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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.          )

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AON CORPORATION

NOTICE OF 2010 ANNUAL MEETING OF STOCKHOLDERS

To the Holders of Common Stock of Aon Corporation:

        The 2010 Annual Meeting of Stockholders of Aon Corporation will be held on Friday, May 21, 2010, at 8:30 A.M (local time), at the Mid-America Club, Aon Center, 200 East Randolph Street, Chicago, Illinois 60601, for the following purposes:

1.

To elect the fourteen nominees named in the attached proxy statement to serve as Directors until our 2011 Annual Meeting of Stockholders. Our Board of Directors unanimously recommends that you vote "FOR" the election of all fourteen nominees.



2.

To ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for the year 2010. Our Board of Directors unanimously recommends that you vote "FOR" the ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm.



3.

To transact such other business as may properly come before the 2010 Annual Meeting of Stockholders or any adjournment or postponement thereof.

        Only holders of common stock at the close of business on March 24, 2010 are entitled to notice of and to vote at the 2010 Annual Meeting of Stockholders and any adjournment or postponement thereof. A list of the stockholders entitled to vote at the 2010 Annual Meeting will be available for inspection, for any purpose germane to the 2010 Annual Meeting, both at the 2010 Annual Meeting and during normal business hours at our corporate offices for ten days prior to the 2010 Annual Meeting.

        Pursuant to the rules of the Securities and Exchange Commission (the "SEC"), we provide access to our proxy materials through the Internet. As a result, we will mail, on or before April 7, 2010, a Notice of Internet Availability of Proxy Materials to our stockholders of record and beneficial owners at the close of business on March 24, 2010 who have not previously requested paper copies of the proxy materials. On the date of mailing of the Notice of Internet Availability of Proxy Materials, all stockholders of record and beneficial owners will be able to access the proxy materials on a website referred to and at the URL address included in the Notice of Internet Availability of Proxy Materials and in the proxy statement. These proxy materials will be available free of charge.

Chicago, Illinois
April 7, 2010

        Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting of Stockholders to be held on May 21, 2010. Our Proxy Statement for the 2010 Annual Meeting of Stockholders and the Annual Report to Stockholders for the fiscal year ended December 31, 2009 are available at http://www.envisionreports.com/AON if you are a stockholder of record, and http://www.edocumentview.com/AON if you are a beneficial owner.

        Your vote is important. Whether or not you plan to attend the 2010 Annual Meeting of Stockholders, please vote as promptly as possible by telephone, through the Internet or by requesting a paper proxy card to complete, sign and return by mail.

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Aon Corporation
200 East Randolph Street
Chicago, Illinois 60601

PROXY STATEMENT
ANNUAL MEETING OF STOCKHOLDERS – MAY 21, 2010

INFORMATION ABOUT THIS PROXY STATEMENT AND THE 2010 ANNUAL MEETING

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        The Board of Directors of Aon Corporation ("Aon" or the "Company") is soliciting your proxy to vote at the 2010 Annual Meeting of Stockholders (the "Annual Meeting") to be held at the Mid-America Club, Aon Center, 200 East Randolph Street, Chicago Illinois 60601, at 8:30 a.m. (local time), on Friday, May 21, 2010, and at any adjournment or postponement thereof.

        As permitted by the rules of the Securities and Exchange Commission (the "SEC"), we are making our proxy materials, including the Notice of 2010 Annual Meeting of Stockholders, this proxy statement and the accompanying proxy card, and our Annual Report to Stockholders (collectively, the "proxy materials"), available to stockholders electronically via the Internet on April 7, 2010. On the same date, we began mailing to our stockholders a Notice of Internet Availability of Proxy Materials (the "Notice of Internet Availability") containing instructions on how to access our proxy materials and vote online. If you received a Notice of Internet Availability, you will not receive a printed copy of the proxy materials unless you have previously made a permanent election to receive these materials in hard copy. Instead, the Notice of Internet Availability instructs you as to how you may access and review all of the important information contained in the proxy materials. The Notice of Internet Availability also instructs you as to how you may submit your proxy on the Internet. If you received a Notice of Internet Availability by mail and would like to receive a printed copy of our proxy materials, you should follow the instructions for requesting such materials included in the Notice of Internet Availability.

        Aon's Annual Report to Stockholders, which contains Aon's Annual Report on Form 10-K, including consolidated financial statements for the year ended December 31, 2009 but excluding exhibits, accompanies this proxy statement. Requests for copies of exhibits to Aon's Annual Report on Form 10-K should be submitted to the Office of the Secretary, Aon Corporation, 200 East Randolph Street, Chicago, Illinois 60601. Exhibits will be furnished upon payment of a nominal fee (which fee will be limited to the expenses we incur in providing you with the requested exhibits). Aon's Annual Report on Form 10-K, including exhibits, are also available free of charge through our website (http://www.aon.com).

Why did I receive these proxy materials?

        We have made these proxy materials available to you on the Internet or, upon your request, have delivered printed versions of these materials to you by mail, in connection with the solicitation of proxies for use at the Annual Meeting, and at any adjournment or postponement thereof.

        The Notice of Internet Availability was first mailed on or before April 7, 2010 to stockholders of record as of March 24, 2010 (the "Record Date").

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What matters will be presented for consideration at the Annual Meeting?

        Action will be taken at the Annual Meeting with respect to the following items:

1.

The election of the fourteen nominees named in this proxy statement to serve as Directors until our 2011 Annual Meeting of Stockholders.



2.

The ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm for the year 2010.

Will any other matters be decided at the Annual Meeting?

        At the date of this proxy statement, we do not know of any other matters to be raised at the Annual Meeting other than those described in this proxy statement. If any other matters are properly presented at the Annual Meeting for consideration, the individuals named in the proxy card will vote on such matters in their discretion.

Who is entitled to vote at the Annual Meeting?

        Holders of our common stock, par value $1.00 per share (the "Common Stock") as of the close of business on March 24, 2010, are entitled to vote at the Annual Meeting. As of that date, there were 269,203,709 shares of Common Stock outstanding and entitled to vote. Each share of Common Stock is entitled to one vote on each matter properly brought before the Annual Meeting.

        What is the difference between holding shares of Common Stock as a stockholder of record and as a beneficial owner?

        If your shares of Common Stock are registered directly in your name with Aon's transfer agent, Computershare Trust Company, N.A., you are considered, with respect to those shares of Common Stock, the stockholder of record, and these proxy materials are being made available or sent directly to you by Aon.

        If your shares of Common Stock are held in a stock brokerage account or by a broker, bank or other nominee, you are considered the beneficial owner of shares held in street name, and these proxy materials are being made available or forwarded to you by your broker, bank or other nominee who is considered, with respect to those shares, the stockholder of record. As the beneficial owner, you have the right to direct your broker, bank or other nominee on how to vote your shares of Common Stock by following the instructions for voting on the proxy card or Notice of Internet Availability.

How do I vote?

        If you are a stockholder of record, you may vote using any of the following methods:

•

By telephone using the toll-free telephone number shown on the proxy card;



•

Through the Internet as instructed on the proxy card or the Notice of Internet Availability;



•

If you received proxy materials by mail or if you request a paper proxy card by telephone or through the Internet, you may elect to vote by mail by completing and signing the proxy card and returning it in the prepaid envelope provided; or



•

By written ballot at the Annual Meeting.

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        Telephone and Internet voting facilities for stockholders of record will be available 24 hours a day. If you vote by telephone or through the Internet, your vote must be received by 11:59 p.m., Eastern Time, on Thursday, May 20, 2010, the day before the Annual Meeting. If you properly cast your vote by telephone, through the Internet or by executing and returning a paper proxy card, and your vote is not subsequently revoked, your Common Stock will be voted in accordance with your instructions. If you execute and return a proxy card but do not give instructions, your proxy will be voted as follows: FOR the election of all nominees for Director named in this proxy statement, FOR the ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm for the year 2010, and otherwise in accordance with the judgment of the person or persons voting the proxy on any other matter properly brought before the Annual Meeting.

        If you are a beneficial owner, you should follow the voting directions provided by your broker, bank or other nominee. You may submit voting instructions by telephone or through the Internet to your broker, bank or other nominee, or request and return a paper proxy card. If you hold shares through the Aon Savings Plan, the plan trustees will vote according to the instructions received from you provided your voting instruction is received by 11:59 p.m., Eastern Time, on Wednesday, May 19, 2010.

        We will distribute written ballots to anyone who wants to vote at the Annual Meeting. If you are a beneficial owner, you must obtain a legal proxy from your broker, bank or other nominee and present it to the inspectors of election with your ballot to be able to vote at the Annual Meeting.

        What should I do if I receive more than one notice of internet availability of proxy materials or proxy card?

        If you own shares of Common Stock directly in your name as a registered holder and other shares of Common Stock as a beneficial owner through a broker, bank or other nominee, or if you own shares of Common Stock through more than one broker, bank or nominee, you may receive multiple Notices of Internet Availability or, if you request proxy materials to be delivered to you by mail, multiple proxy cards. It is necessary for you to vote, sign and return all of the proxy cards or follow the instructions for any alternative voting procedure on each of the Notices of Internet Availability you receive in order to vote all of the shares you own. If you request proxy materials to be delivered to you by mail, each proxy card you receive will come with its own prepaid return envelope. If you vote by mail make sure you return each proxy card in the return envelope which accompanied that proxy card.

How is a quorum determined?

        The presence of the holders of a majority of the shares of Common Stock issued and outstanding and entitled to vote at the Annual Meeting, present in person or represented by proxy, is necessary to constitute a quorum. Abstentions and broker non-votes will be counted as present and entitled to vote for purposes of determining a quorum at the Annual Meeting.

What is a broker non-vote?

        If you own your shares through a broker, bank or other nominee, and you don't vote, the bank, broker or other nominee may vote your shares in its discretion on certain routine matters. With respect to certain non-discretionary matters, your broker, bank or other nominee is not permitted to vote your shares for you. A broker non-vote occurs when a broker, bank or other nominee holding shares of Common Stock on your behalf, does not vote on a particular proposal because it has not received instructions from you and does not have discretionary voting power with respect to that proposal.

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        Under the rules of the New York Stock Exchange (the "NYSE"), if you are a beneficial owner, your broker, bank or other nominee has discretion to vote your shares of Common Stock if it does not receive instructions from you on the ratification of the appointment of our independent registered public accounting firm. In the past, if you were a beneficial owner and you did not provide instructions as to how you wanted your shares of Common Stock voted with respect to the election of Directors, your broker, bank or other nominee was allowed to vote your shares of Common Stock. However, in 2009, the rules of the NYSE were revised to categorize voting in director elections as a non-discretionary matter. As a result, if you are a beneficial owner, your broker, bank or other nominee no longer has discretion to vote your shares of Common Stock if it does not receive instructions from you with respect to the election of Directors.

What are the voting requirements to elect Directors and approve each of the proposals?

        The election of each of the fourteen nominees for Director named in this proxy statement will be decided by a majority of the votes cast with respect to such Director, which means that the number of votes cast for a nominee for Director must exceed the number of votes cast against that nominee for Director. Abstentions and broker non-votes will not be counted as a vote either for or against a nominee for Director.

        Except as otherwise required by applicable law or our Second Amended and Restated Certificate of Incorporation, as amended, any other proposal properly presented at a meeting in which a quorum is present will be decided by the affirmative vote of the holders of a majority of the Common Stock present in person or represented by proxy and entitled to vote on the proposal at that meeting. Accordingly, the ratification of the appointment of our independent registered public accounting firm will be decided by the vote of the holders of a majority of the Common Stock present in person or represented by proxy and entitled to vote on this proposal. For the ratification of the appointment of our independent registered public accounting firm, a stockholder who submits a properly executed ballot or proxy is considered present and entitled to vote, so an abstention will have the effect of a vote against the proposal.

Can I change my vote?

        If you are a stockholder of record, you can change your vote or revoke your proxy at any time before the Annual Meeting by:

•

Entering a later-dated vote by telephone or through the Internet;



•

Delivering a valid, later-dated proxy card;



•

Sending written notice to the Office of the Secretary of Aon; or



•

Voting by ballot in person at the Annual Meeting.

        If you are a beneficial owner of shares of Common Stock, you may submit new voting instructions by contacting your broker, bank or other nominee. You may also vote in person at the Annual Meeting if you obtain a legal proxy as described above under "How do I vote?"

        All shares of Common Stock that have been properly voted and not revoked will be voted at the Annual Meeting. Attending the Annual Meeting without taking further action will not automatically revoke your prior telephone or Internet vote or your proxy.

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Will the Annual Meeting be webcast?

        You may listen to the Annual Meeting on the World Wide Web by logging on to our website at www.aon.com and following the on-screen instructions. We have included our website address in this proxy statement for reference purposes only. The information contained on our website is not incorporated by reference into this proxy statement.

Who can attend the Annual Meeting?

        Stockholders as of the close of business on March 24, 2010, which is the record date for voting, may attend the Annual Meeting.

What do I need to do to attend the Annual Meeting?

        If you are a stockholder of record, you do not need to take any additional action in order to attend the Annual Meeting. If you are a beneficial owner of shares of Common Stock and would like to attend the Annual Meeting, you will need to bring an account statement or other acceptable evidence of ownership of your Common Stock as of the close of business on March 24, 2010, which is the record date for voting. Alternatively, you may contact the broker, bank or other nominee in whose name your Common Stock is registered and obtain a proxy to bring to the Annual Meeting.

Who will pay the costs of this proxy solicitation?

        We will pay the expenses of the preparation of proxy materials and the solicitation of proxies for the Annual Meeting. In addition to the solicitation of proxies by mail, solicitation may be made on our behalf by certain Directors, officers or employees of Aon and our subsidiaries telephonically, electronically or by other means of communication, and by Georgeson Shareholder Communications Inc., whom we have hired to assist in the solicitation and distribution of proxies. Directors, officers and employees of Aon and our subsidiaries will receive no additional compensation for such solicitation. Georgeson will receive a fee of $7,000 for its services. We will also reimburse banks, brokers and other nominees for reasonable expenses incurred by them in forwarding proxy materials to beneficial owners.

Who will count the vote?

        Representatives of our transfer agent, Computershare Trust Company, N.A., will count the vote and serve as inspectors of election.

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PRINCIPAL HOLDERS OF VOTING SECURITIES

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        As of February 26, 2010, the beneficial owners of 5% or more of our Common Stock entitled to vote at the Annual Meeting and known to us were:

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(1)

Based upon information contained in a Schedule 13G filed with the SEC on February 11, 2010 pursuant to Rule 13d-1(b) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). Capital World Investors ("Capital World"), a division of Capital Research and Management Company ("CRMC"), is a registered investment adviser and has: (a) sole voting power as to 5,885,500 shares of Common Stock; (b) shared voting power as to 0 shares of Common Stock; (c) sole dispositive power as to 25,337,742 shares of Common Stock; and (d) shared dispositive power as to 0 shares of Common Stock. All of the shares of Common Stock covered by the Schedule 13G are deemed to be beneficially owned by Capital World as a result of CRMC acting as investment adviser to various investment companies. As permitted by Rule 13d-4 of the Exchange Act, Capital World disclaims beneficial ownership of the shares of Common Stock covered by the Schedule 13G.

(2)

Includes 4,240,157 shares of Common Stock beneficially owned by Mr. Ryan and 12,385,846 shares of Common Stock beneficially owned and attributed to Mr. Ryan pursuant to trusts for the benefit of family members. Also includes 471,922 shares of Common Stock owned by a charitable foundation of which Mr. Ryan is a member and for which he has sole voting and shared investment control. Also includes 7,833 shares of Common Stock representing a beneficial interest in shares of Common Stock of the Aon Common Stock Fund of the Aon Supplemental Savings Plan attributable to Mr. Ryan. Under the terms of the Aon Supplemental Savings Plan, as a participant in such plan, Mr. Ryan is entitled to direct the manner in which the trustees will vote the shares of Common Stock attributed to him; in addition, all shares of Common Stock for which voting instructions are not received are voted by the trustees in the same proportion as the shares of Common Stock for which voting instructions are received. Also includes 232,765 shares of Common Stock that Mr. Ryan has the right to acquire pursuant to presently exercisable employee stock options, or stock options that will become exercisable or stock awards that will vest within 60 days following February 26, 2010.

(3)

Based upon information contained in a Schedule 13G filed with the SEC on February 11, 2010 pursuant to Rule 13d-1(b) of the Exchange Act. T. Rowe Price Associates, Inc. ("Price Associates") is a registered investment adviser and has: (a) sole voting power as to 3,244,788 shares of Common

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Stock; (b) shared voting power as to 0 shares of Common Stock; (c) sole dispositive power as to 17,250,176 shares of Common Stock; and (d) shared dispositive power as to 0 shares of Common Stock. These shares of Common Stock are owned by various individual and institutional investors, with respect to which Price Associates serves as investment adviser with power to direct investments and sole power to vote certain of the shares of Common Stock. Although Price Associates is deemed to be the beneficial owner of such shares of Common Stock for the reporting requirements of the Exchange Act, Price Associates expressly disclaims beneficial ownership of the shares of Common Stock covered by the Schedule 13G.

(4)

Based upon information contained in a Schedule 13G filed February 12, 2010 pursuant to Rule 13d-1(b) of the Exchange Act. State Street Bank and Trust Company ("State Street") is a parent holding company or control person in accordance with Rule 13d-1(B)(i)(II)(G) of the Exchange Act that acts in various fiduciary capacities with respect to certain benefit plans of Aon. State Street has: (a) sole voting power as to 0 shares of Common Stock; (b) shared voting power as to 14,352,616 shares of Common Stock; (c) sole dispositive power as to 0 shares of Common Stock; and (d) shared dispositive power as to 14,352,616 shares of Common Stock. State Street expressly disclaims beneficial ownership of all shares of Common Stock reported in the Schedule 13G pursuant to Rule 13d-4 of the Exchange Act.

(5)

Based upon information contained in a Schedule 13G filed February 5, 2010 pursuant to Rule 13d-1(b) of the Exchange Act. Southeastern Asset Management, Inc. ("Southeastern") is a registered investment adviser and has: (a) sole voting power as to 6,156,918 shares of Common Stock; (b) shared voting power as to 6,410,200 shares of Common Stock; (c) no voting power as to 1,244,000 shares of Common Stock; (d) sole dispositive power as to 7,400,918 shares of Common Stock; (e) shared dispositive power as to 6,410,200 shares of Common Stock; and (f) no dispositive power as to 0 shares of Common Stock. All of the shares of Common Stock covered by the Schedule 13G are owned legally by Southeastern's investment advisory clients and none are owned directly or indirectly by Southeastern. As permitted by Rule 13d-4 of the Exchange Act, Southeastern disclaims beneficial ownership of the shares of Common Stock covered by the Schedule 13G.

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PROPOSAL 1—ELECTION OF DIRECTORS

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        Fourteen Directors are to be elected at the Annual Meeting. All of the current members of our Board of Directors (the "Board") are standing for election. With respect to Mr. Case, his employment agreement provides that he will be nominated for election as a Director at each annual meeting of stockholders during the period of his employment. The term of each Director expires at the next Annual Meeting of Stockholders, and each Director will continue in office until the election and qualification of his or her respective successor or until his or her earlier death, removal or resignation. The Board consists of a number of Directors as is fixed from time to time by resolution adopted by the Board as provided in our bylaws. The Board currently is authorized to have up to twenty-one members.

        All nominees are currently Directors of Aon. All nominees for Director have consented to be named and have agreed to serve as Directors if elected. The Governance/Nominating Committee recommended to the full Board that each Director be nominated to serve for an additional term.

        Each of the fourteen Directors will be elected by the vote of a majority of the votes cast with respect to such Director, which means that the number of votes cast for a Director must exceed the number of votes cast against that Director. A stockholder may: (i) vote for the election of a nominee for Director; (ii) vote against the election of a nominee for Director; or (iii) abstain from voting for a nominee for Director.

        Unless a proxy directs to the contrary, it is intended that the proxies will be voted FOR the election of the fourteen nominees for Director named on the following pages, to hold office until the next Annual Meeting of Stockholders or until their respective successors are duly elected and qualified. We have no reason to believe that any of the nominees will not be available to serve as a Director. However, if any of them should become unavailable to serve for any reason, the proxies will be voted for such substitute nominees as may be designated by the Board.

        Aon values a number of attributes and criteria when identifying candidates to serve as a Director, including professional background, expertise, reputation for integrity, business, financial and management experience, leadership capabilities and diversity. In addition to the specific experience and qualifications set forth below, we believe all of the nominees are individuals with a reputation for integrity, demonstrate strong leadership capabilities and are able to work collaboratively to make contributions to the Board and management.

        Set forth on the following pages is biographical and other background information concerning each nominee for election as a Director. This information includes each nominee's principal occupation as well as a discussion of the specific experience, qualifications, attributes, and skills of each nominee that led to the Board's conclusion that each nominee should serve as a Director. In addition, set forth below is the period during which each nominee has served as a Director of Aon, including service as a Director of Ryan Insurance Group, Inc. ("Ryan Group"), which merged with Aon in 1982. The information presented below has been confirmed by each nominee for purposes of its inclusion in this proxy statement. Ages shown for all Directors are as of December 31, 2009.

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        OUR BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE "FOR" THE ELECTION OF ALL NOMINEES.

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

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        The following table sets forth the number of shares of Common Stock beneficially owned as of February 26, 2010 by each Director and nominee, by each of the named executive officers of Aon as set forth in the Summary Compensation Table for Fiscal Years 2009, 2008 and 2007 in this proxy statement, and by all Directors, nominees and executive officers of Aon as a group. As used in this proxy statement, beneficially owned means a person has, or may have within 60 days, the sole or shared power to vote or direct the voting of a security and/or the sole or shared investment power with respect to a security (i.e., the power to dispose or direct the disposition of a security). Therefore, the table does not include the "phantom stock" shares held by or attributable to any individual under our benefit plans. Information with respect to shares attributable to Aon's Directors under various deferral accounts is set forth in the section captioned "2009 Director Compensation."

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CORPORATE GOVERNANCE

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        The Board has adopted Governance Guidelines (the "Governance Guidelines"), which, along with the Committee charters, the Code of Business Conduct, which sets forth standards of conduct for employees, officers and Directors, and the Code of Ethics for Senior Financial Officers, provide the framework for the governance of Aon. The Board provides oversight of Aon's overall performance, strategic direction, and executive management team performance. The Board also approves major initiatives and transactions and advises on key financial and business matters. The Board is kept apprised of Aon's progress on a regular basis through Board and Committee meetings, discussions with management, operating and financial reports provided by the Chief Executive Officer and Chief Financial Officer, and other material distributed to the Directors throughout the year.

        The Governance Guidelines require that Aon have a majority of Directors who meet the categorical independence standards adopted by the Board, which must meet or exceed the independence requirements of the NYSE. The Governance Guidelines further provide that each of the Audit, Governance/Nominating and Organization and Compensation Committees will be composed entirely of independent Directors. The principal responsibilities of each Committee are described in this proxy statement in the section captioned "Board of Directors and Committees."

Director Independence

        In accordance with the rules of the NYSE, the Board has adopted categorical independence standards, which either meet or exceed the independence requirements of the NYSE corporate governance standards, to provide assistance in the determination of director independence. The categorical standards are set forth below and provide that a Director of Aon will not qualify as an independent Director if:

(i)

The Director is, or has been within the last three years, an employee of Aon, or an immediate family member of the Director is, or has been within the last three years, an executive officer, of Aon;



(ii)

The Director has received, or has an immediate family member who has received, during any twelve-month period within the last three years, more than $120,000 in direct compensation from Aon, other than director and committee fees and pension or other forms of deferred compensation for prior service (provided such compensation is not contingent in any way on continued service);



(iii)

(A) The Director is a current partner or employee of a firm that is Aon's internal or external auditor; (B) the Director has an immediate family member who is a current partner of such a firm; (C) the Director has an immediate family member who is a current employee of such a firm and personally works on Aon's audit; or (D) the Director or an immediate family member was within the last three years a partner or employee of such a firm and personally worked on Aon's audit within that time;



(iv)

The Director or an immediate family member is, or has been within the last three years, employed as an executive officer of another company where any of Aon's present executive officers at the same time serves or served on that company's compensation committee;



(v)

The Director is a current employee, or an immediate family member is a current executive officer, of a company that has made payments to, or received payments from, Aon for

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property or services in an amount which, in any of the last three fiscal years, exceeded the greater of $1 million or 2% of such other company's consolidated gross revenues; or

(vi)

The Director, or the spouse of a Director, serves as an executive officer of a charitable organization to which Aon's charitable contributions in the last fiscal year, excluding those made under Aon's matching gift program, exceeded the greater of $1 million or two percent (2%) of such organization's consolidated gross revenues.

        For purposes of the categorical standards, "immediate family member" is defined to include a Director's spouse, parents, children, siblings, mothers and fathers-in-law, sons and daughters-in-law, brothers and sisters-in-law, and anyone (other than domestic employees) who shares the Director's home.

        In connection with the determination of director independence, the Governance/Nominating Committee reviewed the categorical standards adopted by the Board together with other applicable legal requirements and the rules of the NYSE. The Committee also reviewed information compiled from the responses to questionnaires completed by each of Aon's Directors, information derived from Aon's corporate and financial records, information available from public records, and information received from other relevant parties. Following this review, the Committee delivered a report to the full Board of Directors, and the Board made its determination of director independence.

        As a result of this review, the Board affirmatively determined that each of the following Directors does not have a material relationship with Aon and is independent under the categorical standards adopted by the Board, applicable legal requirements and the rules of the NYSE: Mr. Conti, Mr. Jannotta, Mr. Kalff, Mr. Knight, Mr. Losh, Mr. Martin, Mr. McKenna, Mr. Morrison, General Myers, Mr. Notebaert, Mr. Rogers, Ms. Santona and Dr. Woo. Mr. Case is considered a management Director because of his position as President and Chief Executive Officer of Aon.

        In determining that each of the non-employee Directors is independent, the Board also considered the following relationships that it deemed were immaterial to such Director's independence.

        With respect to Mr. Conti, Mr. Jannotta, Mr. Knight, Mr. Martin, Mr. McKenna, Mr. Rogers, Ms. Santona and Dr. Woo, the Board considered that, in the ordinary course of business, Aon has sold services to, or purchased services from, a company (or other entity) at which these Directors is an executive officer (or, in the case of Mr. Martin, is Of Counsel and in the case of Dr. Woo, is Dean of the College of Business), and in each case the amount paid to or received from one of these entities in any of the previous three fiscal years was below one percent (1%) of Aon's or the other company's annual revenue.

        With respect to Mr. Knight, the Board considered personal investments made by Mr. Jannotta and Mr. McKenna, as well as by the Aon Pension Fund, in a privately held fund managed by Mr. Knight. The Board determined that the investments were immaterial and did not impair the independence of any non-management Director.

        The Board considered that Mr. Martin, Mr. McKenna, Mr. Morrison, Mr. Rogers and Ms. Santona serve on the boards of various not-for-profit entities with executive officers of Aon.

        With respect to Mr. Jannotta, Mr. Knight, Mr. Martin, Mr. McKenna, Mr. Morrison, General Myers, Mr. Notebaert, Mr. Rogers and Ms. Santona, the Board considered that Aon made charitable contributions in 2009 to organizations in which the Director or a Director's spouse serves as an officer, director or trustee.

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        With respect to Mr. Rogers, the Board considered that Mr. Rogers was a member of the Board of Directors of Chicago 2016 during 2009. With respect to Mr. McKenna, the Board considered that Mr. McKenna served as co-chair of the fundraising Chicago 2016 Development Committee, which was a committee whose primary function was fundraising, and which had no governing or decision-making authority. For information regarding Aon's contributions to Chicago 2016 in 2009, see the section captioned "Certain Relationships and Related Transactions" in this proxy statement.

Majority Voting

        Aon's by-laws require that Directors be elected by majority vote in uncontested elections. In January 2009, the Board approved an amendment to Aon's by-laws to provide that, in a contested election, Directors will be elected by plurality vote. In addition, in March 2009, the Board adopted revisions to the Governance Guidelines requiring any incumbent Director who fails to receive a majority of the votes cast in an uncontested election to immediately offer to tender his or her resignation to the Board. The Board will then determine, through a process overseen by the Governance/Nominating Committee, whether to accept the resignation, reject the resignation, or take other action. The Board will act on the recommendation of the Governance/Nominating Committee, and promptly disclose its decision and the rationale behind it in a Form 8-K filed with the SEC.

Board Meetings

        The Board met six times in 2009. All incumbent Directors attended at least seventy-five (75%) of the meetings of the Board and all Committees of the Board on which they served.

Meetings of Non-Management Directors

        In accordance with NYSE rules and the Governance Guidelines, non-management Directors meet regularly in executive session without management. Lester B. Knight, the Company's non-Executive Chairman, chairs these executive sessions.

Stock Ownership Guidelines for Non-Management Directors

        In July 2006, the Board of Directors adopted Stock Ownership Guidelines for Non-Management Directors that were subsequently updated and revised in July 2008. The Guidelines require each non-management Director to hold an investment position in Common Stock (including vested deferred stock units) equal to three times the annual Director retainer. The Guidelines provide a transition period of five years for non-management Directors to achieve the ownership guidelines level; provided, however that each new non-management Director is expected to hold 1,000 shares of Common Stock within the first year of joining the Board or transitioning from a management Director to a non-management Director. Shares held by non-management Directors in deferred accounts will be included when determining if the target ownership level has been achieved.

Attendance at Annual Meeting

        The Governance Guidelines provide that Directors are expected to attend the Annual Meeting of Stockholders. All of our Board members attended the 2009 Annual Meeting of Stockholders held on May 15, 2009, with the exception of Edgar D. Jannotta and Carolyn Y. Woo.

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Communications with the Board of Directors

        Stockholders and other interested parties may communicate with the Board of Directors by contacting the non-management Directors of Aon Corporation, c/o Office of the Secretary, 200 East Randolph Street, Chicago, IL 60601. Alternatively, stockholders and other interested parties may communicate with Aon's non-management Directors via electronic mail to the following address: corporate_governance@aon.com.

        The non-management Directors have established procedures for handling communications from stockholders and other interested parties. Communications are distributed to the Chairman of the Governance/Nominating Committee, the full Board of Directors, the non-management Directors or to any individual Director or Directors as appropriate, depending on the facts and circumstances outlined in the communication. Solicitations, spam, junk mail and mass mailings, resumes and other forms of job inquiries, business solicitations or advertisements and frivolous or inappropriate communications will not be forwarded, but will be made available to any non-management Director upon request.

Code of Business Conduct/Code of Ethics for Senior Financial Officers

        The Board has adopted a code of business conduct that applies to our Directors, officers and employees. The Code of Business Conduct can be found on our web site at http://www.aon.com/about-aon/corporate-governance/guidelines-policies/code-of-business-conduct.jsp and is available in print copy to any stockholder who makes a written request to the Office of the Secretary.

        In addition, the Board has adopted a Code of Ethics for Senior Financial Officers that applies to the principal executive officer and the senior financial officers of Aon and our subsidiaries. The Code of Ethics for Senior Financial Officers can be found on our web site at http:///www.aon.com/about-aon/corporate-governance/guidelines-policies/code-of-ethics-for-senior-financial-officers.jsp.

        We intend to disclose future amendments to, or waivers from, certain provisions of both the Code of Business Conduct and the Code of Ethics for Senior Financial Officers on our website promptly following the date of such amendment or waiver.

Board Leadership Structure and Role in Risk Oversight

        Since April 4, 2005, the positions of Chief Executive Officer and Chairman of the Board of Directors have been held by separate individuals. On April 4, 2005, Gregory C. Case was named Aon's President and Chief Executive Officer, and Patrick G. Ryan, who had served as Aon's Chief Executive Officer prior to that time, became the Executive Chairman of Aon's Board of Directors. After having served as Aon's Chief Executive Officer since 1982 and as Aon's Chairman since 1990, Mr. Ryan moved into the Executive Chairman position to continue to provide executive leadership to Aon and to facilitate the transition of the management of day-to-day operations to Mr. Case. Effective August 1, 2008, upon the retirement of Mr. Ryan, Lester B. Knight was elected Non-Executive Chairman of Aon's Board of Directors. The position of Non-Executive Chairman is independent from Aon management. As Non-Executive Chairman, Mr. Knight sets the agendas for and presides over the Board meetings and also chairs executive sessions of the non-management Directors of the Board. The Chief Executive Officer is also a member of the Board and participates in its meetings. The Board of Directors believes the separation of the positions of Chief Executive Officer and Chairman is the appropriate structure at this time, as it allows the Chief Executive Officer to focus on the management of Aon and the Chairman to ensure that the Board is focused on its oversight responsibilities, including independent oversight of Aon management.

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        Risk is inherent with every business, and how well a business manages risk can ultimately determine its success. We face a number of risks, including economic risks, financial risks, legal and regulatory risks, and others, such as the impact of competition. Management is responsible for the day-to-day management of risks that Aon faces, while the Board of Directors, as a whole and through its Committees, has responsibility for the oversight of risk management. In its risk oversight role, Aon's Board of Directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate and functioning as designed.

        The Board believes that establishing the right "tone at the top" and full and open communication between management and the Board are essential for effective risk management and oversight. Senior management attends Board meetings and is available to address any questions or concerns raised by the Board on risk management-related and any other matters. The Board of Directors receives presentations from senior management on strategic matters involving our operations.

        While the Board is ultimately responsible for risk oversight at Aon, Aon's Board Committees assist the Board in fulfilling its oversight responsibilities in certain areas of risk. The Board of Directors has delegated to the Audit Committee through its charter the primary responsibility for the oversight of risks facing Aon. The charter provides that the Audit Committee will discuss guidelines and policies with respect to risk assessment and risk management and will discuss Aon's major financial risk exposures and the steps management has taken to monitor and control such exposures. The Audit Committee also has general oversight responsibility for Aon's compliance with legal, regulatory and ethics requirements, which represent many of the most significant risks that Aon faces. The Audit Committee annually reviews legal, regulatory and ethics policies and programs, including Aon's Code of Business Conduct. In addition, the Audit Committee periodically reviews with Aon management any material correspondence with, or other action by, regulators or governmental agencies, and also periodically reviews with Aon's General Counsel legal matters that may have a material impact on Aon's financial statements or compliance policies. Aon's senior management periodically reviews with the Audit Committee the major risks facing Aon and the steps management has taken to monitor and mitigate those risks.

        In light of the breadth and number of responsibilities that the Audit Committee must oversee, and the importance of the evaluation and management of risk related to Aon's compliance programs and policies, the Board formed the Compliance Committee, which is currently a standing subcommittee of the Audit Committee, to oversee Aon's implementation of compliance policies, programs and procedures that are designed to be responsive to the various compliance and regulatory risks facing Aon and to assist the Audit Committee in fulfilling its oversight responsibility for Aon's legal, regulatory and ethics policies and programs. In addition to its general oversight of Aon's legal and regulatory compliance policies, programs and procedures, the Compliance Committee is also responsible for the ongoing monitoring of Aon's efforts to implement and comply with its legal obligations arising under certain regulatory settlement agreements.

        While the Board's primary oversight of risk is with the Audit Committee, the Board has delegated to other Committees the oversight of risks within their areas of responsibility and expertise. For example, the Organization and Compensation Committee reviews the risks associated with Aon's compensation practices, including an annual review of Aon's risk assessment of its compensation policies and practices for its employees. The Finance Committee reviews significant financial exposures and contingent liabilities of Aon, including Aon's capital structure, its credit ratings and its cost of capital, long-term benefit obligations, and Aon's use of or investment in financial products, including derivatives used to manage risk related to foreign currencies, commodities, and interest rates. In

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addition, the Finance Committee reviews proposed mergers, acquisitions and divestitures; monitors the financial performance of completed mergers and acquisitions; and oversees the financial, investment and actuarial policies and objectives of Aon's ERISA-qualified benefit plans, reviews the investment performance of those plans, and periodically reviews the investment performance of, and makes recommendations regarding investment guidelines for, non-U.S. benefit and retirement plans. The Finance Committee also reviews Aon's major insurance programs. The Governance/Nominating Committee oversees the risks associated with Aon's overall governance and its succession planning process to confirm that Aon has a slate of future, qualified candidates for key management positions.

        The Board believes that its oversight of risks, primarily through delegation to the Audit Committee, but also through delegation to other Committees to oversee specific risks within their areas of responsibility and expertise, and the sharing of information with the full Board, is appropriate for a company like Aon that is a provider of risk management services, insurance and reinsurance brokerage and human capital and management consulting. The Chair of each Committee that oversees risk provides a summary of the matters discussed with the Committee to the full Board following each Committee meeting. The minutes of each Committee meeting are also provided to all Board members.

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BOARD OF DIRECTORS AND COMMITTEES

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        The Board of Directors has appointed standing Committees, including Executive, Audit, Governance/Nominating, Finance and Organization and Compensation Committees. The Audit Committee has also established the Compliance Committee as a standing sub-committee of the Audit Committee. The charters of the Audit, Compliance, Governance/Nominating, Finance and Organization and Compensation Committees are available on the corporate governance section of our website at http://www.aon.com/about-aon/corporate-governance/guidelines-policies/board-committees-charters.jsp. The Governance Guidelines are also available on the corporate governance section of our website at http://www.aon.com/about-aon/corporate-governance/guidelines-policies/aon-corporation-governance-guidelines.jsp.

        Membership on the Committees since the last Annual Meeting in 2009 has been as follows:

(1)

Chair.

Executive Committee

        When the Board of Directors is not in session, the Executive Committee is empowered to exercise the power and authority in the management of the business and affairs of Aon as would be exercised by the Board of Directors, subject to certain exceptions. The Executive Committee acted by unanimous written consent on two occasions in 2009.

Audit Committee

        In 2009, the Audit Committee met nine times. The Board of Directors has determined that each of the members of the Audit Committee is independent as defined by the rules of the NYSE. In addition, as required by the rules of the NYSE, all of the Committee members are financially literate. The Board of Directors has determined that each of John W. Rogers, Jr., the Chairman of our Audit Committee, Fulvio Conti, Robert S. Morrison and Richard C. Notebaert is an "audit committee financial expert" within the meaning of rules promulgated by the SEC. The primary purposes of the Audit Committee are to assist the Board with the oversight of: (i) the integrity of Aon's financial statements and financial reporting process; (ii) Aon's compliance with legal and regulatory requirements and ethics programs established by management and the Board; (iii) the engagement of the independent auditor, and its qualifications, independence and performance; and (iv) the performance of Aon's internal audit function. In discharging this role, the Audit Committee is authorized to retain outside counsel or other experts as it deems appropriate to carry out its duties and responsibilities.

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        The Audit Committee charter can be found on the corporate governance section of our website at http://www.aon.com/about-aon/corporate-governance/guidelines-policies/board-charters/amended-restated-audit-committee-charter.jsp. Additional information regarding the Audit Committee's responsibilities may be found in this proxy statement in the section captioned "Report of the Audit Committee."

Compliance Committee

        The Compliance Committee is a standing sub-committee of the Audit Committee, which has general oversight responsibility for Aon's legal, regulatory and ethics policies and programs. The primary purposes of the Compliance Committee are to: (i) oversee Aon's implementation of compliance policies, programs and procedures that are designed to be responsive to the various compliance and regulatory risks facing Aon; (ii) monitor Aon's effort to implement various legal obligations arising from certain regulatory settlement agreements; and (iii) assist the Audit Committee in fulfilling its oversight responsibilities for Aon's legal, regulatory and ethics policies and programs. The Compliance Committee reports regularly to the Audit Committee regarding its activities. Each member of the Compliance Committee is independent as defined in the independence standards of the NYSE. The Compliance Committee met four times during 2009.

Finance Committee

        The Finance Committee is responsible for assisting the Board with monitoring and overseeing Aon's balance sheet, including the capital management strategy, capital structure, investments, returns and related policies. The Finance Committee also reviews proposed mergers, acquisitions and divestitures in accordance with policies established by the Board. In addition, the Finance Committee oversees the investment policies and objectives of Aon's ERISA-qualified benefit plans, and reviews the investment performance of non-U.S. benefit and retirement plans. The Finance Committee met four times during 2009.

Governance/Nominating Committee

        The Governance/Nominating Committee identifies and recommends to the Board of Directors candidates for service on the Board, reviews and recommends the renomination of incumbent Directors, reviews and recommends Committee appointments and leads the annual performance evaluation of the Board and its Committees. In addition, the Governance/Nominating Committee develops and recommends governance guidelines for Aon to the Board of Directors, reviews related party transactions, periodically reviews management succession planning and periodically reviews compliance with stock ownership guidelines. Each member of the Governance/Nominating Committee is independent as defined in the independence standards of the NYSE. The Governance/Nominating Committee met six times during 2009.

        The Governance/Nominating Committee considers recommendations for Director candidates from Aon's Directors and executive officers. In addition, the Governance/Nominating Committee will consider stockholders' recommendations. Recommendations, together with the name and address of the stockholder making the recommendation, relevant biographical information regarding the proposed candidate, and a description of any arrangement or understanding between the stockholder and the proposed nominee, should be sent to our Secretary. Consistent with the Governance Guidelines, the Governance/Nominating Committee considers a number of criteria in evaluating Director candidates, including professional background, expertise, reputation for integrity, business experience, leadership

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capabilities and potential contributions to the Board of Directors and Aon's management. The Governance/Nominating Committee also considers whether a potential nominee would satisfy the independence standards of the NYSE.

        The Board of Directors also values diversity as a factor in selecting nominees to serve on the Board, and believes that the diversity which exists in its composition provides significant benefit to the Board and Aon. Although there is no specific policy on diversity, the Governance/Nominating Committee considers the criteria noted above in selecting nominees for Directors, including members from diverse backgrounds who combine a broad spectrum of experience and expertise with a reputation for integrity. Such considerations may include gender, race, national origin, functional background, executive or professional experience, and international experience. The effectiveness of the nomination process, including the criteria used for selecting nominees for Directors, is evaluated by the Board each year as part of its annual self-evaluation process and by the Governance/Nominating Committee as it evaluates and identifies Director candidates.

        When a vacancy exists on the Board of Directors due to the expansion of the size of the Board of Directors or the resignation or retirement of an existing Director, the Governance/Nominating Committee identifies and evaluates potential Director nominees. The Governance/Nominating Committee has sole authority to retain and terminate any search firm to be used to identify Director candidates and sole authority to approve such search firm's fees and other retention terms.

        Candidates for Director are evaluated using the criteria discussed above and the existing composition of the Board of Directors, including its size, structure, backgrounds and areas of expertise of existing Directors and the number of independent and management Directors. The Governance/Nominating Committee also considers the specific needs of the various Board Committees. The Governance/Nominating Committee recommends potential Director candidates to the full Board of Directors, which is responsible for final approval of any Director candidate. This process is the same for Director candidates who are recommended by our stockholders.

        Recommendations for Director candidates to stand for election at the 2011 Annual Meeting of Stockholders must be submitted in writing to the Secretary of Aon, 200 East Randolph Street, Chicago, IL 60601. Recommendations will be forwarded to the Chairman of the Governance/Nominating Committee for review and consideration.

Organization and Compensation Committee

        The Organization and Compensation Committee (the "Compensation Committee") assists the Board in carrying out its overall responsibilities with regard to executive compensation, including oversight of the determination and administration of Aon's philosophy, policies, programs and plans for executive officers and non-management Directors. The Compensation Committee annually reviews and determines the compensation of Aon's executive officers, including Aon's Chief Executive Officer subject to the input of the independent members of the Board. The Compensation Committee consults with the Chief Executive Officer on, and directly approves, the compensation of other executive officers, including special hiring and severance arrangements. The Compensation Committee administers the Aon Stock Incentive Plan (and its predecessor plans), including granting stock options and stock awards (other than awards to the Chief Executive Officer and the current Non-Executive Chairman, which awards are approved by the independent members of the Board) and interpreting the plan, and has general administrative responsibility with respect to Aon's other U.S. employee benefit programs. In addition, the Compensation Committee reviews and makes recommendations to the Board concerning Directors' compensation and certain amendments to U.S. employee benefit plans or

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equity plans. The Compensation Committee also reviews and discusses the compensation disclosures contained in Aon's Annual Report on Form 10-K and proxy statement. The Compensation Committee may delegate its authority to sub-committees when appropriate, although it did not do so in 2009. The Compensation Committee met ten times during 2009. The Compensation Committee charter can be found on the corporate governance section of our website at http://www.aon.com/about-aon/corporate-governance/guidelines-policies/board-charters/organization-compensation-committee-charter.jsp.

Process of Determining Executive Compensation

        The role of Aon management is to assist the Compensation Committee in managing the Company's executive and Director compensation programs. Direct responsibilities of management include, but are not limited to:

•

Recommending compensation increases, short and long-term incentive awards and, where applicable, severance benefits for executive officers other than the Chief Executive Officer;



•

Providing an ongoing review of the effectiveness of the Company's compensation programs and aligning the programs with the Company's objectives;



•

Designing and recommending the amendment of long-term and short-term cash and equity-based incentive plans; and



•

Designing and recommending the amendment of U.S. employee benefit plans.

        In the first quarter of 2010, the independent non-employee Directors evaluated the performance, and reviewed the compensation, of the Chief Executive Officer. At that time, the Compensation Committee evaluated the performance and reviewed the compensation of all other executive officers. The Compensation Committee also approved for each executive officer a target annual incentive for 2010 performance and the specific corporate performance metric that Aon's performance would be measured against for 2010.

        In connection with this annual compensation review, management presented the Compensation Committee with compensation tally sheets reporting compensation paid for 2009 and competitive pay data, where available, as a market check. The Compensation Committee also reviewed and considered the overall performance of Aon against a target that was established for 2009 culminating in certain compensation decisions made by the Compensation Committee during the first quarter of 2010. The Compensation Committee's decisions with respect to the compensation of our executive officers are described in this proxy statement in the section captioned "Compensation Discussion and Analysis."

Relationship with Executive Compensation Consultant

        Since 2005, the Compensation Committee has retained Frederic W. Cook & Co., Inc. as its independent executive compensation consultant. The consultant provides expertise on various matters coming before the Compensation Committee. The consultant is engaged by, and reports directly to, the Compensation Committee. The consultant does not advise Aon's management or receive other compensation from Aon. George Paulin, the Chief Executive Officer of Frederic W. Cook & Co., Inc., typically participates in all meetings of the Compensation Committee during which executive compensation matters are discussed and communicates between meetings with the Chairman of the Compensation Committee. During 2009, the consultant assisted the Compensation Committee by: providing insights and advice regarding Aon's compensation philosophy, objectives and strategy; developing criteria for identification of Aon's peer group for executive compensation and company

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performance review purposes; reviewing management's proposals for the design of short-term cash and long-term equity incentive compensation programs; providing insights and advice regarding the amendment and restatement of the Chief Executive Officer's employment agreement and change-in-control agreement; and advising on and providing comments on management's recommendations regarding executive officers' bonuses for 2009 and equity-based awards granted in 2009. Management periodically retains other consulting firms to provide pay survey data and other non-executive compensation services that may be presented to or reviewed by the Compensation Committee.

Review of Compensation Policies and Practices

        Although recently there has been increased scrutiny of risk and whether companies' compensation programs contribute to unnecessary risk taking, we believe that we have historically maintained a level of prudence associated with our compensation programs and will continue to do so. We engage in a process to evaluate whether our executive and broad-based compensation programs contribute to unnecessary risk-taking and have concluded that the risks arising from these programs are not reasonably likely to have a material adverse effect on Aon.

Compensation Committee Interlocks and Insider Participation

        During 2009, the Compensation Committee was composed of Richard C. Notebaert (Chairman), Edgar D. Jannotta, J. Michael Losh, Andrew J. McKenna, Robert S. Morrison and Richard B. Myers. No member of the Compensation Committee was, during 2009 or previously, an officer or employee of Aon or any of its subsidiaries. In addition, during 2009, there were no compensation committee interlocks required to be disclosed.

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REPORT OF THE AUDIT COMMITTEE

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        The Audit Committee oversees Aon's financial reporting process on behalf of the Board of Directors. Management has the primary responsibility for establishing and maintaining adequate internal financial controls, for preparing the financial statements and for the reporting process. Ernst & Young LLP ("E&Y"), Aon's independent registered public accounting firm for 2009, is responsible for expressing opinions on the conformity of Aon's audited financial statements with generally accepted accounting principles and the effectiveness of Aon's internal control over financial reporting.

        In this context, the Audit Committee reviewed and discussed with management and E&Y the audited financial statements for the year ended December 31, 2009, as well as management's assessment of the effectiveness of Aon's internal control over financial reporting and E&Y's evaluation of Aon's internal control over financial reporting. The Audit Committee has discussed with E&Y the matters that are required to be discussed by Auditing Standards, the SEC and other regulatory agencies (Communication with Audit Committees).

        In addition, the Audit Committee has discussed with E&Y the independence of that firm from Aon and its management, including the matters in the written disclosures required by Rule 3526 of the Public Company Accounting Oversight Board (Communication with Audit Committees Concerning Independence). The Audit Committee has also considered whether E&Y's provision of non-audit services to Aon is compatible with maintaining E&Y's independence. The Audit Committee has concluded that E&Y is independent from Aon and its management.

        The Audit Committee discussed with Aon's internal auditors and E&Y the overall scope and plans for their respective audits. The Audit Committee meets with the internal and independent auditors, with and without management present, to discuss the results of their examinations, their evaluations of Aon's internal controls, and the overall quality of Aon's financial reporting.

        In reliance on the reviews and discussions referred to above, and subject to the limitations on the role and responsibilities of the Audit Committee referred to above, the Audit Committee recommended to the Board of Directors (and the Board has approved) that the audited financial statements be included in the Annual Report on Form 10-K for the year ended December 31, 2009 for filing with the SEC. The Audit Committee has approved, and the Board of Directors has requested that stockholders ratify, the selection of E&Y as our independent registered public accounting firm for the year 2010.

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PROPOSAL 2—RATIFICATION OF APPOINTMENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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        The Audit Committee has appointed Ernst & Young LLP ("E&Y") as Aon's independent registered public accounting firm for the year 2010, subject to ratification by our stockholders. E&Y was first retained as Aon's independent registered public accounting firm in February 1986. Although this appointment is not required to be submitted to a vote of the stockholders, the Board of Directors believes it appropriate as a matter of policy to request that the stockholders ratify the appointment of the independent registered public accounting firm for the year 2010. In the event this proposal does not receive the affirmative vote of the holders of a majority of the shares entitled to vote and present in person or represented by proxy at the Annual Meeting, the Audit Committee will reconsider the appointment, but may decide to maintain its appointment of E&Y.

        We anticipate that a representative of E&Y will be present at the Annual Meeting. The representative will be given the opportunity to make a statement if he or she desires to do so, and is expected to be available to respond to any appropriate questions that may be submitted by stockholders at the Annual Meeting.

        OUR BOARD OF DIRECTORS AND AUDIT COMMITTEE UNANIMOUSLY RECOMMEND THAT YOU VOTE "FOR" THE RATIFICATION OF THE APPOINTMENT OF ERNST & YOUNG LLP AS OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM FOR 2010.

        Audit Fees.    Fees for audit services totaled approximately $17.9 million in 2009 and $19.5 million in 2008. For both years, audit fees included services associated with the annual audit, including fees related to Sarbanes-Oxley Section 404, the reviews of Aon's documents filed with the SEC, and statutory audits required domestically and internationally. Fees for required statutory audits and attestation reports in various domestic and foreign jurisdictions included in the amounts above were approximately $9.3 million in 2009 and $10.1 million in 2008, respectively.

        Audit-Related Fees.    Fees for audit-related services totaled approximately $1.6 million in 2009 and $2.4 million in 2008. Audit-related fees include services such as employee benefit plan audits, other attestation services, due diligence in connection with acquisitions and accounting consultations not included in audit fees.

        Tax Fees.    Fees for tax services, including tax compliance, tax advice and tax planning totaled approximately $2.2 million in 2009 and $2.9 million in 2008.

        All Other Fees.    Fees for all other services not included above totaled $0 in 2009 and approximately $0.1 million in 2008.

Audit Committee's Pre-Approval Policies and Procedures

        The Audit Committee pre-approves all audit and permissible non-audit services provided by the independent registered public accounting firm. These services may include audit services, audit-related services, tax services and other services. Each pre-approval provides details regarding the particular service or category of service to be provided and is subject to a specific engagement authorization. The Audit Committee requires that the independent registered public accounting firm and management report on the actual fees charged by the independent registered public accounting firm for each category of service at Audit Committee meetings held during the year.

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        The Audit Committee acknowledges that circumstances may arise throughout the year that require the engagement of the independent registered public accounting firm to provide additional services not contemplated in the Audit Committee's initial pre-approval process that occurs on an annual basis. In those circumstances, the Audit Committee requires that specific pre-approval be obtained before engaging the independent registered public accounting firm. The Audit Committee has delegated pre-approval authority to the Chairman of the Audit Committee for those instances when pre-approval is needed prior to a scheduled Audit Committee meeting. Such pre-approvals are reported to the Audit Committee at the next scheduled Audit Committee meeting.

        All audit and non-audit services provided by the independent registered public accounting firm during 2009 were pre-approved in accordance with Aon's pre-approval policy as described above.

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COMPENSATION COMMITTEE REPORT

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        The Organization and Compensation Committee of the Board of Directors of Aon has reviewed and discussed with management the Compensation Discussion and Analysis required by Item 402(b) of Regulation S-K and set forth in this proxy statement.

        Based on its review and discussions with management, the Organization and Compensation Committee recommended to the Board of Directors that the Compensation Discussion and Analysis be included in this proxy statement and Aon's Annual Report on Form 10-K.

        This Report is provided by the Organization and Compensation Committee, which is composed entirely of the following independent Directors:

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EXECUTIVE COMPENSATION

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Compensation Discussion and Analysis

Introduction

        This Compensation Discussion and Analysis ("CD&A") describes and analyzes our executive compensation program. It should be read in conjunction with the executive compensation tables and corresponding footnotes that follow, as it provides context for the amounts shown in the tables and the footnote disclosures.

        This CD&A is arranged in the following four sections:

•

Executive Summary of the CD&A



•

Discussion of our compensation objectives and process



•

Explanation of compensation components and analysis of 2009 pay decisions



•

Other policies and practices as they relate to our executive compensation program

        While the discussion focuses primarily on compensation awarded to our named executive officers, we address Aon's compensation programs as they apply to other employees where it enhances an understanding of our compensation philosophy. In this proxy statement, the reference to our "named executive officers" means Gregory C. Case, our President and Chief Executive Officer (our "CEO"); Christa Davies, our Executive Vice President and Chief Financial Officer (our "CFO"); Messrs. Appel, McGill and Dail, our three other most highly compensated executive officers for 2009; and Mr. Devine, who would have been among our most highly compensated executive officers except that he was not serving as an executive officer as of December 31, 2009.

Executive Summary

        Who We Are    We are a global professional services firm with over 36,000 employees worldwide focused exclusively on risk advice and human capital consulting.

        Our Performance    In 2009 we delivered strong results despite a soft market and very challenging economic environment. Net income attributable to Aon stockholders from continuing operations increased 7% per share and total pretax margin increased 80 basis points.

        We continued to execute on our goals of strategically investing in long-term growth and managing expenses. We further aligned our core product portfolio around risk advice and human capital solutions through key sales and acquisitions. We are well positioned for future growth. Our world-class leadership in risk advice and human capital solutions drove these operational accomplishments.

        Against a multi-year backdrop of weak economic conditions globally, we view our longer range results as particularly impressive compared to the results of our industry peers and the benchmark S&P 500. Over the last three calendar years, our stock price return was a positive 8.5%, compared to the returns of our primary industry peers, including Marsh & McLennan Companies, Inc. (-28.0%) and Willis Group Holdings Limited (-33.6%), as well as the benchmark S&P 500 (-21.4%).

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        Our Compensation    We awarded our named executive officers for their dedication and achievement in 2009 with compensation directly linked to performance. Namely:

•

Aon's performance was the principal consideration for the bonuses awarded for 2009. Our CEO received an annual bonus of $3,000,000. This represents 100% of his 2009 target annual bonus. The remaining named executive officers (excluding Mr. Devine, who was ineligible for a bonus under his transition agreement) received, on average, 114% of their target annual bonuses.



•

No base salary adjustments were made for any named executive officer in 2009.



•

In early 2010, we settled performance share units granted to certain of our named executive officers in 2007. Those units were linked to 2007-2009 Aon performance. The units were settled, and shares of Common Stock were awarded, at 200% of target due to the Company's superior performance over that three-year period, as measured by cumulative adjusted Earnings Per Share ("EPS") from continuing operations. Our cumulative adjusted EPS for the period far exceeded the target.



•

In 2009 we granted similar performance share units to each of our named executive officers, the values of which are wholly dependent on Aon's performance (and, in the case of Messrs. Appel and Dail, a portion of which are dependent on their specific business unit performance) for 2009-2011.

        Extension of Our CEO's Contract and Reduction in his Change-in-Control Protection    During 2009, the Organization and Compensation Committee of Aon's Board of Directors (the "Committee") undertook an extensive review of our CEO's employment agreement and change-in-control protection. Aon entered into an amended and restated employment agreement with our CEO, extending the term of his employment by five years. The parties also entered into an amended and restated change-in-control agreement that significantly reduced the financial protection to be afforded to our CEO in the event of the termination of his employment in connection with a change-in-control of Aon. Among other changes, Aon's obligation to provide a tax-gross up payment was completely eliminated and our CEO further agreed to cap his cash and non-equity change-in-control benefits at a level that would be fully deductible by Aon.

        These and other compensation decisions are explained below.

        We believe our compensation program achieved its purpose in 2009.

Compensation Objectives and Process

Objectives of our Compensation Program

        We continue our quest to build, and continuously improve upon, the pre-eminent risk advice and human capital management firm in the world. We accomplish this by providing clients with world-class advice, solutions, innovation and execution. To achieve those objectives, we must be the destination of choice for the best talent. Our compensation program supports this vision and business strategy and fundamentally aligns the financial interests of our executives with those of our stockholders. This is true in both our short and long term programs. We strive to maximize stockholders' return primarily through growth in pre-tax income from continuing operations and adjusted EPS.

        We have a guiding philosophy with regard to our variable components of compensation, such as equity-based awards and annual bonuses. This philosophy dictates that our stockholders should always benefit first before any element of our executives' variable compensation is earned or paid. For

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example, under our annual bonus program a minimum level of corporate performance must be achieved before any bonus is payable. We carefully set that minimum each year. Even if the minimum level is achieved, the Committee reserves the sole discretion to exercise negative discretion to the extent it deems reasonable and prudent under the circumstances.

Use of Peer Group as a Market Check of Target Total Direct Compensation

        We set executive compensation at levels that are appropriate and competitive for global professional services firms within our market sector and the general industry marketplace. We review annual financial reports filed by our peer group. We also annually review the levels of executive officer compensation from global pay surveys provided by Hewitt Associates, Inc. For purposes of doing a market check, and not for purposes of doing true benchmarking to specific percentiles, we look at peer group compensation data. We compare the target total direct compensation (defined as base salary plus target bonus plus equity-based awards) for our named executive officers to the target total direct compensation for executives at selected peer companies where job descriptions are sufficiently similar to those of our executives to permit comparison.

        From January 1, 2009 until November 19, 2009, we utilized the same peer group as for 2008. That group consisted of the following companies:

        The peer group was originally selected in 2007 based upon three criteria which each one met at such time. They are global financial services industry companies or major consulting firms with whom we compete for executive talent or financial capital. With the exception of Willis Group Holdings Limited, which is a direct competitor, the peer group is generally comprised of companies that are, or were, between one-third and three times our size in revenues. Lastly, each company provides public disclosure regarding its executive compensation. This peer group represents seven financial industry Global Industry Classification Standard sub-sectors.

        Beginning mid-year 2009, we undertook a review of the composition of our peer group because such a review had not been conducted since 2007, and we wanted to ensure the peer group provides adequate benchmarks. The updated peer group members were selected based upon three criteria. They are global financial services industry companies or major consulting firms with whom we compete for executive talent or financial capital. With the exception of Willis Group Holdings Limited, which is a direct competitor, and Accenture, the peer group is generally comprised of companies that are between one-third and three times our size in average market capitalization (as calculated over most recent eight quarters to reduce volatility). Lastly, each company provides public disclosure regarding its executive compensation.

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        After discussions with its compensation consultant, the Committee approved the following peer group effective November 19, 2009, for use as a reference point in future compensation decisions:

        Companies continuing from the prior peer group are identified with a "C" and those newly added to this peer group are identified with an "N". This updated peer group represents eight financial industry Global Industry Classification Standard sub-sectors.

How We Determine Total Compensation

        As described above, market data is helpful in determining the competitive level of various elements of total direct compensation. However, for 2009 we did not generally have a specific market target for the total compensation to be delivered to each executive officer. We did not specifically target a certain percentile of total compensation or a particular component or subset of compensation with regard to the benchmark. We did not use a specific formula to set total compensation either in relation to market data, the relative mix of pay components or otherwise. A decision regarding one component of compensation had only an indirect link to decisions regarding other pay components.

        We do, from time to time, factor internal pay fairness considerations into compensation decisions. We describe herein those considerations regarding 2009 compensation decisions related to our named executive officers.

        We generally targeted a competitive level and mix of total direct compensation elements using market data simply as a reference point. This was not a mechanical process. Rather, we used our judgment and business experience. Overall, our intent was to manage the various elements of total compensation together so that the emphasis was on our variable components of pay, including long term equity awards and annual bonus that fluctuate based on the performance of Aon.

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        Performance-based compensation for 2009 of our named executive officers that remain on our executive management committee ranged from 71%-85% of total direct compensation, based on the grant date fair values of the long-term equity awards as valued in accordance with FASB ASC Topic 718, as follows:

(1)

The amounts in this column are the sums of: (A) the cash portion of the executive's bonus paid for 2009 performance plus (B) the grant date fair value, determined in accordance with FASB ASC Topic 718, of all performance-based equity awards granted to the executive during 2009.

(2)

The amounts in this column are the sums of: (A) the executive's 2009 base salary; (B) any other non-performance based direct compensation paid for 2009 service; and (C) the sum shown in Column B.

        This supplemental table is not required by the SEC. It is provided to demonstrate the link between performance and our executives' total direct compensation. Please refer to the Summary Compensation Table for Fiscal Years 2009, 2008 and 2007 for complete disclosure of the total compensation of our named executive officers, according to the SEC requirements.

        As the chart demonstrates, we strive to link our executive's pay to performance at greater rates for our more senior executives. Given the responsibility of our Chief Executive Officer to drive performance results for Aon, and his success in achieving those results as further described below, 85% of Mr. Case's total direct compensation for 2009 was linked directly to the performance of Aon.

Our Use of Tally Sheets

        In connection with our annual compensation review process, as described in the section of this proxy statement captioned "Board of Directors and Committees—Organization and Compensation Committee—Process of Determining Executive Compensation," the Committee reviews compensation tally sheets. The tally sheets assign dollar amounts to each component of the executive's compensation, including outstanding equity awards, current bonus and base salary, deferred compensation, employee benefits (including supplemental pension benefits), perquisites and potential change-in-control severance payments. The tally sheets are presented to the Committee to ensure it is aware of all compensation elements and the value of such elements.

Involvement of Mr. Case in the Compensation Process

        Each year the Committee approves all elements of compensation for Aon's named executive officers, other executive officers and any non-executive officers that report directly to our CEO. These decisions are typically made during the annual compensation review process conducted in the first calendar quarter. The Committee solicits certain recommendations from each of Mr. Case, our Global

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Head of Human Resources, and the independent members of Aon's Board who do not serve on the Committee.

        Mr. Case recommends to the Committee the equity award, annual bonus and base salary adjustment, if any, for the executive and non-executive officers who report directly to him. He has direct knowledge of the contributions made by those executive officers to Aon and he shares this knowledge with the Committee. Mr. Case supports his recommendations by providing performance evaluations for his direct reports.

        During the annual review process, Mr. Case and the Chairman of the Committee work together on Mr. Case's annual evaluation report, which summarizes Mr. Case's qualitative and quantitative performance. The report is considered in the determination of Mr. Case's compensation, along with other factors, including the Committee's own assessment of Mr. Case's performance, relevant market data and Aon's overall performance.

        The Committee has the ultimate authority to make compensation decisions. The Committee discusses its preliminary compensation decisions with the independent members of the Board who do not serve on the Committee. This process garners valuable input from those Directors regarding the executives' performance. The sharing of performance review information also aids the Directors in carrying out their succession planning responsibilities. After considering input from those Directors, the Committee makes its final determination.

        Mr. Case, together with our Global Head of Human Resources and our Chief Financial Officer, makes recommendations to the Committee relating to the corporate performance targets to be established under Aon's Shareholder-Approved Plan (as defined below under "Compensation Components and Analysis of 2009 Pay Decisions—Components of Total Compensation—Performance-Based Annual Bonus" and long-term equity incentive programs. The Committee reviews such recommendations with its independent executive compensation consultant and reserves the ultimate authority to set such targets and to determine whether such goals were achieved.

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Compensation Components and Analysis of 2009 Pay Decisions

Components of Total Compensation

        The table below describes our rationale for providing each of the key components of our compensation program and the factors that we consider in determining the amounts for a given year.

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Equity-Based Awards

        The Aon Stock Incentive Plan, as amended and restated in 2006 and as further amended from time to time (the "Stock Plan"), authorizes the grant of a variety of equity compensation awards. It authorizes the issuance of performance awards, stock options and restricted stock units—the three forms of equity compensation granted to our named executive officers in 2009.

        Performance Awards    In the first quarter of 2009, we granted performance share units to our executive officers, including each named executive officer, pursuant to our "Leadership Performance Program" ("LPP 4") and, with regard to Messrs. Appel and Dail only, under the newly-established "Aon Benfield Performance Program ("ABPP"). LPP 4 and ABPP are sub-plans of the Stock Plan. Both programs are intended to further strengthen the relationship between capital accumulation for our executives and long-term Aon financial performance and stockholder value.

        The performance share units awarded under both programs are payable in shares of Common Stock. The nominal value of the awards was determined and approved by the Committee. The number of target performance share units was calculated on the date of grant based on that day's closing price of Common Stock, in accordance with the terms of the Stock Plan. With regard to LPP 4, the number of target performance share units represented 80% of the nominal value of LPP 4 awards, with the remainder of such value granted in stock options (as described below). The ABPP grants were comprised exclusively of performance share units. Additional terms and conditions applicable to the performance share units, including the vesting provisions, are described in the section captioned "Potential Payments on Termination or Change-in-Control" contained in this proxy statement.

        LPP 4    Each of our named executive officers received an award under LPP 4. The units will be earned and settled in a range of 0% to 200% of target value based on performance results over a three-year performance period. The performance period began January 1, 2009, and will end on December 31, 2011. The performance results will be measured against the specified cumulative adjusted EPS target for 2009-2011. After adjustments, the cumulative target ranges from $8.85, below which no payout will occur, to $10.15, which would yield a payout of 200% of the target award value. A result of $9.25 in cumulative adjusted EPS would yield a payout, and settlement in shares of Common Stock, at 100% of target. This target represents a 4.5% increase over the adjusted baseline for a similar Leadership Performance Program established for the performance period 2008-2010 ("LPP 3"). The target represents an aggressive, yet achievable, performance goal.

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        ABPP    Messrs. Appel and Dail each have significant management responsibility for our Aon Benfield reinsurance brokerage unit. They are the only named executive officers to receive awards under the ABPP, which was created for such unit. The ABPP was established as a management integration tool following our acquisition of Benfield Group Limited ("Benfield"). It aligns the senior leaders from the Aon reinsurance brokerage unit with those senior leaders of the former Benfield reinsurance brokerage unit under a common performance-based long-term equity incentive program. The units will be settled in a range of 0% to 200% of target value based on performance results of the business unit over a three-year period. The performance period began January 1, 2009 and will end on December 31, 2011. The performance results will be measured against the specified cumulative adjusted three-year business unit pre-tax income for the performance period 2009-2011. When the ABPP was established, this target represented an aggressive, yet achievable, performance goal.

        Award Values and Features    In determining the individual awards under LPP 4 and ABPP, the Committee reviewed peer group market data, where available, for each executive to determine the appropriate long-term value of such awards. For example, the market data relevant to Mr. Case supported a larger award to him than the awards granted to the other named executive officers. The Committee decided to make smaller awards under LPP 4 to Messrs. Appel and Dail as compared to the awards to the other named executive officers given that both of these named executive officers were also granted awards under the ABPP. The Committee chose to grant these named executive officers awards under both programs, in lieu of an award under the ABPP only, because it wanted them to maintain significant focus on the success of Aon as a whole.

        The Committee determined that combining performance share units with stock options (as described below) under LPP 4, as was done in the three prior years, continues to provide the requisite incentive for the executives to achieve specific corporate performance goals that enhance the value of Aon's stock. The Committee determined that performance share units should be the exclusive form of award under the ABPP since most of the 80 recipients of such awards do not have Aon-wide management responsibility and, thus, their incentive should be tied to business unit performance.

        The Committee's selection under both programs of three-year performance periods and cumulative financial performance metrics provides the award recipients a reasonable period of time within which to achieve and sustain challenging long-term growth objectives.

        The Committee did not consider the number or value of equity-based awards previously granted to, or currently held by, our named executive officers in determining individual awards for 2009. Past awards were granted to induce performance in prior years. As a result, they were not viewed as significant in determining the 2009 awards to the named executive officers. The awards we granted under LPP 4 formed the fourth layer of consecutive three-year performance awards for certain of our named executive officers.

        Settlement of LPP 2 In early 2010, we determined the actual achievement under our second Leadership Performance Program, covering the performance period January 1, 2007 through December 31, 2009 ("LPP 2"). We settled the performance share units in shares of Common Stock. The cumulative adjusted EPS from continuing operations target ranged from $7.32, below which no payout was due to occur, to $8.52, which would have yielded a payout at 200% of the target award value. A result of $7.77 in cumulative adjusted EPS from continuing operations would have yielded a payout at 100% of target. This target represented an 11.3% increase over the adjusted baseline for a similar Leadership Performance Program established for the performance period 2006-2008 ("LPP 1").

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Our actual cumulative adjusted EPS from continuing operations for the three-year period were $8.93, resulting in a payout at 200% of target.

        The annual EPS from continuing operations results for LPP 2 include adjustments detailed by the plan and approved by the Committee. The adjustments allowed by the plan are specific to events or issues outside of management's control or significant one-time transactions that can affect EPS results. These include the following as detailed by the plan: change in accounting policy; gain/loss on disposition of assets or business; charge for goodwill impairment; extraordinary legal/regulatory settlements; effects of natural or man-made disasters (e.g. World Trade Center); hyperinflation (e.g. >15%); change in statutory tax rates/regulations; charges from Board-approved restructuring programs; results of discontinued operations held for sale after sale closing; other extraordinary, unusual or infrequently occurring items—as defined by GAAP. For each year of the performance period associated with LPP 2 adjustments to EPS from continuing operations were approved by the Committee because they were significant one-time transactions or outside management's control, as follows: charges associated with our restructuring plans; write-down of deferred taxes related to changes in future statutory tax rates and the amendment of the APB exemption status of Combined Insurance Company of America ("CICA") following sale announcement; gains on sale of land, businesses or discontinued operations; costs related to our acquisition of Benfield and sale of CICA; operating results of discontinued operations held for sale before sale closing; and pension curtailment gain/loss net of tax. Any such adjustment made in connection with a fiscal year's EPS will be reflected in the adjusted EPS from continuing operations for that year under each of the Leadership Performance Programs that cover such year. Each of our named executive officers other than Ms. Davies participated in LPP 2.

        We do not pay dividends or dividend equivalents on performance share units.

        LPP 5    On November 13, 2009, Aon entered into amended and restated employment and change-in-control agreements with Mr. Case, which agreements are described in the narrative section captioned "Employment Agreements and Other Compensation Arrangements" that follows the Grants of Plan-Based Awards in Fiscal Year 2009 table and in the section captioned "Potential Payments on Termination and Change-in-Control." As a reflection of Mr. Case's exceptional performance to date and his commitment to the extended term as set forth in the employment agreement, Aon provided him with an additional award valued at $10 million under the leadership performance program to be established for the performance period beginning January 1, 2010 and ending December 31, 2012 ("LPP 5"). The additional award will be earned on the same performance criteria and weightings as the regular award Aon awarded to him under LPP 5. None of the other named executive officers had a contractual entitlement to such an award.

        Stock Options    In the first quarter of 2009 in connection with LPP 4, we granted stock options to our named executive officers. Stock options represented 20% of the total value of LPP 4 awards, converted on a 3:1 basis using a Black-Scholes valuation. The stock options vest ratably over the three-year performance period. Additional terms and conditions applicable to the stock options are described in the section captioned "Potential Payments on Termination and Change-in-Control" contained in this proxy statement. We grant stock options as an additional way to motivate our executive officers. The stock options provide value to our executive officers only if our stock price increases.

        Restricted Stock Units    In the first quarter of 2009 we granted time-vested restricted stock units to each of our named executive officers other than Ms. Davies in connection with Aon's Incentive Stock Program. That program provides executives with a portion of their 2008 annual bonus in the form of

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restricted stock units. The primary goals of the program are to further focus the employees' attention on the longer-term performance of Aon as a whole, and to further promote employee retention and stock ownership.

        Also in the first quarter of 2009, we granted time-vested restricted stock units to Messrs. Appel and Devine in connection with the negotiation and execution of amendments to their employment agreements. The restricted stock units granted to Mr. Devine were forfeited and canceled as of November 18, 2009 pursuant to the transition agreement entered into between Aon and Mr. Devine as of such date, which agreement is described in this proxy statement in the narrative section captioned "Employment Agreement and Other Compensation Arrangements" that follows the Grants of Plan-Based Awards in Fiscal Year 2009 table.

        Each of the time-vested restricted stock units granted in connection with our Incentive Stock Program will vest ratably over a three-year period, and the time-vested restricted stock units granted to Messrs. Appel and Devine were to vest in 25% equal installments on the second through fifth anniversaries of the grant date. Vesting of all such restricted stock units is contingent on the executive's continued employment and other conditions as described in the section captioned "Potential Payments on Termination and Change-in-Control" contained in this proxy statement. The restricted stock units are settled in shares of Common Stock. We provide dividend equivalents on unvested restricted stock units in cash at the time actual dividends are declared for stockholders.

Performance-Based Annual Bonus

        Shareholder-Approved Plan    For purposes of ensuring the deductibility of bonuses for our named executive officers, Aon's stockholders have approved a plan pursuant to which we award annual bonuses that meet the criteria under Code Section 162(m) as "performance-based" pay. That plan is called our Senior Officer Incentive Compensation Plan, as amended and restated in 2006 (the "Shareholder-Approved Plan"). Pursuant to this plan, the Committee annually sets a Company-wide performance target (expressed in US dollars) and minimum achievement threshold (expressed as a percentage). If the metric is not achieved for any given year, no bonuses are payable under the Shareholder-Approved Plan.

        If the metric is achieved, the Shareholder-Approved Plan allows for the payment of deductible bonuses to our executive officers up to a cap. The cap is the lesser of $5 million or the maximum bonus otherwise established by the Committee for such executive officer. For 2009, the Committee established a cap of 300% of each named executive officer's target bonus. In the first quarter of 2009 we set bonus eligibility for our named executive officers as a target percentage of the executive's base salary at year-end. The target bonus for Mr. Case was subsequently increased from 150% to 200% of base salary pursuant to the amended and restated employment agreement between Aon and Mr. Case, dated November 13, 2009. The target bonuses and the applicable cap for each of our named executive officers are shown in the chart below under the heading "Determination of 2009 Bonuses."

        The Shareholder-Approved Plan does not provide guidelines or formulas for determining the actual bonuses payable to our executive officers once the metric is achieved. Rather, the Committee retains sole discretion for determining the actual bonuses payable. If the metric is achieved, the Shareholder-Approved Plan would allow the Committee to award a bonus equal to the cap or allow it to exercise negative discretion to award a lesser amount. As explained below, for 2009 we adopted the "Executive Committee Incentive Plan" as a set of guidelines for consideration by the Committee in determining actual bonuses to be paid if the metric under the Shareholder-Approved Plan was achieved.

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        2009 Metric Under Shareholder-Approved Plan    In the first quarter of 2009, the Committee determined that the 2009 Aon-wide performance target would be budgeted pre-tax income from continuing operations ("PTI") of $1,309 million, excluding restructuring charges and Benfield amortization expense. The Committee set the minimum achievement threshold at 85% of such target, or $1,113 million, as adjusted for extraordinary, unusual or infrequently occurring items. The Committee selected PTI as the measure to emphasize performance of Aon as a whole and directly link executives' awards to Aon's key business initiatives of delivering distinctive client value and achieving operational excellence. In combination with the performance targets established under each of LPP 1 through LPP 4 (i.e. cumulative EPS), we believe the targets balanced the executives' short and long-term perspective appropriately.

        The 2009 PTI target was set at a level substantially higher than Aon's 2008 actual adjusted PTI. We also considered the past performance of our peer group in setting the target. We believe that the 2009 target was achievable but challenging. We set the minimum threshold at 85% because we believed performance below that level would not create sufficient value for our stockholders and, therefore, should not result in bonus payments.

        2009 Performance    During the first quarter of 2010, the Committee determined that Aon's 2009 PTI, after permitted adjustments for extraordinary or unusual items, was $1,298 million, or 99.5% of target. This exceeded the minimum threshold established under the Shareholder-Approved Plan.

        Executive Committee Incentive Plan    In the first quarter of 2009, the Committee approved a set of guidelines for funding the total bonus pool under the Shareholder-Approved Plan for the 12 executives that comprised Aon's executive management committee. That group included each of the named executive officers. Mr. Devine was included in this group until his resignation from such committee effective November 18, 2009. The rationale for establishing funding guidelines was to provide executives with a clearer connection between the expected reward and the required performance, as well as for bonus accrual purposes.

        The funding formula was based on Aon's performance as measured by (i) achievement of budgeted PTI; (ii) growth in PTI in 2009 as compared to 2008; and (iii) organic revenue growth. To align with the Shareholder-Approved Plan, the formula provided that no funding was to occur unless Aon achieved the minimum threshold of 85% of the 2009 PTI target. If that minimum threshold was achieved, the formula provided for adjustments to funding to account for year over year growth in PTI, 2009 organic revenue growth and other permissible adjustments. After consideration of each of these factors, the resulting bonus pool funding level is determined, and the funding level can range from 0% to 300%.

        The budgeted 2009 PTI growth rate was 3.1% over 2008 PTI. The incentive pool funding was determined by the aggregate of each executive management committee member's individual targeted bonus multiplied by a percentage varying from 0% to 300% depending on Aon's actual growth in PTI as compared to 2008. The plan provided that the funding level could be further increased up to 20% or reduced by 10% depending on Aon's 2009 organic revenue growth. The actual 2009 PTI growth over 2008 PTI was 3%. In 2009 Aon experienced negative organic revenue growth of 1%. In the last half of 2009, the Committee approved two discretionary reductions to the funded pool of 10% each, while maintaining the pre-established performance targets, on account of the extraordinary market conditions. After application of the PTI growth metric, the organic revenue growth factor, and the two discretionary reductions, the resulting bonus pool was determined to be funded at 108.7%.

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        The actual size of the incentive pool equals the aggregate target bonuses multiplied by the percentage the pool was funded after application of the formula, as described above. For 2009, based on a funding level of 108.7%, the total incentive pool for members of the executive management committee was $14,848,955.

        Determination of 2009 Bonuses    Consistent with the Shareholder-Approved Plan, the bonus program for the executive management committee provides that the Committee has sole discretion to determine each executive's actual bonus amount as long as the corporate performance threshold was achieved. As explained above, for 2009 the threshold was achieved and, thus, the Committee had discretion to pay bonuses at the cap level or a lesser amount. It was anticipated that the Committee would consider in determining the executive's actual bonus, among other factors, the bonus for such executive at the pool funding level as well as executive's targeted bonus allocation. However, the Committee reserved, and for 2009 exercised, the discretion to set bonuses at levels higher or lower than the funded or targeted allocations.

        The Committee chose to exercise negative discretion with regard to each of the named executive officers. In other words, none of the named executive officers received their maximum bonus of the lesser of $5 million or 3 times their target bonus. In fact, each officer received only in the range of 100%—129% of their target bonus. The following table sets forth the target bonus, cap, funded bonus, and actual bonus paid to each of our named executive officers:

        The Committee's rationale in determining the actual bonus awards was as follows:

•

In order for an officer to get a bonus in excess of the target bonus, there needed to be certain exceptional factors.



•

With regard to Messrs. Case, Appel and McGill, the Committee determined it was appropriate to award a bonus at the officer's target bonus level based on Aon's solid overall performance as reported.



•

With regard to Ms. Davies, the Committee determined it was appropriate to award a bonus greater than the funded and target bonus levels taking into consideration (i) Aon's solid overall performance as reported and (ii) the Committee's assessment that Ms. Davies significantly strengthened the global financial function and team. The Committee did not utilize a formula for determining the amount of bonus to be awarded greater than the funded bonus level.



•

With regard to Mr. Dail, the Committee determined it was appropriate to award a bonus greater than Mr. Dail's funded and target bonus level taking into consideration (i) Aon's solid overall performance as reported and (ii) the Committee's assessment that Mr. Dail was highly effective on the Aon Benfield transition team, which team was responsible for the reported success of being ahead of schedule and below cost on the restructuring program. The Committee did not

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utilize a formula for determining the amount of bonus to be awarded greater than the funded bonus level.

        For 2009, generally all annual bonuses for executive officers are payable 65% in cash and 35% in restricted stock units.

Other Policies and Practices

Internal Pay Fairness Considerations for Other Executive Officers

        In determining an executive officer's target bonus or long-term performance award value, the Committee will, from time to time, consider internal pay fairness factors. However, the Committee has not adopted a broad internal pay equity policy pursuant to which each executive officer's compensation, or one or more components thereof, is tied to or targeted against the compensation of other executive officers.

Base Salary

        Base salary is a fixed component of compensation and is initially set at a level based primarily upon the executive's job scope or level of responsibility. The base salaries of our senior-most executives are adjusted rarely, as our general practice is to increase other components of pay based upon superior performance. However, base salaries may be adjusted to, among other things, recognize a significant change in job function or responsibilities or to bring the fixed component of an executive's total compensation in line with his or her peers at Aon or the industry generally.

        No base salary adjustments were made for our named executive officers during 2009.

Personal Benefits and Executive Benefits

Personal Benefits

        During 2009 we provided personal benefits to our named executive officers as a component of their total compensation. We do not emphasize personal benefits in our executive compensation practices. With regard to certain forms of personal benefits, such as tax equalization payments and expatriate allowances, that are typically provided by our competitors to their executives when asked to work in locations other than their home countries, we feel we must provide these personal benefits to our executives who work outside of their home countries to attract and retain the best talent.

Executive Benefits

        In addition to Aon's broad-based employee benefit programs that are available to Aon employees generally (such as health coverage, 401(k) salary deferrals, etc.), each of our named executive officers is eligible to participate in a deferred compensation program, a supplemental pension program and a supplemental savings plan. In addition, Aon provides an executive health screening program available to all members of Aon's executive management committee, including the named executive officers. Additional information regarding certain of our executive benefits is set forth in the table captioned Pension Benefits in Fiscal 2009 contained in this proxy statement.

Deferred Compensation Program

        We maintain a Deferred Compensation Plan ("DCP") that allows certain employees, including our named executive officers, to defer receipt of their salary and/or annual incentive payments into

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Common Stock or accounts that mirror several different investment funds. Participants may defer up to 75% of salary and up to 100% of their annual bonus until the date(s) they have specified in accordance with the DCP's distribution provisions. Under the DCP we do not credit above-market interest on deferred compensation, as that term is defined in the U.S. Internal Revenue Code of 1986, as amended (the "Internal Revenue Code").

        We are not required to make any contributions to the DCP. We do not fund the DCP, and participants have an unsecured contractual commitment by Aon to pay the amounts due under the DCP. When such payments are due, the distributions will be made from our general assets. We have purchased corporate-owned life insurance to offset a portion of this liability.

U.S. Supplemental Pension Program

        The supplemental pension program is a non-qualified, deferred compensation plan that provided eligible U.S. employees, including executives hired on or before December 31, 2003, with the opportunity to receive benefits that could not be earned under the qualified pension plan because of tax limitations and the specific provisions of such plan. Effective April 1, 2009, benefit accruals for all participants were frozen and no addition benefits will accrue after such date.

U.S. Supplemental Savings Plan

        The Supplemental Savings Plan is a non-qualified, deferred compensation plan that provides eligible employees, including executives, with the opportunity to receive contributions that could not be credited under the Savings Plan because of tax limitations and the specific provisions of such plan.

Supplemental Retirement Program for Mr. McGill

        Mr. McGill has been an expatriate from the U.K. on assignment in the U.S. since 2006. While on assignment, he participates in our standard retirement programs available to eligible employees generally, but full participation in our U.K. defined contribution scheme while in the U.S is not viable. In order to eliminate any lost benefits that might otherwise result from his assignment, our U.K. subsidiary that employs Mr. McGill, Aon Limited, had agreed that upon his retirement or return to work in the U.K., it would compare contributions that might otherwise have been paid into the U.K. scheme but were lost, recognizing his U.S.-based compensation and service, and pay those contributions through a supplemental retirement program. The parties amended this arrangement such that, effective July 1, 2009, the Company's obligation to make contributions to Mr. McGill's personal pension plan in the U.K. will cease. In addition, effective January 1, 2010, the Company will be obligated to make an annual cash lump sum payment in partial replacement of the personal pension benefits referenced above. Such amount will be in the US dollar equivalent of GB 45,000 pounds per annum. The Committee approved such changes in order to increase tax efficiency.

Post-Termination Compensation

        We believe that the provision of change-in-control severance agreements and other transitional compensation arrangements are critical to recruit talented employees and to secure the continued employment and dedication of our existing employees. All or nearly all of the companies with which we compete for talent have similar arrangements in place for their senior executives. While we consider these agreements to be necessary, the terms of these agreements are not considered as part of the compensation strategy when the Committee annually determines the compensation for the named executive officers. Additional information about post-termination compensation is set forth in the

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section captioned "Potential Payments on Termination or Change-in-Control" contained in this proxy statement.

Severance Agreements regarding Change-in-Control

        Beginning in 2005, we entered into change-in-control severance agreements with certain of our key executive officers, including each of our named executive officers. The agreements are intended to secure the continued service, and to ensure the dedication and objectivity of these executives in the event of an actual or threatened change-in-control of Aon. The agreements provide that covered executives receive certain severance benefits upon qualifying terminations of employment in connection with or within two years following a change-in-control of Aon. Thus, the agreements require a "double trigger"—a qualifying change-in-control of Aon and a qualifying termination of the executive's employment—in order for severance benefits to become payable. As adopted in 2005, the agreements also provide for excise tax gross-up protection in the event the executive becomes subject to tax under Section 280G of the Code in connection with such double trigger.

        Effective November 13, 2009, our Board of Directors approved an amended and restated change-in-control agreement for Mr. Case. The Committee had recommended the changes to the Board to better align with market practice. The Committee determined that while the agreement generally was consistent with prevailing norms, the elimination of the excise tax gross-up protection and a reduction in the potential severance payments and benefits could, and should, be made without jeopardizing the retentive value of the agreement. The principal modifications were: (1) the complete elimination of Aon's obligation to provide a gross-up to Mr. Case in connection with excise taxes imposed by Section 4999 of the Internal Revenue Code of 1986, as amended (the "Code"); and (2) capping Mr. Case's cash and non-equity award payments to the "safe harbor" amount under Code Section 280G, such that the cash and non-equity payments are not deemed to be "excess parachute payments" and are deductible. Additional information regarding the change-in-control agreements for Mr. Case and the other named executive officers is set forth in the section captioned "Potential Payments on Termination or Change-in-Control" contained in this proxy statement.

Amendment of Mr. McGill's employment arrangement

        In the third quarter of 2009, Aon Limited and Mr. McGill amended their employment arrangement to extend the duration of his overseas assignment through January 1, 2013. Pursuant to the amendment, Mr. McGill's base salary was fixed in U.S. dollars to alleviate the administrative burdens related to significant shifts in the foreign exchange rate between the U.S. and the U.K. Effective January 1, 2010, Mr. McGill will no longer be eligible for a tax gross-up on his annual expatriate allowance and he will no longer be eligible to participate in Aon's tax equalization policy for expatriates. Additional changes to his pension arrangement are described below in the table captioned Pension Benefits in Fiscal 2009 and the accompanying narrative, and under the caption McGill Agreement in the narrative accompanying the Nonqualified Deferred Compensation in Fiscal 2009 Table.

Transition Agreement with Mr. Devine

        In the fourth quarter of 2009 we entered into a transition agreement with Mr. Devine. The agreement is described in this proxy statement in the narrative section captioned "Employment Agreement and Other Compensation Arrangements" that follows the Grants of Plan-Based Awards in Fiscal Year 2009 table. As a result of his resignation, and pursuant to the transition agreement,

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Mr. Devine waived the right to receive change-in-control coverage under our standard change-in-control agreement. In approving the transition agreement with Mr. Devine, the Committee considered Mr. Devine's overall contributions to Aon during his four years of service and his commitment to develop a charitable organization to foster the link the between sports and the betterment of disadvantaged children, a mission Aon also supports through its Manchester United sponsorship.

Severance Benefits Pursuant to Employment Agreements

        We have entered into agreements with certain executive officers that provide for post-employment severance benefits and transitional compensation if the officer's employment terminates for a qualifying event or circumstance unrelated to a change-in-control of Aon, such as being terminated without "cause" as such term is defined in the operative agreement. Additional information regarding such post-employment severance or transitional compensation for Mr. Case and the other named executive officers is set forth in the section captioned "Potential Payments on Termination or Change-in-Control" contained in this proxy statement.

Practices Regarding the Grant of Equity Awards

        We typically grant stock options and other forms of equity awards at regularly scheduled meetings of the Committee. Equity awards granted to Mr. Case are typically awarded at regularly scheduled meetings of our Board of Directors by the independent members of the Board. During 2009, all equity awards granted to our named executive officers were awarded by the Committee (or, with regard to Mr. Case, the independent members of the Board) at regularly scheduled meetings or special meetings and valued at such dates. We do not have a policy or practice with respect to coordinating grant dates for equity awards with the release of material non-public information.

Recovery of Prior Performance-Based Equity Awards or Cash Bonuses

        We do not have a policy with respect to adjustment or recovery of equity awards or cash payments if relevant Aon performance measures upon which such awards or payments were based are restated or otherwise adjusted in a manner that would have resulted in a reduced award or payment. Under those circumstances, the Committee would evaluate whether recovery was appropriate based upon the facts and circumstances surrounding the restatement or adjustment.

Stock Ownership Guidelines

        In 2006 we adopted stock ownership guidelines, which were revised in July 2008, applicable to Aon's Chief Executive Officer, Chief Financial Officer and members of Aon's executive management committee. The guidelines are designed to increase executives' equity stakes in Aon and to align executives' interests more closely with those of our stockholders. The guidelines provide that the Chief Executive Officer should attain an investment position in Common Stock equal to four times annual base salary and each other executive officer, including the remainder of our named executive officers, should attain an investment position in Common Stock equal to two times annual base salary. These investment levels should generally be achieved within five years. Shares of Common Stock counted toward these guidelines include: any shares owned outright; shares obtained and held upon the exercise of stock options or the vesting of restricted stock units; shares held through the Savings Plan; shares held through our employee stock purchase plan; "phantom" stock held under the DCP, if such

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distribution is paid in shares of Common Stock; and "phantom" stock held under the Supplemental Savings Plan.

Role of the Compensation Consultant

        The Committee has retained Frederic W. Cook & Co., Inc. as its independent executive compensation consultant. The role of the compensation consultant is described in this proxy statement under "Board of Directors and Committees—Organization and Compensation Committee—Relationship with Executive Compensation Consultant."

Impact of Tax Treatment

        Section 162(m) of the Internal Revenue Code provides that a public corporation may take a deduction for compensation in excess of $1 million for its chief executive officer and certain of its other highest paid executive officers only if specific and detailed criteria are satisfied. Other sections of the Internal Revenue Code could result in adverse tax consequences to Aon and/or the executive related to certain change-in-control payments or the receipt of deferred compensation. Among other factors, we consider the company deductibility of compensation paid to the named executive officers.

        We recognize that the deductibility of some types of compensation payments can depend upon the timing of an executive's vesting or exercise of previously granted rights. The deductibility of compensation is also affected by interpretations of and changes in applicable tax laws and regulations as well as other factors beyond our control. Also, in some circumstances, factors other than tax deductibility are more important in determining the forms and levels of executive compensation most appropriate and in the best interests of Aon and its stockholders.

        For these and other reasons, we have determined that we will make a reasonable effort to administer Aon's compensation program in a tax-effective manner; however, we have from time to time approved elements of compensation for certain executive officers that are not fully deductible or result in adverse tax consequences to the executive and we reserve the right to do so in the future, when appropriate. For instance, we cannot deduct the portion of base salary in excess of $1 million that we paid to certain executive officers.

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Historical Compensation of Executive Officers

        The executive compensation disclosure contained in this section reflects compensation information for the years ended December 31, 2009, December 31, 2008 and December 31, 2007. The following Summary Compensation Table contains compensation information for: (1) Mr. Case, who served as our Chief Executive Officer during 2009, (2) Ms. Davies, who served as our Chief Financial Officer during 2009, (3) Messrs. McGill, Appel and Dail, who were our three other most highly compensated executive officers serving as of December 31, 2009, and (4) Mr. Devine, who served as our Executive Vice President and President—Aon Risk Services through November 18, 2009, and who would have been among our most highly compensated executive officers except that he was not serving as an executive officer as of December 31, 2009. We refer to these six individuals in this proxy statement as our "named executive officers." No compensation information is provided for Ms. Davies or Mr. Devine for 2007 as they each became a named executive officer in 2008 and no compensation information is provided for Mr. Dail for 2007 or 2008 as he became a named executive officer in 2009.

Summary Compensation Table for Fiscal Years 2009, 2008 and 2007

(1)

For purposes of this table, the amounts set forth with respect to Mr. McGill in column (c) for all of 2007 and 2008, and for a portion of 2009, have been converted from British pounds sterling to U.S. dollars based on the conversion rate in effect at the time of each of Mr. McGill's monthly salary payments. During 2009, Mr. McGill was paid in British pounds sterling through July 31, 2009 and in U.S. dollars for the remainder of 2009.

(2)

Except for Ms. Davies in 2008, none of the named executive officers received any payments for 2009, 2008 or 2007 that would be characterized as "bonus" payments under the rules of the SEC. As the amount of the

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2008 bonus paid to Ms. Davies was guaranteed pursuant to her employment agreement, this payment is reported in column (d) as a "bonus" payment. See the section captioned "Employment Agreements and Other Compensation Arrangements" following the Grants of Plan-Based Awards in Fiscal Year 2009 table for more information on this agreement. Cash amounts earned by the named executive officers in 2009, 2008 and 2007 as short-term incentive compensation are shown in column (g) "Non-Equity Incentive Plan Compensation."

(3)

The amounts shown in column (e) reflect the aggregate grant date fair value computed in accordance with FASB ASC Topic 718 for grants made in 2009, 2008 and 2007, respectively, of restricted stock unit awards and performance share unit awards granted to the named executive officers pursuant to the Aon Stock Plan, and its sub-plans, specifically, the Incentive Stock Program or "ISP," the Leadership Performance Program or "LPP" and the Aon Benfield Performance Plan or "ABPP," disregarding adjustments for forfeiture assumptions, and do not reflect amounts actually paid to, or realized by, the named executive officers in 2009, 2008 or 2007 or prior years. The ABPP was adopted during 2009 and, therefore, no grants under it are reflected in the table for 2008 or 2007. Of the named executive officers, only Messrs. Appel and Dail participate in the ABPP. Reflected in column (e) for each of 2009, 2008 and 2007 is the grant date fair value of the LPP grants and, if applicable, ABPP grants, made on March 19, 2009 for the LPP (for each of the named executive officers other than Mr. Case), March 20, 2009 for the LPP (for Mr. Case only), April 22, 2009 for the ABPP (for Messrs. Appel and Dail only), March 13, 2008 for the LPP, March 15, 2007 for the LPP (for each of the named executive officers other than Mr. Case), and March 16, 2007 for the LPP (for Mr. Case only), respectively, calculated in accordance with FASB ASC Topic 718 based on the probable outcome of the performance conditions at the time of grant with respect to performance share unit awards granted pursuant to the LPP and ABPP, which is the dollar value attributed to the original share amount of the award multiplied by 100% for 2009, 100% for 2008 and 100% for 2007 for the LPP and 150% for 2009 for the ABPP.

Set forth below are the grant date fair values of the performance share unit awards granted under the LPP and ABPP calculated assuming (i) the probable outcome of the performance conditions for each program as discussed in the prior paragraph, which amount is included in column (e) of this Summary Compensation Table and (ii) achievement of the maximum levels of performance (which is the dollar value attributed to the original award multiplied by 200% for each of 2009, 2008 and 2007 for the LPP and 200% for 2009 for the ABPP). Messrs. Appel and Dail were the only named executive officers who were granted performance share unit awards under the ABPP in 2009.

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