Exhibit 24

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Gregory C. Case

Gregory C. Case

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Fulvio Conti

Fulvio Conti

2

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Cheryl A. Francis

Cheryl A. Francis

3

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Judson C. Green

Judson C. Green

4

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Edgar D. Jannotta

Edgar D. Jannotta

5

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Jan Kalff

Jan Kalff

6

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Lester B. Knight

Lester B. Knight

7

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ J. Michael Losh

J. Michael Losh

8

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ R. Eden Martin

R. Eden Martin

9

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Andrew J. McKenna

Andrew J. McKenna

10

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Robert S. Morrison

Robert S. Morrison

11

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Richard B. Myers

Richard B. Myers

12

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Richard C. Notebaert

Richard C. Notebaert

13

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ John W. Rogers, Jr.

John W. Rogers, Jr.

14

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Gloria Santona

Gloria Santona

15

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned, being a director or officer of Aon Corporation, a Delaware corporation (the “Company”), hereby severally constitutes and appoints Gregory C. Case, Christa Davies and Jennifer L. Kraft and each of them, with full power to act without the others, his or her true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned’s name, place and stead, in any and all capacities, to sign a Registration Statement on Form S-8 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the offering from time to time by the Company of shares of common stock pursuant to the Aon Corporation 2011 Incentive Plan and the Aon Corporation 2011 Employee Stock Purchase Plan, any and all amendments and supplements thereto or to the prospectus contained therein (including all post-effective amendments) and any additional registration statement pursuant to Rule 462(b) of the Securities Act and any and all amendments thereto, and to file the same, with all exhibits thereto, and all other documents in connection therewith, with the Securities and Exchange Commission, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done to the end that such Registration Statement or additional registration statement comply with the Securities Act, and the applicable rules and regulations adopted or issued pursuant thereto, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

IN WITNESS WHEREOF, the undersigned has signed his or her name effective as of June 8, 2011.

/s/ Carolyn Y. Woo

Carolyn Y. Woo

16