POWER OF ATTORNEY

I, Andrew J. McKenna ("Grantor"), hereby confirm, constitute and
appoint each of Ram Padmanabhan, Matthew M. Rice and Michele Welsh,
or any of them signing singly, and with full power of substitution,
as the true and lawful attorney-in-fact of Grantor to:

1.       prepare, execute in Grantor's name and on Grantor's
behalf, and submit to the United States Securities and Exchange
Commission (the "SEC") a Form ID, including amendments thereto,
and any other documents necessary or appropriate to obtain codes
and passwords enabling the undersigned to make electronic filings
with the SEC of reports required by Section 16(a) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act")
or any rule or regulation promulgated by the SEC;

2.       execute for and on behalf of Grantor, in Grantor's
capacity as an officer, director or greater than ten percent
stockholder of Aon Corporation (the "Company"), Forms 3, 4 and 5,
including but not limited to any amendments thereto, in accordance
with Section 16(a) of the Exchange Act, and the rules promulgated
thereunder, which may be necessary or desirable as a result of
Grantor's ownership of or transaction in securities of the
Company; and

3.     do and perform any and all acts for and on behalf of
Grantor which may be necessary or desirable to complete and
execute any such Form 3, 4 or 5 or any amendments thereto, and
timely file such form with the SEC and any other stock exchange or
similar authority.

Grantor hereby grants to each such attorney-in-fact full power and
authority to do and perform any and every act and thing whatsoever
requisite, necessary or proper to be done in the exercise of any
of the rights and powers herein granted, as fully to all intents
and purposes as the undersigned might or could do if personally
present, with full power of substitution or revocation, hereby
ratifying and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully do or
cause to be done by virtue of this power of attorney and the
rights and powers herein granted.  Grantor acknowledges that the
foregoing attorneys-in-fact, in serving in such capacity at the
request of Grantor, are not assuming, nor is the Company assuming,
any of Grantor's responsibilities to comply with Section 16 of the
Exchange Act.

This Power of Attorney shall be effective on the date set forth
below and shall continue in full force and effect until the date
on which Grantor shall cease to be subject to Section 16 of the
Exchange Act and the rules promulgated thereunder or until such
earlier date on which written notification executed by Grantor is
filed with the SEC expressly revoking this Power of Attorney.

Grantor hereby revokes all prior powers of attorney that are in
effect and filed with the SEC.


IN WITNESS WHEREOF, Grantor has caused this Power of Attorney to
be executed as of this 16th day of September, 2011.


Signature:     /s/ Andrew J. McKenna
                  Andrew J. McKenna