POWER OF ATTORNEY
I, Gregory J. Besio ('Grantor'), hereby confirm,
constitute and appoint each of Jennifer L. Kraft and
Richard E. Barry, or either 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 stock 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 19th day of July,
2007.


Signature:   /s/ Gregory J. Besio
		Gregory J. Besio