SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
Under the Securities Exchange Act of 1934
(Initial Filing)*
Aon Corporation
________________________________________________________
(Name of Issuer)
Common Stock
_______________________________________________________
(Title of Class and Securities)
037389103
_______________________________________________________
(CUSIP Number of Class of Securities)
Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:
/X/ Rule 13d-1(b)
/ / Rule 13d-1(c)
/ / Rule 13d-1(d)
* The remainder of this cover page shall be filled out for a
reporting person's initial filing on this form with respect to the
subject class of securities, and for any subsequent amendment
containing information which would alter the disclosures provided
in a prior page.
The information required in the remainder of this cover page shall
not be deemed to be "filed" for the purpose of Section 18 of the
Securities Exchange Act of 1934 ("Act") or otherwise subject to the
liabilities of that section of the Act but shall be subject to all
other provisions of the Act (however, see the Notes).
(Continued on following page(s))
CUSIP No. 037389103 13G
_____________________________________________________________________________
(1) NAMES OF REPORTING PERSONS
Southeastern Asset Management, Inc. I.D. No. 62-0951781
_____________________________________________________________________________
(2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:
(a)
(b) X
_____________________________________________________________________________
(3) SEC USE ONLY
_____________________________________________________________________________
(4) CITIZENSHIP OR PLACE OF ORGANIZATION
Tennessee
_____________________________________________________________________________
:(5) SOLE VOTING POWER
: (Discretionary Accounts)
NUMBER OF SHARES BENEFICIALLY : 6,156,918 shares
OWNED BY EACH REPORTING PERSON __________________________________________
WITH :(6) SHARED OR NO VOTING POWER
6,410,200 shares (Shared)
1,244,000 shares (No Vote)
__________________________________________
:(7) SOLE DISPOSITIVE POWER
(Discretionary Accounts)
: 7,400,918 shares
__________________________________________
:(8) SHARED DISPOSITIVE POWER
: 6,410,200 shares (Shared)
0 shares (None)
_____________________________________________________________________________
(9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
13,811,118 shares
_____________________________________________________________________________
(10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES
CERTAIN SHARES
_____________________________________________________________________________
(11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
5.0 %
_____________________________________________________________________________
(12) TYPE OF REPORTING PERSON
IA
_____________________________________________________________________________
CUSIP No. 037389103 13G
_____________________________________________________________________________
(1) NAMES OF REPORTING PERSONS
O. Mason Hawkins I.D. No. XXX-XX-XXXX
_____________________________________________________________________________
(2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP:
(a)
(b) X
_____________________________________________________________________________
(3) SEC USE ONLY
_____________________________________________________________________________
(4) CITIZENSHIP OR PLACE OF ORGANIZATION
Citizen of United States
_____________________________________________________________________________
:(5) SOLE VOTING POWER
: (Discretionary Accounts)
NUMBER OF SHARES BENEFICIALLY : None
OWNED BY EACH REPORTING PERSON __________________________________________
WITH :(6) SHARED VOTING POWER
: None
__________________________________________
:(7) SOLE DISPOSITIVE POWER
: None
__________________________________________
:(8) SHARED DISPOSITIVE POWER
: None
_____________________________________________________________________________
(9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
None (See Item 3)
_____________________________________________________________________________
(10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 9 EXCLUDES
CERTAIN SHARES
_____________________________________________________________________________
(11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
0.0%
_____________________________________________________________________________
(12) TYPE OF REPORTING PERSON
IN
_____________________________________________________________________________
Item 1.
(a). Name of Issuer: Aon Corporation
(b). Address of Issuer's Principal Executive Offices:
200 E. Randolph Street
Chicago, Illinois 60601
Item 2.
(a) and (b). Names and Principal Business Addresses of Persons
Filing:
(1) Southeastern Asset Management, Inc.
6410 Poplar Ave., Suite 900
Memphis, TN 38119
(2) Mr. O. Mason Hawkins
Chairman of the Board and C.E.O.
Southeastern Asset Management, Inc.
6410 Poplar Ave., Suite 900
Memphis, TN 38119
(c). Citizenship:
Southeastern Asset Management, Inc. - A Tennessee corporation
Mr. O. Mason Hawkins - U.S. Citizen
(d). Title of Class of Securities: Common stock (the
"Securities").
(e). Cusip Number: 037389103
Item 3. If this statement is filed pursuant to Rules 13d-1 (b) or
13d-2 (b), check whether the person filing is a:
(e) Investment Adviser registered under Section 203 of the
Investment Advisers Act of 1940. This statement is being filed
by Southeastern Asset Management, Inc. as a registered investment
adviser. All of the securities covered by this report are owned
legally by Southeastern's investment advisory clients and none
are owned directly or indirectly by Southeastern. As permitted
by Rule 13d-4, the filing of this statement shall not be construed
as an admission that Southeastern Asset Management, Inc. is the
beneficial owner of any of the securities covered by this statement.
(g) Parent Holding Company. This statement is also being filed by
Mr. O. Mason Hawkins, Chairman of the Board and C.E.O. of
Southeastern Asset Management, Inc. in the event he could be
deemed to be a controlling person of that firm as the result of
his official positions with or ownership of its voting securities.
The existence of such control is expressly disclaimed. Mr. Hawkins
does not own directly or indirectly any securities covered by
this statement for his own account. As permitted by Rule 13d-4,
the filing of this statement shall not be construed as an admission
that Mr. Hawkins is the beneficial owner of any of the securities
covered by this statement.
Item 4. Ownership:
(a). Amount Beneficially Owned: (At 12/31/09)
13,811,118 shares
(b). Percent of Class:
5.0 %
Above percentage is based on 273,922,587 shares of common
stock outstanding.
(c). Number of shares as to which such person has:
(i). sole power to vote or to direct the vote:
6,156,918 shares
(ii). shared or no power to vote or to direct the vote:
Shared - 6,410,200 shares.
Securities owned by the following series of Longleaf
Partners Funds Trust, an open-end management
investment company registered under the Investment
Company Act of 1940, as follows:
Longleaf Partners Fund - 6,410,200
No Power to Vote - 1,244,000 shares.
(iii). sole power to dispose or to direct the disposition
of:
7,400,918 shares
(iv). shared or no power to dispose or to direct the
disposition of:
Shared - 6,410,200 shares
Securities owned by the following series of Longleaf
Partners Funds Trust, an open-end management
investment company registered under the Investment
Company Act of 1940, as follows:
Longleaf Partners Fund - 6,410,200
No Power - 0 shares.
Item 5. Ownership of Five Percent or Less of a Class: N/A
Item 6. Ownership of More Than Five Percent on Behalf of Another
Person: N/A
Item 7. Identification and Classification of the Subsidiary Which
Acquired the Security Being Reported on By the Parent
Holding Company: N/A
Item 8. Identification and Classification of Members of the Group:
N/A
Item 9. Notice of Dissolution of Group: N/A
Item 10. Certification:
By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired in the
ordinary course of business and were not acquired for the purpose
and do not have the effect of changing or influencing the control
of the issuer of such securities and were not acquired in
connection with or as a participant in any transaction having such
purposes or effect.
Signatures
After reasonable inquiry and to the best of the knowledge and
belief of the undersigned, the undersigned certifies that the
information set forth in this statement is true, complete, and
correct.
Dated: February 5, 2010
Southeastern Asset Management, Inc.
By /s/ Andrew R. McCarroll
_______________________________________________
Andrew R. McCarroll
Vice President and General Counsel
O. Mason Hawkins, Individually
/s/ O. Mason Hawkins
_______________________________________________
Joint Filing Agreement
In accordance with Rule 13d-1(k) under the Securities Exchange Act
of 1934, the persons or entities named below agree to the joint
filing on behalf of each of them of this Schedule 13G with respect
to the Securities of the Issuer and further agree that this joint
filing agreement be included as an exhibit to this Schedule 13G. In
evidence thereof, the undersigned hereby execute this Agreement as
of February 5, 2010.
Southeastern Asset Management, Inc.
By /s/ Andrew R. McCarroll
______________________________________________
Andrew R. McCarroll
Vice President and General Counsel
O. Mason Hawkins, Individually
/s/ O. Mason Hawkins
_______________________________________________
1
AON13G.doc
SCHEDULE 13G - Aon Corporation ("Issuer")
Initial Filing
2
AON13G.doc