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


                                 SCHEDULE 13G


                  Under the Securities Exchange Act of 1934*


                                AON Corporation
--------------------------------------------------------------------------------
                               (Name of Issuer)

                                 Common Stock
--------------------------------------------------------------------------------
                        (Title of Class of Securities)

                                   037389103
                        ------------------------------
                                (CUSIP Number)

                               December 31, 2001
--------------------------------------------------------------------------------
            (Date of Event Which Requires Filing of this Statement)


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 cover 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).

                               Page 1 of 4 Pages



  -------------------
  CUSIP NO. 037389103                13G
  -------------------


------------------------------------------------------------------------------
      NAMES OF REPORTING PERSONS.
 1    I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS

        Barrow, Hanley, Mewhinney & Strauss, Inc.
        752403190

------------------------------------------------------------------------------
      CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions)
 2                                                              (a) [_]
                                                                (b) [_]

------------------------------------------------------------------------------
      SEC USE ONLY
 3


------------------------------------------------------------------------------
      CITIZENSHIP OR PLACE OF ORGANIZATION
 4
        A Nevada corporation

------------------------------------------------------------------------------
                          SOLE VOTING POWER
                     5
     NUMBER OF                      shares

      SHARES       -----------------------------------------------------------
                          SHARED VOTING POWER
   BENEFICIALLY      6
                                     shares
     OWNED BY
                   -----------------------------------------------------------
       EACH               SOLE DISPOSITIVE POWER
                     7
    REPORTING                        shares

      PERSON       -----------------------------------------------------------
                          SHARED DISPOSITIVE POWER
       WITH          8
                          ----
------------------------------------------------------------------------------
      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 9                 shares

------------------------------------------------------------------------------
      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
10    (See Instructions)
                                                                    [_]

------------------------------------------------------------------------------
      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
11


------------------------------------------------------------------------------
      TYPE OF REPORTING PERSON (See Instructions)
12          IA


------------------------------------------------------------------------------

                               Page 2 of 4 Pages



     SCHEDULE 13G
     ------------

Item 1(a) Name of Issuer:
                   AON Corporation

     1(b) Address of Issuer's Principal Executive Offices:
                   123 North Wacker Drive
                   Chicago, IL 60606

Item 2(a) Name of Person Filing:
                   Barrow, Hanley, Mewhinney & Strauss, Inc.

     2(b) Address of Principal Business Office or, if none, Residence:
                   One McKinney Plaza
                   3232 McKinney Avenue, 15th Floor
                   Dallas, TX 75204-2429

     2(c) Citizenship:
                   A Nevada corporation

     2(d) Title of Class of Securities:
                   Common Stock

     2(e) CUSIP Number:
                   037389103

Item 3.   If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b):
                   The reporting person is an Investment Adviser registered
                   under Section 203 of the Investment Advisers Act of 1940.

Item 4.   Ownership:

     4(a) Amount beneficially owned:
                              shares

     4(b) Percent of class:


     4(c) Number of shares as to which the person has:

          (i)   Sole power to vote or to direct the vote:
                             shares

          (ii)  Shared power to vote or to direct the vote:
                              shares

          (iii) Sole power to dispose or to direct the disposition of:
                              shares

          (iv)  Shared power to dispose or to direct the disposition of:
                   ----

Item 5.   Ownership of Five Percent or Less of a Class:
                   If this statement is being filed to report the fact that as
                   of the date hereof the reporting person has ceased to be the
                   beneficial owner of more than five percent of the class of
                   securities, check the following: [X]

                               Page 3 of 4 Pages



Item 6.   Ownership of More than Five Percent on Behalf of Another Person:

                   The right to receive or the power to direct the receipt of
                   dividends from, or the proceeds from the sale of, the common
                   stock is held by certain clients of the reporting person,
                   none of which has such right or power with respect to five
                   percent or more of the common stock.

Item 7.   Identification and Classification of the Subsidiary which Acquired the
          Security Being Reported on by the Parent Holding Company:
                   Not Applicable.

Item 8.   Identification and Classification of Members of the Group:
                   Not Applicable.

Item 9.   Notice of Dissolution of a Group:
                   Not Applicable.

Item 10.  Certification:

                   By signing below the undersigned certifies that, to the best
                   of its knowledge and belief, the securities referred to above
                   were acquired in the ordinary course of business and were not
                   acquired for the purpose of 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 purpose or effect.

After reasonable inquiry and to the best of its knowledge and belief, the
undersigned certifies that the information set forth in this statement is true,
complete and correct.

                                       BARROW, HANLEY, MEWHINNEY & STRAUSS, INC.


                                       By: /s/ James P. Barrow
                                           -------------------------------------
                                           Name: James P. Barrow
                                           Title: President
February 8, 2002
         -


                               Page 4 of 4 Pages