June 24, 2004





Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C.   20549

         RE:      REPORT ON FORM 11-K FOR THE AON SAVINGS PLAN
                  REGISTRANT:  AON CORPORATION
                  COMMISSION FILE NO.:  1-7933


Gentlemen and Ladies:

         Enclosed with this EDGAR transmission is the above referenced Form 11-K
for the Aon Savings Plan.

         Please  contact  the  undersigned  at  312/381-3165  if  you  have  any
questions.

Very truly yours,


/S/ MAXINE  G. BONN

Maxine G. Bonn
Counsel

MGB/rjr
Enclosures


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 11-K





  X      Annual Report Pursuant to Section 15(d) of the Securities
-----             Exchange Act of 1934

                  For the fiscal year ended December 31, 2003

                                       OR

                  Transition Report Pursuant to Section 15(d) of the
-----             Securities Exchange Act of 1934



                  A.       Full  title of the plan and the  address of the plan,
                           if different from the issuer named below:

                                Aon Savings Plan


                  B.       Name of the issuer of the securities held pursuant to
                           the plan and the address of its  principal  executive
                           office:


                                 Aon Corporation
                              200 E. Randolph Drive
                             Chicago, Illinois 60601








                               S I G N A T U R E S

Pursuant to the  requirements of the Securities  Exchange Act of 1934, the Plan,
by the Plan  Administrator,  the Committee,  has caused this annual report to be
signed on its  behalf by the  undersigned,  thereunto  duly  authorized,  in the
County of Cook and the State of Illinois on the 24th day of June, 2004.


AON SAVINGS PLAN

BY THE COMMITTEE



/s/ THOMAS STACHURA                         /s/ JOHN A. RESCHKE
------------------------                    -------------------------
Thomas Stachura                             John A. Reschke



                 FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULE

                                AON SAVINGS PLAN

                     Years Ended December 31, 2003 and 2002

                      With Report of Independent Registered

                             Public Accounting Firm

                    Employer Identification Number 36-3051915

                                   Plan # 020






                                AON SAVINGS PLAN

                 FINANCIAL STATEMENTS AND SUPPLEMENTAL SCHEDULE

                     Years ended December 31, 2003 and 2002


                                    CONTENTS



Report of Independent Registered Public Accounting Firm                        1

Financial Statements

         Statement of Assets Available for Benefits
         at December 31, 2003                                                  2

         Statement of Assets Available for Benefits
         At December 31, 2002                                                  3

         Statement of Changes in Assets Available for Benefits
         for the year ended December 31, 2003                                  4

         Statement of Changes in Assets Available for Benefits
         for the year ended December 31, 2002                                  5

Notes to Financial Statements                                                  6

Supplemental Schedule:

         Schedule H, Line 4i - Schedule of Assets (Held At
         End of Year)                                                         13



             Report of Independent Registered Public Accounting Firm


The Participants and Administrative Committee
Aon Savings Plan


We have audited the accompanying  statements of assets available for benefits of
the Aon  Savings  Plan  as of  December  31,  2003  and  2002,  and the  related
statements of changes in assets available for benefits for the years then ended.
These financial statements are the responsibility of the Plan's management.  Our
responsibility  is to express an opinion on these financial  statements based on
our audits.

We conducted our audits in accordance  with the standards of the Public  Company
Accounting Oversight Board (United States). Those standards require that we plan
and perform the audit to obtain reasonable assurance about whether the financial
statements are free of material misstatement.  An audit includes examining, on a
test basis,  evidence  supporting  the amounts and  disclosures in the financial
statements.  An audit also includes assessing the accounting principles used and
significant  estimates  made by  management,  as well as evaluating  the overall
financial  statement  presentation.   We  believe  that  our  audits  provide  a
reasonable basis for our opinion.

In our opinion,  the financial  statements  referred to above present fairly, in
all material respects, the assets available for benefits of the Plan at December
31, 2003 and 2002, and the changes in its assets  available for benefits for the
years  then  ended,  in  conformity  with  U.S.  generally  accepted  accounting
principles.

Our audits  were  performed  for the  purpose of forming an opinion on the basic
financial statements taken as a whole. The accompanying supplemental schedule of
assets (held at end of year) as of December 31, 2003,  is presented for purposes
of additional  analysis and is not a required part of the financial  statements,
but is supplementary information required by the Department of Labor's Rules and
Regulations for Reporting and Disclosure  under the Employee  Retirement  Income
Security Act of 1974. This  supplemental  schedule is the  responsibility of the
Plan's management.  The supplemental schedule has been subjected to the auditing
procedures  applied in our audits of the basic financial  statements and, in our
opinion,  is fairly  stated in all  material  respects  in relation to the basic
financial statements taken as a whole.




May 17, 2004                                          Ernst & Young LLP
Chicago, IL


                                      - 1 -



                                                                                       Employer Plan Identification # 36-3051915
                                                                                       Plan # 020


                                                                                           AON SAVINGS PLAN
                                                                           STATEMENT OF ASSETS AVAILABLE FOR BENEFITS
                                                                                         DECEMBER 31, 2003
                                                                                           (in thousands)
                                                                           ------------------------------------------------------




                                                                                          
     ASSETS:

     Investments, at Fair Value:
          Aon Corporation Common Stock                                                       $                           302,540
          Brokerage Accounts-Other Common and
             Preferred Stocks and Mutual Funds                                                                             8,327
          Investments in Mutual Funds:
             AIM Liquid Asset Fund                                                                                       249,360
             Vanguard REIT Index Fund                                                                                     53,303
             Vanguard Admiral Intermediate Term Treasury Fund                                                             76,522
             INVESCO Dynamics Fund                                                                                        31,136
             Dodge & Cox Common Stock Fund                                                                               105,230
             PIMCO Total Return Fund                                                                                      40,609
             Montag & Caldwell Growth Fund                                                                                15,855
             Managers Special Equity Fund                                                                                 35,821
             Templeton Emerging Markets Fund                                                                              16,645
          Investments in Collective Trusts:
             INVESCO Asset Allocation Fund                                                                               136,138
             INVESCO 500 Index Fund                                                                                      229,043
             INVESCO International Equity Fund                                                                            40,756
          Short-Term Investment Funds                                                                                      2,065
          Participant Loans                                                                                               21,239
                                                                                               ----------------------------------

                                                                                                                       1,364,589


     Company Contribution Receivable                                                                                      54,148

                                                                                               ----------------------------------
     ASSETS AVAILABLE FOR BENEFITS                                                           $                         1,418,737
                                                                                               ==================================



          See notes to financial statements.




                                      - 2 -




                                                                                       Employer Plan Identification # 36-3051915
                                                                                       Plan # 020



                                                                                          AON SAVINGS PLAN
                                                                            STATEMENT OF ASSETS AVAILABLE FOR BENEFITS
                                                                                          DECEMBER 31, 2002
                                                                                           (in thousands)
                                                                           ------------------------------------------------------


                                                                                                   ESOP
                                                                              SAVINGS            ALLOCATED
     ASSETS:                                                                   PLAN               ACCOUNT              TOTAL
                                                                           ----------------    ----------------    --------------

                                                                                                        
     Investments, at Fair Value:
          Aon Corporation Common Stock                                   $       144,755     $       110,361     $       255,116
          Brokerage Accounts-Other Common and
             Preferred Stocks and Mutual Funds                                     4,917                   -               4,917
          Investments in Mutual Funds:
             AIM Liquid Asset Fund                                               248,777                   -             248,777
             Vanguard REIT Index Fund                                             32,568                   -              32,568
             Vanguard Admiral Intermediate Term Treasury Fund                     85,778                   -              85,778
             INVESCO Dynamics Fund                                                16,124                   -              16,124
             Dodge & Cox Common Stock Fund                                        50,682                   -              50,682
             PIMCO Total Return Fund                                              31,799                   -              31,799
             Montag & Caldwell Growth Fund                                         7,595                   -               7,595
             Managers Special Equity Fund                                         13,666                   -              13,666
             Templeton Emerging Markets Fund                                       2,916                   -               2,916
          Investments in Collective Trusts:
             INVESCO Asset Allocation Fund                                       117,128                   -             117,128
             INVESCO 500 Index Fund                                              171,542                   -             171,542
             INVESCO International Equity Fund                                    28,247                   -              28,247
          Short-Term Investment Funds                                              1,499                   -               1,499
          Participant Loans                                                       18,957                   -              18,957
                                                                           ----------------    ----------------    --------------

                                                                                 976,950             110,361           1,087,311


     Company Contribution Receivable                                              30,437              17,760              48,197

                                                                           ----------------    ----------------    --------------
     ASSETS AVAILABLE FOR BENEFITS                                       $     1,007,387     $       128,121     $     1,135,508
                                                                           ================    ================    ==============



          See notes to financial statements.


                                      - 3 -




                                                                                  Employer Plan Identification # 36-3051915
                                                                                  Plan #020


                                                                            AON SAVINGS PLAN
                                                          STATEMENT OF CHANGES IN ASSETS AVAILABLE FOR BENEFITS
                                                                         YEAR ENDED DECEMBER 31, 2003
                                                                              (in thousands)
                                                      ------------------------------------------------------------------------


                                                                                        
   NET INVESTMENT INCOME
      Interest Income                                                                      $                            1,355
      Net Realized and Unrealized Appreciation
        in Fair Value of Investments                                                                                  201,742
      Aon Corporation Dividends                                                                                         7,948
      Other Dividends                                                                                                  14,705
      Management and Administrative Fees                                                                               (3,076)
                                                                                             ---------------------------------

   TOTAL NET INVESTMENT INCOME                                                                                        222,674

   CONTRIBUTIONS
      Company                                                                                                          54,148
      Participants                                                                                                     90,764
      Rollovers                                                                                                         7,580
                                                                                             ---------------------------------

   TOTAL CONTRIBUTIONS                                                                                                152,492

   OTHER CHANGES
      Benefit Payments                                                                                                (98,081)
      Plan Mergers                                                                                                      6,144
                                                                                             ---------------------------------


   TOTAL OTHER CHANGES                                                                                                (91,937)
                                                                                             ---------------------------------

   NET INCREASE IN ASSETS AVAILABLE
       FOR BENEFITS                                                                                                   283,229

   ASSETS AVAILABLE FOR BENEFITS
        AT BEGINNING OF YEAR                                                                                        1,135,508

                                                                                             ---------------------------------
   ASSETS AVAILABLE FOR BENEFITS
        AT END OF YEAR                                                                     $                        1,418,737
                                                                                             =================================


       See notes to financial statements.



                                      - 4 -



                                                                                  Employer Plan Identification # 36-3051915
                                                                                  Plan #020


                                                                             AON SAVINGS PLAN
                                                          STATEMENT OF CHANGES IN ASSETS AVAILABLE FOR BENEFITS
                                                                         YEAR ENDED DECEMBER 31, 2002
                                                                               (in thousands)
                                                      ------------------------------------------------------------------------

                                                                                                 ESOP
                                                                             SAVINGS           ALLOCATED
                                                                              PLAN              ACCOUNT             TOTAL
                                                                          --------------     --------------     --------------

                                                                                                     
   NET INVESTMENT LOSS
      Interest Income                                                   $         1,529    $             1    $         1,530
      Net Realized and Unrealized Depreciation
       in Fair Value of Investments                                            (204,840)           (97,587)          (302,427)
      Aon Corporation Dividends                                                   5,933              4,788             10,721
      Other Dividends                                                            15,603                  -             15,603
      Management and Administrative Fees                                         (1,891)              (136)            (2,027)
                                                                          --------------     --------------     --------------

   TOTAL NET INVESTMENT LOSS                                                   (183,666)           (92,934)          (276,600)

   CONTRIBUTIONS
      Company                                                                    30,437             17,760             48,197
      Participants                                                               86,106                  -             86,106
      Rollovers                                                                  11,172                  -             11,172
                                                                          --------------     --------------     --------------

   TOTAL CONTRIBUTIONS                                                          127,715             17,760            145,475

   ALLOCATIONS

      ESOP Diversification                                                        1,352             (1,352)                 -
                                                                          --------------     --------------     --------------

   TOTAL ALLOCATIONS                                                              1,352             (1,352)                 -

   OTHER CHANGES

   Benefit Payments                                                            (106,506)           (14,045)          (120,551)
   Plan Merger                                                                    1,614                  -              1,614

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

   TOTAL OTHER CHANGES                                                         (104,892)           (14,045)          (118,937)
                                                                          --------------     --------------     --------------

   NET DECREASE IN ASSETS AVAILABLE
       FOR BENEFITS                                                            (159,491)           (90,571)          (250,062)

   ASSETS AVAILABLE FOR BENEFITS
        AT BEGINNING OF YEAR                                                  1,166,878            218,692          1,385,570

                                                                          --------------     --------------     --------------
   ASSETS AVAILABLE FOR BENEFITS
        AT END OF YEAR                                                  $     1,007,387    $       128,121    $     1,135,508
                                                                          ==============     ==============     ==============


       See notes to financial statements.



                                      - 5 -



                                       Employer Plan Identification # 36-3051915
                                       Plan # 020




                                AON SAVINGS PLAN

                          NOTES TO FINANCIAL STATEMENTS

                     Years Ended December 31, 2003 and 2002

1.       DESCRIPTION OF PLAN

         GENERAL

         The Aon  Savings  Plan  (the  Plan)  was  authorized  by the  Board  of
         Directors of Aon  Corporation  (the Company or Plan  Sponsor).  It is a
         defined  contribution  plan  with  a  salary  deferral  feature  and an
         employee stock  ownership  (ESOP)  feature.  The Plan is subject to the
         provisions  of the  Employee  Retirement  Income  Security  Act of 1974
         (ERISA).  Effective  January 1, 2003,  the ASI Solutions,  Inc.  401(k)
         Retirement  Plan and the McLagan  Partners Inc.  401(k) Profit  Sharing
         Plan were  merged into the Plan and as a result,  assets  approximating
         $6.1 million were transferred to the Plan.  Effective  January 1, 2002,
         the FESC  Employees  Savings Plan merged into the Plan and as a result,
         assets approximating $1.6 million were transferred into the Plan.

         Prior to 2003,  certain  Plan  assets  were held by the Aon  Funds,  an
         affiliated,  open-end management investment company.  Assets in the Aon
         Funds were  liquidated  in 2002.  The assets of the ESOP portion of the
         Plan  are   invested   primarily   in  common  stock  of  the  Company.
         Additionally,  certain  assets are  invested by the  Trustees as deemed
         advisable in order for the Plan to meet its cash flow needs.

         Prior to 2003, the Plan presented a separate ESOP Allocated  Account in
         its financial  statements because the assets of the ESOP portion of the
         Plan (which were comprised of the ESOP Allocated Fund investment in Aon
         common  stock and  receivables  from the  Company)  were  considered  a
         non-participant directed investment. Effective January 1, 2003, the Aon
         Common Stock Fund and the ESOP Allocated Fund were merged into a single
         fund  called the Aon Common  Stock  ESOP  Fund.  Participants  have the
         option to reinvest  dividends in additional  shares of Aon common stock
         in the  Plan or  receive  dividends  in cash.  Additionally,  effective
         January 1, 2003,  participants are allowed to immediately diversify any
         Company matching  contributions  allocated to the Aon Common Stock ESOP
         Fund. As a result, the ESOP Allocated Account is no longer considered a
         non-participant   directed   investment   and  has  not  been  reported
         separately in the 2003 financial statements.


                                     - 6 -



1.       DESCRIPTION OF PLAN (CONTINUED)

         The   following   description   of  the  Plan   provides  only  general
         information.  Participants of the Plan should refer to the Summary Plan
         Description for a more complete description of the Plan.

         ELIGIBILITY AND PARTICIPATION

         Employees other than field sales agents or employees  scheduled to work
         less than 20 hours per week are  immediately  eligible to  participate.
         Field sales agents and  employees  scheduled to work less than 20 hours
         per week are  eligible  to  participate  after  completing  one year of
         service.  Participants must complete one year of service to be eligible
         for Company matching contributions.

         CONTRIBUTIONS

         PARTICIPANT  - Participant  contributions  are made by means of regular
         payroll deductions.  Non-highly compensated participants, as defined by
         the  Internal  Revenue  Code  (IRC),  may  elect to make  contributions
         between  1% and 16% of their  compensation,  as  defined  by the  Plan.
         Highly  compensated  participants,  as defined by the IRC, may elect to
         make contributions between 1% and 8% of their compensation,  as defined
         by the Plan.  Participant  contributions are limited to amounts allowed
         by  the  Internal  Revenue  Service  (IRS).  Accordingly,  the  maximum
         participant  contribution  was $12,000 in 2003 and $11,000 in 2002.  In
         addition to regular participant  contributions,  catch-up contributions
         of up to  $2,000  for 2003 and  $1,000  for 2002 were  allowed  for any
         participants who were age 50 or older during the Plan year.

         COMPANY - The Company  contributes an amount equal to 100% of the first
         3% of a participant's  compensation  that a participant  contributes to
         the Plan (75% of a participant's compensation up to 4% for employees of
         Aon  Human  Capital  Services,   LLC).  The  Company  makes  a  further
         contribution  to the ESOP  portion  of the  Plan  equal to 75% (50% for
         field sales agents) of the next 3% of a participant's compensation that
         is contributed to the Plan. In 2003, the ESOP  contribution was made in
         cash. In 2002, the ESOP contribution was made in shares of common stock
         of the Company.  Employees of Aon Human Capital  Services,  LLC are not
         eligible  for  the  ESOP   contribution.   The  Plan  requires  that  a
         participant be employed for at least one year and be actively  employed
         as of the last day of the Plan  year in  order  to  receive  a  Company
         contribution.

         INVESTMENT OPTIONS

         Contributions  to the  Plan  may  be  invested  in  any of the  various
         investment  alternatives  offered by the Plan in any whole percentages.
         Additionally,  a Self-Managed  Account is offered whereby  participants
         can invest their  self-directed  contributions in various stock, mutual
         funds and other investments.


                                      - 7 -


1.       DESCRIPTION OF PLAN (CONTINUED)

         PARTICIPANT ACCOUNTS

         Each   participant's   account  is  credited  with  the   participant's
         contribution and allocations of a) the Company's contributions, b) Plan
         earnings  (losses),  and c)  forfeitures  of  terminated  participants'
         non-vested accounts.  The benefit to which a participant is entitled is
         the benefit that can be provided from the participant's account.

         VESTING

         For the ESOP portion of the Plan, a participant vests in 20% increments
         per year and becomes 100% vested after completion of five years of plan
         service.  Forfeitures  of  non-vested  accounts  are  allocated  to the
         remaining  participants.   Forfeitures  are  only  allocated  to  those
         participants who received a Company contribution.

         For the non-ESOP portion of the Plan,  participants are fully vested in
         their  contributions plus actual earnings thereon.  Participants become
         100% vested in the remainder of their account  balance after five years
         of  plan  service,  according  to a  graded  schedule.  Forfeitures  of
         non-vested accounts are allocated to the remaining participants.

         The  total  amount  of  forfeitures   allocated  to  participants   was
         $1,074,000 and $1,049,000 for 2003 and 2002, respectively.

         BENEFIT PAYMENTS

         For the ESOP portion of the Plan, a participant's  entire account shall
         be paid to the participant or designated beneficiary in a lump sum upon
         normal retirement,  permanent  disability or death. The participant may
         elect payment in the form of Company common stock or cash.

         For the non-ESOP  portion,  on  termination  of service,  a participant
         shall  be paid a lump  sum  amount  equal  to the  value  of his or her
         account. The participant will receive payment in the form of cash only.

         PLAN TERMINATION

         Although it has not  expressed any intent to do so, the Company has the
         right under the Plan to discontinue its  contributions  at any time and
         to terminate the Plan subject to the provisions of ERISA.  In the event
         of Plan  termination,  participants  will  become  100% vested in their
         accounts.

                                      - 8 -



1.       DESCRIPTION OF PLAN (CONTINUED)

         PARTICIPANT LOANS

         Under the loan provision of the Plan, each participant is permitted one
         loan in a twelve month period and the outstanding  balance of all loans
         made to a  participant  may not  exceed the lesser of $50,000 or 50% of
         the vested  portion of the  participant's  account,  excluding the ESOP
         portion of the account.  The interest rate for each loan is equal to 1%
         plus the prime rate as quoted in The Wall  Street  Journal for the last
                                          --- ----  ------  -------
         day of the  month  preceding  the loan  request.  Loans  are made for a
         period of up to five years,  except for  residential  loans that have a
         fixed repayment period of up to fifteen years.

2.       SIGNIFICANT ACCOUNTING POLICIES

         BASIS OF ACCOUNTING

         The  financial  statements of the Plan are prepared on an accrual basis
         in accordance with U.S. generally accepted accounting principles.

         INVESTMENT VALUATION AND INCOME RECOGNITION

         Investments are carried at fair value, which for marketable  securities
         is based on quotations obtained from national securities  exchanges and
         various  other   sources.   Participant   loans  are  valued  at  their
         outstanding balances, which approximate fair value.

         Interest  income is recorded as earned.  Dividend income is recorded on
         the ex-dividend  date.  Realized gains or losses on investments are the
         difference  between the proceeds  received and the cost of  investments
         sold as determined on a first-in,  first-out  basis.  The change in the
         difference  between fair value and the cost of  investments is reported
         as unrealized appreciation or depreciation of investments.

         ADMINISTRATIVE EXPENSES

         Administrative   expenses  of  the  Plan,  including  expenses  of  the
         Trustees,  are paid from the Plan assets, except to the extent that the
         Company,  at its  discretion,  may  decide  to pay such  expenses.  The
         Company did not pay any Plan expenses in 2003 or 2002.

         USE OF ESTIMATES

         The  preparation  of the financial  statements in conformity  with U.S.
         generally accepted  accounting  principles  requires management to make
         estimates  and  assumptions  that  affect the  amounts  reported in the
         financial  statements  and  accompanying  notes.  Actual  results could
         differ from those estimates.


                                      - 9 -



3.       INVESTMENTS

         Institutional  Trust  Company (ITC) is custodian of the Plan assets and
         Trustee for all Plan assets except the Aon Common Stock ESOP shares and
         the  self-managed  brokerage  accounts.  For the Aon Common  Stock ESOP
         shares and self-managed brokerage accounts, State Street Bank and Trust
         Company is the Trustee. The Trustees are named fiduciaries under ERISA.
         As used herein,  Trustee  refers to ITC and State Street Bank and Trust
         Company individually and collectively.

         During  2003 and 2002 the  Plan's  investments  (including  investments
         bought,  sold and held during the year)  appreciated  (depreciated)  in
         fair value as follows (in thousands):






                                                                               December 31
                                                                  2003                             2002
                                           ---------------------------------------------------------------------------
                                                                  Net Realized                      Net Realized
                                                                and Unrealized                    and Unrealized
                                                                  Appreciation                      Appreciation
                                                                (Depreciation)                    (Depreciation)
                                                                 in Fair Value                     in Fair Value
                                                                of Investments                    of Investments
                                                       Fair             During           Fair             During
                                                       Value          the Year           Value          the Year

                                                                                     
Investments, at fair value:
Aon Corporation Common Stock                   $        302,540 $        65,964 $        255,116 $       (215,483)
Brokerage Accounts-Other
  Common and Preferred Stocks
  and Mutual Funds                                        8,327           2,337            4,917           (2,298)
Investments in Mutual Funds:
  Aon Government Securities Fund                              -               -                -             1,618
  Aon Asset Allocation Fund                                   -               -                -           (4,877)
  AIM Liquid Asset Fund                                 249,360               -          248,777                 -
  Vanguard REIT Index Fund                               53,303          10,518           32,568           (1,430)
  INVESCO Dynamics Fund                                  31,136           7,901           16,124           (8,044)
  Dodge & Cox Common Stock Fund                         105,230          19,582           50,682           (7,024)
  PIMCO Total Return Fund                                40,609              37           31,799               284
  Montag & Caldwell Growth Fund                          15,855           1,894            7,595           (2,151)
  Managers Special Equity Fund                           35,821           8,334           13,666           (3,992)
  Templeton Emerging Markets
      Fund                                               16,645           3,267            2,916             (326)
  Vanguard Admiral Intermediate
      Term Treasury Fund                                 76,522         (3,003)           85,778             1,443
Investments in Collective Trusts:
  INVESCO Asset Allocation Fund                         136,138          23,219          117,128           (3,644)
  INVESCO 500 Index Fund                                229,043          51,876          171,542          (52,658)
  INVESCO Core-Balanced Fund                                  -               -                -             (550)
  INVESCO International
        Equity Fund                                      40,756           9,816           28,247           (3,295)
Short-Term Investment Funds                               2,065               -            1,499                 -
                                               --------------------------------------------------------------------
  Total                                        $    1,343,350   $       201,742 $      1,068,354 $       (302,427)
                                               --------------------------------------------------------------------


                                     - 10 -


3.       INVESTMENTS (CONTINUED)

         The fair value of individual  investments  that represent 5% or more of
         the Plan's assets is as follows (in thousands):



                                                                           December 31
                                                             -------------------------------------
                                                                   2003                    2002
                                                                   ----                    ----
                                                                                 
         Aon Corporation, Common Stock                        $    302,540             $   255,116*
         Investments in Mutual Funds:
           AIM Liquid Asset Fund                                   249,360                 248,777
           Dodge & Cox Common Stock Fund                           105,230                     **
           Vanguard Admiral Intermediate Term
              Treasury Fund                                         76,522                  85,778
         Investments in Collective Trusts:
           INVESCO 500 Index Fund                                  229,043                 171,542
           INVESCO Asset Allocation Fund                           136,138                 117,128


         *Includes $202,435 of non-participant directed investments in 2002.

         **Below 5% threshold.





4.       INCOME TAX STATUS

         The Plan has received a determination letter from the IRS dated October
         1, 2003, stating that the Plan is qualified under section 401(a) of the
         IRC  and,  therefore,  the  related  trust  is  exempt  from  taxation.
         Subsequent to this issuance of the determination  letter,  the Plan was
         amended. Once qualified,  the Plan is required to operate in conformity
         with the IRC to maintain  its  qualification.  The Plan  Administrative
         Committee  believes the Plan is being  operated in compliance  with the
         applicable  requirements of the IRC and,  therefore,  believes that the
         Plan, as amended, is qualified and the related trust is tax exempt.

5.       RISKS AND UNCERTAINTIES

         The  Plan  invests  in  various   investment   securities.   Investment
         securities are exposed to various risks such as interest  rate,  market
         and credit  risks.  Due to the level of risk  associated  with  certain
         investment securities,  it is at least reasonably possible that changes
         in the values of investment  securities will occur in the near term and
         that  such  changes  could  materially  affect  participants'   account
         balances and the amounts reported in the statements of assets available
         for benefits.


                                     - 11 -



6.       SUBSEQUENT EVENTS

         Effective  January 1, 2004, the Company  contributes an amount equal to
         50% of a participant's compensation that participant contributes, up to
         6% of compensation  (75% of a  participant's  compensation up to 4% for
         employees  of Aon Human  Capital  Services LLC and 100% of the first 3%
         for employees of Human Resources  Outsourcing Group). This contribution
         will be made concurrent with participant contributions. The Company may
         make an additional contribution at its discretion but may not exceed 6%
         of a participant's compensation.

         Effective  January 1, 2004,  non-highly  compensated  participants  may
         elect to make contributions up to 25% of their compensation, as defined
         by the Plan  and  highly  compensated  participants  may  elect to make
         contributions  up to 10% of their  compensation  subject to limitations
         allowed by the IRS.

         Effective  January 1, 2004, the Aon Retirement  Account was established
         as a separate  account under the Aon Savings Plan.  The Aon  Retirement
         Account is intended for  employees  hired after January 1, 2004 who are
         not  eligible  for  participation  in the  Aon  Pension  Plan.  The Aon
         Retirement  Account is to be funded entirely by Company  contributions.
         No employee  contributions  will be allowed.  Participants  will become
         vested in their balances in the Aon Retirement Account after five years
         of service.


                                     - 12 -



                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020


                                                  AON SAVINGS PLAN
                           Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                 December 31, 2003

                                                             Number of Shares
                                                             ----------------                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
AON COMMON STOCK ESOP FUND
--------------------------

                                                                                           
COMMON STOCK

     Aon Corporation
     Common Stock, 1.00 par*                                  12,538,939                         $        302,422
                                                                                                    ==============


MONEY MARKET FUND
-----------------

MUTUAL FUND

     Investments held in the AIM
     Liquid Asset Fund                                       249,359,859                         $        249,360
                                                                                                    ==============


TOTAL RETURN FUND
-----------------

COLLECTIVE TRUST

     Investments held in the INVESCO
     Asset Allocation Fund*                                   11,705,777                         $        136,138
                                                                                                    ==============


COMMON STOCK INDEX FUND
-----------------------

COLLECTIVE TRUST

     Investments held in the INVESCO
     500 Index Fund*                                           8,185,969                         $        229,043
                                                                                                    ==============


REAL ESTATE SECURITIES FUND
---------------------------

MUTUAL FUND

     Investments held in the Vanguard
     REIT Index Fund                                           3,511,400                         $         53,303
                                                                                                    ==============




                                                       - 13 -




                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020
                                                  AON SAVINGS PLAN
                           Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                 December 31, 2003
                                                    (continued)

                                                             Number of Shares
                                                             ----------------                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
INVESCO DYNAMICS FUND
---------------------

                                                                                           
MUTUAL FUND

     Investments held in the INVESCO
     Dynamics Fund*                                            2,112,353                         $         31,136
                                                                                                    ==============


DODGE & COX COMMON STOCK FUND
-----------------------------

MUTUAL FUND

     Investments held in the Dodge & Cox
     Common Stock Fund                                           924,856                         $        105,230
                                                                                                    ==============


PIMCO TOTAL RETURN FUND
-----------------------

MUTUAL FUND

     Investments held in the PIMCO
     Total Return Fund                                         3,791,707                         $         40,609
                                                                                                    ==============


MONTAG & CALDWELL GROWTH FUND
-----------------------------

MUTUAL FUND

     Investments held in the Montag & Caldwell
     Growth Fund                                                 724,610                         $         15,855
                                                                                                    ==============


MANAGERS SPECIAL EQUITY FUND
----------------------------

MUTUAL FUND

     Investments held in the Managers
     Special Equity Fund                                         456,375                         $         35,821
                                                                                                    ==============



                                                          - 14 -




                                                                                Employer Identification #  36-3051915
                                                                                Plan #  020
                                                  AON SAVINGS PLAN
                           Schedule H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)
                                                 December 31, 2003
                                                    (continued)

                                                             Number of Shares
                                                             ----------------                       Current Value
Identity of Issuer                                           Principal Amount                        (thousands)
------------------------------------------------------------------------------------------------------------------
TEMPLETON EMERGING MARKETS FUND
-------------------------------

                                                                                           
MUTUAL FUND

     Investments held in the Templeton
     Emerging Markets Fund                                     1,367,698                         $         16,645
                                                                                                    ==============

VANGUARD ADMIRAL INTERMEDIATE TERM
----------------------------------
    TREASURY FUND
    -------------

MUTUAL FUND

     Investments held in the Vanguard Admiral
     Intermediate Term Treasury Fund                           6,712,475                         $         76,522
                                                                                                    ==============

INVESCO INTERNATIONAL EQUITY FUND
---------------------------------

COLLECTIVE TRUST

     Investments held in the INVESCO
     International Equity Fund*                                1,926,083                         $         40,756
                                                                                                    ==============

OTHER COMMON AND PREFERRED STOCKS AND MUTUAL FUNDS (SELF-MANAGED FUNDS)
-----------------------------------------------------------------------

BROKERAGE ACCOUNTS

     Investments held in other common and preferred
     stocks and mutual funds and other investments             8,327,090                         $          8,327
                                                                                                    ==============

    Investments held in Aon Corporation
    Common Stock*                                              4,919                             $            118
                                                                                                    ==============

    Investment held in the State Street
    Short-Term Investment Fund*                                2,064,534                         $          2,065
                                                                                                    ==============


PARTICIPANT LOANS (5.00% - 10.5%)                                      -                         $         21,239
                                                                                                    ==============

                                                                                                 $      1,364,589
                                                                                                    ==============
    *Party in interest transaction not prohibited by ERISA.



                                                       - 15 -


            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM


We consent to the incorporation by reference in the Registration Statement (Form
S-8 No.  33-27894)  pertaining to the Aon Savings Plan of Aon Corporation of our
report dated May 17, 2004, with respect to the financial statements and schedule
of the Aon Savings Plan  included in this annual report (Form 11-K) for the year
ended December 31, 2003.




June 21, 2004                                            Ernst & Young LLP
Chicago, IL