Debt	9 Months Ended
Sep. 30, 2013
Debt Disclosure [Abstract]
Debt	Debt The Company uses proceeds from the commercial paper market from time to time in order to meet short-term working capital needs and from time to time to retire other debt obligations. At September 30, 2013, the Company had $511 million in commercial paper outstanding as compared to $50 million of commercial paper outstanding at December 31, 2012. The increase was largely attributable to the use of commercial paper proceeds to repay the remaining balance outstanding of the term credit loan facility due October 2013. The weighted average commercial paper outstanding for the three and nine months ended September 30, 2013 was $524 million and $349 million, respectively. The weighted average interest rate of the commercial paper outstanding for the three and nine months ended September 30, 2013 was 0.33% and 0.35%, respectively. During the quarter ended September 30, 2013, the €500 million ($674 million) debt securities due July 2014 were classified as Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position as the date of maturity is less than one year. On March 8, 2013, the Company issued $90 million in aggregate principal amount of 4.250% Notes Due 2042. The 4.250% Notes Due 2042 constitute a further issuance of, and were consolidated to form a single series of debt securities with, the $166 million aggregate principal amount of the 4.250% Notes Due 2042 issued by Aon plc on December 12, 2012 (collectively, the "Original Notes"). The Original Notes were unconditionally guaranteed as to the payment of principal and interest by Aon Corporation. On April 15, 2013, an S-4 registration statement registering $256 million in aggregate principal amount of 4.250% Notes Due 2042 (the "Exchange Notes") under the Securities Act of 1933, as amended (the "Securities Act"), was declared effective by the Securities and Exchange Commission. The Exchange Notes were exchanged for the Original Notes. The form and terms of the Exchange Notes are substantially identical in all material respects to those of the Original Notes except that the Exchange Notes are registered under the Securities Act and the transfer restrictions, registration rights and related additional interest provisions applicable to the Original Notes do not apply to the Exchange Notes. Like the Original Notes, the Exchange Notes were issued by Aon plc and unconditionally guaranteed by Aon Corporation. All Original Notes were exchanged for Exchange Notes in the second quarter 2013. On April 29, 2013, the Company amended its Euro Facility agreement to add Aon plc as an additional borrower. On May 8, 2013, the Company established a multi-currency commercial paper program in aggregate principal amount of up to €650 million. Aon Corporation is a guarantor under the program. On May 21, 2013, the Company issued $250 million in aggregate principal amount of 4.45% Notes Due 2043. The 4.45% Notes Due 2043 were issued by Aon plc and fully and unconditionally guaranteed by Aon Corporation. The Company used the proceeds of the issuance to repay commercial paper borrowings and for general corporate purposes.

Debt

The Company uses proceeds from the commercial paper market from time to time in order to meet short-term working capital needs and from time to time to retire other debt obligations. At September 30, 2013, the Company had $511 million in commercial paper outstanding as compared to $50 million of commercial paper outstanding at December 31, 2012. The increase was largely attributable to the use of commercial paper proceeds to repay the remaining balance outstanding of the term credit loan facility due October 2013. The weighted average commercial paper outstanding for the three and nine months ended September 30, 2013 was $524 million and $349 million, respectively. The weighted average interest rate of the commercial paper outstanding for the three and nine months ended September 30, 2013 was 0.33% and 0.35%, respectively.

During the quarter ended September 30, 2013, the €500 million ($674 million) debt securities due July 2014 were classified as Short-term debt and current portion of long-term debt in the Condensed Consolidated Statements of Financial Position as the date of maturity is less than one year.

On March 8, 2013, the Company issued $90 million in aggregate principal amount of 4.250% Notes Due 2042. The 4.250% Notes Due 2042 constitute a further issuance of, and were consolidated to form a single series of debt securities with, the $166 million aggregate principal amount of the 4.250% Notes Due 2042 issued by Aon plc on December 12, 2012 (collectively, the "Original Notes"). The Original Notes were unconditionally guaranteed as to the payment of principal and interest by Aon Corporation.

On April 15, 2013, an S-4 registration statement registering $256 million in aggregate principal amount of 4.250% Notes Due 2042 (the "Exchange Notes") under the Securities Act of 1933, as amended (the "Securities Act"), was declared effective by the Securities and Exchange Commission. The Exchange Notes were exchanged for the Original Notes. The form and terms of the Exchange Notes are substantially identical in all material respects to those of the Original Notes except that the Exchange Notes are registered under the Securities Act and the transfer restrictions, registration rights and related additional interest provisions applicable to the Original Notes do not apply to the Exchange Notes. Like the Original Notes, the Exchange Notes were issued by Aon plc and unconditionally guaranteed by Aon Corporation. All Original Notes were exchanged for Exchange Notes in the second quarter 2013.

On April 29, 2013, the Company amended its Euro Facility agreement to add Aon plc as an additional borrower. On May 8, 2013, the Company established a multi-currency commercial paper program in aggregate principal amount of up to €650 million. Aon Corporation is a guarantor under the program.

On May 21, 2013, the Company issued $250 million in aggregate principal amount of 4.45% Notes Due 2043. The 4.45% Notes Due 2043 were issued by Aon plc and fully and unconditionally guaranteed by Aon Corporation. The Company used the proceeds of the issuance to repay commercial paper borrowings and for general corporate purposes.