Debt	6 Months Ended
Jun. 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. At June 30, 2013, the Company had $347 million in commercial paper outstanding as compared to $50 million of commercial paper outstanding at December 31, 2012. The weighted average commercial paper outstanding for the three and six months ended June 30, 2013 was $358 million and $261 million, respectively. The weighted average interest rate of the commercial paper outstanding for the three and six months ended June 30, 2013 was 0.35% and 0.37%, respectively. 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 are to be 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. During the second quarter 2013, the Company used available funds to repay $306 million of the term loan credit facility due October 2013.

Debt

The Company uses proceeds from the commercial paper market from time to time in order to meet short-term working capital needs. At June 30, 2013, the Company had $347 million in commercial paper outstanding as compared to $50 million of commercial paper outstanding at December 31, 2012. The weighted average commercial paper outstanding for the three and six months ended June 30, 2013 was $358 million and $261 million, respectively. The weighted average interest rate of the commercial paper outstanding for the three and six months ended June 30, 2013 was 0.35% and 0.37%, respectively.

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 are to be 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.

During the second quarter 2013, the Company used available funds to repay $306 million of the term loan credit facility due October 2013.