Managed Investment Entities (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012 collateralizedloanobligations	Dec. 31, 2011	Sep. 30, 2012 Variable Interest Entity, Primary Beneficiary [Member]	Dec. 31, 2011 Variable Interest Entity, Primary Beneficiary [Member]	Mar. 31, 2012 New CLO Formed in March 2012 [Member]	Oct. 31, 2012 New CLO Formed In October 2012 [Member]
Variable Interest Entity [Line Items]
Aggregate fair value of investment in collateralized loan obligations			$ 240	$ 98
Aggregate fair value of investment in collateralized loan obligations, most subordinate debt tranches			96
Face amount of liabilities					410	450
Face amount of liabilities purchased by subsidiaries of AFG					39	35
Managed Investment Entities (Textual) [Abstract]
Percentage of investment of most subordinate debt tranche, Minimum	7.50%
Percentage of investment of most subordinate debt tranche, Maximum	51.20%
Number of collateralized loan obligation entities	8
Difference between aggregate unpaid principal balance and fair value of CLOs' fixed maturity investments	33	120
Difference between aggregate unpaid principal balance and fair value of CLOs' debt	151	306
Aggregate unpaid principal balance of CLO loans in default	12	7
Carrying amount of CLO loans in default	$ 5	$ 2