Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Professional Stock	Jun. 30, 2011	Dec. 31, 2011
Fair Value Measurements (Textual) [Abstract]
Fair value of assets transferred from Level 1 to Level 2			$ 35
Number of preferred stocks transferred from Level 1 to Level 2			6
Level 3 assets as a percentage of total assets measured at fair value			4.00%
Percentage of level 3 assets that were priced using non-binding broker quotes			89.00%
Percentage of internally developed Level 3 assets to total assets			1.00%
Total realized/unrealized losses included in net income on liabilities still outstanding	14	10	51	71
AFG's internal investment professionals			20
Level 3 assets that were priced using non-binding broker quotes			952
Percentage of internally developed Level 3 assets to Shareholders' equity			2.00%
Fair value of derivatives in annuity benefits accumulated measured using a discounted cash flow approach	$ 512		$ 512		$ 395