Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Professional Stock	Sep. 30, 2011	Dec. 31, 2011
Fair Value Measurements (Textual) [Abstract]
AFG's internal investment professionals			20
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			90.00%
Percentage of internally developed Level 3 assets to total assets			1.00%
Total realized/unrealized losses included in net income on liabilities still outstanding	49	89	99	19
Level 3 assets that were priced using non-binding broker quotes			907
Percentage of internally developed Level 3 assets to Shareholders' equity			3.00%
Fair value of derivatives in annuity benefits accumulated measured using a discounted cash flow approach	$ 497		$ 497		$ 361