Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended							12 Months Ended
	Dec. 31, 2012 Professional	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Preferred Stock [Member] Stock	Mar. 31, 2012 Preferred Stock [Member] Stock	Dec. 31, 2012 Perpetual Preferred Stock [Member] Stock	Dec. 31, 2012 Redeemable Preferred Stock [Member] Stock	Dec. 31, 2012 Embedded Derivative Financial Instruments, Majority of Future Years [Member] Minimum [Member]	Dec. 31, 2012 Embedded Derivative Financial Instruments, Majority of Future Years [Member] Maximum [Member]	Dec. 31, 2012 Embedded Derivative Financial Instruments [Member] Minimum [Member]	Dec. 31, 2012 Embedded Derivative Financial Instruments [Member] Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
AFG's internal investment professionals	20
Number of preferred stocks transferred from Level 1 to Level 2				1	6
Fair value of assets transferred from Level 1 to Level 2				$ 6	$ 35
Number of perpetual preferred stocks transferred from Level 2 to Level 1						2
Fair value of assets transferred from Level 2 to Level 1						16	2
Number of redeemable preferred stocks transferred from Level 2 to Level 1							1
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%
Level 3 assets that were priced using non-binding broker quotes	920
Percentage of internally developed Level 3 assets to total assets	1.00%
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	465	361
Unobservable input surrenders used in Level 3 fair value determination								5.00%	12.00%	4.00%	20.00%
Total realized/unrealized losses included in net income on liabilities still outstanding	$ 125	$ 3	$ 213