Fair Value Measurements (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 Professional	Mar. 31, 2012	Dec. 31, 2012
Fair Value Measurements (Textual) [Abstract]
AFG's internal investment professionals	20
Level 3 assets as a percentage of total assets measured at fair value	3.00%
Percentage of level 3 assets that were priced using non-binding broker quotes	95.00%
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	$ 555		$ 465
Total realized/unrealized losses included in net income on liabilities still outstanding	18	39
Preferred Stock [Member]
Fair Value Measurements (Textual) [Abstract]
Number of preferred stocks transferred from Level 1 to Level 2		6
Fair value of assets transferred from Level 1 to Level 2		$ 35
Embedded Derivative Financial Instruments, Majority of Future Years [Member] | Minimum [Member]
Fair Value Measurements (Textual) [Abstract]
Unobservable input surrenders used in Level 3 fair value determination	5.00%
Embedded Derivative Financial Instruments, Majority of Future Years [Member] | Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
Unobservable input surrenders used in Level 3 fair value determination	12.00%
Embedded Derivative Financial Instruments [Member] | Minimum [Member]
Fair Value Measurements (Textual) [Abstract]
Unobservable input surrenders used in Level 3 fair value determination	4.00%
Embedded Derivative Financial Instruments [Member] | Maximum [Member]
Fair Value Measurements (Textual) [Abstract]
Unobservable input surrenders used in Level 3 fair value determination	20.00%