Derivatives (Details) (Not Designated as Hedging Instrument [Member], USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	$ 145	$ 199
Derivative liability, at fair value	356	204
MBS with embedded derivatives [Member] | Fixed Maturities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	98	101
Interest rate swaptions [Member] | Other Investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	7	21
Indexed annuities embedded derivative [Member] | Annuity benefits accumulated [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	332	190
Equity index call options [Member] | Other Investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	40	77
Reinsurance contracts embedded derivative [Member] | Other Liabilities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	$ 24	$ 14