Derivatives (Details) (Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	$ 244	$ 170
Derivative liability, at fair value	505	418
MBS with embedded derivatives [Member] | Fixed Maturities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	102	99
Interest rate swaptions [Member] | Other Investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	5	5
Indexed annuities embedded derivative [Member] | Annuity benefits accumulated [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	483	395
Equity index call options [Member] | Other Investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	137	66
Reinsurance contracts embedded derivative [Member] | Other Liabilities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	$ 22	$ 23