Derivatives (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	$ 448	$ 499
Derivative liability, at fair value	1,267	1,173
MBS with embedded derivatives [Member] | Fixed maturities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	170	158
Public company warrants [Member] | Equity securities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	0	19
Interest rate swaptions [Member] | Other investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	0	0
Fixed-indexed annuities (embedded derivative) [Member] | Annuity benefits accumulated [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	1,258	1,160
Equity index call options [Member] | Other investments [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	278	322
Reinsurance contracts (embedded derivative) [Member] | Other liabilities [Member]
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	$ 9	$ 13