Derivatives - Derivatives that do not qualify for hedge accounting under GAAP included in the Balance Sheet at fair value (Details) - Not Designated as Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	$ 570	$ 375
Derivative liability, at fair value	1,701	1,376
MBS with embedded derivatives | Fixed maturities
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	120	130
Public company warrants | Equity securities
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	3	4
Fixed-indexed annuities (embedded derivative) | Annuity benefits accumulated
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	1,688	1,369
Equity index call options | Other investments
Derivatives included in AFG' s Balance Sheet at fair value
Derivative asset, at fair value	447	241
Reinsurance contracts (embedded derivative) | Other liabilities
Derivatives included in AFG' s Balance Sheet at fair value
Derivative liability, at fair value	$ 13	$ 7