Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]
Special charges to increase asbestos and environmental reserves	$ 30

Special charges to increase asbestos and environmental reserves.

No definition available.

Name:	afg_SpecialChargesToIncreaseAsbestosAndEnvironmentalReserves
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration