Deferred Policy Acquisition Costs (Details Textual) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Deferred Policy Acquisition Costs (Textual) [Abstract]
Accumulated amortization of present value of future profits	$ 204	$ 195

The cumulative amount of amortization of present value of future profits that has been recognized in the Income Statement.

No definition available.

Name:	afg_AccumulatedAmortizationOfPresentValueOfFutureProfits
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant