Deferred Policy Acquisition Costs (Details Textual) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Deferred Policy Acquisition Costs Disclosures [Abstract]
Accumulated amortization of present value of future profits	$ 188	$ 184

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