Segments of Operations (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Segments of Operations (Textual) [Abstract]
Earnings (losses) of managed investment entities attributable to noncontrolling interests	$ (28)	$ (35)
Other Segment [Member]
Segments of Operations (Textual) [Abstract]
Earnings (losses) of managed investment entities attributable to noncontrolling interests	$ (28)	$ (35)

Earnings (losses) of variable interest entities attributable to noncontrolling interests.

No definition available.

Name:	afg_EarningsLossesOfVariableInterestEntitiesAttributableToNoncontrollingInterests
Namespace Prefix:	afg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration