Managed Investment Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Gains (losses) on change in fair value of assets/liabilities (a):
Assets	$ 55	$ 29
Liabilities	(84)	(62)
Management fees paid to AFG	4	3
Collateralized loan obligations' earnings (losses) attributable to:
AFG shareholders	5	6
Noncontrolling interests	$ (28)	$ (35)