Income Taxes (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended				3 Months Ended		12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Positive Outcome of Litigation [Member]	Dec. 31, 2012 Tax Litigation Settlement [Member]	Sep. 30, 2012 Tax Litigation Settlement [Member]	Dec. 31, 2012 AFG [Member]	Dec. 31, 2011 AFG [Member]	Dec. 31, 2010 AFG [Member]	Dec. 31, 2011 Charge for valuation allowance [Member]	Dec. 31, 2011 Charge for valuation allowance related to prior year losses [Member]
Income Tax Reconciliation [Line Items]
Statutory rate of income taxes			35.00%
Income (losses) subject to tax in foreign jurisdictions			$ (5)	$ (31)	$ (12)
Charge for valuation allowance against deferred tax assets		34										44	34
Operating loss carryforwards, valuation allowance		50		50
Period of discretionary appeal						90 days
Tax benefit related to settlement of litigation							39	28
Expected refund of tax and interest paid related to tax settlements								17
Cash payments for income taxes			277	157	196
Decrease in related accrued interest		15	1	15
Change in AFG's liability for uncertain tax positions of prior year	10		46	0	0
Change in AFG's liability for uncertain tax positions of current year, uncertainty as to timing of tax return inclusion of income related to certain secuties			3	7	16
Change in AFG's liability for uncertain tax positions of current year related to deductibility of certain expenses			2
Change in AFG's liability for uncertain tax positions of prior year related to resolution of tax case			36
Change in AFG's related liability for interest for uncertain tax positions			14
Unrecognized tax benefits that would impact effective tax rate			3
Interest included in tax provision									$ (14)	$ 3	$ 2