Insurance (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Net Investment Income of AFG's Insurance Group
Investment income	$ 1,312		$ 1,241		$ 1,191
AFG Insurance Group [Member]
Net Investment Income of AFG's Insurance Group
Investment income	1,306		1,233		1,184
Investment expenses	(31)	[1]	(34)	[1]	(25)	[1]
Net investment income	1,275		1,199		1,159
Fixed maturities [Member] | AFG Insurance Group [Member]
Net Investment Income of AFG's Insurance Group
Investment income	1,215		1,142		1,112
Equity securities [Member] | AFG Insurance Group [Member]
Net Investment Income of AFG's Insurance Group
Investment income	31		26		11
Other [Member] | AFG Insurance Group [Member]
Net Investment Income of AFG's Insurance Group
Investment income	$ 60		$ 65		$ 61

[1] Included primarily in “Other operating and general expenses” in the Statement of Earnings.