Condensed Financial Information of Parent Company (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Activities:
Net earnings attributable to shareholders	$ 50	$ 226	$ 99	$ 113	$ 109	$ 97	$ 48	$ 88	$ 488	$ 342	$ 482
Adjustments:
Net cash provided by operating activities									817	667	864
Investing Activities:
Net cash used in investing activities									(1,425)	(2,439)	(1,705)
Financing Activities:
Additional long-term borrowings									372	2	159
Reductions of long-term debt									(365)	(20)	(39)
Issuances of Common Stock									46	39	32
Repurchases of Common Stock									(415)	(315)	(292)
Cash dividends paid on Common Stock									(90)	(67)	(63)
Net cash provided by (used in) financing activities									989	1,997	820
Net Change in Cash and Cash Equivalents									381	225	(21)
Cash and cash equivalents at beginning of year				1,324				1,099	1,324	1,099	1,120
Cash and cash equivalents at end of year	1,705				1,324				1,705	1,324	1,099
AFG [Member]
Operating Activities:
Net earnings attributable to shareholders									488	342	482
Adjustments:
Equity in net earnings of subsidiaries									(515)	(439)	(551)
Dividends from subsidiaries									417	542	550
Other operating activities, net									(10)	17	0
Net cash provided by operating activities									380	462	481
Investing Activities:
Purchases of investments, property and equipment									(11)	(54)	(13)
Returns of capital from (capital contributions to) subsidiaries									(273)	(27)	(97)
Proceeds from maturities and redemptions of investments									0	4	0
Proceeds from sales of investments, property and equipment									0	5	0
Net cash used in investing activities									(284)	(72)	(110)
Financing Activities:
Additional long-term borrowings									344	0	128
Reductions of long-term debt									(115)	0	0
Issuances of Common Stock									44	37	31
Repurchases of Common Stock									(415)	(315)	(292)
Cash dividends paid on Common Stock									(90)	(67)	(63)
Other financing activities, net									0	0	(2)
Net cash provided by (used in) financing activities									(232)	(345)	(198)
Net Change in Cash and Cash Equivalents									(136)	45	173
Cash and cash equivalents at beginning of year				415				370	415	370	197
Cash and cash equivalents at end of year	$ 279				$ 415				$ 279	$ 415	$ 370