Shareholders' Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Components of accumulated other comprehensive income
Accumulated other comprehensive income, net unrealized gains on securities, beginning balance	$ 705	$ 509	$ 578	$ 491
Other comprehensive income, net unrealized gains on securities, pre-tax	101	151	301	179
Other comprehensive income, net unrealized gains on securities, tax	(35)	(53)	(105)	(63)
Other comprehensive income, net unrealized gains on securities, noncontrolling interests		(2)	(3)	(2)
Other comprehensive income, net unrealized gains on securities, net of tax, attributable to parent	66	96	193	114
Accumulated other comprehensive income, net unrealized gains on securities, ending balance	771	605	771	605
Accumulated other comprehensive income, foreign currency translation adjustments, beginning balance	16	19	10	12
Other comprehensive income, foreign currency translation adjustments, pre-tax	(8)	(2)	(1)	5
Other comprehensive income, foreign currency translation adjustments, noncontrolling interests	1
Other comprehensive income, foreign currency translation adjustments, net of tax, attributable to parent	(7)	(2)	(1)	5
Accumulated other comprehensive income, foreign currency translation adjustments, ending balance	9	17	9	17
Accumulated other comprehensive income, pension and other postretirement plans adjustments, beginning balance	(7)	(8)	(8)	(8)
Other comprehensive income, pension and other postretirement plans adjustments, pre-tax		1	1	1
Other comprehensive income, pension and other postretirement plans adjustments, net of tax, attributable to parent		1	1	1
Accumulated other comprehensive income, pension and other postretirement plans adjustments, ending balance	(7)	(7)	(7)	(7)
Accumulated other comprehensive income, total, beginning balance	714	520	580	495
Other comprehensive income, total, pre-tax	93	150	301	185
Other comprehensive income, total, tax	(35)	(53)	(105)	(63)
Other comprehensive income, total, noncontrolling interests	1	(2)	(3)	(2)
Other comprehensive income, total, net of tax, attributable to parent	59	95	193	120
Accumulated other comprehensive income, total, ending balance	$ 773	$ 615	$ 773	$ 615