Shareholders' Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Components of accumulated other comprehensive income
Accumulated other comprehensive income, net unrealized gains on securities, beginning balance	$ 578	$ 491
Other comprehensive income, net unrealized gains on securities, pre-tax	200	28
Other comprehensive income, net unrealized gains on securities, tax	(70)	(10)
Other comprehensive income, net unrealized gains on securities, noncontrolling interests	(3)
Other comprehensive income, net unrealized gains on securities, net of tax	127	18
Accumulated other comprehensive income, net unrealized gains on securities, ending balance	705	509
Accumulated other comprehensive income, foreign currency translation adjustments, beginning balance	10	12
Other comprehensive income, foreign currency translation adjustments, pre-tax	7	7
Other comprehensive income, foreign currency translation adjustments, noncontrolling interests	(1)
Other comprehensive income, foreign currency translation adjustments, net of tax	6	7
Accumulated other comprehensive income, foreign currency translation adjustments, ending balance	16	19
Accumulated other comprehensive income, pension and other postretirement plans adjustments, beginning balance	(8)	(8)
Other comprehensive income, pension and other postretirement plans adjustments, pre-tax	1
Other comprehensive income, pension and other postretirement plans adjustments, net of tax	1
Accumulated other comprehensive income, pension and other postretirement plans adjustments, ending balance	(7)	(8)
Accumulated other comprehensive income, total, Beginning balance	580	495
Other comprehensive income, total, pre-tax	208	35
Other comprehensive income, total, tax	(70)	(10)
Other comprehensive income, total, noncontrolling interests	(4)
Other comprehensive income, net of tax	138	25
Other comprehensive income, total, net of tax	134	25
Accumulated other comprehensive income, total, ending balance	$ 714	$ 520