Shareholders' Equity (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Components of accumulated other comprehensive income
Accumulated other comprehensive income, net unrealized gains on securities, beginning balance	$ 578	[1]	$ 491	[1]	$ 167
Other comprehensive income, net unrealized gains on securities, pretax	388		141		507
Other comprehensive income, net unrealized gains on securities, tax	(136)		(49)		(177)
Other comprehensive income, net unrealized gains on securities, noncontrolling interests	(7)		(5)		(2)
Other comprehensive income, net unrealized gains on securities, net of tax, attributable to parent	245		87		328
Other change in accumulated other comprehensive income, available for sale securities adjustments					(4)	[2]
Accumulated other comprehensive income, net unrealized gains on securities, ending balance	823	[1]	578	[1]	491	[1]
Accumulated other comprehensive income, foreign currency translation adjustments, beginning balance	10		12		5
Other comprehensive income, foreign currency translation adjustments, pretax	6		(1)		8
Other comprehensive income, foreign currency translation adjustments, noncontrolling interests	(1)		(1)		0
Other comprehensive income, foreign currency translation adjustments, net of tax, attributable to parent	5		(2)		8
Other change in accumulated other comprehensive income, foreign currency translation adjustments	(1)	[2]			(1)	[2]
Accumulated other comprehensive income, foreign currency translation adjustments, ending balance	14		10		12
Accumulated other comprehensive income, pension and other postretirement plans adjustments, beginning balance	(8)		(8)		(8)
Other comprehensive income, pension and other postretirement plans adjustments, pretax	2		0		0
Other comprehensive income, pension and other postretirement plans adjustments, net of tax, attributable to parent	(2)		0		0
Accumulated other comprehensive income, pension and other postretirement plans adjustments, ending balance	(6)		(8)		(8)
Accumulated other comprehensive income (loss), total, beginning balance	580		495		164
Other comprehensive income, total, pretax	396		140		515
Other comprehensive income, total, tax	(136)		(49)		(177)
Other comprehensive income, total, noncontrolling interests	(8)		(6)		(2)
Other comprehensive income, total, net of tax, attributable to parent	252		85		336
Other change in accumulated other comprehensive income, total	(1)	[2]			(5)	[2]
Accumulated other comprehensive income (loss), total, ending balance	$ 831		$ 580		$ 495

[1] Includes net unrealized gains of $33 million at December 31, 2012 compared to net unrealized losses of $16 million and $11 million at December 31, 2011 and 2010, respectively, related to securities for which only the credit portion of an other-than-temporary impairment has been recorded in earnings.

[2] Other reflects the cumulative effect of accounting change in 2010 and the acquisition of noncontrolling interest in a subsidiary in 2012.