Investments (Credit Losses Recognized in Net Income on Debt Securities) (Detail) (Debt Securities, USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Debt Securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Cumulative credit losses, beginning balance	$ 610	$ 755	$ 646	$ 784
Other-than-temporary impairments not previously recognized	6	1	8	4
Increases related to other-than-temporary impairments previously recognized	19	17	32	48
Securities sold, paid down or disposed	(47)	(47)	(98)	(110)
Cumulative credit losses, ending balance	$ 588	$ 726	$ 588	$ 726