Summary of Credit-Related Impairment Losses on Other-Than-Temporarily-Impaired Securities With Bifurcated Losses (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Schedule of Investments [Line Items]
Cumulative credit loss impairments, beginning of period	$ 4	$ 13	$ 13	$ 24
Credit losses for which an other-than-temporary impairment was previously recognized	0	1	0	1
Securities sold during period	(4)	(1)	(13)	(12)
Cumulative credit loss impairments, end of period	$ 0	$ 13	$ 0	$ 13