Accretable Balance of Structured Investment Securities and Other Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Changes In Amortized Cost And Accretable Balance Investments [Line Items]
Balance at beginning of period	$ 93	$ 117		$ 100		$ 139
Accretion	(3)	(4)		(11)		(13)
Disposals	(90)			(90)
Other		(6)	[1]	1	[1]	(19)	[1]
Balance at end of period		$ 107				$ 107

[1] Primarily represents changes in projected future cash flows related to variable rates on certain investment securities.