Changes in Accretable Balance for Purchased Impaired Loans (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
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 2,431		$ 3,015		$ 2,619		$ 2,890
Purchases					13		100
Accretion	(109)		(110)		(337)		(337)
Disposals	(37)		(43)		(135)		(47)
Reclassifications (to)/from nonaccretable difference (a)	58	[1]	(170)	[1]	191	[1]	117	[1]
Other	(14)		(7)		(22)		(38)
Balance at end of period	$ 2,329		$ 2,685		$ 2,329		$ 2,685

[1] Primarily relates to changes in expected credit performance.