Loans and Allowance for Credit Losses - Changes in Accretable Balance for Purchased Impaired Loans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Deteriorated Loans Transferred in [Abstract]
Balance at beginning of period	$ 1,076	$ 1,487	$ 1,309	$ 1,655
Accretion	(91)	(105)	(289)	(336)
Disposals	(32)	(34)	(102)	(103)
Reclassifications from nonaccretable difference	120	38	157	172
Other	1		(1)	(2)
Balance at end of period	$ 1,074	$ 1,386	$ 1,074	$ 1,386