Loans and Allowance for Credit Losses - Changes in Accretable Balance for Purchased Impaired Loans (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Deteriorated Loans Transferred in [Abstract]
Balance at beginning of period	$ 1,187	$ 1,584	$ 1,309	$ 1,655
Accretion	(100)	(120)	(198)	(231)
Disposals	(43)	(29)	(70)	(69)
Reclassifications from nonaccretable difference	32	53	37	134
Other		(1)	(2)	(2)
Balance at end of period	$ 1,076	$ 1,487	$ 1,076	$ 1,487