Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 280	$ 270	$ 338
Total Loans	59,876	57,381	54,457
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	51	13	95
Forgiveness of principal	2	2	5
Other	1	25	7
Total	54	40	107
Total Loans	44,272	41,381
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	132	140	130
Forgiveness of principal	8	4	5
Other	86	86	96
Total	226	230	$ 231
Total Loans	$ 15,604	$ 16,000