Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 268	$ 270	$ 294
Total Loans	57,953	57,381	55,445
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	12	13	49
Forgiveness of principal	2	2	5
Other	25	25	7
Total	39	40	61
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	140	140	142
Forgiveness of principal	4	4	5
Other	85	86	86
Total	$ 229	$ 230	$ 233