Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 287	$ 270	$ 264
Total Loans	60,085	57,381	56,155
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	58	13	24
Forgiveness of principal	2	2	5
Other	1	25	6
Total	61	40	35
Total Loans	44,274	41,381	40,130
Consumer Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	139	140	140
Forgiveness of principal	4	4	4
Other	83	86	85
Total	226	230	229
Total Loans	$ 15,811	$ 16,000	$ 16,025