Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Total commercial and consumer TDRs	$ 41	$ 12	$ 81	$ 81
Total loans	85,528	60,085	85,528	60,085	$ 59,876
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	9	1	28	48
Forgiveness of principal	0	0	0	0
Other	24	0	24	0
Total	33	1	52	48
Total loans	61,384	44,274	61,384	44,274	44,272
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Interest rate reduction	3	6	9	21
Forgiveness of principal	0	0	0	0
Other	5	5	20	12
Total	8	11	29	33
Total loans	$ 24,144	$ 15,811	$ 24,144	$ 15,811	$ 15,604