Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,377	$ 4,329	$ 4,357	$ 4,306
Provision for credit losses	360	325	1,055	982
Loans charged-off	433	398	1,287	1,210
Less recoveries of loans charged-off	(103)	(83)	(282)	(263)
Net loans charged-off	330	315	1,005	947
Other changes		(1)		(3)
Balance at end of period	4,407	4,338	4,407	4,338
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,395	1,473	1,450	1,287
Provision for credit losses	71	90	169	438
Loans charged-off	115	104	315	322
Less recoveries of loans charged-off	(32)	(17)	(79)	(73)
Net loans charged-off	83	87	236	249
Balance at end of period	1,383	1,476	1,383	1,476
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	856	748	812	724
Provision for credit losses	(12)	34	21	53
Loans charged-off	2	9	7	19
Less recoveries of loans charged-off	(9)	(8)	(25)	(23)
Net loans charged-off	(7)	1	(18)	(4)
Balance at end of period	851	781	851	781
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	455	544	510	631
Provision for credit losses	2	(12)	(33)	(63)
Loans charged-off	16	19	49	67
Less recoveries of loans charged-off	(9)	(7)	(22)	(19)
Net loans charged-off	7	12	27	48
Balance at end of period	450	520	450	520
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	648	643	617	743
Provision for credit losses	84	37	234	42
Loans charged-off	86	84	263	243
Less recoveries of loans charged-off	(26)	(30)	(84)	(84)
Net loans charged-off	60	54	179	159
Balance at end of period	672	626	672	626
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	990	884	934	883
Provision for credit losses	216	178	666	514
Loans charged-off	214	182	653	559
Less recoveries of loans charged-off	(27)	(21)	(72)	(64)
Net loans charged-off	187	161	581	495
Other changes				(1)
Balance at end of period	1,019	901	1,019	901
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	4,344	4,292	4,323	4,268
Provision for credit losses	361	327	1,057	984
Loans charged-off	433	398	1,287	1,210
Less recoveries of loans charged-off	(103)	(83)	(282)	(263)
Net loans charged-off	330	315	1,005	947
Other changes				(1)
Balance at end of period	4,375	4,304	4,375	4,304
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	33	37	34	38
Provision for credit losses	(1)	(2)	(2)	(2)
Other changes		(1)		(2)
Balance at end of period	$ 32	$ 34	$ 32	$ 34