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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,411	$ 4,377	$ 4,417	$ 4,357
Provision for credit losses	343	360	1,011	1,055
Loans charged-off	428	433	1,318	1,287
Less recoveries of loans charged-off	(100)	(103)	(317)	(282)
Net loans charged-off	328	330	1,001	1,005
Other changes			(1)
Balance at end of period	4,426	4,407	4,426	4,407
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,391	1,395	1,372	1,450
Provision for credit losses	88	71	225	169
Loans charged-off	88	115	265	315
Less recoveries of loans charged-off	(22)	(32)	(81)	(79)
Net loans charged-off	66	83	184	236
Balance at end of period	1,413	1,383	1,413	1,383
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	812	856	831	812
Provision for credit losses	(12)	(12)	(34)	21
Loans charged-off	1	2	6	7
Less recoveries of loans charged-off	(10)	(9)	(18)	(25)
Net loans charged-off	(9)	(7)	(12)	(18)
Balance at end of period	809	851	809	851
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	436	455	449	510
Provision for credit losses	8	2	6	(33)
Loans charged-off	12	16	37	49
Less recoveries of loans charged-off	(8)	(9)	(22)	(22)
Net loans charged-off	4	7	15	27
Balance at end of period	440	450	440	450
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	667	648	678	617
Provision for credit losses	41	84	156	234
Loans charged-off	96	86	283	263
Less recoveries of loans charged-off	(35)	(26)	(96)	(84)
Net loans charged-off	61	60	187	179
Balance at end of period	647	672	647	672
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,082	990	1,056	934
Provision for credit losses	221	216	668	666
Loans charged-off	231	214	727	653
Less recoveries of loans charged-off	(25)	(27)	(100)	(72)
Net loans charged-off	206	187	627	581
Balance at end of period	1,097	1,019	1,097	1,019
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	4,388	4,344	4,386	4,323
Provision for credit losses	346	361	1,021	1,057
Loans charged-off	428	433	1,318	1,287
Less recoveries of loans charged-off	(100)	(103)	(317)	(282)
Net loans charged-off	328	330	1,001	1,005
Balance at end of period	4,406	4,375	4,406	4,375
Covered Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	23	33	31	34
Provision for credit losses	(3)	(1)	(10)	(2)
Other changes			(1)
Balance at end of period	$ 20	$ 32	$ 20	$ 32