Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Delinquency Status of those that Continue to Accrue Interest and are Nonperforming (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 275,925	$ 269,994
Accruing 30-89 Days Past Due	1,110	1,081
Accruing 90 Days or More Past Due	649	764
Nonperforming	1,035	1,368
Total loans, excluding covered loans	275,457	269,371
Total loans	278,719	273,207
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	96,389	92,588
Accruing 30-89 Days Past Due	218	263
Accruing 90 Days or More Past Due	52	52
Nonperforming	269	483
Total loans, excluding covered loans	96,928	93,386
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	41,242	42,922
Accruing 30-89 Days Past Due	62	44
Accruing 90 Days or More Past Due	4	8
Nonperforming	122	124
Total loans, excluding covered loans	41,430	43,098
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	58,581	56,372
Accruing 30-89 Days Past Due	155	151
Accruing 90 Days or More Past Due	107	156
Nonperforming	474	595
Total loans, excluding covered loans	59,317	57,274
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	56,282	53,340
Accruing 30-89 Days Past Due	331	284
Accruing 90 Days or More Past Due	83	83
Nonperforming	163	157
Total loans, excluding covered loans	56,859	53,864
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20,375	21,209
Accruing 30-89 Days Past Due	296	284
Accruing 90 Days or More Past Due	251	253
Nonperforming	1	3
Total loans, excluding covered loans	20,923	21,749
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	272,869	266,431
Accruing 30-89 Days Past Due	1,062	1,026
Accruing 90 Days or More Past Due	497	552
Nonperforming	1,029	1,362
Total loans, excluding covered loans	275,457	269,371
Covered Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,056	3,563
Accruing 30-89 Days Past Due	48	55
Accruing 90 Days or More Past Due	152	212
Nonperforming	6	6
Total loans	$ 3,262	$ 3,836