Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class, Including Delinquency Status of those that Continue to Accrue Interest and are Nonperforming (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 294,781	$ 294,716
Accruing 30-89 Days Past Due	737	1,290
Accruing 90 Days or More Past Due	376	477
Nonperforming	1,018	1,224
Total loans	296,912	297,707
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	103,019	102,127
Accruing 30-89 Days Past Due	171	314
Accruing 90 Days or More Past Due	40	55
Nonperforming	291	375
Total loans	103,521	102,871
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	38,423	38,676
Accruing 30-89 Days Past Due	32	183
Accruing 90 Days or More Past Due	3	2
Nonperforming	312	450
Total loans	38,770	39,311
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	72,830	75,529
Accruing 30-89 Days Past Due	174	244
Accruing 90 Days or More Past Due	118	137
Nonperforming	244	245
Total loans	73,366	76,155
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	59,003	56,466
Accruing 30-89 Days Past Due	203	318
Accruing 90 Days or More Past Due	62	86
Nonperforming	171	154
Total loans	59,439	57,024
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,506	21,918
Accruing 30-89 Days Past Due	157	231
Accruing 90 Days or More Past Due	153	197
Total loans	$ 21,816	$ 22,346