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	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 291,898	$ 294,716
Accruing 30-89 Days Past Due	925	1,290
Accruing 90 Days or More Past Due	476	477
Nonperforming	1,128	1,224
Total loans	294,427	297,707
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	103,557	102,127
Accruing 30-89 Days Past Due	193	314
Accruing 90 Days or More Past Due	61	55
Nonperforming	347	375
Total loans	104,158	102,871
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	37,953	38,676
Accruing 30-89 Days Past Due	119	183
Accruing 90 Days or More Past Due	4	2
Nonperforming	356	450
Total loans	38,432	39,311
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	73,024	75,529
Accruing 30-89 Days Past Due	204	244
Accruing 90 Days or More Past Due	143	137
Nonperforming	253	245
Total loans	73,624	76,155
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	56,878	56,466
Accruing 30-89 Days Past Due	221	318
Accruing 90 Days or More Past Due	70	86
Nonperforming	172	154
Total loans	57,341	57,024
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20,486	21,918
Accruing 30-89 Days Past Due	188	231
Accruing 90 Days or More Past Due	198	197
Total loans	$ 20,872	$ 22,346