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, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 307,481	$ 293,596
Accruing 30-89 Days Past Due	1,227	1,209
Accruing 90 Days or More Past Due	556	605
Nonperforming	1,071	692
Total loans	310,335	296,102
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	119,316	103,273
Accruing 30-89 Days Past Due	399	307
Accruing 90 Days or More Past Due	90	79
Nonperforming	456	204
Total loans	120,261	103,863
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	40,776	39,627
Accruing 30-89 Days Past Due	103	34
Accruing 90 Days or More Past Due	2	3
Nonperforming	195	82
Total loans	41,076	39,746
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	70,731	70,071
Accruing 30-89 Days Past Due	241	154
Accruing 90 Days or More Past Due	115	120
Nonperforming	242	241
Total loans	71,329	70,586
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	55,890	56,463
Accruing 30-89 Days Past Due	254	393
Accruing 90 Days or More Past Due	90	97
Nonperforming	178	165
Total loans	56,412	57,118
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	20,768	24,162
Accruing 30-89 Days Past Due	230	321
Accruing 90 Days or More Past Due	259	306
Total loans	$ 21,257	$ 24,789