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, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 315,633	$ 293,596
Accruing 30-89 Days Past Due	1,278	1,209
Accruing 90 Days or More Past Due	579	605
Nonperforming	815	692
Total loans	318,305	296,102
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	125,576	103,273
Accruing 30-89 Days Past Due	352	307
Accruing 90 Days or More Past Due	80	79
Nonperforming	309	204
Total loans	126,317	103,863
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	40,795	39,627
Accruing 30-89 Days Past Due	82	34
Accruing 90 Days or More Past Due	2	3
Nonperforming	101	82
Total loans	40,980	39,746
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	70,660	70,071
Accruing 30-89 Days Past Due	164	154
Accruing 90 Days or More Past Due	108	120
Nonperforming	243	241
Total loans	71,175	70,586
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	56,408	56,463
Accruing 30-89 Days Past Due	387	393
Accruing 90 Days or More Past Due	95	97
Nonperforming	162	165
Total loans	57,052	57,118
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,194	24,162
Accruing 30-89 Days Past Due	293	321
Accruing 90 Days or More Past Due	294	306
Total loans	$ 22,781	$ 24,789