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, 2022	Dec. 31, 2021
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 318,934	$ 312,028
Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	316,863	309,520
Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	856	1,202
Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	450	472
Nonperforming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	765	834
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	117,470	112,023
Commercial [Member] | Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	116,986	111,270
Commercial [Member] | Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	234	530
Commercial [Member] | Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	76	49
Commercial [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	174	174
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	39,191	39,053
Commercial Real Estate [Member] | Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	38,888	38,678
Commercial Real Estate [Member] | Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	86	80
Commercial Real Estate [Member] | Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1	11
Commercial Real Estate [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	216	284
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	78,487	76,493
Residential Mortgages [Member] | Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	78,028	75,962
Residential Mortgages [Member] | Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	105	124
Residential Mortgages [Member] | Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	140	181
Residential Mortgages [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	214	226
Other Retail [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	61,623	61,959
Other Retail [Member] | Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	61,157	61,468
Other Retail [Member] | Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	237	275
Other Retail [Member] | Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	68	66
Other Retail [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	161	150
Credit Card [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	22,163	22,500
Credit Card [Member] | Current [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	21,804	22,142
Credit Card [Member] | Accruing 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	194	193
Credit Card [Member] | Accruing 90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 165	$ 165