Loans and Allowance for Credit Losses - Loans by Portfolio Class, Including Delinquency Status (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 381,819		$ 379,832
Loans purchased from GNMA mortgage pools
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest income on nonperforming loans	4	$ 5
Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,685		1,793
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	378,092		375,950
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,246		1,279
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	796		810
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	144,081		139,484
Commercial | Commercial | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	616		670
Commercial | Commercial | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	143,066		138,362
Commercial | Commercial | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	303		356
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	96		96
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	48,334		48,859
Commercial | Commercial real estate | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	780		824
Commercial | Commercial real estate | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	47,490		47,948
Commercial | Commercial real estate | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	59		78
Commercial | Commercial real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	5		9
Consumer | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	118,907		118,813
Consumer | Residential mortgages | Loans purchased from GNMA mortgage pools
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 days past due purchased from Government National Mortgage Association mortgage pools, classified as current	512		660
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools, classified as current	2,500		2,300
Consumer | Residential mortgages | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	141		152
Consumer | Residential mortgages | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	118,242		118,267
Consumer | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	295		188
Consumer | Residential mortgages | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	229		206
Consumer | Credit card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,223		30,350
Consumer | Credit card | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	0		0
Consumer | Credit card | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	28,432		29,487
Consumer | Credit card | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	382		428
Consumer | Credit card | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	409		435
Consumer | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	41,274		42,326
Consumer | Other retail | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	148		147
Consumer | Other retail | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	40,862		41,886
Consumer | Other retail | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	207		229
Consumer | Other retail | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 57		$ 64