Loans and Allowance for Credit Losses - Loans by Portfolio Class, Including Delinquency Status (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 382,517		$ 382,517		$ 379,832
Loans purchased from GNMA mortgage pools
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest income on nonperforming loans	4	$ 5	14	$ 16
Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,610		1,610		1,793
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	378,962		378,962		375,950
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,105		1,105		1,279
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	840		840		810
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	148,414		148,414		139,484
Commercial | Commercial | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	733		733		670
Commercial | Commercial | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	147,310		147,310		138,362
Commercial | Commercial | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	283		283		356
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	88		88		96
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	48,244		48,244		48,859
Commercial | Commercial real estate | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	579		579		824
Commercial | Commercial real estate | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	47,571		47,571		47,948
Commercial | Commercial real estate | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	75		75		78
Commercial | Commercial real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	19		19		9
Consumer | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	115,046		115,046		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	626		626		660
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools, classified as current	2,400		2,400		2,300
Consumer | Residential mortgages | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	143		143		152
Consumer | Residential mortgages | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	114,443		114,443		118,267
Consumer | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	162		162		188
Consumer | Residential mortgages | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	298		298		206
Consumer | Credit card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	30,594		30,594		30,350
Consumer | Credit card | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	0		0		0
Consumer | Credit card | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,801		29,801		29,487
Consumer | Credit card | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	409		409		428
Consumer | Credit card | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	384		384		435
Consumer | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	40,219		40,219		42,326
Consumer | Other retail | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	155		155		147
Consumer | Other retail | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	39,837		39,837		41,886
Consumer | Other retail | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	176		176		229
Consumer | Other retail | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 51		$ 51		$ 64