Loans and Allowance for Credit Losses - Loans by Portfolio Class, Including Delinquency Status (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 374,588		$ 373,835
Loans purchased from GNMA mortgage pools
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest income on nonperforming loans	5	$ 4
Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,741		1,449
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	371,033		370,316
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,100		1,372
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	714		698
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	134,726		131,881
Commercial | Commercial | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	549		376
Commercial | Commercial | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	133,763		130,925
Commercial | Commercial | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	309		464
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	105		116
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	52,677		53,455
Commercial | Commercial real estate | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	900		777
Commercial | Commercial real estate | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	51,753		52,619
Commercial | Commercial real estate | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	22		55
Commercial | Commercial real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2		4
Consumer | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	116,079		115,530
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	491		595
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools, classified as current	1,800		2,000
Consumer | Residential mortgages | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	155		158
Consumer | Residential mortgages | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	115,636		115,067
Consumer | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	143		169
Consumer | Residential mortgages | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	145		136
Consumer | Credit card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	27,844		28,560
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	27,058		27,779
Consumer | Credit card | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	390		406
Consumer | Credit card | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	396		375
Consumer | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	43,262		44,409
Consumer | Other retail | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	137		138
Consumer | Other retail | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	42,823		43,926
Consumer | Other retail | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	236		278
Consumer | Other retail | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 66		$ 67