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, 2024	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 374,164	$ 374,164		$ 373,835
Loans purchased from GNMA mortgage pools
Financing Receivable, Recorded Investment, Past Due [Line Items]
Interest income on nonperforming loans	5	16	$ 12
Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,809	1,809		1,449
Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	370,382	370,382		370,316
30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	1,235	1,235		1,372
90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	738	738		698
Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	133,638	133,638		131,881
Commercial | Commercial | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	585	585		376
Commercial | Commercial | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	132,626	132,626		130,925
Commercial | Commercial | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	335	335		464
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	92	92		116
Commercial | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	50,619	50,619		53,455
Commercial | Commercial real estate | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	925	925		777
Commercial | Commercial real estate | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	49,604	49,604		52,619
Commercial | Commercial real estate | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	81	81		55
Commercial | Commercial real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	9	9		4
Consumer | Residential mortgages
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	118,034	118,034		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	607	607		595
Loans 90 days or more past due purchased from Government National Mortgage Association mortgage pools, classified as current	2,000	2,000		2,000
Consumer | Residential mortgages | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	154	154		158
Consumer | Residential mortgages | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	117,530	117,530		115,067
Consumer | Residential mortgages | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	171	171		169
Consumer | Residential mortgages | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	179	179		136
Consumer | Credit card
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	29,037	29,037		28,560
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	28,215	28,215		27,779
Consumer | Credit card | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	426	426		406
Consumer | Credit card | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	396	396		375
Consumer | Other retail
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	42,836	42,836		44,409
Consumer | Other retail | Nonperforming
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	145	145		138
Consumer | Other retail | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	42,407	42,407		43,926
Consumer | Other retail | 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	222	222		278
Consumer | Other retail | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 62	$ 62		$ 67