Loans and Allowance for Credit Losses - Loan Modifications that Defaulted (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	$ 42	$ 12	$ 114	$ 18
Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	99	24	167	28
Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	248	14	315	16
Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	55	6	98	8
Payment Delay and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	49	7	91	7
Interest Rate Reduction and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	5		6
Interest Rate Reduction, Payment Delay and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	1	1	1
Total loans, excluding loans purchased from GNMA mortgage pools | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	42	12	114	18
Total loans, excluding loans purchased from GNMA mortgage pools | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	2	4	13	5
Total loans, excluding loans purchased from GNMA mortgage pools | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	198	5	235	6
Total loans, excluding loans purchased from GNMA mortgage pools | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	0	4	1
Loans purchased from GNMA mortgage pools | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Loans purchased from GNMA mortgage pools | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	97	20	154	23
Loans purchased from GNMA mortgage pools | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	50	9	80	10
Loans purchased from GNMA mortgage pools | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	54	6	94	7
Commercial | Commercial | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	8	2	20	3
Commercial | Commercial | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Commercial | Commercial | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	13	0	13	0
Commercial | Commercial | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Commercial | Commercial real estate | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	0		0
Commercial | Commercial real estate | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0		0
Commercial | Commercial real estate | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	180		204
Commercial | Commercial real estate | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0		0
Consumer | Residential mortgages | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Consumer | Residential mortgages | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	2	4	12	5
Consumer | Residential mortgages | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	1	3	1
Consumer | Residential mortgages | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	0	4	1
Consumer | Credit card | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	33	10	92	15
Consumer | Credit card | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Consumer | Credit card | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Consumer | Credit card | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	0	0
Consumer | Other retail | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	0	2	0
Consumer | Other retail | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0	1	0
Consumer | Other retail | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	5	4	15	5
Consumer | Other retail | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	$ 0	$ 0	$ 0	$ 0