Loans and Allowance for Credit Losses - Loan Modifications that Defaulted (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	$ 45	$ 35
Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	85	83
Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	54	40
Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	70	44
Payment Delay and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	41	43
Interest Rate Reduction and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	27
Interest Rate Reduction, Payment Delay and Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	2	1
Total loans, excluding loans purchased from GNMA mortgage pools | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	45	35
Total loans, excluding loans purchased from GNMA mortgage pools | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	6
Total loans, excluding loans purchased from GNMA mortgage pools | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	20	9
Total loans, excluding loans purchased from GNMA mortgage pools | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	2
Loans purchased from GNMA mortgage pools | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0
Loans purchased from GNMA mortgage pools | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	84	77
Loans purchased from GNMA mortgage pools | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	34	31
Loans purchased from GNMA mortgage pools | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	70	42
Commercial | Commercial | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	9	6
Commercial | Commercial | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0
Commercial | Commercial | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	16	0
Commercial | Commercial | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	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	0	0
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
Consumer | Residential mortgages | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	5
Consumer | Residential mortgages | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	3
Consumer | Residential mortgages | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	2
Consumer | Credit card | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	35	29
Consumer | Credit card | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0
Consumer | Credit card | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0
Consumer | Credit card | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	0
Consumer | Other retail | Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans that defaulted	1	0
Consumer | Other retail | Payment Delay
Financing Receivable, Modified [Line Items]
Loans that defaulted	0	1
Consumer | Other retail | Term Extension
Financing Receivable, Modified [Line Items]
Loans that defaulted	4	6
Consumer | Other retail | Multiple Modifications
Financing Receivable, Modified [Line Items]
Loans that defaulted	$ 0	$ 0