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