Loans and Card Member Receivables - Modifications Subsequently Defaulted (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	$ 74	$ 0	$ 103	$ 0
Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	1		2
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	57		80
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	16		21
Card Member Loans | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	40		56
Card Member Loans | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	17		24
Card Member Loans | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Loans | Interest Rate Reduction and Term Extension | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Loans | Interest Rate Reduction and Term Extension | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Loans | Interest Rate Reduction and Term Extension | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Loans | Interest Rate Reduction | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	40		56
Card Member Loans | Interest Rate Reduction | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	17		24
Card Member Loans | Interest Rate Reduction | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Receivables | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	5		6
Card Member Receivables | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	11		15
Card Member Receivables | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Receivables | Interest Rate Reduction and Term Extension | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Receivables | Interest Rate Reduction and Term Extension | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Receivables | Interest Rate Reduction and Term Extension | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Card Member Receivables | Term Extension | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	5		6
Card Member Receivables | Term Extension | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	11		15
Card Member Receivables | Term Extension | Corporate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Other Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	1		2
Other Loans | Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	1		2
Other Loans | Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	0		0
Other Loans | Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	$ 0		$ 0