Loans and Card Member Receivables - Modifications Subsequently Defaulted (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	$ 95	$ 0	$ 134	$ 0
Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	2		2
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	75		108
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	18		24
Card Member Loans | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	52		75
Card Member Loans | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	23		33
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	52		75
Card Member Loans | Interest Rate Reduction | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	23		33
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	6		8
Card Member Receivables | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	12		16
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	6		8
Card Member Receivables | Term Extension | Small Business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	12		16
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	2		2
Other Loans | Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Account balance	2		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