Loans and Card Member Receivables - Summary (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 139,203	$ 139,674
Financing receivable, reserves for credit losses	5,592	5,679	$ 5,271	$ 5,118
Financing receivables, net	133,611	133,995
Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	105,213	107,646
Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	33,903	31,991
Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	87	37
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	9,678	9,232
Financing receivable, reserves for credit losses	244	194	136	126
Financing receivables, net	9,434	9,038
Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	58,503	59,411
Financing receivable, reserves for credit losses	148	171	$ 151	$ 174
Financing receivables, net	58,355	59,240
Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	23,211	25,431
Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,631	18,619
Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	16,661	15,361
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	26,667	28,278
Variable Interest Entity, Primary Beneficiary | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	26,700	28,300
Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	4,205	3,927
Variable Interest Entity, Primary Beneficiary | Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 4,200	$ 3,900