Loans and Card Member Receivables - Summary (Details) - USD ($) $ in Millions	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 142,275		$ 139,674
Financing receivable, reserves for credit losses	5,767	$ 5,592	5,679	$ 5,321	$ 5,271	$ 5,118
Financing receivables, net	136,508		133,995
Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	109,160		107,646
Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	33,072		31,991
Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	43		37
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	10,103		9,232
Financing receivable, reserves for credit losses	272	244	194	140	136	126
Financing receivables, net	9,831		9,038
Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	59,598		59,411
Financing receivable, reserves for credit losses	193	$ 148	171	$ 171	$ 151	$ 174
Financing receivables, net	59,405		59,240
Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	24,598		25,431
Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,982		18,619
Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	16,018		15,361
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	26,664		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	3,952		3,927
Variable Interest Entity, Primary Beneficiary | Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 4,000		$ 3,900