Loans and Card Member Receivables - Aging (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due	30 days
Financing receivables, gross	$ 144,814	$ 139,674
Loans and receivables threshold period for write off	180 days
Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 110,957	107,646
Loans over 90 days past due and accruing interest	470	435
Non-accruals	430	464
Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	33,818	31,991
Loans over 90 days past due and accruing interest	141	132
Non-accruals	143	135
Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	38	37
Loans over 90 days past due and accruing interest	0	0
Non-accruals	$ 0	0
Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due	30 days
Financing receivables, gross	$ 61,023	59,411
Loans and receivables threshold period for write off	180 days
Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 24,446	25,431
Loans over 90 days past due and accruing interest	0	0
Non-accruals	0	0
Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	19,189	18,619
Loans over 90 days past due and accruing interest	0	0
Non-accruals	0	0
Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	17,388	15,361
Loans over 90 days past due and accruing interest	0	0
Non-accruals	0	0
Current | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	109,430	106,155
Current | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	33,295	31,510
Current | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	24,214	25,255
Current | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,981	18,400
30 to 59 Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	460	437
30 to 59 Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	168	151
30 to 59 Days Past Due | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	63	58
30 to 59 Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	75	77
60 to 89 Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	335	329
60 to 89 Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	119	107
60 to 89 Days Past Due | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	49	39
60 to 89 Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	45	54
90+ Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	732	725
90+ Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	236	223
90+ Days Past Due | Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	0	0
90+ Days Past Due | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	120	79
90+ Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	88	88
90+ Days Past Due | Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 65	$ 65