Loans and Card Member Receivables - Aging (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due	30 days
Financing receivables, gross	$ 134,548	$ 125,995
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	$ 102,236	98,111
90+ days past due and still accruing interest	409	393
Non-accruals	391	344
Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	32,275	27,833
90+ days past due and still accruing interest	125	109
Non-accruals	116	95
Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	37	51
90+ days past due and still 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	$ 59,042	60,411
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	$ 23,426	25,578
90+ days past due and still accruing interest	0	0
Non-accruals	0	0
Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,925	19,286
90+ days past due and still accruing interest	0	0
Non-accruals	0	0
Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	16,691	15,547
90+ days past due and still accruing interest	0	0
Non-accruals	0	0
Current | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	100,819	96,779
Current | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	31,813	27,444
Current | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	23,245	25,355
Current | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,704	19,020
30 to 59 Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	446	420
30 to 59 Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	154	133
30 to 59 Days Past Due | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	59	70
30 to 59 Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	83	104
60 to 89 Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	327	298
60 to 89 Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	108	85
60 to 89 Days Past Due | Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	41	47
60 to 89 Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	51	62
90+ Days Past Due | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	644	614
90+ Days Past Due | Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	200	171
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	81	106
90+ Days Past Due | Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	87	100
90+ Days Past Due | Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 67	$ 67