Reserves for Credit Losses - Changes in Loan Reserve (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions for credit losses	$ 1,356	$ 1,233	$ 3,893	$ 3,486
Card Member Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	5,321	4,390	5,118	3,747
Provisions for credit losses	1,114	982	3,098	2,691
Other	6	(12)	(7)	5
Ending Balance	5,588	4,721	5,588	4,721
Card Member Loans \| Principal
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	(701)	(525)	(2,159)	(1,412)
Recoveries	192	138	530	396
Card Member Loans \| Interest and fees
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	$ (152)	$ (114)	$ (462)	$ (310)

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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