Reserves for Credit Losses - Changes in Loan Reserve (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions for credit losses	$ 1,150	$ 1,269
Card Member Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	5,679	5,118	$ 5,118
Provisions for credit losses	901	1,014
Other	8	(6)
Ending Balance	5,592	5,271	$ 5,679
Card Member Loans | Principal
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	(818)	(705)
Recoveries	221	159
Card Member Loans | Interest and fees
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	$ (178)	$ (150)