Reserves for Credit Losses - Changes in Loan Reserve (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions for credit losses	$ 1,269	$ 1,055
Card Member Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	5,118	3,747
Provisions for credit losses	1,014	786
Other	(6)	6
Ending Balance	5,271	4,053
Card Member Loans | Principal
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	(705)	(397)
Recoveries	159	128
Card Member Loans | Interest and fees
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Net write-offs	$ (150)	$ (89)