Reserves for Losses - Changes in Card Member Receivables Reserve for Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in the Card Member receivable reserve for losses
Balance, January 1	$ 167	$ 145	$ 110
Provisions	216	243	238
Other credits	13	53	58
Net write-offs	(229)	(238)	(198)
Other debits	(5)	(36)	(63)
Balance, December 31	162	167	145
Participation interests in Card Member receivables purchased from affiliates	2,700	9,800	9,400
Allowance for card member receivables, recoveries of bad debts	125	119	95
Participation interest in card member receivables sold to affiliates	$ 1,100	$ 6,200	$ 9,400