Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in the Card Member receivable reserve for losses
Balance, January 1	$ 145	$ 110
Provisions	62	60
Other credits	28	10
Net write-offs	(56)	(47)
Other debits	0	(5)
Balance, March 31	$ 179	$ 128