Reserves (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Changes in the Card Member receivable reserve for losses
Balance, January 1	$ 145	$ 110
Provisions	119	113
Other credits	32	33
Net write-offs	(119)	(94)
Other debits	(20)	(16)
Balance, June 30	$ 157	$ 146