Reserves (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the Card Member receivable reserve for losses
Balance, January 1	$ 110	$ 114	$ 94
Provisions	238	145	160
Other credits	58	20	32
Net write-offs	(198)	(146)	(157)
Other debits	(63)	(23)	(15)
Balance, December 31	$ 145	$ 110	$ 114