Reserves (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Changes in the Card Member receivable reserve for losses
Balance, January 1	$ 145	$ 110
Provisions	186	171
Other credits	51	35
Net write-offs	(173)	(142)
Other debits	(26)	(16)
Balance, September 30	$ 183	$ 158