Reserves for Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Changes in the Card Member loans reserve for losses
Balance, January 1			$ 1,223	$ 1,028
Card Member loans - provisions	$ 404	$ 285	741	512
Card Member loans net write-offs - principal			(557)	(437)
Card Member loans net write-offs - interest and fees			(106)	(80)
Card Member loans reserves for losses - other			19	68
Balance, September 30	$ 1,320	$ 1,091	$ 1,320	$ 1,091