Reserves for Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in the Card Member loans reserve for losses
Balance, January 1			$ 1,223	$ 1,028
Card Member loans - provisions	$ 531	$ 319	1,272	831
Card Member loans net write-offs - principal			(856)	(687)
Card Member loans net write-offs - interest and fees			(163)	(128)
Card Member loans reserves for losses - other			26	70
Balance, September 30	$ 1,502	$ 1,114	$ 1,502	$ 1,114