Reserves for Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in the Card Member loans reserve for losses
Balance, January 1	$ 1,223	$ 1,028
Card Member loans - provisions	337	227
Card Member loans net write-offs - principal	(272)	(214)
Card Member loans net write-offs - interest and fees	(51)	(40)
Card Member loans reserves for losses - other	11	11
Balance, September 30	$ 1,248	$ 1,012