Reserves For Losses (Details 1) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Card Member Loans And Related Reserves Evaluated Separately And Collectively For Impairment [Abstract]
Card Member loans evaluated individually for impairment	$ 347	$ 346
Reserves on Card Member loans evaluated individually for impairment	57	60
Card Member loans evaluated collectively for impairment	67,531	64,919
Reserves on Card Member loans evaluated collectively for impairment	$ 1,445	$ 1,163