Reserves For Losses (Details 1) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Card Member Loans And Related Reserves Evaluated Separately And Collectively For Impairment [Abstract]
Card Member loans evaluated individually for impairment	$ 397	$ 367
Reserves on Card Member loans evaluated individually for impairment	60	57
Card Member loans evaluated collectively for impairment	72,423	73,032
Reserves on Card Member loans evaluated collectively for impairment	$ 1,726	$ 1,649