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Reserves For Losses (Details 1) - Card member loans evaluated separately and collectively for impairment [Member] - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Card Member Loans And Related Reserves Evaluated Separately And Collectively For Impairment [Line Items]      
Card Member loans evaluated separately for impairment $ 367 $ 346 $ 279
Reserves on Card Member loans evaluated separately for impairment 57 60 53
Card Member loans evaluated collectively for impairment 73,032 64,919 58,294
Reserves on Card Member loans evaluated collectively for impairment $ 1,649 $ 1,163 $ 975