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Reserves for Losses (Details 3) - Card Member Receivables Evaluated Separately And Collectively For Impairment [Member] - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Card Member Receivables And Related Reserves Evaluated Separately and Collectively For Impairment [Line Items]      
Card Member receivables evaluated separately for impairment $ 80 $ 55 $ 33
Reserves on Card Member receivables evaluated separately for impairment 3 28 20
Card Member receivables evaluated collectively for impairment 53,967 47,253 44,100
Reserves on Card Member receivables evaluated collectively for impairment $ 518 $ 439 $ 442