Reserves (Details Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserves For Losses (Textuals) [Abstract]
Participation interests in Card Member receivables purchased from affiliates	$ 9,400	$ 5,400	$ 5,800
Allowance for Card Member Receivables, Recoveries of Bad Debts	95	91	100
Allowance for Card Member Loans, Recoveries of Bad Debts	1	1	1
Participation Interest in Card Member Receivables Sold to Affiliates	$ 9,400	$ 5,700	$ 2,600