Reserves For Losses (Details Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Card Member Receivables, Recoveries of Bad Debts	$ 359	$ 391	$ 401
Allowance for Card Member Loans, Recoveries of Bad Debts	409	379	418
Allowance for Card Member Receivables, Recoveries of Bad Debts - TDR	(2)	16	60
Allowance for Card Member Loans, Recoveries of Bad Debts - TDR	30	34	41
Loans Transferred From Held For Sale To Held For Investment		265
Cardmember Reserves For Loans Held For Investments		67
Foreign Currency Translation Adjustments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Card Member receivable reserves for losses - Other	12	(12)	(16)
Card Member loans reserves for losses - other	8	(10)	(20)
Other Items [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Card Member receivable reserves for losses - Other	(17)	(5)	(11)
Card Member loans reserves for losses - other	$ 15	$ 8	$ 10