Reserves (Details Textuals) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Reserves For Losses (Textuals) [Abstract]
Participation interests in Card Member receivables purchased from affiliates	$ 6,000.0	$ 3,400.0
Allowance for Card Member Receivables, Recoveries of Bad Debts	70.0	71.0
Allowance for Card Member Loans, Recoveries of Bad Debts	1.0	1.0
Participation Interest in Card Member Receivables Sold to Affiliates	$ 2,600.0	$ 4,700.0