Reserves Textuals (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reserves For Losses (Textuals) [Abstract]
Participation interests in Card Member receivables purchased from affiliates	$ 9,800.0	$ 9,400.0	$ 5,400.0
Allowance for Card Member Receivables, Recoveries of Bad Debts	119.0	95.0	91.0
Allowance for Card Member Loans, Recoveries of Bad Debts	1.8	1.0	1.0
Participation Interest in Card Member Receivables Sold to Affiliates	$ 6,200.0	$ 9,400.0	$ 5,700.0