Reserves Textuals (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Reserves For Losses (Textuals) [Abstract]
Participation interests in Card Member receivables purchased from affiliates	$ 2,700.0	$ 5,500.0
Allowance for Card Member Receivables, Recoveries of Bad Debts	64.0	55.0
Allowance for Card Member Loans, Recoveries of Bad Debts	1.0	1.0
Participation Interest in Card Member Receivables Sold to Affiliates	$ 1,100.0	$ 3,400.0