Reserves for Credit Losses (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions	$ (24.0)	$ 173.0	$ (38.0)	$ 276.0
Card Member Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	24.0	18.0	20.0	17.0
Provisions	0.0	9.0	8.0	12.0
Net write-offs	(3.0)	(4.0)	(7.0)	(6.0)
Ending Balance	21.0	23.0	21.0	23.0
Recoveries	$ 0.8	$ 0.5	$ 1.5	$ 1.0