Reserves for Credit Losses (Details 3) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provisions	$ 29.0	$ (12.0)	$ (9.0)	$ 264.0
Card Member Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	21.0	23.0	20.0	17.0
Provisions	4.0	4.0	12.0	16.0
Net write-offs	(2.0)	(5.0)	(9.0)	(11.0)
Ending Balance	23.0	22.0	23.0	22.0
Recoveries	$ 1.1	$ 0.6	$ 2.6	$ 2.0