Loans Receivable (Schedule of Loans Receivable) - USD ($) $ in Millions	Sep. 30, 2021		Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 9,685.8	[1],[2]		$ 10,124.8
Allowance for credit losses	(3,103.2)			(3,336.9)
Loans receivable, net	6,582.6		$ 6,768.1	6,787.9	$ 6,865.2	$ 6,749.8	$ 6,685.2
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	5,776.6	[1]		5,869.6
Allowance for credit losses	(1,746.0)			(1,702.1)
Loans receivable, net	4,030.6		4,135.9	4,167.5	4,222.9	4,187.2	4,195.3
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	3,909.2	[2]		4,255.2
Allowance for credit losses	(1,357.2)			(1,634.8)
Loans receivable, net	$ 2,552.0		$ 2,632.2	$ 2,620.4	$ 2,642.3	$ 2,562.6	$ 2,489.9

[1] As Consumer Loans are aggregated by Dealer for purposes of recognizing revenue and measuring credit losses, the Dealer Loan amount was estimated by allocating the balance of each Dealer Loan to the underlying Consumer Loans based on the forecasted future collections of each Consumer Loan.

[2] As certain Consumer Loans are aggregated by Dealer or month of purchase for purposes of recognizing revenue and measuring credit losses, the Purchased Loan amount was estimated by allocating the balance of certain Purchased Loans to the underlying Consumer Loans based on the forecasted future collections of each Consumer Loan.