Loans Receivable Loans Receivable (Summary of Provision for Credit Losses) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 21.3	$ 354.7
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	(0.1)	168.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	21.4	186.6
New Consumer Loan Assignments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	131.8	157.9
New Consumer Loan Assignments [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	54.7	64.8
New Consumer Loan Assignments [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	77.1	93.1
Forecast Changes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	(110.5)	196.8
Forecast Changes [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	(54.8)	103.3
Forecast Changes [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ (55.7)	$ 93.5