Loans Receivable Loans Receivable (Summary of Provision for Credit Losses) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 139.4	$ 15.4	$ 494.1	$ 29.9
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	61.1	14.5	229.2	26.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	78.3	0.9	264.9	3.8
New Consumer Loan Assignments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	154.2	0.0	312.1	0.0
New Consumer Loan Assignments [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	60.9	0.0	125.7	0.0
New Consumer Loan Assignments [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	93.3	$ 0.0	186.4	$ 0.0
Forecast Changes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	(14.8)		182.0
Forecast Changes [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	0.2		103.5
Forecast Changes [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ (15.0)		$ 78.5