Loans Receivable Loans Receivable (Summary of Provision for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 354.7	$ 14.5
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	168.1	11.6
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	186.6	$ 2.9
New Consumer Loan Assignments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	157.9
New Consumer Loan Assignments [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	64.8
New Consumer Loan Assignments [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	93.1
Forecast Changes [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	196.8
Forecast Changes [Member] | Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	103.3
Forecast Changes [Member] | Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 93.5