Loans Receivable (Schedule of Consumer Loans Performance) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 2,943.6	$ 2,719.8	$ 2,518.1	$ 2,408.2
Allowance for credit losses	(210.4)	(206.9)	(200.1)	(195.4)
Loans receivable, net	2,733.2	2,512.9
Loan Pool Performance Meets Or Exceeds Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	1,321.4	1,262.8
Loans receivable, net	1,321.4	1,262.8
Loan Pool Performance Less Than Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	1,622.2	1,457.0
Allowance for credit losses	(210.4)	(206.9)
Loans receivable, net	1,411.8	1,250.1
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,564.3	2,389.8	2,247.0	2,155.5
Allowance for credit losses	(201.6)	(198.1)	(190.8)	(185.7)
Loans receivable, net	2,362.7	2,191.7
Dealer Loans [Member] | Loan Pool Performance Meets Or Exceeds Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	986.5	945.1
Loans receivable, net	986.5	945.1
Dealer Loans [Member] | Loan Pool Performance Less Than Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	1,577.8	1,444.7
Allowance for credit losses	(201.6)	(198.1)
Loans receivable, net	1,376.2	1,246.6
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	379.3	330.0	271.1	252.7
Allowance for credit losses	(8.8)	(8.8)	(9.3)	(9.7)
Loans receivable, net	370.5	321.2
Purchased Loans [Member] | Loan Pool Performance Meets Or Exceeds Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	334.9	317.7
Loans receivable, net	334.9	317.7
Purchased Loans [Member] | Loan Pool Performance Less Than Initial Estimates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	44.4	12.3
Allowance for credit losses	(8.8)	(8.8)
Loans receivable, net	$ 35.6	$ 3.5