Loans Receivable (Schedule of Loans Receivable) (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
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
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