Loans Receivable (Schedule of Loans Receivable) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 3,189.7	$ 3,052.6	$ 2,719.8	$ 2,615.6	$ 2,562.8	$ 2,408.2
Allowance for credit losses	(230.2)	(217.9)	(206.9)	(208.2)	(204.8)	(195.4)
Loans receivable, net	2,959.5		2,512.9
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,726.5	2,634.8	2,389.8	2,315.3	2,279.0	2,155.5
Allowance for credit losses	(221.8)	(209.4)	(198.1)	(199.1)	(195.8)	(185.7)
Loans receivable, net	2,504.7		2,191.7
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	463.2	417.8	330.0	300.3	283.8	252.7
Allowance for credit losses	(8.4)	$ (8.5)	(8.8)	$ (9.1)	$ (9.0)	$ (9.7)
Loans receivable, net	$ 454.8		$ 321.2