Loans Receivable (Schedule of Loans Receivable) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 3,052.6	$ 2,943.6	$ 2,719.8	$ 2,562.8	$ 2,518.1	$ 2,408.2
Allowance for credit losses	(217.9)	(210.4)	(206.9)	(204.8)	(200.1)		$ (195.4)
Loans receivable, net	2,834.7		2,512.9
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,634.8	2,564.3	2,389.8	2,279.0	2,247.0	2,155.5
Allowance for credit losses	(209.4)	(201.6)	(198.1)	(195.8)	(190.8)		(185.7)
Loans receivable, net	2,425.4		2,191.7
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	417.8	379.3	330.0	283.8	271.1	$ 252.7
Allowance for credit losses	(8.5)	$ (8.8)	(8.8)	$ (9.0)	$ (9.3)		$ (9.7)
Loans receivable, net	$ 409.3		$ 321.2