Loans Receivable (Schedule of Loans Receivable) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 2,562.8	$ 2,518.1	$ 2,408.2	$ 2,278.5	$ 2,210.3	$ 2,109.9
Allowance for credit losses	(204.8)	(200.1)	(195.4)	(185.8)	(181.7)	(176.4)
Loans receivable, net	2,358.0		2,212.8
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,279.0	2,247.0	2,155.5	2,041.4	1,973.1	1,869.4
Allowance for credit losses	(195.8)	(190.8)	(185.7)	(175.5)	(172.9)	(167.4)
Loans receivable, net	2,083.2		1,969.8
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	283.8	271.1	252.7	237.1	237.2	240.5
Allowance for credit losses	(9.0)	(9.3)	(9.7)	(10.3)	(8.8)	(9.0)
Loans receivable, net	$ 274.8		$ 243.0