Loans Receivable (Schedule of Loans Receivable) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	$ 2,615.6	$ 2,562.8	$ 2,408.2	$ 2,354.3	$ 2,278.5	$ 2,109.9
Allowance for credit losses	(208.2)	(204.8)	(195.4)	(190.9)	(185.8)	(176.4)
Loans receivable, net	2,407.4		2,212.8
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	2,315.3	2,279.0	2,155.5	2,110.0	2,041.4	1,869.4
Allowance for credit losses	(199.1)	(195.8)	(185.7)	(180.8)	(175.5)	(167.4)
Loans receivable, net	2,116.2		1,969.8
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable	300.3	283.8	252.7	244.3	237.1	240.5
Allowance for credit losses	(9.1)	(9.0)	(9.7)	(10.1)	(10.3)	(9.0)
Loans receivable, net	$ 291.2		$ 243.0