Loans Receivable (Summary of Changes In Allowance for Credit Losses) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		$ 429.4	$ 320.4
Provision for credit losses		23.4	20.5
Allowance for Loan and Lease Losses, Adjustments, Other		0.0
Write-offs		(6.4)	(3.2)
Recoveries	[1],[2]	2.0	0.3
Balance, end of period		448.4	338.0
Dealer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		366.0	309.3
Provision for credit losses		18.7	17.2
Allowance for Loan and Lease Losses, Adjustments, Other		(2.9)
Write-offs		(4.3)	(3.0)
Recoveries	[1],[2]	1.8	0.3
Balance, end of period		379.3	323.8
Purchased Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		63.4	11.1
Provision for credit losses		4.7	3.3
Allowance for Loan and Lease Losses, Adjustments, Other		2.9
Write-offs		(2.1)	(0.2)
Recoveries	[1],[2]	0.2	0.0
Balance, end of period		$ 69.1	$ 14.2

[1] Represents collections received on previously written off Loans.

[2] Represents collections received on previously written off Loans.