Loans Receivable (Summary of Changes In Allowance for Credit Losses) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		$ 448.4	$ 338.0	$ 429.4	$ 320.4
Provision for credit losses		1.8	21.8	25.2	42.3
Transfers		0.0		0.0
Write-offs		(15.4)	(6.2)	(21.8)	(9.4)
Recoveries	[1],[2]	0.9	0.5	2.9	0.8
Balance, end of period		435.7	354.1	435.7	354.1
Dealer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		379.3	323.8	366.0	309.3
Provision for credit losses		3.2	18.2	21.9	35.4
Transfers		(2.7)		(5.6)
Write-offs		(14.5)	(5.5)	(18.8)	(8.5)
Recoveries	[1],[2]	0.6	0.4	2.4	0.7
Balance, end of period		365.9	336.9	365.9	336.9
Purchased Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		69.1	14.2	63.4	11.1
Provision for credit losses		(1.4)	3.6	3.3	6.9
Transfers		2.7		5.6
Write-offs		(0.9)	(0.7)	(3.0)	(0.9)
Recoveries	[1],[2]	0.3	0.1	0.5	0.1
Balance, end of period		$ 69.8	$ 17.2	$ 69.8	$ 17.2

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

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