Loans Receivable (Summary of Changes In Allowance for Credit Losses) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		$ 435.7	$ 354.1	$ 429.4	$ 320.4
Provision for credit losses		14.0	25.7	39.2	68.0
Transfers		0.0		0.0
Write-offs		(2.7)	(4.1)	(24.5)	(13.5)
Recoveries	[1],[2]	0.6	0.5	3.5	1.3
Balance, end of period		447.6	376.2	447.6	376.2
Dealer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		365.9	336.9	366.0	309.3
Provision for credit losses		12.4	20.2	34.3	55.6
Transfers		(3.1)		(8.7)
Write-offs		(2.5)	(2.9)	(21.3)	(11.4)
Recoveries	[1],[2]	0.3	0.4	2.7	1.1
Balance, end of period		373.0	354.6	373.0	354.6
Purchased Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		69.8	17.2	63.4	11.1
Provision for credit losses		1.6	5.5	4.9	12.4
Transfers		3.1		8.7
Write-offs		(0.2)	(1.2)	(3.2)	(2.1)
Recoveries	[1],[2]	0.3	0.1	0.8	0.2
Balance, end of period		$ 74.6	$ 21.6	$ 74.6	$ 21.6

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

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