Loans Receivable (Summary of Changes In Allowance for Credit Losses) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		$ 354.1	$ 276.9	$ 320.4	$ 243.6
Provision for credit losses		25.7	22.8	68.0	62.8
Write-offs		(4.1)	(3.3)	(13.5)	(10.7)
Recoveries	[1],[2]	0.5	0.4	1.3	1.1
Balance, end of period		376.2	296.8	376.2	296.8
Dealer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		336.9	268.2	309.3	235.1
Provision for credit losses		20.2	21.6	55.6	61.3
Write-offs		(2.9)	(3.1)	(11.4)	(10.4)
Recoveries	[1],[2]	0.4	0.3	1.1	1.0
Balance, end of period		354.6	287.0	354.6	287.0
Purchased Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period		17.2	8.7	11.1	8.5
Provision for credit losses		5.5	1.2	12.4	1.5
Write-offs		(1.2)	(0.2)	(2.1)	(0.3)
Recoveries	[1],[2]	0.1	0.1	0.2	0.1
Balance, end of period		$ 21.6	$ 9.8	$ 21.6	$ 9.8

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

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