Loans Receivable (Summary Of Changes In Allowance For Credit Losses) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		$ 320.4		$ 243.6		$ 206.9
Provision for credit losses		129.3		90.2		41.5
Transfers	[1]	0.0
Write-offs		(22.1)		(14.8)		(6.6)
Recoveries	[3]	1.8	[2]	1.4	[1]	1.8	[1]
Balance, end of period		429.4		320.4		243.6
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		309.3		235.1		198.1
Provision for credit losses		103.4		87.3		41.8
Transfers	[1]	(31.8)
Write-offs		(16.4)		(14.4)		(6.4)
Recoveries	[3]	1.5	[2]	1.3	[2]	1.6	[1]
Balance, end of period		366.0		309.3		235.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		11.1		8.5		8.8
Provision for credit losses		25.9		2.9		(0.3)
Transfers	[1]	31.8
Write-offs		(5.7)		(0.4)		(0.2)
Recoveries	[3]	0.3	[2]	0.1	[1]	0.2	[1]
Balance, end of period		$ 63.4		$ 11.1		$ 8.5

[1] Under our Portfolio Program, certain events may result in Dealers forfeiting their rights to Dealer Holdback. We transfer the Dealer’s outstanding Dealer Loan balance to Purchased Loans in the period this forfeiture occurs. Beginning in the fourth quarter of 2017, we also transfer the related allowance for credit losses balance to Purchased Loans in the period this forfeiture occurs.

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

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