Loans Receivable (Summary Of Changes In Loans Receivable) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period			$ 6,225.2	$ 5,049.0	$ 4,207.0
New Consumer Loan assignments	[1]		3,772.2	3,595.8	2,873.1
Principal collected on Loans receivable			(2,971.2)	(2,576.7)	(2,189.5)
Accelerated Dealer Holdback payments			(58.8)	(52.6)	(47.1)
Dealer Holdback payments			138.5	128.9	131.6
Transfers	[2]		0.0	0.0	0.0
Write-offs			(4.9)	(28.6)	(22.1)
Recoveries	[3],[4]		2.6	4.2	1.8
Balance, end of period		$ 5,049.0	7,221.2	6,225.2	5,049.0
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period			4,141.0	3,518.1	3,209.0
New Consumer Loan assignments	[1]		2,424.5	2,414.8	1,968.3
Principal collected on Loans receivable			(2,049.4)	(1,873.0)	(1,729.9)
Accelerated Dealer Holdback payments			(58.8)	(52.6)	(47.1)
Dealer Holdback payments			138.5	128.9	131.6
Transfers	[2]	(89.0)	(87.2)	(78.2)	(93.1)
Write-offs			(4.4)	(25.2)	(16.4)
Recoveries	[3],[4]		1.5	3.0	1.5
Balance, end of period		3,518.1	4,623.3	4,141.0	3,518.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period			2,084.2	1,530.9	998.0
New Consumer Loan assignments	[1]		1,347.7	1,181.0	904.8
Principal collected on Loans receivable			(921.8)	(703.7)	(459.6)
Accelerated Dealer Holdback payments			0.0	0.0	0.0
Dealer Holdback payments			0.0	0.0	0.0
Transfers	[2]		87.2	78.2	93.1
Write-offs			(0.5)	(3.4)	(5.7)
Recoveries	[3],[4]		1.1	1.2	0.3
Balance, end of period		$ 1,530.9	$ 2,597.9	$ 2,084.2	$ 1,530.9

[1] The Dealer Loans amount represents advances paid to Dealers on Consumer Loans assigned under our Portfolio Program.  The Purchased Loans amount represents one-time payments made to Dealers to purchase Consumer Loans assigned under our Purchase Program.

[2] 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 and the related allowance for credit losses balance to Purchased Loans in the period this forfeiture occurs.

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

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