Loans Receivable (Summary Of Changes In Loans Receivable and Allowance for Credit Losses) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		$ 6,685.2	$ 5,763.3	$ 4,619.6
Adoption of CECL	[1]	0.0
Finance Charges Revenue		(1,562.4)	(1,369.4)	(1,176.8)
Provision for credit losses		556.9	76.4	56.9
New Consumer Loan assignments		3,641.2	3,772.2	3,595.8
Principal collected on Loans receivable		(4,741.4)	(4,349.5)	(3,762.3)
Accelerated Dealer Holdback payments		(45.9)	(58.8)	(52.6)
Dealer Holdback payments		142.6	138.5	128.9
Transfers	[2]	0.0	0.0	0.0
Write-offs		0.0	0.0	0.0
Recoveries	[3]	0.0	0.0	0.0
Deferral of Loan Origination Costs		8.9	8.9	8.8
Balance, end of period		6,787.9	6,685.2	5,763.3
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		7,221.2	6,225.2	5,049.0
Adoption of CECL	[1]	(2,463.6)
Finance Charges Revenue		(2,304.9)	(1,369.4)	(1,176.8)
Provision for credit losses		0.0	0.0	0.0
New Consumer Loan assignments		3,641.2	3,772.2	3,595.8
Principal collected on Loans receivable		(4,741.4)	(4,349.5)	(3,762.3)
Accelerated Dealer Holdback payments		(45.9)	(58.8)	(52.6)
Dealer Holdback payments		142.6	138.5	128.9
Transfers	[2]	0.0	0.0	0.0
Write-offs		(964.9)	(4.9)	(28.6)
Recoveries	[3]	(2.8)	(2.6)	(4.2)
Deferral of Loan Origination Costs		8.9	8.9	8.8
Balance, end of period		10,124.8	7,221.2	6,225.2
Allowance for Credit Losses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		536.0	461.9	429.4
Adoption of CECL	[1]	(2,463.6)
Finance Charges Revenue		(742.5)	0.0	0.0
Provision for credit losses		556.9	76.4	56.9
New Consumer Loan assignments		0.0	0.0	0.0
Principal collected on Loans receivable		0.0	0.0	0.0
Accelerated Dealer Holdback payments		0.0	0.0	0.0
Dealer Holdback payments		0.0	0.0	0.0
Transfers	[2]	0.0	0.0	0.0
Write-offs		(964.9)	(4.9)	(28.6)
Recoveries	[3]	(2.8)	(2.6)	(4.2)
Deferral of Loan Origination Costs		0.0	0.0	0.0
Balance, end of period		3,336.9	536.0	461.9
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		4,195.3	3,762.9	3,152.1
Adoption of CECL	[1]	0.0
Finance Charges Revenue		(945.9)	(888.7)	(807.5)
Provision for credit losses		239.7	65.9	48.0
New Consumer Loan assignments		2,207.8	2,424.5	2,414.8
Principal collected on Loans receivable		(3,059.1)	(2,947.0)	(2,689.3)
Accelerated Dealer Holdback payments		(45.9)	(58.8)	(52.6)
Dealer Holdback payments		142.6	138.5	128.9
Transfers	[2]	(80.1)	(74.1)	(64.5)
Write-offs		0.0	0.0	0.0
Recoveries	[3]	0.0	0.0	0.0
Deferral of Loan Origination Costs		8.9	8.9	8.8
Balance, end of period		4,167.5	4,195.3	3,762.9
Dealer Loans [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		4,623.3	4,141.0	3,518.1
Adoption of CECL	[1]	(940.2)
Finance Charges Revenue		(1,313.9)	(888.7)	(807.5)
Provision for credit losses		0.0	0.0	0.0
New Consumer Loan assignments		2,207.8	2,424.5	2,414.8
Principal collected on Loans receivable		(3,059.1)	(2,947.0)	(2,689.3)
Accelerated Dealer Holdback payments		(45.9)	(58.8)	(52.6)
Dealer Holdback payments		142.6	138.5	128.9
Transfers	[2]	(119.8)	(87.2)	(78.2)
Write-offs		(235.1)	(4.4)	(25.2)
Recoveries	[3]	(1.0)	(1.5)	(3.0)
Deferral of Loan Origination Costs		8.9	8.9	8.8
Balance, end of period		5,869.6	4,623.3	4,141.0
Dealer Loans [Member] | Allowance for Credit Losses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		428.0	378.1	366.0
Adoption of CECL	[1]	(940.2)
Finance Charges Revenue		(368.0)	0.0	0.0
Provision for credit losses		239.7	65.9	48.0
New Consumer Loan assignments		0.0	0.0	0.0
Principal collected on Loans receivable		0.0	0.0	0.0
Accelerated Dealer Holdback payments		0.0	0.0	0.0
Dealer Holdback payments		0.0	0.0	0.0
Transfers	[2]	(39.7)	(13.1)	(13.7)
Write-offs		(235.1)	(4.4)	(25.2)
Recoveries	[3]	(1.0)	(1.5)	(3.0)
Deferral of Loan Origination Costs		0.0	0.0	0.0
Balance, end of period		1,702.1	428.0	378.1
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		2,489.9	2,000.4	1,467.5
Adoption of CECL	[1]	0.0
Finance Charges Revenue		(616.5)	(480.7)	(369.3)
Provision for credit losses		317.2	10.5	8.9
New Consumer Loan assignments		1,433.4	1,347.7	1,181.0
Principal collected on Loans receivable		(1,682.3)	(1,402.5)	(1,073.0)
Accelerated Dealer Holdback payments		0.0	0.0	0.0
Dealer Holdback payments		0.0	0.0	0.0
Transfers	[2]	(80.1)	(74.1)	(64.5)
Write-offs		0.0	0.0	0.0
Recoveries	[3]	0.0	0.0	0.0
Deferral of Loan Origination Costs		0.0	0.0	0.0
Balance, end of period		2,620.4	2,489.9	2,000.4
Purchased Loans [Member] | Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		2,597.9	2,084.2	1,530.9
Adoption of CECL	[1]	(1,523.4)
Finance Charges Revenue		(991.0)	(480.7)	(369.3)
Provision for credit losses		0.0	0.0	0.0
New Consumer Loan assignments		1,433.4	1,347.7	1,181.0
Principal collected on Loans receivable		(1,682.3)	(1,402.5)	(1,073.0)
Accelerated Dealer Holdback payments		0.0	0.0	0.0
Dealer Holdback payments		0.0	0.0	0.0
Transfers	[2]	(119.8)	(87.2)	(78.2)
Write-offs		(729.8)	(0.5)	(3.4)
Recoveries	[3]	(1.8)	(1.1)	(1.2)
Deferral of Loan Origination Costs		0.0	0.0	0.0
Balance, end of period		4,255.2	2,597.9	2,084.2
Purchased Loans [Member] | Allowance for Credit Losses [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance, beginning of period		108.0	83.8	63.4
Adoption of CECL	[1]	(1,523.4)
Finance Charges Revenue		(374.5)	0.0	0.0
Provision for credit losses		317.2	10.5	8.9
New Consumer Loan assignments		0.0	0.0	0.0
Principal collected on Loans receivable		0.0	0.0	0.0
Accelerated Dealer Holdback payments		0.0	0.0	0.0
Dealer Holdback payments		0.0	0.0	0.0
Transfers	[2]	(39.7)	(13.1)	(13.7)
Write-offs		(729.8)	(0.5)	(3.4)
Recoveries	[3]	(1.8)	(1.1)	(1.2)
Deferral of Loan Origination Costs		0.0	0.0	0.0
Balance, end of period		$ 1,634.8	$ 108.0	$ 83.8

[1] Represents the gross-up of Loans receivable and allowance for credit losses on January 1, 2020 upon the adoption of CECL for the present value of the difference between contractual future net cash flows and expected future net cash flows discounted at the effective interest rate.

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

[3] The Dealer Loans amount represents net cash flows received (collections less any related Dealer Holdback payments) on Dealer Loans that were previously written off in full. The Purchased Loans amount represents collections received on Purchased Loans that were previously written off in full