Loans Receivable (Summary of Changes in Accretable Yield) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Certain Loans Acquired in Transfer Not Accounted for as Loans Accretable Yield Movement Schedule [Roll Forward]
Balance, beginning of period		$ 1,494.8	$ 1,246.5	$ 1,330.7	$ 1,072.8
New Consumer Loan assignments	[1]	285.3	276.7	883.7	832.0
Accretion	[2]	(261.7)	(226.2)	(755.8)	(648.7)
Provision for credit losses		25.7	22.8	68.0	62.8
Forecast changes		5.5	(6.0)	22.4	(6.2)
Transfers	[3]	0.8	1.7	1.4	2.8
Balance, end of period		1,550.4	1,315.5	1,550.4	1,315.5
Dealer Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Loans Accretable Yield Movement Schedule [Roll Forward]
Balance, beginning of period		1,038.4	963.2	982.6	874.2
New Consumer Loan assignments	[1]	192.6	196.1	599.1	613.8
Accretion	[2]	(194.7)	(183.1)	(575.5)	(537.2)
Provision for credit losses		20.2	21.6	55.6	61.3
Forecast changes		(1.9)	(7.6)	(6.8)	(21.1)
Transfers	[3]	(0.5)	(0.8)	(0.9)	(1.6)
Balance, end of period		1,054.1	989.4	1,054.1	989.4
Purchased Loans [Member]
Certain Loans Acquired in Transfer Not Accounted for as Loans Accretable Yield Movement Schedule [Roll Forward]
Balance, beginning of period		456.4	283.3	348.1	198.6
New Consumer Loan assignments	[1]	92.7	80.6	284.6	218.2
Accretion	[2]	(67.0)	(43.1)	(180.3)	(111.5)
Provision for credit losses		5.5	1.2	12.4	1.5
Forecast changes		7.4	1.6	29.2	14.9
Transfers	[3]	1.3	2.5	2.3	4.4
Balance, end of period		$ 496.3	$ 326.1	$ 496.3	$ 326.1

[1] The Dealer Loans amount represents the net cash flows expected at the time of assignment on Consumer Loans assigned under our Portfolio Program, less the related advances paid to Dealers. The Purchased Loans amount represents the net cash flows expected at the time of assignment on Consumer Loans assigned under our Purchase Program, less the related one-time payments made to Dealers.

[2] Represents finance charges excluding the amortization of deferred direct origination costs for Dealer Loans.

[3] 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 expected future net cash flows to Purchased Loans in the period this forfeiture occurs.