Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Other income	$ 7.0	$ 15.9	$ 35.2	$ 51.6
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	4.1	8.8	22.3	27.3
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.1	3.0	5.7	9.5
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	2.0	2.6	6.7
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7	1.4	2.5	3.5
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	0.6	1.5	2.0
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	$ 0.1	0.6	$ 0.7
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	5.2		27.4
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	4.1		22.3
Transferred over Time [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred over Time [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4		2.6
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7		2.5
Transferred over Time [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred over Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Other income	1.8		7.8
Transferred at Point in Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred at Point in Time [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.1		5.7
Transferred at Point in Time [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred at Point in Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Transferred at Point in Time [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5		1.5
Transferred at Point in Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2		0.6
Third Party Providers [Member]
Disaggregation of Revenue [Line Items]
Other income	4.7		25.5
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	4.1		22.3
Third Party Providers [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Third Party Providers [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4		2.6
Third Party Providers [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Third Party Providers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Third Party Providers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2		0.6
Dealers [Member]
Disaggregation of Revenue [Line Items]
Other income	2.3		9.7
Dealers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Dealers [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.1		5.7
Dealers [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.0
Dealers [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7		2.5
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5		1.5
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0		$ 0.0