Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Other income	$ 13.9	$ 16.0	$ 28.2	$ 35.7
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	10.0	8.1	18.2	18.5
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.8	3.1	4.6	6.5
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	2.4	2.2	4.7
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.9	1.1	1.8	2.1
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	0.7	1.0	1.4
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	$ 0.1	0.4	$ 0.6
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	11.4		22.2
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	10.0		18.2
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	0.5		2.2
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.9		1.8
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	2.5		6.0
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	1.8		4.6
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		1.0
Transferred at Point in Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2		0.4
Third Party Providers [Member]
Disaggregation of Revenue [Line Items]
Other income	10.7		20.8
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	10.0		18.2
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	0.5		2.2
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		0.4
Dealers [Member]
Disaggregation of Revenue [Line Items]
Other income	3.2		7.4
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	1.8		4.6
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	0.9		1.8
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5		1.0
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0		$ 0.0