Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Other income	$ 10.5	$ 13.9	$ 22.2	$ 28.2
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	7.2	10.0	15.4	18.2
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.9	1.8	4.1	4.6
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.5	0.7	2.2
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7	0.9	1.1	1.8
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.5	0.7	1.0
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0	$ 0.2	0.2	$ 0.4
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	8.3		17.2
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	7.2		15.4
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		0.7
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7		1.1
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	2.2		5.0
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	1.9		4.1
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	0.3		0.7
Transferred at Point in Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0		0.2
Third Party Providers [Member]
Disaggregation of Revenue [Line Items]
Other income	7.6		16.3
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	7.2		15.4
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		0.7
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	0.0		0.2
Dealers [Member]
Disaggregation of Revenue [Line Items]
Other income	2.9		5.9
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	1.9		4.1
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		1.1
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3		0.7
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0		$ 0.0