Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Other income	$ 12.6	$ 7.0	$ 34.8	$ 35.2
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	9.6	4.1	25.0	22.3
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.9	1.1	6.0	5.7
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	0.4	0.9	2.6
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	0.7	1.6	2.5
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	0.5	0.9	1.5
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	$ 0.2	0.4	$ 0.6
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	10.3		27.5
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	9.6		25.0
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	0.2		0.9
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5		1.6
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	2.3		7.3
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		6.0
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	0.2		0.9
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	10.0		26.3
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	9.6		25.0
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	0.2		0.9
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	2.6		8.5
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		6.0
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	0.5		1.6
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2		0.9
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0		$ 0.0