Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Other income	$ 17.8	$ 11.7
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	14.7	8.2
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	2.0	2.2
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.3
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.4
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.4
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0	$ 0.2
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	15.4
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	14.7
Transferred over Time [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred over Time [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4
Transferred over Time [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Other income	2.4
Transferred at Point in Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred at Point in Time [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	2.0
Transferred at Point in Time [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred at Point in Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred at Point in Time [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4
Third Party Providers [Member]
Disaggregation of Revenue [Line Items]
Other income	15.0
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	14.7
Third Party Providers [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Third Party Providers [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3
Third Party Providers [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Third Party Providers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Dealers [Member]
Disaggregation of Revenue [Line Items]
Other income	2.8
Dealers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Dealers [Member] | Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	2.0
Dealers [Member] | Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Dealers [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.4