Other Income (Disaggregation of Revenue) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Other income	$ 11.7	$ 14.3
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	8.2	8.2
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	2.2	2.8
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	1.7
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.9
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.5
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	$ 0.2
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	8.9
Transferred over Time [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	8.2
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 over Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.0
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Other income	2.8
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	2.2
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
Transferred at Point in Time [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2
Third Party Providers [Member]
Disaggregation of Revenue [Line Items]
Other income	8.7
Third Party Providers [Member] | Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	8.2
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
Third Party Providers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2
Dealers [Member]
Disaggregation of Revenue [Line Items]
Other income	3.0
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	2.2
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
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0