Other Income (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Other income	$ 14.3	$ 19.7
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	8.2	10.4
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	2.8	3.4
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	1.7	2.3
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.9	1.0
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	0.7
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	$ 0.5
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Other income	10.8
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	1.7
Transferred over Time [Member] | Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.9
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	3.5
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	2.8
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	0.5
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	10.1
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	1.7
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	4.2
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	2.8
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	0.9
Dealers [Member] | Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5
Dealers [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0