Other income (Schedule of Other Income) - 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
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
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.3
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0	$ 0.2