Other income (Schedule of Other Income) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Other income	$ 23.3	$ 12.6	$ 57.5	$ 34.8
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	13.7	9.6	41.3	25.0
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	7.1	1.9	11.0	6.0
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	1.9	0.2	2.9	0.9
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.5	1.4	1.6
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.2	0.9	0.9
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0	$ 0.2	$ 0.0	$ 0.4