Other income (Schedule of Other Income) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Other income	$ 12.6	$ 7.0	$ 34.8	$ 35.2
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	9.6	4.1	25.0	22.3
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.9	1.1	6.0	5.7
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.5	0.7	1.6	2.5
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	0.5	0.9	1.5
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.2	0.4	0.9	2.6
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.2	$ 0.2	$ 0.4	$ 0.6