Other income (Schedule of Other Income) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Other income	$ 10.5	$ 13.9	$ 22.2	$ 28.2
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other income	7.2	10.0	15.4	18.2
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	1.9	1.8	4.1	4.6
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other income	0.7	0.9	1.1	1.8
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other income	0.3	0.5	0.7	1.0
Interest [Member]
Disaggregation of Revenue [Line Items]
Other income	0.4	0.5	0.7	2.2
Other [Member]
Disaggregation of Revenue [Line Items]
Other income	$ 0.0	$ 0.2	$ 0.2	$ 0.4