Other income (Schedule of Other Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Other Income	$ 53.1	$ 49.6	$ 68.6
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other Income	40.2	33.5	37.9
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	7.8	7.1	12.0
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	1.9	3.0	4.7
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other Income	1.3	1.9	2.5
Interest Income [Member]
Disaggregation of Revenue [Line Items]
Other Income	1.2	2.9	8.5
GPS-SID Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	0.0	0.0	1.9
Other [Member]
Disaggregation of Revenue [Line Items]
Other Income	$ 0.7	$ 1.2	$ 1.1