Other income (Schedule of Other Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Other Income	$ 49.6	$ 68.6	$ 62.4
Ancillary Product Profit Sharing [Member]
Disaggregation of Revenue [Line Items]
Other Income	33.5	37.9	30.6
Remarketing Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	7.1	12.0	11.2
Interest Income [Member]
Disaggregation of Revenue [Line Items]
Other Income	2.9	8.5	5.0
Dealer Enrollment Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	3.0	4.7	4.3
Dealer Support Products And Services [Member]
Disaggregation of Revenue [Line Items]
Other Income	1.9	2.5	4.1
GPS-SID Fees [Member]
Disaggregation of Revenue [Line Items]
Other Income	0.0	1.9	6.4
Other [Member]
Disaggregation of Revenue [Line Items]
Other Income	$ 1.2	$ 1.1	$ 0.8