Stockholders' equity - Tax Effects Related to Each Component of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	$ 12.0	$ (19.8)	$ (5.3)
Tax Benefit (Expense)	(2.8)	4.4	0.9
Total other comprehensive income (loss), net of tax	9.2	(15.4)	(4.4)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	4.3	(5.0)	(3.7)
Tax Benefit (Expense)	(0.6)	0.7	0.5
Total other comprehensive income (loss), net of tax	3.7	(4.3)	(3.2)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	8.9	(13.0)	(2.0)
Tax Benefit (Expense)	(2.4)	3.6	0.4
Total other comprehensive income (loss), net of tax	6.5	(9.4)	(1.6)
Foreign Currency Translation Losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pretax	(1.2)	(1.8)	0.4
Tax Benefit (Expense)	0.2	0.1	0.0
Total other comprehensive income (loss), net of tax	$ (1.0)	$ (1.7)	$ 0.4