Accounts receivable - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Revenue recognized in excess of billings on services contracts or unbilled accounts receivable	$ 73.1	$ 63.3
Allowance for doubtful accounts	8.0	9.2
Provision for doubtful accounts reported in selling, general and administrative expenses, (income) expense	(0.6)	(0.3)	$ (1.6)
Long-term receivables	$ 49.1	$ 84.4