Income taxes - Total Income (Loss) From Continuing Operations Before Income Taxes and Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income (loss) from continuing operations before income taxes
United States	$ (177.2)	$ (443.5)	$ (316.3)
Foreign	114.6	(18.2)	44.5
Loss from continuing operations before income taxes	(62.6)	(461.7)	(271.8)
Current
United States	15.9	9.1	7.3
Foreign	34.7	38.1	51.5
Total	50.6	47.2	58.8
Deferred
Foreign	(8.3)	(59.1)	(13.4)
Total provision (benefit) for income taxes	$ 42.3	$ (11.9)	$ 45.4