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, 2023	Dec. 31, 2022	Dec. 31, 2021
Income (loss) before income taxes
United States	$ (545.5)	$ (177.2)	$ (443.5)
Foreign	197.7	114.6	(18.2)
Loss before income taxes	(347.8)	(62.6)	(461.7)
Current
United States	8.8	15.9	9.1
Foreign	46.0	34.7	38.1
Total	54.8	50.6	47.2
Deferred
Foreign	24.5	(8.3)	(59.1)
Total provision (benefit) for income taxes	$ 79.3	$ 42.3	$ (11.9)