Income taxes - Components of Comprehensive Provision for Income Taxes Allocation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income taxes
U.S.	$ (16.6)	$ 169.8	$ 53.2
Non-U.S.	(26.4)	74.4	(72.7)
Income (loss) before income taxes	$ (43.0)	$ 244.2	$ (19.5)