Income taxes - Components of Comprehensive Provision for Income Taxes Allocation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Income Tax [Line Items]
United States	$ 169.8	$ 53.2	$ 81.4
Non-U.S. subsidiaries	74.4	(72.7)	88.5
Income (loss) before income taxes	244.2	(19.5)	169.9
Expected tax expense (benefit) at U.S. federal statutory income tax rate of 21%	$ 51.3	$ (4.1)	$ 35.7
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%
Non-U.S. tax rates	$ 0.1	$ (6.3)	$ 2.0
Incremental net tax benefit on earnings and losses of U.S. and non-U.S. tax group companies	11.3	(13.9)	(1.7)
Valuation allowance	10.7
Global intangible low-tax income, net	3.4	(0.4)	1.8
U.S. state income taxes, net	2.6	0.6	1.5
Adjustment to the reserve for uncertain tax positions, net	0.5	(0.7)	(2.9)
Nondeductible expenses	3.2	1.2	1.0
Other, net	(0.2)	(1.0)	(0.6)
Income tax expense (benefit)	82.9	(24.6)	36.8
Comprehensive provision (benefit) for income taxes allocable to:
Net income (loss)	82.9	(24.6)	36.8
Other comprehensive income (loss):
Currency translation	(3.9)	0.4	(3.3)
Total	86.5	(32.1)	95.1
Pension Plans
Other comprehensive income (loss):
Pension plans	$ 7.5	(7.6)	60.7
OPEB
Other comprehensive income (loss):
Pension plans		$ (0.3)	$ 0.9