Income taxes - Components of Income Taxes and Comprehensive Provision for Income Taxes Allocation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Income Tax [Line Items]
U.S.	$ (1.5)	$ 44.1	$ 25.5
Non-U.S.	(71.4)	89.8	127.9
Income (loss) before income taxes	(72.9)	133.9	153.4
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 21%	$ (15.3)	28.1	32.2
U.S. Federal statutory income tax rate	21.00%
Non-U.S. tax rates	$ (6.3)	2.1	4.6
Incremental net tax benefit on earnings and losses of U.S. and non-U.S. companies	(4.7)	(0.5)	(3.9)
Valuation allowance, net	2.6	(3.6)	3.1
Global intangible low-tax income, net	(0.3)	2.1	2.8
Adjustment to the reserve for uncertain tax positions, net	(0.5)	(0.4)
Nondeductible expenses	1.0	0.9	1.0
U.S. state income taxes and other, net	(0.3)	0.7	0.7
Income tax expense (benefit)	(23.8)	29.4	40.5
Current payable:
U.S. federal and state	2.0	10.7	4.6
Non-U.S.	13.5	20.1	21.6
Total	15.5	30.8	26.2
U.S. federal and state	(3.7)	(3.0)	3.3
Non-U.S.	(35.6)	1.6	11.0
Total	(39.3)	(1.4)	14.3
Comprehensive provision for income taxes (benefit) allocable to:
Net income (loss)	(23.8)	29.4	40.5
Other comprehensive income (loss):
Total	(30.7)	79.1	64.5
Defined benefit pension plans
Other comprehensive income (loss):
Pension plans	(6.7)	49.3	$ 24.0
OPEB Plans
Other comprehensive income (loss):
Pension plans	$ (0.2)	$ 0.4