Income taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disclosure Income Taxes Components Of Comprehensive Provision For Income Taxes Allocation [Abstract]
Expected tax expense (benefit) at U.S. federal statutory income tax rate of 21%	$ 25.2	$ (2.0)	$ 36.9	$ (5.5)
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
Non-U.S. tax rates	$ 0.5	$ (1.9)	$ 0.4	$ (4.3)
Incremental net tax benefit on earnings and losses of U.S. and non-U.S. tax group companies	4.5	(4.4)	0.2	(9.5)
Global intangible low-tax income, net	1.5		2.9	0.1
Valuation allowance, net	1.3		3.8
Adjustment to the reserve for uncertain tax positions, net	0.2	0.1	0.4	(0.6)
Adjustment of prior year taxes, net		(0.1)		(0.5)
Nondeductible expenses	0.5	0.2	1.1	0.7
U.S. state income taxes and other, net	0.6	0.3	0.9	(0.2)
Income tax expense (benefit)	34.3	(7.8)	46.6	(19.8)
Comprehensive provision (benefit) for income taxes allocable to:
Net income (loss)	34.3	(7.8)	46.6	(19.8)
Other comprehensive income (loss):
Currency translation	0.7	(0.2)	(1.4)	(1.6)
Pension plans	0.2	0.3	0.8	1.4
Other	0.2	(0.1)		(0.4)
Total	$ 35.4	$ (7.8)	$ 46.0	$ (20.4)