Income taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule Of Income Tax [Line Items]
Expected tax expense (benefit) at U.S. federal statutory income tax rate of 21%	$ (2.0)	$ 10.3	$ (5.5)	$ 39.6
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	21.00%
Non-U.S. tax rates	$ (1.9)	$ (2.0)	$ (4.3)	$ 1.3
Incremental net tax (benefit) on earnings and losses of U.S. and non-U.S. tax group companies	(4.4)	1.2	(9.5)	(0.1)
Valuation allowance	0.2	(3.5)	1.2	(3.3)
Global intangible low-tax income, net	0.0	0.5	0.1	1.9
Adjustment to the reserve for uncertain tax positions, net	0.1	0.5	(0.6)	0.1
Adjustment of prior year taxes, net	(0.1)	0.0	(0.5)	0.0
Nondeductible expenses	0.2	0.6	0.7	1.2
U.S. state income taxes and other, net	0.3	0.6	(0.2)	1.4
Income tax expense	(7.6)	8.2	(18.6)	42.1
Comprehensive provision for income taxes allocable to:
Net income (loss)	(7.6)	8.2	(18.6)	42.1
Other comprehensive income (loss):
Currency translation	(0.2)	(3.0)	(1.6)	(6.4)
Other	(0.1)	0.0	(0.4)	0.2
Total	(7.6)	6.5	(19.2)	40.0
Pension Plans
Other comprehensive income (loss):
Defined benefit plans	$ 0.3	$ 1.3	$ 1.4	$ 4.1