Income taxes - Components of Net Deferred Tax Asset (Liability) (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Tax effect of temporary differences related to:
Inventories	$ 1.4
Lease assets	5.7	$ 5.3
Accrued OPEB costs	2.1	2.0
Accrued pension costs	26.9	22.0
Accrued environmental liabilities	22.6	25.9
Other deductible differences	14.1	12.0
Investments in subsidiaries and affiliates	10.5	6.7
Tax loss and tax credit carryforwards	119.6	82.6
Valuation allowance	(18.2)	(16.5)
Adjusted gross deferred tax assets	184.7	140.0
Netting of items by tax jurisdiction, assets	(117.7)	(99.5)
Net noncurrent deferred tax asset (liability)	67.0	40.5
Tax effect of temporary differences related to:
Inventories		(5.3)
Property and equipment	(62.9)	(62.8)
Lease liabilities	(5.7)	(5.4)
Other taxable differences	(15.3)	(15.8)
Investments in subsidiaries and affiliates	(54.7)	(62.3)
Tax on unremitted earnings of non-U.S. subsidiaries	(10.9)	(11.4)
Adjusted gross deferred tax liabilities	(149.5)	(163.0)
Netting of items by tax jurisdiction, liabilities	117.7	99.5
Net noncurrent deferred tax asset (liability)	$ (31.8)	$ (63.5)