Income taxes - Components of Net Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Income taxes
Inventories	$ 1.1
Lease assets (liabilities)	5.7	$ 5.3
Accrued OPEB costs	1.8	1.7
Accrued pension costs	26.8	21.6
Other accrued liabilities and deductible differences	16.9	15.3
Tax loss and tax credit carryforwards	107.7	70.7
Valuation allowance	(6.4)	(3.8)
Adjusted gross deferred tax assets (liabilities)	153.6	110.8
Netting by tax jurisdiction	(70.3)	(58.8)
Net noncurrent deferred tax asset (liability)	83.3	52.0
Inventories, Liabilities		(5.5)
Property and equipment, Liabilities	(59.3)	(59.1)
Lease, Liabilities	(5.7)	(5.4)
Other taxable differences	(3.5)	(3.9)
Tax on unremitted earnings of non-U.S. subsidiaries	(10.8)	(11.3)
Adjusted gross deferred tax, Liabilities	(79.3)	(85.2)
Netting by tax jurisdiction, Liabilities	70.3	58.8
Net noncurrent deferred tax, Liability	$ (9.0)	$ (26.4)