Income taxes - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Dec. 10, 2024	Dec. 31, 2024	Dec. 31, 2017	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2018
Income Taxes Disclosure [Line Items]
Nondeductible Portion of Interest Carryforwards		$ 23.1		$ 23.1	$ 14.7
Unpaid Transition Tax		18.5		18.5
Income tax expense (benefit)				82.9	(24.6)	$ 36.8
Deferred income taxes		53.8		$ 53.8	67.0
Period for which opertaing loss carryforward is utilized				3 years
Deferred income tax asset valuation allowance		14.1		$ 14.1	3.5
Business interest income, adjusted taxable income				30.00%
Current income taxes expense (benefit)				$ 39.5	26.1	36.4
Deferred income taxes expense (benefit)		16.5		43.4	(50.7)	0.4
Pre transition gain	$ 77.1
Deferred income taxes		57.7		57.7	17.1
Unrecognized tax benefits impact on effective tax rate		3.2		3.2
Contran
Income Taxes Disclosure [Line Items]
Income taxes payable current		16.9		16.9	10.2
Chemicals
Income Taxes Disclosure [Line Items]
Deferred income taxes expense (benefit)				2.5
Germany
Income Taxes Disclosure [Line Items]
Deferred income tax asset valuation allowance		0.0		0.0
Belgium
Income Taxes Disclosure [Line Items]
Deferred income tax asset valuation allowance		8.2		$ 8.2
Canada
Income Taxes Disclosure [Line Items]
Operating loss carryforwards, expiration period				20 years
European Subsidiaries | Chemicals | Transition Tax
Income Taxes Disclosure [Line Items]
Current income tax expense provisional pursuant to transition tax			$ 74.1
Income tax liability payable period							8 years
Corporate Tax Purposes | Germany
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		70.8		$ 70.8
Net operating loss carryforwards		447.3		447.3
Corporate Tax Purposes | Belgium
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		18.0		18.0
Net operating loss carryforwards		72.0		72.0
Corporate Tax Purposes | Canada
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		4.3		4.3
Net operating loss carryforwards		28.9		28.9
Trade Tax Purposes | Germany
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		4.4		4.4
Net operating loss carryforwards		40.1		40.1
Provincial Tax Purposes | Canada
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		3.6		3.6
Net operating loss carryforwards		31.1		31.1
Direct Investment in Subsidiary | Kronos
Income Taxes Disclosure [Line Items]
Deferred income taxes expense (benefit)				4.6	$ (6.4)	$ 1.2
Deferred income taxes		49.6		49.6
Direct Investment in Subsidiary | Kronos | Maximum
Income Taxes Disclosure [Line Items]
Deferred income taxes		$ 153.6		$ 153.6