Business combinations - Assets acquired and liabilities assumed (Details) - USD ($) $ in Millions	Jul. 16, 2024	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Allocation of purchase price to identifiable assets acquired and liabilities assumed:
Goodwill		$ 382.3	$ 382.3	$ 379.7
Louisiana Pigment Company, L.P. (LPC)
Consideration:
Fair value of investment in TiO2 manufacturing joint venture	$ 178.2
Louisiana Pigment Company, L.P. (LPC) | Kronos
Consideration:
Cash consideration	185.0
Working capital adjustment	(11.0)
Earn-out liability	4.2
Total fair value of consideration	178.2
Fair value of investment in TiO2 manufacturing joint venture	178.2
Total	356.4
Allocation of purchase price to identifiable assets acquired and liabilities assumed:
Cash and cash equivalents	21.3
Restricted cash	1.3
Accounts and other receivables, net	0.2
Inventories, net	82.0
Prepaid expenses and other	0.6
Other assets	10.7
Property and equipment	268.5
Accounts payable and accrued liabilities	(21.7)
Other noncurrent liabilities	(6.4)
Deferred tax liability	(2.7)
Total net identifiable assets acquired	353.8
Goodwill	2.6
Total	$ 356.4