Related party transactions - Additional Information (Details) € in Millions, shares in Millions, $ in Millions			1 Months Ended	12 Months Ended
	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Feb. 29, 2024 USD ($)	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Related Party Transaction [Line Items]
Subordinated, Unsecured Term Loan from Contran				$ 53.7
Kronos | Subordinated, unsecured term loan from Contran
Related Party Transaction [Line Items]
Subordinated, Unsecured Term Loan from Contran	$ 53.7	€ 50.0		53.7
Contran | Intercorporate Services Agreements Fees
Related Party Transaction [Line Items]
Related party transaction				39.5	$ 37.8	$ 41.2
Contran | Combined Information Technology Data Recovery Program
Related Party Transaction [Line Items]
Related party transaction				0.4	0.4	0.3
Contran | Pledge Fee Received
Related Party Transaction [Line Items]
Revenue and other income from related party transactions				0.9	0.8	1.2
Contran | Kronos | Sublease Agreement
Related Party Transaction [Line Items]
Payment for sublease rent and related ancillary services				$ 0.7	0.6	0.5
Contran | Kronos | Stock Pledged as Collateral
Related Party Transaction [Line Items]
Stock pledged as collateral | shares				16.7
Contran | Contran Credit Facility
Related Party Transaction [Line Items]
Interest on borrowings and unused commitment fees under credit facilities				$ 6.3	10.3	9.2
Contran and Other Affiliates
Related Party Transaction [Line Items]
Related party transaction cash paid for insurance premium				29.7	29.3	25.2
LPC
Related Party Transaction [Line Items]
Purchase of Ti02 from LPC					231.7	225.6
Sales of feedstock ore to LPC					$ 135.1	$ 106.9
Related Party [Member] | Kronos | Subordinated, unsecured term loan from Contran | Contran
Related Party Transaction [Line Items]
Subordinated, Unsecured Term Loan from Contran			$ 53.7
Interest expense				$ 5.1