Long-term debt - Subordinated, Unsecured Term Loan from Contran (Details) - Kronos Worldwide, Inc. - Subordinated, unsecured term loan from Contran € in Millions, $ in Millions	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Feb. 06, 2024 USD ($)
Debt Instrument [Line Items]
Proceeds from Issuance of Unsecured Debt	$ 53.7	€ 50.0
Line of credit maximum borrowing capacity			$ 225.0
Long-term promissory note fixed interest rate			11.50%