Long-term debt - Subordinated, Unsecured Term Loan from Contran (Details) € in Millions, $ in Millions					3 Months Ended
	Feb. 14, 2024 USD ($)	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Feb. 06, 2024 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)
Debt Instrument [Line Items]
Loan from Contran					$ 53.7	$ 0.0
Kronos Worldwide, Inc. | Subordinated, unsecured term loan from Contran
Debt Instrument [Line Items]
Loan from Contran	$ 53.7	$ 53.7	€ 50.0
Line of credit maximum borrowing capacity				$ 225.0
Long-term promissory note fixed interest rate				11.50%
Kronos Worldwide, Inc. | Subordinated, unsecured term loan from Contran | Contran
Debt Instrument [Line Items]
Interest rate on outstanding borrowings				2.00%