Long-term debt - Subordinated, Unsecured Term Loan from Contran (Details) € in Millions, $ in Millions			1 Months Ended		12 Months Ended
	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Jul. 31, 2024	Feb. 29, 2024	Dec. 31, 2024 USD ($)	Aug. 31, 2024
Debt Instrument [Line Items]
Kronos term loan from Contran					$ 53.7
Kronos Worldwide | Subordinated, unsecured term loan from Contran
Debt Instrument [Line Items]
Kronos term loan from Contran	$ 53.7	€ 50.0			$ 53.7
Interest rate			11.50%			9.54%
Interest rate spread			2.00%	2.00%