Long-term debt - Kronos 3.75 Senior Secured Notes - Additional Information (Details) - Kronos Worldwide - 3.75% Senior Secured Notes due 2025 - Kronos International, Inc € in Millions, $ in Millions	Jun. 30, 2025 EUR (€)	Jun. 30, 2025 USD ($)	Dec. 31, 2024
Debt Instrument [Line Items]
Debt instrument interest rate	3.75%	3.75%	3.75%
Debt instrument principal amount | €	€ 75
Principal amount outstanding | $		$ 87.9