Long-term debt - Valhi Contran Credit Facility - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2025 USD ($)
Debt Instrument [Line Items]
Repayments of credit facility	$ 112.1
VALHI, INC. | Contran Credit Facility
Debt Instrument [Line Items]
Debt instrument, Interest rate at period end	8.50%
Debt instrument, interest rate during period	8.50%
Borrowings	$ 0.0
Repayments of credit facility	5.4
Amount available for borrowing	$ 110.8