Long-term debt - Valhi Contran Credit Facility - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2025 USD ($)
Debt Instrument [Line Items]
Repayments of credit facility	$ 280.9
VALHI, INC. | Contran Credit Facility
Debt Instrument [Line Items]
Borrowings	0.0
Repayments of credit facility	$ 11.5
Debt instrument, interest rate during period	8.50%
Debt instrument, Interest rate at period end	8.50%
Amount available for borrowing	$ 116.9