Long-term debt - Valhi Contran Credit Facility - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Repayments of credit facility	$ 123.9	$ 0.0
VALHI, INC. | Contran Credit Facility
Debt Instrument [Line Items]
Borrowings	0.0
Repayments of credit facility	$ 48.3
Debt instrument, interest rate during period	9.48%
Debt instrument, Interest rate at period end	9.00%
Amount available for borrowing	$ 104.9