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Long-Term Debt - Valhi Contran Credit Facility - Additional Information (Detail)
$ in Millions
6 Months Ended
Jun. 30, 2021
USD ($)
Debt Instrument [Line Items]  
Borrowings of credit facility $ 0.0
Repaid credit facility $ 28.0
VALHI, INC. | Contran Credit Facility  
Debt Instrument [Line Items]  
Debt instrument, Interest rate at period end 4.25%
Debt instrument, Interest rate during period 4.25%
Amount available for borrowing $ 77.3