Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Long-term debt
Total debt	$ 786.4	$ 794.3
Less current maturities	(3.1)	(4.9)
Total long-term debt	783.3	789.4
VALHI, INC. | Contran Credit Facility
Long-term debt
Total debt	309.2	313.0
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Long-term debt
Total debt	443.8	442.6
Tremont | Promissory Note
Long-term debt
Total debt		2.0
BMI | Bank loan | Western Alliance Bank
Long-term debt
Total debt	16.2	17.2
LandWell | Unsecured Debt
Long-term debt
Total debt		1.6
LandWell | Unsecured Debt | Western Alliance Bank
Long-term debt
Total debt	14.5	15.0
Other Subsidiary | Other
Long-term debt
Total debt	2.7	2.9
Subsidiary
Long-term debt
Total debt	$ 477.2	$ 481.3