Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Long-term debt
Total debt	$ 783.5	$ 794.3
Less current maturities	(3.8)	(4.9)
Total long-term debt	779.7	789.4
VALHI, INC. | Contran Credit Facility
Long-term debt
Total debt	313.0	313.0
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Long-term debt
Total debt	435.1	442.6
Tremont | Promissory Note
Long-term debt
Total debt	0.5	2.0
BMI | Bank loan | Western Alliance Bank
Long-term debt
Total debt	17.2	17.2
LandWell | Unsecured Debt
Long-term debt
Total debt		1.6
LandWell | Unsecured Debt | Western Alliance Bank
Long-term debt
Total debt	14.9	15.0
Other Subsidiary | Other
Long-term debt
Total debt	2.8	2.9
Subsidiary
Long-term debt
Total debt	$ 470.5	$ 481.3