Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Long-term debt
Total debt	$ 794.3	$ 800.4
Less current maturities	(4.9)	(2.9)
Total long-term debt	789.4	797.5
VALHI, INC. | Contran Credit Facility
Long-term debt
Total debt	313.0	314.3
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Long-term debt
Total debt	442.6	452.4
BMI | Bank loan | Western Alliance Bank
Long-term debt
Total debt	17.2	18.0
Tremont | Promissory Note
Long-term debt
Total debt	2.0	9.4
LandWell | Unsecured Debt
Long-term debt
Total debt	1.6	2.1
LandWell | Unsecured Debt | Western Alliance Bank
Long-term debt
Total debt	15.0
Other Subsidiary | Other
Long-term debt
Total debt	2.9	4.2
Subsidiary
Long-term debt
Total debt	$ 481.3	$ 486.1