Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2017
Long-term debt
Total debt	$ 800.4		$ 1,043.1
Less current maturities	2.9		1.6
Total long-term debt	797.5		1,041.5
VALHI, INC.
Long-term debt
Total debt	314.3		534.3
VALHI, INC. | Snake River
Long-term debt
Total debt		$ 250.0
VALHI, INC. | Contran Credit Facility
Long-term debt
Total debt	314.3		284.3
VALHI, INC. | Notes Payable, Other Payables | Snake River
Long-term debt
Total debt			250.0
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Long-term debt
Total debt	452.4		471.1
Tremont | Promissory Note
Long-term debt
Total debt	9.4		13.1
BMI | 2018 Notes Payable to Banks | Western Alliance Bank
Long-term debt
Total debt	18.0		18.8
LandWell | Unsecured Debt
Long-term debt
Total debt	2.1		2.5
Other Subsidiary | Other
Long-term debt
Total debt	4.2		3.3
Subsidiary
Long-term debt
Total debt	$ 486.1		$ 508.8