Long-Term Debt - Long-Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Long-term debt
Total debt	$ 811.3	$ 1,043.1
Less current maturities	1.6	1.6
Total long-term debt	809.7	1,041.5
VALHI, INC.
Long-term debt
Total debt	314.3	534.3
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	463.0	471.1
Tremont | Promissory Note
Long-term debt
Total debt	10.9	13.1
BMI | Bank loan | Western Alliance Bank
Long-term debt
Total debt	18.0	18.8
LandWell | Unsecured Debt
Long-term debt
Total debt	2.3	2.5
Other Subsidiary | Other
Long-term debt
Total debt	2.8	3.3
Subsidiary
Long-term debt
Total debt	$ 497.0	$ 508.8