Financial Instruments - Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due September 15, 2025 | Kronos International, Inc
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	$ 471.1
Long term debt, fair value	495.1
Kronos Worldwide, Inc. | Term Loan | 2014 Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount		$ 335.9
Long term debt, fair value		334.6
VALHI, INC. | Contran Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	284.3	278.9
Long term debt, fair value	284.3	278.9
VALHI, INC. | Term Loan | Snake River
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	250.0	250.0
Long term debt, fair value	250.0	250.0
Tremont | Promissory Note
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	13.1	14.5
Long term debt, fair value	13.1	14.5
BMI | Bank note payable | Meadows Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	18.8	8.4
Long term debt, fair value	19.7	8.5
LandWell | Unsecured Debt
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	2.5	2.9
Long term debt, fair value	2.5	2.9
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	461.7	174.8
Deferred payment obligation	9.3	9.0
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	461.7	174.8
Deferred payment obligation	$ 9.3	$ 9.0