Financial Instruments - Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
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	$ 448.8	$ 485.7
Long term debt, fair value	460.2	499.9
VALHI, INC. | Contran Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	172.9	270.7
Long term debt, fair value	172.9	270.7
BMI | Bank note payable | Meadows Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	15.4	16.3
Long term debt, fair value	15.9	16.9
LandWell | Bank note payable
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	13.5	14.2
Long term debt, fair value	13.5	14.2
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	792.9	570.3
Deferred payment obligation		1.3
Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	$ 792.9	570.3
Deferred payment obligation		$ 1.3