Fair Value Measurements and Financial Instruments - Financial Instruments not Carried at Fair Value (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Reported Value Measurement [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	$ 733.2	$ 792.9
Estimate of Fair Value Measurement [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash, cash equivalents and restricted cash equivalents	733.2	792.9
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	415.1	448.8
Long term debt, fair value	372.6	460.2
VALHI, INC. | Contran Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	153.4	172.9
Long term debt, fair value	153.4	172.9
BMI | Bank note payable | Meadows Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	14.3	15.4
Long term debt, fair value	14.8	15.9
LandWell | Bank note payable
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long term debt, carrying amount	13.2	13.5
Long term debt, fair value	$ 13.2	$ 13.5