Fair value measurements and financial instruments - Financial Instruments not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Reported Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions
Cash, cash equivalents and restricted cash equivalents	$ 231.5	$ 378.6
Estimate of Fair Value Measurement
Fair Value Balance Sheet Grouping Financial Statement Captions
Cash, cash equivalents and restricted cash equivalents	231.5	378.6
Kronos Worldwide | Kronos International, Inc
Fair Value Balance Sheet Grouping Financial Statement Captions
Long term debt, carrying amount	43.2	10.0
Long term debt, fair value	43.2	10.0
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc
Fair Value Balance Sheet Grouping Financial Statement Captions
Long term debt, carrying amount	379.1	365.4
Long term debt, fair value	412.2	403.4
Kronos Worldwide | 3.75% Senior Secured Notes due 2025 | Kronos International, Inc
Fair Value Balance Sheet Grouping Financial Statement Captions
Long term debt, carrying amount	81.2	78.3
Long term debt, fair value	80.7	77.9
LandWell | Bank note payable
Fair Value Balance Sheet Grouping Financial Statement Captions
Long term debt, carrying amount	11.4	11.4
Long term debt, fair value	$ 11.4	$ 11.4