Noncontrolling interest in subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 344.9	$ 340.5
Kronos Worldwide
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	196.4	197.6
NL Industries
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	75.1	75.1
CompX International
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	18.3	18.0
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	26.9	25.0
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 28.2	$ 24.8