Noncontrolling interest in subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 358.5	$ 343.0
Kronos Worldwide
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	215.9	210.3
NL Industries
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	81.7	81.5
CompX International
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	19.4	19.0
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	22.0	18.7
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 19.5	$ 13.5