Noncontrolling interest in subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 321.6	$ 325.7
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	202.5	209.0
NL Industries, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	76.6	76.9
CompX International Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	22.0	22.0
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	12.0	11.0
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 8.5	$ 6.8