Noncontrolling interest in subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 324.4	$ 325.7
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	202.4	209.0
NL Industries, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	77.5	76.9
CompX International Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	22.1	22.0
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	13.7	11.0
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 8.7	$ 6.8