Noncontrolling interest in subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 344.1	$ 325.7
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	216.2	209.0
NL Industries, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	79.7	76.9
CompX International Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	18.9	22.0
Basic Management Inc
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	16.7	11.0
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 12.6	$ 6.8