Noncontrolling Interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 9.7	$ 13.5
Kronos Worldwide, Inc.
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	3.8	5.2
NL
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	2.3	0.3
CompX
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	0.6	0.6
BMI
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	1.1	2.8
LandWell
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 1.9	$ 4.6