Noncontrolling Interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 15.5	$ 4.0	$ 34.1	$ 22.4
Kronos Worldwide, Inc.
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			15.8	10.2
NL
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			6.2	1.8
CompX
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			1.8	1.1
BMI
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			4.0	4.4
LandWell
Noncontrolling interest in net income of subsidiaries:
Noncontrolling interest in net income of subsidiaries			$ 6.3	$ 4.9