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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries	$ 5.5	$ 18.0	$ 32.7	$ 73.4
Kronos Worldwide, Inc.
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			35.3	60.0
NL Industries
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			(7.4)	11.4
CompX International
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			1.6	1.2
BMI
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			1.1	0.3
LandWell
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			$ 2.1	$ 0.5