Noncontrolling interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income (Loss) of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries	$ 18.0	$ 6.0	$ 73.4	$ 4.3
Kronos Worldwide, Inc.
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			60.0	3.8
NL Industries
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			11.4	1.0
CompX International
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			1.2	1.0
BMI
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			0.3	(1.2)
LandWell
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income (loss) of subsidiaries			$ 0.5	$ (0.3)