Noncontrolling interest in Subsidiaries - Schedule of Noncontrolling Interest in Net Income of Subsidiaries (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries	$ 8.7	$ 46.3	$ 27.2	$ 55.4
Kronos Worldwide, Inc.
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries			29.0	45.6
NL Industries
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries			(4.8)	8.4
CompX International
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries			1.1	0.9
BMI
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries			0.7	0.2
LandWell
Noncontrolling interest in net income (loss) of subsidiaries:
Noncontrolling interest in net income of subsidiaries			$ 1.2	$ 0.3