Noncontrolling Interest in Subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 297.7	$ 243.5
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	178.8	134.5
NL Industries
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	53.0	44.3
CompX International
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	17.0	16.4
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	24.8	24.6
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 24.1	$ 23.7