Noncontrolling Interest in Subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 319.2	$ 243.5
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	196.4	134.5
NL Industries
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	56.3	44.3
CompX International
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	17.3	16.4
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	25.0	24.6
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 24.2	$ 23.7