Noncontrolling Interest in Subsidiaries - Noncontrolling Interest in Net Assets of Subsidiaries (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 342.3	$ 243.5
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	204.9	134.5
NL Industries
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	71.1	44.3
CompX International
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	17.8	16.4
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	26.0	24.6
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 22.5	$ 23.7