Noncontrolling Interest in Subsidiaries - Noncontrolling Interest in Subsidiaries (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 323.0	$ 336.3
Kronos Worldwide, Inc.
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	198.3	211.0
NL
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	53.7	54.4
CompX
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	14.7	14.4
BMI
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	31.8	31.7
LandWell
Noncontrolling interest in net assets:
Noncontrolling interest in subsidiaries	$ 24.5	$ 24.8