Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 360.2	$ 443.5	$ 725.3	$ 863.6
Cost of sales	313.7	349.7	601.4	689.3
Income (loss) from operations	(10.4)	44.3	21.8	70.3
Income tax expense	145.1	6.8	154.5	14.7
Net income (loss)	$ (159.8)	$ 33.1	$ (141.4)	$ 47.4