Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 441.4	$ 356.1	$ 811.2	$ 674.5
Cost of sales	311.6	300.6	578.0	578.6
Income from operations	70.1	10.5	122.4	10.2
Income tax expense (benefit)	(131.1)	3.9	(120.1)	2.5
Net income (loss)	$ 196.5	$ 1.7	$ 233.3	$ (2.1)