Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Detail) - Kronos - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Net sales	$ 1,729.0	$ 1,364.3	$ 1,348.8
Cost of sales	1,170.1	1,107.3	1,156.5
Income (loss) from operations	330.4	81.1	(1.1)
Income tax expense (benefit)	(48.8)	17.9	142.8
Net income (loss)	$ 354.5	$ 43.3	$ (173.6)