Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 479.6	$ 466.0
Cost of sales	357.8	280.7
Gross margin	121.8	185.3
Operating income	60.4	118.8
Securities earnings	3.1	8.3
Insurance recoveries	0.3	0.2
Gain on land sales		12.5
Changes in market value of Valhi common stock held by subsidiaries	1.1	(0.3)
Other components of net periodic pension and OPEB cost	(4.1)	(3.7)
General expenses, net	(7.9)	(14.0)
Interest expense	(10.3)	(15.4)
Income from continuing operations before income taxes	42.6	106.4
Chemicals
Segment Reporting Information [Line Items]
Net sales	436.5	430.4
Cost of sales	327.7	256.1
Gross margin	108.8	174.3
Operating income	52.8	110.6
Component Products
Segment Reporting Information [Line Items]
Net sales	31.2	28.4
Cost of sales	21.5	18.9
Gross margin	9.7	9.5
Operating income	4.4	4.4
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	11.9	7.2
Cost of sales	8.6	5.7
Gross margin	3.3	1.5
Operating income	$ 3.2	$ 3.8