Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 459.3	$ 479.6
Cost of sales	359.6	357.8
Gross margin	99.7	121.8
Operating income	71.0	60.4
Securities earnings	1.6	3.1
Insurance recoveries	1.6	0.3
Changes in market value of Valhi common stock held by subsidiaries	(2.4)	1.1
Other components of net periodic pension expense	(4.7)	(4.1)
General expenses, net	(8.1)	(7.9)
Interest expense	(9.7)	(10.3)
Income before income taxes	49.3	42.6
Chemicals
Segment Reporting Information [Line Items]
Net sales	421.0	436.5
Cost of sales	333.3	327.7
Gross margin	87.7	108.8
Operating income	46.8	52.8
Component Products
Segment Reporting Information [Line Items]
Net sales	32.3	31.2
Cost of sales	21.9	21.5
Gross margin	10.4	9.7
Operating income	5.0	4.4
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	6.0	11.9
Cost of sales	4.4	8.6
Gross margin	1.6	3.3
Operating income	$ 19.2	$ 3.2