Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net sales	$ 458.6	$ 475.2	$ 1,332.9	$ 1,483.5
Cost of sales	368.9	376.8	1,039.5	1,140.0
Gross margin	89.7	98.4	293.4	343.5
Operating income	28.9	41.4	139.2	167.6
Securities earnings	0.9	2.6	3.5	9.0
Insurance recoveries		0.2	1.6	5.2
Gain on land sales		4.4		4.4
Changes in market value of Valhi common stock held by subsidiaries	0.7	(3.1)	(2.2)	(0.1)
Other components of net periodic pension expense	(5.2)	(4.1)	(14.9)	(12.3)
Litigation settlement expense, net		0.3		(19.3)
General expenses, net	(8.4)	(9.5)	(25.5)	(28.2)
Interest expense	(8.9)	(10.3)	(27.4)	(30.7)
Income before income taxes	8.0	21.9	74.3	95.6
Chemicals
Segment Reporting Information [Line Items]
Net sales	416.9	437.4	1,223.9	1,358.4
Cost of sales	337.3	350.3	961.8	1,053.4
Gross margin	79.6	87.1	262.1	305.0
Operating income	21.6	36.3	104.3	139.6
Component Products
Segment Reporting Information [Line Items]
Net sales	28.4	29.7	84.5	94.6
Cost of sales	21.1	20.2	59.4	64.6
Gross margin	7.3	9.5	25.1	30.0
Operating income	2.1	4.3	9.5	14.3
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	13.3	8.1	24.5	30.5
Cost of sales	10.5	6.3	18.3	22.0
Gross margin	2.8	1.8	6.2	8.5
Operating income	$ 5.2	$ 0.8	$ 25.4	$ 13.7