Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Net sales	$ 415.0	$ 528.6	$ 874.3	$ 1,008.2
Cost of sales	311.0	405.4	670.6	763.2
Gross margin	104.0	123.2	203.7	245.0
Operating income	39.3	65.9	110.3	126.3
Securities earnings	1.0	3.3	2.6	6.4
Insurance recoveries		4.7	1.6	5.0
Changes in market value of Valhi common stock held by subsidiaries	(0.5)	1.9	(2.9)	3.0
Other components of net periodic pension expense	(5.0)	(4.1)	(9.7)	(8.2)
Litigation settlement expense, net		(19.6)		(19.6)
General expenses, net	(9.0)	(10.8)	(17.1)	(18.7)
Interest expense	(8.8)	(10.1)	(18.5)	(20.4)
Income before income taxes	17.0	31.2	66.3	73.8
Chemicals
Segment Reporting Information [Line Items]
Net sales	386.0	484.5	807.0	921.0
Cost of sales	291.1	375.4	624.5	703.1
Gross margin	94.9	109.1	182.5	217.9
Operating income	35.9	50.5	82.7	103.3
Component Products
Segment Reporting Information [Line Items]
Net sales	23.8	33.7	56.1	64.9
Cost of sales	16.4	22.8	38.3	44.3
Gross margin	7.4	10.9	17.8	20.6
Operating income	2.4	5.6	7.4	10.0
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	5.2	10.4	11.2	22.3
Cost of sales	3.5	7.2	7.8	15.8
Gross margin	1.7	3.2	3.4	6.5
Operating income	$ 1.0	$ 9.8	$ 20.2	$ 13.0