Business segment information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Business segment information [Line Items]
Net sales	$ 559.7	$ 507.1	$ 1,090.3	$ 999.8
Cost of sales	438.4	441.6	882.7	880.2
Gross margin	121.3	65.5	207.6	119.6
Operating income	54.8	12.0	86.3	14.5
Interest income and other	5.5	4.7	11.2	9.6
Gain on land sales		1.5	0.0	1.5
Other components of net periodic pension and OPEB expense	(0.6)	(7.5)	(1.2)	(8.7)
Changes in market value of Valhi common stock held by subsidiaries	0.1	(1.1)	0.6	(2.2)
General expenses, net	(10.3)	(9.5)	(18.1)	(17.4)
Interest expense	(11.9)	(7.2)	(23.2)	(14.2)
Income (loss) before income taxes	37.6	(7.1)	55.6	(16.9)
Insurance recoveries			0.2	2.2
Chemicals
Business segment information [Line Items]
Net sales	500.5	443.2	979.3	869.5
Cost of sales	400.7	399.4	808.6	795.2
Gross margin	99.8	43.8	170.7	74.3
Operating income	40.5	(2.6)	63.3	(17.7)
Insurance recoveries		0.5		2.2
Component products
Business segment information [Line Items]
Net sales	35.9	36.6	73.9	77.8
Cost of sales	24.8	26.3	53.1	54.8
Gross margin	11.1	10.3	20.8	23.0
Operating income	5.1	4.4	8.8	11.4
Real estate management and development
Business segment information [Line Items]
Net sales	23.3	27.3	37.1	52.5
Cost of sales	12.9	15.9	21.0	30.2
Gross margin	10.4	11.4	16.1	22.3
Operating income	$ 9.2	$ 10.2	$ 14.2	$ 20.8