Business and geographic segments - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Net sales	$ 507.1	$ 634.6	$ 999.8	$ 1,263.6
Cost of sales	441.6	487.9	880.2	946.2
Gross margin	65.5	146.7	119.6	317.4
Operating income (loss)	12.0	71.9	14.5	172.6
Interest income and other	4.7	1.4	9.6	2.3
Gain on land sales	1.5		1.5
Other components of net periodic pension and OPEB expense	(7.5)	(3.3)	(8.7)	(6.6)
Changes in market value of Valhi common stock held by subsidiaries	(1.1)	3.9	(2.2)	4.0
General expenses, net	(9.5)	(10.5)	(17.4)	(18.7)
Interest expense	(7.2)	(7.0)	(14.2)	(13.9)
Income (loss) before income taxes	(7.1)	56.4	(16.9)	139.7
Insurance recoveries			2.2
Fixed asset impairment		16.0		16.0
Chemicals
Segment Reporting Information [Line Items]
Net sales	443.2	565.3	869.5	1,128.2
Cost of sales	399.4	445.1	795.2	859.0
Gross margin	43.8	120.2	74.3	269.2
Operating income (loss)	(2.6)	69.2	(17.7)	155.6
Insurance recoveries	0.5		2.2
Component Products
Segment Reporting Information [Line Items]
Net sales	36.6	41.6	77.8	83.7
Cost of sales	26.3	28.0	54.8	58.0
Gross margin	10.3	13.6	23.0	25.7
Operating income (loss)	4.4	7.7	11.4	14.0
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	27.3	27.7	52.5	51.7
Cost of sales	15.9	14.8	30.2	29.2
Gross margin	11.4	12.9	22.3	22.5
Operating income (loss)	$ 10.2	(5.0)	$ 20.8	$ 3.0
Fixed asset impairment		$ 16.0