Business and geographic segments - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2021	Jun. 30, 2021	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net sales										$ 1,921.7	$ 2,222.5	$ 2,296.4
Cost of sales										1,676.5	1,732.1	1,716.2
Gross margin										245.2	490.4	580.2
Operating income										34.2	239.4	318.6
Interest income and other										21.3	10.4	4.0
Gain on land sales							$ 10.4	$ 5.6	$ 1.5	1.5		16.0
Other components of net periodic pension and OPEB expense										(11.8)	(13.9)	(17.0)
Changes in market value of Valhi common stock held by subsidiaries										(1.7)	(1.6)	3.3
General expenses, net										(34.7)	(36.5)	(34.6)
Interest expense										(28.3)	(27.9)	(32.5)
Income (loss) before income taxes										(19.5)	169.9	257.8
Restructuring Costs	$ 5.8
Insurance recoveries										3.0	2.8	0.1
Fixed asset impairment	$ 3.8					$ 16.4				3.8
Chemicals
Segment Reporting Information [Line Items]
Net sales										1,666.5	1,930.2	1,939.4
Cost of sales										1,502.7	1,540.2	1,494.5
Gross margin										163.8	390.0	444.9
Operating income										(41.1)	174.6	200.8
Insurance recoveries		$ 2.5	$ 2.5	$ 2.5	$ 2.7
Component products
Segment Reporting Information [Line Items]
Net sales										161.3	166.6	140.8
Cost of sales										112.1	117.8	98.1
Gross margin										49.2	48.8	42.7
Operating income										25.4	25.4	20.5
Real estate management and development
Segment Reporting Information [Line Items]
Net sales										93.9	125.7	216.2
Cost of sales										61.7	74.1	123.6
Gross margin										32.2	51.6	92.6
Operating income										$ 49.9	$ 39.4	$ 97.3