Business and geographic segments - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Net sales	$ 468.9		$ 556.3		$ 1,468.7	$ 1,819.9
Cost of sales	408.3		435.9		1,288.5	1,382.1
Gross margin	60.6		120.4		180.2	437.8
Operating income	2.5		69.4		17.0	242.0
Interest income and other	4.9		3.3		14.5	5.6
Gain on land sales	0.0	$ 1.5	0.0		1.5	0.0
Other components of net periodic pension and OPEB expense	(1.3)		(3.2)		(10.0)	(9.8)
Changes in market value of Valhi common stock held by subsidiaries	0.1		(4.9)		(2.1)	(0.9)
General expenses, net	(8.5)		(8.6)		(25.9)	(27.3)
Interest expense	(7.2)		(7.0)		(21.4)	(20.9)
Income (loss) before income taxes	(9.5)		49.0		(26.4)	188.7
Insurance recoveries			2.7		2.5	2.7
Fixed asset impairment	0.0		0.4		0.0	16.4
Chemicals
Segment Reporting Information [Line Items]
Net sales	396.9		459.6		1,266.4	1,587.8
Cost of sales	362.8		376.0		1,158.0	1,235.0
Gross margin	34.1		83.6		108.4	352.8
Operating income	(21.8)		34.3		(39.5)	189.9
Insurance recoveries	0.3		2.7		2.5
Component products
Segment Reporting Information [Line Items]
Net sales	40.3		42.9		118.1	126.6
Cost of sales	27.7		30.9		82.5	88.9
Gross margin	12.6		12.0		35.6	37.7
Operating income	6.6		6.0		18.0	20.0
Real estate management and development
Segment Reporting Information [Line Items]
Net sales	31.7		53.8		84.2	105.5
Cost of sales	17.8		29.0		48.0	58.2
Gross margin	13.9		24.8		36.2	47.3
Operating income	$ 17.7		$ 29.1		$ 38.5	$ 32.1
Fixed asset impairment				$ 16.4