Business segment information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Business segment information [Line Items]
Net sales	$ 530.6	$ 492.7
Cost of sales	444.3	438.6
Gross margin	86.3	54.1
Operating income	31.5	2.5
Interest income and other	5.7	4.9
Other components of net periodic pension and OPEB expense	(0.6)	(1.2)
Changes in market value of Valhi common stock held by subsidiaries	0.5	(1.1)
General expenses, net	(7.8)	(7.9)
Interest expense	(11.3)	(7.0)
Income (loss) before income taxes	18.0	(9.8)
Insurance recoveries		1.7
Chemicals
Business segment information [Line Items]
Net sales	478.8	426.3
Cost of sales	407.9	395.8
Gross margin	70.9	30.5
Operating income	22.8	(15.1)
Insurance recoveries		1.7
Component products
Business segment information [Line Items]
Net sales	38.0	41.2
Cost of sales	28.3	28.5
Gross margin	9.7	12.7
Operating income	3.7	7.0
Real estate management and development
Business segment information [Line Items]
Net sales	13.8	25.2
Cost of sales	8.1	14.3
Gross margin	5.7	10.9
Operating income	$ 5.0	$ 10.6