Business segment information - Segment Operating Performance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Business segment information
Net sales	$ 538.6	$ 530.6
Cost of sales	416.1	444.3
Gross margin	122.5	86.3
Operating income	50.1	31.5
Interest income and other	4.3	5.7
Other components of net periodic pension and OPEB expense	(0.8)	(0.6)
Changes in market value of Valhi common stock held by subsidiaries	(1.7)	0.5
General expenses, net	(7.9)	(7.8)
Interest expense	(13.2)	(11.3)
Income before income taxes	30.8	18.0
Chemicals
Business segment information
Net sales	489.8	478.8
Cost of sales	383.4	407.9
Gross margin	106.4	70.9
Operating income	41.2	22.8
Component products
Business segment information
Net sales	40.3	38.0
Cost of sales	28.1	28.3
Gross margin	12.2	9.7
Operating income	5.9	3.7
Real estate management and development
Business segment information
Net sales	8.5	13.8
Cost of sales	4.6	8.1
Gross margin	3.9	5.7
Operating income	$ 3.0	$ 5.0