Business and geographic segments - Segment Operating Performance (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jul. 16, 2024	Jun. 30, 2022	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Business and geographic segments
Net sales			$ 2,104.8	$ 1,921.7	$ 2,222.5
Cost of sales			1,680.3	1,676.5	1,732.1
Gross margin			424.5	245.2	490.4
Operating income			210.7	34.2	239.4
Interest income and other			22.0	21.3	10.4
Gain on remeasurement of investment in TiO2 manufacturing joint venture	$ 64.5		64.5
Insurance recoveries			1.4	3.0	2.8
Gain on land sales			0.5	1.5
Other components of net periodic pension and OPEB expense			(2.6)	(11.8)	(13.9)
Changes in market value of Valhi common stock held by subsidiaries			1.9	(1.7)	(1.6)
General expenses, net			(4.3)	(35.2)	(36.6)
Interest expense			(49.9)	(28.3)	(27.9)
Income (loss) before income taxes			244.2	(19.5)	169.9
Restructuring Costs			2.0	5.8
Fixed asset impairment				3.8
N L Industries Inc
Business and geographic segments
Insurance recoveries			1.4	0.5	0.1
Basic Management Inc
Business and geographic segments
Fixed asset impairment		$ 16.4
Chemicals
Business and geographic segments
Net sales			1,887.1	1,666.5	1,930.2
Cost of sales			1,530.1	1,502.7	1,540.2
Gross margin			357.0	163.8	390.0
Operating income			138.5	(41.1)	174.6
Insurance recoveries				2.5	2.7
Component products
Business and geographic segments
Net sales			145.9	161.3	166.6
Cost of sales			104.6	112.1	117.8
Gross margin			41.3	49.2	48.8
Operating income			17.0	25.4	25.4
Real estate management and development
Business and geographic segments
Net sales			71.8	93.9	125.7
Cost of sales			45.6	61.7	74.1
Gross margin			26.2	32.2	51.6
Operating income			$ 55.2	$ 49.9	$ 39.4