Business and Geographic Segments - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 388.7	$ 455.2	$ 510.2	$ 466.0	$ 495.9	$ 496.5	$ 481.7	$ 405.3	$ 1,820.1	$ 1,879.4	$ 1,519.4
Cost of sales									1,210.9	1,266.5	1,211.5
Gross margin	107.2	132.7	184.0	185.3	185.3	161.5	141.2	114.0	609.2	612.9	307.9
Operating income	$ 52.7	$ 69.2	$ 130.0	$ 118.8	$ 130.0	103.1	$ 83.1	$ 64.1	370.7	380.3	119.2
Securities earnings									38.5	29.5	27.2
Insurance recoveries									1.3	0.4	0.4
Gain on land sales									12.5
Other components of net periodic pension expense									(14.5)	(17.7)	(11.5)
Litigation settlement expense, net									(62.0)
Changes in market value of Valhi common stock held by subsidiaries									(12.2)
General expenses, net									(42.4)	(34.7)	(37.6)
Loss on prepayment of debt						$ (7.1)				(7.1)
Interest expense									(55.7)	(58.9)	(58.1)
Income from continuing operations before income taxes									236.2	291.8	39.6
Depreciation and amortization									58.4	59.0	67.5
Capital expenditures									61.4	71.3	58.9
Chemicals
Segment Reporting Information [Line Items]
Net sales									1,661.9	1,729.0	1,364.3
Cost of sales									1,101.7	1,161.2	1,101.5
Gross margin									560.2	567.8	262.8
Operating income									342.9	358.5	102.8
Chemicals | Operating Segment
Segment Reporting Information [Line Items]
Depreciation and amortization									52.0	43.4	42.6
Capital expenditures									56.3	64.3	53.0
Component Products
Segment Reporting Information [Line Items]
Net sales									118.2	112.0	108.9
Cost of sales									79.9	77.2	73.8
Gross margin									38.3	34.8	35.1
Operating income									17.8	15.2	15.6
Component Products | Operating Segment
Segment Reporting Information [Line Items]
Depreciation and amortization									3.5	3.7	3.7
Capital expenditures									3.1	2.8	3.2
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales									40.0	38.4	46.2
Cost of sales									29.3	28.1	36.2
Gross margin									10.7	10.3	10.0
Operating income									10.0	6.6	0.8
Real Estate Management And Development | Operating Segment
Segment Reporting Information [Line Items]
Depreciation and amortization									2.9	3.0	2.9
Capital expenditures									1.9	3.3	2.0
Waste Management | Operating Segment
Segment Reporting Information [Line Items]
Depreciation and amortization										8.9	18.3
Capital expenditures									$ 0.1	$ 0.9	$ 0.7