Business Segment Information - Segment Operating Performance (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 528.6	$ 510.2	$ 1,008.2	$ 976.2
Cost of sales	405.4	326.2	763.2	606.9
Gross margin	123.2	184.0	245.0	369.3
Operating income	65.9	130.0	126.3	248.8
Securities earnings	3.3	8.5	6.4	16.8
Insurance recoveries	4.7	0.2	5.0	0.4
Gain on land sales				12.5
Changes in market value of Valhi common stock held by subsidiaries	1.9	(3.8)	3.0	(4.1)
Other components of net periodic pension and OPEB expense	(4.1)	(3.8)	(8.2)	(7.5)
Litigation settlement expense	(19.6)	(62.0)	(19.6)	(62.0)
General expenses, net	(10.8)	(11.1)	(18.7)	(25.1)
Interest expense	(10.1)	(16.0)	(20.4)	(31.4)
Income from continuing operations before income taxes	31.2	42.0	73.8	148.4
Chemicals
Segment Reporting Information [Line Items]
Net sales	484.5	471.8	921.0	902.2
Cost of sales	375.4	300.5	703.1	556.6
Gross margin	109.1	171.3	217.9	345.6
Operating income	50.5	123.6	103.3	234.2
Component Products
Segment Reporting Information [Line Items]
Net sales	33.7	32.4	64.9	60.8
Cost of sales	22.8	21.2	44.3	40.1
Gross margin	10.9	11.2	20.6	20.7
Operating income	5.6	6.0	10.0	10.4
Real Estate Management And Development
Segment Reporting Information [Line Items]
Net sales	10.4	6.0	22.3	13.2
Cost of sales	7.2	4.5	15.8	10.2
Gross margin	3.2	1.5	6.5	3.0
Operating income	$ 9.8	$ 0.4	$ 13.0	$ 4.2