Quarterly Results of Operations - Schedule of Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ 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
Disclosure Quarterly Results Of Operations Schedule Of Quarterly Results Of Operations [Abstract]
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
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
Net income (loss) from continuing operations	28.4	148.3	20.0	70.2	162.8	62.2	163.3	23.5	266.9	411.8	21.0
Amounts attributable to Valhi stockholders:
Income (loss) from continuing operations	22.3	142.8	11.3	51.7	141.1	44.2	117.0	14.4	228.1	316.7	8.1
Income (loss) from discontinued operations	(4.6)	0.7	0.4	37.6	(1.0)	1.7	(108.2)	(1.7)	34.1	(109.2)	(24.0)
Net income (loss) attributable to Valhi stockholders	$ 17.7	$ 143.5	$ 11.7	$ 89.3	$ 140.1	$ 45.9	$ 8.8	$ 12.7	$ 262.2	$ 207.5	$ (15.9)
Earnings per share:
Income (loss) from continuing operations	$ 0.07	$ 0.42	$ 0.03	$ 0.15	$ 0.41	$ 0.13	$ 0.34	$ 0.04	$ 0.67	$ 0.93	$ 0.02
Loss from discontinued operations	(0.01)			0.11			(0.31)		0.10	(0.32)	(0.07)
Net income (loss) per share	$ 0.06	$ 0.42	$ 0.03	$ 0.26	$ 0.41	$ 0.13	$ 0.03	$ 0.04	$ 0.77	$ 0.61	$ (0.05)

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