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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Quarterly Results Of Operations Schedule Of Quarterly Results Of Operations [Abstract]
Net sales	$ 495.9	$ 496.5	$ 481.7	$ 405.3	$ 390.5	$ 393.1	$ 387.5	$ 348.3	$ 1,879.4	$ 1,519.4	$ 1,487.9
Gross margin	185.3	161.5	141.2	114.0	101.4	85.7	64.7	48.4	602.0	300.2	228.4
Operating income	125.4	98.6	78.8	60.1	55.2	34.8	16.9	0.5	362.9	107.4	21.1
Net income (loss) from continuing operations	162.8	62.2	163.3	23.5	24.1	13.3	(2.4)	(14.0)	411.8	21.0	(149.4)
Amounts attributable to Valhi stockholders:
Income (loss) from continuing operations	141.1	44.2	117.0	14.4	15.5	7.3	(3.2)	(11.5)	316.7	8.1	(111.9)
Loss from discontinued operations	(1.0)	1.7	(108.2)	(1.7)	(6.3)	(4.3)	(5.5)	(7.9)	(109.2)	(24.0)	(21.7)
Net income (loss) attributable to Valhi stockholders	$ 140.1	$ 45.9	$ 8.8	$ 12.7	$ 9.2	$ 3.0	$ (8.7)	$ (19.4)	$ 207.5	$ (15.9)	$ (133.6)
Earnings per share:
Income (loss) from continuing operations	$ 0.41	$ 0.13	$ 0.34	$ 0.04	$ 0.05	$ 0.02	$ (0.01)	$ (0.04)	$ 0.93	$ 0.02	$ (0.33)
Loss from discontinued operations			(0.31)		(0.02)	(0.01)	(0.01)	(0.02)	(0.32)	(0.07)	(0.06)
Net income (loss) per share	$ 0.41	$ 0.13	$ 0.03	$ 0.04	$ 0.03	$ 0.01	$ (0.02)	$ (0.06)	$ 0.61	$ (0.05)	$ (0.39)