Valhi Stockholders' Equity - Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ 958.6
Balance at end of period	946.4
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.6	$ 1.7
Balance at end of period	1.6	1.7
Currency Translation
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(91.5)	(72.2)
Other comprehensive income	(4.5)	4.2
Balance at end of period	(96.0)	(68.0)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(55.0)	(120.9)
Other comprehensive income	0.6	1.8
Balance at end of period	(54.4)	(119.1)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.0	0.1
Other comprehensive income	(0.2)	(0.1)
Balance at end of period	0.8
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(143.9)	(191.3)
Other comprehensive income	(4.1)	5.9
Balance at end of period	$ (148.0)	$ (185.4)