Valhi Stockholders' Equity - Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	$ 829.5
Other comprehensive income	47.4	$ 28.1	$ 1.3
Plan settlement	0.2
Balance at end of period	958.6	829.5
Marketable Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	1.7	1.8	1.7
Other comprehensive income	(0.1)	(0.1)	0.1
Balance at end of period	1.6	1.7	1.8
Currency Translation
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(72.2)	(67.4)	(76.8)
Other comprehensive income	(19.3)	(4.8)	9.4
Balance at end of period	(91.5)	(72.2)	(67.4)
Accumulated Defined Benefit Plans Adjustment | Defined Benefit Pension Plans
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(120.9)	(154.1)	(146.6)
Other comprehensive income	7.3	10.7	9.8
Net actuarial gain (loss) arising during the year	58.4	22.5	(17.3)
Balance at end of period	(55.0)	(120.9)	(154.1)
Accumulated Defined Benefit Plans Adjustment | OPEB
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	0.1	0.3	1.0
Other comprehensive income	(0.5)	(0.3)	(0.8)
Net actuarial gain (loss) arising during the year	1.4	0.1	0.1
Balance at end of period	1.0	0.1	0.3
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at beginning of period	(191.3)	(219.4)	(220.7)
Balance at end of period	$ (143.9)	$ (191.3)	$ (219.4)