Valhi Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2012
Schedule Of Stockholders Equity [Line Items]
Treasury stock, shares	13,200,000	13,200,000	13,200,000
Percentage of shares held by majority-owned subsidiary that has to be considered for voting purpose	100.00%
Preferred stock, par value	$ 0.01	$ 0.01
Director Plan
Schedule Of Stockholders Equity [Line Items]
Number of shares authorized					200,000
Shares awarded under new plan	50,000	14,500	12,000
Common stock available for future grant	74,000
Series A Preferred Stock
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares outstanding	5,000
Preferred stock liquidation preference, per share	$ 133,466.75
Preferred stock, aggregate liquidation preference	$ 667.3
Preferred stock, par value	$ 0.01
Non-cumulative dividend on preferred stock	6.00%
NL
Schedule Of Stockholders Equity [Line Items]
Treasury stock, shares	14,400,000	14,400,000
Unrealized loss of shares attributable to noncontrolling interest	$ 0.2	$ 12.2
NL | Director Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	113,150
Kronos Worldwide, Inc.
Schedule Of Stockholders Equity [Line Items]
Shares available for purchase	1,690,000
Treasury stock, shares	1,700,000	1,700,000
Unrealized loss of shares attributable to noncontrolling interest	$ 0.2	$ 12.2
Kronos Worldwide, Inc. | Director Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	140,900
CompX | Director Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	149,050
Common stock
Schedule Of Stockholders Equity [Line Items]
Shares available for purchase				10,000,000