Valhi Stockholders' Equity - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2019
Schedule Of Stockholders Equity [Line Items]
Treasury stock, shares	1,100,000	1,100,000	1,100,000
Percentage of shares held by majority-owned subsidiary that has to be considered for voting purpose	100.00%
Director Stock Plan
Schedule Of Stockholders Equity [Line Items]
Number of shares authorized				200,000	100,000
Shares awarded under plan	7,500	6,300
Common stock available for future grant	70,800
N L Industries Inc
Schedule Of Stockholders Equity [Line Items]
Treasury stock, shares		1,200,000
Unrealized gain (loss) on sale of shares attributable to noncontrolling interest	$ 2.7	$ 1.9	$ (1.7)
N L Industries Inc | Director Stock Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	170,750
Kronos
Schedule Of Stockholders Equity [Line Items]
Shares available for purchase	1,017,518
Treasury stock, shares	100,000
Unrealized gain (loss) on sale of shares attributable to noncontrolling interest	$ 2.7	$ 1.9	$ 1.7
Kronos | Director Stock Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	71,000
Comp X | Director Stock Plan
Schedule Of Stockholders Equity [Line Items]
Common stock available for future grant	115,150
Common Stock [Member]
Schedule Of Stockholders Equity [Line Items]
Shares available for purchase	334,000					833,333