Valhi Stockholders' Equity - Schedule of Common Stock Outstanding (Detail) - shares shares in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Stockholders Equity [Line Items]
Shares of common stock, Issued, beginning balance	355.3	355.3
Shares of common stock, Issued, ending balance	355.3	355.3
Shares of common stock, Treasury, beginning balance	(13.2)	(13.2)
Shares of common stock, Treasury, ending balance	(13.2)	(13.2)
Shares of common stock, Outstanding, beginning balance	355.3
Shares of common stock, Outstanding, ending balance	355.3	355.3
Excluding Stock Ownership By Subsidiary Considered To Be Held In Treasury
Schedule Of Stockholders Equity [Line Items]
Shares of common stock, Outstanding, beginning balance	342.0	342.0
Shares of common stock, Outstanding, ending balance	342.0	342.0