Noncontrolling interest in subsidiaries - Changes in Ownership Interest in Subsidiaries (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net income attributable to Valhi stockholders	$ 3.5	$ 23.0	$ 44.3	$ 89.0	$ 55.6	$ 71.5	$ 52.4	$ 38.0	$ 159.8	$ 217.5	$ 50.3
Transfers from noncontrolling interest:
Issuance of subsidiary stock									0.2	0.4	87.8
Net income attributable to Valhi stockholders and change from noncontrolling interest in subsidiaries									$ 160.0	$ 217.9	$ 138.1