Income Taxes - Additional Information (Detail) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		3 Months Ended
	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2014 Cash tax benefit USD ($)	Jun. 30, 2014 U.S. Income Tax Audit USD ($)	Dec. 31, 2013 Kronos Worldwide, Inc. Bank Of Montreal CAD	Jun. 30, 2014 Canada Canadian Income Tax Audit USD ($)	Jun. 30, 2014 Canada Foreign Line of Credit Kronos Worldwide, Inc. Bank Of Montreal CAD
Income Taxes Disclosure [Line Items]
Letter of credit collateralized						7.9		0.3
Unrecognized tax benefits	5.6		5.6
Non-cash income tax benefit recognized related to release of portion of reserve for uncertain tax positions					3.1		3.0
Aggregate letters of credit cancelled								7.6
Provision (benefit) for income taxes related to previous periods	$ (2.0)	$ 1.0	$ (1.8)	$ 2.0