Income taxes - Additional Information (Detail) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended						3 Months Ended	12 Months Ended		12 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2012 Proposed adjustment to certain foreign tax liabilities [Member] USD ($)	Dec. 31, 2012 Proposed adjustment to certain foreign tax liabilities [Member] CAD	Mar. 31, 2010 Germany [Member] USD ($)	Dec. 31, 2012 France [Member] USD ($)	Sep. 30, 2012 France [Member]	Dec. 31, 2012 Taiwan [Member] USD ($)	Dec. 31, 2012 Chemicals [Member] USD ($)	Dec. 31, 2012 Kronos Worldwide, Inc. [Member] German corporate [Member] USD ($)	Dec. 31, 2012 Kronos Worldwide, Inc. [Member] Trade tax purposes [Member] USD ($)
Income Taxes Disclosure [Line Items]
Surtax on dividend distributions											3.00%
Distributed dividend										$ 8.9
Undistributed earnings			1,000.0	978.0						10.8
Net incremental tax benefit	11.1	8.4											3.1
Tax related to non-cash dividend distributions												8.0
Provision for income taxes				17.2
Realized non-cash income tax benefit			51.5	95.3	(11.1)				35.2
Letter of credit collateralized								7.5
Potential tax liability full amount for the proposed adjustment							16.0
Unrecognized tax benefits impact on effective tax rate			27.9	23.5	32.2
Unrecognized tax benefits			33.4	23.0	37.4	31.8
Increase (decrease) in unrecognized tax benefits			(4.4)
Accrued interest and penalties during the period			0.9	0.6	0.8
Accrued interest and penalties end of the period			4.1	3.9
Net operating loss carryforwards														744	100
Deferred income tax asset valuation allowance			$ 0