Income Taxes - Additional Information (Detail) $ in Millions			3 Months Ended							6 Months Ended			12 Months Ended
	Dec. 31, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 CAD ($)
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate														35.00%	35.00%	35.00%
Income tax examination, description														Tax authorities may in the future examine certain of our U.S. and non-U.S. tax returns and have or may propose tax deficiencies, including penalties and interest. Because of the inherent uncertainties involved in settlement initiatives and court and tax proceedings, we cannot guarantee that these tax matters will be resolved in our favor, and therefore our potential exposure, if any, is also uncertain.
Deferred income tax benefit from change in enacted tax rate														$ 77,100,000
Current income tax expense provisional pursuant to transition tax			$ 76,200,000											76,200,000
Increase (decrease) in non-cash deferred income tax asset valuation allowance														(205,400,000)	$ (2,200,000)	$ 159,000,000
Income taxes	$ 5,100,000		25,100,000			$ 5,100,000				$ 25,100,000				25,100,000	5,100,000
Non-cash income tax benefit related to reversal of reserve for uncertain tax positions						7,200,000
Deferred income taxes expense (benefit)														(245,800,000)	(26,400,000)	89,100,000
Unrecognized tax benefits impact on effective tax rate			13,100,000							13,100,000				13,100,000
Increase (decrease) in unrecognized tax benefits			1,800,000							1,800,000				1,800,000
Accrued interest and penalties during the period														2,100,000	1,600,000	$ 1,300,000
Accrued interest and penalties end of the period	5,200,000		1,500,000			5,200,000				1,500,000				$ 1,500,000	5,200,000
US-Canada APA
Income Taxes Disclosure [Line Items]
Current U.S. income tax benefit															$ (3,400,000)
Canada - Germany APA
Income Taxes Disclosure [Line Items]
U.S.-Canada Advance Pricing Agreement, description														During the third quarter of 2017, our Canadian subsidiary executed and finalized an Advance Pricing Agreement with the Competent Authority for Canada (the “Canada-Germany APA”) effective for tax years 2005 - 2017. Pursuant to the terms of the Canada-Germany APA, the Canadian and German tax authorities agreed to certain prior year changes to taxable income of our Canadian and German subsidiaries.
Non-cash income tax benefit related to reversal of reserve for uncertain tax positions				$ 8,100,000										$ 8,600,000
Canada - Germany APA | Earliest Tax Year
Income Taxes Disclosure [Line Items]
Effective tax year														2005
Canada - Germany APA | Latest Tax Year
Income Taxes Disclosure [Line Items]
Effective tax year														2017
Scenario Plan
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate													21.00%
Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance					$ (149,900,000)
Effect of Currency Exchange Rates
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance														$ 13,700,000
Transition Tax | Maximum
Income Taxes Disclosure [Line Items]
Percentage of annual usage limitation on net operating loss carryforward														80.00%
Germany | Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance					(141,900,000)
Belgium | Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance					(8,000,000)
Germany and Belgian
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance														$ (186,700,000)
Germany and Belgian | Current Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance										(24,100,000)	$ (12,700,000)
One Non-U.S. subsidiary | Expected Future Periods Net Operating Loss Utilization | Valuation Allowance of Deferred Tax Assets | Non Cash Deferred Income Tax Benefit
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance			(18,700,000)
Kronos Worldwide, Inc. | US-Canada APA | Earliest Tax Year
Income Taxes Disclosure [Line Items]
Effective tax year															2005
Kronos Worldwide, Inc. | US-Canada APA | Latest Tax Year
Income Taxes Disclosure [Line Items]
Effective tax year															2015
Kronos Worldwide, Inc. | Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	(173,000,000)				$ (149,900,000)
Kronos Worldwide, Inc. | Germany | Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	(153,000,000)
Kronos Worldwide, Inc. | Belgium | Expected Future Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance	(20,000,000)
Kronos Worldwide, Inc. | Germany and Belgian | Current Periods Net Operating Loss Utilization
Income Taxes Disclosure [Line Items]
Increase (decrease) in non-cash deferred income tax asset valuation allowance		$ 150,300,000									$ (12,700,000)	$ 8,700,000			$ (2,200,000)
European Subsidiaries | Transition Tax
Income Taxes Disclosure [Line Items]
Current income tax expense provisional pursuant to transition tax			76,200,000
Income tax liability payable period														8 years
European Subsidiaries | Transition Tax | Income Tax Payable | Contran
Income Taxes Disclosure [Line Items]
Current income tax expense payable in increments over remainder of eight year period			70,100,000							70,100,000				$ 70,100,000
European Subsidiaries | Transition Tax | Income Tax Receivable | Contran
Income Taxes Disclosure [Line Items]
Current income tax expense payable in next fiscal year			6,100,000							6,100,000				6,100,000
European and Canadian Subsidiaries | Undistributed Earnings Previously Considered to be Permanently Reinvested
Income Taxes Disclosure [Line Items]
Aggregate provisional non-cash deferred income tax expense (benefit)			5,300,000
Kronos Canadian Subsidiary | US-Canada APA
Income Taxes Disclosure [Line Items]
Income taxes	$ 2,300,000					$ 2,300,000									2,300,000		$ 3
Corporate Tax Purposes | Kronos Worldwide, Inc. | Germany
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards			652,000,000							652,000,000				652,000,000
Corporate Tax Purposes | Kronos Worldwide, Inc. | Belgium
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards			50,000,000							50,000,000				50,000,000
Trade Tax Purposes | Kronos Worldwide, Inc. | Germany
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards			500,000							500,000				500,000
Canada Revenue Agency and German Federal Central Tax Office | Germany | Canada - Germany APA
Income Taxes Disclosure [Line Items]
Non-cash income tax benefit related to increase in German NOLs				2,600,000
Cash tax refund				$ 600,000
Direct investment in subsidiary excess carrying amount | Kronos Worldwide, Inc.
Income Taxes Disclosure [Line Items]
Deferred income taxes expense (benefit)							$ (29,300,000)	$ (29,300,000)	$ (29,300,000)					22,100,000	$ 6,500,000
Direct Investment in Subsidiary | Kronos Worldwide, Inc.
Income Taxes Disclosure [Line Items]
Deferred income tax liability			157,600,000							157,600,000				157,600,000
Direct Investment in Subsidiary | Kronos Worldwide, Inc. | Maximum
Income Taxes Disclosure [Line Items]
Deferred income tax liability			$ 173,000,000							$ 173,000,000				$ 173,000,000