Income Taxes - Additional Information (Detail) CAD in Millions, $ in Millions	1 Months Ended	3 Months Ended				12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2013 CAD
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate						35.00%	35.00%	35.00%
Equity ownership percentage		50.00%				50.00%
Non-cash income tax benefit recognized related to completion of audit					$ 3.2
Unrecognized tax benefits impact on effective tax rate	$ 29.2	$ 23.4				$ 23.4	$ 24.2	$ 29.2
Increase (decrease) in unrecognized tax benefits		6.6				6.6
Accrued interest and penalties during the period						1.3	1.2	1.3
Accrued interest and penalties end of the period		4.2				4.2	4.1
Deferred income taxes						85.7	10.0	$ (114.8)
U.S. Income Tax Audit
Income Taxes Disclosure [Line Items]
Non-cash income tax benefit recognized related to completion of audit							3.1
Kronos Worldwide, Inc. | Bank Of Montreal
Income Taxes Disclosure [Line Items]
Letter of credit collateralized | CAD									CAD 7.9
Kronos Worldwide, Inc. | Direct investment in subsidiary excess carrying amount
Income Taxes Disclosure [Line Items]
Deferred income taxes		29.3	$ 29.3	$ 29.3
Canada | Canadian Income Tax Audit
Income Taxes Disclosure [Line Items]
Non-cash income tax benefit recognized related to completion of audit							$ 3.0
Germany | Kronos Worldwide, Inc. | Corporate Tax Purposes
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		683.0				683.0
Germany | Kronos Worldwide, Inc. | Trade Tax Purposes
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		96.0				96.0
Belgium | Kronos Worldwide, Inc. | Corporate Tax Purposes
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards		86.0				86.0
Germany and Belgian | Kronos Worldwide, Inc.
Income Taxes Disclosure [Line Items]
Deferred income tax asset valuation allowance		$ 159.0	$ 8.7	$ 150.3		159.0
Increase in deferred income tax valuation allowance						$ 9.8
BMI
Income Taxes Disclosure [Line Items]
Equity ownership percentage	32.00%							32.00%	32.00%
Parent company ownership interest	63.00%							63.00%	63.00%
Incremental tax (benefit) on earnings of non-U.S. and non-tax group companies	$ (11.1)