Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate		35.00%	35.00%
Deferred income taxes		$ 90.2	$ 6.5
Non-cash income tax benefit recognized related to release of portion of reserve for uncertain tax positions		2.4
Increase (decrease) in unrecognized tax benefits		6.4
Chemicals | Employee Severance
Income Taxes Disclosure [Line Items]
Restructuring charges	$ 21.1	21.5
Kronos Worldwide, Inc. | Germany and Belgian
Income Taxes Disclosure [Line Items]
Deferred income tax asset valuation allowance	$ 150.3	2.3
Kronos Worldwide, Inc. | Direct investment in subsidiary excess carrying amount
Income Taxes Disclosure [Line Items]
Deferred income taxes		$ 29.7
Kronos Worldwide, Inc. | Corporate Purposes | German
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards				$ 738.0
Kronos Worldwide, Inc. | Corporate Purposes | Belgian
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards				87.0
Kronos Worldwide, Inc. | Trade Tax Purposes | German
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards				$ 94.0