Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate		35.00%	35.00%
Deferred income taxes		$ 96.1	$ (7.4)
Non-cash income tax benefit recognized related to release of portion of reserve for uncertain tax positions		2.9
Kronos Worldwide, Inc. | Germany and Belgian
Income Taxes Disclosure [Line Items]
Deferred income tax asset valuation allowance	$ 150.3	$ 150.3
Kronos Worldwide, Inc. | Direct investment in subsidiary excess carrying amount
Income Taxes Disclosure [Line Items]
Deferred income taxes	$ 29.3
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