Income Taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule Of Income Tax [Line Items]
Expected tax expense, at U.S. federal statutory income tax rate of 21%	$ 8.9	$ 22.4
Incremental net tax (benefit) on earnings and losses of non-U.S. and non-tax group companies	(0.2)	4.1
Non-U.S. tax rates	2.3	7.0
Valuation allowance	1.0	0.3
Global intangible low-tax income, net	0.7
Adjustment to the reserve for uncertain tax positions, net	0.5	1.6
U.S. state income taxes and other, net	1.0	2.2
Income tax expense	14.2	36.2
Comprehensive provision for income taxes (benefit) allocable to:
Income from continuing operations	14.2	36.2
Discontinued operations		20.1
Retained earnings – change in accounting principle		1.1
Other comprehensive income (loss):
Currency translation		1.4
Total	15.7	60.2
Kronos Worldwide, Inc. | Canada-Germany APA
Schedule Of Income Tax [Line Items]
Canada – Germany APA		(1.4)
Pension Plans
Other comprehensive income (loss):
Defined benefit plans	1.6	1.5
OPEB Plans
Other comprehensive income (loss):
Defined benefit plans	$ (0.1)	$ (0.1)