Income Taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule Of Income Tax [Line Items]
Expected tax expense (benefit), at U.S. federal statutory income tax rate of 35%	$ 27.7	$ 4.0	$ 2.3	$ (9.3)
Incremental net tax on earnings and losses of non-U.S., U.S. and non-tax group companies	8.9	4.9	57.2	7.6
Non-U.S. tax rates	(3.5)	(1.0)	(8.2)	(1.4)
Valuation allowance	(7.8)	(0.8)	(170.4)	2.1
Adjustment to the reserve for uncertain tax positions, net	(7.7)	0.5	(6.6)	1.1
Nondeductible expenses	0.9	0.7	1.7	1.3
Domestic production activities deduction	(1.0)	0.2	(3.1)	(0.6)
U.S. state income taxes	0.5	(0.3)	(4.2)	(0.8)
Other, net	0.4	(0.1)	0.3	(0.3)
Income tax expense (benefit)	15.2	2.6	(134.2)	(5.8)
Comprehensive provision for income taxes (benefit) allocable to:
Income tax expense (benefit)	15.2	2.6	(134.2)	(5.8)
Other comprehensive income (loss):
Marketable securities	(0.5)	0.8	(1.0)	1.0
Currency translation	10.6	1.8	28.7	3.6
Interest rate swap	1.3	0.5	1.4	(2.2)
Total	28.0	6.3	(100.8)	(1.5)
Kronos Worldwide, Inc. | US Canada APA
Schedule Of Income Tax [Line Items]
U.S. Canada APA		(5.5)		(5.5)
Kronos Worldwide, Inc. | Canada Germany APA
Schedule Of Income Tax [Line Items]
U.S. Canada APA	(3.2)		(3.2)
Pension Plans
Other comprehensive income (loss):
Defined benefit plans	1.6	0.8	4.7	2.5
OPEB Plans
Other comprehensive income (loss):
Defined benefit plans	$ (0.2)	$ (0.2)	$ (0.4)	$ (0.6)