Income Taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Income Tax [Line Items]
United States		$ 26.7	$ (8.2)	$ (3.5)
Non-U.S. subsidiaries		265.1	47.8	(38.4)
Income (loss) from continuing operations before income taxes		291.8	39.6	(41.9)
Expected tax expense (benefit) at U.S. federal statutory income tax rate of 35%		102.1	13.8	(14.7)
Non-U.S. tax rates		(13.1)	(4.3)	0.6
Incremental net tax expense (benefit) on earnings and losses of non-U.S. and non-tax group companies		14.8	8.2	(37.6)
Valuation allowance		(205.4)	(2.2)	159.0
Transition tax	$ 76.2	76.2
Change in federal tax rate		(77.1)
U.S. state income taxes, net		3.5	1.7	(1.1)
Adjustment to the reserve for uncertain tax positions, net		(18.2)	7.2	0.8
Nondeductible expenses		2.2	1.9	2.5
Domestic production activities deduction		(3.8)	(3.8)	(1.3)
Other, net		(1.2)	(0.5)	(0.7)
Provision for income taxes (benefit)		(120.0)	18.6	107.5
Comprehensive provision for income taxes (benefit) allocable to:
Income (loss) from continuing operations		(120.0)	18.6	107.5
Discontinued operations		(67.1)	(12.6)	(10.1)
Other comprehensive income (loss):
Marketable securities		2.8	2.1	(4.1)
Currency translation		31.1	(3.4)	(17.3)
Interest rate swap		1.6	0.2	(1.7)
Total		(143.6)	(0.6)	78.0
Pension Plans
Other comprehensive income (loss):
Defined benefit plans		8.6	(5.0)	4.1
OPEB Plans
Other comprehensive income (loss):
Defined benefit plans		$ (0.6)	(0.5)	$ (0.4)
Kronos Worldwide, Inc. | US-Canada APA
Schedule Of Income Tax [Line Items]
U.S. – Canada APA			$ (3.4)