Income Taxes - Components of Comprehensive Provision for Income Taxes Allocation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Income Tax [Line Items]
United States	$ 45.2	$ 23.5	$ (22.5)
Non-U.S. subsidiaries	55.4	81.2	258.7
Income from continuing operations before income taxes	100.6	104.7	236.2
Expected tax expense at U.S. federal statutory income tax rate of 21%	21.1	22.0	49.6
Non-U.S. tax rates	0.5	5.2	20.8
Incremental net tax benefit on earnings and losses of U.S. and non-U.S. tax group companies	(8.7)	(4.5)	(167.8)
Valuation allowance	3.8	4.5
Transition tax			(2.1)
Global intangible low-tax income, net	2.2	1.8	4.0
Tax rate changes	(0.2)	4.7	58.8
U.S. state income taxes, net	0.9	(0.3)	0.6
Adjustment to the reserve for uncertain tax positions, net	(3.8)	(5.1)	4.1
Nondeductible expenses	1.0	1.5	3.0
Refund of prior tax payments, net		(2.1)
Other, net	(0.9)	(1.2)	(0.3)
Income tax expense (benefit)	15.9	26.5	(30.7)
Comprehensive provision for income taxes (benefit) allocable to:
Income tax expense (benefit)	15.9	26.5	(30.7)
Discontinued operations	0.6		23.7
Retained earnings-change in accounting principle			1.1
Other comprehensive income (loss):
Currency translation	1.6	(0.2)	(4.2)
Total	10.4	10.2	(15.2)
Pension Plans
Other comprehensive income (loss):
Defined benefit plans	(7.3)	(15.6)	(4.7)
Other
Other comprehensive income (loss):
Defined benefit plans	$ (0.4)	$ (0.5)	(0.4)
Kronos Worldwide, Inc. | Canada - Germany APA
Schedule Of Income Tax [Line Items]
APA			$ (1.4)