Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Taxes Disclosure [Line Items]
U.S. federal statutory income tax rate	21.00%	21.00%		21.00%	21.00%
Non-cash income tax benefit			$ 1.4
Aggregate provisional non-cash deferred income tax expense		$ 3.4
Deferred income tax benefit from change in enacted tax rate		$ 59.7			$ 59.7
Effective income tax rate		38.00%			38.90%
Provision for income taxes includes non-cash deferred income tax expense				$ 6.7	$ 3.0
Business interest income, adjusted taxable income				30.00%
Increase (decrease) in unrecognized tax benefits	$ (3.7)			$ (3.7)
Kronos Worldwide, Inc.
Income Taxes Disclosure [Line Items]
Incremental tax benefit				1.4
Direct Investment in Subsidiary | Kronos Worldwide, Inc.
Income Taxes Disclosure [Line Items]
Deferred income tax liability						$ 40.7
Deferred income taxes expense (benefit)		$ 113.0		$ 3.3	$ 19.2
Direct Investment in Subsidiary | Kronos Worldwide, Inc. | Maximum
Income Taxes Disclosure [Line Items]
Deferred income tax liability						$ 155.4