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Related Party Transactions - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contran \| Intercorporate Services Agreements Fees
Related Party Transaction [Line Items]
Related party transaction	$ 41.3	$ 43.9	$ 39.6
Contran \| Combined Information Technology Data Recovery Program
Related Party Transaction [Line Items]
Related party transaction	0.3	0.2	0.3
Contran \| Pledge Fee Received
Related Party Transaction [Line Items]
Revenue and other income from related party transactions	1.4	1.9	3.1
Contran \| Tremont \| Deferred Payment \| Present Value
Related Party Transaction [Line Items]
Guarantee Obligations, estimated exposure	9.9
Contran \| Tremont \| Deferred Payment \| Face Value
Related Party Transaction [Line Items]
Guarantee Obligations, estimated exposure	11.1
Contran \| Tremont \| Promissory Notes
Related Party Transaction [Line Items]
Guarantee Obligations, estimated exposure	2.0
Contran \| Kronos Worldwide, Inc. \| Sublease Agreement
Related Party Transaction [Line Items]
Payment for sublease rent and related ancillary services	$ 0.4	0.1
Contran \| Kronos Worldwide, Inc. \| Stock Pledged as Collateral
Related Party Transaction [Line Items]
Stock pledged as collateral	21.7
Contran \| Revolving Credit Facility
Related Party Transaction [Line Items]
Interest on borrowings and unused commitment fees under credit facilities	$ 14.2	19.9	18.9
Contran and Other Affiliates
Related Party Transaction [Line Items]
Related party transaction cash received for insurance premium		0.7	5.4
Related party transaction cash paid for insurance premium	23.1
LPC
Related Party Transaction [Line Items]
Purchase of Ti02 from LPC	167.8	176.2	165.9
Sales of feedstock ore to LPC	$ 84.2	$ 84.1	$ 66.9