Accounts Payable and Accrued Liabilities - Components of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts Payable And Accrued Liabilities [Line Items]
Accounts payable	$ 132.0	$ 111.0
Employee benefits	30.3	27.8
Accrued sales discounts and rebates	14.6	29.1
Operating lease liabilities	$ 6.3	$ 6.7
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Total	Total
Other	$ 28.3	$ 41.3
Total	238.0	243.8
Louisiana Pigment Company, L.P.
Accounts Payable And Accrued Liabilities [Line Items]
Payables to affiliate	16.8	19.3
Valhi | Income taxes
Accounts Payable And Accrued Liabilities [Line Items]
Payables to affiliate	$ 9.7	$ 8.6