Long-term debt - Kronos 9.50 Senior Secured Notes - Additional Information (Detail) $ in Millions					9 Months Ended
	Jul. 30, 2024 USD ($)	Feb. 14, 2024 USD ($)	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 EUR (€)	Aug. 31, 2024	Jul. 31, 2024	Jul. 30, 2024 EUR (€)	Jul. 17, 2024 USD ($)	Jul. 16, 2024 USD ($)	Jun. 30, 2024 USD ($)	Feb. 14, 2024 EUR (€)	Dec. 31, 2023 USD ($)
Debt Instrument [Line Items]
Kronos term loan from Contran					$ 53.7	$ 0.0
3.75% Senior Secured Notes due 2025
Debt Instrument [Line Items]
Remaining outstanding | €														€ 75,000,000
Kronos Worldwide, Inc. | On or Before March 15, 2026
Debt Instrument [Line Items]
Debt instrument, redemption price percentage			109.50%	109.50%
Kronos Worldwide, Inc. | Global Revolver Credit Facility
Debt Instrument [Line Items]
Line of credit maximum borrowing capacity											$ 300.0	$ 225.0	$ 300.0
Kronos Worldwide, Inc. | Kronos International, Inc
Debt Instrument [Line Items]
Long term debt, carrying amount					$ 25.0
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029
Debt Instrument [Line Items]
Debt instrument interest rate				9.50%						9.50%
Debt instrument principal amount | €				€ 276,174,000						€ 75,000,000
Debt Instrument Exchanged, Principal Amount of Each Instrument | €				850
Debt Instrument Exchanged, Cash Paid For Each Instrument | €				€ 150
Premium percentage										107.50%
Net proceeds from issuance	$ 90.0
Debt instrument, redemption price percentage			100.00%	100.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | On or After March 15, 2026
Debt Instrument [Line Items]
Debt instrument, redemption price percentage			104.75%	104.75%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | On or After March 15, 2028
Debt Instrument [Line Items]
Debt instrument, redemption price percentage			100.00%	100.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | On or Before March 15, 2026
Debt Instrument [Line Items]
Debt instrument, percentage of debt that may be redeemed			40.00%	40.00%
Minimum redemption outstanding debt percentage				50.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | Certain Change Of control events
Debt Instrument [Line Items]
Debt instrument redemption price percent if experiences certain specified change of control events			101.00%	101.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc
Debt Instrument [Line Items]
Debt instrument interest rate					9.50%		9.50%			9.50%					9.50%
Debt instrument, payment terms					bear interest at 9.50% per annum, payable semi-annually on March 15 and September 15 of each year, payments began on September 15, 2024
Frequency of debt instrument payment					semi-annually
Debt instrument, date of first semi-annual interest payment			--03-15	--03-15
Debt instrument, date of second semi-annual interest payment			--09-15	--09-15
Debt Instrument, date of first required semi-annual payment			Sep. 15, 2024	Sep. 15, 2024
Long term debt, carrying amount					$ 391.7		€ 351,174,000
Unamortized debt issuance costs					7.1
Unamortized premium | €							€ 5,400,000
Debt issuance costs, gross					$ 7.9
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Direct Domestic Subsidiary of KII and Guarantors | Collateral Pledged
Debt Instrument [Line Items]
Parent company ownership interest				100.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Foreign Subsidiary Directly Owned by KII or any Guarantor | Collateral Pledged
Debt Instrument [Line Items]
Parent company ownership interest				65.00%
Kronos Worldwide, Inc. | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Foreign Subsidiary Directly Owned by KII or any Guarantor | Collateral Pledged | Non-voting Common Stock
Debt Instrument [Line Items]
Parent company ownership interest				100.00%
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due 2025
Debt Instrument [Line Items]
Debt instrument interest rate				3.75%
Debt instrument principal amount | €				€ 325,000,000
Cash consideration		$ 52.6		48,750,000
Debt instrument, par value | €				1,000
Kronos Worldwide, Inc. | 3.75% Senior Secured Notes due 2025 | Kronos International, Inc
Debt Instrument [Line Items]
Debt instrument interest rate					3.75%		3.75%								3.75%
Debt instrument principal amount | €							€ 75,000,000
Long term debt, carrying amount					$ 83.9										$ 440.9
Interest charge included in interest expense					$ 1.5
Kronos Worldwide, Inc. | Subordinated, unsecured term loan from Contran
Debt Instrument [Line Items]
Debt instrument interest rate								9.54%	11.50%
Debt instrument principal amount | €				€ 50,000,000.0
Kronos term loan from Contran			$ 53.7
Kronos Worldwide, Inc. | Senior notes | Kronos International, Inc
Debt Instrument [Line Items]
Maximum amount of other indebtedness default before triggering customary default provisions			$ 50.0