Long-term debt - Kronos 9.50 Senior Secured Notes - Additional Information (Details) € in Thousands, $ in Millions					3 Months Ended	12 Months Ended
	Sep. 15, 2025 USD ($)	Jul. 30, 2024 USD ($)	Feb. 12, 2024 USD ($)	Feb. 12, 2024 EUR (€)	Mar. 31, 2024 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2025 EUR (€)	Sep. 30, 2025 EUR (€)	Sep. 15, 2025 EUR (€)	Jul. 30, 2024 EUR (€)	Jul. 17, 2024 USD ($)	Jul. 16, 2024 USD ($)	Feb. 12, 2024 EUR (€)
Long-term debt
Additional principal amount						$ 88.0	$ 80.2
9.50% Senior Secured Notes due 2029
Long-term debt
Premium percentage		107.50%									107.50%
9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Direct Domestic Subsidiary of KII and Guarantors | Collateral Pledged [Member]
Long-term debt
Parent company ownership interest			100.00%											100.00%
9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Foreign Subsidiary Directly Owned by KII or any Guarantor | Collateral Pledged [Member]
Long-term debt
Parent company ownership interest			65.00%											65.00%
Kronos Worldwide | Global Revolver Credit Facility
Long-term debt
Line of credit maximum borrowing capacity		$ 300.0										$ 300.0	$ 225.0
Kronos Worldwide | Kronos International, Inc
Long-term debt
Long term debt, carrying amount							$ 10.0
Kronos Worldwide | 9.50% Senior Secured Notes due 2029
Long-term debt
Debt instrument interest rate		9.50%	9.50%			9.50%		9.50%		9.50%	9.50%			9.50%
Principal amount			$ 53.7
Debt instrument principal amount | €										€ 75,000	€ 75,000			€ 276,174
Premium percentage		107.50%								105.00%	107.50%
Net proceeds from issuance	$ 90.0	$ 90.0
Debt instrument, redemption price percentage			100.00%	100.00%
Debt issuance costs	$ 1.7
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | Prior to March 15, 2026
Long-term debt
Debt instrument, redemption price percentage			100.00%	100.00%
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | On or After March 15, 2028
Long-term debt
Debt instrument, redemption price percentage			104.75%	104.75%
Debt instrument, percentage of debt that may be redeemed			40.00%	40.00%
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | On or Before March 15, 2026
Long-term debt
Debt instrument, redemption price percentage			109.50%	109.50%
Minimum redemption outstanding debt percentage			50.00%											50.00%
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | Certain Change Of control events
Long-term debt
Debt instrument redemption price percent if experiences certain specified change of control events			101.00%	101.00%
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc
Long-term debt
Debt instrument interest rate			9.50%			9.50%	9.50%	9.50%						9.50%
Debt instrument principal amount | €										€ 351,174
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	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
Debt instrument maturity date			Mar. 15, 2029	Mar. 15, 2029
Unamortized premium						$ 9.0
Unamortized debt issuance costs						6.9
Long term debt, carrying amount						$ 503.7	$ 365.4	€ 426,174
Kronos Worldwide | 9.50% Senior Secured Notes due 2029 | Kronos International, Inc | Foreign Subsidiary Directly Owned by KII or any Guarantor | Collateral Pledged [Member] | Nonvoting Common Stock [Member]
Long-term debt
Parent company ownership interest			100.00%											100.00%
Kronos Worldwide | 3.75% Senior Secured Notes due 2025
Long-term debt
Debt instrument interest rate			3.75%							3.75%				3.75%
Debt instrument principal amount | €										€ 75,000				€ 325,000
Cash consideration			$ 52.6	€ 48,750
Kronos Worldwide | 3.75% Senior Secured Notes due 2025 | Kronos International, Inc
Long-term debt
Debt instrument interest rate						3.75%	3.75%	3.75%	3.75%
Debt instrument principal amount | €								€ 75,000	€ 75,000
Interest charge included in interest expense					$ 1.5
Long term debt, carrying amount							$ 78.3
Kronos Worldwide | Senior notes | Kronos International, Inc
Long-term debt
Maximum amount of other indebtedness default before triggering customary default provisions			$ 50.0