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Organization and basis of presentation - Additional Information (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Significant Accounting Policies [Line Items]
Special dividends paid per share	$ 0.21	$ 0.43
Kronos
Significant Accounting Policies [Line Items]
Parent company ownership interest	31.00%
Parent Company [Member] | Valhi Inc
Significant Accounting Policies [Line Items]
Parent company ownership interest	83.00%
Parent Company [Member] | Valhi Inc | Contran Corporation
Significant Accounting Policies [Line Items]
Parent company ownership interest	91.00%

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- Definition

Significant accounting policies.

+ References

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- Definition

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481687/323-10-50-3

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