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Business segment information - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Business segment information
Number of reportable segment not disclosed		true
Chemicals
Business segment information
Accelerated depreciation	$ 4.0		$ 14.0
Charge related to workforce reductions			2.0
Chemicals \| Louisiana Pigment Company, L.P. (LPC)
Business segment information
Transaction costs			$ 2.2
Kronos \| Valhi Incorporation
Business segment information
Direct ownership percentage by parent		50.00%
Kronos \| NL Industries
Business segment information
Indirect controlling interest in subsidiary		31.00%
NL Industries \| Valhi Incorporation
Business segment information
Direct ownership percentage by parent		83.00%
LandWell \| Valhi Incorporation
Business segment information
Direct ownership percentage by parent		27.00%
LandWell \| Basic Management Inc
Business segment information
Indirect controlling interest in subsidiary		50.00%
Basic Management Inc \| Valhi Incorporation
Business segment information
Direct ownership percentage by parent		63.00%