Organization and basis of presentation - Additional Information (Details)	Mar. 31, 2026
Contran \| Valhi Incorporation
Organization and basis of presentation
Parent company ownership interest	91.00%

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant