XML 50 R40.htm IDEA: XBRL DOCUMENT
v3.25.3

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% |

X
- Definition Significant accounting policies. + References No definition available. + Details
Name: | nl_SignificantAccountingPoliciesLineItems
Namespace Prefix: | nl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Special dividends paid during the period for each share of common stock outstanding. + References No definition available. + Details
Name: | nl_SpecialDividendsPaidPerShare
Namespace Prefix: | nl_
Data Type: | dtr-types:perShareItemType
Balance Type: | na
Period Type: | duration

X
- 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 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=nl_KronosWorldwideIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_OwnershipAxis=nl_ValhiIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=nl_ContranCorporationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |