<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>162</ContextCount>
  <ElementCount>247</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>38</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>5</UnitCount>
  <MyReports>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedBalanceSheets</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00200 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfIncome</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00300 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00400 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfEquity</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00405 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfEquityParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00500 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Organization and basis of presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOrganizationAndBasisOfPresentation</Role>
      <ShortName>Organization and basis of presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Segment information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Accounts and other receivables, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccountsAndOtherReceivablesNet</Role>
      <ShortName>Accounts and other receivables, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Inventories, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInventoriesNet</Role>
      <ShortName>Inventories, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Marketable securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureMarketableSecurities</Role>
      <ShortName>Marketable securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Investment in Kronos Worldwide, Inc.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideInc</Role>
      <ShortName>Investment in Kronos Worldwide, Inc.</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Other assets, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherAssetsNet</Role>
      <ShortName>Other assets, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Accrued and other current liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccruedAndOtherCurrentLiabilities</Role>
      <ShortName>Accrued and other current liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Long-term debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureLongTermDebt</Role>
      <ShortName>Long-term debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Other noncurrent liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherNoncurrentLiabilities</Role>
      <ShortName>Other noncurrent liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Revenue recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureRevenueRecognition</Role>
      <ShortName>Revenue recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Employee benefit plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureEmployeeBenefitPlans</Role>
      <ShortName>Employee benefit plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Income taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Stockholders' equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureStockholdersEquity</Role>
      <ShortName>Stockholders' equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Commitments and contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Financial instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureFinancialInstruments</Role>
      <ShortName>Financial instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11701 - Disclosure - Recent Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureRecentAccountingPronouncements</Role>
      <ShortName>Recent Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>20102 - Disclosure - Organization and basis of presentation (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureOrganizationAndBasisOfPresentationPolicies</Role>
      <ShortName>Organization and basis of presentation (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.nl-ind.com/role/DisclosureRecentAccountingPronouncements</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>30203 - Disclosure - Segment information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureSegmentInformationTables</Role>
      <ShortName>Segment information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/role/DisclosureSegmentInformation</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Accounts and other receivables, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccountsAndOtherReceivablesNetTables</Role>
      <ShortName>Accounts and other receivables, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccountsAndOtherReceivablesNet</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>30403 - Disclosure - Inventories, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInventoriesNetTables</Role>
      <ShortName>Inventories, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInventoriesNet</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Marketable securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureMarketableSecuritiesTables</Role>
      <ShortName>Marketable securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureMarketableSecurities</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Investment in Kronos Worldwide, Inc. (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideIncTables</Role>
      <ShortName>Investment in Kronos Worldwide, Inc. (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideInc</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Other assets, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherAssetsNetTables</Role>
      <ShortName>Other assets, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherAssetsNet</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Accrued and other current liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccruedAndOtherCurrentLiabilitiesTables</Role>
      <ShortName>Accrued and other current liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccruedAndOtherCurrentLiabilities</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Other noncurrent liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherNoncurrentLiabilitiesTables</Role>
      <ShortName>Other noncurrent liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherNoncurrentLiabilities</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Revenue recognition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureRevenueRecognitionTables</Role>
      <ShortName>Revenue recognition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureRevenueRecognition</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Employee benefit plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureEmployeeBenefitPlansTables</Role>
      <ShortName>Employee benefit plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureEmployeeBenefitPlans</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>31303 - Disclosure - Income taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxes</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Stockholders' equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureStockholdersEquityTables</Role>
      <ShortName>Stockholders' equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureStockholdersEquity</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Commitments and contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>31603 - Disclosure - Financial instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureFinancialInstrumentsTables</Role>
      <ShortName>Financial instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureFinancialInstruments</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Organization and basis of presentation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureOrganizationAndBasisOfPresentationAdditionalInformationDetails</Role>
      <ShortName>Organization and basis of presentation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Segment information - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureSegmentInformationAdditionalInformationDetails</Role>
      <ShortName>Segment information - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40202 - Disclosure - Segment information - Differences Between Segment Profit and Amounts Included in Net Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureSegmentInformationDifferencesBetweenSegmentProfitAndAmountsIncludedInNetIncomeDetails</Role>
      <ShortName>Segment information - Differences Between Segment Profit and Amounts Included in Net Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Accounts and other receivables, net - Schedule of Accounts Notes Loans and Financing Receivable (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccountsAndOtherReceivablesNetScheduleOfAccountsNotesLoansAndFinancingReceivableDetails</Role>
      <ShortName>Accounts and other receivables, net - Schedule of Accounts Notes Loans and Financing Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Inventories, net - Schedule of Inventories, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInventoriesNetScheduleOfInventoriesNetDetails</Role>
      <ShortName>Inventories, net - Schedule of Inventories, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Marketable securities - Schedule of Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureMarketableSecuritiesScheduleOfMarketableSecuritiesDetails</Role>
      <ShortName>Marketable securities - Schedule of Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40502 - Disclosure - Marketable securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureMarketableSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Marketable securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Investment in Kronos Worldwide, Inc. - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideIncAdditionalInformationDetails</Role>
      <ShortName>Investment in Kronos Worldwide, Inc. - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Investment in Kronos Worldwide, Inc. - Changes in Carrying Value of Investment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideIncChangesInCarryingValueOfInvestmentDetails</Role>
      <ShortName>Investment in Kronos Worldwide, Inc. - Changes in Carrying Value of Investment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40603 - Disclosure - Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideIncSelectedFinancialInformationOfKronosBalanceSheetDetails</Role>
      <ShortName>Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Balance Sheet (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40604 - Disclosure - Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureInvestmentInKronosWorldwideIncSelectedFinancialInformationOfKronosIncomeStatementDetails</Role>
      <ShortName>Investment in Kronos Worldwide, Inc. - Selected Financial Information of Kronos Income Statement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Other assets, net - Schedule of Other Assets, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherAssetsNetScheduleOfOtherAssetsNetDetails</Role>
      <ShortName>Other assets, net - Schedule of Other Assets, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Accrued and other current liabilities - Schedule of Accrued and Other Current Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureAccruedAndOtherCurrentLiabilitiesScheduleOfAccruedAndOtherCurrentLiabilitiesDetails</Role>
      <ShortName>Accrued and other current liabilities - Schedule of Accrued and Other Current Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Long-term debt - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureLongTermDebtAdditionalInformationDetails</Role>
      <ShortName>Long-term debt - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Other noncurrent liabilities - Summary of Other Noncurrent Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureOtherNoncurrentLiabilitiesSummaryOfOtherNoncurrentLiabilitiesDetails</Role>
      <ShortName>Other noncurrent liabilities - Summary of Other Noncurrent Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Revenue recognition - Schedule of Disaggregation of Net Sales By Reporting Unit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureRevenueRecognitionScheduleOfDisaggregationOfNetSalesByReportingUnitDetails</Role>
      <ShortName>Revenue recognition - Schedule of Disaggregation of Net Sales By Reporting Unit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Employee benefit plans - Components of Net Periodic Defined Benefit Cost (Income) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureEmployeeBenefitPlansComponentsOfNetPeriodicDefinedBenefitCostIncomeDetails</Role>
      <ShortName>Employee benefit plans - Components of Net Periodic Defined Benefit Cost (Income) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>41202 - Disclosure - Employee benefit plans - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureEmployeeBenefitPlansAdditionalInformationDetails</Role>
      <ShortName>Employee benefit plans - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Income taxes - Component of Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxesComponentOfIncomeTaxesDetails</Role>
      <ShortName>Income taxes - Component of Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>41302 - Disclosure - Income taxes - Components of Comprehensive Provision (Benefit) for Income Taxes Allocation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxesComponentsOfComprehensiveProvisionBenefitForIncomeTaxesAllocationDetails</Role>
      <ShortName>Income taxes - Components of Comprehensive Provision (Benefit) for Income Taxes Allocation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>41303 - Disclosure - Income taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>41304 - Disclosure - Income Taxes - Component of Income Taxes - Additional (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/role/DisclosureIncomeTaxesComponentOfIncomeTaxesAdditionalDetails</Role>
      <ShortName>Income Taxes - Component of Income Taxes - Additional (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Stockholders' equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureStockholdersEquityScheduleOfChangesInAccumulatedOtherComprehensiveLossDetails</Role>
      <ShortName>Stockholders' equity - Schedule of Changes in Accumulated Other Comprehensive Loss (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesChangesInAccruedEnvironmentalRemediationAndRelatedCostsDetails</Role>
      <ShortName>Commitments and contingencies - Changes in Accrued Environmental Remediation and Related Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Commitments and contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>Commitments and contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="nl-20250630x10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Financial instruments - Summary of Financial Instruments Not Carried at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nl-ind.com/20210930/taxonomy/role/DisclosureFinancialInstrumentsSummaryOfFinancialInstrumentsNotCarriedAtFairValueDetails</Role>
      <ShortName>Financial instruments - Summary of Financial Instruments Not Carried at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>nl-20250630.xsd</File>
    <File>nl-20250630_cal.xml</File>
    <File>nl-20250630_def.xml</File>
    <File>nl-20250630_lab.xml</File>
    <File>nl-20250630_pre.xml</File>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="nl-20250630x10q.htm">nl-20250630x10q.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="2">http://fasb.org/srt/2024</BaseTaxonomy>
    <BaseTaxonomy items="683">http://fasb.org/us-gaap/2024</BaseTaxonomy>
    <BaseTaxonomy items="30">http://xbrl.sec.gov/dei/2024</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
