<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>507</ContextCount>
  <ElementCount>399</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>105</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>75000 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>75010 - Statement - Unaudited Interim Condensed Statements of Consolidated Financial Position</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedInterimCondensedStatementsOfConsolidatedFinancialPosition</Role>
      <ShortName>Unaudited Interim Condensed Statements of Consolidated Financial Position</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>75020 - Statement - Unaudited Interim Condensed Consolidated Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedInterimCondensedConsolidatedStatementsOfOperations3</Role>
      <ShortName>Unaudited Interim Condensed Consolidated Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>75030 - Statement - Unaudited Interim Condensed Statements of Consolidated Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedInterimCondensedStatementsOfConsolidatedComprehensiveIncomeLoss</Role>
      <ShortName>Unaudited Interim Condensed Statements of Consolidated Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>75050 - Statement - Unaudited Interim Condensed Statements of Consolidated Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedInterimCondensedStatementsOfConsolidatedCashFlows</Role>
      <ShortName>Unaudited Interim Condensed Statements of Consolidated Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>75060 - Statement - Unaudited Condensed Statements of Changes in Consolidated Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedCondensedStatementsOfChangesInConsolidatedShareholdersEquity</Role>
      <ShortName>Unaudited Condensed Statements of Changes in Consolidated Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>75070 - Statement - Unaudited Condensed Statements of Changes in Consolidated Shareholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/StatementUnauditedCondensedStatementsOfChangesInConsolidatedShareholdersEquityParenthetical</Role>
      <ShortName>Unaudited Condensed Statements of Changes in Consolidated Shareholders' Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>995455 - Disclosure - The Company</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/TheCompany</Role>
      <ShortName>The Company</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>995465 - Disclosure - Accounting principles</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/AccountingPrinciples</Role>
      <ShortName>Accounting principles</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>995475 - Disclosure - Scope of consolidation and non-consolidated entities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureScopeOfConsolidationAndNonconsolidatedEntities1</Role>
      <ShortName>Scope of consolidation and non-consolidated entities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>995485 - Disclosure - Information concerning the Group's Consolidated Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperations</Role>
      <ShortName>Information concerning the Group's Consolidated Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>995495 - Disclosure - Impairment tests</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/ImpairmentTests</Role>
      <ShortName>Impairment tests</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>995505 - Disclosure - Right-of-use assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/RightOfUseAssets</Role>
      <ShortName>Right-of-use assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>995515 - Disclosure - Property, plant and equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/PropertyPlantAndEquipment</Role>
      <ShortName>Property, plant and equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>995525 - Disclosure - Non-current financial assets and other non-current assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncurrentFinancialAssetsAndOtherNoncurrentAssets1</Role>
      <ShortName>Non-current financial assets and other non-current assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>995535 - Disclosure - Trade Receivables and Other Current Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureTradeReceivablesAndOtherCurrentAssets1</Role>
      <ShortName>Trade Receivables and Other Current Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>995545 - Disclosure - Financial assets and liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialAssetsAndLiabilities1</Role>
      <ShortName>Financial assets and liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995555 - Disclosure - Current financial assets and Cash and cash equivalents</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/CurrentFinancialAssetsAndCashAndCashEquivalents</Role>
      <ShortName>Current financial assets and Cash and cash equivalents</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>995565 - Disclosure - Financial liabilities and lease debts</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebts</Role>
      <ShortName>Financial liabilities and lease debts</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>995575 - Disclosure - Other current liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/OtherCurrentLiabilities</Role>
      <ShortName>Other current liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>995585 - Disclosure - Deferred income and contract liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureDeferredIncomeAndContractLiabilities</Role>
      <ShortName>Deferred income and contract liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>995595 - Disclosure - Share capital and premium related to the share capitals</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureShareCapitalAndPremiumRelatedToTheShareCapitals1</Role>
      <ShortName>Share capital and premium related to the share capitals</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>995605 - Disclosure - Non-cash stock-based compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensation1</Role>
      <ShortName>Non-cash stock-based compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995615 - Disclosure - Earnings per share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/EarningsPerShare</Role>
      <ShortName>Earnings per share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995625 - Disclosure - Provisions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/Provisions</Role>
      <ShortName>Provisions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>995635 - Disclosure - Off-balance sheet commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureOffbalanceSheetCommitments1</Role>
      <ShortName>Off-balance sheet commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>995645 - Disclosure - Related parties and other major shareholders</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureRelatedPartiesAndOtherMajorShareholders</Role>
      <ShortName>Related parties and other major shareholders</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995655 - Disclosure - Subsequent events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/SubsequentEvents</Role>
      <ShortName>Subsequent events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>995665 - Disclosure - Accounting principles (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/AccountingPrinciplesPolicies</Role>
      <ShortName>Accounting principles (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/AccountingPrinciples</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>995685 - Disclosure - Information concerning the Group's Consolidated Operations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsTables</Role>
      <ShortName>Information concerning the Group's Consolidated Operations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperations</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>995695 - Disclosure - Right-of-use assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/RightOfUseAssetsTables</Role>
      <ShortName>Right-of-use assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/RightOfUseAssets</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995705 - Disclosure - Property, plant and equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/PropertyPlantAndEquipmentTables</Role>
      <ShortName>Property, plant and equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/PropertyPlantAndEquipment</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995715 - Disclosure - Non-current financial assets and other non-current assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncurrentFinancialAssetsAndOtherNoncurrentAssetsTables</Role>
      <ShortName>Non-current financial assets and other non-current assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncurrentFinancialAssetsAndOtherNoncurrentAssets1</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995725 - Disclosure - Trade receivables and other current assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureTradeReceivablesAndOtherCurrentAssetsTables</Role>
      <ShortName>Trade receivables and other current assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995735 - Disclosure - Financial assets and liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialAssetsAndLiabilitiesTables</Role>
      <ShortName>Financial assets and liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialAssetsAndLiabilities1</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995745 - Disclosure - Current financial assets and Cash and cash equivalents (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/CurrentFinancialAssetsAndCashAndCashEquivalentsTables</Role>
      <ShortName>Current financial assets and Cash and cash equivalents (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/CurrentFinancialAssetsAndCashAndCashEquivalents</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995755 - Disclosure - Financial liabilities and lease debts (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsTables</Role>
      <ShortName>Financial liabilities and lease debts (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebts</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>995765 - Disclosure - Other current liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/OtherCurrentLiabilitiesTables</Role>
      <ShortName>Other current liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/OtherCurrentLiabilities</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>995775 - Disclosure - Deferred Income and contract liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureDeferredIncomeAndContractLiabilitiesTables</Role>
      <ShortName>Deferred Income and contract liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>995785 - Disclosure - Share capital and premium related to the share capitals (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureShareCapitalAndPremiumRelatedToTheShareCapitalsTables</Role>
      <ShortName>Share capital and premium related to the share capitals (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureShareCapitalAndPremiumRelatedToTheShareCapitals1</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>995795 - Disclosure - Non-cash stock-based compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationTables</Role>
      <ShortName>Non-cash stock-based compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensation1</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>995805 - Disclosure - Earnings per share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/EarningsPerShareTables</Role>
      <ShortName>Earnings per share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/EarningsPerShare</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>995815 - Disclosure - Provisions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/ProvisionsTables</Role>
      <ShortName>Provisions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/Provisions</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>995825 - Disclosure - Off-balance sheet commitments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureOffbalanceSheetCommitmentsTables</Role>
      <ShortName>Off-balance sheet commitments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureOffbalanceSheetCommitments1</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>995835 - Disclosure - Related parties and other major shareholders (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureRelatedPartiesAndOtherMajorShareholdersTables</Role>
      <ShortName>Related parties and other major shareholders (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cellectis.com/20260630/taxonomy/role/DisclosureRelatedPartiesAndOtherMajorShareholders</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>995845 - Disclosure - Accounting Principles - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/AccountingPrinciplesAdditionalInformationDetail</Role>
      <ShortName>Accounting Principles - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>995855 - Disclosure - Scope of Consolidation and Non-Consolidated Entities - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureScopeOfConsolidationAndNonconsolidatedEntitiesAdditionalInformationDetail</Role>
      <ShortName>Scope of Consolidation and Non-Consolidated Entities - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>995865 - Disclosure - Information Concerning the Group's Consolidated Operations - Revenues by Nature (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsRevenuesByNatureDetail</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Revenues by Nature (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>995875 - Disclosure - Information Concerning the Group's Consolidated Operations - Revenues by Country of Origin and Other Income (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsRevenuesByCountryOfOriginAndOtherIncomeDetail</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Revenues by Country of Origin and Other Income (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>995885 - Disclosure - Information Concerning the Group's Consolidated Operations - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsAdditionalInformationDetail</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>995895 - Disclosure - Information Concerning the Group's Consolidated Operations - Details of Operating Expenses by Nature (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsDetailsOfOperatingExpensesByNatureDetail</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Details of Operating Expenses by Nature (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>995905 - Disclosure - Information Concerning the Group's Consolidated Operations - Details of Financial Income and Expenses (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/InformationConcerningTheGroupsConsolidatedOperationsDetailsOfFinancialIncomeAndExpensesDetail</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Details of Financial Income and Expenses (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>995915 - Disclosure - Information Concerning the Group's Consolidated Operations - Summary of Income Tax Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureInformationConcerningTheGroupsConsolidatedOperationsSummaryOfIncomeTaxExpensesDetails</Role>
      <ShortName>Information Concerning the Group's Consolidated Operations - Summary of Income Tax Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>995925 - Disclosure - Impairment Tests - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/ImpairmentTestsAdditionalInformationDetail</Role>
      <ShortName>Impairment Tests - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>995935 - Disclosure - Right-of-use Assets - Details Information About Breakdown Of Right Of Use Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/RightOfUseAssetsDetailsInformationAboutBreakdownOfRightOfUseAssetsDetail</Role>
      <ShortName>Right-of-use Assets - Details Information About Breakdown Of Right Of Use Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>995945 - Disclosure - Property, Plant and Equipment - Disclosure of Property, Plant and Equipment (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/PropertyPlantAndEquipmentDisclosureOfPropertyPlantAndEquipmentDetail</Role>
      <ShortName>Property, Plant and Equipment - Disclosure of Property, Plant and Equipment (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>995955 - Disclosure - Non-current Financial Assets and Other Non-current Assets - Summary of Non-current Financial Assets and Other Non-current Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncurrentFinancialAssetsAndOtherNoncurrentAssetsSummaryOfNoncurrentFinancialAssetsAndOtherNoncurrentAssetsDetail</Role>
      <ShortName>Non-current Financial Assets and Other Non-current Assets - Summary of Non-current Financial Assets and Other Non-current Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>995965 - Disclosure - Non-current Financial Assets and Other Non-current Assets - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncurrentFinancialAssetsAndOtherNoncurrentAssetsAdditionalInformationDetail</Role>
      <ShortName>Non-current Financial Assets and Other Non-current Assets - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>995975 - Disclosure - Trade Receivables and Other Current Assets - Disclosure of Trade Receivables (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/TradeReceivablesAndOtherCurrentAssetsDisclosureOfTradeReceivablesDetail</Role>
      <ShortName>Trade Receivables and Other Current Assets - Disclosure of Trade Receivables (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>995985 - Disclosure - Trade Receivables and Other Current Assets - Disclosure of Subsidies Receivables (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/TradeReceivablesAndOtherCurrentAssetsDisclosureOfSubsidiesReceivablesDetail</Role>
      <ShortName>Trade Receivables and Other Current Assets - Disclosure of Subsidies Receivables (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>995995 - Disclosure - Trade Receivables and Other Current Assets - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/TradeReceivablesAndOtherCurrentAssetsAdditionalInformationDetail</Role>
      <ShortName>Trade Receivables and Other Current Assets - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>996005 - Disclosure - Trade Receivables and Other Current Assets - Disclosure of Other Current Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/TradeReceivablesAndOtherCurrentAssetsDisclosureOfOtherCurrentAssetsDetail</Role>
      <ShortName>Trade Receivables and Other Current Assets - Disclosure of Other Current Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>996015 - Disclosure - Financial Assets and Liabilities - Summary of Financial Assets and Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialAssetsAndLiabilitiesSummaryOfFinancialAssetsAndLiabilitiesDetail</Role>
      <ShortName>Financial Assets and Liabilities - Summary of Financial Assets and Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>996025 - Disclosure - Current Financial Assets and Cash and Cash Equivalents - Summary of Current Financial Assets and Cash and Cash Equivalents (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/CurrentFinancialAssetsAndCashAndCashEquivalentsSummaryOfCurrentFinancialAssetsAndCashAndCashEquivalentsDetail</Role>
      <ShortName>Current Financial Assets and Cash and Cash Equivalents - Summary of Current Financial Assets and Cash and Cash Equivalents (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>996035 - Disclosure - Current Financial Assets and Cash and Cash Equivalents - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureCurrentFinancialAssetsAndCashAndCashEquivalentsAdditionalInformationDetail</Role>
      <ShortName>Current Financial Assets and Cash and Cash Equivalents - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>996045 - Disclosure - Current Financial Assets and Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/CurrentFinancialAssetsAndCashAndCashEquivalentsSummaryOfCashAndCashEquivalentsDetail</Role>
      <ShortName>Current Financial Assets and Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>996055 - Disclosure - Financial Liabilities and Lease Debts - Schedule of Financial Liabilities and Lease Debts (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsScheduleOfFinancialLiabilitiesAndLeaseDebtsDetail</Role>
      <ShortName>Financial Liabilities and Lease Debts - Schedule of Financial Liabilities and Lease Debts (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>996065 - Disclosure - Financial Liabilities and Lease Debts - Schedule of reconciliation of movements of liabilities to cash flows arising from financing liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsScheduleOfReconciliationOfMovementsOfLiabilitiesToCashFlowsArisingFromFinancingLiabilitiesDetai</Role>
      <ShortName>Financial Liabilities and Lease Debts - Schedule of reconciliation of movements of liabilities to cash flows arising from financing liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>996075 - Disclosure - Financial Liabilities and Lease Debts - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsAdditionalInformationDetail</Role>
      <ShortName>Financial Liabilities and Lease Debts - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>996085 - Disclosure - Financial Liabilities and Lease Debts - Summary of Assumptions and Results of the Warrant Valuation (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsSummaryOfAssumptionsAndResultsOfTheWarrantValuationDetail</Role>
      <ShortName>Financial Liabilities and Lease Debts - Summary of Assumptions and Results of the Warrant Valuation (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>996095 - Disclosure - Financial Liabilities and Lease Debts - Disclosure of Sensitivity on the Expected Volatility (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsDisclosureOfSensitivityOnTheExpectedVolatilityDetail</Role>
      <ShortName>Financial Liabilities and Lease Debts - Disclosure of Sensitivity on the Expected Volatility (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>996105 - Disclosure - Financial Liabilities and Lease Debts - Schedule Representing Remaining Contractual Maturities of Financial Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureFinancialLiabilitiesAndLeaseDebtsScheduleRepresentingRemainingContractualMaturitiesOfFinancialLiabilitiesDetail</Role>
      <ShortName>Financial Liabilities and Lease Debts - Schedule Representing Remaining Contractual Maturities of Financial Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>996115 - Disclosure - Other Current Liabilities - Summary of Other Current Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/OtherCurrentLiabilitiesSummaryOfOtherCurrentLiabilitiesDetail</Role>
      <ShortName>Other Current Liabilities - Summary of Other Current Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>996125 - Disclosure - Deferred Income and Contract Liabilities - Summary of Deferred income and Contract Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureDeferredIncomeAndContractLiabilitiesSummaryOfDeferredIncomeAndContractLiabilitiesDetail</Role>
      <ShortName>Deferred Income and Contract Liabilities - Summary of Deferred income and Contract Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>996135 - Disclosure - Deferred Income and Contract Liabilities - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureDeferredIncomeAndContractLiabilitiesAdditionalInformationDetail</Role>
      <ShortName>Deferred Income and Contract Liabilities - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>996145 - Disclosure - Share Capital and Premium Related to the Share Capitals - Schedule of Share Capital Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureShareCapitalAndPremiumRelatedToTheShareCapitalsScheduleOfShareCapitalInformationDetail</Role>
      <ShortName>Share Capital and Premium Related to the Share Capitals - Schedule of Share Capital Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>996155 - Disclosure - Share Capital and Premium Related to the Share Capitals - Schedule of Share Capital Information (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureShareCapitalAndPremiumRelatedToTheShareCapitalsScheduleOfShareCapitalInformationParentheticalDetail</Role>
      <ShortName>Share Capital and Premium Related to the Share Capitals - Schedule of Share Capital Information (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>996165 - Disclosure - Non-cash stock-based compensation - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationAdditionalInformationDetail</Role>
      <ShortName>Non-cash stock-based compensation - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>996175 - Disclosure - Non-cash stock-based compensation - Summary of assumptions Vesting Details (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationSummaryOfAssumptionsVestingDetailsDetail</Role>
      <ShortName>Non-cash stock-based compensation - Summary of assumptions Vesting Details (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>996185 - Disclosure - Non-cash stock-based compensation - Summary of Information on Stock Option Activity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationSummaryOfInformationOnStockOptionActivityDetail</Role>
      <ShortName>Non-cash stock-based compensation - Summary of Information on Stock Option Activity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>996195 - Disclosure - Non-cash stock-based compensation - Summary of Information on Warrants Activity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationSummaryOfInformationOnWarrantsActivityDetail</Role>
      <ShortName>Non-cash stock-based compensation - Summary of Information on Warrants Activity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>996205 - Disclosure - Non-cash stock-based compensation - Summary of Number of Shares Outstanding and Weighted Average Grant Date Fair Value (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureNoncashStockbasedCompensationSummaryOfNumberOfSharesOutstandingAndWeightedAverageGrantDateFairValueDetail</Role>
      <ShortName>Non-cash stock-based compensation - Summary of Number of Shares Outstanding and Weighted Average Grant Date Fair Value (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>996215 - Disclosure - Earnings Per Share - Details of Earnings Per Share (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/EarningsPerShareDetailsOfEarningsPerShareDetail</Role>
      <ShortName>Earnings Per Share - Details of Earnings Per Share (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>996225 - Disclosure - Provisions - Summary of Provisions (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureProvisionsSummaryOfProvisionsDetail</Role>
      <ShortName>Provisions - Summary of Provisions (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>996245 - Disclosure - Off-balance Sheet Commitments - Schedule of Off-balance Sheet Commitments (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureOffbalanceSheetCommitmentsScheduleOfOffbalanceSheetCommitmentsDetail</Role>
      <ShortName>Off-balance Sheet Commitments - Schedule of Off-balance Sheet Commitments (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>996255 - Disclosure - Off-Balance Sheet Commitments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureOffbalanceSheetCommitmentsAdditionalInformationDetails</Role>
      <ShortName>Off-Balance Sheet Commitments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>996265 - Disclosure - Related parties and other major shareholders - Schedule of Outstanding Balances with Related Parties (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureRelatedPartiesAndOtherMajorShareholdersScheduleOfOutstandingBalancesWithRelatedPartiesDetails</Role>
      <ShortName>Related parties and other major shareholders - Schedule of Outstanding Balances with Related Parties (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>996275 - Disclosure - Related parties and other major shareholders - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureRelatedPartiesAndOtherMajorShareholdersAdditionalInformationDetails</Role>
      <ShortName>Related parties and other major shareholders - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="clls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>996285 - Disclosure - Subsequent events - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cellectis.com/20260630/taxonomy/role/DisclosureSubsequentEventsAdditionalInformationDetails</Role>
      <ShortName>Subsequent events - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="6-K/A" isDefinitelyFs="true" isIfrs="true" isUsgaap="true" original="clls-20260630.htm">clls-20260630.htm</File>
    <File doctype="6-K/A" isDefinitelyFs="true" isIfrs="true" isUsgaap="true" original="clls-ex99_1.htm">clls-ex99_1.htm</File>
    <File>clls-20260630.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="10">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
    <BaseTaxonomy items="1108">https://xbrl.ifrs.org/taxonomy/2025-03-27/ifrs-full</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
