<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:cef="http://xbrl.sec.gov/cef/2024"
  xmlns:dei="http://xbrl.sec.gov/dei/2024"
  xmlns:iso4217="http://www.xbrl.org/2003/iso4217"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:us-gaap="http://fasb.org/us-gaap/2024"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="iisf-20240331.xsd" xlink:type="simple"/>
    <context id="c0">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001976685</identifier>
        </entity>
        <period>
            <startDate>2023-04-01</startDate>
            <endDate>2024-03-31</endDate>
        </period>
    </context>
    <context id="c1">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001976685</identifier>
        </entity>
        <period>
            <startDate>2024-03-31</startDate>
            <endDate>2024-03-31</endDate>
        </period>
    </context>
    <context id="c2">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001976685</identifier>
        </entity>
        <period>
            <instant>2024-03-31</instant>
        </period>
    </context>
    <unit id="shares">
        <measure>shares</measure>
    </unit>
    <unit id="usdPershares">
        <divide>
            <unitNumerator>
                <measure>iso4217:USD</measure>
            </unitNumerator>
            <unitDenominator>
                <measure>shares</measure>
            </unitDenominator>
        </divide>
    </unit>
    <dei:DocumentType contextRef="c0" id="ixv-3377">N-CSR</dei:DocumentType>
    <dei:EntityRegistrantName contextRef="c0" id="ixv-3378">Institutional Investment Strategy Fund</dei:EntityRegistrantName>
    <cef:OutstandingSecurityHeldShares contextRef="c1" decimals="0" id="ixv-3379" unitRef="shares">305359</cef:OutstandingSecurityHeldShares>
    <us-gaap:NetAssetValuePerShare
      contextRef="c2"
      decimals="2"
      id="ixv-3380"
      unitRef="usdPershares">10.21</us-gaap:NetAssetValuePerShare>
    <dei:AmendmentFlag contextRef="c0" id="ixv-3383">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey contextRef="c0" id="ixv-3384">0001976685</dei:EntityCentralIndexKey>
    <dei:EntityInvCompanyType contextRef="c0" id="ixv-3385">N-2</dei:EntityInvCompanyType>
</xbrl>
