<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.24.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>305</ContextCount>
  <ElementCount>42</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>33</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="d884259dncsr.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>030000 - Disclosure - Form N-CSR Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/oef/role/NcsrCover</Role>
      <ShortName>Form N-CSR Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="d884259dncsr.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>030001 - Disclosure - Shareholder Report</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/oef/role/ShareholderReport</Role>
      <ShortName>Shareholder Report</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="d884259dncsr.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>040010 - Disclosure - Shareholder Report, Line Graph (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/oef/role/ShareholderReportLineGraphDetails</Role>
      <ShortName>Shareholder Report, Line Graph (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="d884259dncsr.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>040020 - Disclosure - Shareholder Report, Holdings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/oef/role/ShareholderReportHoldingsDetails</Role>
      <ShortName>Shareholder Report, Holdings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>4</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="N-CSR" isDefinitelyNotFs="true" isNcsr="true" isOEF="true" isRRorOEF="true" isUsgaap="true" original="d884259dncsr.htm">d884259dncsr.htm</File>
    <File>nifi-20241029.xsd</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g884259g00m02.jpg</File>
    <File>g884259g00m08.jpg</File>
    <File>g884259g00m14.jpg</File>
    <File>g884259g00m20.jpg</File>
    <File>g884259g00m31.jpg</File>
    <File>g884259g00m36.jpg</File>
    <File>g884259g00s01.jpg</File>
    <File>g884259g00s02.jpg</File>
    <File>g884259g00s03.jpg</File>
    <File>g884259g05m01.jpg</File>
    <File>g884259g05m02.jpg</File>
    <File>g884259g11m01.jpg</File>
    <File>g884259g11m02.jpg</File>
    <File>g884259g17m01.jpg</File>
    <File>g884259g17m02.jpg</File>
    <File>g884259g19w55.jpg</File>
    <File>g884259g44n51.jpg</File>
    <File>g884259g55a55.jpg</File>
    <File>g884259g55b55.jpg</File>
    <File>g884259g64g38.jpg</File>
    <File>g884259g66h11.jpg</File>
    <File>g884259g69z13.jpg</File>
    <File>g884259g75s64.jpg</File>
    <File>g884259g85u20.jpg</File>
    <File>g884259g95r54.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="14">http://fasb.org/us-gaap/2023</BaseTaxonomy>
    <BaseTaxonomy items="13">http://xbrl.sec.gov/dei/2023</BaseTaxonomy>
    <BaseTaxonomy items="637">http://xbrl.sec.gov/oef/2023</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
