<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>41</ContextCount>
  <ElementCount>178</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>25</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="d206782d485bpos.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000000 - Document - Document and Entity Information {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nuveen.com/role/DocumentDocumentandEntityInformationElements000000</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="d206782d485bpos.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>000021 - Disclosure - Risk/Return Detail Data {Elements} - Nuveen Minnesota Intermediate Municipal Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nuveen.com/role/DisclosureRiskReturnDetailDataElementsNuveenMinnesotaIntermediateMunicipalBondFund000021</Role>
      <ShortName>Risk/Return Detail Data- Nuveen Minnesota Intermediate Municipal Bond Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="d206782d485bpos.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>000041 - Disclosure - Risk/Return Detail Data {Elements} - Nuveen Minnesota Municipal Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nuveen.com/role/DisclosureRiskReturnDetailDataElementsNuveenMinnesotaMunicipalBondFund000041</Role>
      <ShortName>Risk/Return Detail Data- Nuveen Minnesota Municipal Bond Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="d206782d485bpos.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>000061 - Disclosure - Risk/Return Detail Data {Elements} - Nuveen Nebraska Municipal Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nuveen.com/role/DisclosureRiskReturnDetailDataElementsNuveenNebraskaMunicipalBondFund000061</Role>
      <ShortName>Risk/Return Detail Data- Nuveen Nebraska Municipal Bond Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="d206782d485bpos.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>000081 - Disclosure - Risk/Return Detail Data {Elements} - Nuveen Oregon Intermediate Municipal Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.nuveen.com/role/DisclosureRiskReturnDetailDataElementsNuveenOregonIntermediateMunicipalBondFund000081</Role>
      <ShortName>Risk/Return Detail Data- Nuveen Oregon Intermediate Municipal Bond Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>5</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="485BPOS" original="d206782d485bpos.htm">d206782d485bpos.htm</File>
    <File>d206782dex99d5.htm</File>
    <File>d206782dex99d8.htm</File>
    <File>d206782dex99e2.htm</File>
    <File>d206782dex99j.htm</File>
    <File>d206782dex99p1.htm</File>
    <File>nifi-20210928.xsd</File>
    <File>nifi-20210928_cal.xml</File>
    <File>nifi-20210928_def.xml</File>
    <File>nifi-20210928_lab.xml</File>
    <File>nifi-20210928_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g206782img_37982788fed64.jpg</File>
    <File>g206782img_b340178604774.jpg</File>
    <File>g206782img_b62eb23cfec24.jpg</File>
    <File>g206782img_d97c8ace37564.jpg</File>
    <File>g206782img_e1568add81db4.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/rr/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
