<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.2.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>30</ContextCount>
  <ElementCount>82</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>20</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="amifi-20220928.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.ABglobal.com/role/DocumentDocumentandEntityInformationElements000000</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="amifi-20220928.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>000021 - Disclosure - Risk/Return Detail Data {Elements} - AB National Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/DisclosureRiskReturnDetailDataElementsABNationalPortfolio000021</Role>
      <ShortName>Risk/Return Detail Data- AB National Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="amifi-20220928.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>000041 - Disclosure - Risk/Return Detail Data {Elements} - AB High Income Municipal Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/DisclosureRiskReturnDetailDataElementsABHighIncomeMunicipalPortfolio</Role>
      <ShortName>Risk/Return Detail Data- AB High Income Municipal Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="amifi-20220928.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>000061 - Disclosure - Risk/Return Detail Data {Elements} - AB California Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/DisclosureRiskReturnDetailDataElementsABCaliforniaPortfolio000061</Role>
      <ShortName>Risk/Return Detail Data- AB California Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="amifi-20220928.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>000161 - Disclosure - Risk/Return Detail Data {Elements} - AB New York Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/DisclosureRiskReturnDetailDataElementsABNewYorkPortfolio000161</Role>
      <ShortName>Risk/Return Detail Data- AB New York Portfolio</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="amifi-20220928.htm">amifi-20220928.htm</File>
    <File>amifi-20220928.xsd</File>
    <File>amifi-20220928_cal.xml</File>
    <File>amifi-20220928_def.xml</File>
    <File>amifi-20220928_lab.xml</File>
    <File>amifi-20220928_pre.xml</File>
    <File>d9759127_ex99-j.htm</File>
    <File>d9759127_ex99h-8.htm</File>
    <File>d9765628_ex99-i.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g12c59.jpg</File>
    <File>g16c63.jpg</File>
    <File>g19d95.jpg</File>
    <File>g19t59.jpg</File>
    <File>g20r22.jpg</File>
    <File>g22c48.jpg</File>
    <File>g31a51.jpg</File>
    <File>g49d54.jpg</File>
    <File>g67z55.jpg</File>
    <File>g70a28.jpg</File>
    <File>g71b29.jpg</File>
    <File>g71m70.jpg</File>
    <File>g78d41.jpg</File>
    <File>g78f52.jpg</File>
    <File>image_010.jpg</File>
    <File>image_011.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="8">http://xbrl.sec.gov/dei/2021</BaseTaxonomy>
    <BaseTaxonomy items="479">http://xbrl.sec.gov/rr/2021</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
