<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>30</ContextCount>
  <ElementCount>173</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>20</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001 - Document - Document and Entity Information  {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/DocumentAndEntityInformationElements</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0003 - Disclosure - Risk/Return Detail Data {Elements} - AB National Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/RiskReturnDetailDataElementsAbNationalPortfolio</Role>
      <ShortName>Risk/Return Detail Data- AB National Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>0005 - Disclosure - Risk/Return Detail Data {Elements} - AB High Income Municipal Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/RiskReturnDetailDataElementsAbHighIncomeMunicipalPortfolio</Role>
      <ShortName>Risk/Return Detail Data- AB High Income Municipal Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>0007 - Disclosure - Risk/Return Detail Data {Elements} - AB California Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/RiskReturnDetailDataElementsAbCaliforniaPortfolio</Role>
      <ShortName>Risk/Return Detail Data- AB California Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>0009 - Disclosure - Risk/Return Detail Data {Elements} - AB New York Portfolio</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.ABglobal.com/role/RiskReturnDetailDataElementsAbNewYorkPortfolio</Role>
      <ShortName>Risk/Return Detail Data- AB New York Portfolio</ShortName>
      <MenuCategory></MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="amifi-20210930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>040000 - Disclosure - Risk/Return Detail Data {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/RiskReturnDetailData</Role>
      <ShortName>Risk/Return Detail Data</ShortName>
      <MenuCategory></MenuCategory>
      <Position>6</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-20210930.htm">amifi-20210930.htm</File>
    <File>amifi-20210930.xsd</File>
    <File>amifi-20210930_cal.xml</File>
    <File>amifi-20210930_def.xml</File>
    <File>amifi-20210930_lab.xml</File>
    <File>amifi-20210930_pre.xml</File>
    <File>d8940275_ex99-4.htm</File>
    <File>d8940275_ex99-j.htm</File>
    <File>d8940531_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_004.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>
