<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>10</ContextCount>
  <ElementCount>167</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>9</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="tm2131914-1_485bposseq1.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000001 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mfs.com/20211228/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory></MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="tm2131914-1_485bposseq1.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>020000 - Document - Risk/Return Summary {Unlabeled} - MFS Intrinsic Value Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mfs.com/20211228/role/DocumentRiskReturnSummaryUnlabeledMFSIntrinsicValueFund</Role>
      <ShortName>Risk/Return Summary- MFS Intrinsic Value Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="tm2131914-1_485bposseq1.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>020005 - Disclosure - Risk/Return Detail Data {Elements} - MFS Intrinsic Value Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mfs.com/20211228/role/DisclosureRiskReturnDetailDataElementsMFSIntrinsicValueFund</Role>
      <ShortName>Risk/Return Detail Data- MFS Intrinsic Value Fund</ShortName>
      <MenuCategory></MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="tm2131914-1_485bposseq1.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.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>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="485BPOS" original="tm2131914-1_485bposseq1.htm">tm2131914-1_485bposseq1.htm</File>
    <File>ck0000318874-20211228.xsd</File>
    <File>ck0000318874-20211228_cal.xml</File>
    <File>ck0000318874-20211228_def.xml</File>
    <File>ck0000318874-20211228_lab.xml</File>
    <File>ck0000318874-20211228_pre.xml</File>
    <File>tm2131914d1_ex99-i.htm</File>
    <File>tm2131914d1_ex99-n2.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g304193bg01i001.gif</File>
    <File>g319142bi01i001.gif</File>
    <File>g319143bi01i001.gif</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2021</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/rr/2021</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
