2.4.0.8000001 - Document - Document and Entity Informationtruefalsefalse1false falsefalsedefaulthttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:001true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:2false 2dei_DocumentTypedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00485BPOSfalsefalsefalsedei:submissionTypeItemTypestringThe type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word "Other".No definition available.false0Document Type3false 2dei_DocumentPeriodEndDatedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse002013-03-31falsefalsetruexbrli:dateItemTypedateThe end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD.No definition available.false0Document Period End Date4false 2dei_EntityRegistrantNamedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFS MUNICIPAL SERIES TRUSTfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringThe exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 false0Registrant Name5false 2dei_EntityCentralIndexKeydei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse000000751656falsefalsefalsedei:centralIndexKeyItemTypenaA unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation 12B -Number 240 -Section 12b -Subsection 1 false0Central Index Key6false 2dei_AmendmentFlagdei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsexbrli:booleanItemTypenaIf the value is true, then the document is an amendment to previously-filed/accepted document.No definition available.false0Amendment Flag7false 2dei_DocumentCreationDatedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse002013-07-26falsefalsetruexbrli:dateItemTypedateThe date the document was made available and submitted, in CCYY-MM-DD format. The date of submission, date of acceptance by the recipient, and the document effective date are all potentially different.No definition available.false0Document Creation Date8false 2dei_DocumentEffectiveDatedei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse002013-07-29falsefalsetruexbrli:dateItemTypedateThe date when a document, upon receipt and acceptance, becomes officially effective, in CCYY-MM-DD format. Usually it is a system-assigned date time value, but it may be declared by the submitter in some cases.No definition available.false0Document Effective Date9false 2rr_ProspectusDaterr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse002013-07-29falsefalsetruexbrli:dateItemTypedateThe date of the prospectus.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Form -Number N-1A -Chapter A -Section 1 -Subsection a -Paragraph 3 false0Prospectus Date10false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse2false truefalseS000002521Member_C000006957Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Alabama Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002521Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006957Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Alabama Municipal Bond Fund | A11true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:12false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFALXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol13false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse3false truefalseS000002521Member_C000006958Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Alabama Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002521Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006958Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Alabama Municipal Bond Fund | B14true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:15false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBABXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol16false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse4false truefalseS000002529Member_C000006976Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Arkansas Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002529Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006976Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Arkansas Municipal Bond Fund | A17true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:18false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFARXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol19false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse5false truefalseS000002529Member_C000006977Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Arkansas Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002529Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006977Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Arkansas Municipal Bond Fund | B20true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:21false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBARXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol22false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse6false truefalseS000002530Member_C000006978Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS California Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002530Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006978Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS California Municipal Bond Fund | A23true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:24false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MCFTXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol25false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse7false truefalseS000002530Member_C000006979Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS California Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002530Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006979Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS California Municipal Bond Fund | B26true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:27false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBCAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol28false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse8false truefalseS000002530Member_C000006980Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS California Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002530Memberdei_LegalEntityAxisexplicitMemberfalsefalseCrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006980Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS California Municipal Bond Fund | C29true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:30false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MCCAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol31false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse9false truefalseS000002532Member_C000006983Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Georgia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002532Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006983Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Georgia Municipal Bond Fund | A32true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:33false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MMGAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol34false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse10false truefalseS000002532Member_C000006984Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Georgia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002532Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006984Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Georgia Municipal Bond Fund | B35true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:36false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBGAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol37false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse11false truefalseS000002533Member_C000006985Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Maryland Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002533Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006985Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Maryland Municipal Bond Fund | A38true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:39false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFSMXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol40false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse12false truefalseS000002533Member_C000006986Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Maryland Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002533Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006986Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Maryland Municipal Bond Fund | B41true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:42false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBMDXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol43false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse13false truefalseS000002534Member_C000006987Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Massachusetts Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002534Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006987Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Massachusetts Municipal Bond Fund | A44true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:45false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFSSXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol46false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse14false truefalseS000002534Member_C000006988Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Massachusetts Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002534Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006988Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Massachusetts Municipal Bond Fund | B47true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:48false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBMAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol49false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse15false truefalseS000002535Member_C000006989Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Mississippi Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002535Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006989Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Mississippi Municipal Bond Fund | A50true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:51false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MISSXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol52false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse16false truefalseS000002535Member_C000006990Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Mississippi Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002535Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006990Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Mississippi Municipal Bond Fund | B53true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:54false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBMSXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol55false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse17false truefalseS000002522Member_C000006959Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS New York Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002522Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006959Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS New York Municipal Bond Fund | A56true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:57false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MSNYXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol58false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse18false truefalseS000002522Member_C000006960Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS New York Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002522Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006960Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS New York Municipal Bond Fund | B59true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:60false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBNYXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol61false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse19false truefalseS000002522Member_C000006961Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS New York Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002522Memberdei_LegalEntityAxisexplicitMemberfalsefalseCrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006961Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS New York Municipal Bond Fund | C62true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:63false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MCNYXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol64false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse20false truefalseS000002523Member_C000006962Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS North Carolina Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002523Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006962Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS North Carolina Municipal Bond Fund | A65true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:66false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MSNCXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol67false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse21false truefalseS000002523Member_C000006963Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS North Carolina Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002523Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006963Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS North Carolina Municipal Bond Fund | B68true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:69false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBNCXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol70false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse22false truefalseS000002523Member_C000006964Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS North Carolina Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002523Memberdei_LegalEntityAxisexplicitMemberfalsefalseCrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006964Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS North Carolina Municipal Bond Fund | C71true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:72false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MCNCXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol73false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse23false truefalseS000002524Member_C000006965Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Pennsylvania Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002524Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006965Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Pennsylvania Municipal Bond Fund | A74true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:75false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFPAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol76false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse24false truefalseS000002524Member_C000006966Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Pennsylvania Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002524Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006966Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Pennsylvania Municipal Bond Fund | B77true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:78false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBPAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol79false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse25false truefalseS000002525Member_C000006967Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS South Carolina Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002525Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006967Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS South Carolina Municipal Bond Fund | A80true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:81false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFSCXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol82false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse26false truefalseS000002525Member_C000006968Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS South Carolina Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002525Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006968Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS South Carolina Municipal Bond Fund | B83true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:84false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBSCXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol85false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse27false truefalseS000002526Member_C000006969Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Tennessee Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002526Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006969Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Tennessee Municipal Bond Fund | A86true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:87false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MSTNXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol88false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse28false truefalseS000002526Member_C000006970Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Tennessee Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002526Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006970Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Tennessee Municipal Bond Fund | B89true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:90false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBTNXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol91false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse29false truefalseS000002527Member_C000006971Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Virginia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002527Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006971Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Virginia Municipal Bond Fund | A92true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:93false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MSVAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol94false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse30false truefalseS000002527Member_C000006972Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Virginia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002527Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006972Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Virginia Municipal Bond Fund | B95true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:96false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBVAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol97false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse31false truefalseS000002527Member_C000006973Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS Virginia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002527Memberdei_LegalEntityAxisexplicitMemberfalsefalseCrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006973Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS Virginia Municipal Bond Fund | C98true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:99false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MVACXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol100false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse32false truefalseS000002528Member_C000006974Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS West Virginia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002528Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006974Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS West Virginia Municipal Bond Fund | A101true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:102false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFWVXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol103false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse33false truefalseS000002528Member_C000006975Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseMFS West Virginia Municipal Bond Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002528Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006975Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0MFS West Virginia Municipal Bond Fund | B104true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:105false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MBWVXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol106false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse34false truefalsedoc_Class_A_B_C_and_I_ProspectusMember_S000002536Member_C000006991Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A, B, C, and I Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A_B_C_and_I_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseArr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006991Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A, B, C, and I Prospectus | MFS Municipal Income Fund | A107true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:108false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MFIAXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol109false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse35false truefalsedoc_Class_A_B_C_and_I_ProspectusMember_S000002536Member_C000006992Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A, B, C, and I Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A_B_C_and_I_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseBrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006992Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A, B, C, and I Prospectus | MFS Municipal Income Fund | B110true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:111false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MMIBXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol112false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse36false truefalsedoc_Class_A_B_C_and_I_ProspectusMember_S000002536Member_C000006993Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A, B, C, and I Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A_B_C_and_I_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseCrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000006993Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A, B, C, and I Prospectus | MFS Municipal Income Fund | C113true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:114false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MMICXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol115false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse37false truefalsedoc_Class_A_B_C_and_I_ProspectusMember_S000002536Member_C000105400Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A, B, C, and I Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A_B_C_and_I_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseIrr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000105400Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A, B, C, and I Prospectus | MFS Municipal Income Fund | I116true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:117false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MIMIXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol118false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse38false truefalsedoc_Class_A1_and_B1_ProspectusMember_S000002536Member_C000042676Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A1 and B1 Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A1_and_B1_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseA1rr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000042676Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A1 and B1 Prospectus | MFS Municipal Income Fund | A1119true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:120false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MMIDXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading Symbol121false 0truefalsetruefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalse39false truefalsedoc_Class_A1_and_B1_ProspectusMember_S000002536Member_C000042677Memberhttp://www.sec.gov/CIK0000751656duration2013-03-31T00:00:002013-03-31T00:00:00falsefalseClass A1 and B1 Prospectusdei_DocumentInformationDocumentAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_doc_Class_A1_and_B1_ProspectusMemberdei_DocumentInformationDocumentAxisexplicitMemberfalsefalseMFS Municipal Income Funddei_LegalEntityAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_S000002536Memberdei_LegalEntityAxisexplicitMemberfalsefalseB1rr_ProspectusShareClassAxisxbrldihttp://xbrl.org/2006/xbrldick0000751656_C000042677Memberrr_ProspectusShareClassAxisexplicitMembernanafalse0Class A1 and B1 Prospectus | MFS Municipal Income Fund | B1122true 1rr_RiskReturnAbstractrr_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Risk/Return:123false 2dei_TradingSymboldei_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00MMIGXfalsefalsefalsexbrli:normalizedStringItemTypenormalizedstringTrading symbol of an instrument as listed on an exchange.No definition available.false0Trading SymbolfalseDocument and Entity InformationUnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://mfs.com/20130726/role/DocumentAndEntityInformation1123