v3.26.1
Label Element Value
Risk/Return: oef_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Mar. 31, 2026
Registrant Name dei_EntityRegistrantName MFS® MUNICIPAL SERIES TRUST
Entity Central Index Key dei_EntityCentralIndexKey 0000751656
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Jul. 28, 2026
Document Effective Date dei_DocumentEffectiveDate Jul. 29, 2026
Entity Investment Company Type dei_EntityInvCompanyType N-1A
Prospectus Date oef_ProspectusDate Jul. 29, 2026
Prospectus Summary | MFS Alabama Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFALX
Prospectus Summary | MFS Alabama Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBABX
Prospectus Summary | MFS Alabama Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLALX
Prospectus Summary | MFS Alabama Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPOLX
Prospectus Summary | MFS Arkansas Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFARX
Prospectus Summary | MFS Arkansas Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBARX
Prospectus Summary | MFS Arkansas Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MARLX
Prospectus Summary | MFS Arkansas Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPRAX
Prospectus Summary | MFS California Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCFTX
Prospectus Summary | MFS California Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBCAX
Prospectus Summary | MFS California Municipal Bond Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCCAX
Prospectus Summary | MFS California Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCAVX
Prospectus Summary | MFS California Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPOAX
Prospectus Summary | MFS Georgia Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMGAX
Prospectus Summary | MFS Georgia Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBGAX
Prospectus Summary | MFS Georgia Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MGATX
Prospectus Summary | MFS Georgia Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPGOX
Prospectus Summary | MFS Maryland Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFSMX
Prospectus Summary | MFS Maryland Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBMDX
Prospectus Summary | MFS Maryland Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMDIX
Prospectus Summary | MFS Maryland Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPMDX
Prospectus Summary | MFS Massachusetts Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFSSX
Prospectus Summary | MFS Massachusetts Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBMAX
Prospectus Summary | MFS Massachusetts Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MTALX
Prospectus Summary | MFS Massachusetts Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPMAX
Prospectus Summary | MFS Mississippi Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MISSX
Prospectus Summary | MFS Mississippi Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBMSX
Prospectus Summary | MFS Mississippi Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMSTX
Prospectus Summary | MFS Mississippi Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPMSX
Prospectus Summary | MFS Municipal Income Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFIAX
Prospectus Summary | MFS Municipal Income Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMIBX
Prospectus Summary | MFS Municipal Income Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMICX
Prospectus Summary | MFS Municipal Income Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIMIX
Prospectus Summary | MFS Municipal Income Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPMNX
Prospectus Summary | MFS Municipal Income Fund | Class A1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMIDX
Prospectus Summary | MFS Municipal Income Fund | Class B1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MMIGX
Prospectus Summary | MFS Municipal Intermediate Fund | A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIUAX
Prospectus Summary | MFS Municipal Intermediate Fund | C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIUCX
Prospectus Summary | MFS Municipal Intermediate Fund | I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIUIX
Prospectus Summary | MFS Municipal Intermediate Fund | R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIURX
Prospectus Summary | MFS New York Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSNYX
Prospectus Summary | MFS New York Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBNYX
Prospectus Summary | MFS New York Municipal Bond Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCNYX
Prospectus Summary | MFS New York Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MNYLX
Prospectus Summary | MFS New York Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPNYX
Prospectus Summary | MFS North Carolina Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSNCX
Prospectus Summary | MFS North Carolina Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBNCX
Prospectus Summary | MFS North Carolina Municipal Bond Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCNCX
Prospectus Summary | MFS North Carolina Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MNCLX
Prospectus Summary | MFS North Carolina Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPNCX
Prospectus Summary | MFS Pennsylvania Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFPAX
Prospectus Summary | MFS Pennsylvania Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBPAX
Prospectus Summary | MFS Pennsylvania Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPALX
Prospectus Summary | MFS Pennsylvania Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPPAX
Prospectus Summary | MFS South Carolina Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFSCX
Prospectus Summary | MFS South Carolina Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBSCX
Prospectus Summary | MFS South Carolina Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MTSCX
Prospectus Summary | MFS South Carolina Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPOCX
Prospectus Summary | MFS Virginia Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSVAX
Prospectus Summary | MFS Virginia Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBVAX
Prospectus Summary | MFS Virginia Municipal Bond Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MVACX
Prospectus Summary | MFS Virginia Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIVAX
Prospectus Summary | MFS Virginia Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPVOX
Prospectus Summary | MFS West Virginia Municipal Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MFWVX
Prospectus Summary | MFS West Virginia Municipal Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MBWVX
Prospectus Summary | MFS West Virginia Municipal Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MWVIX
Prospectus Summary | MFS West Virginia Municipal Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MPWVX