v3.26.3
Label Element Value
Risk/Return: oef_RiskReturnAbstract  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Jun. 30, 2026
Registrant Name dei_EntityRegistrantName MFS® SERIES TRUST XVII
Entity Central Index Key dei_EntityCentralIndexKey 0000867969
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Oct. 27, 2026
Document Effective Date dei_DocumentEffectiveDate Oct. 28, 2026
Entity Investment Company Type dei_EntityInvCompanyType N-1A
Prospectus Date oef_ProspectusDate Oct. 28, 2026
MFS International Equity Fund | A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIEJX
MFS International Equity Fund | I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIEKX
MFS International Equity Fund | R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIEIX