Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Apr. 30, 2012
Registrant Name	dei_EntityRegistrantName	MFS SERIES TRUST XV
Central Index Key	dei_EntityCentralIndexKey	0000764719
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Aug. 27, 2012
Document Effective Date	dei_DocumentEffectiveDate	Aug. 28, 2012
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| A
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MCSAX
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| B
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| C
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| I
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MCSIX
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| R1
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| R2
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| R3
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| R4
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	N/A (Currently Not Offered)
MFS COMMODITY STRATEGY FUND (Prospectus Summary) \| MFS COMMODITY STRATEGY FUND \| R5
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	MCSRX

If the value is true, then the document is an amendment to previously-filed/accepted document.

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

The 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.

+ References

No definition available.

+ Details

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Namespace Prefix:	dei_
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- Definition

The 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.

+ References

No definition available.

+ Details

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- Definition

The 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.

+ References

No definition available.

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The 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".

+ References

No definition available.

+ Details

Name:	dei_DocumentType
Namespace Prefix:	dei_
Data Type:	dei:submissionTypeItemType
Balance Type:	na
Period Type:	duration

- Definition

A unique 10-digit SEC-issued value to identify entities that have filed disclosures with the SEC. It is commonly abbreviated as CIK.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation 12B

-Number 240

-Section 12b

-Subsection 1

+ Details

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Namespace Prefix:	dei_
Data Type:	dei:centralIndexKeyItemType
Balance Type:	na
Period Type:	duration

- Definition

The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation 12B

-Number 240

-Section 12b

-Subsection 1

+ Details

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- Definition

Trading symbol of an instrument as listed on an exchange.

+ References

No definition available.

+ Details

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Namespace Prefix:	dei_
Data Type:	xbrli:normalizedStringItemType
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- Details

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