485BPOS

As filed with the Securities and Exchange Commission on November 16, 2012

1933 Act File No. 2-36431

1940 Act File No. 811-2032

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C.  20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

POST-EFFECTIVE AMENDMENT NO. 54

AND

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940

AMENDMENT NO. 44

MFS® SERIES TRUST XVI

(Exact Name of Registrant as Specified in Charter)

500 Boylston Street, Boston, Massachusetts 02116

(Address of Principal Executive Offices)

Registrant’s Telephone Number, including Area Code: 617-954-5000

Susan S. Newton, Massachusetts Financial Services Company,

500 Boylston Street, Boston, Massachusetts 02116

(Name and Address of Agent for Service)

APPROXIMATE DATE OF PROPOSED PUBLIC OFFERING:

It is proposed that this filing will become effective (check appropriate box)

x immediately upon filing pursuant to paragraph (b)

o on [date] pursuant to paragraph (b)

o 60 days after filing pursuant to paragraph (a)(i)

o on [date] pursuant to paragraph (a)(i)

o 75 days after filing pursuant to paragraph (a)(ii)

o on [date] pursuant to paragraph (a)(ii) of rule 485.

If appropriate, check the following box:

o this post-effective amendment designates a new effective date for a previously filed post-effective amendment

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment to the Registration Statement to be signed on its behalf by the undersigned, thereto duly authorized, in the City of Boston and The Commonwealth of Massachusetts on the 16th November, 2012.

MFS® SERIES TRUST XVI
By:	JOHN M. CORCORAN*
Name:	John M. Corcoran
Title:	President

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to its Registration Statement has been signed below by the following persons in the capacities indicated on November 16, 2012.

SIGNATURE	TITLE
JOHN M. CORCORAN*	President (Principal Executive Officer)
John M. Corcoran
DAVID L. DILORENZO*	Principal Financial and Accounting Officer
David L. DiLorenzo
ROBERT E. BUTLER*	Trustee
Robert E. Butler
MAUREEN R. GOLDFARB*	Trustee
Maureen R. Goldfarb
DAVID H. GUNNING*	Trustee
David H. Gunning
WILLIAM R. GUTOW*	Trustee
William R. Gutow

MICHAEL HEGARTY*	Trustee
Michael Hegarty
JOHN P. KAVANAUGH*	Trustee
John P. Kavanaugh
ROBERT J. MANNING*	Trustee
Robert J. Manning
J. DALE SHERRATT*	Trustee
J. Dale Sherratt
LAURIE J. THOMSEN*	Trustee
Laurie J. Thomsen
ROBERT W. UEK*	Trustee
Robert W. Uek

*By:	SUSAN S. NEWTON
Name:	Susan S. Newton
	as Attorney-in-fact
Executed by Susan S. Newton on behalf of those indicated pursuant to a Power of Attorney, dated September 11, 2012 (Trustees), and a Power of Attorney, dated September 11, 2012 (Corcoran) (DiLorenzo); filed herewith.

MFS Series Trust I

MFS Series Trust II

MFS Series Trust III

MFS Series Trust IV

MFS Series Trust V

MFS Series Trust VI

MFS Series Trust VII

MFS Series Trust VIII

MFS Series Trust IX

MFS Series Trust X

MFS Series Trust XI

MFS Series Trust XII

MFS Series Trust XIII

MFS Series Trust XIV

MFS Series Trust XV

MFS Series Trust XVI

Massachusetts Investors Growth Stock Fund

Massachusetts Investors Trust

MFS Institutional Trust

MFS Municipal Series Trust

MFS Variable Insurance Trust

MFS Variable Insurance Trust II

MFS California Municipal Fund

MFS Charter Income Trust

MFS Government Markets Income Trust

MFS High Income Municipal Trust

MFS High Yield Municipal Trust

MFS InterMarket Income Trust I

MFS Intermediate High Income Fund

MFS Intermediate Income Trust

MFS Investment Grade Municipal Trust

MFS Multimarket Income Trust

MFS Municipal Income Trust

MFS Special Value Trust

(each a “Registrant”)

POWER OF ATTORNEY

The undersigned, a Trustee of each of the above-mentioned Registrants, hereby severally constitutes and appoints Mark N. Polebaum, Susan S. Newton, Christopher R. Bohane, Thomas H. Connors, Brian E. Langenfeld and Susan A. Pereira, and each of them singly, as true and lawful attorneys, with full power to them and each of them to sign for each of the undersigned, in the names of, and in the capacities indicated below, any

Registration Statement and any and all amendments thereto and to file the same with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission for the purpose of registering the Registrant as a management investment company under the Investment Company Act of 1940 and/or the shares issued by the Registrant under the Securities Act of 1933 granting unto my said attorneys, and each of them, acting alone, full power and authority to do and perform each and every act and thing requisite or necessary or desirable to be done in the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys or any of them may lawfully do or cause to be done by virtue thereof.

IN WITNESS WHEREOF, the undersigned have hereunto set their hand on this 11th day of September, 2012.

ROBERT E. BUTLER	Trustee
Robert E. Butler
MAUREEN R. GOLDFARB	Trustee
Maureen R. Goldfarb
DAVID H. GUNNING	Trustee
David H. Gunning
WILLIAM R. GUTOW	Trustee
William R. Gutow
MICHAEL HEGARTY	Trustee
Michael Hegarty
JOHN P. KAVANAUGH	Trustee
John P. Kavanaugh
ROBERT J. MANNING	Trustee
Robert J. Manning
J. DALE SHERRATT	Trustee
J. Dale Sherratt

LAURIE J. THOMSEN	Trustee
Laurie J. Thomsen
ROBERT W. UEK	Trustee
Robert W. Uek

MFS Series Trust I

MFS Series Trust II

MFS Series Trust III

MFS Series Trust IV

MFS Series Trust V

MFS Series Trust VI

MFS Series Trust VII

MFS Series Trust VIII

MFS Series Trust IX

MFS Series Trust X

MFS Series Trust XI

MFS Series Trust XII

MFS Series Trust XIII

MFS Series Trust XIV

MFS Series Trust XV

MFS Series Trust XVI

Massachusetts Investors Growth Stock Fund

Massachusetts Investors Trust

MFS Institutional Trust

MFS Municipal Series Trust

MFS Variable Insurance Trust

MFS Variable Insurance Trust II

MFS California Municipal Fund

MFS Charter Income Trust

MFS Government Markets Income Trust

MFS High Income Municipal Trust

MFS High Yield Municipal Trust

MFS InterMarket Income Trust I

MFS Intermediate High Income Fund

MFS Intermediate Income Trust

MFS Investment Grade Municipal Trust

MFS Multimarket Income Trust

MFS Municipal Income Trust

MFS Special Value Trust

(each a “Registrant”)

POWER OF ATTORNEY

The undersigned, being the President and Principal Executive Officer, and Treasurer and Principal Financial and Accounting Officer, respectively, of each of the above-mentioned Registrants, hereby severally constitutes and appoints Mark N. Polebaum, Susan S. Newton, Christopher R. Bohane, Thomas H. Connors, Brian E. Langenfeld and Susan A. Pereira, and each of them singly, as true and lawful attorneys, with full power to them and each of them to sign for each of the undersigned, in the names of, and in the capacities indicated below, any Registration Statement and any and all amendments thereto and to file the same with all exhibits thereto, and other documents in connection therewith, with the Securities and

Exchange Commission for the purpose of registering the Registrant as a management investment company under the Investment Company Act of 1940 and/or the shares issued by the Registrant under the Securities Act of 1933 granting unto my said attorneys, and each of them, acting alone, full power and authority to do and perform each and every act and thing requisite or necessary or desirable to be done in the premises, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that said attorneys or any of them may lawfully do or cause to be done by virtue thereof.

IN WITNESS WHEREOF, the undersigned have hereunto set their hand on this 11th day of September, 2012.

JOHN M. CORCORAN	President (Principal Executive Officer)
John M. Corcoran
DAVID L. DILORENZO	Principal Financial and Accounting Officer
David L. DiLorenzo

MFS SERIES TRUST XVI

MFS® GLOBAL MULTI-ASSET FUND

INDEX TO EXHIBITS

EXHIBIT NO.	DESCRIPTION OF EXHIBIT	PAGE NO.
101	Risk/Return summary of the fund’s prospectus as an Interactive Data File using eXtensible Business Reporting Language (“XBRL”)

XML

MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return.

Fees and Expenses

This table describes the fees and expenses that you may pay when you buy and
hold shares of the fund. The annual fund operating expenses for Class R5 shares
are based on estimated "Other Expenses" for the current fiscal year expressed as
a percentage of the fund's estimated average net assets during the period.
  
You may qualify for sales charge reductions if you and certain members of your
family invest, or agree to invest in the future, at least $50,000 in MFS Funds.
More information about these and other waivers and reductions is available from
your financial intermediary and in "Sales Charges and Waivers or Reductions" on
page 11 of the fund's prospectus and "Waivers of Sales Charges" on page I-13 of
the fund's statement of additional information Part I.

Shareholder Fees (fees paid directly from your investment):

Shareholder Fees MFS Global Multi-Asset Fund	A		B	C	I	R1	R2	R3	R4	R5
Shareholder Fees Column [Text]	A		B	C	I	ALL R	ALL R	ALL R	ALL R	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	5.75%		none	none	none	none	none	none	none	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	1.00%	[1]	4.00%	1.00%	none	none	none	none	none	none

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Annual Fund Operating Expenses MFS Global Multi-Asset Fund		A	B	C	I	R1	R2	R3	R4	R5
Operating Expenses Column [Text]		A	B	C	I	R1	R2	R3	R4	R5
Management Fee		0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%	0.72%
Distribution and/or Service (12b-1) Fees		0.25%	1.00%	1.00%	none	1.00%	0.50%	0.25%	none	none
Other Expenses		1.06%	1.06%	1.06%	1.06%	1.06%	1.06%	1.06%	1.06%	1.04%
Acquired (Underlying) Fund Fees and Expenses		0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%	0.17%
Total Annual Fund Operating Expenses		2.20%	2.95%	2.95%	1.95%	2.95%	2.45%	2.20%	1.95%	1.93%
Fee Reductions and/or Expense Reimbursements	[1]	(0.76%)	(0.76%)	(0.76%)	(0.76%)	(0.76%)	(0.76%)	(0.76%)	(0.76%)	(0.75%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		1.44%	2.19%	2.19%	1.19%	2.19%	1.69%	1.44%	1.19%	1.18%

Example

This example is intended to help you compare the cost of investing in the fund
with the cost of investing in other mutual funds.
  
The example assumes that: you invest $10,000 in the fund for the time periods
indicated and you redeem your shares at the end of the time periods (unless
otherwise indicated); your investment has a 5% return each year; and the fund's
operating expenses remain the same.

Although your actual costs will likely be higher or lower, under these assumptions your costs would be:

Expense Example MFS Global Multi-Asset Fund (USD $)	Expense Example, By Year, Column [Text]	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
A	Class A Shares	713	1,155	1,621	2,907
B	Class B Shares	622	1,141	1,686	3,039
C	Class C Shares	322	841	1,486	3,217
I	Class I Shares	121	539	982	2,213
R1	Class R1 Shares	222	841	1,486	3,217
R2	Class R2 Shares	172	691	1,237	2,729
R3	Class R3 Shares	147	615	1,110	2,475
R4	Class R4 Shares	121	539	982	2,213
R5	Class R5 Shares	120	533	972	2,193

Expense Example, No Redemption MFS Global Multi-Asset Fund (USD $)	Expense Example, No Redemption, By Year, Column [Text]	Expense Example, No Redemption, 1 Year	Expense Example, No Redemption, 3 Years	Expense Example, No Redemption, 5 Years	Expense Example, No Redemption, 10 Years
B	Class B Shares assuming no redemption at end of period	222	841	1,486	3,039
C	Class C Shares assuming no redemption at end of period	222	841	1,486	3,217

Portfolio Turnover

The fund pays transaction costs, such as commissions, when it buys and sells
securities (or "turns over" its portfolio). A higher portfolio turnover rate
may indicate higher transaction costs and may result in higher taxes when
shares are held in a taxable account. These transaction costs, which are not
reflected in "Annual Fund Operating Expenses" or in the "Example," affect the
fund's performance.  During the most recent fiscal year, the fund's portfolio
turnover rate was 48% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
seeks to achieve the fund's objective by generating returns from (1) a strategic
allocation to a mix of asset classes, (2) individual security selection of U.S.
and foreign issuers within those asset classes, and (3) a tactical asset
allocation overlay to manage the fund's exposure to asset classes, markets, and
currencies primarily using derivative instruments. Derivatives include futures,
forward contracts, options, structured securities, inverse floating rate
instruments, and swaps.

The fund's performance may not be correlated with the performance of the asset
classes, markets, or currencies represented by the individual investments
selected by MFS.

Strategic Asset Class Allocation:  MFS determines the percentages of the fund's
assets to be invested in the general asset classes of bonds and stocks, as well as
in other less-traditional asset classes that MFS believes provide diversification
benefits when added to a portfolio consisting of bonds and stocks, such as
commodity-related investments and real estate-related investments. As of October
28, 2012, the fund's target strategic exposures among asset classes were as follows:
15% in inflation-adjusted debt instruments; 35% in other debt instruments; 30% in
equity securities; 15% in commodity-related investments; and 5% in real
estate-related investments.

Debt instruments include corporate bonds, U.S. Government securities, asset-backed
securities, municipal instruments, foreign government securities, inflation-adjusted
bonds, and other obligations to repay money borrowed.  Equity securities include
common stocks, preferred stocks, securities convertible into stocks, and depositary
receipts for those securities.

MFS may invest the fund's assets in other mutual funds advised by MFS that invest
in such asset classes instead of investing directly in such assets.

The strategic asset class allocations have been selected for investment over
longer time periods, but may be changed without shareholder approval or notice.
The actual strategic asset class weightings can deviate due to market movements
and cash flows.  MFS periodically rebalances the fund's strategic asset class
weightings.  These target asset class weightings do not reflect the fund's cash
balance; some portion of the fund's portfolio will be held in cash due to
collateral requirements associated with the fund's derivative transactions,
purchase and redemption activity, and other short term cash needs.

Individual Security Selection:

In selecting direct investments for the fund, MFS may invest the fund's assets in
U.S. and foreign securities, including emerging market securities.

Of the fund's investments in debt instruments, MFS primarily invests the fund's
assets in investment grade debt instruments, but may also invest in less than
investment grade quality debt instruments (lower quality debt instruments).

MFS generally seeks to diversify the fund's equity investments in terms of market
capitalization (e.g., small, mid, large cap), style (e.g., growth, value), and
location (e.g., U.S., foreign). These allocations may vary significantly from
time to time.

MFS may invest a large percentage of the fund's assets in issuers in a single
country, a small number of countries, or a particular geographic region.

While MFS may use derivatives for any investment purpose, to the extent MFS uses
derivatives as part of its individual security selection process, MFS expects to
use derivatives primarily to increase or decrease exposure to a particular market,
segment of the market, or security, to increase or decrease interest rate or
currency exposure, or as alternatives to direct investments.

A team of investment professionals selects investments for the fund. MFS allocates
the fund's assets to investment professionals by investment strategy. MFS uses a
bottom-up investment approach to buying and selling investments for the fund.
Investments are selected primarily based on fundamental analysis of individual
issuers and instruments. Quantitative models that systematically evaluate issuers
and instruments may also be considered.

Tactical Asset Allocation Overlay:  MFS employs a top-down tactical asset allocation
process to adjust the fund's exposure to asset classes, markets and currencies based
on its assessment of the relative attractiveness of such asset classes, markets and
currencies. MFS manages the fund's exposure to asset classes, markets and currencies
primarily through the use of derivative instruments.

In managing the tactical overlay, MFS uses proprietary quantitative models and may
increase or decrease the fund's exposure to asset classes, markets and/or currencies
resulting from MFS' individual security selection based on MFS' assessment of the
risk/return potential of such asset classes, markets and/or currencies. After taking
into account the tactical overlay, the fund's exposure to the various asset classes,
markets, and/or currencies may vary significantly from time to time. MFS may also
expose the fund to asset classes, markets and/or currencies in which its individual
security selection has resulted in no or little exposure (e.g., the high yield bond
market).

MFS may adjust the fund's net exposure to asset classes, markets and/or currencies
by taking net short positions in an asset class, market or currency if MFS believes
the risk/return potential of such asset class, market or currency is unattractive.  
Alternatively, MFS may cause the fund to take net long positions in an asset class,
market or currency if MFS believes such asset class, market or currency appears
attractive. After taking into account the tactical overlay, the fund's net exposures
to the asset classes referenced below, which may include exposure to U.S. and foreign
issuers, will normally fall within the following ranges:

Asset Class                                                          Range   
Inflation-adjusted debt instruments                               -5% to 35%
Debt instruments, excluding inflation-adjusted debt instruments    0% to 70%
Equity securities                                                  0% to 60%
Commodity-related investments                                     -5% to 35%
Real estate-related investments                                   -10% to 20%

MFS' tactical asset allocation process for the fund will typically make extensive use
of derivatives.

MFS may also use derivatives to seek to limit the fund's exposure to certain extreme
market events.

Principal Risks

As with any mutual fund, the fund may not achieve its objective and/or you could
lose money on your investment in the fund. An investment in the fund is not a
bank deposit and is not insured or guaranteed by the Federal Deposit Insurance
Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Investment Selection and Allocation Risk:  MFS' investment analysis, its
selection of investments, its assessment of the risk/return potential of asset
classes, markets and currencies, and its adjustments to the fund's exposure to
asset classes, markets, and currencies through the use of derivatives and
underlying funds may not produce the intended results and/or can lead to an
investment focus that results in the fund underperforming other funds with
similar investment strategies and/or underperforming the markets in which the
fund invests.

Investment Strategy Risk:  The fund's strategy to manage its exposure to asset
classes, markets, and currencies may not produce the intended results. In
addition, the strategies MFS may implement to limit the fund's exposure to
certain extreme market events may not work as intended, and the costs associated
with such strategies will reduce the fund's returns.

Interest Rate Risk:  The price of a debt instrument falls when interest rates
rise and rises when interest rates fall. Instruments with longer maturities, or
that do not pay current interest, are more sensitive to interest rate changes.

Credit Risk:  The price of a debt instrument depends, in part, on the credit
quality of the issuer, borrower, counterparty, or underlying collateral or
assets and the terms of the instrument. The price of a debt instrument can
decline in response to changes in the financial condition of the issuer,
borrower, counterparty, or underlying collateral or assets, or changes in
specific or general market, economic, industry, political, regulatory,
geopolitical, or other conditions.

Lower quality debt instruments (commonly referred to as "high yield securities"
or "junk bonds") can involve a substantially greater risk of default or can
already be in default, and their values can decline significantly. Lower quality
debt instruments are regarded as having predominantly speculative characteristics.
Lower quality debt instruments tend to be more sensitive to adverse news about
the issuer, or the market or economy in general, than higher quality debt
instruments.

Stock Market/Company Risk:  Stock markets are volatile and can decline
significantly in response to issuer, market, economic, industry, political,
regulatory, geopolitical, and other conditions, as well as to investor
perceptions of these conditions. The price of an equity security can decrease
significantly in response to these conditions, and these conditions can affect a
single issuer or type of security, issuers within a broad market sector,
industry or geographic region, or the market in general.

Derivatives Risk:  Derivatives can be highly volatile and involve risks in
addition to the risks of the underlying indicator(s) on which the derivative is
based. Gains or losses from derivatives can be substantially greater than the
derivatives' original cost.  Derivatives can involve leverage.

Commodity Risk:  The value of commodities may be more volatile than the value of
equity securities or debt instruments and their value may be affected by changes
in overall market movements, commodity index volatility, changes in interest
rates, or factors affecting a particular industry or commodity. The price of a
commodity may be affected by demand/supply imbalances in the market for the
commodity.

Real Estate-Related Investment Risk:  The risks of investing in real estate-related
securities include certain risks associated with the direct ownership of real
estate and the real estate industry in general. These include risks related to
general, regional and local economic conditions; fluctuations in interest rates;
property tax rates, zoning laws, environmental regulations and other governmental
action; cash flow dependency; increased operating expenses; lack of availability
of mortgage funds; losses due to natural disasters; overbuilding; losses due to
casualty or condemnation; changes in property values and rental rates; and other
factors.  The securities of smaller real estate-related issuers can be more
volatile and less liquid than securities of larger issuers and their issuers can
have more limited financial resources.

Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially
emerging markets, through issuers or currencies can involve additional risks
relating to market, economic, political, regulatory, geopolitical, or other
conditions. These factors can make foreign investments, especially those in
emerging markets, more volatile and less liquid than U.S. investments. In
addition, foreign markets can react differently to these conditions than the
U.S. market. Emerging markets can have less developed markets, greater custody
and operational risk, and less developed legal, regulatory, and accounting
systems, and greater political, social, and economic instability than developed
markets.

Currency Risk:  The value of foreign currencies relative to the U.S. dollar
fluctuates in response to market, economic, political, regulatory, geopolitical
or other conditions, and a decline in the value of a foreign currency versus the
U.S. dollar reduces the value in U.S. dollars of investments denominated in that
foreign currency.

Geographic Concentration Risk:  The fund's performance could be closely tied to
the market, currency, economic, political, regulatory, geopolitical, or other
conditions in the countries or regions in which the fund invests and could be
more volatile than the performance of more geographically-diversified funds.
  
Prepayment/Extension Risk:  Instruments subject to prepayment and/or extension
can reduce the potential for gain for the instrument's holders if the instrument
is prepaid and increase the potential for loss if the maturity of the instrument
is extended.

Inflation-Adjusted Debt Instruments Risk:  Interest payments on inflation-adjusted
debt instruments can be unpredictable and vary based on the level of inflation. If
inflation is negative, principal and income can both decline.

Municipal Risk:  The price of a municipal instrument can be volatile and
significantly affected by adverse tax or court rulings, legislative or political
changes, changes in specific or general market and economic conditions, and the
financial condition of municipal issuers and insurers. Because many municipal
instruments are issued to finance similar projects, conditions in these
industries can significantly affect the fund and the overall municipal market.

Tax Risk:  In order to qualify as a regulated investment company (RIC) under the
Internal Revenue Code of 1986, as amended, the fund must meet certain requirements
regarding the source of its income, the diversification of its assets, and the
distribution of its income. If the fund were to fail to qualify as a RIC and became
subject to federal income tax, shareholders of the fund would be subject to the risk
of diminished returns.

Leveraging Risk:  Leverage involves investment exposure in an amount exceeding
the initial investment. Leverage can cause increased volatility by magnifying
gains or losses.

Counterparty and Third Party Risk:  Transactions involving a counterparty or third
party other than the issuer of the instrument are subject to the credit risk of the
counterparty or third party, and to the counterparty's or third party's ability to
perform in accordance with the terms of the transaction.

Liquidity Risk:  It may not be possible to sell certain investments, types of
investments, and/or segments of the market at any particular time or at an
acceptable price.

Performance Information

The bar chart and performance table are not included because the fund has not had
a full calendar year of operations.

[1] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.

[1] Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity, investment related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles), such that "Total Annual Fund Operating Expenses" do not exceed 1.27% of the fund's average daily net assets annually for each of Class A and Class R3 shares, 2.02% of the fund's average daily net assets annually for each of Class B, Class C, and Class R1 shares, 1.02% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.52% of the fund's average daily net assets annually for Class R2 shares, and 1.01% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2013.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Oct. 28, 2012
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Summary of Key Information
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund's investment objective is to seek total return.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. The annual fund operating expenses for Class R5 shares are based on estimated "Other Expenses" for the current fiscal year expressed as a percentage of the fund's estimated average net assets during the period.    You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in "Sales Charges and Waivers or Reductions" on page 11 of the fund's prospectus and "Waivers of Sales Charges" on page I-13 of the fund's statement of additional information Part I.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-10-31
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in "Annual Fund Operating Expenses" or in the "Example," affect the fund's performance.  During the most recent fiscal year, the fund's portfolio turnover rate was 48% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	48.00%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	The annual fund operating expenses for Class R5 shares are based on estimated "Other Expenses" for the current fiscal year expressed as a percentage of the fund's estimated average net assets during the period.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.    The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund's operating expenses remain the same.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund's objective by generating returns from (1) a strategic allocation to a mix of asset classes, (2) individual security selection of U.S. and foreign issuers within those asset classes, and (3) a tactical asset allocation overlay to manage the fund's exposure to asset classes, markets, and currencies primarily using derivative instruments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. The fund's performance may not be correlated with the performance of the asset classes, markets, or currencies represented by the individual investments selected by MFS. Strategic Asset Class Allocation:  MFS determines the percentages of the fund's assets to be invested in the general asset classes of bonds and stocks, as well as in other less-traditional asset classes that MFS believes provide diversification benefits when added to a portfolio consisting of bonds and stocks, such as commodity-related investments and real estate-related investments. As of October 28, 2012, the fund's target strategic exposures among asset classes were as follows: 15% in inflation-adjusted debt instruments; 35% in other debt instruments; 30% in equity securities; 15% in commodity-related investments; and 5% in real estate-related investments. Debt instruments include corporate bonds, U.S. Government securities, asset-backed securities, municipal instruments, foreign government securities, inflation-adjusted bonds, and other obligations to repay money borrowed.  Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for those securities. MFS may invest the fund's assets in other mutual funds advised by MFS that invest in such asset classes instead of investing directly in such assets. The strategic asset class allocations have been selected for investment over longer time periods, but may be changed without shareholder approval or notice. The actual strategic asset class weightings can deviate due to market movements and cash flows.  MFS periodically rebalances the fund's strategic asset class weightings.  These target asset class weightings do not reflect the fund's cash balance; some portion of the fund's portfolio will be held in cash due to collateral requirements associated with the fund's derivative transactions, purchase and redemption activity, and other short term cash needs. Individual Security Selection: In selecting direct investments for the fund, MFS may invest the fund's assets in U.S. and foreign securities, including emerging market securities. Of the fund's investments in debt instruments, MFS primarily invests the fund's assets in investment grade debt instruments, but may also invest in less than investment grade quality debt instruments (lower quality debt instruments). MFS generally seeks to diversify the fund's equity investments in terms of market capitalization (e.g., small, mid, large cap), style (e.g., growth, value), and location (e.g., U.S., foreign). These allocations may vary significantly from time to time. MFS may invest a large percentage of the fund's assets in issuers in a single country, a small number of countries, or a particular geographic region. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives as part of its individual security selection process, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments. A team of investment professionals selects investments for the fund. MFS allocates the fund's assets to investment professionals by investment strategy. MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers and instruments. Quantitative models that systematically evaluate issuers and instruments may also be considered. Tactical Asset Allocation Overlay:  MFS employs a top-down tactical asset allocation process to adjust the fund's exposure to asset classes, markets and currencies based on its assessment of the relative attractiveness of such asset classes, markets and currencies. MFS manages the fund's exposure to asset classes, markets and currencies primarily through the use of derivative instruments. In managing the tactical overlay, MFS uses proprietary quantitative models and may increase or decrease the fund's exposure to asset classes, markets and/or currencies resulting from MFS' individual security selection based on MFS' assessment of the risk/return potential of such asset classes, markets and/or currencies. After taking into account the tactical overlay, the fund's exposure to the various asset classes, markets, and/or currencies may vary significantly from time to time. MFS may also expose the fund to asset classes, markets and/or currencies in which its individual security selection has resulted in no or little exposure (e.g., the high yield bond market). MFS may adjust the fund's net exposure to asset classes, markets and/or currencies by taking net short positions in an asset class, market or currency if MFS believes the risk/return potential of such asset class, market or currency is unattractive.   Alternatively, MFS may cause the fund to take net long positions in an asset class, market or currency if MFS believes such asset class, market or currency appears attractive. After taking into account the tactical overlay, the fund's net exposures to the asset classes referenced below, which may include exposure to U.S. and foreign issuers, will normally fall within the following ranges: Asset Class                                                          Range    Inflation-adjusted debt instruments                               -5% to 35% Debt instruments, excluding inflation-adjusted debt instruments    0% to 70% Equity securities                                                  0% to 60% Commodity-related investments                                     -5% to 35% Real estate-related investments                                   -10% to 20% MFS' tactical asset allocation process for the fund will typically make extensive use of derivatives. MFS may also use derivatives to seek to limit the fund's exposure to certain extreme market events.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The principal risks of investing in the fund are: Investment Selection and Allocation Risk:  MFS' investment analysis, its selection of investments, its assessment of the risk/return potential of asset classes, markets and currencies, and its adjustments to the fund's exposure to asset classes, markets, and currencies through the use of derivatives and underlying funds may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests. Investment Strategy Risk:  The fund's strategy to manage its exposure to asset classes, markets, and currencies may not produce the intended results. In addition, the strategies MFS may implement to limit the fund's exposure to certain extreme market events may not work as intended, and the costs associated with such strategies will reduce the fund's returns. Interest Rate Risk:  The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes. Credit Risk:  The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, or other conditions. Lower quality debt instruments (commonly referred to as "high yield securities" or "junk bonds") can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments. Stock Market/Company Risk:  Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general. Derivatives Risk:  Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives' original cost.  Derivatives can involve leverage. Commodity Risk:  The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity. Real Estate-Related Investment Risk:  The risks of investing in real estate-related securities include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates; property tax rates, zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.  The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources. Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, political, regulatory, geopolitical, or other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, and less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets. Currency Risk:  The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, political, regulatory, geopolitical or other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency. Geographic Concentration Risk:  The fund's performance could be closely tied to the market, currency, economic, political, regulatory, geopolitical, or other conditions in the countries or regions in which the fund invests and could be more volatile than the performance of more geographically-diversified funds.    Prepayment/Extension Risk:  Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument's holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended. Inflation-Adjusted Debt Instruments Risk:  Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline. Municipal Risk:  The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market. Tax Risk:  In order to qualify as a regulated investment company (RIC) under the Internal Revenue Code of 1986, as amended, the fund must meet certain requirements regarding the source of its income, the diversification of its assets, and the distribution of its income. If the fund were to fail to qualify as a RIC and became subject to federal income tax, shareholders of the fund would be subject to the risk of diminished returns. Leveraging Risk:  Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. Counterparty and Third Party Risk:  Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty's or third party's ability to perform in accordance with the terms of the transaction. Liquidity Risk:  It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.
Risk Lose Money [Text]	rr_RiskLoseMoney	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and performance table are not included because the fund has not had a full calendar year of operations.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	The bar chart and performance table are not included because the fund has not had a full calendar year of operations.
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | A
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	A
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.75%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[1]
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	A
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.20%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.44%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	713
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	1,155
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,621
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,907
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | B
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	B
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.00%
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	B
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.95%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	2.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	622
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	1,141
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,686
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	3,039
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	222
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	841
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	1,486
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	3,039
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | C
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	C
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	C
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.95%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	2.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	322
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	841
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,486
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	3,217
Expense Example, No Redemption, 1 Year	rr_ExpenseExampleNoRedemptionYear01	222
Expense Example, No Redemption, 3 Years	rr_ExpenseExampleNoRedemptionYear03	841
Expense Example, No Redemption, 5 Years	rr_ExpenseExampleNoRedemptionYear05	1,486
Expense Example, No Redemption, 10 Years	rr_ExpenseExampleNoRedemptionYear10	3,217
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | I
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	I
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	I
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.95%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	121
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	539
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	982
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,213
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R1
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	R1
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.95%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	2.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	222
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	841
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,486
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	3,217
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R2
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	R2
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.45%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.69%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	172
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	691
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,237
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,729
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R3
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	R3
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.20%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.44%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	147
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	615
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	1,110
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,475
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R4
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	R4
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.95%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.76%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	121
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	539
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	982
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,213
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R5
Risk Return [Abstract]	rr_RiskReturnAbstract
Shareholder Fees Column [Text]	rr_ShareholderFeesColumnName	ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Operating Expenses Column [Text]	rr_OperatingExpensesColumnName	R5
Management Fee	rr_ManagementFeesOverAssets	0.72%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	1.04%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.17%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.93%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.75%)	[2]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.18%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	120
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	533
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	972
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	2,193

[1] On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.

[2] Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity, investment related expenses, and fees and expenses associated with investments in investment companies and other similar investment vehicles), such that "Total Annual Fund Operating Expenses" do not exceed 1.27% of the fund's average daily net assets annually for each of Class A and Class R3 shares, 2.02% of the fund's average daily net assets annually for each of Class B, Class C, and Class R1 shares, 1.02% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.52% of the fund's average daily net assets annually for Class R2 shares, and 1.01% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least October 31, 2013.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Jun. 30, 2012
Registrant Name	dei_EntityRegistrantName	MFS SERIES TRUST XVI
Central Index Key	dei_EntityCentralIndexKey	0000063067
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Oct. 25, 2012
Document Effective Date	dei_DocumentEffectiveDate	Oct. 28, 2012
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | A
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMAX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | B
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMBX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | C
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMCX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | I
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMIX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R1
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMRX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R2
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMSX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R3
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMTX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R4
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMUX
MFS Global Multi-Asset Fund (Prospectus Summary) | MFS Global Multi-Asset Fund | R5
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	GLMVX