485BPOS

As filed with the Securities and Exchange Commission on December 31, 2012

1933 Act File No. 333-59093

1940 Act File No. 811-08879

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C.  20549

FORM N-1A

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933

POST-EFFECTIVE AMENDMENT NO. 36

AND

REGISTRATION STATEMENT

UNDER THE INVESTMENT COMPANY ACT OF 1940

AMENDMENT NO. 37

MFS® VARIABLE INSURANCE TRUST III

(formerly, SUN CAPITAL ADVISERS TRUST®)

(Exact name of registrant as specified in charter)

111 Huntington Avenue, Boston, Massachusetts  02199

(Address of principal executive offices)

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

Susan S. Newton, Massachusetts Financial Services Company

111 Huntington Avenue, Boston, Massachusetts  02199

(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 31st day of December, 2012

MFS® VARIABLE INSURANCE TRUST III
(formerly, Sun Capital Advisers Trust®)
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 December 31, 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 December 7, 2012 (Trustees), and a Power of Attorney, dated December 7, 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 Variable Insurance Trust III

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 7th day of December, 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 Variable Insurance Trust III

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 7th day of December, 2012.

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

MFS VARIABLE INSURANCE TRUST III

MFS® BLENDED RESEARCH SMALL CAP EQUITY PORTFOLIO (formerly, SCSM BlackRock Small Cap Index Fund)

MFS® CONSERVATIVE ALLOCATION PORTFOLIO (formerly, SCSM Ibbotson Conservative Fund)

MFS® GLOBAL REAL ESTATE PORTFOLIO (formerly, Sun Capital Global Real Estate Fund)

MFS® GROWTH ALLOCATION PORTFOLIO (formerly, SCSM Ibbotson Growth Fund)

MFS® INFLATION-ADJUSTED BOND PORTFOLIO (formerly, SCSM BlackRock Inflation Protected Bond Fund)

MFS® LIMITED MATURITY PORTFOLIO (formerly, SCSM Goldman Sachs Short Duration Fund)

MFS® MID CAP VALUE PORTFOLIO (formerly, SCSM Goldman Sachs Mid Cap Value Fund)

MFS® MODERATE ALLOCATION PORTFOLIO (formerly, SCSM Ibbotson Balanced Fund)

MFS® NEW DISCOVERY VALUE PORTFOLIO (formerly, SCSM Columbia Small Cap Value Fund)

INDEX TO EXHIBITS

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

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio
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 that exceeds the rate of inflation over the long-term, with an emphasis on current income, but also considering capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 430% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	430.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in inflation-adjusted debt instruments and other instruments with similar economic characteristics to these instruments. MFS currently intends to focus the fund's investments in inflation-adjusted debt instruments issued by the U.S. Treasury. MFS may also invest the fund's assets in other inflation-adjusted debt instruments, other instruments with similar economic characteristics to these instruments, including derivatives, and non-inflation-adjusted 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 may invest the fund's assets in U.S. and foreign securities. The fund is a non-diversified fund. This means that MFS may invest a relatively large percentage of the fund's assets in a single issuer or a small number of issuers. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. MFS allocates the fund's assets across maturities and types of debt instruments based on its evaluation of U.S. and foreign macroeconomic factors, including interest rates, inflation rates, and monetary and fiscal policies. 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 instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.
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: 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. U.S. Government securities not supported as to the payment of principal or interest by the U.S. Treasury are subject to greater credit risk than are U.S. Government securities supported by the U.S. Treasury. Foreign Risk: Exposure to foreign 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. 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. Non-Diversification Risk: Because MFS may invest a relatively large percentage of the fund's assets in a single issuer or small number of issuers, the fund's performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds. 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.    Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.    Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Because MFS may invest a relatively large percentage of the fund's assets in a single issuer or small number of issuers, the fund's performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds.
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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012 was 5.64%. During the period(s) shown in the bar chart, the highest quarterly return was 3.95% (for the calendar quarter ended September 30, 2011) and the lowest quarterly return was (1.15)% (for the calendar quarter ended December 31, 2010).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays US Treasury Inflation-Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays US Treasury Inflation-Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Barclays World Government Inflation-Linked Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays World Government Inflation-Linked Bond Index
1 Year	rr_AverageAnnualReturnYear01	10.65%
Since Inception	rr_AverageAnnualReturnSinceInception	6.41%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Barclays US Treasury Inflation-Protected Securities Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays US Treasury Inflation-Protected Securities Index
1 Year	rr_AverageAnnualReturnYear01	13.56%
Since Inception	rr_AverageAnnualReturnSinceInception	8.33%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.59%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	60
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	189
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	329
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	738
Annual Return 2009	rr_AnnualReturn2009	8.72%
Annual Return 2010	rr_AnnualReturn2010	5.24%
Annual Return 2011	rr_AnnualReturn2011	11.90%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	5.64%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2011
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	3.95%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.15%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	11.90%
Since Inception	rr_AverageAnnualReturnSinceInception	7.59%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

XML

MFS New Discovery Value Portfolio (Second Prospectus Summary) | MFS New Discovery Value Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements
with MFS. If the fees and expenses imposed by the insurance company that issued
your variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses		MFS New Discovery Value Portfolio Service Class
Management Fee		0.90%
Distribution and/or Service (12b-1) Fees		0.25%
Other Expenses		0.25%
Total Annual Fund Operating Expenses		1.40%
Fee Reductions and/or Expense Reimbursements	[1]	(0.10%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		1.30%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.
  
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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS New Discovery Value Portfolio Service Class	132	422	745	1,661

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. 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 50% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests the fund's assets primarily in equity securities. Equity
securities include common stocks, preferred stocks, securities convertible into
stocks, and depositary receipts for such securities.

MFS focuses on investing the fund's assets in the stocks of companies it
believes are undervalued compared to their perceived worth (value companies).

While MFS may invest the fund's assets in companies of any size, MFS generally
focuses on companies with small capitalizations.

MFS may invest the fund's assets in foreign securities.

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. Quantitative models that systematically evaluate issuers may
also be considered.

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:
  
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.

Value Company Risk: The stocks of value companies can continue to be
undervalued for long periods of time and not realize their expected value and
can be more volatile than the market in general.
  
Small Cap Risk: The stocks of small cap companies can be more volatile than
stocks of larger companies.
  
Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012 was 7.23%.
During the period(s) shown in the bar chart, the highest quarterly return was
22.29% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (21.52)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS New Discovery Value Portfolio	Label	1 Year	Since Inception	Inception Date
Service Class	Service Class Shares	(6.50%)	5.16%	Oct. 01, 2008
Russell 2000 Value Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Value Index	(5.50%)	1.96%	Oct. 01, 2008

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.30% of the fund's average daily net assets annually for Service Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Mid Cap Value Portfolio (First Prospectus Summary) | MFS Mid Cap Value Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 50% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	50.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in issuers with medium market capitalizations. MFS generally defines medium market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell Midcap Value Index over the last 13 months at the time of purchase. As of October 31, 2012, the range of the Russell Midcap Value Index was between $26.1 million and $18.7 billion. MFS normally invests the fund's assets primarily in equity securities. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. MFS focuses on investing the fund's assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies). MFS may invest the fund's assets in foreign securities. 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. Quantitative models that systematically evaluate issuers may also be considered.
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: 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. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. Mid Cap Risk: The stocks of mid cap companies can be more volatile than stocks of larger companies. Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 13.85%. During the period(s) shown in the bar chart, the highest quarterly return was 22.59% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (17.30)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Mid Cap Value Portfolio (First Prospectus Summary) | MFS Mid Cap Value Portfolio | Russell Midcap Value Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell Midcap Value Index
1 Year	rr_AverageAnnualReturnYear01	(1.38%)
Since Inception	rr_AverageAnnualReturnSinceInception	3.25%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008
MFS Mid Cap Value Portfolio (First Prospectus Summary) | MFS Mid Cap Value Portfolio | Initial Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.75%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.08%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.83%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	85
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	265
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	460
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,025
Annual Return 2009	rr_AnnualReturn2009	25.68%
Annual Return 2010	rr_AnnualReturn2010	22.13%
Annual Return 2011	rr_AnnualReturn2011	2.47%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	13.85%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.59%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(17.30%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	2.47%
Since Inception	rr_AverageAnnualReturnSinceInception	2.53%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Limited Maturity Portfolio (Second Prospectus Summary) | MFS Limited Maturity Portfolio
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 with an emphasis on current income, but also considering capital preservation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 154% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	154.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests the fund's assets primarily in debt instruments. 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. The fund's dollar-weighted average effective maturity will normally not exceed five years. MFS generally invests substantially all of the fund's assets in investment grade debt instruments. MFS invests the fund's assets in U.S. securities and U.S. dollar-denominated foreign securities. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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 exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. 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 instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.
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: 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. Foreign Risk: Exposure to foreign 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. 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. 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. Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. 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. 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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.
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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 2.21%. During the period(s) shown in the bar chart, the highest quarterly return was 1.49% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (0.42)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Limited Maturity Portfolio (Second Prospectus Summary) | MFS Limited Maturity Portfolio | Barclays 1-3 Year U.S. Government/Credit Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays 1-3 Year U.S. Government/Credit Bond Index
1 Year	rr_AverageAnnualReturnYear01	1.59%
Since Inception	rr_AverageAnnualReturnSinceInception	2.73%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008
MFS Limited Maturity Portfolio (Second Prospectus Summary) | MFS Limited Maturity Portfolio | Service Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.40%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.07%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.72%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	74
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	230
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	401
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	894
Annual Return 2009	rr_AnnualReturn2009	3.52%
Annual Return 2010	rr_AnnualReturn2010	2.16%
Annual Return 2011	rr_AnnualReturn2011	0.17%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	2.21%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.49%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(0.42%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	0.17%
Since Inception	rr_AverageAnnualReturnSinceInception	2.31%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS New Discovery Value Portfolio (Second Prospectus Summary) | MFS New Discovery Value Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 50% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	50.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher.    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; 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) normally invests the fund's assets primarily in equity securities. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. MFS focuses on investing the fund's assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies). While MFS may invest the fund's assets in companies of any size, MFS generally focuses on companies with small capitalizations. MFS may invest the fund's assets in foreign securities. 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. Quantitative models that systematically evaluate issuers may also be considered.
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:    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. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.    Small Cap Risk: The stocks of small cap companies can be more volatile than stocks of larger companies.    Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012 was 7.23%. During the period(s) shown in the bar chart, the highest quarterly return was 22.29% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (21.52)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS New Discovery Value Portfolio (Second Prospectus Summary) | MFS New Discovery Value Portfolio | Russell 2000 Value Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Value Index
1 Year	rr_AverageAnnualReturnYear01	(5.50%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.96%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS New Discovery Value Portfolio (Second Prospectus Summary) | MFS New Discovery Value Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.90%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.25%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.40%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.10%)	[1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.30%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2014-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	132
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	422
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	745
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,661
Annual Return 2009	rr_AnnualReturn2009	30.07%
Annual Return 2010	rr_AnnualReturn2010	21.33%
Annual Return 2011	rr_AnnualReturn2011	(6.50%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	7.23%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.29%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.52%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	(6.50%)
Since Inception	rr_AverageAnnualReturnSinceInception	5.16%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.30% of the fund's average daily net assets annually for Service Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

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MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a moderate level of risk relative to the other MFS Asset
Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS
Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS
Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Moderate Allocation Portfolio Initial Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.04%
Acquired (Underlying) Fund Fees and Expenses	0.81%
Total Annual Fund Operating Expenses	0.85%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Moderate Allocation Portfolio Initial Class	87	271	471	1,049

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. 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 7% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes by
investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.

As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:

Bond Funds:                              41%
MFS Global Governments Portfolio          5%
MFS Government Securities Portfolio      10%
MFS High Yield Portfolio                  5%
MFS Inflation-Adjusted Bond Portfolio     5%
MFS Limited Maturity Portfolio            4%
MFS Research Bond Series                 12%
Specialty Funds:                          3%
MFS Global Real Estate Portfolio          3%
International Stock Funds:               13%
MFS Emerging Markets Equity Portfolio     0%
MFS International Growth Portfolio        3%
MFS International Value Portfolio         3%
MFS Research International Portfolio      7%
U.S. Stock Funds:                        43%
MFS Growth Series                         9%
MFS Mid Cap Growth Series                 7%
MFS Mid Cap Value Portfolio               7%
MFS New Discovery Series                1.5%
MFS New Discovery Value Portfolio       1.5%
MFS Research Series                       8%
MFS Value Series                          9%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.

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.

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, 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.

Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

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.

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.

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 and property tax rates; shifts in 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.

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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies.  The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 9.30%.
During the period(s) shown in the bar chart, the highest quarterly return was
13.40% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (11.11)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Moderate Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Initial Class	Initial Class Shares		(1.56%)	6.87%	Oct. 01, 2008
Standard & Poor's 500 Stock Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index		2.11%	4.65%	Oct. 01, 2008
Dow Jones Moderate U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderate U.S. Relative Risk Portfolio Index		3.32%	7.54%	Oct. 01, 2008
MFS Moderate Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Moderate Allocation Fund Blended Index	[1]	2.22%	5.77%	Oct. 01, 2008

Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS
Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S.
Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500
Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect
the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Moderate Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (41%) Standard & Poor's 500 Stock Index; (13%) MSCI EAFE (Europe, Australasia, Far East) Index; (3%) The Dow Jones-UBS Commodity Index; (2%) FTSE EPRA/NAREIT Developed Real Estate Index; and (41%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a conservative level of risk relative to the other MFS Asset Allocation Portfolios.  (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 7% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	7.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was: Bond Funds:                             62% MFS Global Governments Portfolio         8% MFS Government Securities Portfolio     10% MFS High Yield Portfolio                 5% MFS Inflation-Adjusted Bond Portfolio   10% MFS Limited Maturity Portfolio          12% MFS Research Bond Series                17% Specialty Funds:                         2% MFS Global Real Estate Portfolio         2% International Stock Funds:               8% MFS Emerging Markets Equity Portfolio    0% MFS International Growth Portfolio       2% MFS International Value Portfolio        2% MFS Research International Portfolio     4% U.S. Stock Funds:                       28% MFS Growth Series                        6% MFS Mid Cap Growth Series                4% MFS Mid Cap Value Portfolio              4% MFS New Discovery Series                 1% MFS New Discovery Value Portfolio        1% MFS Research Series                      6% MFS Value Series                         6%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective. 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. 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, 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. 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. 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 and property tax rates; shifts in 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. 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. Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 7.89%. During the period(s) shown in the bar chart, the highest quarterly return was 9.51% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (7.38)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index because MFS believes the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index because MFS believes the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio | Barclays U.S. Aggregate Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index
1 Year	rr_AverageAnnualReturnYear01	7.84%
Since Inception	rr_AverageAnnualReturnSinceInception	7.68%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio | Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	5.07%
Since Inception	rr_AverageAnnualReturnSinceInception	7.76%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio | MFS Conservative Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees expenses or taxes) MFS Conservative Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	4.58%
Since Inception	rr_AverageAnnualReturnSinceInception	6.52%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.05%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.74%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.04%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	106
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	331
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	574
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,271
Annual Return 2009	rr_AnnualReturn2009	19.22%
Annual Return 2010	rr_AnnualReturn2010	9.64%
Annual Return 2011	rr_AnnualReturn2011	0.63%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	7.89%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	9.51%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(7.38%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	0.63%
Since Inception	rr_AverageAnnualReturnSinceInception	5.97%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (28%) Standard & Poor's 500 Stock Index; (8%) MSCI EAFE (Europe, Australasia, Far East) Index; (1%) The Dow Jones-UBS Commodity Index; (1%) FTSE EPRA/NAREIT Developed Real Estate Index; and (62%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

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MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return that exceeds the rate of
inflation over the long-term, with an emphasis on current income, but also
considering capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Inflation-Adjusted Bond Portfolio Initial Class
Management Fee	0.50%
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.09%
Total Annual Fund Operating Expenses	0.59%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Inflation-Adjusted Bond Portfolio Initial Class	60	189	329	738

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. 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 430% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in inflation-adjusted
debt instruments and other instruments with similar economic characteristics to
these instruments.

MFS currently intends to focus the fund's investments in inflation-adjusted debt
instruments issued by the U.S. Treasury. MFS may also invest the fund's assets
in other inflation-adjusted debt instruments, other instruments with similar
economic characteristics to these instruments, including derivatives, and
non-inflation-adjusted 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 may invest the fund's assets in U.S. and foreign securities.

The fund is a non-diversified fund. This means that MFS may invest a relatively
large percentage of the fund's assets in a single issuer or a small number of
issuers.

While MFS may use derivatives for any investment purpose, to the extent MFS uses
derivatives, 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. Derivatives include futures, forward contracts, options, structured
securities, inverse floating rate instruments, and swaps.

MFS allocates the fund's assets across maturities and types of debt instruments
based on its evaluation of U.S. and foreign macroeconomic factors, including
interest rates, inflation rates, and monetary and fiscal policies.

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 instruments and their issuers. Quantitative models that systematically
evaluate instruments may also be considered. In structuring the fund, MFS may also
consider top-down factors.

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:

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.

U.S. Government securities not supported as to the payment of principal or
interest by the U.S. Treasury are subject to greater credit risk than are U.S.
Government securities supported by the U.S. Treasury.

Foreign Risk: Exposure to foreign 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.

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.

Non-Diversification Risk: Because MFS may invest a relatively large percentage
of the fund's assets in a single issuer or small number of issuers, the fund's
performance could be closely tied to the value of that one issuer or issuers,
and could be more volatile than the performance of diversified funds.

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.
  
Leveraging Risk: Leverage involves investment exposure in an amount exceeding
the initial investment. Leverage can cause increased volatility by magnifying
gains or losses.
  
Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012 was 5.64%.
During the period(s) shown in the bar chart, the highest quarterly return was
3.95% (for the calendar quarter ended September 30, 2011) and the lowest
quarterly return was (1.15)% (for the calendar quarter ended December 31, 2010).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Inflation-Adjusted Bond Portfolio	Label	1 Year	Since Inception	Inception Date
Initial Class	Initial Class Shares	11.90%	7.59%	Oct. 01, 2008
Barclays World Government Inflation-Linked Bond Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays World Government Inflation-Linked Bond Index	10.65%	6.41%	Oct. 01, 2008
Barclays US Treasury Inflation-Protected Securities Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays US Treasury Inflation-Protected Securities Index	13.56%	8.33%	Oct. 01, 2008

Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond
Index replaced the Barclays US Treasury Inflation-Protected Securities Index
because MFS believes the Barclays World Government Inflation-Linked Bond Index
better reflects the fund's current investment strategies.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a moderate level of risk relative to the other MFS Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 7% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	7.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was: Bond Funds:                              41% MFS Global Governments Portfolio          5% MFS Government Securities Portfolio      10% MFS High Yield Portfolio                  5% MFS Inflation-Adjusted Bond Portfolio     5% MFS Limited Maturity Portfolio            4% MFS Research Bond Series                 12% Specialty Funds:                          3% MFS Global Real Estate Portfolio          3% International Stock Funds:               13% MFS Emerging Markets Equity Portfolio     0% MFS International Growth Portfolio        3% MFS International Value Portfolio         3% MFS Research International Portfolio      7% U.S. Stock Funds:                        43% MFS Growth Series                         9% MFS Mid Cap Growth Series                 7% MFS Mid Cap Value Portfolio               7% MFS New Discovery Series                1.5% MFS New Discovery Value Portfolio       1.5% MFS Research Series                       8% MFS Value Series                          9%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective. 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. 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, 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. Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. 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. 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. 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 and property tax rates; shifts in 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. 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 9.13%. During the period(s) shown in the bar chart, the highest quarterly return was 13.43% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (11.20)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio | Standard & Poor's 500 Stock Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
1 Year	rr_AverageAnnualReturnYear01	2.11%
Since Inception	rr_AverageAnnualReturnSinceInception	4.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio | Dow Jones Moderate U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderate U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	3.32%
Since Inception	rr_AverageAnnualReturnSinceInception	7.54%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio | MFS Moderate Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Moderate Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	2.22%
Since Inception	rr_AverageAnnualReturnSinceInception	5.77%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.04%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.10%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	112
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	350
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	606
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,340
Annual Return 2009	rr_AnnualReturn2009	23.65%
Annual Return 2010	rr_AnnualReturn2010	11.82%
Annual Return 2011	rr_AnnualReturn2011	(1.81%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	9.13%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	13.43%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(11.20%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	(1.81%)
Since Inception	rr_AverageAnnualReturnSinceInception	6.58%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Moderate Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (41%) Standard & Poor's 500 Stock Index; (13%) MSCI EAFE (Europe, Australasia, Far East) Index; (3%) The Dow Jones-UBS Commodity Index; (2%) FTSE EPRA/NAREIT Developed Real Estate Index; and (41%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Global Real Estate Portfolio (Second Prospectus Summary) | MFS Global Real Estate Portfolio
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 27% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	27.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in U.S. and foreign real estate-related investments. MFS normally invests the fund's assets primarily in equity securities. MFS generally focuses the fund's investments in equity real estate investment trusts ("REITs") as well as similar entities formed under the laws of non-U.S. countries, but may also invest in mortgage REITs, hybrid REITs and other U.S. and foreign real estate-related investments, including emerging market real estate-related investments. MFS may invest the fund's assets in real estate-related investments of any size.  However, issuers of real estate-related investments tend to be small-to-medium-sized. MFS typically allocates the fund's investments across various geographic areas, REIT managers and property types, but may from time to time focus the fund's investments in any one or a few of these areas. 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. MFS selects investments by analyzing the fundamental and relative values of potential investments.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund's net assets in U.S. and foreign real estate-related investments.
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: Real Estate-Related Investment Risk: The fund's performance will be closely tied to the performance of real estate-related investments and as a result, can be more volatile than the performance of more broadly-diversified funds. The risks of investing in real estate-related investments 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 and property tax rates; shifts in 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. Small to Medium Cap Risk: 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. 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. 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, 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.    The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 20.93%. During the period(s) shown in the bar chart, the highest quarterly return was 34.75% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (39.09)% (for the calendar quarter ended December 31, 2008).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Global Real Estate Portfolio (Second Prospectus Summary) | MFS Global Real Estate Portfolio | FTSE EPRA/NAREIT Developed Real Estate Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) FTSE EPRA/NAREIT Developed Real Estate Index
1 Year	rr_AverageAnnualReturnYear01	(5.82%)
5 Years	rr_AverageAnnualReturnYear05	(5.28%)
10 Years	rr_AverageAnnualReturnYear10	9.50%
MFS Global Real Estate Portfolio (Second Prospectus Summary) | MFS Global Real Estate Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.90%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.10%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.25%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.20%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2014-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	122
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	386
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	676
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,502
Annual Return 2005	rr_AnnualReturn2005	9.37%
Annual Return 2006	rr_AnnualReturn2006	38.64%
Annual Return 2007	rr_AnnualReturn2007	(13.34%)
Annual Return 2008	rr_AnnualReturn2008	(44.89%)
Annual Return 2009	rr_AnnualReturn2009	29.83%
Annual Return 2010	rr_AnnualReturn2010	14.94%
Annual Return 2011	rr_AnnualReturn2011	(7.74%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	20.93%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	34.75%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(39.09%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	(7.74%)
5 Years	rr_AverageAnnualReturnYear05	(8.04%)
10 Years	rr_AverageAnnualReturnYear10	6.44%

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.20% of the fund's average daily net assets annually for Service Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Limited Maturity Portfolio (First Prospectus Summary) | MFS Limited Maturity Portfolio
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 with an emphasis on current income, but also considering capital preservation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 154% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	154.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests the fund's assets primarily in debt instruments. 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. The fund's dollar-weighted average effective maturity will normally not exceed five years. MFS generally invests substantially all of the fund's assets in investment grade debt instruments. MFS invests the fund's assets in U.S. securities and U.S. dollar-denominated foreign securities. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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 exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. 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 instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.
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: 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. Foreign Risk: Exposure to foreign 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. 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. 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. Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. 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. 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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.
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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 2.40%. During the period(s) shown in the bar chart, the highest quarterly return was 1.55% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (0.32)% (for the calendar quarter ended December 31, 2010).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Limited Maturity Portfolio (First Prospectus Summary) | MFS Limited Maturity Portfolio | Barclays 1-3 Year U.S. Government/Credit Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays 1-3 Year U.S. Government/Credit Bond Index
1 Year	rr_AverageAnnualReturnYear01	1.59%
Since Inception	rr_AverageAnnualReturnSinceInception	2.73%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008
MFS Limited Maturity Portfolio (First Prospectus Summary) | MFS Limited Maturity Portfolio | Initial Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.40%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.07%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.47%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	48
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	151
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	263
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	591
Annual Return 2009	rr_AnnualReturn2009	3.78%
Annual Return 2010	rr_AnnualReturn2010	2.41%
Annual Return 2011	rr_AnnualReturn2011	0.53%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	2.40%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.55%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(0.32%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	0.53%
Since Inception	rr_AverageAnnualReturnSinceInception	2.59%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio
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 that exceeds the rate of inflation over the long-term, with an emphasis on current income, but also considering capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 430% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	430.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher.    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; 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) normally invests at least 80% of the fund's net assets in inflation-adjusted debt instruments and other instruments with similar economic characteristics to these instruments. MFS currently intends to focus the fund's investments in inflation-adjusted debt instruments issued by the U.S. Treasury. MFS may also invest the fund's assets in other inflation-adjusted debt instruments, other instruments with similar economic characteristics to these instruments, including derivatives, and non-inflation-adjusted 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 may invest the fund's assets in U.S. and foreign securities. The fund is a non-diversified fund. This means that MFS may invest a relatively large percentage of the fund's assets in a single issuer or a small number of issuers. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, 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. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. MFS allocates the fund's assets across maturities and types of debt instruments based on its evaluation of U.S. and foreign macroeconomic factors, including interest rates, inflation rates, and monetary and fiscal policies. 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 instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.
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: 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. U.S. Government securities not supported as to the payment of principal or interest by the U.S. Treasury are subject to greater credit risk than are U.S. Government securities supported by the U.S. Treasury. Foreign Risk: Exposure to foreign 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. 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. Non-Diversification Risk: Because MFS may invest a relatively large percentage of the fund's assets in a single issuer or small number of issuers, the fund's performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds. 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.    Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.    Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Because MFS may invest a relatively large percentage of the fund's assets in a single issuer or small number of issuers, the fund's performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds.
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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012 was 5.41%. During the period(s) shown in the bar chart, the highest quarterly return was 3.95% (for the calendar quarter ended September 30, 2011) and the lowest quarterly return was (1.33)% (for the calendar quarter ended December 31, 2010).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays US Treasury Inflation-Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays US Treasury Inflation-Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Barclays World Government Inflation-Linked Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays World Government Inflation-Linked Bond Index
1 Year	rr_AverageAnnualReturnYear01	10.65%
Since Inception	rr_AverageAnnualReturnSinceInception	6.41%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Barclays US Treasury Inflation-Protected Securities Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays US Treasury Inflation-Protected Securities Index
1 Year	rr_AverageAnnualReturnYear01	13.56%
Since Inception	rr_AverageAnnualReturnSinceInception	8.33%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.09%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.84%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	86
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	268
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	466
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,037
Annual Return 2009	rr_AnnualReturn2009	8.34%
Annual Return 2010	rr_AnnualReturn2010	4.91%
Annual Return 2011	rr_AnnualReturn2011	11.70%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	5.41%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2011
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	3.95%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.33%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	11.70%
Since Inception	rr_AverageAnnualReturnSinceInception	7.30%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

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MFS Limited Maturity Portfolio (First Prospectus Summary) | MFS Limited Maturity Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return with an emphasis
on current income, but also considering capital preservation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Limited Maturity Portfolio Initial Class shares
Management Fee	0.40%
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.07%
Total Annual Fund Operating Expenses	0.47%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Limited Maturity Portfolio Initial Class shares	48	151	263	591

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. 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 154% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests the fund's assets primarily in debt instruments.

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.

The fund's dollar-weighted average effective maturity will normally not exceed
five years.

MFS generally invests substantially all of the fund's assets in investment grade
debt instruments.

MFS invests the fund's assets in U.S. securities and U.S. dollar-denominated
foreign securities.

While MFS may use derivatives for any investment purpose, to the extent MFS uses
derivatives, 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 exposure, or as alternatives to direct investments.
Derivatives include futures, forward contracts, options, structured securities,
inverse floating rate instruments, and swaps.

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 instruments and their issuers. Quantitative models that systematically
evaluate instruments may also be considered. In structuring the fund, MFS may
also consider top-down factors.

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:

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.

Foreign Risk: Exposure to foreign 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.

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.

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.

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

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.

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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

Performance Information

The bar chart and performance table below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 2.40%.
During the period(s) shown in the bar chart, the highest quarterly return was
1.55% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (0.32)% (for the calendar quarter ended December 31, 2010).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Limited Maturity Portfolio	Label	1 Year	Since Inception	Inception Date
Initial Class shares	Initial Class Shares	0.53%	2.59%	Mar. 07, 2008
Barclays 1-3 Year U.S. Government/Credit Bond Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays 1-3 Year U.S. Government/Credit Bond Index	1.59%	2.73%	Mar. 07, 2008

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Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a greater than moderate level of risk relative to the other MFS Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 16% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	16.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was: Bond Funds:                             21% MFS Global Governments Portfolio         4% MFS Government Securities Portfolio      0% MFS High Yield Portfolio                 5% MFS Inflation-Adjusted Bond Portfolio    5% MFS Limited Maturity Portfolio           2% MFS Research Bond Series                 5% Specialty Funds:                         5% MFS Global Real Estate Portfolio         5% International Stock Funds:              20% MFS Emerging Markets Equity Portfolio    1% MFS International Growth Portfolio       5% MFS International Value Portfolio        5% MFS Research International Portfolio     9% U.S. Stock Funds:                       54% MFS Growth Series                       11% MFS Mid Cap Growth Series                9% MFS Mid Cap Value Portfolio              9% MFS New Discovery Series                 2% MFS New Discovery Value Portfolio        2% MFS Research Series                     10% MFS Value Series                        11%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective. 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. 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, 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. Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.    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 nstruments. 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. 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 and property tax rates; shifts in 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. 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 10.87%.  During the period(s) shown in the bar chart, the highest quarterly return was 16.85% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (14.70)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio | Standard & Poor's 500 Stock Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
1 Year	rr_AverageAnnualReturnYear01	2.11%
Since Inception	rr_AverageAnnualReturnSinceInception	4.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio | Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	1.45%
Since Inception	rr_AverageAnnualReturnSinceInception	7.04%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio | MFS Growth Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Growth Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	(0.24%)
Since Inception	rr_AverageAnnualReturnSinceInception	4.79%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.88%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.94%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	96
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	300
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	520
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,155
Annual Return 2009	rr_AnnualReturn2009	27.17%
Annual Return 2010	rr_AnnualReturn2010	13.80%
Annual Return 2011	rr_AnnualReturn2011	(3.66%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	10.87%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.85%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(14.70%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	(3.66%)
Since Inception	rr_AverageAnnualReturnSinceInception	6.75%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Growth Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (52%) Standard & Poor's 500 Stock Index; (20%) MSCI EAFE (Europe, Australasia, Far East) Index; (4%); The Dow Jones-UBS Commodity Index; (3%) FTSE EPRA/NAREIT Developed Real Estate Index; and (21%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return that exceeds the rate of
inflation over the long-term, with an emphasis on current income, but also
considering capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Inflation-Adjusted Bond Portfolio Service Class
Management Fee	0.50%
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.09%
Total Annual Fund Operating Expenses	0.84%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.
  
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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Inflation-Adjusted Bond Portfolio Service Class	86	268	466	1,037

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. 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 430% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in inflation-adjusted
debt instruments and other instruments with similar economic characteristics to
these instruments.

MFS currently intends to focus the fund's investments in inflation-adjusted debt
instruments issued by the U.S. Treasury. MFS may also invest the fund's assets
in other inflation-adjusted debt instruments, other instruments with similar
economic characteristics to these instruments, including derivatives, and
non-inflation-adjusted 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 may invest the fund's assets in U.S. and foreign securities.

The fund is a non-diversified fund. This means that MFS may invest a relatively
large percentage of the fund's assets in a single issuer or a small number of
issuers.

While MFS may use derivatives for any investment purpose, to the extent MFS uses
derivatives, 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. Derivatives include futures, forward contracts, options, structured
securities, inverse floating rate instruments, and swaps.

MFS allocates the fund's assets across maturities and types of debt instruments
based on its evaluation of U.S. and foreign macroeconomic factors, including
interest rates, inflation rates, and monetary and fiscal policies.

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 instruments and their issuers. Quantitative models that systematically
evaluate instruments may also be considered. In structuring the fund, MFS may
also consider top-down factors.

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:

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.

U.S. Government securities not supported as to the payment of principal or
interest by the U.S. Treasury are subject to greater credit risk than are U.S.
Government securities supported by the U.S. Treasury.

Foreign Risk: Exposure to foreign 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.

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.

Non-Diversification Risk: Because MFS may invest a relatively large percentage
of the fund's assets in a single issuer or small number of issuers, the fund's
performance could be closely tied to the value of that one issuer or issuers,
and could be more volatile than the performance of diversified funds.

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.
  
Leveraging Risk: Leverage involves investment exposure in an amount exceeding
the initial investment. Leverage can cause increased volatility by magnifying
gains or losses.
  
Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012 was 5.41%.
During the period(s) shown in the bar chart, the highest quarterly return was
3.95% (for the calendar quarter ended September 30, 2011) and the lowest
quarterly return was (1.33)% (for the calendar quarter ended December 31, 2010).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Inflation-Adjusted Bond Portfolio	Label	1 Year	Since Inception	Inception Date
Service Class	Service Class Shares	11.70%	7.30%	Oct. 01, 2008
Barclays World Government Inflation-Linked Bond Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays World Government Inflation-Linked Bond Index	10.65%	6.41%	Oct. 01, 2008
Barclays US Treasury Inflation-Protected Securities Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays US Treasury Inflation-Protected Securities Index	13.56%	8.33%	Oct. 01, 2008

Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond
Index replaced the Barclays US Treasury Inflation-Protected Securities Index
because MFS believes the Barclays World Government Inflation-Linked Bond Index
better reflects the fund's current investment strategies.

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MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a greater than moderate level of risk relative to the other MFS
Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are
MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and
MFS Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Growth Allocation Portfolio Service Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.06%
Acquired (Underlying) Fund Fees and Expenses	0.88%
Total Annual Fund Operating Expenses	1.19%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Growth Allocation Portfolio Service Class	121	378	654	1,443

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. 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 16% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes
by investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.

As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:

Bond Funds:                             21%
MFS Global Governments Portfolio         4%
MFS Government Securities Portfolio      0%
MFS High Yield Portfolio                 5%
MFS Inflation-Adjusted Bond Portfolio    5%
MFS Limited Maturity Portfolio           2%
MFS Research Bond Series                 5%
Specialty Funds:                         5%
MFS Global Real Estate Portfolio         5%
International Stock Funds:              20%
MFS Emerging Markets Equity Portfolio    1%
MFS International Growth Portfolio       5%
MFS International Value Portfolio        5%
MFS Research International Portfolio     9%
U.S. Stock Funds:                       54%
MFS Growth Series                       11%
MFS Mid Cap Growth Series                9%
MFS Mid Cap Value Portfolio              9%
MFS New Discovery Series                 2%
MFS New Discovery Value Portfolio        2%
MFS Research Series                     10%
MFS Value Series                        11%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.

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.

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, 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.
  
Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

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.

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.

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 and property tax rates; shifts in 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.

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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was
10.59%.  During the period(s) shown in the bar chart, the highest quarterly
return was 16.75% (for the calendar quarter ended June 30, 2009) and the lowest
quarterly return was (14.69)% (for the calendar quarter ended September 30,
2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Growth Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Service Class	Service Class Shares		(3.90%)	6.51%	Oct. 01, 2008
Standard & Poor's 500 Stock Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index		2.11%	4.65%	Oct. 01, 2008
Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index		1.45%	7.04%	Oct. 01, 2008
MFS Growth Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Growth Allocation Fund Blended Index	[1]	(0.24%)	4.79%	Oct. 01, 2008

Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the
MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately
Aggressive U.S. Relative Risk Portfolio Index because MFS believes the
Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended
Index better reflect the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Growth Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (52%) Standard & Poor's 500 Stock Index; (20%) MSCI EAFE (Europe, Australasia, Far East) Index; (4%); The Dow Jones-UBS Commodity Index; (3%) FTSE EPRA/NAREIT Developed Real Estate Index; and (21%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Global Real Estate Portfolio (First Prospectus Summary) | MFS Global Real Estate Portfolio
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 27% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	27.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in U.S. and foreign real estate-related investments. MFS normally invests the fund's assets primarily in equity securities. MFS generally focuses the fund's investments in equity real estate investment trusts ("REITs") as well as similar entities formed under the laws of non-U.S. countries, but may also invest in mortgage REITs, hybrid REITs and other U.S. and foreign real estate-related investments, including emerging market real estate-related investments. MFS may invest the fund's assets in real estate-related investments of any size.  However, issuers of real estate-related investments tend to be small-to-medium-sized. MFS typically allocates the fund's investments across various geographic areas, REIT managers and property types, but may from time to time focus the fund's investments in any one or a few of these areas. 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. MFS selects investments by analyzing the fundamental and relative values of potential investments.
Strategy Portfolio Concentration [Text]	rr_StrategyPortfolioConcentration	MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund's net assets in U.S. and foreign real estate-related investments.
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: Real Estate-Related Investment Risk: The fund's performance will be closely tied to the performance of real estate-related investments and as a result, can be more volatile than the performance of more broadly-diversified funds. The risks of investing in real estate-related investments 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 and property tax rates; shifts in 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. Small to Medium Cap Risk: 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. 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. 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, 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.    The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 21.23%. During the period(s) shown in the bar chart, the highest quarterly return was 34.82% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (39.05)% (for the calendar quarter ended December 31, 2008).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Global Real Estate Portfolio (First Prospectus Summary) | MFS Global Real Estate Portfolio | FTSE EPRA/NAREIT Developed Real Estate Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) FTSE EPRA/NAREIT Developed Real Estate Index
1 Year	rr_AverageAnnualReturnYear01	(5.82%)
5 Years	rr_AverageAnnualReturnYear05	(5.28%)
10 Years	rr_AverageAnnualReturnYear10	9.50%
MFS Global Real Estate Portfolio (First Prospectus Summary) | MFS Global Real Estate Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.90%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.10%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.00%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.05%)	[1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.95%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2014-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	97
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	308
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	542
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,215
Annual Return 2002	rr_AnnualReturn2002	4.04%
Annual Return 2003	rr_AnnualReturn2003	35.95%
Annual Return 2004	rr_AnnualReturn2004	33.32%
Annual Return 2005	rr_AnnualReturn2005	9.67%
Annual Return 2006	rr_AnnualReturn2006	38.96%
Annual Return 2007	rr_AnnualReturn2007	(13.13%)
Annual Return 2008	rr_AnnualReturn2008	(44.73%)
Annual Return 2009	rr_AnnualReturn2009	30.09%
Annual Return 2010	rr_AnnualReturn2010	15.28%
Annual Return 2011	rr_AnnualReturn2011	(7.59%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	21.23%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	34.82%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(39.05%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	(7.59%)
5 Years	rr_AverageAnnualReturnYear05	(7.82%)
10 Years	rr_AverageAnnualReturnYear10	6.70%

[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), such that "Total Annual Fund Operating Expenses" do not exceed 0.95% of the fund's average daily net assets annually for Initial Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

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MFS Blended Research Small Cap Equity Portfolio (Second Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Blended Research Small Cap Equity Portfolio Service Class
Management Fee	0.40%
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.11%
Total Annual Fund Operating Expenses	0.76%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Blended Research Small Cap Equity Portfolio Service Class	78	243	422	942

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. 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 37% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in equity securities of
issuers with small market capitalizations. MFS generally defines small market
capitalization issuers as issuers with market capitalizations similar to those
of issuers included in the Russell 2000 Index over the last 13 months at the
time of purchase. As of October 31, 2012, the range of the Russell 2000 Index
was between $10.4 million and $4.1 billion.

Equity securities include common stocks, preferred stocks, securities convertible
into stocks, and depositary receipts for such securities.

In selecting investments for the fund, MFS is not constrained to any particular
investment style. MFS may invest the fund's assets in the stocks of companies it
believes to have above average earnings growth potential compared to other
companies (growth companies), in the stocks of companies it believes are
undervalued compared to their perceived worth (value companies), or in a
combination of growth and value companies.

MFS may invest the fund's assets in foreign securities.

MFS uses a bottom-up approach to buying and selling investments for the fund.
Investments are selected based on fundamental analysis of individual issuers and
quantitative models that systematically evaluate issuers.

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:

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.

Small Cap Risk: The stocks of small cap companies can be more volatile than
stocks of larger companies.

Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis, its development and use of
quantitative models, and its selection of investments 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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and using a passive investment strategy.
The fund's past performance does not necessarily indicate how the fund will
perform in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 13.54%.
During the period(s) shown in the bar chart, the highest quarterly return was
31.20% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (26.91)% (for the calendar quarter ended December 31, 2008).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Blended Research Small Cap Equity Portfolio	Label	1 Year	5 Years	10 Years
Service Class	Service Class Shares	(5.09%)	(0.54%)	4.25%
Russell 2000 Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Index	(4.18%)	0.15%	5.62%

XML

MFS Global Real Estate Portfolio (Second Prospectus Summary) | MFS Global Real Estate Portfolio

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 hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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 Real Estate Portfolio Service Class
Management Fee		0.90%
Distribution and/or Service (12b-1) Fees		0.25%
Other Expenses		0.10%
Total Annual Fund Operating Expenses		1.25%
Fee Reductions and/or Expense Reimbursements	[1]	(0.05%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		1.20%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Global Real Estate Portfolio Service Class	122	386	676	1,502

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. 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 27% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in U.S. and foreign real
estate-related investments.

MFS normally invests the fund's assets primarily in equity securities.

MFS generally focuses the fund's investments in equity real estate investment
trusts ("REITs") as well as similar entities formed under the laws of non-U.S.
countries, but may also invest in mortgage REITs, hybrid REITs and other U.S.
and foreign real estate-related investments, including emerging market real
estate-related investments.

MFS may invest the fund's assets in real estate-related investments of any
size.  However, issuers of real estate-related investments tend to be
small-to-medium-sized.

MFS typically allocates the fund's investments across various geographic areas,
REIT managers and property types, but may from time to time focus the fund's
investments in any one or a few of these areas.

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.

MFS selects investments by analyzing the fundamental and relative values of
potential investments.

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:

Real Estate-Related Investment Risk: The fund's performance will be closely
tied to the performance of real estate-related investments and as a result, can
be more volatile than the performance of more broadly-diversified funds. The
risks of investing in real estate-related investments 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 and property tax rates; shifts in
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.

Small to Medium Cap Risk: 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.

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.

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, 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.
  
The fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle through
which an investment in the fund is made were included, they would reduce the returns
shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 20.93%.
During the period(s) shown in the bar chart, the highest quarterly return was
34.75% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (39.09)% (for the calendar quarter ended December 31, 2008).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Global Real Estate Portfolio	Label	1 Year	5 Years	10 Years
Service Class	Service Class Shares	(7.74%)	(8.04%)	6.44%
FTSE EPRA/NAREIT Developed Real Estate Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) FTSE EPRA/NAREIT Developed Real Estate Index	(5.82%)	(5.28%)	9.50%

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.20% of the fund's average daily net assets annually for Service Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

XML

MFS Blended Research Small Cap Equity Portfolio (First Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Blended Research Small Cap Equity Portfolio Initial Class
Management Fee	0.40%
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.11%
Total Annual Fund Operating Expenses	0.51%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Blended Research Small Cap Equity Portfolio Initial Class	52	164	285	640

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. 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 37% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in equity securities of
issuers with small market capitalizations. MFS generally defines small market
capitalization issuers as issuers with market capitalizations similar to those
of issuers included in the Russell 2000 Index over the last 13 months at the
time of purchase. As of October 31, 2012, the range of the Russell 2000 Index
was between $10.4 million and $4.1 billion.

Equity securities include common stocks, preferred stocks, securities convertible
into stocks, and depositary receipts for such securities.

In selecting investments for the fund, MFS is not constrained to any particular
investment style. MFS may invest the fund's assets in the stocks of companies
it believes to have above average earnings growth potential compared to other
companies (growth companies), in the stocks of companies it believes are
undervalued compared to their perceived worth (value companies), or in a
combination of growth and value companies.

MFS may invest the fund's assets in foreign securities.

MFS uses a bottom-up approach to buying and selling investments for the fund.
Investments are selected based on fundamental analysis of individual issuers and
quantitative models that systematically evaluate issuers.

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:

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.

Small Cap Risk: The stocks of small cap companies can be more volatile than
stocks of larger companies.

Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis, its development and use of
quantitative models, and its selection of investments 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and using a passive investment strategy. The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 13.81%.
During the period(s) shown in the bar chart, the highest quarterly return was
31.28% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (26.91)% (for the calendar quarter ended December 31, 2008).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Blended Research Small Cap Equity Portfolio	Label	1 Year	5 Years	10 Years
Initial Class	Initial Class Shares	(4.87%)	(0.21%)	4.56%
Russell 2000 Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Index	(4.18%)	0.15%	5.62%

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MFS New Discovery Value Portfolio (First Prospectus Summary) | MFS New Discovery Value Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements
with MFS. If the fees and expenses imposed by the insurance company that issued
your variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses		MFS New Discovery Value Portfolio Initial Class
Management Fee		0.90%
Distribution and/or Service (12b-1) Fees		none
Other Expenses		0.25%
Total Annual Fund Operating Expenses		1.15%
Fee Reductions and/or Expense Reimbursements	[1]	(0.10%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		1.05%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS New Discovery Value Portfolio Initial Class	107	344	612	1,378

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. 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 50% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests the fund's assets primarily in equity securities. Equity
securities include common stocks, preferred stocks, securities convertible into
stocks, and depositary receipts for such securities.

MFS focuses on investing the fund's assets in the stocks of companies it
believes are undervalued compared to their perceived worth (value companies).

While MFS may invest the fund's assets in companies of any size, MFS generally
focuses on companies with small capitalizations.

MFS may invest the fund's assets in foreign securities.

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. Quantitative models that systematically evaluate issuers may
also be considered.

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:

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.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

Small Cap Risk: The stocks of small cap companies can be more volatile than
stocks of larger companies.
  
Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.
  
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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.
  
Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012 was 7.42%.
During the period(s) shown in the bar chart, the highest quarterly return was
22.44% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (21.49)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS New Discovery Value Portfolio	Label	1 Year	Since Inception	Inception Date
Initial Class	Initial Class Shares	(6.32%)	5.43%	Oct. 01, 2008
Russell 2000 Value Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Value Index	(5.50%)	1.96%	Oct. 01, 2008

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.05% of the fund's average daily net assets annually for Initial Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

XML

MFS Limited Maturity Portfolio (Second Prospectus Summary) | MFS Limited Maturity Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek total return with an emphasis on
current income, but also considering capital preservation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Limited Maturity Portfolio Service Class shares
Management Fee	0.40%
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.07%
Total Annual Fund Operating Expenses	0.72%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Limited Maturity Portfolio Service Class shares	74	230	401	894

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. 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 154% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests the fund's assets primarily in debt instruments.

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.

The fund's dollar-weighted average effective maturity will normally not exceed
five years.

MFS generally invests substantially all of the fund's assets in investment grade
debt instruments.

MFS invests the fund's assets in U.S. securities and U.S. dollar-denominated
foreign securities.

While MFS may use derivatives for any investment purpose, to the extent MFS uses
derivatives, 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 exposure, or as alternatives to direct investments.
Derivatives include futures, forward contracts, options, structured securities,
inverse floating rate instruments, and swaps.

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 instruments and their issuers. Quantitative models that systematically
evaluate instruments may also be considered. In structuring the fund, MFS may
also consider top-down factors.

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:

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.

Foreign Risk: Exposure to foreign 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.

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.

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.

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

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.

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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

Performance Information

The bar chart and performance table below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's past
performance does not necessarily indicate how the fund will perform in the future.
Updated performance is available at mfs.com or by calling 1-877-411-3325. If the
fees and expenses imposed by the investment vehicle through which an investment in
the fund is made were included, they would reduce the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 2.21%.
During the period(s) shown in the bar chart, the highest quarterly return was
1.49% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (0.42)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Limited Maturity Portfolio	Label	1 Year	Since Inception	Inception Date
Service Class shares	Service Class Shares	0.17%	2.31%	Mar. 07, 2008
Barclays 1-3 Year U.S. Government/Credit Bond Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays 1-3 Year U.S. Government/Credit Bond Index	1.59%	2.73%	Mar. 07, 2008

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Blended Research Small Cap Equity Portfolio (First Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 37% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	37.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in equity securities of issuers with small market capitalizations. MFS generally defines small market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell 2000 Index over the last 13 months at the time of purchase. As of October 31, 2012, the range of the Russell 2000 Index was between $10.4 million and $4.1 billion. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. In selecting investments for the fund, MFS is not constrained to any particular investment style. MFS may invest the fund's assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. MFS may invest the fund's assets in foreign securities. MFS uses a bottom-up approach to buying and selling investments for the fund. Investments are selected based on fundamental analysis of individual issuers and quantitative models that systematically evaluate issuers.
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: 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. Small Cap Risk: The stocks of small cap companies can be more volatile than stocks of larger companies. Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis, its development and use of quantitative models, and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and using a passive investment strategy. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 13.81%. During the period(s) shown in the bar chart, the highest quarterly return was 31.28% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (26.91)% (for the calendar quarter ended December 31, 2008).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Blended Research Small Cap Equity Portfolio (First Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Russell 2000 Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Index
1 Year	rr_AverageAnnualReturnYear01	(4.18%)
5 Years	rr_AverageAnnualReturnYear05	0.15%
10 Years	rr_AverageAnnualReturnYear10	5.62%
MFS Blended Research Small Cap Equity Portfolio (First Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.40%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.51%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	52
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	164
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	285
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	640
Annual Return 2002	rr_AnnualReturn2002	(20.61%)
Annual Return 2003	rr_AnnualReturn2003	41.62%
Annual Return 2004	rr_AnnualReturn2004	18.43%
Annual Return 2005	rr_AnnualReturn2005	4.33%
Annual Return 2006	rr_AnnualReturn2006	13.60%
Annual Return 2007	rr_AnnualReturn2007	(1.44%)
Annual Return 2008	rr_AnnualReturn2008	(37.99%)
Annual Return 2009	rr_AnnualReturn2009	36.77%
Annual Return 2010	rr_AnnualReturn2010	24.46%
Annual Return 2011	rr_AnnualReturn2011	(4.87%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	13.81%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	31.28%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(26.91%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	(4.87%)
5 Years	rr_AverageAnnualReturnYear05	(0.21%)
10 Years	rr_AverageAnnualReturnYear10	4.56%

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS New Discovery Value Portfolio (First Prospectus Summary) | MFS New Discovery Value Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 50% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	50.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests the fund's assets primarily in equity securities. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. MFS focuses on investing the fund's assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies). While MFS may invest the fund's assets in companies of any size, MFS generally focuses on companies with small capitalizations. MFS may invest the fund's assets in foreign securities. 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. Quantitative models that systematically evaluate issuers may also be considered.
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: 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. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. Small Cap Risk: The stocks of small cap companies can be more volatile than stocks of larger companies.    Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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.    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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.    Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012 was 7.42%. During the period(s) shown in the bar chart, the highest quarterly return was 22.44% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (21.49)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS New Discovery Value Portfolio (First Prospectus Summary) | MFS New Discovery Value Portfolio | Russell 2000 Value Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Value Index
1 Year	rr_AverageAnnualReturnYear01	(5.50%)
Since Inception	rr_AverageAnnualReturnSinceInception	1.96%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS New Discovery Value Portfolio (First Prospectus Summary) | MFS New Discovery Value Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.90%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.25%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.15%
Fee Reductions and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.10%)	[1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.05%
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2014-12-31
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	107
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	344
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	612
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,378
Annual Return 2009	rr_AnnualReturn2009	30.52%
Annual Return 2010	rr_AnnualReturn2010	21.62%
Annual Return 2011	rr_AnnualReturn2011	(6.32%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	7.42%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.44%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(21.49%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	(6.32%)
Since Inception	rr_AverageAnnualReturnSinceInception	5.43%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[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), such that "Total Annual Fund Operating Expenses" do not exceed 1.05% of the fund's average daily net assets annually for Initial Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a moderate level of risk relative to the other MFS Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 7% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	7.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was: Bond Funds:                              41% MFS Global Governments Portfolio          5% MFS Government Securities Portfolio      10% MFS High Yield Portfolio                  5% MFS Inflation-Adjusted Bond Portfolio     5% MFS Limited Maturity Portfolio            4% MFS Research Bond Series                 12% Specialty Funds:                          3% MFS Global Real Estate Portfolio          3% International Stock Funds:               13% MFS Emerging Markets Equity Portfolio     0% MFS International Growth Portfolio        3% MFS International Value Portfolio         3% MFS Research International Portfolio      7% U.S. Stock Funds:                        43% MFS Growth Series                         9% MFS Mid Cap Growth Series                 7% MFS Mid Cap Value Portfolio               7% MFS New Discovery Series                1.5% MFS New Discovery Value Portfolio       1.5% MFS Research Series                       8% MFS Value Series                          9%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective. 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. 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, 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. Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. 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. 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. 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 and property tax rates; shifts in 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. 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies.  The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 9.30%. During the period(s) shown in the bar chart, the highest quarterly return was 13.40% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (11.11)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio | Standard & Poor's 500 Stock Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
1 Year	rr_AverageAnnualReturnYear01	2.11%
Since Inception	rr_AverageAnnualReturnSinceInception	4.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio | Dow Jones Moderate U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderate U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	3.32%
Since Inception	rr_AverageAnnualReturnSinceInception	7.54%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio | MFS Moderate Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Moderate Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	2.22%
Since Inception	rr_AverageAnnualReturnSinceInception	5.77%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.04%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.81%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.85%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	87
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	271
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	471
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,049
Annual Return 2009	rr_AnnualReturn2009	23.91%
Annual Return 2010	rr_AnnualReturn2010	12.18%
Annual Return 2011	rr_AnnualReturn2011	(1.56%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	9.30%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	13.40%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(11.11%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	(1.56%)
Since Inception	rr_AverageAnnualReturnSinceInception	6.87%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Moderate Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (41%) Standard & Poor's 500 Stock Index; (13%) MSCI EAFE (Europe, Australasia, Far East) Index; (3%) The Dow Jones-UBS Commodity Index; (2%) FTSE EPRA/NAREIT Developed Real Estate Index; and (41%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
Document Type	dei_DocumentType	485BPOS
Document Period End Date	dei_DocumentPeriodEndDate	Dec. 31, 2011
Registrant Name	dei_EntityRegistrantName	MFS VARIABLE INSURANCE TRUST III
Central Index Key	dei_EntityCentralIndexKey	0001065698
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Dec. 07, 2012
Document Effective Date	dei_DocumentEffectiveDate	Dec. 10, 2012
MFS Blended Research Small Cap Equity Portfolio (First Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCOSX
MFS Blended Research Small Cap Equity Portfolio (Second Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCOMX
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCIMX
MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SIMSX
MFS Global Real Estate Portfolio (First Prospectus Summary) | MFS Global Real Estate Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCREX
MFS Global Real Estate Portfolio (Second Prospectus Summary) | MFS Global Real Estate Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SRESX
MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SIBGX
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SIGSX
MFS Inflation-Adjusted Bond Portfolio (First Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCBIX
MFS Inflation-Adjusted Bond Portfolio (Second Prospectus Summary) | MFS Inflation-Adjusted Bond Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SBISX
MFS Limited Maturity Portfolio (First Prospectus Summary) | MFS Limited Maturity Portfolio | Initial Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SGSSX
MFS Limited Maturity Portfolio (Second Prospectus Summary) | MFS Limited Maturity Portfolio | Service Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SGSDX
MFS Mid Cap Value Portfolio (First Prospectus Summary) | MFS Mid Cap Value Portfolio | Initial Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCGMX
MFS Mid Cap Value Portfolio (Second Prospectus Summary) | MFS Mid Cap Value Portfolio | Service Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SGMCX
MFS Moderate Allocation Portfolio (First Prospectus Summary) | MFS Moderate Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCIBX
MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SIBSX
MFS New Discovery Value Portfolio (First Prospectus Summary) | MFS New Discovery Value Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SCDSX
MFS New Discovery Value Portfolio (Second Prospectus Summary) | MFS New Discovery Value Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Trading Symbol	dei_TradingSymbol	SDSSX

XML

MFS Mid Cap Value Portfolio (Second Prospectus Summary) | MFS Mid Cap Value Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Mid Cap Value Portfolio Service Class shares
Management Fee	0.75%
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.08%
Total Annual Fund Operating Expenses	1.08%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Mid Cap Value Portfolio Service Class shares	110	343	595	1,317

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. 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 50% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in issuers with medium
market capitalizations. MFS generally defines medium market capitalization
issuers as issuers with market capitalizations similar to those of issuers
included in the Russell Midcap Value Index over the last 13 months at the time
of purchase. As of October 31, 2012, the range of the Russell Midcap Value Index
was between $26.1 million and $18.7 billion.

MFS normally invests the fund's assets primarily in equity securities. Equity
securities include common stocks, preferred stocks, securities convertible into
stocks, and depositary receipts for such securities.

MFS focuses on investing the fund's assets in the stocks of companies it
believes are undervalued compared to their perceived worth (value companies).

MFS may invest the fund's assets in foreign securities.

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. Quantitative models that systematically evaluate issuers may
also be considered.

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:

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.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

Mid Cap Risk: The stocks of mid cap companies can be more volatile than stocks
of larger companies.

Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's past
performance does not necessarily indicate how the fund will perform in the future.
Updated performance is available at mfs.com or by calling 1-877-411-3325. If the
fees and expenses imposed by the investment vehicle through which an investment in
the fund is made were included, they would reduce the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 13.62%.
During the period(s) shown in the bar chart, the highest quarterly return was
22.50% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (17.29)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Mid Cap Value Portfolio	Label	1 Year	Since Inception	Inception Date
Service Class shares	Service Class Shares	2.34%	2.26%	Mar. 07, 2008
Russell Midcap Value Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell Midcap Value Index	(1.38%)	3.25%	Mar. 07, 2008

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a conservative level of risk relative to the other MFS Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 7% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	7.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher.    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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure.    As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was:    Bond Funds:                             62% MFS Global Governments Portfolio         8% MFS Government Securities Portfolio     10% MFS High Yield Portfolio                 5% MFS Inflation-Adjusted Bond Portfolio   10% MFS Limited Maturity Portfolio          12% MFS Research Bond Series                17% Specialty Funds:                         2% MFS Global Real Estate Portfolio         2% International Stock Funds:               8% MFS Emerging Markets Equity Portfolio    0% MFS International Growth Portfolio       2% MFS International Value Portfolio        2% MFS Research International Portfolio     4% U.S. Stock Funds:                       28% MFS Growth Series                        6% MFS Mid Cap Growth Series                4% MFS Mid Cap Value Portfolio              4% MFS New Discovery Series                 1% MFS New Discovery Value Portfolio        1% MFS Research Series                      6% MFS Value Series                         6%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective.    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. 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, 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.    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.    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 and property tax rates; shifts in 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.    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.    Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general.    Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than 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.    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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.    Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 8.07%. During the period(s) shown in the bar chart, the highest quarterly return was 9.66% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (7.39)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index because MFS believes the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index because MFS believes the Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio | Barclays U.S. Aggregate Bond Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index
1 Year	rr_AverageAnnualReturnYear01	7.84%
Since Inception	rr_AverageAnnualReturnSinceInception	7.68%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio | Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	5.07%
Since Inception	rr_AverageAnnualReturnSinceInception	7.76%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio | MFS Conservative Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Conservative Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	4.58%
Since Inception	rr_AverageAnnualReturnSinceInception	6.52%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio | Initial Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.05%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.74%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.79%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	81
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	252
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	439
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	978
Annual Return 2009	rr_AnnualReturn2009	19.37%
Annual Return 2010	rr_AnnualReturn2010	9.92%
Annual Return 2011	rr_AnnualReturn2011	0.97%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	8.07%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	9.66%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(7.39%)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
1 Year	rr_AverageAnnualReturnYear01	0.97%
Since Inception	rr_AverageAnnualReturnSinceInception	6.24%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (28%) Standard & Poor's 500 Stock Index; (8%) MSCI EAFE (Europe, Australasia, Far East) Index; (1%) The Dow Jones-UBS Commodity Index; (1%) FTSE EPRA/NAREIT Developed Real Estate Index; and (62%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

XML

Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Blended Research Small Cap Equity Portfolio (Second Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 37% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	37.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in equity securities of issuers with small market capitalizations. MFS generally defines small market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell 2000 Index over the last 13 months at the time of purchase. As of October 31, 2012, the range of the Russell 2000 Index was between $10.4 million and $4.1 billion. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. In selecting investments for the fund, MFS is not constrained to any particular investment style. MFS may invest the fund's assets in the stocks of companies it believes to have above average earnings growth potential compared to other companies (growth companies), in the stocks of companies it believes are undervalued compared to their perceived worth (value companies), or in a combination of growth and value companies. MFS may invest the fund's assets in foreign securities. MFS uses a bottom-up approach to buying and selling investments for the fund. Investments are selected based on fundamental analysis of individual issuers and quantitative models that systematically evaluate issuers.
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: 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. Small Cap Risk: The stocks of small cap companies can be more volatile than stocks of larger companies. Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis, its development and use of quantitative models, and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and using a passive investment strategy. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 13.54%. During the period(s) shown in the bar chart, the highest quarterly return was 31.20% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (26.91)% (for the calendar quarter ended December 31, 2008).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Blended Research Small Cap Equity Portfolio (Second Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Russell 2000 Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Index
1 Year	rr_AverageAnnualReturnYear01	(4.18%)
5 Years	rr_AverageAnnualReturnYear05	0.15%
10 Years	rr_AverageAnnualReturnYear10	5.62%
MFS Blended Research Small Cap Equity Portfolio (Second Prospectus Summary) | MFS Blended Research Small Cap Equity Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.40%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.11%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.76%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	78
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	243
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	422
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	942
Annual Return 2007	rr_AnnualReturn2007	(2.11%)
Annual Return 2008	rr_AnnualReturn2008	(38.14%)
Annual Return 2009	rr_AnnualReturn2009	36.50%
Annual Return 2010	rr_AnnualReturn2010	24.07%
Annual Return 2011	rr_AnnualReturn2011	(5.09%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	13.54%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	31.20%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(26.91%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	(5.09%)
5 Years	rr_AverageAnnualReturnYear05	(0.54%)
10 Years	rr_AverageAnnualReturnYear10	4.25%

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MFS Conservative Allocation Portfolio (First Prospectus Summary) | MFS Conservative Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a conservative level of risk relative to the other MFS Asset
Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS
Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS
Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Conservative Allocation Portfolio Initial Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.05%
Acquired (Underlying) Fund Fees and Expenses	0.74%
Total Annual Fund Operating Expenses	0.79%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.
  
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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Conservative Allocation Portfolio Initial Class	81	252	439	978

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. 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 7% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes
by investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.
  
As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:
  
Bond Funds:                             62%
MFS Global Governments Portfolio         8%
MFS Government Securities Portfolio     10%
MFS High Yield Portfolio                 5%
MFS Inflation-Adjusted Bond Portfolio   10%
MFS Limited Maturity Portfolio          12%
MFS Research Bond Series                17%
Specialty Funds:                         2%
MFS Global Real Estate Portfolio         2%
International Stock Funds:               8%
MFS Emerging Markets Equity Portfolio    0%
MFS International Growth Portfolio       2%
MFS International Value Portfolio        2%
MFS Research International Portfolio     4%
U.S. Stock Funds:                       28%
MFS Growth Series                        6%
MFS Mid Cap Growth Series                4%
MFS Mid Cap Value Portfolio              4%
MFS New Discovery Series                 1%
MFS New Discovery Value Portfolio        1%
MFS Research Series                      6%
MFS Value Series                         6%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.
  
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.

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, 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.
  
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.
  
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 and property tax rates; shifts in 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.
  
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.
  
Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.
  
Value Company Risk: The stocks of value companies can continue to be
undervalued for long periods of time and not realize their expected value
and can be more volatile than 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.
  
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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.
  
Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 8.07%.
During the period(s) shown in the bar chart, the highest quarterly return was
9.66% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (7.39)% (for the calendar quarter ended September 30,
2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Conservative Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Initial Class	Initial Class Shares		0.97%	6.24%	Oct. 01, 2008
Barclays U.S. Aggregate Bond Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index		7.84%	7.68%	Oct. 01, 2008
Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index		5.07%	7.76%	Oct. 01, 2008
MFS Conservative Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Conservative Allocation Fund Blended Index	[1]	4.58%	6.52%	Oct. 01, 2008

Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS
Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately
Conservative U.S. Relative Risk Portfolio Index because MFS believes the
Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund
Blended Index better reflect the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (28%) Standard & Poor's 500 Stock Index; (8%) MSCI EAFE (Europe, Australasia, Far East) Index; (1%) The Dow Jones-UBS Commodity Index; (1%) FTSE EPRA/NAREIT Developed Real Estate Index; and (62%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

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Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Mid Cap Value Portfolio (Second Prospectus Summary) | MFS Mid Cap Value Portfolio
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 capital appreciation.
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 50% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	50.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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) normally invests at least 80% of the fund's net assets in issuers with medium market capitalizations. MFS generally defines medium market capitalization issuers as issuers with market capitalizations similar to those of issuers included in the Russell Midcap Value Index over the last 13 months at the time of purchase. As of October 31, 2012, the range of the Russell Midcap Value Index was between $26.1 million and $18.7 billion. MFS normally invests the fund's assets primarily in equity securities. Equity securities include common stocks, preferred stocks, securities convertible into stocks, and depositary receipts for such securities. MFS focuses on investing the fund's assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies). MFS may invest the fund's assets in foreign securities. 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. Quantitative models that systematically evaluate issuers may also be considered.
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: 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. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. Mid Cap Risk: The stocks of mid cap companies can be more volatile than stocks of larger companies. Foreign Risk: Exposure to foreign 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. Investment Selection Risk: MFS' investment analysis and its selection of investments 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 13.62%. During the period(s) shown in the bar chart, the highest quarterly return was 22.50% (for the calendar quarter ended September 30, 2009) and the lowest quarterly return was (17.29)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Mid Cap Value Portfolio (Second Prospectus Summary) | MFS Mid Cap Value Portfolio | Russell Midcap Value Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell Midcap Value Index
1 Year	rr_AverageAnnualReturnYear01	(1.38%)
Since Inception	rr_AverageAnnualReturnSinceInception	3.25%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008
MFS Mid Cap Value Portfolio (Second Prospectus Summary) | MFS Mid Cap Value Portfolio | Service Class shares
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.75%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.08%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.08%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	110
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	343
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	595
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,317
Annual Return 2009	rr_AnnualReturn2009	25.38%
Annual Return 2010	rr_AnnualReturn2010	21.62%
Annual Return 2011	rr_AnnualReturn2011	2.34%
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	13.62%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.50%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(17.29%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	2.34%
Since Inception	rr_AverageAnnualReturnSinceInception	2.26%
Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 07, 2008

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MFS Moderate Allocation Portfolio (Second Prospectus Summary) | MFS Moderate Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a moderate level of risk relative to the other MFS Asset
Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS
Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS
Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Moderate Allocation Portfolio Service Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.04%
Acquired (Underlying) Fund Fees and Expenses	0.81%
Total Annual Fund Operating Expenses	1.10%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Moderate Allocation Portfolio Service Class	112	350	606	1,340

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. 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 7% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes
by investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.

As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:

Bond Funds:                              41%
MFS Global Governments Portfolio          5%
MFS Government Securities Portfolio      10%
MFS High Yield Portfolio                  5%
MFS Inflation-Adjusted Bond Portfolio     5%
MFS Limited Maturity Portfolio            4%
MFS Research Bond Series                 12%
Specialty Funds:                          3%
MFS Global Real Estate Portfolio          3%
International Stock Funds:               13%
MFS Emerging Markets Equity Portfolio     0%
MFS International Growth Portfolio        3%
MFS International Value Portfolio         3%
MFS Research International Portfolio      7%
U.S. Stock Funds:                        43%
MFS Growth Series                         9%
MFS Mid Cap Growth Series                 7%
MFS Mid Cap Value Portfolio               7%
MFS New Discovery Series                1.5%
MFS New Discovery Value Portfolio       1.5%
MFS Research Series                       8%
MFS Value Series                          9%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.

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.

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, 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.

Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

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.

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.

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 and property tax rates; shifts in 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.

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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 9.13%.
During the period(s) shown in the bar chart, the highest quarterly return was
13.43% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (11.20)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Moderate Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Service Class	Service Class Shares		(1.81%)	6.58%	Oct. 01, 2008
Standard & Poor's 500 Stock Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index		2.11%	4.65%	Oct. 01, 2008
Dow Jones Moderate U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderate U.S. Relative Risk Portfolio Index		3.32%	7.54%	Oct. 01, 2008
MFS Moderate Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Moderate Allocation Fund Blended Index	[1]	2.22%	5.77%	Oct. 01, 2008

Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS
Moderate Allocation Fund Blended Index replaced the Dow Jones Moderate U.S.
Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500
Stock Index and the MFS Moderate Allocation Fund Blended Index better reflect
the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Moderate Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (41%) Standard & Poor's 500 Stock Index; (13%) MSCI EAFE (Europe, Australasia, Far East) Index; (3%) The Dow Jones-UBS Commodity Index; (2%) FTSE EPRA/NAREIT Developed Real Estate Index; and (41%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

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MFS Global Real Estate Portfolio (First Prospectus Summary) | MFS Global Real Estate Portfolio

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 hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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 Real Estate Portfolio Initial Class
Management Fee		0.90%
Distribution and/or Service (12b-1) Fees		none
Other Expenses		0.10%
Total Annual Fund Operating Expenses		1.00%
Fee Reductions and/or Expense Reimbursements	[1]	(0.05%)
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements		0.95%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Global Real Estate Portfolio Initial Class	97	308	542	1,215

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. 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 27% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in U.S. and foreign
real estate-related investments.

MFS normally invests the fund's assets primarily in equity securities.

MFS generally focuses the fund's investments in equity real estate investment
trusts ("REITs") as well as similar entities formed under the laws of non-U.S.
countries, but may also invest in mortgage REITs, hybrid REITs and other U.S.
and foreign real estate-related investments, including emerging market real
estate-related investments.

MFS may invest the fund's assets in real estate-related investments of any
size.  However, issuers of real estate-related investments tend to be
small-to-medium-sized.

MFS typically allocates the fund's investments across various geographic areas,
REIT managers and property types, but may from time to time focus the fund's
investments in any one or a few of these areas.

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.

MFS selects investments by analyzing the fundamental and relative values of
potential investments.

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:

Real Estate-Related Investment Risk: The fund's performance will be closely
tied to the performance of real estate-related investments and as a result, can
be more volatile than the performance of more broadly-diversified funds. The
risks of investing in real estate-related investments 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 and property tax rates; shifts in
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.

Small to Medium Cap Risk: 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.

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.

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, 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.
  
The fund's past performance does not necessarily indicate how the fund will
perform in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle through
which an investment in the fund is made were included, they would reduce the returns
shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 21.23%.
During the period(s) shown in the bar chart, the highest quarterly return was
34.82% (for the calendar quarter ended June 30, 2009) and the lowest quarterly
return was (39.05)% (for the calendar quarter ended December 31, 2008).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Global Real Estate Portfolio	Label	1 Year	5 Years	10 Years
Initial Class	Initial Class Shares	(7.59%)	(7.82%)	6.70%
FTSE EPRA/NAREIT Developed Real Estate Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) FTSE EPRA/NAREIT Developed Real Estate Index	(5.82%)	(5.28%)	9.50%

[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), such that "Total Annual Fund Operating Expenses" do not exceed 0.95% of the fund's average daily net assets annually for Initial Class shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2014.

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Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 10, 2012
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio
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 investment objective of the fund is to seek a high level of total return consistent with a greater than moderate level of risk relative to the other MFS Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS Growth Allocation Portfolio.)
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 hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
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):
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. 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 16% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	16.00%
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. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. 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; 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	The fund is designed to provide diversification among different asset classes by investing its assets in other mutual funds advised by MFS (Massachusetts Financial Services Company, the fund's investment adviser), referred to as underlying funds. The underlying funds are selected following a two stage asset allocation process. The first stage is a strategic asset allocation to determine the percentage of the fund's assets to be invested in the general asset classes of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an allocation to underlying funds that have less traditional investment strategies that MFS believes provide diversification benefits when added to a portfolio consisting of stock and bond funds (referred to as Specialty Funds) based on the risk/return potential of the different asset classes and the risk profile of the fund. The second stage involves the actual selection of underlying funds to represent the asset classes based on underlying fund classifications, historical risk, performance, and other factors. Within the stock fund allocations, MFS seeks to diversify globally (by including domestic and international underlying funds), in terms of market capitalization (by including large, mid, and small capitalization underlying funds), and by style (by including both growth and value underlying funds). Within the bond fund allocation, MFS includes underlying funds with varying degrees of interest rate and credit exposure. As of December 10, 2012, the fund's target allocation among asset classes and the underlying funds was: Bond Funds:                             21% MFS Global Governments Portfolio         4% MFS Government Securities Portfolio      0% MFS High Yield Portfolio                 5% MFS Inflation-Adjusted Bond Portfolio    5% MFS Limited Maturity Portfolio           2% MFS Research Bond Series                 5% Specialty Funds:                         5% MFS Global Real Estate Portfolio         5% International Stock Funds:              20% MFS Emerging Markets Equity Portfolio    1% MFS International Growth Portfolio       5% MFS International Value Portfolio        5% MFS Research International Portfolio     9% U.S. Stock Funds:                       54% MFS Growth Series                       11% MFS Mid Cap Growth Series                9% MFS Mid Cap Value Portfolio              9% MFS New Discovery Series                 2% MFS New Discovery Value Portfolio        2% MFS Research Series                     10% MFS Value Series                        11%
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, and its assessment of the risk/return potential of asset classes 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. Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes the fund to the risks of the underlying funds. Each underlying fund pursues its own investment objective and strategies and may not achieve its objective. 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. 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, 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.    Growth Company Risk: The stocks of growth companies can be more sensitive to the company's earnings and more volatile than the market in general. Value Company Risk: The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general. 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. 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. 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 and property tax rates; shifts in 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. 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. 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 below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. The fund's past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Service Class Bar Chart.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the nine-month period ended September 30, 2012, was 10.59%.  During the period(s) shown in the bar chart, the highest quarterly return was 16.75% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (14.69)% (for the calendar quarter ended September 30, 2011).
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index better reflect the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	Reflects no deduction for fees, expenses or taxes
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index because MFS believes the Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended Index better reflect the fund's current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2011)
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio | Standard & Poor's 500 Stock Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
1 Year	rr_AverageAnnualReturnYear01	2.11%
Since Inception	rr_AverageAnnualReturnSinceInception	4.65%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio | Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index
1 Year	rr_AverageAnnualReturnYear01	1.45%
Since Inception	rr_AverageAnnualReturnSinceInception	7.04%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio | MFS Growth Allocation Fund Blended Index
Risk Return [Abstract]	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Growth Allocation Fund Blended Index	[1]
1 Year	rr_AverageAnnualReturnYear01	(0.24%)
Since Inception	rr_AverageAnnualReturnSinceInception	4.79%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
MFS Growth Allocation Portfolio (Second Prospectus Summary) | MFS Growth Allocation Portfolio | Service Class
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	none
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.06%
Acquired (Underlying) Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.88%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.19%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	121
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	378
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	654
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	1,443
Annual Return 2009	rr_AnnualReturn2009	26.75%
Annual Return 2010	rr_AnnualReturn2010	13.61%
Annual Return 2011	rr_AnnualReturn2011	(3.90%)
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Sep. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	10.59%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	16.75%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(14.69%)
Label	rr_AverageAnnualReturnLabel	Service Class Shares
1 Year	rr_AverageAnnualReturnYear01	(3.90%)
Since Inception	rr_AverageAnnualReturnSinceInception	6.51%
Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

[1] As of December 31, 2011, the MFS Growth Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (52%) Standard & Poor's 500 Stock Index; (20%) MSCI EAFE (Europe, Australasia, Far East) Index; (4%); The Dow Jones-UBS Commodity Index; (3%) FTSE EPRA/NAREIT Developed Real Estate Index; and (21%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

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MFS Mid Cap Value Portfolio (First Prospectus Summary) | MFS Mid Cap Value Portfolio

Summary of Key Information

Investment Objective

The fund's investment objective is to seek capital appreciation.

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Mid Cap Value Portfolio Initial Class shares
Management Fee	0.75%
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.08%
Total Annual Fund Operating Expenses	0.83%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Mid Cap Value Portfolio Initial Class shares	85	265	460	1,025

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. 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 50% of the average value of its portfolio.

Principal Investment Strategies

MFS (Massachusetts Financial Services Company, the fund's investment adviser)
normally invests at least 80% of the fund's net assets in issuers with medium
market capitalizations. MFS generally defines medium market capitalization
issuers as issuers with market capitalizations similar to those of issuers
included in the Russell Midcap Value Index over the last 13 months at the time
of purchase. As of October 31, 2012, the range of the Russell Midcap Value Index
was between $26.1 million and $18.7 billion.

MFS normally invests the fund's assets primarily in equity securities. Equity
securities include common stocks, preferred stocks, securities convertible into
stocks, and depositary receipts for such securities.

MFS focuses on investing the fund's assets in the stocks of companies it
believes are undervalued compared to their perceived worth (value companies).

MFS may invest the fund's assets in foreign securities.

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. Quantitative models that systematically evaluate issuers may
also be considered.

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:

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.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than the market in general.

Mid Cap Risk: The stocks of mid cap companies can be more volatile than stocks
of larger companies.

Foreign Risk: Exposure to foreign 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.

Investment Selection Risk: MFS' investment analysis and its selection of
investments 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 13.85%.
During the period(s) shown in the bar chart, the highest quarterly return was
22.59% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (17.30)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Mid Cap Value Portfolio	Label	1 Year	Since Inception	Inception Date
Initial Class shares	Initial Class Shares	2.47%	2.53%	Mar. 07, 2008
Russell Midcap Value Index	Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell Midcap Value Index	(1.38%)	3.25%	Mar. 07, 2008

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MFS Growth Allocation Portfolio (First Prospectus Summary) | MFS Growth Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a greater than moderate level of risk relative to the other MFS
Asset Allocation Portfolios. (The MFS Asset Allocation Portfolios currently are
MFS Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and
MFS Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your
expenses would be higher.

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

Annual Fund Operating Expenses	MFS Growth Allocation Portfolio Initial Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	none
Other Expenses	0.06%
Acquired (Underlying) Fund Fees and Expenses	0.88%
Total Annual Fund Operating Expenses	0.94%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Growth Allocation Portfolio Initial Class	96	300	520	1,155

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. 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 16% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes
by investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.

As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:

Bond Funds:                             21%
MFS Global Governments Portfolio         4%
MFS Government Securities Portfolio      0%
MFS High Yield Portfolio                 5%
MFS Inflation-Adjusted Bond Portfolio    5%
MFS Limited Maturity Portfolio           2%
MFS Research Bond Series                 5%
Specialty Funds:                         5%
MFS Global Real Estate Portfolio         5%
International Stock Funds:              20%
MFS Emerging Markets Equity Portfolio    1%
MFS International Growth Portfolio       5%
MFS International Value Portfolio        5%
MFS Research International Portfolio     9%
U.S. Stock Funds:                       54%
MFS Growth Series                       11%
MFS Mid Cap Growth Series                9%
MFS Mid Cap Value Portfolio              9%
MFS New Discovery Series                 2%
MFS New Discovery Value Portfolio        2%
MFS Research Series                     10%
MFS Value Series                        11%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.

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.

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, 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.

Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.

Value Company Risk: The stocks of value companies can continue to be
undervalued for long periods of time and not realize their expected value
and can be more volatile than the market in general.
  
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
nstruments.

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.

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 and property tax rates; shifts in 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.

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.

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 below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another
adviser or subadviser was responsible for selecting investments for the fund
under a different investment objective and different investment strategies. The
fund's past performance does not necessarily indicate how the fund will perform
in the future. Updated performance is available at mfs.com or by calling
1-877-411-3325. If the fees and expenses imposed by the investment vehicle
through which an investment in the fund is made were included, they would reduce
the returns shown.

Initial Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was
10.87%.  During the period(s) shown in the bar chart, the highest quarterly
return was 16.85% (for the calendar quarter ended June 30, 2009) and the lowest
quarterly return was (14.70)% (for the calendar quarter ended September 30,
2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Growth Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Initial Class	Initial Class Shares		(3.66%)	6.75%	Oct. 01, 2008
Standard & Poor's 500 Stock Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index		2.11%	4.65%	Oct. 01, 2008
Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, Dow Jones Moderately Aggressive U.S. Relative Risk Portfolio Index		1.45%	7.04%	Oct. 01, 2008
MFS Growth Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Growth Allocation Fund Blended Index	[1]	(0.24%)	4.79%	Oct. 01, 2008

Effective December 8, 2012, the Standard & Poor's 500 Stock Index and the
MFS Growth Allocation Fund Blended Index replaced the Dow Jones Moderately
Aggressive U.S. Relative Risk Portfolio Index because MFS believes the
Standard & Poor's 500 Stock Index and the MFS Growth Allocation Fund Blended
Index better reflect the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Growth Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (52%) Standard & Poor's 500 Stock Index; (20%) MSCI EAFE (Europe, Australasia, Far East) Index; (4%); The Dow Jones-UBS Commodity Index; (3%) FTSE EPRA/NAREIT Developed Real Estate Index; and (21%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.

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MFS Conservative Allocation Portfolio (Second Prospectus Summary) | MFS Conservative Allocation Portfolio

Summary of Key Information

Investment Objective

The investment objective of the fund is to seek a high level of total return
consistent with a conservative level of risk relative to the other MFS Asset
Allocation Portfolios.  (The MFS Asset Allocation Portfolios currently are MFS
Conservative Allocation Portfolio, MFS Moderate Allocation Portfolio, and MFS
Growth Allocation Portfolio.)

Fees and Expenses

This table describes the fees and expenses that you may pay when you hold shares
of the fund. Expenses have been adjusted to reflect current fee arrangements and
the management fee set forth in the fund's Investment Advisory Agreement with
MFS. If the fees and expenses imposed by the insurance company that issued your
variable contracts through which the fund is offered were included, your expenses
would be higher.

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

Annual Fund Operating Expenses	MFS Conservative Allocation Portfolio Service Class
Management Fee	none
Distribution and/or Service (12b-1) Fees	0.25%
Other Expenses	0.05%
Acquired (Underlying) Fund Fees and Expenses	0.74%
Total Annual Fund Operating Expenses	1.04%

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. If the fees and expenses
imposed by the investment vehicle through which an investment in the fund is
made were included, your expenses would be higher.

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; 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 (USD $)	Expense Example, with Redemption, 1 Year	Expense Example, with Redemption, 3 Years	Expense Example, with Redemption, 5 Years	Expense Example, with Redemption, 10 Years
MFS Conservative Allocation Portfolio Service Class	106	331	574	1,271

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. 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 7% of the average value of its portfolio.

Principal Investment Strategies

The fund is designed to provide diversification among different asset classes
by investing its assets in other mutual funds advised by MFS (Massachusetts
Financial Services Company, the fund's investment adviser), referred to as
underlying funds. The underlying funds are selected following a two stage asset
allocation process. The first stage is a strategic asset allocation to determine
the percentage of the fund's assets to be invested in the general asset classes
of Bond Funds, International Stock Funds, and U.S. Stock Funds, as well as an
allocation to underlying funds that have less traditional investment strategies
that MFS believes provide diversification benefits when added to a portfolio
consisting of stock and bond funds (referred to as Specialty Funds) based on the
risk/return potential of the different asset classes and the risk profile of the
fund. The second stage involves the actual selection of underlying funds to
represent the asset classes based on underlying fund classifications, historical
risk, performance, and other factors. Within the stock fund allocations, MFS
seeks to diversify globally (by including domestic and international underlying
funds), in terms of market capitalization (by including large, mid, and small
capitalization underlying funds), and by style (by including both growth and
value underlying funds). Within the bond fund allocation, MFS includes
underlying funds with varying degrees of interest rate and credit exposure.

As of December 10, 2012, the fund's target allocation among asset classes and
the underlying funds was:

Bond Funds:                             62%
MFS Global Governments Portfolio         8%
MFS Government Securities Portfolio     10%
MFS High Yield Portfolio                 5%
MFS Inflation-Adjusted Bond Portfolio   10%
MFS Limited Maturity Portfolio          12%
MFS Research Bond Series                17%
Specialty Funds:                         2%
MFS Global Real Estate Portfolio         2%
International Stock Funds:               8%
MFS Emerging Markets Equity Portfolio    0%
MFS International Growth Portfolio       2%
MFS International Value Portfolio        2%
MFS Research International Portfolio     4%
U.S. Stock Funds:                       28%
MFS Growth Series                        6%
MFS Mid Cap Growth Series                4%
MFS Mid Cap Value Portfolio              4%
MFS New Discovery Series                 1%
MFS New Discovery Value Portfolio        1%
MFS Research Series                      6%
MFS Value Series                         6%

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, and its assessment of the risk/return potential of
asset classes 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.

Underlying Funds Risk: MFS' strategy of investing in underlying funds exposes
the fund to the risks of the underlying funds. Each underlying fund pursues its
own investment objective and strategies and may not achieve its objective.

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.

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, 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.

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.

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 and property tax rates; shifts in 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.

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.

Growth Company Risk: The stocks of growth companies can be more sensitive to
the company's earnings and more volatile than the market in general.

Value Company Risk: The stocks of value companies can continue to be undervalued
for long periods of time and not realize their expected value and can be more
volatile than 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.

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 below are intended to provide some indication
of the risks of investing in the fund by showing changes in the fund's performance
over time and how the fund's performance over time compares with that of a broad
measure of market performance.

Performance prior to December 8, 2012, reflects time periods when another adviser
or subadviser was responsible for selecting investments for the fund under a
different investment objective and different investment strategies. The fund's
past performance does not necessarily indicate how the fund will perform in the
future. Updated performance is available at mfs.com or by calling 1-877-411-3325.
If the fees and expenses imposed by the investment vehicle through which an
investment in the fund is made were included, they would reduce the returns shown.

Service Class Bar Chart.

The total return for the nine-month period ended September 30, 2012, was 7.89%.
During the period(s) shown in the bar chart, the highest quarterly return was
9.51% (for the calendar quarter ended September 30, 2009) and the lowest
quarterly return was (7.38)% (for the calendar quarter ended September 30, 2011).

Performance Table.

Average Annual Total Returns (for the Periods Ended December 31, 2011)

Average Annual Total Returns MFS Conservative Allocation Portfolio	Label		1 Year	Since Inception	Inception Date
Service Class	Service Class Shares		0.63%	5.97%	Oct. 01, 2008
Barclays U.S. Aggregate Bond Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index		7.84%	7.68%	Oct. 01, 2008
Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Dow Jones Moderately Conservative U.S. Relative Risk Portfolio Index		5.07%	7.76%	Oct. 01, 2008
MFS Conservative Allocation Fund Blended Index	Index Comparisons (Reflects no deduction for fees expenses or taxes) MFS Conservative Allocation Fund Blended Index	[1]	4.58%	6.52%	Oct. 01, 2008

Effective December 8, 2012, the Barclays U.S. Aggregate Bond Index and the MFS
Conservative Allocation Fund Blended Index replaced the Dow Jones Moderately
Conservative U.S. Relative Risk Portfolio Index because MFS believes the
Barclays U.S. Aggregate Bond Index and the MFS Conservative Allocation Fund
Blended Index better reflect the fund's current investment strategies.

[1] As of December 31, 2011, the MFS Conservative Allocation Fund Blended Index (the "Blended Index") consisted of the following indices and weightings: (28%) Standard & Poor's 500 Stock Index; (8%) MSCI EAFE (Europe, Australasia, Far East) Index; (1%) The Dow Jones-UBS Commodity Index; (1%) FTSE EPRA/NAREIT Developed Real Estate Index; and (62%) Barclays U.S. Aggregate Bond Index. The underlying indices and weightings of the Blended Index may have differed during the period, and may differ in the future.