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Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MFS Total Return Series 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.  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):
Management Fee rr_ManagementFeesOverAssets 0.75%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.05%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.80%
Fee Reductions and /or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.03%) [1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.77%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 2014-04-30
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 22% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 22.00%
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:
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 79
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 252
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 441
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 987
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

MFS (Massachusetts Financial Services Company, the fund’s investment adviser) invests the fund’s assets in equity securities and debt instruments. Equity securities include common stocks, preferred stocks, securities convertible into stocks, equity interests in real estate investment trusts (REITs), and depositary receipts for such securities. 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. MFS seeks to invest between 40% and 75% of the fund’s assets in equity securities and at least 25% of the fund’s assets in fixed-income senior 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 large capitalizations.


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


Of the fund’s investments in debt instruments, MFS generally invests substantially all of these investments in investment grade debt instruments.


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 uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers and instruments. Quantitative models that systematically evaluate issuers and instruments may also be considered.

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.


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, and other conditions.


Foreign Risk:  Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and 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.


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 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 and one or more other measures of performance for markets in which the fund may invest.


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 and one or more other measures of performance for markets in which the fund may invest.
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.
Annual Return 2003 rr_AnnualReturn2003 16.32%
Annual Return 2004 rr_AnnualReturn2004 11.32%
Annual Return 2005 rr_AnnualReturn2005 2.82%
Annual Return 2006 rr_AnnualReturn2006 11.95%
Annual Return 2007 rr_AnnualReturn2007 4.17%
Annual Return 2008 rr_AnnualReturn2008 (22.13%)
Annual Return 2009 rr_AnnualReturn2009 18.03%
Annual Return 2010 rr_AnnualReturn2010 9.93%
Annual Return 2011 rr_AnnualReturn2011 1.77%
Annual Return 2012 rr_AnnualReturn2012 11.26%
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

The total return for the three-month period ended March 31, 2013 was 7.23%. During the period(s) shown in the bar chart, the highest quarterly return was 11.56% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (11.94)% (for the calendar quarter ended December 31, 2008).

Year to Date Return, Label rr_YearToDateReturnLabel The total return for the three-month period ended
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2013
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 11.56%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (11.94%)
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, 2012)
Label rr_AverageAnnualReturnLabel Initial Class Shares
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.26%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.73%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.91%
Standard & Poor’s 500 Stock Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.00%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.66%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 7.10%
Barclays U.S. Aggregate Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Aggregate Bond Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 4.21%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.95%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.18%
MFS Total Return Blended Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) MFS Total Return Blended Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.31% [2]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.81% [2]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.62% [2]
[1] Massachusetts Financial Services Company has agreed in writing to reduce its management fee to 0.70% of the fund's average daily net assets annually in excess of $1 billion and 0.65% of the fund's average daily net assets annually in excess of $2.5 billion to $3 billion. This written agreement will remain in effect until modified by the fund's Board of Trustees, but such agreement will continue until at least April 30, 2014.
[2] As of December 31, 2012, the MFS Total Return Blended Index (the "Blended Index") consisted of the following indices and weightings: 60% Standard & Poor's 500 Stock Index and 40% Barclays U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the period, and may differ in the future.