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Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MFS Technology Portfolio 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.  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 0.46%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.21%
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 1.16%
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 62% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 62.00%
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 $ 118
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 379
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 660
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,462
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 securities of issuers principally engaged in offering, using or developing products, processes, or services that will provide or will benefit significantly from technological advances and improvements. These issuers are in such fields as computer systems and software, networking and telecommunications, internet, business services, and electronics.


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) or the stocks of companies it believes are undervalued compared to their perceived worth (value companies). However, companies that benefit from technological advancements and improvements often are growth companies.


MFS normally invests the fund’s assets primarily in U.S. and foreign equity securities, including emerging market equity securities. 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.


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.


MFS may invest the fund’s assets in companies of any size.


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. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.


MFS may enter into short sales.


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.

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 securities of issuers principally engaged in offering, using or developing products, processes, or services that will provide or will benefit significantly from technological advances and improvements. These issuers are in such fields as computer systems and software, networking and telecommunications, internet, business services, and electronics.
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.


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.


Technology Concentration Risk:  The fund’s performance will be closely tied to the performance of technology issuers and, as a result, can be more volatile than the performance of more broadly-diversified funds. The price of stocks in the technology sector can be very volatile due to the rapid pace of product change, technological developments, and other factors.


Short Sale Risk:  A security sold short is closed out at a loss if the price of the security sold short increases between the time of the short sale and closing out the short position. It may not be possible to close out a short position at any particular time or at an acceptable price. Short sales can involve leverage. Investing the proceeds from short sale positions in other securities subjects the fund to the risks of the securities purchased with the proceeds in addition to the risks of the securities sold short.


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


Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially emerging 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. 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, industry, political, regulatory, geopolitical, and 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, and 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.


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.


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 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 45.39%
Annual Return 2004 rr_AnnualReturn2004 2.44%
Annual Return 2005 rr_AnnualReturn2005 6.19%
Annual Return 2006 rr_AnnualReturn2006 21.97%
Annual Return 2007 rr_AnnualReturn2007 20.22%
Annual Return 2008 rr_AnnualReturn2008 (50.92%)
Annual Return 2009 rr_AnnualReturn2009 76.64%
Annual Return 2010 rr_AnnualReturn2010 20.63%
Annual Return 2011 rr_AnnualReturn2011 1.17%
Annual Return 2012 rr_AnnualReturn2012 14.60%
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

The total return for the three-month period ended March 31, 2013 was 6.05%. During the period(s) shown in the bar chart, the highest quarterly return was 25.71% (for the calendar quarter ended June 30, 2009) and the lowest quarterly return was (32.70)% (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 6.05%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 25.71%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (32.70%)
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 14.60%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.93%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 10.89%
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%
Standard & Poor’s North American Technology Sector Index
  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's North American Technology Sector Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.23%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.54%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 9.40%
[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 1.00% 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 April 30, 2014.