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MFS Limited Maturity Portfolio  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MFS® Limited Maturity 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 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. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor 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 40% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 40.00%
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 insurance company that issued your variable contracts or other eligible investor 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 U.S. Government securities, corporate bonds, foreign government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), 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 quality debt instruments.

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

MFS normally invests the fund's assets across different industries, sectors, countries, and regions, but MFS may invest a significant percentage of the fund’s assets in issuers in a single industry, sector, country, or region.

MFS may invest a significant 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 exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, and swaps.

MFS uses an active 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 screening tools that systematically evaluate instruments may also be considered. In structuring the fund, MFS also considers top-down factors.
Risk [Heading] rr_RiskHeading Principal Risks
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 (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

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 insurance company that issued your variable contracts or other eligible investor 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 (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
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 three-month period ended March 31, 2025, was 1.68%. During the period(s) shown in the bar chart, the highest quarterly return was 5.19% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (3.09)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading rr_PerformanceTableHeading Performance Table.
Average Annual Return, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (For the Periods Ended December 31, 2024)
MFS Limited Maturity Portfolio | Principal Risks  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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:
MFS Limited Maturity Portfolio | Risk Lose Money [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
MFS Limited Maturity Portfolio | Risk Not Insured [Member]  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock 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.
MFS Limited Maturity Portfolio | Investment Selection Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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. In addition, to the extent MFS considers quantitative tools in managing the fund, such tools may not produce the intended results.

MFS Limited Maturity Portfolio | Debt Market Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Debt Market Risk: Debt markets can be volatile and can decline significantly in response to changes in, or investor perceptions of, issuer, market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These conditions can affect a single instrument, issuer, or borrower, a particular type of instrument, issuer, or borrower, a segment of the debt markets or the debt markets generally. Certain events can have a dramatic adverse effect on debt markets and may lead to periods of high volatility and reduced liquidity in a debt market or segment of a debt market.

MFS Limited Maturity Portfolio | Interest Rate Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Interest Rate Risk: In general, the price of a debt instrument falls when interest rates rise and rises when interest rates fall. Interest rate risk is generally greater for instruments with longer maturities or durations, or that do not pay current interest.
MFS Limited Maturity Portfolio | Credit Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Credit Risk: The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in, or perceptions of, the financial condition of the issuer, borrower, counterparty, or other entity, or underlying collateral or assets, or changes in, or perceptions of, specific or general market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. Debt instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could negatively affect the market value and liquidity of a debt instrument.
MFS Limited Maturity Portfolio | Foreign Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Foreign Risk: Exposure to foreign markets through issuers can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions. These factors can make foreign investments, especially those tied economically to countries with developing economies or countries subject to sanctions or the threat of new or modified sanctions, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market.
MFS Limited Maturity Portfolio | Focus Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Focus Risk: Issuers in a single industry, sector, country, or region can react similarly to market, currency, political, economic, regulatory, geopolitical, environmental, public health, and other conditions, and the fund's performance will be affected by the conditions in the industries, sectors, countries, and regions to which the fund is exposed.

If MFS invests a significant percentage of the fund's assets in a single issuer or small number of issuers, the fund’s performance could be more volatile than the performance of more diversified funds.

MFS Limited Maturity Portfolio | Prepayment/Extension Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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.

MFS Limited Maturity Portfolio | Derivatives Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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.
MFS Limited Maturity Portfolio | Leveraging Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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

MFS Limited Maturity Portfolio | Counterparty and Third Party Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

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 or willingness to perform in accordance with the terms of the transaction.
MFS Limited Maturity Portfolio | Liquidity Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Liquidity Risk: It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs.

MFS Limited Maturity Portfolio | Large Shareholder Risk  
Risk/Return: rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock

Large Shareholder Risk: From time to time, shareholders of the fund (which may include institutional investors, financial intermediaries, or other MFS funds) may make relatively large redemptions or purchases of fund shares. These transactions may cause the fund to sell securities or invest additional cash, as the case may be, at disadvantageous prices. Redemptions of a large number of shares also may increase transaction and other costs or have adverse tax consequences for shareholders of the fund by requiring a sale of portfolio securities. Purchases of a large number of shares may adversely affect the fund's performance to the extent that it takes time to invest new cash and the fund maintains a larger cash position than it ordinarily would.
MFS Limited Maturity Portfolio | Bloomberg U.S. Aggregate Bond Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel Bloomberg U.S. Aggregate Bond Index
1 Year rr_AverageAnnualReturnYear01 1.25%
5 Years rr_AverageAnnualReturnYear05 (0.33%)
10 Years rr_AverageAnnualReturnYear10 1.35%
MFS Limited Maturity Portfolio | Bloomberg 1-3 Year U.S. Government/Credit Bond Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel Bloomberg 1-3 Year U.S. Government/Credit Bond Index
1 Year rr_AverageAnnualReturnYear01 4.36%
5 Years rr_AverageAnnualReturnYear05 1.58%
10 Years rr_AverageAnnualReturnYear10 1.63%
MFS Limited Maturity Portfolio | Initial Class Shares  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol N/A
Management Fee rr_ManagementFeesOverAssets 0.40%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.09%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.49%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.01%) [1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.48%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination April 30, 2026
1 Year rr_ExpenseExampleYear01 $ 49
3 Years rr_ExpenseExampleYear03 156
5 Years rr_ExpenseExampleYear05 273
10 Years rr_ExpenseExampleYear10 $ 615
Annual Return 2015 rr_AnnualReturn2015 0.48%
Annual Return 2016 rr_AnnualReturn2016 1.68%
Annual Return 2017 rr_AnnualReturn2017 1.73%
Annual Return 2018 rr_AnnualReturn2018 1.28%
Annual Return 2019 rr_AnnualReturn2019 5.19%
Annual Return 2020 rr_AnnualReturn2020 4.34%
Annual Return 2021 rr_AnnualReturn2021 0.16%
Annual Return 2022 rr_AnnualReturn2022 (4.14%)
Annual Return 2023 rr_AnnualReturn2023 6.08%
Annual Return 2024 rr_AnnualReturn2024 5.30%
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, 2025
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 1.68%
Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.19%
Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.09%)
1 Year rr_AverageAnnualReturnYear01 5.30%
5 Years rr_AverageAnnualReturnYear05 2.27%
10 Years rr_AverageAnnualReturnYear10 2.17%
MFS Limited Maturity Portfolio | Service Class Shares  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol N/A
Management Fee rr_ManagementFeesOverAssets 0.40%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.09%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74%
Fee Reductions and/or Expense Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.01%) [1]
Total Annual Fund Operating Expenses After Fee Reductions and/or Expense Reimbursements rr_NetExpensesOverAssets 0.73%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination April 30, 2026
1 Year rr_ExpenseExampleYear01 $ 75
3 Years rr_ExpenseExampleYear03 236
5 Years rr_ExpenseExampleYear05 410
10 Years rr_ExpenseExampleYear10 $ 917
1 Year rr_AverageAnnualReturnYear01 5.02%
5 Years rr_AverageAnnualReturnYear05 2.03%
10 Years rr_AverageAnnualReturnYear10 1.92%
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least April 30, 2026.