| Label | Element | Value |
|---|---|---|
| MFS High Yield Pooled Portfolio | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk/Return [Heading] | oef_RiskReturnHeading | MFS® High Yield Pooled Portfolio Summary of Key Information |
| Objective [Heading] | oef_ObjectiveHeading | Investment Objective |
| Objective, Primary [Text Block] | oef_ObjectivePrimaryTextBlock | The fund’s investment objective is to seek total return with an emphasis on high current income, but also considering capital appreciation. |
| Expense Heading [Optional Text] | oef_ExpenseHeading | Fees and Expenses |
| Expense Narrative [Text Block] | oef_ExpenseNarrativeTextBlock | This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. |
| Shareholder Fees Caption [Optional Text] | oef_ShareholderFeesCaption | Shareholder Fees (fees paid directly from your investment): |
| Operating Expenses Caption [Optional Text] | oef_OperatingExpensesCaption | Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment): |
| Portfolio Turnover [Heading] | oef_PortfolioTurnoverHeading | Portfolio Turnover |
| Portfolio Turnover [Text Block] | oef_PortfolioTurnoverTextBlock | The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 50% of the average value of its portfolio. |
| Portfolio Turnover, Rate | oef_PortfolioTurnoverRate | 50.00% |
| Expense Example [Heading] | oef_ExpenseExampleHeading | Example |
| Expense Example Narrative [Text Block] | oef_ExpenseExampleNarrativeTextBlock | This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods; your investment has a 5% return each year; and the fund’s operating expenses remain the same. |
| Expense Example by, Year, Caption [Text] | oef_ExpenseExampleByYearCaption | Although your actual costs will likely be higher or lower, under these assumptions your costs would be: |
| Strategy [Heading] | oef_StrategyHeading | Principal Investment Strategies |
| Strategy Narrative [Text Block] | oef_StrategyNarrativeTextBlock | MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund’s net assets in high yielding debt instruments. Debt instruments include corporate debt instruments, foreign government securities, floating rate loans, and other obligations to repay money borrowed. High yield debt instruments are debt instruments that are below investment grade quality. Below investment grade quality debt instruments are debt instruments rated BB+ or lower by S&P or Fitch, or Ba1 or lower by Moody’s, or comparably rated by another Nationally Recognized Statistical Rating Organization ("NRSRO"). MFS may invest the fund’s assets in other types of debt instruments. MFS may invest up to 100% of the fund’s assets in below investment grade quality debt instruments. MFS may invest the fund’s assets in foreign securities. MFS normally invests the fund's assets across different industries and sectors, but MFS may invest a significant percentage of the fund's assets in issuers in a single industry or sector. 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. For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes. |
| Bar Chart and Performance Table [Heading] | oef_BarChartAndPerformanceTableHeading | Performance Information |
| Performance Narrative [Text Block] | oef_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 (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606. |
| Performance Information Illustrates Variability of Returns [Text] | oef_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] | oef_PerformanceAvailabilityPhone | 1-800-225-2606 |
| Performance Availability Website Address [Text] | oef_PerformanceAvailabilityWebSiteAddress | mfs.com |
| Performance Past Does Not Indicate Future [Text] | oef_PerformancePastDoesNotIndicateFuture | The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. |
| Bar Chart [Heading] | oef_BarChartHeading | Bar Chart. |
| Bar Chart Narrative [Text Block] | oef_BarChartNarrativeTextBlock | The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown. |
| Bar Chart Does Not Reflect Sales Loads [Text] | oef_BarChartDoesNotReflectSalesLoads | The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown. |
| Bar Chart Closing [Text Block] | oef_BarChartClosingTextBlock | The total return for the three-month period ended March 31, 2026, was (0.40)%. During the period(s) shown in the bar chart, the highest quarterly return was 7.30% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was (10.58)% (for the calendar quarter ended March 31, 2020). |
| Performance Table Heading | oef_PerformanceTableHeading | Performance Table. |
| Index No Deduction for Fees, Expenses, or Taxes [Text] | oef_IndexNoDeductionForFeesExpensesTaxes | Reflects no deduction for fees, expenses, or taxes |
| Performance Table Not Relevant to Tax Deferred | oef_PerformanceTableNotRelevantToTaxDeferred | Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). |
| Performance Table One Class of after Tax Shown [Text] | oef_PerformanceTableOneClassOfAfterTaxShown | The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown. |
| Performance Table Closing [Text Block] | oef_PerformanceTableClosingTextBlock | After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown. |
| Average Annual Return, Caption [Optional Text] | oef_AverageAnnualReturnCaption | Average Annual Total Returns (For the Periods Ended December 31, 2025) |
| MFS High Yield Pooled Portfolio | Principal Risks | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Risk Lose Money [Member] | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Risk Not Insured [Member] | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Investment Selection Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Debt Market Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Interest Rate Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Credit Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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. Below investment grade 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. Below investment grade quality debt instruments are regarded as having predominantly speculative characteristics. Below investment grade 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. |
| MFS High Yield Pooled Portfolio | Foreign Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_RiskTextBlock | Foreign Risk: Exposure to foreign markets through issuers or currencies 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 High Yield Pooled Portfolio | Focus Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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. Furthermore, investments in particular industries, sectors, countries, or regions may be more volatile than the broader market as a whole. |
| MFS High Yield Pooled Portfolio | Prepayment/Extension Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Derivatives Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Leveraging Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Counterparty and Third Party Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Liquidity Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Large Shareholder Risk | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Risk [Text Block] | oef_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 High Yield Pooled Portfolio | Bloomberg U.S. Aggregate Bond Index | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Bloomberg U.S. Aggregate Bond Index |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 7.30% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | (0.36%) |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 2.01% |
| MFS High Yield Pooled Portfolio | Bloomberg U.S. Corporate High-Yield 2% Issuer Capped Index | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Bloomberg U.S. Corporate High-Yield 2% Issuer Capped Index |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.62% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 4.50% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.52% |
| MFS High Yield Pooled Portfolio | Fund Shares | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Trading Symbol | dei_TradingSymbol | HYPPX |
| Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) | oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice | 0.00% |
| Maximum Deferred Sales Charge (as a percentage of Offering Price) | oef_MaximumDeferredSalesChargeOverOfferingPrice | 0.00% |
| Management Fees (as a percentage of Assets) | oef_ManagementFeesOverAssets | 0.00% |
| Other Expenses (as a percentage of Assets): | oef_OtherExpensesOverAssets | 0.03% |
| Expenses (as a percentage of Assets) | oef_ExpensesOverAssets | 0.03% |
| Expense Example, with Redemption, 1 Year | oef_ExpenseExampleYear01 | $ 3 |
| Expense Example, with Redemption, 3 Years | oef_ExpenseExampleYear03 | 10 |
| Expense Example, with Redemption, 5 Years | oef_ExpenseExampleYear05 | 17 |
| Expense Example, with Redemption, 10 Years | oef_ExpenseExampleYear10 | $ 39 |
| Year to Date Return, Label [Optional Text] | oef_YearToDateReturnLabel | The total return for the three-month period ended |
| Bar Chart, Year to Date Return, Date | oef_BarChartYearToDateReturnDate | Mar. 31, 2026 |
| Bar Chart, Year to Date Return | oef_BarChartYearToDateReturn | (0.40%) |
| Highest Quarterly Return, Label [Optional Text] | oef_HighestQuarterlyReturnLabel | highest quarterly return |
| Highest Quarterly Return, Date | oef_BarChartHighestQuarterlyReturnDate | Dec. 31, 2023 |
| Highest Quarterly Return | oef_BarChartHighestQuarterlyReturn | 7.30% |
| Lowest Quarterly Return, Label [Optional Text] | oef_LowestQuarterlyReturnLabel | lowest quarterly return |
| Lowest Quarterly Return, Date | oef_BarChartLowestQuarterlyReturnDate | Mar. 31, 2020 |
| Lowest Quarterly Return | oef_BarChartLowestQuarterlyReturn | (10.58%) |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Returns Before Taxes |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 9.44% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 4.61% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.19% |
| Annual Return [Percent] | oef_AnnlRtrPct | 14.49% |
| Annual Return [Percent] | oef_AnnlRtrPct | 7.30% |
| Annual Return [Percent] | oef_AnnlRtrPct | (2.25%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 15.44% |
| Annual Return [Percent] | oef_AnnlRtrPct | 5.01% |
| Annual Return [Percent] | oef_AnnlRtrPct | 4.16% |
| Annual Return [Percent] | oef_AnnlRtrPct | (9.86%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 13.34% |
| Annual Return [Percent] | oef_AnnlRtrPct | 7.56% |
| Annual Return [Percent] | oef_AnnlRtrPct | 9.44% |
| MFS High Yield Pooled Portfolio | Fund Shares | After Taxes on Distributions | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Returns After Taxes on Distributions |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.36% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 1.93% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 3.53% |
| MFS High Yield Pooled Portfolio | Fund Shares | After Taxes on Distributions and Sales | ||
| Risk/Return: | oef_RiskReturnAbstract | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Returns After Taxes on Distributions and Sale of Fund Shares |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 5.51% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 2.31% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 3.57% |