v3.26.1
Label Element Value
MFS High Income Fund  
Risk/Return: oef_RiskReturnAbstract  
Risk/Return [Heading] oef_RiskReturnHeading MFS® High Income Fund 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. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.

You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds. More information about these and other waivers and reductions is available from your financial intermediary and in “Sales Charges and Waivers and Reductions” on page 11 and “Appendix A – Waivers and Reductions of Sales Charges” on page A-1 of the fund’s prospectus.

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 51% of the average value of its portfolio.
Portfolio Turnover, Rate oef_PortfolioTurnoverRate 51.00%
Expense Breakpoint Discounts [Text] oef_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if, with respect to Class A shares, you and certain members of your family invest, or agree to invest in the future, at least $100,000 in MFS funds.
Expense Breakpoint, Minimum Investment Required [Amount] oef_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
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 (unless otherwise indicated); 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 income debt instruments. Debt instruments include corporate debt instruments, foreign government securities, floating rate loans, and other obligations to repay money borrowed. High income 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 Class A 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 (0.68)%. During the period(s) shown in the bar chart, the highest quarterly return was 7.00% (for the calendar quarter ended March 31, 2019) and the lowest quarterly return was (10.23)% (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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | 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 Income Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHITX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.25%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1]
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.86%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.85%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expenses Deferred Charges [Text Block] oef_ExpensesDeferredChargesTextBlock This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 508
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 687
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 881
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,440
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 (0.68%)
Highest Quarterly Return, Label [Optional Text] oef_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date oef_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return oef_BarChartHighestQuarterlyReturn 7.00%
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 (10.23%)
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.07%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.81%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.79%
Annual Return [Percent] oef_AnnlRtrPct 13.38%
Annual Return [Percent] oef_AnnlRtrPct 6.13%
Annual Return [Percent] oef_AnnlRtrPct (3.30%)
Annual Return [Percent] oef_AnnlRtrPct 14.43%
Annual Return [Percent] oef_AnnlRtrPct 4.42%
Annual Return [Percent] oef_AnnlRtrPct 3.20%
Annual Return [Percent] oef_AnnlRtrPct (10.56%)
Annual Return [Percent] oef_AnnlRtrPct 12.18%
Annual Return [Percent] oef_AnnlRtrPct 6.58%
Annual Return [Percent] oef_AnnlRtrPct 8.69%
MFS High Income Fund | Class A | 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 1.52%
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.55%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.58%
MFS High Income Fund | Class A | 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 2.35%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.12%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.68%
MFS High Income Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIBX
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 4.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.61%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 563 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 807 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 1,075 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,709 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 163 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 507 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 875 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,709 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.53%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.55%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.65%
MFS High Income Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHICX
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 1.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.61%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 263 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 507 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 875 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,709 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 163 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 507 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 875 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,709 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 6.88%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.94%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.62%
MFS High Income Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIIX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.61%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 61
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 194
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 339
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 761
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.96%
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.96%
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.51%
MFS High Income Fund | Class R1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIGX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.61%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 163
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 507
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 875
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,910
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.53%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.46%
MFS High Income Fund | Class R2  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MIHRX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.11%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.10%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 112
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 352
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 611
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,351
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.08%
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.32%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.92%
MFS High Income Fund | Class R3  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIHX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.86%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.85%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 87
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 273
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 476
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,060
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.70%
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.64%
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.21%
MFS High Income Fund | Class R4  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIJX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.16%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.61%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 61
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 194
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 339
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 761
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 8.95%
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.97%
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.54%
MFS High Income Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MHIKX
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 0.45%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.06%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.51%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.01%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.50%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination May 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 51
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 163
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 284
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 640
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 9.07%
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.08%
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.62%
[1] This contingent deferred sales charge (CDSC) applies to shares purchased without an initial sales charge and redeemed within 18 months of purchase.
[2] 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 May 31, 2027.
[3] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.