v3.26.1
Label Element Value
MFS Total Return Bond Fund  
Risk/Return: oef_RiskReturnAbstract  
Risk/Return [Heading] oef_RiskReturnHeading MFS® Total Return Bond 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 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 13 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 48% of the average value of its portfolio (22% excluding to be announced (TBA) transactions).
Portfolio Turnover, Rate oef_PortfolioTurnoverRate 48.00%
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 debt instruments. Debt instruments include corporate bonds, U.S. Government securities, foreign government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), municipal instruments, and other obligations to repay money borrowed.

MFS primarily invests the fund’s assets in investment grade quality debt instruments, but may also invest the fund’s assets in below investment grade quality debt instruments.

MFS may purchase or sell securities for the fund on a when-issued, delayed delivery, or forward commitment basis where payment and delivery take place at a future settlement date, including mortgage-backed securities purchased or sold in the TBA market.

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.

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.

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.

Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block] fnd_NmRule35d1TermDfnSmryTextBlock Debt instruments include corporate bonds, U.S. Government securities, foreign government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), municipal instruments, and other obligations to repay money borrowed.
Rule 35d-1 Eighty Percent Investment Policy [Text Block] fnd_NmRule35d1EightyPctInvstmntPlcyTextBlock MFS (Massachusetts Financial Services Company, the fund’s investment adviser) normally invests at least 80% of the fund’s net assets in debt instruments.
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 a broad measure of market performance.

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 a broad measure of market performance.
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 six-month period ended June 30, 2026, was 0.88%. During the period(s) shown in the bar chart, the highest quarterly return was 7.04% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was (6.05)% (for the calendar quarter ended June 30, 2022).
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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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.

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 Total Return Bond 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 Total Return Bond Fund | Municipal Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax changes or court rulings, legislative or political changes, changes in specific or general market and economic conditions and developments, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in certain industries can significantly affect the fund and the overall municipal market. Municipal instruments may be more susceptible to downgrades or defaults during economic downturns or similar periods of economic stress, which in turn could affect the market values and marketability of many or all municipal obligations of issuers in a state, U.S. territory, or possession.

In addition, because some municipal obligations may be secured or guaranteed by banks and other institutions, the risk associated with investments in such municipal securities could increase if the banking or financial sector suffers an economic downturn and/or if the credit ratings of the institutions issuing the guarantee are downgraded or at risk of being downgraded by a national rating organization. If such events occur, the value of the security could decrease or the value could be lost entirely, and it may be difficult or impossible to sell the security at the time and the price that normally prevails in the market.

MFS Total Return Bond Fund | When-Issued, Delayed Delivery, and Forward Commitment Transaction Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

When-Issued, Delayed Delivery, and Forward Commitment Transaction Risk: The purchaser in a when-issued, delayed delivery or forward commitment transaction assumes the rights and risks of ownership, including the risks of price and yield fluctuations and the risk that the security will not be issued or delivered as anticipated. When-issued, delayed delivery, and forward commitment transactions can involve leverage. TBA transactions may significantly increase the fund's portfolio turnover rate.
MFS Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond 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 Total Return Bond Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBFX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.77%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.17%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.60%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 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 $ 484
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 644
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 819
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,323
Year to Date Return, Label [Optional Text] oef_YearToDateReturnLabel The total return for the six-month period ended
Bar Chart, Year to Date Return, Date oef_BarChartYearToDateReturnDate Jun. 30, 2026
Bar Chart, Year to Date Return oef_BarChartYearToDateReturn 0.88%
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 7.04%
Lowest Quarterly Return, Label [Optional Text] oef_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date oef_BarChartLowestQuarterlyReturnDate Jun. 30, 2022
Lowest Quarterly Return oef_BarChartLowestQuarterlyReturn (6.05%)
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.62%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.88%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.97%
Annual Return [Percent] oef_AnnlRtrPct 3.54%
Annual Return [Percent] oef_AnnlRtrPct 4.08%
Annual Return [Percent] oef_AnnlRtrPct (1.28%)
Annual Return [Percent] oef_AnnlRtrPct 9.89%
Annual Return [Percent] oef_AnnlRtrPct 8.68%
Annual Return [Percent] oef_AnnlRtrPct (1.06%)
Annual Return [Percent] oef_AnnlRtrPct (13.96%)
Annual Return [Percent] oef_AnnlRtrPct 7.06%
Annual Return [Percent] oef_AnnlRtrPct 2.30%
Annual Return [Percent] oef_AnnlRtrPct 7.17%
MFS Total Return Bond 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 0.92%
Average Annual Return, Percent oef_AvgAnnlRtrPct (2.32%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.64%
MFS Total Return Bond 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 1.52%
Average Annual Return, Percent oef_AvgAnnlRtrPct (1.27%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.93%
MFS Total Return Bond Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBBX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.52%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.17%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.35%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 537 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 764 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 1,013 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,595 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 137 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 464 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 813 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,595 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.26%
Average Annual Return, Percent oef_AvgAnnlRtrPct (1.12%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.81%
MFS Total Return Bond Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBCX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.52%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 248 [3]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 473 [3]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 822 [3]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,604 [3]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 148 [3]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 473 [3]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 822 [3]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,604 [3]
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.16%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.87%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.72%
MFS Total Return Bond Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBIX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.52%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 160
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 284
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 646
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.33%
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.57%
MFS Total Return Bond Fund | Class R1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBGX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.52%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 1.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 148
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 473
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 822
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,807
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 6.16%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.87%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.54%
MFS Total Return Bond Fund | Class R2  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRRRX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.02%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.95%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 318
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 556
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,242
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 6.80%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.36%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.06%
MFS Total Return Bond Fund | Class R3  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBHX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.77%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.70%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 72
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 239
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 421
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 948
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.07%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.11%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.31%
MFS Total Return Bond Fund | Class R4  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBJX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.52%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.07%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 160
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 284
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 646
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.22%
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.12%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.57%
MFS Total Return Bond Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MRBKX
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 0.39%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.03%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.42%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.06%) [2]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.36%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination August 31, 2027
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 37
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 129
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 229
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 524
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Returns Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.32%
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.23%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.67%
[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 reduce its management fee to 0.40% of the fund’s average daily net assets annually up to $2.5 billion. This written agreement will remain in effect until modified by the fund’s Board of Trustees, but such agreement will continue until at least August 31, 2027. 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 August 31, 2027. MFS Fund Distributors, Inc. (MFD), has agreed in writing to waive the Class A and Class B service fee to 0.15% of each class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least August 31, 2027. MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, certain tax reclaim recovery expenses (including contingency fees and closing agreement expenses), 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 0.60% of the class' average daily net assets annually for Class A shares, 1.35% of the class' average daily net assets annually for Class B shares, 1.45% of the class' average daily net assets annually for each of Class C and Class R1 shares, 0.45% of the class' average daily net assets annually for each of Class I and Class R4 shares, 0.95% of the class' average daily net assets annually for Class R2 shares, 0.70% of the class' average daily net assets annually for Class R3 shares, and 0.36% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least August 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.