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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
ProspectusDate rr_ProspectusDate Aug. 28, 2011
MFS Bond Fund (Prospectus Summary) | MFS Bond Fund
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return, Heading rr_RiskReturnHeading Summary of Key Information
Investment Objective, Heading rr_ObjectiveHeading Investment Objective
investment Objective, Primary rr_ObjectivePrimaryTextBlock 
The fund's investment objective is to seek total return with an emphasis on
current income, but also considering capital appreciation.
Expense, Heading rr_ExpenseHeading Fees and Expenses
Expense, Narrative rr_ExpenseNarrativeTextBlock 
This table describes the fees and expenses that you may pay when you buy and
hold shares of the fund.

You may qualify for sales charge reductions if you and certain members of your
family invest, or agree to invest in the future, at least $50,000 in MFS Funds.
More information about these and other waivers and reductions is available from
your financial intermediary and in "Sales Charges and Waivers or Reductions" on
page 8 of the fund's prospectus and "Waivers of Sales Charges" on page 12 of the
fund's statement of additional information Part I.
Shareholder Fees, Caption rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses, Caption rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Portfolio Turnover, Heading rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover rr_PortfolioTurnoverTextBlock 
The fund pays transaction costs, such as commissions, when it buys and sells
securities (or "turns over" its portfolio). A higher portfolio turnover rate may
indicate higher transaction costs 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 58% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 58.00%
Expense Breakpoint, Discounts rr_ExpenseBreakpointDiscounts You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in "Sales Charges and Waivers or Reductions" on page 8 of the fund's prospectus and "Waivers of Sales Charges" on page 12 of the fund's statement of additional information Part I.
Expense Breakpoint, Minimum Investment Required Amount rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example, Heading rr_ExpenseExampleHeading Example
Expense Example, Narrative rr_ExpenseExampleNarrativeTextBlock 
This example is intended to help you compare the cost of investing in the fund
with the cost of investing in other mutual funds.

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 rr_ExpenseExampleByYearCaption Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Investment Strategy, Heading rr_StrategyHeading Principal Investment Strategies
Investment Strategy, Narrative rr_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.

MFS invests the majority of the fund's assets in corporate debt instruments, but
may also invest in other types of debt instruments. MFS primarily invests the
fund's assets in investment grade debt instruments, but may also invest in lower
quality debt instruments.

MFS may invest the fund's assets in foreign securities, including emerging
market securities.

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 or currency exposure, or as alternatives to direct
investments. Derivatives include futures, forward contracts, options, structured
securities, inverse floating rate instruments, and swaps.

MFS uses a bottom-up investment approach to buying and selling investments for
the fund. Investments are selected primarily based on fundamental analysis of
individual instruments and their issuers in light of issuers' current financial
condition and current market, economic, political, and regulatory conditions.
Factors considered may include the instrument's credit quality, collateral
characteristics, and indenture provisions, and the issuer's management ability,
capital structure, leverage, and ability to meet its current obligations.
Quantitative models that systematically evaluate the structure of the debt
instrument and its features may also be considered.
Risk, Heading rr_RiskHeading Principal Risks
Risk, Narrative rr_RiskNarrativeTextBlock 
As with any mutual fund, the fund may not achieve its objective and/or you could
lose money on your investment in the fund. An investment in the fund is not a
bank deposit and is not insured or guaranteed by the Federal Deposit Insurance
Corporation or any other governmental agency.

The principal risks of investing in the fund are:

Interest Rate Risk:  The price of a debt instrument falls when interest rates
rise and rises when interest rates fall. Instruments with longer maturities, or
that do not pay current interest, are more sensitive to interest rate changes.

Credit Risk:  The price of a debt instrument depends, in part, on the credit
quality of the issuer, borrower, counterparty, or underlying collateral and can
decline in response to changes in the financial condition of the issuer,
borrower, counterparty, or underlying collateral, or changes in specific or
general market, economic, industry, political, regulatory, geopolitical, or
other conditions.

Lower 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. Lower quality
debt instruments are regarded as having predominantly speculative
characteristics. Lower 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.

Foreign and Emerging Markets Risk:  Exposure to foreign markets, especially
emerging markets, through issuers or currencies can involve additional risks
relating to market, economic, political, regulatory, geopolitical, or other
conditions. These factors can make foreign investments, especially those in
emerging markets, more volatile and less liquid than U.S. investments. In
addition, foreign markets can react differently to these conditions than the
U.S. market. Emerging markets can have less developed markets and less developed
legal, regulatory, and accounting systems, and greater political, social, and
economic instability than developed markets.

Currency Risk:  The value of foreign currencies relative to the U.S. dollar
fluctuates in response to market, economic, political, regulatory, geopolitical
or other conditions, and a decline in the value of a foreign currency versus the
U.S. dollar reduces the value in U.S. dollars of investments denominated in that
foreign currency.

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.

Inflation-Adjusting Risk:  Interest payments on inflation-adjusted debt
instruments can be unpredictable and vary based on the level of inflation. If
inflation is negative, principal and income can both decline.

Municipal Risk:  The price of a municipal instrument can be volatile and
significantly affected by adverse tax or court rulings, legislative or political
changes, changes in specific or general market and economic conditions, and the
financial condition of municipal issuers and insurers. Because many municipal
instruments are issued to finance similar projects, conditions in these
industries can significantly affect the fund and the overall municipal market.

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.

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

Liquidity Risk:  It may not be possible to sell certain investments, types of
investments, and/or segments of the market at any particular time or at an
acceptable price.

Counterparty and Third Party Risk:  Transactions involving a counterparty or
third party other than the issuer of the instrument are subject to the credit
risk of the counterparty or third party, and to the counterparty's or third
party's ability to perform in accordance with the terms of the transaction.

Investment Selection Risk:  The MFS analysis of an investment can be incorrect
and 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.
Risk, Lose Money rr_RiskLoseMoney As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
Risk, Not Insured Depository Institution rr_RiskNotInsuredDepositoryInstitution An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table, Heading rr_BarChartAndPerformanceTableHeading Performance Information
Performance, Narrative rr_PerformanceNarrativeTextBlock 
The bar chart and performance table below are intended to provide some
indication of the risks of investing in the fund by showing changes in the
fund's performance over time and how the fund's performance over time compares
with that of a broad measure of market performance and one or more other
measures of performance for markets in which the fund may invest.

The fund's past performance (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 rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.
Performance, Availability Phone Number rr_PerformanceAvailabilityPhone 1-800-225-2606
Performance, Availability Website Address rr_PerformanceAvailabilityWebSiteAddress mfs.com
Performance, Past Does Not Indicate Future rr_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 rr_BarChartHeading Class A Bar Chart.
Bar Chart, Narrative rr_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 rr_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 rr_BarChartClosingTextBlock 
The total return for the six-month period ended June 30, 2011 was 3.85%. During
the period(s) shown in the bar chart, the highest quarterly return was 11.30%
(for the calendar quarter ended June 30, 2009) and the lowest quarterly return
was (5.18)% (for the calendar quarter ended September 30, 2008).
Performance Table, Heading rr_PerformanceTableHeading Performance Table.
Index No Deduction for Fees, Expenses, Taxes rr_IndexNoDeductionForFeesExpensesTaxes Reflects no deduction for fees, expenses or taxes
Performance Table, Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table, Not Relevant to Tax Deferred rr_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-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table, One Class of after Tax Shown rr_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 rr_PerformanceTableClosingTextBlock 
After-tax returns are calculated using the historical highest individual 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-deferred arrangements, such as
401(k) plans or individual retirement accounts. 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 Returns, Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (for the Periods Ended December 31, 2010)
MFS Bond Fund (Prospectus Summary) | MFS Bond Fund | A
  
Risk/Return: rr_RiskReturnAbstract  
Year to Date Return, Label rr_YearToDateReturnLabel The total return for the six-month period
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2011
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 3.85%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 11.30%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.18%)
MFS Bond Fund | Barclays Capital U.S. Credit Bond Index
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays Capital U.S. Credit Bond Index
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 8.47%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.98%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.55%
MFS Bond Fund | A
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
A
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.75%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [1]
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
A
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.85%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 558
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 733
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 924
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,474
Annual Return 2001 rr_AnnualReturn2001 7.78%
Annual Return 2002 rr_AnnualReturn2002 8.64%
Annual Return 2003 rr_AnnualReturn2003 9.46%
Annual Return 2004 rr_AnnualReturn2004 6.07%
Annual Return 2005 rr_AnnualReturn2005 1.71%
Annual Return 2006 rr_AnnualReturn2006 4.93%
Annual Return 2007 rr_AnnualReturn2007 3.51%
Annual Return 2008 rr_AnnualReturn2008 (9.98%)
Annual Return 2009 rr_AnnualReturn2009 28.37%
Annual Return 2010 rr_AnnualReturn2010 11.22%
Average Annual Returns, Label rr_AverageAnnualReturnLabel A Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 5.94%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.86%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.28%
MFS Bond Fund | A | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel A Shares Returns After Taxes on Distributions
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 3.89%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.81%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.11%
MFS Bond Fund | A | After Taxes on Distributions and Sales
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel A Shares Returns After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 3.81%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 3.75%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 4.04%
MFS Bond Fund | B
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
B
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
B
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.60%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 563
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 805
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 1,071
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,699
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 163
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 505
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 871
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,699
Average Annual Returns, Label rr_AverageAnnualReturnLabel B Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 6.42%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.82%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.21%
MFS Bond Fund | C
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
C
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
C
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.60%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 263
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 505
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 871
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,900
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 163
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 505
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 871
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 1,900
Average Annual Returns, Label rr_AverageAnnualReturnLabel C Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 9.42%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.16%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.06%
MFS Bond Fund | I
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
I AND W
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
I
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.60%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 61
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 192
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 335
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 750
Average Annual Returns, Label rr_AverageAnnualReturnLabel I Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.50%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 7.18%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 7.11%
MFS Bond Fund | W
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
I AND W
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
W
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.10%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.70%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 72
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 224
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 390
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 871
Average Annual Returns, Label rr_AverageAnnualReturnLabel W Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01  
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05  
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10  
MFS Bond Fund | R1
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
R1
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.60%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 163
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 505
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 871
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,900
Average Annual Returns, Label rr_AverageAnnualReturnLabel R1 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.42%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.10%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.90%
MFS Bond Fund | R2
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
R2
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.10%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 112
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 350
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 606
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,340
Average Annual Returns, Label rr_AverageAnnualReturnLabel R2 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 10.87%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.59%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.42%
MFS Bond Fund | R3
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
R3
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.85%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 87
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 271
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 471
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 1,049
Average Annual Returns, Label rr_AverageAnnualReturnLabel R3 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.22%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.87%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.69%
MFS Bond Fund | R4
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees, Column Name rr_ShareholderFeesColumnName 
ALL R
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is less) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Operating Expenses, Column Name rr_OperatingExpensesColumnName 
R4
Management Fee rr_ManagementFeesOverAssets 0.39%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.21%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.60%
Expense Example, With Redemption, 1 Year rr_ExpenseExampleYear01 61
Expense Example, With Redemption, 3 Years rr_ExpenseExampleYear03 192
Expense Example, With Redemption, 5 Years rr_ExpenseExampleYear05 335
Expense Example, With Redemption, 10 Years rr_ExpenseExampleYear10 $ 750
Average Annual Returns, Label rr_AverageAnnualReturnLabel R4 Shares Returns Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 11.50%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 7.16%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 6.99%
[1] On shares purchased without an initial sales charge and redeemed within 24 months of purchase.