Label

Element

Value

Risk/Return:

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Supplement [Text Block]

ck0000751656_SupplementTextBlock

SUPPLEMENT TO PROSPECTUS
The date of this supplement is November 28, 2014.

MFS® Alabama Municipal Bond Fund

Risk/Return [Heading]

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MFS® Alabama Municipal Bond Fund

Expense [Heading]

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Effective immediately, the second paragraph of the sub-section entitled "Fees and Expenses" beneath the main heading "Summary of Key Information" is restated in its entirety as follows:

Expense Narrative [Text Block]

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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 (at least $100,000 effective December 29, 2014) 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 H-1 of the fund’s Statement of Additional Information (“SAI”).

Effective immediately, the following is added after the table entitled “Shareholder Fees (fees paid directly from your investment)” in the sub-section entitled “Fees and Expenses” beneath the main heading “Summary of Key Information”:

Effective December 29, 2014, the Maximum Sales Charge on Class A shares will be reduced to 4.25%.

Expense Breakpoint Discounts [Text]

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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 (at least $100,000 effective December 29, 2014) in MFS Funds.

Expense Breakpoint, Minimum Investment Required [Amount]

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$ 50,000

Expense Example [Heading]

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Effective December 29, 2014, the row for Class A shares in the third paragraph of the sub-section entitled "Example" beneath the main heading "Summary of Key Information" is restated in its entirety as follows:

Bar Chart and Performance Table [Heading]

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Effective December 29, 2014, the rows for Class A shares in the "Performance Table" in the sub-section entitled "Performance Information" beneath the main heading "Summary of Key Information" are restated in their entirety as follows:

Caption

rr_AverageAnnualReturnCaption

Average Annual Total Returns (For the Periods Ended December 31, 2013)

A

Risk/Return:

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Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

516

Expense Example, with Redemption, 3 Years

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733

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

969

Expense Example, with Redemption, 10 Years

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$ 1,643

Label

rr_AverageAnnualReturnLabel

A Shares Returns Before Taxes

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

(8.77%)

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.51%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

3.08%

A | After Taxes on Distributions

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

A Shares Returns After Taxes on Distributions

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

(8.77%)

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.45%

Average Annual Returns, 10 Years

rr_AverageAnnualReturnYear10

3.01%

A | After Taxes on Distributions and Sale of Fund Shares

Risk/Return:

rr_RiskReturnAbstract

Label

rr_AverageAnnualReturnLabel

A Shares Returns After Taxes on Distributions and Sale of Fund Shares

Average Annual Returns, 1 Year

rr_AverageAnnualReturnYear01

(3.43%)

Average Annual Returns, 5 Years

rr_AverageAnnualReturnYear05

4.43%

Average Annual Returns, 10 Years

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3.29%