Shareholder Report

12 Months Ended

Mar. 31, 2026

USD ($)

Holding

Shareholder Report [Line Items]

Document Type

N-CSR

Amendment Flag

false

Registrant Name

MFS MUNICIPAL SERIES TRUST

Entity Central Index Key

0000751656

Entity Investment Company Type

N-1A

Document Period End Date

Mar. 31, 2026

C000194226 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® AlabamaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPOLX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Alabama Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$61	0.60%

Expenses Paid, Amount

$ 61

Expense Ratio, Percent

0.60%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Alabama Municipal Bond Fund (fund) provided a total return of 4.32%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the health care sector, most notably within A-rated securities, strengthened relative returns. Bond selection within the education sector, primarily within AA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.32%	0.67%	1.95%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 70,721,615

Holdings Count | Holding

156

Advisory Fees Paid, Amount

$ 298,721

^[1]

Investment Company Portfolio Turnover

14.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	70,721,615	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	156	Average Effective Duration (yrs):	8.9
Total Management Fee ($)#:	298,721
Portfolio Turnover Rate (%):	14

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.7%
Money Market Funds	2.3%

Industries

General Obligations - General Purpose	16.5%
Universities - Colleges	12.6%
Water & Sewer Utility Revenue	9.5%
Sales & Excise Tax Revenue	8.2%
Tax - Other	8.0%
Healthcare Revenue - Hospitals	7.1%
Single Family Housing - State	6.5%
General Obligations - Schools	5.5%
Utilities - Other	4.9%
State & Local Agencies	4.6%
Other Industries	14.3%

Composition including fixed income credit
quality

AAA	1.4%
AA	45.0%
A	31.8%
BBB	12.7%
BB	0.6%
B	0.3%
Not Rated	5.9%
Money Market Funds	2.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169758 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® AlabamaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MLALX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Alabama Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$66	0.65%

Expenses Paid, Amount

$ 66

Expense Ratio, Percent

0.65%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Alabama Municipal Bond Fund (fund) provided a total return of 4.27%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the health care sector, most notably within A-rated securities, strengthened relative returns. Bond selection within the education sector, primarily within AA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.27%	0.61%	1.88%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 70,721,615

Holdings Count | Holding

156

Advisory Fees Paid, Amount

$ 298,721

^[2]

Investment Company Portfolio Turnover

14.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	70,721,615	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	156	Average Effective Duration (yrs):	8.9
Total Management Fee ($)#:	298,721
Portfolio Turnover Rate (%):	14

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.7%
Money Market Funds	2.3%

Industries

General Obligations - General Purpose	16.5%
Universities - Colleges	12.6%
Water & Sewer Utility Revenue	9.5%
Sales & Excise Tax Revenue	8.2%
Tax - Other	8.0%
Healthcare Revenue - Hospitals	7.1%
Single Family Housing - State	6.5%
General Obligations - Schools	5.5%
Utilities - Other	4.9%
State & Local Agencies	4.6%
Other Industries	14.3%

Composition including fixed income credit quality

AAA	1.4%
AA	45.0%
A	31.8%
BBB	12.7%
BB	0.6%
B	0.3%
Not Rated	5.9%
Money Market Funds	2.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006958 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® AlabamaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBABX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Alabama Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$168	1.65%

Expenses Paid, Amount

$ 168

Expense Ratio, Percent

1.65%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Alabama Municipal Bond Fund (fund) provided a total return of 3.21%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the health care sector, most notably within A-rated securities, strengthened relative returns. Bond selection within the education sector, primarily within AA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.21%	(0.40)%	0.88%
B with CDSC (declining over six years from 4% to 0%)×	(0.79)%	(0.77)%	0.88%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 70,721,615

Holdings Count | Holding

156

Advisory Fees Paid, Amount

$ 298,721

^[3]

Investment Company Portfolio Turnover

14.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	70,721,615	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	156	Average Effective Duration (yrs):	8.9
Total Management Fee ($)#:	298,721
Portfolio Turnover Rate (%):	14

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.7%
Money Market Funds	2.3%

Industries

General Obligations - General Purpose	16.5%
Universities - Colleges	12.6%
Water & Sewer Utility Revenue	9.5%
Sales & Excise Tax Revenue	8.2%
Tax - Other	8.0%
Healthcare Revenue - Hospitals	7.1%
Single Family Housing - State	6.5%
General Obligations - Schools	5.5%
Utilities - Other	4.9%
State & Local Agencies	4.6%
Other Industries	14.3%

Composition including fixed income credit quality

AAA	1.4%
AA	45.0%
A	31.8%
BBB	12.7%
BB	0.6%
B	0.3%
Not Rated	5.9%
Money Market Funds	2.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006957 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® AlabamaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFALX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Alabama Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$92	0.90%

Expenses Paid, Amount

$ 92

Expense Ratio, Percent

0.90%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Alabama Municipal Bond Fund (fund) provided a total return of 3.87%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the health care sector, most notably within A-rated securities, strengthened relative returns. Bond selection within the education sector, primarily within AA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.87%	0.34%	1.63%
A with initial sales charge (4.25%)	(0.55)%	(0.53)%	1.19%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 70,721,615

Holdings Count | Holding

156

Advisory Fees Paid, Amount

$ 298,721

^[4]

Investment Company Portfolio Turnover

14.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	70,721,615	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	156	Average Effective Duration (yrs):	8.9
Total Management Fee ($)#:	298,721
Portfolio Turnover Rate (%):	14

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.7%
Money Market Funds	2.3%

Industries

General Obligations - General Purpose	16.5%
Universities - Colleges	12.6%
Water & Sewer Utility Revenue	9.5%
Sales & Excise Tax Revenue	8.2%
Tax - Other	8.0%
Healthcare Revenue - Hospitals	7.1%
Single Family Housing - State	6.5%
General Obligations - Schools	5.5%
Utilities - Other	4.9%
State & Local Agencies	4.6%
Other Industries	14.3%

Composition including fixed income credit quality

AAA	1.4%
AA	45.0%
A	31.8%
BBB	12.7%
BB	0.6%
B	0.3%
Not Rated	5.9%
Money Market Funds	2.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006959 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® New YorkMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MSNYX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS New York Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$85	0.83%

Expenses Paid, Amount

$ 85

Expense Ratio, Percent

0.83%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS New York Municipal Bond Fund (fund) provided a total return of 3.64%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the special tax, industrial revenue, housing, and local sectors strengthened relative returns, most notably within AA and AAA-rated securities.
  • The fund's greater exposure to the housing sector was another contributor to the fund's relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also hurt relative results.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.64%	0.51%	1.86%
A with initial sales charge (4.25%)	(0.77)%	(0.35)%	1.42%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 186,997,483

Holdings Count | Holding

183

Advisory Fees Paid, Amount

$ 789,505

^[5]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	186,997,483	Average Effective Maturity (yrs):	20.7
Total Number of Holdings:	183	Average Effective Duration (yrs):	9.1
Total Management Fee ($)#:	789,505
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Healthcare Revenue - Hospitals	14.3%
Multi-Family Housing Revenue	14.0%
Tax - Other	7.7%
Airport Revenue	7.2%
Miscellaneous Revenue - Other	5.6%
Transportation - Special Tax	5.4%
Universities - Colleges	5.1%
State & Local Agencies	4.9%
Water & Sewer Utility Revenue	4.4%
Secondary Schools	4.4%
Other Industries	25.3%

Composition including fixed income credit
quality

AAA	4.4%
AA	33.2%
A	26.1%
BBB	21.3%
BB	2.4%
B	2.3%
CCC	0.1%
CC	0.7%
Not Rated	7.8%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006960 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® New YorkMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBNYX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS New York Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$160	1.58%

Expenses Paid, Amount

$ 160

Expense Ratio, Percent

1.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS New York Municipal Bond Fund (fund) provided a total return of 2.87%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the special tax, industrial revenue, housing, and local sectors strengthened relative returns, most notably within AA and AAA-rated securities.
  • The fund's greater exposure to the housing sector was another contributor to the fund's relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also hurt relative results.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.87%	(0.26)%	1.10%
B with CDSC (declining over six years from 4% to 0%)×	(1.13)%	(0.61)%	1.10%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 186,997,483

Holdings Count | Holding

183

Advisory Fees Paid, Amount

$ 789,505

^[6]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	186,997,483	Average Effective Maturity (yrs):	20.7
Total Number of Holdings:	183	Average Effective Duration (yrs):	9.1
Total Management Fee ($)#:	789,505
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Healthcare Revenue - Hospitals	14.3%
Multi-Family Housing Revenue	14.0%
Tax - Other	7.7%
Airport Revenue	7.2%
Miscellaneous Revenue - Other	5.6%
Transportation - Special Tax	5.4%
Universities - Colleges	5.1%
State & Local Agencies	4.9%
Water & Sewer Utility Revenue	4.4%
Secondary Schools	4.4%
Other Industries	25.3%

Composition including fixed income credit quality

AAA	4.4%
AA	33.2%
A	26.1%
BBB	21.3%
BB	2.4%
B	2.3%
CCC	0.1%
CC	0.7%
Not Rated	7.8%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006961 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® New YorkMunicipal Bond Fund

Class Name

Class C

Trading Symbol

MCNYX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS New York Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$160	1.58%

Expenses Paid, Amount

$ 160

Expense Ratio, Percent

1.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS New York Municipal Bond Fund (fund) provided a total return of 2.87%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the special tax, industrial revenue, housing, and local sectors strengthened relative returns, most notably within AA and AAA-rated securities.
  • The fund's greater exposure to the housing sector was another contributor to the fund's relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also hurt relative results.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
C without sales charge	2.87%	(0.23)%	1.10%
C with CDSC (1% for 12 months)×	1.87%	(0.23)%	1.10%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 186,997,483

Holdings Count | Holding

183

Advisory Fees Paid, Amount

$ 789,505

^[7]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	186,997,483	Average Effective Maturity (yrs):	20.7
Total Number of Holdings:	183	Average Effective Duration (yrs):	9.1
Total Management Fee ($)#:	789,505
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Healthcare Revenue - Hospitals	14.3%
Multi-Family Housing Revenue	14.0%
Tax - Other	7.7%
Airport Revenue	7.2%
Miscellaneous Revenue - Other	5.6%
Transportation - Special Tax	5.4%
Universities - Colleges	5.1%
State & Local Agencies	4.9%
Water & Sewer Utility Revenue	4.4%
Secondary Schools	4.4%
Other Industries	25.3%

Composition including fixed income credit quality

AAA	4.4%
AA	33.2%
A	26.1%
BBB	21.3%
BB	2.4%
B	2.3%
CCC	0.1%
CC	0.7%
Not Rated	7.8%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169759 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® New YorkMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MNYLX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS New York Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$59	0.58%

Expenses Paid, Amount

$ 59

Expense Ratio, Percent

0.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS New York Municipal Bond Fund (fund) provided a total return of 3.89%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the special tax, industrial revenue, housing, and local sectors strengthened relative returns, most notably within AA and AAA-rated securities.
  • The fund's greater exposure to the housing sector was another contributor to the fund's relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also hurt relative results.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.89%	0.76%	2.12%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 186,997,483

Holdings Count | Holding

183

Advisory Fees Paid, Amount

$ 789,505

^[8]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	186,997,483	Average Effective Maturity (yrs):	20.7
Total Number of Holdings:	183	Average Effective Duration (yrs):	9.1
Total Management Fee ($)#:	789,505
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Healthcare Revenue - Hospitals	14.3%
Multi-Family Housing Revenue	14.0%
Tax - Other	7.7%
Airport Revenue	7.2%
Miscellaneous Revenue - Other	5.6%
Transportation - Special Tax	5.4%
Universities - Colleges	5.1%
State & Local Agencies	4.9%
Water & Sewer Utility Revenue	4.4%
Secondary Schools	4.4%
Other Industries	25.3%

Composition including fixed income credit
quality

AAA	4.4%
AA	33.2%
A	26.1%
BBB	21.3%
BB	2.4%
B	2.3%
CCC	0.1%
CC	0.7%
Not Rated	7.8%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194228 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® New YorkMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPNYX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS New York Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$51	0.50%

Expenses Paid, Amount

$ 51

Expense Ratio, Percent

0.50%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS New York Municipal Bond Fund (fund) provided a total return of 3.98%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the special tax, industrial revenue, housing, and local sectors strengthened relative returns, most notably within AA and AAA-rated securities.
  • The fund's greater exposure to the housing sector was another contributor to the fund's relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also hurt relative results.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	3.98%	0.86%	2.13%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 186,997,483

Holdings Count | Holding

183

Advisory Fees Paid, Amount

$ 789,505

^[9]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	186,997,483	Average Effective Maturity (yrs):	20.7
Total Number of Holdings:	183	Average Effective Duration (yrs):	9.1
Total Management Fee ($)#:	789,505
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Healthcare Revenue - Hospitals	14.3%
Multi-Family Housing Revenue	14.0%
Tax - Other	7.7%
Airport Revenue	7.2%
Miscellaneous Revenue - Other	5.6%
Transportation - Special Tax	5.4%
Universities - Colleges	5.1%
State & Local Agencies	4.9%
Water & Sewer Utility Revenue	4.4%
Secondary Schools	4.4%
Other Industries	25.3%

Composition including fixed income credit
quality

AAA	4.4%
AA	33.2%
A	26.1%
BBB	21.3%
BB	2.4%
B	2.3%
CCC	0.1%
CC	0.7%
Not Rated	7.8%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194230 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® North CarolinaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPNCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS North Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$53	0.52%

Expenses Paid, Amount

$ 53

Expense Ratio, Percent

0.52%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS North Carolina Municipal Bond Fund (fund) provided a total return of 4.07%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and health care sectors strengthened relative results, most notably within AA, AAA and BBB-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.07%	0.89%	2.03%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 546,644,837

Holdings Count | Holding

304

Advisory Fees Paid, Amount

$ 2,182,504

^[10]

Investment Company Portfolio Turnover

6.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	546,644,837	Average Effective Maturity (yrs):	18.9
Total Number of Holdings:	304	Average Effective Duration (yrs):	8.8
Total Management Fee ($)#:	2,182,504
Portfolio Turnover Rate (%):	6

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.1%
Money Market Funds	2.9%

Industries

Water & Sewer Utility Revenue	17.6%
Single Family Housing - State	10.1%
State & Local Agencies	9.8%
Universities - Colleges	9.7%
Healthcare Revenue - Long Term Care	8.8%
Healthcare Revenue - Hospitals	7.5%
Airport Revenue	7.0%
Multi-Family Housing Revenue	4.9%
General Obligations - General Purpose	3.9%
Toll Roads	3.8%
Other Industries	14.0%

Composition including fixed income credit quality

AAA	9.1%
AA	52.9%
A	14.2%
BBB	12.7%
BB	0.4%
B	0.0%
CCC	0.4%
Not Rated	7.4%
Money Market Funds	2.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169760 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® North CarolinaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MNCLX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS North Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$60	0.59%

Expenses Paid, Amount

$ 60

Expense Ratio, Percent

0.59%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS North Carolina Municipal Bond Fund (fund) provided a total return of 3.99%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and health care sectors strengthened relative results, most notably within AA, AAA and BBB-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.99%	0.82%	1.97%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 546,644,837

Holdings Count | Holding

304

Advisory Fees Paid, Amount

$ 2,182,504

^[11]

Investment Company Portfolio Turnover

6.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	546,644,837	Average Effective Maturity (yrs):	18.9
Total Number of Holdings:	304	Average Effective Duration (yrs):	8.8
Total Management Fee ($)#:	2,182,504
Portfolio Turnover Rate (%):	6

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.1%
Money Market Funds	2.9%

Industries

Water & Sewer Utility Revenue	17.6%
Single Family Housing - State	10.1%
State & Local Agencies	9.8%
Universities - Colleges	9.7%
Healthcare Revenue - Long Term Care	8.8%
Healthcare Revenue - Hospitals	7.5%
Airport Revenue	7.0%
Multi-Family Housing Revenue	4.9%
General Obligations - General Purpose	3.9%
Toll Roads	3.8%
Other Industries	14.0%

Composition including fixed income credit
quality

AAA	9.1%
AA	52.9%
A	14.2%
BBB	12.7%
BB	0.4%
B	0.0%
CCC	0.4%
Not Rated	7.4%
Money Market Funds	2.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006964 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® North CarolinaMunicipal Bond Fund

Class Name

Class C

Trading Symbol

MCNCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS North Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$161	1.59%

Expenses Paid, Amount

$ 161

Expense Ratio, Percent

1.59%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS North Carolina Municipal Bond Fund (fund) provided a total return of 2.91%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and health care sectors strengthened relative results, most notably within AA, AAA and BBB-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
C without sales charge	2.91%	(0.19)%	0.94%
C with CDSC (1% for 12 months)×	1.91%	(0.19)%	0.94%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 546,644,837

Holdings Count | Holding

304

Advisory Fees Paid, Amount

$ 2,182,504

^[12]

Investment Company Portfolio Turnover

6.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	546,644,837	Average Effective Maturity (yrs):	18.9
Total Number of Holdings:	304	Average Effective Duration (yrs):	8.8
Total Management Fee ($)#:	2,182,504
Portfolio Turnover Rate (%):	6

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.1%
Money Market Funds	2.9%

Industries

Water & Sewer Utility Revenue	17.6%
Single Family Housing - State	10.1%
State & Local Agencies	9.8%
Universities - Colleges	9.7%
Healthcare Revenue - Long Term Care	8.8%
Healthcare Revenue - Hospitals	7.5%
Airport Revenue	7.0%
Multi-Family Housing Revenue	4.9%
General Obligations - General Purpose	3.9%
Toll Roads	3.8%
Other Industries	14.0%

Composition including fixed income credit
quality

AAA	9.1%
AA	52.9%
A	14.2%
BBB	12.7%
BB	0.4%
B	0.0%
CCC	0.4%
Not Rated	7.4%
Money Market Funds	2.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006963 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® North CarolinaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBNCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS North Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$161	1.59%

Expenses Paid, Amount

$ 161

Expense Ratio, Percent

1.59%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS North Carolina Municipal Bond Fund (fund) provided a total return of 2.91%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and health care sectors strengthened relative results, most notably within AA, AAA and BBB-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.91%	(0.19)%	0.94%
B with CDSC (declining over six years from 4% to 0%)×	(1.09)%	(0.56)%	0.94%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 546,644,837

Holdings Count | Holding

304

Advisory Fees Paid, Amount

$ 2,182,504

^[13]

Investment Company Portfolio Turnover

6.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	546,644,837	Average Effective Maturity (yrs):	18.9
Total Number of Holdings:	304	Average Effective Duration (yrs):	8.8
Total Management Fee ($)#:	2,182,504
Portfolio Turnover Rate (%):	6

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.1%
Money Market Funds	2.9%

Industries

Water & Sewer Utility Revenue	17.6%
Single Family Housing - State	10.1%
State & Local Agencies	9.8%
Universities - Colleges	9.7%
Healthcare Revenue - Long Term Care	8.8%
Healthcare Revenue - Hospitals	7.5%
Airport Revenue	7.0%
Multi-Family Housing Revenue	4.9%
General Obligations - General Purpose	3.9%
Toll Roads	3.8%
Other Industries	14.0%

Composition including fixed income credit
quality

AAA	9.1%
AA	52.9%
A	14.2%
BBB	12.7%
BB	0.4%
B	0.0%
CCC	0.4%
Not Rated	7.4%
Money Market Funds	2.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006962 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® North CarolinaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MSNCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS North Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$86	0.84%

Expenses Paid, Amount

$ 86

Expense Ratio, Percent

0.84%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS North Carolina Municipal Bond Fund (fund) provided a total return of 3.68%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and health care sectors strengthened relative results, most notably within AA, AAA and BBB-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.68%	0.57%	1.70%
A with initial sales charge (4.25%)	(0.73)%	(0.30)%	1.26%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 546,644,837

Holdings Count | Holding

304

Advisory Fees Paid, Amount

$ 2,182,504

^[14]

Investment Company Portfolio Turnover

6.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	546,644,837	Average Effective Maturity (yrs):	18.9
Total Number of Holdings:	304	Average Effective Duration (yrs):	8.8
Total Management Fee ($)#:	2,182,504
Portfolio Turnover Rate (%):	6

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.1%
Money Market Funds	2.9%

Industries

Water & Sewer Utility Revenue	17.6%
Single Family Housing - State	10.1%
State & Local Agencies	9.8%
Universities - Colleges	9.7%
Healthcare Revenue - Long Term Care	8.8%
Healthcare Revenue - Hospitals	7.5%
Airport Revenue	7.0%
Multi-Family Housing Revenue	4.9%
General Obligations - General Purpose	3.9%
Toll Roads	3.8%
Other Industries	14.0%

Composition including fixed income credit
quality

AAA	9.1%
AA	52.9%
A	14.2%
BBB	12.7%
BB	0.4%
B	0.0%
CCC	0.4%
Not Rated	7.4%
Money Market Funds	2.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006967 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® South CarolinaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFSCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS South Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$88	0.86%

Expenses Paid, Amount

$ 88

Expense Ratio, Percent

0.86%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS South Carolina Municipal Bond Fund (fund) provided a total return of 3.82%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, leasing, and education sectors strengthened relative returns, most notably within AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.82%	0.37%	1.55%
A with initial sales charge (4.25%)	(0.59)%	(0.50)%	1.11%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 239,482,607

Holdings Count | Holding

220

Advisory Fees Paid, Amount

$ 966,673

^[15]

Investment Company Portfolio Turnover

21.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	239,482,607	Average Effective Maturity (yrs):	20.3
Total Number of Holdings:	220	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	966,673
Portfolio Turnover Rate (%):	21

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.1%
Money Market Funds	3.9%

Industries

Water & Sewer Utility Revenue	12.7%
Healthcare Revenue - Hospitals	12.5%
Single Family Housing - State	10.6%
State & Local Agencies	10.3%
Universities - Colleges	6.8%
General Obligations - Schools	5.1%
Multi-Family Housing Revenue	5.1%
Utilities - Other	4.5%
Utilities - Municipal Owned	4.3%
Airport Revenue	3.7%
Other Industries	20.5%

Composition including fixed income credit quality

AAA	12.1%
AA	36.5%
A	30.7%
BBB	7.5%
BB	2.0%
B	0.1%
Not Rated	7.2%
Money Market Funds	3.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006968 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® South CarolinaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBSCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS South Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$162	1.60%

Expenses Paid, Amount

$ 162

Expense Ratio, Percent

1.60%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS South Carolina Municipal Bond Fund (fund) provided a total return of 2.96%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, leasing, and education sectors strengthened relative returns, most notably within AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.96%	(0.40)%	0.80%
B with CDSC (declining over six years from 4% to 0%)×	(1.04)%	(0.76)%	0.80%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 239,482,607

Holdings Count | Holding

220

Advisory Fees Paid, Amount

$ 966,673

^[16]

Investment Company Portfolio Turnover

21.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	239,482,607	Average Effective Maturity (yrs):	20.3
Total Number of Holdings:	220	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	966,673
Portfolio Turnover Rate (%):	21

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.1%
Money Market Funds	3.9%

Industries

Water & Sewer Utility Revenue	12.7%
Healthcare Revenue - Hospitals	12.5%
Single Family Housing - State	10.6%
State & Local Agencies	10.3%
Universities - Colleges	6.8%
General Obligations - Schools	5.1%
Multi-Family Housing Revenue	5.1%
Utilities - Other	4.5%
Utilities - Municipal Owned	4.3%
Airport Revenue	3.7%
Other Industries	20.5%

Composition including fixed income credit quality

AAA	12.1%
AA	36.5%
A	30.7%
BBB	7.5%
BB	2.0%
B	0.1%
Not Rated	7.2%
Money Market Funds	3.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169762 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® South CarolinaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MTSCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS South Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$62	0.61%

Expenses Paid, Amount

$ 62

Expense Ratio, Percent

0.61%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS South Carolina Municipal Bond Fund (fund) provided a total return of 4.02%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, leasing, and education sectors strengthened relative returns, most notably within AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.02%	0.60%	1.81%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 239,482,607

Holdings Count | Holding

220

Advisory Fees Paid, Amount

$ 966,673

^[17]

Investment Company Portfolio Turnover

21.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	239,482,607	Average Effective Maturity (yrs):	20.3
Total Number of Holdings:	220	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	966,673
Portfolio Turnover Rate (%):	21

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.1%
Money Market Funds	3.9%

Industries

Water & Sewer Utility Revenue	12.7%
Healthcare Revenue - Hospitals	12.5%
Single Family Housing - State	10.6%
State & Local Agencies	10.3%
Universities - Colleges	6.8%
General Obligations - Schools	5.1%
Multi-Family Housing Revenue	5.1%
Utilities - Other	4.5%
Utilities - Municipal Owned	4.3%
Airport Revenue	3.7%
Other Industries	20.5%

Composition including fixed income credit
quality

AAA	12.1%
AA	36.5%
A	30.7%
BBB	7.5%
BB	2.0%
B	0.1%
Not Rated	7.2%
Money Market Funds	3.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194234 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® South CarolinaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPOCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS South Carolina Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$55	0.54%

Expenses Paid, Amount

$ 55

Expense Ratio, Percent

0.54%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS South Carolina Municipal Bond Fund (fund) provided a total return of 4.10%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, leasing, and education sectors strengthened relative returns, most notably within AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.10%	0.67%	1.88%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 239,482,607

Holdings Count | Holding

220

Advisory Fees Paid, Amount

$ 966,673

^[18]

Investment Company Portfolio Turnover

21.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	239,482,607	Average Effective Maturity (yrs):	20.3
Total Number of Holdings:	220	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	966,673
Portfolio Turnover Rate (%):	21

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.1%
Money Market Funds	3.9%

Industries

Water & Sewer Utility Revenue	12.7%
Healthcare Revenue - Hospitals	12.5%
Single Family Housing - State	10.6%
State & Local Agencies	10.3%
Universities - Colleges	6.8%
General Obligations - Schools	5.1%
Multi-Family Housing Revenue	5.1%
Utilities - Other	4.5%
Utilities - Municipal Owned	4.3%
Airport Revenue	3.7%
Other Industries	20.5%

Composition including fixed income credit
quality

AAA	12.1%
AA	36.5%
A	30.7%
BBB	7.5%
BB	2.0%
B	0.1%
Not Rated	7.2%
Money Market Funds	3.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194238 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® VirginiaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPVOX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$51	0.50%

Expenses Paid, Amount

$ 51

Expense Ratio, Percent

0.50%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Virginia Municipal Bond Fund (fund) provided a total return of 3.89%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of security selection and a greater exposure to the housing sector strengthened relative returns, most notably within AAA-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	3.89%	0.72%	1.99%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 345,095,722

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 1,519,081

^[19]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	345,095,722	Average Effective Maturity (yrs):	18.6
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.4
Total Management Fee ($)#:	1,519,081
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.9%
Money Market Funds	2.1%

Industries

Healthcare Revenue - Hospitals	14.1%
Multi-Family Housing Revenue	13.9%
Water & Sewer Utility Revenue	9.0%
State & Local Agencies	8.8%
General Obligations - General Purpose	8.2%
Toll Roads	6.8%
Universities - Colleges	6.2%
Sales & Excise Tax Revenue	6.0%
Utilities - Other	3.5%
Healthcare Revenue - Long Term Care	3.5%
Other Industries	17.9%

Composition including fixed income credit quality

AAA	12.7%
AA	49.5%
A	17.2%
BBB	11.1%
BB	1.2%
B	0.4%
CCC	0.5%
Not Rated	5.3%
Money Market Funds	2.1%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169764 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® VirginiaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MIVAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$59	0.58%

Expenses Paid, Amount

$ 59

Expense Ratio, Percent

0.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Virginia Municipal Bond Fund (fund) provided a total return of 3.69%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of security selection and a greater exposure to the housing sector strengthened relative returns, most notably within AAA-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.69%	0.61%	1.91%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 345,095,722

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 1,519,081

^[20]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	345,095,722	Average Effective Maturity (yrs):	18.6
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.4
Total Management Fee ($)#:	1,519,081
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.9%
Money Market Funds	2.1%

Industries

Healthcare Revenue - Hospitals	14.1%
Multi-Family Housing Revenue	13.9%
Water & Sewer Utility Revenue	9.0%
State & Local Agencies	8.8%
General Obligations - General Purpose	8.2%
Toll Roads	6.8%
Universities - Colleges	6.2%
Sales & Excise Tax Revenue	6.0%
Utilities - Other	3.5%
Healthcare Revenue - Long Term Care	3.5%
Other Industries	17.9%

Composition including fixed income credit
quality

AAA	12.7%
AA	49.5%
A	17.2%
BBB	11.1%
BB	1.2%
B	0.4%
CCC	0.5%
Not Rated	5.3%
Money Market Funds	2.1%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006973 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® VirginiaMunicipal Bond Fund

Class Name

Class C

Trading Symbol

MVACX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$160	1.58%

Expenses Paid, Amount

$ 160

Expense Ratio, Percent

1.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS Virginia Municipal Bond Fund (fund) provided a total return of 2.66%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of security selection and a greater exposure to the housing sector strengthened relative returns, most notably within AAA-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
C without sales charge	2.66%	(0.38)%	0.89%
C with CDSC (1% for 12 months)×	1.66%	(0.38)%	0.89%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 345,095,722

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 1,519,081

^[21]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	345,095,722	Average Effective Maturity (yrs):	18.6
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.4
Total Management Fee ($)#:	1,519,081
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.9%
Money Market Funds	2.1%

Industries

Healthcare Revenue - Hospitals	14.1%
Multi-Family Housing Revenue	13.9%
Water & Sewer Utility Revenue	9.0%
State & Local Agencies	8.8%
General Obligations - General Purpose	8.2%
Toll Roads	6.8%
Universities - Colleges	6.2%
Sales & Excise Tax Revenue	6.0%
Utilities - Other	3.5%
Healthcare Revenue - Long Term Care	3.5%
Other Industries	17.9%

Composition including fixed income credit
quality

AAA	12.7%
AA	49.5%
A	17.2%
BBB	11.1%
BB	1.2%
B	0.4%
CCC	0.5%
Not Rated	5.3%
Money Market Funds	2.1%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006972 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® VirginiaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBVAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$160	1.58%

Expenses Paid, Amount

$ 160

Expense Ratio, Percent

1.58%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Virginia Municipal Bond Fund (fund) provided a total return of 2.66%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of security selection and a greater exposure to the housing sector strengthened relative returns, most notably within AAA-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.66%	(0.38)%	0.89%
B with CDSC (declining over six years from 4% to 0%)×	(1.34)%	(0.74)%	0.89%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 345,095,722

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 1,519,081

^[22]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	345,095,722	Average Effective Maturity (yrs):	18.6
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.4
Total Management Fee ($)#:	1,519,081
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.9%
Money Market Funds	2.1%

Industries

Healthcare Revenue - Hospitals	14.1%
Multi-Family Housing Revenue	13.9%
Water & Sewer Utility Revenue	9.0%
State & Local Agencies	8.8%
General Obligations - General Purpose	8.2%
Toll Roads	6.8%
Universities - Colleges	6.2%
Sales & Excise Tax Revenue	6.0%
Utilities - Other	3.5%
Healthcare Revenue - Long Term Care	3.5%
Other Industries	17.9%

Composition including fixed income credit
quality

AAA	12.7%
AA	49.5%
A	17.2%
BBB	11.1%
BB	1.2%
B	0.4%
CCC	0.5%
Not Rated	5.3%
Money Market Funds	2.1%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006971 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® VirginiaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MSVAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$84	0.83%

Expenses Paid, Amount

$ 84

Expense Ratio, Percent

0.83%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Virginia Municipal Bond Fund (fund) provided a total return of 3.42%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of security selection and a greater exposure to the housing sector strengthened relative returns, most notably within AAA-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.42%	0.36%	1.65%
A with initial sales charge (4.25%)	(0.97)%	(0.50)%	1.21%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 345,095,722

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 1,519,081

^[23]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	345,095,722	Average Effective Maturity (yrs):	18.6
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.4
Total Management Fee ($)#:	1,519,081
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.9%
Money Market Funds	2.1%

Industries

Healthcare Revenue - Hospitals	14.1%
Multi-Family Housing Revenue	13.9%
Water & Sewer Utility Revenue	9.0%
State & Local Agencies	8.8%
General Obligations - General Purpose	8.2%
Toll Roads	6.8%
Universities - Colleges	6.2%
Sales & Excise Tax Revenue	6.0%
Utilities - Other	3.5%
Healthcare Revenue - Long Term Care	3.5%
Other Industries	17.9%

Composition including fixed income credit
quality

AAA	12.7%
AA	49.5%
A	17.2%
BBB	11.1%
BB	1.2%
B	0.4%
CCC	0.5%
Not Rated	5.3%
Money Market Funds	2.1%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006974 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® West VirginiaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFWVX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS West Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$89	0.87%

Expenses Paid, Amount

$ 89

Expense Ratio, Percent

0.87%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS West Virginia Municipal Bond Fund (fund) provided a total return of 3.77%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, special tax, and leasing sectors strengthened relative returns, most notably within AAA and AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • Security selection within the health care sector was another area of relative underperformance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.77%	0.64%	1.69%
A with initial sales charge (4.25%)	(0.64)%	(0.23)%	1.25%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 83,788,269

Holdings Count | Holding

136

Advisory Fees Paid, Amount

$ 375,449

^[24]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	83,788,269	Average Effective Maturity (yrs):	18.0
Total Number of Holdings:	136	Average Effective Duration (yrs):	7.7
Total Management Fee ($)#:	375,449
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Hospitals	16.0%
Single Family Housing - State	14.6%
Water & Sewer Utility Revenue	12.2%
State & Local Agencies	9.2%
Universities - Colleges	8.1%
General Obligations - General Purpose	8.1%
Sales & Excise Tax Revenue	6.9%
Miscellaneous Revenue - Other	5.1%
General Obligations - Schools	4.5%
Tax - Other	3.7%
Other Industries	10.0%

Composition including fixed income credit
quality

AAA	14.6%
AA	32.0%
A	31.3%
BBB	8.9%
BB	2.3%
B	0.1%
Not Rated	9.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006975 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® West VirginiaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBWVX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS West Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$164	1.62%

Expenses Paid, Amount

$ 164

Expense Ratio, Percent

1.62%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS West Virginia Municipal Bond Fund (fund) provided a total return of 3.00%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, special tax, and leasing sectors strengthened relative returns, most notably within AAA and AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • Security selection within the health care sector was another area of relative underperformance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.00%	(0.11)%	0.92%
B with CDSC (declining over six years from 4% to 0%)×	(1.00)%	(0.47)%	0.92%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 83,788,269

Holdings Count | Holding

136

Advisory Fees Paid, Amount

$ 375,449

^[25]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	83,788,269	Average Effective Maturity (yrs):	18.0
Total Number of Holdings:	136	Average Effective Duration (yrs):	7.7
Total Management Fee ($)#:	375,449
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Hospitals	16.0%
Single Family Housing - State	14.6%
Water & Sewer Utility Revenue	12.2%
State & Local Agencies	9.2%
Universities - Colleges	8.1%
General Obligations - General Purpose	8.1%
Sales & Excise Tax Revenue	6.9%
Miscellaneous Revenue - Other	5.1%
General Obligations - Schools	4.5%
Tax - Other	3.7%
Other Industries	10.0%

Composition including fixed income credit
quality

AAA	14.6%
AA	32.0%
A	31.3%
BBB	8.9%
BB	2.3%
B	0.1%
Not Rated	9.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169765 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® West VirginiaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MWVIX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS West Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$63	0.62%

Expenses Paid, Amount

$ 63

Expense Ratio, Percent

0.62%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS West Virginia Municipal Bond Fund (fund) provided a total return of 4.10%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, special tax, and leasing sectors strengthened relative returns, most notably within AAA and AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • Security selection within the health care sector was another area of relative underperformance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.10%	0.92%	1.95%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 83,788,269

Holdings Count | Holding

136

Advisory Fees Paid, Amount

$ 375,449

^[26]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	83,788,269	Average Effective Maturity (yrs):	18.0
Total Number of Holdings:	136	Average Effective Duration (yrs):	7.7
Total Management Fee ($)#:	375,449
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Hospitals	16.0%
Single Family Housing - State	14.6%
Water & Sewer Utility Revenue	12.2%
State & Local Agencies	9.2%
Universities - Colleges	8.1%
General Obligations - General Purpose	8.1%
Sales & Excise Tax Revenue	6.9%
Miscellaneous Revenue - Other	5.1%
General Obligations - Schools	4.5%
Tax - Other	3.7%
Other Industries	10.0%

Composition including fixed income credit quality

AAA	14.6%
AA	32.0%
A	31.3%
BBB	8.9%
BB	2.3%
B	0.1%
Not Rated	9.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194240 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® West VirginiaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPWVX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS West Virginia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$56	0.55%

Expenses Paid, Amount

$ 56

Expense Ratio, Percent

0.55%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS West Virginia Municipal Bond Fund (fund) provided a total return of 4.17%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within the housing, special tax, and leasing sectors strengthened relative returns, most notably within AAA and AA-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.
  • Security selection within the health care sector was another area of relative underperformance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.17%	0.99%	2.03%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 83,788,269

Holdings Count | Holding

136

Advisory Fees Paid, Amount

$ 375,449

^[27]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	83,788,269	Average Effective Maturity (yrs):	18.0
Total Number of Holdings:	136	Average Effective Duration (yrs):	7.7
Total Management Fee ($)#:	375,449
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Hospitals	16.0%
Single Family Housing - State	14.6%
Water & Sewer Utility Revenue	12.2%
State & Local Agencies	9.2%
Universities - Colleges	8.1%
General Obligations - General Purpose	8.1%
Sales & Excise Tax Revenue	6.9%
Miscellaneous Revenue - Other	5.1%
General Obligations - Schools	4.5%
Tax - Other	3.7%
Other Industries	10.0%

Composition including fixed income credit
quality

AAA	14.6%
AA	32.0%
A	31.3%
BBB	8.9%
BB	2.3%
B	0.1%
Not Rated	9.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194242 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® ArkansasMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPRAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Arkansas Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$54	0.53%

Expenses Paid, Amount

$ 54

Expense Ratio, Percent

0.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Arkansas Municipal Bond Fund (fund) provided a total return of 4.31%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • From a quality perspective, favorable bond selection within AA-rated securities also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.31%	0.77%	1.96%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 140,288,015

Holdings Count | Holding

184

Advisory Fees Paid, Amount

$ 615,574

^[28]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	140,288,015	Average Effective Maturity (yrs):	17.2
Total Number of Holdings:	184	Average Effective Duration (yrs):	7.5
Total Management Fee ($)#:	615,574
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.3%
Money Market Funds	0.7%

Industries

Sales & Excise Tax Revenue	19.7%
Water & Sewer Utility Revenue	17.0%
Healthcare Revenue - Hospitals	12.2%
Universities - Colleges	12.0%
General Obligations - Schools	8.5%
Single Family Housing - State	7.9%
Miscellaneous Revenue - Other	5.4%
Utilities - Other	4.0%
Tax - Other	3.3%
Tobacco	2.6%
Other Industries	6.7%

Composition including fixed income credit
quality

AAA	2.6%
AA	59.8%
A	18.0%
BBB	8.3%
BB	3.5%
B	0.1%
Not Rated	7.0%
Money Market Funds	0.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169766 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® ArkansasMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MARLX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Arkansas Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$61	0.60%

Expenses Paid, Amount

$ 61

Expense Ratio, Percent

0.60%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Arkansas Municipal Bond Fund (fund) provided a total return of 4.23%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • From a quality perspective, favorable bond selection within AA-rated securities also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.23%	0.69%	1.84%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 140,288,015

Holdings Count | Holding

184

Advisory Fees Paid, Amount

$ 615,574

^[29]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	140,288,015	Average Effective Maturity (yrs):	17.2
Total Number of Holdings:	184	Average Effective Duration (yrs):	7.5
Total Management Fee ($)#:	615,574
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.3%
Money Market Funds	0.7%

Industries

Sales & Excise Tax Revenue	19.7%
Water & Sewer Utility Revenue	17.0%
Healthcare Revenue - Hospitals	12.2%
Universities - Colleges	12.0%
General Obligations - Schools	8.5%
Single Family Housing - State	7.9%
Miscellaneous Revenue - Other	5.4%
Utilities - Other	4.0%
Tax - Other	3.3%
Tobacco	2.6%
Other Industries	6.7%

Composition including fixed income credit
quality

AAA	2.6%
AA	59.8%
A	18.0%
BBB	8.3%
BB	3.5%
B	0.1%
Not Rated	7.0%
Money Market Funds	0.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006977 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® ArkansasMunicipal Bond Fund

Class Name

CLASS B

Trading Symbol

MBARX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Arkansas Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$147	1.45%

Expenses Paid, Amount

$ 147

Expense Ratio, Percent

1.45%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Arkansas Municipal Bond Fund (fund) provided a total return of 3.35%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • From a quality perspective, favorable bond selection within AA-rated securities also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.35%	(0.15)%	1.00%
B with CDSC (declining over six years from 4% to 0%)×	(0.65)%	(0.51)%	1.00%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 140,288,015

Holdings Count | Holding

184

Advisory Fees Paid, Amount

$ 615,574

^[30]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	140,288,015	Average Effective Maturity (yrs):	17.2
Total Number of Holdings:	184	Average Effective Duration (yrs):	7.5
Total Management Fee ($)#:	615,574
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.3%
Money Market Funds	0.7%

Industries

Sales & Excise Tax Revenue	19.7%
Water & Sewer Utility Revenue	17.0%
Healthcare Revenue - Hospitals	12.2%
Universities - Colleges	12.0%
General Obligations - Schools	8.5%
Single Family Housing - State	7.9%
Miscellaneous Revenue - Other	5.4%
Utilities - Other	4.0%
Tax - Other	3.3%
Tobacco	2.6%
Other Industries	6.7%

Composition including fixed income credit
quality

AAA	2.6%
AA	59.8%
A	18.0%
BBB	8.3%
BB	3.5%
B	0.1%
Not Rated	7.0%
Money Market Funds	0.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006976 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® ArkansasMunicipal Bond Fund

Class Name

CLASS A

Trading Symbol

MFARX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Arkansas Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$71	0.70%

Expenses Paid, Amount

$ 71

Expense Ratio, Percent

0.70%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Arkansas Municipal Bond Fund (fund) provided a total return of 4.13%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • From a quality perspective, favorable bond selection within AA-rated securities also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	4.13%	0.59%	1.75%
A with initial sales charge (4.25%)	(0.30)%	(0.28)%	1.31%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 140,288,015

Holdings Count | Holding

184

Advisory Fees Paid, Amount

$ 615,574

^[31]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	140,288,015	Average Effective Maturity (yrs):	17.2
Total Number of Holdings:	184	Average Effective Duration (yrs):	7.5
Total Management Fee ($)#:	615,574
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.3%
Money Market Funds	0.7%

Industries

Sales & Excise Tax Revenue	19.7%
Water & Sewer Utility Revenue	17.0%
Healthcare Revenue - Hospitals	12.2%
Universities - Colleges	12.0%
General Obligations - Schools	8.5%
Single Family Housing - State	7.9%
Miscellaneous Revenue - Other	5.4%
Utilities - Other	4.0%
Tax - Other	3.3%
Tobacco	2.6%
Other Industries	6.7%

Composition including fixed income credit
quality

AAA	2.6%
AA	59.8%
A	18.0%
BBB	8.3%
BB	3.5%
B	0.1%
Not Rated	7.0%
Money Market Funds	0.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006978 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® CaliforniaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MCFTX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS California Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Material Fund Change Notice [Text Block]

This report describes certain changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$68	0.67%

Expenses Paid, Amount

$ 68

Expense Ratio, Percent

0.67%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS California Municipal Bond Fund (fund) provided a total return of 3.64%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AAA-rated securities, also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities within the education sector also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.64%	0.52%	2.04%
A with initial sales charge (4.25%)	(0.76)%	(0.35)%	1.59%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Material Change Date

Aug. 01, 2025

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 790,370,826

Holdings Count | Holding

435

Advisory Fees Paid, Amount

$ 3,138,229

^[32]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	790,370,826	Average Effective Maturity (yrs):	19.8
Total Number of Holdings:	435	Average Effective Duration (yrs):	9.2
Total Management Fee ($)#:	3,138,229
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.8%
Money Market Funds	4.2%

Industries

Multi-Family Housing Revenue	14.2%
General Obligations - Schools	13.3%
Healthcare Revenue - Hospitals	11.0%
Airport Revenue	10.1%
Utilities - Other	8.9%
State & Local Agencies	5.2%
Tax Assessment	4.8%
Secondary Schools	4.1%
Water & Sewer Utility Revenue	3.6%
Universities - Colleges	3.5%
Other Industries	17.1%

Composition including fixed income credit
quality

AAA	0.8%
AA	47.9%
A	22.6%
BBB	12.3%
BB	2.1%
B	0.2%
Not Rated	9.9%
Money Market Funds	4.2%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

Material Fund Change [Text Block]

MATERIAL FUND CHANGES

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Effective August 1, 2025, for Class A shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.65% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Material Fund Change Expenses [Text Block]

Effective August 1, 2025, for Class A shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.65% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Summary of Change Legend [Text Block]

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Updated Prospectus Phone Number

1‑800‑225‑2606

Updated Prospectus Web Address

funds.mfs.com

C000006979 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® CaliforniaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBCAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS California Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Material Fund Change Notice [Text Block]

This report describes certain changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$144	1.42%

Expenses Paid, Amount

$ 144

Expense Ratio, Percent

1.42%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS California Municipal Bond Fund (fund) provided a total return of 2.88%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AAA-rated securities, also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities within the education sector also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.88%	(0.22)%	1.28%
B with CDSC (declining over six years from 4% to 0%)×	(1.12)%	(0.58)%	1.28%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Material Change Date

Aug. 01, 2025

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 790,370,826

Holdings Count | Holding

435

Advisory Fees Paid, Amount

$ 3,138,229

^[33]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	790,370,826	Average Effective Maturity (yrs):	19.8
Total Number of Holdings:	435	Average Effective Duration (yrs):	9.2
Total Management Fee ($)#:	3,138,229
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.8%
Money Market Funds	4.2%

Industries

Multi-Family Housing Revenue	14.2%
General Obligations - Schools	13.3%
Healthcare Revenue - Hospitals	11.0%
Airport Revenue	10.1%
Utilities - Other	8.9%
State & Local Agencies	5.2%
Tax Assessment	4.8%
Secondary Schools	4.1%
Water & Sewer Utility Revenue	3.6%
Universities - Colleges	3.5%
Other Industries	17.1%

Composition including fixed income credit
quality

AAA	0.8%
AA	47.9%
A	22.6%
BBB	12.3%
BB	2.1%
B	0.2%
Not Rated	9.9%
Money Market Funds	4.2%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

Material Fund Change [Text Block]

MATERIAL FUND CHANGES

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Effective August 1, 2025, for Class B shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 1.40% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Material Fund Change Expenses [Text Block]

Effective August 1, 2025, for Class B shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 1.40% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Summary of Change Legend [Text Block]

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Updated Prospectus Phone Number

1‑800‑225‑2606

Updated Prospectus Web Address

funds.mfs.com

C000006980 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® CaliforniaMunicipal Bond Fund

Class Name

Class C

Trading Symbol

MCCAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS California Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Material Fund Change Notice [Text Block]

This report describes certain changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$159	1.57%

Expenses Paid, Amount

$ 159

Expense Ratio, Percent

1.57%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS California Municipal Bond Fund (fund) provided a total return of 2.72%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AAA-rated securities, also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities within the education sector also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
C without sales charge	2.72%	(0.40)%	1.11%
C with CDSC (1% for 12 months)×	1.72%	(0.40)%	1.11%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Material Change Date

Aug. 01, 2025

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 790,370,826

Holdings Count | Holding

435

Advisory Fees Paid, Amount

$ 3,138,229

^[34]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	790,370,826	Average Effective Maturity (yrs):	19.8
Total Number of Holdings:	435	Average Effective Duration (yrs):	9.2
Total Management Fee ($)#:	3,138,229
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.8%
Money Market Funds	4.2%

Industries

Multi-Family Housing Revenue	14.2%
General Obligations - Schools	13.3%
Healthcare Revenue - Hospitals	11.0%
Airport Revenue	10.1%
Utilities - Other	8.9%
State & Local Agencies	5.2%
Tax Assessment	4.8%
Secondary Schools	4.1%
Water & Sewer Utility Revenue	3.6%
Universities - Colleges	3.5%
Other Industries	17.1%

Composition including fixed income credit quality

AAA	0.8%
AA	47.9%
A	22.6%
BBB	12.3%
BB	2.1%
B	0.2%
Not Rated	9.9%
Money Market Funds	4.2%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

Material Fund Change [Text Block]

MATERIAL FUND CHANGES

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Effective August 1, 2025, for Class C shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 1.55% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Material Fund Change Expenses [Text Block]

Effective August 1, 2025, for Class C shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 1.55% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Summary of Change Legend [Text Block]

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Updated Prospectus Phone Number

1‑800‑225‑2606

Updated Prospectus Web Address

funds.mfs.com

C000169767 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® CaliforniaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MCAVX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS California Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Material Fund Change Notice [Text Block]

This report describes certain changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$57	0.56%

Expenses Paid, Amount

$ 57

Expense Ratio, Percent

0.56%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS California Municipal Bond Fund (fund) provided a total return of 3.74%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AAA-rated securities, also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities within the education sector also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.74%	0.60%	2.11%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Material Change Date

Aug. 01, 2025

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 790,370,826

Holdings Count | Holding

435

Advisory Fees Paid, Amount

$ 3,138,229

^[35]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	790,370,826	Average Effective Maturity (yrs):	19.8
Total Number of Holdings:	435	Average Effective Duration (yrs):	9.2
Total Management Fee ($)#:	3,138,229
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.8%
Money Market Funds	4.2%

Industries

Multi-Family Housing Revenue	14.2%
General Obligations - Schools	13.3%
Healthcare Revenue - Hospitals	11.0%
Airport Revenue	10.1%
Utilities - Other	8.9%
State & Local Agencies	5.2%
Tax Assessment	4.8%
Secondary Schools	4.1%
Water & Sewer Utility Revenue	3.6%
Universities - Colleges	3.5%
Other Industries	17.1%

Composition including fixed income credit quality

AAA	0.8%
AA	47.9%
A	22.6%
BBB	12.3%
BB	2.1%
B	0.2%
Not Rated	9.9%
Money Market Funds	4.2%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

Material Fund Change [Text Block]

MATERIAL FUND CHANGES

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Effective August 1, 2025, for Class I shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.55% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Material Fund Change Expenses [Text Block]

Effective August 1, 2025, for Class I shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.55% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Summary of Change Legend [Text Block]

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Updated Prospectus Phone Number

1‑800‑225‑2606

Updated Prospectus Web Address

funds.mfs.com

C000194244 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® CaliforniaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPOAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS California Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Material Fund Change Notice [Text Block]

This report describes certain changes to the Fund that occurred during the reporting period.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$51	0.50%

Expenses Paid, Amount

$ 51

Expense Ratio, Percent

0.50%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS California Municipal Bond Fund (fund) provided a total return of 3.81%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AAA-rated securities, also strengthened relative returns.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.
  • The fund's out-of-benchmark exposure to Not Rated securities within the education sector also weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	3.81%	0.65%	2.13%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Material Change Date

Aug. 01, 2025

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 790,370,826

Holdings Count | Holding

435

Advisory Fees Paid, Amount

$ 3,138,229

^[36]

Investment Company Portfolio Turnover

15.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	790,370,826	Average Effective Maturity (yrs):	19.8
Total Number of Holdings:	435	Average Effective Duration (yrs):	9.2
Total Management Fee ($)#:	3,138,229
Portfolio Turnover Rate (%):	15

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.8%
Money Market Funds	4.2%

Industries

Multi-Family Housing Revenue	14.2%
General Obligations - Schools	13.3%
Healthcare Revenue - Hospitals	11.0%
Airport Revenue	10.1%
Utilities - Other	8.9%
State & Local Agencies	5.2%
Tax Assessment	4.8%
Secondary Schools	4.1%
Water & Sewer Utility Revenue	3.6%
Universities - Colleges	3.5%
Other Industries	17.1%

Composition including fixed income credit
quality

AAA	0.8%
AA	47.9%
A	22.6%
BBB	12.3%
BB	2.1%
B	0.2%
Not Rated	9.9%
Money Market Funds	4.2%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

Material Fund Change [Text Block]

MATERIAL FUND CHANGES

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Effective August 1, 2025, for Class R6 shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.49% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Material Fund Change Expenses [Text Block]

Effective August 1, 2025, for Class R6 shares, the investment adviser has agreed in writing to pay a portion of the fund’s total annual operating 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 (including interest expense and fees associated with investments in inverse floating rate instruments), such that total operating expenses do not exceed 0.49% annually of the class’s average daily net assets. This written agreement will continue until modified by the fund’s Board of Trustees, but such agreement will continue at least until July 31, 2026.

Summary of Change Legend [Text Block]

This is a summary of certain changes to the fund since April 1, 2025. For more complete information, you may review the fund's prospectus as amended, which is available at funds.mfs.com or upon request at 1‑800‑225‑2606.

Updated Prospectus Phone Number

1‑800‑225‑2606

Updated Prospectus Web Address

funds.mfs.com

C000194246 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® GeorgiaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPGOX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Georgia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$60	0.59%

Expenses Paid, Amount

$ 60

Expense Ratio, Percent

0.59%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Georgia Municipal Bond Fund (fund) provided a total return of 4.28%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the education sector, most notably within both A and AA-rated securities, strengthened relative returns. Bond selection within the housing sector, primarily within AAA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • The fund's out-of-benchmark exposure to Not Rated securities weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.28%	0.77%	1.92%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 124,221,589

Holdings Count | Holding

198

Advisory Fees Paid, Amount

$ 488,892

^[37]

Investment Company Portfolio Turnover

13.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	124,221,589	Average Effective Maturity (yrs):	19.9
Total Number of Holdings:	198	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	488,892
Portfolio Turnover Rate (%):	13

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.4%
Money Market Funds	4.6%

Industries

Water & Sewer Utility Revenue	12.2%
Healthcare Revenue - Hospitals	11.9%
Universities - Colleges	11.4%
Utilities - Municipal Owned	7.7%
Multi-Family Housing Revenue	7.2%
Single Family Housing - State	7.1%
Miscellaneous Revenue - Other	6.8%
Sales & Excise Tax Revenue	4.3%
General Obligations - General Purpose	4.2%
Utilities - Other	4.1%
Other Industries	18.5%

Composition including fixed income credit quality

AAA	7.7%
AA	46.6%
A	27.4%
BBB	8.1%
BB	0.5%
B	0.0%
Not Rated	5.1%
Money Market Funds	4.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169768 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® GeorgiaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MGATX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Georgia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$66	0.65%

Expenses Paid, Amount

$ 66

Expense Ratio, Percent

0.65%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Georgia Municipal Bond Fund (fund) provided a total return of 4.33%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the education sector, most notably within both A and AA-rated securities, strengthened relative returns. Bond selection within the housing sector, primarily within AAA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • The fund's out-of-benchmark exposure to Not Rated securities weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.33%	0.72%	1.88%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 124,221,589

Holdings Count | Holding

198

Advisory Fees Paid, Amount

$ 488,892

^[38]

Investment Company Portfolio Turnover

13.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	124,221,589	Average Effective Maturity (yrs):	19.9
Total Number of Holdings:	198	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	488,892
Portfolio Turnover Rate (%):	13

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.4%
Money Market Funds	4.6%

Industries

Water & Sewer Utility Revenue	12.2%
Healthcare Revenue - Hospitals	11.9%
Universities - Colleges	11.4%
Utilities - Municipal Owned	7.7%
Multi-Family Housing Revenue	7.2%
Single Family Housing - State	7.1%
Miscellaneous Revenue - Other	6.8%
Sales & Excise Tax Revenue	4.3%
General Obligations - General Purpose	4.2%
Utilities - Other	4.1%
Other Industries	18.5%

Composition including fixed income credit quality

AAA	7.7%
AA	46.6%
A	27.4%
BBB	8.1%
BB	0.5%
B	0.0%
Not Rated	5.1%
Money Market Funds	4.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006984 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® GeorgiaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBGAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Georgia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$168	1.65%

Expenses Paid, Amount

$ 168

Expense Ratio, Percent

1.65%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Georgia Municipal Bond Fund (fund) provided a total return of 3.23%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the education sector, most notably within both A and AA-rated securities, strengthened relative returns. Bond selection within the housing sector, primarily within AAA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • The fund's out-of-benchmark exposure to Not Rated securities weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.23%	(0.28)%	0.88%
B with CDSC (declining over six years from 4% to 0%)×	(0.77)%	(0.65)%	0.88%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 124,221,589

Holdings Count | Holding

198

Advisory Fees Paid, Amount

$ 488,892

^[39]

Investment Company Portfolio Turnover

13.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	124,221,589	Average Effective Maturity (yrs):	19.9
Total Number of Holdings:	198	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	488,892
Portfolio Turnover Rate (%):	13

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.4%
Money Market Funds	4.6%

Industries

Water & Sewer Utility Revenue	12.2%
Healthcare Revenue - Hospitals	11.9%
Universities - Colleges	11.4%
Utilities - Municipal Owned	7.7%
Multi-Family Housing Revenue	7.2%
Single Family Housing - State	7.1%
Miscellaneous Revenue - Other	6.8%
Sales & Excise Tax Revenue	4.3%
General Obligations - General Purpose	4.2%
Utilities - Other	4.1%
Other Industries	18.5%

Composition including fixed income credit quality

AAA	7.7%
AA	46.6%
A	27.4%
BBB	8.1%
BB	0.5%
B	0.0%
Not Rated	5.1%
Money Market Funds	4.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006983 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® GeorgiaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MMGAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Georgia Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$92	0.90%

Expenses Paid, Amount

$ 92

Expense Ratio, Percent

0.90%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Georgia Municipal Bond Fund (fund) provided a total return of 4.00%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.
  • Security selection within the education sector, most notably within both A and AA-rated securities, strengthened relative returns. Bond selection within the housing sector, primarily within AAA-rated securities, also helped relative performance.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • The fund's out-of-benchmark exposure to Not Rated securities weakened relative returns.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	4.00%	0.48%	1.64%
A with initial sales charge (4.25%)	(0.42)%	(0.39)%	1.20%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 124,221,589

Holdings Count | Holding

198

Advisory Fees Paid, Amount

$ 488,892

^[40]

Investment Company Portfolio Turnover

13.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	124,221,589	Average Effective Maturity (yrs):	19.9
Total Number of Holdings:	198	Average Effective Duration (yrs):	9.0
Total Management Fee ($)#:	488,892
Portfolio Turnover Rate (%):	13

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	95.4%
Money Market Funds	4.6%

Industries

Water & Sewer Utility Revenue	12.2%
Healthcare Revenue - Hospitals	11.9%
Universities - Colleges	11.4%
Utilities - Municipal Owned	7.7%
Multi-Family Housing Revenue	7.2%
Single Family Housing - State	7.1%
Miscellaneous Revenue - Other	6.8%
Sales & Excise Tax Revenue	4.3%
General Obligations - General Purpose	4.2%
Utilities - Other	4.1%
Other Industries	18.5%

Composition including fixed income credit
quality

AAA	7.7%
AA	46.6%
A	27.4%
BBB	8.1%
BB	0.5%
B	0.0%
Not Rated	5.1%
Money Market Funds	4.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006985 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MarylandMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFSMX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Maryland Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$88	0.86%

Expenses Paid, Amount

$ 88

Expense Ratio, Percent

0.86%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Maryland Municipal Bond Fund (fund) provided a total return of 3.83%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AA-rated securities, strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.83%	0.65%	1.84%
A with initial sales charge (4.25%)	(0.58)%	(0.22)%	1.40%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 156,942,333

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 645,294

^[41]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	156,942,333	Average Effective Maturity (yrs):	17.8
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.0
Total Management Fee ($)#:	645,294
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.7%
Money Market Funds	3.3%

Industries

Healthcare Revenue - Hospitals	16.4%
State & Local Agencies	15.1%
Multi-Family Housing Revenue	11.1%
General Obligations - General Purpose	9.9%
Single Family Housing - State	6.3%
Universities - Colleges	3.9%
Tax Assessment	3.9%
Water & Sewer Utility Revenue	3.5%
Utilities - Other	3.3%
Transportation - Special Tax	2.9%
Other Industries	20.4%

Composition including fixed income credit
quality

AAA	12.0%
AA	38.7%
A	26.5%
BBB	11.0%
BB	0.6%
B	0.0%
CCC	0.1%
Not Rated	7.8%
Money Market Funds	3.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006986 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MarylandMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBMDX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Maryland Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$164	1.61%

Expenses Paid, Amount

$ 164

Expense Ratio, Percent

1.61%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Maryland Municipal Bond Fund (fund) provided a total return of 3.17%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AA-rated securities, strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.17%	(0.10)%	1.09%
B with CDSC (declining over six years from 4% to 0%)×	(0.83)%	(0.46)%	1.09%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 156,942,333

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 645,294

^[42]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	156,942,333	Average Effective Maturity (yrs):	17.8
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.0
Total Management Fee ($)#:	645,294
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.7%
Money Market Funds	3.3%

Industries

Healthcare Revenue - Hospitals	16.4%
State & Local Agencies	15.1%
Multi-Family Housing Revenue	11.1%
General Obligations - General Purpose	9.9%
Single Family Housing - State	6.3%
Universities - Colleges	3.9%
Tax Assessment	3.9%
Water & Sewer Utility Revenue	3.5%
Utilities - Other	3.3%
Transportation - Special Tax	2.9%
Other Industries	20.4%

Composition including fixed income credit
quality

AAA	12.0%
AA	38.7%
A	26.5%
BBB	11.0%
BB	0.6%
B	0.0%
CCC	0.1%
Not Rated	7.8%
Money Market Funds	3.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169769 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MarylandMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MMDIX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Maryland Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$62	0.61%

Expenses Paid, Amount

$ 62

Expense Ratio, Percent

0.61%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Maryland Municipal Bond Fund (fund) provided a total return of 4.14%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AA-rated securities, strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.14%	0.90%	2.10%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 156,942,333

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 645,294

^[43]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	156,942,333	Average Effective Maturity (yrs):	17.8
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.0
Total Management Fee ($)#:	645,294
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.7%
Money Market Funds	3.3%

Industries

Healthcare Revenue - Hospitals	16.4%
State & Local Agencies	15.1%
Multi-Family Housing Revenue	11.1%
General Obligations - General Purpose	9.9%
Single Family Housing - State	6.3%
Universities - Colleges	3.9%
Tax Assessment	3.9%
Water & Sewer Utility Revenue	3.5%
Utilities - Other	3.3%
Transportation - Special Tax	2.9%
Other Industries	20.4%

Composition including fixed income credit quality

AAA	12.0%
AA	38.7%
A	26.5%
BBB	11.0%
BB	0.6%
B	0.0%
CCC	0.1%
Not Rated	7.8%
Money Market Funds	3.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194249 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MarylandMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPMDX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Maryland Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$56	0.55%

Expenses Paid, Amount

$ 56

Expense Ratio, Percent

0.55%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Maryland Municipal Bond Fund (fund) provided a total return of 4.10%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • The combination of an overweight exposure and favorable security selection within the housing sector, most notably within AA-rated securities, strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.10%	0.97%	2.13%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 156,942,333

Holdings Count | Holding

230

Advisory Fees Paid, Amount

$ 645,294

^[44]

Investment Company Portfolio Turnover

9.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	156,942,333	Average Effective Maturity (yrs):	17.8
Total Number of Holdings:	230	Average Effective Duration (yrs):	8.0
Total Management Fee ($)#:	645,294
Portfolio Turnover Rate (%):	9

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	96.7%
Money Market Funds	3.3%

Industries

Healthcare Revenue - Hospitals	16.4%
State & Local Agencies	15.1%
Multi-Family Housing Revenue	11.1%
General Obligations - General Purpose	9.9%
Single Family Housing - State	6.3%
Universities - Colleges	3.9%
Tax Assessment	3.9%
Water & Sewer Utility Revenue	3.5%
Utilities - Other	3.3%
Transportation - Special Tax	2.9%
Other Industries	20.4%

Composition including fixed income credit
quality

AAA	12.0%
AA	38.7%
A	26.5%
BBB	11.0%
BB	0.6%
B	0.0%
CCC	0.1%
Not Rated	7.8%
Money Market Funds	3.3%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194252 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MississippiMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPMSX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Mississippi Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$61	0.60%

Expenses Paid, Amount

$ 61

Expense Ratio, Percent

0.60%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Mississippi Municipal Bond Fund (fund) provided a total return of 4.60%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors was a primary contributor to relative returns, most notably within AA and BBB-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.60%	0.53%	1.75%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 61,615,928

Holdings Count | Holding

130

Advisory Fees Paid, Amount

$ 278,561

^[45]

Investment Company Portfolio Turnover

7.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	61,615,928	Average Effective Maturity (yrs):	18.1
Total Number of Holdings:	130	Average Effective Duration (yrs):	8.2
Total Management Fee ($)#:	278,561
Portfolio Turnover Rate (%):	7

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

Single Family Housing - State	15.8%
General Obligations - Schools	13.5%
Universities - Colleges	13.5%
General Obligations - General Purpose	13.4%
Water & Sewer Utility Revenue	10.5%
State & Local Agencies	5.9%
Sales & Excise Tax Revenue	5.1%
Tax - Other	4.4%
Healthcare Revenue - Hospitals	3.3%
Multi-Family Housing Revenue	3.0%
Other Industries	10.7%

Composition including fixed income credit
quality

AA	70.0%
A	13.0%
BBB	8.1%
BB	0.3%
B	0.1%
Not Rated	7.6%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169771 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MississippiMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MMSTX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Mississippi Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$67	0.66%

Expenses Paid, Amount

$ 67

Expense Ratio, Percent

0.66%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Mississippi Municipal Bond Fund (fund) provided a total return of 4.43%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors was a primary contributor to relative returns, most notably within AA and BBB-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.43%	0.45%	1.67%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 61,615,928

Holdings Count | Holding

130

Advisory Fees Paid, Amount

$ 278,561

^[46]

Investment Company Portfolio Turnover

7.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	61,615,928	Average Effective Maturity (yrs):	18.1
Total Number of Holdings:	130	Average Effective Duration (yrs):	8.2
Total Management Fee ($)#:	278,561
Portfolio Turnover Rate (%):	7

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

Single Family Housing - State	15.8%
General Obligations - Schools	13.5%
Universities - Colleges	13.5%
General Obligations - General Purpose	13.4%
Water & Sewer Utility Revenue	10.5%
State & Local Agencies	5.9%
Sales & Excise Tax Revenue	5.1%
Tax - Other	4.4%
Healthcare Revenue - Hospitals	3.3%
Multi-Family Housing Revenue	3.0%
Other Industries	10.7%

Composition including fixed income credit
quality

AA	70.0%
A	13.0%
BBB	8.1%
BB	0.3%
B	0.1%
Not Rated	7.6%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006990 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MississippiMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBMSX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Mississippi Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$144	1.41%

Expenses Paid, Amount

$ 144

Expense Ratio, Percent

1.41%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Mississippi Municipal Bond Fund (fund) provided a total return of 3.65%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors was a primary contributor to relative returns, most notably within AA and BBB-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.65%	(0.29)%	0.92%
B with CDSC (declining over six years from 4% to 0%)×	(0.35)%	(0.65)%	0.92%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 61,615,928

Holdings Count | Holding

130

Advisory Fees Paid, Amount

$ 278,561

^[47]

Investment Company Portfolio Turnover

7.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	61,615,928	Average Effective Maturity (yrs):	18.1
Total Number of Holdings:	130	Average Effective Duration (yrs):	8.2
Total Management Fee ($)#:	278,561
Portfolio Turnover Rate (%):	7

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

Single Family Housing - State	15.8%
General Obligations - Schools	13.5%
Universities - Colleges	13.5%
General Obligations - General Purpose	13.4%
Water & Sewer Utility Revenue	10.5%
State & Local Agencies	5.9%
Sales & Excise Tax Revenue	5.1%
Tax - Other	4.4%
Healthcare Revenue - Hospitals	3.3%
Multi-Family Housing Revenue	3.0%
Other Industries	10.7%

Composition including fixed income credit
quality

AA	70.0%
A	13.0%
BBB	8.1%
BB	0.3%
B	0.1%
Not Rated	7.6%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006989 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MississippiMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MISSX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Mississippi Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$78	0.76%

Expenses Paid, Amount

$ 78

Expense Ratio, Percent

0.76%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Mississippi Municipal Bond Fund (fund) provided a total return of 4.32%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors was a primary contributor to relative returns, most notably within AA and BBB-rated securities.
  • The fund's longer duration stance enhanced relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	4.32%	0.37%	1.57%
A with initial sales charge (4.25%)	(0.11)%	(0.49)%	1.13%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 61,615,928

Holdings Count | Holding

130

Advisory Fees Paid, Amount

$ 278,561

^[48]

Investment Company Portfolio Turnover

7.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	61,615,928	Average Effective Maturity (yrs):	18.1
Total Number of Holdings:	130	Average Effective Duration (yrs):	8.2
Total Management Fee ($)#:	278,561
Portfolio Turnover Rate (%):	7

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

Single Family Housing - State	15.8%
General Obligations - Schools	13.5%
Universities - Colleges	13.5%
General Obligations - General Purpose	13.4%
Water & Sewer Utility Revenue	10.5%
State & Local Agencies	5.9%
Sales & Excise Tax Revenue	5.1%
Tax - Other	4.4%
Healthcare Revenue - Hospitals	3.3%
Multi-Family Housing Revenue	3.0%
Other Industries	10.7%

Composition including fixed income credit
quality

AA	70.0%
A	13.0%
BBB	8.1%
BB	0.3%
B	0.1%
Not Rated	7.6%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006991 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class A

Trading Symbol

MFIAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$79	0.78%

Expenses Paid, Amount

$ 79

Expense Ratio, Percent

0.78%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Municipal Income Fund (fund) provided a total return of 3.65%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.65%	0.79%	2.21%
A with initial sales charge (4.25%)	(0.75)%	(0.08)%	1.77%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[49]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000042676 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class A1

Trading Symbol

MMIDX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A1	$54	0.53%

Expenses Paid, Amount

$ 54

Expense Ratio, Percent

0.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A1 shares of the MFS Municipal Income Fund (fund) provided a total return of 3.92%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A1 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A1 without sales charge	3.92%	1.05%	2.47%
A1 with initial sales charge (4.25%)	(0.50)%	0.17%	2.03%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a1 for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[50]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006992 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class B

Trading Symbol

MMIBX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$155	1.53%

Expenses Paid, Amount

$ 155

Expense Ratio, Percent

1.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Municipal Income Fund (fund) provided a total return of 2.89%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.89%	0.04%	1.45%
B with CDSC (declining over six years from 4% to 0%)×	(1.11)%	(0.31)%	1.45%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[51]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit
quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000042677 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class B1

Trading Symbol

MMIGX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B1	$130	1.28%

Expenses Paid, Amount

$ 130

Expense Ratio, Percent

1.28%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B1 shares of the MFS Municipal Income Fund (fund) provided a total return of 3.27%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B1 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B1 without sales charge	3.27%	0.31%	1.71%
B1 with CDSC (declining over six years from 4% to 0%)×	(0.73)%	(0.04)%	1.71%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b1 for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[52]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit
quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006993 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class C

Trading Symbol

MMICX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$155	1.53%

Expenses Paid, Amount

$ 155

Expense Ratio, Percent

1.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS Municipal Income Fund (fund) provided a total return of 2.88%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
C without sales charge	2.88%	0.05%	1.45%
C with CDSC (1% for 12 months)×	1.89%	0.05%	1.45%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[53]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit
quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000105400 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class I

Trading Symbol

MIMIX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$54	0.53%

Expenses Paid, Amount

$ 54

Expense Ratio, Percent

0.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Municipal Income Fund (fund) provided a total return of 3.90%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.90%	1.03%	2.46%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[54]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit
quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194254 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® Municipal Income Fund

Class Name

Class R6

Trading Symbol

MPMNX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Income Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$47	0.46%

Expenses Paid, Amount

$ 47

Expense Ratio, Percent

0.46%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Municipal Income Fund (fund) provided a total return of 3.98%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • An overweight position and security selection within the housing sector contributed to relative performance. Favorable security selection within both the industrial revenue and leasing sectors also benefited relative returns. The fund's overweight position to lower-quality bonds within the power and healthcare sectors was also a positive factor for relative performance. Security selection within these sectors also supported relative results.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's overweight exposure to the long end (maturities of 20 or more years) of the yield curve, detracted from relative performance as bond yields rose most in that segment of the curve.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	3.98%	1.11%	2.48%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 6,956,477,715

Holdings Count | Holding

2,285

Advisory Fees Paid, Amount

$ 21,856,873

^[55]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	6,956,477,715	Average Effective Maturity (yrs):	19.7
Total Number of Holdings:	2,285	Average Effective Duration (yrs):	8.5
Total Management Fee ($)#:	21,856,873
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	97.6%
Money Market Funds	2.4%

Industries

Healthcare Revenue - Hospitals	15.9%
Airport Revenue	8.9%
Utilities - Other	7.9%
Multi-Family Housing Revenue	7.7%
Healthcare Revenue - Long Term Care	6.2%
Miscellaneous Revenue - Other	4.3%
Single Family Housing - State	4.3%
General Obligations - Schools	4.2%
State & Local Agencies	4.1%
Universities - Colleges	3.9%
Other Industries	30.2%

Composition including fixed income credit
quality

AAA	4.5%
AA	30.7%
A	33.9%
BBB	14.8%
BB	3.4%
B	0.7%
CCC	0.2%
CC	0.2%
Not Rated	9.2%
Money Market Funds	2.4%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000227172 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MunicipalIntermediate Fund

Class Name

Class R6

Trading Symbol

MIURX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Intermediate Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$39	0.38%

Expenses Paid, Amount

$ 39

Expense Ratio, Percent

0.38%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Municipal Intermediate Fund (fund) provided a total return of 5.09%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg Municipal 1-15 Year Index, generated a return of 4.49%.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. The fund’s benchmark, the Bloomberg Municipal 1-15 Year Index, generated a solid 4.5% return. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.35%, higher than the five-year average of 2.77%.

• Top contributors to performance relative to the Bloomberg Municipal 1-15 Year Index:
  • The fund's overweight exposure to A-rated and lower-rated securities benefited relative performance. Favorable security selection and overweight exposures to the healthcare and housing sectors also strengthened relative returns. Security selection within the local general obligation, special tax, and transportation sectors further benefited relative results.
  • The fund's long duration stance was another positive factor for relative returns as rates inside 15-years declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal 1-15 Year Index:
  • Yield curve positioning detracted from relative performance as the fund was underweight key rates 10-years and in, which performed best.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 

*For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.

Share Class	1-yr	Life*
R6 without sales charge	5.09%	1.51%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.68%
Bloomberg Municipal 1-15 Year Index ∆	4.49%	1.07%

*	For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

May 18, 2021

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 386,686,704

Holdings Count | Holding

661

Advisory Fees Paid, Amount

$ 1,081,525

^[56]

Investment Company Portfolio Turnover

10.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	386,686,704	Average Effective Maturity (yrs):	10.7
Total Number of Holdings:	661	Average Effective Duration (yrs):	6.2
Total Management Fee ($)#:	1,081,525
Portfolio Turnover Rate (%):	10

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Long Term Care	11.7%
Healthcare Revenue - Hospitals	10.9%
Utilities - Other	8.7%
Multi-Family Housing Revenue	8.4%
Airport Revenue	7.4%
Student Loan Revenue	5.7%
Secondary Schools	4.9%
Universities - Colleges	4.8%
Miscellaneous Revenue - Other	3.2%
State & Local Agencies	3.0%
Other Industries	29.7%

Composition including fixed income credit
quality

AAA	1.4%
AA	29.7%
A	33.8%
BBB	19.5%
BB	6.1%
B	0.6%
CCC	0.1%
Not Rated	7.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000227171 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MunicipalIntermediate Fund

Class Name

Class I

Trading Symbol

MIUIX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Intermediate Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$46	0.45%

Expenses Paid, Amount

$ 46

Expense Ratio, Percent

0.45%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Municipal Intermediate Fund (fund) provided a total return of 5.02%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg Municipal 1-15 Year Index, generated a return of 4.49%.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. The fund’s benchmark, the Bloomberg Municipal 1-15 Year Index, generated a solid 4.5% return. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.35%, higher than the five-year average of 2.77%.

• Top contributors to performance relative to the Bloomberg Municipal 1-15 Year Index:
  • The fund's overweight exposure to A-rated and lower-rated securities benefited relative performance. Favorable security selection and overweight exposures to the healthcare and housing sectors also strengthened relative returns. Security selection within the local general obligation, special tax, and transportation sectors further benefited relative results.
  • The fund's long duration stance was another positive factor for relative returns as rates inside 15-years declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal 1-15 Year Index:
  • Yield curve positioning detracted from relative performance as the fund was underweight key rates 10-years and in, which performed best.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 

*For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.

Share Class	1-yr	Life*
I without sales charge	5.02%	1.47%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.68%
Bloomberg Municipal 1-15 Year Index ∆	4.49%	1.07%

*	For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

May 18, 2021

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 386,686,704

Holdings Count | Holding

661

Advisory Fees Paid, Amount

$ 1,081,525

^[57]

Investment Company Portfolio Turnover

10.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	386,686,704	Average Effective Maturity (yrs):	10.7
Total Number of Holdings:	661	Average Effective Duration (yrs):	6.2
Total Management Fee ($)#:	1,081,525
Portfolio Turnover Rate (%):	10

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Long Term Care	11.7%
Healthcare Revenue - Hospitals	10.9%
Utilities - Other	8.7%
Multi-Family Housing Revenue	8.4%
Airport Revenue	7.4%
Student Loan Revenue	5.7%
Secondary Schools	4.9%
Universities - Colleges	4.8%
Miscellaneous Revenue - Other	3.2%
State & Local Agencies	3.0%
Other Industries	29.7%

Composition including fixed income credit
quality

AAA	1.4%
AA	29.7%
A	33.8%
BBB	19.5%
BB	6.1%
B	0.6%
CCC	0.1%
Not Rated	7.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000227169 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MunicipalIntermediate Fund

Class Name

Class C

Trading Symbol

MIUCX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Intermediate Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
C	$148	1.45%

Expenses Paid, Amount

$ 148

Expense Ratio, Percent

1.45%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class C shares of the MFS Municipal Intermediate Fund (fund) provided a total return of 4.00%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg Municipal 1-15 Year Index, generated a return of 4.49%.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. The fund’s benchmark, the Bloomberg Municipal 1-15 Year Index, generated a solid 4.5% return. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.35%, higher than the five-year average of 2.77%.

• Top contributors to performance relative to the Bloomberg Municipal 1-15 Year Index:
  • The fund's overweight exposure to A-rated and lower-rated securities benefited relative performance. Favorable security selection and overweight exposures to the healthcare and housing sectors also strengthened relative returns. Security selection within the local general obligation, special tax, and transportation sectors further benefited relative results.
  • The fund's long duration stance was another positive factor for relative returns as rates inside 15-years declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal 1-15 Year Index:
  • Yield curve positioning detracted from relative performance as the fund was underweight key rates 10-years and in, which performed best.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class C over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. 

*For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.

Share Class	1-yr	Life*
C without sales charge	4.00%	0.47%
C with CDSC (1% for 12 months)×	3.00%	0.47%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.68%
Bloomberg Municipal 1-15 Year Index ∆	4.49%	1.07%

*	For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

Performance Inception Date

May 18, 2021

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/c for more recent performance information.

Net Assets

$ 386,686,704

Holdings Count | Holding

661

Advisory Fees Paid, Amount

$ 1,081,525

^[58]

Investment Company Portfolio Turnover

10.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	386,686,704	Average Effective Maturity (yrs):	10.7
Total Number of Holdings:	661	Average Effective Duration (yrs):	6.2
Total Management Fee ($)#:	1,081,525
Portfolio Turnover Rate (%):	10

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Long Term Care	11.7%
Healthcare Revenue - Hospitals	10.9%
Utilities - Other	8.7%
Multi-Family Housing Revenue	8.4%
Airport Revenue	7.4%
Student Loan Revenue	5.7%
Secondary Schools	4.9%
Universities - Colleges	4.8%
Miscellaneous Revenue - Other	3.2%
State & Local Agencies	3.0%
Other Industries	29.7%

Composition including fixed income credit quality

AAA	1.4%
AA	29.7%
A	33.8%
BBB	19.5%
BB	6.1%
B	0.6%
CCC	0.1%
Not Rated	7.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000227170 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MunicipalIntermediate Fund

Class Name

Class A

Trading Symbol

MIUAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Municipal Intermediate Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$72	0.70%

Expenses Paid, Amount

$ 72

Expense Ratio, Percent

0.70%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Municipal Intermediate Fund (fund) provided a total return of 4.77%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index. The fund's other benchmark, the Bloomberg Municipal 1-15 Year Index, generated a return of 4.49%.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. The fund’s benchmark, the Bloomberg Municipal 1-15 Year Index, generated a solid 4.5% return. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.35%, higher than the five-year average of 2.77%.

• Top contributors to performance relative to the Bloomberg Municipal 1-15 Year Index:
  • The fund's overweight exposure to A-rated and lower-rated securities benefited relative performance. Favorable security selection and overweight exposures to the healthcare and housing sectors also strengthened relative returns. Security selection within the local general obligation, special tax, and transportation sectors further benefited relative results.
  • The fund's long duration stance was another positive factor for relative returns as rates inside 15-years declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal 1-15 Year Index:
  • Yield curve positioning detracted from relative performance as the fund was underweight key rates 10-years and in, which performed best.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests. This graph includes the deduction of the maximum applicable sales charge.

*For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of (i) a broad measure of market performance and (ii) an additional index that MFS believes more closely reflects the market segments in which the fund invests, over the same periods.

Share Class	1-yr	Life*
A without sales charge	4.77%	1.22%
A with initial sales charge (4.25%)	0.32%	0.32%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.68%
Bloomberg Municipal 1-15 Year Index ∆	4.49%	1.07%

*	For the period from the commencement of the class's investment operations, May 18, 2021 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

May 18, 2021

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 386,686,704

Holdings Count | Holding

661

Advisory Fees Paid, Amount

$ 1,081,525

^[59]

Investment Company Portfolio Turnover

10.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	386,686,704	Average Effective Maturity (yrs):	10.7
Total Number of Holdings:	661	Average Effective Duration (yrs):	6.2
Total Management Fee ($)#:	1,081,525
Portfolio Turnover Rate (%):	10

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.4%
Money Market Funds	1.6%

Industries

Healthcare Revenue - Long Term Care	11.7%
Healthcare Revenue - Hospitals	10.9%
Utilities - Other	8.7%
Multi-Family Housing Revenue	8.4%
Airport Revenue	7.4%
Student Loan Revenue	5.7%
Secondary Schools	4.9%
Universities - Colleges	4.8%
Miscellaneous Revenue - Other	3.2%
State & Local Agencies	3.0%
Other Industries	29.7%

Composition including fixed income credit quality

AAA	1.4%
AA	29.7%
A	33.8%
BBB	19.5%
BB	6.1%
B	0.6%
CCC	0.1%
Not Rated	7.2%
Money Market Funds	1.6%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006987 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MassachusettsMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFSSX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Massachusetts Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$83	0.82%

Expenses Paid, Amount

$ 83

Expense Ratio, Percent

0.82%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Massachusetts Municipal Bond Fund (fund) provided a total return of 3.61%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both AA and BBB-rated securities strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.61%	0.46%	1.72%
A with initial sales charge (4.25%)	(0.79)%	(0.41)%	1.28%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 408,933,457

Holdings Count | Holding

270

Advisory Fees Paid, Amount

$ 1,715,367

^[60]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	408,933,457	Average Effective Maturity (yrs):	18.3
Total Number of Holdings:	270	Average Effective Duration (yrs):	7.9
Total Management Fee ($)#:	1,715,367
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Universities - Colleges	17.9%
Healthcare Revenue - Hospitals	17.6%
General Obligations - General Purpose	13.4%
Sales & Excise Tax Revenue	7.3%
Multi-Family Housing Revenue	5.8%
Airport Revenue	5.2%
Transportation - Special Tax	5.1%
Student Loan Revenue	4.7%
Single Family Housing - State	4.4%
Utilities - Other	3.5%
Other Industries	13.4%

Composition including fixed income credit
quality

AAA	4.9%
AA	48.8%
A	19.3%
BBB	18.9%
BB	1.8%
B	0.0%
Not Rated	4.6%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006988 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MassachusettsMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBMAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Massachusetts Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$159	1.57%

Expenses Paid, Amount

$ 159

Expense Ratio, Percent

1.57%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Massachusetts Municipal Bond Fund (fund) provided a total return of 2.85%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both AA and BBB-rated securities strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	2.85%	(0.30)%	0.95%
B with CDSC (declining over six years from 4% to 0%)×	(1.15)%	(0.66)%	0.95%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 408,933,457

Holdings Count | Holding

270

Advisory Fees Paid, Amount

$ 1,715,367

^[61]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	408,933,457	Average Effective Maturity (yrs):	18.3
Total Number of Holdings:	270	Average Effective Duration (yrs):	7.9
Total Management Fee ($)#:	1,715,367
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Universities - Colleges	17.9%
Healthcare Revenue - Hospitals	17.6%
General Obligations - General Purpose	13.4%
Sales & Excise Tax Revenue	7.3%
Multi-Family Housing Revenue	5.8%
Airport Revenue	5.2%
Transportation - Special Tax	5.1%
Student Loan Revenue	4.7%
Single Family Housing - State	4.4%
Utilities - Other	3.5%
Other Industries	13.4%

Composition including fixed income credit
quality

AAA	4.9%
AA	48.8%
A	19.3%
BBB	18.9%
BB	1.8%
B	0.0%
Not Rated	4.6%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169770 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MassachusettsMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MTALX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Massachusetts Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$58	0.57%

Expenses Paid, Amount

$ 58

Expense Ratio, Percent

0.57%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Massachusetts Municipal Bond Fund (fund) provided a total return of 3.91%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both AA and BBB-rated securities strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	3.91%	0.70%	1.96%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 408,933,457

Holdings Count | Holding

270

Advisory Fees Paid, Amount

$ 1,715,367

^[62]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	408,933,457	Average Effective Maturity (yrs):	18.3
Total Number of Holdings:	270	Average Effective Duration (yrs):	7.9
Total Management Fee ($)#:	1,715,367
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Universities - Colleges	17.9%
Healthcare Revenue - Hospitals	17.6%
General Obligations - General Purpose	13.4%
Sales & Excise Tax Revenue	7.3%
Multi-Family Housing Revenue	5.8%
Airport Revenue	5.2%
Transportation - Special Tax	5.1%
Student Loan Revenue	4.7%
Single Family Housing - State	4.4%
Utilities - Other	3.5%
Other Industries	13.4%

Composition including fixed income credit
quality

AAA	4.9%
AA	48.8%
A	19.3%
BBB	18.9%
BB	1.8%
B	0.0%
Not Rated	4.6%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194250 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® MassachusettsMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPMAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Massachusetts Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$50	0.49%

Expenses Paid, Amount

$ 50

Expense Ratio, Percent

0.49%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Massachusetts Municipal Bond Fund (fund) provided a total return of 4.00%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both AA and BBB-rated securities strengthened relative returns.
  • The fund's longer duration stance also benefited relative performance as interest rates generally declined over the reporting period.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (particularly around maturities of 20 or more years) of the yield curve, held back relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.00%	0.78%	2.02%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 408,933,457

Holdings Count | Holding

270

Advisory Fees Paid, Amount

$ 1,715,367

^[63]

Investment Company Portfolio Turnover

12.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	408,933,457	Average Effective Maturity (yrs):	18.3
Total Number of Holdings:	270	Average Effective Duration (yrs):	7.9
Total Management Fee ($)#:	1,715,367
Portfolio Turnover Rate (%):	12

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	98.3%
Money Market Funds	1.7%

Industries

Universities - Colleges	17.9%
Healthcare Revenue - Hospitals	17.6%
General Obligations - General Purpose	13.4%
Sales & Excise Tax Revenue	7.3%
Multi-Family Housing Revenue	5.8%
Airport Revenue	5.2%
Transportation - Special Tax	5.1%
Student Loan Revenue	4.7%
Single Family Housing - State	4.4%
Utilities - Other	3.5%
Other Industries	13.4%

Composition including fixed income credit
quality

AAA	4.9%
AA	48.8%
A	19.3%
BBB	18.9%
BB	1.8%
B	0.0%
Not Rated	4.6%
Money Market Funds	1.7%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000194232 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® PennsylvaniaMunicipal Bond Fund

Class Name

Class R6

Trading Symbol

MPPAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Pennsylvania Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
R6	$54	0.53%

Expenses Paid, Amount

$ 54

Expense Ratio, Percent

0.53%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class R6 shares of the MFS Pennsylvania Municipal Bond Fund (fund) provided a total return of 4.17%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors strengthened relative returns, most notably within AA and A-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment*

This graph shows the performance of a hypothetical $10,000 investment in Class R6 over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

*For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	Life*
R6 without sales charge	4.17%	0.88%	2.24%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.15%

*	For the period from the commencement of the class's investment operations, August 1, 2017 through March 31, 2026.
∆	Source: FactSet Research Systems Inc.

Performance Inception Date

Aug. 01, 2017

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/r6 for more recent performance information.

Net Assets

$ 189,251,366

Holdings Count | Holding

242

Advisory Fees Paid, Amount

$ 775,831

^[64]

Investment Company Portfolio Turnover

8.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	189,251,366	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	242	Average Effective Duration (yrs):	8.3
Total Management Fee ($)#:	775,831
Portfolio Turnover Rate (%):	8

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

General Obligations - Schools	16.5%
Healthcare Revenue - Hospitals	13.5%
Universities - Colleges	11.6%
Single Family Housing - State	9.6%
Water & Sewer Utility Revenue	6.9%
Healthcare Revenue - Long Term Care	5.6%
General Obligations - General Purpose	4.0%
Airport Revenue	3.8%
Multi-Family Housing Revenue	3.3%
Student Loan Revenue	3.3%
Other Industries	21.0%

Composition including fixed income credit
quality

AAA	0.7%
AA	46.3%
A	28.9%
BBB	12.9%
BB	4.0%
B	0.0%
Not Rated	6.3%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000169761 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® PennsylvaniaMunicipal Bond Fund

Class Name

Class I

Trading Symbol

MPALX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Pennsylvania Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
I	$62	0.61%

Expenses Paid, Amount

$ 62

Expense Ratio, Percent

0.61%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class I shares of the MFS Pennsylvania Municipal Bond Fund (fund) provided a total return of 4.20%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors strengthened relative returns, most notably within AA and A-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class I over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
I without sales charge	4.20%	0.83%	2.22%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/i for more recent performance information.

Net Assets

$ 189,251,366

Holdings Count | Holding

242

Advisory Fees Paid, Amount

$ 775,831

^[65]

Investment Company Portfolio Turnover

8.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	189,251,366	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	242	Average Effective Duration (yrs):	8.3
Total Management Fee ($)#:	775,831
Portfolio Turnover Rate (%):	8

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

General Obligations - Schools	16.5%
Healthcare Revenue - Hospitals	13.5%
Universities - Colleges	11.6%
Single Family Housing - State	9.6%
Water & Sewer Utility Revenue	6.9%
Healthcare Revenue - Long Term Care	5.6%
General Obligations - General Purpose	4.0%
Airport Revenue	3.8%
Multi-Family Housing Revenue	3.3%
Student Loan Revenue	3.3%
Other Industries	21.0%

Composition including fixed income credit
quality

AAA	0.7%
AA	46.3%
A	28.9%
BBB	12.9%
BB	4.0%
B	0.0%
Not Rated	6.3%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006966 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® PennsylvaniaMunicipal Bond Fund

Class Name

Class B

Trading Symbol

MBPAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Pennsylvania Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
B	$147	1.45%

Expenses Paid, Amount

$ 147

Expense Ratio, Percent

1.45%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class B shares of the MFS Pennsylvania Municipal Bond Fund (fund) provided a total return of 3.31%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors strengthened relative returns, most notably within AA and A-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class B over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
B without sales charge	3.31%	(0.02)%	1.36%
B with CDSC (declining over six years from 4% to 0%)×	(0.69)%	(0.38)%	1.36%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆	Source: FactSet Research Systems Inc.
×	Assuming redemption at the end of the applicable period.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/b for more recent performance information.

Net Assets

$ 189,251,366

Holdings Count | Holding

242

Advisory Fees Paid, Amount

$ 775,831

^[66]

Investment Company Portfolio Turnover

8.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	189,251,366	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	242	Average Effective Duration (yrs):	8.3
Total Management Fee ($)#:	775,831
Portfolio Turnover Rate (%):	8

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

General Obligations - Schools	16.5%
Healthcare Revenue - Hospitals	13.5%
Universities - Colleges	11.6%
Single Family Housing - State	9.6%
Water & Sewer Utility Revenue	6.9%
Healthcare Revenue - Long Term Care	5.6%
General Obligations - General Purpose	4.0%
Airport Revenue	3.8%
Multi-Family Housing Revenue	3.3%
Student Loan Revenue	3.3%
Other Industries	21.0%

Composition including fixed income credit
quality

AAA	0.7%
AA	46.3%
A	28.9%
BBB	12.9%
BB	4.0%
B	0.0%
Not Rated	6.3%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

C000006965 [Member]

Shareholder Report [Line Items]

Fund Name

MFS® PennsylvaniaMunicipal Bond Fund

Class Name

Class A

Trading Symbol

MFPAX

Annual or Semi-Annual Statement [Text Block]

This annual shareholder report contains important information about MFS Pennsylvania Municipal Bond Fund for the period of April 1, 2025 to March 31, 2026.

Shareholder Report Annual or Semi-Annual

annual shareholder report

Additional Information [Text Block]

You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.

Additional Information Phone Number

1‑800‑225‑2606

Additional Information Email

orderliterature@mfs.com

Additional Information Website

funds.mfs.com

Expenses [Text Block]

FUND EXPENSES

What were the fund costs for the last year?

(based on a hypothetical $10,000 investment)
Class Name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
A	$72	0.71%

Expenses Paid, Amount

$ 72

Expense Ratio, Percent

0.71%

Factors Affecting Performance [Text Block]

MANAGEMENT'S DISCUSSION OF FUND PERFORMANCE

• For the twelve months ended March 31, 2026, Class A shares of the MFS Pennsylvania Municipal Bond Fund (fund) provided a total return of 3.97%, at net asset value. This compares with a return of 4.29% for the fund’s benchmark, the Bloomberg Municipal Bond Index.

• Considerable progress was made in trade talks between the US and many major trading partners, with a fragile truce between the US and China extended through late 2026. While the US Supreme Court struck down part of the Trump administration’s tariff strategy, the administration began deploying other authorities to largely replace the ones that were ruled unconstitutional.
• Early in the period, moderating inflation pressures allowed many global central banks to ease monetary policy. Amid a difficult policymaking environment and slower job growth, the Federal Reserve resumed easing policy in September and delivered quarter-point rate cuts in October and December before pausing.
• In fixed income markets, previously range-bound global bond yields spiked in reaction to the conflict in the Middle East, as energy-driven inflationary fears appeared to have rattled bond investors. Similarly, US bond market volatility (as measured by the Merrill Lynch Option Volatility Estimate (MOVE) Index) rose off intra-period lows, as uncertainty around the scope and duration of the war raised questions on the long-term growth outlook for global economies. In contrast, global credit spreads widened only marginally, reflecting ongoing strong demand and stable fundamentals.
• The municipal market produced positive returns over the trailing year, characterized by a generally supportive backdrop bookended by periods of elevated volatility that tempered performance. Following a spike in April 2025, bond yield volatility generally trended lower through January of this year providing a tailwind to returns. Additionally, the resumption of Fed rate cuts in late 2025 bolstered fixed income assets, including municipals. In early 2026, strong inflows were a key support to the municipal market, demonstrating resilience despite rising geopolitical risks and faltering returns in the final month of the period. Overall, the investment grade and high yield municipal markets delivered 4.3% and 2.4% returns, respectively. Across the curve, bonds with maturities around the 15-year key rate performed best while the shortest and longest maturity bonds lagged. A positive for income-oriented investors, the yield (yield-to-worst) of the benchmark index ended the period at 3.77%, higher than the five-year average of 3.12%.

• Top contributors to performance relative to the Bloomberg Municipal Bond Index:
  • Security selection within both the housing and local sectors strengthened relative returns, most notably within AA and A-rated securities.

• Top detractors from performance relative to the Bloomberg Municipal Bond Index:
  • Yield curve positioning, particularly the fund's greater exposure to shifts in the long end (centered around maturities of 20 or more years) of the yield curve, weighed on relative performance.

Performance Past Does Not Indicate Future [Text]

The fund’s past performance is not a good predictor of the fund’s future performance.

Line Graph [Table Text Block]

FUND PERFORMANCE

The fund’s past performance is not a good predictor of the fund’s future performance. The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares. The graph and table below assume reinvestment of dividends and capital gain distributions.

Growth of a Hypothetical $10,000 Investment

This graph shows the performance of a hypothetical $10,000 investment in Class A over a ten year period or since inception, if shorter, in comparison to a broad measure of market performance. This graph includes the deduction of the maximum applicable sales charge.

Average Annual Return [Table Text Block]

Average Annual Total Returns through 3/31/26

This table shows the average annual total returns of the class of shares noted for the periods shown, both with (if any) and without sales charges. It also shows the average annual total returns of a broad measure of market performance over the same periods.

Share Class	1-yr	5-yr	10-yr
A without sales charge	3.97%	0.70%	2.11%
A with initial sales charge (4.25%)	(0.45)%	(0.17)%	1.67%
Comparative Benchmark(s)
Bloomberg Municipal Bond Index ∆	4.29%	0.84%	2.16%

∆ Source: FactSet Research Systems Inc.

No Deduction of Taxes [Text Block]

The graph and table below do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

Updated Performance Information Location [Text Block]

Visit mfs.com/perf/a for more recent performance information.

Net Assets

$ 189,251,366

Holdings Count | Holding

242

Advisory Fees Paid, Amount

$ 775,831

^[67]

Investment Company Portfolio Turnover

8.00%

Additional Fund Statistics [Text Block]

FUND STATISTICS AS OF 3/31/26

Net Assets ($):	189,251,366	Average Effective Maturity (yrs):	19.0
Total Number of Holdings:	242	Average Effective Duration (yrs):	8.3
Total Management Fee ($)#:	775,831
Portfolio Turnover Rate (%):	8

# Includes the effect of any management fee waivers, if applicable.

Where the fund holds derivatives, they are not included in the total number of portfolio holdings.

Holdings [Text Block]

PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 3/31/26)

Portfolio structure

Fixed Income	99.1%
Money Market Funds	0.9%

Industries

General Obligations - Schools	16.5%
Healthcare Revenue - Hospitals	13.5%
Universities - Colleges	11.6%
Single Family Housing - State	9.6%
Water & Sewer Utility Revenue	6.9%
Healthcare Revenue - Long Term Care	5.6%
General Obligations - General Purpose	4.0%
Airport Revenue	3.8%
Multi-Family Housing Revenue	3.3%
Student Loan Revenue	3.3%
Other Industries	21.0%

Composition including fixed income credit
quality

AAA	0.7%
AA	46.3%
A	28.9%
BBB	12.9%
BB	4.0%
B	0.0%
Not Rated	6.3%
Money Market Funds	0.9%

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).

Credit Ratings Selection [Text Block]

Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.

[1] Includes the effect of any management fee waivers, if applicable.

[2] Includes the effect of any management fee waivers, if applicable.

[3] Includes the effect of any management fee waivers, if applicable.

[4] Includes the effect of any management fee waivers, if applicable.

[5] Includes the effect of any management fee waivers, if applicable.

[6] Includes the effect of any management fee waivers, if applicable.

[7] Includes the effect of any management fee waivers, if applicable.

[8] Includes the effect of any management fee waivers, if applicable.

[9] Includes the effect of any management fee waivers, if applicable.

[10] Includes the effect of any management fee waivers, if applicable.

[11] Includes the effect of any management fee waivers, if applicable.

[12] Includes the effect of any management fee waivers, if applicable.

[13] Includes the effect of any management fee waivers, if applicable.

[14] Includes the effect of any management fee waivers, if applicable.

[15] Includes the effect of any management fee waivers, if applicable.

[16] Includes the effect of any management fee waivers, if applicable.

[17] Includes the effect of any management fee waivers, if applicable.

[18] Includes the effect of any management fee waivers, if applicable.

[19] Includes the effect of any management fee waivers, if applicable.

[20] Includes the effect of any management fee waivers, if applicable.

[21] Includes the effect of any management fee waivers, if applicable.

[22] Includes the effect of any management fee waivers, if applicable.

[23] Includes the effect of any management fee waivers, if applicable.

[24] Includes the effect of any management fee waivers, if applicable.

[25] Includes the effect of any management fee waivers, if applicable.

[26] Includes the effect of any management fee waivers, if applicable.

[27] Includes the effect of any management fee waivers, if applicable.

[28] Includes the effect of any management fee waivers, if applicable.

[29] Includes the effect of any management fee waivers, if applicable.

[30] Includes the effect of any management fee waivers, if applicable.

[31] Includes the effect of any management fee waivers, if applicable.

[32] Includes the effect of any management fee waivers, if applicable.

[33] Includes the effect of any management fee waivers, if applicable.

[34] Includes the effect of any management fee waivers, if applicable.

[35] Includes the effect of any management fee waivers, if applicable.

[36] Includes the effect of any management fee waivers, if applicable.

[37] Includes the effect of any management fee waivers, if applicable.

[38] Includes the effect of any management fee waivers, if applicable.

[39] Includes the effect of any management fee waivers, if applicable.

[40] Includes the effect of any management fee waivers, if applicable.

[41] Includes the effect of any management fee waivers, if applicable.

[42] Includes the effect of any management fee waivers, if applicable.

[43] Includes the effect of any management fee waivers, if applicable.

[44] Includes the effect of any management fee waivers, if applicable.

[45] Includes the effect of any management fee waivers, if applicable.

[46] Includes the effect of any management fee waivers, if applicable.

[47] Includes the effect of any management fee waivers, if applicable.

[48] Includes the effect of any management fee waivers, if applicable.

[49] Includes the effect of any management fee waivers, if applicable.

[50] Includes the effect of any management fee waivers, if applicable.

[51] Includes the effect of any management fee waivers, if applicable.

[52] Includes the effect of any management fee waivers, if applicable.

[53] Includes the effect of any management fee waivers, if applicable.

[54] Includes the effect of any management fee waivers, if applicable.

[55] Includes the effect of any management fee waivers, if applicable.

[56] Includes the effect of any management fee waivers, if applicable.

[57] Includes the effect of any management fee waivers, if applicable.

[58] Includes the effect of any management fee waivers, if applicable.

[59] Includes the effect of any management fee waivers, if applicable.

[60] Includes the effect of any management fee waivers, if applicable.

[61] Includes the effect of any management fee waivers, if applicable.

[62] Includes the effect of any management fee waivers, if applicable.

[63] Includes the effect of any management fee waivers, if applicable.

[64] Includes the effect of any management fee waivers, if applicable.

[65] Includes the effect of any management fee waivers, if applicable.

[66] Includes the effect of any management fee waivers, if applicable.

[67] Includes the effect of any management fee waivers, if applicable.