v3.26.1
Shareholder Report
 6 Months Ended
Apr. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name MFS SERIES TRUST VIII
Entity Central Index Key 0000819673
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
C000006707 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Fund
Class Name Class A
Trading Symbol MFIOX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
A $36 0.73%
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.73%
Net Assets $ 8,231,624,371
Holdings Count | Holding 524
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,231,624,371 Average Effective Maturity (yrs): 8.7
Total Number of Holdings: 524 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 13
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 4/30/26)
Portfolio structure at value
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 11.7%
AA 6.7%
A 14.3%
BBB 27.5%
BB 6.4%
B 5.1%
CCC 0.6%
C 0.0%
D 0.1%
U.S. Government 25.5%
Federal Agencies 0.0%
Not Rated 0.3%
Money Market Funds 1.8%
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.
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.
C000006708 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Fund
Class Name Class B
Trading Symbol MIOBX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
B $73 1.48%
Expenses Paid, Amount $ 73
Expense Ratio, Percent 1.48%
Net Assets $ 8,231,624,371
Holdings Count | Holding 524
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,231,624,371 Average Effective Maturity (yrs): 8.7
Total Number of Holdings: 524 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 13
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 4/30/26)
Portfolio structure at value
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 11.7%
AA 6.7%
A 14.3%
BBB 27.5%
BB 6.4%
B 5.1%
CCC 0.6%
C 0.0%
D 0.1%
U.S. Government 25.5%
Federal Agencies 0.0%
Not Rated 0.3%
Money Market Funds 1.8%
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.
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.
C000006709 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Fund
Class Name Class C
Trading Symbol MIOCX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
C $73 1.48%
Expenses Paid, Amount $ 73
Expense Ratio, Percent 1.48%
Net Assets $ 8,231,624,371
Holdings Count | Holding 524
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,231,624,371 Average Effective Maturity (yrs): 8.7
Total Number of Holdings: 524 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 13
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 4/30/26)
Portfolio structure at value
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 11.7%
AA 6.7%
A 14.3%
BBB 27.5%
BB 6.4%
B 5.1%
CCC 0.6%
C 0.0%
D 0.1%
U.S. Government 25.5%
Federal Agencies 0.0%
Not Rated 0.3%
Money Market Funds 1.8%
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.
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.
C000006710 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Fund
Class Name Class I
Trading Symbol MFIIX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
I $24 0.48%
Expenses Paid, Amount $ 24
Expense Ratio, Percent 0.48%
Net Assets $ 8,231,624,371
Holdings Count | Holding 524
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,231,624,371 Average Effective Maturity (yrs): 8.7
Total Number of Holdings: 524 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 13
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 4/30/26)
Portfolio structure at value
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 11.7%
AA 6.7%
A 14.3%
BBB 27.5%
BB 6.4%
B 5.1%
CCC 0.6%
C 0.0%
D 0.1%
U.S. Government 25.5%
Federal Agencies 0.0%
Not Rated 0.3%
Money Market Funds 1.8%
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.
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.
C000200511 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Fund
Class Name Class R6
Trading Symbol MFIWX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R6 $19 0.39%
Expenses Paid, Amount $ 19
Expense Ratio, Percent 0.39%
Net Assets $ 8,231,624,371
Holdings Count | Holding 524
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 8,231,624,371 Average Effective Maturity (yrs): 8.7
Total Number of Holdings: 524 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 13
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 4/30/26)
Portfolio structure at value
Fixed Income 98.2%
Money Market Funds 1.8%
Composition including fixed income credit quality
AAA 11.7%
AA 6.7%
A 14.3%
BBB 27.5%
BB 6.4%
B 5.1%
CCC 0.6%
C 0.0%
D 0.1%
U.S. Government 25.5%
Federal Agencies 0.0%
Not Rated 0.3%
Money Market Funds 1.8%
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.
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.
C000126358 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class R6
Trading Symbol MWOKX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R6 $43 0.88%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.88%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006698 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class R4
Trading Symbol MWOJX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R4 $47 0.97%
Expenses Paid, Amount $ 47
Expense Ratio, Percent 0.97%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006705 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class R2
Trading Symbol MGWRX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R2 $72 1.47%
Expenses Paid, Amount $ 72
Expense Ratio, Percent 1.47%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006706 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class R3
Trading Symbol MWOHX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R3 $60 1.22%
Expenses Paid, Amount $ 60
Expense Ratio, Percent 1.22%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006699 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class B
Trading Symbol MWOBX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
B $96 1.97%
Expenses Paid, Amount $ 96
Expense Ratio, Percent 1.97%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006700 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class C
Trading Symbol MWOCX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
C $96 1.97%
Expenses Paid, Amount $ 96
Expense Ratio, Percent 1.97%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006701 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class I
Trading Symbol MWOIX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
I $47 0.97%
Expenses Paid, Amount $ 47
Expense Ratio, Percent 0.97%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006703 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class R1
Trading Symbol MWOGX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
R1 $96 1.97%
Expenses Paid, Amount $ 96
Expense Ratio, Percent 1.97%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
C000006697 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Fund
Class Name Class A
Trading Symbol MWOFX
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Fund for the period of November 1, 2025 to April 30, 2026.
Shareholder Report Annual or Semi-Annual semi-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 six months?
(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 (annualized)
A $60 1.22%
Expenses Paid, Amount $ 60
Expense Ratio, Percent 1.22%
Net Assets $ 835,922,948
Holdings Count | Holding 74
Investment Company Portfolio Turnover 19.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 4/30/26
Net Assets ($): 835,922,948 Portfolio Turnover Rate (%): 19
Total Number of Holdings: 74
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 4/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%
Issuer country weightings
United States 68.6%
Taiwan 6.6%
France 5.9%
Japan 5.1%
China 4.5%
United Kingdom 2.2%
India 2.0%
Canada 2.0%
Switzerland 1.1%
Other Countries 2.0%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 6.6%
Alphabet, Inc., "A" 4.6%
NVIDIA Corp. 4.5%
Microsoft Corp. 3.9%
Visa, Inc., "A" 3.2%
Amazon.com, Inc. 2.7%
Apple, Inc. 2.6%
Tencent Holdings Ltd. 2.5%
L’Oréal S.A. 2.3%
Schneider Electric SE 2.2%