v3.26.3
Performance Management
May 31, 2026
MFS Aggressive Growth Allocation Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Performance Additional Market Index [Text] As of December 31, 2025, the MFS Aggressive Growth Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 60% Standard & Poor's 500 Stock Index; 30% MSCI EAFE (Europe, Australasia, Far East) Index; 5% Bloomberg Commodity Index; and 5% FTSE EPRA Nareit Developed Real Estate Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 8.46%. During the period(s) shown in the bar chart, the highest quarterly return was 18.98% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (20.56)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Aggressive Growth Allocation Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Standard & Poor's 500 Stock Index | Average Annual Return, Label [Optional Text] Standard & Poor's 500 Stock Index      
Standard & Poor's 500 Stock Index | Average Annual Return, Percent   17.88% 14.42% 14.82%
MFS Aggressive Growth Allocation Fund Blended Index | Average Annual Return, Label [Optional Text] MFS Aggressive Growth Allocation Fund Blended Index      
MFS Aggressive Growth Allocation Fund Blended Index | Average Annual Return, Percent   21.38% 12.14% 11.89%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   8.27% 6.72% 9.78%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   6.30% 5.29% 8.50%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   6.10% 4.98% 7.69%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   10.01% 6.87% 9.76%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   12.99% 7.17% 9.76%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   15.17% 8.25% 10.70%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   14.03% 7.18% 9.60%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   14.57% 7.71% 10.14%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   14.86% 7.99% 10.42%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   15.13% 8.25% 10.70%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   15.26% 8.34% 10.74%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

As of December 31, 2025, the MFS Aggressive Growth Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 60% Standard & Poor's 500 Stock Index; 30% MSCI EAFE (Europe, Australasia, Far East) Index; 5% Bloomberg Commodity Index; and 5% FTSE EPRA Nareit Developed Real Estate Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Aggressive Growth Allocation Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 8.46%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 18.98%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (20.56%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Blended Research Growth Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

Performance information prior to March 7, 2022, reflects time periods when the fund was classified as a diversified fund. The fund was reclassified from diversified to non-diversified effective March 7, 2022. The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 7.63%. During the period(s) shown in the bar chart, the highest quarterly return was 25.44% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (19.43)% (for the calendar quarter ended June 30, 2022).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Blended Research Growth Equity Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Russell 3000® Index | Average Annual Return, Label [Optional Text] Russell 3000® Index      
Russell 3000® Index | Average Annual Return, Percent   17.15% 13.15% 14.29%
Russell 1000® Growth Index | Average Annual Return, Label [Optional Text] Russell 1000® Growth Index      
Russell 1000® Growth Index | Average Annual Return, Percent   18.56% 15.32% 18.13%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   9.92% 13.53% 15.29%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   8.22% 11.75% 13.82%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   6.91% 10.29% 12.36%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   11.72% 13.80% 15.30%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   14.75% 14.04% 15.29%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   16.90% 15.18% 16.28%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   15.72% 14.04% 15.11%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   16.27% 14.60% 15.69%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   16.59% 14.88% 15.97%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   16.89% 15.17% 16.27%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   16.95% 15.26% 16.35%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Blended Research Growth Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 7.63%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 25.44%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (19.43%)
Lowest Quarterly Return, Date Jun. 30, 2022
MFS Blended Research Small Cap Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 19.04%. During the period(s) shown in the bar chart, the highest quarterly return was 23.55% (for the calendar quarter ended December 31, 2020) and the lowest quarterly return was (33.59)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Blended Research Small Cap Equity Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Russell 3000® Index | Average Annual Return, Label [Optional Text] Russell 3000® Index      
Russell 3000® Index | Average Annual Return, Percent   17.15% 13.15% 14.29%
Russell 2000® Index | Average Annual Return, Label [Optional Text] Russell 2000® Index      
Russell 2000® Index | Average Annual Return, Percent   12.81% 6.09% 9.62%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   (0.55%) 5.24% 7.84%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   (1.99%) 3.69% 6.62%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   0.71% 3.91% 6.07%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   0.76% 5.37% 7.83%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   3.73% 5.71% 7.83%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   5.79% 6.76% 8.75%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   4.71% 5.71% 7.67%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   5.28% 6.24% 8.21%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   5.52% 6.50% 8.48%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   5.78% 6.76% 8.75%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   5.89% 6.87% 8.85%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Blended Research Small Cap Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 19.04%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 23.55%
Highest Quarterly Return, Date Dec. 31, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (33.59%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Blended Research Mid Cap Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 18.79%. During the period(s) shown in the bar chart, the highest quarterly return was 21.42% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (27.06)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Blended Research Mid Cap Equity Fund
 12 Months Ended 60 Months Ended 112 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Russell 3000® Index | Average Annual Return, Label [Optional Text] Russell 3000® Index      
Russell 3000® Index | Average Annual Return, Percent   17.15% 13.15% 14.30%
Russell 3000® Index | Performance Inception Date       Aug. 19, 2016
Russell Midcap® Index | Average Annual Return, Label [Optional Text] Russell Midcap® Index      
Russell Midcap® Index | Average Annual Return, Percent   10.60% 8.67% 10.58%
Russell Midcap® Index | Performance Inception Date       Aug. 19, 2016
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   1.56% 9.46% 10.10%
Class A | Performance Inception Date       Aug. 19, 2016
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   0.91% 7.21% 8.37%
Class A | After Taxes on Distributions | Performance Inception Date       Aug. 19, 2016
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   1.41% 6.89% 7.70%
Class A | After Taxes on Distributions and Sales | Performance Inception Date       Aug. 19, 2016
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   2.95% 9.65% 10.09%
Class B | Performance Inception Date       Aug. 19, 2016
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   5.98% 9.92% 10.08%
Class C | Performance Inception Date       Aug. 19, 2016
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   8.05% 11.04% 11.08%
Class I | Performance Inception Date       Aug. 19, 2016
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   7.70% 10.14% 10.08%
Class R1 | Performance Inception Date       Aug. 19, 2016
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   7.42% 10.48% 10.52%
Class R2 | Performance Inception Date       Aug. 19, 2016
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   7.70% 10.75% 10.80%
Class R3 | Performance Inception Date       Aug. 19, 2016
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   8.01% 11.04% 11.08%
Class R4 | Performance Inception Date       Aug. 19, 2016
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   8.16% 11.14% 11.17%
Class R6 | Performance Inception Date       Aug. 19, 2016
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Blended Research Mid Cap Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 18.79%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 21.42%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (27.06%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Blended Research Value Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 17.50%. During the period(s) shown in the bar chart, the highest quarterly return was 15.94% (for the calendar quarter ended December 31, 2020) and the lowest quarterly return was (27.36)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Blended Research Value Equity Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Russell 3000® Index | Average Annual Return, Label [Optional Text] Russell 3000® Index      
Russell 3000® Index | Average Annual Return, Percent   17.15% 13.15% 14.29%
Russell 1000® Value Index | Average Annual Return, Label [Optional Text] Russell 1000® Value Index      
Russell 1000® Value Index | Average Annual Return, Percent   15.91% 11.33% 10.53%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   8.40% 10.93% 9.76%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   5.67% 8.62% 8.26%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   6.90% 8.25% 7.65%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   10.22% 11.16% 9.75%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   13.18% 11.42% 9.74%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   15.35% 12.53% 10.68%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   14.99% 12.18% 9.97%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   14.72% 11.97% 10.14%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   15.03% 12.26% 10.41%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   15.32% 12.54% 10.69%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   15.38% 12.63% 10.78%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Blended Research Value Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 17.50%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 15.94%
Highest Quarterly Return, Date Dec. 31, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (27.36%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Conservative Allocation Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Performance Additional Market Index [Text] As of December 31, 2025, the MFS Conservative Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 28% Standard & Poor's 500 Stock Index; 8% MSCI EAFE (Europe, Australasia, Far East) Index; 2% Bloomberg Commodity Index; 2% FTSE EPRA Nareit Developed Real Estate Index; and 60% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 3.82%. During the period(s) shown in the bar chart, the highest quarterly return was 10.75% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (9.33)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Conservative Allocation Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Bloomberg U.S. Aggregate Bond Index | Average Annual Return, Label [Optional Text] Bloomberg U.S. Aggregate Bond Index      
Bloomberg U.S. Aggregate Bond Index | Average Annual Return, Percent   7.30% (0.36%) 2.01%
MFS Conservative Allocation Fund Blended Index | Average Annual Return, Label [Optional Text] MFS Conservative Allocation Fund Blended Index      
MFS Conservative Allocation Fund Blended Index | Average Annual Return, Percent   12.34% 4.82% 6.31%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   3.24% 2.54% 5.30%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   1.25% 1.01% 3.92%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   2.47% 1.46% 3.71%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   4.75% 2.65% 5.29%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   7.73% 3.00% 5.30%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   9.82% 4.04% 6.20%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   8.69% 3.00% 5.14%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   9.25% 3.51% 5.67%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   9.58% 3.78% 5.93%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   9.87% 4.03% 6.20%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   9.89% 4.09% 6.23%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

As of December 31, 2025, the MFS Conservative Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 28% Standard & Poor's 500 Stock Index; 8% MSCI EAFE (Europe, Australasia, Far East) Index; 2% Bloomberg Commodity Index; 2% FTSE EPRA Nareit Developed Real Estate Index; and 60% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Conservative Allocation Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 3.82%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 10.75%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (9.33%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Emerging Markets Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 16.65%. During the period(s) shown in the bar chart, the highest quarterly return was 18.15% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (27.44)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Emerging Markets Equity Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI Emerging Markets Index (net div) | Average Annual Return, Label [Optional Text] MSCI Emerging Markets Index (net div)      
MSCI Emerging Markets Index (net div) | Average Annual Return, Percent   33.57% 4.20% 8.42%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   25.80% 2.84% 6.89%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   25.31% 2.59% 6.71%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   16.02% 2.34% 5.68%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   28.50% 2.94% 6.88%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   31.52% 3.29% 6.88%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   33.82% 4.33% 7.79%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   32.49% 3.29% 6.72%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   33.16% 3.81% 7.25%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   33.49% 4.06% 7.52%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   33.84% 4.33% 7.79%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   33.99% 4.48% 7.93%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Emerging Markets Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 16.65%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 18.15%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (27.44%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS Growth Allocation Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Performance Additional Market Index [Text] As of December 31, 2025, the MFS Growth Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 52% Standard & Poor's 500 Stock Index; 20% MSCI EAFE (Europe, Australasia, Far East) Index; 4% Bloomberg Commodity Index; 4% FTSE EPRA Nareit Developed Real Estate Index; and 20% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 7.09%. During the period(s) shown in the bar chart, the highest quarterly return was 16.76% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (17.73)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Growth Allocation Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Standard & Poor's 500 Stock Index | Average Annual Return, Label [Optional Text] Standard & Poor's 500 Stock Index      
Standard & Poor's 500 Stock Index | Average Annual Return, Percent   17.88% 14.42% 14.82%
MFS Growth Allocation Fund Blended Index | Average Annual Return, Label [Optional Text] MFS Growth Allocation Fund Blended Index      
MFS Growth Allocation Fund Blended Index | Average Annual Return, Percent   17.98% 9.84% 10.24%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   6.83% 5.59% 8.61%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   4.59% 3.91% 7.12%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   5.06% 3.94% 6.55%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   8.46% 5.73% 8.59%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   11.47% 6.05% 8.59%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   13.61% 7.11% 9.52%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   12.47% 6.05% 8.43%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   13.03% 6.58% 8.98%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   13.32% 6.84% 9.25%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   13.57% 7.12% 9.52%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   13.68% 7.18% 9.56%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

As of December 31, 2025, the MFS Growth Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 52% Standard & Poor's 500 Stock Index; 20% MSCI EAFE (Europe, Australasia, Far East) Index; 4% Bloomberg Commodity Index; 4% FTSE EPRA Nareit Developed Real Estate Index; and 20% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Growth Allocation Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 7.09%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 16.76%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (17.73%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS International Diversification Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 8.76%. During the period(s) shown in the bar chart, the highest quarterly return was 17.04% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (19.80)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS International Diversification Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI All Country World (ex-US) Index (net div) | Average Annual Return, Label [Optional Text] MSCI All Country World (ex-US) Index (net div)      
MSCI All Country World (ex-US) Index (net div) | Average Annual Return, Percent   32.39% 7.91% 8.41%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   20.21% 5.26% 8.20%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   18.93% 4.54% 7.62%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   13.02% 4.09% 6.65%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   22.55% 5.39% 8.19%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   25.55% 5.71% 8.19%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   27.81% 6.78% 9.12%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   26.56% 5.72% 8.03%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   27.23% 6.25% 8.58%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   27.54% 6.52% 8.85%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   27.87% 6.78% 9.12%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   27.96% 6.88% 9.21%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS International Diversification Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 8.76%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 17.04%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (19.80%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS International Growth Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 1.82%. During the period(s) shown in the bar chart, the highest quarterly return was 16.93% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (18.71)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS International Growth Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI All Country World (ex-US) Index (net div) | Average Annual Return, Label [Optional Text] MSCI All Country World (ex-US) Index (net div)      
MSCI All Country World (ex-US) Index (net div) | Average Annual Return, Percent   32.39% 7.91% 8.41%
MSCI All Country World (ex-US) Growth Index (net div) | Average Annual Return, Label [Optional Text] MSCI All Country World (ex-US) Growth Index (net div)      
MSCI All Country World (ex-US) Growth Index (net div) | Average Annual Return, Percent   25.65% 4.01% 7.92%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   13.84% 5.59% 8.99%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   12.56% 4.59% 8.29%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   9.28% 4.32% 7.32%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   15.87% 5.73% 8.97%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   18.89% 6.05% 8.98%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   21.08% 7.11% 9.90%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   19.88% 6.05% 8.81%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   20.48% 6.58% 9.36%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   20.78% 6.84% 9.63%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   21.09% 7.12% 9.91%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   21.23% 7.24% 10.03%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS International Growth Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 1.82%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 16.93%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (18.71%)
Lowest Quarterly Return, Date Mar. 31, 2020
MFS International Intrinsic Equity Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) one or more other measures of performance for markets in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) one or more other measures of performance for markets in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 4.91%. During the period(s) shown in the bar chart, the highest quarterly return was 16.58% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (15.15)% (for the calendar quarter ended June 30, 2022).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS International Intrinsic Equity Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI EAFE (Europe, Australasia, Far East) Index (net div) | Average Annual Return, Label [Optional Text] MSCI EAFE (Europe, Australasia, Far East) Index (net div)      
MSCI EAFE (Europe, Australasia, Far East) Index (net div) | Average Annual Return, Percent   31.22% 8.92% 8.18%
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div) | Average Annual Return, Label [Optional Text] MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)      
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div) | Average Annual Return, Percent   42.25% 13.36% 8.69%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   25.17% 5.95% 9.20%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   22.96% 3.57% 7.58%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   16.60% 4.26% 7.24%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   27.79% 6.15% 9.19%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   30.82% 6.42% 9.18%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   33.11% 7.48% 10.12%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   31.80% 6.42% 9.02%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   32.49% 6.95% 9.57%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   32.77% 7.21% 9.84%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   33.16% 7.48% 10.12%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   33.29% 7.60% 10.24%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS International Intrinsic Equity Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 4.91%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 16.58%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (15.15%)
Lowest Quarterly Return, Date Jun. 30, 2022
MFS International Value Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 9.89%. During the period(s) shown in the bar chart, the highest quarterly return was 18.90% (for the calendar quarter ended December 31, 2022) and the lowest quarterly return was (12.28)% (for the calendar quarter ended June 30, 2022).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS International Value Fund
 12 Months Ended 60 Months Ended 66 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI EAFE (Europe, Australasia, Far East) Index (net div) | Average Annual Return, Label [Optional Text] MSCI EAFE (Europe, Australasia, Far East) Index (net div)      
MSCI EAFE (Europe, Australasia, Far East) Index (net div) | Average Annual Return, Percent   31.22% 8.92% 12.03%
MSCI EAFE (Europe, Australasia, Far East) Index (net div) | Performance Inception Date       Jun. 30, 2020
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div) | Average Annual Return, Label [Optional Text] MSCI EAFE (Europe, Australasia, Far East) Value Index (net div)      
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div) | Average Annual Return, Percent   42.25% 13.36% 15.99%
MSCI EAFE (Europe, Australasia, Far East) Value Index (net div) | Performance Inception Date       Jun. 30, 2020
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   31.77% 11.06% 13.84%
Class A | Performance Inception Date       Jun. 30, 2020
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   29.38% 9.88% 12.72%
Class A | After Taxes on Distributions | Performance Inception Date       Jun. 30, 2020
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   20.53% 8.67% 11.06%
Class A | After Taxes on Distributions and Sales | Performance Inception Date       Jun. 30, 2020
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   37.80% 11.55% 14.20%
Class C | Performance Inception Date       Jun. 30, 2020
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   40.07% 12.67% 15.38%
Class I | Performance Inception Date       Jun. 30, 2020
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   38.83% 11.55% 14.20%
Class R1 | Performance Inception Date       Jun. 30, 2020
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   39.47% 12.11% 14.76%
Class R2 | Performance Inception Date       Jun. 30, 2020
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   39.86% 12.40% 15.08%
Class R3 | Performance Inception Date       Jun. 30, 2020
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   40.17% 12.67% 15.40%
Class R4 | Performance Inception Date       Jun. 30, 2020
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   40.20% 12.73% 15.42%
Class R6 | Performance Inception Date       Jun. 30, 2020
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and

after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS International Value Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 9.89%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 18.90%
Highest Quarterly Return, Date Dec. 31, 2022
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (12.28%)
Lowest Quarterly Return, Date Jun. 30, 2022
MFS Managed Wealth Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely corresponds to the fund's principal investment strategies.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely corresponds to the fund's principal investment strategies.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 1.35%. During the period(s) shown in the bar chart, the highest quarterly return was 4.13% (for the calendar quarter ended March 31, 2024) and the lowest quarterly return was (3.28)% (for the calendar quarter ended March 31, 2022).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Managed Wealth Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Standard & Poor's 500 Stock Index | Average Annual Return, Label [Optional Text] Standard & Poor's 500 Stock Index      
Standard & Poor's 500 Stock Index | Average Annual Return, Percent   17.88% 14.42% 14.82%
ICE BofA 0-3 Month U.S. Treasury Bill Index | Average Annual Return, Label [Optional Text] ICE BofA 0-3 Month U.S. Treasury Bill Index      
ICE BofA 0-3 Month U.S. Treasury Bill Index | Average Annual Return, Percent   4.28% 3.23% 2.17%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   1.32% 2.23% 2.98%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   1.18% 2.14% 2.83%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   0.88% 1.72% 2.32%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   2.64% 2.29% 2.89%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   5.68% 2.66% 2.91%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   7.71% 3.68% 3.78%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   6.66% 2.67% 2.75%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   7.15% 3.16% 3.26%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   7.41% 3.43% 3.52%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   7.72% 3.69% 3.78%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   7.79% 3.78% 3.84%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Managed Wealth Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 1.35%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 4.13%
Highest Quarterly Return, Date Mar. 31, 2024
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (3.28%)
Lowest Quarterly Return, Date Mar. 31, 2022
MFS Moderate Allocation Fund  
Prospectus [Line Items]  
Bar Chart and Performance Table [Heading] Performance Information
Performance Narrative [Text Block]

The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.

The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.
Performance Past Does Not Indicate Future [Text] The fund’s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.
Performance Information Illustrates Variability of Returns [Text] The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of (i) a broad measure of market performance and (ii) the performance of an additional index that the adviser believes more closely reflects the market segments in which the fund invests.
Performance Additional Market Index [Text] As of December 31, 2025, the MFS Moderate Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 41% Standard & Poor's 500 Stock Index; 13% MSCI EAFE (Europe, Australasia, Far East) Index; 3% Bloomberg Commodity Index; 3% FTSE EPRA Nareit Developed Real Estate Index; and 40% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.
Bar Chart Narrative [Text Block] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart Does Not Reflect Sales Loads [Text] The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund’s shares. If these sales charges were included, they would reduce the returns shown.
Bar Chart [Heading] Class A Bar Chart.
Bar Chart Closing [Text Block]

The total return for the six-month period ended June 30, 2026, was 5.46%. During the period(s) shown in the bar chart, the highest quarterly return was 13.59% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (13.14)% (for the calendar quarter ended March 31, 2020).
Performance Table Heading Performance Table.
Performance Table Not Relevant to Tax Deferred Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs).
Performance [Table]
Average Annual Total Returns - MFS Moderate Allocation Fund
 12 Months Ended 60 Months Ended 120 Months Ended
May 31, 2026
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Standard & Poor's 500 Stock Index | Average Annual Return, Label [Optional Text] Standard & Poor's 500 Stock Index      
Standard & Poor's 500 Stock Index | Average Annual Return, Percent   17.88% 14.42% 14.82%
MFS Moderate Allocation Fund Blended Index | Average Annual Return, Label [Optional Text] MFS Moderate Allocation Fund Blended Index      
MFS Moderate Allocation Fund Blended Index | Average Annual Return, Percent   15.02% 7.38% 8.36%
Class A | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class A | Average Annual Return, Percent   5.29% 3.99% 6.98%
Class A | After Taxes on Distributions | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions      
Class A | After Taxes on Distributions | Average Annual Return, Percent   2.99% 2.28% 5.46%
Class A | After Taxes on Distributions and Sales | Average Annual Return, Label [Optional Text] Returns After Taxes on Distributions and Sale of Fund Shares      
Class A | After Taxes on Distributions and Sales | Average Annual Return, Percent   3.97% 2.61% 5.12%
Class B | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class B | Average Annual Return, Percent   6.88% 4.12% 6.98%
Class C | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class C | Average Annual Return, Percent   9.89% 4.46% 6.97%
Class I | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class I | Average Annual Return, Percent   12.02% 5.50% 7.89%
Class R1 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R1 | Average Annual Return, Percent   10.85% 4.45% 6.82%
Class R2 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R2 | Average Annual Return, Percent   11.41% 4.97% 7.35%
Class R3 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R3 | Average Annual Return, Percent   11.72% 5.24% 7.63%
Class R4 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R4 | Average Annual Return, Percent   12.01% 5.50% 7.89%
Class R6 | Average Annual Return, Label [Optional Text] Returns Before Taxes      
Class R6 | Average Annual Return, Percent   12.04% 5.56% 7.92%
Average Annual Return, Caption [Optional Text] Average Annual Total Returns (For the Periods Ended December 31, 2025)
Performance Table One Class of after Tax Shown [Text] The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Index No Deduction for Fees, Expenses, or Taxes [Text] Reflects no deduction for fees, expenses, or taxes
Performance Table Closing [Text Block]

As of December 31, 2025, the MFS Moderate Allocation Fund Blended Index (the Blended Index) consisted of the following indices and weightings: 41% Standard & Poor's 500 Stock Index; 13% MSCI EAFE (Europe, Australasia, Far East) Index; 3% Bloomberg Commodity Index; 3% FTSE EPRA Nareit Developed Real Estate Index; and 40% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

After-tax returns are calculated using the historical highest individual U.S. federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-advantaged arrangements, such as 401(k) plans or individual retirement accounts (IRAs). The after-tax returns are shown for only one of the fund’s classes of shares, and after-tax returns for the fund’s other classes of shares will vary from the returns shown.
Performance Availability Website Address [Text] mfs.com
Performance Availability Phone [Text] 1-800-225-2606
MFS Moderate Allocation Fund | Class A  
Prospectus [Line Items]  
Year to Date Return, Label [Optional Text] The total return for the six-month period ended
Bar Chart, Year to Date Return 5.46%
Bar Chart, Year to Date Return, Date Jun. 30, 2026
Highest Quarterly Return, Label [Optional Text] highest quarterly return
Highest Quarterly Return 13.59%
Highest Quarterly Return, Date Jun. 30, 2020
Lowest Quarterly Return, Label [Optional Text] lowest quarterly return
Lowest Quarterly Return (13.14%)
Lowest Quarterly Return, Date Mar. 31, 2020