| Form N-CSR Cover | 6 Months Ended |
| Oct. 31, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | MFS SERIES TRUST XII |
| Entity Central Index Key | 0001330967 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Oct. 31, 2024 |
| Shareholder Report | 6 Months Ended | |
| Oct. 31, 2024 USD ($) Holding | ||
| Shareholder Report [Line Items] | ||
| Document Type | N-CSRS | |
| Amendment Flag | false | |
| Registrant Name | MFS SERIES TRUST XII | |
| Entity Central Index Key | 0001330967 | |
| Entity Investment Company Type | N-1A | |
| Document Period End Date | Oct. 31, 2024 | |
| C000229439 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | LFTMX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [1] |
| Expense Ratio, Percent | 0% | [1] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006795 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class C | |
| Trading Symbol | MLLCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [2] |
| Expense Ratio, Percent | 1% | [2] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000006824 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MLTEX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [3] |
| Expense Ratio, Percent | 1% | [3] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000173919 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MFJEX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [4] |
| Expense Ratio, Percent | 0.25% | [4] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119424 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class C | |
| Trading Symbol | LTTCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [5] |
| Expense Ratio, Percent | 1% | [5] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000236392 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class C | |
| Trading Symbol | MCBCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) C $ 1.36 % | |
| Expenses Paid, Amount | $ 70 | |
| Expense Ratio, Percent | 1.36% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000173232 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | LTMLX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [6] |
| Expense Ratio, Percent | 0% | [6] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000173228 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MLFKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [7] |
| Expense Ratio, Percent | 0% | [7] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000006827 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MLTHX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [8] |
| Expense Ratio, Percent | 0.25% | [8] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000119437 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | LFETX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [9] |
| Expense Ratio, Percent | 0.25% | [9] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000119426 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | LTTRX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [10] |
| Expense Ratio, Percent | 1% | [10] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000006826 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MLTGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [11] |
| Expense Ratio, Percent | 0.50% | [11] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000006794 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class B | |
| Trading Symbol | MLLBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [12] |
| Expense Ratio, Percent | 1% | [12] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000119432 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class B | |
| Trading Symbol | LFEBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [13] |
| Expense Ratio, Percent | 1% | [13] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000173916 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class B | |
| Trading Symbol | MFJBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [14] |
| Expense Ratio, Percent | 0.25% | [14] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006796 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class I | |
| Trading Symbol | MLLIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [15] |
| Expense Ratio, Percent | 0% | [15] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000119452 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | LFISX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [16] |
| Expense Ratio, Percent | 0.50% | [16] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000229443 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class I | |
| Trading Symbol | LFTHX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [17] |
| Expense Ratio, Percent | 0% | [17] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000229438 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | LFTJX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 0.97 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 51 | [18] |
| Expense Ratio, Percent | 0.97% | [18] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119433 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class C | |
| Trading Symbol | LFECX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [19] |
| Expense Ratio, Percent | 1% | [19] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000006833 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MLFEX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [20] |
| Expense Ratio, Percent | 1% | [20] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000119443 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | LTMRX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [21] |
| Expense Ratio, Percent | 1% | [21] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000092198 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class C | |
| Trading Symbol | MFFDX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [22] |
| Expense Ratio, Percent | 1% | [22] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006828 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MLTJX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [23] |
| Expense Ratio, Percent | 0% | [23] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000236393 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MCBHX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) R2 $ 0.86 % | |
| Expenses Paid, Amount | $ 44 | |
| Expense Ratio, Percent | 0.86% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000119423 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class B | |
| Trading Symbol | LTTBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [24] |
| Expense Ratio, Percent | 1% | [24] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000006820 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class A | |
| Trading Symbol | MLTAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [25] |
| Expense Ratio, Percent | 0.25% | [25] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000092196 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class A | |
| Trading Symbol | MFFSX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [26] |
| Expense Ratio, Percent | 0.25% | [26] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000092201 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MFFNX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [27] |
| Expense Ratio, Percent | 0.50% | [27] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119446 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | LTMUX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [28] |
| Expense Ratio, Percent | 0% | [28] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000006836 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MLFHX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [29] |
| Expense Ratio, Percent | 0.25% | [29] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000119429 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | LTTUX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [30] |
| Expense Ratio, Percent | 0% | [30] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000006823 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class I | |
| Trading Symbol | MLTIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [31] |
| Expense Ratio, Percent | 0% | [31] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000173915 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class A | |
| Trading Symbol | MFJAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [32] |
| Expense Ratio, Percent | 0.25% | [32] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119436 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | LFESX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [33] |
| Expense Ratio, Percent | 0.50% | [33] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000119439 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class A | |
| Trading Symbol | LTMAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [34] |
| Expense Ratio, Percent | 0.25% | [34] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000173229 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MFFKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [35] |
| Expense Ratio, Percent | 0% | [35] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006835 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MLFGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [36] |
| Expense Ratio, Percent | 0.50% | [36] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000119453 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | LFITX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [37] |
| Expense Ratio, Percent | 0.25% | [37] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119438 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | LFEUX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [38] |
| Expense Ratio, Percent | 0% | [38] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000006799 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MLLGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [39] |
| Expense Ratio, Percent | 0.50% | [39] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000173921 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MFJTX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [40] |
| Expense Ratio, Percent | 0.25% | [40] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119442 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class I | |
| Trading Symbol | LTMKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [41] |
| Expense Ratio, Percent | 0% | [41] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000119430 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class A | |
| Trading Symbol | LTTAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [42] |
| Expense Ratio, Percent | 0.25% | [42] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000236388 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MCBJX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) R3 $ 0.61 % | |
| Expenses Paid, Amount | $ 32 | |
| Expense Ratio, Percent | 0.61% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000006793 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class A | |
| Trading Symbol | MLLAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [43] |
| Expense Ratio, Percent | 0.25% | [43] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000006822 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class C | |
| Trading Symbol | MLTCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [44] |
| Expense Ratio, Percent | 1% | [44] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000173922 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MFJUX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [45] |
| Expense Ratio, Percent | 0% | [45] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119440 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class B | |
| Trading Symbol | LTMBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [46] |
| Expense Ratio, Percent | 1% | [46] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000173230 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | LTTKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [47] |
| Expense Ratio, Percent | 0% | [47] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000229436 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | LFTLX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.22 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 12 | [48] |
| Expense Ratio, Percent | 0.22% | [48] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000092202 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MFFOX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [49] |
| Expense Ratio, Percent | 0.25% | [49] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119431 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class A | |
| Trading Symbol | LFEAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [50] |
| Expense Ratio, Percent | 0.25% | [50] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000092203 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MFFPX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [51] |
| Expense Ratio, Percent | 0% | [51] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006800 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class R3 | |
| Trading Symbol | MLLHX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [52] |
| Expense Ratio, Percent | 0.25% | [52] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000236387 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MCBMX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com. | |
| Additional Information Website | funds.mfs.com. | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) R6 $ 0.33 % | |
| Expenses Paid, Amount | $ 17 | |
| Expense Ratio, Percent | 0.33% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000119451 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | LFIRX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [53] |
| Expense Ratio, Percent | 1% | [53] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000173917 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class C | |
| Trading Symbol | MFJCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [54] |
| Expense Ratio, Percent | 1% | [54] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000236389 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class A | |
| Trading Symbol | MCBEX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) A $ 0.61 % | |
| Expenses Paid, Amount | $ 32 | |
| Expense Ratio, Percent | 0.61% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000119447 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class A | |
| Trading Symbol | LFIAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [55] |
| Expense Ratio, Percent | 0.25% | [55] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000173225 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MLLKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [56] |
| Expense Ratio, Percent | 0% | [56] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000006801 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MLLJX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [57] |
| Expense Ratio, Percent | 0% | [57] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000006829 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class A | |
| Trading Symbol | MLFAX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [58] |
| Expense Ratio, Percent | 0.25% | [58] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000119427 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | LTTSX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [59] |
| Expense Ratio, Percent | 0.50% | [59] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000119441 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class C | |
| Trading Symbol | LTMDX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [60] |
| Expense Ratio, Percent | 1% | [60] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000119434 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class I | |
| Trading Symbol | LFEDX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [61] |
| Expense Ratio, Percent | 0% | [61] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000229437 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | LFTKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com. You can also request this information by contacting us at 1-800-225-2606 or by sending an e-mail request to orderliterature@mfs.com. | |
| Additional Information Phone Number | 1-800-225-2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.47 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 25 | [62] |
| Expense Ratio, Percent | 0.47% | [62] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119454 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | LFIUX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [63] |
| Expense Ratio, Percent | 0% | [63] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000229440 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class C | |
| Trading Symbol | LFTGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 0.97 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 51 | [64] |
| Expense Ratio, Percent | 0.97% | [64] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119444 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | LTMSX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [65] |
| Expense Ratio, Percent | 0.50% | [65] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000092200 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MFFMX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [66] |
| Expense Ratio, Percent | 1% | [66] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006821 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class B | |
| Trading Symbol | MLTBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [67] |
| Expense Ratio, Percent | 1% | [67] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000236386 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MCBKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) R4 $ 0.37 % | |
| Expenses Paid, Amount | $ 19 | |
| Expense Ratio, Percent | 0.37% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Quality Explanation [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000119450 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class I | |
| Trading Symbol | LFIIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [68] |
| Expense Ratio, Percent | 0% | [68] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006831 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class C | |
| Trading Symbol | MLFCX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [69] |
| Expense Ratio, Percent | 1% | [69] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000173918 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class I | |
| Trading Symbol | MFJIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [70] |
| Expense Ratio, Percent | 0% | [70] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119428 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | LTTTX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [71] |
| Expense Ratio, Percent | 0.25% | [71] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000229442 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | LFTNX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [72] |
| Expense Ratio, Percent | 0% | [72] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000173231 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | LFEKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [73] |
| Expense Ratio, Percent | 0% | [73] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000119448 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class B | |
| Trading Symbol | LFIBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [74] |
| Expense Ratio, Percent | 1% | [74] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119425 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2025 Fund | |
| Class Name | Class I | |
| Trading Symbol | LTTIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [75] |
| Expense Ratio, Percent | 0% | [75] |
| Net Assets | $ 376,138,028 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 376,138,028 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 18.4 % MFS Limited Maturity Fund 18.3 % MFS Inflation-Adjusted Bond Fund 9.9 % MFS Government Securities Fund 9.3 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.2 % MFS Institutional Money Market Portfolio 2.8 % MFS Blended Research International Equity Fund 2.7 % MFS High Income Fund 2.4 % MFS Blended Research Value Equity Fund 2.2 % MFS Value Fund 2.2 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.9 % MFS Blended Research Growth Equity Fund 1.8 % MFS Research Fund 1.8 % MFS Growth Fund 1.8 % MFS Mid Cap Value Fund 1.6 % MFS Mid Cap Growth Fund 1.6 % MFS Research International Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 1.2 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS International Intrinsic Value Fund 0.6 % MFS International Growth Fund 0.6 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % | |
| C000119435 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2035 Fund | |
| Class Name | Class R1 | |
| Trading Symbol | LFERX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [76] |
| Expense Ratio, Percent | 1% | [76] |
| Net Assets | $ 608,746,089 | |
| Holdings Count | Holding | 29 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 608,746,089 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 29 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 7.6 % MFS Government Securities Fund 7.3 % MFS Total Return Bond Fund 7.0 % MFS Inflation-Adjusted Bond Fund 6.5 % MFS Blended Research International Equity Fund 6.4 % MFS Global Opportunistic Bond Fund 4.5 % MFS Blended Research Value Equity Fund 4.3 % MFS Value Fund 4.2 % MFS High Income Fund 4.0 % MFS Blended Research Growth Equity Fund 3.9 % MFS Blended Research Core Equity Fund 3.9 % MFS Research Fund 3.9 % MFS Growth Fund 3.9 % MFS Mid Cap Value Fund 3.8 % MFS Mid Cap Growth Fund 3.7 % MFS Commodity Strategy Fund 3.2 % MFS Global Real Estate Fund 3.1 % MFS Research International Fund 3.0 % MFS Emerging Markets Debt Fund 3.0 % MFS Institutional Money Market Portfolio 2.8 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS International Growth Fund 1.7 % MFS International Intrinsic Value Fund 1.7 % MFS Blended Research Small Cap Equity Fund 1.6 % MFS International New Discovery Fund 1.2 % MFS New Discovery Fund 0.8 % MFS New Discovery Value Fund 0.8 % MFS Emerging Markets Equity Fund 0.1 % MFS Blended Research Emerging Markets Equity Fund 0.1 % | |
| C000006797 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® Income Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MLLEX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R1 $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [77] |
| Expense Ratio, Percent | 1% | [77] |
| Net Assets | $ 595,613,200 | |
| Holdings Count | Holding | 27 | |
| Investment Company Portfolio Turnover | 2% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 595,613,200 Portfolio Turnover Rate (%): 2 Total Number of Holdings: 27 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Limited Maturity Fund 20.2 % MFS Total Return Bond Fund 19.4 % MFS Inflation-Adjusted Bond Fund 10.0 % MFS Government Securities Fund 9.4 % MFS Global Opportunistic Bond Fund 7.0 % MFS Blended Research Mid Cap Equity Fund 3.0 % MFS Institutional Money Market Portfolio 2.7 % MFS Blended Research International Equity Fund 2.4 % MFS High Income Fund 2.0 % MFS Blended Research Value Equity Fund 2.0 % MFS Value Fund 2.0 % MFS Commodity Strategy Fund 2.0 % MFS Global Real Estate Fund 1.9 % MFS Blended Research Core Equity Fund 1.7 % MFS Research Fund 1.6 % MFS Blended Research Growth Equity Fund 1.6 % MFS Growth Fund 1.6 % MFS Mid Cap Value Fund 1.5 % MFS Mid Cap Growth Fund 1.5 % MFS Research International Fund 1.5 % MFS Blended Research Small Cap Equity Fund 1.0 % MFS Emerging Markets Debt Fund 1.0 % MFS Emerging Markets Debt Local Currency Fund 1.0 % MFS New Discovery Fund 0.5 % MFS New Discovery Value Fund 0.5 % MFS International Intrinsic Value Fund 0.5 % MFS International Growth Fund 0.5 % | |
| C000173923 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MFJKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [78] |
| Expense Ratio, Percent | 0% | [78] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000173233 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | LFIKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [79] |
| Expense Ratio, Percent | 0% | [79] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006830 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class B | |
| Trading Symbol | MLFBX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 52 | [80] |
| Expense Ratio, Percent | 1% | [80] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000236390 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class R1 | |
| Trading Symbol | MCBGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) R1 $ 1.36 % | |
| Expenses Paid, Amount | $ 70 | |
| Expense Ratio, Percent | 1.36% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000092199 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class I | |
| Trading Symbol | MFFIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [81] |
| Expense Ratio, Percent | 0% | [81] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000236391 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Core Bond Fund | |
| Class Name | Class I | |
| Trading Symbol | MCBFX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment (annualized) I $ 0.36 % | |
| Expenses Paid, Amount | $ 19 | |
| Expense Ratio, Percent | 0.36% | |
| Net Assets | $ 30,792,124 | |
| Holdings Count | Holding | 307 | |
| Investment Company Portfolio Turnover | 83% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 30,792,124 Average Effective Maturity (yrs): 7.7 Total Number of Holdings: 307 Average Effective Duration (yrs): 6.1 Portfolio Turnover Rate (%): 83 Where the fund holds derivatives, they are not included in the total number of portfolio holdings. | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio structure Fixed Income 95.3 % Money Market Funds 4.7 % Composition including fixed income credit quality AAA 13.0 % AA 5.6 % A 12.8 % BBB 18.0 % U.S. Government 17.6 % Federal Agencies 28.3 % Money Market Funds 4.7 % Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| Credit Ratings Selection [Text Block] | Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change. | |
| C000119445 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2045 Fund | |
| Class Name | Class R3 | |
| Trading Symbol | LTMTX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R3 $ 0.25 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 13 | [82] |
| Expense Ratio, Percent | 0.25% | [82] |
| Net Assets | $ 524,716,460 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 524,716,460 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 9.8 % MFS Blended Research Mid Cap Equity Fund 9.7 % MFS Blended Research Value Equity Fund 5.3 % MFS Value Fund 5.3 % MFS Blended Research Growth Equity Fund 5.0 % MFS Growth Fund 4.9 % MFS Mid Cap Value Fund 4.9 % MFS Mid Cap Growth Fund 4.8 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Commodity Strategy Fund 4.6 % MFS Global Real Estate Fund 4.5 % MFS Research International Fund 3.7 % MFS Inflation-Adjusted Bond Fund 3.4 % MFS International New Discovery Fund 3.1 % MFS International Intrinsic Value Fund 3.1 % MFS International Growth Fund 3.1 % MFS Blended Research Small Cap Equity Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS Total Return Bond Fund 2.1 % MFS High Income Fund 1.6 % MFS Emerging Markets Debt Fund 1.2 % MFS Global Opportunistic Bond Fund 1.2 % MFS New Discovery Fund 1.2 % MFS New Discovery Value Fund 1.2 % MFS Emerging Markets Debt Local Currency Fund 0.8 % MFS Emerging Markets Equity Fund 0.8 % MFS Blended Research Emerging Markets Equity Fund 0.8 % | |
| C000229441 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2065 Fund | |
| Class Name | Class A | |
| Trading Symbol | LFTFX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ A $ 0.22 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 12 | [83] |
| Expense Ratio, Percent | 0.22% | [83] |
| Net Assets | $ 24,586,389 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 18% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 24,586,389 Portfolio Turnover Rate (%): 18 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.1 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Value Fund 5.6 % MFS Blended Research Value Equity Fund 5.6 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Commodity Strategy Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Global Real Estate Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.1 % MFS Research International Fund 4.1 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Inflation-Adjusted Bond Fund 2.6 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Total Return Bond Fund 2.0 % MFS New Discovery Value Fund 1.3 % MFS New Discovery Fund 1.3 % MFS Institutional Money Market Portfolio 1.1 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000173920 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2060 Fund | |
| Class Name | Class R2 | |
| Trading Symbol | MFJGX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R2 $ 0.50 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 26 | [84] |
| Expense Ratio, Percent | 0.50% | [84] |
| Net Assets | $ 205,348,531 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 9% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 205,348,531 Portfolio Turnover Rate (%): 9 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.6 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Intrinsic Value Fund 3.5 % MFS International Growth Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000006832 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class I | |
| Trading Symbol | MLFIX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ I $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [85] |
| Expense Ratio, Percent | 0% | [85] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000006837 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2040 Fund | |
| Class Name | Class R4 | |
| Trading Symbol | MLFJX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R4 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [86] |
| Expense Ratio, Percent | 0% | [86] |
| Net Assets | $ 779,644,550 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 3% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 779,644,550 Portfolio Turnover Rate (%): 3 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research Mid Cap Equity Fund 9.2 % MFS Blended Research International Equity Fund 8.6 % MFS Blended Research Value Equity Fund 5.1 % MFS Value Fund 5.1 % MFS Blended Research Growth Equity Fund 4.7 % MFS Inflation-Adjusted Bond Fund 4.7 % MFS Growth Fund 4.7 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Mid Cap Value Fund 4.6 % MFS Mid Cap Growth Fund 4.5 % MFS Commodity Strategy Fund 4.1 % MFS Global Real Estate Fund 4.0 % MFS High Income Fund 3.6 % MFS Research International Fund 3.5 % MFS Emerging Markets Debt Fund 2.7 % MFS Global Opportunistic Bond Fund 2.7 % MFS International Intrinsic Value Fund 2.6 % MFS International Growth Fund 2.6 % MFS Total Return Bond Fund 2.3 % MFS Institutional Money Market Portfolio 2.2 % MFS International New Discovery Fund 2.2 % MFS Blended Research Small Cap Equity Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 1.8 % MFS New Discovery Fund 1.0 % MFS New Discovery Value Fund 1.0 % MFS Emerging Markets Equity Fund 0.5 % MFS Blended Research Emerging Markets Equity Fund 0.5 % | |
| C000173227 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2030 Fund | |
| Class Name | Class R6 | |
| Trading Symbol | MLTKX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ R6 $ 0.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 0 | [87] |
| Expense Ratio, Percent | 0% | [87] |
| Net Assets | $ 768,229,768 | |
| Holdings Count | Holding | 28 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 768,229,768 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 28 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Total Return Bond Fund 13.1 % MFS Inflation-Adjusted Bond Fund 9.3 % MFS Government Securities Fund 9.3 % MFS Limited Maturity Fund 8.0 % MFS Global Opportunistic Bond Fund 6.6 % MFS Blended Research Mid Cap Equity Fund 4.7 % MFS Blended Research International Equity Fund 4.3 % MFS High Income Fund 4.0 % MFS Blended Research Value Equity Fund 3.2 % MFS Value Fund 3.2 % MFS Institutional Money Market Portfolio 3.0 % MFS Blended Research Growth Equity Fund 2.9 % MFS Blended Research Core Equity Fund 2.9 % MFS Research Fund 2.8 % MFS Growth Fund 2.8 % MFS Mid Cap Value Fund 2.3 % MFS Mid Cap Growth Fund 2.3 % MFS Emerging Markets Debt Fund 2.2 % MFS Commodity Strategy Fund 2.2 % MFS Research International Fund 2.1 % MFS Global Real Estate Fund 2.1 % MFS Emerging Markets Debt Local Currency Fund 2.0 % MFS Blended Research Small Cap Equity Fund 1.1 % MFS International Intrinsic Value Fund 1.1 % MFS International Growth Fund 1.1 % MFS New Discovery Fund 0.6 % MFS New Discovery Value Fund 0.6 % MFS International New Discovery Fund 0.2 % | |
| C000092197 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2050 Fund | |
| Class Name | Class B | |
| Trading Symbol | MFFRX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ B $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [88] |
| Expense Ratio, Percent | 1% | [88] |
| Net Assets | $ 563,796,334 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 4% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 563,796,334 Portfolio Turnover Rate (%): 4 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 10.8 % MFS Blended Research Mid Cap Equity Fund 10.1 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.2 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.1 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.7 % MFS Research Fund 4.7 % MFS Research International Fund 3.9 % MFS International New Discovery Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.4 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.4 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| C000119449 [Member] | ||
| Shareholder Report [Line Items] | ||
| Fund Name | MFS® Lifetime® 2055 Fund | |
| Class Name | Class C | |
| Trading Symbol | LFICX | |
| Annual or Semi-Annual Statement [Text Block] | This semiannual shareholder report | |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report | |
| Additional Information [Text Block] | You can find additional information about the fund at funds.mfs.com | |
| Additional Information Phone Number | 1‑800‑225‑2606 | |
| Additional Information Email | orderliterature@mfs.com | |
| Additional Information Website | funds.mfs.com | |
| Expenses [Text Block] | FUND EXPENSES What were the fund costs for the last six months? (based on a hypothetical $10,000 investment) Class Name Costs of a $10,000 investment ~ Costs paid as a percentage of a $10,000 investment (annualized) ~ C $ 1.00 % ˜ Expenses are direct expenses and do not include underlying fund fees and expenses. | |
| Expenses Paid, Amount | $ 53 | [89] |
| Expense Ratio, Percent | 1% | [89] |
| Net Assets | $ 371,452,215 | |
| Holdings Count | Holding | 24 | |
| Investment Company Portfolio Turnover | 5% | |
| Additional Fund Statistics [Text Block] | FUND STATISTICS AS OF 10/31/24 Net Assets ($): 371,452,215 Portfolio Turnover Rate (%): 5 Total Number of Holdings: 24 | |
| Holdings [Text Block] | PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 10/31/24) Portfolio allocation Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| Largest Holdings [Text Block] | Portfolio holdings MFS Blended Research International Equity Fund 11.0 % MFS Blended Research Mid Cap Equity Fund 10.0 % MFS Blended Research Value Equity Fund 5.5 % MFS Value Fund 5.5 % MFS Blended Research Growth Equity Fund 5.1 % MFS Growth Fund 5.1 % MFS Mid Cap Value Fund 5.0 % MFS Commodity Strategy Fund 5.0 % MFS Mid Cap Growth Fund 5.0 % MFS Global Real Estate Fund 4.9 % MFS Blended Research Core Equity Fund 4.6 % MFS Research Fund 4.6 % MFS International New Discovery Fund 4.0 % MFS Research International Fund 3.9 % MFS International Growth Fund 3.5 % MFS International Intrinsic Value Fund 3.5 % MFS Blended Research Small Cap Equity Fund 2.5 % MFS Inflation-Adjusted Bond Fund 2.5 % MFS Institutional Money Market Portfolio 2.3 % MFS Total Return Bond Fund 1.9 % MFS New Discovery Fund 1.3 % MFS New Discovery Value Fund 1.3 % MFS Emerging Markets Equity Fund 1.0 % MFS Blended Research Emerging Markets Equity Fund 1.0 % | |
| [1]Expenses are direct expenses and do not include underlying fund fees and expenses.[2]Expenses are direct expenses and do not include underlying fund fees and expenses.[3]Expenses are direct expenses and do not include underlying fund fees and expenses.[4]Expenses are direct expenses and do not include underlying fund fees and expenses.[5]Expenses are direct expenses and do not include underlying fund fees and expenses.[6]Expenses are direct expenses and do not include underlying fund fees and expenses.[7]Expenses are direct expenses and do not include underlying fund fees and expenses.[8]Expenses are direct expenses and do not include underlying fund fees and expenses.[9]Expenses are direct expenses and do not include underlying fund fees and expenses.[10]Expenses are direct expenses and do not include underlying fund fees and expenses.[11]Expenses are direct expenses and do not include underlying fund fees and expenses.[12]Expenses are direct expenses and do not include underlying fund fees and expenses.[13]Expenses are direct expenses and do not include underlying fund fees and expenses.[14]Expenses are direct expenses and do not include underlying fund fees and expenses.[15]Expenses are direct expenses and do not include underlying fund fees and expenses.[16]Expenses are direct expenses and do not include underlying fund fees and expenses.[17]Expenses are direct expenses and do not include underlying fund fees and expenses.[18]Expenses are direct expenses and do not include underlying fund fees and expenses.[19]Expenses are direct expenses and do not include underlying fund fees and expenses.[20]Expenses are direct expenses and do not include underlying fund fees and expenses.[21]Expenses are direct expenses and do not include underlying fund fees and expenses.[22]Expenses are direct expenses and do not include underlying fund fees and expenses.[23]Expenses are direct expenses and do not include underlying fund fees and expenses.[24]Expenses are direct expenses and do not include underlying fund fees and expenses.[25]Expenses are direct expenses and do not include underlying fund fees and expenses.[26]Expenses are direct expenses and do not include underlying fund fees and expenses.[27]Expenses are direct expenses and do not include underlying fund fees and expenses.[28]Expenses are direct expenses and do not include underlying fund fees and expenses.[29]Expenses are direct expenses and do not include underlying fund fees and expenses.[30]Expenses are direct expenses and do not include underlying fund fees and expenses.[31]Expenses are direct expenses and do not include underlying fund fees and expenses.[32]Expenses are direct expenses and do not include underlying fund fees and expenses.[33]Expenses are direct expenses and do not include underlying fund fees and expenses.[34]Expenses are direct expenses and do not include underlying fund fees and expenses.[35]Expenses are direct expenses and do not include underlying fund fees and expenses.[36]Expenses are direct expenses and do not include underlying fund fees and expenses.[37]Expenses are direct expenses and do not include underlying fund fees and expenses.[38]Expenses are direct expenses and do not include underlying fund fees and expenses.[39]Expenses are direct expenses and do not include underlying fund fees and expenses.[40]Expenses are direct expenses and do not include underlying fund fees and expenses.[41]Expenses are direct expenses and do not include underlying fund fees and expenses.[42]Expenses are direct expenses and do not include underlying fund fees and expenses.[43]Expenses are direct expenses and do not include underlying fund fees and expenses.[44]Expenses are direct expenses and do not include underlying fund fees and expenses.[45]Expenses are direct expenses and do not include underlying fund fees and expenses.[46]Expenses are direct expenses and do not include underlying fund fees and expenses.[47]Expenses are direct expenses and do not include underlying fund fees and expenses.[48]Expenses are direct expenses and do not include underlying fund fees and expenses.[49]Expenses are direct expenses and do not include underlying fund fees and expenses.[50]Expenses are direct expenses and do not include underlying fund fees and expenses.[51]Expenses are direct expenses and do not include underlying fund fees and expenses.[52]Expenses are direct expenses and do not include underlying fund fees and expenses.[53]Expenses are direct expenses and do not include underlying fund fees and expenses.[54]Expenses are direct expenses and do not include underlying fund fees and expenses.[55]Expenses are direct expenses and do not include underlying fund fees and expenses.[56]Expenses are direct expenses and do not include underlying fund fees and expenses.[57]Expenses are direct expenses and do not include underlying fund fees and expenses.[58]Expenses are direct expenses and do not include underlying fund fees and expenses.[59]Expenses are direct expenses and do not include underlying fund fees and expenses.[60]Expenses are direct expenses and do not include underlying fund fees and expenses.[61]Expenses are direct expenses and do not include underlying fund fees and expenses.[62]Expenses are direct expenses and do not include underlying fund fees and expenses.[63]Expenses are direct expenses and do not include underlying fund fees and expenses.[64]Expenses are direct expenses and do not include underlying fund fees and expenses.[65]Expenses are direct expenses and do not include underlying fund fees and expenses.[66]Expenses are direct expenses and do not include underlying fund fees and expenses.[67]Expenses are direct expenses and do not include underlying fund fees and expenses.[68]Expenses are direct expenses and do not include underlying fund fees and expenses.[69]Expenses are direct expenses and do not include underlying fund fees and expenses.[70]Expenses are direct expenses and do not include underlying fund fees and expenses.[71]Expenses are direct expenses and do not include underlying fund fees and expenses.[72]Expenses are direct expenses and do not include underlying fund fees and expenses.[73]Expenses are direct expenses and do not include underlying fund fees and expenses.[74]Expenses are direct expenses and do not include underlying fund fees and expenses.[75]Expenses are direct expenses and do not include underlying fund fees and expenses.[76]Expenses are direct expenses and do not include underlying fund fees and expenses.[77]Expenses are direct expenses and do not include underlying fund fees and expenses.[78]Expenses are direct expenses and do not include underlying fund fees and expenses.[79]Expenses are direct expenses and do not include underlying fund fees and expenses.[80]Expenses are direct expenses and do not include underlying fund fees and expenses.[81]Expenses are direct expenses and do not include underlying fund fees and expenses.[82]Expenses are direct expenses and do not include underlying fund fees and expenses.[83]Expenses are direct expenses and do not include underlying fund fees and expenses.[84]Expenses are direct expenses and do not include underlying fund fees and expenses.[85]Expenses are direct expenses and do not include underlying fund fees and expenses.[86]Expenses are direct expenses and do not include underlying fund fees and expenses.[87]Expenses are direct expenses and do not include underlying fund fees and expenses.[88]Expenses are direct expenses and do not include underlying fund fees and expenses.[89]Expenses are direct expenses and do not include underlying fund fees and expenses. | ||
| Shareholder Report, Holdings (Details) | Oct. 31, 2024 |
| C000229439 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229439 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229439 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229439 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229439 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229439 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229439 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229439 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229439 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229439 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229439 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229439 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229439 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229439 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229439 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229439 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229439 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229439 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229439 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229439 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229439 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229439 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229439 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229439 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229439 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229439 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229439 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229439 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229439 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000006795 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006795 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006795 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006795 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006795 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006795 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006795 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006795 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006795 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006795 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006795 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006795 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006795 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006795 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006795 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006795 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006795 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006795 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006795 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006795 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006795 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006795 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006795 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006795 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006795 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006795 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006795 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006795 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006795 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006795 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006795 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006795 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000006824 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006824 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006824 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006824 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006824 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006824 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006824 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006824 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006824 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006824 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006824 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006824 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006824 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006824 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006824 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006824 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006824 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006824 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006824 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006824 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006824 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006824 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006824 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006824 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006824 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006824 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006824 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006824 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006824 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006824 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006824 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006824 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006824 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000173919 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173919 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173919 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173919 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173919 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173919 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173919 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173919 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173919 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173919 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173919 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173919 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173919 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173919 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173919 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173919 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173919 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173919 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173919 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173919 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173919 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173919 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173919 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173919 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173919 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173919 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173919 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173919 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173919 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000119424 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119424 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119424 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119424 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119424 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119424 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119424 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119424 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119424 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119424 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119424 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119424 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119424 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119424 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119424 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119424 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119424 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119424 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119424 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119424 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119424 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119424 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119424 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119424 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119424 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119424 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119424 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119424 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119424 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119424 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119424 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119424 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000236392 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236392 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236392 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236392 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236392 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236392 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236392 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236392 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236392 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000173232 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173232 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173232 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000173232 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173232 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000173232 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000173232 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000173232 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000173232 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000173232 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173232 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000173232 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173232 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000173232 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000173232 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173232 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000173232 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000173232 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000173232 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173232 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173232 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000173232 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000173232 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173232 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173232 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173232 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173232 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173232 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000173232 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000173232 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000173232 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000173232 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173232 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000173228 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173228 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173228 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173228 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173228 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000173228 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173228 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173228 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000173228 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000173228 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000173228 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173228 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173228 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173228 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173228 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000173228 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000173228 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173228 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000173228 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000173228 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173228 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173228 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000173228 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173228 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000173228 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000173228 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173228 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173228 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000173228 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000173228 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000173228 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000173228 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173228 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000006827 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006827 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006827 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006827 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006827 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006827 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006827 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006827 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006827 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006827 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006827 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006827 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006827 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006827 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006827 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006827 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006827 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006827 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006827 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006827 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006827 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006827 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006827 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006827 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006827 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006827 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006827 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006827 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006827 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006827 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006827 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006827 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006827 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000119437 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119437 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119437 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119437 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119437 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119437 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119437 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119437 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119437 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119437 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119437 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119437 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119437 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119437 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119437 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119437 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119437 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119437 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119437 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119437 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119437 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119437 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119437 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119437 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119437 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119437 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119437 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119437 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119437 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119437 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119437 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119437 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119437 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119437 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000119426 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119426 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119426 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119426 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119426 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119426 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119426 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119426 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119426 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119426 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119426 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119426 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119426 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119426 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119426 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119426 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119426 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119426 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119426 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119426 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119426 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119426 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119426 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119426 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119426 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119426 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119426 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119426 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119426 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119426 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119426 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119426 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000006826 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006826 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006826 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006826 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006826 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006826 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006826 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006826 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006826 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006826 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006826 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006826 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006826 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006826 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006826 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006826 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006826 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006826 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006826 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006826 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006826 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006826 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006826 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006826 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006826 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006826 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006826 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006826 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006826 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006826 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006826 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006826 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006826 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000006794 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006794 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006794 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006794 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006794 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006794 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006794 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006794 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006794 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006794 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006794 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006794 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006794 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006794 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006794 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006794 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006794 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006794 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006794 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006794 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006794 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006794 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006794 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006794 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006794 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006794 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006794 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006794 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006794 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006794 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006794 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006794 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119432 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119432 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119432 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119432 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119432 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119432 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119432 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119432 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119432 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119432 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119432 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119432 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119432 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119432 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119432 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119432 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119432 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119432 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119432 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119432 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119432 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119432 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119432 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119432 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119432 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119432 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119432 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119432 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119432 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119432 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119432 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119432 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119432 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119432 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000173916 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173916 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173916 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173916 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173916 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173916 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173916 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173916 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173916 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173916 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173916 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173916 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173916 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173916 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173916 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173916 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173916 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173916 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173916 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173916 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173916 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173916 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173916 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173916 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173916 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173916 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173916 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173916 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173916 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000006796 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006796 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006796 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006796 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006796 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006796 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006796 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006796 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006796 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006796 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006796 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006796 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006796 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006796 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006796 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006796 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006796 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006796 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006796 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006796 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006796 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006796 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006796 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006796 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006796 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006796 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006796 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006796 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006796 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006796 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006796 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006796 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119452 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119452 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119452 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119452 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119452 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119452 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119452 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119452 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119452 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119452 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119452 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119452 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119452 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119452 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119452 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119452 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119452 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119452 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119452 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119452 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119452 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119452 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119452 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119452 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119452 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119452 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119452 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119452 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119452 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000229443 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229443 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229443 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229443 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229443 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229443 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229443 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229443 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229443 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229443 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229443 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229443 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229443 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229443 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229443 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229443 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229443 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229443 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229443 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229443 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229443 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229443 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229443 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229443 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229443 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229443 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229443 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229443 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229443 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000229438 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229438 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229438 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229438 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229438 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229438 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229438 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229438 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229438 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229438 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229438 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229438 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229438 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229438 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229438 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229438 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229438 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229438 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229438 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229438 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229438 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229438 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229438 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229438 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229438 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229438 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229438 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229438 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229438 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000119433 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119433 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119433 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119433 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119433 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119433 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119433 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119433 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119433 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119433 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119433 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119433 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119433 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119433 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119433 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119433 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119433 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119433 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119433 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119433 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119433 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119433 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119433 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119433 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119433 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119433 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119433 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119433 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119433 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119433 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119433 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119433 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119433 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119433 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000006833 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006833 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006833 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006833 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006833 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006833 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006833 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006833 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006833 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006833 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006833 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006833 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006833 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006833 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006833 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006833 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006833 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006833 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006833 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006833 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006833 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006833 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006833 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006833 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006833 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006833 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006833 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006833 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006833 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006833 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006833 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006833 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006833 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000119443 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119443 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119443 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119443 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119443 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119443 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119443 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119443 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119443 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119443 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119443 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119443 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119443 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119443 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119443 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119443 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119443 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119443 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119443 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119443 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119443 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119443 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119443 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119443 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119443 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119443 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119443 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119443 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119443 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119443 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119443 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119443 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119443 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000092198 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092198 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092198 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092198 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092198 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092198 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092198 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092198 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092198 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092198 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092198 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092198 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092198 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092198 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092198 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092198 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092198 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092198 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092198 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092198 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092198 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092198 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092198 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092198 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092198 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092198 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092198 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092198 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092198 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000006828 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006828 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006828 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006828 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006828 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006828 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006828 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006828 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006828 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006828 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006828 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006828 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006828 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006828 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006828 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006828 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006828 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006828 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006828 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006828 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006828 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006828 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006828 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006828 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006828 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006828 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006828 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006828 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006828 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006828 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006828 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006828 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006828 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000236393 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236393 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236393 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236393 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236393 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236393 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236393 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236393 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236393 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000119423 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119423 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119423 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119423 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119423 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119423 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119423 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119423 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119423 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119423 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119423 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119423 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119423 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119423 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119423 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119423 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119423 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119423 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119423 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119423 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119423 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119423 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119423 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119423 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119423 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119423 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119423 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119423 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119423 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119423 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119423 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119423 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000006820 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006820 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006820 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006820 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006820 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006820 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006820 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006820 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006820 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006820 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006820 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006820 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006820 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006820 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006820 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006820 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006820 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006820 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006820 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006820 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006820 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006820 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006820 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006820 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006820 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006820 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006820 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006820 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006820 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006820 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006820 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006820 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006820 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000092196 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092196 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092196 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092196 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092196 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092196 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092196 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092196 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092196 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092196 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092196 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092196 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092196 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092196 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092196 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092196 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092196 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092196 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092196 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092196 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092196 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092196 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092196 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092196 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092196 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092196 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092196 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092196 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092196 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000092201 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092201 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092201 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092201 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092201 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092201 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092201 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092201 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092201 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092201 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092201 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092201 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092201 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092201 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092201 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092201 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092201 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092201 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092201 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092201 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092201 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092201 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092201 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092201 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092201 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092201 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092201 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092201 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092201 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000119446 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119446 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119446 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119446 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119446 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119446 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119446 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119446 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119446 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119446 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119446 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119446 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119446 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119446 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119446 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119446 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119446 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119446 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119446 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119446 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119446 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119446 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119446 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119446 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119446 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119446 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119446 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119446 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119446 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119446 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119446 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119446 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119446 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000006836 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006836 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006836 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006836 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006836 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006836 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006836 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006836 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006836 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006836 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006836 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006836 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006836 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006836 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006836 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006836 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006836 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006836 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006836 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006836 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006836 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006836 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006836 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006836 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006836 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006836 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006836 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006836 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006836 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006836 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006836 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006836 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006836 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000119429 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119429 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119429 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119429 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119429 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119429 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119429 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119429 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119429 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119429 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119429 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119429 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119429 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119429 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119429 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119429 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119429 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119429 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119429 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119429 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119429 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119429 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119429 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119429 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119429 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119429 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119429 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119429 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119429 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119429 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119429 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119429 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000006823 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006823 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006823 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006823 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006823 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006823 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006823 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006823 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006823 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006823 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006823 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006823 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006823 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006823 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006823 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006823 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006823 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006823 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006823 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006823 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006823 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006823 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006823 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006823 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006823 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006823 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006823 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006823 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006823 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006823 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006823 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006823 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006823 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000173915 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173915 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173915 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173915 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173915 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173915 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173915 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173915 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173915 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173915 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173915 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173915 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173915 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173915 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173915 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173915 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173915 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173915 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173915 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173915 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173915 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173915 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173915 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173915 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173915 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173915 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173915 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173915 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173915 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000119436 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119436 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119436 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119436 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119436 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119436 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119436 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119436 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119436 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119436 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119436 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119436 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119436 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119436 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119436 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119436 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119436 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119436 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119436 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119436 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119436 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119436 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119436 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119436 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119436 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119436 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119436 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119436 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119436 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119436 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119436 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119436 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119436 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119436 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000119439 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119439 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119439 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119439 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119439 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119439 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119439 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119439 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119439 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119439 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119439 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119439 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119439 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119439 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119439 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119439 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119439 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119439 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119439 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119439 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119439 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119439 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119439 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119439 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119439 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119439 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119439 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119439 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119439 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119439 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119439 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119439 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119439 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000173229 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173229 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173229 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000173229 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173229 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000173229 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173229 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173229 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173229 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173229 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173229 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173229 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173229 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173229 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173229 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173229 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173229 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173229 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173229 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173229 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173229 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173229 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173229 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173229 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173229 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173229 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000173229 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000173229 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173229 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000006835 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006835 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006835 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006835 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006835 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006835 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006835 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006835 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006835 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006835 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006835 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006835 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006835 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006835 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006835 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006835 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006835 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006835 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006835 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006835 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006835 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006835 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006835 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006835 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006835 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006835 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006835 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006835 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006835 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006835 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006835 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006835 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006835 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000119453 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119453 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119453 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119453 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119453 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119453 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119453 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119453 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119453 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119453 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119453 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119453 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119453 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119453 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119453 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119453 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119453 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119453 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119453 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119453 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119453 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119453 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119453 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119453 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119453 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119453 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119453 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119453 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119453 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000119438 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119438 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119438 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119438 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119438 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119438 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119438 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119438 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119438 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119438 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119438 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119438 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119438 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119438 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119438 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119438 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119438 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119438 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119438 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119438 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119438 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119438 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119438 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119438 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119438 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119438 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119438 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119438 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119438 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119438 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119438 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119438 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119438 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119438 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000006799 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006799 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006799 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006799 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006799 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006799 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006799 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006799 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006799 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006799 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006799 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006799 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006799 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006799 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006799 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006799 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006799 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006799 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006799 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006799 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006799 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006799 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006799 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006799 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006799 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006799 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006799 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006799 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006799 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006799 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006799 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006799 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173921 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173921 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173921 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173921 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173921 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173921 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173921 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173921 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173921 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173921 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173921 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173921 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173921 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173921 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173921 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173921 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173921 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173921 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173921 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173921 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173921 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173921 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173921 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173921 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173921 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173921 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173921 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173921 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173921 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000119442 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119442 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119442 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119442 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119442 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119442 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119442 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119442 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119442 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119442 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119442 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119442 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119442 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119442 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119442 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119442 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119442 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119442 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119442 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119442 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119442 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119442 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119442 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119442 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119442 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119442 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119442 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119442 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119442 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119442 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119442 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119442 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119442 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000119430 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119430 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119430 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119430 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119430 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119430 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119430 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119430 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119430 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119430 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119430 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119430 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119430 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119430 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119430 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119430 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119430 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119430 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119430 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119430 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119430 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119430 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119430 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119430 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119430 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119430 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119430 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119430 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119430 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119430 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119430 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119430 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000236388 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236388 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236388 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236388 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236388 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236388 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236388 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236388 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236388 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000006793 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006793 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006793 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006793 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006793 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006793 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006793 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006793 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006793 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006793 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006793 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006793 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006793 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006793 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006793 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006793 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006793 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006793 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006793 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006793 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006793 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006793 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006793 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006793 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006793 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006793 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006793 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006793 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006793 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006793 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006793 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006793 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000006822 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006822 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006822 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006822 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006822 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006822 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006822 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006822 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006822 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006822 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006822 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006822 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006822 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006822 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006822 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006822 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006822 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006822 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006822 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006822 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006822 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006822 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006822 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006822 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006822 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006822 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006822 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006822 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006822 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006822 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006822 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006822 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006822 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000173922 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173922 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173922 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173922 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173922 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173922 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173922 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173922 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173922 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173922 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173922 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173922 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173922 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173922 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173922 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173922 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173922 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173922 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173922 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173922 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173922 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173922 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173922 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173922 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173922 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173922 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173922 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173922 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173922 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000119440 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119440 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119440 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119440 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119440 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119440 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119440 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119440 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119440 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119440 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119440 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119440 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119440 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119440 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119440 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119440 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119440 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119440 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119440 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119440 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119440 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119440 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119440 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119440 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119440 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119440 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119440 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119440 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119440 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119440 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119440 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119440 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119440 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000173230 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173230 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000173230 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173230 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173230 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000173230 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173230 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000173230 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173230 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000173230 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173230 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173230 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000173230 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173230 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000173230 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173230 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000173230 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000173230 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173230 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173230 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000173230 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173230 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000173230 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173230 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000173230 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173230 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000173230 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173230 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173230 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000173230 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000173230 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173230 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000229436 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229436 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229436 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229436 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229436 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229436 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229436 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229436 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229436 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229436 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229436 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229436 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229436 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229436 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229436 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229436 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229436 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229436 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229436 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229436 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229436 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229436 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229436 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229436 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229436 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229436 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229436 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229436 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229436 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000092202 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092202 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092202 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092202 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092202 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092202 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092202 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092202 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092202 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092202 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092202 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092202 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092202 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092202 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092202 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092202 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092202 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092202 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092202 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092202 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092202 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092202 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092202 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092202 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092202 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092202 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092202 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092202 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092202 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000119431 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119431 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119431 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119431 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119431 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119431 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119431 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119431 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119431 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119431 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119431 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119431 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119431 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119431 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119431 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119431 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119431 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119431 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119431 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119431 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119431 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119431 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119431 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119431 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119431 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119431 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119431 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119431 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119431 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119431 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119431 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119431 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119431 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119431 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000092203 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092203 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092203 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092203 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092203 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092203 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092203 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092203 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092203 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092203 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092203 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092203 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092203 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092203 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092203 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092203 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092203 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092203 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092203 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092203 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092203 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092203 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092203 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092203 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092203 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092203 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092203 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092203 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092203 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000006800 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006800 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006800 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006800 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006800 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006800 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006800 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006800 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006800 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006800 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006800 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006800 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006800 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006800 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006800 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006800 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006800 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006800 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006800 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006800 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006800 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006800 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006800 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006800 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006800 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006800 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006800 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006800 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006800 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006800 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006800 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006800 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000236387 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236387 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236387 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236387 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236387 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236387 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236387 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236387 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236387 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000119451 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119451 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119451 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119451 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119451 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119451 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119451 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119451 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119451 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119451 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119451 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119451 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119451 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119451 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119451 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119451 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119451 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119451 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119451 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119451 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119451 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119451 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119451 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119451 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119451 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119451 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119451 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119451 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119451 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000173917 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173917 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173917 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173917 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173917 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173917 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173917 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173917 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173917 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173917 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173917 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173917 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173917 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173917 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173917 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173917 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173917 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173917 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173917 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173917 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173917 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173917 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173917 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173917 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173917 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173917 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173917 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173917 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173917 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000236389 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236389 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236389 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236389 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236389 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236389 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236389 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236389 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236389 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000119447 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119447 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119447 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119447 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119447 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119447 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119447 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119447 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119447 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119447 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119447 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119447 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119447 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119447 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119447 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119447 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119447 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119447 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119447 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119447 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119447 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119447 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119447 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119447 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119447 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119447 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119447 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119447 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119447 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000173225 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173225 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173225 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000173225 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000173225 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173225 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173225 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000173225 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173225 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000173225 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173225 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000173225 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173225 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173225 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173225 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000173225 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000173225 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173225 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173225 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000173225 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000173225 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000173225 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000173225 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173225 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000173225 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000173225 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173225 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173225 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173225 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000173225 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000173225 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000173225 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000006801 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006801 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006801 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006801 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006801 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006801 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006801 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006801 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006801 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006801 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006801 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006801 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006801 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006801 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006801 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006801 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006801 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006801 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006801 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006801 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006801 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006801 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006801 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006801 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006801 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006801 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006801 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006801 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006801 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006801 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006801 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006801 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000006829 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006829 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006829 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006829 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006829 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006829 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006829 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006829 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006829 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006829 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006829 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006829 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006829 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006829 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006829 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006829 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006829 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006829 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006829 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006829 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006829 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006829 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006829 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006829 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006829 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006829 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006829 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006829 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006829 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006829 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006829 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006829 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006829 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000119427 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119427 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119427 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119427 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119427 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119427 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119427 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119427 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119427 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119427 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119427 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119427 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119427 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119427 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119427 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119427 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119427 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119427 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119427 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119427 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119427 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119427 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119427 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119427 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119427 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119427 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119427 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119427 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119427 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119427 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119427 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119427 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119441 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119441 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119441 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119441 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119441 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119441 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119441 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119441 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119441 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119441 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119441 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119441 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119441 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119441 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119441 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119441 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119441 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119441 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119441 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119441 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119441 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119441 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119441 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119441 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119441 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119441 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119441 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119441 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119441 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119441 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119441 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119441 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119441 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000119434 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119434 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119434 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119434 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119434 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119434 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119434 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119434 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119434 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119434 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119434 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119434 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119434 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119434 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119434 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119434 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119434 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119434 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119434 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119434 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119434 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119434 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119434 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119434 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119434 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119434 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119434 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119434 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119434 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119434 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119434 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119434 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119434 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119434 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000229437 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229437 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229437 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229437 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229437 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229437 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229437 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229437 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229437 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229437 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229437 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229437 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229437 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229437 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229437 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229437 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229437 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229437 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229437 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229437 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229437 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229437 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229437 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229437 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229437 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229437 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229437 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229437 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229437 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000119454 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119454 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119454 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119454 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119454 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119454 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119454 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119454 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119454 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119454 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119454 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119454 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119454 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119454 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119454 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119454 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119454 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119454 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119454 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119454 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119454 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119454 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119454 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119454 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119454 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119454 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119454 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119454 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119454 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000229440 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229440 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229440 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229440 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229440 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229440 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229440 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229440 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229440 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229440 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229440 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229440 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229440 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229440 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229440 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229440 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229440 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229440 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229440 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229440 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229440 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229440 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229440 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229440 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229440 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229440 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229440 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229440 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229440 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000119444 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119444 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119444 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119444 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119444 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119444 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119444 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119444 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119444 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119444 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119444 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119444 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119444 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119444 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119444 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119444 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119444 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119444 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119444 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119444 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119444 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119444 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119444 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119444 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119444 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119444 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119444 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119444 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119444 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119444 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119444 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119444 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119444 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000092200 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092200 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092200 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092200 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092200 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092200 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092200 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092200 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092200 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092200 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092200 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092200 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092200 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092200 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092200 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092200 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092200 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092200 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092200 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092200 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092200 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092200 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092200 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092200 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092200 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092200 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092200 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092200 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092200 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000006821 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006821 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006821 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006821 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006821 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006821 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006821 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006821 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006821 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000006821 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006821 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006821 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006821 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000006821 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000006821 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006821 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006821 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000006821 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006821 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006821 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006821 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006821 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000006821 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000006821 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000006821 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000006821 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000006821 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000006821 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006821 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000006821 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000006821 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000006821 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006821 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000236386 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236386 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236386 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236386 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236386 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236386 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236386 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236386 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236386 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000119450 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119450 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119450 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119450 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119450 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119450 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119450 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119450 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119450 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119450 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119450 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119450 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119450 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119450 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119450 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119450 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119450 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119450 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119450 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119450 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119450 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119450 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119450 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119450 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119450 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119450 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119450 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119450 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119450 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000006831 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006831 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006831 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006831 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006831 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006831 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006831 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006831 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006831 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006831 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006831 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006831 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006831 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006831 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006831 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006831 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006831 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006831 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006831 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006831 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006831 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006831 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006831 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006831 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006831 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006831 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006831 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006831 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006831 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006831 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006831 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006831 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006831 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000173918 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173918 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173918 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173918 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173918 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173918 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173918 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173918 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173918 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173918 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173918 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173918 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173918 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173918 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173918 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173918 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173918 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173918 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173918 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173918 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173918 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173918 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173918 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173918 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173918 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173918 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173918 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173918 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173918 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000119428 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119428 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119428 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119428 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119428 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119428 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119428 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119428 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119428 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119428 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119428 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119428 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119428 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119428 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119428 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119428 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119428 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119428 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119428 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119428 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119428 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119428 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119428 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119428 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119428 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119428 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119428 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119428 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119428 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119428 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119428 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119428 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000229442 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229442 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229442 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229442 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229442 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229442 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229442 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229442 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229442 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229442 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229442 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229442 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229442 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229442 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229442 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229442 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229442 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229442 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229442 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229442 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229442 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229442 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229442 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229442 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229442 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229442 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229442 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229442 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229442 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000173231 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000173231 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173231 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000173231 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173231 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000173231 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000173231 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000173231 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000173231 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173231 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000173231 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000173231 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000173231 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173231 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000173231 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000173231 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000173231 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000173231 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000173231 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000173231 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000173231 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000173231 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000173231 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000173231 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173231 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000173231 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000173231 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000173231 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173231 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000173231 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000173231 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000173231 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000173231 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173231 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000119448 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119448 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119448 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119448 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119448 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119448 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119448 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119448 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119448 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119448 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119448 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119448 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119448 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119448 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119448 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119448 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119448 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119448 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119448 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119448 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119448 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119448 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119448 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119448 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119448 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119448 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119448 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119448 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119448 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000119425 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119425 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119425 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119425 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119425 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119425 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119425 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119425 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119425 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000119425 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119425 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119425 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119425 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119425 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000119425 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119425 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.40% |
| C000119425 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000119425 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119425 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119425 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000119425 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119425 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.30% |
| C000119425 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119425 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119425 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000119425 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000119425 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119425 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119425 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.10% |
| C000119425 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 67.70% |
| C000119425 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119425 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119435 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119435 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119435 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.50% |
| C000119435 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119435 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119435 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119435 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.20% |
| C000119435 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.60% |
| C000119435 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000119435 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7.30% |
| C000119435 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119435 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000119435 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119435 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000119435 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119435 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119435 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119435 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000119435 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000119435 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000119435 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.80% |
| C000119435 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.10% |
| C000119435 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.40% |
| C000119435 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119435 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119435 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119435 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119435 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119435 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119435 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.30% |
| C000119435 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 42.40% |
| C000119435 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 34.30% |
| C000119435 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000119435 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 14.20% |
| C000006797 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006797 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006797 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000006797 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006797 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006797 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006797 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000006797 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006797 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.40% |
| C000006797 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006797 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006797 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006797 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006797 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006797 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006797 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 19.40% |
| C000006797 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006797 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000006797 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.50% |
| C000006797 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000006797 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.70% |
| C000006797 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.20% |
| C000006797 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006797 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 7% |
| C000006797 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006797 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000006797 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000006797 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000006797 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18.50% |
| C000006797 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 70% |
| C000006797 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006797 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173923 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173923 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173923 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173923 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173923 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173923 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173923 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173923 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173923 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173923 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173923 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173923 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173923 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173923 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173923 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173923 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173923 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173923 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173923 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173923 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173923 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173923 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173923 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173923 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173923 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173923 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173923 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173923 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173923 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000173233 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173233 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173233 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173233 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173233 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173233 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173233 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173233 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000173233 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173233 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173233 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173233 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000173233 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173233 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173233 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173233 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173233 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173233 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173233 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000173233 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173233 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173233 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173233 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173233 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173233 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173233 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000173233 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173233 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173233 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
| C000006830 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006830 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006830 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006830 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006830 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006830 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006830 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006830 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006830 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006830 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006830 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006830 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006830 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006830 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006830 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006830 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006830 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006830 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006830 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006830 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006830 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006830 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006830 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006830 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006830 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006830 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006830 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006830 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006830 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006830 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006830 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006830 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006830 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000236390 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236390 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236390 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236390 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236390 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236390 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236390 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236390 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236390 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000092199 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092199 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092199 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092199 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092199 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092199 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092199 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092199 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092199 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092199 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092199 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092199 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092199 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092199 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092199 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092199 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092199 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092199 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092199 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092199 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092199 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092199 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092199 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092199 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092199 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092199 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092199 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092199 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092199 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000236391 [Member] | Fitch, BBB Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 18% |
| C000236391 [Member] | Fitch, AA Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000236391 [Member] | Fitch, A Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 12.80% |
| C000236391 [Member] | Money Market Funds Quality [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236391 [Member] | Moody's, Aaa Rating [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13% |
| C000236391 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000236391 [Member] | Federal Agencies [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000236391 [Member] | Fixed Income Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 95.30% |
| C000236391 [Member] | US Government Debt Securities [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.60% |
| C000119445 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119445 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119445 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000119445 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119445 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119445 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119445 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119445 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.70% |
| C000119445 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119445 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119445 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.70% |
| C000119445 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119445 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.30% |
| C000119445 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119445 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.60% |
| C000119445 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.80% |
| C000119445 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000119445 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.10% |
| C000119445 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119445 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119445 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.80% |
| C000119445 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.80% |
| C000119445 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119445 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119445 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119445 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.20% |
| C000119445 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000119445 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000119445 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.10% |
| C000119445 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54% |
| C000119445 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.30% |
| C000119445 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000119445 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 24.40% |
| C000229441 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229441 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229441 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000229441 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229441 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229441 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229441 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229441 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229441 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229441 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229441 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.60% |
| C000229441 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000229441 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229441 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000229441 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000229441 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229441 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000229441 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000229441 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11.10% |
| C000229441 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229441 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000229441 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000229441 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229441 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000229441 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000229441 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.90% |
| C000229441 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000229441 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000229441 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 28.30% |
| C000173920 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173920 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000173920 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173920 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173920 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173920 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173920 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173920 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000173920 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173920 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000173920 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000173920 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000173920 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173920 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000173920 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000173920 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173920 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000173920 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000173920 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000173920 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173920 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000173920 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000173920 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000173920 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000173920 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000173920 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.80% |
| C000173920 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000173920 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173920 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.60% |
| C000006832 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006832 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006832 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006832 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006832 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006832 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006832 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006832 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006832 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006832 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006832 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006832 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006832 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006832 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006832 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006832 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006832 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006832 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006832 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006832 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006832 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006832 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006832 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006832 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006832 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006832 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006832 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006832 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006832 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006832 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006832 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006832 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006832 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000006837 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006837 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006837 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006837 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006837 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006837 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006837 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006837 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.20% |
| C000006837 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.80% |
| C000006837 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006837 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000006837 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006837 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000006837 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006837 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.60% |
| C000006837 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.50% |
| C000006837 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000006837 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.60% |
| C000006837 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.10% |
| C000006837 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000006837 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.50% |
| C000006837 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.60% |
| C000006837 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006837 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000006837 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.70% |
| C000006837 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000006837 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000006837 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000006837 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.10% |
| C000006837 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 51.40% |
| C000006837 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 17.80% |
| C000006837 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000006837 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 20.50% |
| C000173227 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000173227 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000173227 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000173227 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000173227 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000173227 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000173227 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000173227 [Member] | MFS Emerging Markets Debt Local Currency Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2% |
| C000173227 [Member] | MFS Government Securities Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.30% |
| C000173227 [Member] | MFS Emerging Markets Debt Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173227 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000173227 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173227 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.20% |
| C000173227 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.20% |
| C000173227 [Member] | MFS High Income Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000173227 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173227 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 13.10% |
| C000173227 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000173227 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.20% |
| C000173227 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000173227 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000173227 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.90% |
| C000173227 [Member] | MFS Limited Maturity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8% |
| C000173227 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.10% |
| C000173227 [Member] | MFS Global Opportunistic Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 6.60% |
| C000173227 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 0.60% |
| C000173227 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.80% |
| C000173227 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.10% |
| C000173227 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000173227 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 29.40% |
| C000173227 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 54.50% |
| C000173227 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3% |
| C000173227 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 8.80% |
| C000092197 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092197 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.20% |
| C000092197 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.40% |
| C000092197 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092197 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.40% |
| C000092197 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092197 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092197 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.10% |
| C000092197 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092197 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092197 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000092197 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000092197 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092197 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000092197 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000092197 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000092197 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000092197 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000092197 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10.80% |
| C000092197 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092197 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000092197 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000092197 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.70% |
| C000092197 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000092197 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000092197 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 56% |
| C000092197 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.30% |
| C000092197 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000092197 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.50% |
| C000119449 [Member] | MFS New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119449 [Member] | MFS Blended Research Growth Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119449 [Member] | MFS Inflation Adjusted Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119449 [Member] | MFS Institutional Money Market Portfolio [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119449 [Member] | MFS International Intrinsic Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119449 [Member] | MFS Blended Research Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119449 [Member] | MFS Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119449 [Member] | MFS Blended Research Mid Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 10% |
| C000119449 [Member] | MFS Research International Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.90% |
| C000119449 [Member] | MFS Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.10% |
| C000119449 [Member] | MFS Blended Research Value Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5.50% |
| C000119449 [Member] | MFS International New Discovery Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4% |
| C000119449 [Member] | MFS Mid Cap Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119449 [Member] | MFS Total Return Bond Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.90% |
| C000119449 [Member] | MFS International Growth Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 3.50% |
| C000119449 [Member] | MFS Commodity Strategy Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119449 [Member] | MFS Mid Cap Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 5% |
| C000119449 [Member] | MFS Emerging Markets Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1% |
| C000119449 [Member] | MFS Blended Research International Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 11% |
| C000119449 [Member] | MFS Blended Research Core Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119449 [Member] | MFS Blended Research Small Cap Equity Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.50% |
| C000119449 [Member] | MFS New Discovery Value Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 1.30% |
| C000119449 [Member] | MFS Research Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.60% |
| C000119449 [Member] | MFS Global Real Estate Fund [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.90% |
| C000119449 [Member] | Non Traditional Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 9.90% |
| C000119449 [Member] | U S Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 55.50% |
| C000119449 [Member] | Bond Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 4.40% |
| C000119449 [Member] | Money Market Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 2.30% |
| C000119449 [Member] | International Stock Funds [Member] | |
| Holdings [Line Items] | |
| Percent of Total Investments | 27.90% |
