v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name MFS VARIABLE INSURANCE TRUST II
Entity Central Index Key 0000719269
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
C000007238 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Corporate Bond Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $44 0.88%
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.88%
Net Assets $ 126,518,455
Holdings Count | Holding 414
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 126,518,455 Average Effective Maturity (yrs): 9.5
Total Number of Holdings: 414 Average Effective Duration (yrs): 6.6
Portfolio Turnover Rate (%): 26
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 6/30/26)
Portfolio structure
Fixed Income 98.8%
Money Market Funds 1.2%
Issuer country weightings
United States 71.8%
United Kingdom 4.2%
Canada 3.6%
Australia 2.6%
Japan 2.4%
Mexico 2.2%
Ireland 1.7%
Switzerland 1.7%
Germany 1.4%
Other Countries 8.4%
Composition including fixed income credit quality
AAA 3.1%
AA 2.2%
A 31.0%
BBB 52.0%
BB 7.4%
B 2.3%
D 0.1%
U.S. Government 0.7%
Not Rated 0.0%
Money Market Funds 1.2%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007237 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Corporate Bond Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Corporate Bond Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $31 0.63%
Expenses Paid, Amount $ 31
Expense Ratio, Percent 0.63%
Net Assets $ 126,518,455
Holdings Count | Holding 414
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 126,518,455 Average Effective Maturity (yrs): 9.5
Total Number of Holdings: 414 Average Effective Duration (yrs): 6.6
Portfolio Turnover Rate (%): 26
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 6/30/26)
Portfolio structure
Fixed Income 98.8%
Money Market Funds 1.2%
Issuer country weightings
United States 71.8%
United Kingdom 4.2%
Canada 3.6%
Australia 2.6%
Japan 2.4%
Mexico 2.2%
Ireland 1.7%
Switzerland 1.7%
Germany 1.4%
Other Countries 8.4%
Composition including fixed income credit quality
AAA 3.1%
AA 2.2%
A 31.0%
BBB 52.0%
BB 7.4%
B 2.3%
D 0.1%
U.S. Government 0.7%
Not Rated 0.0%
Money Market Funds 1.2%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007239 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $28 0.57%
Expenses Paid, Amount $ 28
Expense Ratio, Percent 0.57%
Net Assets $ 256,989,758
Holdings Count | Holding 593
Investment Company Portfolio Turnover 72.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 256,989,758 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 593 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 72
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 6/30/26)
Portfolio structure
Fixed Income 94.1%
Money Market Funds 5.9%
Composition including fixed income credit quality
AAA 5.8%
AA 1.6%
A 0.3%
U.S. Government 25.2%
Federal Agencies 61.2%
Money Market Funds 5.9%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007240 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GovernmentSecurities Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Government Securities Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $41 0.82%
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.82%
Net Assets $ 256,989,758
Holdings Count | Holding 593
Investment Company Portfolio Turnover 72.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 256,989,758 Average Effective Maturity (yrs): 6.6
Total Number of Holdings: 593 Average Effective Duration (yrs): 5.5
Portfolio Turnover Rate (%): 72
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 6/30/26)
Portfolio structure
Fixed Income 94.1%
Money Market Funds 5.9%
Composition including fixed income credit
quality
AAA 5.8%
AA 1.6%
A 0.3%
U.S. Government 25.2%
Federal Agencies 61.2%
Money Market Funds 5.9%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007242 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® High Yield Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS High Yield Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $48 0.97%
Expenses Paid, Amount $ 48
Expense Ratio, Percent 0.97%
Net Assets $ 213,333,200
Holdings Count | Holding 369
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 213,333,200 Average Effective Maturity (yrs): 3.9
Total Number of Holdings: 369 Average Effective Duration (yrs): 2.9
Portfolio Turnover Rate (%): 26
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 6/30/26)
Portfolio structure
Fixed Income 97.1%
Money Market Funds 2.8%
Equities 0.1%
Composition including fixed income credit 
quality
BBB 1.3%
BB 48.8%
B 36.0%
CCC 10.7%
CC 0.1%
D 0.2%
Not Rated 0.0%
Non-Fixed Income 0.1%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000007241 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® High Yield Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS High Yield Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $36 0.72%
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.72%
Net Assets $ 213,333,200
Holdings Count | Holding 369
Investment Company Portfolio Turnover 26.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 213,333,200 Average Effective Maturity (yrs): 3.9
Total Number of Holdings: 369 Average Effective Duration (yrs): 2.9
Portfolio Turnover Rate (%): 26
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 6/30/26)
Portfolio structure
Fixed Income 97.1%
Money Market Funds 2.8%
Equities 0.1%
Composition including fixed income credit quality
BBB 1.3%
BB 48.8%
B 36.0%
CCC 10.7%
CC 0.1%
D 0.2%
Not Rated 0.0%
Non-Fixed Income 0.1%
Money Market Funds 2.8%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
Credit Ratings Selection [Text Block]
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
C000007243 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® InternationalGrowth Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS International Growth Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $44 0.88%
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.88%
Net Assets $ 380,951,790
Holdings Count | Holding 83
Investment Company Portfolio Turnover 12.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 380,951,790 Portfolio Turnover Rate (%): 12
Total Number of Holdings: 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 6/30/26)
Portfolio structure
Equities 99.0%
Money Market Funds 1.0%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 7.6%
Schneider Electric SE 4.2%
Resonac Holdings Corp. 3.6%
Nestle S.A. 3.1%
Tencent Holdings Ltd. 2.9%
AstraZeneca PLC 2.8%
Novartis AG 2.8%
SAP SE 2.7%
Rolls-Royce Holdings PLC 2.6%
Linde PLC 2.5%
Issuer country weightings
Taiwan 11.5%
France 11.1%
United Kingdom 11.0%
Japan 10.9%
Germany 8.4%
Switzerland 7.2%
Canada 7.1%
Netherlands 4.8%
United States 4.6%
Other Countries 23.4%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 7.6%
Schneider Electric SE 4.2%
Resonac Holdings Corp. 3.6%
Nestle S.A. 3.1%
Tencent Holdings Ltd. 2.9%
AstraZeneca PLC 2.8%
Novartis AG 2.8%
SAP SE 2.7%
Rolls-Royce Holdings PLC 2.6%
Linde PLC 2.5%
C000007244 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® InternationalGrowth Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS International Growth Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $57 1.13%
Expenses Paid, Amount $ 57
Expense Ratio, Percent 1.13%
Net Assets $ 380,951,790
Holdings Count | Holding 83
Investment Company Portfolio Turnover 12.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 380,951,790 Portfolio Turnover Rate (%): 12
Total Number of Holdings: 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 6/30/26)
Portfolio structure
Equities 99.0%
Money Market Funds 1.0%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 7.6%
Schneider Electric SE 4.2%
Resonac Holdings Corp. 3.6%
Nestle S.A. 3.1%
Tencent Holdings Ltd. 2.9%
AstraZeneca PLC 2.8%
Novartis AG 2.8%
SAP SE 2.7%
Rolls-Royce Holdings PLC 2.6%
Linde PLC 2.5%
Issuer country weightings
Taiwan 11.5%
France 11.1%
United Kingdom 11.0%
Japan 10.9%
Germany 8.4%
Switzerland 7.2%
Canada 7.1%
Netherlands 4.8%
United States 4.6%
Other Countries 23.4%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 7.6%
Schneider Electric SE 4.2%
Resonac Holdings Corp. 3.6%
Nestle S.A. 3.1%
Tencent Holdings Ltd. 2.9%
AstraZeneca PLC 2.8%
Novartis AG 2.8%
SAP SE 2.7%
Rolls-Royce Holdings PLC 2.6%
Linde PLC 2.5%
C000007246 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® International IntrinsicEquity Portfolio(formerly MFS® International Intrinsic Value Portfolio)
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS International Intrinsic Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Material Fund Change Notice [Text Block]
This report describes certain changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website insurancefunds.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)
Service Class $58 1.14%
Expenses Paid, Amount $ 58
Expense Ratio, Percent 1.14%
Material Change Date Apr. 30, 2026
Net Assets $ 1,535,416,709
Holdings Count | Holding 92
Investment Company Portfolio Turnover 9.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 1,535,416,709 Portfolio Turnover Rate (%): 9
Total Number of Holdings: 92
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 6/30/26)
Portfolio structure
Equities 95.6%
Money Market Funds 4.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.4%
Franco-Nevada Corp. 3.3%
Schneider Electric SE 3.0%
Legrand S.A. 2.9%
TotalEnergies SE 2.5%
Deutsche Boerse AG 2.3%
NatWest Group PLC 2.3%
Resona Holdings, Inc. 2.2%
UBS Group AG 2.2%
CaixaBank S.A. 1.9%
Issuer country weightings
United Kingdom 16.2%
France 14.8%
Japan 13.5%
Switzerland 9.5%
United States 7.9%
Germany 7.6%
Canada 7.5%
Ireland 4.8%
Taiwan 4.4%
Other Countries 13.8%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.4%
Franco-Nevada Corp. 3.3%
Schneider Electric SE 3.0%
Legrand S.A. 2.9%
TotalEnergies SE 2.5%
Deutsche Boerse AG 2.3%
NatWest Group PLC 2.3%
Resona Holdings, Inc. 2.2%
UBS Group AG 2.2%
CaixaBank S.A. 1.9%
Material Fund Change [Text Block]
MATERIAL FUND CHANGES
This is a summary of certain changes to the fund since January 1, 2026. For more complete information, you may review the fund's prospectus as amended, which is available at insurancefunds.mfs.com or upon request at 1‑800‑225‑2606.
Effective April 30, 2026, the MFS International Intrinsic Value Portfolio was renamed to the MFS International Intrinsic Equity Portfolio. In connection with the name change, the fund adopted a policy to invest at least 80% of its assets in equity securities.
Material Fund Change Name [Text Block] Effective April 30, 2026, the MFS International Intrinsic Value Portfolio was renamed to the MFS International Intrinsic Equity Portfolio.
Material Fund Change Strategies [Text Block] In connection with the name change, the fund adopted a policy to invest at least 80% of its assets in equity securities.
Summary of Change Legend [Text Block]
This is a summary of certain changes to the fund since January 1, 2026. For more complete information, you may review the fund's prospectus as amended, which is available at insurancefunds.mfs.com or upon request at 1‑800‑225‑2606.
Updated Prospectus Phone Number 1‑800‑225‑2606
Updated Prospectus Web Address insurancefunds.mfs.com
C000007245 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® International IntrinsicEquity Portfolio(formerly MFS® International Intrinsic Value Portfolio)
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS International Intrinsic Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.mfs.com. You can also request this information by contacting us at 1‑800‑225‑2606 or by sending an e-mail request to orderliterature@mfs.com.
Material Fund Change Notice [Text Block]
This report describes certain changes to the Fund that occurred during the reporting period.
Additional Information Phone Number 1‑800‑225‑2606
Additional Information Email orderliterature@mfs.com
Additional Information Website insurancefunds.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)
Initial Class $45 0.89%
Expenses Paid, Amount $ 45
Expense Ratio, Percent 0.89%
Material Change Date Apr. 30, 2026
Net Assets $ 1,535,416,709
Holdings Count | Holding 92
Investment Company Portfolio Turnover 9.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 1,535,416,709 Portfolio Turnover Rate (%): 9
Total Number of Holdings: 92
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 6/30/26)
Portfolio structure
Equities 95.6%
Money Market Funds 4.4%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.4%
Franco-Nevada Corp. 3.3%
Schneider Electric SE 3.0%
Legrand S.A. 2.9%
TotalEnergies SE 2.5%
Deutsche Boerse AG 2.3%
NatWest Group PLC 2.3%
Resona Holdings, Inc. 2.2%
UBS Group AG 2.2%
CaixaBank S.A. 1.9%
Issuer country weightings
United Kingdom 16.2%
France 14.8%
Japan 13.5%
Switzerland 9.5%
United States 7.9%
Germany 7.6%
Canada 7.5%
Ireland 4.8%
Taiwan 4.4%
Other Countries 13.8%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.4%
Franco-Nevada Corp. 3.3%
Schneider Electric SE 3.0%
Legrand S.A. 2.9%
TotalEnergies SE 2.5%
Deutsche Boerse AG 2.3%
NatWest Group PLC 2.3%
Resona Holdings, Inc. 2.2%
UBS Group AG 2.2%
CaixaBank S.A. 1.9%
Material Fund Change [Text Block]
MATERIAL FUND CHANGES
This is a summary of certain changes to the fund since January 1, 2026. For more complete information, you may review the fund's prospectus as amended, which is available at insurancefunds.mfs.com or upon request at 1‑800‑225‑2606.
Effective April 30, 2026, the MFS International Intrinsic Value Portfolio was renamed to the MFS International Intrinsic Equity Portfolio. In connection with the name change, the fund adopted a policy to invest at least 80% of its assets in equity securities.
Material Fund Change Name [Text Block] Effective April 30, 2026, the MFS International Intrinsic Value Portfolio was renamed to the MFS International Intrinsic Equity Portfolio.
Material Fund Change Strategies [Text Block] In connection with the name change, the fund adopted a policy to invest at least 80% of its assets in equity securities.
Summary of Change Legend [Text Block]
This is a summary of certain changes to the fund since January 1, 2026. For more complete information, you may review the fund's prospectus as amended, which is available at insurancefunds.mfs.com or upon request at 1‑800‑225‑2606.
Updated Prospectus Phone Number 1‑800‑225‑2606
Updated Prospectus Web Address insurancefunds.mfs.com
C000007247 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Massachusetts InvestorsGrowth Stock Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Massachusetts Investors Growth Stock Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $35 0.72%
Expenses Paid, Amount $ 35
Expense Ratio, Percent 0.72%
Net Assets $ 856,656,941
Holdings Count | Holding 55
Investment Company Portfolio Turnover 24.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 856,656,941 Portfolio Turnover Rate (%): 24
Total Number of Holdings: 55
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 6/30/26)
Portfolio structure
Equities 98.8%
Money Market Funds 1.2%
Equity sectors
Information Technology 35.6%
Financials 13.6%
Health Care 12.4%
Communication Services 11.6%
Industrials 10.9%
Consumer Discretionary 7.1%
Consumer Staples 4.3%
Utilities 2.1%
Materials 1.1%
Real Estate 0.1%
Top ten holdings
NVIDIA Corp. 13.3%
Alphabet, Inc., "A" 10.2%
Broadcom, Inc. 4.8%
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.8%
Amphenol Corp., "A" 4.0%
Visa, Inc., "A" 3.7%
Apple, Inc. 3.1%
Aon PLC 2.7%
Moody's Corp. 2.5%
Hubbell, Inc. 2.4%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 13.3%
Alphabet, Inc., "A" 10.2%
Broadcom, Inc. 4.8%
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.8%
Amphenol Corp., "A" 4.0%
Visa, Inc., "A" 3.7%
Apple, Inc. 3.1%
Aon PLC 2.7%
Moody's Corp. 2.5%
Hubbell, Inc. 2.4%
C000007248 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Massachusetts InvestorsGrowth Stock Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Massachusetts Investors Growth Stock Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $47 0.97%
Expenses Paid, Amount $ 47
Expense Ratio, Percent 0.97%
Net Assets $ 856,656,941
Holdings Count | Holding 55
Investment Company Portfolio Turnover 24.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 856,656,941 Portfolio Turnover Rate (%): 24
Total Number of Holdings: 55
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 6/30/26)
Portfolio structure
Equities 98.8%
Money Market Funds 1.2%
Equity sectors
Information Technology 35.6%
Financials 13.6%
Health Care 12.4%
Communication Services 11.6%
Industrials 10.9%
Consumer Discretionary 7.1%
Consumer Staples 4.3%
Utilities 2.1%
Materials 1.1%
Real Estate 0.1%
Top ten holdings
NVIDIA Corp. 13.3%
Alphabet, Inc., "A" 10.2%
Broadcom, Inc. 4.8%
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.8%
Amphenol Corp., "A" 4.0%
Visa, Inc., "A" 3.7%
Apple, Inc. 3.1%
Aon PLC 2.7%
Moody's Corp. 2.5%
Hubbell, Inc. 2.4%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 13.3%
Alphabet, Inc., "A" 10.2%
Broadcom, Inc. 4.8%
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 4.8%
Amphenol Corp., "A" 4.0%
Visa, Inc., "A" 3.7%
Apple, Inc. 3.1%
Aon PLC 2.7%
Moody's Corp. 2.5%
Hubbell, Inc. 2.4%
C000007250 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Blended Research®Core Equity Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Blended Research Core Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $29 0.55%
Expenses Paid, Amount $ 29
Expense Ratio, Percent 0.55%
Net Assets $ 391,603,409
Holdings Count | Holding 112
Investment Company Portfolio Turnover 18.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 391,603,409 Portfolio Turnover Rate (%): 18
Total Number of Holdings: 112
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 6/30/26)
Portfolio structure
Equities 99.5%
Money Market Funds 0.5%
Equity sectors
Information Technology 37.7%
Financials 12.6%
Consumer Discretionary 10.1%
Communication Services 9.4%
Health Care 9.0%
Industrials 8.0%
Consumer Staples 4.7%
Utilities 3.0%
Energy 2.6%
Real Estate 1.4%
Materials 1.0%
Top ten holdings
NVIDIA Corp. 8.8%
Apple, Inc. 7.8%
Microsoft Corp. 4.2%
Amazon.com, Inc. 4.0%
Alphabet, Inc., "A" 2.6%
Broadcom, Inc. 2.6%
Lam Research Corp. 2.4%
Johnson & Johnson 2.3%
Alphabet, Inc., "C" 2.1%
Micron Technology, Inc. 2.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 8.8%
Apple, Inc. 7.8%
Microsoft Corp. 4.2%
Amazon.com, Inc. 4.0%
Alphabet, Inc., "A" 2.6%
Broadcom, Inc. 2.6%
Lam Research Corp. 2.4%
Johnson & Johnson 2.3%
Alphabet, Inc., "C" 2.1%
Micron Technology, Inc. 2.1%
C000007249 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Blended Research®Core Equity Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Blended Research Core Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $16 0.30%
Expenses Paid, Amount $ 16
Expense Ratio, Percent 0.30%
Net Assets $ 391,603,409
Holdings Count | Holding 112
Investment Company Portfolio Turnover 18.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 391,603,409 Portfolio Turnover Rate (%): 18
Total Number of Holdings: 112
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 6/30/26)
Portfolio structure
Equities 99.5%
Money Market Funds 0.5%
Equity sectors
Information Technology 37.7%
Financials 12.6%
Consumer Discretionary 10.1%
Communication Services 9.4%
Health Care 9.0%
Industrials 8.0%
Consumer Staples 4.7%
Utilities 3.0%
Energy 2.6%
Real Estate 1.4%
Materials 1.0%
Top ten holdings
NVIDIA Corp. 8.8%
Apple, Inc. 7.8%
Microsoft Corp. 4.2%
Amazon.com, Inc. 4.0%
Alphabet, Inc., "A" 2.6%
Broadcom, Inc. 2.6%
Lam Research Corp. 2.4%
Johnson & Johnson 2.3%
Alphabet, Inc., "C" 2.1%
Micron Technology, Inc. 2.1%
MFS uses the Global Industry Classification Standard (GICS®) for sector/industry reporting. MFS has applied its own internal sector/industry classification methodology for equity securities and non-equity securities that are unclassified by GICS.
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 8.8%
Apple, Inc. 7.8%
Microsoft Corp. 4.2%
Amazon.com, Inc. 4.0%
Alphabet, Inc., "A" 2.6%
Broadcom, Inc. 2.6%
Lam Research Corp. 2.4%
Johnson & Johnson 2.3%
Alphabet, Inc., "C" 2.1%
Micron Technology, Inc. 2.1%
C000007255 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® U.S. GovernmentMoney Market Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS U.S. Government Money Market Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $22 0.45%
Expenses Paid, Amount $ 22
Expense Ratio, Percent 0.45%
Net Assets $ 248,477,599
Holdings Count | Holding 23
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 248,477,599
Total Number of Holdings: 23
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 6/30/26)
Portfolio structure
U.S. Treasury and U.S. Government Agency Securities and Equivalents 67.8%
Repurchase Agreements, collateralized by U.S. Treasury and/or U.S. Government Agency Securities 32.2%
Composition including fixed income credit quality
A-1+ 50.5%
A-1 40.1%
U.S. Government 9.4%
Maturity breakdown
0 - 7 days 37.0%
8 - 29 days 23.4%
30 - 59 days 11.7%
60 - 89 days 12.7%
90 - 365 days 15.2%
Ratings are assigned to portfolio securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. Ratings are shown in the S&P scale. All ratings are subject to change. The fund did not hold unrated securities. The fund is not rated by these agencies.
Credit Ratings Selection [Text Block]
Ratings are assigned to portfolio securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. Ratings are shown in the S&P scale. All ratings are subject to change. The fund did not hold unrated securities. The fund is not rated by these agencies.
C000007256 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® U.S. GovernmentMoney Market Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS U.S. Government Money Market Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $22 0.45%
Expenses Paid, Amount $ 22
Expense Ratio, Percent 0.45%
Net Assets $ 248,477,599
Holdings Count | Holding 23
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 248,477,599
Total Number of Holdings: 23
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL INVESTMENTS AS OF 6/30/26)
Portfolio structure
U.S. Treasury and U.S. Government Agency Securities and Equivalents 67.8%
Repurchase Agreements, collateralized by U.S. Treasury and/or U.S. Government Agency Securities 32.2%
Composition including fixed income credit quality
A-1+ 50.5%
A-1 40.1%
U.S. Government 9.4%
Maturity breakdown
0 - 7 days 37.0%
8 - 29 days 23.4%
30 - 59 days 11.7%
60 - 89 days 12.7%
90 - 365 days 15.2%
Ratings are assigned to portfolio securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. Ratings are shown in the S&P scale. All ratings are subject to change. The fund did not hold unrated securities. The fund is not rated by these agencies.
Credit Ratings Selection [Text Block]
Ratings are assigned to portfolio securities utilizing ratings from Moody’s, Fitch, and Standard & Poor’s rating agencies and applying the following hierarchy: If all three agencies provide a rating, the middle rating (after dropping the highest and lowest ratings) is assigned; if two of the three agencies rate a security, the lower of the two is assigned. Ratings are shown in the S&P scale. All ratings are subject to change. The fund did not hold unrated securities. The fund is not rated by these agencies.
C000007262 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® ResearchInternational Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Research International Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $59 1.14%
Expenses Paid, Amount $ 59
Expense Ratio, Percent 1.14%
Net Assets $ 369,664,564
Holdings Count | Holding 118
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 369,664,564 Portfolio Turnover Rate (%): 13
Total Number of Holdings: 118
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 6/30/26)
Portfolio structure
Equities 98.2%
Money Market Funds 1.8%
Top ten holdings
Mizuho Financial Group, Inc. 3.0%
Schneider Electric SE 2.9%
Tokyo Electron Ltd. 2.8%
ASML Holding N.V. 2.7%
Taiwan Semiconductor Manufacturing Co. Ltd. 2.3%
Novartis AG 2.2%
Hitachi Ltd. 2.1%
TotalEnergies SE 1.8%
Linde PLC 1.8%
AstraZeneca PLC 1.8%
Issuer country weightings
Japan 23.7%
United Kingdom 15.9%
France 11.4%
Switzerland 7.1%
Netherlands 6.5%
United States 6.0%
Germany 5.8%
Italy 3.1%
Australia 2.6%
Other Countries 17.9%
Largest Holdings [Text Block]
Top ten holdings
Mizuho Financial Group, Inc. 3.0%
Schneider Electric SE 2.9%
Tokyo Electron Ltd. 2.8%
ASML Holding N.V. 2.7%
Taiwan Semiconductor Manufacturing Co. Ltd. 2.3%
Novartis AG 2.2%
Hitachi Ltd. 2.1%
TotalEnergies SE 1.8%
Linde PLC 1.8%
AstraZeneca PLC 1.8%
C000007261 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® ResearchInternational Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Research International Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $46 0.89%
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.89%
Net Assets $ 369,664,564
Holdings Count | Holding 118
Investment Company Portfolio Turnover 13.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 369,664,564 Portfolio Turnover Rate (%): 13
Total Number of Holdings: 118
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 6/30/26)
Portfolio structure
Equities 98.2%
Money Market Funds 1.8%
Top ten holdings
Mizuho Financial Group, Inc. 3.0%
Schneider Electric SE 2.9%
Tokyo Electron Ltd. 2.8%
ASML Holding N.V. 2.7%
Taiwan Semiconductor Manufacturing Co. Ltd. 2.3%
Novartis AG 2.2%
Hitachi Ltd. 2.1%
TotalEnergies SE 1.8%
Linde PLC 1.8%
AstraZeneca PLC 1.8%
Issuer country weightings
Japan 23.7%
United Kingdom 15.9%
France 11.4%
Switzerland 7.1%
Netherlands 6.5%
United States 6.0%
Germany 5.8%
Italy 3.1%
Australia 2.6%
Other Countries 17.9%
Largest Holdings [Text Block]
Top ten holdings
Mizuho Financial Group, Inc. 3.0%
Schneider Electric SE 2.9%
Tokyo Electron Ltd. 2.8%
ASML Holding N.V. 2.7%
Taiwan Semiconductor Manufacturing Co. Ltd. 2.3%
Novartis AG 2.2%
Hitachi Ltd. 2.1%
TotalEnergies SE 1.8%
Linde PLC 1.8%
AstraZeneca PLC 1.8%
C000007263 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Research Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Research Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $44 0.85%
Expenses Paid, Amount $ 44
Expense Ratio, Percent 0.85%
Net Assets $ 75,162,837
Holdings Count | Holding 123
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 75,162,837 Portfolio Turnover Rate (%): 20
Total Number of Holdings: 123
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 6/30/26)
Portfolio structure
Equities 99.2%
Money Market Funds 0.8%
Top ten holdings
NVIDIA Corp. 5.5%
Taiwan Semiconductor Manufacturing Co. Ltd. 4.3%
Apple, Inc. 4.0%
Alphabet, Inc., "A" 3.3%
Amazon.com, Inc. 3.2%
Microsoft Corp. 3.2%
Broadcom, Inc. 2.7%
SK hynix, Inc. 2.6%
ASML Holding N.V. 1.8%
Mastercard, Inc., "A" 1.7%
Issuer country weightings
United States 57.5%
Japan 7.2%
United Kingdom 6.1%
Taiwan 4.3%
France 4.1%
Netherlands 3.8%
Switzerland 2.9%
South Korea 2.6%
Canada 2.1%
Other Countries 9.4%
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 5.5%
Taiwan Semiconductor Manufacturing Co. Ltd. 4.3%
Apple, Inc. 4.0%
Alphabet, Inc., "A" 3.3%
Amazon.com, Inc. 3.2%
Microsoft Corp. 3.2%
Broadcom, Inc. 2.7%
SK hynix, Inc. 2.6%
ASML Holding N.V. 1.8%
Mastercard, Inc., "A" 1.7%
C000007264 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Research Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Research Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $57 1.10%
Expenses Paid, Amount $ 57
Expense Ratio, Percent 1.10%
Net Assets $ 75,162,837
Holdings Count | Holding 123
Investment Company Portfolio Turnover 20.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 75,162,837 Portfolio Turnover Rate (%): 20
Total Number of Holdings: 123
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 6/30/26)
Portfolio structure
Equities 99.2%
Money Market Funds 0.8%
Top ten holdings
NVIDIA Corp. 5.5%
Taiwan Semiconductor Manufacturing Co. Ltd. 4.3%
Apple, Inc. 4.0%
Alphabet, Inc., "A" 3.3%
Amazon.com, Inc. 3.2%
Microsoft Corp. 3.2%
Broadcom, Inc. 2.7%
SK hynix, Inc. 2.6%
ASML Holding N.V. 1.8%
Mastercard, Inc., "A" 1.7%
Issuer country weightings
United States 57.5%
Japan 7.2%
United Kingdom 6.1%
Taiwan 4.3%
France 4.1%
Netherlands 3.8%
Switzerland 2.9%
South Korea 2.6%
Canada 2.1%
Other Countries 9.4%
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 5.5%
Taiwan Semiconductor Manufacturing Co. Ltd. 4.3%
Apple, Inc. 4.0%
Alphabet, Inc., "A" 3.3%
Amazon.com, Inc. 3.2%
Microsoft Corp. 3.2%
Broadcom, Inc. 2.7%
SK hynix, Inc. 2.6%
ASML Holding N.V. 1.8%
Mastercard, Inc., "A" 1.7%
C000007268 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $46 0.92%
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.92%
Net Assets $ 37,273,389
Holdings Count | Holding 260
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 37,273,389 Average Effective Maturity (yrs): 8.5
Total Number of Holdings: 260 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 22
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 6/30/26)
Portfolio structure
Fixed Income 99.6%
Money Market Funds 0.4%
Composition including fixed income credit quality
AAA 12.0%
AA 8.7%
A 14.9%
BBB 29.9%
BB 5.9%
B 5.1%
CCC 0.4%
C 0.0%
U.S. Government 21.0%
Federal Agencies 0.0%
Not Rated 1.7%
Money Market Funds 0.4%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007267 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Income Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Income Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $33 0.67%
Expenses Paid, Amount $ 33
Expense Ratio, Percent 0.67%
Net Assets $ 37,273,389
Holdings Count | Holding 260
Investment Company Portfolio Turnover 22.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 37,273,389 Average Effective Maturity (yrs): 8.5
Total Number of Holdings: 260 Average Effective Duration (yrs): 5.8
Portfolio Turnover Rate (%): 22
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 6/30/26)
Portfolio structure
Fixed Income 99.6%
Money Market Funds 0.4%
Composition including fixed income credit quality
AAA 12.0%
AA 8.7%
A 14.9%
BBB 29.9%
BB 5.9%
B 5.1%
CCC 0.4%
C 0.0%
U.S. Government 21.0%
Federal Agencies 0.0%
Not Rated 1.7%
Money Market Funds 0.4%
Ratings are assigned using Moody’s, Fitch, and Standard & Poor’s and applying a hierarchy: If all 3 agencies rate a security, the middle rating is assigned; if 2 agencies rate a security, the lower rating is assigned. If none of the 3 agencies rate a security, we use DBRS Morningstar. If none of the 4 agencies rate a security, we use Kroll Bond Rating Agency. Ratings are shown in the S&P and Fitch scale (e.g., AAA). All ratings are subject to change.
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.
C000007271 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Technology Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Technology Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $45 0.82%
Expenses Paid, Amount $ 45
Expense Ratio, Percent 0.82%
Net Assets $ 252,485,052
Holdings Count | Holding 48
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 252,485,052 Portfolio Turnover Rate (%): 21
Total Number of Holdings: 48
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 6/30/26)
Portfolio structure
Equities 94.1%
Money Market Funds 5.9%
Top ten holdings
Alphabet, Inc., "A" 8.4%
Broadcom, Inc. 7.1%
Apple, Inc. 6.9%
NVIDIA Corp. 6.6%
Microsoft Corp. 4.7%
Lam Research Corp. 4.4%
Applied Materials, Inc. 4.3%
Advanced Micro Devices 3.6%
KLA Corp. 3.1%
Cisco Systems, Inc. 3.0%
Top five industries
Semiconductor & Electronic Components 41.0%
Hardware, Peripherals, & Assembly 22.5%
Software 20.3%
Interactive Media Services 11.6%
Electrical Equipment 3.0%
For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).
Largest Holdings [Text Block]
Top ten holdings
Alphabet, Inc., "A" 8.4%
Broadcom, Inc. 7.1%
Apple, Inc. 6.9%
NVIDIA Corp. 6.6%
Microsoft Corp. 4.7%
Lam Research Corp. 4.4%
Applied Materials, Inc. 4.3%
Advanced Micro Devices 3.6%
KLA Corp. 3.1%
Cisco Systems, Inc. 3.0%
C000007272 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Technology Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Technology Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $58 1.07%
Expenses Paid, Amount $ 58
Expense Ratio, Percent 1.07%
Net Assets $ 252,485,052
Holdings Count | Holding 48
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 252,485,052 Portfolio Turnover Rate (%): 21
Total Number of Holdings: 48
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 6/30/26)
Portfolio structure
Equities 94.1%
Money Market Funds 5.9%
Top ten holdings
Alphabet, Inc., "A" 8.4%
Broadcom, Inc. 7.1%
Apple, Inc. 6.9%
NVIDIA Corp. 6.6%
Microsoft Corp. 4.7%
Lam Research Corp. 4.4%
Applied Materials, Inc. 4.3%
Advanced Micro Devices 3.6%
KLA Corp. 3.1%
Cisco Systems, Inc. 3.0%
Top five industries
Semiconductor & Electronic Components 41.0%
Hardware, Peripherals, & Assembly 22.5%
Software 20.3%
Interactive Media Services 11.6%
Electrical Equipment 3.0%
For purposes of these classifications, MFS uses its own internal sector/industry classification methodology, which may deviate from classification methodologies used by other industry participants (e.g., the Global Industry Classification Standard).
Largest Holdings [Text Block]
Top ten holdings
Alphabet, Inc., "A" 8.4%
Broadcom, Inc. 7.1%
Apple, Inc. 6.9%
NVIDIA Corp. 6.6%
Microsoft Corp. 4.7%
Lam Research Corp. 4.4%
Applied Materials, Inc. 4.3%
Advanced Micro Devices 3.6%
KLA Corp. 3.1%
Cisco Systems, Inc. 3.0%
C000007282 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Core Equity Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Core Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $53 1.03%
Expenses Paid, Amount $ 53
Expense Ratio, Percent 1.03%
Net Assets $ 294,159,536
Holdings Count | Holding 178
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 294,159,536 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 178
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 6/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Global equity sectors
Technology 33.1%
Capital Goods 14.3%
Financial Services 12.8%
Consumer Cyclicals 10.4%
Communication Services 10.0%
Health Care 9.3%
Energy 6.0%
Consumer Staples 2.7%
Top ten holdings
NVIDIA Corp. 7.3%
Apple, Inc. 5.4%
Alphabet, Inc., "A" 5.1%
Amazon.com, Inc. 4.4%
Microsoft Corp. 4.2%
Broadcom, Inc. 3.4%
Meta Platforms, Inc., "A" 2.2%
JPMorgan Chase & Co. 1.8%
Arista Networks, Inc. 1.8%
Johnson & Johnson 1.5%
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 7.3%
Apple, Inc. 5.4%
Alphabet, Inc., "A" 5.1%
Amazon.com, Inc. 4.4%
Microsoft Corp. 4.2%
Broadcom, Inc. 3.4%
Meta Platforms, Inc., "A" 2.2%
JPMorgan Chase & Co. 1.8%
Arista Networks, Inc. 1.8%
Johnson & Johnson 1.5%
C000007281 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Core Equity Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Core Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $40 0.78%
Expenses Paid, Amount $ 40
Expense Ratio, Percent 0.78%
Net Assets $ 294,159,536
Holdings Count | Holding 178
Investment Company Portfolio Turnover 31.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 294,159,536 Portfolio Turnover Rate (%): 31
Total Number of Holdings: 178
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 6/30/26)
Portfolio structure
Equities 98.6%
Money Market Funds 1.4%
Global equity sectors
Technology 33.1%
Capital Goods 14.3%
Financial Services 12.8%
Consumer Cyclicals 10.4%
Communication Services 10.0%
Health Care 9.3%
Energy 6.0%
Consumer Staples 2.7%
Top ten holdings
NVIDIA Corp. 7.3%
Apple, Inc. 5.4%
Alphabet, Inc., "A" 5.1%
Amazon.com, Inc. 4.4%
Microsoft Corp. 4.2%
Broadcom, Inc. 3.4%
Meta Platforms, Inc., "A" 2.2%
JPMorgan Chase & Co. 1.8%
Arista Networks, Inc. 1.8%
Johnson & Johnson 1.5%
Largest Holdings [Text Block]
Top ten holdings
NVIDIA Corp. 7.3%
Apple, Inc. 5.4%
Alphabet, Inc., "A" 5.1%
Amazon.com, Inc. 4.4%
Microsoft Corp. 4.2%
Broadcom, Inc. 3.4%
Meta Platforms, Inc., "A" 2.2%
JPMorgan Chase & Co. 1.8%
Arista Networks, Inc. 1.8%
Johnson & Johnson 1.5%
C000007285 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Emerging MarketsEquity Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Emerging Markets Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $66 1.23%
Expenses Paid, Amount $ 66
Expense Ratio, Percent 1.23%
Net Assets $ 44,149,860
Holdings Count | Holding 96
Investment Company Portfolio Turnover 25.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 44,149,860 Portfolio Turnover Rate (%): 25
Total Number of Holdings: 96
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 6/30/26)
Portfolio structure
Equities 98.7%
Money Market Funds 1.3%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 14.0%
Samsung Electronics Co. Ltd. 11.0%
Tencent Holdings Ltd. 4.3%
SK hynix, Inc. 3.2%
Hon Hai Precision Industry Co. Ltd. 3.0%
Alibaba Group Holding Ltd. 2.8%
HDFC Bank Ltd. 2.3%
ASE Technology Holding Co. Ltd 2.2%
MediaTek, Inc. 2.2%
Delta Electronics, Inc. 2.0%
Issuer country weightings
Taiwan 24.3%
South Korea 21.4%
China 19.4%
India 12.4%
Brazil 3.3%
Hong Kong 2.6%
Saudi Arabia 2.6%
United States 2.6%
United Arab Emirates 2.0%
Other Countries 9.4%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 14.0%
Samsung Electronics Co. Ltd. 11.0%
Tencent Holdings Ltd. 4.3%
SK hynix, Inc. 3.2%
Hon Hai Precision Industry Co. Ltd. 3.0%
Alibaba Group Holding Ltd. 2.8%
HDFC Bank Ltd. 2.3%
ASE Technology Holding Co. Ltd 2.2%
MediaTek, Inc. 2.2%
Delta Electronics, Inc. 2.0%
C000007286 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Emerging MarketsEquity Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Emerging Markets Equity Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $80 1.48%
Expenses Paid, Amount $ 80
Expense Ratio, Percent 1.48%
Net Assets $ 44,149,860
Holdings Count | Holding 96
Investment Company Portfolio Turnover 25.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 44,149,860 Portfolio Turnover Rate (%): 25
Total Number of Holdings: 96
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 6/30/26)
Portfolio structure
Equities 98.7%
Money Market Funds 1.3%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 14.0%
Samsung Electronics Co. Ltd. 11.0%
Tencent Holdings Ltd. 4.3%
SK hynix, Inc. 3.2%
Hon Hai Precision Industry Co. Ltd. 3.0%
Alibaba Group Holding Ltd. 2.8%
HDFC Bank Ltd. 2.3%
ASE Technology Holding Co. Ltd 2.2%
MediaTek, Inc. 2.2%
Delta Electronics, Inc. 2.0%
Issuer country weightings
Taiwan 24.3%
South Korea 21.4%
China 19.4%
India 12.4%
Brazil 3.3%
Hong Kong 2.6%
Saudi Arabia 2.6%
United States 2.6%
United Arab Emirates 2.0%
Other Countries 9.4%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd. 14.0%
Samsung Electronics Co. Ltd. 11.0%
Tencent Holdings Ltd. 4.3%
SK hynix, Inc. 3.2%
Hon Hai Precision Industry Co. Ltd. 3.0%
Alibaba Group Holding Ltd. 2.8%
HDFC Bank Ltd. 2.3%
ASE Technology Holding Co. Ltd 2.2%
MediaTek, Inc. 2.2%
Delta Electronics, Inc. 2.0%
C000007288 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GlobalGovernments Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Governments Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $46 0.94%
Expenses Paid, Amount $ 46
Expense Ratio, Percent 0.94%
Net Assets $ 77,632,606
Holdings Count | Holding 70
Investment Company Portfolio Turnover 35.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 77,632,606 Average Effective Maturity (yrs): 8.9
Total Number of Holdings: 70 Average Effective Duration (yrs): 6.6
Portfolio Turnover Rate (%): 35
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 6/30/26)
Portfolio structure
Fixed Income 97.5%
Money Market Funds 2.5%
Issuer country weightings
United States 42.6%
Japan 10.7%
Italy 8.1%
United Kingdom 8.0%
France 6.5%
Greece 5.3%
Canada 3.5%
Spain 3.2%
Lithuania 3.0%
Other Countries 9.1%
Composition including fixed income credit quality
AAA 6.0%
AA 8.9%
A 24.1%
BBB 15.4%
BB 1.9%
B 0.5%
U.S. Government 39.3%
Federal Agencies 0.5%
Not Rated 0.9%
Money Market Funds 2.5%
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.
C000007287 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® GlobalGovernments Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Governments Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $34 0.69%
Expenses Paid, Amount $ 34
Expense Ratio, Percent 0.69%
Net Assets $ 77,632,606
Holdings Count | Holding 70
Investment Company Portfolio Turnover 35.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 77,632,606 Average Effective Maturity (yrs): 8.9
Total Number of Holdings: 70 Average Effective Duration (yrs): 6.6
Portfolio Turnover Rate (%): 35
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 6/30/26)
Portfolio structure
Fixed Income 97.5%
Money Market Funds 2.5%
Issuer country weightings
United States 42.6%
Japan 10.7%
Italy 8.1%
United Kingdom 8.0%
France 6.5%
Greece 5.3%
Canada 3.5%
Spain 3.2%
Lithuania 3.0%
Other Countries 9.1%
Composition including fixed income credit quality
AAA 6.0%
AA 8.9%
A 24.1%
BBB 15.4%
BB 1.9%
B 0.5%
U.S. Government 39.3%
Federal Agencies 0.5%
Not Rated 0.9%
Money Market Funds 2.5%
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.
C000007289 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $43 0.88%
Expenses Paid, Amount $ 43
Expense Ratio, Percent 0.88%
Net Assets $ 47,197,888
Holdings Count | Holding 72
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 47,197,888 Portfolio Turnover Rate (%): 21
Total Number of Holdings: 72
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 6/30/26)
Portfolio structure
Equities 98.8%
Money Market Funds 1.2%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 7.3%
Alphabet, Inc., "A" 4.8%
NVIDIA Corp. 4.5%
Amazon.com, Inc. 3.8%
Visa, Inc., "A" 3.3%
Amphenol Corp., "A" 2.4%
L’Oréal S.A. 2.4%
Schneider Electric SE 2.3%
Aon PLC 2.3%
Tencent Holdings Ltd. 2.2%
Issuer country weightings
United States 67.6%
Taiwan 7.3%
France 6.0%
Japan 5.6%
China 4.2%
United Kingdom 2.4%
India 2.1%
Canada 1.7%
Switzerland 1.2%
Other Countries 1.9%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 7.3%
Alphabet, Inc., "A" 4.8%
NVIDIA Corp. 4.5%
Amazon.com, Inc. 3.8%
Visa, Inc., "A" 3.3%
Amphenol Corp., "A" 2.4%
L’Oréal S.A. 2.4%
Schneider Electric SE 2.3%
Aon PLC 2.3%
Tencent Holdings Ltd. 2.2%
C000007290 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global Growth Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Growth Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $55 1.13%
Expenses Paid, Amount $ 55
Expense Ratio, Percent 1.13%
Net Assets $ 47,197,888
Holdings Count | Holding 72
Investment Company Portfolio Turnover 21.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 47,197,888 Portfolio Turnover Rate (%): 21
Total Number of Holdings: 72
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 6/30/26)
Portfolio structure
Equities 98.8%
Money Market Funds 1.2%
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 7.3%
Alphabet, Inc., "A" 4.8%
NVIDIA Corp. 4.5%
Amazon.com, Inc. 3.8%
Visa, Inc., "A" 3.3%
Amphenol Corp., "A" 2.4%
L’Oréal S.A. 2.4%
Schneider Electric SE 2.3%
Aon PLC 2.3%
Tencent Holdings Ltd. 2.2%
Issuer country weightings
United States 67.6%
Taiwan 7.3%
France 6.0%
Japan 5.6%
China 4.2%
United Kingdom 2.4%
India 2.1%
Canada 1.7%
Switzerland 1.2%
Other Countries 1.9%
Largest Holdings [Text Block]
Top ten holdings
Taiwan Semiconductor Manufacturing Co. Ltd., ADR 7.3%
Alphabet, Inc., "A" 4.8%
NVIDIA Corp. 4.5%
Amazon.com, Inc. 3.8%
Visa, Inc., "A" 3.3%
Amphenol Corp., "A" 2.4%
L’Oréal S.A. 2.4%
Schneider Electric SE 2.3%
Aon PLC 2.3%
Tencent Holdings Ltd. 2.2%
C000007292 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global TacticalAllocation Portfolio
Class Name Service Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Tactical Allocation Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Service Class $51 1.02%
Expenses Paid, Amount $ 51
Expense Ratio, Percent 1.02%
Net Assets $ 315,554,461
Holdings Count | Holding 1,160
Investment Company Portfolio Turnover 43.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 315,554,461 Portfolio Turnover Rate (%): 43
Total Number of Holdings: 1,160
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL NET ASSETS AS OF 6/30/26)
Portfolio Structure Tactical Overlay (b)
Active Security
Selection (a)		 Long Short Net Market
Exposure (c)
Fixed Income U.S. 20.9% 26.8% (6.0)% 41.7%
Emerging Markets 18.2% 0.0% 0.0% 18.2%
Japan 1.6% 8.7% 0.0% 10.3%
Europe ex-U.K. 17.4% 0.0% (9.3)% 8.1%
United Kingdom 4.6% 3.1% 0.0% 7.7%
North America ex-U.S. 4.2% 1.3% 0.0% 5.5%
Supranational 0.1% 0.0% 0.0% 0.1%
Developed - Middle East/Africa 0.1% 0.0% 0.0% 0.1%
Asia/Pacific ex-Japan 2.1% 0.0% (9.1)% (7.0)%
Total 69.2% 39.9% (24.4)% 84.7%
Equity U.S. Small/Mid Cap 9.5% 0.0% (0.1)% 9.4%
Europe ex-U.K. 7.6% 1.6% (2.0)% 7.2%
U.S. Large Cap 8.5% 0.0% (2.1)% 6.4%
United Kingdom 3.8% 2.1% 0.0% 5.9%
Japan 2.8% 1.9% 0.0% 4.7%
Emerging Markets 2.3% 2.0% (1.4)% 2.9%
North America ex-U.S. 0.6% 2.1% 0.0% 2.7%
Asia/Pacific ex-Japan 0.6% 1.3% (3.7)% (1.8)%
Total 35.7% 11.0% (9.3)% 37.4%
Real Estate-related U.S. 0.6% 0.0% 0.0% 0.6%
Non-U.S. 0.4% 0.0% 0.0% 0.4%
Total 1.0% 0.0% 0.0% 1.0%
Cash Cash & Cash Equivalents (d) 1.5%
Other (e) (24.6)%
Total Net Exposure Summary 100.0%
(a) Represents the actively managed portion of the portfolio and for purposes of this presentation, components include the value of securities, less any securities sold short. The bond component will include any accrued interest amounts. This also reflects the equivalent exposure of certain derivative positions. These amounts may be negative from time to time.
(b) Represents the tactical overlay portion of the portfolio which is how the fund manages its exposure to markets and currencies through the use of derivative positions. Percentages reflect the equivalent exposure of those derivative positions.
(c) For purposes of this presentation, the components include the value of securities, less any securities sold short, and reflect the impact of the equivalent exposure of all derivative positions. These amounts may be negative from time to time. The bond component will include any accrued interest amounts.
(d) Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities.
(e) Other includes currency derivatives and/or the offsetting of the leverage produced by derivative positions.
Portfolio Composition presents the value of securities, including equivalent exposure of derivative positions. Equivalent exposure is a reasonable approximation of the amount of the underlying asset the portfolio would have to hold to have the same price sensitivity of the derivative contract. Bonds include any accrued interest amounts.
Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.
Exposure Basis Explanation [Text Block]
(a) Represents the actively managed portion of the portfolio and for purposes of this presentation, components include the value of securities, less any securities sold short. The bond component will include any accrued interest amounts. This also reflects the equivalent exposure of certain derivative positions. These amounts may be negative from time to time.
(b) Represents the tactical overlay portion of the portfolio which is how the fund manages its exposure to markets and currencies through the use of derivative positions. Percentages reflect the equivalent exposure of those derivative positions.
(c) For purposes of this presentation, the components include the value of securities, less any securities sold short, and reflect the impact of the equivalent exposure of all derivative positions. These amounts may be negative from time to time. The bond component will include any accrued interest amounts.
(d) Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities.
(e) Other includes currency derivatives and/or the offsetting of the leverage produced by derivative positions.
Portfolio Composition presents the value of securities, including equivalent exposure of derivative positions. Equivalent exposure is a reasonable approximation of the amount of the underlying asset the portfolio would have to hold to have the same price sensitivity of the derivative contract. Bonds include any accrued interest amounts.
Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.
C000007291 [Member]  
Shareholder Report [Line Items]  
Fund Name MFS® Global TacticalAllocation Portfolio
Class Name Initial Class
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semiannual shareholder report contains important information about MFS Global Tactical Allocation Portfolio for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the fund at insurancefunds.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 insurancefunds.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)
Initial Class $39 0.77%
Expenses Paid, Amount $ 39
Expense Ratio, Percent 0.77%
Net Assets $ 315,554,461
Holdings Count | Holding 1,160
Investment Company Portfolio Turnover 43.00%
Additional Fund Statistics [Text Block]
FUND STATISTICS AS OF 6/30/26
Net Assets ($): 315,554,461 Portfolio Turnover Rate (%): 43
Total Number of Holdings: 1,160
Holdings [Text Block]
PORTFOLIO COMPOSITION (BASED ON TOTAL NET ASSETS AS OF 6/30/26)
Portfolio Structure Tactical Overlay (b)
Active Security
Selection (a)		 Long Short Net Market
Exposure (c)
Fixed Income U.S. 20.9% 26.8% (6.0)% 41.7%
Emerging Markets 18.2% 0.0% 0.0% 18.2%
Japan 1.6% 8.7% 0.0% 10.3%
Europe ex-U.K. 17.4% 0.0% (9.3)% 8.1%
United Kingdom 4.6% 3.1% 0.0% 7.7%
North America ex-U.S. 4.2% 1.3% 0.0% 5.5%
Supranational 0.1% 0.0% 0.0% 0.1%
Developed - Middle East/Africa 0.1% 0.0% 0.0% 0.1%
Asia/Pacific ex-Japan 2.1% 0.0% (9.1)% (7.0)%
Total 69.2% 39.9% (24.4)% 84.7%
Equity U.S. Small/Mid Cap 9.5% 0.0% (0.1)% 9.4%
Europe ex-U.K. 7.6% 1.6% (2.0)% 7.2%
U.S. Large Cap 8.5% 0.0% (2.1)% 6.4%
United Kingdom 3.8% 2.1% 0.0% 5.9%
Japan 2.8% 1.9% 0.0% 4.7%
Emerging Markets 2.3% 2.0% (1.4)% 2.9%
North America ex-U.S. 0.6% 2.1% 0.0% 2.7%
Asia/Pacific ex-Japan 0.6% 1.3% (3.7)% (1.8)%
Total 35.7% 11.0% (9.3)% 37.4%
Real Estate-related U.S. 0.6% 0.0% 0.0% 0.6%
Non-U.S. 0.4% 0.0% 0.0% 0.4%
Total 1.0% 0.0% 0.0% 1.0%
Cash Cash & Cash Equivalents (d) 1.5%
Other (e) (24.6)%
Total Net Exposure Summary 100.0%
(a) Represents the actively managed portion of the portfolio and for purposes of this presentation, components include the value of securities, less any securities sold short. The bond component will include any accrued interest amounts. This also reflects the equivalent exposure of certain derivative positions. These amounts may be negative from time to time.
(b) Represents the tactical overlay portion of the portfolio which is how the fund manages its exposure to markets and currencies through the use of derivative positions. Percentages reflect the equivalent exposure of those derivative positions.
(c) For purposes of this presentation, the components include the value of securities, less any securities sold short, and reflect the impact of the equivalent exposure of all derivative positions. These amounts may be negative from time to time. The bond component will include any accrued interest amounts.
(d) Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities.
(e) Other includes currency derivatives and/or the offsetting of the leverage produced by derivative positions.
Portfolio Composition presents the value of securities, including equivalent exposure of derivative positions. Equivalent exposure is a reasonable approximation of the amount of the underlying asset the portfolio would have to hold to have the same price sensitivity of the derivative contract. Bonds include any accrued interest amounts.
Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.
Exposure Basis Explanation [Text Block]
(a) Represents the actively managed portion of the portfolio and for purposes of this presentation, components include the value of securities, less any securities sold short. The bond component will include any accrued interest amounts. This also reflects the equivalent exposure of certain derivative positions. These amounts may be negative from time to time.
(b) Represents the tactical overlay portion of the portfolio which is how the fund manages its exposure to markets and currencies through the use of derivative positions. Percentages reflect the equivalent exposure of those derivative positions.
(c) For purposes of this presentation, the components include the value of securities, less any securities sold short, and reflect the impact of the equivalent exposure of all derivative positions. These amounts may be negative from time to time. The bond component will include any accrued interest amounts.
(d) Cash & Cash Equivalents includes any cash, investments in money market funds, short-term securities, and other assets less liabilities.
(e) Other includes currency derivatives and/or the offsetting of the leverage produced by derivative positions.
Portfolio Composition presents the value of securities, including equivalent exposure of derivative positions. Equivalent exposure is a reasonable approximation of the amount of the underlying asset the portfolio would have to hold to have the same price sensitivity of the derivative contract. Bonds include any accrued interest amounts.
Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.