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

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Performance Information Illustrates Variability of Returns [Text]

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

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was 1.13%. During the period(s) shown in the bar chart, the highest quarterly return was 23.70% (for the calendar quarter ended December 31, 2020) and the lowest quarterly return was (33.45)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS Blended Research Small Cap Equity Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Russell 3000® Index \| Average Annual Return, Label [Optional Text]	Russell 3000® Index
Russell 3000® Index \| Average Annual Return, Percent		17.15%	13.15%	14.29%
Russell 2000® Index \| Average Annual Return, Label [Optional Text]	Russell 2000® Index
Russell 2000® Index \| Average Annual Return, Percent		12.81%	6.09%	9.62%
Initial Class Shares \| Average Annual Return, Percent		5.76%	6.92%	9.10%
Service Class Shares \| Average Annual Return, Percent		5.49%	6.62%	8.82%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Phone [Text]

1-877-411-3325

Prospectus [Line Items]

Bar Chart, Year to Date Return

1.13%

Highest Quarterly Return, Label [Optional Text]

highest quarterly return

Highest Quarterly Return, Date

Dec. 31, 2020

Lowest Quarterly Return

(33.45%)

Bar Chart and Performance Table [Heading]

Performance Information

Performance Past Does Not Indicate Future [Text]

The fund’s past performance does not necessarily indicate how the fund will perform in the future.

Performance Additional Market Index [Text]

As of December 31, 2025, the MFS Conservative Allocation Portfolio Blended Index (the Blended Index) consisted of the following indices and weightings: 29% Standard & Poor’s 500 Stock Index; 9% MSCI EAFE (Europe, Australasia, Far East) Index (net div); 2% FTSE EPRA Nareit Developed Real Estate Index (net div); and 60% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was (1.23)%. During the period(s) shown in the bar chart, the highest quarterly return was 10.49% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (9.41)% (for the calendar quarter ended June 30, 2022).

Performance [Table]

Average Annual Total Returns - MFS Conservative Allocation Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Bloomberg U.S. Aggregate Bond Index \| Average Annual Return, Label [Optional Text]	Bloomberg U.S. Aggregate Bond Index
Bloomberg U.S. Aggregate Bond Index \| Average Annual Return, Percent		7.30%	(0.36%)	2.01%
MFS Conservative Allocation Portfolio Blended Index \| Average Annual Return, Label [Optional Text]	MFS Conservative Allocation Portfolio Blended Index
MFS Conservative Allocation Portfolio Blended Index \| Average Annual Return, Percent		12.50%	4.70%	6.29%
Initial Class Shares \| Average Annual Return, Percent		10.00%	3.09%	5.70%
Service Class Shares \| Average Annual Return, Percent		9.72%	2.83%	5.43%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Website Address [Text]

mfs.com

Year to Date Return, Label [Optional Text]

The total return for the three-month period ended

Bar Chart, Year to Date Return, Date

Mar. 31, 2026

Highest Quarterly Return

10.49%

Lowest Quarterly Return, Label [Optional Text]

lowest quarterly return

Lowest Quarterly Return, Date

Jun. 30, 2022

Prospectus [Line Items]

Performance Narrative [Text Block]

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

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Performance Information Illustrates Variability of Returns [Text]

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

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was (1.26)%. During the period(s) shown in the bar chart, the highest quarterly return was 16.58% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was (23.07)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS Global Real Estate Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
MSCI All Country World Index (net div) \| Average Annual Return, Label [Optional Text]	MSCI All Country World Index (net div)
MSCI All Country World Index (net div) \| Average Annual Return, Percent		22.34%	11.19%	11.72%
FTSE EPRA Nareit Developed Real Estate Index (net div) \| Average Annual Return, Label [Optional Text]	FTSE EPRA Nareit Developed Real Estate Index (net div)
FTSE EPRA Nareit Developed Real Estate Index (net div) \| Average Annual Return, Percent		9.57%	2.76%	3.25%
Initial Class Shares \| Average Annual Return, Percent		3.53%	1.32%	5.01%
Service Class Shares \| Average Annual Return, Percent		3.30%	1.08%	4.76%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Phone [Text]

1-877-411-3325

Prospectus [Line Items]

Bar Chart, Year to Date Return

(1.26%)

Highest Quarterly Return, Label [Optional Text]

highest quarterly return

Highest Quarterly Return, Date

Dec. 31, 2023

Lowest Quarterly Return

(23.07%)

Bar Chart and Performance Table [Heading]

Performance Information

Performance Past Does Not Indicate Future [Text]

The fund’s past performance does not necessarily indicate how the fund will perform in the future.

Performance Additional Market Index [Text]

As of December 31, 2025, the MFS Growth Allocation Portfolio Blended Index (the Blended Index) consisted of the following indices and weightings: 54% Standard & Poor’s 500 Stock Index; 21% MSCI EAFE (Europe, Australasia, Far East) Index (net div); 5% FTSE EPRA Nareit Developed Real Estate Index (net div); and 20% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was (2.07)%. During the period(s) shown in the bar chart, the highest quarterly return was 16.78% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (16.60)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS Growth Allocation Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Standard & Poor's 500 Stock Index \| Average Annual Return, Label [Optional Text]	Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index \| Average Annual Return, Percent		17.88%	14.42%	14.82%
MFS Growth Allocation Portfolio Blended Index \| Average Annual Return, Label [Optional Text]	MFS Growth Allocation Portfolio Blended Index
MFS Growth Allocation Portfolio Blended Index \| Average Annual Return, Percent		18.09%	9.73%	10.37%
Initial Class Shares \| Average Annual Return, Percent		12.18%	6.19%	9.22%
Service Class Shares \| Average Annual Return, Percent		11.87%	5.93%	8.95%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Website Address [Text]

mfs.com

Year to Date Return, Label [Optional Text]

The total return for the three-month period ended

Bar Chart, Year to Date Return, Date

Mar. 31, 2026

Highest Quarterly Return

16.78%

Lowest Quarterly Return, Label [Optional Text]

lowest quarterly return

Lowest Quarterly Return, Date

Mar. 31, 2020

Prospectus [Line Items]

Performance Narrative [Text Block]

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

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Performance Information Illustrates Variability of Returns [Text]

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

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was (0.37)%. During the period(s) shown in the bar chart, the highest quarterly return was 8.49% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was (12.69)% (for the calendar quarter ended June 30, 2022).

Performance [Table]

Average Annual Total Returns - MFS Inflation-Adjusted Bond Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Bloomberg Global Aggregate Index \| Average Annual Return, Label [Optional Text]	Bloomberg Global Aggregate Index
Bloomberg Global Aggregate Index \| Average Annual Return, Percent		8.17%	(2.15%)	1.26%
Bloomberg World Government Inflation-Linked Bond Index \| Average Annual Return, Label [Optional Text]	Bloomberg World Government Inflation-Linked Bond Index
Bloomberg World Government Inflation-Linked Bond Index \| Average Annual Return, Percent		8.80%	(2.17%)	1.68%
Initial Class Shares \| Average Annual Return, Percent		8.63%	(3.09%)	1.10%
Service Class Shares \| Average Annual Return, Percent		8.17%	(3.35%)	0.84%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Phone [Text]

1-877-411-3325

Prospectus [Line Items]

Bar Chart, Year to Date Return

(0.37%)

Highest Quarterly Return, Label [Optional Text]

highest quarterly return

Highest Quarterly Return, Date

Dec. 31, 2023

Lowest Quarterly Return

(12.69%)

Bar Chart and Performance Table [Heading]

Performance Information

Performance Past Does Not Indicate Future [Text]

The fund’s past performance does not necessarily indicate how the fund will perform in the future.

Bar Chart [Heading]

Initial Class Bar Chart.

Performance Table Heading

Performance Table.

Average Annual Return, Caption [Optional Text]

Average Annual Total Returns (For the Periods Ended December 31, 2025)

Performance Availability Website Address [Text]

mfs.com

Year to Date Return, Label [Optional Text]

The total return for the three-month period ended

Bar Chart, Year to Date Return, Date

Mar. 31, 2026

Highest Quarterly Return

5.19%

Lowest Quarterly Return, Label [Optional Text]

lowest quarterly return

Lowest Quarterly Return, Date

Mar. 31, 2020

Prospectus [Line Items]

Performance Narrative [Text Block]

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

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Performance Information Illustrates Variability of Returns [Text]

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

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was 1.09%. During the period(s) shown in the bar chart, the highest quarterly return was 19.90% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (31.01)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS Mid Cap Value Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Russell 3000® Index \| Average Annual Return, Label [Optional Text]	Russell 3000® Index
Russell 3000® Index \| Average Annual Return, Percent		17.15%	13.15%	14.29%
Russell Midcap® Value Index \| Average Annual Return, Label [Optional Text]	Russell Midcap® Value Index
Russell Midcap® Value Index \| Average Annual Return, Percent		11.05%	9.83%	9.78%
Initial Class Shares \| Average Annual Return, Percent		5.98%	10.18%	9.95%
Service Class Shares \| Average Annual Return, Percent		5.75%	9.90%	9.69%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Phone [Text]

1-877-411-3325

Prospectus [Line Items]

Bar Chart, Year to Date Return

1.09%

Highest Quarterly Return, Label [Optional Text]

highest quarterly return

Highest Quarterly Return, Date

Jun. 30, 2020

Lowest Quarterly Return

(31.01%)

Bar Chart and Performance Table [Heading]

Performance Information

Performance Past Does Not Indicate Future [Text]

The fund’s past performance does not necessarily indicate how the fund will perform in the future.

Performance Additional Market Index [Text]

As of December 31, 2025, the MFS Moderate Allocation Portfolio Blended Index (the Blended Index) consisted of the following indices and weightings: 43% Standard & Poor’s 500 Stock Index; 14% MSCI EAFE (Europe, Australasia, Far East) Index (net div); 3% FTSE EPRA Nareit Developed Real Estate Index (net div); and 40% Bloomberg U.S. Aggregate Bond Index. The components and weightings of the Blended Index may have differed during the periods and may differ in the future.

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was (1.68)%. During the period(s) shown in the bar chart, the highest quarterly return was 13.62% (for the calendar quarter ended June 30, 2020) and the lowest quarterly return was (12.32)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS Moderate Allocation Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Standard & Poor's 500 Stock Index \| Average Annual Return, Label [Optional Text]	Standard & Poor's 500 Stock Index
Standard & Poor's 500 Stock Index \| Average Annual Return, Percent		17.88%	14.42%	14.82%
MFS Moderate Allocation Portfolio Blended Index \| Average Annual Return, Label [Optional Text]	MFS Moderate Allocation Portfolio Blended Index
MFS Moderate Allocation Portfolio Blended Index \| Average Annual Return, Percent		15.20%	7.36%	8.52%
Initial Class Shares \| Average Annual Return, Percent		11.29%	4.82%	7.62%
Service Class Shares \| Average Annual Return, Percent		10.96%	4.55%	7.35%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Website Address [Text]

mfs.com

Year to Date Return, Label [Optional Text]

The total return for the three-month period ended

Bar Chart, Year to Date Return, Date

Mar. 31, 2026

Highest Quarterly Return

13.62%

Lowest Quarterly Return, Label [Optional Text]

lowest quarterly return

Lowest Quarterly Return, Date

Mar. 31, 2020

Prospectus [Line Items]

Performance Narrative [Text Block]

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

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available at mfs.com or by calling 1-877-411-3325. If the fees and expenses imposed by the insurance company that issued your variable contracts or other eligible investor through which an investment in the fund is made were included, they would reduce the returns shown.

Performance Information Illustrates Variability of Returns [Text]

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

Bar Chart Closing [Text Block]

The total return for the three-month period ended March 31, 2026, was 1.49%. During the period(s) shown in the bar chart, the highest quarterly return was 31.09% (for the calendar quarter ended December 31, 2020) and the lowest quarterly return was (34.08)% (for the calendar quarter ended March 31, 2020).

Performance [Table]

Average Annual Total Returns - MFS New Discovery Value Portfolio		12 Months Ended	60 Months Ended	120 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2025
Russell 3000® Index \| Average Annual Return, Label [Optional Text]	Russell 3000® Index
Russell 3000® Index \| Average Annual Return, Percent		17.15%	13.15%	14.29%
Russell 2000® Value Index \| Average Annual Return, Label [Optional Text]	Russell 2000® Value Index
Russell 2000® Value Index \| Average Annual Return, Percent		12.59%	8.88%	9.27%
Initial Class Shares \| Average Annual Return, Percent		3.08%	8.48%	10.58%
Service Class Shares \| Average Annual Return, Percent		2.88%	8.22%	10.30%

Index No Deduction for Fees, Expenses, or Taxes [Text]

Reflects no deduction for fees, expenses, or taxes

Performance Availability Phone [Text]

1-877-411-3325

Prospectus [Line Items]

Bar Chart, Year to Date Return

1.49%

Highest Quarterly Return, Label [Optional Text]

highest quarterly return

Highest Quarterly Return, Date

Dec. 31, 2020

Lowest Quarterly Return

(34.08%)