Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	MFS Inflation-Adjusted Bond Portfolio Summary of Key Information
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund’s investment objective is to seek total return that exceeds the rate of inflation over the long-term, with an emphasis on current income, but also considering capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay when you hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund’s Investment Advisory Agreement with MFS. If the fees and expenses imposed by the insurance company that issued your variable contracts through which the fund is offered were included, your expenses would be higher.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Management Fee	rr_ManagementFeesOverAssets	0.50%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.08%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.58%
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs. These transaction costs, which are not reflected in “Annual Fund Operating Expenses” or in the “Example,” affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 520% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	520.00%
Expenses Restated to Reflect Current [Text]	rr_ExpensesRestatedToReflectCurrent	Expenses have been adjusted to reflect current fee arrangements and the management fee set forth in the fund's Investment Advisory Agreement with MFS.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. If the fees and expenses imposed by the investment vehicle through which an investment in the fund is made were included, your expenses would be higher. The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods; your investment has a 5% return each year; and the fund’s operating expenses remain the same.
Expense Example by, Year, Caption [Text]	rr_ExpenseExampleByYearCaption	Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 59
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	186
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	324
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 726
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	MFS (Massachusetts Financial Services Company, the fund’s investment adviser) normally invests at least 80% of the fund’s net assets in inflation-adjusted debt instruments and other instruments with similar economic characteristics. MFS currently intends to focus the fund’s investments in inflation-adjusted debt instruments issued by U.S. and foreign governments. MFS may also invest the fund’s assets in inflation-adjusted debt instruments of other issuers, other instruments with similar economic characteristics to these instruments, including derivatives, and non-inflation-adjusted debt instruments. MFS primarily invests the fund’s assets in investment grade debt instruments, but may also invest in less than investment grade quality debt instruments (lower quality debt instruments). MFS may invest the fund’s assets in U.S. and foreign securities. The fund is a non-diversified fund. This means that MFS may invest a relatively large percentage of the fund’s assets in a single issuer or a small number of issuers. While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps. MFS allocates the fund’s assets across maturities and types of debt instruments based on its evaluation of U.S. and foreign macroeconomic factors, including interest rates, inflation rates, and monetary and fiscal policies. MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. The principal risks of investing in the fund are: Interest Rate Risk: The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes. Credit Risk: The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions. Lower quality debt instruments (commonly referred to as “high yield securities” or “junk bonds”) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments. U.S. Government securities not supported as to the payment of principal or interest by the U.S. Treasury are subject to greater credit risk than are U.S. Government securities supported by the U.S. Treasury. Foreign Risk: Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Prepayment/Extension Risk: Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument’s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended. Inflation-Adjusted Debt Instruments Risk: Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline. Non-Diversification Risk: Because MFS may invest a relatively large percentage of the fund’s assets in a single issuer or small number of issuers, the fund’s performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds. Derivatives Risk: Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s) on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives’ original cost. Derivatives can involve leverage. Leveraging Risk: Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses. Investment Selection Risk: MFS’ investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests. Counterparty and Third Party Risk: Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty’s or third party’s ability to perform in accordance with the terms of the transaction. Liquidity Risk: It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.
Risk Lose Money [Text]	rr_RiskLoseMoney	As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.
Risk Nondiversified Status [Text]	rr_RiskNondiversifiedStatus	Because MFS may invest a relatively large percentage of the fund's assets in a single issuer or small number of issuers, the fund's performance could be closely tied to the value of that one issuer or issuers, and could be more volatile than the performance of diversified funds.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund’s performance over time and how the fund’s performance over time compares with that of a broad measure of market performance. Performance prior to December 8, 2012, reflects time periods when another adviser or subadviser was responsible for selecting investments for the fund under a different investment objective and different investment strategies. 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 investment vehicle through which an investment in the fund is made were included, they would reduce the returns shown.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-877-411-3325
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	mfs.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	The fund's past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Initial Class Bar Chart.
Annual Return 2009	rr_AnnualReturn2009	8.72%
Annual Return 2010	rr_AnnualReturn2010	5.24%
Annual Return 2011	rr_AnnualReturn2011	11.90%
Annual Return 2012	rr_AnnualReturn2012	7.74%
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	The total return for the three-month period ended March 31, 2013 was (1.42)%. During the period(s) shown in the bar chart, the highest quarterly return was 3.95% (for the calendar quarter ended September 30, 2011) and the lowest quarterly return was (1.15)% (for the calendar quarter ended December 31, 2010).
Year to Date Return, Label	rr_YearToDateReturnLabel	The total return for the three-month period ended
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2013
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	(1.42%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest quarterly return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2011
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	3.95%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest quarterly return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.15%)
Performance Table Heading	rr_PerformanceTableHeading	Performance Table.
Performance Table Market Index Changed	rr_PerformanceTableMarketIndexChanged	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays U.S. Treasury Inflation Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund's current investment strategies.
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	(Reflects no deduction for fees, expenses or taxes)
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Effective December 8, 2012, the Barclays World Government Inflation-Linked Bond Index replaced the Barclays U.S. Treasury Inflation Protected Securities Index because MFS believes the Barclays World Government Inflation-Linked Bond Index better reflects the fund’s current investment strategies.
Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the Periods Ended December 31, 2012)
Label	rr_AverageAnnualReturnLabel	Initial Class Shares
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	7.74%
Average Annual Returns, Life	rr_AverageAnnualReturnSinceInception	7.62%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
Barclays World Government Inflation-Linked Bond Index
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays World Government Inflation-Linked Bond Index
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	6.95%
Average Annual Returns, Life	rr_AverageAnnualReturnSinceInception	6.55%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008
Barclays U.S. Treasury Inflation Protected Securities Index
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Treasury Inflation Protected Securities Index
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	6.98%
Average Annual Returns, Life	rr_AverageAnnualReturnSinceInception	8.02%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 01, 2008

If the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Form

-Number N-1A

-Chapter A

-Section 4

-Subsection b

-Paragraph 2

-Subparagraph instructions

-Clause 3

-Exhibit a