Label	Element	Value
MFS® Commodity Strategy Fund
Risk/Return:	rr_RiskReturnAbstract
Supplement [Text Block]	ck0000764719_SupplementTextBlock	SUPPLEMENT TO PROSPECTUS The date of this supplement is May 31, 2013. MFS® Commodity Strategy Fund Effective immediately, the sub-section entitled “Principal Investment Strategies” beneath the main heading "Summary of Key Information" is restated in its entirety as follows:
Risk/Return [Heading]	rr_RiskReturnHeading	MFS® Commodity Strategy Fund
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund’s objective by providing exposure to the commodities markets. The fund normally invests significantly in commodity-linked derivatives and debt instruments. Commodities are assets with tangible properties, including oil, natural gas, agricultural products, and industrial and other precious metals. The fund’s investments in commodity-linked derivatives provide exposure to the investment returns of the commodities markets without investing directly in commodities. MFS primarily invests the fund’s investments in commodity-linked derivatives in commodity-linked notes, but may also invest in other commodity-linked derivatives, such as commodity-linked futures, options, and swaps. In addition to direct investments in commodity-linked derivatives, MFS may also invest up to 25% of the fund’s assets in a wholly-owned and controlled subsidiary (“Subsidiary”) that will invest primarily in commodity-linked derivatives (such as commodity-linked futures, options, and swaps) and debt instruments. MFS does not currently intend to invest the fund's assets in commodity-linked futures, options, swaps, or a Subsidiary. MFS allocates the fund’s investments in commodity-linked derivatives among a variety of different commodity sectors based on quantitative analysis. Of the fund’s investments in debt instruments, MFS generally invests substantially all of these investments in investment grade debt instruments. MFS may invest the fund’s assets in foreign securities. In addition to the commodity-linked derivatives described above, 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 uses a bottom-up investment approach to buying and selling debt 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. Effective immediately, the sub-section entitled “Principal Risks” beneath the main heading "Summary of Key Information" is restated in its entirety as follows:
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: Commodity Risk: The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity. To the extent the fund focuses its investments in a particular asset of the commodities market, the fund will be more susceptible to risks associated with that particular asset. Commodity-Linked Note Risk: Commodity-linked notes have characteristics of debt instruments and derivatives and are subject to the risks associated with investing in those types of investments. Commodity-linked notes can be highly volatile and less liquid than other types of investments. 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. Tax Risk: In order to qualify as a regulated investment company (RIC) under the Internal Revenue Code, the fund must meet certain requirements regarding the source of its income, the diversification of its assets, and the distribution of its income. If the fund were to fail to qualify as a RIC and became subject to federal income tax, shareholders of the fund would be subject to the risk of diminished returns. 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, or other conditions. Foreign Risk: Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, political, regulatory, geopolitical, or 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. Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market. 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 and Allocation Risk: MFS’ investment analysis, its selection of investments, and its assessment of the risk/return potential of commodity sectors may not produce the intended results and 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. Financial Services Exposure Risk: Events that affect the financial services sector may have a significant adverse effect on the fund. 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. Subsidiary Risk: The Subsidiary will not be registered as an investment company under the Investment Company Act of 1940 (the “Act”) and will not be subject to all of the investor protections of the Act. Changes in the laws impacting the fund or the Subsidiary could negatively affect the fund and its shareholders. By investing in the Subsidiary, the fund is exposed to all the risks associated with the Subsidiary’s investments.
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 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.

Label

Element

Value

MFS® Commodity Strategy Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

ck0000764719_SupplementTextBlock

SUPPLEMENT TO PROSPECTUS
The date of this supplement is May 31, 2013.

MFS® Commodity Strategy Fund

Effective immediately, the sub-section entitled “Principal Investment Strategies” beneath the main heading "Summary of Key Information" is restated in its entirety as follows:

Risk/Return [Heading]

rr_RiskReturnHeading

MFS® Commodity Strategy Fund

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

MFS (Massachusetts Financial Services Company, the fund's investment adviser) seeks to achieve the fund’s objective by providing exposure to the commodities markets. The fund normally invests significantly in commodity-linked derivatives and debt instruments. Commodities are assets with tangible properties, including oil, natural gas, agricultural products, and industrial and other precious metals. The fund’s investments in commodity-linked derivatives provide exposure to the investment returns of the commodities markets without investing directly in commodities.

MFS primarily invests the fund’s investments in commodity-linked derivatives in commodity-linked notes, but may also invest in other commodity-linked derivatives, such as commodity-linked futures, options, and swaps. In addition to direct investments in commodity-linked derivatives, MFS may also invest up to 25% of the fund’s assets in a wholly-owned and controlled subsidiary (“Subsidiary”) that will invest primarily in commodity-linked derivatives (such as commodity-linked futures, options, and swaps) and debt instruments. MFS does not currently intend to invest the fund's assets in commodity-linked futures, options, swaps, or a Subsidiary.

MFS allocates the fund’s investments in commodity-linked derivatives among a variety of different commodity sectors based on quantitative analysis.

Of the fund’s investments in debt instruments, MFS generally invests substantially all of these investments in investment grade debt instruments.

MFS may invest the fund’s assets in foreign securities.

In addition to the commodity-linked derivatives described above, 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 uses a bottom-up investment approach to buying and selling debt 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.

Effective immediately, the sub-section entitled “Principal Risks” beneath the main heading "Summary of Key Information" is restated in its entirety as follows:

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:

Commodity Risk: The value of commodities may be more volatile than the value of equity securities or debt instruments and their value may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, or factors affecting a particular industry or commodity. The price of a commodity may be affected by demand/supply imbalances in the market for the commodity. To the extent the fund focuses its investments in a particular asset of the commodities market, the fund will be more susceptible to risks associated with that particular asset.

Commodity-Linked Note Risk: Commodity-linked notes have characteristics of debt instruments and derivatives and are subject to the risks associated with investing in those types of investments. Commodity-linked notes can be highly volatile and less liquid than other types of investments.

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.

Tax Risk: In order to qualify as a regulated investment company (RIC) under the Internal Revenue Code, the fund must meet certain requirements regarding the source of its income, the diversification of its assets, and the distribution of its income. If the fund were to fail to qualify as a RIC and became subject to federal income tax, shareholders of the fund would be subject to the risk of diminished returns.

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, or other conditions.

Foreign Risk: Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, political, regulatory, geopolitical, or 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.

Municipal Risk: The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market.

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 and Allocation Risk: MFS’ investment analysis, its selection of investments, and its assessment of the risk/return potential of commodity sectors may not produce the intended results and 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.

Financial Services Exposure Risk: Events that affect the financial services sector may have a significant adverse effect on the fund.

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.

Subsidiary Risk: The Subsidiary will not be registered as an investment company under the Investment Company Act of 1940 (the “Act”) and will not be subject to all of the investor protections of the Act. Changes in the laws impacting the fund or the Subsidiary could negatively affect the fund and its shareholders. By investing in the Subsidiary, the fund is exposed to all the risks associated with the Subsidiary’s investments.

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 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.