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MFS U.S. Government Cash Reserve Fund  
Risk/Return: oef_RiskReturnAbstract  
Risk/Return [Heading] oef_RiskReturnHeading MFS® U.S. Government Cash Reserve Fund Summary of Key Information
Objective [Heading] oef_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] oef_ObjectivePrimaryTextBlock

The fund’s investment objective is to seek current income consistent with preservation of capital and liquidity.

Expense Heading [Optional Text] oef_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] oef_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay when you buy, hold, and sell shares of the fund. Investors may also pay commissions or other fees to their financial intermediaries when they buy, hold, and sell shares of the fund, which are not reflected below.
Shareholder Fees Caption [Optional Text] oef_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Optional Text] oef_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):
Expense Example [Heading] oef_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] oef_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.

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 (unless otherwise indicated); your investment has a 5% return each year; and the fund’s operating expenses remain the same.

Expense Example by, Year, Caption [Text] oef_ExpenseExampleByYearCaption Although your actual costs will likely be higher or lower, under these assumptions your costs would be:
Strategy [Heading] oef_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] oef_StrategyNarrativeTextBlock

MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 99.5% of the fund’s total assets in cash, U.S. Government money market instruments, and/or repurchase agreements collateralized by cash or U.S. Government securities. MFS normally invests at least 80% of the fund’s net assets in U.S. Government money market instruments and repurchase agreements collateralized by U.S. Government securities. U.S. Government money market instruments are short-term instruments issued or guaranteed as to the payment of principal and interest by the U.S. Treasury, by an agency or instrumentality of the U.S. Government, or by a U.S. Government-sponsored entity that pay a fixed, variable, or floating interest rate. U.S. Government securities include mortgage-backed securities and other types of asset-backed securities issued or guaranteed by the U.S. Treasury, by an agency or instrumentality of the U.S. Government, or by a U.S. Government-sponsored entity.

In buying and selling investments for the fund, MFS follows U.S. Securities and Exchange Commission (SEC) rules for money market funds regarding credit quality, diversification, liquidity, and maturity. MFS stresses maintaining a stable $1.00 per share price, liquidity, and income.

For purposes of the fund's 80% policy, net assets include the amount of any borrowings for investment purposes.
Bar Chart and Performance Table [Heading] oef_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] oef_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.

The fund’s past performance does not necessarily indicate how the fund will perform in the future. Updated performance is available online at mfs.com or by calling 1-800-225-2606.

Performance Information Illustrates Variability of Returns [Text] oef_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.
Performance Availability Phone [Text] oef_PerformanceAvailabilityPhone 1-800-225-2606
Performance Availability Website Address [Text] oef_PerformanceAvailabilityWebSiteAddress mfs.com
Performance Past Does Not Indicate Future [Text] oef_PerformancePastDoesNotIndicateFuture The fund’s past performance does not necessarily indicate how the fund will perform in the future.
Bar Chart [Heading] oef_BarChartHeading Class A Bar Chart.
Bar Chart Closing [Text Block] oef_BarChartClosingTextBlock

The total return for the nine-month period ended September 30, 2025, was 2.96%. During the period(s) shown in the bar chart, the highest quarterly return was 1.25% (for the calendar quarter ended December 31, 2023) and the lowest quarterly return was 0.00% (for the calendar quarter ended March 31, 2022).
Performance Table Heading oef_PerformanceTableHeading Performance Table.
Average Annual Return, Caption [Optional Text] oef_AverageAnnualReturnCaption Average Annual Total Returns (For the Periods Ended December 31, 2024)
MFS U.S. Government Cash Reserve Fund | Principal Risks  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Principal Risks

You could lose money by investing in the fund. Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The fund’s sponsor is not required to reimburse the fund for losses, and you should not expect that the sponsor will provide financial support to the fund at any time, including during periods of market stress.

The principal risks of investing in the fund are:
MFS U.S. Government Cash Reserve Fund | Risk Lose Money [Member]  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock You could lose money by investing in the fund.
MFS U.S. Government Cash Reserve Fund | Risk Not Insured [Member]  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock An investment in the fund is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
MFS U.S. Government Cash Reserve Fund | Risk Money Market Fund May Not Preserve Dollar [Member]  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock Although the fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so.
MFS U.S. Government Cash Reserve Fund | Interest Rate Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Interest Rate Risk: In general, the price of a money market instrument falls when interest rates rise and rises when interest rates fall. A major or unexpected increase in interest rates could cause the fund's share price to decrease to below $1.00 per share. In addition, a low or negative interest rate environment may prevent the fund from providing a positive yield and could impair the fund's ability to maintain a stable $1.00 per share.
MFS U.S. Government Cash Reserve Fund | Credit and Market Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Credit and Market Risk: The value of a money market instrument depends on the credit quality of the issuer, borrower, counterparty, or other entity responsible for payment. The value of a money market instrument can also decline in response to changes in, or perceptions of, the financial condition of the issuer or borrower, changes in, or perceptions of, specific market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions that affect a particular type of instrument, issuer, or borrower, and changes in, or perceptions of, general market, economic, industry, political, regulatory, geopolitical, environmental, public health, and other conditions.
MFS U.S. Government Cash Reserve Fund | Investment Selection Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

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. In addition, to the extent MFS considers quantitative tools in managing the fund, such tools may not produce the intended results.

MFS U.S. Government Cash Reserve Fund | Redemption Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Redemption Risk: Large or frequent redemptions could cause the fund's share price to decrease to below $1.00 per share.
MFS U.S. Government Cash Reserve Fund | Focus Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Focus Risk: If MFS invests a significant percentage of the fund's assets in a single issuer or small number of issuers, the fund’s performance could be more volatile than the performance of more diversified funds.

MFS U.S. Government Cash Reserve Fund | Counterparty and Third Party Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

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 or willingness to perform in accordance with the terms of the transaction.
MFS U.S. Government Cash Reserve Fund | Liquidity Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Liquidity Risk: It may be difficult to value, and it may not be possible to sell, certain investments, types of investments, and/or investments in certain segments of the market, and the fund may have to sell certain of these investments at prices or times that are not advantageous in order to meet redemptions or other cash needs.

MFS U.S. Government Cash Reserve Fund | Large Shareholder Risk  
Risk/Return: oef_RiskReturnAbstract  
Risk [Text Block] oef_RiskTextBlock

Large Shareholder Risk: From time to time, shareholders of the fund (which may include institutional investors, financial intermediaries, or other MFS funds) may make relatively large redemptions or purchases of fund shares. These transactions may cause the fund to sell securities or invest additional cash, as the case may be, at disadvantageous prices. Redemptions of a large number of shares also may increase transaction and other costs or have adverse tax consequences for shareholders of the fund by requiring a sale of portfolio securities. Purchases of a large number of shares may adversely affect the fund's performance to the extent that it takes time to invest new cash and the fund maintains a larger cash position than it ordinarily would.
MFS U.S. Government Cash Reserve Fund | Class A  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MSRXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.83%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.38%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 227
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 423
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 990
Year to Date Return, Label [Optional Text] oef_YearToDateReturnLabel The total return for the nine-month period ended
Bar Chart, Year to Date Return, Date oef_BarChartYearToDateReturnDate Sep. 30, 2025
Bar Chart, Year to Date Return oef_BarChartYearToDateReturn 2.96%
Highest Quarterly Return, Label [Optional Text] oef_HighestQuarterlyReturnLabel highest quarterly return
Highest Quarterly Return, Date oef_BarChartHighestQuarterlyReturnDate Dec. 31, 2023
Highest Quarterly Return oef_BarChartHighestQuarterlyReturn 1.25%
Lowest Quarterly Return, Label [Optional Text] oef_LowestQuarterlyReturnLabel lowest quarterly return
Lowest Quarterly Return, Date oef_BarChartLowestQuarterlyReturnDate Mar. 31, 2022
Lowest Quarterly Return oef_BarChartLowestQuarterlyReturn none
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
Annual Return [Percent] oef_AnnlRtrPct none
Annual Return [Percent] oef_AnnlRtrPct 0.01%
Annual Return [Percent] oef_AnnlRtrPct 0.20%
Annual Return [Percent] oef_AnnlRtrPct 1.12%
Annual Return [Percent] oef_AnnlRtrPct 1.46%
Annual Return [Percent] oef_AnnlRtrPct 0.17%
Annual Return [Percent] oef_AnnlRtrPct 0.01%
Annual Return [Percent] oef_AnnlRtrPct 1.19%
Annual Return [Percent] oef_AnnlRtrPct 4.59%
Annual Return [Percent] oef_AnnlRtrPct 4.87%
MFS U.S. Government Cash Reserve Fund | Class B  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCRXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 4.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.58%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (1.13%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 446 [2]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 688 [2]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 953 [2]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,579 [2]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 46 [2]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 388 [2]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 753 [2]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,579 [2]
Average Annual Return, Percent oef_AvgAnnlRtrPct 0.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.77%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class C  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MCCXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 1.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.58%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (1.13%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 146 [2]
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 388 [2]
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 753 [2]
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 1,579 [2]
Expense Example, No Redemption, 1 Year oef_ExpenseExampleNoRedemptionYear01 46 [2]
Expense Example, No Redemption, 3 Years oef_ExpenseExampleNoRedemptionYear03 388 [2]
Expense Example, No Redemption, 5 Years oef_ExpenseExampleNoRedemptionYear05 753 [2]
Expense Example, No Redemption, 10 Years oef_ExpenseExampleNoRedemptionYear10 $ 1,579 [2]
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class I  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRHXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.58%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.13%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 173
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 311
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 713
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class R1  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRVXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.58%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (1.13%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 388
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 753
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,782
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class R2  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRMXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 1.08%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.63%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 281
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 534
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 1,260
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class R3  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRJXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.83%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.38%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 227
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 423
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 990
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class R4  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRKXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.58%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.13%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.45%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 46
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 173
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 311
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 713
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.35%
MFS U.S. Government Cash Reserve Fund | Class R6  
Risk/Return: oef_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol CRRXX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 0.00%
Maximum Deferred Sales Charge (as a percentage of Offering Price) oef_MaximumDeferredSalesChargeOverOfferingPrice 0.00%
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.13%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.53%
Fee Waiver or Reimbursement oef_FeeWaiverOrReimbursementOverAssets (0.16%) [1]
Net Expenses (as a percentage of Assets) oef_NetExpensesOverAssets 0.37%
Fee Waiver or Reimbursement over Assets, Date of Termination oef_FeeWaiverOrReimbursementOverAssetsDateOfTermination December 31, 2026
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 38
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 154
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 280
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 650
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.92%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.18%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.37%
[1] Massachusetts Financial Services Company (MFS) has agreed in writing to waive at least 0.01% of the fund's management fee as part of an agreement pursuant to which MFS has agreed to reduce its management fee by a specified amount if certain MFS mutual fund assets exceed thresholds agreed to by MFS and the fund's Board of Trustees. The agreement to waive at least 0.01% of the management fee will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2026. MFS Fund Distributors, Inc. (MFD), has agreed in writing to waive the Class B, Class C, Class R1, and Class R2 distribution fee to 0.00% of each class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2026. MFD has agreed in writing to waive the Class A, Class B, Class C, Class R1, Class R2, and Class R3 service fee to 0.00% of each class' average daily net assets annually until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2026. MFS has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 0.45% of the class' average daily net assets annually for each of Class A, Class B, Class C, Class I, Class R1, Class R2, Class R3, and Class R4 shares, and 0.37% of the class' average daily net assets annually for Class R6 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least December 31, 2026.
[2] Shares automatically convert to Class A shares approximately eight years after purchase; therefore, the expense examples reflect Class A share expenses after eight years.