v3.25.2
Risk/Return Detail Data - FidelitySeriesTreasuryBillIndexFund-PRO - USD ($)
 12 Months Ended 48 Months Ended 60 Months Ended 84 Months Ended 96 Months Ended 120 Months Ended
Jun. 28, 2025
Jun. 28, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Jun. 28, 2025
 [18]
Jun. 28, 2025
Jun. 28, 2025
Jun. 28, 2025
Jun. 28, 2025
FidelityGovernmentMoneyMarketFundFidelityMoneyMarketFund-PremiumComboPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Premium Class                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.11%                                
Expenses (as a percentage of Assets) 0.36%                                
Fee Waiver or Reimbursement [1] (0.04%)                                
Net Expenses (as a percentage of Assets) 0.32%                                
Expense Example, with Redemption, 1 Year $ 33                                
Expense Example, with Redemption, 3 Years 110                                
Expense Example, with Redemption, 5 Years 197                                
Expense Example, with Redemption, 10 Years $ 450                                
Annual Return, Inception Date Apr. 06, 2015                                
Average Annual Return, Label [Optional Text]   Premium Class                              
Average Annual Return, Percent   5.02%                       2.29%     1.61% [2]
Annual Return [Percent]     5.02% 4.88% 1.37% 0.01% 0.29% 1.95% 1.58% 0.61% 0.13%            
FidelityGovernmentMoneyMarketFundFidelityMoneyMarketFund-PremiumComboPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /Premium                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.02%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.29%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityGovernmentMoneyMarketFundFidelityMoneyMarketFund-PremiumComboPRO | Fidelity Money Market Fund | Fidelity Money Market Fund - Premium Class                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.11%                                
Expenses (as a percentage of Assets) 0.36%                                
Fee Waiver or Reimbursement [3] (0.06%)                                
Net Expenses (as a percentage of Assets) 0.30%                                
Expense Example, with Redemption, 1 Year $ 31                                
Expense Example, with Redemption, 3 Years 107                                
Expense Example, with Redemption, 5 Years 194                                
Expense Example, with Redemption, 10 Years $ 448                                
Annual Return, Inception Date Apr. 06, 2015                                
Average Annual Return, Label [Optional Text]   Premium Class                              
Average Annual Return, Percent   5.11%                       2.40%     1.79% [4]
Annual Return [Percent]     5.11% 5.00% 1.58% 0.01% 0.42% 2.13% 1.87% 1.01% 0.48%            
FidelityGovernmentMoneyMarketFundFidelityMoneyMarketFund-PremiumComboPRO | Fidelity Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Money Market Fund /Premium                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Investing in U.S. dollar-denominated money market securities of domestic and foreign issuers and repurchase agreements. Investing more than 25% of total assets in the financial services industries. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.03%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.32%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2021                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityGovernmentMoneyMarketFund-K6PRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Class K6                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.02%                                
Expenses (as a percentage of Assets) 0.27%                                
Fee Waiver or Reimbursement [5] (0.02%)                                
Net Expenses (as a percentage of Assets) 0.25%                                
Expense Example, with Redemption, 1 Year $ 26                                
Expense Example, with Redemption, 3 Years 84                                
Expense Example, with Redemption, 5 Years 149                                
Expense Example, with Redemption, 10 Years $ 341                                
Annual Return, Inception Date Jan. 24, 2018                                
Average Annual Return, Label [Optional Text]   Class K6                              
Average Annual Return, Percent   5.09%                       2.34% 2.20% [6]    
Annual Return [Percent]     5.09% 4.95% 1.43% 0.01% 0.32% 2.02%                  
FidelityGovernmentMoneyMarketFund-K6PRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /K6                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.401k.com and log in for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.401k.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.03%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.31%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2021                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityGovernmentMoneyMarketFund-DailyMoneyPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Daily Money Class                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.25%                                
Other Expenses (as a percentage of Assets): 0.21%                                
Expenses (as a percentage of Assets) 0.71%                                
Fee Waiver or Reimbursement [7] (0.01%)                                
Net Expenses (as a percentage of Assets) 0.70%                                
Expense Example, with Redemption, 1 Year $ 72                                
Expense Example, with Redemption, 3 Years 226                                
Expense Example, with Redemption, 5 Years 394                                
Expense Example, with Redemption, 10 Years $ 881                                
Annual Return, Inception Date Apr. 06, 2015                                
Average Annual Return, Label [Optional Text]   Daily Money Class                              
Average Annual Return, Percent   4.62%                       2.07%     1.36% [8]
Annual Return [Percent]     4.62% 4.49% 1.12% 0.01% 0.19% 1.56% 1.19% 0.24% 0.01%            
FidelityGovernmentMoneyMarketFund-DailyMoneyPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /Daily Money                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit institutional.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] institutional.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.92%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.19%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityGovernmentMoneyMarketFund-AdvisorMPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Class M                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.25%                                
Other Expenses (as a percentage of Assets): 0.21%                                
Expenses (as a percentage of Assets) 0.71%                                
Fee Waiver or Reimbursement [9] (0.01%)                                
Net Expenses (as a percentage of Assets) 0.70%                                
Expense Example, with Redemption, 1 Year $ 72                                
Expense Example, with Redemption, 3 Years 226                                
Expense Example, with Redemption, 5 Years 394                                
Expense Example, with Redemption, 10 Years $ 881                                
Annual Return, Inception Date Jul. 06, 2017                                
Average Annual Return, Label [Optional Text]   Advisor M Class                              
Average Annual Return, Percent   4.62%                       2.07%   1.77% [10]  
Annual Return [Percent]     4.62% 4.48% 1.12% 0.01% 0.20% 1.58% 1.20%                
FidelityGovernmentMoneyMarketFund-AdvisorMPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /Advisor M                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit institutional.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] institutional.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.92%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.19%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2021                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityFlexGovernmentMoneyMarketFund-PRO | Fidelity Flex Government Money Market Fund | Fidelity Flex Government Money Market Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.00%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.00%                                
Expenses (as a percentage of Assets) [11] 0.00%                                
Expense Example, with Redemption, 1 Year $ 0                                
Expense Example, with Redemption, 3 Years 0                                
Expense Example, with Redemption, 5 Years 0                                
Expense Example, with Redemption, 10 Years $ 0                                
Annual Return, Inception Date Mar. 08, 2017                                
Average Annual Return, Label [Optional Text]   Fidelity Flex® Government Money Market Fund                              
Average Annual Return, Percent   5.37%                       2.54%   2.26% [12]  
Annual Return [Percent]     5.37% 5.22% 1.67% 0.07% 0.49% 2.27% 1.91%                
FidelityFlexGovernmentMoneyMarketFund-PRO | Fidelity Flex Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund: Fidelity Flex® Government Money Market Fund                                
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity Flex® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions , which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. This example does not include any fees paid at the fee-based account or plan level. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. The performance shown does not reflect the impact of any fees paid at the fee-based account or plan level. Visit www.401k.com and log in or www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.401k.com and log in or www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.09%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.37%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Jun. 30, 2021                                
Lowest Quarterly Return 0.01%                                
Performance Table Heading Average Annual Returns                                
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.17%                                
Expenses (as a percentage of Assets) 0.42%                                
Expense Example, with Redemption, 1 Year $ 43                                
Expense Example, with Redemption, 3 Years 135                                
Expense Example, with Redemption, 5 Years 235                                
Expense Example, with Redemption, 10 Years $ 530                                
Average Annual Return, Label [Optional Text]   Fidelity® Government Money Market Fund                              
Average Annual Return, Percent   4.92%                       2.23%     1.50%
Annual Return [Percent]     4.92% 4.78% 1.31% 0.01% 0.26% 1.84% 1.47% 0.51% 0.04% 0.01%          
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /Fidelity® Government Money Market Fund                                
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.99%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.26%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Money Market Fund | Fidelity Money Market Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.17%                                
Expenses (as a percentage of Assets) 0.42%                                
Expense Example, with Redemption, 1 Year $ 43                                
Expense Example, with Redemption, 3 Years 135                                
Expense Example, with Redemption, 5 Years 235                                
Expense Example, with Redemption, 10 Years $ 530                                
Average Annual Return, Label [Optional Text]   Fidelity® Money Market Fund                              
Average Annual Return, Percent   4.98%                       2.32%     1.66%
Annual Return [Percent]     4.98% 4.87% 1.49% 0.01% 0.36% 2.01% 1.75% 0.89% 0.36% 0.01%          
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Money Market Fund /Fidelity® Money Market Fund                                
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Investing in U.S. dollar-denominated money market securities of domestic and foreign issuers and repurchase agreements. Investing more than 25% of total assets in the financial services industries. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.00%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.29%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Treasury Only Money Market Fund | Fidelity Treasury Only Money Market Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.42%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.00%                                
Expenses (as a percentage of Assets) 0.42%                                
Expense Example, with Redemption, 1 Year $ 43                                
Expense Example, with Redemption, 3 Years 135                                
Expense Example, with Redemption, 5 Years 235                                
Expense Example, with Redemption, 10 Years $ 530                                
Average Annual Return, Label [Optional Text]   Fidelity® Treasury Only Money Market Fund                              
Average Annual Return, Percent   4.90%                       2.19%     1.47%
Annual Return [Percent]     4.90% 4.65% 1.26% 0.01% 0.26% 1.81% 1.47% 0.47% 0.01% 0.01%          
FidelityHerefordStreetTrustFunds-RetailComboPRO | Fidelity Treasury Only Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Treasury Only Money Market Fund /Fidelity® Treasury Only Money Market Fund                                
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Treasury Only Money Market Fund seeks as high a level of current income as is consistent with the security of principal and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash and U.S. Treasury securities. Normally investing in securities whose interest is exempt from state and local income taxes. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Treasury securities. Treasury securities are high-quality securities issued or guaranteed by the U.S. Treasury. Treasury securities are backed by the full faith and credit of the U.S. Treasury. Treasury securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.98%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.27%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityGovernmentMoneyMarketFund-CapitalReservesPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Capital Reserves Class                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.50%                                
Other Expenses (as a percentage of Assets): 0.21%                                
Expenses (as a percentage of Assets) 0.96%                                
Fee Waiver or Reimbursement [13] (0.01%)                                
Net Expenses (as a percentage of Assets) 0.95%                                
Expense Example, with Redemption, 1 Year $ 97                                
Expense Example, with Redemption, 3 Years 305                                
Expense Example, with Redemption, 5 Years 530                                
Expense Example, with Redemption, 10 Years $ 1,177                                
Annual Return, Inception Date Apr. 06, 2015                                
Average Annual Return, Label [Optional Text]   Capital Reserves Class                              
Average Annual Return, Percent   4.36%                       1.92%     1.22% [14]
Annual Return [Percent]     4.36% 4.23% 0.97% 0.01% 0.14% 1.31% 0.94% 0.09% 0.01%            
FidelityGovernmentMoneyMarketFund-CapitalReservesPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /Capital Reserves                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit institutional.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] institutional.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.86%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.13%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityTreasuryDigitalFund-PRO | Fidelity Treasury Digital Fund | Fidelity Treasury Digital Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): [15] 0.00%                                
Expenses (as a percentage of Assets) 0.25%                                
Fee Waiver or Reimbursement [16] (0.07%)                                
Net Expenses (as a percentage of Assets) 0.18%                                
Expense Example, with Redemption, 1 Year $ 18                                
Expense Example, with Redemption, 3 Years $ 63                                
FidelityTreasuryDigitalFund-PRO | Fidelity Treasury Digital Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund/Class: Fidelity® Treasury Digital Fund/Liquidity                                 
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Treasury Digital Fund seeks to obtain as high a level of current income as is consistent with the preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2027                                
Other Expenses, New Fund, Based on Estimates [Text] Based on estimated amounts for the current fiscal year.                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash and U.S. Treasury securities.Normally investing in securities whose interest is exempt from state and local income taxes.Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Treasury securities. Treasury securities are high-quality securities issued or guaranteed by the U.S. Treasury. Treasury securities are backed by the full faith and credit of the U.S. Treasury. Treasury securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] Performance history will be available for the fund after the fund has been in operation for one calendar year.                                
Performance One Year or Less [Text] Performance history will be available for the fund after the fund has been in operation for one calendar year.                                
FidelityGovernmentMoneyMarketFund-ClassSPRO | Fidelity Government Money Market Fund | Fidelity Government Money Market Fund - Class S                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.25%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.21%                                
Expenses (as a percentage of Assets) 0.46%                                
Fee Waiver or Reimbursement [17] (0.04%)                                
Net Expenses (as a percentage of Assets) 0.42%                                
Expense Example, with Redemption, 1 Year $ 43                                
Expense Example, with Redemption, 3 Years 142                                
Expense Example, with Redemption, 5 Years 252                                
Expense Example, with Redemption, 10 Years $ 574                                
Annual Return, Inception Date Dec. 02, 2021                                
Average Annual Return, Label [Optional Text]   Class S                              
Average Annual Return, Percent   4.92%                     3.55%        
Annual Return [Percent]     4.92% 4.78% 1.31%                        
FidelityGovernmentMoneyMarketFund-ClassSPRO | Fidelity Government Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Government Money Market Fund /S                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Government Money Market Fund seeks as high a level of current income as is consistent with preservation of capital and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Fee Waiver or Reimbursement over Assets, Date of Termination Aug. 31, 2026                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash, U.S. Government securities and/or repurchase agreements that are collateralized fully (i.e., collateralized by cash or government securities). Investing in U.S. Government securities issued by entities that are chartered or sponsored by Congress but whose securities are neither issued nor guaranteed by the U.S. Treasury. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Government securities and repurchase agreements for those securities. U.S. Government securities are high-quality securities issued or guaranteed by the U.S. Treasury or by an agency or instrumentality of the U.S. Government. U.S. Government securities may be backed by the full faith and credit of the U.S. Treasury, the right to borrow from the U.S. Treasury, or the agency or instrumentality issuing or guaranteeing the security. Certain issuers of U.S. Government securities, including Fannie Mae, Freddie Mac, and the Federal Home Loan Banks, are sponsored or chartered by Congress but their securities are neither issued nor guaranteed by the U.S. Treasury. The issuer usually pays a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. A repurchase agreement is an agreement to buy a security at one price and a simultaneous agreement to sell it back at an agreed-upon price. A repurchase agreement entered into by the fund may be collateralized by U.S. Government securities or cash.                                 
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.99%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.26%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelityTreasuryOnlyMoneyMarketFund-ClassOUSPRO | Fidelity Treasury Only Money Market Fund | Fidelity Treasury Only Money Market Fund - Class OUS                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.37%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): [19] 0.00%                                
Expenses (as a percentage of Assets) 0.37%                                
Expense Example, with Redemption, 1 Year $ 38                                
Expense Example, with Redemption, 3 Years 119                                
Expense Example, with Redemption, 5 Years 208                                
Expense Example, with Redemption, 10 Years $ 468                                
FidelityTreasuryOnlyMoneyMarketFund-ClassOUSPRO | Fidelity Treasury Only Money Market Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Treasury Only Money Market Fund /OUS                                  
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Treasury Only Money Market Fund seeks as high a level of current income as is consistent with the security of principal and liquidity.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Other Expenses, New Fund, Based on Estimates [Text] Based on estimated amounts for the current fiscal year.                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 99.5% of total assets in cash and U.S. Treasury securities. Normally investing in securities whose interest is exempt from state and local income taxes. Investing in compliance with industry-standard regulatory requirements for money market funds for the quality, maturity, liquidity, and diversification of investments. In addition, the fund normally invests at least 80% of its assets in U.S. Treasury securities. Treasury securities are high-quality securities issued or guaranteed by the U.S. Treasury. Treasury securities are backed by the full faith and credit of the U.S. Treasury. Treasury securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of Fidelity ® Treasury Only Money Market Fund, a class of shares of the fund, from year to year.   Past performance is not an indication of future performance. Visit www.fidelity.com for more recent performance information for Fidelity® Treasury Only Money Market Fund, a class of shares of the fund. Performance history will be available at www.netbenefits.com for Class OUS after Class OUS has been in operation for one calendar year.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of Fidelity ® Treasury Only Money Market Fund, a class of shares of the fund, from year to year.                                
Performance One Year or Less [Text] Performance history will be available at www.netbenefits.com for Class OUS after Class OUS has been in operation for one calendar year.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Bar Chart, Returns for Class Not Offered in Prospectus [Text] * The returns shown above are for Fidelity® Treasury Only Money Market Fund, a class of shares of the fund that is not offered through this prospectus. Class OUS   would have substantially similar annual returns to Fidelity® Treasury Only Money Market Fund because the classes are invested in the same portfolio of securities. Class OUS's   returns would differ from Fidelity® Treasury Only Money Market Fund's returns only to the extent that the classes do not have the same expenses.                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 0.98%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Dec. 31, 2023                                
Highest Quarterly Return 1.27%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return none                                
Performance Table Heading Average Annual Returns                                
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund | Fidelity Series Treasury Bill Index Fund                                  
Prospectus Line Items                                  
Management Fees (as a percentage of Assets) 0.00%                                
Distribution and Service (12b-1) Fees 0.00%                                
Other Expenses (as a percentage of Assets): 0.00%                                
Expenses (as a percentage of Assets) 0.00%                                
Expense Example, with Redemption, 1 Year $ 0                                
Expense Example, with Redemption, 3 Years 0                                
Expense Example, with Redemption, 5 Years 0                                
Expense Example, with Redemption, 10 Years $ 0                                
Annual Return, Inception Date Aug. 17, 2018                                
Average Annual Return, Label [Optional Text]   Return Before Taxes                              
Average Annual Return, Percent   5.33%                       2.52% 2.48% [20]    
Annual Return [Percent]     5.33% 5.13% 1.32% 0.06% 0.85% 2.44%                  
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund                                  
Prospectus Line Items                                  
Risk/Return [Heading] Fund Summary Fund: Fidelity® Series Treasury Bill Index Fund                                
Objective [Heading] Investment Objective                                
Objective, Primary [Text Block] Fidelity® Series Treasury Bill Index Fund seeks a high level of current income consistent with preservation of capital.                                
Expense Heading [Optional Text] Fee Table                                
Expense Narrative [Text Block] The following table describes the fees and expenses that may be incurred when you buy, hold, and sell shares of the fund.                                
Shareholder Fees Caption [Optional Text] Shareholder fees                                
Shareholder Fee, Other $ 0                                
Operating Expenses Caption [Optional Text] Annual Operating Expenses                                
Portfolio Turnover [Heading] Portfolio Turnover                                
Portfolio Turnover [Text Block] 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 and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 0 % of the average value of its portfolio.                                
Portfolio Turnover, Rate none                                
Expense Example Narrative [Text Block] This example helps compare the cost of investing in the fund with the cost of investing in other funds. Let's say, hypothetically, that the annual return for shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund are exactly as described in the fee table. This example illustrates the effect of fees and expenses, but is not meant to suggest actual or expected fees and expenses or returns, all of which may vary. For every $10,000 you invested, here's how much you would pay in total expenses if you sell all of your shares at the end of each time period indicated:                                
Strategy [Heading] Principal Investment Strategies                                
Strategy Narrative [Text Block] Normally investing at least 80% of assets in securities included in the Bloomberg U.S. 3-6 Month Treasury Bill Index . The index is a market capitalization-weighted index of investment-grade, fixed-rate public obligations of the U.S. Treasury with maturities from 3 up to (but not including) 6 months, excluding zero coupon strips. Effective December 11, 2025, derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives. Using statistical sampling techniques based on duration, maturity, interest rate sensitivity, security structure, and credit quality to attempt to replicate the returns of the Bloomberg U.S. 3-6 Month Treasury Bill Index using a smaller number of securities.                                
Bar Chart and Performance Table [Heading] Performance                                
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance (before and after taxes) is not an indication of future performance. The performance shown does not reflect the impact of any fees paid at the fee-based account or plan level, if applicable. Visit www.fidelity.com for more recent performance information.                                
Performance Information Illustrates Variability of Returns [Text] The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time.                                
Performance Availability Website Address [Text] www.fidelity.com                                
Performance Past Does Not Indicate Future [Text] Past performance (before and after taxes) is not an indication of future performance.                                
Bar Chart [Heading] Year-by-Year Returns                                
Year to Date Return, Label [Optional Text]    Year-to-Date Return                                
Bar Chart, Year to Date Return, Date Mar. 31, 2025                                
Bar Chart, Year to Date Return 1.07%                                
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                                
Highest Quarterly Return, Date Sep. 30, 2024                                
Highest Quarterly Return 1.52%                                
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                                
Lowest Quarterly Return, Date Mar. 31, 2022                                
Lowest Quarterly Return (0.04%)                                
Performance Table Heading Average Annual Returns                                
Performance Table Uses Highest Federal Rate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes.                                
Performance Table Not Relevant to Tax Deferred The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan).                                
Performance Table Explanation after Tax Higher Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.                                
Performance Table Narrative After-tax returns are calculated using the historical highest individual federal marginal income tax rates, but do not reflect the impact of state or local taxes. Actual after-tax returns may differ depending on your individual circumstances. The after-tax returns shown are not relevant if you hold your shares in a retirement account or in another tax-deferred arrangement, such as an employee benefit plan (profit sharing, 401(k), or 403(b) plan). Return After Taxes on Distributions and Sale of Fund Shares may be higher than other returns for the same period due to a tax benefit of realizing a capital loss upon the sale of fund shares.                                
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund | After Taxes on Distributions | Fidelity Series Treasury Bill Index Fund                                  
Prospectus Line Items                                  
Average Annual Return, Label [Optional Text]   Return After Taxes on Distributions                              
Average Annual Return, Percent   3.27%                       1.46% 1.44% [20]    
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund | After Taxes on Distributions and Sales | Fidelity Series Treasury Bill Index Fund                                  
Prospectus Line Items                                  
Average Annual Return, Label [Optional Text]   Return After Taxes on Distributions and Sale of Fund Shares                              
Average Annual Return, Percent   3.22%                       1.48% 1.46% [20]    
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund | LB151                                  
Prospectus Line Items                                  
Average Annual Return, Label [Optional Text]   Bloomberg U.S. 3-6 Month Treasury Bill Index                              
Average Annual Return, Percent   5.33%                       2.52% 2.49%    
FidelitySeriesTreasuryBillIndexFund-PRO | Fidelity Series Treasury Bill Index Fund | LB001                                  
Prospectus Line Items                                  
Average Annual Return, Label [Optional Text]   Bloomberg U.S. Aggregate Bond Index                              
Average Annual Return, Percent   1.25%                       (0.33%) 1.24%    
Document Type 485BPOS                                
Registrant Name Fidelity Hereford Street Trust                                
[1]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Premium Class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.32% (the Expense Cap). If at any time during the current fiscal year expenses for Premium Class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[2]
A From April 6, 2015 .
[3]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Premium Class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.30% (the Expense Cap). If at any time during the current fiscal year expenses for Premium Class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[4]
A From April 6, 2015 .
[5]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Class K6 of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.25% (the Expense Cap). If at any time during the current fiscal year expenses for Class K6 of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[6]
A From January 24, 2018 .
[7]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Daily Money Class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.70% (the Expense Cap). If at any time during the current fiscal year expenses for Daily Money Class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[8]
A From April 6, 2015 .
[9]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Advisor M Class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.70% (the Expense Cap). If at any time during the current fiscal year expenses for Advisor M Class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[10]
A From July 6, 2017 .
[11]
A The fund is available only to certain fee-based accounts and advisory programs offered by Fidelity. Advisory account clients, retirement plans, plan sponsors and/or plan participants typically pay an advisory fee that generally covers investment advisory and administrative services.
[12]
A From March 8, 2017 .
[13]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Capital Reserves Class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.95% (the Expense Cap). If at any time during the current fiscal year expenses for Capital Reserves Class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[14]
A From April 6, 2015 .
[15] ABased on estimated amounts for the current fiscal year.
[16] BFidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Liquidity class of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, proxy and shareholder meeting expenses, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.18% (the Expense Cap). If at any time during the current fiscal year expenses for Liquidity class of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2027. FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[17]
A Fidelity Management & Research Company LLC (FMR) has contractually agreed to reimburse Class S of the fund to the extent that total operating expenses (excluding interest, certain taxes, fees and expenses of the Independent Trustees, extraordinary expenses, and acquired fund fees and expenses (including fees and expenses associated with a wholly owned subsidiary), if any, as well as non-operating expenses such as brokerage commissions and fees and expenses associated with the fund's securities lending program, if applicable), as a percentage of its average net assets, exceed 0.42% (the Expense Cap). If at any time during the current fiscal year expenses for Class S of the fund fall below the Expense Cap, FMR reserves the right to recoup through the end of the fiscal year any expenses that were reimbursed during the current fiscal year up to, but not in excess of, the Expense Cap. This arrangement will remain in effect through August 31, 2026 . FMR may not terminate this arrangement before the expiration date without the approval of the Board of Trustees and may extend it in its discretion after that date.
[18]
A From December 2, 2021 .
[19]
A Based on estimated amounts for the current fiscal year.
[20]
A From August 17, 2018 .