Risk/Return Detail Data - FidelityIntermediateMunicipalIncomeFund-ETFClassPRO - USD ($) |
12 Months Ended | 60 Months Ended | 120 Months Ended | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 12, 2026 |
Jun. 12, 2026 |
Dec. 31, 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 |
Jun. 12, 2026 |
Jun. 12, 2026 |
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| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | Fidelity Intermediate Municipal Income Fund - ETF Class | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Management Fees (as a percentage of Assets) | 0.26% | |||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.00% | |||||||||||||||||
| Other Expenses (as a percentage of Assets): | [1] | 0.05% | ||||||||||||||||
| Expenses (as a percentage of Assets) | 0.31% | |||||||||||||||||
| Fee Waiver or Reimbursement | [2] | (0.01%) | ||||||||||||||||
| Net Expenses (as a percentage of Assets) | 0.30% | |||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 31 | |||||||||||||||||
| Expense Example, with Redemption, 3 Years | 98 | |||||||||||||||||
| Expense Example, with Redemption, 5 Years | 172 | |||||||||||||||||
| Expense Example, with Redemption, 10 Years | $ 391 | |||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return Before Taxes | |||||||||||||||||
| Average Annual Return, Percent | 5.04% | 1.27% | 2.29% | |||||||||||||||
| Annual Return [Percent] | 5.04% | 1.37% | 5.51% | (6.27%) | 1.14% | 4.54% | 6.55% | 1.19% | 4.48% | (0.01%) | ||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Risk/Return [Heading] | Fund Summary Fund /Class: Fidelity® Intermediate Municipal Income Fund /ETF Class | |||||||||||||||||
| Objective [Heading] | Investment Objective | |||||||||||||||||
| Objective, Primary [Text Block] | Fidelity® Intermediate Municipal Income Fund seeks as high a level of current income, exempt from federal income tax, as is consistent with the 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's ETF Class. 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 | Apr. 30, 2028 | |||||||||||||||||
| 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 15 % of the average value of its portfolio. | |||||||||||||||||
| Portfolio Turnover, Rate | 15.00% | |||||||||||||||||
| 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's ETF Class with the cost of investing in other funds or classes. Let's say, hypothetically, that the annual return for ETF Class shares of the fund is 5% and that the fees and the annual operating expenses for shares of the fund's ETF Class 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 ETF Class 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 municipal securities whose interest is exempt from federal income tax. The municipal securities in which the fund invests are normally investment-grade (those of medium and high quality). Municipal debt securities are issued to raise money for a variety of public and private purposes, including general financing for state and local governments, financing for eligible non-profit organizations, or financing for a specific project or public facility. Municipal debt securities in which the fund invests include securities issued by U.S. territories and possessions, general obligation bonds of municipalities, local or state governments, project or revenue-specific bonds, or pre-refunded or escrowed bonds, municipal money market securities, and synthetic securities. Municipal securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. Investment grade securities in which the fund invests include securities or issuers rated at least BBB- or its equivalent by at least one nationally recognized statistical ratings organization (NRSRO), or, if unrated, determined by the Adviser to be of comparable quality. 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. Managing the fund to have similar overall interest rate risk to the supplemental index (see "Additional Index Information" section of the prospectus). Normally maintaining a dollar-weighted average maturity between three and 10 years. Allocating assets across different market sectors and maturities. Potentially investing more than 25% of total assets in municipal securities that finance similar types of projects. Analyzing the credit quality of the issuer, security-specific features, current and potential future valuation, and trading opportunities to select 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 ETF Class shares are a new class of shares for which performance information is not available, and therefore, for periods prior to the inception of the ETF Class shares, the bar chart and table show performance information for the Fidelity® Intermediate Municipal Income Fund shares of the fund, a mutual fund class of shares of the fund not offered in this Prospectus. Returns of the ETF Class shares of the fund may vary from the returns of the Fidelity® Intermediate Municipal Income Fund shares due to differences in expenses. The information illustrates the changes in the performance of Fidelity® Intermediate Municipal Income Fund, a class of shares of the fund, from year to year and compares the performance of this class to the performance of a securities market index and additional indexes over various periods of time. The additional indexes have 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. Visit www.fidelity.com for more recent performance information for Fidelity® Intermediate Municipal Income Fund, a class of shares of the fund. Performance history will be available at www.fidelity.com for ETF Class after ETF Class 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® Intermediate Municipal Income Fund, a class of shares of the fund, from year to year and compares the performance of this class to the performance of a securities market index and additional indexes over various periods of time. | |||||||||||||||||
| Performance One Year or Less [Text] | Performance history will be available at www.fidelity.com for ETF Class after ETF Class 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 (before and after taxes) 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® Intermediate Municipal Income Fund, a class of shares of the fund that is not offered through this prospectus. ETF Class would have substantially similar annual returns to Fidelity® Intermediate Municipal Income Fund because the classes are invested in the same portfolio of securities. ETF Class's returns would differ from Fidelity® Intermediate Municipal Income 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, 2026 | |||||||||||||||||
| Bar Chart, Year to Date Return | (0.47%) | |||||||||||||||||
| Highest Quarterly Return, Label [Optional Text] | Highest Quarter Return | |||||||||||||||||
| Highest Quarterly Return, Date | Dec. 31, 2023 | |||||||||||||||||
| Highest Quarterly Return | 6.06% | |||||||||||||||||
| Lowest Quarterly Return, Label [Optional Text] | Lowest Quarter Return | |||||||||||||||||
| Lowest Quarterly Return, Date | Mar. 31, 2022 | |||||||||||||||||
| Lowest Quarterly Return | (5.05%) | |||||||||||||||||
| 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 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. 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. | |||||||||||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | After Taxes on Distributions | Fidelity Intermediate Municipal Income Fund - ETF Class | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions | |||||||||||||||||
| Average Annual Return, Percent | 5.03% | 1.26% | 2.26% | |||||||||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | After Taxes on Distributions and Sales | Fidelity Intermediate Municipal Income Fund - ETF Class | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions and Sale of Fund Shares | |||||||||||||||||
| Average Annual Return, Percent | 4.16% | 1.50% | 2.31% | |||||||||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | IXWQ5 | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Bloomberg 3-15 Year Blend (2-17) Municipal Bond Index | |||||||||||||||||
| Average Annual Return, Percent | 5.30% | 1.10% | 2.34% | |||||||||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | F0083 | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Fidelity Intermediate Municipal Income Linked Index℠ | |||||||||||||||||
| Average Annual Return, Percent | 5.30% | 1.18% | 2.28% | |||||||||||||||
| FidelityIntermediateMunicipalIncomeFund-ETFClassPRO | Fidelity Intermediate Municipal Income Fund | LB015 | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Bloomberg Municipal Bond Index | |||||||||||||||||
| Average Annual Return, Percent | 4.25% | 0.80% | 2.34% | |||||||||||||||
| Document Type | 485BPOS | |||||||||||||||||
| Registrant Name | Fidelity School Street Trust | |||||||||||||||||
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