Risk/Return Detail Data - FidelityShort-TermBondFund-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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| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | Fidelity Short-Term Bond Fund - ETF Class | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Management Fees (as a percentage of Assets) | 0.20% | |||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.00% | |||||||||||||||||
| Other Expenses (as a percentage of Assets): | [1] | 0.01% | ||||||||||||||||
| Expenses (as a percentage of Assets) | 0.21% | |||||||||||||||||
| Fee Waiver or Reimbursement | [2] | (0.01%) | ||||||||||||||||
| Net Expenses (as a percentage of Assets) | 0.20% | |||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 20 | |||||||||||||||||
| Expense Example, with Redemption, 3 Years | 66 | |||||||||||||||||
| Expense Example, with Redemption, 5 Years | 117 | |||||||||||||||||
| Expense Example, with Redemption, 10 Years | $ 266 | |||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return Before Taxes | |||||||||||||||||
| Average Annual Return, Percent | 5.47% | 2.16% | 2.25% | |||||||||||||||
| Annual Return [Percent] | 5.47% | 4.71% | 5.34% | (3.62%) | (0.73%) | 3.70% | 4.20% | 1.19% | 1.15% | 1.45% | ||||||||
| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Risk/Return [Heading] | Fund Summary Fund /Class: Fidelity® Short-Term Bond Fund /ETF Class | |||||||||||||||||
| Objective [Heading] | Investment Objective | |||||||||||||||||
| Objective, Primary [Text Block] | Fidelity® Short-Term Bond Fund seeks to obtain 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'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 | Dec. 31, 2027 | |||||||||||||||||
| 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 59 % of the average value of its portfolio. | |||||||||||||||||
| Portfolio Turnover, Rate | 59.00% | |||||||||||||||||
| 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 investment-grade debt securities (those of medium and high quality) of all types and repurchase agreements for those securities. Debt securities are used by issuers to borrow money. 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. Debt securities include corporate bonds, government securities (including Treasury securities), repurchase agreements, money market securities, mortgage and other asset-backed securities, loans and loan participations, and other securities, such as hybrids and synthetic securities, believed to have debt-like characteristics (e.g., securities classified as Tier 2 Regulatory capital, securities that rank above share capital in an insolvency waterfall, securities with maturity dates and non-cancellable interest payment structures). 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. 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. 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 Bloomberg U.S. 1-3 Year Government/Credit Bond Index. Normally maintaining a dollar-weighted average maturity of three years or less. Allocating assets across different market sectors and maturities. Investing in domestic and foreign issuers. Analyzing the credit quality of the issuer, security-specific features, current and potential future valuation, and trading opportunities to select investments. Engaging in transactions that have a leveraging effect on the fund, including investments in derivatives - such as swaps (interest rate, total return, and credit default), options, and futures contracts - and forward-settling securities, to adjust the fund's risk exposure. Investing in Fidelity's Central funds (specialized investment vehicles used by Fidelity® funds to invest in particular security types or investment disciplines) consistent with the asset classes discussed above. | |||||||||||||||||
| 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® Short-Term Bond 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® Short-Term Bond Fund shares due to differences in expenses. The information illustrates the changes in the performance of Fidelity® Short-Term Bond 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 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. Visit www.fidelity.com for more recent performance information for Fidelity® Short-Term Bond 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® Short-Term Bond 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 an additional index 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® Short-Term Bond 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® Short-Term Bond Fund because the classes are invested in the same portfolio of securities. ETF Class's returns would differ from Fidelity® Short-Term Bond 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 | 0.26% | |||||||||||||||||
| Highest Quarterly Return, Label [Optional Text] | Highest Quarter Return | |||||||||||||||||
| Highest Quarterly Return, Date | Jun. 30, 2020 | |||||||||||||||||
| Highest Quarterly Return | 2.98% | |||||||||||||||||
| Lowest Quarterly Return, Label [Optional Text] | Lowest Quarter Return | |||||||||||||||||
| Lowest Quarterly Return, Date | Mar. 31, 2022 | |||||||||||||||||
| Lowest Quarterly Return | (2.50%) | |||||||||||||||||
| 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. | |||||||||||||||||
| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | After Taxes on Distributions | Fidelity Short-Term Bond Fund - ETF Class | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions | |||||||||||||||||
| Average Annual Return, Percent | 3.65% | 1.05% | 1.32% | |||||||||||||||
| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | After Taxes on Distributions and Sales | Fidelity Short-Term Bond 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 | 3.21% | 1.18% | 1.33% | |||||||||||||||
| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | LB013 | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Bloomberg U.S. 1-3 Year Government/Credit Bond Index | |||||||||||||||||
| Average Annual Return, Percent | 5.35% | 1.97% | 2.09% | |||||||||||||||
| FidelityShort-TermBondFund-ETFClassPRO | Fidelity Short-Term Bond Fund | LB001 | ||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Bloomberg U.S. Aggregate Bond Index | |||||||||||||||||
| Average Annual Return, Percent | 7.30% | (0.36%) | 2.01% | |||||||||||||||
| Document Type | 485BPOS | |||||||||||||||||
| Registrant Name | Fidelity Salem Street Trust | |||||||||||||||||
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