Risk/Return Detail Data - FidelityGNMAFund-PRO - USD ($) |
12 Months Ended | 60 Months Ended | 120 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 29, 2026 |
Sep. 29, 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 |
Sep. 29, 2026 |
Sep. 29, 2026 |
|
| FidelityGNMAFund-PRO | Fidelity GNMA Fund | Fidelity GNMA Fund | ||||||||||||||
| Prospectus Line Items | ||||||||||||||
| Management Fees (as a percentage of Assets) | 0.28% | |||||||||||||
| Distribution and Service (12b-1) Fees | 0.00% | |||||||||||||
| Other Expenses (as a percentage of Assets): | 0.17% | |||||||||||||
| Expenses (as a percentage of Assets) | 0.45% | |||||||||||||
| Expense Example, with Redemption, 1 Year | $ 46 | |||||||||||||
| Expense Example, with Redemption, 3 Years | 144 | |||||||||||||
| Expense Example, with Redemption, 5 Years | 252 | |||||||||||||
| Expense Example, with Redemption, 10 Years | $ 567 | |||||||||||||
| Average Annual Return, Label [Optional Text] | Return Before Taxes | |||||||||||||
| Average Annual Return, Percent | 7.88% | 0.21% | 1.43% | |||||||||||
| Annual Return [Percent] | 7.88% | 1.02% | 5.43% | (11.28%) | (0.85%) | 3.74% | 5.71% | 0.61% | 1.74% | 1.63% | ||||
| FidelityGNMAFund-PRO | Fidelity GNMA Fund | ||||||||||||||
| Prospectus Line Items | ||||||||||||||
| Risk/Return [Heading] | Fund Summary Fund: Fidelity® GNMA Fund | |||||||||||||
| Objective [Heading] | Investment Objective | |||||||||||||
| Objective, Primary [Text Block] | Fidelity® GNMA Fund seeks a high level of current income, consistent with prudent investment risk. In seeking current income, the fund may also consider the potential for capital gain. | |||||||||||||
| 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 | |||||||||||||
| 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 620 % of the average value of its portfolio. | |||||||||||||
| Portfolio Turnover, Rate | 620.00% | |||||||||||||
| 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 Ginnie Maes and repurchase agreements for Ginnie Maes. Ginnie Maes are U.S. Government securities that represent interests in pools of mortgage loans. Their principal and interest payments are fully guaranteed by the U.S. Government. 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. Investing in other U.S. Government securities and instruments related to U.S. 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. Managing the fund to have similar overall interest rate risk to the Bloomberg GNMA Index. Allocating assets across different market sectors and maturities. 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. | |||||||||||||
| 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. 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 | Jun. 30, 2026 | |||||||||||||
| Bar Chart, Year to Date Return | 1.50% | |||||||||||||
| Highest Quarterly Return, Label [Optional Text] | Highest Quarter Return | |||||||||||||
| Highest Quarterly Return, Date | Dec. 31, 2023 | |||||||||||||
| Highest Quarterly Return | 7.51% | |||||||||||||
| Lowest Quarterly Return, Label [Optional Text] | Lowest Quarter Return | |||||||||||||
| Lowest Quarterly Return, Date | Sep. 30, 2022 | |||||||||||||
| Lowest Quarterly Return | (4.97%) | |||||||||||||
| 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. | |||||||||||||
| FidelityGNMAFund-PRO | Fidelity GNMA Fund | After Taxes on Distributions | Fidelity GNMA Fund | ||||||||||||||
| Prospectus Line Items | ||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions | |||||||||||||
| Average Annual Return, Percent | 6.28% | (0.90%) | 0.42% | |||||||||||
| FidelityGNMAFund-PRO | Fidelity GNMA Fund | After Taxes on Distributions and Sales | Fidelity GNMA Fund | ||||||||||||||
| Prospectus Line Items | ||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions and Sale of Fund Shares | |||||||||||||
| Average Annual Return, Percent | 4.64% | (0.32%) | 0.65% | |||||||||||
| FidelityGNMAFund-PRO | Fidelity GNMA Fund | LB020 | ||||||||||||||
| Prospectus Line Items | ||||||||||||||
| Average Annual Return, Label [Optional Text] | Bloomberg GNMA Index | |||||||||||||
| Average Annual Return, Percent | 8.08% | 0.23% | 1.50% | |||||||||||
| FidelityGNMAFund-PRO | Fidelity GNMA 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 Income Fund | |||||||||||||