Risk/Return Detail Data - SelectUtilitiesPortfolio-AMCIZPro - USD ($) |
12 Months Ended | 60 Months Ended | 120 Months Ended | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2025 |
Sep. 30, 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 |
Sep. 30, 2025 |
Sep. 30, 2025 |
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| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | Fidelity Advisor Utilities Fund - Class A | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Maximum Cumulative Sales Charge (as a percentage of Offering Price) | 5.75% | |||||||||||||||||||
| Maximum Deferred Sales Charge (as a percentage) | [1] | 0.00% | ||||||||||||||||||
| Management Fees (as a percentage of Assets) | [2] | 0.68% | ||||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.25% | |||||||||||||||||||
| Other Expenses (as a percentage of Assets): | [2] | 0.02% | ||||||||||||||||||
| Expenses (as a percentage of Assets) | 0.95% | |||||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 666 | |||||||||||||||||||
| Expense Example, with Redemption, 3 Years | 860 | |||||||||||||||||||
| Expense Example, with Redemption, 5 Years | 1,070 | |||||||||||||||||||
| Expense Example, with Redemption, 10 Years | 1,674 | |||||||||||||||||||
| Expense Example, No Redemption, 1 Year | 666 | |||||||||||||||||||
| Expense Example, No Redemption, 3 Years | 860 | |||||||||||||||||||
| Expense Example, No Redemption, 5 Years | 1,070 | |||||||||||||||||||
| Expense Example, No Redemption, 10 Years | $ 1,674 | |||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return Before Taxes | |||||||||||||||||||
| Average Annual Return, Percent | 28.73% | 9.64% | 9.72% | |||||||||||||||||
| Annual Return [Percent] | 28.73% | (1.17%) | 5.22% | 17.68% | 0.57% | 22.66% | 8.58% | 17.96% | 14.00% | (10.89%) | ||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | Fidelity Advisor Utilities Fund - Class M | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Maximum Cumulative Sales Charge (as a percentage of Offering Price) | 3.50% | |||||||||||||||||||
| Maximum Deferred Sales Charge (as a percentage) | [1] | 0.00% | ||||||||||||||||||
| Management Fees (as a percentage of Assets) | [2] | 0.68% | ||||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.50% | |||||||||||||||||||
| Other Expenses (as a percentage of Assets): | [2] | 0.02% | ||||||||||||||||||
| Expenses (as a percentage of Assets) | 1.20% | |||||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 468 | |||||||||||||||||||
| Expense Example, with Redemption, 3 Years | 718 | |||||||||||||||||||
| Expense Example, with Redemption, 5 Years | 987 | |||||||||||||||||||
| Expense Example, with Redemption, 10 Years | 1,754 | |||||||||||||||||||
| Expense Example, No Redemption, 1 Year | 468 | |||||||||||||||||||
| Expense Example, No Redemption, 3 Years | 718 | |||||||||||||||||||
| Expense Example, No Redemption, 5 Years | 987 | |||||||||||||||||||
| Expense Example, No Redemption, 10 Years | $ 1,754 | |||||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | Fidelity Advisor Utilities Fund - Class C | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Maximum Cumulative Sales Charge (as a percentage of Offering Price) | 0.00% | |||||||||||||||||||
| Maximum Deferred Sales Charge (as a percentage) | [3] | 1.00% | ||||||||||||||||||
| Management Fees (as a percentage of Assets) | [2] | 0.68% | ||||||||||||||||||
| Distribution and Service (12b-1) Fees | 1.00% | |||||||||||||||||||
| Other Expenses (as a percentage of Assets): | [2] | 0.02% | ||||||||||||||||||
| Expenses (as a percentage of Assets) | 1.70% | |||||||||||||||||||
| Expenses Deferred Charges [Text Block] | On Class C shares redeemed less than one year after purchase. | |||||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 273 | |||||||||||||||||||
| Expense Example, with Redemption, 3 Years | 536 | |||||||||||||||||||
| Expense Example, with Redemption, 5 Years | 923 | |||||||||||||||||||
| Expense Example, with Redemption, 10 Years | 1,810 | |||||||||||||||||||
| Expense Example, No Redemption, 1 Year | 173 | |||||||||||||||||||
| Expense Example, No Redemption, 3 Years | 536 | |||||||||||||||||||
| Expense Example, No Redemption, 5 Years | 923 | |||||||||||||||||||
| Expense Example, No Redemption, 10 Years | $ 1,810 | |||||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | Fidelity Advisor Utilities Fund - Class I | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Maximum Cumulative Sales Charge (as a percentage of Offering Price) | 0.00% | |||||||||||||||||||
| Maximum Deferred Sales Charge (as a percentage) | 0.00% | |||||||||||||||||||
| Management Fees (as a percentage of Assets) | [2] | 0.68% | ||||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.00% | |||||||||||||||||||
| Other Expenses (as a percentage of Assets): | [2] | 0.02% | ||||||||||||||||||
| Expenses (as a percentage of Assets) | 0.70% | |||||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 72 | |||||||||||||||||||
| Expense Example, with Redemption, 3 Years | 224 | |||||||||||||||||||
| Expense Example, with Redemption, 5 Years | 390 | |||||||||||||||||||
| Expense Example, with Redemption, 10 Years | 871 | |||||||||||||||||||
| Expense Example, No Redemption, 1 Year | 72 | |||||||||||||||||||
| Expense Example, No Redemption, 3 Years | 224 | |||||||||||||||||||
| Expense Example, No Redemption, 5 Years | 390 | |||||||||||||||||||
| Expense Example, No Redemption, 10 Years | $ 871 | |||||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | Fidelity Advisor Utilities Fund - Class Z | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Maximum Cumulative Sales Charge (as a percentage of Offering Price) | 0.00% | |||||||||||||||||||
| Maximum Deferred Sales Charge (as a percentage) | 0.00% | |||||||||||||||||||
| Management Fees (as a percentage of Assets) | [2] | 0.56% | ||||||||||||||||||
| Distribution and Service (12b-1) Fees | 0.00% | |||||||||||||||||||
| Other Expenses (as a percentage of Assets): | [2] | 0.02% | ||||||||||||||||||
| Expenses (as a percentage of Assets) | 0.58% | |||||||||||||||||||
| Expense Example, with Redemption, 1 Year | $ 59 | |||||||||||||||||||
| Expense Example, with Redemption, 3 Years | 186 | |||||||||||||||||||
| Expense Example, with Redemption, 5 Years | 324 | |||||||||||||||||||
| Expense Example, with Redemption, 10 Years | 726 | |||||||||||||||||||
| Expense Example, No Redemption, 1 Year | 59 | |||||||||||||||||||
| Expense Example, No Redemption, 3 Years | 186 | |||||||||||||||||||
| Expense Example, No Redemption, 5 Years | 324 | |||||||||||||||||||
| Expense Example, No Redemption, 10 Years | $ 726 | |||||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Risk/Return [Heading] | Fund Summary Fund /Class: Utilities Portfolio /Fidelity Advisor® Utilities Fund A, M, C, I, Z | |||||||||||||||||||
| Objective [Heading] | Investment Objective | |||||||||||||||||||
| Objective, Primary [Text Block] | Utilities Portfolio seeks capital appreciation. | |||||||||||||||||||
| 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. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $ 50,000 in the fund or certain other Fidelity ® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 19 of the prospectus and in the sales charge waiver appendix to the prospectus. | |||||||||||||||||||
| Shareholder Fees Caption [Optional Text] | Shareholder fees | |||||||||||||||||||
| 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 69 % of the average value of its portfolio. | |||||||||||||||||||
| Portfolio Turnover, Rate | 69.00% | |||||||||||||||||||
| Expenses Deferred Charges [Text Block] | Class A and Class M purchases of $1 million or more will not be subject to a front-end sales charge. Such Class A and Class M purchases may be subject, upon redemption, to a contingent deferred sales charge (CDSC) of 1.00% and 0.25%, respectively. | |||||||||||||||||||
| Expense Breakpoint Discounts [Text] | You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $ 50,000 in the fund or certain other Fidelity ® funds. More information about these and other discounts is available from your investment professional and in the "Fund Distribution" section beginning on page 19 of the prospectus | |||||||||||||||||||
| Expense Breakpoint, Minimum Investment Required [Amount] | $ 50,000 | |||||||||||||||||||
| 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 and if you hold your shares: | |||||||||||||||||||
| Strategy [Heading] | Principal Investment Strategies | |||||||||||||||||||
| Strategy Narrative [Text Block] | Normally investing primarily in common stocks. Normally investing at least 80% of assets in securities of companies principally engaged in the utilities industry and companies deriving a majority of their revenues from their utility operations. These companies may include, for example, companies that produce electricity, including nuclear and non-nuclear facilities; companies that distribute and transmit natural and manufactured gas; water treatment and other utility companies; companies that operate as independent power producers, gas and power marketing and trading specialists and/or integrated energy merchants; and companies that engage in the generation and distribution of electricity using renewable sources. For purposes of the fund's policy to normally invest at least 80% of its assets in securities of companies principally engaged in the business activity or activities identified for the fund, Fidelity may consider a company to be principally engaged in the designated business activity or activities based on: (i) the level of a company's assets, income, sales, or profits that are committed to, derived from, or related to the designated business activity or activities, or (ii) whether a third party has given the company an industry or sector classification consistent with the designated business activity or activities. Whether a company is principally engaged in the designated business activity or activities can be determined under any of these factors. 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. Investing in domestic and foreign issuers. Using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments. | |||||||||||||||||||
| Strategy Portfolio Concentration [Text] | Normally investing at least 80% of assets in securities of companies principally engaged in the utilities industry and companies deriving a majority of their revenues from their utility operations. | |||||||||||||||||||
| 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 Utilities Portfolio, 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 Utilities Portfolio, a class of shares of the fund. Performance history will be available at institutional.fidelity.com for Class A, Class M, Class C, Class I, and Class Z after Class A, Class M, Class C, Class I, and Class Z have been in operation for one calendar year. | |||||||||||||||||||
| Performance Information Illustrates Variability of Returns [Text] | The information illustrates the changes in the performance of Utilities Portfolio, 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 institutional.fidelity.com for Class A, Class M, Class C, Class I, and Class Z after Class A, Class M, Class C, Class I, and Class Z have 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 Utilities Portfolio, a class of shares of the fund that is not offered through this prospectus. Class A, Class M, Class C, Class I, and Class Z would have substantially similar annual returns to Utilities Portfolio because the classes are invested in the same portfolio of securities. Class A's, Class M's, Class C's, Class I's, and Class Z's returns would differ from Utilities Portfolio'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 | Jun. 30, 2025 | |||||||||||||||||||
| Bar Chart, Year to Date Return | 6.37% | |||||||||||||||||||
| Highest Quarterly Return, Label [Optional Text] | Highest Quarter Return | |||||||||||||||||||
| Highest Quarterly Return, Date | Sep. 30, 2024 | |||||||||||||||||||
| Highest Quarterly Return | 18.70% | |||||||||||||||||||
| Lowest Quarterly Return, Label [Optional Text] | Lowest Quarter Return | |||||||||||||||||||
| Lowest Quarterly Return, Date | Mar. 31, 2020 | |||||||||||||||||||
| Lowest Quarterly Return | (17.71%) | |||||||||||||||||||
| 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. | |||||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | After Taxes on Distributions | Fidelity Advisor Utilities Fund - Class A | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions | |||||||||||||||||||
| Average Annual Return, Percent | 26.48% | 8.43% | 8.54% | |||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | After Taxes on Distributions and Sales | Fidelity Advisor Utilities Fund - Class A | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Average Annual Return, Label [Optional Text] | Return After Taxes on Distributions and Sale of Fund Shares | |||||||||||||||||||
| Average Annual Return, Percent | 18.09% | 7.37% | 7.63% | |||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | F1528 | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Average Annual Return, Label [Optional Text] | MSCI U.S. IMI Utilities 25-50 Index | |||||||||||||||||||
| Average Annual Return, Percent | 23.20% | 6.14% | 8.30% | |||||||||||||||||
| SelectUtilitiesPortfolio-AMCIZPro | Select Utilities Portfolio | SP001 | ||||||||||||||||||||
| Prospectus Line Items | ||||||||||||||||||||
| Average Annual Return, Label [Optional Text] | S&P 500® Index | |||||||||||||||||||
| Average Annual Return, Percent | 25.02% | 14.53% | 13.10% | |||||||||||||||||
| Document Type | 485BPOS | |||||||||||||||||||
| Registrant Name | Fidelity Select Portfolios | |||||||||||||||||||
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