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Risk/Return Detail Data - FidelityMagellanFund-RetailPRO - USD ($)
 12 Months Ended 60 Months Ended 72 Months Ended 120 Months Ended
May 30, 2025
May 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
May 30, 2025
May 30, 2025
May 30, 2025
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | Fidelity Advisor Magellan 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] 0.61%                            
Distribution and Service (12b-1) Fees 0.25%                            
Other Expenses (as a percentage of Assets): 0.03%                            
Expenses (as a percentage of Assets) 0.89%                            
Expense Example, with Redemption, 1 Year $ 661                            
Expense Example, with Redemption, 3 Years 843                            
Expense Example, with Redemption, 5 Years 1,040                            
Expense Example, with Redemption, 10 Years 1,608                            
Expense Example, No Redemption, 1 Year 661                            
Expense Example, No Redemption, 3 Years 843                            
Expense Example, No Redemption, 5 Years 1,040                            
Expense Example, No Redemption, 10 Years $ 1,608                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | Fidelity Advisor Magellan 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] 0.60%                            
Distribution and Service (12b-1) Fees 0.50%                            
Other Expenses (as a percentage of Assets): 0.03%                            
Expenses (as a percentage of Assets) 1.13%                            
Expense Example, with Redemption, 1 Year $ 461                            
Expense Example, with Redemption, 3 Years 697                            
Expense Example, with Redemption, 5 Years 950                            
Expense Example, with Redemption, 10 Years 1,677                            
Expense Example, No Redemption, 1 Year 461                            
Expense Example, No Redemption, 3 Years 697                            
Expense Example, No Redemption, 5 Years 950                            
Expense Example, No Redemption, 10 Years $ 1,677                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | Fidelity Advisor Magellan 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] 0.61%                            
Distribution and Service (12b-1) Fees 1.00%                            
Other Expenses (as a percentage of Assets): 0.05%                            
Expenses (as a percentage of Assets) 1.66%                            
Expenses Deferred Charges [Text Block] On Class C shares redeemed less than one year after purchase.                            
Expense Example, with Redemption, 1 Year $ 269                            
Expense Example, with Redemption, 3 Years 523                            
Expense Example, with Redemption, 5 Years 902                            
Expense Example, with Redemption, 10 Years 1,760                            
Expense Example, No Redemption, 1 Year 169                            
Expense Example, No Redemption, 3 Years 523                            
Expense Example, No Redemption, 5 Years 902                            
Expense Example, No Redemption, 10 Years $ 1,760                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | Fidelity Advisor Magellan 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] 0.60%                            
Distribution and Service (12b-1) Fees 0.00%                            
Other Expenses (as a percentage of Assets): 0.02%                            
Expenses (as a percentage of Assets) 0.62%                            
Expense Example, with Redemption, 1 Year $ 63                            
Expense Example, with Redemption, 3 Years 199                            
Expense Example, with Redemption, 5 Years 346                            
Expense Example, with Redemption, 10 Years 774                            
Expense Example, No Redemption, 1 Year 63                            
Expense Example, No Redemption, 3 Years 199                            
Expense Example, No Redemption, 5 Years 346                            
Expense Example, No Redemption, 10 Years $ 774                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | Fidelity Advisor Magellan 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] 0.48%                            
Distribution and Service (12b-1) Fees 0.00%                            
Other Expenses (as a percentage of Assets): 0.07%                            
Expenses (as a percentage of Assets) 0.55%                            
Expense Example, with Redemption, 1 Year $ 56                            
Expense Example, with Redemption, 3 Years 176                            
Expense Example, with Redemption, 5 Years 307                            
Expense Example, with Redemption, 10 Years 689                            
Expense Example, No Redemption, 1 Year 56                            
Expense Example, No Redemption, 3 Years 176                            
Expense Example, No Redemption, 5 Years 307                            
Expense Example, No Redemption, 10 Years $ 689                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund                              
Prospectus Line Items                              
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Magellan® Fund /Fidelity Advisor® Magellan® Fund A, M, C, I, Z                              
Objective [Heading] Investment Objective                            
Objective, Primary [Text Block] Fidelity® Magellan® Fund 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 31 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 49 % of the average value of its portfolio.                            
Portfolio Turnover, Rate 49.00%                            
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 31 of the prospectus                            
Expense Breakpoint, Minimum Investment Required [Amount] $ 50,000                            
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. Investing in domestic and foreign issuers. Investing in either "growth" stocks or "value" stocks or both. 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.                            
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® Magellan® 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 over various periods of time. The index description appears 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® Magellan® Fund, 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 Fidelity® Magellan® 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 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                            
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 (5.87%)                            
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                            
Highest Quarterly Return, Date Jun. 30, 2020                            
Highest Quarterly Return 23.95%                            
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                            
Lowest Quarterly Return, Date Jun. 30, 2022                            
Lowest Quarterly Return (17.03%)                            
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.                            
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | SP001                              
Prospectus Line Items                              
Average Annual Return, Label [Optional Text]   S&P 500® Index                          
Average Annual Return, Percent   25.02%                     14.53%   13.10%
FidelityMagellanK6Fund-PRO | Fidelity Magellan K6 Fund | Fidelity Magellan K6 Fund                              
Prospectus Line Items                              
Management Fees (as a percentage of Assets) 0.45%                            
Distribution and Service (12b-1) Fees 0.00%                            
Other Expenses (as a percentage of Assets): 0.00%                            
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                            
Annual Return, Inception Date Jun. 13, 2019                            
Average Annual Return, Label [Optional Text]   Fidelity® Magellan® K6 Fund                          
Average Annual Return, Percent   28.35%                     15.21% 15.78% [4]  
Annual Return [Percent]     28.35% 31.31% (26.85%) 27.46% 29.14%                
FidelityMagellanK6Fund-PRO | Fidelity Magellan K6 Fund                              
Prospectus Line Items                              
Risk/Return [Heading] Fund Summary Fund: Fidelity® Magellan® K6 Fund                            
Objective [Heading] Investment Objective                            
Objective, Primary [Text Block] Fidelity® Magellan® K6 Fund 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 , 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 55 % of the average value of its portfolio.                            
Portfolio Turnover, Rate 55.00%                            
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 primarily in common stocks. Investing in domestic and foreign issuers. Investing in either "growth" stocks or "value" stocks or both. 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.                            
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 over various periods of time. The index description appears in the "Additional Index Information" section of the prospectus. 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 and compares the performance of the fund's shares to the performance of a securities market index over various periods of time.                            
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 (5.78%)                            
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                            
Highest Quarterly Return, Date Jun. 30, 2020                            
Highest Quarterly Return 24.22%                            
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                            
Lowest Quarterly Return, Date Jun. 30, 2022                            
Lowest Quarterly Return (16.78%)                            
Performance Table Heading Average Annual Returns                            
FidelityMagellanK6Fund-PRO | Fidelity Magellan K6 Fund | SP001                              
Prospectus Line Items                              
Average Annual Return, Label [Optional Text]   S&P 500® Index                          
Average Annual Return, Percent   25.02%                     14.53% 15.48%  
FidelityMagellanFund-KPRO | Fidelity Magellan Fund | Fidelity Magellan Fund - Class K                              
Prospectus Line Items                              
Management Fees (as a percentage of Assets) [5] 0.49%                            
Distribution and Service (12b-1) Fees 0.00%                            
Other Expenses (as a percentage of Assets): 0.00%                            
Expenses (as a percentage of Assets) 0.49%                            
Expense Example, with Redemption, 1 Year $ 50                            
Expense Example, with Redemption, 3 Years 157                            
Expense Example, with Redemption, 5 Years 274                            
Expense Example, with Redemption, 10 Years $ 616                            
Average Annual Return, Label [Optional Text]   Class K                          
Average Annual Return, Percent   28.13%                     14.84%   13.15%
Annual Return [Percent]     28.13% 31.05% (27.08%) 26.98% 28.49% 31.31% (5.58%) 26.63% 5.34% 4.16%      
FidelityMagellanFund-KPRO | Fidelity Magellan Fund                              
Prospectus Line Items                              
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Magellan® Fund /K                              
Objective [Heading] Investment Objective                            
Objective, Primary [Text Block] Fidelity® Magellan® Fund 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.                            
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 49 % of the average value of its portfolio.                            
Portfolio Turnover, Rate 49.00%                            
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 primarily in common stocks. Investing in domestic and foreign issuers. Investing in either "growth" stocks or "value" stocks or both. 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.                            
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 over various periods of time. The index description appears in the "Additional Index Information" section of the prospectus. 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 and compares the performance of the fund's shares to the performance of a securities market index over various periods of time.                            
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 (5.80%)                            
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                            
Highest Quarterly Return, Date Jun. 30, 2020                            
Highest Quarterly Return 24.12%                            
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                            
Lowest Quarterly Return, Date Jun. 30, 2022                            
Lowest Quarterly Return (16.97%)                            
Performance Table Heading Average Annual Returns                            
FidelityMagellanFund-KPRO | Fidelity Magellan Fund | SP001                              
Prospectus Line Items                              
Average Annual Return, Label [Optional Text]   S&P 500® Index                          
Average Annual Return, Percent   25.02%                     14.53%   13.10%
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | Fidelity Magellan Fund                              
Prospectus Line Items                              
Management Fees (as a percentage of Assets) [6] 0.56%                            
Distribution and Service (12b-1) Fees 0.00%                            
Other Expenses (as a percentage of Assets): 0.00%                            
Expenses (as a percentage of Assets) 0.56%                            
Expense Example, with Redemption, 1 Year $ 57                            
Expense Example, with Redemption, 3 Years 179                            
Expense Example, with Redemption, 5 Years 313                            
Expense Example, with Redemption, 10 Years $ 701                            
Average Annual Return, Label [Optional Text]   Return Before Taxes                          
Average Annual Return, Percent   28.03%                     14.76%   13.07%
Annual Return [Percent]     28.03% 30.95% (27.15%) 26.98% 28.34% 31.16% (5.60%) 26.51% 5.24% 4.06%      
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund                              
Prospectus Line Items                              
Risk/Return [Heading] Fund Summary Fund /Class: Fidelity® Magellan® Fund /Fidelity® Magellan® Fund                            
Objective [Heading] Investment Objective                            
Objective, Primary [Text Block] Fidelity® Magellan® Fund 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.                            
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 49 % of the average value of its portfolio.                            
Portfolio Turnover, Rate 49.00%                            
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 primarily in common stocks. Investing in domestic and foreign issuers. Investing in either "growth" stocks or "value" stocks or both. 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.                            
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 over various periods of time. The index description appears 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 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 (5.87%)                            
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                            
Highest Quarterly Return, Date Jun. 30, 2020                            
Highest Quarterly Return 23.95%                            
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                            
Lowest Quarterly Return, Date Jun. 30, 2022                            
Lowest Quarterly Return (17.03%)                            
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.                            
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | After Taxes on Distributions | Fidelity Magellan Fund                              
Prospectus Line Items                              
Average Annual Return, Label [Optional Text]   Return After Taxes on Distributions                          
Average Annual Return, Percent   26.21%                     13.10%   11.09%
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | After Taxes on Distributions and Sales | Fidelity Magellan Fund                              
Prospectus Line Items                              
Average Annual Return, Label [Optional Text]   Return After Taxes on Distributions and Sale of Fund Shares                          
Average Annual Return, Percent   17.84%                     11.54%   10.21%
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | 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 Magellan Fund                            
[1]
A 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.
[2]
A The management fee comprises a basic fee, which may vary by class, that is adjusted up or down by a maximum of 0.20% based on the performance of the fund or a designated class of the fund relative to that of the S&P 500® Index. Please see "Fund Services - Fund Management - Advisory Fee(s)" for additional information.
[3]
B On Class C shares redeemed less than one year after purchase.
[4]
A From June 13, 2019 .
[5]
A The management fee comprises a basic fee, which may vary by class, that is adjusted up or down by a maximum of 0.20% based on the performance of the fund or a designated class of the fund relative to that of the S&P 500® Index. Please see "Fund Services - Fund Management - Advisory Fee(s)" for additional information.
[6]
A The management fee comprises a basic fee, which may vary by class, that is adjusted up or down by a maximum of 0.20% based on the performance of the fund or a designated class of the fund relative to that of the S&P 500® Index. Please see "Fund Services - Fund Management - Advisory Fee(s)" for additional information.