v3.26.1
Risk/Return Detail Data - FidelityMagellanFund-RetailPRO - USD ($)
 12 Months Ended 24 Months Ended 60 Months Ended 84 Months Ended 120 Months Ended
May 30, 2026
May 30, 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
May 30, 2026
May 30, 2026
May 30, 2026
May 30, 2026
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] 0.68%                              
Distribution and Service (12b-1) Fees 0.25%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 0.93%                              
Expense Example, with Redemption, 1 Year $ 664                              
Expense Example, with Redemption, 3 Years 854                              
Expense Example, with Redemption, 5 Years 1,060                              
Expense Example, with Redemption, 10 Years 1,652                              
Expense Example, No Redemption, 1 Year 664                              
Expense Example, No Redemption, 3 Years 854                              
Expense Example, No Redemption, 5 Years 1,060                              
Expense Example, No Redemption, 10 Years $ 1,652                              
Annual Return, Inception Date Oct. 08, 2024                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   3.93%                     3.49% [3]      
Annual Return [Percent]     10.27%                          
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] 0.68%                              
Distribution and Service (12b-1) Fees 0.50%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 1.18%                              
Expense Example, with Redemption, 1 Year $ 466                              
Expense Example, with Redemption, 3 Years 712                              
Expense Example, with Redemption, 5 Years 976                              
Expense Example, with Redemption, 10 Years 1,732                              
Expense Example, No Redemption, 1 Year 466                              
Expense Example, No Redemption, 3 Years 712                              
Expense Example, No Redemption, 5 Years 976                              
Expense Example, No Redemption, 10 Years $ 1,732                              
Annual Return, Inception Date Oct. 08, 2024                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   6.13%                     5.24% [4]      
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) [5] 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): 0.00%                              
Expenses (as a percentage of Assets) 1.68%                              
Expenses Deferred Charges [Text Block] On Class C shares redeemed less than one year after purchase.                              
Expense Example, with Redemption, 1 Year $ 271                              
Expense Example, with Redemption, 3 Years 530                              
Expense Example, with Redemption, 5 Years 913                              
Expense Example, with Redemption, 10 Years 1,788                              
Expense Example, No Redemption, 1 Year 171                              
Expense Example, No Redemption, 3 Years 530                              
Expense Example, No Redemption, 5 Years 913                              
Expense Example, No Redemption, 10 Years $ 1,788                              
Annual Return, Inception Date Oct. 08, 2024                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   8.42%                     7.78% [6]      
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] 0.68%                              
Distribution and Service (12b-1) Fees 0.00%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 0.68%                              
Expense Example, with Redemption, 1 Year $ 69                              
Expense Example, with Redemption, 3 Years 218                              
Expense Example, with Redemption, 5 Years 379                              
Expense Example, with Redemption, 10 Years 847                              
Expense Example, No Redemption, 1 Year 69                              
Expense Example, No Redemption, 3 Years 218                              
Expense Example, No Redemption, 5 Years 379                              
Expense Example, No Redemption, 10 Years $ 847                              
Annual Return, Inception Date Oct. 08, 2024                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   10.54%                     8.87% [7]      
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] 0.57%                              
Distribution and Service (12b-1) Fees 0.00%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 0.57%                              
Expense Example, with Redemption, 1 Year $ 58                              
Expense Example, with Redemption, 3 Years 183                              
Expense Example, with Redemption, 5 Years 318                              
Expense Example, with Redemption, 10 Years 714                              
Expense Example, No Redemption, 1 Year 58                              
Expense Example, No Redemption, 3 Years 183                              
Expense Example, No Redemption, 5 Years 318                              
Expense Example, No Redemption, 10 Years $ 714                              
Annual Return, Inception Date Oct. 08, 2024                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   10.69%                     9.01% [8]      
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 54 % of the average value of its portfolio.                              
Portfolio Turnover, Rate 54.00%                              
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 performance of the fund's shares over the past 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 institutional .fidelity.com for more recent performance information .                              
Performance Information Illustrates Variability of Returns [Text] The information illustrates the performance of the fund's shares over the past 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] institutional .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 Narrative [Text Block] The returns in the bar chart do not reflect any applicable sales charges; if sales charges were reflected, returns would be lower than those shown .                              
Bar Chart Does Not Reflect Sales Loads [Text] The returns in the bar chart do not reflect any applicable sales charges; if sales charges were reflected, returns would be lower than those shown .                              
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 (7.68%)                              
Highest Quarterly Return, Label [Optional Text]    Highest Quarter Return                              
Highest Quarterly Return, Date Jun. 30, 2025                              
Highest Quarterly Return 17.68%                              
Lowest Quarterly Return, Label [Optional Text]    Lowest Quarter Return                              
Lowest Quarterly Return, Date Mar. 31, 2025                              
Lowest Quarterly Return (5.95%)                              
Performance Table Heading Average Annual Returns                              
Performance Table Does Reflect Sales Loads Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges.                              
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 One Class of after Tax Shown [Text] After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary.                              
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 Unlike the returns in the bar chart, the returns in the table reflect the maximum applicable sales charges. 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. After-tax returns for Class A are shown in the table below and after-tax returns for other classes will vary. 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 | After Taxes on Distributions | Fidelity Advisor Magellan Fund - Class A                                
Prospectus Line Items                                
Average Annual Return, Label [Optional Text]   Return After Taxes on Distributions                            
Average Annual Return, Percent   1.69%                     1.03% [3]      
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | After Taxes on Distributions and Sales | Fidelity Advisor Magellan 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   3.79%                     2.58% [3]      
FidelityMagellanFund-AMCIZPRO | Fidelity Magellan Fund | SP001                                
Prospectus Line Items                                
Average Annual Return, Label [Optional Text]   S&P 500® Index                            
Average Annual Return, Percent   17.88%                     16.70%      
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   10.90%                       11.75% 15.02% [9]  
Annual Return [Percent]     10.90% 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 57 % of the average value of its portfolio.                              
Portfolio Turnover, Rate 57.00%                              
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, 2026                              
Bar Chart, Year to Date Return (7.51%)                              
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   17.88%                       14.42% 15.84%  
FidelityMagellanFund-KPRO | Fidelity Magellan Fund | Fidelity Magellan Fund - Class K                                
Prospectus Line Items                                
Management Fees (as a percentage of Assets) [10] 0.57%                              
Distribution and Service (12b-1) Fees 0.00%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 0.57%                              
Expense Example, with Redemption, 1 Year $ 58                              
Expense Example, with Redemption, 3 Years 183                              
Expense Example, with Redemption, 5 Years 318                              
Expense Example, with Redemption, 10 Years $ 714                              
Average Annual Return, Label [Optional Text]   Class K                            
Average Annual Return, Percent   10.66%                       11.46%   13.84%
Annual Return [Percent]     10.66% 28.13% 31.05% (27.08%) 26.98% 28.49% 31.31% (5.58%) 26.63% 5.34%        
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 54 % of the average value of its portfolio.                              
Portfolio Turnover, Rate 54.00%                              
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, 2026                              
Bar Chart, Year to Date Return (7.56%)                              
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   17.88%                       14.42%   14.82%
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | Fidelity Magellan Fund                                
Prospectus Line Items                                
Management Fees (as a percentage of Assets) [11] 0.64%                              
Distribution and Service (12b-1) Fees 0.00%                              
Other Expenses (as a percentage of Assets): 0.00%                              
Expenses (as a percentage of Assets) 0.64%                              
Expense Example, with Redemption, 1 Year $ 65                              
Expense Example, with Redemption, 3 Years 205                              
Expense Example, with Redemption, 5 Years 357                              
Expense Example, with Redemption, 10 Years $ 798                              
Average Annual Return, Label [Optional Text]   Return Before Taxes                            
Average Annual Return, Percent   10.58%                       11.39%   13.75%
Annual Return [Percent]     10.58% 28.03% 30.95% (27.15%) 26.98% 28.34% 31.16% (5.60%) 26.51% 5.24%        
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 54 % of the average value of its portfolio.                              
Portfolio Turnover, Rate 54.00%                              
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, 2026                              
Bar Chart, Year to Date Return (7.56%)                              
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   8.21%                       9.32%   11.72%
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   7.81%                       8.63%   10.84%
FidelityMagellanFund-RetailPRO | Fidelity Magellan Fund | SP001                                
Prospectus Line Items                                
Average Annual Return, Label [Optional Text]   S&P 500® Index                            
Average Annual Return, Percent   17.88%                       14.42%   14.82%
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]
A From October 8, 2024 .
[4]
B From October 8, 2024 .
[5]
B On Class C shares redeemed less than one year after purchase.
[6]
C From October 8, 2024 .
[7]
D From October 8, 2024 .
[8]
E From October 8, 2024 .
[9]
A From June 13, 2019 .
[10]
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.
[11]
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.