| Form N-CSR Cover | 6 Months Ended |
| Sep. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Magellan Fund |
| Entity Central Index Key | 0000061397 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Sep. 30, 2024 |
| Shareholder Report | 6 Months Ended |
| Sep. 30, 2024 USD ($) shares | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSRS |
| Amendment Flag | false |
| Registrant Name | Fidelity Magellan Fund |
| Entity Central Index Key | 0000061397 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Sep. 30, 2024 |
| Fidelity Magellan K6 Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Magellan® K6 Fund |
| Class Name | Fidelity® Magellan® K6 Fund |
| Trading Symbol | FMKFX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Magellan® K6 Fund for the period April 1, 2024 to September 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-835-5092 or by sending an e-mail to fidfunddocuments@fidelity.com. |
| Additional Information Phone Number | 1-800-835-5092 |
| Additional Information Email | fidfunddocuments@fidelity.com |
| Additional Information Website | fundresearch.fidelity.com/prospectus/sec |
| Expenses [Text Block] | What were your Fund costs for the last six months? (based on hypothetical $10,000 investment) Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Fidelity® Magellan® K6 Fund $ 0.45 % |
| Expenses Paid, Amount | $ 24 |
| Expense Ratio, Percent | 0.45% |
| Net Assets | $ 316,096,186 |
| Holdings Count | shares | 60 |
| Investment Company Portfolio Turnover | 45% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of September 30, 2024) KEY FACTS Fund Size $ Number of Holdings 60 Portfolio Turnover 45 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 33.8 Industrials 18.0 Health Care 12.2 Financials 10.6 Consumer Discretionary 9.4 Communication Services 8.6 Materials 5.0 Consumer Staples 1.9 Common Stocks 99.5 Short-Term Investments and Net Other Assets (Liabilities) 0.5 ASSET ALLOCATION (% of Fund's net assets) United States 97.8 Canada 1.2 Denmark 1.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Microsoft Corp 7.8 NVIDIA Corp 7.2 Amazon.com Inc 4.6 Meta Platforms Inc Class A 3.9 Alphabet Inc Class A 3.1 Broadcom Inc 3.0 Eli Lilly & Co 2.5 UnitedHealth Group Inc 2.3 Mastercard Inc Class A 2.1 Visa Inc Class A 2.0 38.5 |
| Fidelity Magellan Fund | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Magellan® Fund |
| Class Name | Fidelity® Magellan® Fund |
| Trading Symbol | FMAGX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Magellan® Fund for the period April 1, 2024 to September 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-544-8544 or by sending an e-mail to fidfunddocuments@fidelity.com. |
| Additional Information Phone Number | 1-800-544-8544 |
| Additional Information Email | fidfunddocuments@fidelity.com |
| Additional Information Website | fundresearch.fidelity.com/prospectus/sec |
| Expenses [Text Block] | What were your Fund costs for the last six months? (based on hypothetical $10,000 investment) Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Fidelity® Magellan® Fund $ 0.57 % |
| Expenses Paid, Amount | $ 30 |
| Expense Ratio, Percent | 0.57% |
| Net Assets | $ 36,278,252,982 |
| Holdings Count | shares | 63 |
| Investment Company Portfolio Turnover | 39% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of September 30, 2024) KEY FACTS Fund Size $ Number of Holdings 63 Portfolio Turnover 39 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 33.8 Industrials 17.9 Health Care 12.2 Financials 10.6 Consumer Discretionary 9.4 Communication Services 8.6 Materials 5.0 Consumer Staples 1.9 Common Stocks 99.4 Short-Term Investments and Net Other Assets (Liabilities) 0.6 ASSET ALLOCATION (% of Fund's net assets) United States 97.8 Canada 1.2 Denmark 1.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Microsoft Corp 7.8 NVIDIA Corp 7.2 Amazon.com Inc 4.6 Meta Platforms Inc Class A 3.9 Alphabet Inc Class A 3.1 Broadcom Inc 3.0 Eli Lilly & Co 2.5 UnitedHealth Group Inc 2.3 Mastercard Inc Class A 2.1 Visa Inc Class A 2.0 38.5 |
| Fidelity Magellan Fund - Class K | |
| Shareholder Report [Line Items] | |
| Fund Name | Fidelity® Magellan® Fund |
| Class Name | Fidelity® Magellan® Fund Class K |
| Trading Symbol | FMGKX |
| Annual or Semi-Annual Statement [Text Block] | This semi-annual shareholder report contains information about Fidelity® Magellan® Fund for the period April 1, 2024 to September 30, 2024. |
| Shareholder Report Annual or Semi-Annual | semi-annual shareholder report |
| Additional Information [Text Block] | You can find additional information about the Fund at fundresearch.fidelity.com/prospectus/sec. You can also request this information by contacting us at 1-800-835-5092 or by sending an e-mail to fidfunddocuments@fidelity.com. |
| Additional Information Phone Number | 1-800-835-5092 |
| Additional Information Email | fidfunddocuments@fidelity.com |
| Additional Information Website | fundresearch.fidelity.com/prospectus/sec |
| Expenses [Text Block] | What were your Fund costs for the last six months? (based on hypothetical $10,000 investment) Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Class K $ 0.50 % |
| Expenses Paid, Amount | $ 26 |
| Expense Ratio, Percent | 0.50% |
| Net Assets | $ 36,278,252,982 |
| Holdings Count | shares | 63 |
| Investment Company Portfolio Turnover | 39% |
| Additional Fund Statistics [Text Block] | Key Fund Statistics (as of September 30, 2024) KEY FACTS Fund Size $ Number of Holdings 63 Portfolio Turnover 39 % |
| Holdings [Text Block] | MARKET SECTORS (% of Fund's net assets) Information Technology 33.8 Industrials 17.9 Health Care 12.2 Financials 10.6 Consumer Discretionary 9.4 Communication Services 8.6 Materials 5.0 Consumer Staples 1.9 Common Stocks 99.4 Short-Term Investments and Net Other Assets (Liabilities) 0.6 ASSET ALLOCATION (% of Fund's net assets) United States 97.8 Canada 1.2 Denmark 1.0 GEOGRAPHIC DIVERSIFICATION (% of Fund's net assets) |
| Largest Holdings [Text Block] | TOP HOLDINGS (% of Fund's net assets) Microsoft Corp 7.8 NVIDIA Corp 7.2 Amazon.com Inc 4.6 Meta Platforms Inc Class A 3.9 Alphabet Inc Class A 3.1 Broadcom Inc 3.0 Eli Lilly & Co 2.5 UnitedHealth Group Inc 2.3 Mastercard Inc Class A 2.1 Visa Inc Class A 2.0 38.5 |
| Shareholder Report, Holdings (Details) | Sep. 30, 2024 |
| Fidelity Magellan K6 Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| Fidelity Magellan K6 Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.20% |
| Fidelity Magellan K6 Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Magellan K6 Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Fidelity Magellan K6 Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Magellan K6 Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Magellan K6 Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Magellan K6 Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Magellan K6 Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Fidelity Magellan K6 Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity Magellan K6 Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| Fidelity Magellan K6 Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 33.80% |
| Fidelity Magellan K6 Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity Magellan K6 Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 18% |
| Fidelity Magellan K6 Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| Fidelity Magellan K6 Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| Fidelity Magellan K6 Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Fidelity Magellan K6 Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| Fidelity Magellan K6 Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.80% |
| Fidelity Magellan K6 Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Fidelity Magellan K6 Fund | Denmark | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Magellan K6 Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.50% |
| Fidelity Magellan K6 Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.50% |
| Fidelity Magellan Fund | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| Fidelity Magellan Fund | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.20% |
| Fidelity Magellan Fund | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Magellan Fund | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Fidelity Magellan Fund | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Magellan Fund | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Magellan Fund | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Magellan Fund | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Magellan Fund | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Fidelity Magellan Fund | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity Magellan Fund | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| Fidelity Magellan Fund | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 33.80% |
| Fidelity Magellan Fund | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity Magellan Fund | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.90% |
| Fidelity Magellan Fund | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| Fidelity Magellan Fund | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| Fidelity Magellan Fund | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Fidelity Magellan Fund | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| Fidelity Magellan Fund | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.80% |
| Fidelity Magellan Fund | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Fidelity Magellan Fund | Denmark | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Magellan Fund | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.40% |
| Fidelity Magellan Fund | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
| Fidelity Magellan Fund - Class K | TH0Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.80% |
| Fidelity Magellan Fund - Class K | TH1Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.20% |
| Fidelity Magellan Fund - Class K | TH2Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 4.60% |
| Fidelity Magellan Fund - Class K | TH3Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Fidelity Magellan Fund - Class K | TH4Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.10% |
| Fidelity Magellan Fund - Class K | TH5Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3% |
| Fidelity Magellan Fund - Class K | TH6Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Fidelity Magellan Fund - Class K | TH7Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| Fidelity Magellan Fund - Class K | TH8Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.10% |
| Fidelity Magellan Fund - Class K | TH9Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2% |
| Fidelity Magellan Fund - Class K | MSFinancialsSectorMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| Fidelity Magellan Fund - Class K | Information Technology Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 33.80% |
| Fidelity Magellan Fund - Class K | Healthcare Sector | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 12.20% |
| Fidelity Magellan Fund - Class K | Industrial Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 17.90% |
| Fidelity Magellan Fund - Class K | Materials Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| Fidelity Magellan Fund - Class K | Consumer Discretionary Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
| Fidelity Magellan Fund - Class K | Consumer Staples Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.90% |
| Fidelity Magellan Fund - Class K | Communications Sector Member | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 8.60% |
| Fidelity Magellan Fund - Class K | United States | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 97.80% |
| Fidelity Magellan Fund - Class K | Canada | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.20% |
| Fidelity Magellan Fund - Class K | Denmark | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1% |
| Fidelity Magellan Fund - Class K | AACommonStocksMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 99.40% |
| Fidelity Magellan Fund - Class K | AAShortTermInvestmentsandNetOtherAssetsLiabilitiesMember | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 0.60% |
