v3.24.4
Risk/Return Detail Data - FidelityGrowthCompanyK6Fund-PRO
Jan. 29, 2025
USD ($)
Risk/Return:  
Registrant Name Fidelity Mt. Vernon Street Trust
FidelityGrowthCompanyK6Fund-PRO | Fidelity Growth Company K6 Fund  
Risk/Return:  
Risk/Return [Heading] Fund Summary Fund: Fidelity® Growth Company K6 Fund
Objective [Heading] Investment Objective
Objective, Primary [Text Block] Fidelity® Growth Company K6 Fund seeks capital appreciation.
Expense [Heading] 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 [Text] Shareholder fees
(fees paid directly from your investment) none
Operating Expenses Caption [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 22 % of the average value of its portfolio.
Portfolio Turnover, Rate 22.00%
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 companies that Fidelity Management & Research Company LLC (FMR) believes have above-average growth potential (stocks of these companies are often called "growth" stocks). Investing in domestic and foreign issuers. Using fundamental analysis of factors such as each issuer's financial condition and industry position, as well as market and economic conditions, to select investments. Effective December 11, 2025, normally investing at least 80% of assets in securities of growth companies. Growth companies are companies the Adviser believes have above average growth potential. The Adviser considers a number of factors in determining a company's growth potential, such as whether the company is included in a third-party growth benchmark or classified as a growth company by a third-party vendor, if the company's projected earnings per share growth, sales growth per share or free cash flow growth or its trailing earnings per share growth is above the equity market median, if the company's research and development expenses exceed sales, general and administrative expenses, or if the company is raising capital to grow, fund or expand its business. A company's growth potential can be determined under any of these factors. Derivative instruments that provide investment exposure to the investments above or exposure to one or more market risk factors associated with such investments are included in the fund's 80% policy, consistent with the fund's investment policies and limitations with respect to investments in derivatives.
Risk [Heading] Principal Investment Risks
Bar Chart and Performance Table [Heading] Performance
Performance Narrative [Text Block] The following information is intended to help you understand the risks of investing in the fund. The information illustrates the changes in the performance of the fund's shares from year to year and compares the performance of the fund's shares to the performance of a securities market index and an additional index over various periods of time. The additional index has characteristics relevant to the fund's investment strategies. Index descriptions appear in the "Additional Index Information" section of the prospectus. Past performance 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 and an additional 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
Highest Quarterly Return, Label    Highest Quarter Return
Highest Quarterly Return, Date Jun. 30, 2020
Highest Quarterly Return 40.26%
Lowest Quarterly Return, Label    Lowest Quarter Return
Lowest Quarterly Return, Date Jun. 30, 2022
Lowest Quarterly Return (25.10%)
Performance Table Heading Average Annual Returns
FidelityGrowthCompanyK6Fund-PRO | Fidelity Growth Company K6 Fund | Fidelity Growth Company K6 Fund  
Risk/Return:  
Management fee 0.45%
Distribution and/or Service (12b-1) fees none
Other expenses none
Total annual operating expenses 0.45%
1 year $ 46
3 years 144
5 years 252
10 years $ 567
Annual Return, Inception Date Jun. 13, 2019
2020 68.77%
2021 22.09%
2022 (32.62%)
2023 46.02%
2024 38.36%
FidelityGrowthCompanyK6Fund-PRO | Fidelity Growth Company K6 Fund | Return Before Taxes | Fidelity Growth Company K6 Fund  
Risk/Return:  
Label Fidelity® Growth Company K6 Fund
Past 1 year 38.36%
Past 5 years 22.91%
Since Inception 23.48% [1]
FidelityGrowthCompanyK6Fund-PRO | Fidelity Growth Company K6 Fund | RS003  
Risk/Return:  
Label Russell 3000® Index
Past 1 year 23.81%
Past 5 years 13.86%
Since Inception 14.77%
FidelityGrowthCompanyK6Fund-PRO | Fidelity Growth Company K6 Fund | RS007  
Risk/Return:  
Label Russell 3000® Growth Index
Past 1 year 32.46%
Past 5 years 18.25%
Since Inception 19.00%
[1]
A From June 13, 2019 .