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Risk Return Abstract rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName First Trust Exchange-Traded Fund
Prospectus Date rr_ProspectusDate May 01, 2025
First Trust Morningstar Dividend Leaders Index Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading <span style="color:#000000;font-family:Arial;font-size:12.60pt;font-weight:bold;">First Trust Morningstar Dividend Leaders Index Fund (FDL)</span>
Objective [Heading] rr_ObjectiveHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Investment Objective</span>
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The First Trust Morningstar Dividend Leaders Index Fund (the “Fund”) seeks investment results that correspond generally to the price and yield (before the Fund’s fees and expenses) of an equity index called the Morningstar® Dividend Leaders IndexSM (the “Index”).
Expense [Heading] rr_ExpenseHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Fees and Expenses of the Fund</span>
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock The following table describes the fees and expenses you may pay if you buy, hold and sell shares of the Fund. Investors may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and example below.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Shareholder Fees</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(fees paid directly from your investment)</span>
Operating Expenses Caption [Text] rr_OperatingExpensesCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-weight:bold;">Annual Fund Operating Expenses</span> <br/><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(expenses that you pay each year as a percentage of the value of your investment)</span>
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination <span style="font-family:Arial;font-size:8.10pt;font-style:italic;">April 30, </span><span style="font-family:Arial;font-size:8.10pt;font-style:italic;">2026</span>
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Portfolio Turnover</span>
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock 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 fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 46% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 46.00%
Expense Example [Heading] rr_ExpenseExampleHeading <span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;font-weight:bold;">Example</span>
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock The example below is intended to help you compare the cost of investing in the Fund with the cost of investing in other funds.The example assumes that you invest $10,000 in the Fund for the time periods indicated and then hold or sell all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain at current levels. The example assumes that the Fund’s investment advisor’s agreement to waive fees and/or pay the Fund’s expenses to the extent necessary to prevent the operating expenses of the Fund (excluding interest expense, brokerage commissions and other trading expenses, acquired fund fees and expenses, taxes, and extraordinary expenses) from exceeding 0.45% of average daily net assets will be terminated following April 30, 2026. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock The Fund will normally invest at least 90% of its net assets (including investment borrowings) in the securities that comprise the Index. The Fund, using an indexing investment approach, attempts to replicate, before fees and expenses, the performance of the Index. The Index is developed, maintained and sponsored by Morningstar, Inc. (the “Index Provider”). The Index Provider serves as the index calculation agent. The Index Provider continually reviews the Index methodology to account for factors such as evolving market trends, feedback received from market participants or as an endeavor to adopt evolving best practices in the industry. Such reviews may cause the Index Provider to change the Index construction or calculation methodology, as well as the Index's treatment of various corporate actions. Such changes can impact the Index’s selection universe, portfolio composition or the Index’s on-going maintenance. The Index is designed to target the 100 highest-yielding stocks from the Morningstar Dividend Composite Index, which screens for records of consistent dividend payments and stocks' capacity to sustain their dividends. The securities comprising the Morningstar® US Market IndexSM (the “Base Index”) serve as the Fund’s selection universe. The Base Index measures the performance of large-, mid- and small-cap stocks in the U.S., representing the top 97% of the investable universe by market capitalization. According to the Index Provider, to be eligible for inclusion in the Base Index, a security must be listed on a qualifying U.S. securities exchange and be issued by a company incorporated in the United States or its territories and whose primary stock market activities are conducted in the United States. Securities issued by companies incorporated outside the United States and its territories may nonetheless be included in the Base Index if the company files a Form 10-K/10-Q or equivalents, and its primary business activities, as measured by the geographic distribution of revenue and assets, are conducted in the United States. The Base Index also excludes securities based on liquidity standards, among other criteria, determined by the Index Provider. From this universe, according to the Index Provider, the Index further excludes any securities issuing dividend payments that do not constitute qualifying income (i.e., real estate investment trusts). In order to be eligible for inclusion in the Index, a security must also have a positive dividend yield, a five-year dividend per share growth greater than or equal to 0 and a dividend coverage ratio greater than 1. A security’s coverage ratio equals its one-year forecast of earnings per share divided by its indicated dividend per share. All remaining securities are then ranked by indicated dividend yield and the top 100 securities are selected for inclusion in the Index. The Index weights the component securities based upon an indicated dividend dollar weighted methodology. Weights are adjusted so that no individual security has a weight of greater than 10% and securities with a weight of more than 5% do not collectively exceed 50% of the entire portfolio. The Index is rebalanced quarterly and reconstituted annually and the Fund will make corresponding changes to its portfolio shortly after the Index changes are made public. The Index’s quarterly rebalance schedule may cause the Fund to experience a higher rate of portfolio turnover. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. As of March 31, 2025, the Index was composed of 95 securities. The Fund’s investments will change as the Index changes and, as a result, the Fund may have significant investments in jurisdictions or investment sectors that it may not have had as of March 31, 2025. To the extent the Fund invests a significant portion of its assets in a given jurisdiction or investment sector, the Fund may be exposed to the risks associated with that jurisdiction or investment sector.
Risk [Heading] rr_RiskHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Risks</span>
Risk Caption rr_RiskCaption <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">You could lose money by investing in the Fund.</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">An investment in the Fund is not a deposit of a bank and is not insured or </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;"> There can be no assurance that </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">the Fund’s investment objective will be achieved. The order of the below risk factors does not indicate the significance of any </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">particular risk factor.</span>
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading <span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Annual Total Return</span>
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund and Index returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of the Index, a broad-based securities market index and a market index. The Fund’s performance information is accessible on the Fund’s website at http://www.ftportfolios.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns <span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">The bar chart and table below illustrate the annual calendar year returns of the Fund based on net asset value as well as the average annual Fund and Index returns. The bar chart and table provide an indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year-to-year and by showing how the Fund’s average annual total returns based on net asset value compared to those of the Index, a </span><span style="font-family:Arial;font-size:9.00pt;">broad-based securities market index and a market index. </span>
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress <span style="font-family:Arial;font-size:9.00pt;">http://www.ftportfolios.com</span>
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.</span>
Bar Chart [Heading] rr_BarChartHeading <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">First Trust Morningstar Dividend Leaders Index Fund</span> <br/><span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Calendar Year Total Returns as of 12/31</span>
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock During the periods shown in the chart above:ReturnPeriod EndedBest Quarter15.31%June 30, 2020Worst Quarter-30.57%March 31, 2020
Performance Table Heading rr_PerformanceTableHeading <span style="font-family:Arial;font-size:9.90pt;font-weight:bold;">Average Annual Total Returns for the Periods Ended December 31, 2024</span>
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate <span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax.</span>
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0%;">Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts </span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">(</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;font-style:italic;">IRAs</span><span style="color:#000000;font-family:Arial;font-size:9.00pt;">) or employee-sponsored retirement plans.</span>
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher <span style="font-family:Arial;font-size:9.00pt;">Returns after taxes on distributions reflect the taxed return on the payment of dividends </span><span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for </span><span style="font-family:Arial;font-size:9.00pt;">an index do not include expenses, which are deducted from Fund returns, or taxes.</span>
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.All after-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of any state or local tax.Returns after taxes on distributions reflect the taxed return on the payment of dividends and capital gains. Returns after taxes on distributions and sale of shares assume you sold your shares at period end, and, therefore, are also adjusted for any capital gains or losses incurred. Returns for an index do not include expenses, which are deducted from Fund returns, or taxes.Your own actual after-tax returns will depend on your specific tax situation and may differ from what is shown here. After-tax returns are not relevant to investors who hold Fund shares in tax-deferred accounts such as individual retirement accounts (IRAs) or employee-sponsored retirement plans.
First Trust Morningstar Dividend Leaders Index Fund | Risk Lose Money [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock You could lose money by investing in the Fund.
First Trust Morningstar Dividend Leaders Index Fund | Risk Not Insured Depository Institution [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
First Trust Morningstar Dividend Leaders Index Fund | Authorized Participant Concentration Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock AUTHORIZED PARTICIPANT CONCENTRATION RISK. Only an authorized participant may engage in creation or redemption transactions directly with the Fund. A limited number of institutions act as authorized participants for the Fund. To the extent that these institutions exit the business or are unable to proceed with creation and/or redemption orders and no other authorized participant steps forward to create or redeem, the Fund’s shares may trade at a premium or discount (the difference between the market price of the Fund's shares and the Fund's net asset value) and possibly face delisting and the bid/ask spread (the difference between the price that someone is willing to pay for shares of the Fund at a specific point in time versus the price at which someone is willing to sell) on the Fund’s shares may widen.
First Trust Morningstar Dividend Leaders Index Fund | Current Market Conditions Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock CURRENT MARKET CONDITIONS RISK. Current market conditions risk is the risk that a particular investment, or shares of the Fund in general, may fall in value due to current market conditions. As a means to fight inflation, which remains at elevated levels, the Federal Reserve and certain foreign central banks have raised interest rates; however, the Federal Reserve has recently lowered interest rates and may continue to do so. U.S. regulators have proposed several changes to market and issuer regulations which would directly impact the Fund, and any regulatory changes could adversely impact the Fund’s ability to achieve its investment strategies or make certain investments. Recent and potential future bank failures could result in disruption to the broader banking industry or markets generally and reduce confidence in financial institutions and the economy as a whole, which may also heighten market volatility and reduce liquidity. Additionally, challenges in commercial real estate markets, including rising interest rates, declining valuations and increasing vacancies, could have a broader impact on financial markets. The ongoing adversarial political climate in the United States, as well as political and diplomatic events both domestic and abroad, have and may continue to have an adverse impact the U.S. regulatory landscape, markets and investor behavior, which could have a negative impact on the Fund’s investments and operations. The change in administration resulting from the 2024 United States national elections could result in significant impacts to international trade relations, tax and immigration policies, and other aspects of the national and international political and financial landscape, which could affect, among other things, inflation and the securities markets generally. Other unexpected political, regulatory and diplomatic events within the U.S. and abroad may affect investor and consumer confidence and may adversely impact financial markets and the broader economy. For example, ongoing armed conflicts between Russia and Ukraine in Europe and among Israel, Iran, Hamas and other militant groups in the Middle East, have caused and could continue to cause significant market disruptions and volatility within the markets in Russia, Europe, the Middle East and the United States. The hostilities and sanctions resulting from those hostilities have and could continue to have a significant impact on certain Fund investments as well as Fund performance and liquidity. The economies of the United States and its trading partners, as well as the financial markets generally, may be adversely impacted by trade disputes, including the imposition of tariffs, and other matters. For example, the United States has imposed trade barriers and restrictions on China. In addition, the Chinese government is engaged in a longstanding dispute with Taiwan, continually threatening an invasion. If the political climate between the United States and China does not improve or continues to deteriorate, if China were to attempt invading Taiwan, or if other geopolitical conflicts develop or worsen, economies, markets and individual securities may be adversely affected, and the value of the Fund’s assets may go down. A public health crisis and the ensuing policies enacted by governments and central banks may cause significant volatility and uncertainty in global financial markets, negatively impacting global growth prospects. As the COVID-19 global pandemic illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. Advancements in technology may also adversely impact markets and the overall performance of the Fund. For instance, the economy may be significantly impacted by the advanced development and increased regulation of artificial intelligence. Additionally, cyber security breaches of both government and non-government entities could have negative impacts on infrastructure and the ability of such entities, including the Fund, to operate properly. These events, and any other future events, may adversely affect the prices and liquidity of the Fund’s portfolio investments and could result in disruptions in the trading markets.
First Trust Morningstar Dividend Leaders Index Fund | Cyber Security Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock CYBER SECURITY RISK. The Fund is susceptible to operational risks through breaches in cyber security. A breach in cyber security refers to both intentional and unintentional events that may cause the Fund to lose proprietary information, suffer data corruption or lose operational capacity. Such events could cause the Fund to incur regulatory penalties, reputational damage, additional compliance costs associated with corrective measures and/or financial loss. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems through “hacking” or malicious software coding but may also result from outside attacks such as denial-of-service attacks through efforts to make network services unavailable to intended users. In addition, cyber security breaches of the issuers of securities in which the Fund invests or the Fund’s third-party service providers, such as its administrator, transfer agent, custodian, or sub-advisor, as applicable, can also subject the Fund to many of the same risks associated with direct cyber security breaches. Although the Fund has established risk management systems designed to reduce the risks associated with cyber security, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers or third-party service providers.
First Trust Morningstar Dividend Leaders Index Fund | Dividends Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock DIVIDENDS RISK. The Fund’s investment in dividend-paying securities could cause the Fund to underperform similar funds that invest without consideration of an issuer’s track record of paying dividends. Companies that issue dividend-paying securities are not required to continue to pay dividends on such securities. Therefore, there is the possibility that such companies could reduce or eliminate the payment of dividends in the future, which could negatively affect the Fund’s performance.
First Trust Morningstar Dividend Leaders Index Fund | Equity Securities Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock EQUITY SECURITIES RISK. The value of the Fund's shares will fluctuate with changes in the value of the equity securities in which it invests. Equity securities prices fluctuate for several reasons, including changes in investors’ perceptions of the financial condition of an issuer or the general condition of the relevant equity market, such as market volatility, or when political or economic events affecting an issuer occur. Common stock prices may be particularly sensitive to rising interest rates, as the cost of capital rises and borrowing costs increase. Equity securities may decline significantly in price over short or extended periods of time, and such declines may occur in the equity market as a whole, or they may occur in only a particular country, company, industry or sector of the market.
First Trust Morningstar Dividend Leaders Index Fund | Index Concentration Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock INDEX CONCENTRATION RISK. The Fund will be concentrated in an industry or a group of industries to the extent that the Index is so concentrated. To the extent that the Fund invests a significant percentage of its assets in a single asset class or the securities of issuers within the same country, state, region, industry or sector, an adverse economic, business or political development may affect the value of the Fund’s investments more than if the Fund were more broadly diversified. A significant exposure makes the Fund more susceptible to any single occurrence and may subject the Fund to greater market risk than a fund that is more broadly diversified. There may be instances in which the Index, for a variety of reasons including changes in the prices of individual securities held by the Fund, has a larger exposure to a small number of stocks or a single stock relative to the rest of the stocks in the Index. Under such circumstances, the Fund will not deviate from the Index except in rare circumstances or in an immaterial way and therefore the Fund’s returns would be more greatly influenced by the returns of the stock(s) with the larger exposure.
First Trust Morningstar Dividend Leaders Index Fund | Index Or Model Constituent Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock INDEX OR MODEL CONSTITUENT RISK. The Fund may be a constituent of one or more indices or ETF models. As a result, the Fund may be included in one or more index-tracking exchange-traded funds or mutual funds. Being a component security of such a vehicle could greatly affect the trading activity involving the Fund’s shares, the size of the Fund and the market volatility of the Fund. Inclusion in an index could increase demand for the Fund and removal from an index could result in outsized selling activity in a relatively short period of time. As a result, the Fund’s net asset value could be negatively impacted and the Fund’s market price may be below the Fund’s net asset value during certain periods. In addition, index rebalances may potentially result in increased trading activity in the Fund's shares.
First Trust Morningstar Dividend Leaders Index Fund | Index Provider Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock INDEX PROVIDER RISK. There is no assurance that the Index Provider, or any agents that act on its behalf, will compile the Index accurately, or that the Index will be determined, maintained, constructed, reconstituted, rebalanced, composed, calculated or disseminated accurately. The Index Provider and its agents do not provide any representation or warranty in relation to the quality, accuracy or completeness of data in the Index, and do not guarantee that the Index will be calculated in accordance with its stated methodology. The Advisor’s mandate as described in this prospectus is to manage the Fund consistently with the Index provided by the Index Provider. The Advisor relies upon the Index provider and its agents to accurately compile, maintain, construct, reconstitute, rebalance, compose, calculate and disseminate the Index accurately. Therefore, losses or costs associated with any Index Provider or agent errors generally will be borne by the Fund and its shareholders. To correct any such error, the Index Provider or its agents may carry out an unscheduled rebalance of the Index or other modification of Index constituents or weightings. When the Fund in turn rebalances its portfolio, any transaction costs and market exposure arising from such portfolio rebalancing will be borne by the Fund and its shareholders. Unscheduled rebalances also expose the Fund to additional tracking error risk. Errors in respect of the quality, accuracy and completeness of the data used to compile the Index may occur from time to time and may not be identified and corrected by the Index Provider for a period of time or at all, particularly where the Index is less commonly used as a benchmark by funds or advisors. For example, during a period where the Index contains incorrect constituents, the Fund tracking the Index would have market exposure to such constituents and would be underexposed to the Index’s other constituents. Such errors may negatively impact the Fund and its shareholders. The Index Provider and its agents rely on various sources of information to assess the criteria of issuers included in the Index, including information that may be based on assumptions and estimates. Neither the Fund nor the Advisor can offer assurances that the Index’s calculation methodology or sources of information will provide an accurate assessment of included issuers. Unusual market conditions or issuer-specific events may cause the Index Provider to postpone a scheduled rebalance, exclude or substitute a security in the Index or undertake other measures which could cause the Index to vary from its normal or expected composition. The postponement of a scheduled rebalance in a time of market volatility could mean that constituents that would otherwise be removed at rebalance due to changes in market capitalizations, issuer credit ratings, or other reasons may remain, causing the performance and constituents of the Index to vary from those expected under normal conditions. Apart from scheduled rebalances, the Index Provider or its agents may carry out additional ad hoc rebalances to the Index due to unusual market conditions or in order, for example, to correct an error in the selection of index constituents.
First Trust Morningstar Dividend Leaders Index Fund | Inflation Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock INFLATION RISK. Inflation risk is the risk that the value of assets or income from investments will be less in the future as inflation decreases the value of money. As inflation increases, the present value of the Fund’s assets and distributions may decline.
First Trust Morningstar Dividend Leaders Index Fund | Large Capitalization Companies Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock LARGE CAPITALIZATION COMPANIES RISK. Large capitalization companies may grow at a slower rate and be less able to adapt to changing market conditions than smaller capitalization companies. Thus, the return on investment in securities of large capitalization companies may be less than the return on investment in securities of small and/or mid capitalization companies. The performance of large capitalization companies also tends to trail the overall market during different market cycles.
First Trust Morningstar Dividend Leaders Index Fund | Market Maker Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MARKET MAKER RISK. The Fund faces numerous market trading risks, including the potential lack of an active market for Fund shares due to a limited number of market markers. Decisions by market makers or authorized participants to reduce their role or step away from these activities in times of market stress could inhibit the effectiveness of the arbitrage process in maintaining the relationship between the underlying values of the Fund’s portfolio securities and the Fund’s market price. The Fund may rely on a small number of third-party market makers to provide a market for the purchase and sale of shares. Any trading halt or other problem relating to the trading activity of these market makers could result in a dramatic change in the spread between the Fund’s net asset value and the price at which the Fund’s shares are trading on the Exchange, which could result in a decrease in value of the Fund’s shares. This reduced effectiveness could result in Fund shares trading at a discount to net asset value and also in greater than normal intraday bid-ask spreads for Fund shares.
First Trust Morningstar Dividend Leaders Index Fund | Market Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock MARKET RISK. Market risk is the risk that a particular investment, or shares of the Fund in general, may fall in value. Securities are subject to market fluctuations caused by real or perceived adverse economic, political, and regulatory factors or market developments, changes in interest rates and perceived trends in securities prices. Shares of the Fund could decline in value or underperform other investments. In addition, local, regional or global events such as war, acts of terrorism, market manipulation, government defaults, government shutdowns, regulatory actions, political changes, diplomatic developments, the imposition of sanctions and other similar measures, spread of infectious diseases or other public health issues, recessions, natural disasters, or other events could have a significant negative impact on the Fund and its investments. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares, the liquidity of an investment, and may result in increased market volatility. During any such events, the Fund’s shares may trade at increased premiums or discounts to their net asset value, the bid/ask spread on the Fund’s shares may widen and the returns on investment may fluctuate.
First Trust Morningstar Dividend Leaders Index Fund | Non Correlation Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock NON-CORRELATION RISK. The Fund’s return may not match the return of the Index for a number of reasons. The Fund incurs operating expenses not applicable to the Index, and may incur costs in buying and selling securities, especially when rebalancing the Fund’s portfolio holdings to reflect changes in the composition of the Index. In addition, the Fund’s portfolio holdings may not exactly replicate the securities included in the Index or the ratios between the securities included in the Index. Additionally, in order to comply with its investment strategies and policies, the Fund portfolio may deviate from the composition of the Index. Accordingly, the Fund's return may underperform the return of the Index.
First Trust Morningstar Dividend Leaders Index Fund | Risk Nondiversified [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock NON-DIVERSIFICATION RISK. The Fund is classified as “non-diversified” under the Investment Company Act of 1940, as amended (the "1940 Act"). As a result, the Fund is only limited as to the percentage of its assets which may be invested in the securities of any one issuer by the diversification requirements imposed by the Internal Revenue Code of 1986, as amended. The Fund may invest a relatively high percentage of its assets in a limited number of issuers. As a result, the Fund may be more susceptible to a single adverse economic or regulatory occurrence affecting one or more of these issuers, experience increased volatility and be highly invested in certain issuers.
First Trust Morningstar Dividend Leaders Index Fund | Operational Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock OPERATIONAL RISK. The Fund is subject to risks arising from various operational factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third-parties, failed or inadequate processes and technology or systems failures. The Fund relies on third-parties for a range of services, including custody. Any delay or failure relating to engaging or maintaining such service providers may affect the Fund’s ability to meet its investment objective. Although the Fund and the Fund's investment advisor seek to reduce these operational risks through controls and procedures, there is no way to completely protect against such risks.
First Trust Morningstar Dividend Leaders Index Fund | Passive Investment Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock PASSIVE INVESTMENT RISK. The Fund is not actively managed. The Fund invests in securities included in or representative of the Index regardless of investment merit. The Fund generally will not attempt to take defensive positions in declining markets. In the event that the Index is no longer calculated, the Index license is terminated or the identity or character of the Index is materially changed, the Fund will seek to engage a replacement index.
First Trust Morningstar Dividend Leaders Index Fund | Portfolio Turnover Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock PORTFOLIO TURNOVER RISK. High portfolio turnover may result in the Fund paying higher levels of transaction costs and may generate greater tax liabilities for shareholders. Portfolio turnover risk may cause the Fund’s performance to be less than expected.
First Trust Morningstar Dividend Leaders Index Fund | Premium Discount Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock PREMIUM/DISCOUNT RISK. The market price of the Fund’s shares will generally fluctuate in accordance with changes in the Fund’s net asset value as well as the relative supply of and demand for shares on the Exchange. The Fund’s investment advisor cannot predict whether shares will trade below, at or above their net asset value because the shares trade on the Exchange at market prices and not at net asset value. Price differences may be due, in large part, to the fact that supply and demand forces at work in the secondary trading market for shares will be closely related, but not identical, to the same forces influencing the prices of the holdings of the Fund trading individually or in the aggregate at any point in time. However, given that shares can only be purchased and redeemed in Creation Units, and only to and from broker-dealers and large institutional investors that have entered into participation agreements (unlike shares of closed-end funds, which frequently trade at appreciable discounts from, and sometimes at premiums to, their net asset value), the Fund’s investment advisor believes that large discounts or premiums to the net asset value of shares should not be sustained. During stressed market conditions, the market for the Fund’s shares may become less liquid in response to deteriorating liquidity in the market for the Fund’s underlying portfolio holdings, which could in turn lead to differences between the market price of the Fund’s shares and their net asset value and the bid/ask spread on the Fund’s shares may widen.
First Trust Morningstar Dividend Leaders Index Fund | Smaller Companies Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock SMALLER COMPANIES RISK. Small and/or mid capitalization companies may be more vulnerable to adverse general market or economic developments, and their securities may be less liquid and may experience greater price volatility than larger, more established companies as a result of several factors, including limited trading volumes, fewer products or financial resources, management inexperience and less publicly available information. Accordingly, such companies are generally subject to greater market risk than larger, more established companies.
First Trust Morningstar Dividend Leaders Index Fund | Trading Issues Risk [Member]  
Risk Return Abstract rr_RiskReturnAbstract  
Risk [Text Block] rr_RiskTextBlock TRADING ISSUES RISK. Trading in Fund shares on the Exchange may be halted due to market conditions or for reasons that, in the view of the Exchange, make trading in shares inadvisable. In addition, trading in Fund shares on the Exchange is subject to trading halts caused by extraordinary market volatility pursuant to the Exchange’s “circuit breaker” rules. There can be no assurance that the requirements of the Exchange necessary to maintain the listing of the Fund will continue to be met or will remain unchanged. The Fund may have difficulty maintaining its listing on the Exchange in the event the Fund’s assets are small, the Fund does not have enough shareholders, or if the Fund is unable to proceed with creation and/or redemption orders.
First Trust Morningstar Dividend Leaders Index Fund | First Trust Morningstar Dividend Leaders Index Fund  
Risk Return Abstract rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)[ctag:span_t-rule1] rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Management Fees[ctag:span_t-indent1] rr_ManagementFeesOverAssets 0.30% [1]
Distribution and Service (12b-1) Fees[ctag:span_t-indent1] rr_DistributionAndService12b1FeesOverAssets none
Other Expenses[ctag:span_t-indent1] rr_OtherExpensesOverAssets 0.13%
Acquired Fund Fees and Expenses[ctag:span_t-indent1-rule] rr_AcquiredFundFeesAndExpensesOverAssets none
Total Annual Fund Operating Expenses[ctag:span_t-indent1-rule3] rr_ExpensesOverAssets 0.43%
Fee Waiver and Expense Reimbursement[ctag:span_t-indent1-rule] rr_FeeWaiverOrReimbursementOverAssets none [2]
Total Annual Fund Operating Expenses After Fee Waiver and Expense Reimbursement[ctag:span_t-indent1-rule3] rr_NetExpensesOverAssets 0.43%
1 Year rr_ExpenseExampleNoRedemptionYear01 $ 44
3 Years rr_ExpenseExampleNoRedemptionYear03 138
5 Years rr_ExpenseExampleNoRedemptionYear05 241
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 542
2015 rr_AnnualReturn2015 2.73%
2016 rr_AnnualReturn2016 20.67%
2017 rr_AnnualReturn2017 11.97%
2018 rr_AnnualReturn2018 (5.87%)
2019 rr_AnnualReturn2019 24.36%
2020 rr_AnnualReturn2020 (4.42%)
2021 rr_AnnualReturn2021 24.76%
2022 rr_AnnualReturn2022 6.71%
2023 rr_AnnualReturn2023 2.90%
2024 rr_AnnualReturn2024 16.98%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Best Quarter</span>
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.31%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel <span style="color:#000000;font-family:Arial;font-size:9.00pt;margin-left:0.0pt;">Worst Quarter</span>
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (30.57%)
1 Year rr_AverageAnnualReturnYear01 16.98%
5 Years rr_AverageAnnualReturnYear05 8.90%
10 Years rr_AverageAnnualReturnYear10 9.55%
Since Inception rr_AverageAnnualReturnSinceInception 7.94%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 09, 2006
First Trust Morningstar Dividend Leaders Index Fund | After tax on distributions | First Trust Morningstar Dividend Leaders Index Fund  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 14.97%
5 Years rr_AverageAnnualReturnYear05 7.01%
10 Years rr_AverageAnnualReturnYear10 7.78%
Since Inception rr_AverageAnnualReturnSinceInception 6.30%
First Trust Morningstar Dividend Leaders Index Fund | After tax on distributions and sale of fund shares | First Trust Morningstar Dividend Leaders Index Fund  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 10.02%
5 Years rr_AverageAnnualReturnYear05 6.03%
10 Years rr_AverageAnnualReturnYear10 6.80%
Since Inception rr_AverageAnnualReturnSinceInception 5.65%
First Trust Morningstar Dividend Leaders Index Fund | S&P 500® Index (reflects no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 25.02%
5 Years rr_AverageAnnualReturnYear05 14.53%
10 Years rr_AverageAnnualReturnYear10 13.10%
Since Inception rr_AverageAnnualReturnSinceInception 10.62%
First Trust Morningstar Dividend Leaders Index Fund | Morningstar® Dividend Leaders Index(SM) (reflects no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 17.49%
5 Years rr_AverageAnnualReturnYear05 9.45%
10 Years rr_AverageAnnualReturnYear10 10.10%
Since Inception rr_AverageAnnualReturnSinceInception 8.48%
First Trust Morningstar Dividend Leaders Index Fund | Russell 1000® Value Index (reflects no deduction for fees, expenses or taxes)  
Risk Return Abstract rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 14.37%
5 Years rr_AverageAnnualReturnYear05 8.68%
10 Years rr_AverageAnnualReturnYear10 8.49%
Since Inception rr_AverageAnnualReturnSinceInception 7.81%
[1] The management fee paid to First Trust Advisors L.P., the Fund’s investment advisor, may be reduced at certain levels of Fund net assets (“breakpoints”). The Fund's contractual management fee absent any breakpoints is 0.30%. See the Fund’s Statement of Additional Information for more information on the breakpoints.
[2] First Trust Advisors L.P., the Fund’s investment advisor, has agreed to waive fees and/or reimburse Fund expenses to the extent that the operating expenses of the Fund (excluding interest expense, brokerage commissions and other trading expenses, acquired fund fees and expenses, taxes and extraordinary expenses) exceed 0.45% of its average daily net assets (the “Expense Cap”) at least through April 30, 2026. The agreement may be terminated by the Trust, on behalf of the Fund, at any time and by the Fund’s investment advisor only after April 30, 2026 upon 60 days’ written notice.