First Trust Horizon Managed Volatility Domestic ETF Investment Strategy - First Trust Horizon Managed Volatility Domestic ETF	Jul. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Investment Strategies</span>
Strategy Narrative [Text Block]	Under normal market conditions, the Fund seeks to achieve its investment objective by investing at least 80% of its net assets (including investment borrowings) in common stocks of domestic companies listed and traded on U.S. national securities exchanges that Horizon Investments, LLC (“Horizon” or the “Sub-Advisor”) believes exhibit low future expected volatility. The goal of this strategy is to capture upside price movements in rising markets and reduce downside risk when markets decline. To implement this strategy, the Sub-Advisor employs volatility forecasting models to forecast future expected volatility. The strategy is largely quantitative and rules-based, but also includes multiple parameters over which the Sub-Advisor may exercise discretion (including, but not limited to, the number of holdings and the weightings of particular holdings) in connection with its active management of the Fund. To begin, the Sub-Advisor gathers pricing and generates return data for the starting universe, which is comprised of common stocks of large cap domestic companies listed and traded on U.S. national securities exchanges. The Sub-Advisor then conducts volatility forecasts for securities comprising the starting universe and ranks them from low to high based on their volatility forecasts. The Sub-Advisor targets 50-200 securities for inclusion in the portfolio based on future expected volatility. Once the final portfolio is selected, the Sub-Advisor gives larger weights to securities with lower future expected volatility and has the ability to adjust how aggressive the weighting scheme is depending on market conditions. The Sub-Advisor periodically rebalances and reallocates the portfolio using this methodology, which may result in higher levels of portfolio turnover. As of October 31, 2025, the Fund had significant investments in information technology companies, although this may change from time to time. 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.
Strategy Portfolio Concentration [Text]	<span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">As of October 31, 2025, the Fund had significant investments in information technology companies, although this may change from time to time.</span>

First Trust Horizon Managed Volatility Domestic ETF Investment Strategy - First Trust Horizon Managed Volatility Domestic ETF

Jul. 31, 2025

<span style="color:#000000;font-family:Arial;font-size:9.90pt;font-weight:bold;">Principal Investment Strategies</span>

Strategy Narrative [Text Block]

Under normal market conditions, the Fund seeks to achieve its investment objective by investing at least 80% of its net assets (including investment borrowings) in common stocks of domestic companies listed and traded on U.S. national securities exchanges that Horizon Investments, LLC (“Horizon” or the “Sub-Advisor”) believes exhibit low future expected volatility. The goal of this strategy is to capture upside price movements in rising markets and reduce downside risk when markets decline. To implement this strategy, the Sub-Advisor employs volatility forecasting models to forecast future expected volatility. The strategy is largely quantitative and rules-based, but also includes multiple parameters over which the Sub-Advisor may exercise discretion (including, but not limited to, the number of holdings and the weightings of particular holdings) in connection with its active management of the Fund. To begin, the Sub-Advisor gathers pricing and generates return data for the starting universe, which is comprised of common stocks of large cap domestic companies listed and traded on U.S. national securities exchanges. The Sub-Advisor then conducts volatility forecasts for securities comprising the starting universe and ranks them from low to high based on their volatility forecasts. The Sub-Advisor targets 50-200 securities for inclusion in the portfolio based on future expected volatility. Once the final portfolio is selected, the Sub-Advisor gives larger weights to securities with lower future expected volatility and has the ability to adjust how aggressive the weighting scheme is depending on market conditions. The Sub-Advisor periodically rebalances and reallocates the portfolio using this methodology, which may result in higher levels of portfolio turnover. As of October 31, 2025, the Fund had significant investments in information technology companies, although this may change from time to time. 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.

Strategy Portfolio Concentration [Text]

<span style="font-family:Arial;font-size:9.00pt;margin-left:0%;">As of October 31, 2025, the Fund had significant investments in information technology companies, although this may change from time to time.</span>