First Trust Short Duration High Income Fund Investment Strategy - First Trust Short Duration High Income Fund	Oct. 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 invests at least 80% of its net assets (including investment borrowings) in high yield debt securities and bank loans that are rated below-investment grade or unrated. High yield debt securities are below-investment grade debt securities, commonly known as “junk bonds.” For purposes of determining whether a security is below-investment grade, the lowest available rating is used. The Fund has a short duration investment strategy, which seeks to maintain, under normal market conditions, a blended (or weighted average) portfolio duration of three years or less. Duration is a mathematical calculation of the average life of a debt security (or portfolio of debt securities) that serves as a measure of its price risk. In general, each year of duration represents an expected 1% change in the value of a security for every 1% immediate change in interest rates. For example, if a portfolio of bank loans and fixed income securities has an average duration of three years, its value can be expected to fall about 3% if interest rates rise by 1%. Conversely, the portfolio’s value can be expected to rise about 3% if interest rates fall by 1%. As a result, prices of instruments with shorter durations tend to be less sensitive to interest rate changes than instruments with longer durations. As the value of a security changes over time, so will its duration. Bank loans have relatively low durations, i.e., close to zero, which means that the interest rates on loans reset approximately every 30-90 days, on average, however, the inclusion of Secured Overnight Financing Rate ("SOFR") or similar reference rate floors on certain senior loans or other factors may cause interest rate duration to be longer than 90 days. Accordingly, the Fund’s investment in such securities will likely reduce the blended duration of the portfolio and in turn the Fund’s overall interest rate sensitivity. “Average duration” is the measure of a debt instrument’s or a portfolio’s price sensitivity with respect to changes in market yields. The blended duration is the sum of the dollar weighted average duration of the Fund’s positions. Under normal market conditions, the Fund may invest up to 15% of its net assets in non-U.S. securities denominated in non-U.S. currencies. The Fund may also invest in investment grade debt securities, covenant-lite loans, floating rate securities and companies with various market capitalizations.

First Trust Short Duration High Income Fund Investment Strategy - First Trust Short Duration High Income Fund

Oct. 31, 2025

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

Under normal market conditions, the Fund invests at least 80% of its net assets (including investment borrowings) in high yield debt securities and bank loans that are rated below-investment grade or unrated. High yield debt securities are below-investment grade debt securities, commonly known as “junk bonds.” For purposes of determining whether a security is below-investment grade, the lowest available rating is used. The Fund has a short duration investment strategy, which seeks to maintain, under normal market conditions, a blended (or weighted average) portfolio duration of three years or less. Duration is a mathematical calculation of the average life of a debt security (or portfolio of debt securities) that serves as a measure of its price risk. In general, each year of duration represents an expected 1% change in the value of a security for every 1% immediate change in interest rates. For example, if a portfolio of bank loans and fixed income securities has an average duration of three years, its value can be expected to fall about 3% if interest rates rise by 1%. Conversely, the portfolio’s value can be expected to rise about 3% if interest rates fall by 1%. As a result, prices of instruments with shorter durations tend to be less sensitive to interest rate changes than instruments with longer durations. As the value of a security changes over time, so will its duration. Bank loans have relatively low durations, i.e., close to zero, which means that the interest rates on loans reset approximately every 30-90 days, on average, however, the inclusion of Secured Overnight Financing Rate ("SOFR") or similar reference rate floors on certain senior loans or other factors may cause interest rate duration to be longer than 90 days. Accordingly, the Fund’s investment in such securities will likely reduce the blended duration of the portfolio and in turn the Fund’s overall interest rate sensitivity. “Average duration” is the measure of a debt instrument’s or a portfolio’s price sensitivity with respect to changes in market yields. The blended duration is the sum of the dollar weighted average duration of the Fund’s positions. Under normal market conditions, the Fund may invest up to 15% of its net assets in non-U.S. securities denominated in non-U.S. currencies. The Fund may also invest in investment grade debt securities, covenant-lite loans, floating rate securities and companies with various market capitalizations.