Janus Henderson Small Cap Value Fund Performance Management - Class D Shares [Member] - Janus Henderson Small Cap Value Fund	Jun. 30, 2025
Prospectus [Line Items]
Bar Chart and Performance Table [Heading]	<span style="color:#FFFFFF;font-family:Times New Roman;font-size:10.45pt;font-weight:bold;margin-left:0.0pt;text-transform:uppercase;">Performance information</span>
Performance Narrative [Text Block]	The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more additional indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janushenderson.com/allfunds or by calling 1-800-525-3713.
Performance Past Does Not Indicate Future [Text]	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.</span>
Performance Information Illustrates Variability of Returns [Text]	<span style="font-family:Times New Roman;font-size:9.50pt;">The bar chart depicts the change in performance from year to year during the periods indicated. </span><span style="font-family:Times New Roman;font-size:9.50pt;">The table compares the </span><span style="font-family:Times New Roman;font-size:9.50pt;">Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more additional indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions.</span>
Performance Additional Market Index [Text]	<span style="font-family:Times New Roman;font-size:9.50pt;">The table compares the </span><span style="font-family:Times New Roman;font-size:9.50pt;">Fund’s average annual returns for the periods indicated to a broad-based securities market index, as well as to one or more additional indices that have investment characteristics similar to those of the Fund. All figures assume reinvestment of dividends and distributions.</span>
Bar Chart [Heading]	Annual Total Returns for Class D Shares (calendar year-end)
Bar Chart Closing [Text Block]	Best Quarter:4th Quarter 202025.65%Worst Quarter:1st Quarter 2020– 32.58%
Year to Date Return, Label [Optional Text]	<span style="font-family:Times New Roman;font-size:9.50pt;">Class D Shares’ year-to-date return as of the calendar quarter ended September 30, 2025 was 4.66%.</span>
Performance Table Heading	Average Annual Total Returns (periods ended 12/31/24)
Performance Table Narrative	The Fund’s broad-based benchmark index is the Russell 3000 Index, due to regulatory requirements. The Fund’s additional benchmark index is the Russell 2000 Value Index, which has investment characteristics similar to those of the Fund. The indices are described below.•The Russell 3000 Index measures the performance of the largest 3,000 U.S. companies.•The Russell 2000 Value Index measures the performance of those Russell 2000 companies with lower price-to-book ratios and lower forecasted growth values.After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-advantaged account, such as a 401(k) plan or an IRA.
Performance Table Uses Highest Federal Rate	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. </span>
Performance Table Not Relevant to Tax Deferred	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">Actual after-tax returns depend on your individual tax situation and may differ from those </span><span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;">shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-advantaged account, such as a 401(k) plan or an IRA.</span>
Performance Table Explanation after Tax Higher	<span style="color:#000000;font-family:Times New Roman;font-size:7.60pt;">If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.</span>
Performance Table Closing [Text Block]	Updated performance information is available at janushenderson.com/allfunds or by calling 1-800-525-3713.
Performance Availability Website Address [Text]	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">janushenderson.com/allfunds</span>
Performance Availability Phone [Text]	<span style="color:#000000;font-family:Times New Roman;font-size:9.50pt;font-style:italic;">1-800-525-3713</span>
Class D
Prospectus [Line Items]
Bar Chart, Year to Date Return	4.66%
Bar Chart, Year to Date Return, Date	Sep. 30, 2025
Highest Quarterly Return, Label [Optional Text]	Best Quarter
Highest Quarterly Return	25.65%
Highest Quarterly Return, Date	Dec. 31, 2020
Lowest Quarterly Return, Label [Optional Text]	Worst Quarter
Lowest Quarterly Return	(32.58%)
Lowest Quarterly Return, Date	Mar. 31, 2020