v3.25.1
Document And Entity Information - shares
3 Months Ended
Mar. 31, 2025
Apr. 29, 2025
Document Information [Line Items]    
Entity Central Index Key 0001274173  
Entity Registrant Name JANUS HENDERSON GROUP PLC  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q1  
Document Fiscal Year Focus 2025  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2025  
Document Transition Report false  
Entity File Number 001-38103  
Entity Incorporation, State or Country Code Y9  
Entity Tax Identification Number 98-1376360  
Entity Address, Address Line One 201 Bishopsgate  
Entity Address, City or Town London  
Entity Address, Country GB  
Entity Address, Postal Zip Code EC2M3AE  
City Area Code 44  
Local Phone Number (0) 20 7818 1818  
Title of 12(b) Security Common Stock, $1.50 Per Share Par Value  
Trading Symbol JHG  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   157,557,812