| Document And Entity Information | Oct. 31, 2024 |
| Document Information [Line Items] | |
| Entity, Registrant Name | JANUS HENDERSON GROUP PLC |
| Document, Type | 8-K |
| Document, Period End Date | Oct. 31, 2024 |
| 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 | (0) 20 |
| Local Phone Number | 7818 1818 |
| Title of 12(b) Security | Common Stock, $1.50 Per Share Par Value |
| Trading Symbol | JHG |
| Security Exchange Name | NYSE |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001274173 |
