XML 59 R47.htm IDEA: XBRL DOCUMENT
v3.25.1

Note 4 - Investments - Investment Gains (Losses), Net (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2025 | Mar. 31, 2024
Investment gains (losses), net | $ (5.5) | $ 22.5
Seeded Investment Products and Hedges, Net [Member] |  |
Investment gains (losses), net | 5.8 | 11.9
Third-party Ownership Interests in Seeded Investment Products [Member] |  |
Investment gains (losses), net | (3.3) | 10.5
Equity Method Investments [Member] |  |
Investment gains (losses), net | (1.7) | (1.4)
Other Security Investments [Member] |  |
Investment gains (losses), net | $ (6.3) | $ 1.5

X
- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 + Details
Name: | us-gaap_GainLossOnInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_InvestmentTypeAxis=jhg_SeededInvestmentProductsAndHedgesNetMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=jhg_ThirdpartyOwnershipInterestsInSeededInvestmentProductsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_EquityMethodInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_OtherAggregatedInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |