Represent the amount of performance fees generated that would be a part of the sales consideration.

No definition available.

Name:	jhg_AmountOfPerformanceFeesGeneratedAsPartOfConsideration
Namespace Prefix:	jhg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the business combination contingent consideration forecasting revenues term.

+ References

No definition available.

+ Details

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Namespace Prefix:	jhg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Consideration for the sale was based on percentage share of the management and performance fees generated by investee.

+ References

No definition available.

+ Details

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Namespace Prefix:	jhg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of performance taken to considered for calculation of consideration of sale of investee assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	jhg_PeriodOfPerformanceOfInvesteeForRecognizingConsideration
Namespace Prefix:	jhg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of asset recognized arising from contingent consideration in a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6411-128476

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116859824&loc=d3e6819-128478

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Fair Value Measurements - Disposal of Volantis (Details) £ in Millions, $ in Millions		6 Months Ended
	Apr. 01, 2017 GBP (£)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Dispositions
Revenue forecasting period		3 years
Volantis \| Discontinued Operations, Disposed of by Sale
Dispositions
Percentage of share for consideration of sale	10.00%
Period of performance of investee for recognizing consideration	3 years
Fair value of contingent consideration		$ 0.8	$ 2.9
Business Combination, Contingent Consideration, Asset		$ 0.8	$ 2.9
Certain fund
Dispositions
Percentage of share for consideration of sale	50.00%
Performance fee threshold \| £	£ 12