Name:	jhg_AccumulatedShareBasedCompensationCosts
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of increase in additional paid in capital (APIC) resulting from the reduction in par value.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

This line items represents the information pertaining to basis of presentation.

No definition available.

Name:	jhg_BasisOfPresentationLineItems
Namespace Prefix:	jhg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This item represents the gain (loss) on purchase, issue, sale or cancellation of Henderson's own equity shares.

No definition available.

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

Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(30)(a)(1))
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Period Type:	instant

Amount of increase to additional paid-in capital (APIC) for recognition of cost for award under share-based payment arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 20
-Section 55
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-Publisher FASB
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-Section 35
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Face amount or stated value per share of common stock.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
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Name:	us-gaap_CommonStockParOrStatedValuePerShare
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Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Aggregate par or stated value of issued nonredeemable common stock (or common stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable common shares, par value and other disclosure concepts are in another section within stockholders' equity.

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-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_CommonStockValue
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Period Type:	instant

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

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

- References

No definition available.

Name:	us-gaap_FiniteLivedIntangibleAssetsNetAbstract
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Data Type:	xbrli:stringItemType
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Period Type:	duration

Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

No definition available.

Name:	us-gaap_NumberOfReportingUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The cash inflow associated with the amount received from the stock plan during the period.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 14
-Subparagraph (a)
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Name:	us-gaap_ProceedsFromStockPlans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 4
-Subparagraph (SAB TOPIC 4.C)
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