Document And Entity Information Statistical Measurement [Axis] Note To Financial Statement Details Textual EBP, Basis of Accounting [Policy Text Block] Significant Accounting Policies Note 1 - Description of Plan Note 3 - Fair Value Measurements Note 4 - Nonparticipant-directed Investments us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAllocatedSharesForEsop Transfers to participant-directed investments Schedule H - Line 4a Schedule H - Line 4(i) Note 1 - Description of Plan - Vesting Percentage (Details) Note 3 - Fair Value Measurements - Schedule of Fair Value Measurements (Details) Note 4 - Nonparticipant-directed Investments - Schedule of Nonparticipant-directed Investments (Details) Minimum [Member] Schedule H - Line 4a - Schedule of Delinquent Participant Contributions (Details) Schedule H - Line 4(i) - Schedule of Assets (Held at End of Year) (Details) Statistical Measurement [Domain] Schedule H - Line 4(i) - Schedule of Assets (Held at End of Year) 2 (Details) Maximum [Member] Notes To Financial Statements Notes To Financial Statements [Abstract] EBP, Investment, Fair Value and NAV [Text Block] EBP, Related Party and Party-in-Interest Transactions [Table] Accounting Policies [Abstract] us-gaap-ebp_EbpPlanName EBP, Plan Name EBP, Risk and Uncertainty [Policy Text Block] EBP, Contingency [Text Block] EBP, Contingency [Table] us-gaap-ebp_EbpRiskAndUncertaintyConcentrationOfInvestmentAtFairValueToNetAssetsPercentage EBP, Risk and Uncertainty, Concentration of Investment at Fair Value to Net Assets, Percentage Investment, Identifier [Axis] Statement [Table] Fair Value Hierarchy and NAV [Domain] Statement of Financial Position [Abstract] EBP, Participant-Directed and Nonparticipant-Directed Status [Domain] jhg_PolicyTable Mutual Fund [Member] EBP, Schedule of Asset Held for Investment [Text Block] EBP, Nonparticipant-Directed Investment [Table] EBP, Expense [Policy Text Block] dei_DocumentType Document Type us-gaap-ebp_EmployeeBenefitPlanInvestmentExcludingPlanInterestInMasterTrustCost EBP, Investment, Excluding Plan Interest in Master Trust, Cost Document Information [Line Items] Document Information [Table] EBP, Schedule of Delinquent Participant Contribution [Text Block] EBP, Trustee [Member] Entity Interactive Data Current us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionLateRepaymentIncluded EBP, Schedule of Delinquent Participant Contribution, Late Repayment Included [true false] Statement [Line Items] Fair Value Hierarchy and NAV [Axis] EBP, Nonparticipant-Directed Investment [Text Block] EBP, Payment to Participant [Policy Text Block] us-gaap-ebp_EmployeeBenefitPlanTaxDeterminationLetterObtained EBP, Tax Determination Letter, Obtained [true false] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecrease Total deductions us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit Net assets available for benefits Beginning of year End of year us-gaap_PolicyTextBlockAbstract Accounting Policies Participants us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Retirement Plan Tax Status [Domain] us-gaap_TableTextBlock Notes Tables Qualified Plan [Member] us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionNotCorrected EBP, Schedule of Delinquent Participant Contribution, Not Corrected Document Fiscal Period Focus EBP, Note Receivable from Participant [Policy Text Block] Document Fiscal Year Focus dei_AmendmentFlag Amendment Flag Common Stock [Member] dei_DocumentPeriodEndDate Document Period End Date us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContribution Total contributions us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionPendingCorrectionInVfcp EBP, Schedule of Delinquent Participant Contribution, Pending Correction in VFCP Legal Entity [Axis] EBP, Schedule of Asset Held for Investment [Table] us-gaap-ebp_EmployeeBenefitPlanParticipantLoanMaturityDate EBP, Asset Held for Investment, Participant Loan, Maturity Date us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionTransferredLateToPlan EBP, Schedule of Delinquent Participant Contribution, Transferred Late to Plan Notes receivable from participants Entity Tax Identification Number Entity [Domain] Interest income on notes receivable from participants dei_EntityCentralIndexKey Entity Central Index Key Net appreciation in fair value of investments Net appreciation in fair value of investments dei_EntityRegistrantName Entity Registrant Name EBP, Contribution [Policy Text Block] Entity Current Reporting Status EBP, Description of Plan [Text Block] EBP, Net Asset Available for Benefit EBP, Nonparticipant-Directed [Member] Current Fiscal Year End Date us-gaap-ebp_EmployeeBenefitPlanTaxDeterminationLetterDate EBP, Tax Determination Letter, Date EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Entity Shell Company Entity Emerging Growth Company Entity Small Business Investments [Domain] EBP, Employer, Common Stock [Member] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForPaymentToParticipant Benefits paid to participants Benefits paid to participants Participant rollovers Sponsor us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestment Net investment income us-gaap-ebp_EmployeeBenefitPlanTaxQualificationStatusExtensibleEnumeration EBP, Tax Qualification Status [Extensible Enumeration] Interest-Bearing Deposits [Member] EBP, Participant-Directed and Nonparticipant-Directed Status [Axis] Statement of Stockholders' Equity [Abstract] us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForAdministrativeExpense EBP, Forfeited Nonvested Account, Decrease from Administrative Expense Total cash and investments us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount EBP, Forfeited Nonvested Account us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionCorrectedOutsideVfcp EBP, Schedule of Delinquent Participant Contribution, Corrected Outside VFCP EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Equity Components [Axis] Class of Stock [Axis] Equity Component [Domain] Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 [Member] EBP, Self-Directed Brokerage Account [Member] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForDividendIncomeOnInvestment Dividends reinvested Fair Value, Inputs, Level 1 [Member] EBP 43-1804048 003 [Member] Represents information pertaining to the employee benefit plan 003. us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecrease Net increase in net assets us-gaap-ebp_EmployeeBenefitPlanScheduleOfDelinquentParticipantContributionCorrected EBP, Schedule of Delinquent Participant Contribution, Corrected Deductions from net assets attributed to: jhg_EBPParticipantYearsOfServiceEligibleForTransferIntoParticipantdirectedInvestments EBP, Participant, Years of Service Eligible for Transfer into Participant-directed Investments The number of years of service required for a participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) to transfer funds into participant-directed investments. jhg_EBPParticipantMinimumAgeForCatchupDeferralContributions EBP, Participant, Minimum Age for Catch-up Deferral Contributions The minimum age of participant to make voluntary catch-up contributions to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPEmployerContributionParticipantCompensationMatchedQualifiedStudentLoanPaymentsPercentage EBP, Employer Contribution, Participant Compensation Matched, Qualified Student Loan Payments, Percentage Percentage of participant qualified student loan payments eligible for employer matching contribution for participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPParticipantBalanceEligibleForTransferToParticipantdirectedInvestments EBP, Participant, Balance Eligible For Transfer to Participant-directed Investments Percentage of participant balance in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) eligible to be transferred into participant-directed investments. us-gaap-ebp_EmployeeBenefitPlanParticipantLoanInterestRate EBP, Asset Held for Investment, Participant Loan, Interest Rate jhg_EBPEmployerContributionMatchingPercentageOnQualifiedStudentLoanPayments EBP, Employer Contribution, Matching Percentage on Qualified Student Loan Payments Percentage of employer matching contribution on qualified student loan payments in eligible participant contribution to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccountDecreaseForEmployerContribution EBP, Forfeited Nonvested Account, Decrease from Employer Contribution EBP, Participant-Directed [Member] jhg_EBPParticipantContributionPretaxMaximumAnnualCompensationToTotalCompensationAftertaxPercentage EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, After-tax, Percentage Percentage of maximum after-tax annual compensation that participant in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), is permitted to contribute to total pretax annual compensation. Contributions to net assets attributed to: jhg_EBPParticipantYearsOfServiceUntilFullVestingPercentage EBP, Participant, Years of Service Until Full Vesting Percentage The standard years of service required for participants employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) to achieve full vesting. jhg_EBPMinimumAgeOfParticipantToTakeInServiceDistribution EBP, Minimum Age of Participant to Take In Service Distribution Minimum age of participant required to take in service distribution in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPParticipantPercentageVestedUponRetirementAgeEliminationDisabilityOrDeath EBP, Participant, Percentage Vested Upon Retirement Age, Elimination, Disability, or Death The vesting percentage in an employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) upon reaching retirement age, elimination, disability, or death. jhg_EBPParticipantMaximumCatchupContributionSecureAct EBP, Participant Maximum Catch-up Contribution, Secure Act Secure Act limit of maximum amount of catch-up contribution that is permitted to contribute to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Additions to net assets attributed to: jhg_EBPParticipantSelfContributionsVestedPercentage EBP, Participant, Self Contributions, Vested Percentage The percentage of participant self contributions that are vested in an employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Net assets available for benefits: jhg_EBPParticipantMaximumCatchupContributionIRSLimit EBP, Participant Maximum Catch-up Contribution, IRS Limit IRS limit of maximum amount of catch-up contribution that is permitted to contribute to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Dividends and interest jhg_EBPParticipantAgeForSecureActContributions EBP, Participant, Age for Secure Act Contributions The required age of participant to make Secure Act 2.0 contributions to employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPVestingYearsOfServiceTrancheTwo EBP, Vesting, Years of Service, Tranche Two Number of vesting years of service in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche two. jhg_EBPVestingYearsOfServiceTrancheThree EBP, Vesting, Years of Service, Tranche Three Number of vesting years of service in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche three. Investments, Fair Value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value EBP, Summary of Employer Contribution Vesting Schedule [Table Text Block] Tabular disclosure of vesting schedule of employer contribution in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPVestingYearsOfServiceTrancheOne Years of Service (Year) Number of vesting years of service in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche one. jhg_EBPAssetHeldForInvestmentParticipantLoanVariableRatePrime EBP, Asset Held for Investment, Participant Loan, Variable Rate, Prime Variable Interest rate on prime rate for participant loan in schedule of asset held for investment of employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPTerminationOfPlanVestedPercentage EBP, Termination of Plan, Vested Percentage Vesting percentage in accounts in case of employee benefit plan (EBP) plan termination. jhg_EBPTerminationVestedBalanceToCashOut EBP, Termination, Vested Balance to Cash Out Amount of vested balance at termination to cash out in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPTerminationVestedBalanceToRollAccount EBP, Termination, Vested Balance to Roll Account Amount of vested balance at termination in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) to roll account. jhg_EBPVestingPercentageTrancheFive EBP, Vesting Percentage, Tranche Five Vesting percentage in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche five. EBP, Nonparticipant-Directed Investment [Table Text Block] EBP, Tax Status [Policy Text Block] Disclosure of accounting policy for income status for employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). jhg_EBPVestingPercentageTrancheThree EBP, Vesting Percentage, Tranche Three EBP, Vesting Percentage, Tranche Three jhg_EBPVestingPercentageTrancheFour EBP, Vesting Percentage, Tranche Four EBP, Vesting Percentage, Tranche Four jhg_EBPVestingPercentageTrancheOne Vesting Percentage Vesting percentage in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche one. us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecreaseForAdministrativeExpense Plan expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense jhg_EBPVestingPercentageTrancheTwo EBP, Vesting Percentage, Tranche Two Vesting percentage in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche two. Cash and investments: jhg_EBPVestingYearsOfServiceTrancheFour EBP, Vesting, Years of Service, Tranche Four Number of vesting years of service in employee stock purchase, saving, or similar plan (employee benefit plan (EBP)), tranche four. jhg_EBPVestingYearsOfServiceTrancheFive EBP, Vesting, Years of Service, Tranche Five EBP, Vesting, Years of Service, Tranche Five jhg_EBPChangeInNetAssetAvailableForBenefitDecreaseFromForfeitures Forfeitures Amount of decrease in net asset available for benefit from forfeitures incurred by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). EBP, Accounting Policy [Table] Receivables: EBP, Description of Plan [Table] us-gaap-ebp_EmployeeBenefitPlanReceivable Total receivables EBP, Schedule of Delinquent Participant Contribution [Table] Cash [Member] us-gaap-ebp_EmployeeBenefitPlanPlanNumber EBP, Plan Number EBP, Investment, Current Value, Type [Extensible Enumeration] Investment Type [Axis] us-gaap-ebp_EmployeeBenefitPlanEmployerContributionMatchingPercentage EBP, Employer Contribution, Matching Percentage EBP, Investment, Number of Shares (in shares) EBP, Investment, Number of Shares EBP, Use of Estimate [Policy Text Block] us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingAmount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount Employee Benefit Plan, Schedule of Delinquent Participant Contribution [Text Block] The entire disclosure for schedule of delinquent participant contribution for employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Schedule of Assets [Text Block] The entire disclosure for schedule of asset held for investment for employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). us-gaap-ebp_EmployeeBenefitPlanParticipantContributionPretaxMaximumAnnualCompensationToTotalCompensationPercentage EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage EBP, Related Party and Party-in-Interest [Domain] EBP, Subsequent Event [Policy Text Block] EBP, Summary of Accounting Policy [Text Block] EBP, Investment [Policy Text Block] Sponsor contributions EBP, Related Party and Party-in-Interest [Axis] us-gaap-ebp_EmployeeBenefitPlanNoteReceivableFromParticipantAccountMaximumBorrowingToTotalAccountPercentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage us-gaap-ebp_EmployeeBenefitPlanEmployerContributionParticipantCompensationMatchedPercentage EBP, Employer Contribution, Participant Compensation Matched, Percentage Money Market Funds [Member] EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Investment, Fair Value and NAV [Table Text Block] EBP, Investment, Fair Value and NAV [Table]