-- None. No documentation exists for this element. --

No definition available.

Name:	jll_FairValueAbstract
Namespace Prefix:	jll_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Investments in Real Estate Ventures, at Fair Value, Additions

+ References

No definition available.

+ Details

Name:	jll_InvestmentsinRealEstateVenturesatFairValueAdditions
Namespace Prefix:	jll_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Investments in Real Estate Ventures, at Fair Value, Distributions

+ References

No definition available.

+ Details

Name:	jll_InvestmentsinRealEstateVenturesatFairValueDistributions
Namespace Prefix:	jll_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Investments in Real Estate Ventures, at Fair Value, Foreign Currency Translation

+ References

No definition available.

+ Details

Name:	jll_InvestmentsinRealEstateVenturesatFairValueForeignCurrencyTranslation
Namespace Prefix:	jll_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of separate property or fund co-investments.

+ References

No definition available.

+ Details

Name:	jll_NumberOfSeparatePropertyOrFundCoInvestments
Namespace Prefix:	jll_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

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

- Definition

Amount of investment in equity method investee and investment in and advance to affiliate.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

+ Details

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

- Definition

Amount of unrealized gain (loss) on investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

+ Details

Name:	us-gaap_UnrealizedGainLossOnInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_InvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jll_JLLTechnologiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jll_LasalleInvestmentCompanyIiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jll_LasalleInvestmentManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=jll_OtherInvestmentsAndAdvanceToAffiliatesSubsidiariesAssociatesAndJointVenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investments (Details) $ in Millions	3 Months Ended
Investments (Details) $ in Millions	Mar. 31, 2024 USD ($) investment	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of separate property or fund co-investments \| investment	49
Investments	$ 816.2		$ 816.6
Fair Value [Abstract]
Fair value investments at beginning of the period	740.8	$ 794.9
Investments in Real Estate Ventures, at Fair Value, Additions	18.8	32.8
Investments in Real Estate Ventures, at Fair Value, Distributions	(6.4)	(6.6)
Unrealized Gain (Loss) on Investments	(3.1)	(3.3)
Investments in Real Estate Ventures, at Fair Value, Foreign Currency Translation	(6.3)	7.7
Fair value investments at end of the period	743.8	825.5
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member]
Fair Value [Abstract]
Fair value investments at beginning of the period	367.3	452.0
Fair value investments at end of the period	369.7	$ 73.1
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member] \| Investments [Member]
Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	3.2
JLL Technologies
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	12.5
Investments	402.3		397.6
LaSalle Investment Company II [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	60.3
LaSalle Investment Management
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	332.7
Investments	382.5		388.3
Other Investments and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures
Schedule of Equity Method Investments [Line Items]
Investments	$ 31.4		$ 30.7