Business Segments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Reimbursement Revenues	$ 1,949.8	$ 1,756.1	$ 5,727.1	$ 5,160.6
Segment revenue:
Revenue	4,495.6	3,969.8	12,582.7	11,428.7
Revenue Before Reimbursements	2,545.8	2,213.7	6,855.6	6,268.1
Operating expenses:
Depreciation and amortization	53.6	42.7	145.6	131.1
Operating Income (Loss)	171.6	190.9	347.1	394.5
Equity in earnings (losses)	17.1	3.4	32.3	27.2
Segment Reconciling Items:
Revenue	4,495.6	3,969.8	12,582.7	11,428.7
Total segment operating expenses before restructuring and acquisition charges	2,304.2	2,019.1	6,394.2	5,880.3
Cost of Reimbursable Expenses	1,949.8	1,756.1	5,727.1	5,160.6
Segment Operating Expenses before Restructuring and acquisition	4,254.0	3,775.2	12,121.3	11,040.9
Segment Reporting Information Operating Income Before Restructuring Charges	241.6	194.6	461.4	387.8
Restructuring and acquisition charges	70.0	3.7	114.3	(6.7)
Operating Income (Loss)	171.6	190.9	347.1	394.5
Assets	13,077.9		13,077.9		$ 10,025.5
Reportable Subsegments [Member]
Segment revenue:
Real Estate Revenues, Net	1,815.4	1,591.4	4,764.5	4,366.4
Operating expenses:
Gross contract vendor and subcontractor costs reimbursement	717.7	617.0	2,073.7	1,892.4
Reportable Subsegments [Member] \| Americas [Member]
Segment Reporting Information [Line Items]
Reimbursement Revenues	1,430.3	1,251.5	4,184.8	3,659.6
Segment revenue:
Revenue	2,687.6	2,201.6	7,401.3	6,295.1
Revenue Before Reimbursements	1,257.3	950.1	3,216.5	2,635.5
Derivative, Gain (Loss) on Derivative, Net	12.7	5.3	17.4	9.3
Real Estate Revenues, Net	1,043.8	774.1	2,618.8	2,165.8
Operating expenses:
Compensation, operating and administrative expenses	1,045.6	821.2	2,770.1	2,306.8
Depreciation and amortization	35.3	24.5	88.9	77.1
Operating Expenses, Excluding Reimbursed Expenses	1,080.9	845.7	2,859.0	2,383.9
Gross contract vendor and subcontractor costs reimbursement	200.8	170.7	580.3	460.4
Total fee based segment operating expenses	880.1	675.0	2,278.7	1,923.5
General Contractor Cost	(200.8)	(170.7)	(580.3)	(460.4)
Operating Income (Loss)	176.4	104.4	357.5	251.6
Equity in earnings (losses)	1.5	0.1	1.6	0.6
Operating Income (Loss), Including Income (Loss) from Equity Method Investments	177.9	104.5	359.1	252.2
Segment Reconciling Items:
Revenue	2,687.6	2,201.6	7,401.3	6,295.1
Operating Income (Loss)	176.4	104.4	357.5	251.6
Reportable Subsegments [Member] \| EMEA [Member]
Segment Reporting Information [Line Items]
Reimbursement Revenues	174.1	171.0	492.4	480.0
Segment revenue:
Revenue	862.6	805.6	2,404.3	2,435.8
Revenue Before Reimbursements	688.5	634.6	1,911.9	1,955.8
Real Estate Revenues, Net	401.0	396.7	1,097.0	1,135.4
Operating expenses:
Compensation, operating and administrative expenses	664.6	611.7	1,896.1	1,931.4
Depreciation and amortization	10.1	11.8	32.7	34.7
Operating Expenses, Excluding Reimbursed Expenses	674.7	623.5	1,928.8	1,966.1
Gross contract vendor and subcontractor costs reimbursement	287.5	237.9	814.9	820.4
Total fee based segment operating expenses	387.2	385.6	1,113.9	1,145.7
General Contractor Cost	(287.5)	(237.9)	(814.9)	(820.4)
Operating Income (Loss)	13.8	11.1	(16.9)	(10.3)
Equity in earnings (losses)	0.0	0.0	(1.0)	0.0
Operating Income (Loss), Including Income (Loss) from Equity Method Investments	13.8	11.1	(17.9)	(10.3)
Segment Reconciling Items:
Revenue	862.6	805.6	2,404.3	2,435.8
Operating Income (Loss)	13.8	11.1	(16.9)	(10.3)
Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment Reporting Information [Line Items]
Reimbursement Revenues	343.6	330.0	1,044.3	1,007.8
Segment revenue:
Revenue	833.8	790.0	2,437.7	2,314.2
Revenue Before Reimbursements	490.2	460.0	1,393.4	1,306.4
Real Estate Revenues, Net	264.9	252.3	726.0	698.0
Operating expenses:
Compensation, operating and administrative expenses	452.9	432.6	1,316.0	1,245.1
Depreciation and amortization	6.5	5.6	19.3	17.0
Operating Expenses, Excluding Reimbursed Expenses	459.4	438.2	1,335.3	1,262.1
Gross contract vendor and subcontractor costs reimbursement	225.3	207.7	667.4	608.4
Total fee based segment operating expenses	234.1	230.5	667.9	653.7
General Contractor Cost	(225.3)	(207.7)	(667.4)	(608.4)
Operating Income (Loss)	30.8	21.8	58.1	44.3
Equity in earnings (losses)	0.7	1.0	1.4	2.0
Operating Income (Loss), Including Income (Loss) from Equity Method Investments	31.5	22.8	59.5	46.3
Segment Reconciling Items:
Revenue	833.8	790.0	2,437.7	2,314.2
Operating Income (Loss)	30.8	21.8	58.1	44.3
Investment Management [Member]
Segment Reporting Information [Line Items]
Reimbursement Revenues	1.8	3.6	5.6	13.2
Segment revenue:
Revenue	111.6	172.6	339.4	383.6
Revenue Before Reimbursements	109.8	169.0	333.8	370.4
Real Estate Revenues, Net	105.7	168.3	322.7	367.2
Operating expenses:
Compensation, operating and administrative expenses	87.5	110.9	266.4	265.9
Depreciation and amortization	1.7	0.8	4.7	2.3
Operating Expenses, Excluding Reimbursed Expenses	89.2	111.7	271.1	268.2
Gross contract vendor and subcontractor costs reimbursement	4.1	0.7	11.1	3.2
Total fee based segment operating expenses	85.1	111.0	260.0	265.0
General Contractor Cost	(4.1)	(0.7)	(11.1)	(3.2)
Operating Income (Loss)	20.6	57.3	62.7	102.2
Equity in earnings (losses)	14.9	2.3	30.3	24.6
Operating Income (Loss), Including Income (Loss) from Equity Method Investments	35.5	59.6	93.0	126.8
Segment Reconciling Items:
Revenue	111.6	172.6	339.4	383.6
Operating Income (Loss)	20.6	57.3	62.7	102.2
Leasing [Member] \| Reportable Subsegments [Member] \| Americas [Member]
Segment revenue:
Revenue	472.7	424.0	1,354.3	1,151.4
Segment Reconciling Items:
Revenue	472.7	424.0	1,354.3	1,151.4
Leasing [Member] \| Reportable Subsegments [Member] \| EMEA [Member]
Segment revenue:
Revenue	72.2	80.1	190.3	211.9
Segment Reconciling Items:
Revenue	72.2	80.1	190.3	211.9
Leasing [Member] \| Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment revenue:
Revenue	59.4	69.3	161.5	165.2
Segment Reconciling Items:
Revenue	59.4	69.3	161.5	165.2
Capital Markets [Member] \| Reportable Subsegments [Member] \| Americas [Member]
Segment revenue:
Revenue	323.2	115.6	553.1	344.4
Segment Reconciling Items:
Revenue	323.2	115.6	553.1	344.4
Capital Markets [Member] \| Reportable Subsegments [Member] \| EMEA [Member]
Segment revenue:
Revenue	106.2	108.9	248.7	288.1
Segment Reconciling Items:
Revenue	106.2	108.9	248.7	288.1
Capital Markets [Member] \| Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment revenue:
Revenue	50.6	39.5	128.2	122.2
Segment Reconciling Items:
Revenue	50.6	39.5	128.2	122.2
Property & Facility Management [Member] \| Reportable Subsegments [Member] \| Americas [Member]
Segment revenue:
Revenue	1,386.3	1,271.5	4,119.2	3,713.4
Segment Reconciling Items:
Revenue	1,386.3	1,271.5	4,119.2	3,713.4
Property & Facility Management [Member] \| Reportable Subsegments [Member] \| EMEA [Member]
Segment revenue:
Revenue	387.1	336.3	1,137.0	1,078.9
Segment Reconciling Items:
Revenue	387.1	336.3	1,137.0	1,078.9
Property & Facility Management [Member] \| Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment revenue:
Revenue	539.4	529.2	1,630.6	1,590.6
Segment Reconciling Items:
Revenue	539.4	529.2	1,630.6	1,590.6
Project & Development Services [Member] \| Reportable Subsegments [Member] \| Americas [Member]
Segment revenue:
Revenue	406.0	304.7	1,091.5	848.8
Segment Reconciling Items:
Revenue	406.0	304.7	1,091.5	848.8
Project & Development Services [Member] \| Reportable Subsegments [Member] \| EMEA [Member]
Segment revenue:
Revenue	234.2	220.1	633.9	663.5
Segment Reconciling Items:
Revenue	234.2	220.1	633.9	663.5
Project & Development Services [Member] \| Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment revenue:
Revenue	145.7	108.7	393.9	309.8
Segment Reconciling Items:
Revenue	145.7	108.7	393.9	309.8
Advisory, Consulting and Other [Member] \| Reportable Subsegments [Member] \| Americas [Member]
Segment revenue:
Revenue	99.4	85.8	283.2	237.1
Segment Reconciling Items:
Revenue	99.4	85.8	283.2	237.1
Advisory, Consulting and Other [Member] \| Reportable Subsegments [Member] \| EMEA [Member]
Segment revenue:
Revenue	62.9	60.2	194.4	193.4
Segment Reconciling Items:
Revenue	62.9	60.2	194.4	193.4
Advisory, Consulting and Other [Member] \| Reportable Subsegments [Member] \| Asia Pacific [Member]
Segment revenue:
Revenue	38.7	43.3	123.5	126.4
Segment Reconciling Items:
Revenue	38.7	43.3	123.5	126.4
Advisory Fees [Member] \| Investment Management [Member]
Segment revenue:
Revenue	79.9	68.0	237.0	205.0
Segment Reconciling Items:
Revenue	79.9	68.0	237.0	205.0
Transaction Fees & Other [Member] \| Investment Management [Member]
Segment revenue:
Revenue	14.2	9.8	43.7	33.2
Segment Reconciling Items:
Revenue	14.2	9.8	43.7	33.2
Incentive Fees [Member] \| Investment Management [Member]
Segment revenue:
Revenue	17.5	94.8	58.7	145.4
Segment Reconciling Items:
Revenue	$ 17.5	$ 94.8	$ 58.7	$ 145.4

The total amount of compensation and benefits, and operating, administrative and other expenses.

No definition available.

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

- Definition

Cost associated with reimbursable revenue. This occurs when a services entity incurs expenses on behalf of the client and passes through the cost of reimbursable expense to a client.

+ References

No definition available.

+ Details

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

- Definition

The aggregate costs related to general contracting services.

+ References

No definition available.

+ Details

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

- Definition

Reimbursement for contract vendor and subcontractor costs that is deducted from gross revenue.

+ References

No definition available.

+ Details

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

- Definition

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services, less vendor and subcontractor costs, which are reimbursed by the client.

+ References

No definition available.

+ Details

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

- Definition

Operating Expenses, Excluding expenses directly reimbursed by customers

+ References

No definition available.

+ Details

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

- Definition

Operating Income (Loss), Including Income (Loss) from Equity Method Investments

+ References

No definition available.

+ Details

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

- Definition

The aggregate revenue from real estate operations during the reporting period.

+ References

No definition available.

+ Details

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

- Definition

Repayment received or receivable for expenses incurred on behalf of a client or customer.

+ References

No definition available.

+ Details

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

- Definition

Revenue Before Reimbursements

+ References

No definition available.

+ Details

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

- Definition

Segment Operating Expenses before Restructuring and Acquisition

+ References

No definition available.

+ Details

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

- Definition

Total segment operating expenses, which includes compensation, operating and administrative expenses, and depreciation and amortization. Does not include restructuring charges.

+ References

No definition available.

+ Details

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

- Definition

Operating Income Before Restructuring Charges

+ References

No definition available.

+ Details

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

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(11))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(12))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

+ Details

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

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan and expenses resulting from the write-down of assets. Excludes expenses related to a business combination, a discontinued operation or an asset retirement obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8933-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(1))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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

- 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

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_ReportableSubsegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=srt_AmericasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=us-gaap_EMEAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=srt_AsiaPacificMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=jll_InvestmentManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_LeasingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_CapitalMarketsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_PropertyFacilityManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_ProjectDevelopmentServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_AdvisoryConsultingandOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_AdvisoryFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_TransactionFeesOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	jll_BusinessLineAxis=jll_IncentiveFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: