Investments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) investment	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) investment	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of separate property or fund co-investments | investment	55		55
Property, Plant and Equipment, Net, consolidated VIE	$ 731.7		$ 731.7		$ 740.0
Investments	901.9		901.9		745.7
Total assets	15,272.3		15,272.3		15,505.0
Other Liabilities, Current	269.4		269.4		218.1
Total liabilities	9,118.4		9,118.4		9,083.8
Total liabilities and equity	15,272.3		15,272.3		15,505.0
Revenue	5,278.4	$ 4,495.0	10,079.8	$ 8,532.1
Net income	335.5	199.4	479.4	301.8
Fair Value [Abstract]
Fair value investments at beginning of the period			639.6	340.3
Investments in Real Estate Ventures, at Fair Value, Additions			121.8	98.6
Investments in Real Estate Ventures, at Fair Value, Distributions			(21.4)	(15.9)
Unrealized Gain (Loss) on Investments			65.3	85.1
Investments in Real Estate Ventures, at Fair Value, Foreign Currency Translation			(19.2)	(3.1)
Fair value investments at end of the period	786.1	505.0	786.1	505.0
JLL Technologies
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	344.9		344.9
Investments	$ 511.6		$ 511.6		353.6
LaSalle Investment Company II [Member]
Schedule of Equity Method Investments [Line Items]
Partnership ownership interest (in hundredths)	48.78%		48.78%
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 60.3		$ 60.3
LaSalle Investment Management
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	344.9		344.9
Investments	356.1		356.1		354.6
Other Investments and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures
Schedule of Equity Method Investments [Line Items]
Investments	34.2		34.2		37.5
Consolidated Variable Interest Entities [Member]
Schedule of Equity Method Investments [Line Items]
Property, Plant and Equipment, Net, consolidated VIE	187.4		187.4		184.7
Investments	10.6		10.6		10.2
Other Assets, consolidated VIE	25.6		25.6		17.7
Total assets	223.6		223.6		212.6
Other Liabilities, Current	2.2		2.2		2.1
Loans Payable, Fair Value Disclosure, consolidated VIE	111.9		111.9		107.5
Total liabilities	114.1		114.1		109.6
Members' Equity, consolidated VIE	109.5		109.5		103.0
Total liabilities and equity	223.6		223.6		$ 212.6
Revenue	5.1	2.9	8.6	5.5
Other Expenses, consolidated VIE	(6.0)	(3.5)	(11.7)	(6.7)
Gains (Losses) on Sales of Investment Real Estate, consolidated VIE	142.3	0.0	142.3	0.0
Net income	$ 141.4	$ (0.6)	$ 139.2	$ (1.2)