Investments in Real Estate Ventures (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) investment	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) investment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Document Period End Date			Sep. 30, 2020
Number of separate property or fund co-investments \| investment	48		48
Property, Plant and Equipment, Net, consolidated VIE	$ 675.4		$ 675.4		$ 701.9
Investments in real estate ventures	389.6		389.6		404.2
Total assets	13,902.1		13,902.1		13,672.6
Other Liabilities, Current	313.6		313.6		203.2
Total liabilities	8,608.0		8,608.0		8,459.3
Total liabilities and equity	13,902.1		13,902.1		13,672.6
Revenue	3,978.1	$ 4,495.6	11,744.5	$ 12,582.7
Net income	134.6	129.3	166.5	261.8
Fair Value [Abstract]
Fair value investments at beginning of the period			328.6	247.3
Investments in Real Estate Ventures, at Fair Value, Additions			36.8	67.1
Investments in Real Estate Ventures, at Fair Value, Distributions			58.8	39.2
Unrealized Gain (Loss) on Investments			(9.1)	29.8
Investments in Real Estate Ventures, at Fair Value, Foreign Currency Translation			1.5	(0.8)
Fair value investments at end of the period	$ 299.0	304.2	$ 299.0	304.2
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	$ 60.4		$ 60.4
Exclusive of LaSalle Investment Company II [Member]
Schedule of Equity Method Investments [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	338.8		338.8
Consolidated Variable Interest Entities [Member]
Schedule of Equity Method Investments [Line Items]
Property, Plant and Equipment, Net, consolidated VIE	132.9		132.9		126.3
Investments in real estate ventures	9.2		9.2		13.2
Other Assets, consolidated VIE	9.6		9.6		14.3
Total assets	151.7		151.7		153.8
Other Liabilities, Current	2.6		2.6		3.2
Loans Payable, Fair Value Disclosure, consolidated VIE	71.3		71.3		69.7
Total liabilities	73.9		73.9		72.9
Members' Equity, consolidated VIE	77.8		77.8		80.9
Total liabilities and equity	151.7		151.7		$ 153.8
Revenue	3.6	1.9	10.8	4.9
Other Expenses, consolidated VIE	(3.7)	(2.1)	(11.9)	(5.3)
Gains (Losses) on Sales of Investment Real Estate, consolidated VIE	3.1	0.0	15.3	0.0
Net income	$ 3.0	$ (0.2)	$ 14.2	$ (0.4)

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