Organization (Details) $ in Millions, ft² in Billions	12 Months Ended
Dec. 31, 2021 USD ($) ft² employee	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of employees \| employee	98,000
Number of employees whose costs are reimbursed by clients \| employee	44,500
Portfolio of property and corporate facility management (in square feet) \| ft²	5.4
Assets under management by LaSalle Investment Management	$ 76,600.0
Product Information [Line Items]
Revenue:	19,367.0	$ 16,589.9	$ 17,983.2
Real Estate Services: Leasing [Member]
Product Information [Line Items]
Revenue:	2,794.0	1,884.2	2,524.0
Real Estate Services: Capital Markets and Hotels [Member]
Product Information [Line Items]
Revenue:	2,193.5	1,407.4	1,542.2
Real Estate Services: Property & Facilities Management [Member]
Product Information [Line Items]
Revenue:	10,222.7	9,485.4	9,364.7
Real Estate Services: Project & Development Services [Member]
Product Information [Line Items]
Revenue:	2,684.9	2,530.1	3,121.5
Real Estate Services: Advisory, Consulting and Other [Member]
Product Information [Line Items]
Revenue:	971.8	861.0	904.7
LaSalle Investment Management [Member]
Product Information [Line Items]
Revenue:	$ 500.1	$ 421.8	$ 526.1