Transactions with Affiliates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Interests in Real Estate Ventures [Member]
Related Party Transaction [Line Items]
Revenues from affiliates	$ 251.3	$ 195.1	$ 143.3
Receivables due from affiliates	20.3	32.9
Employees [Member]
Related Party Transaction [Line Items]
Receivables due from affiliates	185.5	140.1
Employees [Member] | Loans related to co-investments [Member]
Related Party Transaction [Line Items]
Receivables due from affiliates	16.0	13.4
Employees [Member] | Travel, relocation and other miscellaneous advances [Member]
Related Party Transaction [Line Items]
Receivables due from affiliates	$ 169.5	$ 126.7