Unconsolidated Investments - Cash Distributions by Investment Type and Location (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Operating	$ 24.7
Investing	42.6	$ 69.0
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	16.4
Investing	29.0
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.8
Investing	2.3
Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	7.3
Investing	7.8
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.2
Investing	3.5
Western U.S. [Member]
Schedule of Equity Method Investments [Line Items]
Operating	24.6
Investing	40.4
Western U.S. [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	16.3
Investing	26.8
Western U.S. [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.8
Investing	2.3
Western U.S. [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	7.3
Investing	7.8
Western U.S. [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.2
Investing	3.5
Japan [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.1
Investing	2.2
Japan [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.1
Investing	2.2
Japan [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	0.0
Japan [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	0.0
Japan [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	$ 0.0