Unconsolidated Investments - Cash Distributions by Investment Type and Location (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Schedule of Equity Method Investments [Line Items]
Operating	$ 44.8
Investing	105.5	$ 105.9
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	25.9
Investing	28.0
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	15.0
Investing	39.0
Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	3.9
Investing	6.1
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	32.4
Western U.S. [Member]
Schedule of Equity Method Investments [Line Items]
Operating	28.3
Investing	66.6
Western U.S. [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	19.7
Investing	25.5
Western U.S. [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	4.7
Investing	2.6
Western U.S. [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	3.9
Investing	6.1
Western U.S. [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	32.4
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Operating	16.5
Investing	38.9
Ireland [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	6.2
Investing	2.5
Ireland [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	10.3
Investing	36.4
Ireland [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	0.0
Ireland [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.0
Investing	$ 0.0