Unconsolidated Investments - Cash Distributions by Investment Type and Location (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Operating	$ 15.7
Investing	79.3	$ 5.6
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	10.3
Investing	8.8
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	2.9
Investing	35.0
Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	2.1
Investing	4.6
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.4
Investing	30.9
Western U.S. [Member]
Schedule of Equity Method Investments [Line Items]
Operating	12.3
Investing	44.4
Western U.S. [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	8.6
Investing	6.3
Western U.S. [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.2
Investing	2.6
Western U.S. [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	2.1
Investing	4.6
Western U.S. [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	0.4
Investing	30.9
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Operating	3.4
Investing	34.9
Ireland [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.7
Investing	2.5
Ireland [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.7
Investing	32.4
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