UNCONSOLIDATED INVESTMENTS - Cash Distributions by Investment Type and Location (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 property
Schedule of Equity Method Investments [Line Items]
Operating	$ 74.1
Investing	115.0
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	57.0
Investing	91.5
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	4.5
Investing	4.8
Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	11.2
Investing	13.6
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.4
Investing	5.1
Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Operating	66.6
Investing	111.2
Western United States [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	50.6
Investing	91.5
Western United States [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	3.4
Investing	1.0
Western United States [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Operating	11.2
Investing	13.6
Western United States [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.4
Investing	5.1
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Operating	7.5
Investing	3.8
Ireland [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Operating	6.4
Investing	0.0
Ireland [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Operating	1.1
Investing	3.8
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
Joint Venture [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Number of real estate properties sold | property	3
Multifamily [Member] | Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Number of real estate properties sold | property		6
Multifamily [Member] | Joint Venture [Member] | Western United States [Member]
Schedule of Equity Method Investments [Line Items]
Number of real estate properties sold | property	3