Unconsolidated Investments - Schedule of Joint Ventures (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 1,256.4	$ 1,334.6
Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	569.3	609.2
Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	267.4	266.2
Hotel [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	76.9	72.8
Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	140.6	139.6
Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	202.2	246.8
Western U.S. [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	726.6	767.8
Western U.S. [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	238.1	230.5
Western U.S. [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	76.6	78.1
Western U.S. [Member] | Hotel [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	76.9	72.8
Western U.S. [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	132.8	139.6
Western U.S. [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	202.2	246.8
Ireland [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	474.2	518.1
Ireland [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	331.2	378.7
Ireland [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	141.5	139.4
Ireland [Member] | Hotel [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0.0	0.0
Ireland [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	1.5	0.0
Ireland [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0.0	0.0
United Kingdom [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	55.6	48.7
United Kingdom [Member] | Multifamily [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0.0	0.0
United Kingdom [Member] | Commercial [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	49.3	48.7
United Kingdom [Member] | Hotel [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	0.0	0.0
United Kingdom [Member] | Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	6.3	0.0
United Kingdom [Member] | Residential and Other [Member]
Schedule of Equity Method Investments [Line Items]
Investments in joint ventures	$ 0.0	$ 0.0