Real Estate and In-Place Lease Value - Gains on Sale of Real Estate, Net (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($) property
Real Estate [Line Items]
Gain on sale of real estate, net | $	$ 47.7	$ 252.3
Gain (loss) on sale of real estate and cost of real estate sold | $		252.4
Gain (loss) on sale of properties, attributable to noncontrolling interest | $		$ 116.6
Multifamily [Member] | United Kingdom [Member]
Real Estate [Line Items]
Number of real estate properties sold	1
Retail [Member] | United Kingdom [Member]
Real Estate [Line Items]
Number of real estate properties sold	13
Retail [Member] | Western U.S. [Member]
Real Estate [Line Items]
Number of real estate properties sold		5
Industrial Property [Member] | United Kingdom [Member]
Real Estate [Line Items]
Number of real estate properties sold	1
Office Property [Member] | United Kingdom [Member]
Real Estate [Line Items]
Number of real estate properties sold	1
Commercial [Member] | United Kingdom [Member]
Real Estate [Line Items]
Number of real estate properties sold		6