Real Estate and In-Place Lease Value - Gains on Sale of Real Estate, Net (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) property	Mar. 31, 2019 USD ($) property
Real Estate [Line Items]
Gain on sale of real estate, net | $	$ 44.2	$ 34.8
Gain (loss) on sale of properties, attributable to noncontrolling interest | $		11.4
Gain on sale of real estate and cost of real estate sold | $		$ 34.9
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	11
Retail [Member] | Western U.S. [Member]
Real Estate [Line Items]
Number of real estate properties sold		3
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		4