Schedule III - SCHEDULE OF REAL ESTATE AND ACCUMULATED DEPRECIATION (Activity of real Estate and Accumulated Depreciation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate [Roll Forward]
Gross amount at beginning	$ 15,960.1	$ 15,349.0	$ 14,277.0
Acquisitions	887.0	721.4	499.7
Discretionary capital projects	258.1	173.5	120.7
Discretionary ground lease purchases	189.8	180.4	150.4
Redevelopment capital expenditures	213.6	177.3	138.8
Capital improvements	161.2	94.0	65.6
Start-up capital expenditures	71.3	113.1	158.1
Other additions	45.2	(3.0)	106.4
Total additions	1,826.2	1,456.7	1,239.7
Cost of real estate sold or disposed	(304.6)	(395.7)	(246.5)
Other deductions	(52.4)	(449.9)	78.8
Total deductions	(357.0)	(845.6)	(167.7)
Balance at end	17,429.3	15,960.1	15,349.0
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward]
Gross amount of accumulated depreciation at beginning	(5,724.7)	(5,181.2)	(4,548.1)
Depreciation	(768.4)	(751.4)	(718.7)
Other additions	0.0	0.0	0.0
Total additions	(768.4)	(751.4)	(718.7)
Amount of accumulated depreciation for assets sold or disposed	121.4	129.3	100.7
Other deductions	(10.5)	78.6	(15.1)
Total deductions	110.9	207.9	85.6
Balance at end	$ (6,382.2)	$ (5,724.7)	$ (5,181.2)