Schedule III - Real Estate and Accumulated Depreciation-Overall Summary (Details)	Dec. 31, 2020 USD ($) Property ApartmentUnit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Overall summary of real estate and accumulated depreciation
Investment in Real Estate, Gross	$ 27,203,325,000	$ 27,533,607,000	$ 26,511,022,000	$ 26,026,896,000
Accumulated Depreciation	$ (7,859,657,000)	$ (7,276,786,000)	$ (6,696,281,000)	$ (6,040,378,000)
Investment in Real Estate - Wholly Owned Unencumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	246
Units | ApartmentUnit	64,363
Investment in Real Estate, Gross	$ 22,528,561,227
Accumulated Depreciation	(6,521,859,521)
Investment in Real Estate, Net	16,006,701,706
Encumbrances	$ 0
Investment in Real Estate - Wholly Owned Encumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	42
Units | ApartmentUnit	10,127
Investment in Real Estate, Gross	$ 3,704,582,050
Accumulated Depreciation	(1,032,587,859)
Investment in Real Estate, Net	2,671,994,191
Encumbrances	$ 2,088,144,904
Wholly Owned Properties
Overall summary of real estate and accumulated depreciation
Properties | Property	288
Units | ApartmentUnit	74,490
Investment in Real Estate, Gross	$ 26,233,143,277
Accumulated Depreciation	(7,554,447,380)
Investment in Real Estate, Net	18,678,695,897
Encumbrances	$ 2,088,144,904
Investment in Real Estate - Partially Owned Unencumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	14
Units | ApartmentUnit	2,699
Investment in Real Estate, Gross	$ 672,990,027
Accumulated Depreciation	(231,543,640)
Investment in Real Estate, Net	441,446,387
Encumbrances	$ 0
Investment in Real Estate - Partially Owned Encumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	2
Units | ApartmentUnit	700
Investment in Real Estate, Gross	$ 297,191,796
Accumulated Depreciation	(73,666,183)
Investment in Real Estate, Net	223,525,613
Encumbrances	$ 205,744,819
NONCONTROLLING INTERESTS - PARTIALLY OWNED PROPERTIES
Overall summary of real estate and accumulated depreciation
Properties | Property	16
Units | ApartmentUnit	3,399
Investment in Real Estate, Gross	$ 970,181,823
Accumulated Depreciation	(305,209,823)
Investment in Real Estate, Net	664,972,000
Encumbrances	$ 205,744,819
Unencumbered Properties [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	260
Units | ApartmentUnit	67,062
Investment in Real Estate, Gross	$ 23,201,551,254
Accumulated Depreciation	(6,753,403,161)
Investment in Real Estate, Net	16,448,148,093
Encumbrances	$ 0
Encumbered Properties [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	44
Units | ApartmentUnit	10,827
Investment in Real Estate, Gross	$ 4,001,773,846
Accumulated Depreciation	(1,106,254,042)
Investment in Real Estate, Net	2,895,519,804
Encumbrances	$ 2,293,889,723
Total Consolidated Investment in Real Estate [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	304
Units | ApartmentUnit	77,889
Investment in Real Estate, Gross	$ 27,203,325,100
Accumulated Depreciation	(7,859,657,203)
Investment in Real Estate, Net	19,343,667,897
Encumbrances	$ 2,293,889,723