Schedule III - Real Estate and Accumulated Depreciation-Overall Summary (Details)	Dec. 31, 2017 USD ($) Property ApartmentUnit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Overall summary of real estate and accumulated depreciation
Investment in Real Estate, Gross	$ 26,026,896,000	$ 25,386,425,000	$ 28,542,697,000	$ 27,675,383,000
Accumulated Depreciation	$ (6,040,378,000)	$ (5,360,389,000)	$ (6,084,616,000)	$ (5,432,805,000)
Investment in Real Estate - Wholly Owned Unencumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	215
Units | ApartmentUnit	55,954
Investment in Real Estate, Gross	$ 19,776,737,815
Accumulated Depreciation	(4,363,244,353)
Investment in Real Estate, Net	15,413,493,462
Encumbrances	$ 0
Investment in Real Estate - Wholly Owned Encumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	71
Units | ApartmentUnit	18,497
Investment in Real Estate, Gross	$ 5,600,381,309
Accumulated Depreciation	(1,440,591,113)
Investment in Real Estate, Net	4,159,790,196
Encumbrances	$ 3,316,375,422
Wholly Owned Properties
Overall summary of real estate and accumulated depreciation
Properties | Property	286
Units | ApartmentUnit	74,451
Investment in Real Estate, Gross	$ 25,377,119,124
Accumulated Depreciation	(5,803,835,466)
Investment in Real Estate, Net	19,573,283,658
Encumbrances	$ 3,316,375,422
Investment in Real Estate - Partially Owned Unencumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	9
Units | ApartmentUnit	1,527
Investment in Real Estate, Gross	$ 289,986,862
Accumulated Depreciation	(108,651,639)
Investment in Real Estate, Net	181,335,223
Encumbrances	$ 0
Investment in Real Estate - Partially Owned Encumbered [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	8
Units | ApartmentUnit	1,688
Investment in Real Estate, Gross	$ 359,790,405
Accumulated Depreciation	(127,891,086)
Investment in Real Estate, Net	231,899,319
Encumbrances	$ 302,346,576
NONCONTROLLING INTERESTS – PARTIALLY OWNED PROPERTIES
Overall summary of real estate and accumulated depreciation
Properties | Property	17
Units | ApartmentUnit	3,215
Investment in Real Estate, Gross	$ 649,777,267
Accumulated Depreciation	(236,542,725)
Investment in Real Estate, Net	413,234,542
Encumbrances	$ 302,346,576
Unencumbered Properties [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	224
Units | ApartmentUnit	57,481
Investment in Real Estate, Gross	$ 20,066,724,677
Accumulated Depreciation	(4,471,895,992)
Investment in Real Estate, Net	15,594,828,685
Encumbrances	$ 0
Encumbered Properties [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	79
Units | ApartmentUnit	20,185
Investment in Real Estate, Gross	$ 5,960,171,714
Accumulated Depreciation	(1,568,482,199)
Investment in Real Estate, Net	4,391,689,515
Encumbrances	$ 3,618,721,998
Total Consolidated Investment in Real Estate [Member]
Overall summary of real estate and accumulated depreciation
Properties | Property	303
Units | ApartmentUnit	77,666
Investment in Real Estate, Gross	$ 26,026,896,391
Accumulated Depreciation	(6,040,378,191)
Investment in Real Estate, Net	19,986,518,200
Encumbrances	$ 3,618,721,998