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Real Estate and Accumulated Depreciation - Overall Summary and Encumbrances Reconciliation (Details) | 12 Months Ended |
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Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2013 USD ($) | Dec. 31, 2015 USD ($)
Real Estate and Accumulated Depreciation [Line Items] |  |  |  |
Number of Units in Real Estate Property |  |  |  | 109,652
Overall summary of real estate and accumulated depreciation |  |  |  |
Accumulated Depreciation | $ (5,432,805,000) | $ (4,807,709,000) | $ (4,912,221,000) | $ (6,084,616,000)
Changes in total real estate |  |  |  |
Balance, beginning of year | 27,675,383,000 | 26,800,948,000 | 21,008,429,000 |
Acquisitions and development | 964,645,000 | 1,121,423,000 | 9,273,492,000 |
Improvements | 186,104,000 | 191,243,000 | 139,950,000 |
Dispositions and other | (283,435,000) | (438,231,000) | (3,620,923,000) |
Balance, end of year | 28,542,697,000 | 27,675,383,000 | 26,800,948,000 |
Changes in accumulated depreciation |  |  |  |
Balance, beginning of year | (5,432,805,000) | (4,807,709,000) | (4,912,221,000) |
Depreciation | 765,895,000 | 758,861,000 | 1,013,353,000 |
Dispositions and other | (114,084,000) | (133,765,000) | (1,117,865,000) |
Balance, end of year | (6,084,616,000) | $ (5,432,805,000) | $ (4,807,709,000) |
EQR-Fanwell 2007 LP [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 300,000,000
Real Estate and Accumulated Depreciation Encumbrances Reconciliation [Abstract] |  |  |  |
Number of Properties Encumbered |  |  |  | 4
EQR-Fanwell 2007 LP [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 0
EQR-Fanwell 2007 LP [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 300,000,000
EQR-Wellfan 2008 LP [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 550,000,000
Real Estate and Accumulated Depreciation Encumbrances Reconciliation [Abstract] |  |  |  |
Number of Properties Encumbered |  |  |  | 10
EQR-Wellfan 2008 LP [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 0
EQR-Wellfan 2008 LP [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 550,000,000
Fannie Mae Pool 3 [Domain] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 462,400,525
Real Estate and Accumulated Depreciation Encumbrances Reconciliation [Abstract] |  |  |  |
Number of Properties Encumbered |  |  |  | 5
Fannie Mae Pool 3 [Domain] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 24,223,525
Fannie Mae Pool 3 [Domain] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 438,177,000
Archstone Master Property [Domain] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 800,000,000
Real Estate and Accumulated Depreciation Encumbrances Reconciliation [Abstract] |  |  |  |
Number of Properties Encumbered |  |  |  | 13
Archstone Master Property [Domain] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 0
Archstone Master Property [Domain] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 800,000,000
Portfolio Entity Encumbrances [Member] |  |  |  |
Real Estate and Accumulated Depreciation Encumbrances Reconciliation [Abstract] |  |  |  |
Number of Properties Encumbered |  |  |  | 32
Individual Property Encumbrances [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 2,451,484,639
Individual Property Encumbrances [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 319,205,053
Individual Property Encumbrances [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 2,132,279,586
Real Estate Held For Sale-Individual Property Encumbrances [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 140,985,116
Real Estate Held For Sale-Individual Property Encumbrances [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 0
Real Estate Held For Sale-Individual Property Encumbrances [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 140,985,116
Investment in Real Estate - Wholly Owned Unencumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 211
Units |  |  |  | 52,513
Investment in Real Estate, Gross |  |  |  | $ 17,437,812,582
Accumulated Depreciation | (3,224,397,212) |  |  | (3,224,397,212)
Investment in Real Estate Net |  |  |  | 14,213,415,370
Encumbrances |  |  |  | $ 0
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (3,224,397,212) |  |  |
Investment in Real Estate - Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 87
Units |  |  |  | 23,686
Investment in Real Estate, Gross |  |  |  | $ 7,054,964,658
Accumulated Depreciation | (1,464,311,726) |  |  | (1,464,311,726)
Investment in Real Estate Net |  |  |  | 5,590,652,932
Encumbrances |  |  |  | $ 4,220,456,586
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (1,464,311,726) |  |  |
Investment in Real Estate - Wholly Owned Properties [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 298
Units |  |  |  | 76,199
Investment in Real Estate, Gross |  |  |  | $ 24,492,777,240
Accumulated Depreciation | (4,688,708,938) |  |  | (4,688,708,938)
Investment in Real Estate Net |  |  |  | 19,804,068,302
Encumbrances |  |  |  | $ 4,220,456,586
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (4,688,708,938) |  |  |
Investment in Real Estate - Partially Owned Unencumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 9
Units |  |  |  | 1,661
Investment in Real Estate, Gross |  |  |  | $ 262,146,372
Accumulated Depreciation | (96,031,075) |  |  | (96,031,075)
Investment in Real Estate Net |  |  |  | 166,115,297
Encumbrances |  |  |  | $ 0
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (96,031,075) |  |  |
Investment in Real Estate - Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 10
Units |  |  |  | 2,110
Investment in Real Estate, Gross |  |  |  | $ 427,427,967
Accumulated Depreciation | (120,665,999) |  |  | (120,665,999)
Investment in Real Estate Net |  |  |  | 306,761,968
Encumbrances |  |  |  | $ 343,428,578
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (120,665,999) |  |  |
NONCONTROLLING INTERESTS – PARTIALLY OWNED PROPERTIES |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 19
Units |  |  |  | 3,771
Investment in Real Estate, Gross |  |  |  | $ 689,574,339
Accumulated Depreciation | (216,697,074) |  |  | (216,697,074)
Investment in Real Estate Net |  |  |  | 472,877,265
Encumbrances |  |  |  | $ 343,428,578
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (216,697,074) |  |  |
Total Consolidated Investment in Real Estate [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 317
Units |  |  |  | 79,970
Investment in Real Estate, Gross |  |  |  | $ 25,182,351,579
Accumulated Depreciation | (4,905,406,012) |  |  | (4,905,406,012)
Investment in Real Estate Net |  |  |  | 20,276,945,567
Encumbrances |  |  |  | 4,563,885,164
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (4,905,406,012) |  |  |
Total Consolidated Investment in Real Estate [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 343,428,578
Total Consolidated Investment in Real Estate [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 4,220,456,586
Real Estate Held For Sale - Wholly Owned Unencumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 68
Units |  |  |  | 21,494
Investment in Real Estate, Gross |  |  |  | $ 3,118,799,507
Accumulated Depreciation | (1,075,431,644) |  |  | (1,075,431,644)
Investment in Real Estate Net |  |  |  | 2,043,367,863
Encumbrances |  |  |  | $ 0
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (1,075,431,644) |  |  |
Real Estate Held For Sale - Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 4
Units |  |  |  | 1,768
Investment in Real Estate, Gross |  |  |  | $ 241,545,360
Accumulated Depreciation | (103,778,656) |  |  | (103,778,656)
Investment in Real Estate Net |  |  |  | 137,766,704
Encumbrances |  |  |  | $ 140,985,116
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (103,778,656) |  |  |
Total Real Estate Held For Sale [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 72
Units |  |  |  | 23,262
Investment in Real Estate, Gross |  |  |  | $ 3,360,344,867
Accumulated Depreciation | (1,179,210,300) |  |  | (1,179,210,300)
Investment in Real Estate Net |  |  |  | 2,181,134,567
Encumbrances |  |  |  | $ 140,985,116
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (1,179,210,300) |  |  |
Unencumbered Properties [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 288
Units |  |  |  | 75,668
Investment in Real Estate, Gross |  |  |  | $ 20,818,758,461
Accumulated Depreciation | (4,395,859,931) |  |  | (4,395,859,931)
Investment in Real Estate Net |  |  |  | 16,422,898,530
Encumbrances |  |  |  | $ 0
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (4,395,859,931) |  |  |
Encumbered Properties [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 101
Units |  |  |  | 27,564
Investment in Real Estate, Gross |  |  |  | $ 7,723,937,985
Accumulated Depreciation | (1,688,756,381) |  |  | (1,688,756,381)
Investment in Real Estate Net |  |  |  | 6,035,181,604
Encumbrances |  |  |  | $ 4,704,870,280
Changes in accumulated depreciation |  |  |  |
Balance, end of year | (1,688,756,381) |  |  |
Total Investment in Real Estate and Real Estate Held For Sale [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Properties |  |  |  | 389
Units |  |  |  | 103,232
Investment in Real Estate, Gross |  |  |  | $ 28,542,696,446
Accumulated Depreciation | (6,084,616,312) |  |  | (6,084,616,312)
Investment in Real Estate Net |  |  |  | 22,458,080,134
Encumbrances |  |  |  | 4,704,870,280
Changes in accumulated depreciation |  |  |  |
Balance, end of year | $ (6,084,616,312) |  |  |
Total Investment in Real Estate and Real Estate Held For Sale [Member] | Partially Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | 343,428,578
Total Investment in Real Estate and Real Estate Held For Sale [Member] | Wholly Owned Encumbered [Member] |  |  |  |
Overall summary of real estate and accumulated depreciation |  |  |  |
Encumbrances |  |  |  | $ 4,361,441,702

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