CONSOLIDATED STATEMENTS OF CASH FLOWS OF ERP OPERATING LIMITED PARTNERSHIP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 908,018	$ 658,683	$ 1,905,353
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	765,895	758,861	1,013,353
Amortization of deferred financing costs	10,801	11,088	22,425
Amortization of above/below market leases	3,382	3,222	898
Amortization of discounts and premiums on debt	(9,492)	(13,520)	(156,439)
Amortization of deferred settlements on derivative instruments	18,075	16,334	19,607
Write-off of pursuit costs	3,208	3,607	5,184
(Income) loss from investments in unconsolidated entities	(15,025)	7,952	58,156
Distributions from unconsolidated entities – return on capital	4,741	5,570	2,481
Net (gain) on sales of investment securities and other investments	(526)	(57)	(4,203)
Net (gain) on sales of real estate properties	(335,134)	(212,685)	0
Net loss (gain) on sales of land parcels	1	(5,277)	(12,227)
Net (gain) on sales of discontinued operations	0	(179)	(2,036,505)
Realized/unrealized loss (gain) on derivative instruments	3,055	(60)	70
Compensation paid with Company Common Shares	34,607	27,543	35,474
Changes in assets and liabilities:
(Increase) decrease in deposits – restricted	(1,794)	(1,740)	3,684
Decrease in mortgage deposits	258	1,452	1,813
(Increase) decrease in other assets	(41,803)	21,773	3,742
(Decrease) increase in accounts payable and accrued expenses	(1,667)	17,797	6,229
(Decrease) increase in accrued interest payable	(4,319)	11,231	(9,219)
Increase in other liabilities	12,269	8,437	15,401
Increase (decrease) in security deposits	1,949	4,041	(6,361)
Net cash provided by operating activities	1,356,499	1,324,073	868,916
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisition of Archstone, net of cash acquired	0	0	(4,000,875)
Investment in real estate – acquisitions	(331,336)	(469,989)	(108,308)
Investment in real estate – development/other	(653,897)	(530,387)	(377,442)
Capital expenditures to real estate	(182,113)	(185,957)	(135,816)
Non-real estate capital additions	(3,991)	(5,286)	(4,134)
Interest capitalized for real estate and unconsolidated entities under development	(59,885)	(52,782)	(47,321)
Proceeds from disposition of real estate, net	504,748	522,647	4,551,454
Investments in unconsolidated entities	(23,019)	(15,768)	(66,471)
Distributions from unconsolidated entities – return of capital	51,144	103,793	25,471
Proceeds from sale of investment securities	2,535	57	4,878
Decrease in deposits on real estate acquisitions and investments, net	17,874	33,004	143,694
(Increase) decrease in mortgage deposits	(531)	798	7,893
Consolidation of previously unconsolidated properties	0	(44,796)	0
Net cash (used for) investing activities	(678,471)	(644,666)	(6,977)
CASH FLOWS FROM FINANCING ACTIVITIES:
Debt financing costs	(6,425)	(10,982)	(16,526)
Mortgage deposits	(8,588)	(7,699)	(5,631)
Mortgage notes payable:
Proceeds	0	0	902,886
Lump sum payoffs	(359,244)	(88,788)	(2,532,682)
Scheduled principal repayments	(9,275)	(11,869)	(12,658)
Notes, net:
Proceeds	746,391	1,194,277	1,245,550
Lump sum payoffs	(300,000)	(1,250,000)	(400,000)
Line of credit and commercial paper:
Line of credit proceeds	3,770,000	7,167,000	9,832,000
Line of credit repayments	(4,103,000)	(6,949,000)	(9,717,000)
Commercial paper proceeds	3,931,227	0	0
Commercial paper repayments	(3,545,028)	0	0
(Payments on) settlement of derivative instruments	(13,938)	(758)	(44,063)
Proceeds from EQR's Employee Share Purchase Plan (ESPP)	4,404	3,392	3,401
Proceeds from exercise of EQR options	59,508	82,573	17,252
OP units repurchased and retired	0	(1,777)	0
Payments for Repurchase of Redeemable Preferred Stock	(12,720)	0	0
Payments for the Premium on Redemption of Preferred Shares/Preference Units	(3,486)	0	0
Payment of offering costs	(79)	(41)	(1,047)
Other financing activities, net	(49)	(49)	(48)
Acquisition of Noncontrolling Interests – Partially Owned Properties	0	(5,501)	0
Contributions – Noncontrolling Interests – Partially Owned Properties	0	5,684	27,660
Contributions - Limited Partners	3	3	5
Distributions:
Preference Units	(3,357)	(4,145)	(4,145)
OP Units – General Partner	(784,748)	(776,659)	(681,610)
OP Units – Limited Partners	(30,869)	(30,744)	(27,897)
Noncontrolling Interests – Partially Owned Properties	(6,559)	(7,778)	(6,442)
Net cash (used for) financing activities	(675,832)	(692,861)	(1,420,995)
Net increase (decrease) in cash and cash equivalents	2,196	(13,454)	(559,056)
Cash and cash equivalents, beginning of year	40,080	53,534	612,590
Cash and cash equivalents, end of year	42,276	40,080	53,534
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	436,748	443,125	722,963
Net cash paid for income and other taxes	1,264	1,517	1,152
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	0	28,910	0
Amortization of deferred financing costs:
Investment in real estate, net	0	0	(152)
Deferred financing costs, net	10,801	11,088	22,577
Amortization of discounts and premiums on debt:
Mortgage notes payable	(13,126)	(15,904)	(158,625)
Notes, net	2,557	2,384	2,186
Line of credit and commercial paper	1,077	0	0
Amortization of deferred settlements on derivative instruments:
Other liabilities	(169)	(534)	(534)
Accumulated other comprehensive income	18,244	16,868	20,141
Write-off of pursuit costs [Abstract]
Investment in real estate, net	2,804	2,541	4,956
Write-off of pursuit costs	3,208	3,607	5,184
Other assets	74	1,066	203
(Income) loss from investments in unconsolidated entities:
Investments in unconsolidated entities	(17,340)	4,610	53,066
Other liabilities	2,315	3,342	5,090
Distributions from unconsolidated entities return on capital:
Investments in unconsolidated entities	4,606	5,360	2,448
Other liabilities	135	210	33
Realized/unrealized loss (gain) on derivative instruments:
Other assets	(3,573)	10,160	(17,139)
Notes, net	2,058	1,597	(1,523)
Other liabilities	2,351	21,489	(39)
Accumulated other comprehensive income	2,219	(33,306)	18,771
Acquisition of Archstone, net of cash acquired:
Investment in real estate, net	0	39,929	(8,687,355)
Investments in unconsolidated entities	0	(33,993)	(225,568)
Deposits - restricted	0	0	(528)
Escrow deposits - mortgage	0	0	(37,582)
Deferred financing costs, net	0	0	(25,780)
Other assets	0	(2,586)	(215,622)
Mortgage notes payable	0	0	3,076,876
Accounts payable and accrued expenses	0	(146)	16,984
Accrued interest payable	0	0	11,305
Other liabilities	0	(3,204)	117,299
Security deposits	0	0	10,965
Issuance of OP Units	0	0	1,929,868
Noncontrolling Interests - Partially Owned Properties	0	0	28,263
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(59,885)	(52,717)	(45,533)
Investments in unconsolidated entities	0	(65)	(1,788)
Investments in unconsolidated entities:
Investments in unconsolidated entities	(1,404)	(6,318)	(13,656)
Other liabilities	(21,615)	(9,450)	(52,815)
Consolidation of previously unconsolidated properties:
Investment in real estate, net	331,336	469,989	108,308
Investments in unconsolidated entities	(23,019)	(15,768)	(66,471)
Accounts payable and accrued expenses	(1,667)	17,797	6,229
(Payments on) settlement of derivative instruments:
Other assets	1,848	6,623	(50)
Other liabilities	(15,786)	(7,381)	(44,013)
Other:
Foreign currency translation adjustments	327	552	(613)
Unconsolidated Properties [Member]
Changes in assets and liabilities:
(Decrease) increase in accounts payable and accrued expenses	0	1,987	0
CASH FLOWS FROM INVESTING ACTIVITIES:
Investment in real estate – acquisitions	0	64,319	0
Investments in unconsolidated entities	0	(847)	0
Consolidation of previously unconsolidated properties:
Investment in real estate, net	0	(64,319)	0
Investments in unconsolidated entities	0	(847)	0
Accounts payable and accrued expenses	0	1,987	0
Other Liabilities	0	18,383	0
Land [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Write-off of pursuit costs	330	0	25
Write-off of pursuit costs [Abstract]
Write-off of pursuit costs	330	0	25
ERPOP [Member]
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	908,018	658,683	1,905,353
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	765,895	758,861	1,013,353
Amortization of deferred financing costs	10,801	11,088	22,425
Amortization of above/below market leases	3,382	3,222	898
Amortization of discounts and premiums on debt	(9,492)	(13,520)	(156,439)
Amortization of deferred settlements on derivative instruments	18,075	16,334	19,607
Write-off of pursuit costs	3,208	3,607	5,184
(Income) loss from investments in unconsolidated entities	(15,025)	7,952	58,156
Distributions from unconsolidated entities – return on capital	4,741	5,570	2,481
Net (gain) on sales of investment securities and other investments	(526)	(57)	(4,203)
Net (gain) on sales of real estate properties	(335,134)	(212,685)	0
Net loss (gain) on sales of land parcels	1	(5,277)	(12,227)
Net (gain) on sales of discontinued operations	0	(179)	(2,036,505)
Realized/unrealized loss (gain) on derivative instruments	3,055	(60)	70
Compensation paid with Company Common Shares	34,607	27,543	35,474
Changes in assets and liabilities:
(Increase) decrease in deposits – restricted	(1,794)	(1,740)	3,684
Decrease in mortgage deposits	258	1,452	1,813
(Increase) decrease in other assets	(41,803)	21,773	3,742
(Decrease) increase in accounts payable and accrued expenses	(1,667)	17,797	6,229
(Decrease) increase in accrued interest payable	(4,319)	11,231	(9,219)
Increase in other liabilities	12,269	8,437	15,401
Increase (decrease) in security deposits	1,949	4,041	(6,361)
Net cash provided by operating activities	1,356,499	1,324,073	868,916
CASH FLOWS FROM INVESTING ACTIVITIES:
Acquisition of Archstone, net of cash acquired	0	0	(4,000,875)
Investment in real estate – acquisitions	(331,336)	(469,989)	(108,308)
Investment in real estate – development/other	(653,897)	(530,387)	(377,442)
Capital expenditures to real estate	(182,113)	(185,957)	(135,816)
Non-real estate capital additions	(3,991)	(5,286)	(4,134)
Interest capitalized for real estate and unconsolidated entities under development	(59,885)	(52,782)	(47,321)
Proceeds from disposition of real estate, net	504,748	522,647	4,551,454
Investments in unconsolidated entities	(23,019)	(15,768)	(66,471)
Distributions from unconsolidated entities – return of capital	51,144	103,793	25,471
Proceeds from sale of investment securities	2,535	57	4,878
Decrease in deposits on real estate acquisitions and investments, net	17,874	33,004	143,694
(Increase) decrease in mortgage deposits	(531)	798	7,893
Consolidation of previously unconsolidated properties	0	(44,796)	0
Net cash (used for) investing activities	(678,471)	(644,666)	(6,977)
CASH FLOWS FROM FINANCING ACTIVITIES:
Debt financing costs	(6,425)	(10,982)	(16,526)
Mortgage deposits	(8,588)	(7,699)	(5,631)
Mortgage notes payable:
Proceeds	0	0	902,886
Lump sum payoffs	(359,244)	(88,788)	(2,532,682)
Scheduled principal repayments	(9,275)	(11,869)	(12,658)
Notes, net:
Proceeds	746,391	1,194,277	1,245,550
Lump sum payoffs	(300,000)	(1,250,000)	(400,000)
Line of credit and commercial paper:
Line of credit proceeds	3,770,000	7,167,000	9,832,000
Line of credit repayments	(4,103,000)	(6,949,000)	(9,717,000)
Commercial paper proceeds	3,931,227	0	0
Commercial paper repayments	(3,545,028)	0	0
(Payments on) settlement of derivative instruments	(13,938)	(758)	(44,063)
Proceeds from EQR's Employee Share Purchase Plan (ESPP)	4,404	3,392	3,401
Proceeds from exercise of EQR options	59,508	82,573	17,252
OP units repurchased and retired	0	(1,777)	0
Payments for Repurchase of Redeemable Preferred Stock	(12,720)	0	0
Payments for the Premium on Redemption of Preferred Shares/Preference Units	(3,486)	0	0
Payment of offering costs	(79)	(41)	(1,047)
Other financing activities, net	(49)	(49)	(48)
Acquisition of Noncontrolling Interests – Partially Owned Properties	0	(5,501)	0
Contributions – Noncontrolling Interests – Partially Owned Properties	0	5,684	27,660
Contributions - Limited Partners	3	3	5
Distributions:
Preference Units	(3,357)	(4,145)	(4,145)
OP Units – General Partner	(784,748)	(776,659)	(681,610)
OP Units – Limited Partners	(30,869)	(30,744)	(27,897)
Noncontrolling Interests – Partially Owned Properties	(6,559)	(7,778)	(6,442)
Net cash (used for) financing activities	(675,832)	(692,861)	(1,420,995)
Net increase (decrease) in cash and cash equivalents	2,196	(13,454)	(559,056)
Cash and cash equivalents, beginning of year	40,080	53,534	612,590
Cash and cash equivalents, end of year	42,276	40,080	53,534
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	436,748	443,125	722,963
Net cash paid for income and other taxes	1,264	1,517	1,152
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	0	28,910	0
Amortization of deferred financing costs:
Investment in real estate, net	0	0	(152)
Deferred financing costs, net	10,801	11,088	22,577
Amortization of discounts and premiums on debt:
Mortgage notes payable	(13,126)	(15,904)	(158,625)
Notes, net	2,557	2,384	2,186
Line of credit and commercial paper	1,077	0	0
Amortization of deferred settlements on derivative instruments:
Other liabilities	(169)	(534)	(534)
Accumulated other comprehensive income	18,244	16,868	20,141
Write-off of pursuit costs [Abstract]
Investment in real estate, net	2,804	2,541	4,956
Write-off of pursuit costs	3,208	3,607	5,184
Other assets	74	1,066	203
(Income) loss from investments in unconsolidated entities:
Investments in unconsolidated entities	(17,340)	4,610	53,066
Other liabilities	2,315	3,342	5,090
Distributions from unconsolidated entities return on capital:
Investments in unconsolidated entities	4,606	5,360	2,448
Other liabilities	135	210	33
Realized/unrealized loss (gain) on derivative instruments:
Other assets	(3,573)	10,160	(17,139)
Notes, net	2,058	1,597	(1,523)
Other liabilities	2,351	21,489	(39)
Accumulated other comprehensive income	2,219	(33,306)	18,771
Acquisition of Archstone, net of cash acquired:
Investment in real estate, net	0	39,929	(8,687,355)
Investments in unconsolidated entities	0	(33,993)	(225,568)
Deposits - restricted	0	0	(528)
Escrow deposits - mortgage	0	0	(37,582)
Deferred financing costs, net	0	0	(25,780)
Other assets	0	(2,586)	(215,622)
Mortgage notes payable	0	0	3,076,876
Accounts payable and accrued expenses	0	(146)	16,984
Accrued interest payable	0	0	11,305
Other liabilities	0	(3,204)	117,299
Security deposits	0	0	10,965
Issuance of OP Units	0	0	1,929,868
Noncontrolling Interests - Partially Owned Properties	0	0	28,263
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(59,885)	(52,717)	(45,533)
Investments in unconsolidated entities	0	(65)	(1,788)
Investments in unconsolidated entities:
Investments in unconsolidated entities	(1,404)	(6,318)	(13,656)
Other liabilities	(21,615)	(9,450)	(52,815)
Consolidation of previously unconsolidated properties:
Investment in real estate, net	331,336	469,989	108,308
Investments in unconsolidated entities	(23,019)	(15,768)	(66,471)
Accounts payable and accrued expenses	(1,667)	17,797	6,229
(Payments on) settlement of derivative instruments:
Other assets	1,848	6,623	(50)
Other liabilities	(15,786)	(7,381)	(44,013)
Other:
Foreign currency translation adjustments	327	552	(613)
ERPOP [Member] | Unconsolidated Properties [Member]
Changes in assets and liabilities:
(Decrease) increase in accounts payable and accrued expenses	0	1,987	0
CASH FLOWS FROM INVESTING ACTIVITIES:
Investment in real estate – acquisitions	0	64,319	0
Investments in unconsolidated entities	0	(847)	0
Consolidation of previously unconsolidated properties:
Investment in real estate, net	0	(64,319)	0
Investments in unconsolidated entities	0	(847)	0
Accounts payable and accrued expenses	0	1,987	0
Other Liabilities	0	18,383	0
ERPOP [Member] | Land [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Write-off of pursuit costs	330	0	25
Write-off of pursuit costs [Abstract]
Write-off of pursuit costs	$ 330	$ 0	$ 25