CONSOLIDATED STATEMENTS OF CASH FLOWS OF ERP OPERATING LIMITED PARTNERSHIP (Unaudited) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 1,397,766,000	$ 260,482,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	550,488,000	348,106,000
Amortization of deferred financing costs	11,529,000	7,037,000
Amortization of Intangible Assets	1,216,000	0
Amortization of discounts and premiums on debt	(23,031,000)	(3,538,000)
Amortization of deferred settlements on derivative instruments	11,830,000	6,935,000
Write-off of pursuit costs	3,365,000	3,565,000
Income Loss from Investments in Unconsolidated Entities Adjustment	54,540,000	0
Distributions from unconsolidated entities - return on capital	588,000	240,000
Gain Loss On Sale Of Land Parcels	(14,616,000)	0
Net (gain) on sales of discontinued operations	(1,588,874,000)	(204,053,000)
Unrealized (gain) loss on derivative instruments	24,000	(1,000)
Compensation paid with Company Common Shares	22,089,000	16,878,000
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	(12,220,000)	(1,330,000)
Increase (decrease) in mortgage deposits	789,000	(992,000)
(Increase) in other assets	(4,695,000)	(23,017,000)
Increase in accounts payable and accrued expenses	25,956,000	35,794,000
(Decrease) in accrued interest payable	(1,396,000)	(5,426,000)
Increase (decrease) in other liabilities	(11,449,000)	141,090,000
Increase in security deposits	(6,080,000)	2,979,000
Net cash provided by operating activities	417,819,000	584,749,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to Acquire Businesses, Net of Cash Acquired	(4,000,875,000)	0
Investment in real estate - acquisitions	(108,308,000)	(520,775,000)
Investment in real estate - development/other	(154,576,000)	(78,210,000)
Improvements to real estate	(57,253,000)	(68,319,000)
Additions to non-real estate property	(2,801,000)	(4,700,000)
Interest capitalized for real estate and unconsolidated entities under development	(20,006,000)	(10,055,000)
Proceeds from disposition of real estate, net	3,764,000,000	333,015,000
Investments in unconsolidated entities	(53,687,000)	(5,420,000)
(Increase) in deposits on real estate acquisitions and investments, net	65,869,000	(40,539,000)
Decrease in mortgage deposits	5,089,000	2,285,000
Acquisition of Noncontrolling Interests – Partially Owned Properties	0	(87,000)
Net cash (used for) provided by investing activities	(562,548,000)	(392,805,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(18,006,000)	(4,283,000)
Mortgage Deposits	(2,208,000)	260,000
Mortgage notes payable:
Proceeds from Issuance of Long-term Debt	683,000	0
Restricted cash	0	214,000
Scheduled principal repayments	(6,336,000)	(7,575,000)
Notes, net:
Proceeds from Notes Payable	1,245,550,000	0
Lump sum payoffs	(400,000,000)	(253,858,000)
Line of Credit Facility:
Proceeds	8,413,000,000	105,000,000
Repayments	(8,413,000,000)	(70,000,000)
Payments for (Proceeds from) Hedge, Financing Activities	(44,013,000)	0
Proceeds from exercise of options	13,885,000	31,281,000
Payment of offering costs	(744,000)	(1,907,000)
Proceeds from (Payments for) Other Financing Activities	(33,000)	(33,000)
Contributions - Noncontrolling Interests - Partially Owned Properties	6,769,000	2,935,000
Contributions - Noncontrolling Interests - Operating Partnership	5,000	5,000
Distributions:
Noncontrolling Interests – Partially Owned Properties	(4,404,000)	(2,225,000)
Net cash (used for) financing activities	(315,297,000)	(531,280,000)
Net (decrease) increase in cash and cash equivalents	(460,026,000)	(339,336,000)
Cash and cash equivalents, beginning of period	612,590,000	383,921,000
Cash and cash equivalents, end of period	152,564,000	44,585,000
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	319,992,000	236,600,000
Net cash paid for income and other taxes	1,028,000	454,000
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	0	106,600,000
Valuation Of O P Units Issued	0	66,606,000
AmortizationOfDeferredFinancingCosts [Abstract]
Amortization Of Deferred Financing Costs Investment In Real Estate Net	(1,000)	0
Amortization Of Deferred Financing Costs Deferred Financing Costs Net	11,530,000	7,037,000
Amortization of discounts and premiums on debt:
Mortgage notes payable	(24,083,000)	(4,664,000)
Notes, net	1,052,000	1,126,000
Amortization of deferred settlements on derivative instruments:
Other liabilities	(268,000)	(268,000)
Losses reclassified into earnings from other comprehensive income	12,098,000	7,203,000
Loss From Investments In Unconsolidated Entities [Abstract]
Income Loss From Equity Method Investments Merger	49,507,000	0
Other Liabilities Loss From Investments in unconsolidated entities	5,033,000	0
Unrealized (gain) loss on derivative instruments:
Other assets	(10,753,000)	4,663,000
Mortgage notes payable	0	(2,589,000)
Notes, net	(1,523,000)	(2,074,000)
Other liabilities	(37,000)	8,641,000
Unrealized holding (losses) arising during the period	12,337,000	(8,642,000)
Acquisition of Archstone, net of cash acquired [Abstract]
Acquisition of Archstone Investment in Real Estate Net	(8,713,217,000)	0
Acquisition of Archstone Investments in Unconsolidated Entities	(214,677,000)	0
Acquisition of Archstone Deposits Restricted	(474,000)	0
Acquisition of Archstone Escrow Deposits Mortgage	(35,898,000)	0
Acquisition of Archstone Deferred Financing Costs	(25,780,000)	0
Acquisition of Archstone Other Assets	(203,008,000)	0
Acquisition of Archstone Mortgage Notes Payable	3,076,876,000	0
Acquisition of Archstone Accounts Payable And Accrued Liabilities	17,576,000	0
Acqusition of Archstone Interest Payable	11,256,000	0
Acquisition of Archstone Other Liabilities	117,391,000	0
Acquisition of Archstone Security Deposits	10,949,000	0
Acquisition of Archstone Common Shares Issued	1,929,868,000	0
Acquisition of Archstone Noncontrolling Interests Partially Owned Properties	28,263,000	0
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(19,195,000)	(9,676,000)
Investment in unconsolidated entities	(811,000)	(379,000)
Investments in unconsolidated entities	(4,371,000)	(5,420,000)
Investments in unconsolidated entities other liabilities	(49,316,000)	0
Other:
Receivable For Common Shares OP Units Issued	0	28,457,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(941,000)	0
OPERATING PARTNERSHIP
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	1,397,766,000	260,482,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	550,488,000	348,106,000
Amortization of deferred financing costs	11,529,000	7,037,000
Amortization of Intangible Assets	1,216,000	0
Amortization of discounts and premiums on debt	(23,031,000)	(3,538,000)
Amortization of deferred settlements on derivative instruments	11,830,000	6,935,000
Write-off of pursuit costs	3,365,000	3,565,000
Income Loss from Investments in Unconsolidated Entities Adjustment	54,540,000	0
Distributions from unconsolidated entities - return on capital	588,000	240,000
Gain Loss On Sale Of Land Parcels	(14,616,000)	0
Net (gain) on sales of discontinued operations	(1,588,874,000)	(204,053,000)
Unrealized (gain) loss on derivative instruments	24,000	(1,000)
Compensation paid with Company Common Shares	22,089,000	16,878,000
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	(12,220,000)	(1,330,000)
Increase (decrease) in mortgage deposits	789,000	(992,000)
(Increase) in other assets	(4,695,000)	(23,017,000)
Increase in accounts payable and accrued expenses	25,956,000	35,794,000
(Decrease) in accrued interest payable	(1,396,000)	(5,426,000)
Increase (decrease) in other liabilities	(11,449,000)	141,090,000
Increase in security deposits	(6,080,000)	2,979,000
Net cash provided by operating activities	417,819,000	584,749,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to Acquire Businesses, Net of Cash Acquired	(4,000,875,000)	0
Investment in real estate - acquisitions	(108,308,000)	(520,775,000)
Investment in real estate - development/other	(154,576,000)	(78,210,000)
Improvements to real estate	(57,253,000)	(68,319,000)
Additions to non-real estate property	(2,801,000)	(4,700,000)
Interest capitalized for real estate and unconsolidated entities under development	(20,006,000)	(10,055,000)
Proceeds from disposition of real estate, net	3,764,000,000	333,015,000
Investments in unconsolidated entities	(53,687,000)	(5,420,000)
(Increase) in deposits on real estate acquisitions and investments, net	65,869,000	(40,539,000)
Decrease in mortgage deposits	5,089,000	2,285,000
Acquisition of Noncontrolling Interests – Partially Owned Properties	0	(87,000)
Net cash (used for) provided by investing activities	(562,548,000)	(392,805,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(18,006,000)	(4,283,000)
Mortgage Deposits	(2,208,000)	260,000
Mortgage notes payable:
Proceeds from Issuance of Long-term Debt	683,000	0
Restricted cash	0	214,000
Lump sum payoffs	(697,897,000)	(198,763,000)
Scheduled principal repayments	(6,336,000)	(7,575,000)
Notes, net:
Proceeds from Notes Payable	1,245,550,000	0
Lump sum payoffs	(400,000,000)	(253,858,000)
Line of Credit Facility:
Proceeds	8,413,000,000	105,000,000
Repayments	(8,413,000,000)	(70,000,000)
Payments for (Proceeds from) Hedge, Financing Activities	(44,013,000)	0
Proceeds from sale of OP Units	0	152,058,000
Proceeds from EQR's Employee Share Purchase Plan (ESPP)	2,363,000	4,523,000
Proceeds from exercise of options	13,885,000	31,281,000
Payment of offering costs	(744,000)	(1,907,000)
Proceeds from (Payments for) Other Financing Activities	(33,000)	(33,000)
Contributions - Noncontrolling Interests - Partially Owned Properties	6,769,000	2,935,000
Contributions - Noncontrolling Interests - Operating Partnership	5,000	5,000
Distributions:
OP Units - General Partner	(393,347,000)	(269,755,000)
Preference Units	(1,036,000)	(6,933,000)
OP Units - Limited Partners	(16,528,000)	(12,224,000)
Noncontrolling Interests – Partially Owned Properties	(4,404,000)	(2,225,000)
Net cash (used for) financing activities	(315,297,000)	(531,280,000)
Net (decrease) increase in cash and cash equivalents	(460,026,000)	(339,336,000)
Cash and cash equivalents, beginning of period	612,590,000	383,921,000
Cash and cash equivalents, end of period	152,564,000	44,585,000
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	319,992,000	236,600,000
Net cash paid for income and other taxes	1,028,000	454,000
Real estate acquisitions/dispositions/other:
Mortgage loans assumed	0	106,600,000
Valuation Of O P Units Issued	0	66,606,000
AmortizationOfDeferredFinancingCosts [Abstract]
Amortization Of Deferred Financing Costs Investment In Real Estate Net	(1,000)	0
Amortization Of Deferred Financing Costs Deferred Financing Costs Net	11,530,000	7,037,000
Amortization of discounts and premiums on debt:
Mortgage notes payable	(24,083,000)	(4,664,000)
Notes, net	1,052,000	1,126,000
Amortization of deferred settlements on derivative instruments:
Other liabilities	(268,000)	(268,000)
Losses reclassified into earnings from other comprehensive income	12,098,000	7,203,000
Loss From Investments In Unconsolidated Entities [Abstract]
Income Loss From Equity Method Investments Merger	49,507,000	0
Other Liabilities Loss From Investments in unconsolidated entities	5,033,000	0
Unrealized (gain) loss on derivative instruments:
Other assets	(10,753,000)	4,663,000
Mortgage notes payable	0	(2,589,000)
Notes, net	(1,523,000)	(2,074,000)
Other liabilities	(37,000)	8,641,000
Unrealized holding (losses) arising during the period	12,337,000	(8,642,000)
Acquisition of Archstone, net of cash acquired [Abstract]
Acquisition of Archstone Investment in Real Estate Net	(8,713,217,000)	0
Acquisition of Archstone Investments in Unconsolidated Entities	(214,677,000)	0
Acquisition of Archstone Deposits Restricted	(474,000)	0
Acquisition of Archstone Escrow Deposits Mortgage	(35,898,000)	0
Acquisition of Archstone Deferred Financing Costs	(25,780,000)	0
Acquisition of Archstone Other Assets	(203,008,000)	0
Acquisition of Archstone Mortgage Notes Payable	3,076,876,000	0
Acquisition of Archstone Accounts Payable And Accrued Liabilities	17,576,000	0
Acqusition of Archstone Interest Payable	11,256,000	0
Acquisition of Archstone Other Liabilities	117,391,000	0
Acquisition of Archstone Security Deposits	10,949,000	0
Acquisition of Archstone Common Shares Issued	1,929,868,000	0
Acquisition of Archstone Noncontrolling Interests Partially Owned Properties	28,263,000	0
Interest capitalized for real estate and unconsolidated entities under development:
Investment in real estate, net	(19,195,000)	(9,676,000)
Investment in unconsolidated entities	(811,000)	(379,000)
Investments in unconsolidated entities	(4,371,000)	(5,420,000)
Investments in unconsolidated entities other liabilities	(49,316,000)	0
Other:
Receivable For Common Shares OP Units Issued	0	28,457,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	$ (941,000)	$ 0