CONSOLIDATED STATEMENTS OF CASH FLOWS OF ERP OPERATING LIMITED PARTNERSHIP (Unaudited) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 1,061,034,000	$ 152,167,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	220,038,000	175,108,000
Amortization of deferred financing costs	7,176,000	2,974,000
Amortization of Intangible Assets	292,000	0
Amortization of discounts and premiums on debt	(7,071,000)	(1,567,000)
Amortization of deferred settlements on derivative instruments	8,139,000	3,429,000
Write-off of pursuit costs	2,533,000	1,034,000
Income (Loss) from Equity Method Investments	(355,000)	0
Income Loss from Investments in Unconsolidated Entities Adjustment	46,366,000	0
Distributions from unconsolidated entities - return on capital	257,000	89,000
Net (gain) on sales of discontinued operations	(1,198,922,000)	(132,956,000)
Unrealized (gain) loss on derivative instruments	0	(1,000)
Compensation paid with Company Common Shares	10,236,000	8,968,000
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	(1,733,000)	2,768,000
Increase (decrease) in mortgage deposits	1,651,000	(782,000)
(Increase) in other assets	(15,220,000)	(12,262,000)
Increase in accounts payable and accrued expenses	47,498,000	41,616,000
(Decrease) in accrued interest payable	1,039,000	(8,632,000)
Increase (decrease) in other liabilities	(18,437,000)	(16,878,000)
Increase in security deposits	(5,268,000)	182,000
Net cash provided by operating activities	193,514,000	234,245,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to Acquire Businesses, Net of Cash Acquired	(4,000,643,000)	0
Investment in real estate - acquisitions	0	(183,112,000)
Investment in real estate - development/other	(65,232,000)	(35,876,000)
Improvements to real estate	(26,599,000)	(30,225,000)
Additions to non-real estate property	(1,942,000)	(2,229,000)
Interest capitalized for real estate and unconsolidated entities under development	(8,413,000)	(4,996,000)
Proceeds from disposition of real estate, net	2,955,398,000	204,272,000
Investments in unconsolidated entities	(283,000)	(2,396,000)
(Increase) in deposits on real estate acquisitions and investments, net	101,668,000	(27,386,000)
Decrease in mortgage deposits	4,473,000	83,000
Net cash (used for) provided by investing activities	(1,041,573,000)	(81,865,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(13,869,000)	(4,227,000)
Mortgage Deposits Financing Activities	(632,000)	(37,000)
Mortgage notes payable:
Restricted cash	0	209,000
Scheduled principal repayments	(3,244,000)	(3,970,000)
Notes, net:
Proceeds from Notes Payable	750,000,000	0
Lump sum payoffs	0	(253,858,000)
Line of Credit Facility:
Proceeds	5,850,000,000	0
Repayments	5,455,000,000	0
Proceeds from exercise of EQR options	7,174,000	18,938,000
Payment of offering costs	(406,000)	(1,887,000)
Contributions - Noncontrolling Interests - Partially Owned Properties	3,299,000	921,000
Contributions - Noncontrolling Interests - Operating Partnership	3,000	5,000
Distributions:
Noncontrolling Interests – Partially Owned Properties	(3,345,000)	(1,762,000)
Net cash (used for) financing activities	291,556,000	(316,673,000)
Net (decrease) increase in cash and cash equivalents	(556,503,000)	(164,293,000)
Cash and cash equivalents, beginning of period	612,590,000	383,921,000
Cash and cash equivalents, end of period	56,087,000	219,628,000
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	182,356,000	125,435,000
Net cash paid for income and other taxes	483,000	560,000
AmortizationOfDeferredFinancingCosts [Abstract]
Amortization Of Deferred Financing Costs Investment In Real Estate Net	(1,000)	0
Amortization Of Deferred Financing Costs Deferred Financing Costs Net	7,177,000	2,974,000
Amortization of discounts and premiums on debt:
Mortgage notes payable	(7,557,000)	(2,153,000)
Notes, net	486,000	586,000
Amortization of deferred settlements on derivative instruments:
Other liabilities	(133,000)	(134,000)
Accumulated other comprehensive income	(8,272,000)	(3,563,000)
Loss From Investments In Unconsolidated Entities [Abstract]
Income Loss From Equity Method Investments Merger	42,213,000	0
Other Liabilities Loss From Investments in unconsolidated entities	4,153,000	0
Unrealized (gain) loss on derivative instruments:
Other assets	1,471,000	1,300,000
Mortgage notes payable	0	(588,000)
Notes, net	(1,471,000)	(712,000)
Other liabilities	(2,814,000)	(3,219,000)
Unrealized holding (losses) arising during the period	2,814,000	3,218,000
Acquisition of Archstone, net of cash acquired [Abstract]
Acquisition of Archstone Investment in real estate, net	(8,707,967,000)	0
Acquisition of Archstone Investments in Unconsolidated Entities	(218,197,000)	0
Acquisition of Archstone Restricted Cash and Cash Equivalents	(474,000)	0
Acquisition of Archstone Escrow Deposits For Mortgage And Replacement Reserves	(35,898,000)	0
Acquisition of Archstone Deferred Finance Costs, Net	(25,780,000)	0
Acquisition of Archstone Other Assets	(204,523,000)	0
Acquisition of Archstone Secured Debt	3,076,876,000	0
Acquisition of Archstone Accounts Payable And Accrued Liabilities	17,593,000	0
Acquisition 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	(8,089,000)	(4,827,000)
Investment in unconsolidated entities	(324,000)	(169,000)
Other:
Receivable For Common Shares Issued	0	28,457,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	873,000	0
OPERATING PARTNERSHIP
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	1,061,034,000	152,167,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	220,038,000	175,108,000
Amortization of deferred financing costs	7,176,000	2,974,000
Amortization of Intangible Assets	292,000	0
Amortization of discounts and premiums on debt	(7,071,000)	(1,567,000)
Amortization of deferred settlements on derivative instruments	8,139,000	3,429,000
Write-off of pursuit costs	2,533,000	1,034,000
Income (Loss) from Equity Method Investments	(355,000)	0
Income Loss from Investments in Unconsolidated Entities Adjustment	46,366,000	0
Distributions from unconsolidated entities - return on capital	257,000	89,000
Net (gain) on sales of discontinued operations	(1,198,922,000)	(132,956,000)
Unrealized (gain) loss on derivative instruments	0	(1,000)
Compensation paid with Company Common Shares	10,236,000	8,968,000
Changes in assets and liabilities:
(Increase) decrease in deposits - restricted	1,733,000	(2,768,000)
Increase (decrease) in mortgage deposits	1,651,000	(782,000)
(Increase) in other assets	15,220,000	12,262,000
Increase in accounts payable and accrued expenses	47,498,000	41,616,000
(Decrease) in accrued interest payable	1,039,000	(8,632,000)
Increase (decrease) in other liabilities	(18,437,000)	(16,878,000)
Increase in security deposits	(5,268,000)	182,000
Net cash provided by operating activities	193,514,000	234,245,000
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to Acquire Businesses, Net of Cash Acquired	(4,000,643,000)	0
Investment in real estate - acquisitions	0	(183,112,000)
Investment in real estate - development/other	(65,232,000)	(35,876,000)
Improvements to real estate	(26,599,000)	(30,225,000)
Additions to non-real estate property	(1,942,000)	(2,229,000)
Interest capitalized for real estate and unconsolidated entities under development	(8,413,000)	(4,996,000)
Proceeds from disposition of real estate, net	2,955,398,000	204,272,000
Investments in unconsolidated entities	(283,000)	(2,396,000)
(Increase) in deposits on real estate acquisitions and investments, net	101,668,000	(27,386,000)
Decrease in mortgage deposits	4,473,000	83,000
Net cash (used for) provided by investing activities	(1,041,573,000)	(81,865,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Loan and bond acquisition costs	(13,869,000)	(4,227,000)
Mortgage Deposits Financing Activities	(632,000)	(37,000)
Mortgage notes payable:
Restricted cash	0	209,000
Lump sum payoffs	(584,020,000)	(47,800,000)
Scheduled principal repayments	(3,244,000)	(3,970,000)
Notes, net:
Proceeds from Notes Payable	750,000,000	0
Lump sum payoffs	0	(253,858,000)
Line of Credit Facility:
Proceeds	5,850,000,000	0
Repayments	(5,455,000,000)	0
Proceeds from sale of OP Units	0	152,058,000
Proceeds from EQR's Employee Share Purchase Plan (ESPP)	1,763,000	4,210,000
Proceeds from exercise of EQR options	7,174,000	18,938,000
Payment of offering costs	(406,000)	(1,887,000)
Contributions - Noncontrolling Interests - Partially Owned Properties	3,299,000	921,000
Contributions - Noncontrolling Interests - Operating Partnership	3,000	5,000
Distributions:
OP Units - General Partner	(249,330,000)	(168,350,000)
Preference Units	0	(3,466,000)
OP Units - Limited Partners	(10,837,000)	(7,657,000)
Noncontrolling Interests – Partially Owned Properties	(3,345,000)	(1,762,000)
Net cash (used for) financing activities	291,556,000	(316,673,000)
Net (decrease) increase in cash and cash equivalents	(556,503,000)	(164,293,000)
Cash and cash equivalents, beginning of period	612,590,000	383,921,000
Cash and cash equivalents, end of period	56,087,000	219,628,000
SUPPLEMENTAL INFORMATION:
Cash paid for interest, net of amounts capitalized	182,356,000	125,435,000
Net cash paid for income and other taxes	483,000	560,000
AmortizationOfDeferredFinancingCosts [Abstract]
Amortization Of Deferred Financing Costs Investment In Real Estate Net	(1,000)	0
Amortization Of Deferred Financing Costs Deferred Financing Costs Net	7,177,000	2,974,000
Amortization of discounts and premiums on debt:
Mortgage notes payable	(7,557,000)	(2,153,000)
Notes, net	486,000	586,000
Amortization of deferred settlements on derivative instruments:
Other liabilities	(133,000)	(134,000)
Accumulated other comprehensive income	8,272,000	3,563,000
Loss From Investments In Unconsolidated Entities [Abstract]
Income Loss From Equity Method Investments Merger	42,213,000	0
Other Liabilities Loss From Investments in unconsolidated entities	4,153,000	0
Unrealized (gain) loss on derivative instruments:
Other assets	1,471,000	1,300,000
Mortgage notes payable	0	(588,000)
Notes, net	(1,471,000)	(712,000)
Other liabilities	(2,814,000)	(3,219,000)
Unrealized holding (losses) arising during the period	2,814,000	3,218,000
Acquisition of Archstone, net of cash acquired [Abstract]
Acquisition of Archstone Investment in real estate, net	(8,707,967,000)	0
Acquisition of Archstone Investments in Unconsolidated Entities	(218,197,000)	0
Acquisition of Archstone Restricted Cash and Cash Equivalents	(474,000)	0
Acquisition of Archstone Escrow Deposits For Mortgage And Replacement Reserves	(35,898,000)	0
Acquisition of Archstone Deferred Finance Costs, Net	(25,780,000)	0
Acquisition of Archstone Other Assets	(204,523,000)	0
Acquisition of Archstone Secured Debt	3,076,876,000	0
Acquisition of Archstone Accounts Payable And Accrued Liabilities	17,593,000	0
Acquisition 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	(8,089,000)	(4,827,000)
Investment in unconsolidated entities	(324,000)	(169,000)
Other:
Receivable For Common Shares Issued	0	28,457,000
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	$ 873,000	$ 0