Investments in Partially Owned Entities (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Nov. 01, 2012	Dec. 31, 2011	Dec. 31, 2010
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	19		19
Partially Owned Consolidated Units	3,475		3,475
ASSETS
Investment in real estate	$ 21,151,576,000		$ 21,151,576,000			$ 20,407,946,000
Accumulated depreciation	(4,880,808,000)		(4,880,808,000)			(4,539,583,000)
Investment in real estate, net	16,270,768,000		16,270,768,000			15,868,363,000
Cash and cash equivalents	45,623,000	45,986,000	45,623,000	45,986,000		383,921,000	431,408,000
Deposits - restricted	120,440,000		120,440,000			152,237,000
Escrow deposits - mortgage	10,462,000		10,462,000			10,692,000
Deferred financing costs, net	38,823,000		38,823,000			44,608,000
Other assets	164,523,000		164,523,000			187,155,000
Total assets	16,668,545,000		16,668,545,000			16,659,303,000
LIABILITIES AND EQUITY
Total Debt	3,948,115,000		3,948,115,000			4,111,487,000
Accounts payable and accrued expenses	105,602,000		105,602,000			35,206,000
Accrued interest payable	78,869,000		78,869,000			88,121,000
Other liabilities	370,046,000		370,046,000			291,289,000
Security deposits	68,758,000		68,758,000			65,286,000
Total liabilities	10,040,476,000		10,040,476,000			10,380,042,000
Noncontrolling Interests - Partially Owned Properties	75,428,000		75,428,000			74,306,000
Total liabilities and equity	16,668,545,000		16,668,545,000			16,659,303,000
Debt-Secured:
Debt Instrument, Interest Rate, Stated Percentage	6.625%		6.625%		5.50%
Partially Owned Property Income Statement Schedule
Operating revenue	556,144,000	493,872,000	1,609,963,000	1,423,818,000
Depreciation	167,406,000	159,691,000	509,338,000	467,416,000
General and administrative/other	10,096,000	10,121,000	37,178,000	32,462,000
Operating income	184,127,000	144,814,000	489,790,000	395,750,000
Interest and Other Income	70,087,000	5,313,000	70,516,000	6,598,000
Interest:
Expense incurred, net	(113,876,000)	(112,449,000)	(347,452,000)	(350,957,000)
Amortization of Financing Costs	(3,338,000)	(4,650,000)	(10,319,000)	(11,900,000)
Income before income and other taxes, net gain on sales of land parcels and discontinued operations	132,906,000	30,500,000	181,857,000	30,173,000
Income and other tax (expense) benefit	(222,000)	(283,000)	(627,000)	(669,000)
Net income	236,323,000	112,977,000	496,805,000	827,796,000
Investments In Partially Owned Entities (Textuals) [Abstract]
Joint Venture Partner Ownership Percentage	80.00%		80.00%
Number of Joint Ventures	2		2
Partners Payments To Acquire Equity Method Investments			40,100,000
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Project Cost	232,800,000		232,800,000
Number of joint venture loans	2		2
Land purchase price	76,100,000		76,100,000
Business Acquisition, Cost of Acquired Entity, Purchase Price	968,545,000		968,545,000
Investment in Joint Venture	194,700,000		194,700,000
Variable Interest Entity Joint Venture Partner Ownership Percentage	50.00%		50.00%
Disposed Properties			20
Disposed Units			5,337
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	103,394,000	76,864,000	307,447,000	759,100,000
Consolidated Development Projects Held for and or Under Development [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	0		0
Partially Owned Consolidated Units	0		0
ASSETS
Investment in real estate	149,888,000		149,888,000
Accumulated depreciation	0		0
Investment in real estate, net	149,888,000		149,888,000
Cash and cash equivalents	5,475,000		5,475,000
Deposits - restricted	43,601,000		43,601,000
Deferred financing costs, net	0		0
Other assets	5,811,000		5,811,000
Total assets	204,775,000		204,775,000
LIABILITIES AND EQUITY
Total Debt	0		0
Accounts payable and accrued expenses	222,000		222,000
Accrued interest payable	0		0
Other liabilities	1,269,000		1,269,000
Security deposits	0		0
Total liabilities	1,491,000		1,491,000
Noncontrolling Interests - Partially Owned Properties	82,776,000		82,776,000
EQR equity	120,508,000		120,508,000
Total equity	203,284,000		203,284,000
Total liabilities and equity	204,775,000		204,775,000
Debt-Secured:
Debt Ownership	0		0
Noncontrolling Ownership	0		0
Partially Owned Property Income Statement Schedule
Operating revenue			0
Operating Expenses			121,000
Net operating (loss) income			(121,000)
Depreciation			0
General and administrative/other			93,000
Operating income			(214,000)
Interest and Other Income			2,000
Other Nonoperating Income (Expense)			(248,000)
Interest:
Expense incurred, net			0
Amortization of Financing Costs			0
Income before income and other taxes, net gain on sales of land parcels and discontinued operations			(460,000)
Income and other tax (expense) benefit			(25,000)
Net income			(485,000)
Consolidated Other [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	19		19
Partially Owned Consolidated Units	3,475		3,475
ASSETS
Investment in real estate	452,473,000		452,473,000
Accumulated depreciation	(155,820,000)		(155,820,000)
Investment in real estate, net	296,653,000		296,653,000
Cash and cash equivalents	15,641,000		15,641,000
Deposits - restricted	5,000		5,000
Deferred financing costs, net	1,055,000		1,055,000
Other assets	153,000		153,000
Total assets	313,507,000		313,507,000
LIABILITIES AND EQUITY
Total Debt	200,337,000		200,337,000
Accounts payable and accrued expenses	2,273,000		2,273,000
Accrued interest payable	782,000		782,000
Other liabilities	1,107,000		1,107,000
Security deposits	1,506,000		1,506,000
Total liabilities	206,005,000		206,005,000
Noncontrolling Interests - Partially Owned Properties	(7,348,000)		(7,348,000)
EQR equity	114,850,000		114,850,000
Total equity	107,502,000		107,502,000
Total liabilities and equity	313,507,000		313,507,000
Debt-Secured:
Debt Ownership	159,068,000		159,068,000
Noncontrolling Ownership	41,269,000		41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue			46,432,000
Operating Expenses			14,789,000
Net operating (loss) income			31,643,000
Depreciation			11,516,000
General and administrative/other			39,000
Operating income			20,088,000
Interest and Other Income			100,000
Other Nonoperating Income (Expense)			0
Interest:
Expense incurred, net			(7,040,000)
Amortization of Financing Costs			(125,000)
Income before income and other taxes, net gain on sales of land parcels and discontinued operations			13,023,000
Income and other tax (expense) benefit			(75,000)
Net income			12,948,000
Partially Owned Properties [Member]
ASSETS
Investment in real estate	602,361,000		602,361,000
Accumulated depreciation	(155,820,000)		(155,820,000)
Investment in real estate, net	446,541,000		446,541,000
Cash and cash equivalents	21,116,000		21,116,000
Deposits - restricted	43,606,000		43,606,000
Deferred financing costs, net	1,055,000		1,055,000
Other assets	5,964,000		5,964,000
Total assets	518,282,000		518,282,000
LIABILITIES AND EQUITY
Total Debt	200,337,000		200,337,000
Accounts payable and accrued expenses	2,495,000		2,495,000
Accrued interest payable	782,000		782,000
Other liabilities	2,376,000		2,376,000
Security deposits	1,506,000		1,506,000
Total liabilities	207,496,000		207,496,000
Noncontrolling Interests - Partially Owned Properties	75,428,000		75,428,000
EQR equity	235,358,000		235,358,000
Total equity	310,786,000		310,786,000
Total liabilities and equity	518,282,000		518,282,000
Debt-Secured:
Debt Ownership	159,068,000		159,068,000
Noncontrolling Ownership	41,269,000		41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue			46,432,000
Operating Expenses			14,910,000
Net operating (loss) income			31,522,000
Depreciation			11,516,000
General and administrative/other			132,000
Operating income			19,874,000
Interest and Other Income			102,000
Other Nonoperating Income (Expense)			(248,000)
Interest:
Expense incurred, net			(7,040,000)
Amortization of Financing Costs			(125,000)
Income before income and other taxes, net gain on sales of land parcels and discontinued operations			12,563,000
Income and other tax (expense) benefit			(100,000)
Net income			12,463,000
Unconsolidated Institutional Joint Ventures [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	0		0
Partially Owned Consolidated Units	0		0
ASSETS
Investment in real estate	143,996,000		143,996,000
Accumulated depreciation	0		0
Investment in real estate, net	143,996,000		143,996,000
Cash and cash equivalents	155,000		155,000
Deposits - restricted	0		0
Deferred financing costs, net	6,000		6,000
Other assets	0		0
Total assets	144,157,000		144,157,000
LIABILITIES AND EQUITY
Total Debt	50,934,000		50,934,000
Accounts payable and accrued expenses	4,995,000		4,995,000
Accrued interest payable	204,000		204,000
Other liabilities	117,000		117,000
Security deposits	1,000		1,000
Total liabilities	56,251,000		56,251,000
Noncontrolling Interests - Partially Owned Properties	70,428,000		70,428,000
EQR equity	17,478,000		17,478,000
Total equity	87,906,000		87,906,000
Total liabilities and equity	144,157,000		144,157,000
Debt-Secured:
Debt Ownership	10,187,000		10,187,000
Noncontrolling Ownership	40,747,000		40,747,000
Partially Owned Property Income Statement Schedule
Operating revenue			2,000
Operating Expenses			112,000
Net operating (loss) income			(110,000)
Depreciation			0
General and administrative/other			0
Operating income			(110,000)
Interest and Other Income			0
Other Nonoperating Income (Expense)			0
Interest:
Expense incurred, net			0
Amortization of Financing Costs			0
Income before income and other taxes, net gain on sales of land parcels and discontinued operations			(110,000)
Income and other tax (expense) benefit			0
Net income			(110,000)
Joint Venture Partner [Member]
LIABILITIES AND EQUITY
Noncontrolling Interests - Partially Owned Properties	81,800,000		81,800,000
Investments In Partially Owned Entities (Textuals) [Abstract]
Land purchase price	57,900,000		57,900,000
Business Acquisition, Cost of Acquired Entity, Purchase Price	75,700,000		75,700,000
Disposed Properties			2
Disposed Units			441
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax			(21,500,000)
Nexus Sawgrass [Member]
LIABILITIES AND EQUITY
Total Debt	19,100,000		19,100,000
Debt-Secured:
Debt Instrument, Interest Rate, Stated Percentage	5.60%		5.60%
Debt Instrument, Maturity Date			Jan. 01, 2021
Investments In Partially Owned Entities (Textuals) [Abstract]
Maximum Debt Commitment	47,100,000		47,100,000
Domain [Member]
LIABILITIES AND EQUITY
Total Debt	31,800,000		31,800,000
Debt-Secured:
Debt Instrument, Interest Rate, Stated Percentage	5.75%		5.75%
Debt Instrument, Maturity Date			Jan. 01, 2022
Investments In Partially Owned Entities (Textuals) [Abstract]
Maximum Debt Commitment	98,600,000		98,600,000
Company's Portion [Member]
Investments In Partially Owned Entities (Textuals) [Abstract]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 102,500,000		$ 102,500,000