Investments in Partially Owned Entities (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	21
Partially Owned Consolidated Units	3,916
ASSETS
Investment in real estate	$ 20,537,091,000		$ 20,407,946,000
Accumulated depreciation	(4,658,994,000)		(4,539,583,000)
Investment in real estate, net	15,878,097,000		15,868,363,000
Cash and cash equivalents	219,628,000	306,072,000	383,921,000	431,408,000
Deposits - restricted	182,182,000		152,237,000
Escrow deposits - mortgage	11,428,000		10,692,000
Deferred financing costs, net	45,861,000		44,608,000
Other assets	129,248,000		187,155,000
Total assets	16,481,247,000		16,659,303,000
LIABILITIES AND EQUITY
Total Debt	4,056,976,000		4,111,487,000
Accounts payable and accrued expenses	77,055,000		35,206,000
Accrued interest payable	79,489,000		88,121,000
Other liabilities	261,448,000		291,289,000
Security deposits	65,468,000		65,286,000
Total liabilities	10,005,069,000		10,380,042,000
Noncontrolling Interests - Partially Owned Properties	73,915,000		74,306,000
Total liabilities and equity	16,481,247,000		16,659,303,000
Partially Owned Property Income Statement Schedule
Operating revenue	527,659,000	466,356,000
Depreciation	174,737,000	158,455,000
General and administrative/other	13,688,000	11,433,000
Operating income	146,152,000	115,953,000
Interest and Other Income	172,000	1,011,000
Interest:
Expense incurred, net	(118,703,000)	(120,528,000)
Amortization of Financing Costs	(2,974,000)	(3,005,000)
Income (loss) before income and other taxes and discontinued operations	17,580,000	(8,729,000)
Income and other tax (expense) benefit	(191,000)	(184,000)
Net income	152,167,000	133,066,000
Investments In Partially Owned Entities (Textuals) [Abstract]
Joint Venture Partner Ownership Percentage	80.00%
Number of Joint Ventures	2
Partners Payments To Acquire Equity Method Investments	40,100,000
Equity Method Investment, Ownership Percentage	20.00%
Project Cost	232,800,000
Number of joint venture loans	2
Equity Method Investment Remaining Funding Obligation	3,000,000
Land purchase price	76,100,000
Business Acquisition, Cost of Acquired Entity, Purchase Price	182,840,000
Investment in Joint Venture	186,300,000
Variable Interest Entity Joint Venture Partner Ownership Percentage	50.00%
Consolidated Development Projects Held for and or Under Development [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	0
Partially Owned Consolidated Units	0
ASSETS
Investment in real estate	162,547,000
Accumulated depreciation	0
Investment in real estate, net	162,547,000
Cash and cash equivalents	2,448,000
Deposits - restricted	43,586,000
Escrow deposits - mortgage	0
Deferred financing costs, net	0
Other assets	5,766,000
Total assets	214,347,000
LIABILITIES AND EQUITY
Total Debt	0
Accounts payable and accrued expenses	7,000
Accrued interest payable	0
Other liabilities	1,272,000
Security deposits	0
Total liabilities	1,279,000
Noncontrolling Interests - Partially Owned Properties	79,011,000
EQR equity	134,057,000
Total equity	213,068,000
Total liabilities and equity	214,347,000
Debt-Secured:
Debt Ownership	0
Noncontrolling Ownership	0
Partially Owned Property Income Statement Schedule
Operating revenue	0
Real Estate Operating Expenses	(18,000)
Net operating (loss) income	18,000
Depreciation	0
General and administrative/other	4,000
Operating income	14,000
Interest and Other Income	1,000
Other Nonoperating Income (Expense)	(61,000)
Interest:
Expense incurred, net	0
Amortization of Financing Costs	0
Income (loss) before income and other taxes and discontinued operations	(46,000)
Income and other tax (expense) benefit	(26,000)
Net income	(72,000)
Consolidated Development Projects Completed and Stabalized [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	2
Partially Owned Consolidated Units	441
ASSETS
Investment in real estate	114,595,000
Accumulated depreciation	(13,269,000)
Investment in real estate, net	101,326,000
Cash and cash equivalents	1,243,000
Deposits - restricted	2,295,000
Escrow deposits - mortgage	70,000
Deferred financing costs, net	37,000
Other assets	115,000
Total assets	105,086,000
LIABILITIES AND EQUITY
Total Debt	33,175,000
Accounts payable and accrued expenses	431,000
Accrued interest payable	104,000
Other liabilities	51,000
Security deposits	111,000
Total liabilities	33,872,000
Noncontrolling Interests - Partially Owned Properties	1,079,000
EQR equity	70,135,000
Total equity	71,214,000
Total liabilities and equity	105,086,000
Debt-Secured:
Debt Ownership	33,175,000
Noncontrolling Ownership	0
Partially Owned Property Income Statement Schedule
Operating revenue	2,349,000
Real Estate Operating Expenses	375,000
Net operating (loss) income	1,974,000
Depreciation	1,042,000
General and administrative/other	2,000
Operating income	930,000
Interest and Other Income	1,000
Other Nonoperating Income (Expense)	0
Interest:
Expense incurred, net	(337,000)
Amortization of Financing Costs	(107,000)
Income (loss) before income and other taxes and discontinued operations	487,000
Income and other tax (expense) benefit	0
Net income	487,000
Consolidated Other [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties	19
Partially Owned Consolidated Units	3,475
ASSETS
Investment in real estate	450,120,000
Accumulated depreciation	(148,177,000)
Investment in real estate, net	301,943,000
Cash and cash equivalents	11,515,000
Deposits - restricted	5,000
Escrow deposits - mortgage	0
Deferred financing costs, net	1,125,000
Other assets	147,000
Total assets	314,735,000
LIABILITIES AND EQUITY
Total Debt	200,337,000
Accounts payable and accrued expenses	1,925,000
Accrued interest payable	782,000
Other liabilities	889,000
Security deposits	1,483,000
Total liabilities	205,416,000
Noncontrolling Interests - Partially Owned Properties	(6,175,000)
EQR equity	115,494,000
Total equity	109,319,000
Total liabilities and equity	314,735,000
Debt-Secured:
Debt Ownership	159,068,000
Noncontrolling Ownership	41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue	15,045,000
Real Estate Operating Expenses	4,871,000
Net operating (loss) income	10,174,000
Depreciation	3,872,000
General and administrative/other	13,000
Operating income	6,289,000
Interest and Other Income	0
Other Nonoperating Income (Expense)	0
Interest:
Expense incurred, net	(2,346,000)
Amortization of Financing Costs	(54,000)
Income (loss) before income and other taxes and discontinued operations	3,889,000
Income and other tax (expense) benefit	(21,000)
Net income	3,868,000
Partially Owned Properties [Member]
ASSETS
Investment in real estate	727,262,000
Accumulated depreciation	(161,446,000)
Investment in real estate, net	565,816,000
Cash and cash equivalents	15,206,000
Deposits - restricted	45,886,000
Escrow deposits - mortgage	70,000
Deferred financing costs, net	1,162,000
Other assets	6,028,000
Total assets	634,168,000
LIABILITIES AND EQUITY
Total Debt	233,512,000
Accounts payable and accrued expenses	2,363,000
Accrued interest payable	886,000
Other liabilities	2,212,000
Security deposits	1,594,000
Total liabilities	240,567,000
Noncontrolling Interests - Partially Owned Properties	73,915,000
EQR equity	319,686,000
Total equity	393,601,000
Total liabilities and equity	634,168,000
Debt-Secured:
Debt Ownership	192,243,000
Noncontrolling Ownership	41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue	17,394,000
Real Estate Operating Expenses	5,228,000
Net operating (loss) income	12,166,000
Depreciation	4,914,000
General and administrative/other	19,000
Operating income	7,233,000
Interest and Other Income	2,000
Other Nonoperating Income (Expense)	(61,000)
Interest:
Expense incurred, net	(2,683,000)
Amortization of Financing Costs	(161,000)
Income (loss) before income and other taxes and discontinued operations	4,330,000
Income and other tax (expense) benefit	(47,000)
Net income	4,283,000
Joint Venture Partner [Member]
LIABILITIES AND EQUITY
Noncontrolling Interests - Partially Owned Properties	76,705,068
Investments In Partially Owned Entities (Textuals) [Abstract]
Land purchase price	57,900,000
Business Acquisition, Cost of Acquired Entity, Purchase Price	75,700,000
Company's Portion [Member]
Investments In Partially Owned Entities (Textuals) [Abstract]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 102,500,000