Investments in Partially Owned Entities (Details) (USD $)	3 Months Ended							12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Aug. 23, 2006
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties								19
Partially Owned Consolidated Units								3,475
ASSETS
Investment in real estate				$ 20,407,946,000				$ 21,008,429,000	$ 20,407,946,000
Accumulated depreciation				(4,539,583,000)				(4,912,221,000)	(4,539,583,000)
Investment in real estate, net				15,868,363,000				16,096,208,000	15,868,363,000
Cash and cash equivalents				383,921,000				612,590,000	383,921,000	431,408,000	193,288,000
Deposits - restricted				152,237,000				250,442,000	152,237,000
Deferred financing costs, net				44,608,000				44,382,000	44,608,000
Other assets				187,155,000				170,372,000	187,155,000
Total assets				16,659,303,000				17,201,000,000	16,659,303,000
LIABILITIES AND EQUITY
Mortgage notes payable				4,111,487,000				3,898,369,000	4,111,487,000
Accounts payable and accrued expenses				35,206,000				38,372,000	35,206,000
Accrued interest payable				88,121,000				76,223,000	88,121,000
Other liabilities				291,289,000				304,518,000	291,289,000
Security deposits				65,286,000				66,988,000	65,286,000
Total liabilities				10,380,042,000				9,275,521,000	10,380,042,000
Noncontrolling Interests - Partially Owned Properties				74,306,000				77,688,000	74,306,000
Total liabilities and equity				16,659,303,000				17,201,000,000	16,659,303,000
Partially Owned Property Income Statement Schedule
Operating revenue								2,123,715,000	1,883,491,000	1,674,709,000
Depreciation								664,082,000	612,579,000	581,469,000
General and Administrative Expense								47,248,000	43,605,000	39,881,000
Operating income	179,867,000	158,988,000	140,889,000	154,722,000	142,781,000	134,130,000	110,042,000	667,958,000	541,675,000	348,210,000
Interest and Other Income								150,547,000	7,965,000	5,118,000
Interest:
Expense incurred, net								457,666,000	464,277,000	460,748,000
Amortization of Financing Costs								21,370,000	16,766,000	9,576,000
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations								312,108,000	54,305,000	(128,788,000)
Income and other tax (expense) benefit								(539,000)	(728,000)	(291,000)
Net gain on sales of discontinued operations								548,278,000	826,489,000	297,956,000
Net income								881,204,000	935,197,000	295,983,000
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
Business Acquisition, Cost of Acquired Entity, Purchase Price				1,597,111,000				1,047,545,000	1,597,111,000
Investment in Joint Venture								203,500,000
Debt Instrument, Interest Rate, Stated Percentage												3.85%
Disposed Properties								35	47
Disposed Units								9,012	14,345
Variable Interest Entity Joint Venture Partner Ownership Percentage								5,000,000
Nexus Sawgrass [Member]
Investments In Partially Owned Entities (Textuals) [Abstract]
Maximum Debt Commitment								48,700,000
Long-term Debt								29,800,000
Debt Instrument, Interest Rate, Stated Percentage								5.60%
Domain [Member]
Investments In Partially Owned Entities (Textuals) [Abstract]
Maximum Debt Commitment								98,600,000
Long-term Debt								46,900,000
Debt Instrument, Interest Rate, Stated Percentage								5.75%
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								161,820,000
Accumulated depreciation								0
Investment in real estate, net								161,820,000
Cash and cash equivalents								3,884,000
Deposits - restricted								43,609,000
Deferred financing costs, net								0
Other assets								5,839,000
Total assets								215,152,000
LIABILITIES AND EQUITY
Mortgage notes payable								0
Accounts payable and accrued expenses								686,000
Accrued interest payable								0
Other liabilities								1,238,000
Security deposits								0
Total liabilities								1,924,000
Noncontrolling Interests - Partially Owned Properties								85,006,000
EQR equity								128,222,000
Total equity								213,228,000
Total liabilities and equity								215,152,000
Debt-Secured:
Debt Ownership								0
Noncontrolling Ownership								0
Partially Owned Property Income Statement Schedule
Operating revenue								0
Real Estate Operating Expenses								170,000
Net operating (loss) income								(170,000)
Depreciation								0
General and Administrative Expense								213,000
Operating income								(383,000)
Interest and Other Income								2,000
Other Nonoperating Income (Expense)								(264,000)
Interest:
Expense incurred, net								0
Amortization of Financing Costs								0
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations								(645,000)
Income and other tax (expense) benefit								(25,000)
Net gain on sales of discontinued operations								15,000
Net income								(655,000)
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								453,235,000
Accumulated depreciation								(159,651,000)
Investment in real estate, net								293,584,000
Cash and cash equivalents								17,221,000
Deposits - restricted								5,000
Deferred financing costs, net								1,019,000
Other assets								171,000
Total assets								312,000,000
LIABILITIES AND EQUITY
Mortgage notes payable								200,337,000
Accounts payable and accrued expenses								693,000
Accrued interest payable								782,000
Other liabilities								1,096,000
Security deposits								1,483,000
Total liabilities								204,391,000
Noncontrolling Interests - Partially Owned Properties								(7,318,000)
EQR equity								114,927,000
Total equity								107,609,000
Total liabilities and equity								312,000,000
Debt-Secured:
Debt Ownership								159,068,000
Noncontrolling Ownership								41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue								62,405,000
Real Estate Operating Expenses								19,480,000
Net operating (loss) income								42,925,000
Depreciation								15,346,000
General and Administrative Expense								157,000
Operating income								27,422,000
Interest and Other Income								100,000
Other Nonoperating Income (Expense)								0
Interest:
Expense incurred, net								(9,386,000)
Amortization of Financing Costs								(160,000)
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations								17,976,000
Income and other tax (expense) benefit								(75,000)
Net gain on sales of discontinued operations								0
Net income								17,901,000
Partially Owned Properties [Member]
ASSETS
Investment in real estate								615,055,000
Accumulated depreciation								(159,651,000)
Investment in real estate, net								455,404,000
Cash and cash equivalents								21,105,000
Deposits - restricted								43,614,000
Deferred financing costs, net								1,019,000
Other assets								6,010,000
Total assets								527,152,000
LIABILITIES AND EQUITY
Mortgage notes payable								200,337,000
Accounts payable and accrued expenses								1,379,000
Accrued interest payable								782,000
Other liabilities								2,334,000
Security deposits								1,483,000
Total liabilities								206,315,000
Noncontrolling Interests - Partially Owned Properties								77,688,000
EQR equity								243,149,000
Total equity								320,837,000
Total liabilities and equity								527,152,000
Debt-Secured:
Debt Ownership								159,068,000
Noncontrolling Ownership								41,269,000
Partially Owned Property Income Statement Schedule
Operating revenue								62,405,000
Real Estate Operating Expenses								19,650,000
Net operating (loss) income								42,755,000
Depreciation								15,346,000
General and Administrative Expense								370,000
Operating income								27,039,000
Interest and Other Income								102,000
Other Nonoperating Income (Expense)								(264,000)
Interest:
Expense incurred, net								(9,386,000)
Amortization of Financing Costs								(160,000)
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations								17,331,000
Income and other tax (expense) benefit								(100,000)
Net gain on sales of discontinued operations								15,000
Net income								17,246,000
Investments In Partially Owned Entities (Textuals) [Abstract]
Disposed Properties								2
Disposed Units								441
Joint Venture Company Portion [Member]
Interest:
Net gain on sales of discontinued operations								(21,300,000)
Unconsolidated Properties [Member]
Partially Owned Property Balance Sheet Schedule
Partially Owned Consolidated Properties								0
Partially Owned Consolidated Units								0
ASSETS
Investment in real estate								171,041,000
Accumulated depreciation								0
Investment in real estate, net								171,041,000
Cash and cash equivalents								214,000
Deposits - restricted								0
Deferred financing costs, net								6,000
Other assets								22,000
Total assets								171,283,000
LIABILITIES AND EQUITY
Mortgage notes payable								76,634,000
Accounts payable and accrued expenses								6,550,000
Accrued interest payable								342,000
Other liabilities								108,000
Security deposits								3,000
Total liabilities								83,637,000
Noncontrolling Interests - Partially Owned Properties								70,428,000
EQR equity								17,218,000
Total equity								87,646,000
Total liabilities and equity								171,283,000
Debt-Secured:
Debt Ownership								15,327,000
Noncontrolling Ownership								61,307,000
Partially Owned Property Income Statement Schedule
Operating revenue								7,000
Real Estate Operating Expenses								244,000
Net operating (loss) income								(237,000)
Depreciation								0
General and Administrative Expense								0
Operating income								(237,000)
Interest and Other Income								0
Other Nonoperating Income (Expense)								0
Interest:
Expense incurred, net								0
Amortization of Financing Costs								0
Income (loss) before income and other taxes, (loss) from investments in unconsolidated entities, net gain (loss) on sales of unconsolidated entities and land parcels and discontinued operations								(237,000)
Income and other tax (expense) benefit								0
Net gain on sales of discontinued operations								0
Net income								(237,000)
Joint Venture Partner [Member]
LIABILITIES AND EQUITY
Noncontrolling Interests - Partially Owned Properties								84,000,000
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
Company's Portion [Member]
Investments In Partially Owned Entities (Textuals) [Abstract]
Land purchase price				76,100,000					76,100,000
Business Acquisition, Cost of Acquired Entity, Purchase Price				$ 102,500,000					$ 102,500,000