Business (Details)	Sep. 30, 2011 Apartment State Property MilitaryHouse
Property/Unit schedule
Wholly Owned Properties	394
Wholly Owned Apartment Units	110,194
Partially Owned Consolidated Properties	21
Partially Owned Consolidated Apartment Units	3,916
Military Housing Properties	2
Military Housing Apartment Units	4,901
Total Properties	417
Total Apartment Units	119,011
Business (Textuals) [Abstract]
EQR's Ownership percentage in ERPOP	95.60%
Properties owned	417
States in which properties owned are located	15
Units owned	119,011

Business.

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Total number of rental properties that represent military housing but are not consolidated by the Company.

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Total number of units associated with rental properties that represent military housing but are not consolidated by the Company

Total number of rental properties that are partially owned and consolidated by the Company.

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Total number of units associated with rental properties that are partially owned and consolidated by the Company.

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Schedule of properties and units.

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Total number of rental properties that are wholly owned and consolidated by the Company.

Total number of units associated with rental properties that are wholly owned and consolidated by the Company.

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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The number of real estate properties owned as of the balance sheet date.

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The number of states the entity operates in as of the balance sheet date.

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The number of units in a real estate property owned as of the balance sheet date.

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