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Business (Details)	Mar. 31, 2015
Noncontrolling Interest, Ownership Percentage by Parent	96.20%us-gaap_MinorityInterestOwnershipPercentageByParent
Number of Real Estate Properties	389us-gaap_NumberOfRealEstateProperties
Number of States in which Entity Operates	12us-gaap_NumberOfStatesInWhichEntityOperates
Number of Units in Real Estate Property	108,793us-gaap_NumberOfUnitsInRealEstateProperty
Consolidated Properties [Member]
Number of Real Estate Properties	362us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = us-gaap_ConsolidatedPropertiesMember
Number of Units in Real Estate Property	97,825us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_RealEstatePropertiesAxis = us-gaap_ConsolidatedPropertiesMember
Master-Leased Properties [Member]
Number of Real Estate Properties	3us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = eqr_MasterLeasedPropertiesMember
Number of Units in Real Estate Property	853us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_RealEstatePropertiesAxis = eqr_MasterLeasedPropertiesMember
Partially Owned Properties [Member]
Number of Real Estate Properties	19us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = us-gaap_PartiallyOwnedPropertiesMember
Number of Units in Real Estate Property	3,771us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_RealEstatePropertiesAxis = us-gaap_PartiallyOwnedPropertiesMember
Unconsolidated Properties [Member]
Number of Real Estate Properties	3us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = us-gaap_UnconsolidatedPropertiesMember
Number of Units in Real Estate Property	1,281us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_RealEstatePropertiesAxis = us-gaap_UnconsolidatedPropertiesMember
Military Housing [Member]
Number of Real Estate Properties	2us-gaap_NumberOfRealEstateProperties / us-gaap_RealEstatePropertiesAxis = eqr_MilitaryHousingMember
Number of Units in Real Estate Property	5,063us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_RealEstatePropertiesAxis = eqr_MilitaryHousingMember

X

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfUnitsInRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_RealEstatePropertiesAxis=eqr_MasterLeasedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RealEstatePropertiesAxis=eqr_MilitaryHousingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_ConsolidatedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_PartiallyOwnedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RealEstatePropertiesAxis=us-gaap_UnconsolidatedPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: