Business - Additional Information (Details)	Sep. 30, 2017 State Property ApartmentUnit
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of States in which Entity Operates \| State	10
Properties \| Property	305
Apartment Units \| ApartmentUnit	78,302
ERPOP [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	96.40%

Organization consolidation and presentation of financial statements disclosure.

No definition available.

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

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
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The number of real estate properties owned as of the balance sheet date.

No definition available.

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

No definition available.

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

No definition available.

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

Name:	dei_LegalEntityAxis=eqr_ERPOPMember
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