Business - Additional Information (Details)	Jun. 30, 2021 State Property ApartmentUnit
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of states in which entity operates \| State	9
Properties \| Property	303
Apartment units \| ApartmentUnit	78,107
ERPOP [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Noncontrolling interest, ownership percentage by parent	96.70%

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.

Name:	us-gaap_NumberOfRealEstateProperties
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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:	srt_OwnershipAxis=eqr_ERPOPMember
Namespace Prefix:
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Period Type: