Commitments and Contingencies - Additional Information (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) Property ApartmentUnit Agreement	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commitments And Contingencies [Abstract]
Projects in various stages of development \| Property	2
Partially owned projects in various stages of development \| Property	1
Units in various stages of development \| ApartmentUnit	824
Consolidated project under development commitment fund \| $	$ 421.2
Various stages of development with estimated completion dates ranging through September 30, 2021	Sep. 30, 2021
Number of joint venture agreements \| Agreement	2
Compensation expense, recognized \| $	$ 0.4	$ 0.3	$ 0.4

Commitments and Contingencies.

No definition available.

Name:	eqr_CommitmentsAndContingenciesAbstract
Namespace Prefix:	eqr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the company's remaining funding obligation (i.e. total project costs less book value) for consolidated projects that are under development.

+ References

No definition available.

+ Details

Name:	eqr_ConsolidatedProjectUnderDevelopmentCommitmentFund
Namespace Prefix:	eqr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of joint venture agreements.

+ References

No definition available.

+ Details

Name:	eqr_NumberOfJointVentureAgreements
Namespace Prefix:	eqr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of partially owned projects in various stages of development.

+ References

No definition available.

+ Details

Name:	eqr_NumberOfPartiallyOwnedProjectsInVariousStagesOfDevelopment
Namespace Prefix:	eqr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of open development projects. May include projects that are held for and/or under development, completed and not stabilized or completed and stabilized. These projects are consolidated.

+ References

No definition available.

+ Details

Name:	eqr_NumberOfProjectsInVariousStagesOfDevelopment
Namespace Prefix:	eqr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Total number of units that are associated with open development projects. May include projects that are held for and/or under development, completed and not stabilized or completed and stabilized. These units are consolidated.

+ References

No definition available.

+ Details

Name:	eqr_NumberOfUnitsInVariousStagesOfDevelopment
Namespace Prefix:	eqr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the latest completion date for the current projects under development.

+ References

No definition available.

+ Details

Name:	eqr_VariousStagesOfDevelopmentDateMaturity
Namespace Prefix:	eqr_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 30
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration