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Commitments and Contingencies - Additional Information (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2019 USD ($) Property ApartmentUnit
Accrual for environmental loss contingencies | $ | $ 4.3
Number of properties with environmental reserves | 3
Projects in various stages of development | 3
Units in various stages of development | ApartmentUnit | 691
Consolidated project under development commitment fund | $ | $ 388.4
Various stages of development with estimated completion dates ranging through September 30, 2021 | Sep. 30, 2021
Partially Owned Properties - Unconsolidated |
Number of unconsolidated projects | 2

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- 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
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Namespace Prefix: | eqr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- 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

X
- Definition Number of properties with environmental reserves. + References No definition available. + Details
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Namespace Prefix: | eqr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total number of unconsolidated open development projects. May include projects that are held for and/or under development, completed and not stabilized or completed and stabilized. + References No definition available. + Details
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Namespace Prefix: | eqr_
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Balance Type: | na
Period Type: | instant

X
- 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
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Namespace Prefix: | eqr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the latest completion date for the current projects under development. + References No definition available. + Details
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Namespace Prefix: | eqr_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 + Details
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Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |