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Investments in Partially Owned Entities - Summary of Companys Investment in Unconsolidated Entities (Parenthetical) (Details) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 ApartmentUnit JointVenture | Sep. 30, 2019 ApartmentUnit
Variable Interest Entity [Line Items] |  |
Apartment units |  | 80,299
Operating Property [Member] | Unconsolidated Non-VIE [Member] |  |
Variable Interest Entity [Line Items] |  |
Apartment units | 945 |
Number of joint ventures under agreements | JointVenture | 2 |

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- Definition Number of joint ventures. + References No definition available. + Details
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Namespace Prefix: | eqr_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of units in a real estate property owned as of the balance sheet date. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_MajorityOwnedSubsidiaryUnconsolidatedMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |