Business - Additional Information (Details)	Dec. 31, 2017 State Property ApartmentUnit
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of states in which entity operates \| State	10
Properties	305
Apartment units \| ApartmentUnit	78,611
Number of operating properties under long-term ground leases	14
ERPOP [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Noncontrolling interest, ownership percentage by parent	96.40%

Number of operating properties for which the Company owns the building and improvements and leases the underlying land under long-term ground leases.

No definition available.

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

Organization consolidation and presentation of financial statements disclosure.

No definition available.

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

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

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

The number of real estate properties owned as of the balance sheet date.

No definition available.

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

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

No definition available.

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

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
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: