Debt - Mortgage Notes Payable - Summary of Mortgage Notes Payable Activity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Mortgage notes payable, net beginning balance	$ 1,941,610	$ 2,385,470
Proceeds	519,204	295,771	$ 96,935
Lump sum payoffs	(160,522)	(743,021)	(1,347,939)
Scheduled principal repayments	(7,759)	(6,808)
Amortization of premiums/ discounts	2,234	8,618	20,144
Amortization of deferred financing costs, net	(877)	1,580
Mortgage notes payable, net ending balance	2,293,890	1,941,610	2,385,470
Fixed Rate Debt [Member] \| Secured – Conventional [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net beginning balance	1,574,699	1,885,407
Proceeds	495,000	288,120
Lump sum payoffs	(160,522)	(584,536)
Scheduled principal repayments	(7,759)	(6,308)
Amortization of premiums/ discounts	988	(7,999)
Amortization of deferred financing costs, net	(1,315)	15
Mortgage notes payable, net ending balance	1,901,091	1,574,699	1,885,407
Floating Rate Debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net beginning balance	366,911	500,063
Proceeds	24,204	7,651
Lump sum payoffs		(158,485)
Scheduled principal repayments		(500)
Amortization of premiums/ discounts	1,246	16,617
Amortization of deferred financing costs, net	438	1,565
Mortgage notes payable, net ending balance	392,799	366,911	500,063
Floating Rate Debt [Member] \| Secured – Conventional [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net beginning balance	7,050	6,357
Proceeds	24,204	7,651
Lump sum payoffs		(5,920)
Scheduled principal repayments		(500)
Amortization of deferred financing costs, net	240	(538)
Mortgage notes payable, net ending balance	31,494	7,050	6,357
Floating Rate Debt [Member] \| Secured – Tax Exempt [Member]
Debt Instrument [Line Items]
Mortgage notes payable, net beginning balance	359,861	493,706
Lump sum payoffs		(152,565)
Amortization of premiums/ discounts	1,246	16,617
Amortization of deferred financing costs, net	198	2,103
Mortgage notes payable, net ending balance	$ 361,305	$ 359,861	$ 493,706

Amount of amortization of other deferred financing costs net associated with mortgage notes payable, net.

No definition available.

Name:	eqr_AmortizationOfDeferredFinancingCostsNetMortgageNotesPayableNet
Namespace Prefix:	eqr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The component of interest expense representing the noncash expenses charged against earnings in the period to amortize debt discount and premium associated with the mortgage notes payable during the period.

+ References

No definition available.

+ Details

Name:	eqr_AmortizationOfDiscountsAndPremiumsOnDebtMortgageNotesPayable
Namespace Prefix:	eqr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow from the lump sum payment of collateralized debt obligations (backed by pledge, mortgage or other lien in the entity's assets).

+ References

No definition available.

+ Details

Name:	eqr_MortgageNotesPayableLumpSumPayOffs
Namespace Prefix:	eqr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from borrowings supported by a written promise to pay an obligation that is collateralized (backed by pledge, mortgage or other lien in the entity's assets).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_SecuredDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=eqr_FixedRateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=eqr_SecuredConventionalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=eqr_FloatingRateDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=eqr_SecuredTaxExemptMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: