Debt - Mortgage Notes Payable - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Mortgage notes payable	$ 2,894,344	$ 3,618,722
Debt instrument, maturity date	Jan. 10, 2022
Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 1,700
Write off of deferred debt issuance cost	1,600
Write off unamortized (premium) discount	$ (200)
Debt instrument, maturity date	May 28, 2061
Weighted average interest rate	4.24%
Mortgages [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.10%
Mortgages [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.90%
Conventional Mortgage Loan [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 43,700
Debt instrument, maturity year	2018
Bonds [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 131,900
Debt instrument maturity year, start	2028
Debt instrument maturity year, end	2042
Credit enhanced debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 563,500
Fannie Mae Pool 3 [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 550,000
Debt instrument, interest rate, stated percentage	6.08%
Debt instrument, maturity year	2020
Prepayment penalty charges	$ 22,100

Debt instrument maturity year.

No definition available.

Name:	eqr_DebtInstrumentMaturityYear
Namespace Prefix:	eqr_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity year, end.

+ References

No definition available.

+ Details

Name:	eqr_DebtInstrumentMaturityYearEnd
Namespace Prefix:	eqr_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity year, start.

+ References

No definition available.

+ Details

Name:	eqr_DebtInstrumentMaturityYearStart
Namespace Prefix:	eqr_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents charges to interest expense related to the extinguishment of borrowing before maturity.

+ References

No definition available.

+ Details

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

- Definition

Amount of write off of unamortized discount premium net.

+ References

No definition available.

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- 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

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&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://www.xbrl.org/2003/role/presentationRef
-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=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=eqr_FannieMaePool3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: