Debt - Mortgage Notes Payable - Additional Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) Property	Dec. 31, 2016 USD ($) Property
Debt Instrument [Line Items]
Mortgage notes payable	$ 3,618,722	$ 4,119,181
Debt instrument, maturity date	Jan. 10, 2022
Historical cost, net of accumulated depreciation, of encumbered properties	$ 4,400,000	5,000,000
Noncash or part noncash acquisition, debt assumed		$ 43,400
Properties acquired \| Property	4	4
Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 10,700	$ 8,500
Write off of deferred debt issuance cost	300	1,600
Write off unamortized (premium) discount	$ 700	$ 20,700
Debt instrument, maturity date	May 28, 2061	May 28, 2061
Weighted average interest rate	4.33%	4.34%
Properties acquired \| Property		1
Mortgages [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	0.10%	0.10%
Mortgages [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	6.90%	7.20%
Conventional Mortgage Loan [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 193,400	$ 75,900
Prepayment penalty charges	$ 1,500	2,200
Debt instrument maturity year, start	2017
Debt instrument maturity year, end	2048
Credit enhanced debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 598,600	601,900
Bonds [Member]
Debt Instrument [Line Items]
Repayments of long-term debt		65,500
Prepayment penalty charges		$ 200
Debt instrument maturity year, start		2026
Debt instrument maturity year, end		2037
Mortgage Loan - Floating Rate [Member]
Debt Instrument [Line Items]
Repayments of long-term debt		$ 900
Fannie Mae Pool 3 [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 300,000	$ 440,800
Debt instrument, interest rate, stated percentage	5.987%	6.256%
Debt instrument, maturity year	2019	2017
Prepayment penalty charges	$ 10,800	$ 29,300

Debt instrument maturity year.

No definition available.

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

- Definition

Debt instrument maturity year, end.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Debt instrument maturity year, start.

+ References

No definition available.

+ Details

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- Definition

Represents a total which may include the following: land available-for-development, investments in building and building improvements, developments-in-process, and furniture and fixtures for properties that are encumbered by mortgages.

+ References

No definition available.

+ Details

Name:	eqr_HistoricalCostOfEncumberedProperties
Namespace Prefix:	eqr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total number of property or properties acquired from unaffiliated third parties during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of write off of unamortized discount premium net.

+ References

No definition available.

+ Details

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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

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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

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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

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Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

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Balance Type:	credit
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

+ Details

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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

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+ Details

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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

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- Details

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- Details

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- Details

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- Details

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