Debt - Mortgage Notes Payable - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Mortgage notes payable	$ 2,385,470	$ 3,618,722
Debt instrument, maturity date	Jan. 10, 2022
Weighted average interest rate	4.25%	4.35%
Historical cost, net of accumulated depreciation, of encumbered properties	$ 3,200,000	$ 4,400,000
ERPOP [Member]
Debt Instrument [Line Items]
Mortgage notes payable	2,385,470	3,618,722
Mortgages [Member]
Debt Instrument [Line Items]
Mortgage notes payable	$ 6,600
Repayments of long-term debt		$ 10,700
Debt instrument, maturity date	May 28, 2061	May 28, 2061
Write off of deferred debt issuance cost	$ 3,000	$ 300
Write off unamortized (premium) discount	$ 16,300	$ (700)
Weighted average interest rate	4.15%	4.33%
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%	6.90%
Conventional Mortgage Loan [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 43,700	$ 193,400
Debt instrument, maturity year	2018
Prepayment penalty charges		$ 1,500
Debt instrument maturity year, start		2017
Debt instrument maturity year, end		2048
Bonds [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 254,200
Debt instrument maturity year, start	2028
Debt instrument maturity year, end	2042
New Floating Rate Tax Exempt Mortgage Bond [Member] \| ERPOP [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Apr. 01, 2042
Proceeds from issuance of long-term debt	$ 96,900
Credit enhanced debt [Member]
Debt Instrument [Line Items]
Mortgage notes payable	440,700	$ 598,600
Fannie Mae Pool 3 [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 550,000	$ 300,000
Debt instrument, interest rate, stated percentage	6.08%	5.987%
Debt instrument, maturity year	2020	2019
Prepayment penalty charges	$ 22,100	$ 10,800
Freddie Mac Loan Pool [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Repayments of long-term debt	$ 500,000
Debt instrument, interest rate, stated percentage	5.19%
Debt instrument, maturity date	Oct. 01, 2019

Debt instrument maturity year.

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity year, end.

+ References

No definition available.

+ Details

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Namespace Prefix:	eqr_
Data Type:	xbrli:gYearItemType
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

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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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Balance Type:	debit
Period Type:	duration

- Definition

Amount of write off of unamortized discount premium net.

+ References

No definition available.

+ Details

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- Definition

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

+ References

Reference 1: 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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- 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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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the 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 14
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

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Balance Type:	debit
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- 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
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- 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
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+ Details

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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

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