Derivative and Other Fair Value Instruments (Details 1) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Derivatives designated as hedging instruments:
Total	$ 78,530	$ 75,123
Derivatives designated as hedging instruments:
Total	232,613	97,210
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1)
Derivatives designated as hedging instruments:
Total	67,949	59,326
Derivatives designated as hedging instruments:
Total	66,444	58,132
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1) \| Fair Value Hedges [Member] \| Other Assets [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value	0
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1) \| Forward Starting Swaps [Member] \| Other Liabilities [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value	0
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1) \| Other Assets [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	66,444	58,132
Available for sale investment securities	1,505	1,194
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1) \| Other Liabilities [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	66,444	58,132
Quoted Priced in Active Markets for Identical Assets/ Liabilities (Level 1) \| Mezzanine [Member]
Derivatives designated as hedging instruments:
Redeemable Noncontrolling interests - operating partnership/redeemable limited partners	0
Significant Other Observable Inputs (Level 2)
Derivatives designated as hedging instruments:
Total	10,581	15,797
Derivatives designated as hedging instruments:
Total	166,169	39,078
Significant Other Observable Inputs (Level 2) \| Fair Value Hedges [Member] \| Other Assets [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value	10,581	12,521
Significant Other Observable Inputs (Level 2) \| Forward Starting Swaps [Member] \| Other Assets [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value		3,276
Significant Other Observable Inputs (Level 2) \| Forward Starting Swaps [Member] \| Other Liabilities [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value	166,169	37,756
Significant Other Observable Inputs (Level 2) \| Development Cash Flow Hedges [Member] \| Other Liabilities [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value		1,322
Significant Other Observable Inputs (Level 2) \| Other Assets [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	0
Available for sale investment securities	0
Significant Other Observable Inputs (Level 2) \| Other Liabilities [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	0
Significant Other Observable Inputs (Level 2) \| Mezzanine [Member]
Derivatives designated as hedging instruments:
Redeemable Noncontrolling interests - operating partnership/redeemable limited partners	378,798	383,540
Significant Unobservable Inputs (Level 3)
Derivatives designated as hedging instruments:
Total	0
Derivatives designated as hedging instruments:
Total	0
Significant Unobservable Inputs (Level 3) \| Other Assets [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value	0
Supplemental Executive Retirement Plan	0
Available for sale investment securities	0
Significant Unobservable Inputs (Level 3) \| Other Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value	0
Supplemental Executive Retirement Plan	0
Significant Unobservable Inputs (Level 3) \| Mezzanine [Member]
Derivatives designated as hedging instruments:
Redeemable Noncontrolling interests - operating partnership/redeemable limited partners	0
Fair Value Hedges [Member] \| Other Assets [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value	10,581	12,521
Forward Starting Swaps [Member] \| Other Assets [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative asset, fair value		3,276
Forward Starting Swaps [Member] \| Other Liabilities [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value	166,169	37,756
Development Cash Flow Hedges [Member] \| Other Liabilities [Member] \| Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative liability, fair value		1,322
Other Assets [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	66,444	58,132
Available for sale investment securities	1,505	1,194
Other Liabilities [Member]
Derivatives designated as hedging instruments:
Supplemental Executive Retirement Plan	66,444	58,132
Mezzanine [Member]
Derivatives designated as hedging instruments:
Redeemable Noncontrolling interests - operating partnership/redeemable limited partners	$ 378,798	$ 383,540

Fair value as of the balance sheet date of non-controlling interests which are redeemable by the parent at a fixed or determinable price on a fixed or determinable date, at the option of the holder of the non-controlling interest, or upon occurrence of an event that is not solely within the control of the parent.

Name:	eqr_RedeemableNoncontrollingInterestOperatingPartnershipLiabilityFairValueDisclosure
Namespace Prefix:	eqr
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

+ References

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

+ Details

Name:	us-gaap_OtherAssetsFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ Details

Name:	us-gaap_OtherLiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant