Derivative and Other Fair Value Instruments (Details 2) (USD $) In Thousands	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Amount of Gain/(Loss) Recognized in Income on Derivative	$ (1,940)	$ 9,842
Amount of Gain/ (Loss) Recognized in Income on Hedged Item	1,940	(9,842)
Interest Rate Swap [Member]
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Hedged Item	Fixed rate debt	Fixed rate debt
Interest Rate Swap [Member] \| Interest Expense [Member]
Schedule of Location of Fair Value/Cash flow Hedges on Statement of Operations
Amount of Gain/(Loss) Recognized in Income on Derivative	(1,940)	9,842
Amount of Gain/ (Loss) Recognized in Income on Hedged Item	$ 1,940	$ (9,842)

Derivative instruments gain loss in statement of financial performances.

Name:	eqr_DerivativeInstrumentsGainLossInStatementOfFinancialPerformancesAbstract
Namespace Prefix:	eqr
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the hedged item related to the derivative. Includes the type of instrument hedged, contract amount, term, and so forth.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579240-113959

+ Details

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

- Definition

Amount of unrealized gain (loss) included in earnings for the period related to the fair value of the hedged item in an interest rate fair value hedge, which was offset by the gain (loss) on the hedging instrument to the extent that the fair value hedge is determined to be effective.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph a(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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5618551-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959

+ Details

Name:	us-gaap_IncreaseDecreaseInFairValueOfHedgedItemInInterestRateFairValueHedge
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of unrealized gain (loss) related to the fair value of interest rate derivatives designated as fair value hedging instruments. Recognized in earnings and offsets the gain (loss) on the hedged item to the extent that the fair value hedge is determined to be effective.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5618551-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624171-113959

+ Details

Name:	us-gaap_IncreaseDecreaseInFairValueOfInterestRateFairValueHedgingInstruments
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration