Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2012
Summary of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X promulgated under the Securities Act of 1933, as amended. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) and certain reclassifications considered necessary for a fair presentation have been included. Certain reclassifications have been made to the prior period financial statements in order to conform to the current year presentation. Operating results for the nine months ended September 30, 2012 are not necessarily indicative of the results that may be expected for the year ending December 31, 2012. In preparation of the Company’s financial statements in conformity with accounting principles generally accepted in the United States, management makes estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates. The balance sheets at December 31, 2011 have been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. For further information, including definitions of capitalized terms not defined herein, refer to the consolidated financial statements and footnotes thereto included in the Company’s and the Operating Partnership's annual report on Form 10-K for the year ended December 31, 2011. Income and Other Taxes Due to the structure of EQR as a REIT and the nature of the operations of its operating properties, no provision for federal income taxes has been made at the EQR level. In addition, ERPOP generally is not liable for federal income taxes as the partners recognize their proportionate share of income or loss in their tax returns; therefore no provision for federal income taxes has been made at the ERPOP level. Historically, the Company has generally only incurred certain state and local income, excise and franchise taxes. The Company has elected Taxable REIT Subsidiary (“TRS”) status for certain of its corporate subsidiaries and as a result, these entities will incur both federal and state income taxes on any taxable income of such entities after consideration of any net operating losses. Deferred tax assets and liabilities applicable to the TRS are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. These assets and liabilities are measured using enacted tax rates for which the temporary differences are expected to be recovered or settled. The effects of changes in tax rates on deferred tax assets and liabilities are recognized in earnings in the period enacted. The Company’s deferred tax assets are generally the result of differing depreciable lives on capitalized assets and the timing of expense recognition for certain accrued liabilities. As of September 30, 2012, the Company has recorded a deferred tax asset of approximately $31.7 million, which is fully offset by a valuation allowance due to the uncertainty in forecasting future TRS taxable income. Other The Company is the controlling partner in various consolidated partnerships owning 19 properties and 3,475 apartment units and various completed and uncompleted development properties having a noncontrolling interest book value of $75.4 million at September 30, 2012. The Company is required to make certain disclosures regarding noncontrolling interests in consolidated limited-life subsidiaries. Of the consolidated entities described above, the Company is the controlling partner in limited-life partnerships owning six properties having a noncontrolling interest deficit balance of $6.0 million. These six partnership agreements contain provisions that require the partnerships to be liquidated through the sale of their assets upon reaching a date specified in each respective partnership agreement. The Company, as controlling partner, has an obligation to cause the property owning partnerships to distribute the proceeds of liquidation to the Noncontrolling Interests in these Partially Owned Properties only to the extent that the net proceeds received by the partnerships from the sale of their assets warrant a distribution based on the partnership agreements. As of September 30, 2012, the Company estimates the value of Noncontrolling Interest distributions for these six properties would have been approximately $33.3 million (“Settlement Value”) had the partnerships been liquidated. This Settlement Value is based on estimated third party consideration realized by the partnerships upon disposition of the six Partially Owned Properties and is net of all other assets and liabilities, including yield maintenance on the mortgages encumbering the properties, that would have been due on September 30, 2012 had those mortgages been prepaid. Due to, among other things, the inherent uncertainty in the sale of real estate assets, the amount of any potential distribution to the Noncontrolling Interests in the Company’s Partially Owned Properties is subject to change. To the extent that the partnerships’ underlying assets are worth less than the underlying liabilities, the Company has no obligation to remit any consideration to the Noncontrolling Interests in these Partially Owned Properties. Effective January 1, 2011, companies are required to separately disclose purchases, sales, issuances and settlements on a gross basis in the reconciliation of recurring Level 3 fair value measurements. This does not have a material effect on the Company’s consolidated results of operations or financial position. See Note 9 for further discussion. Effective January 1, 2012, companies are required to separately disclose the amounts and reasons for any transfers of assets and liabilities into and out of Level 1 and Level 2 of the fair value hierarchy. For fair value measurements using significant unobservable inputs (Level 3), companies are required to disclose quantitative information about the significant unobservable inputs used for all Level 3 measurements and a description of the Company’s valuation processes in determining fair value. In addition, companies are required to provide a qualitative discussion about the sensitivity of recurring Level 3 measurements to changes in the unobservable inputs disclosed, including the interrelationship between inputs. Companies are also required to disclose information about when the current use of a non-financial asset measured at fair value differs from its highest and best use and the hierarchy classification for items whose fair value is not recorded on the balance sheet but is disclosed in the notes. This does not have a material effect on the Company's consolidated results of operations or financial position. See Note 9 for further discussion.

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X promulgated under the Securities Act of 1933, as amended. Accordingly, they do not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) and certain reclassifications considered necessary for a fair presentation have been included. Certain reclassifications have been made to the prior period financial statements in order to conform to the current year presentation. Operating results for the nine months ended September 30, 2012 are not necessarily indicative of the results that may be expected for the year ending December 31, 2012.

In preparation of the Company’s financial statements in conformity with accounting principles generally accepted in the United States, management makes estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements as well as the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates.

The balance sheets at December 31, 2011 have been derived from the audited financial statements at that date but does not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements.

For further information, including definitions of capitalized terms not defined herein, refer to the consolidated financial statements and footnotes thereto included in the Company’s and the Operating Partnership's annual report on Form 10-K for the year ended December 31, 2011.

Income and Other Taxes

Due to the structure of EQR as a REIT and the nature of the operations of its operating properties, no provision for federal income taxes has been made at the EQR level. In addition, ERPOP generally is not liable for federal income taxes as the partners recognize their proportionate share of income or loss in their tax returns; therefore no provision for federal income taxes has been made at the ERPOP level. Historically, the Company has generally only incurred certain state and local income, excise and franchise taxes. The Company has elected Taxable REIT Subsidiary (“TRS”) status for certain of its corporate subsidiaries and as a result, these entities will incur both federal and state income taxes on any taxable income of such entities after consideration of any net operating losses.

Deferred tax assets and liabilities applicable to the TRS are recognized for future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. These assets and liabilities are measured using enacted tax rates for which the temporary differences are expected to be recovered or settled. The effects of changes in tax rates on deferred tax assets and liabilities are recognized in earnings in the period enacted. The Company’s deferred tax assets are generally the result of differing depreciable lives on capitalized assets and the timing of expense recognition for certain accrued liabilities. As of September 30, 2012, the Company has recorded a deferred tax asset of approximately $31.7 million, which is fully offset by a valuation allowance due to the uncertainty in forecasting future TRS taxable income.

Other

The Company is the controlling partner in various consolidated partnerships owning 19 properties and 3,475 apartment units and various completed and uncompleted development properties having a noncontrolling interest book value of $75.4 million at September 30, 2012. The Company is required to make certain disclosures regarding noncontrolling interests in consolidated limited-life subsidiaries. Of the consolidated entities described above, the Company is the controlling partner in limited-life partnerships owning six properties having a noncontrolling interest deficit balance of $6.0 million. These six partnership agreements contain provisions that require the partnerships to be liquidated through the sale of their assets upon reaching a date specified in each respective partnership agreement. The Company, as controlling partner, has an obligation to cause the property owning partnerships to distribute the proceeds of liquidation to the Noncontrolling Interests in these Partially Owned Properties only to the extent that the net proceeds received by the partnerships from the sale of their assets warrant a distribution based on the partnership agreements. As of September 30, 2012, the Company estimates the value of Noncontrolling Interest distributions for these six properties would have been approximately $33.3 million (“Settlement Value”) had the partnerships been liquidated. This Settlement Value is based on estimated third party consideration realized by the partnerships upon disposition of the six Partially Owned Properties and is net of all other assets and liabilities, including yield maintenance on the mortgages encumbering the properties, that would have been due on September 30, 2012 had those mortgages been prepaid. Due to, among other things, the inherent uncertainty in the sale of real estate assets, the amount of any potential distribution to the Noncontrolling Interests in the Company’s Partially Owned Properties is subject to change. To the extent that the partnerships’ underlying assets are worth less than the underlying liabilities, the Company has no obligation to remit any consideration to the Noncontrolling Interests in these Partially Owned Properties.

Effective January 1, 2011, companies are required to separately disclose purchases, sales, issuances and settlements on a gross basis in the reconciliation of recurring Level 3 fair value measurements. This does not have a material effect on the Company’s consolidated results of operations or financial position. See Note 9 for further discussion.

Effective January 1, 2012, companies are required to separately disclose the amounts and reasons for any transfers of assets and liabilities into and out of Level 1 and Level 2 of the fair value hierarchy. For fair value measurements using significant unobservable inputs (Level 3), companies are required to disclose quantitative information about the significant unobservable inputs used for all Level 3 measurements and a description of the Company’s valuation processes in determining fair value. In addition, companies are required to provide a qualitative discussion about the sensitivity of recurring Level 3 measurements to changes in the unobservable inputs disclosed, including the interrelationship between inputs. Companies are also required to disclose information about when the current use of a non-financial asset measured at fair value differs from its highest and best use and the hierarchy classification for items whose fair value is not recorded on the balance sheet but is disclosed in the notes. This does not have a material effect on the Company's consolidated results of operations or financial position. See Note 9 for further discussion.