Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 12, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Registrant Name	EQUITY RESIDENTIAL
Entity Central Index Key	0000906107
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	EQR
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Public Float			$ 21.7
Entity Common Stock, Shares Outstanding		372,663,215
Entity File Number	1-12252
Entity Tax Identification Number	13-3675988
Entity Address, Address Line One	Two North Riverside Plaza
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	312
Local Phone Number	474-1300
Entity Incorporation, State or Country Code	MD
Title of 12(b) Security	Common Shares of Beneficial Interest,$0.01 Par Value (Equity Residential)
Security Exchange Name	NYSE
Document Annual Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference	Part III incorporates by reference certain information that will be contained in Equity Residential’s Proxy Statement relating to its 2021 Annual Meeting of Shareholders, which Equity Residential intends to file no later than 120 days after the end of its fiscal year ended December 31, 2020, and thus these items have been omitted in accordance with General Instruction G(3) to Form 10-K.  Equity Residential is the general partner and 96.4% owner of ERP Operating Limited Partnership.
ERPOP [Member]
Document Information [Line Items]
Entity Registrant Name	ERP OPERATING LIMITED PARTNERSHIP
Entity Central Index Key	0000931182
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
No Trading Symbol Flag	true
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	0-24920
Entity Tax Identification Number	36-3894853
Entity Address, Address Line One	Two North Riverside Plaza
Entity Address, City or Town	Chicago
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60606
City Area Code	312
Local Phone Number	474-1300
Entity Incorporation, State or Country Code	IL
Title of 12(b) Security	7.57% Notes due August 15, 2026(ERP Operating Limited Partnership)
Security Exchange Name	NYSE
Document Annual Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
ICFR Auditor Attestation Flag	true