Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 22, 2021
Document Information [Line Items]
Entity Registrant Name	EQUITY RESIDENTIAL
Entity Central Index Key	0000906107
Document Type	10-Q
Document Period End Date	Sep. 30, 2021
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	EQR
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		375,016,222
Entity Current Reporting Status	Yes
Entity Shell Company	false
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 Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
ERPOP [Member]
Document Information [Line Items]
Entity Registrant Name	ERP OPERATING LIMITED PARTNERSHIP
Entity Central Index Key	0000931182
Document Type	10-Q
Document Period End Date	Sep. 30, 2021
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
No Trading Symbol Flag	true
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell 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 Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes