Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 27, 2018
Document And Entity Information [Line Items]
Entity Registrant Name	EQUITY RESIDENTIAL
Entity Central Index Key	0000906107
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Trading Symbol	EQR
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		368,213,717
ERPOP [Member]
Document And Entity Information [Line Items]
Entity Registrant Name	ERP OPERATING LIMITED PARTNERSHIP
Entity Central Index Key	0000931182
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer