| Cover Page | Dec. 17, 2020 |
| Document Information [Line Items] | |
| Entity Registrant Name | EQUITY RESIDENTIAL |
| Entity Central Index Key | 0000906107 |
| Document Type | 8-K |
| Document Period End Date | Dec. 17, 2020 |
| Amendment Flag | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Shares of Beneficial Interest, $0.01 Par Value (Equity Residential) |
| Trading Symbol | EQR |
| Security Exchange Name | NYSE |
| ERPOP [Member] | |
| Document Information [Line Items] | |
| Entity Registrant Name | ERP OPERATING LIMITED PARTNERSHIP |
| Entity Central Index Key | 0000931182 |
| Document Type | 8-K |
| Document Period End Date | Dec. 17, 2020 |
| 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 Incorporation, State or Country Code | IL |
| Title of 12(b) Security | 7.57% Notes due August 15, 2026 (ERP Operating Limited Partnership) |
| No Trading Symbol Flag | true |
| Security Exchange Name | NYSE |
