| Document and Entity Information Document | Apr. 28, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Apr. 28, 2022 |
| Entity Registrant Name | EASTERN BANKSHARES, INC. |
| Entity Central Index Key | 0001810546 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | MA |
| Entity File Number | 001-39610 |
| Entity Tax Identification Number | 84-4199750 |
| Entity Address, Address Line One | 265 Franklin Street |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02110 |
| City Area Code | 800 |
| Local Phone Number | 327-8376 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | EBC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
