| Document and Entity Information Statement | Feb. 12, 2021 |
| Entity Information [Line Items] | |
| Amendment Flag | false |
| Document Type | 8-K |
| Document Period End Date | Feb. 12, 2021 |
| Entity Registrant Name | WEBSTER FINANCIAL CORPORATION |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-31486 |
| Entity Tax Identification Number | 06-1187536 |
| Entity Address, Address Line One | 145 Bank Street |
| Entity Address, City or Town | Waterbury |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06702 |
| City Area Code | 203 |
| Local Phone Number | 578-2202 |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000801337 |
