| Document and Entity Information | Jul. 15, 2021 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | People's United Financial, Inc. |
| Amendment Flag | false |
| Entity Central Index Key | 0001378946 |
| Document Type | 8-K |
| Document Period End Date | Jul. 15, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-33326 |
| Entity Tax Identification Number | 20-8447891 |
| Entity Address, Address Line One | 850 Main Street |
| Entity Address, City or Town | Bridgeport |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06604 |
| City Area Code | (203) |
| Local Phone Number | 338-7171 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $0.01 par value per share |
| Trading Symbol | PBCT |
| Security Exchange Name | NASDAQ |
| Series A Preferred Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series A, $0.01 par value per share |
| Trading Symbol | PBCTP |
| Security Exchange Name | NASDAQ |
