Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity Registrant Name	People's United Financial, Inc.
Entity File Number	001-33326
Entity Incorporation, State or Country Code	DE
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
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 6,690
Entity Common Stock, Shares Outstanding		433,739,103
Documents Incorporated by Reference	Portions of the Proxy Statement for the Annual Meeting of Shareholders to be held on May 21, 2020, are incorporated by reference into Part III.
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001378946
Current Fiscal Year End Date	--12-31
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	PBCT
Security Exchange Name	NASDAQ
Series A Preferred Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series A, $0.01 par value per share
Trading Symbol	PBCTP
Security Exchange Name	NASDAQ