Employee Benefit Plans (Policies)	3 Months Ended
Mar. 31, 2020
People's United Employee Pension and Other Postretirement Plans	People’s United Employee Pension and Other Postretirement Plans People’s United maintains a qualified noncontributory defined benefit pension plan (the “People’s Qualified Plan”) that covers substantially all full-time and part-time employees who (i) meet certain age and length of service requirements and (ii) were employed by the Bank prior to August 14, 2006. Benefits are based upon the employee’s years of credited service and either the average compensation for the last five years or the average compensation for the five consecutive years of the last ten years that produce the highest average. New employees of the Bank starting on or after August 14, 2006 are not eligible to participate in the People’s Qualified Plan. Instead, the Bank makes contributions on behalf of these employees to a qualified defined contribution plan in an annual amount equal to 3% of the employee’s eligible compensation. Employee participation in this plan is restricted to employees who (i) are at least 18 years of age and (ii) worked at least 1,000 hours in a year. Both full-time and part-time employees are eligible to participate as long as they meet these requirements. In July 2011, the Bank amended the People’s Qualified Plan to “freeze”, effective December 31, 2011, the accrual of pension benefits for People’s Qualified Plan participants. As such, participants will not earn any additional benefits after that date. Instead, effective January 1, 2012, the Bank began making contributions on behalf of these participants to a qualified defined contribution plan in an annual amount equal to 3% of the employee’s eligible compensation. In addition to the People’s Qualified Plan, People’s United continues to maintain qualified defined benefit pension plans that cover (i) former First Connecticut Bancorp, Inc. employees who meet certain eligibility requirements (the “First Connecticut Qualified Plan”) and (ii) former United Financial Bancorp, Inc. employees who meet certain eligibility requirements (the “United Financial Qualified Plan”). All benefits under these plans were frozen effective February 28, 2013 and December 31, 2012, respectively. People’s United’s funding policy is to contribute the amounts required by applicable regulations, although additional amounts may be contributed from time to time. People’s United also maintains (i) unfunded, nonqualified supplemental plans to provide retirement benefits to certain senior officers (the “People’s Supplemental Plans”) and (ii) an unfunded plan that provides retirees with optional medical, dental and life insurance benefits (the “People’s Postretirement Plan”). People’s United accrues the cost of these postretirement benefits over the employees’ years of service to the date of their eligibility for such benefit. People’s United also continues to maintain: (1) for certain eligible former First Connecticut Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “First Connecticut Supplemental Plan”) and (ii) unfunded plans that provide medical, dental and life insurance benefits (the “First Connecticut Postretirement Plans”); (2) for certain eligible former BSB Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “BSB Bancorp Supplemental Plan”) and (ii) unfunded plans that provide life insurance benefits (the “BSB Bancorp Post Retirement Welfare (Life Insurance) Plan”); and (3) for certain former United Financial Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “United Financial Supplemental Plan”) and (ii) unfunded plans that provide medical, dental and life insurance benefits (the “United Financial Postretirement Benefit Plan”).
Employee Stock Ownership Plan	Employee Stock Ownership Plan In April 2007, People’s United established an ESOP. At that time, People’s United loaned the ESOP $216.8 million to purchase 10,453,575 shares of People’s United common stock in the open market. In order for the ESOP to repay the loan, People’s United expects to make annual cash contributions of approximately $18.8 million until 2036. Such cash contributions may be reduced by the cash dividends paid on unallocated ESOP shares, which, for the three months ended March 31, 2020, totaled $1.1 million. At March 31, 2020, the loan balance totaled $171.8 million. Employee participation in this plan is restricted to those employees who (i) are at least 18 years of age and (ii) worked at least 1,000 hours within 12 months of their hire date or any plan year (January 1 to December 31) after their date of hire. Employees meeting the aforementioned eligibility criteria during the plan year must continue to be employed as of the last day of the plan year in order to receive an allocation of shares for that plan year. Shares of People’s United common stock are held by the ESOP and allocated to eligible participants annually based upon a percentage of each participant’s eligible compensation. Since the ESOP was established, a total of 4,616,996 shares of People’s United common stock have been allocated or committed to be released to participants’ accounts. At March 31, 2020, 5,836,579 shares of People’s United common stock, with a fair value of $64.5 million at that date, have not been allocated or committed to be released. Compensation expense related to the ESOP is recognized at an amount equal to the number of common shares committed to be released by the ESOP for allocation to participants’ accounts multiplied by the average fair value of People’s United’s common stock during the reporting period. The difference between the fair value of the shares of People’s United’s common stock committed to be released and the cost of those common shares is recorded as a credit to additional paid-in capital (if fair value exceeds cost) or, to the extent that no such credits remain in additional paid-in capital, as a charge to retained earnings (if fair value is less than cost). Expense recognized for the ESOP totaled $1.2 million and $1.4 million for the three months ended March 31, 2020 and 2019, respectively.
Recurring
Fair Value Measurements	Recurring Fair Value Measurements Trading Debt Securities, Equity Securities and Debt Securities Available-For-Sale When available, People’s United uses quoted market prices for identical securities received from an independent, nationally-recognized, third-party pricing service (as discussed further below) to determine the fair value of investment securities such as U.S. Treasury and agency securities and equity securities that are included in Level 1. When quoted market prices for identical securities are unavailable, People’s United uses prices provided by the independent pricing service based on recent trading activity and other observable information including, but not limited to, market interest rate curves, referenced credit spreads and estimated prepayment rates where applicable. These investments include certain U.S. and government agency debt securities, corporate and municipal debt securities, and GSE mortgage-backed and CMO securities, all of which are included in Level 2. The Company’s available-for-sale debt securities are primarily comprised of GSE mortgage-backed securities. The fair value of these securities is based on prices obtained from the independent pricing service. The pricing service uses various techniques to determine pricing for the Company’s mortgage-backed securities, including option pricing and discounted cash flow analysis. The inputs include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, benchmark securities, bids, offers, reference data, monthly payment information and collateral performance. At both March 31, 2020 and December 31, 2019, the entire available-for-sale mortgage-backed securities portfolio was comprised of GSE mortgage-backed and CMO securities with original final maturities ranging from 10 to 40 years. An active market exists for securities that are similar to the Company’s GSE mortgage-backed and CMO securities, making observable inputs readily available.
Nonrecurring
Fair Value Measurements	Non-Recurring Fair Value Measurements Loans Held-for-Sale Loans held-for-sale are recorded at the lower of amortized cost or fair value and are therefore measured at fair value on a non-recurring basis. When available, People’s United uses observable secondary market data, including pricing on recent closed market transactions for loans with similar characteristics. Accordingly, such loans are classified as Level 2 measurements. When observable data is unavailable, valuation methodologies using current market interest rate data adjusted for inherent credit risk are used, and such loans are included in Level 3. REO and Repossessed Assets REO and repossessed assets are recorded at the lower of cost or fair value, less estimated selling costs, and are therefore measured at fair value on a non-recurring basis. People’s United has estimated the fair values of these assets using Level 3 inputs, such as independent third-party appraisals and price opinions. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%. Assets that are acquired through loan default are recorded as held-for-sale initially at the lower of the recorded investment in the loan or fair value (less estimated selling costs) upon the date of foreclosure/repossession. Subsequent to foreclosure/repossession, valuations are updated periodically and the carrying amounts of these assets may be reduced further. Mortgage Servicing Rights Mortgage servicing rights are evaluated for impairment based upon the fair value of the servicing rights as compared to their amortized cost. The fair value of mortgage servicing rights is based on a valuation model that calculates the present value of estimated net servicing income. This model incorporates certain assumptions that market participants would likely use in estimating future net servicing income, such as interest rates, prepayment speeds and the cost to service (including delinquency and foreclosure costs), all of which require a degree of management judgment. Adjustments are only recorded when the discounted cash flows derived from the valuation model are less than the carrying value of the asset. As such, mortgage servicing rights are subject to measurement at fair value on a non-recurring basis and are classified as Level 3 assets. Collateral Dependent / Impaired Loans (periods prior to January 1, 2020) The Company’s approach to determining the fair value of collateral dependent loans is described in Note 3, “Loans”. At March 31, 2020, collateral dependent loans with an amortized cost of $15.2 million had a corresponding ACL (determined using a Level 3 measurement approach) of $8.9 million. The provision for credit losses associated with collateral dependent loans totaled $3.9 million for the three months ended March 31, 2020. Prior to the Company's adoption of the CECL standard, loan impairment was deemed to exist when full repayment of principal and interest according to the contractual terms of the loan was no longer probable. Impaired loans were reported based on one of three measures: (i) the present value of expected future cash flows discounted at the loan’s original effective interest rate; (ii) the loan’s observable market price; or (iii) the fair value of the collateral (less estimated cost to sell) if the loan is collateral dependent. Accordingly, certain impaired loans may have been subject to measurement at fair value on a  non-recurring basis. People’s United has estimated the fair values of these assets using Level 3 inputs, such as discounted cash flows based on inputs that are largely unobservable and, instead, reflect management’s own estimates of the assumptions a market participant would use in pricing such loans and/or the fair value of collateral based on independent third-party appraisals for  collateral dependent loans. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%.

Employee Benefit Plans (Policies)

3 Months Ended

Mar. 31, 2020

People's United Employee Pension and Other Postretirement Plans

People’s United Employee Pension and Other Postretirement Plans

People’s United maintains a qualified noncontributory defined benefit pension plan (the “People’s Qualified Plan”) that covers substantially all full-time and part-time employees who (i) meet certain age and length of service requirements and (ii) were employed by the Bank prior to August 14, 2006. Benefits are based upon the employee’s years of credited service and either the average compensation for the last five years or the average compensation for the five consecutive years of the last ten years that produce the highest average.

New employees of the Bank starting on or after August 14, 2006 are not eligible to participate in the People’s Qualified Plan. Instead, the Bank makes contributions on behalf of these employees to a qualified defined contribution plan in an annual amount equal to 3% of the employee’s eligible compensation. Employee participation in this plan is restricted to employees who (i) are at least 18 years of age and (ii) worked at least 1,000 hours in a year. Both full-time and part-time employees are eligible to participate as long as they meet these requirements.

In July 2011, the Bank amended the People’s Qualified Plan to “freeze”, effective December 31, 2011, the accrual of pension benefits for People’s Qualified Plan participants. As such, participants will not earn any additional benefits after that date. Instead, effective January 1, 2012, the Bank began making contributions on behalf of these participants to a qualified defined contribution plan in an annual amount equal to 3% of the employee’s eligible compensation.

In addition to the People’s Qualified Plan, People’s United continues to maintain qualified defined benefit pension plans that cover (i) former First Connecticut Bancorp, Inc. employees who meet certain eligibility requirements (the “First Connecticut Qualified Plan”) and (ii) former United Financial Bancorp, Inc. employees who meet certain eligibility requirements (the “United Financial Qualified Plan”). All benefits under these plans were frozen effective February 28, 2013 and December 31, 2012, respectively.

People’s United’s funding policy is to contribute the amounts required by applicable regulations, although additional amounts may be contributed from time to time.

People’s United also maintains (i) unfunded, nonqualified supplemental plans to provide retirement benefits to certain senior officers (the “People’s Supplemental Plans”) and (ii) an unfunded plan that provides retirees with optional medical, dental and life insurance benefits (the “People’s Postretirement Plan”). People’s United accrues the cost of these postretirement benefits over the employees’ years of service to the date of their eligibility for such benefit. People’s United also continues to maintain: (1) for certain eligible former First Connecticut Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “First Connecticut Supplemental Plan”) and (ii) unfunded plans that provide medical, dental and life insurance benefits (the “First Connecticut Postretirement Plans”); (2) for certain eligible former BSB Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “BSB Bancorp Supplemental Plan”) and (ii) unfunded plans that provide life insurance benefits (the “BSB Bancorp Post Retirement Welfare (Life Insurance) Plan”); and (3) for certain former United Financial Bancorp, Inc. employees (i) an unfunded, nonqualified supplemental retirement plan (the “United Financial Supplemental Plan”) and (ii) unfunded plans that provide medical, dental and life insurance benefits (the “United Financial Postretirement Benefit Plan”).

Employee Stock Ownership Plan

In April 2007, People’s United established an ESOP. At that time, People’s United loaned the ESOP $216.8 million to purchase 10,453,575 shares of People’s United common stock in the open market. In order for the ESOP to repay the loan, People’s United expects to make annual cash contributions of approximately $18.8 million until 2036. Such cash contributions may be reduced by the cash dividends paid on unallocated ESOP shares, which, for the three months ended March 31, 2020, totaled $1.1 million. At March 31, 2020, the loan balance totaled $171.8 million.

Employee participation in this plan is restricted to those employees who (i) are at least 18 years of age and (ii) worked at least 1,000 hours within 12 months of their hire date or any plan year (January 1 to December 31) after their date of hire. Employees meeting the aforementioned eligibility criteria during the plan year must continue to be employed as of the last day of the plan year in order to receive an allocation of shares for that plan year.

Shares of People’s United common stock are held by the ESOP and allocated to eligible participants annually based upon a percentage of each participant’s eligible compensation. Since the ESOP was established, a total of 4,616,996 shares of People’s United common stock have been allocated or committed to be released to participants’ accounts. At March 31, 2020, 5,836,579 shares of People’s United common stock, with a fair value of $64.5 million at that date, have not been allocated or committed to be released.

Compensation expense related to the ESOP is recognized at an amount equal to the number of common shares committed to be released by the ESOP for allocation to participants’ accounts multiplied by the average fair value of People’s United’s common stock during the reporting period. The difference between the fair value of the shares of People’s United’s common stock committed to be released and the cost of those common shares is recorded as a credit to additional paid-in capital (if fair value exceeds cost) or, to the extent that no such credits remain in additional paid-in capital, as a charge to retained earnings (if fair value is less than cost). Expense recognized for the ESOP totaled $1.2 million and $1.4 million for the three months ended March 31, 2020 and 2019, respectively.

Recurring

Fair Value Measurements

Recurring Fair Value Measurements

Trading Debt Securities, Equity Securities and Debt Securities Available-For-Sale

When available, People’s United uses quoted market prices for identical securities received from an independent, nationally-recognized, third-party pricing service (as discussed further below) to determine the fair value of investment securities such as U.S. Treasury and agency securities and equity securities that are included in Level 1. When quoted market prices for identical securities are unavailable, People’s United uses prices provided by the independent pricing service based on recent trading activity and other observable information including, but not limited to, market interest rate curves, referenced credit spreads and estimated prepayment rates where applicable. These investments include certain U.S. and government agency debt securities, corporate and municipal debt securities, and GSE mortgage-backed and CMO securities, all of which are included in Level 2.

The Company’s available-for-sale debt securities are primarily comprised of GSE mortgage-backed securities. The fair value of these securities is based on prices obtained from the independent pricing service. The pricing service uses various techniques to determine pricing for the Company’s mortgage-backed securities, including option pricing and discounted cash flow analysis. The inputs include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, benchmark securities, bids, offers, reference data, monthly payment information and collateral performance. At both March 31, 2020 and December 31, 2019, the entire available-for-sale mortgage-backed securities portfolio was comprised of GSE mortgage-backed and CMO securities with original final maturities ranging from 10 to 40 years. An active market exists for securities that are similar to the Company’s GSE mortgage-backed and CMO securities, making observable inputs readily available.

Nonrecurring

Fair Value Measurements

Non-Recurring Fair Value Measurements

Loans Held-for-Sale

Loans held-for-sale are recorded at the lower of amortized cost or fair value and are therefore measured at fair value on a non-recurring basis. When available, People’s United uses observable secondary market data, including pricing on recent closed market transactions for loans with similar characteristics. Accordingly, such loans are classified as Level 2 measurements. When observable data is unavailable, valuation methodologies using current market interest rate data adjusted for inherent credit risk are used, and such loans are included in Level 3.

REO and Repossessed Assets

REO and repossessed assets are recorded at the lower of cost or fair value, less estimated selling costs, and are therefore measured at fair value on a non-recurring basis. People’s United has estimated the fair values of these assets using Level 3 inputs, such as independent third-party appraisals and price opinions. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%. Assets that are acquired through loan default are recorded as held-for-sale initially at the lower of the recorded investment in the loan or fair value (less estimated selling costs) upon the date of foreclosure/repossession. Subsequent to foreclosure/repossession, valuations are updated periodically and the carrying amounts of these assets may be reduced further.

Mortgage Servicing Rights

Mortgage servicing rights are evaluated for impairment based upon the fair value of the servicing rights as compared to their amortized cost. The fair value of mortgage servicing rights is based on a valuation model that calculates the present value of estimated net servicing income. This model incorporates certain assumptions that market participants would likely use in estimating future net servicing income, such as interest rates, prepayment speeds and the cost to service (including delinquency and foreclosure costs), all of which require a degree of management judgment. Adjustments are only recorded when the discounted cash flows derived from the valuation model are less than the carrying value of the asset. As such, mortgage servicing rights are subject to measurement at fair value on a non-recurring basis and are classified as Level 3 assets.

Collateral Dependent / Impaired Loans (periods prior to January 1, 2020)

The Company’s approach to determining the fair value of collateral dependent loans is described in Note 3, “Loans”. At March 31, 2020, collateral dependent loans with an amortized cost of $15.2 million had a corresponding ACL (determined using a Level 3 measurement approach) of $8.9 million. The provision for credit losses associated with collateral dependent loans totaled $3.9 million for the three months ended March 31, 2020.

Prior to the Company's adoption of the CECL standard, loan impairment was deemed to exist when full repayment of principal and interest according to the contractual terms of the loan was no longer probable. Impaired loans were reported based on one of three measures: (i) the present value of expected future cash flows discounted at the loan’s original effective interest rate; (ii) the loan’s observable market price; or (iii) the fair value of the collateral (less estimated cost to sell) if the loan is collateral dependent. Accordingly, certain impaired loans may have been subject to measurement at fair value on a  non-recurring basis.

People’s United has estimated the fair values of these assets using Level 3 inputs, such as discounted cash flows based on inputs that are largely unobservable and, instead, reflect management’s own estimates of the assumptions a market participant would use in pricing such loans and/or the fair value of collateral based on independent third-party appraisals for  collateral dependent loans. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%.