People's United Financial (PBCT) 10-Q 9 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	PBCT
Entity Registrant Name	People's United Financial, Inc.
Entity Central Index Key	1,378,946
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		346,251,605

Consolidated Statements of Cond

Consolidated Statements of Condition - (Unaudited) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 414.1	$ 432.4
Short-term investments (note 3)	302.5	181.7
Total cash and cash equivalents	716.6	614.1
Securities (note 3):
Trading account securities, at fair value	8.3	6.8
Securities available for sale, at fair value	3,197.5	4,409.9
Securities held to maturity, at amortized cost (fair value of $3.44 billion and $2.01 billion)	3,387.6	2,005.4
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	320.9	315.8
Total securities	6,914.3	6,737.9
Loans held for sale	15	39.3
Loans (note 4):
Total loans	32,384.5	29,744.9
Less allowance for loan losses	(233.4)	(229.3)
Total loans, net	32,151.1	29,515.6
Goodwill (note 7)	2,411.4	1,992.7
Bank-owned life insurance	405.6	349.1
Premises and equipment, net	264.7	244.5
Other acquisition-related intangible assets (note 7)	156.5	149.4
Other assets (notes 1, 4 and 12)	963	967.2
Total assets	43,998.2	40,609.8
Deposits:
Non-interest-bearing	7,655.3	6,660.8
Savings	4,513.1	4,397.7
Interest-bearing checking and money market	15,143.1	14,260.1
Time	5,235.8	4,542.2
Total deposits	32,547.3	29,860.8
Borrowings:
Federal Home Loan Bank advances	3,074.1	3,061.1
Federal funds purchased	543	617
Customer repurchase agreements	295.8	343.3
Other borrowings	231.1	35.4
Total borrowings	4,144	4,056.8
Notes and debentures	906.2	1,030.1
Other liabilities (notes 1 and 12)	654.6	520.2
Total liabilities	38,252.1	35,467.9
Commitments and contingencies (notes 1 and 9)
Stockholders' Equity (notes 2, 5 and 8)
Preferred stock ($0.01 par value; 50.0 million shares authorized; 10.0 million shares issued and outstanding at both dates)	244.1	244.1
Common stock ($0.01 par value; 1.95 billion shares authorized; 433.6 million shares and 405.0 million shares issued)	4.3	4
Additional paid-in capital	5,972.2	5,446.1
Retained earnings	996.4	949.3
Unallocated common stock of Employee Stock Ownership Plan, at cost (6.7 million shares and 7.0 million shares)	(139.1)	(144.6)
Accumulated other comprehensive loss	(169.7)	(195)
Treasury stock, at cost (89.0 million shares and 89.1 million shares)	(1,162.1)	(1,162)
Total stockholders' equity	5,746.1	5,141.9
Total liabilities and stockholders' equity	43,998.2	40,609.8
Commercial [Member]
Loans (note 4):
Total loans	23,510.8	21,404.9
Less allowance for loan losses	(203.5)	(204.9)
Retail Loans [Member]
Loans (note 4):
Total loans	8,873.7	8,340
Less allowance for loan losses	(29.9)	(24.4)
Commercial Real Estate Loan [Member] | Commercial [Member]
Loans (note 4):
Total loans	11,180.5	10,247.3
Commercial and Industrial [Member] | Commercial [Member]
Loans (note 4):
Total loans	8,624.7	8,125.1
Equipment Financing [Member] | Commercial [Member]
Loans (note 4):
Total loans	3,705.6	3,032.5
Residential Mortgage Loan [Member] | Retail Loans [Member]
Loans (note 4):
Total loans	6,781	6,216.7
Home Equity and Other Consumer [Member] | Retail Loans [Member]
Loans (note 4):
Total loans	$ 2,092.7	$ 2,123.3

Consolidated Statements of Con3

Consolidated Statements of Condition - (Unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Securities held to maturity, at fair value	$ 3,435.6	$ 2,012.6
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	10,000,000	10,000,000
Preferred stock, shares outstanding	10,000,000	10,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,950,000,000	1,950,000,000
Common stock, shares issued	433,600,000	405,000,000
Unallocated common stock of Employee Stock Ownership Plan, shares	6,707,711	7,000,000
Treasury stock, shares	89,000,000	89,100,000

Consolidated Statements of Inco

Consolidated Statements of Income - (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest and dividend income:
Commercial real estate	$ 105.6	$ 85.7	$ 299.5	$ 257.8
Residential mortgage	52.5	45.7	154.1	133.4
Home equity and other consumer	21	18.4	59.3	55.4
Total interest on loans	300.6	249.5	836.2	735.7
Securities	37.2	34.2	112.1	103.4
Short-term investments	1.1	0.4	2.7	1.1
Loans held for sale	0.3	0.4	0.7	0.8
Total interest and dividend income	339.2	284.5	951.7	841
Interest expense:
Deposits	34.4	25.2	92.4	75.8
Borrowings	12.7	6.1	28.9	16.4
Notes and debentures	7.5	7.9	22.3	23.4
Total interest expense	54.6	39.2	143.6	115.6
Net interest income	284.6	245.3	808.1	725.4
Provision for loan losses (note 4)	7	8.4	18.5	28.9
Net interest income after provision for loan losses	277.6	236.9	789.6	696.5
Non-interest income:
Bank service charges	25.3	25.3	73.8	73.8
Investment management fees	16.9	11.6	49.2	34.1
Operating lease income	10.9	11.2	32.1	31.7
Commercial banking lending fees	7	7.1	26.7	24.4
Insurance revenue	9.7	9.8	26.3	26.1
Cash management fees	6.8	6.5	19.6	18.8
Brokerage commissions	2.8	3.2	9.2	9.4
Net gains on sales of residential mortgage loans	1.1	1.9	2.7	3.7
Net security (losses) gains (note 3)			(15.6)	0.1
Other non-interest income	8.8	14.2	41.6	36.4
Total non-interest income	89.3	90.8	265.6	258.5
Non-interest expense (note 2):
Compensation and benefits	128	116.1	383.6	341.6
Occupancy and equipment	40.2	37.7	118.6	112.6
Professional and outside services	19.2	17.7	62.8	51.5
Regulatory assessments	10.3	9.9	29.8	27.1
Operating lease expense	8.8	9.7	26.3	28
Amortization of other acquisition-related intangible assets (note 7)	7.9	5.8	22.1	17.4
Other non-interest expense	22.7	24.5	77.3	73.4
Total non-interest expense	237.1	221.4	720.5	651.6
Income before income tax expense	129.8	106.3	334.7	303.4
Income tax expense (notes 1 and 14)	39	32.6	103.8	98.3
Net income	90.8	73.7	230.9	205.1
Preferred stock dividend	3.5		10.5
Net income available to common shareholders	$ 87.3	$ 73.7	$ 220.4	$ 205.1
Earnings per common share (note 6):
Basic	$ 0.26	$ 0.24	$ 0.67	$ 0.68
Diluted	$ 0.26	$ 0.24	$ 0.67	$ 0.68
Commercial and Industrial [Member]
Interest and dividend income:
Interest and fee income	$ 80	$ 66.9	$ 218.7	$ 190
Equipment Financing [Member]
Interest and dividend income:
Interest and fee income	$ 41.5	$ 32.8	$ 104.6	$ 99.1

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 90.8	$ 73.7	$ 230.9	$ 205.1
Other comprehensive income (loss), net of tax:
Net actuarial loss and prior service credit related to pension and other postretirement plans	0.9	0.9	2.8	2.8
Net unrealized gains and losses on securities available for sale	3.6	(1.7)	21	52.3
Amortization of unrealized losses on securities transferred to held to maturity	0.6	0.5	1.6	1.5
Net unrealized gains and losses on derivatives accounted for as cash flow hedges	(0.2)	0.2	(0.1)	0.2
Total other comprehensive income (loss), net of tax (note 5)	4.9	(0.1)	25.3	56.8
Total comprehensive income	$ 95.7	$ 73.6	$ 256.2	$ 261.9

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - (Unaudited) - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Unallocated ESOP Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2015	$ 4,731.6		$ 3.9	$ 5,337.7	$ 880.8	$ (151.8)	$ (177.2)	$ (1,161.8)
Net income	205.1				205.1
Total other comprehensive income, net of tax (note 5)	56.8						56.8
Cash dividends on common stock	(154.1)				(154.1)
Restricted stock and performance-based share awards	7			7.1	0.1			(0.2)
Employee Stock Ownership Plan common committed to be released (note 8)	4				(1.4)	5.4
Common stock repurchased and retired upon vesting of restricted stock awards	(3.2)				(3.2)
Stock option exercises and related tax benefits	15.1		0.1	15
Ending Balance at Sep. 30, 2016	4,862.3		4	5,359.8	927.3	(146.4)	(120.4)	(1,162)
Beginning Balance at Dec. 31, 2016	5,141.9	$ 244.1	4	5,446.1	949.3	(144.6)	(195)	(1,162)
Net income	230.9				230.9
Total other comprehensive income, net of tax (note 5)	25.3						25.3
Common stock issued in Suffolk Bancorp acquisition (note 2)	484.8		0.2	484.6
Cash dividends on common stock	(169.3)				(169.3)
Cash dividends on preferred stock	(10.5)				(10.5)
Restricted stock and performance-based share awards	9			9.1				(0.1)
Employee Stock Ownership Plan common committed to be released (note 8)	4.8				(0.7)	5.5
Common stock repurchased and retired upon vesting of restricted stock awards	(3.3)				(3.3)
Stock option exercises and related tax benefits	32.5		0.1	32.4
Ending Balance at Sep. 30, 2017	$ 5,746.1	$ 244.1	$ 4.3	$ 5,972.2	$ 996.4	$ (139.1)	$ (169.7)	$ (1,162.1)

Consolidated Statements of Cha7

Consolidated Statements of Changes in Stockholders' Equity - (Unaudited) (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash dividends on common stock, per share	$ 0.5150	$ 0.5075
Retained Earnings [Member]
Cash dividends on common stock, per share	$ 0.5150	$ 0.5075

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash Flows from Operating Activities:
Net income	$ 230.9	$ 205.1
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of premises and equipment	29.3	27.6
Expense related to operating leases	26.3	28
Amortization of other acquisition-related intangible assets	22.1	17.4
Provision for loan losses	18.5	28.9
Expense related to share-based awards	13.4	11.4
Employee Stock Ownership Plan common stock committed to be released	4.8	4
Net security losses (gains)	15.6	(0.1)
Net gains on sales of residential mortgage loans	(2.7)	(3.7)
Originations of loans held-for-sale	(212.5)	(296.1)
Proceeds from sales of loans held-for-sale	239.5	287.8
Net increase in trading account securities	(1.5)	(0.1)
Excess income tax benefits from stock option exercises (note 14)	1.3
Net changes in other assets and other liabilities	15.3	(23.8)
Net cash provided by operating activities	400.3	286.4
Cash Flows from Investing Activities:
Proceeds from principal repayments and maturities of securities available for sale	456.1	680.2
Proceeds from sales of securities available for sale	1,016.2	249.9
Proceeds from principal repayments and maturities of securities held to maturity	92.1	83.6
Purchases of securities available for sale	(237.6)	(1,228.3)
Purchases of securities held to maturity	(1,235.9)	(286.8)
Net redemptions (purchases) of Federal Reserve Bank stock	17.6	(9.1)
Net purchases of Federal Home Loan Bank stock	(19.9)	(1)
Proceeds from sales of loans	8.4	2.8
Loan disbursements, net of principal collections	(325.4)	(944.8)
Purchases of loans		(30.6)
Purchases of premises and equipment	(6.7)	(14.9)
Purchases of leased equipment	(20.5)	(14.3)
Proceeds from sales of real estate owned	8.6	8
Return of premium on bank-owned life insurance, net	1.7	1.7
Net cash acquired in acquisitions	28.9
Net cash used in investing activities	(216.4)	(1,503.6)
Cash Flows from Financing Activities:
Net increase in deposits	834.1	1,238.1
Net (decrease) increase in borrowings with terms of three months or less	(279.4)	131.2
Repayments of borrowings with terms of more than three months	(356.1)	(0.2)
Repayment of notes and debentures	(125)
Cash dividends paid on common stock	(169.3)	(154.1)
Cash dividends paid on preferred stock	(10.5)
Common stock repurchases	(3.3)	(3.2)
Proceeds from stock options exercised	28.1	10.4
Net cash (used in) provided by financing activities	(81.4)	1,222.2
Net increase in cash and cash equivalents	102.5	5
Cash and cash equivalents at beginning of period	614.1	715.3
Cash and cash equivalents at end of period	716.6	720.3
Supplemental Information:
Interest payments	138.4	114.3
Unsettled purchases of securities	110.5	9.7
Income tax payments	100.1	86.1
Real estate properties acquired by foreclosure	9.3	$ 17.9
Assets acquired and liabilities assumed in acquisitions (note 2):
Non-cash assets, excluding goodwill and other acquisition-related intangibles	2,642.1
Liabilities	2,634.1
Common stock issued in Suffolk Bancorp acquisition	$ 484.8

General

General	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
General	NOTE 1. GENERAL In the opinion of management, the accompanying unaudited consolidated financial statements of People’s United Financial, Inc. (“People’s United” or the “Company”) have been prepared to reflect all adjustments necessary to present fairly the financial position and results of operations as of the dates and for the periods shown. All significant intercompany transactions and balances are eliminated in consolidation. Certain reclassifications have been made to prior period amounts to conform to the current period presentation. In preparing the consolidated financial statements, management is required to make significant estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses. Actual results could differ from management’s current estimates, as a result of changing conditions and future events. Several accounting estimates are particularly critical and are susceptible to significant near-term change, including the allowance for loan losses and asset impairment judgments, such as the recoverability of goodwill and other intangible assets. These accounting estimates are reviewed with the Audit Committee of the Board of Directors. The judgments used by management in applying critical accounting policies may be affected by economic conditions, which may result in changes to future financial results. For example, subsequent evaluations of the loan portfolio, in light of the factors then prevailing, may result in significant changes in the allowance for loan losses in future periods, and the inability to collect outstanding principal may result in increased loan losses. Note 1 to People’s United’s audited consolidated financial statements included in the Annual Report on Form 10-K People’s United holds ownership interests in limited partnerships formed to develop and operate affordable housing units for lower income tenants throughout its franchise area. The underlying partnerships, which are considered variable interest entities (“VIEs”), are not consolidated into the Company’s Consolidated Financial Statements. These investments have historically played a role in enabling People’s United Bank, National Association (the “Bank”) to meet its Community Reinvestment Act requirements while, at the same time, providing federal income tax credits. Affordable housing investments, including all legally binding commitments to fund future investments, are included in other assets in the Consolidated Statements of Condition ($250.0 million and $195.2 million at September 30, 2017 and December 31, 2016, respectively). Included in other liabilities in the Consolidated Statements of Condition is a liability for all legally binding unfunded commitments to fund future investments ($109.6 million and $92.5 million at those dates). The cost of the Company’s investments is amortized on a straight-line basis over the period during which the related federal income tax credits are realized (generally ten years). Amortization expense, which is included as a component of income tax expense, totaled $4.2 million and $3.0 million for the three months ended September 30, 2017 and 2016, respectively, and $12.3 million and $8.9 million for the nine months ended September 30, 2017 and 2016, respectively. Certain information and footnote disclosures normally included in consolidated financial statements prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) have been omitted or condensed. As a result, the accompanying consolidated financial statements should be read in conjunction with People’s United’s Annual Report on Form 10-K

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Acquisitions	NOTE 2 – ACQUISITIONS LEAF Commercial Capital, Inc. Effective August 1, 2017, the Bank completed its acquisition of LEAF Commercial Capital, Inc. (“LEAF”) a Philadelphia-based commercial equipment finance company. The fair value of the consideration transferred in the LEAF acquisition consisted of approximately $220 million in cash. The assets acquired and liabilities assumed in this transaction were recorded by People’s United at their estimated fair values as of the effective date and People’s United’s results of operations for the three and nine months ended September 30, 2017 include the results of LEAF beginning with the effective date. The excess of the purchase price over the estimated fair value of the net assets acquired was recorded as goodwill, which was allocated to the Commercial Banking segment. Merger-related expenses recorded during the nine months ended September 30, 2017 related to the LEAF acquisition totaled $2.2 million, including fees for investment advisory, legal and valuation services. The acquisition-date estimated fair values of the assets acquired and liabilities assumed in the acquisition of LEAF are summarized as follows: (in millions) Assets: Cash and cash equivalents $ 74.9 Loans 717.9 Goodwill 148.4 Trade name intangible 0.9 Premises and equipment 2.4 Non-compete 0.2 Other assets 13.0 Total assets $ 957.7 Liabilities: Borrowings $ 708.1 Other liabilities 29.6 Total liabilities $ 737.7 Total purchase price $ 220.0 Prior to the acquisition, and in connection with its previous revolving warehouse debt facilities and term note securitization transactions, LEAF established bankruptcy-remote special-purpose entities (“SPEs”) that issued term debt to institutional investors. These SPEs were VIEs, of which LEAF was deemed the primary beneficiary, and, therefore, the related financings were treated as secured borrowings with the SPEs consolidated in LEAF’s financial statements. Following the Company’s acquisition of LEAF, approximately $460 million of LEAF’s borrowings were repaid prior to September 30, 2017, including all but one remaining securitization, which can be repaid without penalty in 2018. Net deferred tax assets totaling $3.9 million were established in connection with recording the related purchase accounting adjustments (other than goodwill). Fair value adjustments to assets acquired (other than loans, see Note 4) and liabilities assumed are generally amortized on a straight-line basis over periods consistent with the average life, useful life and/or contractual term of the related assets and liabilities. Suffolk Bancorp Effective April 1, 2017, People’s United completed its acquisition of Suffolk Bancorp (“Suffolk”) based in Riverhead, New York. The fair value of the consideration transferred in the Suffolk acquisition totaled approximately $485 million and consisted of approximately 26.6 million shares of People’s United common stock. At the acquisition date, Suffolk operated 27 branches in the greater Long Island area. The assets acquired and liabilities assumed in this transaction were recorded by People’s United at their estimated fair values as of the effective date and People’s United’s results of operations for the nine months ended September 30, 2017 include the results of Suffolk beginning with the effective date. The excess of the purchase price over the estimated fair value of the net assets acquired was recorded as goodwill, which was allocated to the Commercial Banking and Retail Banking segments. Merger-related expenses recorded during the nine months ended September 30, 2017 and 2016 related to the Suffolk acquisition totaled $26.5 million and $1.9 million, respectively, including: (i) fees for investment advisory, legal, accounting and valuation services; (ii) costs associated with contract terminations and branch closings; and (iii) compensatory charges. The acquisition-date estimated fair values of the assets acquired and liabilities assumed in the acquisition of Suffolk are summarized as follows: (in millions) Assets: Cash and cash equivalents $ 174.0 Securities 167.4 Loans 1,617.5 Goodwill 270.3 Core deposit intangible 28.1 Premises and equipment 40.4 Bank-owned life insurance 54.1 Other real estate owned 0.5 Other assets 28.9 Total assets $ 2,381.2 Liabilities: Deposits $ 1,852.4 Borrowings 15.1 Other liabilities 28.9 Total liabilities $ 1,896.4 Total purchase price $ 484.8 Net deferred tax liabilities totaling $0.3 million were established in connection with recording the related purchase accounting adjustments (other than goodwill). Fair value adjustments to assets acquired (other than loans, see Note 4) and liabilities assumed are generally amortized on a straight-line basis over periods consistent with the average life, useful life and/or contractual term of the related assets and liabilities. The preceding summaries include adjustments to record the acquired assets and assumed liabilities at their respective fair values based on management’s best estimate using the information available at the time of the respective acquisition. While there may be changes in the respective acquisition-date fair values of certain balance sheet amounts and other items, management does not expect that such changes, if any, will be material. Fair values of the major categories of assets acquired and liabilities assumed were determined as follows: Cash and Cash Equivalents The fair values of cash and cash equivalents approximate the respective carrying amounts because the instruments are payable on demand or have short-term maturities. Securities The fair values of securities acquired were based on quoted market prices. If a quoted market price for a certain security was not available, then a quoted price for a similar security in active markets was used to estimate fair value. Loans Loans acquired in connection with these acquisitions were recorded at fair value with no carryover of either LEAF’s or Suffolk’s previously established allowance for loan losses. Fair value of the loans was determined using market participant assumptions in estimating the amount and timing of both principal and interest cash flows expected to be collected as adjusted for an estimate of future credit losses and prepayments and then applying a market-based discount rate to those cash flow. The acquired loans were evaluated upon the respective acquisition dates and classified as either purchased performing or purchased credit impaired (“PCI”) (see Note 4). In the aggregate, loans totaling $57 million were deemed PCI and were recorded at a discount from the corresponding outstanding principal balance of $67 million. The remaining acquired loans were deemed purchased performing and had a fair value of $2.28 billion and an outstanding principal balance of $2.32 billion, resulting in a discount that will be accreted over the remaining lives of the loans. Included in the Consolidated Statements of Income for the nine months ended September 30, 2017 is approximately $44 million of interest income attributable to these acquisitions since the respective acquisition dates. Core Deposit Intangible The core deposit intangible represents the value of the relationships with deposit customers. The fair value was estimated based on a discounted cash flow methodology that gave appropriate consideration to expected customer attrition rates, net maintenance costs of the deposit base, the alternative cost of funds and the interest cost associated with customer deposits. The core deposit intangible will be amortized using an accelerated amortization method over a 6-year Deposits The fair values of acquired savings and transaction deposit accounts were assumed to approximate the respective carrying amounts as these accounts have no stated maturity and are payable on demand. Time deposits were valued based on the present value of the contractual cash flows over the remaining period to maturity using a market rate. Borrowings The fair values of Federal Home Loan Bank (“FHLB”) advances and other borrowings, including securitizations, represent contractual repayments discounted using interest rates currently available on borrowings with similar characteristics and remaining maturities. The following table presents selected unaudited pro forma financial information of the Company reflecting the acquisitions of Suffolk and LEAF assuming the acquisitions were completed as of the beginning of the respective periods: Nine Months Ended (in millions, except per common share data) 2017 2016 Selected Financial Results: Net interest income $ 835.9 $ 797.3 Provision for loan losses 18.5 28.9 Non-interest 275.5 275.5 Non-interest 720.6 707.1 Net income 258.0 227.7 Net income applicable to common shareholders 247.5 227.7 Basic and diluted earnings per common share $ 0.73 $ 0.69 The selected unaudited pro forma financial information is presented for illustrative purposes only and is not necessarily indicative of the financial results of the combined companies had the acquisitions actually been completed at the beginning of the periods presented, nor does it indicate future results for any other interim or full-year period. Merger-related expenses attributable to the acquisitions that were incurred by People’s United, Suffolk and LEAF during the nine months ended September 30, 2017 and 2016 are not reflected in the selected unaudited pro forma financial information. Pro forma basic and diluted earnings per common share (“EPS”) were calculated using People’s United’s actual weighted-average common shares outstanding for the periods presented, plus the incremental common shares issued, assuming the acquisitions occurred at the beginning of the periods presented. Recent acquisitions have been undertaken with the objective of expanding the Company’s business, both geographically and through product offerings, as well as realizing synergies and economies of scale by combining with the acquired entities. For these reasons, a market-based premium was paid for the acquired entities which, in turn, resulted in the recognition of goodwill, representing the excess of the respective purchase prices over the estimated fair value of the net assets acquired (see Note 7). All of People’s United’s tax deductible goodwill was created in transactions in which the Company purchased the assets of the target (as opposed to purchasing the issued and outstanding stock of the target). At September 30, 2017 and December 31, 2016, tax deductible goodwill totaled $73.2 million and $77.9 million, respectively.

Securities and Short-Term Inves

Securities and Short-Term Investments	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Securities and Short-Term Investments	NOTE 3. SECURITIES AND SHORT-TERM INVESTMENTS The amortized cost, gross unrealized gains and losses, and fair value of People’s United’s securities available for sale and securities held to maturity are as follows: As of September 30, 2017 (in millions) Amortized Gross Gross Fair Securities available for sale: Debt securities: U.S. Treasury and agency $ 760.9 $ 0.1 $ (19.1 ) $ 741.9 GSE (1) mortgage-backed securities 2,450.1 11.5 (15.0 ) 2,446.6 Total debt securities 3,211.0 11.6 (34.1 ) 3,188.5 Equity securities (3) 9.6 — (0.6 ) 9.0 Total securities available for sale $ 3,220.6 $ 11.6 $ (34.7 ) $ 3,197.5 Securities held to maturity: Debt securities: State and municipal $ 1,999.2 $ 60.7 $ (8.5 ) $ 2,051.4 GSE mortgage-backed securities 1,344.6 1.5 (6.5 ) 1,339.6 Corporate 42.3 0.8 — 43.1 Other 1.5 — — 1.5 Total securities held to maturity $ 3,387.6 $ 63.0 $ (15.0 ) $ 3,435.6 (1) Government sponsored enterprise (2) Collateralized mortgage obligations (3) During the quarter ended March 31, 2017, the Company exchanged its ownership interest in a non-marketable As of December 31, 2016 (in millions) Amortized Gross Gross Fair Securities available for sale: Debt securities: U.S. Treasury and agency $ 889.9 $ 0.3 $ (30.5 ) $ 859.7 GSE mortgage-backed securities 3,573.1 15.0 (38.1 ) 3,550.0 Total debt securities 4,463.0 15.3 (68.6 ) 4,409.7 Equity securities 0.2 — — 0.2 Total securities available for sale $ 4,463.2 $ 15.3 $ (68.6 ) $ 4,409.9 Securities held to maturity: Debt securities: State and municipal $ 1,499.1 $ 33.9 $ (23.5 ) $ 1,509.5 GSE mortgage-backed securities 500.8 — (3.2 ) 497.6 Corporate 4.0 — — 4.0 Other 1.5 — — 1.5 Total securities held to maturity $ 2,005.4 $ 33.9 $ (26.7 ) $ 2,012.6 Securities available for sale with a fair value of $2.92 billion and $1.83 billion at September 30, 2017 and December 31, 2016, respectively, were pledged as collateral for public deposits and for other purposes. The following table is a summary of the amortized cost and fair value of debt securities as of September 30, 2017, based on remaining period to contractual maturity. Information for GSE mortgage-backed securities and CMOs is based on the final contractual maturity dates without considering repayments and prepayments. Available for Sale Held to Maturity (in millions) Amortized Fair Amortized Fair U.S. Treasury and agency: Within 1 year $ 1.0 $ 1.0 $ — $ — After 1 but within 5 years 361.3 355.0 — — After 5 but within 10 years 398.6 385.9 — — Total 760.9 741.9 — — GSE mortgage-backed securities and CMOs: After 1 but within 5 years — — 69.4 69.4 After 5 but within 10 years 604.6 613.9 834.3 830.4 After 10 years 1,845.5 1,832.7 440.9 439.8 Total 2,450.1 2,446.6 1,344.6 1,339.6 State and municipal: Within 1 year — — 18.7 18.7 After 1 but within 5 years — — 114.1 117.4 After 5 but within 10 years — — 343.2 363.2 After 10 years — — 1,523.2 1,552.1 Total — — 1,999.2 2,051.4 Corporate: After 1 but within 5 years — — 5.0 5.0 After 5 but within 10 years — — 37.3 38.1 Total — — 42.3 43.1 Other: After 1 but within 5 years — — 1.5 1.5 Total — — 1.5 1.5 Total: Within 1 year 1.0 1.0 18.7 18.7 After 1 but within 5 years 361.3 355.0 190.0 193.3 After 5 but within 10 years 1,003.2 999.8 1,214.8 1,231.7 After 10 years 1,845.5 1,832.7 1,964.1 1,991.9 Total $ 3,211.0 $ 3,188.5 $ 3,387.6 $ 3,435.6 Management conducts a periodic review and evaluation of the securities portfolio to determine if the decline in fair value of any security is deemed to be other-than-temporary. Other-than-temporary impairment losses are recognized on debt securities when: (i) People’s United has an intention to sell the security; (ii) it is more likely than not that People’s United will be required to sell the security prior to recovery; or (iii) People’s United does not expect to recover the entire amortized cost basis of the security. Other-than-temporary impairment losses on debt securities are reflected in earnings as realized losses to the extent the impairment is related to credit losses of the issuer. The amount of the impairment related to other factors is recognized in other comprehensive income. Management has the ability and intent to hold the securities classified as held to maturity until they mature, at which time People’s United expects to receive full value for the securities. The following tables summarize those securities with unrealized losses, segregated by the length of time the securities have been in a continuous unrealized loss position at the respective dates. Certain unrealized losses totaled less than $0.1 million. Continuous Unrealized Loss Position Less Than 12 Months 12 Months Or Longer Total As of September 30, 2017 (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Securities available for sale: GSE mortgage-backed securities and CMOs $ 1,675.6 $ (12.1 ) $ 133.9 $ (2.9 ) $ 1,809.5 $ (15.0 ) U.S. Treasury and agency 206.6 (3.0 ) 530.1 (16.1 ) 736.7 (19.1 ) Equity securities 9.0 (0.6 ) — — 9.0 (0.6 ) Securities held to maturity: GSE mortgage-backed securities 1,029.5 (6.5 ) — — 1,029.5 (6.5 ) State and municipal 270.3 (1.7 ) 207.5 (6.8 ) 477.8 (8.5 ) Corporate 2.8 — — — 2.8 — Total $ 3,193.8 $ (23.9 ) $ 871.5 $ (25.8 ) $ 4,065.3 $ (49.7 ) Continuous Unrealized Loss Position Less Than 12 Months 12 Months Or Longer Total As of December 31, 2016 (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Securities available for sale: GSE mortgage-backed securities and CMOs $ 2,339.6 $ (26.6 ) $ 396.9 $ (11.5 ) $ 2,736.5 $ (38.1 ) U.S. Treasury and agency 828.3 (30.5 ) — — 828.3 (30.5 ) Securities held to maturity: GSE mortgage-backed securities 497.6 (3.2 ) — — 497.6 (3.2 ) State and municipal 581.7 (23.5 ) — — 581.7 (23.5 ) Total $ 4,247.2 $ (83.8 ) $ 396.9 $ (11.5 ) $ 4,644.1 $ (95.3 ) At September 30, 2017, approximately 27% of the 2,046 securities owned by the Company, consisting of 96 securities classified as available for sale and 453 securities classified as held to maturity, had gross unrealized losses totaling $34.7 million and $15.0 million, respectively. All of the GSE mortgage-backed securities and CMOs had AAA credit ratings and an average contractual maturity of 11 years. The state and municipal securities had an average credit rating of AA and an average maturity of 12 years. The cause of the gross unrealized losses with respect to all of these securities is directly related to changes in interest rates. At this time, management does not intend to sell such securities nor is it more likely than not, based upon available evidence, that management will be required to sell such securities prior to recovery. As such, management believes that all gross unrealized losses within the securities portfolio at September 30, 2017 are temporary impairments. No other-than-temporary impairment losses were recognized in the Consolidated Statements of Income for the three or nine months ended September 30, 2017 or 2016. Security transactions are recorded on the trade date. Realized gains and losses are determined using the specific identification method and reported in non-interest The Bank, as a member of the FHLB of Boston, is currently required to purchase and hold shares of capital stock in the FHLB of Boston (total cost of $139.5 million and $155.0 million at September 30, 2017 and December 31, 2016, respectively) in an amount equal to its membership base investment plus an activity based investment determined according to the Bank’s level of outstanding FHLB advances. As a result of prior acquisitions, the Bank acquired shares of capital stock in the FHLB of New York (total cost of $12.0 million and $11.3 million at September 30, 2017 and December 31, 2016, respectively). Based on the current capital adequacy and liquidity position of both the FHLB of Boston and the FHLB of New York, management believes there is no impairment in the Company’s investment at September 30, 2017 and the cost of the investment approximates fair value. The Bank, as a member of the Federal Reserve Bank system, is currently required to purchase and hold shares of capital stock in the Federal Reserve Bank of New York (the “FRB-NY”) FRB-NY, Included in short-term investments are interest-bearing deposits at the FRB-NY

Loans

Loans	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Loans	NOTE 4. LOANS For purposes of disclosures related to the credit quality of financing receivables and the allowance for loan losses, People’s United has identified two loan portfolio segments, Commercial and Retail, which are comprised of the following loan classes: • Commercial Portfolio • Retail Portfolio Loans acquired in connection with business combinations are referred to as ‘acquired’ loans as a result of the manner in which they are accounted for (see further discussion under ‘Acquired Loans’). All other loans are referred to as ‘originated’ loans. Accordingly, selected credit quality disclosures that follow are presented separately for the ‘originated’ loan portfolio and the ‘acquired’ loan portfolio. People’s United maintains several significant accounting policies with respect to loans, including: • Establishment of the allowance for loan losses (including the identification of ‘impaired’ loans and related impairment measurement considerations); • Income recognition (including the classification of a loan as ‘non-accrual’ • Recognition of loan charge-offs. The Company did not change its application of the accounting policies noted above or its methodology for determining the allowance for loan losses during the nine months ended September 30, 2017. The following table summarizes People’s United’s loans by loan portfolio segment and class: September 30, 2017 December 31, 2016 (in millions) Originated Acquired Total Originated Acquired Total Commercial: Commercial real estate $ 10,194.1 $ 986.4 $ 11,180.5 $ 10,012.6 $ 234.7 $ 10,247.3 Commercial and industrial 7,971.3 653.4 8,624.7 7,939.0 186.1 8,125.1 Equipment financing 3,039.1 666.5 3,705.6 3,020.9 11.6 3,032.5 Total Commercial Portfolio 21,204.5 2,306.3 23,510.8 20,972.5 432.4 21,404.9 Retail: Residential mortgage: Adjustable-rate 5,800.9 147.5 5,948.4 5,453.8 95.3 5,549.1 Fixed-rate 706.7 125.9 832.6 613.5 54.1 667.6 Total residential mortgage 6,507.6 273.4 6,781.0 6,067.3 149.4 6,216.7 Home equity and other consumer: Home equity 1,981.8 59.7 2,041.5 2,044.9 27.7 2,072.6 Other consumer 47.3 3.9 51.2 50.0 0.7 50.7 Total home equity and other consumer 2,029.1 63.6 2,092.7 2,094.9 28.4 2,123.3 Total Retail Portfolio 8,536.7 337.0 8,873.7 8,162.2 177.8 8,340.0 Total loans $ 29,741.2 $ 2,643.3 $ 32,384.5 $ 29,134.7 $ 610.2 $ 29,744.9 Loan origination fees and certain direct loan origination costs are deferred, and the net fee or cost is recognized in interest income as an adjustment of yield. Depending on the loan portfolio, amounts are amortized or accreted using the level yield method over either the actual life or the estimated average life of the loan. Net deferred loan costs, which are included in loans by respective class and accounted for as interest yield adjustments, totaled $73.1 million at September 30, 2017 and $69.9 million at December 31, 2016. The following tables present a summary, by loan portfolio segment, of activity in the allowance for loan losses for the three and nine months ended September 30, 2017 and 2016. With respect to the originated portfolio, an allocation of a portion of the allowance to one segment does not preclude its availability to absorb losses in another segment. Three months ended Commercial Retail September 30, 2017 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 198.3 $ 3.6 $ 201.9 $ 29.6 $ 0.1 $ 29.7 $ 231.6 Charge-offs (4.0 ) (1.0 ) (5.0 ) (1.8 ) — (1.8 ) (6.8 ) Recoveries 0.9 0.1 1.0 0.6 — 0.6 1.6 Net loan charge-offs (3.1 ) (0.9 ) (4.0 ) (1.2 ) — (1.2 ) (5.2 ) Provision for loan losses 4.3 1.3 5.6 1.3 0.1 1.4 7.0 Balance at end of period $ 199.5 $ 4.0 $ 203.5 $ 29.7 $ 0.2 $ 29.9 $ 233.4 Nine months ended Commercial Retail September 30, 2017 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 198.8 $ 6.1 $ 204.9 $ 24.2 $ 0.2 $ 24.4 $ 229.3 Charge-offs (12.0 ) (2.9 ) (14.9 ) (5.1 ) — (5.1 ) (20.0 ) Recoveries 3.8 0.1 3.9 1.7 — 1.7 5.6 Net loan charge-offs (8.2 ) (2.8 ) (11.0 ) (3.4 ) — (3.4 ) (14.4 ) Provision for loan losses 8.9 0.7 9.6 8.9 — 8.9 18.5 Balance at end of period $ 199.5 $ 4.0 $ 203.5 $ 29.7 $ 0.2 $ 29.9 $ 233.4 Three months ended Commercial Retail September 30, 2016 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 189.7 $ 7.2 $ 196.9 $ 23.3 $ 0.2 $ 23.5 $ 220.4 Charge-offs (2.7 ) (0.1 ) (2.8 ) (1.1 ) — (1.1 ) (3.9 ) Recoveries 0.9 — 0.9 0.5 — 0.5 1.4 Net loan charge-offs (1.8 ) (0.1 ) (1.9 ) (0.6 ) — (0.6 ) (2.5 ) Provision for loan losses 7.1 — 7.1 1.3 — 1.3 8.4 Balance at end of period $ 195.0 $ 7.1 $ 202.1 $ 24.0 $ 0.2 $ 24.2 $ 226.3 Nine months ended Commercial Retail September 30, 2016 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 181.8 $ 7.9 $ 189.7 $ 21.1 $ 0.2 $ 21.3 $ 211.0 Charge-offs (10.7 ) (0.4 ) (11.1 ) (6.6 ) — (6.6 ) (17.7 ) Recoveries 1.6 — 1.6 2.5 — 2.5 4.1 Net loan charge-offs (9.1 ) (0.4 ) (9.5 ) (4.1 ) — (4.1 ) (13.6 ) Provision for loan losses 22.3 (0.4 ) 21.9 7.0 — 7.0 28.9 Balance at end of period $ 195.0 $ 7.1 $ 202.1 $ 24.0 $ 0.2 $ 24.2 $ 226.3 The following is a summary, by loan portfolio segment and impairment methodology, of the allowance for loan losses and related portfolio balances: Originated Loans Originated Loans As of Individually Evaluated Collectively Evaluated September 30, 2017 for Impairment for Impairment Acquired Loans (1) Total (in millions) Portfolio Allowance Portfolio Allowance Portfolio Allowance Portfolio Allowance Commercial $ 172.5 $ 5.7 $ 21,032.0 $ 193.8 $ 2,306.3 $ 4.0 $ 23,510.8 $ 203.5 Retail 94.3 2.4 8,442.4 27.3 337.0 0.2 8,873.7 29.9 Total $ 266.8 $ 8.1 $ 29,474.4 $ 221.1 $ 2,643.3 $ 4.2 $ 32,384.5 $ 233.4 Originated Loans Originated Loans As of Individually Evaluated Collectively Evaluated December 31, 2016 for Impairment for Impairment Acquired Loans (1) Total (in millions) Portfolio Allowance Portfolio Allowance Portfolio Allowance Portfolio Allowance Commercial $ 161.8 $ 5.8 $ 20,810.7 $ 193.0 $ 432.4 $ 6.1 $ 21,404.9 $ 204.9 Retail 91.8 3.2 8,070.4 21.0 177.8 0.2 8,340.0 24.4 Total $ 253.6 $ 9.0 $ 28,881.1 $ 214.0 $ 610.2 $ 6.3 $ 29,744.9 $ 229.3 (1) Approximately $3.8 million of the allowance at September 30, 2017 relates to Commercial and Retail PCI loans totaling $406.5 million and $134.7 million, respectively. The remainder of the acquired portfolio represents purchased performing loans with an allowance of approximately $0.4 million at that date. The allowance at December 31, 2016 relates entirely to PCI loans (no acquired loans were purchased performing at that date). The recorded investments, by class of loan, in originated non-performing September 30, December 31, (in millions) 2017 2016 Commercial: Commercial real estate $ 36.7 $ 22.3 Commercial and industrial 34.9 41.5 Equipment financing 54.1 39.4 Total (1) 125.7 103.2 Retail: Residential mortgage 33.8 27.4 Home equity 14.8 17.4 Other consumer — — Total (2) 48.6 44.8 Total $ 174.3 $ 148.0 (1) Reported net of government guarantees totaling $4.0 million and $13.1 million at September 30, 2017 and December 31, 2016, respectively. These government guarantees relate, almost entirely, to guarantees provided by the Small Business Administration as well as selected other Federal agencies and represent the carrying value of the loans that are covered by such guarantees, the extent of which (i.e. full or partial) varies by loan. At September 30, 2017, the principal loan classes to which these government guarantees relate are commercial and industrial loans (95%) and commercial real estate loans (5%). (2) Includes $17.8 million and $9.8 million of loans in the process of foreclosure at September 30, 2017 and December 31, 2016, respectively. The preceding table excludes acquired loans that are (i) accounted for as PCI loans or (ii) covered by a Federal Deposit Insurance Corporation (“FDIC”) loss-share agreement (“LSA”) totaling $24.5 million and $24.7 million at September 30, 2017 and December 31, 2016, respectively. Such loans otherwise meet People’s United’s definition of a non-performing non-performing A loan is generally considered “non-performing” non-accrual non-accrual non-accrual All previously accrued but unpaid interest on non-accrual non-accrual non-accrual A loan is considered impaired when, based on current information and events, it is probable that the Company will be unable to collect all amounts due in accordance with the original contractual terms of the loan agreement, including scheduled principal and interest payments. Impaired loans also include certain loans whose terms have been modified in such a way that they are considered troubled debt restructurings (“TDRs”). Loans are considered TDRs if the borrower is experiencing financial difficulty and is afforded a concession by People’s United, such as, but not limited to: (i) payment deferral; (ii) a reduction of the stated interest rate for the remaining contractual life of the loan; (iii) an extension of the loan’s original contractual term at a stated interest rate lower than the current market rate for a new loan with similar risk; (iv) capitalization of interest; or (v) forgiveness of principal or interest. TDRs may either be accruing or placed on non-accrual non-performing non-accrual non-performing Impairment is evaluated on a collective basis for smaller-balance loans with similar credit risk and on an individual loan basis for other loans. If a loan is deemed to be impaired, a specific valuation allowance is allocated, if necessary, so that the loan is reported (net of the allowance) at the present value of expected future cash flows discounted at the loan’s original effective interest rate or at the fair value of the collateral less cost to sell if repayment is expected solely from the collateral. Interest payments on impaired non-accrual People’s United’s recorded investment in loans classified as TDRs totaled $194.4 million and $189.9 million at September 30, 2017 and December 31, 2016, respectively. The related allowance for loan losses was $4.6 million at September 30, 2017 and $4.2 million at December 31, 2016. Interest income recognized on TDRs totaled $1.4 million and $1.2 million for the three months ended September 30, 2017 and 2016, respectively, and $3.7 million and $3.3 million for the nine months ended September 30, 2017 and 2016, respectively. Fundings under commitments to lend additional amounts to borrowers with loans classified as TDRs were immaterial for the three and nine months ended September 30, 2017 and 2016. Loans that were modified and classified as TDRs during the three and nine months ended September 30, 2017 and 2016 principally involve reduced payment and/or payment deferral, extension of term (generally no more than two years for commercial loans and five years for retail loans) and/or a temporary reduction of interest rate (generally less than 200 basis points). The following tables summarize, by class of loan, the recorded investments in loans modified as TDRs during the three and nine months ended September 30, 2017 and 2016. For purposes of this disclosure, recorded investments represent amounts immediately prior to and subsequent to the restructuring. Three Months Ended September 30, 2017 Pre-Modification Post-Modification Outstanding Outstanding Number Recorded Recorded (dollars in millions) of Contracts Investment Investment Commercial: Commercial real estate (1) 1 $ 0.1 $ 0.1 Commercial and industrial (2) 9 11.6 11.6 Equipment financing (3) 13 8.1 8.1 Total 23 19.8 19.8 Retail: Residential mortgage (4) 17 3.8 3.8 Home equity (5) 19 1.5 1.5 Other consumer — — — Total 36 5.3 5.3 Total 59 $ 25.1 $ 25.1 (1) Represents the following concession: extension of term (1 contract; recorded investment of $0.1 million). (2) Represents the following concessions: extension of term (9 contracts; recorded investment of $11.6 million). (3) Represents the following concessions: reduced payment and/or payment deferral (12 contracts; recorded investment of $8.0 million); or a combination of concessions (1 contract; recorded investment of $0.1 million). (4) Represents the following concessions: loans restructured through bankruptcy (9 contracts; recorded investment of $1.7 million); reduced payment and/or payment deferral (5 contract; recorded investment of $1.7 million); or a combination of concessions (3 contracts; recorded investment of $0.4 million). (5) Represents the following concessions: loans restructured through bankruptcy (10 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (4 contracts; recorded investment of $0.3 million); or a combination of concessions (5 contracts; recorded investment of $0.2 million). Nine Months Ended September 30, 2017 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 8 $ 5.3 $ 5.3 Commercial and industrial (2) 28 39.6 39.6 Equipment financing (3) 54 25.1 25.1 Total 90 70.0 70.0 Retail: Residential mortgage (4) 45 10.8 10.8 Home equity (5) 65 4.5 4.5 Other consumer — — — Total 110 15.3 15.3 Total 200 $ 85.3 $ 85.3 (1) Represents the following concessions: extension of term (5 contracts; recorded investment of $1.4 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $2.2 million); or a temporary rate reduction (1 contract; recorded investment of $1.7 million). (2) Represents the following concessions: extension of term (25 contracts; recorded investment of $29.9 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $9.4 million); or a combination of concessions (1 contract; recorded investment of $0.3 million). (3) Represents the following concessions: reduced payment and/or payment deferral (28 contracts; recorded investment of $17.4 million); or a combination of concessions (26 contracts; recorded investment of $7.7 million). (4) Represents the following concessions: loans restructured through bankruptcy (28 contracts; recorded investment of $4.2 million); reduced payment and/or payment deferral (10 contracts; recorded investment of $3.4 million); or a combination of concessions (7 contracts; recorded investment of $3.2 million). (5) Represents the following concessions: loans restructured through bankruptcy (41 contracts; recorded investment of $2.6 million); reduced payment and/or payment deferral (10 contracts; recorded investment of $0.8 million); or a combination of concessions (14 contracts; recorded investment of $1.1 million). Three Months Ended September 30, 2016 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 7 $ 22.1 $ 22.1 Commercial and industrial (2) 11 4.5 4.5 Equipment financing (3) 22 10.4 10.4 Total 40 37.0 37.0 Retail: Residential mortgage (4) 9 2.9 2.9 Home equity (5) 17 1.2 1.2 Other consumer — — — Total 26 4.1 4.1 Total 66 $ 41.1 $ 41.1 (1) Represents the following concessions: extension of term (5 contracts; recorded investment of $3.3 million); reduced payment and/or payment deferral (1 contract; recorded investment of $1.7 million); or a combination of concessions (1 contract; recorded investment of $17.1 million). (2) Represents the following concessions: extension of term (9 contracts; recorded investment of $4.1 million); or reduced payment and/or payment deferral (2 contracts; recorded investment of $0.4 million). (3) Represents the following concessions: extension of term (6 contracts; recorded investment of $4.3 million); reduced payment and/or payment deferral (13 contracts; recorded investment of $4.7 million); or a combination of concessions (3 contracts; recorded investment of $1.4 million). (4) Represents the following concessions: loans restructured through bankruptcy (6 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (1 contract; recorded investment of $0.7 million); or a combination of concessions (2 contracts; recorded investment of $1.2 million). (5) Represents the following concessions: loans restructured through bankruptcy (11 contracts; recorded investment of $0.5 million); reduced payment and/or payment deferral (1 contract; recorded investment of $0.2 million); or a combination of concessions (5 contracts; recorded investment of $0.5 million). Nine Months Ended September 30, 2016 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 12 $ 25.9 $ 25.9 Commercial and industrial (2) 36 22.9 22.9 Equipment financing (3) 49 21.7 21.7 Total 97 70.5 70.5 Retail: Residential mortgage (4) 47 13.1 13.1 Home equity (5) 50 3.8 3.8 Other consumer — — — Total 97 16.9 16.9 Total 194 $ 87.4 $ 87.4 (1) Represents the following concessions: extension of term (8 contracts; recorded investment of $6.2 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $2.6 million); or a combination of concessions (2 contracts; recorded investment of $17.1 million). (2) Represents the following concessions: extension of term (23 contracts; recorded investment of $12.3 million); reduced payment and/or payment deferral (9 contracts; recorded investment of $9.8 million); or a combination of concessions (4 contracts; recorded investment of $0.8 million). (3) Represents the following concessions: extension of term (17 contracts; recorded investment of $6.3 million); reduced payment and/or payment deferral (25 contracts; recorded investment of $12.5 million); or a combination of concessions (7 contracts; recorded investment of $2.9 million). (4) Represents the following concessions: loans restructured through bankruptcy (18 contracts; recorded investment of $3.2 million); reduced payment and/or payment deferral (11 contracts; recorded investment of $5.5 million); or a combination of concessions (18 contracts; recorded investment of $4.4 million). (5) Represents the following concessions: loans restructured through bankruptcy (31 contracts; recorded investment of $2.1 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $0.3 million); or a combination of concessions (17 contracts; recorded investment of $1.4 million). The following is a summary, by class of loan, of information related to TDRs completed within the previous 12 months that subsequently defaulted during the three and nine months ended September 30, 2017 and 2016. For purposes of this disclosure, the previous 12 months is measured from October 1 of the respective prior year and a default represents a previously-modified loan that became past due 30 days or more during the three or nine months ended September 30, 2017 or 2016. Three Months Ended September 30, 2017 2016 (dollars in millions) Number Recorded Number Recorded Commercial: Commercial real estate — $ — — $ — Commercial and industrial 1 0.1 — — Equipment financing 8 4.2 14 2.2 Total 9 4.3 14 2.2 Retail: Residential mortgage 2 0.9 3 0.6 Home equity 5 0.8 — — Other consumer — — — — Total 7 1.7 3 0.6 Total 16 $ 6.0 17 $ 2.8 Nine Months Ended September 30, 2017 2016 (dollars in millions) Number Recorded Number Recorded Commercial: Commercial real estate — $ — 2 $ 0.9 Commercial and industrial 4 1.5 5 0.6 Equipment financing 15 6.8 20 5.9 Total 19 8.3 27 7.4 Retail: Residential mortgage 9 2.7 10 1.9 Home equity 11 1.3 7 0.5 Other consumer — — — — Total 20 4.0 17 2.4 Total 39 $ 12.3 44 $ 9.8 People’s United’s impaired loans consist of certain loans that have been placed on non-accrual individually-evaluated As of September 30, 2017 As of December 31, 2016 (in millions) Unpaid Recorded Related Unpaid Recorded Related Without a related allowance for loan losses: Commercial: Commercial real estate $ 50.7 $ 46.1 $ — $ 41.4 $ 40.0 $ — Commercial and industrial 39.3 36.7 — 50.7 45.7 — Equipment financing 42.8 39.1 — 38.2 35.3 — Retail: Residential mortgage 66.8 60.0 — 63.6 58.0 — Home equity 23.5 20.0 — 22.4 18.7 — Other consumer — — — — — — Total $ 223.1 $ 201.9 $ — $ 216.3 $ 197.7 $ — With a related allowance for loan losses: Commercial: Commercial real estate $ 13.5 $ 12.8 $ 1.2 $ 12.2 $ 11.4 $ 0.6 Commercial and industrial 25.2 24.6 3.0 25.9 25.0 4.7 Equipment financing 14.1 13.2 1.5 5.0 4.4 0.5 Retail: Residential mortgage 12.4 12.4 1.7 13.1 13.1 2.3 Home equity 1.9 1.9 0.7 2.1 2.0 0.9 Other consumer — — — — — — Total $ 67.1 $ 64.9 $ 8.1 $ 58.3 $ 55.9 $ 9.0 Total impaired loans: Commercial: Commercial real estate $ 64.2 $ 58.9 $ 1.2 $ 53.6 $ 51.4 $ 0.6 Commercial and industrial 64.5 61.3 3.0 76.6 70.7 4.7 Equipment financing 56.9 52.3 1.5 43.2 39.7 0.5 Total 185.6 172.5 5.7 173.4 161.8 5.8 Retail: Residential mortgage 79.2 72.4 1.7 76.7 71.1 2.3 Home equity 25.4 21.9 0.7 24.5 20.7 0.9 Other consumer — — — — — — Total 104.6 94.3 2.4 101.2 91.8 3.2 Total $ 290.2 $ 266.8 $ 8.1 $ 274.6 $ 253.6 $ 9.0 The following tables summarize, by class of loan, the average recorded investment and interest income recognized on impaired loans for the periods indicated. The average recorded investment amounts are based on month-end Three Months Ended September 30, 2017 2016 (in millions) Average Interest Average Interest Commercial: Commercial real estate $ 61.8 $ 0.3 $ 54.1 $ 0.4 Commercial and industrial 59.7 0.7 60.5 0.3 Equipment financing 46.5 0.2 38.2 0.1 Total 168.0 1.2 152.8 0.8 Retail: Residential mortgage 72.4 0.4 71.7 0.4 Home equity 21.8 0.1 21.3 0.1 Other consumer — — — — Total 94.2 0.5 93.0 0.5 Total $ 262.2 $ 1.7 $ 245.8 $ 1.3 Nine Months Ended September 30, 2017 2016 (in millions) Average Interest Average Interest Commercial: Commercial real estate $ 56.9 $ 0.9 $ 58.6 $ 1.1 Commercial and industrial 66.1 1.6 61.9 1.2 Equipment financing 43.0 0.4 35.9 0.2 Total 166.0 2.9 156.4 2.5 Retail: Residential mortgage 71.9 1.3 72.1 1.2 Home equity 21.1 0.3 21.9 0.2 Other consumer — — — — Total 93.0 1.6 94.0 1.4 Total $ 259.0 $ 4.5 $ 250.4 $ 3.9 The following tables summarize, by class of loan, aging information for originated loans: Past Due As of September 30, 2017 (in millions) Current 30-89 90 Days Total Total Commercial: Commercial real estate $ 10,158.6 $ 20.3 $ 15.2 $ 35.5 $ 10,194.1 Commercial and industrial 7,943.2 10.1 18.0 28.1 7,971.3 Equipment financing 2,942.7 88.4 8.0 96.4 3,039.1 Total 21,044.5 118.8 41.2 160.0 21,204.5 Retail: Residential mortgage 6,455.4 31.8 20.4 52.2 6,507.6 Home equity 1,968.5 7.0 6.3 13.3 1,981.8 Other consumer 46.5 0.8 — 0.8 47.3 Total 8,470.4 39.6 26.7 66.3 8,536.7 Total originated loans $ 29,514.9 $ 158.4 $ 67.9 $ 226.3 $ 29,741.2 Included in the “Current” and “30-89 non-performing non-accrual Past Due As of December 31, 2016 (in millions) Current 30-89 90 Days Total Total Commercial: Commercial real estate $ 9,989.9 $ 10.9 $ 11.8 $ 22.7 $ 10,012.6 Commercial and industrial 7,899.2 10.0 29.8 39.8 7,939.0 Equipment financing 2,941.5 68.4 11.0 79.4 3,020.9 Total 20,830.6 89.3 52.6 141.9 20,972.5 Retail: Residential mortgage 6,027.5 22.0 17.8 39.8 6,067.3 Home equity 2,030.3 5.2 9.4 14.6 2,044.9 Other consumer 49.7 0.3 — 0.3 50.0 Total 8,107.5 27.5 27.2 54.7 8,162.2 Total originated loans $ 28,938.1 $ 116.8 $ 79.8 $ 196.6 $ 29,134.7 Included in the “Current” and “30-89 non-performing non-accrual Commercial Credit Quality Indicators The Company utilizes an internal loan risk rating system as a means of monitoring portfolio credit quality and identifying both problem and potential problem loans. Under the Company’s risk rating system, loans not meeting the criteria for problem and potential problem loans as specified below are considered to be “Pass”-rated loans. Problem and potential problem loans are classified as either “Special Mention,” “Substandard” or “Doubtful.” Loans that do not currently expose the Company to sufficient enough risk of loss to warrant classification as either Substandard or Doubtful, but possess weaknesses that deserve management’s close attention, are classified as Special Mention. Substandard loans represent those credits characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. Loans classified as Doubtful possess all the weaknesses inherent in those classified Substandard with the added characteristic that collection or liquidation in full, on the basis of existing facts, conditions and values, is highly questionable and/or improbable. Risk ratings on commercial loans are subject to ongoing monitoring by lending and credit personnel with such ratings updated annually or more frequently, if warranted. The Company’s internal Loan Review function is responsible for independently evaluating the appropriateness of those credit risk ratings in connection with its cyclical reviews, the approach to which is risk-based and determined by reference to underlying portfolio credit quality and the results of prior reviews. Differences in risk ratings noted in conjunction with such periodic portfolio loan reviews, if any, are reported to management each month. Retail Credit Quality Indicators Pools of smaller-balance, homogeneous loans with similar risk and loss characteristics are also assessed for probable losses. These loan pools include residential mortgage, home equity and other consumer loans that are not assigned individual loan risk ratings. Rather, the assessment of these portfolios is based upon a consideration of recent historical loss experience, broader portfolio indicators, including trends in delinquencies, non-performing The portfolio-specific risk characteristics considered include: (i) collateral values/loan-to-value non-stated non-owner For example, to the extent LTV ratios exceed 70% (reflecting a weaker collateral position for the Company) or borrower FICO scores are less than 680 (reflecting weaker financial standing and/or credit history of the customer), the loans are considered to have an increased level of inherent loss. As a result, a loan with a combination of these characteristics would generally be classified as “High” risk. Conversely, as LTV ratios decline (reflecting a stronger collateral position for the Company) or borrower FICO scores exceed 680 (reflecting stronger financial standing and/or credit history of the customer), the loans are considered to have a decreased level of inherent loss. A loan with a combination of these characteristics would generally be classified as “Low” risk. This analysis also considers (i) the extent of underwriting that occurred at the time of origination (direct income verification provides further support for credit decisions) and (ii) the property’s intended use (owner-occupied properties are less likely to default compared to ‘investment-type’ non-owner LTV ratios and FICO scores are determined at origination and updated periodically throughout the life of the loan. LTV ratios are updated for loans 90 days past due and FICO scores are updated for the entire portfolio quarterly. The portfolio stratification (“High”, “Moderate” and “Low” risk) and identification of the corresponding credit quality indicators also occurs quarterly. Commercial and Retail loans are also evaluated to determine whether they are impaired loans. Such loans are included in the tabular disclosures of credit quality indicators that follow. Acquired Loan Credit Quality Indicators Upon acquiring a loan portfolio, the Company’s internal Loan Review function undertakes the process of assigning risk ratings to all commercial loans in accordance with the Company’s established policy, which may differ in certain respects from the risk rating policy of the predecessor company. The length of time necessary to complete this process varies based on the size of the acquired portfolio, the quality of the documentation maintained in the underlying loan files and the extent to which the predecessor company followed a risk rating approach comparable to People’s United’s. As a result, while acquired loans are risk rated, there are occasions when such ratings may be deemed “preliminary” until the Company’s re-rating Acquired loans are initially recorded at fair value, determined based upon an estimate of the amount and timing of both principal and interest cash flows expected to be collected and discounted using a market interest rate. For purchased performing loans, the required allowance for loan losses is determined in a manner similar to that for originated loans with a provision for loan losses only recorded when the required allowance for loan losses exceeds any remaining purchase discount at the loan level. For PCI loans, the difference between contractually required principal and interest payments at the acquisition date and the undiscounted cash flows expected to be collected at the acquisition date is referred to as the “nonaccretable difference”, which includes an estimate of future credit losses expected to be incurred over the life of the loans in each pool. A decrease in the expected cash flows in subsequent periods requires the establishment of an allowance for loan losses at that time. At September 30, 2017 and December 31, 2016, the allowance for loan losses on acquired loans was $4.2 million and $6.3 million, respectively. The following is a summary, by class of loan, of credit quality indicators: As of September 30, 2017 (in millions) Commercial Commercial Equipment Total Commercial: Originated loans: Pass $ 9,926.2 $ 7,588.1 $ 2,619.7 $ 20,134.0 Special mention 129.1 122.8 101.8 353.7 Substandard 137.9 259.6 317.6 715.1 Doubtful 0.9 0.8 — 1.7 Total originated loans 10,194.1 7,971.3 3,039.1 21,204.5 Acquired loans: Pass 940.9 562.2 666.5 2,169.6 Special mention 6.2 42.4 — 48.6 Substandard 38.6 48.8 — 87.4 Doubtful 0.7 — — 0.7 Total acquired loans 986.4 653.4 666.5 2,306.3 Total $ 11,180.5 $ 8,624.7 $ 3,705.6 $ 23,510.8 As of September 30, 2017 (in millions) Residential Home Other Total Retail: Originated loans: Low risk $ 3,259.8 $ 928.2 $ 27.2 $ 4,215.2 Moderate risk 2,715.9 652.2 8.0 3,376.1 High risk 531.9 401.4 12.1 945.4 Total originated loans 6,507.6 1,981.8 47.3 8,536.7 Acquired loans: Low risk 154.9 — — 154.9 Moderate risk 60.2 — — 60.2 High risk 58.3 59.7 3.9 121.9 Total acquired loans 273.4 59.7 3.9 337.0 Total $ 6,781.0 $ 2,041.5 $ 51.2 $ 8,873.7 As of December 31, 2016 (in millions) Commercial Commercial Equipment Total Commercial: Originated loans: Pass $ 9,817.2 $ 7,580.6 $ 2,617.9 $ 20,015.7 Special mention 107.3 121.9 98.8 328.0 Substandard 87.1 233.3 304.2 624.6 Doubtful 1.0 3.2 — 4.2 Total originated loans 10,012.6 7,939.0 3,020.9 20,972.5 Acquired loans: Pass 182.9 155.5 1.0 339.4 Special mention 13.5 3.6 8.6 25.7 Substandard 37.6 27.0 2.0 66.6 Doubtful 0.7 — — 0.7 Total acquired loans 234.7 186.1 11.6 432.4 Total $ 10,247.3 $ 8,125.1 $ 3,032.5 $ 21,404.9 Residential Home Other As of December 31, 2016 (in millions) Mortgage Equity Consumer Total Retail: Originated loans: Low risk $ 3,016.4 $ 950.9 $ 31.1 $ 3,998.4 Moderate risk 2,538.9 663.9 7.2 3,210.0 High risk 512.0 430.1 11.7 953.8 Total originated loans 6,067.3 2,044.9 50.0 8,162.2 Acquired loans: Low risk 75.7 — — 75.7 Moderate risk 27.5 — — 27.5 High risk 46.2 27.7 0.7 74.6 Total acquired loans 149.4 27.7 0.7 177.8 Total $ 6,216.7 $ 2,072.6 $ 50.7 $ 8,340.0 A cquired Loans Loans acquired in a business combination are initially recorded at fair value with no carryover of an acquired entity’s previously established allowance for loan losses. Fair value of the loans is determined using market participant assumptions in estimating the amount and timing of both principal and interest cash flows expected to be collected, as adjusted for an estimate of future credit losses and prepayments, and then applying a market-based discount rate to those cash flows. Acquired loans are evaluated upon acquisition and classified as either purchased performing or PCI. For purchased performing loans, any premium or discount, representing the difference between the fair value and the outstanding principal balance of the loans, is recognized (using the level yield method) as an adjustment to interest income over the remaining period to contractual maturity or until the loan is repaid in full or sold. Subsequent to the acquisition date, the method utilized to estimate the required allowance for loan losses for these loans is similar to that for originated loans. However, a provision for loan losses is only recorded when the required allowance for loan losses exceeds any remaining purchase discount at the loan level. PCI loans represent those acquired loans with specific evidence of deterioration in credit quality since origination and for which it is probable, at acquisition,

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	NOTE 5. STOCKHOLDERS’ EQUITY Preferred Stock People’s United is authorized to issue (i) 50.0 million shares of preferred stock, par value of $0.01 per share, of which 10.0 million shares were outstanding at both September 30, 2017 and December 31, 2016, and (ii) 1.95 billion shares of common stock, par value of $0.01 per share, of which 433.6 million shares and 405.0 million shares were issued at September 30, 2017 and December 31, 2016, respectively. Treasury Stock Treasury stock includes (i) common stock repurchased by People’s United, either directly or through agents, in the open market at prices and terms satisfactory to management in connection with stock repurchases authorized by its Board of Directors (86.4 million shares at both September 30, 2017 and December 31, 2016) and (ii) common stock purchased in the open market by a trustee with funds provided by People’s United and originally intended for awards under the People’s United Financial, Inc. 2007 Recognition and Retention Plan (the “RRP”) (2.6 million and 2.7 million shares at September 30, 2017 and December 31, 2016, respectively). Following shareholder approval of the People’s United Financial, Inc. 2014 Long-Term Incentive Plan in 2014, no new awards may be granted under the RRP. Comprehensive Income Comprehensive income represents the sum of net income and items of “other comprehensive income or loss,” including (on an after-tax The following is a summary of the changes in the components of accumulated other comprehensive loss (“AOCL”), which are included in People’s United’s stockholders’ equity on an after-tax (in millions) Pension Net Unrealized Net Unrealized Net Unrealized Total Balance at December 31, 2016 $ (145.6 ) $ (32.3 ) $ (17.4 ) $ 0.3 $ (195.0 ) Other comprehensive income before reclassifications — 11.1 — 0.3 11.4 Amounts reclassified from AOCL (1) 2.8 9.9 1.6 (0.4 ) 13.9 Current period other comprehensive income 2.8 21.0 1.6 (0.1 ) 25.3 Balance at September 30, 2017 $ (142.8 ) $ (11.3 ) $ (15.8 ) $ 0.2 $ (169.7 ) (in millions) Pension Net Unrealized Net Unrealized Net Unrealized Total Balance at December 31, 2015 $ (140.0 ) $ (17.7 ) $ (19.5 ) $ 0.0 $ (177.2 ) Other comprehensive income (loss) before reclassifications — 52.4 — (0.1 ) 52.3 Amounts reclassified from AOCL (1) 2.8 (0.1 ) 1.5 0.3 4.5 Current period other comprehensive income 2.8 52.3 1.5 0.2 56.8 Balance at September 30, 2016 $ (137.2 ) $ 34.6 $ (18.0 ) $ 0.2 $ (120.4 ) (1) See the following table for details about these reclassifications. The following is a summary of the amounts reclassified from AOCL: Amounts Reclassified from AOCL Three Months Ended Nine Months Ended Affected Line Item in the Statement Where Net Income is Presented (in millions) 2017 2016 2017 2016 Details about components of AOCL: Amortization of pension and other postretirement plans items: Net actuarial loss $ (1.7 ) $ (1.7 ) $ (5.1 ) $ (4.8 ) (1) Prior service credit 0.2 0.2 0.6 0.6 (1) (1.5 ) (1.5 ) (4.5 ) (4.2 ) Income before income tax expense 0.6 0.6 1.7 1.4 Income tax expense (0.9 ) (0.9 ) (2.8 ) (2.8 ) Net income Reclassification adjustment for net realized gains (losses) on securities available for sale — — (15.6 ) 0.1 Income before income tax expense (2) — — 5.7 — Income tax expense — — (9.9 ) 0.1 Net income Amortization of unrealized losses on securities transferred to held to held to maturity (0.9 ) (0.9 ) (2.6 ) (2.4 ) Income before income tax expense (3) 0.3 0.4 1.0 0.9 Income tax expense (0.6 ) (0.5 ) (1.6 ) (1.5 ) Net income Amortization of unrealized gains and losses on cash flow hedges: Interest rate swaps 0.3 (0.1 ) 0.6 (0.6 ) (4) Interest rate locks 0.1 0.1 0.1 0.1 (4) 0.4 — 0.7 (0.5 ) Income before income tax expense (0.2 ) — (0.3 ) 0.2 Income tax expense 0.2 — 0.4 (0.3 ) Net income Total reclassifications for the period $ (1.3 ) $ (1.4 ) $ (13.9 ) $ (4.5 ) (1) Included in the computation of net periodic benefit income (expense) reflected in compensation and benefits expense (see Note 8 for additional details). (2) Included in other non-interest (3) Included in interest and dividend income - securities. (4) Included in interest expense - notes and debentures.

Earnings Per Common Share

Earnings Per Common Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	NOTE 6. EARNINGS PER COMMON SHARE The following is an analysis of People’s United’s basic and diluted EPS, reflecting the application of the two-class Three Months Ended Nine Months Ended September 30, September 30, (in millions, except per common share data) 2017 2016 2017 2016 Net income available to common shareholders $ 87.3 $ 73.7 $ 220.4 $ 205.1 Dividends paid on and undistributed earnings (0.1 ) (0.2 ) (0.4 ) (0.6 ) Earnings attributable to common shareholders $ 87.2 $ 73.5 $ 220.0 $ 204.5 Weighted average common shares outstanding 336.9 302.9 327.6 302.4 Effect of dilutive equity-based awards 1.9 0.4 2.0 0.4 Weighted average common and common-equivalent 338.8 303.3 329.6 302.8 Basic EPS $ 0.26 $ 0.24 $ 0.67 $ 0.68 Diluted EPS $ 0.26 $ 0.24 $ 0.67 $ 0.68 Unvested share-based payment awards, which include the right to receive non-forfeitable two-class two-class All unallocated Employee Stock Ownership Plan (“ESOP”) common shares and all common shares accounted for as treasury shares have been excluded from the calculation of basic and diluted EPS. Anti-dilutive equity-based awards totaling 10.2 million shares and 10.1 million shares for the three and nine months ended September 30, 2017, respectively, and 18.2 million shares for both the three and nine months ended September 30, 2016, have been excluded from the calculation of diluted EPS.

Goodwill and Other Acquisition-

Goodwill and Other Acquisition-Related Intangible Assets	9 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Acquisition-Related Intangible Assets	NOTE 7. GOODWILL AND OTHER ACQUISITION-RELATED INTANGIBLE ASSETS Changes in the carrying amount of People’s United’s goodwill are summarized as follows for the nine months ended September 30, 2017 and 2016: Operating Segment (in millions) Commercial Retail Wealth Total Balance at December 31, 2016 $ 1,222.1 $ 679.6 $ 91.0 $ 1,992.7 Acquisition of: Suffolk 229.8 40.5 — 270.3 LEAF 148.4 — — 148.4 Balance at September 30, 2017 $ 1,600.3 $ 720.1 $ 91.0 $ 2,411.4 Operating Segment (in millions) Commercial Retail Wealth Total Balance at December 31, 2015 $ 1,222.8 $ 681.9 $ 54.0 $ 1,958.7 Acquisition of Eagle Insurance Group, LLC — — 1.4 1.4 Adjustments (0.7 ) (2.3 ) (0.1 ) (3.1 ) Balance at September 30, 2016 $ 1,222.1 $ 679.6 $ 55.3 $ 1,957.0 People’s United’s other acquisition-related intangible assets totaled $156.5 million and $149.4 million at September 30, 2017 and December 31, 2016, respectively. At September 30, 2017, the carrying amounts of other acquisition-related intangible assets were as follows: trade name ($68.1 million); core deposit intangible ($27.9 million); client relationship intangible ($22.5 million); trust relationship intangible ($14.9 million); insurance relationship intangible ($5.4 million); favorable lease agreement ($0.6 million); non-compete Amortization expense of other acquisition-related intangible assets totaled $7.9 million and $5.8 million for the three months ended September 30, 2017 and 2016, respectively, and $22.1 million and $17.4 million for the nine months ended September 30, 2017 and 2016, respectively. Scheduled amortization expense attributable to other acquisition-related intangible assets for the full-year of 2017 and each of the next five years is as follows: $30.0 million in 2017; $19.9 million in 2018; $18.4 million in 2019; $16.8 million in 2020; $15.0 million in 2021; and $13.5 million in 2022. There were no impairment losses relating to goodwill or other acquisition-related

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	NOTE 8. EMPLOYEE BENEFIT 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 a qualified defined benefit pension plan that covers former Chittenden employees who meet certain eligibility requirements (the “Chittenden Qualified Plan”). Effective December 31, 2005, accrued benefits were frozen based on participants’ then-current service and pay levels. Interest continues to be credited on undistributed balances at a crediting rate specified by the Chittenden Qualified Plan. During April 2010, participants who were in payment status as of April 1, 2010, or whose accrued benefit as of that date was scheduled to be paid in the form of an annuity commencing May 1, 2010 based upon elections made by April 15, 2010, were transferred into the People’s Qualified Plan. 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 “Supplemental Plans”) and (ii) an unfunded plan that provides retirees with optional medical, dental and life insurance benefits (the “Other 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. Components of net periodic benefit (income) expense and other amounts recognized in other comprehensive income for the People’s Qualified Plan, the Chittenden Qualified Plan and the Supplemental Plans (together the “Pension Plans”) and the Other Postretirement Plan are as follows: Other Pension Plans Postretirement Plan Three months ended September 30 (in millions) 2017 2016 2017 2016 Net periodic benefit (income) expense: Service cost $ — $ — $ 0.1 $ — Interest cost 4.9 4.7 0.1 0.2 Expected return on plan assets (9.6 ) (8.7 ) — — Recognized net actuarial loss 1.6 1.6 0.1 0.1 Recognized prior service credit (0.2 ) (0.2 ) — — Settlements 1.1 0.3 — — Net periodic benefit (income) expense $ (2.2 ) $ (2.3 ) $ 0.3 $ 0.3 Other Pension Plans Postretirement Plan Nine months ended September 30 (in millions) 2017 2016 2017 2016 Net periodic benefit (income) expense: Service cost $ — $ — $ 0.2 $ 0.2 Interest cost 14.3 14.1 0.4 0.5 Expected return on plan assets (28.3 ) (25.9 ) — — Recognized net actuarial loss 4.9 4.6 0.2 0.2 Recognized prior service credit (0.6 ) (0.6 ) — — Settlements 2.6 0.9 — — Net periodic benefit (income) expense (7.1 ) (6.9 ) 0.8 0.9 Other changes in plan assets and benefit obligations recognized in other comprehensive income: Net actuarial loss (4.9 ) (4.6 ) (0.2 ) (0.2 ) Prior service credit 0.6 0.6 — — Total pre-tax (4.3 ) (4.0 ) (0.2 ) (0.2 ) Total recognized in net periodic benefit $ (11.4 ) $ (10.9 ) $ 0.6 $ 0.7 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 nine months ended September 30, 2017, totaled $3.6 million. At September 30, 2017, the loan balance totaled $184.9 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 3,745,864 shares of People’s United common stock have been allocated or committed to be released to participants’ accounts. At September 30, 2017, 6,707,711 shares of People’s United common stock, with a fair value of $121.7 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 paid-in

Legal Proceedings

Legal Proceedings	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	NOTE 9. LEGAL PROCEEDINGS In the normal course of business, People’s United is subject to various legal proceedings. Management has discussed with legal counsel the nature of these legal proceedings and, based on the advice of counsel and the information currently available, believes that the eventual outcome of these legal proceedings will not have a material adverse effect on its financial condition, results of operations or liquidity.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Segment Information	NOTE 10. SEGMENT INFORMATION See “Segment Results” included in Item 2 for segment information for the three and nine months ended September 30, 2017 and 2016.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	NOTE 11. FAIR VALUE MEASUREMENTS Accounting standards related to fair value measurements define fair value, provide a framework for measuring fair value and establish related disclosure requirements. Broadly, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Accordingly, an “exit price” approach is required in determining fair value. In support of this principle, a fair value hierarchy has been established that prioritizes the inputs used to measure fair value, requiring entities to maximize the use of market or observable inputs (as more reliable measures) and minimize the use of unobservable inputs. Observable inputs reflect market data obtained from independent sources, while unobservable inputs generally require significant management judgment. The three levels within the fair value hierarchy are as follows: • Level 1 – Unadjusted quoted market prices for identical assets or liabilities in active markets that the entity has the ability to access at the measurement date (such as active exchange-traded equity securities or mutual funds and certain U.S. and government agency debt securities). • Level 2 – Observable inputs other than quoted prices included in Level 1, such as: • quoted prices for similar assets or liabilities in active markets (such as U.S. agency and GSE issued mortgage-backed securities and CMOs); • quoted prices for identical or similar assets or liabilities in less active markets (such as certain U.S. and government agency debt securities, and corporate and municipal debt securities that trade infrequently); and • other inputs that (i) are observable for substantially the full term of the asset or liability (e.g. interest rates, yield curves, prepayment speeds, default rates, etc.) or (ii) can be corroborated by observable market data (such as interest rate and currency derivatives and certain other securities). • Level 3 – Valuation techniques that require unobservable inputs that are supported by little or no market activity and are significant to the fair value measurement of the asset or liability (such as pricing models, discounted cash flow methodologies and similar techniques that typically reflect management’s own estimates of the assumptions a market participant would use in pricing the asset or liability). People’s United maintains policies and procedures to value assets and liabilities using the most relevant data available. Described below are the valuation methodologies used by People’s United and the resulting fair values for those financial instruments measured at fair value on both a recurring and a non-recurring Recurring Fair Value Measurements Trading Account Securities and 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 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, GSE residential mortgage-backed securities and CMOs, all of which are included in Level 2. The Company’s available-for-sale available-for-sale 10- 15-year Changes in the prices obtained from the pricing service are analyzed from month to month, taking into consideration changes in market conditions including changes in mortgage spreads, changes in U.S. Treasury security yields and changes in generic pricing of securities with similar duration. As a further point of validation, the Company generates its own month-end 10- 15-year Other Assets As discussed in Note 8, certain unfunded, nonqualified supplemental plans have been established to provide retirement benefits to certain senior officers. People’s United has funded two trusts to provide benefit payments to the extent such benefits are not paid directly by People’s United, the assets of which are included in other assets in the Consolidated Statements of Condition. When available, People’s United determines the fair value of the trust assets using quoted market prices for identical securities received from a third-party nationally recognized pricing service. Derivatives People’s United values its derivatives using internal models that are based on market or observable inputs including interest rate curves and forward/spot prices for selected currencies. Derivative assets and liabilities included in Level 2 represent interest rate swaps/caps, foreign exchange contracts, risk participation agreements, forward commitments to sell residential mortgage loans and interest rate-lock commitments on residential mortgage loans. The following tables summarize People’s United’s financial instruments that are measured at fair value on a recurring basis: ` Fair Value Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Trading account securities: U.S. Treasury $ 8.3 $ — $ — $ 8.3 Securities available for sale: U.S. Treasury and agency 741.9 — — 741.9 GSE mortgage-backed securities and CMOs — 2,446.6 — 2,446.6 Equity securities 9.0 — — 9.0 Other assets: — Exchange-traded funds 35.0 — — 35.0 Fixed income securities — 1.7 — 1.7 Mutual funds 3.6 — — 3.6 Interest rate swaps/caps — 101.9 — 101.9 Foreign exchange contracts — 0.2 — 0.2 Forward commitments to sell residential — 0.6 — 0.6 Total $ 797.8 $ 2,551.0 $ — $ 3,348.8 Financial liabilities: Interest rate swaps/caps $ — $ 60.5 $ — $ 60.5 Risk participation agreements (1) — — — — Foreign exchange contracts — 0.2 — 0.2 Interest rate-lock commitments on residential mortgage loans — 0.7 — 0.7 Total $ — $ 61.4 $ — $ 61.4 Fair Value Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Trading account securities: U.S. Treasury $ 6.8 $ — $ — $ 6.8 Securities available for sale: U.S. Treasury and agency 859.7 — — 859.7 GSE mortgage-backed securities and CMOs — 3,550.0 — 3,550.0 Equity securities — 0.2 — 0.2 Other assets: Exchange-traded funds 32.6 — — 32.6 Fixed income securities — 4.3 — 4.3 Mutual funds 2.7 — — 2.7 Interest rate swaps/caps — 173.1 — 173.1 Foreign exchange contracts — 0.6 — 0.6 Forward commitments to sell residential — 0.3 — 0.3 Total $ 901.8 $ 3,728.5 $ — $ 4,630.3 Financial liabilities: Interest rate swaps/caps $ — $ 121.0 $ — $ 121.0 Risk participation agreements (1) — — — — Foreign exchange contracts — 0.3 — 0.3 Interest rate-lock commitments on residential mortgage loans — 0.4 — 0.4 Total $ — $ 121.7 $ — $ 121.7 (1) At both September 30, 2017 and December 31, 2016, the fair value of risk participation agreements totaled less than $0.1 million (see Note 12). There were no transfers into or out of the Level 1 or Level 2 categories during the nine months ended September 30, 2017 or 2016. Non-Recurring Loans Held for Sale Residential mortgage loans held for sale are recorded at the lower of cost or fair value and are therefore measured at fair value on a non-recurring Impaired Loans Loan impairment is deemed to exist when full repayment of principal and interest according to the contractual terms of the loan is no longer probable. Impaired loans are reported based on one of three measures: the present value of expected future cash flows discounted at the loan’s original effective interest rate; the loan’s observable market price; or the fair value of the collateral (less estimated cost to sell) if the loan is collateral dependent. Accordingly, certain impaired loans may be subject to measurement at fair value on a non-recurring 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%. 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 The following tables summarize People’s United’s assets that are measured at fair value on a non-recurring Fair Value Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Loans held for sale (1) $ — $ 15.0 $ — $ 15.0 Impaired loans (2) — — 64.9 64.9 REO and repossessed assets (3) — — 16.4 16.4 Total $ — $ 15.0 $ 81.3 $ 96.3 Fair Value Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Loans held for sale (1) $ — $ 39.3 $ — $ 39.3 Impaired loans (2) — — 55.9 55.9 REO and repossessed assets (3) — — 19.3 19.3 Total $ — $ 39.3 $ 75.2 $ 114.5 (1) Consists of residential mortgage loans; no fair value adjustments were recorded for the nine months ended September 30, 2017 and 2016. (2) Represents the recorded investment in impaired loans with a related allowance for loan losses measured in accordance with applicable accounting guidance. The total consists of $50.6 million of Commercial loans and $14.3 million of Retail loans at September 30, 2017. The provision for loan losses on impaired loans totaled $4.1 million and $3.5 million for the nine months ended September 30, 2017 and 2016, respectively. (3) Represents: (i) $6.3 million of commercial REO; (ii) $4.7 million of residential REO; and (iii) $5.4 million of repossessed assets at September 30, 2017. Charge-offs to the allowance for loan losses related to loans that were transferred to REO or repossessed assets totaled $2.2 million and $3.3 million for the nine months ended September 30, 2017 and 2016, respectively. Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest Financial Assets and Financial Liabilities Not Measured At Fair Value As discussed previously, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date (an “exit price” approach to fair value). Acceptable valuation techniques (when quoted market prices are not available) that might be used to estimate the fair value of financial instruments include discounted cash flow analyses and comparison to similar instruments. Such estimates are highly subjective and require judgments regarding significant matters such as the amount and timing of future cash flows and the selection of discount rates that appropriately reflect market and credit risks. Changes in these judgments often have a material impact on the fair value estimates. In addition, since these estimates are made as of a specific point in time, they are susceptible to material near-term changes. Fair values estimated in this manner do not reflect any premium or discount that could result from the sale of a large volume of a particular financial instrument, nor do they reflect possible tax ramifications or estimated transaction costs. The following is a description of the principal valuation methods used by People’s United for those financial instruments that are not measured at fair value either on a recurring or non-recurring Cash, Short-Term Investments and Securities Purchased Under Agreements to Resell Cash and due from banks are classified as Level 1. Short-term investments and securities purchased under agreements to resell have fair values that approximate the respective carrying amounts because the instruments are payable on demand or have short-term maturities, and present relatively low credit risk and interest rate risk (“IRR”). As such, these fair values are classified as Level 2. Securities Held to Maturity When available, the fair values of investment securities held to maturity are measured based on quoted market prices for identical securities in active markets and, accordingly, are classified as Level 1 assets. When quoted market prices for identical securities are not available, fair values are estimated based on quoted prices for similar assets in active markets or through the use of pricing models containing observable inputs (i.e. market interest rates, financial information and credit ratings of the issuer, etc.). These fair values are included in Level 2. In cases where there may be limited information available and/or little or no market activity for the underlying security, fair value is estimated using pricing models containing unobservable inputs and classified as Level 3. FHLB and FRB-NY Both FHLB and FRB-NY non-marketable Loans For valuation purposes, the loan portfolio is segregated into its significant categories, which are commercial real estate, commercial and industrial, equipment financing, residential mortgage, home equity and other consumer. These categories are further segregated, where appropriate, into components based on significant financial characteristics such as type of interest rate (fixed or adjustable) and payment status (performing or non-performing). The fair values of performing loans were estimated by discounting the anticipated cash flows from the respective portfolios, assuming future prepayments and using market interest rates for new loans with comparable credit risk. As a result, the valuation method for performing loans, which is consistent with certain guidance provided in accounting standards, does not fully incorporate the “exit price” approach to fair value. The fair values of non-performing Deposit Liabilities The fair values of time deposits represent contractual cash flows discounted at current rates determined by reference to observable inputs including a LIBOR/swap curve over the remaining period to maturity. As such, these fair values are classified as Level 2. The fair values of other deposit liabilities (those with no stated maturity, such as checking and savings accounts) are equal to the carrying amounts payable on demand. Deposit fair values do not include the intangible value of core deposit relationships that comprise a significant portion of People’s United’s deposit base. Management believes that People’s United’s core deposit relationships provide a relatively stable, low-cost Borrowings and Notes and Debentures The fair values of federal funds purchased and customer repurchase agreements are equal to the respective carrying amounts due to the short maturities (generally overnight). The fair values of FHLB advances and other borrowings represent contractual repayments discounted using interest rates currently available on borrowings with similar characteristics and remaining maturities and are classified as Level 2. The fair values of notes and debentures were based on dealer quotes and are classified as Level 2. Lending-Related Financial Instruments The estimated fair values of People’s United’s lending-related financial instruments approximate the respective carrying amounts. Such instruments include commitments to extend credit, unadvanced lines of credit and letters of credit, for which fair values were estimated based on an analysis of the interest rates and fees currently charged to enter into similar transactions, considering the remaining terms of the instruments and the creditworthiness of the potential borrowers. The following tables summarize the carrying amounts, estimated fair values and placement in the fair value hierarchy of People’s United’s financial instruments that are not measured at fair value either on a recurring or non-recurring Estimated Fair Value Carrying Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Cash and due from banks $ 414.1 $ 414.1 $ — $ — $ 414.1 Short-term investments 302.5 — 302.5 — 302.5 Securities held to maturity 3,387.6 — 3,434.1 1.5 3,435.6 FHLB and FRB stock 320.9 — 320.9 — 320.9 Total loans, net (1) 32,086.2 — 6,583.6 25,363.9 31,947.5 Financial liabilities: Time deposits 5,235.8 — 5,232.4 — 5,232.4 Other deposits 27,311.5 — 27,311.5 — 27,311.5 FHLB advances 3,074.1 — 3,076.0 — 3,076.0 Federal funds purchased 543.0 — 543.0 — 543.0 Customer repurchase agreements 295.8 — 295.8 — 295.8 Other borrowings 231.1 — 230.9 — 230.9 Notes and debentures 906.2 — 902.6 — 902.6 (1) Excludes impaired loans totaling $64.9 million measured at fair value on a non-recurring Estimated Fair Value Carrying Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Cash and due from banks $ 432.4 $ 432.4 $ — $ — $ 432.4 Short-term investments 181.7 — 181.7 — 181.7 Securities held to maturity 2,005.4 — 2,011.2 1.5 2,012.7 FHLB and FRB stock 315.8 — 315.8 — 315.8 Total loans, net (1) 29,459.7 — 6,028.4 23,238.1 29,266.5 Financial liabilities: Time deposits 4,542.2 — 4,539.7 — 4,539.7 Other deposits 25,318.6 — 25,318.6 — 25,318.6 FHLB advances 3,061.1 — 3,064.4 — 3,064.4 Federal funds purchased 617.0 — 617.0 — 617.0 Customer repurchase agreements 343.3 — 343.3 — 343.3 Other borrowings 35.4 — 35.4 — 35.4 Notes and debentures 1,030.1 — 1,000.0 — 1,000.0 (1) Excludes impaired loans totaling $55.9 million measured at fair value on a non-recurring

Derivative Financial Instrument

Derivative Financial Instruments and Hedging Activities	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging Activities	NOTE 12. DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES People’s United uses derivative financial instruments as components of its market risk management (principally to manage IRR). Certain other derivatives are entered into in connection with transactions with commercial customers. Derivatives are not used for speculative purposes. All derivatives are recognized as either assets or liabilities in the Consolidated Statements of Condition, reported at fair value and presented on a gross basis. Until a derivative is settled, a favorable change in fair value results in an unrealized gain that is recognized as an asset, while an unfavorable change in fair value results in an unrealized loss that is recognized as a liability. The Company generally applies hedge accounting to its derivatives used for market risk management purposes. Hedge accounting is permitted only if specific criteria are met, including a requirement that a highly effective relationship exist between the derivative instrument and the hedged item, both at inception of the hedge and on an ongoing basis. The hedge accounting method depends upon whether the derivative instrument is classified as a fair value hedge (i.e. hedging an exposure related to a recognized asset or liability, or a firm commitment) or a cash flow hedge (i.e. hedging an exposure related to the variability of future cash flows associated with a recognized asset or liability, or a forecasted transaction). Changes in the fair value of effective fair value hedges are recognized in current earnings (with the change in fair value of the hedged asset or liability also recorded in earnings). Changes in the fair value of effective cash flow hedges are recognized in other comprehensive income (loss) until earnings are affected by the variability in cash flows of the designated hedged item. Ineffective portions of hedge results are recognized in current earnings. Changes in the fair value of derivatives for which hedge accounting is not applied are recognized in current earnings. People’s United formally documents at inception all relationships between the derivative instruments and the hedged items, as well as its risk management objectives and strategies for undertaking the hedge transactions. This process includes linking all derivatives that are designated as hedges to specific assets and liabilities, or to specific firm commitments or forecasted transactions. People’s United also formally assesses, both at inception of the hedge and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting changes in the fair values or cash flows of the hedged items. If it is determined that a derivative is not highly effective or has ceased to be a highly effective hedge, People’s United would discontinue hedge accounting prospectively. Gains or losses resulting from the termination of a derivative accounted for as a cash flow hedge remain in AOCL and are amortized to earnings over the remaining period of the former hedging relationship, provided the hedged item continues to be outstanding or it is probable the forecasted transaction will occur. People’s United uses the dollar offset method, regression analysis and scenario analysis to assess hedge effectiveness at inception and on an ongoing basis. Such methods are chosen based on the nature of the hedge strategy and are used consistently throughout the life of the hedging relationship. Certain derivative financial instruments are offered to commercial customers to assist them in meeting their financing and investing objectives and for their risk management purposes. These derivative financial instruments consist primarily of interest rate swaps, but also include foreign exchange contracts. The interest rate and foreign exchange risks associated with customer interest rate swaps and foreign exchange contracts are mitigated by entering into similar derivatives having essentially offsetting terms with institutional counterparties. Interest rate-lock commitments extended to borrowers relate to the origination of residential mortgage loans. To mitigate the IRR inherent in these commitments, People’s United enters into mandatory delivery and best efforts contracts to sell adjustable-rate and fixed-rate residential mortgage loans (servicing released). Forward commitments to sell and interest rate-lock commitments on residential mortgage loans are considered derivatives and their respective estimated fair values are adjusted based on changes in interest rates. Changes in the fair value of derivatives for which hedge accounting is not applied are recognized in current earnings, including customer derivatives, interest-rate lock commitments and forward sale commitments. By using derivatives, People’s United is exposed to credit risk to the extent that counterparties to the derivative contracts do not perform as required. Should a counterparty fail to perform under the terms of a derivative contract, the Company’s counterparty credit risk is equal to the amount reported as a derivative asset in the Consolidated Statements of Condition. In accordance with the Company’s balance sheet offsetting policy (see Note 13), amounts reported as derivative assets represent derivative contracts in a gain position, without consideration for derivative contracts in a loss position with the same counterparty (to the extent subject to master netting arrangements) and posted collateral. People’s United seeks to minimize counterparty credit risk through credit approvals, limits, monitoring procedures, execution of master netting arrangements and obtaining collateral, where appropriate. Counterparties to People’s United’s derivatives include major financial institutions and exchanges that undergo comprehensive and periodic internal credit analysis as well as maintain investment grade credit ratings from the major credit rating agencies. As such, management believes the risk of incurring credit losses on derivative contracts with those counterparties is remote and losses, if any, would be immaterial. Certain of People’s United’s derivative contracts contain provisions establishing collateral requirements (subject to minimum collateral posting thresholds) based on the Company’s external credit rating. If the Company’s senior unsecured debt rating were to fall below the level generally recognized as investment grade, the counterparties to such derivative contracts could require additional collateral on those derivative transactions in a net liability position (after considering the effect of master netting arrangements and posted collateral). There were no derivative instruments with such credit-related contingent features in a net liability position at September 30, 2017. The following sections further discuss each class of derivative financial instrument used by People’s United, including management’s principal objectives and risk management strategies. Interest Rate Swaps/Caps People’s United may, from time to time, enter into interest rate swaps that are used to manage IRR associated with certain interest-earning assets and interest-bearing liabilities. The Bank has entered into pay floating/receive fixed interest rate swaps to reduce its IRR exposure to the variability in interest cash flows on certain floating-rate commercial loans. The Bank has agreed with the swap counterparties to exchange, at specified intervals, the difference between fixed-rate and floating-rate interest amounts calculated based on notional amounts totaling $210 million. The floating-rate interest payments made under the swaps are calculated using the same floating rate received on the commercial loans. The swaps effectively convert the floating-rate one-month The Bank has entered into a pay floating/receive fixed interest rate swap to hedge the change in fair value due to changes in interest rates of the Bank’s $400 million subordinated notes. The Bank has agreed with the swap counterparty to exchange, at specified intervals, the difference between fixed-rate and floating-rate interest amounts calculated based on a notional amount of $375 million. The fixed-rate interest payments received on the swap will essentially offset the fixed-rate interest payments made on these notes, notwithstanding the notional difference between these notes and the swap. The floating-rate interest amounts paid under the swap are calculated based on three-month LIBOR plus 126.5 basis points. The swap effectively converts the fixed-rate subordinated notes to a floating-rate liability. This swap is accounted for as a fair value hedge. People’s United had previously entered into a pay fixed/receive floating interest rate swap to hedge the LIBOR-based floating rate payments on the Company’s $125 million 5.80% fixed-rate/floating-rate subordinated notes. On February 14, 2017, the Company repaid the subordinated notes and, concurrent with the repayment, the interest rate swap designated to these subordinated notes matured. This swap was accounted for as a cash flow hedge. As a result of the LEAF acquisition, the Company assumed two interest-rate caps with a total notional amount of $150 million, both of which mature in December 2017. Prior to the acquisition, LEAF entered into derivative contracts to reduce potential volatility in its financing costs and to manage its interest rate exposure to changes in one-month LIBOR. Subsequent to the LEAF acquisition, hedge accounting was not applied for these derivatives. Customer Derivatives People’s United enters into interest rate swaps and caps with certain of its commercial customers. In order to minimize its risk, these customer swaps (pay floating/receive fixed) and caps have been offset with essentially matching interest rate swaps (pay fixed/receive floating) and caps with People’s United’s institutional counterparties. Hedge accounting has not been applied for these derivatives. Accordingly, changes in the fair value of all such interest rate swaps and caps are recognized in current earnings. Foreign Exchange Contracts Foreign exchange contracts are commitments to buy or sell foreign currency on a future date at a contractual price. People’s United uses these instruments on a limited basis to (i) eliminate its exposure to fluctuations in currency exchange rates on certain of its commercial loans that are denominated in foreign currencies and (ii) provide foreign exchange contracts on behalf of commercial customers within credit exposure limits. Gains and losses on foreign exchange contracts substantially offset the translation gains and losses on the related loans. Risk Participation Agreements People’s United enters into risk participation agreements under which it may either assume or sell credit risk associated with a borrower’s performance under certain interest rate derivative contracts. In those instances in which People’s United has assumed credit risk, it is not a party to the derivative contract and has entered into the risk participation agreement because it is also a party to the related loan agreement with the borrower. In those instances in which People’s United has sold credit risk, it is a party to the derivative contract and has entered into the risk participation agreement because it sold a portion of the related loan. People’s United manages its credit risk under risk participation agreements by monitoring the creditworthiness of the borrower, based on its normal credit review process. The notional amounts of the risk participation agreements reflect People’s United’s pro-rata Forward Commitments to Sell Residential Mortgage Loans and Related Interest Rate-Lock Commitments People’s United enters into forward commitments to sell adjustable-rate and fixed-rate residential mortgage loans (all to be sold servicing released) in order to reduce the market risk associated with originating loans for sale in the secondary market. In order to fulfill a forward commitment, People’s United delivers originated loans at prices or yields specified by the contract. The risks associated with such contracts arise from the possible inability of counterparties to meet the contract terms or People’s United’s inability to originate the necessary loans. Gains and losses realized on the forward contracts are reported in the Consolidated Statements of Income as a component of the net gains on sales of residential mortgage loans. In the normal course of business, People’s United will commit to an interest rate on a mortgage loan application at the time of application, or anytime thereafter. The risks associated with these interest rate-lock commitments arise if market interest rates change prior to the closing of these loans. Both forward sales commitments and interest rate-lock commitments made to borrowers on held-for-sale Interest Rate Locks In connection with its planned issuance of senior notes in the fourth quarter of 2012, People’s United entered into U.S. Treasury forward interest rate locks (“T-Locks”) 10-year T-Locks net-of-tax ten-year The table below provides a summary of the notional amounts and fair values (presented on a gross basis) of derivatives outstanding: Fair Values (1) Notional Amounts Assets Liabilities (in millions) Type of Sept. 30, Dec. 31, Sept. 30, Dec. 31, Sept. 30, Dec. 31, Derivatives Not Designated as Hedging Instruments: Interest rate swaps/caps: Commercial customers N/A $ 6,101.2 $ 5,612.2 $ 91.5 $ 93.9 $ 39.7 $ 46.9 Institutional counterparties N/A 5,958.2 5,620.2 10.4 65.6 20.8 74.0 Risk participation agreements (2) N/A 383.4 251.9 — — — — Foreign exchange contracts N/A 42.6 101.2 0.2 0.6 0.2 0.3 Forward commitments to sell N/A 26.0 48.6 0.6 0.3 — — Interest rate-lock commitments on residential mortgage loans N/A 31.7 57.0 — — 0.7 0.4 Total 102.7 160.4 61.4 121.6 Derivatives Designated as Hedging Instruments: Interest rate swaps: Subordinated notes Fair value 375.0 375.0 — 13.6 — — Loans Cash flow 210.0 — — — — — Subordinated notes Cash flow — 125.0 — — — 0.1 Total — 13.6 — 0.1 Total fair value of derivatives $ 102.7 $ 174.0 $ 61.4 $ 121.7 (1) Assets are recorded in other assets and liabilities are recorded in other liabilities. (2) Fair value totaled less than $0.1 million at both dates. The following table summarizes the impact of People’s United’s derivatives on pre-tax Amount of Pre-Tax Gain (Loss) Amount of Pre-Tax Gain (Loss) Type of Recognized in Earnings (1) Recognized in AOCL Nine months ended September 30 (in millions) 2017 2016 2017 2016 Derivatives Not Designated as Hedging Instruments: Interest rate swaps/caps: Commercial customers N/A $ 45.4 $ 210.7 $ — $ — Institutional counterparties N/A (39.1 ) (200.3 ) — — Foreign exchange contracts N/A 0.3 (0.6 ) — — Risk participation agreements N/A 0.5 0.1 — — Forward commitments to sell residential mortgage loans N/A 0.1 0.8 — — Interest rate-lock commitments on residential mortgage loans N/A (0.1 ) (1.1 ) — — Total 7.1 9.6 — — Derivatives Designated as Hedging Instruments: Interest rate swaps Fair value 4.5 6.4 — — Interest rate swaps Cash flow 0.6 (0.6 ) — (0.2 ) Interest rate locks Cash flow 0.1 0.1 — — Total 5.2 5.9 — (0.2 ) Total $ 12.3 $ 15.5 $ — $ (0.2 ) (1) Amounts recognized in earnings are recorded in interest income, interest expense or other non-interest non-interest

Balance Sheet Offsetting

Balance Sheet Offsetting	9 Months Ended
	Sep. 30, 2017
Text Block [Abstract]
Balance Sheet Offsetting	NOTE 13. BALANCE SHEET OFFSETTING Assets and liabilities relating to certain financial instruments, including derivatives, may be eligible for offset in the Consolidated Statements of Condition and/or subject to enforceable master netting arrangements or similar agreements. People’s United’s derivative transactions with institutional counterparties are generally executed under International Swaps and Derivative Association (“ISDA”) master agreements, which include “right of set-off” Effective January 3, 2017, the Chicago Mercantile Exchange (“CME”) amended their rulebooks to legally characterize variation margin payments for over-the-counter Collateral (generally in the form of marketable debt securities) pledged by counterparties in connection with derivative transactions is not reported in the Consolidated Statements of Condition unless the counterparty defaults. Collateral that has been pledged by People’s United to counterparties continues to be reported in the Consolidated Statements of Condition unless the Company defaults. The following tables provide a gross presentation, the effects of offsetting, and a net presentation of the Company’s financial instruments that are eligible for offset in the Consolidated Statements of Condition. The collateral amounts in these tables are limited to the outstanding balances of the related asset or liability (after netting is applied) and, therefore, instances of overcollateralization are not presented. The net amounts of the derivative assets and liabilities can be reconciled to the fair value of the Company’s derivative financial instruments in Note 12. The Company’s derivative contracts with commercial customers and customer repurchase agreements are not subject to master netting arrangements and, therefore, have been excluded from the tables below. Gross Gross Net Gross Amounts Not Offset Financial Net As of September 30, 2017 (in millions) Instruments Collateral Amount Financial assets: Interest rate swaps/caps: Counterparty A $ 1.7 $ — $ 1.7 $ (1.7 ) $ — $ — Counterparty B 0.8 — 0.8 (0.8 ) — — Counterparty C 1.4 — 1.4 (1.4 ) — — Counterparty D 2.8 — 2.8 (2.8 ) — — Counterparty E 2.4 — 2.4 — — 2.4 Other counterparties 1.3 — 1.3 (0.3 ) (0.9 ) 0.1 Foreign exchange contracts 0.2 — 0.2 — — 0.2 Total $ 10.6 $ — $ 10.6 $ (7.0 ) $ (0.9 ) $ 2.7 Financial liabilities: Interest rate swaps/caps: Counterparty A $ 3.2 $ — $ 3.2 $ (1.7 ) $ (1.5 ) $ — Counterparty B 6.9 — 6.9 (0.8 ) (6.1 ) — Counterparty C 3.7 — 3.7 (1.4 ) (2.3 ) — Counterparty D 5.9 — 5.9 (2.8 ) (3.1 ) — Other counterparties 1.2 — 1.2 (0.3 ) (0.9 ) — Foreign exchange contracts 0.2 — 0.2 — — 0.2 Total $ 21.1 $ — $ 21.1 $ (7.0 ) $ (13.9 ) $ 0.2 Gross Gross Net Gross Amounts Not Offset Financial Net As of December 31, 2016 (in millions) Instruments Collateral Amount Financial assets: Interest rate swaps/caps: Counterparty A $ 1.9 $ — $ 1.9 $ (1.9 ) $ — $ — Counterparty B 1.0 — 1.0 (1.0 ) — — Counterparty C 1.7 — 1.7 (1.7 ) — — Counterparty D 3.4 — 3.4 (3.4 ) — — Counterparty E 69.6 — 69.6 (50.0 ) (19.6 ) — Other counterparties 1.6 — 1.6 (0.3 ) (1.3 ) — Foreign exchange contracts 0.6 — 0.6 — — 0.6 Total $ 79.8 $ — $ 79.8 $ (58.3 ) $ (20.9 ) $ 0.6 Financial liabilities: Interest rate swaps/caps: Counterparty A $ 4.3 $ — $ 4.3 $ (1.9 ) $ (2.4 ) $ — Counterparty B 7.7 — 7.7 (1.0 ) (6.7 ) — Counterparty C 3.4 — 3.4 (1.7 ) (1.1 ) 0.6 Counterparty D 6.9 — 6.9 (3.4 ) (1.7 ) 1.8 Counterparty E 50.0 — 50.0 (50.0 ) — — Other counterparties 1.8 — 1.8 (0.3 ) (1.5 ) — Foreign exchange contracts 0.3 — 0.3 — — 0.3 Total $ 74.4 $ — $ 74.4 $ (58.3 ) $ (13.4 ) $ 2.7 Resale and repurchase agreements represent agreements to purchase/sell securities subject to an obligation to resell/repurchase the same or similar securities. People’s United accounts for securities resale agreements as secured lending transactions and securities repurchase agreements as secured borrowings since the transferor maintains effective control over the transferred securities and the transfer meets the other criteria for such accounting. The securities are pledged by the transferor as collateral and the transferee has the right, by contract, to repledge that collateral provided the same collateral is returned to the transferor upon maturity of the underlying agreement. The fair value of the pledged collateral approximates the recorded amount of the secured loan or borrowing. Decreases in the fair value of the transferred securities below an established threshold require the transferor to provide additional collateral. The following table shows the extent to which assets and liabilities exchanged under resale and repurchase agreements have been offset in the Consolidated Statements of Condition. These agreements: (i) are entered into simultaneously with the same financial institution counterparty; (ii) have the same principal amounts and inception/maturity dates; and (iii) are subject to a master netting arrangement that contains a conditional right of offset upon default. At September 30, 2017, the Company posted as collateral marketable securities with a fair value of $248.3 million and, in turn, accepted as collateral marketable securities with a fair value of $254.4 million. As of September 30, 2017 (in millions) Gross Gross Net Total resale agreements $ 250.0 $ (250.0 ) $ — Total repurchase agreements $ 250.0 $ (250.0 ) $ —

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2017
Accounting Changes and Error Corrections [Abstract]
New Accounting Standards	NOTE 14. NEW ACCOUNTING STANDARDS Standards effective in 2017 Derivatives and Hedging In March 2016, the Financial Accounting Standards Board (the “FASB”) amended its standards with respect to derivatives and hedging. The first amendment clarifies that a change in the counterparty to a derivative instrument that has been designated as the hedging instrument does not, in and of itself, require dedesignation of that hedging relationship and discontinuation of the application of hedge accounting. This amendment does not require additional disclosures beyond disclosure about a change in accounting principle in the period of adoption. The second amendment clarifies the requirements for assessing whether contingent call (put) options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. An entity performing the assessment is required to assess the embedded call (put) options solely in accordance with a four-step decision sequence and no longer is required to assess whether the event that triggers the ability to exercise the option is related to interest rate or credit risk. These amendments, which are being applied prospectively, became effective for People’s United on January 1, 2017 and did not have a significant impact on the Company’s Consolidated Financial Statements. Investments – Equity Method and Joint Ventures In March 2016, the FASB amended its standards with respect to the equity method of accounting by eliminating the requirement that, upon an investment qualifying for use of the equity method of accounting as a result of an increase in the level of ownership interest or degree of influence, an investor must adjust the investment, results of operations and retained earnings retrospectively, as if the equity method of accounting had been in effect during all previous periods that the investment was held. Rather, under the new guidance, upon qualifying for the equity method of accounting, no retroactive adjustment of the investment is required. Instead, any unrealized holding gain or loss is to be recognized through other comprehensive income on the date the investment qualifies for use of the equity method. This amendment, which is being applied prospectively, became effective for People’s United on January 1, 2017 and did not have a significant impact on the Company’s Consolidated Financial Statements. Stock Compensation In March 2016, the FASB amended its standards with respect to certain aspects of the accounting for share-based year-to-date Standards effective in 2018 Revenue Recognition In May 2014, the FASB amended its standards with respect to revenue recognition. The amended guidance serves to replace all current U.S. GAAP guidance on this topic and eliminate all industry-specific guidance, providing a unified model to determine when and how revenue is recognized. The underlying principle is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The amendments also require enhanced disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from an entity’s contracts with customers. As originally issued, this new guidance, which can be applied retrospectively or through the use of the cumulative effect transition method, was to become effective for fiscal years, and interim periods within those fiscal years, beginning on or after December 15, 2016 (January 1, 2017 for People’s United) and early adoption was not permitted. In July 2015, the FASB approved a one-year The Company will adopt this guidance in the first quarter of 2018 using the modified retrospective method with a cumulative-effect adjustment to opening retained earnings, as appropriate. The Company’s revenue is comprised of net interest income on financial assets and financial liabilities (approximately 75%) and non-interest The Company’s assessment of in-scope Presentation of Deferred Taxes In November 2015, the FASB amended its standards with respect to the presentation of deferred income taxes to eliminate the requirement to separate deferred income tax liabilities and assets into current and noncurrent amounts in a classified statement of condition, thereby simplifying the presentation of deferred income taxes. For public business entities, this new amendment is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017 (January 1, 2018 for People’s United) and may be applied either prospectively or retrospectively to all periods presented. Earlier application of the amendment is permitted as of the beginning of an interim or annual reporting period. The adoption of this amendment is not expected to have a significant impact on the Company’s Consolidated Financial Statements. Recognition and Measurement of Financial Instruments In January 2016, the FASB amended its standards to address certain aspects of recognition, presentation and disclosure of financial instruments. The amended guidance (i) requires that equity investments be measured at fair value with changes in fair value recognized in net income and (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by permitting a qualitative assessment to identify impairment. Both FRB-NY and FHLB stock will continue to be presented at cost. The guidance also contains additional disclosure and presentation requirements associated with financial instruments. Specifically, the standard emphasizes the existing requirement to use “exit price” when determining fair value for disclosure purposes, clarifying that entities should not make use of a practicability exception in determining the fair value of loans. For public business entities, this new guidance is effective in fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017 (January 1, 2018 for People’s United). The cumulative effect transition method will be applied to all outstanding instruments as of the date of adoption, while changes to the accounting for equity investments without readily determinable fair values will be applied prospectively. While the Company continues to monitor the potential impact of the amended guidance on its Consolidated Financial Statements, such impact is indeterminable at this time as it will be dependent upon portfolio composition at the adoption date. As noted in Note 3, at September 30, 2017, the Company’s securities portfolio included equity securities with an amortized cost of $9.6 million and a fair value of $9.0 million. The Company does expect to refine the calculation used to determine the fair value of its held-for-investment Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments In August 2016, the FASB amended its standards to address the classification of certain cash receipts and payments within the statement of cash flows. Specifically, the amended guidance addresses the following: (i) debt prepayment or debt extinguishment costs; (ii) settlement of zero-coupon Asset Derecognition and Accounting for Partial Sales of Nonfinancial Assets In February 2017, the FASB amended its standards to clarify the scope of its guidance on derecognition of a nonfinancial asset and provide additional guidance on the definition of in-substance Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost In March 2017, the FASB amended its standards to (i) require that the service cost component of net benefit cost associated with pension and postretirement plans be reported in the same line item in which the related employees’ compensation cost is reported and (ii) specify that only the service cost component is eligible for capitalization. The other components of net benefit cost, which may not be capitalized, are to be presented separately. For public business entities, this new guidance, which is to be applied retrospectively, is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017 (January 1, 2018 for People’s United) and early adoption is permitted. The adoption of this amendment will result in a reclassification of certain net benefit cost components from compensation and benefits expense to other non-interest Stock Compensation In July 2017, the FASB amended its standards with respect to share-based payment awards to provide explicit guidance pertaining to the provisions of modification accounting. The amendment clarifies that an entity should not account for the effects of a modification if the award’s fair value, vesting conditions and classification (as either debt or equity) are the same immediately before and after the modification. This new guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017 (January 1, 2018 for People’s United) and is to be applied prospectively to awards modified on or after the adoption date. Earlier application of the amendment is permitted. The adoption of this amendment is not expected to have a significant impact on the Company’s Consolidated Financial Statements. Standards effective in 2019 Accounting for Leases In February 2016, the FASB amended its standards with respect to the accounting for leases. The amended guidance serves to replace all current U.S. GAAP guidance on this topic and requires that an operating lease be recognized on the statement of condition as a “right-of-use” The Company has begun its evaluation of the amended guidance including the potential impact on its Consolidated Financial Statements. To date, the Company has identified several areas that are within the scope of the guidance, including its contracts with respect to leased real estate and office equipment. In addition, operating lease agreements entered into with customers by the Company’s equipment financing businesses are also subject to the new guidance. The Company continues to evaluate the impact of the guidance, including determining whether additional contracts exist that are deemed to be in scope. As such, no conclusions have yet been reached regarding the potential impact of adoption on the Company’s Consolidated Financial Statements. The Federal banking agencies have indicated that to the extent a “right-of-use” asset arises due to a lease of a tangible asset (e.g. building or equipment), the asset should: (i) be treated as a tangible asset not subject to deduction from regulatory capital; (ii) risk-weighted at 100%; and (iii) included in total assets for leverage capital purposes. Premium Amortization – Purchased Callable Debt Securities In April 2017, the FASB amended its standards to shorten the amortization period for certain callable debt securities held at a premium, requiring such premiums to be amortized to the earliest call date unless applicable guidance related to certain pools of securities is applied to consider estimated prepayments. Under prior guidance, entities were generally required to amortize premiums on individual, non-pooled Derivatives and Hedging In August 2017, the FASB amended its standards with respect to the accounting for derivatives and hedging, simplifying existing guidance in order to enable companies to more accurately portray the economic effects of risk management activities in the financial statements and enhancing the transparency and understandability of hedge results through improved disclosures. This new guidance is effective for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018 (January 1, 2019 for People’s United) with early adoption permitted. The Company is still evaluating whether to apply the early adoption provisions of the standard. However, given the limited number of derivatives currently designated as hedging instruments, the adoption of this amendment is not expected to have a significant impact on the Company’s Consolidated Financial Statements. Standards effective in 2020 Financial Instruments – Credit Losses In June 2016, the FASB amended its standards with respect to certain aspects of measurement, recognition and disclosure of credit losses on loans and other financial instruments, including available-for-sale While early adoption is permitted, the Company does not expect to elect that option. In preparing for adoption, the Company has established a cross-functional working group comprised of individuals from various disciplines, including credit, risk management, information technology and finance. That working group, which is subject to the Company’s established corporate governance and oversight structure, is currently engaged in: (i) identifying key interpretative issues; (ii) determining the appropriate level of portfolio segmentation; (iii) reviewing historical data so as to identify potential data and resource gaps; and (iv) evaluating existing credit loss forecasting models and processes in order to determine what modifications may be required. In addition, the Company has purchased a third-party vendor solution that will aid in the application of the standard. As a result of the required change in approach toward determining estimated credit losses from the current “incurred loss” model to one based on estimated cash flows over a loan’s contractual life, adjusted for prepayments (a “life of loan” model), the Company expects the new guidance will result in an increase in the allowance for loan losses, particularly for longer duration portfolios. The Company also expects the new guidance may result in an allowance for debt securities. In both cases, the extent of the change is indeterminable at this time as it will be dependent upon portfolio composition and credit quality at the adoption date, as well as economic conditions and forecasts at that time. Further, to date, no guidance has been issued by either the Company’s or the Bank’s primary regulators with respect to how the impact of the amended standard is to be treated for regulatory capital purposes. Simplifying the Test for Goodwill Impairment In January 2017, the FASB amended its standards with respect to goodwill, simplifying how an entity is required to conduct the impairment assessment by eliminating Step 2, which requires a hypothetical purchase price allocation, from the goodwill impairment test. Instead, goodwill impairment will now be measured as the amount by which a reporting unit’s carrying amount exceeds its fair value, not to exceed the carrying amount of goodwill. An entity will still have the option to perform a qualitative assessment to determine if a quantitative impairment test is necessary. For public business entities, this new guidance is effective in fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019 (January 1, 2020 for People’s United) and is to be applied prospectively. Early adoption is permitted for any impairment tests performed after January 1, 2017. The adoption of this amendment is not expected to have a significant impact on the Company’s Consolidated Financial Statements.

Employee Benefit Plans (Policie

Employee Benefit Plans (Policies)	9 Months Ended
	Sep. 30, 2017
Retirement Benefits [Abstract]
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 a qualified defined benefit pension plan that covers former Chittenden employees who meet certain eligibility requirements (the “Chittenden Qualified Plan”). Effective December 31, 2005, accrued benefits were frozen based on participants’ then-current service and pay levels. Interest continues to be credited on undistributed balances at a crediting rate specified by the Chittenden Qualified Plan. During April 2010, participants who were in payment status as of April 1, 2010, or whose accrued benefit as of that date was scheduled to be paid in the form of an annuity commencing May 1, 2010 based upon elections made by April 15, 2010, were transferred into the People’s Qualified Plan. 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 “Supplemental Plans”) and (ii) an unfunded plan that provides retirees with optional medical, dental and life insurance benefits (the “Other 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.
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 nine months ended September 30, 2017, totaled $3.6 million. At September 30, 2017, the loan balance totaled $184.9 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 3,745,864 shares of People’s United common stock have been allocated or committed to be released to participants’ accounts. At September 30, 2017, 6,707,711 shares of People’s United common stock, with a fair value of $121.7 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 paid-in
Fair Value Measurements	FAIR VALUE MEASUREMENTS Accounting standards related to fair value measurements define fair value, provide a framework for measuring fair value and establish related disclosure requirements. Broadly, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. Accordingly, an “exit price” approach is required in determining fair value. In support of this principle, a fair value hierarchy has been established that prioritizes the inputs used to measure fair value, requiring entities to maximize the use of market or observable inputs (as more reliable measures) and minimize the use of unobservable inputs. Observable inputs reflect market data obtained from independent sources, while unobservable inputs generally require significant management judgment. The three levels within the fair value hierarchy are as follows: • Level 1 – Unadjusted quoted market prices for identical assets or liabilities in active markets that the entity has the ability to access at the measurement date (such as active exchange-traded equity securities or mutual funds and certain U.S. and government agency debt securities). • Level 2 – Observable inputs other than quoted prices included in Level 1, such as: • quoted prices for similar assets or liabilities in active markets (such as U.S. agency and GSE issued mortgage-backed securities and CMOs); • quoted prices for identical or similar assets or liabilities in less active markets (such as certain U.S. and government agency debt securities, and corporate and municipal debt securities that trade infrequently); and • other inputs that (i) are observable for substantially the full term of the asset or liability (e.g. interest rates, yield curves, prepayment speeds, default rates, etc.) or (ii) can be corroborated by observable market data (such as interest rate and currency derivatives and certain other securities). • Level 3 – Valuation techniques that require unobservable inputs that are supported by little or no market activity and are significant to the fair value measurement of the asset or liability (such as pricing models, discounted cash flow methodologies and similar techniques that typically reflect management’s own estimates of the assumptions a market participant would use in pricing the asset or liability). People’s United maintains policies and procedures to value assets and liabilities using the most relevant data available. Described below are the valuation methodologies used by People’s United and the resulting fair values for those financial instruments measured at fair value on both a recurring and a non-recurring Recurring Fair Value Measurements Trading Account Securities and 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 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, GSE residential mortgage-backed securities and CMOs, all of which are included in Level 2. The Company’s available-for-sale available-for-sale 10- 15-year Changes in the prices obtained from the pricing service are analyzed from month to month, taking into consideration changes in market conditions including changes in mortgage spreads, changes in U.S. Treasury security yields and changes in generic pricing of securities with similar duration. As a further point of validation, the Company generates its own month-end 10- 15-year Other Assets As discussed in Note 8, certain unfunded, nonqualified supplemental plans have been established to provide retirement benefits to certain senior officers. People’s United has funded two trusts to provide benefit payments to the extent such benefits are not paid directly by People’s United, the assets of which are included in other assets in the Consolidated Statements of Condition. When available, People’s United determines the fair value of the trust assets using quoted market prices for identical securities received from a third-party nationally recognized pricing service. Derivatives People’s United values its derivatives using internal models that are based on market or observable inputs including interest rate curves and forward/spot prices for selected currencies. Derivative assets and liabilities included in Level 2 represent interest rate swaps/caps, foreign exchange contracts, risk participation agreements, forward commitments to sell residential mortgage loans and interest rate-lock commitments on residential mortgage loans. Non-Recurring Loans Held for Sale Residential mortgage loans held for sale are recorded at the lower of cost or fair value and are therefore measured at fair value on a non-recurring Impaired Loans Loan impairment is deemed to exist when full repayment of principal and interest according to the contractual terms of the loan is no longer probable. Impaired loans are reported based on one of three measures: the present value of expected future cash flows discounted at the loan’s original effective interest rate; the loan’s observable market price; or the fair value of the collateral (less estimated cost to sell) if the loan is collateral dependent. Accordingly, certain impaired loans may be subject to measurement at fair value on a non-recurring 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%. 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 Financial Assets and Financial Liabilities Not Measured At Fair Value As discussed previously, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date (an “exit price” approach to fair value). Acceptable valuation techniques (when quoted market prices are not available) that might be used to estimate the fair value of financial instruments include discounted cash flow analyses and comparison to similar instruments. Such estimates are highly subjective and require judgments regarding significant matters such as the amount and timing of future cash flows and the selection of discount rates that appropriately reflect market and credit risks. Changes in these judgments often have a material impact on the fair value estimates. In addition, since these estimates are made as of a specific point in time, they are susceptible to material near-term changes. Fair values estimated in this manner do not reflect any premium or discount that could result from the sale of a large volume of a particular financial instrument, nor do they reflect possible tax ramifications or estimated transaction costs. The following is a description of the principal valuation methods used by People’s United for those financial instruments that are not measured at fair value either on a recurring or non-recurring Cash, Short-Term Investments and Securities Purchased Under Agreements to Resell Cash and due from banks are classified as Level 1. Short-term investments and securities purchased under agreements to resell have fair values that approximate the respective carrying amounts because the instruments are payable on demand or have short-term maturities, and present relatively low credit risk and interest rate risk (“IRR”). As such, these fair values are classified as Level 2. Securities Held to Maturity When available, the fair values of investment securities held to maturity are measured based on quoted market prices for identical securities in active markets and, accordingly, are classified as Level 1 assets. When quoted market prices for identical securities are not available, fair values are estimated based on quoted prices for similar assets in active markets or through the use of pricing models containing observable inputs (i.e. market interest rates, financial information and credit ratings of the issuer, etc.). These fair values are included in Level 2. In cases where there may be limited information available and/or little or no market activity for the underlying security, fair value is estimated using pricing models containing unobservable inputs and classified as Level 3. FHLB and FRB-NY Both FHLB and FRB-NY non-marketable Loans For valuation purposes, the loan portfolio is segregated into its significant categories, which are commercial real estate, commercial and industrial, equipment financing, residential mortgage, home equity and other consumer. These categories are further segregated, where appropriate, into components based on significant financial characteristics such as type of interest rate (fixed or adjustable) and payment status (performing or non-performing). The fair values of performing loans were estimated by discounting the anticipated cash flows from the respective portfolios, assuming future prepayments and using market interest rates for new loans with comparable credit risk. As a result, the valuation method for performing loans, which is consistent with certain guidance provided in accounting standards, does not fully incorporate the “exit price” approach to fair value. The fair values of non-performing Deposit Liabilities The fair values of time deposits represent contractual cash flows discounted at current rates determined by reference to observable inputs including a LIBOR/swap curve over the remaining period to maturity. As such, these fair values are classified as Level 2. The fair values of other deposit liabilities (those with no stated maturity, such as checking and savings accounts) are equal to the carrying amounts payable on demand. Deposit fair values do not include the intangible value of core deposit relationships that comprise a significant portion of People’s United’s deposit base. Management believes that People’s United’s core deposit relationships provide a relatively stable, low-cost Borrowings and Notes and Debentures The fair values of federal funds purchased and customer repurchase agreements are equal to the respective carrying amounts due to the short maturities (generally overnight). The fair values of FHLB advances and other borrowings represent contractual repayments discounted using interest rates currently available on borrowings with similar characteristics and remaining maturities and are classified as Level 2. The fair values of notes and debentures were based on dealer quotes and are classified as Level 2. Lending-Related Financial Instruments The estimated fair values of People’s United’s lending-related financial instruments approximate the respective carrying amounts. Such instruments include commitments to extend credit, unadvanced lines of credit and letters of credit, for which fair values were estimated based on an analysis of the interest rates and fees currently charged to enter into similar transactions, considering the remaining terms of the instruments and the creditworthiness of the potential borrowers.

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2017
Summary of Pro Forma Financial Information Reflecting Acquisition	The following table presents selected unaudited pro forma financial information of the Company reflecting the acquisitions of Suffolk and LEAF assuming the acquisitions were completed as of the beginning of the respective periods: Nine Months Ended (in millions, except per common share data) 2017 2016 Selected Financial Results: Net interest income $ 835.9 $ 797.3 Provision for loan losses 18.5 28.9 Non-interest 275.5 275.5 Non-interest 720.6 707.1 Net income 258.0 227.7 Net income applicable to common shareholders 247.5 227.7 Basic and diluted earnings per common share $ 0.73 $ 0.69
Suffolk Bancorp [Member]
Estimated Fair Values of Assets Acquired and Liabilities Assumed	The acquisition-date estimated fair values of the assets acquired and liabilities assumed in the acquisition of Suffolk are summarized as follows: (in millions) Assets: Cash and cash equivalents $ 174.0 Securities 167.4 Loans 1,617.5 Goodwill 270.3 Core deposit intangible 28.1 Premises and equipment 40.4 Bank-owned life insurance 54.1 Other real estate owned 0.5 Other assets 28.9 Total assets $ 2,381.2 Liabilities: Deposits $ 1,852.4 Borrowings 15.1 Other liabilities 28.9 Total liabilities $ 1,896.4 Total purchase price $ 484.8
LEAF Commercial Capital, Inc. [Member]
Estimated Fair Values of Assets Acquired and Liabilities Assumed	The acquisition-date estimated fair values of the assets acquired and liabilities assumed in the acquisition of LEAF are summarized as follows: (in millions) Assets: Cash and cash equivalents $ 74.9 Loans 717.9 Goodwill 148.4 Trade name intangible 0.9 Premises and equipment 2.4 Non-compete 0.2 Other assets 13.0 Total assets $ 957.7 Liabilities: Borrowings $ 708.1 Other liabilities 29.6 Total liabilities $ 737.7 Total purchase price $ 220.0

Securities and Short-Term Inv25

Securities and Short-Term Investments (Tables)	9 Months Ended
	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Available-for-Sale and Held-to-Maturity Securities Gains (Losses)	The amortized cost, gross unrealized gains and losses, and fair value of People’s United’s securities available for sale and securities held to maturity are as follows: As of September 30, 2017 (in millions) Amortized Gross Gross Fair Securities available for sale: Debt securities: U.S. Treasury and agency $ 760.9 $ 0.1 $ (19.1 ) $ 741.9 GSE (1) mortgage-backed securities 2,450.1 11.5 (15.0 ) 2,446.6 Total debt securities 3,211.0 11.6 (34.1 ) 3,188.5 Equity securities (3) 9.6 — (0.6 ) 9.0 Total securities available for sale $ 3,220.6 $ 11.6 $ (34.7 ) $ 3,197.5 Securities held to maturity: Debt securities: State and municipal $ 1,999.2 $ 60.7 $ (8.5 ) $ 2,051.4 GSE mortgage-backed securities 1,344.6 1.5 (6.5 ) 1,339.6 Corporate 42.3 0.8 — 43.1 Other 1.5 — — 1.5 Total securities held to maturity $ 3,387.6 $ 63.0 $ (15.0 ) $ 3,435.6 (1) Government sponsored enterprise (2) Collateralized mortgage obligations (3) During the quarter ended March 31, 2017, the Company exchanged its ownership interest in a non-marketable As of December 31, 2016 (in millions) Amortized Gross Gross Fair Securities available for sale: Debt securities: U.S. Treasury and agency $ 889.9 $ 0.3 $ (30.5 ) $ 859.7 GSE mortgage-backed securities 3,573.1 15.0 (38.1 ) 3,550.0 Total debt securities 4,463.0 15.3 (68.6 ) 4,409.7 Equity securities 0.2 — — 0.2 Total securities available for sale $ 4,463.2 $ 15.3 $ (68.6 ) $ 4,409.9 Securities held to maturity: Debt securities: State and municipal $ 1,499.1 $ 33.9 $ (23.5 ) $ 1,509.5 GSE mortgage-backed securities 500.8 — (3.2 ) 497.6 Corporate 4.0 — — 4.0 Other 1.5 — — 1.5 Total securities held to maturity $ 2,005.4 $ 33.9 $ (26.7 ) $ 2,012.6
Summary of Amortized Cost and Fair Value of Debt Securities Based on Remaining Period to Contractual Maturity	The following table is a summary of the amortized cost and fair value of debt securities as of September 30, 2017, based on remaining period to contractual maturity. Information for GSE mortgage-backed securities and CMOs is based on the final contractual maturity dates without considering repayments and prepayments. Available for Sale Held to Maturity (in millions) Amortized Fair Amortized Fair U.S. Treasury and agency: Within 1 year $ 1.0 $ 1.0 $ — $ — After 1 but within 5 years 361.3 355.0 — — After 5 but within 10 years 398.6 385.9 — — Total 760.9 741.9 — — GSE mortgage-backed securities and CMOs: After 1 but within 5 years — — 69.4 69.4 After 5 but within 10 years 604.6 613.9 834.3 830.4 After 10 years 1,845.5 1,832.7 440.9 439.8 Total 2,450.1 2,446.6 1,344.6 1,339.6 State and municipal: Within 1 year — — 18.7 18.7 After 1 but within 5 years — — 114.1 117.4 After 5 but within 10 years — — 343.2 363.2 After 10 years — — 1,523.2 1,552.1 Total — — 1,999.2 2,051.4 Corporate: After 1 but within 5 years — — 5.0 5.0 After 5 but within 10 years — — 37.3 38.1 Total — — 42.3 43.1 Other: After 1 but within 5 years — — 1.5 1.5 Total — — 1.5 1.5 Total: Within 1 year 1.0 1.0 18.7 18.7 After 1 but within 5 years 361.3 355.0 190.0 193.3 After 5 but within 10 years 1,003.2 999.8 1,214.8 1,231.7 After 10 years 1,845.5 1,832.7 1,964.1 1,991.9 Total $ 3,211.0 $ 3,188.5 $ 3,387.6 $ 3,435.6
Continuous Unrealized Loss Position on Available-for-Sale and Held-to-Maturities Securities	The following tables summarize those securities with unrealized losses, segregated by the length of time the securities have been in a continuous unrealized loss position at the respective dates. Certain unrealized losses totaled less than $0.1 million. Continuous Unrealized Loss Position Less Than 12 Months 12 Months Or Longer Total As of September 30, 2017 (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Securities available for sale: GSE mortgage-backed securities and CMOs $ 1,675.6 $ (12.1 ) $ 133.9 $ (2.9 ) $ 1,809.5 $ (15.0 ) U.S. Treasury and agency 206.6 (3.0 ) 530.1 (16.1 ) 736.7 (19.1 ) Equity securities 9.0 (0.6 ) — — 9.0 (0.6 ) Securities held to maturity: GSE mortgage-backed securities 1,029.5 (6.5 ) — — 1,029.5 (6.5 ) State and municipal 270.3 (1.7 ) 207.5 (6.8 ) 477.8 (8.5 ) Corporate 2.8 — — — 2.8 — Total $ 3,193.8 $ (23.9 ) $ 871.5 $ (25.8 ) $ 4,065.3 $ (49.7 ) Continuous Unrealized Loss Position Less Than 12 Months 12 Months Or Longer Total As of December 31, 2016 (in millions) Fair Unrealized Fair Unrealized Fair Unrealized Securities available for sale: GSE mortgage-backed securities and CMOs $ 2,339.6 $ (26.6 ) $ 396.9 $ (11.5 ) $ 2,736.5 $ (38.1 ) U.S. Treasury and agency 828.3 (30.5 ) — — 828.3 (30.5 ) Securities held to maturity: GSE mortgage-backed securities 497.6 (3.2 ) — — 497.6 (3.2 ) State and municipal 581.7 (23.5 ) — — 581.7 (23.5 ) Total $ 4,247.2 $ (83.8 ) $ 396.9 $ (11.5 ) $ 4,644.1 $ (95.3 )

Loans (Tables)

Loans (Tables)	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Summary of Loans by Loan Portfolio Segment and Class	The following table summarizes People’s United’s loans by loan portfolio segment and class: September 30, 2017 December 31, 2016 (in millions) Originated Acquired Total Originated Acquired Total Commercial: Commercial real estate $ 10,194.1 $ 986.4 $ 11,180.5 $ 10,012.6 $ 234.7 $ 10,247.3 Commercial and industrial 7,971.3 653.4 8,624.7 7,939.0 186.1 8,125.1 Equipment financing 3,039.1 666.5 3,705.6 3,020.9 11.6 3,032.5 Total Commercial Portfolio 21,204.5 2,306.3 23,510.8 20,972.5 432.4 21,404.9 Retail: Residential mortgage: Adjustable-rate 5,800.9 147.5 5,948.4 5,453.8 95.3 5,549.1 Fixed-rate 706.7 125.9 832.6 613.5 54.1 667.6 Total residential mortgage 6,507.6 273.4 6,781.0 6,067.3 149.4 6,216.7 Home equity and other consumer: Home equity 1,981.8 59.7 2,041.5 2,044.9 27.7 2,072.6 Other consumer 47.3 3.9 51.2 50.0 0.7 50.7 Total home equity and other consumer 2,029.1 63.6 2,092.7 2,094.9 28.4 2,123.3 Total Retail Portfolio 8,536.7 337.0 8,873.7 8,162.2 177.8 8,340.0 Total loans $ 29,741.2 $ 2,643.3 $ 32,384.5 $ 29,134.7 $ 610.2 $ 29,744.9
Summary, by Loan Portfolio Segment, of Activity in Allowance for Loan Losses	The following tables present a summary, by loan portfolio segment, of activity in the allowance for loan losses for the three and nine months ended September 30, 2017 and 2016. With respect to the originated portfolio, an allocation of a portion of the allowance to one segment does not preclude its availability to absorb losses in another segment. Three months ended Commercial Retail September 30, 2017 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 198.3 $ 3.6 $ 201.9 $ 29.6 $ 0.1 $ 29.7 $ 231.6 Charge-offs (4.0 ) (1.0 ) (5.0 ) (1.8 ) — (1.8 ) (6.8 ) Recoveries 0.9 0.1 1.0 0.6 — 0.6 1.6 Net loan charge-offs (3.1 ) (0.9 ) (4.0 ) (1.2 ) — (1.2 ) (5.2 ) Provision for loan losses 4.3 1.3 5.6 1.3 0.1 1.4 7.0 Balance at end of period $ 199.5 $ 4.0 $ 203.5 $ 29.7 $ 0.2 $ 29.9 $ 233.4 Nine months ended Commercial Retail September 30, 2017 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 198.8 $ 6.1 $ 204.9 $ 24.2 $ 0.2 $ 24.4 $ 229.3 Charge-offs (12.0 ) (2.9 ) (14.9 ) (5.1 ) — (5.1 ) (20.0 ) Recoveries 3.8 0.1 3.9 1.7 — 1.7 5.6 Net loan charge-offs (8.2 ) (2.8 ) (11.0 ) (3.4 ) — (3.4 ) (14.4 ) Provision for loan losses 8.9 0.7 9.6 8.9 — 8.9 18.5 Balance at end of period $ 199.5 $ 4.0 $ 203.5 $ 29.7 $ 0.2 $ 29.9 $ 233.4 Three months ended Commercial Retail September 30, 2016 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 189.7 $ 7.2 $ 196.9 $ 23.3 $ 0.2 $ 23.5 $ 220.4 Charge-offs (2.7 ) (0.1 ) (2.8 ) (1.1 ) — (1.1 ) (3.9 ) Recoveries 0.9 — 0.9 0.5 — 0.5 1.4 Net loan charge-offs (1.8 ) (0.1 ) (1.9 ) (0.6 ) — (0.6 ) (2.5 ) Provision for loan losses 7.1 — 7.1 1.3 — 1.3 8.4 Balance at end of period $ 195.0 $ 7.1 $ 202.1 $ 24.0 $ 0.2 $ 24.2 $ 226.3 Nine months ended Commercial Retail September 30, 2016 (in millions) Originated Acquired Total Originated Acquired Total Total Balance at beginning of period $ 181.8 $ 7.9 $ 189.7 $ 21.1 $ 0.2 $ 21.3 $ 211.0 Charge-offs (10.7 ) (0.4 ) (11.1 ) (6.6 ) — (6.6 ) (17.7 ) Recoveries 1.6 — 1.6 2.5 — 2.5 4.1 Net loan charge-offs (9.1 ) (0.4 ) (9.5 ) (4.1 ) — (4.1 ) (13.6 ) Provision for loan losses 22.3 (0.4 ) 21.9 7.0 — 7.0 28.9 Balance at end of period $ 195.0 $ 7.1 $ 202.1 $ 24.0 $ 0.2 $ 24.2 $ 226.3
Summary of Allowance for Loan Losses by Loan Portfolio Segment and Impairment Methodology	The following is a summary, by loan portfolio segment and impairment methodology, of the allowance for loan losses and related portfolio balances: Originated Loans Originated Loans As of Individually Evaluated Collectively Evaluated September 30, 2017 for Impairment for Impairment Acquired Loans (1) Total (in millions) Portfolio Allowance Portfolio Allowance Portfolio Allowance Portfolio Allowance Commercial $ 172.5 $ 5.7 $ 21,032.0 $ 193.8 $ 2,306.3 $ 4.0 $ 23,510.8 $ 203.5 Retail 94.3 2.4 8,442.4 27.3 337.0 0.2 8,873.7 29.9 Total $ 266.8 $ 8.1 $ 29,474.4 $ 221.1 $ 2,643.3 $ 4.2 $ 32,384.5 $ 233.4 Originated Loans Originated Loans As of Individually Evaluated Collectively Evaluated December 31, 2016 for Impairment for Impairment Acquired Loans (1) Total (in millions) Portfolio Allowance Portfolio Allowance Portfolio Allowance Portfolio Allowance Commercial $ 161.8 $ 5.8 $ 20,810.7 $ 193.0 $ 432.4 $ 6.1 $ 21,404.9 $ 204.9 Retail 91.8 3.2 8,070.4 21.0 177.8 0.2 8,340.0 24.4 Total $ 253.6 $ 9.0 $ 28,881.1 $ 214.0 $ 610.2 $ 6.3 $ 29,744.9 $ 229.3 (1) Approximately $3.8 million of the allowance at September 30, 2017 relates to Commercial and Retail PCI loans totaling $406.5 million and $134.7 million, respectively. The remainder of the acquired portfolio represents purchased performing loans with an allowance of approximately $0.4 million at that date. The allowance at December 31, 2016 relates entirely to PCI loans (no acquired loans were purchased performing at that date).
Summarized Recorded Investments, by Class of Loan, in Originated Non-Performing Loans	The recorded investments, by class of loan, in originated non-performing September 30, December 31, (in millions) 2017 2016 Commercial: Commercial real estate $ 36.7 $ 22.3 Commercial and industrial 34.9 41.5 Equipment financing 54.1 39.4 Total (1) 125.7 103.2 Retail: Residential mortgage 33.8 27.4 Home equity 14.8 17.4 Other consumer — — Total (2) 48.6 44.8 Total $ 174.3 $ 148.0 (1) Reported net of government guarantees totaling $4.0 million and $13.1 million at September 30, 2017 and December 31, 2016, respectively. These government guarantees relate, almost entirely, to guarantees provided by the Small Business Administration as well as selected other Federal agencies and represent the carrying value of the loans that are covered by such guarantees, the extent of which (i.e. full or partial) varies by loan. At September 30, 2017, the principal loan classes to which these government guarantees relate are commercial and industrial loans (95%) and commercial real estate loans (5%). (2) Includes $17.8 million and $9.8 million of loans in the process of foreclosure at September 30, 2017 and December 31, 2016, respectively.
Summary of Recorded Investments in TDRs by Class of Loan	The following tables summarize, by class of loan, the recorded investments in loans modified as TDRs during the three and nine months ended September 30, 2017 and 2016. For purposes of this disclosure, recorded investments represent amounts immediately prior to and subsequent to the restructuring. Three Months Ended September 30, 2017 Pre-Modification Post-Modification Outstanding Outstanding Number Recorded Recorded (dollars in millions) of Contracts Investment Investment Commercial: Commercial real estate (1) 1 $ 0.1 $ 0.1 Commercial and industrial (2) 9 11.6 11.6 Equipment financing (3) 13 8.1 8.1 Total 23 19.8 19.8 Retail: Residential mortgage (4) 17 3.8 3.8 Home equity (5) 19 1.5 1.5 Other consumer — — — Total 36 5.3 5.3 Total 59 $ 25.1 $ 25.1 (1) Represents the following concession: extension of term (1 contract; recorded investment of $0.1 million). (2) Represents the following concessions: extension of term (9 contracts; recorded investment of $11.6 million). (3) Represents the following concessions: reduced payment and/or payment deferral (12 contracts; recorded investment of $8.0 million); or a combination of concessions (1 contract; recorded investment of $0.1 million). (4) Represents the following concessions: loans restructured through bankruptcy (9 contracts; recorded investment of $1.7 million); reduced payment and/or payment deferral (5 contract; recorded investment of $1.7 million); or a combination of concessions (3 contracts; recorded investment of $0.4 million). (5) Represents the following concessions: loans restructured through bankruptcy (10 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (4 contracts; recorded investment of $0.3 million); or a combination of concessions (5 contracts; recorded investment of $0.2 million). Nine Months Ended September 30, 2017 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 8 $ 5.3 $ 5.3 Commercial and industrial (2) 28 39.6 39.6 Equipment financing (3) 54 25.1 25.1 Total 90 70.0 70.0 Retail: Residential mortgage (4) 45 10.8 10.8 Home equity (5) 65 4.5 4.5 Other consumer — — — Total 110 15.3 15.3 Total 200 $ 85.3 $ 85.3 (1) Represents the following concessions: extension of term (5 contracts; recorded investment of $1.4 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $2.2 million); or a temporary rate reduction (1 contract; recorded investment of $1.7 million). (2) Represents the following concessions: extension of term (25 contracts; recorded investment of $29.9 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $9.4 million); or a combination of concessions (1 contract; recorded investment of $0.3 million). (3) Represents the following concessions: reduced payment and/or payment deferral (28 contracts; recorded investment of $17.4 million); or a combination of concessions (26 contracts; recorded investment of $7.7 million). (4) Represents the following concessions: loans restructured through bankruptcy (28 contracts; recorded investment of $4.2 million); reduced payment and/or payment deferral (10 contracts; recorded investment of $3.4 million); or a combination of concessions (7 contracts; recorded investment of $3.2 million). (5) Represents the following concessions: loans restructured through bankruptcy (41 contracts; recorded investment of $2.6 million); reduced payment and/or payment deferral (10 contracts; recorded investment of $0.8 million); or a combination of concessions (14 contracts; recorded investment of $1.1 million). Three Months Ended September 30, 2016 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 7 $ 22.1 $ 22.1 Commercial and industrial (2) 11 4.5 4.5 Equipment financing (3) 22 10.4 10.4 Total 40 37.0 37.0 Retail: Residential mortgage (4) 9 2.9 2.9 Home equity (5) 17 1.2 1.2 Other consumer — — — Total 26 4.1 4.1 Total 66 $ 41.1 $ 41.1 (1) Represents the following concessions: extension of term (5 contracts; recorded investment of $3.3 million); reduced payment and/or payment deferral (1 contract; recorded investment of $1.7 million); or a combination of concessions (1 contract; recorded investment of $17.1 million). (2) Represents the following concessions: extension of term (9 contracts; recorded investment of $4.1 million); or reduced payment and/or payment deferral (2 contracts; recorded investment of $0.4 million). (3) Represents the following concessions: extension of term (6 contracts; recorded investment of $4.3 million); reduced payment and/or payment deferral (13 contracts; recorded investment of $4.7 million); or a combination of concessions (3 contracts; recorded investment of $1.4 million). (4) Represents the following concessions: loans restructured through bankruptcy (6 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (1 contract; recorded investment of $0.7 million); or a combination of concessions (2 contracts; recorded investment of $1.2 million). (5) Represents the following concessions: loans restructured through bankruptcy (11 contracts; recorded investment of $0.5 million); reduced payment and/or payment deferral (1 contract; recorded investment of $0.2 million); or a combination of concessions (5 contracts; recorded investment of $0.5 million). Nine Months Ended September 30, 2016 (dollars in millions) Number Pre-Modification Post-Modification Commercial: Commercial real estate (1) 12 $ 25.9 $ 25.9 Commercial and industrial (2) 36 22.9 22.9 Equipment financing (3) 49 21.7 21.7 Total 97 70.5 70.5 Retail: Residential mortgage (4) 47 13.1 13.1 Home equity (5) 50 3.8 3.8 Other consumer — — — Total 97 16.9 16.9 Total 194 $ 87.4 $ 87.4 (1) Represents the following concessions: extension of term (8 contracts; recorded investment of $6.2 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $2.6 million); or a combination of concessions (2 contracts; recorded investment of $17.1 million). (2) Represents the following concessions: extension of term (23 contracts; recorded investment of $12.3 million); reduced payment and/or payment deferral (9 contracts; recorded investment of $9.8 million); or a combination of concessions (4 contracts; recorded investment of $0.8 million). (3) Represents the following concessions: extension of term (17 contracts; recorded investment of $6.3 million); reduced payment and/or payment deferral (25 contracts; recorded investment of $12.5 million); or a combination of concessions (7 contracts; recorded investment of $2.9 million). (4) Represents the following concessions: loans restructured through bankruptcy (18 contracts; recorded investment of $3.2 million); reduced payment and/or payment deferral (11 contracts; recorded investment of $5.5 million); or a combination of concessions (18 contracts; recorded investment of $4.4 million). (5) Represents the following concessions: loans restructured through bankruptcy (31 contracts; recorded investment of $2.1 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $0.3 million); or a combination of concessions (17 contracts; recorded investment of $1.4 million).
Summary of Recorded Investments in TDRs by Class of Loan, Subsequently Defaulted	The following is a summary, by class of loan, of information related to TDRs completed within the previous 12 months that subsequently defaulted during the three and nine months ended September 30, 2017 and 2016. For purposes of this disclosure, the previous 12 months is measured from October 1 of the respective prior year and a default represents a previously-modified loan that became past due 30 days or more during the three or nine months ended September 30, 2017 or 2016. Three Months Ended September 30, 2017 2016 (dollars in millions) Number Recorded Number Recorded Commercial: Commercial real estate — $ — — $ — Commercial and industrial 1 0.1 — — Equipment financing 8 4.2 14 2.2 Total 9 4.3 14 2.2 Retail: Residential mortgage 2 0.9 3 0.6 Home equity 5 0.8 — — Other consumer — — — — Total 7 1.7 3 0.6 Total 16 $ 6.0 17 $ 2.8 Nine Months Ended September 30, 2017 2016 (dollars in millions) Number Recorded Number Recorded Commercial: Commercial real estate — $ — 2 $ 0.9 Commercial and industrial 4 1.5 5 0.6 Equipment financing 15 6.8 20 5.9 Total 19 8.3 27 7.4 Retail: Residential mortgage 9 2.7 10 1.9 Home equity 11 1.3 7 0.5 Other consumer — — — — Total 20 4.0 17 2.4 Total 39 $ 12.3 44 $ 9.8
Summary of Individually-Evaluated Impaired Loans by Class of Loan	People’s United’s impaired loans consist of certain loans that have been placed on non-accrual individually-evaluated As of September 30, 2017 As of December 31, 2016 (in millions) Unpaid Recorded Related Unpaid Recorded Related Without a related allowance for loan losses: Commercial: Commercial real estate $ 50.7 $ 46.1 $ — $ 41.4 $ 40.0 $ — Commercial and industrial 39.3 36.7 — 50.7 45.7 — Equipment financing 42.8 39.1 — 38.2 35.3 — Retail: Residential mortgage 66.8 60.0 — 63.6 58.0 — Home equity 23.5 20.0 — 22.4 18.7 — Other consumer — — — — — — Total $ 223.1 $ 201.9 $ — $ 216.3 $ 197.7 $ — With a related allowance for loan losses: Commercial: Commercial real estate $ 13.5 $ 12.8 $ 1.2 $ 12.2 $ 11.4 $ 0.6 Commercial and industrial 25.2 24.6 3.0 25.9 25.0 4.7 Equipment financing 14.1 13.2 1.5 5.0 4.4 0.5 Retail: Residential mortgage 12.4 12.4 1.7 13.1 13.1 2.3 Home equity 1.9 1.9 0.7 2.1 2.0 0.9 Other consumer — — — — — — Total $ 67.1 $ 64.9 $ 8.1 $ 58.3 $ 55.9 $ 9.0 Total impaired loans: Commercial: Commercial real estate $ 64.2 $ 58.9 $ 1.2 $ 53.6 $ 51.4 $ 0.6 Commercial and industrial 64.5 61.3 3.0 76.6 70.7 4.7 Equipment financing 56.9 52.3 1.5 43.2 39.7 0.5 Total 185.6 172.5 5.7 173.4 161.8 5.8 Retail: Residential mortgage 79.2 72.4 1.7 76.7 71.1 2.3 Home equity 25.4 21.9 0.7 24.5 20.7 0.9 Other consumer — — — — — — Total 104.6 94.3 2.4 101.2 91.8 3.2 Total $ 290.2 $ 266.8 $ 8.1 $ 274.6 $ 253.6 $ 9.0
Schedule of Impaired Financing Receivable	The following tables summarize, by class of loan, the average recorded investment and interest income recognized on impaired loans for the periods indicated. The average recorded investment amounts are based on month-end Three Months Ended September 30, 2017 2016 (in millions) Average Interest Average Interest Commercial: Commercial real estate $ 61.8 $ 0.3 $ 54.1 $ 0.4 Commercial and industrial 59.7 0.7 60.5 0.3 Equipment financing 46.5 0.2 38.2 0.1 Total 168.0 1.2 152.8 0.8 Retail: Residential mortgage 72.4 0.4 71.7 0.4 Home equity 21.8 0.1 21.3 0.1 Other consumer — — — — Total 94.2 0.5 93.0 0.5 Total $ 262.2 $ 1.7 $ 245.8 $ 1.3 Nine Months Ended September 30, 2017 2016 (in millions) Average Interest Average Interest Commercial: Commercial real estate $ 56.9 $ 0.9 $ 58.6 $ 1.1 Commercial and industrial 66.1 1.6 61.9 1.2 Equipment financing 43.0 0.4 35.9 0.2 Total 166.0 2.9 156.4 2.5 Retail: Residential mortgage 71.9 1.3 72.1 1.2 Home equity 21.1 0.3 21.9 0.2 Other consumer — — — — Total 93.0 1.6 94.0 1.4 Total $ 259.0 $ 4.5 $ 250.4 $ 3.9
Summary of Aging Information by Class of Loan	The following tables summarize, by class of loan, aging information for originated loans: Past Due As of September 30, 2017 (in millions) Current 30-89 90 Days Total Total Commercial: Commercial real estate $ 10,158.6 $ 20.3 $ 15.2 $ 35.5 $ 10,194.1 Commercial and industrial 7,943.2 10.1 18.0 28.1 7,971.3 Equipment financing 2,942.7 88.4 8.0 96.4 3,039.1 Total 21,044.5 118.8 41.2 160.0 21,204.5 Retail: Residential mortgage 6,455.4 31.8 20.4 52.2 6,507.6 Home equity 1,968.5 7.0 6.3 13.3 1,981.8 Other consumer 46.5 0.8 — 0.8 47.3 Total 8,470.4 39.6 26.7 66.3 8,536.7 Total originated loans $ 29,514.9 $ 158.4 $ 67.9 $ 226.3 $ 29,741.2 Past Due As of December 31, 2016 (in millions) Current 30-89 90 Days Total Total Commercial: Commercial real estate $ 9,989.9 $ 10.9 $ 11.8 $ 22.7 $ 10,012.6 Commercial and industrial 7,899.2 10.0 29.8 39.8 7,939.0 Equipment financing 2,941.5 68.4 11.0 79.4 3,020.9 Total 20,830.6 89.3 52.6 141.9 20,972.5 Retail: Residential mortgage 6,027.5 22.0 17.8 39.8 6,067.3 Home equity 2,030.3 5.2 9.4 14.6 2,044.9 Other consumer 49.7 0.3 — 0.3 50.0 Total 8,107.5 27.5 27.2 54.7 8,162.2 Total originated loans $ 28,938.1 $ 116.8 $ 79.8 $ 196.6 $ 29,134.7
Summary of Credit Quality Indicators by Class of Loan	The following is a summary, by class of loan, of credit quality indicators: As of September 30, 2017 (in millions) Commercial Commercial Equipment Total Commercial: Originated loans: Pass $ 9,926.2 $ 7,588.1 $ 2,619.7 $ 20,134.0 Special mention 129.1 122.8 101.8 353.7 Substandard 137.9 259.6 317.6 715.1 Doubtful 0.9 0.8 — 1.7 Total originated loans 10,194.1 7,971.3 3,039.1 21,204.5 Acquired loans: Pass 940.9 562.2 666.5 2,169.6 Special mention 6.2 42.4 — 48.6 Substandard 38.6 48.8 — 87.4 Doubtful 0.7 — — 0.7 Total acquired loans 986.4 653.4 666.5 2,306.3 Total $ 11,180.5 $ 8,624.7 $ 3,705.6 $ 23,510.8 As of September 30, 2017 (in millions) Residential Home Other Total Retail: Originated loans: Low risk $ 3,259.8 $ 928.2 $ 27.2 $ 4,215.2 Moderate risk 2,715.9 652.2 8.0 3,376.1 High risk 531.9 401.4 12.1 945.4 Total originated loans 6,507.6 1,981.8 47.3 8,536.7 Acquired loans: Low risk 154.9 — — 154.9 Moderate risk 60.2 — — 60.2 High risk 58.3 59.7 3.9 121.9 Total acquired loans 273.4 59.7 3.9 337.0 Total $ 6,781.0 $ 2,041.5 $ 51.2 $ 8,873.7 As of December 31, 2016 (in millions) Commercial Commercial Equipment Total Commercial: Originated loans: Pass $ 9,817.2 $ 7,580.6 $ 2,617.9 $ 20,015.7 Special mention 107.3 121.9 98.8 328.0 Substandard 87.1 233.3 304.2 624.6 Doubtful 1.0 3.2 — 4.2 Total originated loans 10,012.6 7,939.0 3,020.9 20,972.5 Acquired loans: Pass 182.9 155.5 1.0 339.4 Special mention 13.5 3.6 8.6 25.7 Substandard 37.6 27.0 2.0 66.6 Doubtful 0.7 — — 0.7 Total acquired loans 234.7 186.1 11.6 432.4 Total $ 10,247.3 $ 8,125.1 $ 3,032.5 $ 21,404.9 Residential Home Other As of December 31, 2016 (in millions) Mortgage Equity Consumer Total Retail: Originated loans: Low risk $ 3,016.4 $ 950.9 $ 31.1 $ 3,998.4 Moderate risk 2,538.9 663.9 7.2 3,210.0 High risk 512.0 430.1 11.7 953.8 Total originated loans 6,067.3 2,044.9 50.0 8,162.2 Acquired loans: Low risk 75.7 — — 75.7 Moderate risk 27.5 — — 27.5 High risk 46.2 27.7 0.7 74.6 Total acquired loans 149.4 27.7 0.7 177.8 Total $ 6,216.7 $ 2,072.6 $ 50.7 $ 8,340.0
Summarized Activity in Accretable Yield for Acquired Loan Portfolio	The following table summarizes activity in the accretable yield for the PCI loan portfolio: Three Months Ended Nine Months Ended September 30, September 30, (in millions) 2017 2016 2017 2016 Balance at beginning of period $ 233.4 $ 270.3 $ 255.4 $ 296.0 Acquisitions — — 13.1 — Accretion (7.1 ) (9.0 ) (22.5 ) (31.1 ) Reclassification from nonaccretable difference for loans with improved cash flows (1) — — — — Other changes in expected cash flows (2) — 2.4 (19.7 ) (1.2 ) Balance at end of period $ 226.3 $ 263.7 $ 226.3 $ 263.7 (1) Results in increased interest accretion as a prospective yield adjustment over the remaining life of the corresponding pool of loans. (2) Represents changes in cash flows expected to be collected due to factors other than credit (e.g. changes in prepayment assumptions and/or changes in interest rates on variable rate loans), as well as loan sales, modifications and payoffs.

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Loss	The following is a summary of the changes in the components of accumulated other comprehensive loss (“AOCL”), which are included in People’s United’s stockholders’ equity on an after-tax (in millions) Pension Net Unrealized Net Unrealized Net Unrealized Total Balance at December 31, 2016 $ (145.6 ) $ (32.3 ) $ (17.4 ) $ 0.3 $ (195.0 ) Other comprehensive income before reclassifications — 11.1 — 0.3 11.4 Amounts reclassified from AOCL (1) 2.8 9.9 1.6 (0.4 ) 13.9 Current period other comprehensive income 2.8 21.0 1.6 (0.1 ) 25.3 Balance at September 30, 2017 $ (142.8 ) $ (11.3 ) $ (15.8 ) $ 0.2 $ (169.7 ) (in millions) Pension Net Unrealized Net Unrealized Net Unrealized Total Balance at December 31, 2015 $ (140.0 ) $ (17.7 ) $ (19.5 ) $ 0.0 $ (177.2 ) Other comprehensive income (loss) before reclassifications — 52.4 — (0.1 ) 52.3 Amounts reclassified from AOCL (1) 2.8 (0.1 ) 1.5 0.3 4.5 Current period other comprehensive income 2.8 52.3 1.5 0.2 56.8 Balance at September 30, 2016 $ (137.2 ) $ 34.6 $ (18.0 ) $ 0.2 $ (120.4 ) (1) See the following table for details about these reclassifications.
Summary of Amounts Reclassified from AOCL	The following is a summary of the amounts reclassified from AOCL: Amounts Reclassified from AOCL Three Months Ended Nine Months Ended Affected Line Item in the Statement Where Net Income is Presented (in millions) 2017 2016 2017 2016 Details about components of AOCL: Amortization of pension and other postretirement plans items: Net actuarial loss $ (1.7 ) $ (1.7 ) $ (5.1 ) $ (4.8 ) (1) Prior service credit 0.2 0.2 0.6 0.6 (1) (1.5 ) (1.5 ) (4.5 ) (4.2 ) Income before income tax expense 0.6 0.6 1.7 1.4 Income tax expense (0.9 ) (0.9 ) (2.8 ) (2.8 ) Net income Reclassification adjustment for net realized gains (losses) on securities available for sale — — (15.6 ) 0.1 Income before income tax expense (2) — — 5.7 — Income tax expense — — (9.9 ) 0.1 Net income Amortization of unrealized losses on securities transferred to held to held to maturity (0.9 ) (0.9 ) (2.6 ) (2.4 ) Income before income tax expense (3) 0.3 0.4 1.0 0.9 Income tax expense (0.6 ) (0.5 ) (1.6 ) (1.5 ) Net income Amortization of unrealized gains and losses on cash flow hedges: Interest rate swaps 0.3 (0.1 ) 0.6 (0.6 ) (4) Interest rate locks 0.1 0.1 0.1 0.1 (4) 0.4 — 0.7 (0.5 ) Income before income tax expense (0.2 ) — (0.3 ) 0.2 Income tax expense 0.2 — 0.4 (0.3 ) Net income Total reclassifications for the period $ (1.3 ) $ (1.4 ) $ (13.9 ) $ (4.5 ) (1) Included in the computation of net periodic benefit income (expense) reflected in compensation and benefits expense (see Note 8 for additional details). (2) Included in other non-interest (3) Included in interest and dividend income - securities. (4) Included in interest expense - notes and debentures.

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Common Share, Reflecting Application of Two-Class Method	The following is an analysis of People’s United’s basic and diluted EPS, reflecting the application of the two-class Three Months Ended Nine Months Ended September 30, September 30, (in millions, except per common share data) 2017 2016 2017 2016 Net income available to common shareholders $ 87.3 $ 73.7 $ 220.4 $ 205.1 Dividends paid on and undistributed earnings (0.1 ) (0.2 ) (0.4 ) (0.6 ) Earnings attributable to common shareholders $ 87.2 $ 73.5 $ 220.0 $ 204.5 Weighted average common shares outstanding 336.9 302.9 327.6 302.4 Effect of dilutive equity-based awards 1.9 0.4 2.0 0.4 Weighted average common and common-equivalent 338.8 303.3 329.6 302.8 Basic EPS $ 0.26 $ 0.24 $ 0.67 $ 0.68 Diluted EPS $ 0.26 $ 0.24 $ 0.67 $ 0.68

Goodwill and Other Acquisitio29

Goodwill and Other Acquisition-Related Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in Carrying Amount of Goodwill	Changes in the carrying amount of People’s United’s goodwill are summarized as follows for the nine months ended September 30, 2017 and 2016: Operating Segment (in millions) Commercial Retail Wealth Total Balance at December 31, 2016 $ 1,222.1 $ 679.6 $ 91.0 $ 1,992.7 Acquisition of: Suffolk 229.8 40.5 — 270.3 LEAF 148.4 — — 148.4 Balance at September 30, 2017 $ 1,600.3 $ 720.1 $ 91.0 $ 2,411.4 Operating Segment (in millions) Commercial Retail Wealth Total Balance at December 31, 2015 $ 1,222.8 $ 681.9 $ 54.0 $ 1,958.7 Acquisition of Eagle Insurance Group, LLC — — 1.4 1.4 Adjustments (0.7 ) (2.3 ) (0.1 ) (3.1 ) Balance at September 30, 2016 $ 1,222.1 $ 679.6 $ 55.3 $ 1,957.0

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2017
Retirement Benefits [Abstract]
Components of Net Periodic Benefit (Income) Expense and Other Amounts	Components of net periodic benefit (income) expense and other amounts recognized in other comprehensive income for the People’s Qualified Plan, the Chittenden Qualified Plan and the Supplemental Plans (together the “Pension Plans”) and the Other Postretirement Plan are as follows: Other Pension Plans Postretirement Plan Three months ended September 30 (in millions) 2017 2016 2017 2016 Net periodic benefit (income) expense: Service cost $ — $ — $ 0.1 $ — Interest cost 4.9 4.7 0.1 0.2 Expected return on plan assets (9.6 ) (8.7 ) — — Recognized net actuarial loss 1.6 1.6 0.1 0.1 Recognized prior service credit (0.2 ) (0.2 ) — — Settlements 1.1 0.3 — — Net periodic benefit (income) expense $ (2.2 ) $ (2.3 ) $ 0.3 $ 0.3 Other Pension Plans Postretirement Plan Nine months ended September 30 (in millions) 2017 2016 2017 2016 Net periodic benefit (income) expense: Service cost $ — $ — $ 0.2 $ 0.2 Interest cost 14.3 14.1 0.4 0.5 Expected return on plan assets (28.3 ) (25.9 ) — — Recognized net actuarial loss 4.9 4.6 0.2 0.2 Recognized prior service credit (0.6 ) (0.6 ) — — Settlements 2.6 0.9 — — Net periodic benefit (income) expense (7.1 ) (6.9 ) 0.8 0.9 Other changes in plan assets and benefit obligations recognized in other comprehensive income: Net actuarial loss (4.9 ) (4.6 ) (0.2 ) (0.2 ) Prior service credit 0.6 0.6 — — Total pre-tax (4.3 ) (4.0 ) (0.2 ) (0.2 ) Total recognized in net periodic benefit $ (11.4 ) $ (10.9 ) $ 0.6 $ 0.7

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables summarize People’s United’s financial instruments that are measured at fair value on a recurring basis: ` Fair Value Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Trading account securities: U.S. Treasury $ 8.3 $ — $ — $ 8.3 Securities available for sale: U.S. Treasury and agency 741.9 — — 741.9 GSE mortgage-backed securities and CMOs — 2,446.6 — 2,446.6 Equity securities 9.0 — — 9.0 Other assets: — Exchange-traded funds 35.0 — — 35.0 Fixed income securities — 1.7 — 1.7 Mutual funds 3.6 — — 3.6 Interest rate swaps/caps — 101.9 — 101.9 Foreign exchange contracts — 0.2 — 0.2 Forward commitments to sell residential — 0.6 — 0.6 Total $ 797.8 $ 2,551.0 $ — $ 3,348.8 Financial liabilities: Interest rate swaps/caps $ — $ 60.5 $ — $ 60.5 Risk participation agreements (1) — — — — Foreign exchange contracts — 0.2 — 0.2 Interest rate-lock commitments on residential mortgage loans — 0.7 — 0.7 Total $ — $ 61.4 $ — $ 61.4 Fair Value Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Trading account securities: U.S. Treasury $ 6.8 $ — $ — $ 6.8 Securities available for sale: U.S. Treasury and agency 859.7 — — 859.7 GSE mortgage-backed securities and CMOs — 3,550.0 — 3,550.0 Equity securities — 0.2 — 0.2 Other assets: Exchange-traded funds 32.6 — — 32.6 Fixed income securities — 4.3 — 4.3 Mutual funds 2.7 — — 2.7 Interest rate swaps/caps — 173.1 — 173.1 Foreign exchange contracts — 0.6 — 0.6 Forward commitments to sell residential — 0.3 — 0.3 Total $ 901.8 $ 3,728.5 $ — $ 4,630.3 Financial liabilities: Interest rate swaps/caps $ — $ 121.0 $ — $ 121.0 Risk participation agreements (1) — — — — Foreign exchange contracts — 0.3 — 0.3 Interest rate-lock commitments on residential mortgage loans — 0.4 — 0.4 Total $ — $ 121.7 $ — $ 121.7 (1) At both September 30, 2017 and December 31, 2016, the fair value of risk participation agreements totaled less than $0.1 million (see Note 12).
Assets Measured at Fair Value on Non-Recurring Basis	The following tables summarize People’s United’s assets that are measured at fair value on a non-recurring Fair Value Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Loans held for sale (1) $ — $ 15.0 $ — $ 15.0 Impaired loans (2) — — 64.9 64.9 REO and repossessed assets (3) — — 16.4 16.4 Total $ — $ 15.0 $ 81.3 $ 96.3 Fair Value Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Loans held for sale (1) $ — $ 39.3 $ — $ 39.3 Impaired loans (2) — — 55.9 55.9 REO and repossessed assets (3) — — 19.3 19.3 Total $ — $ 39.3 $ 75.2 $ 114.5 (1) Consists of residential mortgage loans; no fair value adjustments were recorded for the nine months ended September 30, 2017 and 2016. (2) Represents the recorded investment in impaired loans with a related allowance for loan losses measured in accordance with applicable accounting guidance. The total consists of $50.6 million of Commercial loans and $14.3 million of Retail loans at September 30, 2017. The provision for loan losses on impaired loans totaled $4.1 million and $3.5 million for the nine months ended September 30, 2017 and 2016, respectively. (3) Represents: (i) $6.3 million of commercial REO; (ii) $4.7 million of residential REO; and (iii) $5.4 million of repossessed assets at September 30, 2017. Charge-offs to the allowance for loan losses related to loans that were transferred to REO or repossessed assets totaled $2.2 million and $3.3 million for the nine months ended September 30, 2017 and 2016, respectively. Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest
Carrying Amounts and Estimated Fair Values of Financial Instruments	The following tables summarize the carrying amounts, estimated fair values and placement in the fair value hierarchy of People’s United’s financial instruments that are not measured at fair value either on a recurring or non-recurring Estimated Fair Value Carrying Measurements Using As of September 30, 2017 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Cash and due from banks $ 414.1 $ 414.1 $ — $ — $ 414.1 Short-term investments 302.5 — 302.5 — 302.5 Securities held to maturity 3,387.6 — 3,434.1 1.5 3,435.6 FHLB and FRB stock 320.9 — 320.9 — 320.9 Total loans, net (1) 32,086.2 — 6,583.6 25,363.9 31,947.5 Financial liabilities: Time deposits 5,235.8 — 5,232.4 — 5,232.4 Other deposits 27,311.5 — 27,311.5 — 27,311.5 FHLB advances 3,074.1 — 3,076.0 — 3,076.0 Federal funds purchased 543.0 — 543.0 — 543.0 Customer repurchase agreements 295.8 — 295.8 — 295.8 Other borrowings 231.1 — 230.9 — 230.9 Notes and debentures 906.2 — 902.6 — 902.6 (1) Excludes impaired loans totaling $64.9 million measured at fair value on a non-recurring Estimated Fair Value Carrying Measurements Using As of December 31, 2016 (in millions) Level 1 Level 2 Level 3 Total Financial assets: Cash and due from banks $ 432.4 $ 432.4 $ — $ — $ 432.4 Short-term investments 181.7 — 181.7 — 181.7 Securities held to maturity 2,005.4 — 2,011.2 1.5 2,012.7 FHLB and FRB stock 315.8 — 315.8 — 315.8 Total loans, net (1) 29,459.7 — 6,028.4 23,238.1 29,266.5 Financial liabilities: Time deposits 4,542.2 — 4,539.7 — 4,539.7 Other deposits 25,318.6 — 25,318.6 — 25,318.6 FHLB advances 3,061.1 — 3,064.4 — 3,064.4 Federal funds purchased 617.0 — 617.0 — 617.0 Customer repurchase agreements 343.3 — 343.3 — 343.3 Other borrowings 35.4 — 35.4 — 35.4 Notes and debentures 1,030.1 — 1,000.0 — 1,000.0 (1) Excludes impaired loans totaling $55.9 million measured at fair value on a non-recurring

Derivative Financial Instrume32

Derivative Financial Instruments and Hedging Activities (Tables)	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Fair Values of Derivatives Outstanding	The table below provides a summary of the notional amounts and fair values (presented on a gross basis) of derivatives outstanding: Fair Values (1) Notional Amounts Assets Liabilities (in millions) Type of Sept. 30, Dec. 31, Sept. 30, Dec. 31, Sept. 30, Dec. 31, Derivatives Not Designated as Hedging Instruments: Interest rate swaps/caps: Commercial customers N/A $ 6,101.2 $ 5,612.2 $ 91.5 $ 93.9 $ 39.7 $ 46.9 Institutional counterparties N/A 5,958.2 5,620.2 10.4 65.6 20.8 74.0 Risk participation agreements (2) N/A 383.4 251.9 — — — — Foreign exchange contracts N/A 42.6 101.2 0.2 0.6 0.2 0.3 Forward commitments to sell N/A 26.0 48.6 0.6 0.3 — — Interest rate-lock commitments on residential mortgage loans N/A 31.7 57.0 — — 0.7 0.4 Total 102.7 160.4 61.4 121.6 Derivatives Designated as Hedging Instruments: Interest rate swaps: Subordinated notes Fair value 375.0 375.0 — 13.6 — — Loans Cash flow 210.0 — — — — — Subordinated notes Cash flow — 125.0 — — — 0.1 Total — 13.6 — 0.1 Total fair value of derivatives $ 102.7 $ 174.0 $ 61.4 $ 121.7 (1) Assets are recorded in other assets and liabilities are recorded in other liabilities. (2) Fair value totaled less than $0.1 million at both dates.
Impact of Derivatives on Pre-Tax Income and Accumulated Other Comprehensive Loss	The following table summarizes the impact of People’s United’s derivatives on pre-tax Amount of Pre-Tax Gain (Loss) Amount of Pre-Tax Gain (Loss) Type of Recognized in Earnings (1) Recognized in AOCL Nine months ended September 30 (in millions) 2017 2016 2017 2016 Derivatives Not Designated as Hedging Instruments: Interest rate swaps/caps: Commercial customers N/A $ 45.4 $ 210.7 $ — $ — Institutional counterparties N/A (39.1 ) (200.3 ) — — Foreign exchange contracts N/A 0.3 (0.6 ) — — Risk participation agreements N/A 0.5 0.1 — — Forward commitments to sell residential mortgage loans N/A 0.1 0.8 — — Interest rate-lock commitments on residential mortgage loans N/A (0.1 ) (1.1 ) — — Total 7.1 9.6 — — Derivatives Designated as Hedging Instruments: Interest rate swaps Fair value 4.5 6.4 — — Interest rate swaps Cash flow 0.6 (0.6 ) — (0.2 ) Interest rate locks Cash flow 0.1 0.1 — — Total 5.2 5.9 — (0.2 ) Total $ 12.3 $ 15.5 $ — $ (0.2 ) (1) Amounts recognized in earnings are recorded in interest income, interest expense or other non-interest non-interest

Balance Sheet Offsetting (Table

Balance Sheet Offsetting (Tables)	9 Months Ended
	Sep. 30, 2017
Text Block [Abstract]
Summary of Gross Presentation, Financial Instruments that are Eligible for Offset Not Offset in Consolidated Statement of Condition	The Company’s derivative contracts with commercial customers and customer repurchase agreements are not subject to master netting arrangements and, therefore, have been excluded from the tables below. Gross Gross Net Gross Amounts Not Offset Financial Net As of September 30, 2017 (in millions) Instruments Collateral Amount Financial assets: Interest rate swaps/caps: Counterparty A $ 1.7 $ — $ 1.7 $ (1.7 ) $ — $ — Counterparty B 0.8 — 0.8 (0.8 ) — — Counterparty C 1.4 — 1.4 (1.4 ) — — Counterparty D 2.8 — 2.8 (2.8 ) — — Counterparty E 2.4 — 2.4 — — 2.4 Other counterparties 1.3 — 1.3 (0.3 ) (0.9 ) 0.1 Foreign exchange contracts 0.2 — 0.2 — — 0.2 Total $ 10.6 $ — $ 10.6 $ (7.0 ) $ (0.9 ) $ 2.7 Financial liabilities: Interest rate swaps/caps: Counterparty A $ 3.2 $ — $ 3.2 $ (1.7 ) $ (1.5 ) $ — Counterparty B 6.9 — 6.9 (0.8 ) (6.1 ) — Counterparty C 3.7 — 3.7 (1.4 ) (2.3 ) — Counterparty D 5.9 — 5.9 (2.8 ) (3.1 ) — Other counterparties 1.2 — 1.2 (0.3 ) (0.9 ) — Foreign exchange contracts 0.2 — 0.2 — — 0.2 Total $ 21.1 $ — $ 21.1 $ (7.0 ) $ (13.9 ) $ 0.2 Gross Gross Net Gross Amounts Not Offset Financial Net As of December 31, 2016 (in millions) Instruments Collateral Amount Financial assets: Interest rate swaps/caps: Counterparty A $ 1.9 $ — $ 1.9 $ (1.9 ) $ — $ — Counterparty B 1.0 — 1.0 (1.0 ) — — Counterparty C 1.7 — 1.7 (1.7 ) — — Counterparty D 3.4 — 3.4 (3.4 ) — — Counterparty E 69.6 — 69.6 (50.0 ) (19.6 ) — Other counterparties 1.6 — 1.6 (0.3 ) (1.3 ) — Foreign exchange contracts 0.6 — 0.6 — — 0.6 Total $ 79.8 $ — $ 79.8 $ (58.3 ) $ (20.9 ) $ 0.6 Financial liabilities: Interest rate swaps/caps: Counterparty A $ 4.3 $ — $ 4.3 $ (1.9 ) $ (2.4 ) $ — Counterparty B 7.7 — 7.7 (1.0 ) (6.7 ) — Counterparty C 3.4 — 3.4 (1.7 ) (1.1 ) 0.6 Counterparty D 6.9 — 6.9 (3.4 ) (1.7 ) 1.8 Counterparty E 50.0 — 50.0 (50.0 ) — — Other counterparties 1.8 — 1.8 (0.3 ) (1.5 ) — Foreign exchange contracts 0.3 — 0.3 — — 0.3 Total $ 74.4 $ — $ 74.4 $ (58.3 ) $ (13.4 ) $ 2.7
Summary of Collateral Swaps	The following table shows the extent to which assets and liabilities exchanged under resale and repurchase agreements have been offset in the Consolidated Statements of Condition. These agreements: (i) are entered into simultaneously with the same financial institution counterparty; (ii) have the same principal amounts and inception/maturity dates; and (iii) are subject to a master netting arrangement that contains a conditional right of offset upon default. At September 30, 2017, the Company posted as collateral marketable securities with a fair value of $248.3 million and, in turn, accepted as collateral marketable securities with a fair value of $254.4 million. As of September 30, 2017 (in millions) Gross Gross Net Total resale agreements $ 250.0 $ (250.0 ) $ — Total repurchase agreements $ 250.0 $ (250.0 ) $ —

General - Additional Informatio

General - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Affordable housing investments	$ 250		$ 250		$ 195.2
Future contingent commitments	109.6		$ 109.6		$ 92.5
Amortization period			10 years
Amortization expense included in income tax expense	$ 4.2	$ 3	$ 12.3	$ 8.9

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) shares in Millions, $ in Millions	Aug. 01, 2017USD ($)	Apr. 01, 2017USD ($)Branchesshares	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)Securitization	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Interest income on loans acquired			$ 300.6	$ 249.5	$ 836.2	$ 735.7
Loans outstanding principal balance			630.6		630.6		$ 707
Tax deductible goodwill amount			73.2		73.2		$ 77.9
LEAF Commercial Capital, Inc. [Member]
Business Acquisition [Line Items]
Business acquisition cash consideration transferred	$ 220
Business acquisition, date of acquisition agreement	Aug. 1, 2017
Merger-related expenses					2.2
Net deferred tax liabilities			3.9		3.9
Repayment of borrowings					$ 460
Number of remaining securitization which can be repaid without penalty in 2018 | Securitization					1
Loans	$ 717.9
Suffolk Bancorp [Member]
Business Acquisition [Line Items]
Merger-related expenses					$ 26.5	$ 1.9
Net deferred tax liabilities			0.3		$ 0.3
Business acquisition common stock shares | shares		26.6
Business acquisition common stock fair value		$ 485
Number of branches acquired | Branches		27
Loans		$ 1,617.5
Suffolk Bancorp [Member] | Core Deposit Intangible [Member]
Business Acquisition [Line Items]
Amortization period for core deposit intangible					6 years
Businesses Acquired in 2017 [Member]
Business Acquisition [Line Items]
Interest income on loans acquired					$ 44
Businesses Acquired in 2017 [Member] | Purchased Credit Impaired Loans [Member]
Business Acquisition [Line Items]
Loans			57		57
Loans outstanding principal balance			67		67
Businesses Acquired in 2017 [Member] | Purchased Performing Loans [Member]
Business Acquisition [Line Items]
Loans			2,280		2,280
Loans outstanding principal balance			$ 2,320		$ 2,320

Acquisitions - Estimated Fair V

Acquisitions - Estimated Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Aug. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 2,411.4			$ 1,992.7	$ 1,957	$ 1,958.7
LEAF Commercial Capital, Inc. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 74.9
Loans		717.9
Goodwill		148.4
Premises and equipment		2.4
Other assets		13
Total assets		957.7
Liabilities:
Borrowings		708.1
Other liabilities		29.6
Total liabilities		737.7
Total purchase price		220
LEAF Commercial Capital, Inc. [Member] | Trade Name [Member]
Business Acquisition [Line Items]
Core deposit intangible		0.9
LEAF Commercial Capital, Inc. [Member] | Noncompete Agreements [Member]
Business Acquisition [Line Items]
Core deposit intangible		$ 0.2
Suffolk Bancorp [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 174
Securities			167.4
Loans			1,617.5
Goodwill			270.3
Core deposit intangible			28.1
Premises and equipment			40.4
Bank-owned life insurance			54.1
Other real estate owned			0.5
Other assets			28.9
Total assets			2,381.2
Liabilities:
Deposits			1,852.4
Borrowings			15.1
Other liabilities			28.9
Total liabilities			1,896.4
Total purchase price			$ 484.8

Acquisitions - Summary of Pro F

Acquisitions - Summary of Pro Forma Financial Information Reflecting Acquisition (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Selected Financial Results:
Net interest income	$ 835.9	$ 797.3
Provision for loan losses	18.5	28.9
Non-interest income	275.5	275.5
Non-interest expense	720.6	707.1
Net income	258	227.7
Net income applicable to common shareholders	$ 247.5	$ 227.7
Basic and diluted earnings per common share	$ 0.73	$ 0.69

Securities and Short-Term Inv38

Securities and Short-Term Investments - Available-for-Sale and Held-to-Maturity Securities Gains (Losses) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Amortized Cost	$ 3,220.6	$ 4,463.2
Gross Unrealized Gains	11.6	15.3
Gross Unrealized Losses	(34.7)	(68.6)
Fair Value	3,197.5	4,409.9
Held to maturity Securities, Amortized Cost	3,387.6	2,005.4
Securities held to maturity, Gross Unrealized Gains	63	33.9
Securities held to maturity, Gross Unrealized Losses	(15)	(26.7)
Total securities held to maturity, Fair Value	3,435.6	2,012.6
State and Municipal [Member]
Investment Holdings [Line Items]
Held to maturity Securities, Amortized Cost	1,999.2	1,499.1
Securities held to maturity, Gross Unrealized Gains	60.7	33.9
Securities held to maturity, Gross Unrealized Losses	(8.5)	(23.5)
Total securities held to maturity, Fair Value	2,051.4	1,509.5
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Investment Holdings [Line Items]
Amortized Cost	2,450.1	3,573.1
Gross Unrealized Gains	11.5	15
Gross Unrealized Losses	(15)	(38.1)
Fair Value	2,446.6	3,550
Held to maturity Securities, Amortized Cost	1,344.6	500.8
Securities held to maturity, Gross Unrealized Gains	1.5
Securities held to maturity, Gross Unrealized Losses	(6.5)	(3.2)
Total securities held to maturity, Fair Value	1,339.6	497.6
Debt Securities [Member]
Investment Holdings [Line Items]
Amortized Cost	3,211	4,463
Gross Unrealized Gains	11.6	15.3
Gross Unrealized Losses	(34.1)	(68.6)
Fair Value	3,188.5	4,409.7
Equity Securities [Member]
Investment Holdings [Line Items]
Amortized Cost	9.6	0.2
Gross Unrealized Losses	(0.6)
Fair Value	9	0.2
U.S. Treasury and Agency [Member]
Investment Holdings [Line Items]
Amortized Cost	760.9	889.9
Gross Unrealized Gains	0.1	0.3
Gross Unrealized Losses	(19.1)	(30.5)
Fair Value	741.9	859.7
Corporate [Member]
Investment Holdings [Line Items]
Held to maturity Securities, Amortized Cost	42.3	4
Securities held to maturity, Gross Unrealized Gains	0.8
Total securities held to maturity, Fair Value	43.1	4
Other [Member]
Investment Holdings [Line Items]
Held to maturity Securities, Amortized Cost	1.5	1.5
Total securities held to maturity, Fair Value	$ 1.5	$ 1.5

Securities and Short-Term Inv39

Securities and Short-Term Investments - Available-for-Sale and Held-to-Maturity Securities Gains (Losses) (Parenthetical) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Fair value of ownership interest exchanged	$ 10.8

Securities and Short-Term Inv40

Securities and Short-Term Investments - Additional Information (Detail)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2017USD ($)SecuritiesSecurity	Mar. 31, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)SecuritiesSecurity	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Investment [Line Items]
Security available for sale with a fair value pledged with collateral for public deposits	$ 2,920,000,000			$ 2,920,000,000		$ 1,830,000,000
Number of securities available for sale | Security	96			96
Number of securities held to maturity | Securities	453			453
Total number of securities owned | Security				2,046
Percentage of securities available for sale	27.00%			27.00%
Available for sale of securities gross unrealized losses	$ 34,700,000			$ 34,700,000		68,600,000
Held to maturity securities gross unrealized losses	15,000,000			15,000,000
Impairment losses on securities recognized in earnings	0		$ 0	0	$ 0
Amortized cost of mortgage-backed securities	3,211,000,000			3,211,000,000
Impairment of investments				$ 0
Federal Reserve Bank stock percentage				6.00%
Federal Reserve Bank of New York [Member]
Investment [Line Items]
Acquired shares of capital stock	169,400,000			$ 169,400,000		149,500,000
Interest-bearing deposits	259,400,000			$ 259,400,000		$ 169,800,000
Federal funds sold and yield				1.25%		0.75%
Maximum [Member]
Investment [Line Items]
Debt securities with unrealized losses				$ 100,000
State and Municipal [Member]
Investment [Line Items]
Held to maturity securities gross unrealized losses	8,500,000			$ 8,500,000		$ 23,500,000
Available for sale securities average maturity period				12 years
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Investment [Line Items]
Available for sale of securities gross unrealized losses	15,000,000			$ 15,000,000		38,100,000
Held to maturity securities gross unrealized losses	6,500,000			$ 6,500,000		3,200,000
Available for sale securities average maturity period				11 years
Amortized cost of mortgage-backed securities	2,450,100,000			$ 2,450,100,000
U.S. Treasury and CMO Securities [Member]
Investment [Line Items]
Amortized cost of mortgage-backed securities		$ 487,000,000
Gain (loss) on sales of Mortgage Backed Securities		$ 15,700,000
FHLB of Boston [Member]
Investment [Line Items]
Acquired shares of capital stock	139,500,000			139,500,000		155,000,000
FHLB of New York [Member]
Investment [Line Items]
Acquired shares of capital stock	$ 12,000,000			$ 12,000,000		$ 11,300,000

Securities and Short-Term Inv41

Securities and Short-Term Investments - Summary of Amortized Cost and Fair Value of Debt Securities Based on Remaining Period to Contractual Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Available for Sale, Amortized Cost, Within 1 year	$ 1
Available for Sale, Amortized Cost, After 1 but within 5 years	361.3
Available for Sale, Amortized Cost, After 5 but within 10 years	1,003.2
Available for Sale, Amortized Cost, After 10 years	1,845.5
Available for Sale, Amortized Cost, Total	3,211
Available for Sale, Fair Value, Within 1 year	1
Available for Sale, Fair Value, After 1 but within 5 years	355
Available for Sale, Fair Value, After 5 but within 10 years	999.8
Available for Sale, Fair Value, After 10 years	1,832.7
Available for Sale, Fair Value, Total	3,188.5
Held to Maturity, Amortized Cost, Within 1 year	18.7
Held to Maturity, Amortized Cost, After 1 but within 5 years	190
Held to Maturity, Amortized Cost, After 5 but within 10 years	1,214.8
Held to Maturity, Amortized Cost, After 10 years	1,964.1
Held to maturity Securities, Amortized Cost	3,387.6	$ 2,005.4
Held to Maturity, Fair Value, Within 1 year	18.7
Held to Maturity, Fair Value, After 1 but within 5 years	193.3
Held to Maturity, Fair Value, After 5 but within 10 years	1,231.7
Held to Maturity, Fair Value, After 10 years	1,991.9
Held to Maturity, Fair Value, Total	3,435.6	2,012.6
U.S. Treasury and Agency [Member]
Investment [Line Items]
Available for Sale, Amortized Cost, Within 1 year	1
Available for Sale, Amortized Cost, After 1 but within 5 years	361.3
Available for Sale, Amortized Cost, After 5 but within 10 years	398.6
Available for Sale, Amortized Cost, Total	760.9
Available for Sale, Fair Value, Within 1 year	1
Available for Sale, Fair Value, After 1 but within 5 years	355
Available for Sale, Fair Value, After 5 but within 10 years	385.9
Available for Sale, Fair Value, Total	741.9
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Investment [Line Items]
Available for Sale, Amortized Cost, After 5 but within 10 years	604.6
Available for Sale, Amortized Cost, After 10 years	1,845.5
Available for Sale, Amortized Cost, Total	2,450.1
Available for Sale, Fair Value, After 5 but within 10 years	613.9
Available for Sale, Fair Value, After 10 years	1,832.7
Available for Sale, Fair Value, Total	2,446.6
Held to Maturity, Amortized Cost, After 1 but within 5 years	69.4
Held to Maturity, Amortized Cost, After 5 but within 10 years	834.3
Held to Maturity, Amortized Cost, After 10 years	440.9
Held to maturity Securities, Amortized Cost	1,344.6	500.8
Held to Maturity, Fair Value, After 1 but within 5 years	69.4
Held to Maturity, Fair Value, After 5 but within 10 years	830.4
Held to Maturity, Fair Value, After 10 years	439.8
Held to Maturity, Fair Value, Total	1,339.6	497.6
State and Municipal [Member]
Investment [Line Items]
Held to Maturity, Amortized Cost, Within 1 year	18.7
Held to Maturity, Amortized Cost, After 1 but within 5 years	114.1
Held to Maturity, Amortized Cost, After 5 but within 10 years	343.2
Held to Maturity, Amortized Cost, After 10 years	1,523.2
Held to maturity Securities, Amortized Cost	1,999.2	1,499.1
Held to Maturity, Fair Value, Within 1 year	18.7
Held to Maturity, Fair Value, After 1 but within 5 years	117.4
Held to Maturity, Fair Value, After 5 but within 10 years	363.2
Held to Maturity, Fair Value, After 10 years	1,552.1
Held to Maturity, Fair Value, Total	2,051.4	1,509.5
Corporate [Member]
Investment [Line Items]
Held to Maturity, Amortized Cost, After 1 but within 5 years	5
Held to Maturity, Amortized Cost, After 5 but within 10 years	37.3
Held to maturity Securities, Amortized Cost	42.3	4
Held to Maturity, Fair Value, After 1 but within 5 years	5
Held to Maturity, Fair Value, After 5 but within 10 years	38.1
Held to Maturity, Fair Value, Total	43.1	4
Other [Member]
Investment [Line Items]
Held to Maturity, Amortized Cost, After 1 but within 5 years	1.5
Held to maturity Securities, Amortized Cost	1.5	1.5
Held to Maturity, Fair Value, After 1 but within 5 years	1.5
Held to Maturity, Fair Value, Total	$ 1.5	$ 1.5

Securities and Short-Term Inv42

Securities and Short-Term Investments - Continuous Unrealized Loss Position on Available-for-Sale and Held-to-Maturities Securities (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	$ 3,193.8	$ 4,247.2
Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(23.9)	(83.8)
Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	871.5	396.9
Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	(25.8)	(11.5)
Continuous Unrealized Loss Position, Total, Fair Value	4,065.3	4,644.1
Continuous Unrealized Loss Position, Total, Unrealized Losses	(49.7)	(95.3)
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(15)
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Held To Maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	1,029.5	497.6
Held To Maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(6.5)	(3.2)
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Fair Value	1,029.5	497.6
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(6.5)	(3.2)
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	1,675.6	2,339.6
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(12.1)	(26.6)
Available for Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	133.9	396.9
Available for Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	(2.9)	(11.5)
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Fair Value	1,809.5	2,736.5
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(15)	(38.1)
U.S. Treasury and Agency [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	206.6	828.3
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(3)	(30.5)
Available for Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	530.1
Available for Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	(16.1)
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Fair Value	736.7	828.3
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(19.1)	(30.5)
Equity Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	9
Available for Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(0.6)
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Fair Value	9
Available for Sale Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(0.6)
State and Municipal [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Held To Maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	270.3	581.7
Held To Maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	(1.7)	(23.5)
Held To Maturity Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	207.5
Held To Maturity Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	(6.8)
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Fair Value	477.8	581.7
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Unrealized Losses	(8.5)	$ (23.5)
Corporate [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Held To Maturity Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	2.8
Held To Maturity Securities, Continuous Unrealized Loss Position, Total, Fair Value	$ 2.8

Loans - Additional Information

Loans - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)SegmentsRating	Sep. 30, 2016USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2011USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of segments | Segments			2
Net deferred loan costs	$ 73,100,000		$ 73,100,000			$ 69,900,000
Recorded investments, non-performing loans	174,300,000		$ 174,300,000			148,000,000
Number of days of non accrual status			90 days
Accruing interest total	0		$ 0			0
Allowance for loan losses	233,400,000	$ 226,300,000	233,400,000	$ 226,300,000	$ 231,600,000	229,300,000	$ 220,400,000	$ 211,000,000
Interest Income Recognized	1,700,000	1,300,000	$ 4,500,000	3,900,000
Temporary reduction of interest rate for TDRs, basis points			2.00%
Collateral values/LTV ratios, minimum			70.00%
Borrower credit scores, minimum | Rating			680
Principal and interest payments receivable									$ 7,650,000,000
Expected cash flows									7,090,000,000
Loan portfolio fair value									5,420,000,000
Aggregate loan nonaccretable difference									560,100,000
Portfolio accretable yield	226,300,000	263,700,000	$ 226,300,000	263,700,000	233,400,000	255,400,000	270,300,000	296,000,000
Portfolio outstanding balance	630,600,000		630,600,000			707,000,000
Portfolio carrying value	541,200,000		541,200,000			610,200,000
Repossessed assets	5,400,000		5,400,000			7,200,000
Commercial Real Estate Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	21,700,000		21,700,000			10,500,000
Real estate owned	6,300,000		6,300,000			4,000,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	20,700,000		20,700,000			24,800,000
Equipment Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	46,100,000		46,100,000			28,400,000
Residential Mortgage Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate owned	4,700,000		4,700,000			8,100,000
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	125,700,000		125,700,000			103,200,000
Allowance for loan losses	203,500,000	202,100,000	203,500,000	202,100,000	201,900,000	204,900,000	196,900,000	189,700,000
Interest Income Recognized	1,200,000	800,000	2,900,000	2,500,000
Commercial [Member] | Commercial Real Estate Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	36,700,000		36,700,000			22,300,000
Interest Income Recognized	300,000	400,000	900,000	1,100,000
Commercial [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	34,900,000		34,900,000			41,500,000
Interest Income Recognized	700,000	300,000	1,600,000	1,200,000
Commercial [Member] | Equipment Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	54,100,000		54,100,000			39,400,000
Interest Income Recognized	200,000	100,000	400,000	200,000
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	48,600,000		48,600,000			44,800,000
Allowance for loan losses	29,900,000	24,200,000	29,900,000	24,200,000	29,700,000	24,400,000	23,500,000	21,300,000
Interest Income Recognized	500,000	500,000	$ 1,600,000	1,400,000
Duration of extension for payment deferral on TDRs, years			5 years
Retail Loans [Member] | Residential Mortgage Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	33,800,000		$ 33,800,000			27,400,000
Interest Income Recognized	400,000	400,000	$ 1,300,000	1,200,000
Maximum [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Duration of extension for payment deferral on TDRs, years			2 years
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan agreement			6 months
At Acquisition [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Portfolio accretable yield									$ 1,670,000,000
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	24,500,000		$ 24,500,000			24,700,000
Allowance for loan losses	4,200,000		4,200,000			6,300,000
Acquired Loans [Member] | Purchased Performing Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	2,100,000		2,100,000
Acquired Loans [Member] | Purchased Performing Loans [Member] | Subsequent to Acquisition [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	500,000		500,000
Acquired Loans [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	4,000,000	7,100,000	4,000,000	7,100,000	3,600,000	6,100,000	7,200,000	7,900,000
Acquired Loans [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	200,000	200,000	200,000	200,000	$ 100,000	200,000	$ 200,000	$ 200,000
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in originated loans classified as TDRs	194,400,000		194,400,000			189,900,000
Allowance for loan losses	4,600,000		4,600,000			4,200,000
Interest Income Recognized	1,400,000	$ 1,200,000	3,700,000	$ 3,300,000
Foreclosure or Bankruptcy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	$ 21,900,000		$ 21,900,000			$ 17,600,000

Loans - Summary of Loans by Loa

Loans - Summary of Loans by Loan Portfolio Segment and Class (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 32,384.5	$ 29,744.9
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	23,510.8	21,404.9
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,873.7	8,340
Commercial Real Estate Loan [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	11,180.5	10,247.3
Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,624.7	8,125.1
Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,705.6	3,032.5
Residential Mortgage Adjustable Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,948.4	5,549.1
Residential Mortgage Fixed Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	832.6	667.6
Residential Mortgage Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,781	6,216.7
Home Equity Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,041.5	2,072.6
Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	51.2	50.7
Home Equity and Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,092.7	2,123.3
Originated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	29,741.2	29,134.7
Originated [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	21,204.5	20,972.5
Originated [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,536.7	8,162.2
Originated [Member] | Commercial Real Estate Loan [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,194.1	10,012.6
Originated [Member] | Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	7,971.3	7,939
Originated [Member] | Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3,039.1	3,020.9
Originated [Member] | Residential Mortgage Adjustable Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,800.9	5,453.8
Originated [Member] | Residential Mortgage Fixed Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	706.7	613.5
Originated [Member] | Residential Mortgage Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,507.6	6,067.3
Originated [Member] | Home Equity Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,981.8	2,044.9
Originated [Member] | Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	47.3	50
Originated [Member] | Home Equity and Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,029.1	2,094.9
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,643.3	610.2
Acquired Loans [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,306.3	432.4
Acquired Loans [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	337	177.8
Acquired Loans [Member] | Commercial Real Estate Loan [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	986.4	234.7
Acquired Loans [Member] | Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	653.4	186.1
Acquired Loans [Member] | Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	666.5	11.6
Acquired Loans [Member] | Residential Mortgage Adjustable Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	147.5	95.3
Acquired Loans [Member] | Residential Mortgage Fixed Rate [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	125.9	54.1
Acquired Loans [Member] | Residential Mortgage Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	273.4	149.4
Acquired Loans [Member] | Home Equity Loan [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	59.7	27.7
Acquired Loans [Member] | Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	3.9	0.7
Acquired Loans [Member] | Home Equity and Other Consumer [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 63.6	$ 28.4

Loans - Summary, by Loan Portfo

Loans - Summary, by Loan Portfolio Segment, of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 231.6	$ 220.4	$ 229.3	$ 211
Charge-offs	(6.8)	(3.9)	(20)	(17.7)
Recoveries	1.6	1.4	5.6	4.1
Net loan charge-offs	(5.2)	(2.5)	(14.4)	(13.6)
Provision for loan losses	7	8.4	18.5	28.9
Balance at end of period	233.4	226.3	233.4	226.3
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			6.3
Balance at end of period	4.2		4.2
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	201.9	196.9	204.9	189.7
Charge-offs	(5)	(2.8)	(14.9)	(11.1)
Recoveries	1	0.9	3.9	1.6
Net loan charge-offs	(4)	(1.9)	(11)	(9.5)
Provision for loan losses	5.6	7.1	9.6	21.9
Balance at end of period	203.5	202.1	203.5	202.1
Commercial [Member] | Originated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	198.3	189.7	198.8	181.8
Charge-offs	(4)	(2.7)	(12)	(10.7)
Recoveries	0.9	0.9	3.8	1.6
Net loan charge-offs	(3.1)	(1.8)	(8.2)	(9.1)
Provision for loan losses	4.3	7.1	8.9	22.3
Balance at end of period	199.5	195	199.5	195
Commercial [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	3.6	7.2	6.1	7.9
Charge-offs	(1)	(0.1)	(2.9)	(0.4)
Recoveries	0.1		0.1
Net loan charge-offs	(0.9)	(0.1)	(2.8)	(0.4)
Provision for loan losses	1.3		0.7	(0.4)
Balance at end of period	4	7.1	4	7.1
Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	29.7	23.5	24.4	21.3
Charge-offs	(1.8)	(1.1)	(5.1)	(6.6)
Recoveries	0.6	0.5	1.7	2.5
Net loan charge-offs	(1.2)	(0.6)	(3.4)	(4.1)
Provision for loan losses	1.4	1.3	8.9	7
Balance at end of period	29.9	24.2	29.9	24.2
Retail Loans [Member] | Originated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	29.6	23.3	24.2	21.1
Charge-offs	(1.8)	(1.1)	(5.1)	(6.6)
Recoveries	0.6	0.5	1.7	2.5
Net loan charge-offs	(1.2)	(0.6)	(3.4)	(4.1)
Provision for loan losses	1.3	1.3	8.9	7
Balance at end of period	29.7	24	29.7	24
Retail Loans [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	0.1	0.2	0.2	0.2
Provision for loan losses	0.1
Balance at end of period	$ 0.2	$ 0.2	$ 0.2	$ 0.2

Loans - Summary of Allowance fo

Loans - Summary of Allowance for Loan Losses by Loan Portfolio Segment and Impairment Methodology (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	$ 266.8		$ 253.6
Originated Loans Individually Evaluated for Impairment, Allowance	8.1		9
Originated Loans Collectively Evaluated for Impairment, Portfolio	29,474.4		28,881.1
Originated Loans Collectively Evaluated for Impairment, Allowance	221.1		214
Loans, Portfolio	32,384.5		29,744.9
Total Allowance	233.4	$ 231.6	229.3	$ 226.3	$ 220.4	$ 211
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans, Portfolio	2,643.3		610.2
Total Allowance	4.2		6.3
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	172.5		161.8
Originated Loans Individually Evaluated for Impairment, Allowance	5.7		5.8
Originated Loans Collectively Evaluated for Impairment, Portfolio	21,032		20,810.7
Originated Loans Collectively Evaluated for Impairment, Allowance	193.8		193
Loans, Portfolio	23,510.8		21,404.9
Total Allowance	203.5	201.9	204.9	202.1	196.9	189.7
Commercial [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans, Portfolio	2,306.3		432.4
Total Allowance	4	3.6	6.1	7.1	7.2	7.9
Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	94.3		91.8
Originated Loans Individually Evaluated for Impairment, Allowance	2.4		3.2
Originated Loans Collectively Evaluated for Impairment, Portfolio	8,442.4		8,070.4
Originated Loans Collectively Evaluated for Impairment, Allowance	27.3		21
Loans, Portfolio	8,873.7		8,340
Total Allowance	29.9	29.7	24.4	24.2	23.5	21.3
Retail Loans [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans, Portfolio	337		177.8
Total Allowance	$ 0.2	$ 0.1	$ 0.2	$ 0.2	$ 0.2	$ 0.2

Loans - Summary of Allowance 47

Loans - Summary of Allowance for Loan Losses by Loan Portfolio Segment and Impairment Methodology (Parenthetical) (Detail) - USD ($)	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 32,384,500,000		$ 29,744,900,000
Allowance for loan losses	233,400,000	$ 231,600,000	229,300,000	$ 226,300,000	$ 220,400,000	$ 211,000,000
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	23,510,800,000		21,404,900,000
Allowance for loan losses	203,500,000	201,900,000	204,900,000	202,100,000	196,900,000	189,700,000
Commercial [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	406,500,000
Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	8,873,700,000		8,340,000,000
Allowance for loan losses	29,900,000	29,700,000	24,400,000	24,200,000	23,500,000	21,300,000
Retail Loans [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	134,700,000
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,643,300,000		610,200,000
Allowance for loan losses	4,200,000		6,300,000
Acquired Loans [Member] | Commercial and Retail PCI Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loan losses	3,800,000
Acquired Loans [Member] | Purchased Performing Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans			0
Allowance for loan losses	400,000
Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	2,306,300,000		432,400,000
Allowance for loan losses	4,000,000	3,600,000	6,100,000	7,100,000	7,200,000	7,900,000
Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	337,000,000		177,800,000
Allowance for loan losses	$ 200,000	$ 100,000	$ 200,000	$ 200,000	$ 200,000	$ 200,000

Loans - Summarized Recorded Inv

Loans - Summarized Recorded Investments, by Class of Loan, in Originated Non-Performing Loans (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$ 174.3	$ 148
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	125.7	103.2
Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	48.6	44.8
Commercial Real Estate Loan [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	36.7	22.3
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	34.9	41.5
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	54.1	39.4
Residential Mortgage Loan [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	33.8	27.4
Home Equity Loan [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$ 14.8	$ 17.4

Loans - Summarized Recorded I49

Loans - Summarized Recorded Investments, by Class of Loan, in Originated Non-Performing Loans (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Government guarantees	$ 4	$ 13.1
Recorded investments, non-performing loans	174.3	148
Foreclosure [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$ 17.8	$ 9.8
Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Guarantee rate	5.00%
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Guarantee rate	95.00%

Loans - Summary of Recorded Inv

Loans - Summary of Recorded Investments in TDRs by Class of Loan (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	59	66	200	194
Pre-Modification Outstanding Recorded Investment	$ 25.1	$ 41.1	$ 85.3	$ 87.4
Post-Modification Outstanding Recorded Investment	$ 25.1	$ 41.1	$ 85.3	$ 87.4
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	23	40	90	97
Pre-Modification Outstanding Recorded Investment	$ 19.8	$ 37	$ 70	$ 70.5
Post-Modification Outstanding Recorded Investment	$ 19.8	$ 37	$ 70	$ 70.5
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	36	26	110	97
Pre-Modification Outstanding Recorded Investment	$ 5.3	$ 4.1	$ 15.3	$ 16.9
Post-Modification Outstanding Recorded Investment	$ 5.3	$ 4.1	$ 15.3	$ 16.9
Commercial Real Estate Loan [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	1	7	8	12
Pre-Modification Outstanding Recorded Investment	$ 0.1	$ 22.1	$ 5.3	$ 25.9
Post-Modification Outstanding Recorded Investment	$ 0.1	$ 22.1	$ 5.3	$ 25.9
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	9	11	28	36
Pre-Modification Outstanding Recorded Investment	$ 11.6	$ 4.5	$ 39.6	$ 22.9
Post-Modification Outstanding Recorded Investment	$ 11.6	$ 4.5	$ 39.6	$ 22.9
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	13	22	54	49
Pre-Modification Outstanding Recorded Investment	$ 8.1	$ 10.4	$ 25.1	$ 21.7
Post-Modification Outstanding Recorded Investment	$ 8.1	$ 10.4	$ 25.1	$ 21.7
Residential Mortgage Loan [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	17	9	45	47
Pre-Modification Outstanding Recorded Investment	$ 3.8	$ 2.9	$ 10.8	$ 13.1
Post-Modification Outstanding Recorded Investment	$ 3.8	$ 2.9	$ 10.8	$ 13.1
Home Equity Loan [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	19	17	65	50
Pre-Modification Outstanding Recorded Investment	$ 1.5	$ 1.2	$ 4.5	$ 3.8
Post-Modification Outstanding Recorded Investment	$ 1.5	$ 1.2	$ 4.5	$ 3.8

Loans - Summary of Recorded I51

Loans - Summary of Recorded Investments in TDRs by Class of Loan (Parenthetical) (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	59	66	200	194
Recorded investment | $	$ 25.1	$ 41.1	$ 85.3	$ 87.4
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	23	40	90	97
Recorded investment | $	$ 19.8	$ 37	$ 70	$ 70.5
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	1	7	8	12
Recorded investment | $	$ 0.1	$ 22.1	$ 5.3	$ 25.9
Commercial [Member] | Commercial Real Estate Loan [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	1	5	5	8
Recorded investment | $	$ 0.1	$ 3.3	$ 1.4	$ 6.2
Commercial [Member] | Commercial Real Estate Loan [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts		1	2	2
Recorded investment | $		$ 1.7	$ 2.2	$ 2.6
Commercial [Member] | Commercial Real Estate Loan [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts		1		2
Recorded investment | $		$ 17.1		$ 17.1
Commercial [Member] | Commercial Real Estate Loan [Member] | Temporary Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts			1
Recorded investment | $			$ 1.7
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	9	11	28	36
Recorded investment | $	$ 11.6	$ 4.5	$ 39.6	$ 22.9
Commercial [Member] | Commercial and Industrial [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	9	9	25	23
Recorded investment | $	$ 11.6	$ 4.1	$ 29.9	$ 12.3
Commercial [Member] | Commercial and Industrial [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts		2	2	9
Recorded investment | $		$ 0.4	$ 9.4	$ 9.8
Commercial [Member] | Commercial and Industrial [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts			1	4
Recorded investment | $			$ 0.3	$ 0.8
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	13	22	54	49
Recorded investment | $	$ 8.1	$ 10.4	$ 25.1	$ 21.7
Commercial [Member] | Equipment Financing [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts		6		17
Recorded investment | $		$ 4.3		$ 6.3
Commercial [Member] | Equipment Financing [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	12	13	28	25
Recorded investment | $	$ 8	$ 4.7	$ 17.4	$ 12.5
Commercial [Member] | Equipment Financing [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	1	3	26	7
Recorded investment | $	$ 0.1	$ 1.4	$ 7.7	$ 2.9
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	36	26	110	97
Recorded investment | $	$ 5.3	$ 4.1	$ 15.3	$ 16.9
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	17	9	45	47
Recorded investment | $	$ 3.8	$ 2.9	$ 10.8	$ 13.1
Retail Loans [Member] | Residential Mortgage Loan [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	5	1	10	11
Recorded investment | $	$ 1.7	$ 0.7	$ 3.4	$ 5.5
Retail Loans [Member] | Residential Mortgage Loan [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	3	2	7	18
Recorded investment | $	$ 0.4	$ 1.2	$ 3.2	$ 4.4
Retail Loans [Member] | Residential Mortgage Loan [Member] | Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	9	6	28	18
Recorded investment | $	$ 1.7	$ 1	$ 4.2	$ 3.2
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	19	17	65	50
Recorded investment | $	$ 1.5	$ 1.2	$ 4.5	$ 3.8
Retail Loans [Member] | Home Equity Loan [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	4	1	10	2
Recorded investment | $	$ 0.3	$ 0.2	$ 0.8	$ 0.3
Retail Loans [Member] | Home Equity Loan [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	5	5	14	17
Recorded investment | $	$ 0.2	$ 0.5	$ 1.1	$ 1.4
Retail Loans [Member] | Home Equity Loan [Member] | Bankruptcy [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	10	11	41	31
Recorded investment | $	$ 1	$ 0.5	$ 2.6	$ 2.1

Loans - Summary of Recorded I52

Loans - Summary of Recorded Investments in TDRs by Class of Loan, Subsequently Defaulted (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts	Sep. 30, 2017USD ($)Contracts	Sep. 30, 2016USD ($)Contracts
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	16	17	39	44
Recorded Investment | $	$ 6	$ 2.8	$ 12.3	$ 9.8
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	9	14	19	27
Recorded Investment | $	$ 4.3	$ 2.2	$ 8.3	$ 7.4
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts				2
Recorded Investment | $				$ 0.9
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	1		4	5
Recorded Investment | $	$ 0.1		$ 1.5	$ 0.6
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	8	14	15	20
Recorded Investment | $	$ 4.2	$ 2.2	$ 6.8	$ 5.9
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	7	3	20	17
Recorded Investment | $	$ 1.7	$ 0.6	$ 4	$ 2.4
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	2	3	9	10
Recorded Investment | $	$ 0.9	$ 0.6	$ 2.7	$ 1.9
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contracts	5		11	7
Recorded Investment | $	$ 0.8		$ 1.3	$ 0.5

Loans - Summary of Individually

Loans - Summary of Individually-Evaluated Impaired Loans by Class of Loan (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	$ 223.1	$ 216.3
With no related allowance for loan losses, Recorded Investment	201.9	197.7
With a related allowance for loan losses, Unpaid Principal Balance	67.1	58.3
With a related allowance for loan losses, Recorded Investment	64.9	55.9
Unpaid Principal Balance	290.2	274.6
Recorded Investment	266.8	253.6
Related Allowance for Loan Losses	8.1	9
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	185.6	173.4
Recorded Investment	172.5	161.8
Related Allowance for Loan Losses	5.7	5.8
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	50.7	41.4
With no related allowance for loan losses, Recorded Investment	46.1	40
With a related allowance for loan losses, Unpaid Principal Balance	13.5	12.2
With a related allowance for loan losses, Recorded Investment	12.8	11.4
Unpaid Principal Balance	64.2	53.6
Recorded Investment	58.9	51.4
Related Allowance for Loan Losses	1.2	0.6
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	39.3	50.7
With no related allowance for loan losses, Recorded Investment	36.7	45.7
With a related allowance for loan losses, Unpaid Principal Balance	25.2	25.9
With a related allowance for loan losses, Recorded Investment	24.6	25
Unpaid Principal Balance	64.5	76.6
Recorded Investment	61.3	70.7
Related Allowance for Loan Losses	3	4.7
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	42.8	38.2
With no related allowance for loan losses, Recorded Investment	39.1	35.3
With a related allowance for loan losses, Unpaid Principal Balance	14.1	5
With a related allowance for loan losses, Recorded Investment	13.2	4.4
Unpaid Principal Balance	56.9	43.2
Recorded Investment	52.3	39.7
Related Allowance for Loan Losses	1.5	0.5
Retail Loans [Member]
Financing Receivable, Impaired [Line Items]
With a related allowance for loan losses, Recorded Investment	14.3
Unpaid Principal Balance	104.6	101.2
Recorded Investment	94.3	91.8
Related Allowance for Loan Losses	2.4	3.2
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	66.8	63.6
With no related allowance for loan losses, Recorded Investment	60	58
With a related allowance for loan losses, Unpaid Principal Balance	12.4	13.1
With a related allowance for loan losses, Recorded Investment	12.4	13.1
Unpaid Principal Balance	79.2	76.7
Recorded Investment	72.4	71.1
Related Allowance for Loan Losses	1.7	2.3
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Impaired [Line Items]
With no related allowance for loan losses, Unpaid Principal Balance	23.5	22.4
With no related allowance for loan losses, Recorded Investment	20	18.7
With a related allowance for loan losses, Unpaid Principal Balance	1.9	2.1
With a related allowance for loan losses, Recorded Investment	1.9	2
Unpaid Principal Balance	25.4	24.5
Recorded Investment	21.9	20.7
Related Allowance for Loan Losses	$ 0.7	$ 0.9

Loans - Schedule of Impaired Fi

Loans - Schedule of Impaired Financing Receivable (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 262.2	$ 245.8	$ 259	$ 250.4
Interest Income Recognized	1.7	1.3	4.5	3.9
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	168	152.8	166	156.4
Interest Income Recognized	1.2	0.8	2.9	2.5
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	61.8	54.1	56.9	58.6
Interest Income Recognized	0.3	0.4	0.9	1.1
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	59.7	60.5	66.1	61.9
Interest Income Recognized	0.7	0.3	1.6	1.2
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	46.5	38.2	43	35.9
Interest Income Recognized	0.2	0.1	0.4	0.2
Retail Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	94.2	93	93	94
Interest Income Recognized	0.5	0.5	1.6	1.4
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	72.4	71.7	71.9	72.1
Interest Income Recognized	0.4	0.4	1.3	1.2
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	21.8	21.3	21.1	21.9
Interest Income Recognized	$ 0.1	$ 0.1	$ 0.3	$ 0.2

Loans - Summary of Aging Inform

Loans - Summary of Aging Information by Class of Loan (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	$ 32,384.5	$ 29,744.9
Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	29,514.9	28,938.1
Total Past Due	226.3	196.6
Total loans	29,741.2	29,134.7
Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	158.4	116.8
Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	67.9	79.8
Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,873.7	8,340
Retail Loans [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	51.2	50.7
Retail Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	2,041.5	2,072.6
Retail Loans [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	6,781	6,216.7
Retail Loans [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	8,470.4	8,107.5
Total Past Due	66.3	54.7
Total loans	8,536.7	8,162.2
Retail Loans [Member] | Originated [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	46.5	49.7
Total Past Due	0.8	0.3
Total loans	47.3	50
Retail Loans [Member] | Originated [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,968.5	2,030.3
Total Past Due	13.3	14.6
Total loans	1,981.8	2,044.9
Retail Loans [Member] | Originated [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,455.4	6,027.5
Total Past Due	52.2	39.8
Total loans	6,507.6	6,067.3
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	39.6	27.5
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0.8	0.3
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7	5.2
Retail Loans [Member] | Originated [Member] | 30-89 Days [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	31.8	22
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	26.7	27.2
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6.3	9.4
Retail Loans [Member] | Originated [Member] | 90 Days or More [Member] | Residential Mortgage Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20.4	17.8
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	23,510.8	21,404.9
Commercial [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	11,180.5	10,247.3
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	8,624.7	8,125.1
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	3,705.6	3,032.5
Commercial [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	21,044.5	20,830.6
Total Past Due	160	141.9
Total loans	21,204.5	20,972.5
Commercial [Member] | Originated [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,158.6	9,989.9
Total Past Due	35.5	22.7
Total loans	10,194.1	10,012.6
Commercial [Member] | Originated [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,943.2	7,899.2
Total Past Due	28.1	39.8
Total loans	7,971.3	7,939
Commercial [Member] | Originated [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,942.7	2,941.5
Total Past Due	96.4	79.4
Total loans	3,039.1	3,020.9
Commercial [Member] | Originated [Member] | 30-89 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	118.8	89.3
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20.3	10.9
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10.1	10
Commercial [Member] | Originated [Member] | 30-89 Days [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	88.4	68.4
Commercial [Member] | Originated [Member] | 90 Days or More [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	41.2	52.6
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Commercial Real Estate Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15.2	11.8
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	18	29.8
Commercial [Member] | Originated [Member] | 90 Days or More [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 8	$ 11

Loans - Summary of Credit Quali

Loans - Summary of Credit Quality Indicators by Class of Loan (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 32,384.5	$ 29,744.9
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23,510.8	21,404.9
Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,873.7	8,340
Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	21,204.5	20,972.5
Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	20,134	20,015.7
Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	353.7	328
Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	715.1	624.6
Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1.7	4.2
Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,536.7	8,162.2
Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,215.2	3,998.4
Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,376.1	3,210
Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	945.4	953.8
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,643.3	610.2
Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,306.3	432.4
Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,169.6	339.4
Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	48.6	25.7
Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	87.4	66.6
Acquired Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0.7	0.7
Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	337	177.8
Acquired Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	154.9	75.7
Acquired Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	60.2	27.5
Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	121.9	74.6
Commercial Real Estate Loan [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,180.5	10,247.3
Commercial Real Estate Loan [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	10,194.1	10,012.6
Commercial Real Estate Loan [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	9,926.2	9,817.2
Commercial Real Estate Loan [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	129.1	107.3
Commercial Real Estate Loan [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	137.9	87.1
Commercial Real Estate Loan [Member] | Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0.9	1
Commercial Real Estate Loan [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	986.4	234.7
Commercial Real Estate Loan [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	940.9	182.9
Commercial Real Estate Loan [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6.2	13.5
Commercial Real Estate Loan [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	38.6	37.6
Commercial Real Estate Loan [Member] | Acquired Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0.7	0.7
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,624.7	8,125.1
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,971.3	7,939
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,588.1	7,580.6
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	122.8	121.9
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	259.6	233.3
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0.8	3.2
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	653.4	186.1
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	562.2	155.5
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42.4	3.6
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	48.8	27
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,705.6	3,032.5
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,039.1	3,020.9
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,619.7	2,617.9
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	101.8	98.8
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	317.6	304.2
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	666.5	11.6
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	666.5	1
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		8.6
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		2
Residential Mortgage Loan [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,781	6,216.7
Residential Mortgage Loan [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,507.6	6,067.3
Residential Mortgage Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,259.8	3,016.4
Residential Mortgage Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,715.9	2,538.9
Residential Mortgage Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	531.9	512
Residential Mortgage Loan [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	273.4	149.4
Residential Mortgage Loan [Member] | Acquired Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	154.9	75.7
Residential Mortgage Loan [Member] | Acquired Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	60.2	27.5
Residential Mortgage Loan [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	58.3	46.2
Home Equity Loan [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,041.5	2,072.6
Home Equity Loan [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,981.8	2,044.9
Home Equity Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	928.2	950.9
Home Equity Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	652.2	663.9
Home Equity Loan [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	401.4	430.1
Home Equity Loan [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	59.7	27.7
Home Equity Loan [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	59.7	27.7
Other Consumer [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	51.2	50.7
Other Consumer [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47.3	50
Other Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	27.2	31.1
Other Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8	7.2
Other Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	12.1	11.7
Other Consumer [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3.9	0.7
Other Consumer [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 3.9	$ 0.7

Loans - Summarized Activity in

Loans - Summarized Activity in Accretable Yield for Acquired Loan Portfolio (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Receivables [Abstract]
Balance at beginning of period	$ 233.4	$ 270.3	$ 255.4	$ 296
Acquisitions			13.1
Accretion	(7.1)	(9)	(22.5)	(31.1)
Reclassification from nonaccretable difference for loans with improved cash flows	0	0	0	0
Other changes in expected cash flows		2.4	(19.7)	(1.2)
Balance at end of period	$ 226.3	$ 263.7	$ 226.3	$ 263.7

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock par value, per share	$ 0.01	$ 0.01
Common stock, shares authorized	1,950,000,000	1,950,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	433,600,000	405,000,000
Preferred stock, shares outstanding	10,000,000	10,000,000
Number of common stock purchased	89,000,000	89,100,000
Repurchases Authorized by Board of Directors [Member]
Schedule Of Stockholders Equity [Line Items]
Number of common stock purchased	86,400,000	86,400,000
2007 Recognition and Retention Plan [Member]
Schedule Of Stockholders Equity [Line Items]
Number of common stock purchased	2,600,000	2,700,000
2014 Long-Term Incentive Plan [Member] | 2007 Recognition and Retention Plan [Member]
Schedule Of Stockholders Equity [Line Items]
Additional awards under RRP	0
People's United Financial, Inc. [Member]
Schedule Of Stockholders Equity [Line Items]
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock par value, per share	$ 0.01	$ 0.01
Common stock, shares authorized	1,950,000,000	1,950,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	433,600,000	405,000,000
Preferred stock, shares outstanding	10,000,000	10,000,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 5,141.9	$ 4,731.6
Amounts reclassified from AOCL	$ 1.3	$ 1.4	13.9	4.5
Total other comprehensive income , net of tax			25.3	56.8
Ending Balance	5,746.1	4,862.3	5,746.1	4,862.3
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(145.6)	(140)
Amounts reclassified from AOCL			2.8	2.8
Total other comprehensive income , net of tax			2.8	2.8
Ending Balance	(142.8)	(137.2)	(142.8)	(137.2)
Net Unrealized Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(32.3)	(17.7)
Other comprehensive income (loss) before reclassifications			11.1	52.4
Amounts reclassified from AOCL			9.9	(0.1)
Total other comprehensive income , net of tax			21	52.3
Ending Balance	(11.3)	34.6	(11.3)	34.6
Net Unrealized Gain (Losses) On Securities Transferred To Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(17.4)	(19.5)
Amounts reclassified from AOCL			1.6	1.5
Total other comprehensive income , net of tax			1.6	1.5
Ending Balance	(15.8)	(18)	(15.8)	(18)
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			0.3	0
Other comprehensive income (loss) before reclassifications			0.3	(0.1)
Amounts reclassified from AOCL			(0.4)	0.3
Total other comprehensive income , net of tax			(0.1)	0.2
Ending Balance	0.2	0.2	0.2	0.2
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(195)	(177.2)
Other comprehensive income (loss) before reclassifications			11.4	52.3
Amounts reclassified from AOCL			13.9	4.5
Total other comprehensive income , net of tax			25.3	56.8
Ending Balance	$ (169.7)	$ (120.4)	$ (169.7)	$ (120.4)

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Amounts Reclassified from AOCL (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	$ (129.8)	$ (106.3)	$ (334.7)	$ (303.4)
Income tax expense	39	32.6	103.8	98.3
Net income	(90.8)	(73.7)	(230.9)	(205.1)
Interest expense - notes and debentures	7.5	7.9	22.3	23.4
Total reclassifications for the period	(1.3)	(1.4)	(13.9)	(4.5)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss	(1.7)	(1.7)	(5.1)	(4.8)
Prior service credit	0.2	0.2	0.6	0.6
Income before income tax expense	(1.5)	(1.5)	(4.5)	(4.2)
Income tax expense	0.6	0.6	1.7	1.4
Net income	(0.9)	(0.9)	(2.8)	(2.8)
Total reclassifications for the period			(2.8)	(2.8)
Net Unrealized Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense			(15.6)	0.1
Income tax expense			5.7
Net income			(9.9)	0.1
Total reclassifications for the period			(9.9)	0.1
Net Unrealized Gain (Losses) On Securities Transferred To Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	(0.9)	(0.9)	(2.6)	(2.4)
Income tax expense	0.3	0.4	1	0.9
Net income	(0.6)	(0.5)	(1.6)	(1.5)
Total reclassifications for the period			(1.6)	(1.5)
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	0.4		0.7	(0.5)
Income tax expense	(0.2)		(0.3)	0.2
Net income	0.2		0.4	(0.3)
Total reclassifications for the period			0.4	(0.3)
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member] | Interest Rate Locks [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest expense - notes and debentures	0.1	0.1	0.1	0.1
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member] | Interest Rate Swaps/Caps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest expense - notes and debentures	$ (0.3)	$ 0.1	$ (0.6)	$ 0.6

Earnings Per Common Share - Bas

Earnings Per Common Share - Basic and Diluted Earnings Per Common Share, Reflecting Application of Two-Class Method (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 87.3	$ 73.7	$ 220.4	$ 205.1
Dividends paid on and undistributed earnings allocated to participating securities	(0.1)	(0.2)	(0.4)	(0.6)
Earnings attributable to common shareholders	$ 87.2	$ 73.5	$ 220	$ 204.5
Weighted average common shares outstanding for basic EPS	336.9	302.9	327.6	302.4
Effect of dilutive equity-based awards	1.9	0.4	2	0.4
Weighted average common and common-equivalent shares for diluted EPS	338.8	303.3	329.6	302.8
Basic EPS	$ 0.26	$ 0.24	$ 0.67	$ 0.68
Diluted EPS	$ 0.26	$ 0.24	$ 0.67	$ 0.68

Earnings Per Common Share - Add

Earnings Per Common Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Anti-dilutive equity-based awards excluded from calculation of diluted EPS	10.2	18.2	10.1	18.2

Goodwill and Other Acquisitio63

Goodwill and Other Acquisition-Related Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Line Items]
Beginning balance	$ 1,992.7	$ 1,958.7
Adjustments		(3.1)
Ending balance	2,411.4	1,957
Suffolk Bancorp [Member]
Goodwill [Line Items]
Acquisition	270.3
LEAF Commercial Capital, Inc. [Member]
Goodwill [Line Items]
Acquisition	148.4
Eagle Insurance Group, LLC [Member]
Goodwill [Line Items]
Acquisition		1.4
Commercial Banking Loan [Member]
Goodwill [Line Items]
Beginning balance	1,222.1	1,222.8
Adjustments		(0.7)
Ending balance	1,600.3	1,222.1
Commercial Banking Loan [Member] | Suffolk Bancorp [Member]
Goodwill [Line Items]
Acquisition	229.8
Commercial Banking Loan [Member] | LEAF Commercial Capital, Inc. [Member]
Goodwill [Line Items]
Acquisition	148.4
Retail Banking [Member]
Goodwill [Line Items]
Beginning balance	679.6	681.9
Adjustments		(2.3)
Ending balance	720.1	679.6
Retail Banking [Member] | Suffolk Bancorp [Member]
Goodwill [Line Items]
Acquisition	40.5
Wealth Management [Member]
Goodwill [Line Items]
Beginning balance	91	54
Adjustments		(0.1)
Ending balance	$ 91	55.3
Wealth Management [Member] | Eagle Insurance Group, LLC [Member]
Goodwill [Line Items]
Acquisition		$ 1.4

Goodwill and Other Acquisitio64

Goodwill and Other Acquisition-Related Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	$ 156,500,000		$ 156,500,000		$ 149,400,000
Amortization of other acquisition-related intangible assets	7,900,000	$ 5,800,000	22,100,000	$ 17,400,000
Amortization expense attributable to other acquisition-related intangible assets, 2017	30,000,000		30,000,000
Amortization expense attributable to other acquisition-related intangible assets, 2018	19,900,000		19,900,000
Amortization expense attributable to other acquisition-related intangible assets, 2019	18,400,000		18,400,000
Amortization expense attributable to other acquisition-related intangible assets, 2020	16,800,000		16,800,000
Amortization expense attributable to other acquisition-related intangible assets, 2021	15,000,000		15,000,000
Amortization expense attributable to other acquisition-related intangible assets, 2022	13,500,000		13,500,000
Impairment losses relating to goodwill or other acquisition-related intangible assets			0	$ 0
Mutual Fund Management Contracts [Member]
Goodwill And Other Intangible Assets [Line Items]
Mutual fund management contracts (not amortized)	16,500,000		16,500,000
Trade Name [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	68,100,000		68,100,000
Customer Relationships [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	14,900,000		14,900,000
Core Deposit Intangibles [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	27,900,000		27,900,000
Insurance Relationships [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	5,400,000		5,400,000
Client Relationship [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	22,500,000		22,500,000
Favorable Lease Agreement [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	600,000		600,000
Noncompete Agreements [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	$ 600,000		$ 600,000

Employee Benefit Plans - People

Employee Benefit Plans - People's United Employee Pension and Other Postretirement Plans - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Average compensation term on which pension plan benefits are based, in years	5 years
Average compensation term within last ten years on which pension plan benefits are based, in years	5 years
Term considered when determining employee pension benefits, in years	10 years
Minimum age requirement to participate in pension plan, years	18 years
Minimum service hours per year requirement to participate in pension plan	1000 hours
People's Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of covered employee's eligible compensation	3.00%

Employee Benefit Plans - Compon

Employee Benefit Plans - Components of Net Periodic Benefit (Income) Expense and Other Amounts (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Postretirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.1		$ 0.2	$ 0.2
Interest cost	0.1	$ 0.2	0.4	0.5
Recognized net actuarial loss	0.1	0.1	0.2	0.2
Net periodic benefit (income) expense	0.3	0.3	0.8	0.9
Net actuarial loss			(0.2)	(0.2)
Total pre-tax changes recognized in other comprehensive income			(0.2)	(0.2)
Total recognized in net periodic benefit (income) expense and other comprehensive income			0.6	0.7
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	4.9	4.7	14.3	14.1
Expected return on plan assets	(9.6)	(8.7)	(28.3)	(25.9)
Recognized net actuarial loss	1.6	1.6	4.9	4.6
Recognized prior service credit	(0.2)	(0.2)	(0.6)	(0.6)
Settlements	1.1	0.3	2.6	0.9
Net periodic benefit (income) expense	$ (2.2)	$ (2.3)	(7.1)	(6.9)
Net actuarial loss			(4.9)	(4.6)
Prior service credit			0.6	0.6
Total pre-tax changes recognized in other comprehensive income			(4.3)	(4)
Total recognized in net periodic benefit (income) expense and other comprehensive income			$ (11.4)	$ (10.9)

Employee Benefit Plans - Employ

Employee Benefit Plans - Employee Stock Ownership Plan - Additional Information (Detail) - USD ($) $ in Millions	Apr. 30, 2007	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
ESOP, shares to be purchased	10,453,575
ESOP loan	$ 216.8	$ 184.9
Loan repayments expected annual through 2036		18.8
Cash dividends paid on unallocated ESOP shares		$ 3.6
Minimum age requirement to participate in ESOP		18 years
Minimum work experience within 12 months of hire needed to participate in ESOP		1000 hours
ESOP common stock allocated		3,745,864
Unallocated common stock of Employee Stock Ownership Plan, shares		6,707,711		7,000,000
Fair value of deferred ESOP shares		$ 121.7
ESOP compensation expense		$ 4.8	$ 4

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value transfers between level 1 and level 2	$ 0	$ 0
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maturity period of available-for-sale residential mortgage-backed securities portfolio	10 years		15 years
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount to impaired loans	10.00%

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	$ 8.3	$ 6.8
Securities available for sale, at fair value	3,197.5	4,409.9
Other assets	963	967.2
Fair Values, Assets	102.7	174
Fair Values, Liabilities	61.4	121.7
Fair value of total assets measured at fair value on a recurring basis	3,348.8	4,630.3
Fair value of total liabilities measured at fair value on a recurring basis	61.4	121.7
Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	35	32.6
Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.7	4.3
Equity Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	3.6	2.7
US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	8.3	6.8
U.S. Treasury and Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	741.9	859.7
GSE Residential Mortgage-Backed Securities and CMOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	2,446.6	3,550
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	9	0.2
Interest Rate Swaps/Caps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	101.9	173.1
Fair Values, Liabilities	60.5	121
Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	0.2	0.6
Fair Values, Liabilities	0.2	0.3
Forward Commitments to Sell Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	0.6	0.3
Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Liabilities	0.7	0.4
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of total assets measured at fair value on a recurring basis	797.8	901.8
Level 1 [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	35	32.6
Level 1 [Member] | Equity Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	3.6	2.7
Level 1 [Member] | US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	8.3	6.8
Level 1 [Member] | U.S. Treasury and Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	741.9	859.7
Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	9
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of total assets measured at fair value on a recurring basis	2,551	3,728.5
Fair value of total liabilities measured at fair value on a recurring basis	61.4	121.7
Level 2 [Member] | Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.7	4.3
Level 2 [Member] | GSE Residential Mortgage-Backed Securities and CMOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value	2,446.6	3,550
Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value		0.2
Level 2 [Member] | Interest Rate Swaps/Caps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	101.9	173.1
Fair Values, Liabilities	60.5	121
Level 2 [Member] | Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	0.2	0.6
Fair Values, Liabilities	0.2	0.3
Level 2 [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	0.6	0.3
Level 2 [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Liabilities	$ 0.7	$ 0.4

Fair Value Measurements - Ass70

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Risk Participation Agreements [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Derivatives, Net	$ 100,000	$ 100,000

Fair Value Measurements - Ass71

Fair Value Measurements - Assets Measured at Fair Value on Non-Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	$ 15	$ 39.3
Impaired loans	64.9	55.9
REO and repossessed assets	16.4	19.3
Total assets measured at fair value on non-recurring basis	96.3	114.5
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	15	39.3
Total assets measured at fair value on non-recurring basis	15	39.3
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	64.9	55.9
REO and repossessed assets	16.4	19.3
Total assets measured at fair value on non-recurring basis	$ 81.3	$ 75.2

Fair Value Measurements - Ass72

Fair Value Measurements - Assets Measured at Fair Value on Non-Recurring Basis (Parenthetical) (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 64,900,000		$ 64,900,000		$ 55,900,000
Charge-offs to the allowance for loan losses related to loans	7,000,000	$ 8,400,000	18,500,000	$ 28,900,000
Repossessed assets	5,400,000		5,400,000		7,200,000
Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Charge-offs to the allowance for loan losses related to loans			4,100,000	3,500,000
REO and Repossessed Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Charge-offs to the allowance for loan losses related to loans			2,200,000	3,300,000
Nonoperating Income (Expense) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest expense total			(300,000)	2,900,000
Residential Mortgage Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments			0	0
Real estate owned	4,700,000		4,700,000		8,100,000
Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	50,600,000		50,600,000
Commercial Real Estate Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate owned	6,300,000		6,300,000		4,000,000
Retail Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	14,300,000		14,300,000
Charge-offs to the allowance for loan losses related to loans	1,400,000	$ 1,300,000	8,900,000	$ 7,000,000
Retail Loans [Member] | Residential Mortgage Loan [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 12,400,000		$ 12,400,000		$ 13,100,000

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 414.1	$ 432.4
Short-term investments	302.5	181.7
Securities held to maturity	3,387.6	2,005.4
FHLB and FRB stock	320.9	315.8
Time deposits	5,235.8	4,542.2
FHLB advances	3,074.1	3,061.1
Federal funds purchased	543	617
Customer repurchase agreements	295.8	343.3
Other borrowings	231.1	35.4
Notes and debentures	906.2	1,030.1
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	414.1	432.4
Short-term investments	302.5	181.7
Securities held to maturity	3,387.6	2,005.4
FHLB and FRB stock	320.9	315.8
Total loans, net	32,086.2	29,459.7
Time deposits	5,235.8	4,542.2
Other deposits	27,311.5	25,318.6
FHLB advances	3,074.1	3,061.1
Federal funds purchased	543	617
Customer repurchase agreements	295.8	343.3
Other borrowings	231.1	35.4
Notes and debentures	906.2	1,030.1
Estimated Fair Value Measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	414.1	432.4
Short-term investments	302.5	181.7
Securities held to maturity	3,435.6	2,012.7
FHLB and FRB stock	320.9	315.8
Total loans, net	31,947.5	29,266.5
Time deposits	5,232.4	4,539.7
Other deposits	27,311.5	25,318.6
FHLB advances	3,076	3,064.4
Federal funds purchased	543	617
Customer repurchase agreements	295.8	343.3
Other borrowings	230.9	35.4
Notes and debentures	902.6	1,000
Estimated Fair Value Measurements [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	414.1	432.4
Estimated Fair Value Measurements [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	302.5	181.7
Securities held to maturity	3,434.1	2,011.2
FHLB and FRB stock	320.9	315.8
Total loans, net	6,583.6	6,028.4
Time deposits	5,232.4	4,539.7
Other deposits	27,311.5	25,318.6
FHLB advances	3,076	3,064.4
Federal funds purchased	543	617
Customer repurchase agreements	295.8	343.3
Other borrowings	230.9	35.4
Notes and debentures	902.6	1,000
Estimated Fair Value Measurements [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities held to maturity	1.5	1.5
Total loans, net	$ 25,363.9	$ 23,238.1

Fair Value Measurements - Car74

Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Impaired loans	$ 64.9	$ 55.9

Derivative Financial Instrume75

Derivative Financial Instruments and Hedging Activities - Additional Information (Detail)	Feb. 14, 2017USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)
Derivative [Line Items]
Aggregate fair value of derivative instruments		$ 0
Subordinated notes fixed interest rate		5.80%
Repayment of subordinated notes		$ 125,000,000
Unrealized gain on derivatives			$ (200,000)
5.80% Fixed Rate/Floating Rate Subordinated Notes Due 2017 [Member] | People's United Financial, Inc. [Member]
Derivative [Line Items]
Repayment of subordinated notes	$ 125,000,000
Interest Rate Swaps/Caps [Member] | Fair Value [Member]
Derivative [Line Items]
LIBOR basis points		Three-month LIBOR
Notional amount of derivatives		$ 375,000,000
Subordinated notes		$ 400,000,000
Basis points		1.265%
Interest Rate Swaps/Caps [Member] | Cash Flow [Member]
Derivative [Line Items]
Subordinated notes		$ 125,000,000
Interest Rate Swaps/Caps [Member] | Cash Flow [Member] | Loans [Member]
Derivative [Line Items]
LIBOR basis points		One-month LIBOR
Notional amount of derivatives		$ 210,000,000
Treasury Forward Interest Rate Locks ("T-Locks") [Member]
Derivative [Line Items]
Derivative instruments hedge description		To hedge the risk that the 10-year U.S. Treasury yield would rise
Unrealized gain on derivatives		$ 900,000
Period hedged items affected earnings, years		10 years
Treasury Forward Interest Rate Locks ("T-Locks") [Member] | Subordinated Notes [Member]
Derivative [Line Items]
Senior notes issuance		$ 500,000,000
Interest Rate Cap [Member] | LEAF Commercial Capital, Inc. [Member]
Derivative [Line Items]
LIBOR basis points		One-month LIBOR
Notional amount of derivatives		$ 150,000,000
Number of interest-rate caps		2
Interest-rate caps maturity date		2017-12

Derivative Financial Instrume76

Derivative Financial Instruments and Hedging Activities - Schedule of Notional Amounts and Fair Values of Derivatives Outstanding (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total, Derivatives Not Designated as Hedging Instruments, Fair Values, Liabilities	$ 61,400,000	$ 121,600,000
Forward commitments to sell residential mortgage loans	102,700,000	160,400,000
Total, Derivatives Designated as Hedging Instruments, Fair Values, Assets		13,600,000
Total Derivatives Fair value,Assets	102,700,000	174,000,000
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities		100,000
Fair Values, Liabilities	61,400,000	121,700,000
Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	26,000,000	48,600,000
Forward commitments to sell residential mortgage loans	600,000	300,000
Total Derivatives Fair value,Assets	600,000	300,000
Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	31,700,000	57,000,000
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	700,000	400,000
Fair Values, Liabilities	700,000	400,000
Interest Rate Swaps/Caps [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375,000,000
Interest Rate Swaps/Caps [Member] | Cash Flow [Member] | Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	210,000,000
Derivative Assets Designated as Hedging Instruments, Fair Values, Assets	0	0
Interest Rate Swaps/Caps [Member] | Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	6,101,200,000	5,612,200,000
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Assets	91,500,000	93,900,000
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	39,700,000	46,900,000
Interest Rate Swaps/Caps [Member] | Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	5,958,200,000	5,620,200,000
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Assets	10,400,000	65,600,000
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	20,800,000	74,000,000
Interest Rate Swaps/Caps [Member] | Subordinated Notes [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375,000,000	375,000,000
Derivative Assets Designated as Hedging Instruments, Fair Values, Assets		13,600,000
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities	0	0
Interest Rate Swaps/Caps [Member] | Subordinated Notes [Member] | Cash Flow [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts		125,000,000
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities		100,000
Derivative Assets Designated as Hedging Instruments, Fair Values, Assets	0	0
Risk Participation Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	383,400,000	251,900,000
Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	42,600,000	101,200,000
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Assets	200,000	600,000
Total Derivatives Fair value,Assets	200,000	600,000
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Liabilities	200,000	300,000
Fair Values, Liabilities	$ 200,000	$ 300,000

Derivative Financial Instrume77

Derivative Financial Instruments and Hedging Activities - Schedule of Notional Amounts and Fair Values of Derivatives Outstanding (Parenthetical) (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Risk Participation Agreements [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value of Derivatives, Net	$ 100,000	$ 100,000

Derivative Financial Instrume78

Derivative Financial Instruments and Hedging Activities - Impact of Derivatives on Pre-Tax Income and Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	$ 12.3	$ 15.5
Amount of Pre-Tax Gain (Loss) Recognized in AOCL		(0.2)
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	7.1	9.6
Derivatives Not Designated as Hedging Instruments [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	0.1	0.8
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	(0.1)	(1.1)
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps/Caps [Member] | Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	45.4	210.7
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps/Caps [Member] | Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	(39.1)	(200.3)
Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	0.3	(0.6)
Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	0.5	0.1
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	5.2	5.9
Amount of Pre-Tax Gain (Loss) Recognized in AOCL		(0.2)
Derivatives Designated as Hedging Instruments [Member] | Cash Flow [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	0.1	0.1
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps/Caps [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	4.5	6.4
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps/Caps [Member] | Cash Flow [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	$ 0.6	(0.6)
Amount of Pre-Tax Gain (Loss) Recognized in AOCL		$ (0.2)

Balance Sheet Offsetting - Summ

Balance Sheet Offsetting - Summary of Gross Presentation, Financial Instruments that are Eligible for Offset in Consolidated Statement of Condition (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	$ 102.7	$ 174
Financial liabilities, Gross Amount Recognized	61.4	121.7
Financial assets, Gross Amount Recognized	10.6	79.8
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	10.6	79.8
Financial assets, Financial Instruments	(7)	(58.3)
Financial assets, Collateral	(0.9)	(20.9)
Financial assets, Net Amount	2.7	0.6
Financial liabilities, Gross Amount Recognized	21.1	74.4
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	21.1	74.4
Financial liabilities, Financial Instruments	(7)	(58.3)
Financial liabilities, Collateral	(13.9)	(13.4)
Financial liabilities, Net Amount	0.2	2.7
Foreign Exchange Contracts [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.2	0.6
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.2	0.6
Financial assets, Net Amount	0.2	0.6
Financial liabilities, Gross Amount Recognized	0.2	0.3
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	0.2	0.3
Financial liabilities, Net Amount	0.2	0.3
Counterparty A [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	1.7	1.9
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	1.7	1.9
Financial assets, Financial Instruments	(1.7)	(1.9)
Financial liabilities, Gross Amount Recognized	3.2	4.3
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	3.2	4.3
Financial liabilities, Financial Instruments	(1.7)	(1.9)
Financial liabilities, Collateral	(1.5)	(2.4)
Counterparty B [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.8	1
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.8	1
Financial assets, Financial Instruments	(0.8)	(1)
Financial liabilities, Gross Amount Recognized	6.9	7.7
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	6.9	7.7
Financial liabilities, Financial Instruments	(0.8)	(1)
Financial liabilities, Collateral	(6.1)	(6.7)
Counterparty C [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	1.4	1.7
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	1.4	1.7
Financial assets, Financial Instruments	(1.4)	(1.7)
Financial liabilities, Gross Amount Recognized	3.7	3.4
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	3.7	3.4
Financial liabilities, Financial Instruments	(1.4)	(1.7)
Financial liabilities, Collateral	(2.3)	(1.1)
Financial liabilities, Net Amount		0.6
Counterparty D [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	2.8	3.4
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	2.8	3.4
Financial assets, Financial Instruments	(2.8)	(3.4)
Financial liabilities, Gross Amount Recognized	5.9	6.9
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	5.9	6.9
Financial liabilities, Financial Instruments	(2.8)	(3.4)
Financial liabilities, Collateral	(3.1)	(1.7)
Financial liabilities, Net Amount		1.8
Counterparty E [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	2.4	69.6
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	2.4	69.6
Financial assets, Financial Instruments		(50)
Financial assets, Collateral		(19.6)
Financial assets, Net Amount	2.4
Financial liabilities, Gross Amount Recognized		50
Financial liabilities, Gross Amount Offset		0
Financial liabilities, Net Amount Presented		50
Financial liabilities, Financial Instruments		(50)
Other Counterparties [Member] | Interest Rate Swaps/Caps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	1.3	1.6
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	1.3	1.6
Financial assets, Financial Instruments	(0.3)	(0.3)
Financial assets, Collateral	(0.9)	(1.3)
Financial assets, Net Amount	0.1
Financial liabilities, Gross Amount Recognized	1.2	1.8
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	1.2	1.8
Financial liabilities, Financial Instruments	(0.3)	(0.3)
Financial liabilities, Collateral	$ (0.9)	$ (1.5)

Balance Sheet Offsetting - Addi

Balance Sheet Offsetting - Additional Information (Detail) $ in Millions	Sep. 30, 2017USD ($)
US Treasury [Member]
Offsettting Assetsand Liabilities [Line Items]
Fair value of treasury securities	$ 248.3
Mortgage-Backed Securities [Member]
Offsettting Assetsand Liabilities [Line Items]
Fair value of treasury securities	$ 254.4

Balance Sheet Offsetting - Su81

Balance Sheet Offsetting - Summary of Collateral Swaps (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Offsettting Assetsand Liabilities [Line Items]
Total repurchase agreements, Net amounts Presented in the Balance Sheet	$ 295.8	$ 343.3
Collateral Swaps [Member]
Offsettting Assetsand Liabilities [Line Items]
Total resale agreements, Gross Amount Recognized	250
Total resale agreements, Gross Amount Offset in the Balance Sheet	(250)
Total resale agreements, Net amount Presented in the Balance Sheet	0
Total repurchase agreements, Gross Amount Recognized	250
Total repurchase agreements, Gross Amounts Offset in the Balance Sheet	(250)
Total repurchase agreements, Net amounts Presented in the Balance Sheet	$ 0

New Accounting Standards - Addi

New Accounting Standards - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other windfall income tax benefits	$ 1.3
Decrease in effective income tax rate	0.05%
Percentage of interest income on financial assets and financial liabilities	75.00%
Percentage of non-interest income on financial assets and financial liabilities	25.00%
Equity securities, amortized cost	$ 3,220.6	$ 4,463.2
Equity securities, fair value	3,197.5	4,409.9
Equity Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, amortized cost	9.6	0.2
Equity securities, fair value	$ 9	$ 0.2