People's United Financial (PBCT) 10-Q 11 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	PBCT
Entity Registrant Name	People's United Financial, Inc.
Entity Central Index Key	1378946
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		309,109,375

Consolidated_Statements_of_Con

Consolidated Statements of Condition - (Unaudited) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Assets
Cash and due from banks	$306.80	$345.10
Short-term investments (note 2)	250	668.6
Total cash and cash equivalents	556.8	1,013.70
Securities purchased under agreements to resell (note 2)		100
Securities (note 2):
Trading account securities, at fair value	8.3	8.3
Securities available for sale, at fair value	4,356.80	3,993.70
Securities held to maturity, at amortized cost (fair value of $943.9 million and $881.6 million)	897.4	834.3
Federal Home Loan Bank and Federal Reserve Bank stock, at cost	314.2	175.7
Total securities	5,576.70	5,012
Loans held for sale	49.7	34.2
Loans (note 3):
Consumer	2,181.50	2,200.60
Total loans	26,929.30	26,592
Less allowance for loan losses	-200.9	-198.3
Total loans, net	26,728.40	26,393.70
Goodwill (note 6)	1,954.50	1,954.50
Bank-owned life insurance	344.4	343.3
Premises and equipment, net	268.4	277.8
Other acquisition-related intangible assets (note 6)	142.1	148
Other assets (notes 1, 3 and 11)	786.3	719.9
Total assets	36,407.30	35,997.10
Deposits:
Non-interest-bearing	5,761.90	5,655.10
Savings, interest-bearing checking and money market	16,086.40	15,252.40
Time	5,301.60	5,230.70
Total deposits	27,149.90	26,138.20
Borrowings:
Federal Home Loan Bank advances	2,165.90	2,291.70
Federal funds purchased	496	913
Customer repurchase agreements	1	1
Other borrowings	1	1
Total borrowings	3,142.90	3,691.70
Notes and debentures	1,042.30	1,033.50
Other liabilities (note 11)	390.3	500.6
Total liabilities	31,725.40	31,364
Commitments and contingencies (notes 1 and 8)
Stockholders' Equity
Common stock ($0.01 par value; 1.95 billion shares authorized; 397.8 million shares and 396.8 million shares issued)	3.9	3.9
Additional paid-in capital	5,304.20	5,291.20
Retained earnings	833.2	826.7
Accumulated other comprehensive loss (note 4)	-140.6	-168.2
Unallocated common stock of Employee Stock Ownership Plan, at cost (7.6 million shares and 7.7 million shares) (note 7)	-157.2	-159
Treasury stock, at cost (89.0 million shares at both dates) (note 4)	-1,161.60	-1,161.50
Total stockholders' equity	4,681.90	4,633.10
Total liabilities and stockholders' equity	36,407.30	35,997.10
Commercial Customers [Member]
Borrowings:
Customer repurchase agreements	480	486
Commercial [Member]
Loans (note 3):
Commercial	10,226.80	10,055.10
Commercial Real Estate [Member]
Loans (note 3):
Commercial	9,470.40	9,404.30
Residential Mortgage [Member]
Loans (note 3):
Residential mortgage	$5,050.60	$4,932

Consolidated_Statements_of_Con1

Consolidated Statements of Condition - (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Securities held to maturity, at fair value	$943.90	$881.60
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	1.95	1.95
Common stock, shares issued	397,800,000	396,800,000
Unallocated common stock of Employee Stock Ownership Plan, shares	7,578,841	7,700,000
Treasury stock, shares	89,000,000	89,000,000

Consolidated_Statements_of_Inc

Consolidated Statements of Income - (Unaudited) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Interest and dividend income:
Commercial	$88.90	$85.30
Commercial real estate	85.3	88.7
Residential mortgage	40.2	37.8
Consumer	18.1	18.3
Total interest on loans	232.5	230.1
Securities	27.5	25.1
Loans held for sale	0.2	0.1
Short-term investments	0.1	0.1
Total interest and dividend income	260.3	255.4
Interest expense:
Deposits	22.2	19.3
Borrowings	2.6	3.1
Notes and debentures	7.4	5.9
Total interest expense	32.2	28.3
Net interest income	228.1	227.1
Provision for loan losses (note 3)	9.8	9.5
Net interest income after provision for loan losses	218.3	217.6
Non-interest income:
Bank service charges	30.1	30.5
Commercial banking lending fees	12.3	8.8
Investment management fees	10.8	9.8
Operating lease income	10.8	11.3
Insurance revenue	7.6	7.7
Brokerage commissions	3.2	3.2
Net gains on sales of acquired loans	1.9
Net gains on sales of residential mortgage loans	0.7	0.8
Other non-interest income	11.6	7.8
Total non-interest income	89	79.9
Non-interest expense:
Compensation and benefits	114.8	110.4
Occupancy and equipment	38.7	38
Professional and outside services	15.8	15.3
Regulatory assessments	9.3	8.7
Operating lease expense	9.3	11.1
Amortization of other acquisition-related intangible assets (note 6)	5.9	6.2
Other non-interest expense	23.8	27
Total non-interest expense	217.6	216.7
Income before income tax expense	89.7	80.8
Income tax expense	30.5	27.7
Net income	$59.20	$53.10
Earnings per common share (note 5):
Basic	$0.20	$0.18
Diluted	$0.20	$0.18

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income - (Unaudited) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$59.20	$53.10
Other comprehensive income, net of tax:
Net actuarial loss and prior service credit related to pension and other postretirement benefit plans	1.1	0.6
Net unrealized gains and losses on securities available for sale	26.2	16.5
Amortization of unrealized losses on securities transferred to held to maturity	0.5	0.4
Net unrealized gains and losses on derivatives accounted for as cash flow hedges	-0.2	0.1
Current period other comprehensive income (loss)	27.6	17.6
Total comprehensive income	$86.80	$70.70

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders' Equity - (Unaudited) (USD $)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Unallocated ESOP Common Stock [Member]	Treasury Stock [Member]
In Millions
Beginning Balance at Dec. 31, 2013	$4,568.40	$3.90	$5,277	$779	($155.10)	($166.20)	($1,170.20)
Net income	53.1			53.1
Total other comprehensive income, net of tax (note 4)	17.6				17.6
Cash dividends on common stock	-48.6			-48.6
Restricted stock awards	2.7		-4.5	-2.2			9.4
Employee Stock Ownership Plan common stock committed to be released (note 7)	1.3			-0.5		1.8
Common stock repurchased and retired upon vesting of restricted stock awards	-2.6			-2.6
Stock options and related tax benefits	3.9		3.9
Ending Balance at Mar. 31, 2014	4,595.80	3.9	5,276.40	778.2	-137.5	-164.4	-1,160.80
Beginning Balance at Dec. 31, 2014	4,633.10	3.9	5,291.20	826.7	-168.2	-159	-1,161.50
Net income	59.2			59.2
Total other comprehensive income, net of tax (note 4)	27.6				27.6
Cash dividends on common stock	-49.5			-49.5
Restricted stock awards	3.4		3.5				-0.1
Employee Stock Ownership Plan common stock committed to be released (note 7)	1.3			-0.5		1.8
Common stock repurchased and retired upon vesting of restricted stock awards	-2.7			-2.7
Stock options and related tax benefits	9.5		9.5
Ending Balance at Mar. 31, 2015	$4,681.90	$3.90	$5,304.20	$833.20	($140.60)	($157.20)	($1,161.60)

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Stockholders' Equity - (Unaudited) (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash dividends on common stock, per share	$0.17	$0.16
Retained Earnings [Member]
Cash dividends on common stock, per share	$0.17	$0.16

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows - (Unaudited) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Cash Flows from Operating Activities:
Net income	$59.20	$53.10
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Provision for loan losses	9.8	9.5
Depreciation and amortization of premises and equipment	9.7	10
Expense related to operating leases	9.3	11.1
Amortization of other acquisition-related intangible assets	5.9	6.2
Net security gains		-0.1
Net gains on sales of residential mortgage loans	-0.7	-0.8
Net gains on sales of acquired loans	-1.9
Employee Stock Ownership Plan common stock committed to be released	1.3	1.3
Expense related to share-based awards	5	4
Originations of loans held-for-sale	-91.3	-51
Proceeds from sales of loans held-for-sale	76.5	57.7
Net changes in other assets and liabilities	-86.9	-6.9
Net cash (used in) provided by operating activities	-4.1	94.1
Cash Flows from Investing Activities:
Net decrease in securities purchased under agreements to resell	100
Proceeds from principal repayments and maturities of securities available for sale	191.5	161.5
Proceeds from sales of securities available for sale		180.8
Proceeds from principal repayments and maturities of securities held to maturity	1.5	2.1
Purchases of securities available for sale	-597.7	-38.6
Purchases of securities held to maturity	-70.9	-12.9
Purchases of Federal Reserve Bank stock	-138.5
Proceeds from sales of loans	20.8	0.4
Loan disbursements, net of principal collections	-367.5	-252.1
Purchases of premises and equipment	-5.6	-2.8
Purchases of leased equipment	-9.7
Proceeds from sales of real estate owned	3.8	2.6
Return of premiums on bank-owned life insurance, net		0.3
Net cash (used in) provided by investing activities	-872.3	41.3
Cash Flows from Financing Activities:
Net increase in deposits	1,011.70	1,108.20
Net decrease in borrowings with terms of three months or less	-548	-1,168.90
Repayments of borrowings with terms of more than three months	-0.1	-0.1
Cash dividends paid on common stock	-49.5	-48.6
Common stock repurchases	-2.7	-2.6
Proceeds from stock options exercised, including excess income tax benefits	8.1	2.6
Net cash provided by (used in) financing activities	419.5	-109.4
Net (decrease) increase in cash and cash equivalents	-456.9	26
Cash and cash equivalents at beginning of period	1,013.70	474.4
Cash and cash equivalents at end of period	556.8	500.4
Supplemental Information:
Interest payments	32.1	23.9
Unsettled purchases of securities	1.1	26.3
Income tax payments	4.9	4.3
Real estate properties acquired by foreclosure	$6.70	$9.80

General

General	3 Months Ended
	Mar. 31, 2015
Accounting Policies [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, and
	other-than-temporary declines in the fair value of securities. These significant accounting policies and critical estimates are reviewed with the Audit Committee of the Board of Directors.
	The judgments used by management in applying these 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 for the year ended December 31, 2014, as supplemented by this Quarterly Report for the period ended March 31, 2015, provides disclosure of People’s United’s significant accounting policies.
	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, are not consolidated into the Company’s Consolidated Financial Statements. These investments have historically played a role in enabling People’s United Bank, N.A. (the “Bank”) to meet its Community Reinvestment Act requirements while, at the same time, providing federal income tax credits.
	The balance of the Company’s affordable housing investments reflected in the Consolidated Statement of Condition at March 31, 2015 totaled $71.6 million (included in other assets). Future contingent commitments (capital calls) related to such investments, the timing of which cannot be reasonably estimated, totaled $36.1 million at that date. 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 $2.8 million and $2.3 million for the three months ended March 31, 2015 and 2014, 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 for the year ended December 31, 2014. The results of operations for the three months ended March 31, 2015 are not necessarily indicative of the results of operations that may be expected for the entire year or any other interim period.

Securities_and_ShortTerm_Inves

Securities and Short-Term Investments	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities and Short-Term Investments	NOTE 2. 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 March 31, 2015 (in millions)		Amortized		Gross			Gross			Fair
			Cost		Unrealized			Unrealized			Value
					Gains			Losses
	Securities available for sale:
	Debt securities:
	U.S. Treasury and agency		$	299.7	$	1.4		$	—		$	301.1
	GSE (1) residential mortgage-backed securities			4,022.50		52.7			(19.7	)		4,055.50
	and CMOs (2)
	Total debt securities			4,322.20		54.1			(19.7	)		4,356.60
	Equity securities			0.2		—			—			0.2
	Total securities available for sale		$	4,322.40	$	54.1		$	(19.7	)	$	4,356.80
	Securities held to maturity:
	Debt securities:
	State and municipal		$	895.9	$	47.7		$	(1.2	)	$	942.4
	Other			1.5		—			—			1.5
	Total securities held to maturity		$	897.4	$	47.7		$	(1.2	)	$	943.9
		-1	Government sponsored enterprise
		-2	Collateralized mortgage obligations
	As of December 31, 2014 (in millions)		Amortized		Gross			Gross			Fair
			Cost		Unrealized			Unrealized			Value
					Gains			Losses
	Securities available for sale:
	Debt securities:
	U.S. Treasury and agency		$	56.5	$	0.3		$	—		$	56.8
	GSE residential mortgage-backed securities and CMOs			3,943.40		39.7			(46.4	)		3,936.70
	Total debt securities			3,999.90		40			(46.4	)		3,993.50
	Equity securities			0.2		—			—			0.2
	Total securities available for sale		$	4,000.10	$	40		$	(46.4	)	$	3,993.70
	Securities held to maturity:
	Debt securities:
	State and municipal		$	832.8	$	47.4		$	(0.1	)	$	880.1
	Other			1.5		—			—			1.5
	Total securities held to maturity		$	834.3	$	47.4		$	(0.1	)	$	881.6
	The following table is a summary of the amortized cost and fair value of debt securities as of March 31, 2015, based on remaining period to contractual maturity. Information for GSE residential 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
			Cost		Value			Cost			Value
	U.S. Treasury and agency:
	Within 1 year		$	10.9	$	10.9		$	—		$	—
	After 1 but within 5 years			288.8		290.2			—			—
	Total			299.7		301.1			—			—
	GSE residential mortgage-backed securities and CMOs:
	After 1 but within 5 years			18.8		18.9			—			—
	After 5 but within 10 years			792.3		805.7			—			—
	After 10 years			3,211.40		3,230.90			—			—
	Total			4,022.50		4,055.50			—			—
	State and municipal:
	Within 1 year			—		—			3.2			3.2
	After 1 but within 5 years			—		—			20.7			21
	After 5 but within 10 years			—		—			287.3			305.2
	After 10 years			—		—			584.7			613
	Total			—		—			895.9			942.4
	Other:
	After 1 but within 5 years			—		—			1.5			1.5
	Total			—		—			1.5			1.5
	Total:
	Within 1 year			10.9		10.9			3.2			3.2
	After 1 but within 5 years			307.6		309.1			22.2			22.5
	After 5 but within 10 years			792.3		805.7			287.3			305.2
	After 10 years			3,211.40		3,230.90			584.7			613
	Total		$	4,322.20	$	4,356.60		$	897.4		$	943.9
	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. 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 debt securities with unrealized losses, segregated by the length of time the securities have been in a continuous unrealized loss position at the respective dates.
		Continuous Unrealized Loss Position
		Less Than 12 Months					12 Months Or Longer						Total
As of March 31, 2015 (in millions)		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
		Value		Losses			Value			Losses			Value		Losses
Securities available for sale:
GSE residential mortgage-backed securities and CMOs		$	353.2	$	(1.0	)	$	1,094.50		$	(18.7	)	$	1,447.70	$	(19.7	)
Securities held to maturity:
State and municipal			109.1		(1.2	)		—			—			109.1		(1.2	)
Total		$	462.3	$	(2.2	)	$	1,094.50		$	(18.7	)	$	1,556.80	$	(20.9	)
		Continuous Unrealized Loss Position
		Less Than 12 Months					12 Months Or Longer						Total
As of December 31, 2014 (in millions)		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
		Value		Losses			Value			Losses			Value		Losses
Securities available for sale:
GSE residential mortgage-backed securities and CMOs		$	111.9	$	(0.1	)	$	1,744.20		$	(46.3	)	$	1,856.10	$	(46.4	)
Securities held to maturity:
State and municipal			31.8		(0.1	)		—			—			31.8		(0.1	)
Total		$	143.7	$	(0.2	)	$	1,744.20		$	(46.3	)	$	1,887.90	$	(46.5	)
At March 31, 2015, 10% of the 1,207 securities owned by the Company, consisting of 35 securities classified as available for sale and 84 securities classified as held to maturity, had gross unrealized losses totaling $19.7 million and $1.2 million, respectively. All of the GSE residential mortgage-backed securities and CMOs had AAA credit ratings and an average maturity of 12 years. The state and municipal securities had an average credit rating of AA and an average maturity of 16 years. The cause of the temporary impairment with respect to all of these securities is directly related to changes in interest rates.
Management believes that all gross unrealized losses within the securities portfolio at March 31, 2015 and December 31, 2014 are temporary impairments. Management does not intend to sell such securities nor is it more likely than not that management will be required to sell such securities prior to recovery. No other-than-temporary impairment losses were recognized in the Consolidated Statements of Income for the three months ended March 31, 2015 and 2014.
Security transactions are recorded on the trade date. Realized gains and losses are determined using the specific identification method and reported in non-interest income.
Securities available for sale with a fair value of $1.47 billion and $1.43 billion at March 31, 2015 and December 31, 2014, respectively, were pledged as collateral for public deposits and for other purposes.
The Bank, as a member of the Federal Home Loan Bank (“FHLB”) of Boston, is currently required to purchase and hold shares of FHLB capital stock (total cost of $164.4 million at both March 31, 2015 and December 31, 2014) 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 the Smithtown Bancorp, Inc. (“Smithtown”) acquisition completed in 2010, People’s United acquired shares of capital stock in the FHLB of New York (total cost of $11.3 million at both March 31, 2015 and December 31, 2014). 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 March 31, 2015 and the cost of the investment approximates fair value.
The Bank, as a member of the Federal Reserve Bank (“FRB”) system, is currently required to purchase and hold shares of FRB of New York capital stock in an amount equal to six percent of its capital and surplus. In the first quarter of 2015, the Bank purchased FRB capital stock at a total cost of $138.5 million. Based on the current capital adequacy and liquidity position of the FRB of New York, management believes there is no impairment in the Company’s investment at March 31, 2015 and the cost of the investment approximates fair value.
Included in short-term investments are interest-bearing deposits at the FRB of New York totaling $180.1 million at March 31, 2015 and $626.5 million at December 31, 2014. These deposits represent an alternative to overnight federal funds sold and had a yield of 0.25% at both dates.
People’s United accounts for securities purchased under agreements to resell as secured lending transactions. In connection with such agreements, People’s United takes delivery of collateral from all counterparties. The fair value of the collateral securing the agreements outstanding at December 31, 2014 was $100.4 million (no agreements were outstanding at March 31, 2015).

Loans

Loans	3 Months Ended
	Mar. 31, 2015
Receivables [Abstract]
Loans	NOTE 3. 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: commercial real estate; commercial and industrial; and equipment financing.
		•		Retail Portfolio: residential mortgage; home equity; and other consumer.
	Loans acquired in connection with business combinations beginning in 2010 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’ and the treatment of loan origination costs); and
		•		Recognition of loan charge-offs.
	The Company did not change its policies with respect to loans or its methodology for determining the allowance for loan losses during the three months ended March 31, 2015.
	The following table summarizes People’s United’s loans by loan portfolio segment and class:
			March 31, 2015									December 31, 2014
	(in millions)		Originated			Acquired			Total			Originated			Acquired			Total
	Commercial:
	Commercial real estate		$	9,077.80		$	392.6		$	9,470.40		$	8,960.30		$	444		$	9,404.30
	Commercial and industrial			7,131.30			274.2			7,405.50			6,891.10			298.5			7,189.60
	Equipment financing			2,797.80			23.5			2,821.30			2,839.00			26.5			2,865.50
	Total commercial			9,929.10			297.7			10,226.80			9,730.10			325			10,055.10
	Total Commercial Portfolio			19,006.90			690.3			19,697.20			18,690.40			769			19,459.40
	Retail:
	Residential mortgage:
	Adjustable-rate			4,366.30			135.5			4,501.80			4,254.70			139.1			4,393.80
	Fixed-rate			464.4			84.4			548.8			446.8			91.4			538.2
	Total residential mortgage			4,830.70			219.9			5,050.60			4,701.50			230.5			4,932.00
	Consumer:
	Home equity			2,082.70			46.7			2,129.40			2,092.90			50.2			2,143.10
	Other consumer			51			1.1			52.1			56.3			1.2			57.5
	Total consumer			2,133.70			47.8			2,181.50			2,149.20			51.4			2,200.60
	Total Retail Portfolio			6,964.40			267.7			7,232.10			6,850.70			281.9			7,132.60
	Total loans		$	25,971.30		$	958		$	26,929.30		$	25,541.10		$	1,050.90		$	26,592.00
	Net deferred loan costs, which are included in total loans and accounted for as interest yield adjustments, totaled $55.3 million at March 31, 2015 and $54.8 million at December 31, 2014.
	The following table presents a summary, by loan portfolio segment, of activity in the allowance for loan losses. 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.
			Commercial									Retail
	Three Months Ended March 31, 2015 (in millions)		Originated			Acquired			Total			Originated			Acquired			Total			Total
	Balance at beginning of period		$	169.6		$	9.8		$	179.4		$	18.5		$	0.4		$	18.9		$	198.3
	Charge-offs			(6.6	)		—			(6.6	)		(1.5	)		—			(1.5	)		(8.1	)
	Recoveries			0.6			—			0.6			0.3			—			0.3			0.9
	Net loan charge-offs			(6.0	)		—			(6.0	)		(1.2	)		—			(1.2	)		(7.2	)
	Provision for loan losses			9.5			(0.4	)		9.1			0.7			—			0.7			9.8
	Balance at end of period		$	173.1		$	9.4		$	182.5		$	18		$	0.4		$	18.4		$	200.9
			Commercial									Retail
	Three Months Ended March 31, 2014 (in millions)		Originated			Acquired			Total			Originated			Acquired			Total			Total
	Balance at beginning of period		$	158.5		$	9.8		$	168.3		$	19		$	0.5		$	19.5		$	187.8
	Charge-offs			(3.1	)		(1.4	)		(4.5	)		(3.3	)		(0.1	)		(3.4	)		(7.9	)
	Recoveries			0.5			—			0.5			0.4			—			0.4			0.9
	Net loan charge-offs			(2.6	)		(1.4	)		(4.0	)		(2.9	)		(0.1	)		(3.0	)		(7.0	)
	Provision for loan losses			4.1			1.4			5.5			3.9			0.1			4			9.5
	Balance at end of period		$	160		$	9.8		$	169.8		$	20		$	0.5		$	20.5		$	190.3
	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						Acquired Loans						Total
			Individually Evaluated						Collectively Evaluated						(Discounts Related to
			for Impairment						for Impairment						Credit Quality)
	As of March 31, 2015 (in millions)		Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance
	Commercial		$	169.5		$	6.6		$	18,837.40		$	166.5		$	690.3		$	9.4		$	19,697.20		$	182.5
	Retail			97.9			3.9			6,866.50			14.1			267.7			0.4			7,232.10			18.4
	Total		$	267.4		$	10.5		$	25,703.90		$	180.6		$	958.0		$	9.8		$	26,929.30		$	200.9
			Originated Loans						Originated Loans						Acquired Loans						Total
			Individually Evaluated						Collectively Evaluated						(Discounts Related to
			for Impairment						for Impairment						Credit Quality)
	As of December 31, 2014 (in millions)		Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance
	Commercial		$	174.5		$	7.6		$	18,515.90		$	162		$	769		$	9.8		$	19,459.40		$	179.4
	Retail			95			3.9			6,755.70			14.6			281.9			0.4			7,132.60			18.9
	Total		$	269.5		$	11.5		$	25,271.60		$	176.6		$	1,050.90		$	10.2		$	26,592.00		$	198.3
	The recorded investments, by class of loan, of originated non-performing loans are summarized as follows:
(in millions)		March 31,			December 31,
		2015			2014
Commercial:
Commercial real estate		$	43.3		$	60.2
Commercial and industrial			42.6			55.8
Equipment financing			34.9			25.4
Total (1)			120.8			141.4
Retail:
Residential mortgage			37.5			37.6
Home equity			19.4			17.9
Other consumer			0.1			0.1
Total (2)			57			55.6
Total		$	177.8		$	197
-1	Reported net of government guarantees totaling $17.5 million and $17.6 million at March 31, 2015 and December 31, 2014, 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 March 31, 2015, the principal loan classes to which these government guarantees relate are commercial and industrial loans (99%) and commercial real estate loans (1%).
-2	Includes $15.2 million and $18.9 million of loans in the process of foreclosure at March 31, 2015 and December 31, 2014, respectively.
The preceding table excludes acquired loans that are (i) accounted for as purchased credit impaired loans or (ii) covered by an Federal Deposit Insurance Corporation (“FDIC”) loss-share agreement (“LSA”) totaling $72.2 million and $2.6 million, respectively, at March 31, 2015 and $100.6 million and $3.0 million, respectively, at December 31, 2014. Such loans otherwise meet People’s United’s definition of a non-performing loan but are excluded because the loans are included in loan pools that are considered performing and/or credit losses are covered by an FDIC LSA. The discounts arising from recording these loans at fair value were due, in part, to credit quality. The acquired loans are generally accounted for on a pool basis and the accretable yield on the pools is being recognized as interest income over the life of the loans based on expected cash flows at the pool level.
A loan is generally considered “non-performing” when it is placed on non-accrual status. A loan is generally placed on non-accrual status when it becomes 90 days past due as to interest or principal payments. Past due status is based on the contractual payment terms of the loan. A loan may be placed on non-accrual status before it reaches 90 days past due if such loan has been identified as presenting uncertainty with respect to the collectability of interest and principal. A loan past due 90 days or more may remain on accruing status if such loan is both well secured and in the process of collection. There were no loans past due 90 days or more and still accruing interest at March 31, 2015 or December 31, 2014.
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 originated loans whose terms have been modified in such a way that they are considered troubled debt restructurings (“TDRs”). Originated 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. Generally, TDRs are placed on non-accrual status (and reported as non-performing loans) until the loan qualifies for return to accrual status. Loans qualify for return to accrual status once they have demonstrated performance with the restructured terms of the loan agreement for a minimum of six months in the case of a commercial loan or, in the case of a retail loan, when the loan is less than 90 days past due. Loans may continue to be reported as TDRs after they are returned to accrual status. In accordance with regulatory guidance, residential mortgage and home equity loans restructured in connection with the borrower’s bankruptcy and meeting certain criteria are also required to be classified as TDRs, included in non-performing loans and written down to the estimated collateral value, regardless of delinquency status. Acquired loans that are modified are not considered for TDR classification provided they are evaluated for impairment on a pool basis.
People’s United’s recorded investment in originated loans classified as TDRs totaled $192.5 million and $181.6 million at March 31, 2015 and December 31, 2014, respectively. The related allowance for loan losses at March 31, 2015 and December 31, 2014 was $6.7 million and $7.1 million, respectively. Interest income recognized on TDRs totaled $1.1 million and $0.9 million for the three months ended March 31, 2015 and 2014, respectively. Fundings under commitments to lend additional amounts to borrowers with loans classified as TDRs were immaterial for the three months ended March 31, 2015 and 2014. Originated loans that were modified and classified as TDRs during the three months ended March 31, 2015 and 2014 principally involve reduced payment and/or payment deferral, extension of term (generally no more than two years for commercial loans and eight 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 months ended March 31, 2015 and 2014. For purposes of this disclosure, recorded investments represent amounts immediately prior to and subsequent to the restructuring.
		Three Months Ended March 31, 2015
(dollars in millions)		Number			Pre-Modification			Post-Modification
		of Contracts			Outstanding			Outstanding
					Recorded			Recorded
					Investment			Investment
Commercial:
Commercial real estate (1)			8		$	4.9		$	4.9
Commercial and industrial (2)			8			10.1			10.1
Equipment financing (3)			5			7.6			7.6
Total			21			22.6			22.6
Retail:
Residential mortgage (4)			20			5.7			5.7
Home equity (5)			33			2			2
Other consumer			—			—			—
Total			53			7.7			7.7
Total			74		$	30.3		$	30.3
-1	Represents the following concessions: extension of term (8 contracts; recorded investment of $4.9 million).
-2	Represents the following concessions: extension of term (4 contracts; recorded investment of $8.7 million); reduced payment and/or payment deferral (3 contracts; recorded investment of $0.6 million); or a combination of concessions (1 contract; recorded investment of $0.8 million).
-3	Represents the following concessions: reduced payment and/or payment deferral (3 contracts; recorded investment of $5.7 million); or a combination of concessions (2 contracts; recorded investment of $1.9 million).
-4	Represents the following concessions: loans restructured through bankruptcy (6 contracts; recorded investment of $2.4 million); reduced payment and/or payment deferral (4 contracts; recorded investment of $1.5 million); temporary rate reduction (1 contract; recorded investment of $0.2 million); or a combination of concessions (9 contracts; recorded investment of $1.6 million).
-5	Represents the following concessions: loans restructured through bankruptcy (25 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $0.2 million); or a combination of concessions (6 contracts; recorded investment of $0.8 million).
		Three Months Ended March 31, 2014
(dollars in millions)		Number			Pre-Modification			Post-Modification
		of Contracts			Outstanding			Outstanding
					Recorded			Recorded
					Investment			Investment
Commercial:
Commercial real estate (1)			6		$	5		$	5
Commercial and industrial (2)			7			3.4			3.4
Equipment financing (3)			5			2.9			2.9
Total			18			11.3			11.3
Retail:
Residential mortgage (4)			48			16.8			16.8
Home equity (5)			40			3.8			3.8
Other consumer			—			—			—
Total			88			20.6			20.6
Total			106		$	31.9		$	31.9
-1	Represents the following concessions: extension of term (4 contracts; recorded investment of $4.1 million); or a combination of concessions (2 contracts; recorded investment of $0.9 million).
-2	Represents the following concessions: extension of term (3 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 (3 contracts; recorded investment of $1.7 million).
-3	Represents the following concessions: combination of concessions (5 contracts; recorded investment of $2.9 million).
-4	Represents the following concessions: loans restructured through bankruptcy (9 contracts; recorded investment of $3.1 million); extension of term (1 contract; recorded investment of $0.5 million); reduced payment and/or payment deferral (12 contracts; recorded investment of $4.3 million); or a combination of concessions (26 contracts; recorded investment of $8.9 million).
-5	Represents the following concessions: loans restructured through bankruptcy (17 contracts; recorded investment of $2.1 million); reduced payment and/or payment deferral (3 contracts; recorded investment of $0.1 million); temporary rate reduction (1 contract; recorded investment of $0.1 million); or a combination of concessions (19 contracts; recorded investment of $1.5 million).
The following is a summary, by class of loan, of information related to TDRs of originated loans completed within the previous 12 months that subsequently defaulted during the three months ended March 31, 2015 and 2014. For purposes of this disclosure, the previous 12 months is measured from April 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 months ended March 31, 2015 or 2014.
		Three Months Ended March 31,
		2015						2014
(dollars in millions)		Number			Recorded			Number			Recorded
		of Contracts			Investment as of			of Contracts			Investment as of
					Period End						Period End
Commercial:
Commercial real estate			—		$	—			—		$	—
Commercial and industrial			2			0.1			1			1.5
Equipment financing			4			1.3			9			1.4
Total			6			1.4			10			2.9
Retail:
Residential mortgage			17			7.4			24			10.9
Home equity			11			1.2			8			0.9
Other consumer			—			—			—			—
Total			28			8.6			32			11.8
Total			34		$	10			42		$	14.7
People’s United’s impaired loans consist of certain originated loans, including all TDRs. The following table summarizes, by class of loan, information related to individually-evaluated impaired loans within the originated portfolio.
		As of March 31, 2015									As of December 31, 2014
(in millions)		Unpaid			Recorded			Related			Unpaid			Recorded			Related
		Principal			Investment			Allowance			Principal			Investment			Allowance
		Balance						for Loan			Balance						for Loan
								Losses									Losses
Without a related allowance for loan losses:
Commercial:
Commercial real estate		$	54.9		$	53.7		$	—		$	57.1		$	55.8		$	—
Commercial and industrial			60.2			56.9			—			51.7			48.6			—
Equipment financing			34.5			24.5			—			30.2			21.4			—
Retail:
Residential mortgage			66.6			60			—			65.4			58.9			—
Home equity			22.8			19.4			—			21.3			18.3			—
Other consumer			—			—			—			—			—			—
Total		$	239		$	214.5		$	—		$	225.7		$	203		$	—
With a related allowance for loan losses:
Commercial:
Commercial real estate		$	23.1		$	16.2		$	1.7		$	52.1		$	27.8		$	4
Commercial and industrial			8.3			6.4			2.9			21.4			17.4			3.5
Equipment financing			11.9			11.8			2			3.6			3.5			0.1
Retail:
Residential mortgage			16.5			16.4			2.7			15.6			15.3			2.6
Home equity			2.2			2.1			1.2			2.6			2.5			1.3
Other consumer			—			—			—			—			—			—
Total		$	62		$	52.9		$	10.5		$	95.3		$	66.5		$	11.5
Total impaired loans:
Commercial:
Commercial real estate		$	78		$	69.9		$	1.7		$	109.2		$	83.6		$	4
Commercial and industrial			68.5			63.3			2.9			73.1			66			3.5
Equipment financing			46.4			36.3			2			33.8			24.9			0.1
Total			192.9			169.5			6.6			216.1			174.5			7.6
Retail:
Residential mortgage			83.1			76.4			2.7			81			74.2			2.6
Home equity			25			21.5			1.2			23.9			20.8			1.3
Other consumer			—			—			—			—			—			—
Total			108.1			97.9			3.9			104.9			95			3.9
Total		$	301		$	267.4		$	10.5		$	321		$	269.5		$	11.5
The following table summarizes, 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 balances.
		Three Months Ended March 31,
		2015						2014
(in millions)		Average			Interest			Average			Interest
		Recorded			Income			Recorded			Income
		Investment			Recognized			Investment			Recognized
Commercial:
Commercial real estate		$	78		$	0.3		$	74.1		$	0.2
Commercial and industrial			59.5			0.4			37			0.2
Equipment financing			26.8			0.1			28.3			0.3
Total			164.3			0.8			139.4			0.7
Retail:
Residential mortgage			75.6			0.4			69.3			0.3
Home equity			21.5			0.1			16.4			0.1
Other consumer			—			—			—			—
Total			97.1			0.5			85.7			0.4
Total		$	261.4		$	1.3		$	225.1		$	1.1
The following tables summarize, by class of loan, aging information for originated loans:
					Past Due
As of March 31, 2015 (in millions)		Current			30-89			90 Days			Total			Total
					Days			or More						Originated
Commercial:
Commercial real estate		$	9,044.50		$	11.3		$	22		$	33.3		$	9,077.80
Commercial and industrial			7,069.70			20.9			40.7			61.6			7,131.30
Equipment financing			2,729.70			64.1			4			68.1			2,797.80
Total			18,843.90			96.3			66.7			163			19,006.90
Retail:
Residential mortgage			4,781.00			24.9			24.8			49.7			4,830.70
Home equity			2,067.50			5.8			9.4			15.2			2,082.70
Other consumer			50.6			0.3			0.1			0.4			51
Total			6,899.10			31			34.3			65.3			6,964.40
Total originated loans		$	25,743.00		$	127.3		$	101		$	228.3		$	25,971.30
Included in the “Current” and “30-89 Days” categories above are early non-performing commercial real estate loans, commercial and industrial loans, and equipment financing loans totaling $21.4 million, $19.3 million and $30.9 million, respectively, and $22.7 million of retail loans in the process of foreclosure or bankruptcy. These loans are less than 90 days past due but have been placed on non-accrual status as a result of having been identified as presenting uncertainty with respect to the collectability of interest and principal.
					Past Due
As of December 31, 2014 (in millions)		Current			30-89			90 Days			Total			Total
					Days			or More						Originated
Commercial:
Commercial real estate		$	8,908.00		$	17.6		$	34.7		$	52.3		$	8,960.30
Commercial and industrial			6,814.90			32.4			43.8			76.2			6,891.10
Equipment financing			2,793.30			41			4.7			45.7			2,839.00
Total			18,516.20			91			83.2			174.2			18,690.40
Retail:
Residential mortgage			4,647.30			29.1			25.1			54.2			4,701.50
Home equity			2,079.30			5			8.6			13.6			2,092.90
Other consumer			55.8			0.4			0.1			0.5			56.3
Total			6,782.40			34.5			33.8			68.3			6,850.70
Total originated loans		$	25,298.60		$	125.5		$	117		$	242.5		$	25,541.10
Included in the “Current” and “30-89 Days” categories above are early non-performing commercial real estate loans, commercial and industrial loans, and equipment financing loans totaling $25.6 million, $29.5 million and $20.7 million, respectively, and $21.8 million of retail loans in the process of foreclosure or bankruptcy. These loans are less than 90 days past due but have been placed on non-accrual status as a result of having been identified as presenting uncertainty with respect to the collectability of interest and principal.
Commercial Banking 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 loans and portfolio concentrations, and portfolio-specific risk characteristics, the combination of which determines whether a loan is classified as “High”, “Moderate” or “Low” risk.
The portfolio-specific risk characteristics considered include: (i) collateral values/ loan-to-value (“LTV”) ratios (above and below 70%); (ii) borrower credit scores under the FICO scoring system (above and below a score of 680); and (iii) other relevant portfolio risk elements such as income verification at the time of underwriting (stated income vs. non-stated income) and the property’s intended use (owner occupied, non-owner occupied, second home, etc.). In classifying a loan as either “High”, “Moderate” or “Low” risk, the combination of each of the aforementioned risk characteristics is considered for that loan, resulting, effectively, in a “matrix approach” to its risk classification. These risk classifications are reviewed periodically to ensure that they continue to be appropriate in light of changes within the portfolio and/or economic indicators as well as other industry developments.
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 occupied properties, second homes, etc.). Loans not otherwise deemed to be “High” or “Low” risk are classified as “Moderate” risk.
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, which are included in the tabular disclosures of credit quality indicators that follow.
Acquired Loans 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 process has been completed.
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. 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 portfolio. A decrease in the expected cash flows in subsequent periods requires the establishment of an allowance for loan losses at that time. At March 31, 2015 and December 31, 2014, the allowance for loan losses on acquired loans was $9.8 million and $10.2 million, respectively.
The following is a summary, by class of loan, of credit quality indicators:
As of March 31, 2015 (in millions)		Commercial			Commercial			Equipment			Total
		Real Estate			and			Financing
					Industrial
Commercial:
Originated loans:
Pass		$	8,864.90		$	6,672.70		$	2,423.30		$	17,960.90
Special mention			86			142.1			101.8			329.9
Substandard			126.9			314.7			272.7			714.3
Doubtful			—			1.8			—			1.8
Total originated loans			9,077.80			7,131.30			2,797.80			19,006.90
Acquired loans:
Pass			288.1			178.2			6.7			473
Special mention			25.4			20.5			0.6			46.5
Substandard			72.7			59.9			16.2			148.8
Doubtful			6.4			15.6			—			22
Total acquired loans			392.6			274.2			23.5			690.3
Total		$	9,470.4		$	7,405.5		$	2,821.30		$	19,697.20
As of March 31, 2015 (in millions)		Residential			Home			Other			Total
		Mortgage			Equity			Consumer
Retail:
Originated loans:
Low risk		$	2,379.10		$	927.2		$	27		$	3,333.30
Moderate risk			1,943.50			612.4			7.1			2,563.00
High risk			508.1			543.1			16.9			1,068.10
Total originated loans			4,830.70			2,082.70			51			6,964.40
Acquired loans:
Low risk			107.2			—			—			107.2
Moderate risk			47.7			—			—			47.7
High risk			65			46.7			1.1			112.8
Total acquired loans			219.9			46.7			1.1			267.7
Total		$	5,050.6		$	2,129.4		$	52.1		$	7,232.1
As of December 31, 2014 (in millions)		Commercial			Commercial			Equipment			Total
		Real Estate			and			Financing
					Industrial
Commercial:
Originated loans:
Pass		$	8,730.90		$	6,477.40		$	2,481.20		$	17,689.50
Special mention			82.4			114.2			110.6			307.2
Substandard			135.3			297.3			247.2			679.8
Doubtful			11.7			2.2			—			13.9
Total originated loans			8,960.30			6,891.10			2,839.00			18,690.40
Acquired loans:
Pass			302.5			174.5			7.6			484.6
Special mention			20.9			52.8			0.7			74.4
Substandard			113.5			55			18.2			186.7
Doubtful			7.1			16.2			—			23.3
Total acquired loans			444			298.5			26.5			769
Total		$	9,404.3		$	7,189.6		$	2,865.50		$	19,459.40
As of December 31, 2014 (in millions)		Residential			Home			Other			Total
		Mortgage			Equity			Consumer
Retail:
Originated loans:
Low risk		$	2,280.60		$	931.5		$	29.5		$	3,241.60
Moderate risk			1,921.60			597.1			8.3			2,527.00
High risk			499.3			564.3			18.5			1,082.10
Total originated loans			4,701.50			2,092.90			56.3			6,850.70
Acquired loans:
Low risk			107			—			—			107
Moderate risk			50.5			—			—			50.5
High risk			73			50.2			1.2			124.4
Total acquired loans			230.5			50.2			1.2			281.9
Total		$	4,932.0		$	2,143.1		$	57.5		$	7,132.6
Acquired Loans
Acquired loans that have evidence of deterioration in credit quality since origination and for which it is probable, at acquisition, that all contractually required payments will not be collected are initially recorded at fair value without recording an 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 generally accounted for on a pool basis, with pools formed based on the loans’ common risk characteristics, such as loan collateral type and accrual status. Each pool is accounted for as a single asset with a single composite interest rate and an aggregate expectation of cash flows.
Under the accounting model for acquired loans, the excess of cash flows expected to be collected over the carrying amount of the loans, referred to as the “accretable yield”, is accreted into interest income over the life of the loans in each pool using the effective yield method. Accordingly, acquired loans are not subject to classification as non-accrual in the same manner as originated loans. Rather, acquired loans are considered to be accruing loans because their interest income relates to the accretable yield recognized at the pool level and not to contractual interest payments at the loan level. The difference between contractually required principal and interest payments and the cash flows expected to be collected, referred to as the “nonaccretable difference”, includes estimates of both the impact of prepayments and future credit losses expected to be incurred over the life of the loans in each pool. As such, charge-offs on acquired loans are first applied to the nonaccretable difference and then to any allowance for loan losses recognized subsequent to acquisition.
Subsequent to acquisition, actual cash collections are monitored relative to management’s expectations and revised cash flow forecasts are prepared, as warranted. These revised forecasts involve updates, as necessary, of the key assumptions and estimates used in the initial estimate of fair value. Generally speaking, expected cash flows are affected by:
	•		Changes in the expected principal and interest payments over the estimated life – Updates to changes in expected cash flows are driven by the credit outlook and actions taken with borrowers. Changes in expected future cash flows resulting from loan modifications are included in the assessment of expected cash flows;
	•		Changes in prepayment assumptions – Prepayments affect the estimated life of the loans which may change the amount of interest income, and possibly principal, expected to be collected; and
	•		Changes in interest rate indices for variable rate loans – Expected future cash flows are based, as applicable, on the variable rates in effect at the time of the assessment of expected cash flows.
A decrease in expected cash flows in subsequent periods may indicate that the loan pool is impaired, which would require the establishment of an allowance for loan losses by a charge to the provision for loan losses. An increase in expected cash flows in subsequent periods serves, first, to reduce any previously established allowance for loan losses by the increase in the present value of cash flows expected to be collected, and results in a recalculation of the amount of accretable yield for the loan pool. The adjustment of accretable yield due to an increase in expected cash flows is accounted for as a change in estimate. The additional cash flows expected to be collected are reclassified from the nonaccretable difference to the accretable yield, and the amount of periodic accretion is adjusted accordingly over the remaining life of the loans in the pool.
An acquired loan may be resolved either through receipt of payment (in full or in part) from the borrower, the sale of the loan to a third party or foreclosure of the collateral. In the event of a sale of the loan, a gain or loss on sale is recognized and reported within non-interest income based on the difference between the sales proceeds and the carrying amount of the loan. In other cases, individual loans are removed from the pool based on comparing the amount received from its resolution (fair value of the underlying collateral less costs to sell in the case of a foreclosure) with its outstanding balance. Any difference between these amounts is absorbed by the nonaccretable difference established for the entire pool. For loans resolved by payment in full, there is no adjustment of the nonaccretable difference since there is no difference between the amount received at resolution and the outstanding balance of the loan. In these cases, the remaining accretable yield balance is unaffected and any material change in remaining effective yield caused by the removal of the loan from the pool is addressed in connection with the subsequent cash flow re-assessment for the pool. Acquired loans subject to modification are not removed from the pool even if those loans would otherwise be deemed TDRs as the pool, and not the individual loan, represents the unit of account.
At the respective acquisition dates in 2011 and 2010, on an aggregate basis, the acquired loan portfolio had contractually required principal and interest payments receivable of $7.57 billion; expected cash flows of $7.02 billion; and a fair value (initial carrying amount) of $5.36 billion. The difference between the contractually required principal and interest payments receivable and the expected cash flows ($550.9 million) represented the initial nonaccretable difference. The difference between the expected cash flows and fair value ($1.66 billion) represented the initial accretable yield. Both the contractually required principal and interest payments receivable and the expected cash flows reflect anticipated prepayments, determined based on historical portfolio experience. At March 31, 2015, the outstanding principal balance and carrying amount of the acquired loan portfolio were $1.09 billion and $958.0 million, respectively ($1.18 billion and $1.05 billion, respectively, at December 31, 2014). At March 31, 2015, the aggregate remaining nonaccretable difference applicable to acquired loans totaled $89.1 million.
The following table summarizes activity in the accretable yield for the acquired loan portfolio:
		Three Months Ended
		March 31,
(in millions)		2015			2014
Balance at beginning of period		$	396.3		$	639.7
Accretion			(15.3	)		(23.3	)
Reclassification from nonaccretable difference for loans			0.3			5.8
with improved cash flows (1)
Other changes in expected cash flows (2)			(19.7	)		(97.8	)
Balance at end of period		$	361.6		$	524.4
-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.
Other Real Estate Owned and Repossessed Assets (included in Other Assets)
Other real estate owned (“REO”) was comprised of residential and commercial properties totaling $16.5 million and $10.2 million, respectively, at March 31, 2015, and $13.6 million and $11.0 million, respectively, at December 31, 2014. Repossessed assets totaled $4.3 million and $2.5 million at March 31, 2015 and December 31, 2014, respectively.

Stockholders_Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Stockholders' Equity	NOTE 4. STOCKHOLDERS’ EQUITY
	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 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”). Following shareholder approval of the People’s United Financial, Inc. 2014 Long-Term Incentive Plan in the second quarter of 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 basis): (i) net actuarial gains and losses, prior service credits and costs, and transition assets and obligations related to People’s United’s pension and other postretirement benefit plans; (ii) net unrealized gains and losses on securities available for sale; (iii) net unrealized gains and losses on securities transferred to held to maturity; and (iv) net unrealized gains and losses on derivatives accounted for as cash flow hedges. People’s United’s total comprehensive income for the three months ended March 31, 2015 and 2014 is reported in the Consolidated Statements of Comprehensive Income.
	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 basis:
	(in millions)		Pension			Net Unrealized			Net Unrealized			Net Unrealized			Total
			and Other			Gains (Losses)			Gains (Losses)			Gains (Losses)			Accumulated
			Postretirement			on Securities			on Securities			on Derivatives			Other
			Benefits			Available for Sale			Transferred to			Accounted for as			Comprehensive
									Held to Maturity			Cash Flow Hedges			Loss
	Balance at December 31, 2014		$	(142.9	)	$	(3.7	)	$	(21.5	)	$	(0.1	)	$	(168.2	)
	Other comprehensive income (loss) before reclassifications			—			26.2			—			(0.4	)		25.8
	Amounts reclassified from AOCL (1)			1.1			—			0.5			0.2			1.8
	Current period other comprehensive income (loss)			1.1			26.2			0.5			(0.2	)		27.6
	Balance at March 31, 2015		$	(141.8	)	$	22.5		$	(21.0	)	$	(0.3	)	$	(140.6	)
	(in millions)		Pension			Net Unrealized			Net Unrealized			Net Unrealized			Total
			and Other			Gains (Losses)			Gains (Losses)			Gains (Losses)			Accumulated
			Postretirement			on Securities			on Securities			on Derivatives			Other
			Benefits			Available for Sale			Transferred to			Accounted for as			Comprehensive
									Held to Maturity			Cash Flow Hedges			Loss
	Balance at December 31, 2013		$	(85.0	)	$	(46.5	)	$	(23.3	)	$	(0.3	)	$	(155.1	)
	Other comprehensive income (loss) before reclassifications			—			16.6			—			(0.1	)		16.5
	Amounts reclassified from AOCL (1)			0.6			(0.1	)		0.4			0.2			1.1
	Current period other comprehensive income (loss)			0.6			16.5			0.4			0.1			17.6
	Balance at March 31, 2014		$	-84.4		$	(30.0	)	$	(22.9	)	$	(0.2	)	$	(137.5	)
	-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						Affected Line Item
			Three Months Ended March 31,						in the Statement Where
	(in millions)		2015			2014			Net Income is Presented
	Details about components of AOCL:
	Amortization of pension and other postretirement benefits items:
	Net actuarial loss		$	(2.0	)	$	(1.3	)	-1
	Prior service credit			0.3			0.3		-1
				(1.7	)		(1.0	)	Income before income tax expense
				0.6			0.4		Income tax expense
				(1.1	)		(0.6	)	Net income
	Reclassification adjustment for net realized gains on securities available for sale			—			0.1		Income before income tax expense (2)
				—			—		Income tax expense
				—			0.1		Net income
	Amortization of unrealized losses on securities transferred to held to maturity			(0.8	)		(0.7	)	Income before income tax expense (3)
				0.3			0.3		Income tax expense
				(0.5	)		(0.4	)	Net income
	Amortization of unrealized gains and losses on cash flow hedges:
	Interest rate swaps			(0.3	)		(0.3	)	-5
	Interest rate locks (4)			—			—		-5
				(0.3	)		(0.3	)	Income before income tax expense
				0.1			0.1		Income tax expense
				(0.2	)		(0.2	)	Net income
	Total reclassifications for the period		$	(1.8	)	$	(1.1	)
	-1	Included in the computation of net periodic pension cost reflected in compensation and benefits expense (see Note 7 for additional details).
	-2	Included in other non-interest income.
	-3	Included in interest and dividend income - securities.
	-4	Amount reclassified from AOCL totaled less than $0.1 million at both dates.
	-5	Included in interest expense - notes and debentures.

Earnings_Per_Common_Share

Earnings Per Common Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Earnings Per Common Share	NOTE 5. EARNINGS PER COMMON SHARE
	The following is an analysis of People’s United’s basic and diluted earnings per share (“EPS”), reflecting the application of the two-class method, as described below:
		Three Months Ended
		March 31,
	(in millions, except per share data)	2015			2014
	Net income	$	59.2		$	53.1
	Dividends and undistributed earnings allocated to participating securities		(0.3	)		(0.2	)
	Income attributable to common shareholders	$	58.9		$	52.9
	Average common shares outstanding for basic EPS		299.1			297.7
	Effect of dilutive equity-based awards		—			—
	Average common and common-equivalent shares for diluted EPS		299.1			297.7
	Basic EPS	$	0.2		$	0.18
	Diluted EPS	$	0.2		$	0.18
	Unvested share-based payment awards, which include the right to receive non-forfeitable dividends or dividend equivalents, are considered to participate with common stock in undistributed earnings for purposes of computing EPS. Companies that have such participating securities, including People’s United, are required to calculate basic and diluted EPS using the two-class method. Restricted stock awards granted by People’s United are considered participating securities. Calculations of EPS under the two-class method (i) exclude from the numerator any dividends paid or owed on participating securities and any undistributed earnings considered to be attributable to participating securities and (ii) exclude from the denominator the dilutive impact of the participating securities.
	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 21.6 million shares and 18.0 million shares for the three months ended March 31, 2015 and 2014 have been excluded from the calculation of diluted EPS.

Goodwill_and_Other_Acquisition

Goodwill and Other Acquisition-Related Intangible Assets	3 Months Ended
	Mar. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Acquisition-Related Intangible Assets	NOTE 6. GOODWILL AND OTHER ACQUISITION-RELATED INTANGIBLE ASSETS
	People’s United’s goodwill totaled $1.95 billion at both March 31, 2015 and December 31, 2014. At both dates, goodwill was allocated to People’s United’s operating segments as follows: Commercial Banking ($1.22 billion); Retail Banking ($681.9 million); and Wealth Management ($49.8 million).
	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 generally 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.
	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 March 31, 2015 and December 31, 2014, tax deductible goodwill totaled $12.8 million and $13.0 million, respectively, and related, almost entirely, to the Butler Bank acquisition completed in 2010.
	People’s United’s other acquisition-related intangible assets totaled $142.1 million and $148.0 million at March 31, 2015 and December 31, 2014, respectively. At March 31, 2015, the carrying amounts of other acquisition-related intangible assets were as follows: trade name intangible ($85.8 million); core deposit intangible ($33.3 million); trust relationship intangible ($22.1 million); and insurance relationship intangible ($0.9 million).
	Amortization expense of other acquisition-related intangible assets totaled $5.9 million and $6.2 million for the three months ended March 31, 2015 and 2014, respectively. Scheduled amortization expense attributable to other acquisition-related intangible assets for the full-year of 2015 and each of the next five years is as follows: $23.8 million in 2015; $22.7 million in 2016; $21.6 million in 2017; $10.2 million in 2018; $9.4 million in 2019; and $9.0 million in 2020. There were no impairment losses relating to goodwill or other acquisition-related intangible assets recorded during the three months ended March 31, 2015 and 2014.

Employee_Benefit_Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	NOTE 7. EMPLOYEE BENEFIT PLANS
	People’s United Employee Pension and Other Postretirement Benefit Plans
	People’s United maintains a qualified noncontributory defined benefit pension plan (the “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 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 Qualified Plan to “freeze”, effective December 31, 2011, the accrual of pension benefits for 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.
	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. In the first quarter of 2015, the Company made a voluntary employer contribution of $40.0 million to the Qualified Plan as a consequence of lower discount rates and the adoption of updated mortality tables.
	People’s United also maintains (i) unfunded, nonqualified supplemental plans to provide retirement benefits to certain senior officers and (ii) an unfunded plan that provides retirees with optional medical, dental and life insurance benefits (“the other postretirement benefits 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 the net periodic benefit (income) expense and other amounts recognized in other comprehensive income for the plans described above are as follows:
		Pension Benefits						Other
								Postretirement Benefits
	Three Months Ended March 31 (in millions)	2015			2014			2015			2014
	Net periodic benefit (income) expense:
	Service cost	$	—		$	—		$	0.1		$	—
	Interest cost		4.8			4.8			0.1			0.2
	Expected return on plan assets		(7.2	)		(7.1	)		—			—
	Recognized net actuarial loss		1.5			1			0.1			—
	Recognized prior service credit		—			—			(0.1	)		(0.1	)
	Settlements		0.1			0.1			—			—
	Net periodic benefit (income) expense		(0.8	)		(1.2	)		0.2			0.1
	Other changes in plan assets and benefit obligations recognized
	in other comprehensive income:
	Net actuarial loss		(1.5	)		(1.0	)		(0.1	)		—
	Prior service credit		—			—			0.1			0.1
	Total pre-tax changes recognized in		(1.5	)		(1.0	)		—			0.1
	other comprehensive income
	Total recognized in net periodic benefit (income)	$	(2.3	)	$	(2.2	)	$	0.2		$	0.2
	expense and other comprehensive income
	Chittenden Pension Plan
	In addition to the benefit plans described above, People’s United continues to maintain a qualified defined benefit pension plan that covers former Chittenden Corporation employees who meet certain eligibility requirements (the “Chittenden Plan”). Effective December 31, 2005, accrued benefits were frozen based on participants’ then-current service and pay levels. 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 Qualified Plan. Net periodic benefit income for the Chittenden Plan totaled $0.1 million for both the three months ended March 31, 2015 and 2014. In the first quarter of 2015, the Company made a voluntary employer contribution of $10.0 million to the Chittenden Plan as a consequence of lower discount rates and the adoption of updated mortality tables.
	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 totaled $1.3 million for the three months ended March 31, 2015. At March 31, 2015, the loan balance totaled $192.1 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 2,874,734 shares of People’s United common stock have been allocated or committed to be released to participants’ accounts. At March 31, 2015, 7,578,841 shares of People’s United common stock, with a fair value of $115.2 million at that date, have not been allocated or committed to be released.
	Compensation expense related to the ESOP is recognized at an amount equal to the number of common shares committed to be released by the ESOP for allocation to participants’ accounts multiplied by the average fair value of People’s United’s common stock during the reporting period. The difference between the fair value of the shares of People’s United’s common stock committed to be released and the cost of those common shares is recorded as a credit to additional paid-in capital (if fair value exceeds cost) or, to the extent that no such credits remain in additional paid-in capital, as a charge to retained earnings (if fair value is less than cost). Expense recognized for the ESOP totaled $1.3 million for both the three months ended March 31, 2015 and 2014.

Legal_Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	NOTE 8. 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 the pending actions described below, as well as other legal proceedings. Based on the information currently available, advice of counsel, available insurance coverage and the recorded liability for probable legal settlements and costs, People’s United believes that the eventual outcome of these matters will not (individually or in the aggregate) have a material adverse effect on its financial condition, results of operations or liquidity.
	Litigation Relating to the Smithtown Transaction
	On February 25, 2010 and March 29, 2010, Smithtown and several of its officers and directors were named in lawsuits commenced in United States District Court, Eastern District of New York (Waterford Township Police & Fire Retirement v. Smithtown Bancorp, Inc., et al. andYourgal v. Smithtown Bancorp, Inc. et al., respectively) on behalf of a putative class of all persons and entities who purchased Smithtown’s common stock between March 13, 2008 and February 1, 2010, alleging claims under Section 10(b) and Section 20(a) of the Securities Exchange Act of 1934. The plaintiffs allege, among other things, that Smithtown’s loan loss reserve, fair value of its assets, recognition of impaired assets and its internal and disclosure controls were materially false, misleading or incomplete. As a result of the merger of Smithtown with and into People’s United on November 30, 2010, People’s United has become the successor party to Smithtown in this matter.
	Following extensive preliminary filings with the Court by both parties, an agreement in principle to settle this matter was reached on October 23, 2014, subject to completion of appropriate documentation and Court approval. On January 12, 2015, the plaintiffs filed a Motion for Preliminary Approval of the settlement with the Court. On April 17, 2015, the U.S. Magistrate Judge recommended that the Court overseeing the case preliminarily approve of the settlement. The scheduling of a final hearing on the settlement is subject to further approval by the Court. The amount of the agreed-upon settlement has been adequately reserved.
	Other
	The Bank has been named as a defendant in a lawsuit (Marta Farb, on behalf of herself and all others similarly situated v. People’s United Bank) arising from its assessment and collection of overdraft fees on its checking account customers. The Complaint was filed in the Superior Court of Connecticut, Judicial District of Waterbury, on April 22, 2011 and alleges that the Bank engaged in certain unfair practices in the posting of electronic debit card transactions from highest to lowest dollar amount. The Complaint also alleges that such practices were inadequately disclosed to customers and were unfairly used by the Bank for the purpose of generating revenue by maximizing the number of overdrafts a customer is assessed. The Complaint seeks certification of a class of checking account holders residing in Connecticut and who have incurred at least one overdraft fee, injunctive relief, compensatory, punitive and treble damages, disgorgement and restitution of overdraft fees paid, and attorneys’ fees.
	On June 16, 2011, the Bank filed a Motion to Dismiss the Complaint, and on December 7, 2011, that motion was denied by the Court. On April 11, 2012, the plaintiff filed an Amended Complaint, and on May 15, 2012, the Bank filed a Motion to Strike the Amended Complaint. On April 10, 2013, the Bank renewed its Motion to Dismiss the Complaint. On June 6, 2013, the Court denied the Bank’s Motion to Strike and its renewed Motion to Dismiss. On September 23, 2013, the Bank filed its Revised Answer, Special Defenses and Counterclaim to Plaintiff’s Amended Class Action Complaint. A Court hearing on plaintiff’s Motion to Strike certain of the Bank’s Defenses and a Counterclaim was held on January 30, 2014. The Court postponed consideration of that Motion and, on April 28, 2014, held a hearing to consider whether it has jurisdiction to hear the case. On July 28, 2014, the Court dismissed the case in its entirety for lack of subject matter jurisdiction because all of the claims are preempted by federal law. On August 15, 2014, the plaintiff filed a Notice of Appeal. On April 30, 2015, the parties executed a settlement agreement that resolves all claims, counterclaims and appeals in the case, thus concluding this matter. The amount of the agreed-upon settlement has been adequately reserved.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	NOTE 9. SEGMENT INFORMATION
	See “Segment Results” included in Item 2 for segment information for the three months ended March 31, 2015 and 2014.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	NOTE 10. 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 basis, as well as for those financial assets and financial liabilities not measured at fair value but for which fair value is disclosed.
	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, and GSE residential mortgage-backed securities and CMOs, all of which are included in Level 2.
	Substantially all of the Company’s available-for-sale securities represent GSE residential mortgage-backed securities and CMOs. The fair values of these securities are based on prices obtained from the independent pricing service. The pricing service uses various techniques to determine pricing for the Company’s mortgage-backed securities, including option pricing and discounted cash flow analysis. The inputs include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, benchmark securities, bids, offers, reference data, monthly payment information and collateral performance. At both March 31, 2015 and December 31, 2014, the entire available-for-sale residential mortgage-backed securities portfolio was comprised of 10- and 15-year GSE securities. An active market exists for securities that are similar to the Company’s GSE residential mortgage-backed securities and CMOs, making observable inputs readily available.
	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 15-year securities. As a further point of validation, the Company generates its own month-end fair value estimate for all mortgage-backed securities, agency-issued CMOs (also backed by 15-year mortgage-backed securities), and state and municipal securities. While the Company has not adjusted the prices obtained from the independent pricing service, any notable differences between those prices and the Company’s estimates are subject to further analysis. This additional analysis may include a review of prices provided by other independent parties, a yield analysis, a review of average life changes using Bloomberg analytics and a review of historical pricing for the particular security. Based on management’s review of the prices provided by the pricing service, the fair values incorporate observable market inputs used by market participants at the measurement date and, as such, are classified as Level 2 securities.
	Other Assets
	As discussed in Note 7, certain unfunded, nonqualified supplemental benefit 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, 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 March 31, 2015 (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			301.1		—		—		301.1
	GSE residential mortgage-backed securities and CMOs			—		4,055.50		—		4,055.50
	Equity securities			—		0.2		—		0.2
	Other assets:
	Exchange-traded funds			30.7		—		—		30.7
	Fixed income securities			—		5.8		—		5.8
	Mutual funds			1.4		—		—		1.4
	Interest rate swaps			—		176.1		—		176.1
	Foreign exchange contracts			—		1		—		1
	Forward commitments to sell residential mortgage loans			—		0.9		—		0.9
	Total		$	341.5	$	4,239.50	$	—	$	4,581.00
	Financial liabilities:
	Interest rate swaps		$	—	$	128.5	$	—	$	128.5
	Foreign exchange contracts			—		0.5		—		0.5
	Interest rate-lock commitments on residential mortgage loans			—		1.3		—		1.3
	Total		$	—	$	130.3	$	—	$	130.3
			Fair Value Measurements Using
	As of December 31, 2014 (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			56.8		—		—		56.8
	GSE residential mortgage-backed securities and CMOs			—		3,936.70		—		3,936.70
	Equity securities			—		0.2		—		0.2
	Other assets:
	Exchange-traded funds			30.3		—		—		30.3
	Fixed income securities			—		6		—		6
	Mutual funds			0.8		—		—		0.8
	Interest rate swaps			—		131.1		—		131.1
	Foreign exchange contracts			—		0.8		—		0.8
	Forward commitments to sell residential mortgage loans			—		0.5		—		0.5
	Total		$	96.2	$	4,075.30	$	—	$	4,171.50
	Financial liabilities:
	Interest rate swaps		$	—	$	95.8	$	—	$	95.8
	Foreign exchange contracts			—		0.5		—		0.5
	Interest rate-lock commitments on residential mortgage loans			—		0.7		—		0.7
	Total		$	—	$	97	$	—	$	97
As of March 31, 2015 and December 31, 2014, the fair value of risk participation agreements totaled less than $0.1 million (see Note 11).
There were no transfers into or out of the Level 1 or Level 2 categories during the three months ended March 31, 2015 and 2014.
Non-Recurring Fair Value Measurements
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 basis. When available, People’s United uses observable secondary market data, including pricing on recent closed market transactions for loans with similar characteristics. Accordingly, such loans are classified as Level 2 measurements. When observable data is unavailable, valuation methodologies using current market interest rate data adjusted for inherent credit risk are used, and such loans are included in Level 3.
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 basis. People’s United has estimated the fair values of these assets using Level 3 inputs, such as discounted cash flows based on inputs that are largely unobservable and, instead, reflect management’s own estimates of the assumptions a market participant would use in pricing such loans and/or the fair value of collateral based on independent third-party appraisals for collateral-dependent loans. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%.
REO and Repossessed Assets
REO and repossessed assets are recorded at the lower of cost or fair value, less estimated selling costs, and are therefore measured at fair value on a non-recurring basis. People’s United has estimated the fair values of these assets using Level 3 inputs, such as independent third-party appraisals and price opinions. Such appraisals are based on the market and/or income approach to value and are subject to a discount (to reflect estimated cost to sell) that generally approximates 10%. Assets that are acquired through loan default are recorded as held for sale initially at the lower of the recorded investment in the loan or fair value (less estimated selling costs) upon the date of foreclosure/repossession. Subsequent to foreclosure/repossession, valuations are updated periodically and the carrying amounts of these assets may be reduced further.
The following tables summarize People’s United’s assets that are measured at fair value on a non-recurring basis:
		Fair Value Measurements Using
As of March 31, 2015 (in millions)		Level 1		Level 2		Level 3		Total
Loans held for sale (1)		$	—	$	49.7	$	—	$	49.7
Impaired loans (2)			—		—		52.9		52.9
REO and repossessed assets (3)			—		—		31		31
Total		$	—	$	49.7	$	83.9	$	133.6
		Fair Value Measurements Using
As of December 31, 2014 (in millions)		Level 1		Level 2		Level 3		Total
Loans held for sale (1)		$	—	$	34.2	$	—	$	34.2
Impaired loans (2)			—		—		66.5		66.5
REO and repossessed assets (3)			—		—		27.1		27.1
Total		$	—	$	34.2	$	93.6	$	127.8
-1	Consists of residential mortgage loans; no fair value adjustments were recorded for the three months ended March 31, 2015 and 2014.
-2	Represents the recorded investment in originated impaired loans with a related allowance for loan losses measured in accordance with applicable accounting guidance. The total consists of $34.4 million of Commercial loans and $18.5 million of Retail loans at March 31, 2015. The provision for loan losses on impaired loans totaled $2.2 million and $4.0 million for the three months ended March 31, 2015 and 2014, respectively.
-3	Represents: (i) $16.5 million of residential REO; (ii) $10.2 million of commercial REO; and (iii) $4.3 million of repossessed assets at March 31, 2015. Charge-offs to the allowance for loan losses related to loans that were transferred to REO or repossessed assets totaled $0.6 million and $0.7 million for the three months ended March 31, 2015 and 2014, respectively. Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest expense totaled $0.4 million for both periods.
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 basis:
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 Stock
Both FHLB and FRB stock are non-marketable equity securities classified as Level 2 and reported at cost, which equals par value (the amount at which shares have been redeemed in the past in the case of FHLB stock). No significant observable market data is available for either of these securities.
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). Fair values are estimated for each component using a valuation method selected by management.
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 loans were based on recent collateral appraisals or management’s analysis of estimated cash flows discounted at rates commensurate with the credit risk involved. The estimated fair values of residential mortgage loans are classified as Level 2 as a result of the observable market inputs (i.e. market interest rates, prepayment assumptions, etc.) available for this loan type. The fair values of all other loan types are classified as Level 3 as the inputs contained within the respective discounted cash flow models are largely unobservable and, instead, reflect management’s own estimates of the assumptions a market participant would use in pricing such loans. The fair value of home equity lines of credit was based on the outstanding loan balances, and therefore does not reflect the value associated with earnings from future loans to existing customers.
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 funding source that has a substantial intangible value separate from the deposit balances.
Borrowings and Notes and Debentures
The fair values of federal funds purchased and repurchase agreements are equal to the 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 basis:
				Estimated Fair Value
		Carrying		Measurements Using
As of March 31, 2015 (in millions)		Amount		Level 1		Level 2		Level 3		Total
Financial assets:
Cash and due from banks		$	306.8	$	306.8	$	—	$	—	$	306.8
Short-term investments			250		—		250		—		250
Securities held to maturity			897.4		—		942.4		1.5		943.9
FHLB and FRB stock			314.2		—		314.2		—		314.2
Total loans, net (1)			26,675.50		—		4,951.00		21,837.90		26,788.90
Financial liabilities:
Time deposits			5,301.60		—		5,336.60		—		5,336.60
Other deposits			21,848.30		—		21,848.30		—		21,848.30
FHLB advances			2,165.90		—		2,173.40		—		2,173.40
Federal funds purchased			496		—		496		—		496
Customer repurchase agreements			480		—		480		—		480
Repurchase agreements (2)			1		—		1		—		1
Notes and debentures			1,042.30		—		1,043.80		—		1,043.80
-1	Excludes impaired loans totaling $52.9 million measured at fair value on a non-recurring basis.
-2	Included in other borrowings in the Consolidated Statements of Condition.
				Estimated Fair Value
		Carrying		Measurements Using
As of December 31, 2014 (in millions)		Amount		Level 1		Level 2		Level 3		Total
Financial assets:
Cash and due from banks		$	345.1	$	345.1	$	—	$	—	$	345.1
Short-term investments			668.6		—		668.6		—		668.6
Securities purchased under agreements to resell			100		—		100		—		100
Securities held to maturity			834.3		—		880.1		1.5		881.6
FHLB stock			175.7		—		175.7		—		175.7
Total loans, net (1)			26,327.20		—		4,798.50		21,508.80		26,307.30
Financial liabilities:
Time deposits			5,230.70		—		5,262.60		—		5,262.60
Other deposits			20,907.50		—		20,907.50		—		20,907.50
FHLB advances			2,291.70		—		2,298.50		—		2,298.50
Federal funds purchased			913		—		913		—		913
Customer repurchase agreements			486		—		486		—		486
Repurchase agreements (2)			1		—		1		—		1
Notes and debentures			1,033.50		—		1,040.80		—		1,040.80
-1	Excludes impaired loans totaling $66.5 million measured at fair value on a non-recurring basis.
-2	Included in other borrowings in the Consolidated Statements of Condition.

Derivative_Financial_Instrumen

Derivative Financial Instruments and Hedging Activities	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments and Hedging Activities	NOTE 11. 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 accumulated other comprehensive income (loss) 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 IRR associated with customer interest rate swaps is 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 12), 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). The aggregate fair value of derivative instruments with such credit-related contingent features that were in a net liability position at March 31, 2015 was $10.6 million, for which People’s United had posted collateral of $10.1 million in the normal course of business. If the Company’s senior unsecured debt rating had fallen below investment grade as of that date, $0.5 million in additional collateral would have been required.
	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
	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.
	People’s United has entered into a pay fixed/receive floating interest rate swap to hedge the LIBOR-based floating rate payments on the Company’s $125 million subordinated notes (such payments began in February 2012). These notes had a fixed interest rate of 5.80% until February 2012, at which time the interest rate converted to the three-month LIBOR plus 68.5 basis points. People’s United has agreed with the swap counterparty to exchange, at specified intervals, the difference between fixed-rate (1.99%) and floating-rate interest amounts calculated based on a notional amount of $125 million. The floating-rate interest amounts received under the swap are calculated using the same floating-rate paid on these notes. The swap effectively converts the variable-rate subordinated notes to a fixed-rate liability and consequently reduces People’s United’s exposure to increases in interest rates. This swap is accounted for as a cash flow hedge.
	The Bank has entered into a pay floating/receive fixed interest rate swap to hedge the change in fair value of the Bank’s $400 million subordinated notes due to changes in interest rates. 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.
	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”) to hedge the risk that the 10-year U.S. Treasury yield component of the underlying coupon of the fixed rate senior notes would rise prior to establishing the fixed interest rate on the senior notes. Upon pricing the senior notes, the T-Locks were terminated and the unrealized gain of $0.9 million was included (on a net-of-tax basis) as a component of AOCL. The gain is being recognized as a reduction of interest expense over the ten-year period during which the hedged item ($500 million senior note issuance) affects 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 share of the derivative contracts, consistent with its share of the related loans.
	Customer Derivatives
	People’s United enters into interest rate swaps with certain of its commercial customers. In order to minimize its risk, these customer derivatives (pay floating/receive fixed swaps) have been offset with essentially matching interest rate swaps with People’s United’s institutional counterparties (pay fixed/receive floating swaps). Hedge accounting has not been applied for these derivatives. Accordingly, changes in the fair value of all such swaps are recognized in current earnings.
	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 loans are accounted for as derivatives, with changes in fair value recognized in current earnings.
	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	March 31,			Dec. 31,			March 31,			Dec. 31,			March 31,		Dec. 31,
			Hedge	2015			2014			2015			2014			2015		2014
	Derivatives Not Designated as Hedging Instruments:
	Interest rate swaps:
	Commercial customers		N/A	$	3,871.50		$	3,380.20		$	149.1		$	104.2		$	1.7	$	8.3
	Institutional counterparties		N/A		3,871.50			3,380.20			3.3			11.8			125.5		86.5
	Risk participation agreements (2)		N/A		199			150.1			—			—			—		—
	Foreign exchange contracts		N/A		51.6			49.6			1			0.8			0.5		0.5
	Forward commitments to sell residential mortgage loans		N/A		75.8			35.3			0.9			0.5			—		—
	Interest rate-lock commitments on residential mortgage loans		N/A		120.9			57.5			—			—			1.3		0.7
	Total										154.3			117.3			129		96
	Derivatives Designated as Hedging Instruments:
	Interest rate swaps:
	Subordinated notes		Cash flow		125			125			—			—			1.3		1
	Subordinated notes		Fair value		375			375			23.7			15.1			—		—
	Total										23.7			15.1			1.3		1
	Total derivatives									$	178		$	132.4		$	130.3	$	97
	-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 income and AOCL:
				Amount of Pre-Tax Gain (Loss)						Amount of Pre-Tax Gain (Loss)
			Type of	Recognized in Earnings (1)						Recognized in AOCL
	Three Months Ended March 31 (in millions)		Hedge	2015			2014			2015			2014
	Derivatives Not Designated as Hedging Instruments:
	Interest rate swaps:
	Commercial customers		N/A	$	67.7		$	41.1		$	—		$	—
	Institutional counterparties		N/A		(62.5	)		(39.7	)		—			—
	Foreign exchange contracts		N/A		0.2			—			—			—
	Risk participation agreements		N/A		—			—			—			—
	Forward commitments to sell residential mortgage loans		N/A		0.4			0.1			—			—
	Interest rate-lock commitments on residential mortgage loans		N/A		(0.5	)		(0.2	)		—			—
	Total				5.3			1.3			—			—
	Derivatives Designated as Hedging Instruments:
	Interest rate swaps		Cash flow		(0.3	)		(0.3	)		(0.6	)		(0.1	)
	Interest rate locks (2)		Cash flow		—			—			—			—
Interest rate swaps		Fair value		2.5			—			—			—
Total				2.2			(0.3	)		(0.6	)		(0.1	)
Total derivatives			$	7.5		$	1		$	(0.6	)	$	(0.1	)
-1	Amounts recognized in earnings are recorded in interest income, interest expense or other non-interest income for derivatives designated as hedging instruments and in other non-interest income for derivatives not designated as hedging instruments.
-2	Income relating to T-Locks terminated in 2012 totaled less than $0.1 million at both dates.

Balance_Sheet_Offsetting

Balance Sheet Offsetting	3 Months Ended
	Mar. 31, 2015
Text Block [Abstract]
Balance Sheet Offsetting	NOTE 12. 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” provisions that provide for a single net settlement of all interest rate swap positions, as well as collateral, in the event of default on, or the termination of, any one contract. Nonetheless, the Company does not offset asset and liabilities under such arrangements in the Consolidated Statements of Condition.
	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 11. 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
	As of March 31, 2015 (in millions)		Amount		Amount		Amount		Financial			Collateral			Net
			Recognized		Offset		Presented		Instruments						Amount
	Financial assets:
	Interest rate swaps:
	Counterparty A		$	1	$	—	$	1	$	(1.0	)	$	—		$	—
	Counterparty B			0.3		—		0.3		(0.3	)		—			—
	Counterparty C			0.3		—		0.3		(0.3	)		—			—
	Counterparty D			0.7		—		0.7		(0.7	)		—			—
	Counterparty E			24.2		—		24.2		(24.2	)		—			—
	Other counterparties			0.5		—		0.5		(0.5	)		—			—
	Foreign exchange contracts			1		—		1		—			—			1
	Total		$	28	$	—	$	28	$	(27.0	)	$	—		$	1
	Financial liabilities:
	Interest rate swaps:
	Counterparty A		$	11.8	$	—	$	11.8	$	(1.0	)	$	(10.8	)	$	—
	Counterparty B			13.2		—		13.2		(0.3	)		(12.9	)		—
	Counterparty C			6.3		—		6.3		(0.3	)		(6.0	)		—
	Counterparty D			10		—		10		(0.7	)		(8.8	)		0.5
	Counterparty E			79.9		—		79.9		(24.2	)		(55.7	)		—
	Other counterparties			5.6		—		5.6		(0.5	)		(5.1	)		—
	Repurchase agreements (1)			1		—		1		—			(1.0	)		—
	Foreign exchange contracts			0.5		—		0.5		—			—			0.5
	Total		$	128.3	$	—	$	128.3	$	(27.0	)	$	(100.3	)	$	1
	-1	Included in other borrowings in the Consolidated Statements of Condition.
			Gross		Gross		Net		Gross Amounts Not Offset
	As of December 31, 2014 (in millions)		Amount		Amount		Amount		Financial			Collateral			Net
			Recognized		Offset		Presented		Instruments						Amount
	Financial assets:
	Interest rate swaps:
	Counterparty A		$	2.7	$	—	$	2.7	$	(2.7	)	$	—		$	—
	Counterparty B			1.5		—		1.5		(1.5	)		—			—
	Counterparty C			2.5		—		2.5		(2.5	)		—			—
	Counterparty D			3.2		—		3.2		(0.4	)		(2.8	)		—
	Counterparty E			15.7		—		15.7		(15.7	)		—			—
	Other counterparties			1.3		—		1.3		(1.3	)		—			—
	Securities purchased under agreements to resell			100		—		100		—			(100.0	)		—
	Foreign exchange contracts			0.8		—		0.8		—			—			0.8
	Total		$	127.7	$	—	$	127.7	$	(24.1	)	$	(102.8	)	$	0.8
	Financial liabilities:
	Interest rate swaps:
	Counterparty A		$	11.8	$	—	$	11.8	$	(2.7	)	$	(9.1	)	$	—
	Counterparty B			11.8		—		11.8		(1.5	)		(10.3	)		—
	Counterparty C			4.5		—		4.5		(2.5	)		(1.9	)		0.1
	Counterparty D			0.4		—		0.4		(0.4	)		—			—
	Counterparty E			47.8		—		47.8		(15.7	)		(32.1	)		—
	Other counterparties			11.2		—		11.2		(1.3	)		(8.9	)		1
	Repurchase agreements (1)			1		—		1		—			(1.0	)		—
	Foreign exchange contracts			0.5		—		0.5		—			—			0.5
	Total		$	89	$	—	$	89	$	(24.1	)	$	(63.3	)	$	1.6
	-1	Included in other borrowings in the Consolidated Statements of Condition.

New_Accounting_Standards

New Accounting Standards	3 Months Ended
	Mar. 31, 2015
Accounting Changes and Error Corrections [Abstract]
New Accounting Standards	NOTE 13. NEW ACCOUNTING STANDARDS
	Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans Upon Foreclosure
	In January 2014, the Financial Accounting Standards Board (the “FASB”) amended its standards with respect to the accounting for consumer mortgage loans collateralized by residential real estate to clarify that such loans should, upon foreclosure, be reclassified by a creditor as REO when either (i) the creditor obtains legal title to the real estate collateral or (ii) a deed in lieu of foreclosure, conveying all interest in the real estate to the creditor, is completed. In addition, the amendment requires a creditor to provide additional disclosures with respect to (i) the amount of residential real estate meeting the conditions set forth above and (ii) the recorded investment in consumer mortgage loans secured by residential real estate properties that are in the process of foreclosure. This amendment, which is being applied prospectively, became effective for People’s United on January 1, 2015 and did not have a significant impact on the Company’s Consolidated Financial Statements (see Note 3).
	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 proposed, 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 years, beginning on or after December 15, 2016 (January 1, 2017 for People’s United) and early adoption was not permitted. In April 2015, the FASB proposed a one-year deferral of the effective date (to January 1, 2018 for People’s United) with early adoption, as of the original effective date, permitted. The Company is currently evaluating the impact of the amended guidance on the Company’s Consolidated Financial Statements.
	Repurchase Agreements
	In June 2014, the FASB amended its standards with respect to repurchase agreements to (i) require that repurchase-to-maturity transactions be accounted for as secured borrowings, thereby eliminating the possibility of such transactions qualifying for sale accounting treatment, and (ii) eliminate existing guidance for repurchase financings. The amendment also requires enhanced disclosures for certain transactions accounted for as secured borrowings and transfers accounted for as sales when the transferor also retains substantially all of the exposure to the economic return on the transferred financial assets throughout the term of the transaction. In adopting this new guidance, all entities must report changes in accounting for transactions outstanding on the effective date as a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. This amendment became effective for People’s United on January 1, 2015 and did not have a significant impact on the Company’s Consolidated Financial Statements as none of the Company’s repurchase agreements represent repurchase-to-maturity transactions or repurchase financings and all repurchase agreements have been accounted for as secured borrowings.
	Stock Compensation
	In June 2014, the FASB amended its standards with respect to stock compensation to require that a performance target that affects vesting, and that could be achieved after the requisite service period, be treated as a performance condition. As such, the performance target should not be reflected in estimating the grant date fair value of the award. The amendment further clarifies that compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to those periods for which the requisite service has already been rendered. This new guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015 (January 1, 2016 for People’s United) and can be applied either prospectively or retrospectively to all awards outstanding as of the beginning of the earliest annual period presented as an adjustment to opening retained earnings. The adoption of this amendment, for which early adoption is permitted, is not expected to have a significant impact on the Company’s Consolidated Financial Statements.
	Classification of Certain Government-Guaranteed Residential Mortgage Loans upon Foreclosure
	In August 2014, the FASB amended its standards with respect to the classification of certain government-guaranteed residential mortgage loans to clarify that upon foreclosure of mortgage loans within the scope of the standard, a creditor will be required to reclassify the previously existing mortgage loan to a separate receivable from the guarantor, measured at the amount of the guarantee that it expects to collect. This amendment, which is being applied prospectively, became effective for People’s United on January 1, 2015 and did not have a significant impact on the Company’s Consolidated Financial Statements.
	Consolidation
	In February 2015, the FASB amended its standards with respect to the analysis that a reporting entity must perform in determining whether certain types of legal entities should be consolidated. The amendment modifies the evaluation of whether limited partnerships or similar legal entities are variable interest entities (“VIEs”) or voting interest entities, eliminates the presumption that a general partner should consolidate a limited partnership and affects the consolidation analysis of reporting entities that are involved with VIEs, particularly those that have fee arrangements and related party relationships. This new guidance, which can be applied retrospectively or through the use of the cumulative effect transition method, is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015 (January 1, 2016 for People’s United) with early adoption permitted. The Company is currently evaluating the impact of the amended guidance on the Company’s Consolidated Financial Statements.
	Presentation of Debt Issuance Costs
	In April 2015, the FASB amended its standards with respect to the presentation of debt issuance costs by changing the required presentation of such costs from an asset on the balance sheet to a deduction from the related debt liability. For public business entities this new guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015 (January 1, 2016 for People’s United) and is to be applied retrospectively. The adoption of this amendment is not expected to have a significant impact on the Company’s Consolidated Financial Statements.

Securities_and_ShortTerm_Inves1

Securities and Short-Term Investments (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015 (in millions)		Amortized		Gross			Gross			Fair
			Cost		Unrealized			Unrealized			Value
					Gains			Losses
	Securities available for sale:
	Debt securities:
	U.S. Treasury and agency		$	299.7	$	1.4		$	—		$	301.1
	GSE (1) residential mortgage-backed securities			4,022.50		52.7			(19.7	)		4,055.50
	and CMOs (2)
	Total debt securities			4,322.20		54.1			(19.7	)		4,356.60
	Equity securities			0.2		—			—			0.2
	Total securities available for sale		$	4,322.40	$	54.1		$	(19.7	)	$	4,356.80
	Securities held to maturity:
	Debt securities:
	State and municipal		$	895.9	$	47.7		$	(1.2	)	$	942.4
	Other			1.5		—			—			1.5
	Total securities held to maturity		$	897.4	$	47.7		$	(1.2	)	$	943.9
		-1	Government sponsored enterprise
		-2	Collateralized mortgage obligations
	As of December 31, 2014 (in millions)		Amortized		Gross			Gross			Fair
			Cost		Unrealized			Unrealized			Value
					Gains			Losses
	Securities available for sale:
	Debt securities:
	U.S. Treasury and agency		$	56.5	$	0.3		$	—		$	56.8
	GSE residential mortgage-backed securities and CMOs			3,943.40		39.7			(46.4	)		3,936.70
	Total debt securities			3,999.90		40			(46.4	)		3,993.50
	Equity securities			0.2		—			—			0.2
	Total securities available for sale		$	4,000.10	$	40		$	(46.4	)	$	3,993.70
	Securities held to maturity:
	Debt securities:
	State and municipal		$	832.8	$	47.4		$	(0.1	)	$	880.1
	Other			1.5		—			—			1.5
	Total securities held to maturity		$	834.3	$	47.4		$	(0.1	)	$	881.6
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 March 31, 2015, based on remaining period to contractual maturity. Information for GSE residential 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
			Cost		Value			Cost			Value
	U.S. Treasury and agency:
	Within 1 year		$	10.9	$	10.9		$	—		$	—
	After 1 but within 5 years			288.8		290.2			—			—
	Total			299.7		301.1			—			—
	GSE residential mortgage-backed securities and CMOs:
	After 1 but within 5 years			18.8		18.9			—			—
	After 5 but within 10 years			792.3		805.7			—			—
	After 10 years			3,211.40		3,230.90			—			—
	Total			4,022.50		4,055.50			—			—
	State and municipal:
	Within 1 year			—		—			3.2			3.2
	After 1 but within 5 years			—		—			20.7			21
	After 5 but within 10 years			—		—			287.3			305.2
	After 10 years			—		—			584.7			613
	Total			—		—			895.9			942.4
	Other:
	After 1 but within 5 years			—		—			1.5			1.5
	Total			—		—			1.5			1.5
	Total:
	Within 1 year			10.9		10.9			3.2			3.2
	After 1 but within 5 years			307.6		309.1			22.2			22.5
	After 5 but within 10 years			792.3		805.7			287.3			305.2
	After 10 years			3,211.40		3,230.90			584.7			613
	Total		$	4,322.20	$	4,356.60		$	897.4		$	943.9
Continuous Unrealized Loss Position on Available-for-Sale and Held-to-Maturities Securities	The following tables summarize debt securities with unrealized losses, segregated by the length of time the securities have been in a continuous unrealized loss position at the respective dates.
			Continuous Unrealized Loss Position
			Less Than 12 Months					12 Months Or Longer						Total
	As of March 31, 2015 (in millions)		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
			Value		Losses			Value			Losses			Value		Losses
	Securities available for sale:
	GSE residential mortgage-backed securities and CMOs		$	353.2	$	(1.0	)	$	1,094.50		$	(18.7	)	$	1,447.70	$	(19.7	)
	Securities held to maturity:
	State and municipal			109.1		(1.2	)		—			—			109.1		(1.2	)
	Total		$	462.3	$	(2.2	)	$	1,094.50		$	(18.7	)	$	1,556.80	$	(20.9	)
			Continuous Unrealized Loss Position
			Less Than 12 Months					12 Months Or Longer						Total
	As of December 31, 2014 (in millions)		Fair		Unrealized			Fair			Unrealized			Fair		Unrealized
			Value		Losses			Value			Losses			Value		Losses
	Securities available for sale:
	GSE residential mortgage-backed securities and CMOs		$	111.9	$	(0.1	)	$	1,744.20		$	(46.3	)	$	1,856.10	$	(46.4	)
	Securities held to maturity:
	State and municipal			31.8		(0.1	)		—			—			31.8		(0.1	)
	Total		$	143.7	$	(0.2	)	$	1,744.20		$	(46.3	)	$	1,887.90	$	(46.5	)

Loans_Tables

Loans (Tables)	3 Months Ended
	Mar. 31, 2015
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:
			March 31, 2015									December 31, 2014
	(in millions)		Originated			Acquired			Total			Originated			Acquired			Total
	Commercial:
	Commercial real estate		$	9,077.80		$	392.6		$	9,470.40		$	8,960.30		$	444		$	9,404.30
	Commercial and industrial			7,131.30			274.2			7,405.50			6,891.10			298.5			7,189.60
	Equipment financing			2,797.80			23.5			2,821.30			2,839.00			26.5			2,865.50
	Total commercial			9,929.10			297.7			10,226.80			9,730.10			325			10,055.10
	Total Commercial Portfolio			19,006.90			690.3			19,697.20			18,690.40			769			19,459.40
	Retail:
	Residential mortgage:
	Adjustable-rate			4,366.30			135.5			4,501.80			4,254.70			139.1			4,393.80
	Fixed-rate			464.4			84.4			548.8			446.8			91.4			538.2
	Total residential mortgage			4,830.70			219.9			5,050.60			4,701.50			230.5			4,932.00
	Consumer:
	Home equity			2,082.70			46.7			2,129.40			2,092.90			50.2			2,143.10
	Other consumer			51			1.1			52.1			56.3			1.2			57.5
	Total consumer			2,133.70			47.8			2,181.50			2,149.20			51.4			2,200.60
	Total Retail Portfolio			6,964.40			267.7			7,232.10			6,850.70			281.9			7,132.60
	Total loans		$	25,971.30		$	958		$	26,929.30		$	25,541.10		$	1,050.90		$	26,592.00
Summary, by Loan Portfolio Segment, of Activity in Allowance for Loan Losses	The following table presents a summary, by loan portfolio segment, of activity in the allowance for loan losses. 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.
			Commercial									Retail
	Three Months Ended March 31, 2015 (in millions)		Originated			Acquired			Total			Originated			Acquired			Total			Total
	Balance at beginning of period		$	169.6		$	9.8		$	179.4		$	18.5		$	0.4		$	18.9		$	198.3
	Charge-offs			(6.6	)		—			(6.6	)		(1.5	)		—			(1.5	)		(8.1	)
	Recoveries			0.6			—			0.6			0.3			—			0.3			0.9
	Net loan charge-offs			(6.0	)		—			(6.0	)		(1.2	)		—			(1.2	)		(7.2	)
	Provision for loan losses			9.5			(0.4	)		9.1			0.7			—			0.7			9.8
	Balance at end of period		$	173.1		$	9.4		$	182.5		$	18		$	0.4		$	18.4		$	200.9
			Commercial									Retail
	Three Months Ended March 31, 2014 (in millions)		Originated			Acquired			Total			Originated			Acquired			Total			Total
	Balance at beginning of period		$	158.5		$	9.8		$	168.3		$	19		$	0.5		$	19.5		$	187.8
	Charge-offs			(3.1	)		(1.4	)		(4.5	)		(3.3	)		(0.1	)		(3.4	)		(7.9	)
	Recoveries			0.5			—			0.5			0.4			—			0.4			0.9
	Net loan charge-offs			(2.6	)		(1.4	)		(4.0	)		(2.9	)		(0.1	)		(3.0	)		(7.0	)
	Provision for loan losses			4.1			1.4			5.5			3.9			0.1			4			9.5
	Balance at end of period		$	160		$	9.8		$	169.8		$	20		$	0.5		$	20.5		$	190.3
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						Acquired Loans						Total
			Individually Evaluated						Collectively Evaluated						(Discounts Related to
			for Impairment						for Impairment						Credit Quality)
	As of March 31, 2015 (in millions)		Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance
	Commercial		$	169.5		$	6.6		$	18,837.40		$	166.5		$	690.3		$	9.4		$	19,697.20		$	182.5
	Retail			97.9			3.9			6,866.50			14.1			267.7			0.4			7,232.10			18.4
	Total		$	267.4		$	10.5		$	25,703.90		$	180.6		$	958.0		$	9.8		$	26,929.30		$	200.9
			Originated Loans						Originated Loans						Acquired Loans						Total
			Individually Evaluated						Collectively Evaluated						(Discounts Related to
			for Impairment						for Impairment						Credit Quality)
	As of December 31, 2014 (in millions)		Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance			Portfolio			Allowance
	Commercial		$	174.5		$	7.6		$	18,515.90		$	162		$	769		$	9.8		$	19,459.40		$	179.4
	Retail			95			3.9			6,755.70			14.6			281.9			0.4			7,132.60			18.9
	Total		$	269.5		$	11.5		$	25,271.60		$	176.6		$	1,050.90		$	10.2		$	26,592.00		$	198.3
Summarized Recorded Investments, by Class of Loan, of Originated Non-Performing Loans	The recorded investments, by class of loan, of originated non-performing loans are summarized as follows:
	(in millions)		March 31,			December 31,
			2015			2014
	Commercial:
	Commercial real estate		$	43.3		$	60.2
	Commercial and industrial			42.6			55.8
	Equipment financing			34.9			25.4
	Total (1)			120.8			141.4
	Retail:
	Residential mortgage			37.5			37.6
	Home equity			19.4			17.9
	Other consumer			0.1			0.1
	Total (2)			57			55.6
	Total		$	177.8		$	197
	-1	Reported net of government guarantees totaling $17.5 million and $17.6 million at March 31, 2015 and December 31, 2014, 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 March 31, 2015, the principal loan classes to which these government guarantees relate are commercial and industrial loans (99%) and commercial real estate loans (1%).
	-2	Includes $15.2 million and $18.9 million of loans in the process of foreclosure at March 31, 2015 and December 31, 2014, 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 months ended March 31, 2015 and 2014. For purposes of this disclosure, recorded investments represent amounts immediately prior to and subsequent to the restructuring.
			Three Months Ended March 31, 2015
	(dollars in millions)		Number			Pre-Modification			Post-Modification
			of Contracts			Outstanding			Outstanding
						Recorded			Recorded
						Investment			Investment
	Commercial:
	Commercial real estate (1)			8		$	4.9		$	4.9
	Commercial and industrial (2)			8			10.1			10.1
	Equipment financing (3)			5			7.6			7.6
	Total			21			22.6			22.6
	Retail:
	Residential mortgage (4)			20			5.7			5.7
	Home equity (5)			33			2			2
	Other consumer			—			—			—
	Total			53			7.7			7.7
	Total			74		$	30.3		$	30.3
	-1	Represents the following concessions: extension of term (8 contracts; recorded investment of $4.9 million).
	-2	Represents the following concessions: extension of term (4 contracts; recorded investment of $8.7 million); reduced payment and/or payment deferral (3 contracts; recorded investment of $0.6 million); or a combination of concessions (1 contract; recorded investment of $0.8 million).
	-3	Represents the following concessions: reduced payment and/or payment deferral (3 contracts; recorded investment of $5.7 million); or a combination of concessions (2 contracts; recorded investment of $1.9 million).
	-4	Represents the following concessions: loans restructured through bankruptcy (6 contracts; recorded investment of $2.4 million); reduced payment and/or payment deferral (4 contracts; recorded investment of $1.5 million); temporary rate reduction (1 contract; recorded investment of $0.2 million); or a combination of concessions (9 contracts; recorded investment of $1.6 million).
	-5	Represents the following concessions: loans restructured through bankruptcy (25 contracts; recorded investment of $1.0 million); reduced payment and/or payment deferral (2 contracts; recorded investment of $0.2 million); or a combination of concessions (6 contracts; recorded investment of $0.8 million).
			Three Months Ended March 31, 2014
	(dollars in millions)		Number			Pre-Modification			Post-Modification
			of Contracts			Outstanding			Outstanding
						Recorded			Recorded
						Investment			Investment
	Commercial:
	Commercial real estate (1)			6		$	5		$	5
	Commercial and industrial (2)			7			3.4			3.4
	Equipment financing (3)			5			2.9			2.9
	Total			18			11.3			11.3
	Retail:
	Residential mortgage (4)			48			16.8			16.8
	Home equity (5)			40			3.8			3.8
	Other consumer			—			—			—
	Total			88			20.6			20.6
	Total			106		$	31.9		$	31.9
	-1	Represents the following concessions: extension of term (4 contracts; recorded investment of $4.1 million); or a combination of concessions (2 contracts; recorded investment of $0.9 million).
	-2	Represents the following concessions: extension of term (3 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 (3 contracts; recorded investment of $1.7 million).
	-3	Represents the following concessions: combination of concessions (5 contracts; recorded investment of $2.9 million).
	-4	Represents the following concessions: loans restructured through bankruptcy (9 contracts; recorded investment of $3.1 million); extension of term (1 contract; recorded investment of $0.5 million); reduced payment and/or payment deferral (12 contracts; recorded investment of $4.3 million); or a combination of concessions (26 contracts; recorded investment of $8.9 million).
	-5	Represents the following concessions: loans restructured through bankruptcy (17 contracts; recorded investment of $2.1 million); reduced payment and/or payment deferral (3 contracts; recorded investment of $0.1 million); temporary rate reduction (1 contract; recorded investment of $0.1 million); or a combination of concessions (19 contracts; recorded investment of $1.5 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 of originated loans completed within the previous 12 months that subsequently defaulted during the three months ended March 31, 2015 and 2014. For purposes of this disclosure, the previous 12 months is measured from April 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 months ended March 31, 2015 or 2014.
			Three Months Ended March 31,
			2015						2014
	(dollars in millions)		Number			Recorded			Number			Recorded
			of Contracts			Investment as of			of Contracts			Investment as of
						Period End						Period End
	Commercial:
	Commercial real estate			—		$	—			—		$	—
	Commercial and industrial			2			0.1			1			1.5
	Equipment financing			4			1.3			9			1.4
	Total			6			1.4			10			2.9
	Retail:
	Residential mortgage			17			7.4			24			10.9
	Home equity			11			1.2			8			0.9
	Other consumer			—			—			—			—
	Total			28			8.6			32			11.8
	Total			34		$	10			42		$	14.7
Summary of Individually-Evaluated Impaired Loans by Class of Loan	People’s United’s impaired loans consist of certain originated loans, including all TDRs. The following table summarizes, by class of loan, information related to individually-evaluated impaired loans within the originated portfolio.
			As of March 31, 2015									As of December 31, 2014
	(in millions)		Unpaid			Recorded			Related			Unpaid			Recorded			Related
			Principal			Investment			Allowance			Principal			Investment			Allowance
			Balance						for Loan			Balance						for Loan
									Losses									Losses
	Without a related allowance for loan losses:
	Commercial:
	Commercial real estate		$	54.9		$	53.7		$	—		$	57.1		$	55.8		$	—
	Commercial and industrial			60.2			56.9			—			51.7			48.6			—
	Equipment financing			34.5			24.5			—			30.2			21.4			—
	Retail:
	Residential mortgage			66.6			60			—			65.4			58.9			—
	Home equity			22.8			19.4			—			21.3			18.3			—
	Other consumer			—			—			—			—			—			—
	Total		$	239		$	214.5		$	—		$	225.7		$	203		$	—
	With a related allowance for loan losses:
	Commercial:
	Commercial real estate		$	23.1		$	16.2		$	1.7		$	52.1		$	27.8		$	4
	Commercial and industrial			8.3			6.4			2.9			21.4			17.4			3.5
	Equipment financing			11.9			11.8			2			3.6			3.5			0.1
	Retail:
	Residential mortgage			16.5			16.4			2.7			15.6			15.3			2.6
	Home equity			2.2			2.1			1.2			2.6			2.5			1.3
	Other consumer			—			—			—			—			—			—
	Total		$	62		$	52.9		$	10.5		$	95.3		$	66.5		$	11.5
	Total impaired loans:
	Commercial:
	Commercial real estate		$	78		$	69.9		$	1.7		$	109.2		$	83.6		$	4
	Commercial and industrial			68.5			63.3			2.9			73.1			66			3.5
	Equipment financing			46.4			36.3			2			33.8			24.9			0.1
	Total			192.9			169.5			6.6			216.1			174.5			7.6
	Retail:
	Residential mortgage			83.1			76.4			2.7			81			74.2			2.6
	Home equity			25			21.5			1.2			23.9			20.8			1.3
	Other consumer			—			—			—			—			—			—
	Total			108.1			97.9			3.9			104.9			95			3.9
	Total		$	301		$	267.4		$	10.5		$	321		$	269.5		$	11.5
Schedule of Impaired Financing Receivable	The following table summarizes, 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 balances.
			Three Months Ended March 31,
			2015						2014
	(in millions)		Average			Interest			Average			Interest
			Recorded			Income			Recorded			Income
			Investment			Recognized			Investment			Recognized
	Commercial:
	Commercial real estate		$	78		$	0.3		$	74.1		$	0.2
	Commercial and industrial			59.5			0.4			37			0.2
	Equipment financing			26.8			0.1			28.3			0.3
	Total			164.3			0.8			139.4			0.7
	Retail:
	Residential mortgage			75.6			0.4			69.3			0.3
	Home equity			21.5			0.1			16.4			0.1
	Other consumer			—			—			—			—
	Total			97.1			0.5			85.7			0.4
	Total		$	261.4		$	1.3		$	225.1		$	1.1
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 March 31, 2015 (in millions)		Current			30-89			90 Days			Total			Total
						Days			or More						Originated
	Commercial:
	Commercial real estate		$	9,044.50		$	11.3		$	22		$	33.3		$	9,077.80
	Commercial and industrial			7,069.70			20.9			40.7			61.6			7,131.30
	Equipment financing			2,729.70			64.1			4			68.1			2,797.80
	Total			18,843.90			96.3			66.7			163			19,006.90
	Retail:
	Residential mortgage			4,781.00			24.9			24.8			49.7			4,830.70
	Home equity			2,067.50			5.8			9.4			15.2			2,082.70
	Other consumer			50.6			0.3			0.1			0.4			51
	Total			6,899.10			31			34.3			65.3			6,964.40
	Total originated loans		$	25,743.00		$	127.3		$	101		$	228.3		$	25,971.30
						Past Due
	As of December 31, 2014 (in millions)		Current			30-89			90 Days			Total			Total
						Days			or More						Originated
	Commercial:
	Commercial real estate		$	8,908.00		$	17.6		$	34.7		$	52.3		$	8,960.30
	Commercial and industrial			6,814.90			32.4			43.8			76.2			6,891.10
	Equipment financing			2,793.30			41			4.7			45.7			2,839.00
	Total			18,516.20			91			83.2			174.2			18,690.40
	Retail:
	Residential mortgage			4,647.30			29.1			25.1			54.2			4,701.50
	Home equity			2,079.30			5			8.6			13.6			2,092.90
	Other consumer			55.8			0.4			0.1			0.5			56.3
	Total			6,782.40			34.5			33.8			68.3			6,850.70
	Total originated loans		$	25,298.60		$	125.5		$	117		$	242.5		$	25,541.10
Summary of Credit Quality Indicators by Class of Loan	The following is a summary, by class of loan, of credit quality indicators:
	As of March 31, 2015 (in millions)		Commercial			Commercial			Equipment			Total
			Real Estate			and			Financing
						Industrial
	Commercial:
	Originated loans:
	Pass		$	8,864.90		$	6,672.70		$	2,423.30		$	17,960.90
	Special mention			86			142.1			101.8			329.9
	Substandard			126.9			314.7			272.7			714.3
	Doubtful			—			1.8			—			1.8
	Total originated loans			9,077.80			7,131.30			2,797.80			19,006.90
	Acquired loans:
	Pass			288.1			178.2			6.7			473
	Special mention			25.4			20.5			0.6			46.5
	Substandard			72.7			59.9			16.2			148.8
	Doubtful			6.4			15.6			—			22
	Total acquired loans			392.6			274.2			23.5			690.3
	Total		$	9,470.4		$	7,405.5		$	2,821.30		$	19,697.20
	As of March 31, 2015 (in millions)		Residential			Home			Other			Total
			Mortgage			Equity			Consumer
	Retail:
	Originated loans:
	Low risk		$	2,379.10		$	927.2		$	27		$	3,333.30
	Moderate risk			1,943.50			612.4			7.1			2,563.00
	High risk			508.1			543.1			16.9			1,068.10
	Total originated loans			4,830.70			2,082.70			51			6,964.40
	Acquired loans:
	Low risk			107.2			—			—			107.2
	Moderate risk			47.7			—			—			47.7
	High risk			65			46.7			1.1			112.8
	Total acquired loans			219.9			46.7			1.1			267.7
	Total		$	5,050.6		$	2,129.4		$	52.1		$	7,232.1
	As of December 31, 2014 (in millions)		Commercial			Commercial			Equipment			Total
			Real Estate			and			Financing
						Industrial
	Commercial:
	Originated loans:
	Pass		$	8,730.90		$	6,477.40		$	2,481.20		$	17,689.50
	Special mention			82.4			114.2			110.6			307.2
	Substandard			135.3			297.3			247.2			679.8
	Doubtful			11.7			2.2			—			13.9
	Total originated loans			8,960.30			6,891.10			2,839.00			18,690.40
	Acquired loans:
	Pass			302.5			174.5			7.6			484.6
	Special mention			20.9			52.8			0.7			74.4
	Substandard			113.5			55			18.2			186.7
	Doubtful			7.1			16.2			—			23.3
	Total acquired loans			444			298.5			26.5			769
	Total		$	9,404.3		$	7,189.6		$	2,865.50		$	19,459.40
	As of December 31, 2014 (in millions)		Residential			Home			Other			Total
			Mortgage			Equity			Consumer
	Retail:
	Originated loans:
	Low risk		$	2,280.60		$	931.5		$	29.5		$	3,241.60
	Moderate risk			1,921.60			597.1			8.3			2,527.00
	High risk			499.3			564.3			18.5			1,082.10
	Total originated loans			4,701.50			2,092.90			56.3			6,850.70
	Acquired loans:
	Low risk			107			—			—			107
	Moderate risk			50.5			—			—			50.5
	High risk			73			50.2			1.2			124.4
	Total acquired loans			230.5			50.2			1.2			281.9
	Total		$	4,932.0		$	2,143.1		$	57.5		$	7,132.6
Summarized Activity in Accretable Yield for Acquired Loan Portfolio	The following table summarizes activity in the accretable yield for the acquired loan portfolio:
			Three Months Ended
			March 31,
	(in millions)		2015			2014
	Balance at beginning of period		$	396.3		$	639.7
	Accretion			(15.3	)		(23.3	)
	Reclassification from nonaccretable difference for loans			0.3			5.8
	with improved cash flows (1)
	Other changes in expected cash flows (2)			(19.7	)		(97.8	)
	Balance at end of period		$	361.6		$	524.4
	-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)	3 Months Ended
	Mar. 31, 2015
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 basis:
	(in millions)		Pension			Net Unrealized			Net Unrealized			Net Unrealized			Total
			and Other			Gains (Losses)			Gains (Losses)			Gains (Losses)			Accumulated
			Postretirement			on Securities			on Securities			on Derivatives			Other
			Benefits			Available for Sale			Transferred to			Accounted for as			Comprehensive
									Held to Maturity			Cash Flow Hedges			Loss
	Balance at December 31, 2014		$	(142.9	)	$	(3.7	)	$	(21.5	)	$	(0.1	)	$	(168.2	)
	Other comprehensive income (loss) before reclassifications			—			26.2			—			(0.4	)		25.8
	Amounts reclassified from AOCL (1)			1.1			—			0.5			0.2			1.8
	Current period other comprehensive income (loss)			1.1			26.2			0.5			(0.2	)		27.6
	Balance at March 31, 2015		$	(141.8	)	$	22.5		$	(21.0	)	$	(0.3	)	$	(140.6	)
	(in millions)		Pension			Net Unrealized			Net Unrealized			Net Unrealized			Total
			and Other			Gains (Losses)			Gains (Losses)			Gains (Losses)			Accumulated
			Postretirement			on Securities			on Securities			on Derivatives			Other
			Benefits			Available for Sale			Transferred to			Accounted for as			Comprehensive
									Held to Maturity			Cash Flow Hedges			Loss
	Balance at December 31, 2013		$	(85.0	)	$	(46.5	)	$	(23.3	)	$	(0.3	)	$	(155.1	)
	Other comprehensive income (loss) before reclassifications			—			16.6			—			(0.1	)		16.5
	Amounts reclassified from AOCL (1)			0.6			(0.1	)		0.4			0.2			1.1
	Current period other comprehensive income (loss)			0.6			16.5			0.4			0.1			17.6
	Balance at March 31, 2014		$	-84.4		$	(30.0	)	$	(22.9	)	$	(0.2	)	$	(137.5	)
Summary of Amounts Reclassified from AOCL	The following is a summary of the amounts reclassified from AOCL:
			Amounts Reclassified from AOCL						Affected Line Item
			Three Months Ended March 31,						in the Statement Where
	(in millions)		2015			2014			Net Income is Presented
	Details about components of AOCL:
	Amortization of pension and other postretirement benefits items:
	Net actuarial loss		$	(2.0	)	$	(1.3	)	-1
	Prior service credit			0.3			0.3		-1
				(1.7	)		(1.0	)	Income before income tax expense
				0.6			0.4		Income tax expense
				(1.1	)		(0.6	)	Net income
	Reclassification adjustment for net realized gains on securities available for sale			—			0.1		Income before income tax expense (2)
				—			—		Income tax expense
				—			0.1		Net income
	Amortization of unrealized losses on securities transferred to held to maturity			(0.8	)		(0.7	)	Income before income tax expense (3)
				0.3			0.3		Income tax expense
				(0.5	)		(0.4	)	Net income
	Amortization of unrealized gains and losses on cash flow hedges:
	Interest rate swaps			(0.3	)		(0.3	)	-5
	Interest rate locks (4)			—			—		-5
				(0.3	)		(0.3	)	Income before income tax expense
				0.1			0.1		Income tax expense
				(0.2	)		(0.2	)	Net income
	Total reclassifications for the period		$	(1.8	)	$	(1.1	)
	-1	Included in the computation of net periodic pension cost reflected in compensation and benefits expense (see Note 7 for additional details).
	-2	Included in other non-interest income.
	-3	Included in interest and dividend income - securities.
	-4	Amount reclassified from AOCL totaled less than $0.1 million at both dates.
	-5	Included in interest expense - notes and debentures.

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Share, Reflecting Application of Two-Class Method	The following is an analysis of People’s United’s basic and diluted earnings per share (“EPS”), reflecting the application of the two-class method, as described below:
		Three Months Ended
		March 31,
	(in millions, except per share data)	2015			2014
	Net income	$	59.2		$	53.1
	Dividends and undistributed earnings allocated to participating securities		(0.3	)		(0.2	)
	Income attributable to common shareholders	$	58.9		$	52.9
	Average common shares outstanding for basic EPS		299.1			297.7
	Effect of dilutive equity-based awards		—			—
	Average common and common-equivalent shares for diluted EPS		299.1			297.7
	Basic EPS	$	0.2		$	0.18
	Diluted EPS	$	0.2		$	0.18

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Components of Net Periodic Benefit (Income) Expense and Other Amounts	Components of the net periodic benefit (income) expense and other amounts recognized in other comprehensive income for the plans described above are as follows:
		Pension Benefits						Other
								Postretirement Benefits
	Three Months Ended March 31 (in millions)	2015			2014			2015			2014
	Net periodic benefit (income) expense:
	Service cost	$	—		$	—		$	0.1		$	—
	Interest cost		4.8			4.8			0.1			0.2
	Expected return on plan assets		(7.2	)		(7.1	)		—			—
	Recognized net actuarial loss		1.5			1			0.1			—
	Recognized prior service credit		—			—			(0.1	)		(0.1	)
	Settlements		0.1			0.1			—			—
	Net periodic benefit (income) expense		(0.8	)		(1.2	)		0.2			0.1
	Other changes in plan assets and benefit obligations recognized
	in other comprehensive income:
	Net actuarial loss		(1.5	)		(1.0	)		(0.1	)		—
	Prior service credit		—			—			0.1			0.1
	Total pre-tax changes recognized in		(1.5	)		(1.0	)		—			0.1
	other comprehensive income
	Total recognized in net periodic benefit (income)	$	(2.3	)	$	(2.2	)	$	0.2		$	0.2
	expense and other comprehensive income

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015 (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			301.1		—		—		301.1
	GSE residential mortgage-backed securities and CMOs			—		4,055.50		—		4,055.50
	Equity securities			—		0.2		—		0.2
	Other assets:
	Exchange-traded funds			30.7		—		—		30.7
	Fixed income securities			—		5.8		—		5.8
	Mutual funds			1.4		—		—		1.4
	Interest rate swaps			—		176.1		—		176.1
	Foreign exchange contracts			—		1		—		1
	Forward commitments to sell residential mortgage loans			—		0.9		—		0.9
	Total		$	341.5	$	4,239.50	$	—	$	4,581.00
	Financial liabilities:
	Interest rate swaps		$	—	$	128.5	$	—	$	128.5
	Foreign exchange contracts			—		0.5		—		0.5
	Interest rate-lock commitments on residential mortgage loans			—		1.3		—		1.3
	Total		$	—	$	130.3	$	—	$	130.3
			Fair Value Measurements Using
	As of December 31, 2014 (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			56.8		—		—		56.8
	GSE residential mortgage-backed securities and CMOs			—		3,936.70		—		3,936.70
	Equity securities			—		0.2		—		0.2
	Other assets:
	Exchange-traded funds			30.3		—		—		30.3
	Fixed income securities			—		6		—		6
	Mutual funds			0.8		—		—		0.8
	Interest rate swaps			—		131.1		—		131.1
	Foreign exchange contracts			—		0.8		—		0.8
	Forward commitments to sell residential mortgage loans			—		0.5		—		0.5
	Total		$	96.2	$	4,075.30	$	—	$	4,171.50
	Financial liabilities:
	Interest rate swaps		$	—	$	95.8	$	—	$	95.8
	Foreign exchange contracts			—		0.5		—		0.5
	Interest rate-lock commitments on residential mortgage loans			—		0.7		—		0.7
	Total		$	—	$	97	$	—	$	97
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 basis:
			Fair Value Measurements Using
	As of March 31, 2015 (in millions)		Level 1		Level 2		Level 3		Total
	Loans held for sale (1)		$	—	$	49.7	$	—	$	49.7
	Impaired loans (2)			—		—		52.9		52.9
	REO and repossessed assets (3)			—		—		31		31
	Total		$	—	$	49.7	$	83.9	$	133.6
			Fair Value Measurements Using
	As of December 31, 2014 (in millions)		Level 1		Level 2		Level 3		Total
	Loans held for sale (1)		$	—	$	34.2	$	—	$	34.2
	Impaired loans (2)			—		—		66.5		66.5
	REO and repossessed assets (3)			—		—		27.1		27.1
	Total		$	—	$	34.2	$	93.6	$	127.8
	-1	Consists of residential mortgage loans; no fair value adjustments were recorded for the three months ended March 31, 2015 and 2014.
	-2	Represents the recorded investment in originated impaired loans with a related allowance for loan losses measured in accordance with applicable accounting guidance. The total consists of $34.4 million of Commercial loans and $18.5 million of Retail loans at March 31, 2015. The provision for loan losses on impaired loans totaled $2.2 million and $4.0 million for the three months ended March 31, 2015 and 2014, respectively.
	-3	Represents: (i) $16.5 million of residential REO; (ii) $10.2 million of commercial REO; and (iii) $4.3 million of repossessed assets at March 31, 2015. Charge-offs to the allowance for loan losses related to loans that were transferred to REO or repossessed assets totaled $0.6 million and $0.7 million for the three months ended March 31, 2015 and 2014, respectively. Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest expense totaled $0.4 million for both periods.
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 basis:
					Estimated Fair Value
			Carrying		Measurements Using
	As of March 31, 2015 (in millions)		Amount		Level 1		Level 2		Level 3		Total
	Financial assets:
	Cash and due from banks		$	306.8	$	306.8	$	—	$	—	$	306.8
	Short-term investments			250		—		250		—		250
	Securities held to maturity			897.4		—		942.4		1.5		943.9
	FHLB and FRB stock			314.2		—		314.2		—		314.2
	Total loans, net (1)			26,675.50		—		4,951.00		21,837.90		26,788.90
	Financial liabilities:
	Time deposits			5,301.60		—		5,336.60		—		5,336.60
	Other deposits			21,848.30		—		21,848.30		—		21,848.30
	FHLB advances			2,165.90		—		2,173.40		—		2,173.40
	Federal funds purchased			496		—		496		—		496
	Customer repurchase agreements			480		—		480		—		480
	Repurchase agreements (2)			1		—		1		—		1
	Notes and debentures			1,042.30		—		1,043.80		—		1,043.80
	-1	Excludes impaired loans totaling $52.9 million measured at fair value on a non-recurring basis.
	-2	Included in other borrowings in the Consolidated Statements of Condition.
					Estimated Fair Value
			Carrying		Measurements Using
	As of December 31, 2014 (in millions)		Amount		Level 1		Level 2		Level 3		Total
	Financial assets:
	Cash and due from banks		$	345.1	$	345.1	$	—	$	—	$	345.1
	Short-term investments			668.6		—		668.6		—		668.6
	Securities purchased under agreements to resell			100		—		100		—		100
	Securities held to maturity			834.3		—		880.1		1.5		881.6
	FHLB stock			175.7		—		175.7		—		175.7
	Total loans, net (1)			26,327.20		—		4,798.50		21,508.80		26,307.30
	Financial liabilities:
	Time deposits			5,230.70		—		5,262.60		—		5,262.60
	Other deposits			20,907.50		—		20,907.50		—		20,907.50
	FHLB advances			2,291.70		—		2,298.50		—		2,298.50
	Federal funds purchased			913		—		913		—		913
	Customer repurchase agreements			486		—		486		—		486
	Repurchase agreements (2)			1		—		1		—		1
	Notes and debentures			1,033.50		—		1,040.80		—		1,040.80
	-1	Excludes impaired loans totaling $66.5 million measured at fair value on a non-recurring basis.
	-2	Included in other borrowings in the Consolidated Statements of Condition.

Derivative_Financial_Instrumen1

Derivative Financial Instruments and Hedging Activities (Tables)	3 Months Ended
	Mar. 31, 2015
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	March 31,			Dec. 31,			March 31,			Dec. 31,			March 31,		Dec. 31,
			Hedge	2015			2014			2015			2014			2015		2014
	Derivatives Not Designated as Hedging Instruments:
	Interest rate swaps:
	Commercial customers		N/A	$	3,871.50		$	3,380.20		$	149.1		$	104.2		$	1.7	$	8.3
	Institutional counterparties		N/A		3,871.50			3,380.20			3.3			11.8			125.5		86.5
	Risk participation agreements (2)		N/A		199			150.1			—			—			—		—
	Foreign exchange contracts		N/A		51.6			49.6			1			0.8			0.5		0.5
	Forward commitments to sell residential mortgage loans		N/A		75.8			35.3			0.9			0.5			—		—
	Interest rate-lock commitments on residential mortgage loans		N/A		120.9			57.5			—			—			1.3		0.7
	Total										154.3			117.3			129		96
	Derivatives Designated as Hedging Instruments:
	Interest rate swaps:
	Subordinated notes		Cash flow		125			125			—			—			1.3		1
	Subordinated notes		Fair value		375			375			23.7			15.1			—		—
	Total										23.7			15.1			1.3		1
	Total derivatives									$	178		$	132.4		$	130.3	$	97
	-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 income and AOCL:
				Amount of Pre-Tax Gain (Loss)						Amount of Pre-Tax Gain (Loss)
			Type of	Recognized in Earnings (1)						Recognized in AOCL
	Three Months Ended March 31 (in millions)		Hedge	2015			2014			2015			2014
	Derivatives Not Designated as Hedging Instruments:
	Interest rate swaps:
	Commercial customers		N/A	$	67.7		$	41.1		$	—		$	—
	Institutional counterparties		N/A		(62.5	)		(39.7	)		—			—
	Foreign exchange contracts		N/A		0.2			—			—			—
	Risk participation agreements		N/A		—			—			—			—
	Forward commitments to sell residential mortgage loans		N/A		0.4			0.1			—			—
	Interest rate-lock commitments on residential mortgage loans		N/A		(0.5	)		(0.2	)		—			—
	Total				5.3			1.3			—			—
	Derivatives Designated as Hedging Instruments:
	Interest rate swaps		Cash flow		(0.3	)		(0.3	)		(0.6	)		(0.1	)
	Interest rate locks (2)		Cash flow		—			—			—			—
	Interest rate swaps		Fair value		2.5			—			—			—
	Total				2.2			(0.3	)		(0.6	)		(0.1	)
	Total derivatives			$	7.5		$	1		$	(0.6	)	$	(0.1	)
	-1	Amounts recognized in earnings are recorded in interest income, interest expense or other non-interest income for derivatives designated as hedging instruments and in other non-interest income for derivatives not designated as hedging instruments.
	-2	Income relating to T-Locks terminated in 2012 totaled less than $0.1 million at both dates.

Balance_Sheet_Offsetting_Table

Balance Sheet Offsetting (Tables)	3 Months Ended
	Mar. 31, 2015
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
	As of March 31, 2015 (in millions)		Amount		Amount		Amount		Financial			Collateral			Net
			Recognized		Offset		Presented		Instruments						Amount
	Financial assets:
	Interest rate swaps:
	Counterparty A		$	1	$	—	$	1	$	(1.0	)	$	—		$	—
	Counterparty B			0.3		—		0.3		(0.3	)		—			—
	Counterparty C			0.3		—		0.3		(0.3	)		—			—
	Counterparty D			0.7		—		0.7		(0.7	)		—			—
	Counterparty E			24.2		—		24.2		(24.2	)		—			—
	Other counterparties			0.5		—		0.5		(0.5	)		—			—
	Foreign exchange contracts			1		—		1		—			—			1
	Total		$	28	$	—	$	28	$	(27.0	)	$	—		$	1
	Financial liabilities:
	Interest rate swaps:
	Counterparty A		$	11.8	$	—	$	11.8	$	(1.0	)	$	(10.8	)	$	—
	Counterparty B			13.2		—		13.2		(0.3	)		(12.9	)		—
	Counterparty C			6.3		—		6.3		(0.3	)		(6.0	)		—
	Counterparty D			10		—		10		(0.7	)		(8.8	)		0.5
	Counterparty E			79.9		—		79.9		(24.2	)		(55.7	)		—
	Other counterparties			5.6		—		5.6		(0.5	)		(5.1	)		—
	Repurchase agreements (1)			1		—		1		—			(1.0	)		—
	Foreign exchange contracts			0.5		—		0.5		—			—			0.5
	Total		$	128.3	$	—	$	128.3	$	(27.0	)	$	(100.3	)	$	1
	-1	Included in other borrowings in the Consolidated Statements of Condition.
			Gross		Gross		Net		Gross Amounts Not Offset
	As of December 31, 2014 (in millions)		Amount		Amount		Amount		Financial			Collateral			Net
			Recognized		Offset		Presented		Instruments						Amount
	Financial assets:
	Interest rate swaps:
	Counterparty A		$	2.7	$	—	$	2.7	$	(2.7	)	$	—		$	—
	Counterparty B			1.5		—		1.5		(1.5	)		—			—
	Counterparty C			2.5		—		2.5		(2.5	)		—			—
	Counterparty D			3.2		—		3.2		(0.4	)		(2.8	)		—
	Counterparty E			15.7		—		15.7		(15.7	)		—			—
	Other counterparties			1.3		—		1.3		(1.3	)		—			—
	Securities purchased under agreements to resell			100		—		100		—			(100.0	)		—
	Foreign exchange contracts			0.8		—		0.8		—			—			0.8
	Total		$	127.7	$	—	$	127.7	$	(24.1	)	$	(102.8	)	$	0.8
	Financial liabilities:
	Interest rate swaps:
	Counterparty A		$	11.8	$	—	$	11.8	$	(2.7	)	$	(9.1	)	$	—
	Counterparty B			11.8		—		11.8		(1.5	)		(10.3	)		—
	Counterparty C			4.5		—		4.5		(2.5	)		(1.9	)		0.1
	Counterparty D			0.4		—		0.4		(0.4	)		—			—
	Counterparty E			47.8		—		47.8		(15.7	)		(32.1	)		—
	Other counterparties			11.2		—		11.2		(1.3	)		(8.9	)		1
	Repurchase agreements (1)			1		—		1		—			(1.0	)		—
	Foreign exchange contracts			0.5		—		0.5		—			—			0.5
	Total		$	89	$	—	$	89	$	(24.1	)	$	(63.3	)	$	1.6
	-1	Included in other borrowings in the Consolidated Statements of Condition.

General_Additional_Information

General - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Company's housing investment	$786.30		$719.90
Income tax expense (benefit)	30.5	27.7
Affordable Housing Investments [Member]
Description Of Business And Summary Of Significant Accounting Policies [Line Items]
Company's housing investment	71.6
Future contingent commitments	36.1
Amortization period	10 years
Income tax expense (benefit)	$2.80	$2.30

Securities_and_ShortTerm_Inves2

Securities and Short-Term Investments - Available-for-Sale and Held-to-Maturity Securities Gains (Losses) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Investment Holdings [Line Items]
Amortized Cost	$4,322.40	$4,000.10
Gross Unrealized Gains	54.1	40
Gross Unrealized Losses	-19.7	-46.4
Fair Value	4,356.80	3,993.70
Held to maturity Securities, Amortized Cost	897.4	834.3
Securities held to maturity, Gross Unrealized Gains	47.7	47.4
Securities held to maturity, Gross Unrealized Losses	-1.2	-0.1
Total securities held to maturity, Fair Value	943.9	881.6
U.S. Treasury and Agency [Member]
Investment Holdings [Line Items]
Amortized Cost	299.7	56.5
Gross Unrealized Gains	1.4	0.3
Fair Value	301.1	56.8
GSE residential mortgage-backed securities and CMOs [Member]
Investment Holdings [Line Items]
Amortized Cost	4,022.50	3,943.40
Gross Unrealized Gains	52.7	39.7
Gross Unrealized Losses	-19.7	-46.4
Fair Value	4,055.50	3,936.70
Debt Securities [Member]
Investment Holdings [Line Items]
Amortized Cost	4,322.20	3,999.90
Gross Unrealized Gains	54.1	40
Gross Unrealized Losses	-19.7	-46.4
Fair Value	4,356.60	3,993.50
Equity Securities [Member]
Investment Holdings [Line Items]
Amortized Cost	0.2	0.2
Fair Value	0.2	0.2
State and Municipal [Member]
Investment Holdings [Line Items]
Held to maturity Securities, Amortized Cost	895.9	832.8
Securities held to maturity, Gross Unrealized Gains	47.7	47.4
Securities held to maturity, Gross Unrealized Losses	-1.2	-0.1
Total securities held to maturity, Fair Value	942.4	880.1
Other [Member]
Investment Holdings [Line Items]
Held to maturity Securities, Amortized Cost	1.5	1.5
Total securities held to maturity, Fair Value	$1.50	$1.50

Securities_and_ShortTerm_Inves3

Securities and Short-Term Investments - Summary of Amortized Cost and Fair Value of Debt Securities Remaining Period to Contractual Maturity (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Investment [Line Items]
Available for Sale, Amortized Cost, Within 1 year	$10.90
Available for Sale, Amortized Cost, After 1 but within 5 years	307.6
Available for Sale, Amortized Cost, After 5 but within 10 years	792.3
Available for Sale, Amortized Cost, After 10 years	3,211.40
Available for Sale, Amortized Cost, Total	4,322.20
Available for Sale, Fair Value, Within 1 year	10.9
Available for Sale, Fair Value, After 1 but within 5 years	309.1
Available for Sale, Fair Value, After 5 but within 10 years	805.7
Available for Sale, Fair Value, After 10 years	3,230.90
Available for Sale, Fair Value, Total	4,356.60
Held to Maturity, Amortized Cost, Within 1 year	3.2
Held to Maturity, Amortized Cost, After 1 but within 5 years	22.2
Held to Maturity, Amortized Cost, After 5 but within 10 years	287.3
Held to Maturity, Amortized Cost, After 10 years	584.7
Held to maturity Securities, Amortized Cost	897.4	834.3
Held to Maturity, Fair Value, Within 1 year	3.2
Held to Maturity, Fair Value, After 1 but within 5 years	22.5
Held to Maturity, Fair Value, After 5 but within 10 years	305.2
Held to Maturity, Fair Value, After 10 years	613
Held to Maturity, Fair Value, Total	943.9	881.6
U.S. Treasury and Agency [Member]
Investment [Line Items]
Available for Sale, Amortized Cost, Within 1 year	10.9
Available for Sale, Amortized Cost, After 1 but within 5 years	288.8
Available for Sale, Amortized Cost, Total	299.7
Available for Sale, Fair Value, Within 1 year	10.9
Available for Sale, Fair Value, After 5 but within 10 years	290.2
Available for Sale, Fair Value, Total	301.1
GSE residential mortgage-backed securities and CMOs [Member]
Investment [Line Items]
Available for Sale, Amortized Cost, After 1 but within 5 years	18.8
Available for Sale, Amortized Cost, After 5 but within 10 years	792.3
Available for Sale, Amortized Cost, After 10 years	3,211.40
Available for Sale, Amortized Cost, Total	4,022.50
Available for Sale, Fair Value, After 1 but within 5 years	18.9
Available for Sale, Fair Value, After 5 but within 10 years	805.7
Available for Sale, Fair Value, After 10 years	3,230.90
Available for Sale, Fair Value, Total	4,055.50
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
State and Municipal [Member]
Investment [Line Items]
Held to Maturity, Amortized Cost, Within 1 year	3.2
Held to Maturity, Amortized Cost, After 1 but within 5 years	20.7
Held to Maturity, Amortized Cost, After 5 but within 10 years	287.3
Held to Maturity, Amortized Cost, After 10 years	584.7
Held to maturity Securities, Amortized Cost	895.9	832.8
Held to Maturity, Fair Value, Within 1 year	3.2
Held to Maturity, Fair Value, After 1 but within 5 years	21
Held to Maturity, Fair Value, After 5 but within 10 years	305.2
Held to Maturity, Fair Value, After 10 years	613
Held to Maturity, Fair Value, Total	$942.40	$880.10

Securities_and_ShortTerm_Inves4

Securities and Short-Term Investments - Continuous Unrealized Loss Position on Available-for-Sale and Held-to-Maturities Securities (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	$462.30	$143.70
Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	-2.2	-0.2
Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	1,094.50	1,744.20
Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	-18.7	-46.3
Continuous Unrealized Loss Position, Total, Fair Value	1,556.80	1,887.90
Continuous Unrealized Loss Position, Total, Unrealized Losses	-20.9	-46.5
Continuous Unrealized Loss Position, Total, Unrealized Losses	-1.2
GSE residential mortgage-backed securities and CMOs [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	353.2	111.9
Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	-1	-0.1
Continuous Unrealized Loss Position, 12 Months Or Longer, Fair Value	1,094.50	1,744.20
Continuous Unrealized Loss Position, 12 Months Or Longer, Unrealized Losses	-18.7	-46.3
Continuous Unrealized Loss Position, Total, Fair Value	1,447.70	1,856.10
Continuous Unrealized Loss Position, Total, Unrealized Losses	-19.7	-46.4
State and Municipal [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Continuous Unrealized Loss Position, Less Than 12 Months, Fair Value	109.1	31.8
Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	-1.2	-0.1
Continuous Unrealized Loss Position, Total, Fair Value	109.1	31.8
Continuous Unrealized Loss Position, Total, Unrealized Losses	($1.20)	($0.10)

Securities_and_ShortTerm_Inves5

Securities and Short-Term Investments - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
	Security
	Securities
Investment [Line Items]
Number of securities available for sale	35
Number of securities held to maturity	84
Total number of securities owned	1,207
Percentage of securities available for sale	10.00%
Total gross unrealized losses	$19,700,000		$46,400,000
Total gross unrealized losses	1,200,000
Impairment losses on securities recognized in earnings	0	0
Security available for sale with a fair value pledged with collateral for public deposits	1,470,000,000		1,430,000,000
Impairment of investments	0
Purchase of Federal Reserve Bank stock	138,500,000
Federal Reserve Bank stock percentage	6.00%
Securities purchased under agreements to resell	0		100,400,000
State and Municipal [Member]
Investment [Line Items]
Total gross unrealized losses	1,200,000		100,000
Available for sale securities average maturity period	16 years
GSE residential mortgage-backed securities and CMOs [Member]
Investment [Line Items]
Total gross unrealized losses	19,700,000		46,400,000
Available for sale securities average maturity period	12 years
FHLB of Boston [Member]
Investment [Line Items]
Acquired shares of capital stock	164,400,000		164,400,000
FHLB of New York [Member]
Investment [Line Items]
Acquired shares of capital stock	11,300,000		11,300,000
Federal Reserve Bank of New York [Member]
Investment [Line Items]
Interest-bearing deposits	$180,100,000		$626,500,000
Federal funds sold and yield	0.25%		0.25%

Loans_Additional_Information_D

Loans - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
	Rating
	Segments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of segments	2
Net deferred loan costs	$55,300,000		$54,800,000
Recorded investments, non-performing loans	177,800,000		197,000,000
Allowance for loan losses	200,900,000	190,300,000	198,300,000	187,800,000
Interest Income Recognized	1,300,000	1,100,000
Temporary reduction of interest rate for TDRs, basis points	2.00%
Collateral values/LTV ratios, minimum	70.00%
Borrower credit scores, minimum	680
Principal and interest payments receivable					7,570,000,000
Expected cash flows					7,020,000,000
Loan portfolio fair value					5,360,000,000
Aggregate loan nonaccretable difference	89,100,000
Portfolio accretable yield	361,600,000	524,400,000	396,300,000	639,700,000
Portfolio outstanding balance	1,090,000,000		1,180,000,000
Portfolio carrying value	958,000,000		1,050,000,000
Repossessed assets	4,300,000		2,500,000
Expected Cash Flows [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregate loan nonaccretable difference					550,900,000
At Acquisition [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Portfolio accretable yield					1,660,000,000
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	21,400,000		25,600,000
Other real estate owned	10,200,000		11,000,000
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	19,300,000		29,500,000
Equipment Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	30,900,000		20,700,000
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	16,500,000		13,600,000
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	120,800,000		141,400,000
Allowance for loan losses	182,500,000	169,800,000	179,400,000	168,300,000
Interest Income Recognized	800,000	700,000
Commercial [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	43,300,000		60,200,000
Interest Income Recognized	300,000	200,000
Commercial [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	42,600,000		55,800,000
Interest Income Recognized	400,000	200,000
Commercial [Member] | Equipment Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	34,900,000		25,400,000
Interest Income Recognized	100,000	300,000
Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	57,000,000		55,600,000
Allowance for loan losses	18,400,000	20,500,000	18,900,000	19,500,000
Interest Income Recognized	500,000	400,000
Duration of extension for payment deferral on TDRs, months	8 years
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan agreement	6 months
Maximum [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Duration of extension for payment deferral on TDRs, months	2 years
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	9,800,000		10,200,000
Acquired Loans [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	9,400,000	9,800,000	9,800,000	9,800,000
Acquired Loans [Member] | Retail Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	400,000	500,000	400,000	500,000
Purchased Credit Impaired Loans [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	72,200,000		100,600,000
Covered by FDIC Loss-Share [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investments, non-performing loans	2,600,000		3,000,000
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Recorded investment in originated loans classified as TDRs	192,500,000		181,600,000
Allowance for loan losses	6,700,000		7,100,000
Interest Income Recognized	1,100,000	900,000
Foreclosure or Bankruptcy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Early non-performing loans	$22,700,000		$21,800,000

Loans_Summary_of_Loans_by_Loan

Loans - Summary of Loans by Loan Portfolio Segment and Class (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	$2,181.50	$2,200.60
Total Originated	7,232.10	7,132.60
Total loans	26,929.30	26,592
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	19,697.20	19,459.40
Total loans	19,697.20	19,459.40
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	9,470.40	9,404.30
Commercial Real Estate [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	9,470.40	9,404.30
Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	7,405.50	7,189.60
Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	2,821.30	2,865.50
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	10,226.80	10,055.10
Commercial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	10,226.80	10,055.10
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	5,050.60	4,932
Residential Mortgage [Member] | Adjustable-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	4,501.80	4,393.80
Residential Mortgage [Member] | Fixed-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	548.8	538.2
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	2,129.40	2,143.10
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	52.1	57.5
Originated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	2,133.70	2,149.20
Total Originated	6,964.40	6,850.70
Total loans	25,971.30	25,541.10
Originated [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	19,006.90	18,690.40
Originated [Member] | Commercial Real Estate [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	9,077.80	8,960.30
Originated [Member] | Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	7,131.30	6,891.10
Originated [Member] | Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	2,797.80	2,839
Originated [Member] | Commercial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	9,929.10	9,730.10
Originated [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	4,830.70	4,701.50
Originated [Member] | Residential Mortgage [Member] | Adjustable-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	4,366.30	4,254.70
Originated [Member] | Residential Mortgage [Member] | Fixed-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	464.4	446.8
Originated [Member] | Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	2,082.70	2,092.90
Originated [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	51	56.3
Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	47.8	51.4
Total Originated	267.7	281.9
Total loans	958	1,050.90
Acquired Loans [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	690.3	769
Acquired Loans [Member] | Commercial Real Estate [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	392.6	444
Acquired Loans [Member] | Commercial and Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	274.2	298.5
Acquired Loans [Member] | Equipment Financing [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	23.5	26.5
Acquired Loans [Member] | Commercial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Commercial Portfolio	297.7	325
Acquired Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	219.9	230.5
Acquired Loans [Member] | Residential Mortgage [Member] | Adjustable-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	135.5	139.1
Acquired Loans [Member] | Residential Mortgage [Member] | Fixed-Rate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total residential mortgage	84.4	91.4
Acquired Loans [Member] | Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	46.7	50.2
Acquired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	$1.10	$1.20

Loans_Summary_by_Loan_Portfoli

Loans - Summary, by Loan Portfolio Segment, of Activity in Allowance for Loan Losses (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$198.30	$187.80
Charge-offs	-8.1	-7.9
Recoveries	0.9	0.9
Net loan charge-offs	-7.2	-7
Provision for loan losses	9.8	9.5
Balance at end of period	200.9	190.3
Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period			10.2
Balance at end of period	9.8		10.2
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	179.4	168.3
Charge-offs	-6.6	-4.5
Recoveries	0.6	0.5
Net loan charge-offs	-6	-4
Provision for loan losses	9.1	5.5
Balance at end of period	182.5	169.8
Commercial [Member] | Originated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	169.6	158.5
Charge-offs	-6.6	-3.1
Recoveries	0.6	0.5
Net loan charge-offs	-6	-2.6
Provision for loan losses	9.5	4.1
Balance at end of period	173.1	160
Commercial [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	9.8	9.8
Charge-offs		-1.4
Net loan charge-offs		-1.4
Provision for loan losses	-0.4	1.4
Balance at end of period	9.4	9.8
Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	18.9	19.5
Charge-offs	-1.5	-3.4
Recoveries	0.3	0.4
Net loan charge-offs	-1.2	-3
Provision for loan losses	0.7	4
Balance at end of period	18.4	20.5
Retail Loans [Member] | Originated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	18.5	19
Charge-offs	-1.5	-3.3
Recoveries	0.3	0.4
Net loan charge-offs	-1.2	-2.9
Provision for loan losses	0.7	3.9
Balance at end of period	18	20
Retail Loans [Member] | Acquired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period		0.5	0.4
Charge-offs		-0.1
Net loan charge-offs		-0.1
Provision for loan losses		0.1
Balance at end of period	$0.40	$0.50	$0.40

Loans_Summary_of_Allowance_for

Loans - Summary of Allowance for Loan Losses by Loan Portfolio Segment and Impairment Methodology (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	$267.40	$269.50
Originated Loans Individually Evaluated for Impairment, Allowance	10.5	11.5
Originated Loans Collectively Evaluated for Impairment, Portfolio	25,703.90	25,271.60
Originated Loans Collectively Evaluated for Impairment, Allowance	180.6	176.6
Loans, Portfolio	958	1,050.90
Loans, Allowance	9.8	10.2
Total loans	26,929.30	26,592
Total Allowance	200.9	198.3	190.3	187.8
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	169.5	174.5
Originated Loans Individually Evaluated for Impairment, Allowance	6.6	7.6
Originated Loans Collectively Evaluated for Impairment, Portfolio	18,837.40	18,515.90
Originated Loans Collectively Evaluated for Impairment, Allowance	166.5	162
Loans, Portfolio	690.3	769
Loans, Allowance	9.4	9.8
Total loans	19,697.20	19,459.40
Total Allowance	182.5	179.4	169.8	168.3
Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Originated Loans Individually Evaluated for Impairment, Portfolio	97.9	95
Originated Loans Individually Evaluated for Impairment, Allowance	3.9	3.9
Originated Loans Collectively Evaluated for Impairment, Portfolio	6,866.50	6,755.70
Originated Loans Collectively Evaluated for Impairment, Allowance	14.1	14.6
Loans, Portfolio	267.7	281.9
Loans, Allowance	0.4	0.4
Total loans	7,232.10	7,132.60
Total Allowance	$18.40	$18.90	$20.50	$19.50

Loans_Summarized_Recorded_Inve

Loans - Summarized Recorded Investments, by Class of Loan, of Originated Non-Performing Loans (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$177.80	$197
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	120.8	141.4
Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	57	55.6
Commercial Real Estate [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	43.3	60.2
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	42.6	55.8
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	34.9	25.4
Residential Mortgage [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	37.5	37.6
Home Equity [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	19.4	17.9
Consumer [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$0.10	$0.10

Loans_Summarized_Recorded_Inve1

Loans - Summarized Recorded Investments, by Class of Loan, of Originated Non-Performing Loans (Parenthetical) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Government guarantees	$17.50	$17.60
Recorded investments, non-performing loans	177.8	197
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Guarantee rate	1.00%
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Guarantee rate	99.00%
Foreclosure [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investments, non-performing loans	$15.20	$18.90

Loans_Summary_of_Recorded_Inve

Loans - Summary of Recorded Investments in TDRs by Class of Loan (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	Contract	Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	74	106
Pre-Modification Outstanding Recorded Investment	$30.30	$31.90
Post-Modification Outstanding Recorded Investment	30.3	31.9
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	21	18
Pre-Modification Outstanding Recorded Investment	22.6	11.3
Post-Modification Outstanding Recorded Investment	22.6	11.3
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	53	88
Pre-Modification Outstanding Recorded Investment	7.7	20.6
Post-Modification Outstanding Recorded Investment	7.7	20.6
Commercial Real Estate [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	8	6
Pre-Modification Outstanding Recorded Investment	4.9	5
Post-Modification Outstanding Recorded Investment	4.9	5
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	8	7
Pre-Modification Outstanding Recorded Investment	10.1	3.4
Post-Modification Outstanding Recorded Investment	10.1	3.4
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	5	5
Pre-Modification Outstanding Recorded Investment	7.6	2.9
Post-Modification Outstanding Recorded Investment	7.6	2.9
Residential Mortgage [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	20	48
Pre-Modification Outstanding Recorded Investment	5.7	16.8
Post-Modification Outstanding Recorded Investment	5.7	16.8
Home Equity [Member] | Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	33	40
Pre-Modification Outstanding Recorded Investment	2	3.8
Post-Modification Outstanding Recorded Investment	$2	$3.80

Loans_Summary_of_Recorded_Inve1

Loans - Summary of Recorded Investments in TDRs by Class of Loan (Parenthetical) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	Contract	Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts	74	106
Recorded investment	$30.30	$31.90
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	21	18
Recorded investment	22.6	11.3
Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	8	6
Recorded investment	4.9	5
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	8	7
Recorded investment	10.1	3.4
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	5	5
Recorded investment	7.6	2.9
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	53	88
Recorded investment	7.7	20.6
Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	20	48
Recorded investment	5.7	16.8
Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	33	40
Recorded investment	2	3.8
Concessions Extension of Term [Member] | Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	8	4
Recorded investment	4.9	4.1
Concessions Extension of Term [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	3
Recorded investment	8.7	1
Concessions Extension of Term [Member] | Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		1
Recorded investment		0.5
Payment Deferral [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	3	1
Recorded investment	0.6	0.7
Payment Deferral [Member] | Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	3
Recorded investment	5.7
Payment Deferral [Member] | Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	12
Recorded investment	1.5	4.3
Payment Deferral [Member] | Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	2	3
Recorded investment	0.2	0.1
Combination of Concessions [Member] | Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		2
Recorded investment		0.9
Combination of Concessions [Member] | Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	1	3
Recorded investment	0.8	1.7
Combination of Concessions [Member] | Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	2	5
Recorded investment	1.9	2.9
Combination of Concessions [Member] | Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	9	26
Recorded investment	1.6	8.9
Combination of Concessions [Member] | Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	6	19
Recorded investment	0.8	1.5
Bankruptcy [Member] | Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	6	9
Recorded investment	2.4	3.1
Bankruptcy [Member] | Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	25	17
Recorded investment	1	2.1
Temporary Rate Reduction [Member] | Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	1
Recorded investment	0.2
Temporary Rate Reduction [Member] | Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts		1
Recorded investment		$0.10

Loans_Summary_of_Recorded_Inve2

Loans - Summary of Recorded Investments in TDRs by Class of Loan, Subsequently Defaulted (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
	Contracts	Contracts
Financing Receivable, Modifications [Line Items]
Number of Contracts	34	42
Recorded Investment	$10	$14.70
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	6	10
Recorded Investment	1.4	2.9
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	2	1
Recorded Investment	0.1	1.5
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	4	9
Recorded Investment	1.3	1.4
Retail Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	28	32
Recorded Investment	8.6	11.8
Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	17	24
Recorded Investment	7.4	10.9
Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts	11	8
Recorded Investment	$1.20	$0.90

Loans_Summary_of_IndividuallyE

Loans - Summary of Individually-Evaluated Impaired Loans by Class of Loan (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$239	$225.70
Recorded Investment	214.5	203
Unpaid Principal Balance	62	95.3
Recorded Investment	52.9	66.5
Unpaid Principal Balance	301	321
Recorded Investment	267.4	269.5
Related Allowance for Loan Losses	10.5	11.5
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	192.9	216.1
Recorded Investment	169.5	174.5
Related Allowance for Loan Losses	6.6	7.6
Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	54.9	57.1
Recorded Investment	53.7	55.8
Unpaid Principal Balance	23.1	52.1
Recorded Investment	16.2	27.8
Unpaid Principal Balance	78	109.2
Recorded Investment	69.9	83.6
Related Allowance for Loan Losses	1.7	4
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	60.2	51.7
Recorded Investment	56.9	48.6
Unpaid Principal Balance	8.3	21.4
Recorded Investment	6.4	17.4
Unpaid Principal Balance	68.5	73.1
Recorded Investment	63.3	66
Related Allowance for Loan Losses	2.9	3.5
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	34.5	30.2
Recorded Investment	24.5	21.4
Unpaid Principal Balance	11.9	3.6
Recorded Investment	11.8	3.5
Unpaid Principal Balance	46.4	33.8
Recorded Investment	36.3	24.9
Related Allowance for Loan Losses	2	0.1
Retail Loans [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment	18.5
Unpaid Principal Balance	108.1	104.9
Recorded Investment	97.9	95
Related Allowance for Loan Losses	3.9	3.9
Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	66.6	65.4
Recorded Investment	60	58.9
Unpaid Principal Balance	16.5	15.6
Recorded Investment	16.4	15.3
Unpaid Principal Balance	83.1	81
Recorded Investment	76.4	74.2
Related Allowance for Loan Losses	2.7	2.6
Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	22.8	21.3
Recorded Investment	19.4	18.3
Unpaid Principal Balance	2.2	2.6
Recorded Investment	2.1	2.5
Unpaid Principal Balance	25	23.9
Recorded Investment	21.5	20.8
Related Allowance for Loan Losses	$1.20	$1.30

Loans_Schedule_of_Impaired_Fin

Loans - Schedule of Impaired Financing Receivable (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$261.40	$225.10
Interest Income Recognized	1.3	1.1
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	164.3	139.4
Interest Income Recognized	0.8	0.7
Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	78	74.1
Interest Income Recognized	0.3	0.2
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	59.5	37
Interest Income Recognized	0.4	0.2
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	26.8	28.3
Interest Income Recognized	0.1	0.3
Retail Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	97.1	85.7
Interest Income Recognized	0.5	0.4
Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	75.6	69.3
Interest Income Recognized	0.4	0.3
Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	21.5	16.4
Interest Income Recognized	$0.10	$0.10

Loans_Summary_of_Aging_Informa

Loans - Summary of Aging Information by Class of Loan (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	$2,181.50	$2,200.60
Total Originated	7,232.10	7,132.60
Total loans	26,929.30	26,592
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	52.1	57.5
Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	2,129.40	2,143.10
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	5,050.60	4,932
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	9,470.40	9,404.30
Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	25,743	25,298.60
Past Due 30-89 Days	127.3	125.5
Past Due 90 Days or More	101	117
Total Past Due	228.3	242.5
Total Originated	2,133.70	2,149.20
Total Originated	6,964.40	6,850.70
Total loans	25,971.30	25,541.10
Originated [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	51	56.3
Originated [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	2,082.70	2,092.90
Originated [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	4,830.70	4,701.50
Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	7,232.10	7,132.60
Retail Loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	52.1	57.5
Retail Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	2,129.40	2,143.10
Retail Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	5,050.60	4,932
Retail Loans [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	6,899.10	6,782.40
Past Due 30-89 Days	31	34.5
Past Due 90 Days or More	34.3	33.8
Total Past Due	65.3	68.3
Total Originated	6,964.40	6,850.70
Retail Loans [Member] | Originated [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	50.6	55.8
Past Due 30-89 Days	0.3	0.4
Past Due 90 Days or More	0.1	0.1
Total Past Due	0.4	0.5
Total Originated	51	56.3
Retail Loans [Member] | Originated [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,067.50	2,079.30
Past Due 30-89 Days	5.8	5
Past Due 90 Days or More	9.4	8.6
Total Past Due	15.2	13.6
Total Originated	2,082.70	2,092.90
Retail Loans [Member] | Originated [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,781	4,647.30
Past Due 30-89 Days	24.9	29.1
Past Due 90 Days or More	24.8	25.1
Total Past Due	49.7	54.2
Total Originated	4,830.70	4,701.50
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	19,697.20	19,459.40
Total loans	19,697.20	19,459.40
Commercial [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	9,470.40	9,404.30
Commercial [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	7,405.50	7,189.60
Commercial [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Originated	2,821.30	2,865.50
Commercial [Member] | Originated [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	18,843.90	18,516.20
Past Due 30-89 Days	96.3	91
Past Due 90 Days or More	66.7	83.2
Total Past Due	163	174.2
Total Originated	19,006.90	18,690.40
Commercial [Member] | Originated [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	9,044.50	8,908
Past Due 30-89 Days	11.3	17.6
Past Due 90 Days or More	22	34.7
Total Past Due	33.3	52.3
Total Originated	9,077.80	8,960.30
Commercial [Member] | Originated [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	7,069.70	6,814.90
Past Due 30-89 Days	20.9	32.4
Past Due 90 Days or More	40.7	43.8
Total Past Due	61.6	76.2
Total Originated	7,131.30	6,891.10
Commercial [Member] | Originated [Member] | Equipment Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,729.70	2,793.30
Past Due 30-89 Days	64.1	41
Past Due 90 Days or More	4	4.7
Total Past Due	68.1	45.7
Total Originated	$2,797.80	$2,839

Loans_Summary_of_Credit_Qualit

Loans - Summary of Credit Quality Indicators by Class of Loan (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$2,181.50	$2,200.60
Financing Receivable	7,232.10	7,132.60
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	19,697.20	19,459.40
Originated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,964.40	6,850.70
Originated Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,333.30	3,241.60
Originated Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,563	2,527
Originated Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,068.10	1,082.10
Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	19,006.90	18,690.40
Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	17,960.90	17,689.50
Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	329.9	307.2
Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	714.3	679.8
Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1.8	13.9
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47.8	51.4
Financing Receivable	267.7	281.9
Acquired Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	107.2	107
Acquired Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47.7	50.5
Acquired Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	112.8	124.4
Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	690.3	769
Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	473	484.6
Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	46.5	74.4
Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	148.8	186.7
Acquired Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	22	23.3
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	9,470.40	9,404.30
Commercial Real Estate [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	9,470.40	9,404.30
Commercial Real Estate [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	9,077.80	8,960.30
Commercial Real Estate [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,864.90	8,730.90
Commercial Real Estate [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	86	82.4
Commercial Real Estate [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	126.9	135.3
Commercial Real Estate [Member] | Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		11.7
Commercial Real Estate [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	392.6	444
Commercial Real Estate [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	288.1	302.5
Commercial Real Estate [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	25.4	20.9
Commercial Real Estate [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	72.7	113.5
Commercial Real Estate [Member] | Acquired Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6.4	7.1
Commercial and Industrial [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,405.50	7,189.60
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,131.30	6,891.10
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,672.70	6,477.40
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	142.1	114.2
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	314.7	297.3
Commercial and Industrial [Member] | Originated Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1.8	2.2
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	274.2	298.5
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	178.2	174.5
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	20.5	52.8
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	59.9	55
Commercial and Industrial [Member] | Acquired Loans [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	15.6	16.2
Equipment Financing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,821.30	2,865.50
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,797.80	2,839
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,423.30	2,481.20
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	101.8	110.6
Equipment Financing [Member] | Originated Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	272.7	247.2
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23.5	26.5
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6.7	7.6
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0.6	0.7
Equipment Financing [Member] | Acquired Loans [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	16.2	18.2
Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,050.60	4,932
Residential Mortgage [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,050.60	4,932
Residential Mortgage [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,830.70	4,701.50
Residential Mortgage [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,379.10	2,280.60
Residential Mortgage [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,943.50	1,921.60
Residential Mortgage [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	508.1	499.3
Residential Mortgage [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	219.9	230.5
Residential Mortgage [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	219.9	230.5
Residential Mortgage [Member] | Acquired Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	107.2	107
Residential Mortgage [Member] | Acquired Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	47.7	50.5
Residential Mortgage [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65	73
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,129.40	2,143.10
Home Equity [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,129.40	2,143.10
Home Equity [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,082.70	2,092.90
Home Equity [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	927.2	931.5
Home Equity [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	612.4	597.1
Home Equity [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	543.1	564.3
Home Equity [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	46.7	50.2
Home Equity [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	46.7	50.2
Home Equity [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	46.7	50.2
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	52.1	57.5
Consumer [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	52.1	57.5
Consumer [Member] | Originated Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	51	56.3
Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | Low Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	27	29.5
Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | Moderate Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7.1	8.3
Consumer [Member] | Originated Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	16.9	18.5
Consumer [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1.1	1.2
Consumer [Member] | Acquired Loans [Member] | Retail Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1.1	1.2
Consumer [Member] | Acquired Loans [Member] | Retail Loans [Member] | High Risk [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$1.10	$1.20

Loans_Summarized_Activity_in_A

Loans - Summarized Activity in Accretable Yield for Acquired Loan Portfolio (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Receivables [Abstract]
Balance at beginning of period	$396.30	$639.70
Accretion	-15.3	-23.3
Reclassification from nonaccretable difference for loans with improved cash flows	0.3	5.8
Other changes in expected cash flows	-19.7	-97.8
Balance at end of period	$361.60	$524.40

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Schedule Of Stockholders Equity [Line Items]
Amount Reclassified from accumulated other comprehensive loss	($1.80)	($1.10)
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member]
Schedule Of Stockholders Equity [Line Items]
Amount Reclassified from accumulated other comprehensive loss	-0.2	-0.2
Maximum [Member] | Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member] | Interest Rate Locks [Member]
Schedule Of Stockholders Equity [Line Items]
Amount Reclassified from accumulated other comprehensive loss	$0.10	$0.10
2014 Long-Term Incentive Plan [Member]
Schedule Of Stockholders Equity [Line Items]
Additional awards under RRP	0

Stockholders_Equity_Schedule_o

Stockholders' Equity - Schedule of Accumulated Other Comprehensive Loss (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Beginning Balance	($168.20)	($155.10)
Other comprehensive income (loss) before reclassifications	25.8	16.5
Amounts reclassified from AOCL	1.8	1.1
Current period other comprehensive income (loss)	27.6	17.6
Accumulated Other Comprehensive Income Loss Net Of Tax Ending Balance	-140.6	-137.5
Pension and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Beginning Balance	-142.9	-85
Amounts reclassified from AOCL	1.1	0.6
Current period other comprehensive income (loss)	1.1	0.6
Accumulated Other Comprehensive Income Loss Net Of Tax Ending Balance	-141.8	-84.4
Net Unrealized Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Beginning Balance	-3.7	-46.5
Other comprehensive income (loss) before reclassifications	26.2	16.6
Amounts reclassified from AOCL		-0.1
Current period other comprehensive income (loss)	26.2	16.5
Accumulated Other Comprehensive Income Loss Net Of Tax Ending Balance	22.5	-30
Net Unrealized Gain (Losses) On Securities Transferred To Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Beginning Balance	-21.5	-23.3
Amounts reclassified from AOCL	0.5	0.4
Current period other comprehensive income (loss)	0.5	0.4
Accumulated Other Comprehensive Income Loss Net Of Tax Ending Balance	-21	-22.9
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Beginning Balance	-0.1	-0.3
Other comprehensive income (loss) before reclassifications	-0.4	-0.1
Amounts reclassified from AOCL	0.2	0.2
Current period other comprehensive income (loss)	-0.2	0.1
Accumulated Other Comprehensive Income Loss Net Of Tax Ending Balance	($0.30)	($0.20)

Stockholders_Equity_Summary_of

Stockholders' Equity - Summary of Amounts Reclassified from AOCL (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	($89.70)	($80.80)
Income tax expense	30.5	27.7
Net income	-59.2	-53.1
Interest expense - notes and debentures	7.4	5.9
Total reclassifications for the period	-1.8	-1.1
Pension and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss	-2	-1.3
Prior service credit	0.3	0.3
Income before income tax expense	-1.7	-1
Income tax expense	0.6	0.4
Net income	-1.1	-0.6
Total reclassifications for the period	-1.1	-0.6
Net Unrealized Gains (Losses) on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense		0.1
Net income		0.1
Total reclassifications for the period		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	-0.8	-0.7
Income tax expense	0.3	0.3
Net income	-0.5	-0.4
Total reclassifications for the period	-0.5	-0.4
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	-0.3	-0.3
Income tax expense	0.1	0.1
Net income	-0.2	-0.2
Total reclassifications for the period	-0.2	-0.2
Net Unrealized Gains (Losses) on Derivatives Accounted for as Cash Flow Hedges [Member] | Interest Rate Swaps [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Interest expense - notes and debentures	($0.30)	($0.30)

Earnings_Per_Common_Share_Basi

Earnings Per Common Share - Basic and Diluted Earnings Per Share, Reflecting Application of Two-Class Method (Detail) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$59.20	$53.10
Dividends and undistributed earnings allocated to participating securities	-0.3	-0.2
Income attributable to common shareholders	$58.90	$52.90
Average common shares outstanding for basic EPS	299.1	297.7
Effect of dilutive equity-based awards	0	0
Average common and common-equivalent shares for diluted EPS	299.1	297.7
Basic EPS	$0.20	$0.18
Diluted EPS	$0.20	$0.18

Earnings_Per_Common_Share_Addi

Earnings Per Common Share - Additional Information (Detail)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Anti-dilutive equity-based awards excluded from calculation of diluted EPS	21.6	18

Goodwill_and_Other_Acquisition1

Goodwill and Other Acquisition-Related Intangible Assets - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$1,954,500,000		$1,954,500,000
Tax deductible goodwill amount	12,800,000		13,000,000
Other acquisition-related intangible assets	142,100,000		148,000,000
Amortization of other acquisition-related intangible assets	5,900,000	6,200,000
Amortization expense attributable to other acquisition-related intangible assets, 2015	23,800,000
Amortization expense attributable to other acquisition-related intangible assets, 2016	22,700,000
Amortization expense attributable to other acquisition-related intangible assets, 2017	21,600,000
Amortization expense attributable to other acquisition-related intangible assets, 2018	10,200,000
Amortization expense attributable to other acquisition-related intangible assets, 2019	9,400,000
Amortization expense attributable to other acquisition-related intangible assets, 2020	9,000,000
Impairment losses relating to goodwill or other acquisition-related intangible assets	0	0
Trade Name Intangible [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	85,800,000
Core Deposit Intangibles [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	33,300,000
Customer Relationships [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	22,100,000
Insurance Relationships [Member]
Goodwill And Other Intangible Assets [Line Items]
Other acquisition-related intangible assets	900,000
Commercial Banking Loan [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	1,220,000,000		1,220,000,000
Retail Banking [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	681,900,000		681,900,000
Wealth Management [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$49,800,000		$49,800,000

Employee_Benefit_Plans_Additio

Employee Benefit Plans - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended
In Millions, except Share data, unless otherwise specified	Apr. 30, 2007	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Apr. 30, 2007
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
Employer contributions		$40
ESOP, shares to be purchased	10,453,575
ESOP loan	216.8	192.1			216.8
Loan repayments expected annual through 2036		18.8
Cash dividends paid on unallocated ESOP shares		1.3
Minimum age requirement to participate in ESOP		18 years
Minimum amount of hours within in 12 months of hire needed to participate in ESOP		1,000
ESOP common stock allocated		2,874,734
Unallocated common stock of Employee Stock Ownership Plan, shares		7,578,841		7,700,000
Fair value of deferred ESOP shares		115.2
ESOP compensation expense		1.3	1.3
Chittenden Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit income		0.1
Expected employer contributions		$10
Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of covered employee's eligible compensation		3.00%

Employee_Benefit_Plans_Compone

Employee Benefit Plans - Components of Net Periodic Benefit (Income) Expense and Other Amounts (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$4.80	$4.80
Expected return on plan assets	-7.2	-7.1
Recognized net actuarial loss	1.5	1
Settlements	0.1	0.1
Net periodic benefit (income) expense	-0.8	-1.2
Net actuarial loss	-1.5	-1
Total pre-tax changes recognized in other comprehensive income	-1.5	-1
Total recognized in net periodic benefit (income) expense and other comprehensive income	-2.3	-2.2
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1
Interest cost	0.1	0.2
Recognized net actuarial loss	0.1
Recognized prior service credit	-0.1	-0.1
Net periodic benefit (income) expense	0.2	0.1
Net actuarial loss	-0.1
Prior service credit	0.1	0.1
Total pre-tax changes recognized in other comprehensive income		0.1
Total recognized in net periodic benefit (income) expense and other comprehensive income	$0.20	$0.20

Legal_Proceedings_Additional_I

Legal Proceedings - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
Waterford Township Police & Fire Retirement [Member]
Loss Contingencies [Line Items]
Complaint filed date	25-Feb-10
Yourgal [Member]
Loss Contingencies [Line Items]
Complaint filed date	29-Mar-10
Marta Farb, on Behalf of Herself and All Others Similarly Situated Case [Member]
Loss Contingencies [Line Items]
Complaint filed date	22-Apr-11
Dismissal date	28-Jul-14

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value transfers between level 1 and level 2	$0	$0
Maximum [Member] | Risk Participation Agreements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Fair Value, Net	$100,000		100,000
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_Assets

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	$8.30	$8.30
Securities available for sale, at fair value	4,356.80	3,993.70
Other assets	786.3	719.9
Fair Values, Assets	178	132.4
Fair Values, Liabilities	130.3	97
Fair value of total assets measured at fair value on a recurring basis	4,581	4,171.50
Fair value of total liabilities measured at fair value on a recurring basis	130.3	97
US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	8.3	8.3
Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	30.7	30.3
Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	5.8	6
Equity Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.4	0.8
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	301.1	56.8
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	4,055.50	3,936.70
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	0.2
Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	176.1	131.1
Fair Values, Liabilities	128.5	95.8
Forward Commitments to Sell Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	0.9	0.5
Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	1	0.8
Fair Values, Liabilities	0.5	0.5
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	1.3	0.7
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	341.5	96.2
Level 1 [Member] | US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	8.3	8.3
Level 1 [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	30.7	30.3
Level 1 [Member] | Equity Mutual Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.4	0.8
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	301.1	56.8
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	4,239.50	4,075.30
Fair value of total liabilities measured at fair value on a recurring basis	130.3	97
Level 2 [Member] | Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	5.8	6
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	4,055.50	3,936.70
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	0.2
Level 2 [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	176.1	131.1
Fair Values, Liabilities	128.5	95.8
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	0.9	0.5
Level 2 [Member] | Foreign Exchange Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Values, Assets	1	0.8
Fair Values, Liabilities	0.5	0.5
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	$1.30	$0.70

Fair_Value_Measurements_Assets1

Fair Value Measurements - Assets Measured at Fair Value on Non-Recurring Basis (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	$49.70	$34.20
Impaired loans	52.9	66.5
REO and repossessed assets	31	27.1
Total assets measured at fair value on non-recurring basis	133.6	127.8
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale	49.7	34.2
Total assets measured at fair value on non-recurring basis	49.7	34.2
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	52.9	66.5
REO and repossessed assets	31	27.1
Total assets measured at fair value on non-recurring basis	$83.90	$93.60

Fair_Value_Measurements_Assets2

Fair Value Measurements - Assets Measured at Fair Value on Non-Recurring Basis (Parenthetical) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$52,900,000		$66,500,000
Charge-offs to the allowance for loan losses related to loans	9,800,000	9,500,000
Repossessed assets	4,300,000		2,500,000
Write downs and net loss on sale of foreclosed/repossessed assets charged to non-interest expense total	217,600,000	216,700,000
Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments	0	0
Real estate owned	16,500,000
Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	34,400,000
Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Real estate owned	10,200,000		11,000,000
Write Down Net Loss on Sale of Foreclosed Assets [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	400,000	400,000
Retail Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	18,500,000
Charge-offs to the allowance for loan losses related to loans	700,000	4,000,000
Retail Loans [Member] | Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	16,400,000		15,300,000
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	2,200,000	4,000,000
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	$600,000	$700,000

Fair_Value_Measurements_Carryi

Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$306.80	$345.10
Short-term investments	250	668.6
Securities held to maturity	897.4	834.3
FHLB and FRB stock	314.2	175.7
Time deposits	5,301.60	5,230.70
FHLB advances	2,165.90	2,291.70
Federal funds purchased	496	913
Customer repurchase agreements	1	1
Notes and debentures	1,042.30	1,033.50
Securities purchased under agreements to resell		100
Commercial Customers [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	480	486
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	306.8	345.1
Short-term investments	250	668.6
Securities held to maturity	897.4	834.3
FHLB and FRB stock	314.2
Total loans, net	26,675.50	26,327.20
Time deposits	5,301.60	5,230.70
Other deposits	21,848.30	20,907.50
FHLB advances	2,165.90	2,291.70
Federal funds purchased	496	913
Notes and debentures	1,042.30	1,033.50
Securities purchased under agreements to resell		100
FHLB stock		175.7
Carrying Amount [Member] | Commercial Customers [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	480	486
Carrying Amount [Member] | Institutional Counterparties [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	1	1
Estimated Fair Value Measurements [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	306.8	345.1
Short-term investments	250	668.6
Securities held to maturity	943.9	881.6
FHLB and FRB stock	314.2
Total loans, net	26,788.90	26,307.30
Time deposits	5,336.60	5,262.60
Other deposits	21,848.30	20,907.50
FHLB advances	2,173.40	2,298.50
Federal funds purchased	496	913
Notes and debentures	1,043.80	1,040.80
Securities purchased under agreements to resell		100
FHLB stock		175.7
Estimated Fair Value Measurements [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	306.8	345.1
Estimated Fair Value Measurements [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	250	668.6
Securities held to maturity	942.4	880.1
FHLB and FRB stock	314.2
Total loans, net	4,951	4,798.50
Time deposits	5,336.60	5,262.60
Other deposits	21,848.30	20,907.50
FHLB advances	2,173.40	2,298.50
Federal funds purchased	496	913
Notes and debentures	1,043.80	1,040.80
Securities purchased under agreements to resell		100
FHLB stock		175.7
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	21,837.90	21,508.80
Estimated Fair Value Measurements [Member] | Commercial Customers [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	480	486
Estimated Fair Value Measurements [Member] | Commercial Customers [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	480	486
Estimated Fair Value Measurements [Member] | Institutional Counterparties [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	1	1
Estimated Fair Value Measurements [Member] | Institutional Counterparties [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer repurchase agreements	$1	$1

Fair_Value_Measurements_Carryi1

Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Parenthetical) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value Disclosures [Abstract]
Impaired loans	$52.90	$66.50

Derivative_Financial_Instrumen2

Derivative Financial Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2012
Derivative [Line Items]
Aggregate fair value of derivative instruments	$10.60
Collateral posted in normal course of business	10.1
Additional collateral required if senior unsecured debt had fallen below investment grade	0.5
Subordinated notes	125
Subordinated notes fixed interest rate	5.80%
Subordinated Notes [Member]
Derivative [Line Items]
LIBOR basis points	Three-month LIBOR
Basis points	0.69%
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative; fixed-rate (Pay fixed/receive floating interest Interest rate swap)	1.99%
Notional amount of derivatives	125
Interest Rate Swaps [Member] | Fair Value [Member]
Derivative [Line Items]
Subordinated notes	400
LIBOR basis points	Three-month LIBOR
Basis points	1.27%
Notional amount of derivatives	375
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		0.9
Notes and debentures	$500
Period hedged items affected earnings, years		10 years

Derivative_Financial_Instrumen3

Derivative Financial Instruments and Hedging Activities - Schedule of Notional Amounts and Fair Values of Derivatives Outstanding (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Forward commitments to sell residential mortgage loans	$154.30	$117.30
Total, Derivatives Designated as Hedging Instruments, Fair Values, Assets	23.7	15.1
Total Derivatives Fair value,Assets	178	132.4
Total, Derivatives Not Designated as Hedging Instruments, Fair Values, Liabilities	129	96
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities	1.3	1
Fair Values, Liabilities	130.3	97
Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	120.9	57.5
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	1.3	0.7
Fair Values, Liabilities	1.3	0.7
Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	75.8	35.3
Forward commitments to sell residential mortgage loans	0.9	0.5
Risk Participation Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	199	150.1
Interest Rate Swaps [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	125
Interest Rate Swaps [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375
Interest Rate Swaps [Member] | Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	3,871.50	3,380.20
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Assets	149.1	104.2
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	1.7	8.3
Interest Rate Swaps [Member] | Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	3,871.50	3,380.20
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Assets	3.3	11.8
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Liabilities	125.5	86.5
Interest Rate Swaps [Member] | Subordinated Notes [Member] | Cash Flow [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	125	125
Derivative Assets Designated as Hedging Instruments, Fair Values, Assets	0	0
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities	1.3	1
Interest Rate Swaps [Member] | Subordinated Notes [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	375	375
Derivative Assets Designated as Hedging Instruments, Fair Values, Assets	23.7	15.1
Total, Derivatives Designated as Hedging Instruments, Fair Values, Liabilities	0	0
Foreign Exchange Contracts [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Amounts	51.6	49.6
Derivatives Not Designated as Hedging Instruments, Foreign exchange contracts, Fair Values, Assets	1	0.8
Total Derivatives Fair value,Assets	1	0.8
Derivatives Not Designated as Hedging Instruments, Interest rate swaps, Fair Values, Liabilities	0.5	0.5
Fair Values, Liabilities	$0.50	$0.50

Derivative_Financial_Instrumen4

Derivative Financial Instruments and Hedging Activities - Schedule of Notional Amounts and Fair Values of Derivatives Outstanding (Parenthetical) (Detail) (Maximum [Member], Derivatives Not Designated as Hedging Instruments [Member], Risk Participation Agreements [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Maximum [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value of derivatives	$0.10	$0.10

Derivative_Financial_Instrumen5

Derivative Financial Instruments and Hedging Activities - Impact of Derivatives on Pre-Tax Income and Accumulated Other Comprehensive Loss (Detail) (USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	$7.50	$1
Amount of Pre-Tax Gain (Loss) Recognized in AOCL	-0.6		-0.1
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	5.3	1.3
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	-0.5	-0.2
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	0.4	0.1
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Commercial Customers [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	67.7	41.1
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Institutional Counterparties [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	-62.5	-39.7
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	0.2
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	2.2	-0.3
Amount of Pre-Tax Gain (Loss) Recognized in AOCL	-0.6		-0.1
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Cash Flow [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	-0.3	-0.3
Amount of Pre-Tax Gain (Loss) Recognized in AOCL	-0.6		-0.1
Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member] | Fair Value [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of Pre-Tax Gain (Loss) Recognized in Earnings	$2.50

Derivative_Financial_Instrumen6

Derivative Financial Instruments and Hedging Activities - Impact of Derivatives on Pre-Tax Income and Accumulated Other Comprehensive Loss (Parenthetical) (Detail) (Maximum [Member], Derivatives Designated as Hedging Instruments [Member], Treasury Forward Interest Rate Locks ("T-Locks") [Member], USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Maximum [Member] | Derivatives Designated as Hedging Instruments [Member] | Treasury Forward Interest Rate Locks ("T-Locks") [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (loss ) on derivative	$0.10	$0.10

Balance_Sheet_Offsetting_Summa

Balance Sheet Offsetting - Summary of Gross Presentation, Financial Instruments that are Eligible for Offset in Consolidated Statement of Condition (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Offsetting Assets And Liabilities [Line Items]
Financial liabilities, Gross Amount Recognized	$128.30
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	128.3
Financial liabilities, Financial Instruments	-27
Financial liabilities, Collateral	-100.3
Financial liabilities, Net Amount	1
Financial assets, Gross Amount Recognized	28	127.7
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	28	127.7
Financial assets, Financial Instruments	-27	-24.1
Financial assets, Collateral		-102.8
Financial assets, Net Amount	1	0.8
Financial liabilities, Gross Amount Recognized	1	1
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	1	1
Financial liabilities, Financial Instruments	0	0
Financial liabilities, Collateral	-1	-1
Financial liabilities, Net Amount	0	0
Financial assets, Gross Amount Recognized	178	132.4
Financial liabilities, Gross Amount Recognized	130.3	97
Financial assets, Gross Amount Recognized		100
Financial assets, Gross Amount Offset		0
Financial assets, Net Amount Presented		100
Financial assets, Financial Instruments		0
Financial assets, Collateral		-100
Financial assets, Net Amount		0
Foreign Exchange Contracts [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	1	0.8
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	1	0.8
Financial assets, Net Amount	1	0.8
Financial liabilities, Gross Amount Recognized	0.5	0.5
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	0.5	0.5
Financial liabilities, Net Amount	0.5	0.5
Counterparty A [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	1	2.7
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	1	2.7
Financial assets, Financial Instruments	-1	-2.7
Financial liabilities, Gross Amount Recognized	11.8	11.8
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	11.8	11.8
Financial liabilities, Financial Instruments	-1	-2.7
Financial liabilities, Collateral	-10.8	-9.1
Counterparty B [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.3	1.5
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.3	1.5
Financial assets, Financial Instruments	-0.3	-1.5
Financial liabilities, Gross Amount Recognized	13.2	11.8
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	13.2	11.8
Financial liabilities, Financial Instruments	-0.3	-1.5
Financial liabilities, Collateral	-12.9	-10.3
Counterparty C [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.3	2.5
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.3	2.5
Financial assets, Financial Instruments	-0.3	-2.5
Financial liabilities, Gross Amount Recognized	6.3	4.5
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	6.3	4.5
Financial liabilities, Financial Instruments	-0.3	-2.5
Financial liabilities, Collateral	-6	-1.9
Financial liabilities, Net Amount		0.1
Counterparty D [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.7	3.2
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.7	3.2
Financial assets, Financial Instruments	-0.7	-0.4
Financial assets, Collateral		-2.8
Financial liabilities, Gross Amount Recognized	10	0.4
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	10	0.4
Financial liabilities, Financial Instruments	-0.7	-0.4
Financial liabilities, Collateral	-8.8
Financial liabilities, Net Amount	0.5
Counterparty E [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	24.2	15.7
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	24.2	15.7
Financial assets, Financial Instruments	-24.2	-15.7
Financial liabilities, Gross Amount Recognized	79.9	47.8
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	79.9	47.8
Financial liabilities, Financial Instruments	-24.2	-15.7
Financial liabilities, Collateral	-55.7	-32.1
Other Counterparties [Member] | Interest Rate Swaps [Member]
Offsetting Assets And Liabilities [Line Items]
Financial assets, Gross Amount Recognized	0.5	1.3
Financial assets, Gross Amount Offset	0	0
Financial assets, Net Amount Presented	0.5	1.3
Financial assets, Financial Instruments	-0.5	-1.3
Financial liabilities, Gross Amount Recognized	5.6	11.2
Financial liabilities, Gross Amount Offset	0	0
Financial liabilities, Net Amount Presented	5.6	11.2
Financial liabilities, Financial Instruments	-0.5	-1.3
Financial liabilities, Collateral	-5.1	-8.9
Financial liabilities, Net Amount		$1