UIL (UIL) 10-K 26 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 20, 2015	Jun. 30, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	UIL HOLDINGS CORP
Entity Central Index Key	1082510
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$2,137,418,018
Entity Common Stock, Shares Outstanding		56,546,266
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14

CONSOLIDATED_STATEMENT_OF_INCO

CONSOLIDATED STATEMENT OF INCOME (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENT OF INCOME [Abstract]
Operating Revenues	$1,631,943	$1,618,716	$1,486,501
Operation
Purchased power	173,059	139,135	154,546
Natural gas purchased	426,379	438,189	370,234
Operation and maintenance	399,560	384,029	356,277
Transmission wholesale	88,370	88,206	79,469
Depreciation and amortization (Note F)	151,557	189,856	181,348
Taxes - other than income taxes (Note F)	138,271	130,458	114,037
Rate case disallowances	0	8,354	0
Acquisition-related expenses (Note A)	7,344	0	0
Total Operating Expenses	1,384,540	1,378,227	1,255,911
Operating Income	247,403	240,489	230,590
Other Income and (Deductions), net
Acquisition-related bridge facility fees (Note A)	-15,795	0	0
Other income and (deductions) (Note F)	18,020	20,633	25,246
Total Other Income and (Deductions), net	2,225	20,633	25,246
Interest Charges, net
Interest on long-term debt	89,524	87,232	86,469
Other interest, net	4,417	2,106	3,636
Interest Charges, gross	93,941	89,338	90,105
Amortization of debt expense and redemption premiums	2,439	2,431	2,437
Total Interest Charges, net	96,380	91,769	92,542
Income from Equity Investments	13,893	15,272	15,273
Income Before Income Taxes	167,141	184,625	178,567
Income Taxes (Note E)	57,562	69,308	74,866
Net Income (Loss)	109,579	115,317	103,701
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	-14	52	64
Net Income attributable to UIL Holdings	$109,593	$115,265	$103,637
Average Number of Common Shares Outstanding - Basic (in shares)	56,834	52,415	50,831
Average Number of Common Shares Outstanding - Diluted (in shares)	57,136	52,711	51,108
Earnings Per Share of Common Stock - Basic (Note A) (in dollars per share)	$1.93	$2.20	$2.04
Earnings Per Share of Common Stock - Diluted (Note A) (in dollars per share)	$1.92	$2.18	$2.02
Cash Dividends Declared per share of Common Stock (in dollars per share)	$1.73	$1.73	$1.73

CONSOLIDATED_STATEMENT_OF_COMP

CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME [Abstract]
Net Income	$109,579	$115,317	$103,701
Other Comprehensive Income (Loss), net of income taxes
Changes in unrealized gains (losses) related to pension and other post-retirement benefit plans	-815	1,008	-90
Other	3	-24	16
Total Other Comprehensive Income (Loss), net of income taxes	-812	984	-74
Comprehensive Income	108,767	116,301	103,627
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	-14	52	64
Comprehensive Income Attributable to UIL Holdings	$108,781	$116,249	$103,563

CONSOLIDATED_STATEMENT_OF_CASH

CONSOLIDATED STATEMENT OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Cash Flows From Operating Activities
Net income	$109,579		$115,317		$103,701
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	153,996		192,287		183,785
Deferred income taxes	55,959		71,095		68,121
Allowance for funds used during construction (AFUDC) - equity	-8,814		-10,811		-7,480
Stock-based compensation expense (Note A)	5,691		5,283		4,907
Pension expense	31,344		48,798		39,906
Undistributed (earnings) losses in equity investments	-13,294		-15,304		-15,440
Rate case disallowances (Note C)	0		8,354		0
Other regulatory activity, net	41,708		10,945		-16,102
Other non-cash items, net	-4,248		-757		-7,049
Changes in:
Accounts receivable, net	15,089		-9,711		-51,301
Unbilled revenues	-2,766		-9,058		-11,999
Natural gas in storage	2,394		4,850		26,748
Cash distribution received from GenConn	14,004		15,321		19,672
Prepayments	4,350		-3,082		3,450
Accounts payable	49,721		-12,094		-20,221
Interest accrued	504		-494		900
Taxes accrued/refundable, net	-10,273		-1,302		60,614
Accrued liabilities	-8,940		-2,504		16,271
Accrued pension	-35,594		-74,666		-59,317
Accrued other post-employment benefits	-5,016		-8,052		-3,673
Other assets	-1,394		446		3,361
Other liabilities	8,182		347		-4,913
Total Adjustments	292,603		209,891		230,240
Net Cash provided by Operating Activities	402,182		325,208		333,941
Cash Flows from Investing Activities
Plant expenditures including AFUDC debt	-312,153	[1]	-305,178	[1]	-288,633	[1]
Acquisition of Milford LNG	-20,321		0		0
Cash distributions from GenConn	3,928		6,494		1,872
Changes in restricted cash	995		759		3,717
Deposits in New England East West Solution (NEEWS) (Note C)	-8,437		-1,636		-24,059
Other	690		360		844
Net Cash provided by (used in) Investing Activities	-335,298		-299,201		-306,259
Cash Flows from Financing Activities
Issuance of common stock	0		206,516		1,943
Issuances of long-term debt	0		135,000		203,500
Payments on long-term debt	-11,455		-41,455		-109,955
Line of credit borrowings (repayments), net	89,000		-187,000		-48,000
Payment of common stock dividend	-97,708		-87,602		-87,490
Other	-295		-170		-822
Net Cash provided by (used in) Financing Activities	-20,458		25,289		-40,824
Unrestricted Cash and Temporary Cash Investments:
Net change for the period	46,426		51,296		-13,142
Balance at beginning of period	69,153		17,857		30,999
Balance at end of period	115,579		69,153		17,857
Cash paid during the period for:
Interest (net of amount capitalized)	85,317		83,259		81,658
Income taxes	7,594		5,735		4,750
Non-cash investing activity:
Plant expenditures included in ending accounts payable	36,056		33,145		47,475
Plant expenditures funded by deposits in NEEWS	0		-18,469		-6,346
Deposits in New England East West Solution (NEEWS)	$0		$18,469		$6,346
[1]	Capital expenditures are shown on a cash basis. Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.

CONSOLIDATED_BALANCE_SHEET

CONSOLIDATED BALANCE SHEET (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Current Assets
Unrestricted cash and temporary cash investments	$115,579		$69,153
Restricted cash	1,051		2,046
Accounts receivable less allowance of $8,881 and $11,545, respectively	232,887		245,252
Unbilled revenues	95,816		93,050
Current regulatory assets (Note A)	92,764		332,391
Natural gas in storage, at average cost	86,428		79,917
Deferred income taxes	0		21,742
Refundable taxes	15,211		8,244
Current portion of derivative assets (Note A)	6,849		9,098
Prepayments	10,696		14,989
Other	12,815		12,122
Total Current Assets	670,096		888,004
Other investments
Equity investment in GenConn (Note A)	114,195		118,241
Other	25,777		26,348
Total Other investments	139,972		144,589
Net Property, Plant and Equipment (Note A)	3,292,690		3,068,680
Regulatory Assets (Note A)	687,198		703,739
Deferred Charges and Other Assets
Unamortized debt issuance expenses	13,571		15,518
Other long-term receivable	1,490		1,496
Derivative assets (Note A)	20,421		44,349
Goodwill	266,205		266,205
Other	20,292		11,640
Total Deferred Charges and Other Assets	321,979		339,208
Total Assets	5,111,935	[1]	5,144,220	[2]
Current Liabilities
Line of credit borrowings	89,000		0
Current portion of long-term debt	6,526	[3]	11,834	[3]
Accounts payable	217,700		164,416
Dividends payable	24,428		24,392
Accrued liabilities	71,182		78,125
Current regulatory liabilities (Note A)	17,026		261,729
Taxes accrued	20,184		23,490
Interest accrued	22,437		21,933
Deferred income taxes	3,767		0
Current portion of derivative liabilities (Note A)	23,308		26,904
Total Current Liabilities	495,558		612,823
Deferred Income Taxes	585,335		540,542
Regulatory Liabilities (Note A)	491,896		445,092
Other Noncurrent Liabilities
Pension accrued	265,009		170,853
Other post-retirement benefits accrued	85,777		78,539
Derivative liabilities (Note A)	61,766		169,327
Other	46,924		49,047
Total Other Noncurrent Liabilities	459,476		467,766
Commitments and Contingencies (Note J)
Capitalization (Note B)
Long-term debt, net of unamortized discount and premium	1,711,349		1,723,842
Preferred Stock, not subject to mandatory redemption	119		340
Common Stock Equity
Common stock	1,149,985		1,145,950
Paid-in capital	21,587		22,272
Retained earnings	196,907		185,058
Accumulated other comprehensive income (loss)	-277		535
Net Common Stock Equity	1,368,202		1,353,815
Total Capitalization	3,079,670		3,077,997
Total Liabilities and Capitalization	$5,111,935		$5,144,220
[1]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2014.
[2]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2013 and 2012
[3]	Includes the current portion of unamortized premium.

CONSOLIDATED_BALANCE_SHEET_Par

CONSOLIDATED BALANCE SHEET (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current Assets
Allowance for doubtful accounts receivable	$8,881	$11,545

Consolidated_Statement_of_Chan

Consolidated Statement of Changes in Shareholders' Equity (USD $)		Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
In Thousands, except Share data
Balance at Dec. 31, 2011		$931,153	$19,791	$143,792	($375)	$1,094,361
Balance (in shares) at Dec. 31, 2011	[1]	50,645,490
Net income				103,701		103,701
Cash dividends on common stock				-87,529		-87,529
Preferred stock dividends of subsidiary, noncontrolling interests				-64		-64
Issuance of common stock - no par value		5,549				5,549
Issuance of common stock - no par value (in shares)	[1]	229,093
Stock based compensation			609			609
Other comprehensive income (loss), net					-74	-74
Balance at Dec. 31, 2012		936,702	20,400	159,900	-449	1,116,553
Balance (in shares) at Dec. 31, 2012	[1]	50,874,583
Net income				115,317		115,317
Cash dividends on common stock				-90,107		-90,107
Preferred stock dividends of subsidiary, noncontrolling interests				-52		-52
Issuance of common stock - no par value		209,248				209,248
Issuance of common stock - no par value (in shares)	[1]	5,879,260
Stock based compensation			1,872			1,872
Other comprehensive income (loss), net					984	984
Balance at Dec. 31, 2013		1,145,950	22,272	185,058	535	1,353,815
Balance (in shares) at Dec. 31, 2013	[1]	56,753,843
Net income				109,579		109,579
Cash dividends on common stock				-97,744		-97,744
Preferred stock dividends of subsidiary, noncontrolling interests				14		14
Issuance of common stock - no par value		4,035				4,035
Issuance of common stock - no par value (in shares)	[1]	100,616
Stock based compensation			-685			-685
Other comprehensive income (loss), net					-812	-812
Balance at Dec. 31, 2014		$1,149,985	$21,587	$196,907	($277)	$1,368,202
Balance (in shares) at Dec. 31, 2014	[1]	56,854,459
[1]	There were 125,000,000 shares authorized in 2014 and 2013.

Consolidated_Statement_of_Chan1

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statement of Changes in Shareholders' Equity [Abstract]
Cash dividends on common stock (in dollars per share)	$1.73	$1.73	$1.73
Common stock issued (in shares)	83,759	5,797,393	119,627
Other comprehensive income (loss), net of deferred income taxes	($541)	$656	($49)
Common stock, shares authorized (in shares)	125,000,000	125,000,000

STATEMENT_OF_ACCOUNTING_POLICI

STATEMENT OF ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2014
STATEMENT OF ACCOUNTING POLICIES [Abstract]
STATEMENT OF ACCOUNTING POLICIES	(A)  STATEMENT OF ACCOUNTING POLICIES
	UIL Holdings is headquartered in New Haven, Connecticut, where its senior management maintains offices and is responsible for overall planning, operating and financial functions.  The primary business of UIL Holdings is ownership of its operating regulated utility businesses.  The utility businesses consist of the electric distribution and transmission operations of The United Illuminating Company (UI) and the natural gas transportation, distribution and sales operations of The Southern Connecticut Gas Company (SCG), Connecticut Natural Gas Corporation (CNG) and The Berkshire Gas Company (Berkshire, and together with SCG and CNG, the Gas Companies).
	UI is also a party to a joint venture with certain affiliates of NRG Energy, Inc. (NRG affiliates) pursuant to which UI holds 50% of the membership interests in GCE Holding LLC, whose wholly owned subsidiary, GenConn Energy LLC (collectively with GCE Holding LLC, GenConn) operates peaking generation plants in Devon, Connecticut (GenConn Devon) and Middletown, Connecticut (GenConn Middletown).
	Accounting Records
	The accounting records of UIL Holdings are maintained in conformity with generally accepted accounting principles in the United States of America (GAAP).
	The accounting records for UI and the Gas Companies are also maintained in accordance with the uniform systems of accounts prescribed by the Federal Energy Regulatory Commission (FERC), the Connecticut Public Utilities Regulatory Authority (PURA), and the Massachusetts Department of Public Utilities (DPU), as applicable.
	Basis of Presentation
	The financial statements of UIL Holdings are prepared on a consolidated basis and therefore include the accounts of UIL Holdings’ majority-owned subsidiaries noted above.  Intercompany accounts and transactions have been eliminated in consolidation.
	The preparation of financial statements in conformity with GAAP requires management to use estimates and assumptions that affect (1) the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and (2) the reported amounts of revenues and expenses during the reporting period.  Actual results could differ from those estimates.
	Certain immaterial amounts that were reported as such in the Consolidated Financial Statements in previous periods have been reclassified to conform to the current presentation.
	Philadelphia Gas Works
	On March 2, 2014, UIL Holdings entered into an Asset Purchase Agreement (the Asset Purchase Agreement) with the City of Philadelphia pursuant to which UIL Holdings, through a wholly-owned subsidiary, would acquire the operating assets and assume certain liabilities of Philadelphia Gas Works for an initial purchase price of $1.86 billion, subject to adjustment (Acquisition).
	The Acquisition was subject to the satisfaction or waiver of certain customary and other closing conditions for transactions of this type, including approval from the Philadelphia City Council.  On October 27, 2014, the City Council announced that it would not endorse the Acquisition.  In light of the City Council’s announcement, on December 4, 2014 we exercised our contractual right to terminate the Asset Purchase Agreement.
	As of December 31, 2014, UIL Holdings incurred pre-tax acquisition-related expenses of approximately $23.1 million, $7.3 million of which represents legal, investment banking, and due diligence costs that are included in operating expenses and $15.8 million of which are fees associated with a Bridge Term Loan Agreement (Bridge Facility) that is included in other income and (deductions) in the Consolidated Statement of Income.  See Note (D) “Short-Term Credit Arrangements” for additional information about the Bridge Facility.
	Milford LNG Purchase
	On July 31, 2014, United Resources, Inc., a wholly owned subsidiary of UIL Holdings, purchased from Iberdrola USA, Inc. and certain of its subsidiaries, all of the outstanding equity of certain entities (the Purchased Entities) owning (a) a 14.6 million gallon liquefied natural gas (LNG) storage tank operated by SCG and located on property owned by SCG in Milford, Connecticut (the Tank), (b) certain equipment, materials and supplies used in or useful for the operation of the Tank (together with the Tank, the Assets) and (c) the LNG inventory, for a cash purchase price of approximately $20.3 million.  The structure and the pricing of the transaction are intended to maintain the current regulatory structure of the Purchased Entities and the Assets, and have no impact on customers.  The Assets earn a rate of return equal to SCG’s allowed rate of return.
	Allowance for Funds Used During Construction
	In accordance with the uniform systems of accounts, the Company capitalizes allowance for funds used during construction (AFUDC), which represents the approximate cost of debt and equity capital devoted to plant under construction.  The portion of the allowance applicable to borrowed funds and the allowance applicable to equity funds are presented as other income in the Consolidated Statement of Income.  Although the allowance does not represent current cash income, it has been recoverable under the ratemaking process over the service lives of the related properties.  Weighted-average AFUDC rates for 2014, 2013 and 2012 were 6.12%, 9.63% and 5.61%, respectively.
	Asset Retirement Obligations
	The fair value of the liability for an asset retirement obligation (ARO) and/or a conditional ARO is recorded in the period in which it is incurred and the cost is capitalized by increasing the carrying amount of the related long-lived asset.  The liability is adjusted to its present value periodically over time, and the capitalized cost is depreciated over the useful
	life of the related asset.  Upon settlement, the obligation is settled either at its recorded amount or a gain or a loss is incurred.  Any timing differences between rate recovery and depreciation expense are deferred as either a regulatory asset or a regulatory liability.
	The term conditional ARO refers to an entity's legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within the control of the entity.  If an entity has sufficient information to reasonably estimate the fair value of the liability for a conditional ARO, it must recognize that liability at the time the liability is incurred.
	As of December 31, 2014 and 2013, UIL Holdings’ ARO, including estimated conditional AROs, was $18.7 million and $18.5 million, respectively, and consisted primarily of obligations related to the removal or retirement of asbestos, polychlorinated biphenyl (PCB)-contaminated equipment, gas pipeline and cast iron gas mains.  The long-lived assets associated with the AROs are gas storage property, distribution property and other property.  UIL Holdings’ ARO is carried on the balance sheet as other long-term liabilities.
	ARO activity for 2014 and 2013 is as follows:
			2014			2013
			(In Thousands)
	Balance as of December 31		$	18,510		$	18,289
	Liabilities incurred during the year			-			-
	Liabilities settled during the year			(762	)		(740	)
	Accretion			971			961
	Balance as of December 31		$	18,719		$	18,510
	Cash and Temporary Cash Investments
	UIL Holdings considers all of its highly liquid debt instruments with an original maturity of three months or less at the date of purchase to be cash and temporary cash investments.
	Depreciation
	Provisions for depreciation on utility plant for book purposes are computed on a straight‑line basis, using estimated service lives.  For utility plant other than software, service lives are determined by independent engineers and subject to review and approval by PURA and DPU.  Software service life is based upon management’s estimate of useful life.  The aggregate annual provisions for depreciation for the years 2014, 2013 and 2012 were approximately 3.2%, 3.4%, and 3.5%, respectively, of the original cost of depreciable property.
	Derivatives
	UIL Holdings’ regulated subsidiaries are parties to contracts, and involved in transactions, that are derivatives.
	Contracts for Differences (CfDs)
	Pursuant to Connecticut’s 2005 Energy Independence Act, the Connecticut Public Utilities Regulatory Authority (PURA) solicited bids to create new or incremental capacity resources in order to reduce federally mandated congestion charges, and selected four new capacity resources.  To facilitate the transactions between the selected capacity resources and Connecticut electric customers, and provide the commitment necessary for owners of these resources to obtain necessary financing, PURA required that UI and The Connecticut Light and Power Company (CL&P) execute long-term contracts with the selected resources.  In August 2007, PURA approved four CfDs, each of which specifies a capacity quantity and a monthly settlement that reflects the difference between a forward market price and the contract price.  UI executed two of the contracts and CL&P executed the other two contracts.  The costs or benefits of each contract will be paid by or allocated to customers and will be subject to a cost-sharing agreement between UI and CL&P pursuant to which approximately 20% of the cost or benefit is borne by or allocated to UI customers and approximately 80% is borne by or allocated to CL&P customers.
	PURA has determined that costs associated with these CfDs will be fully recoverable by UI and CL&P through electric rates, and in accordance with ASC 980 “Regulated Operations,” UI has deferred recognition of costs (a regulatory asset) or obligations (a regulatory liability).  The CfDs are marked-to-market in accordance with ASC 815 “Derivatives and Hedging.”  For those CfDs signed by CL&P, UI records its approximate 20% portion pursuant to the cost-sharing agreement noted above.  As of December 31, 2014, UI has recorded a gross derivative asset of $27.3 million ($6.6 million of which is related to UI’s portion of the CfD signed by CL&P), a regulatory asset of $64.3 million, a gross derivative liability of $85.1 million ($59.2 million of which is related to UI’s portion of the CfD signed by CL&P) and a regulatory liability of $6.5 million.  See Note (K) “Fair Value of Financial Instruments” for additional CfD information.
	The gross derivative assets and liabilities as of December 31, 2014 and 2013 were as follows:
			December 31,			December 31,
			2014			2013
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,849		$	9,098
	Deferred Charges and Other Assets		$	20,421		$	44,349
	Gross derivative liabilties:
	Current Liabilities		$	23,308		$	26,976
	Noncurrent Liabilities		$	61,766		$	169,327
	The unrealized gains and losses from fair value adjustments to these derivatives, which are recorded in regulatory assets or regulatory liabilities, for years ended December 31, 2014 and 2013 were as follows:
			Year Ended
			December 31,
			2014			2013
			(In Thousands)
	Regulatory Assets - Derivative liabilities		$	(78,510	)	$	(33,819	)
	Regulatory Liabilities - Derivative assets		$	(6,472	)	$	-
	The fluctuations in the balances of the derivatives as well as the related unrealized gains in the year ended December 31, 2014 compared to 2013 are primarily due to increases in forward prices for capacity and reserves as a result of ISO New England market rule changes.
	Weather Insurance Contracts
	On an annual basis, SCG and Berkshire each assess the need for weather insurance contracts for the upcoming heating season in order to provide financial protection from significant weather fluctuations.  According to the terms of such contracts, if temperatures are warmer than normal at a prescribed level for the contract period, a payment is received by the gas company; in addition, under certain of the contracts, if temperatures are colder than normal at a prescribed level for the contract period, the gas company is required to make a payment.  The premiums paid are amortized over the terms of the contracts.  The intrinsic value of the contracts is carried on the balance sheet with changes in value recorded in the income statement as Other Income and (Deductions).  As a result of PURA’s approval of a decoupling mechanism for CNG which went into effect in January 2014, CNG does not enter into weather insurance contracts.
	Earnings per Share
	The following table presents a reconciliation of the basic and diluted earnings per share calculations for the years 2014, 2013 and 2012:
			Year Ended December 31,
			2014			2013			2012
		(In Thousands, except per share amounts)
Numerator:
Net income attributable to UIL Holdings		$	109,593		$	115,265		$	103,637
Less:  Net income allocated to unvested units			63			117			184
Net income attributable to common shareholders		$	109,530		$	115,148		$	103,453
Denominator:
Basic average number of shares outstanding			56,834			52,415			50,831
Effect of dilutive securities			302			296			277
Diluted average number of shares outstanding			57,136			52,711			51,108
Earnings per share:
Basic		$	1.93		$	2.2		$	2.04
Diluted		$	1.92		$	2.18		$	2.02
All outstanding options to purchase shares of common stock during 2013 and 2012 were included in the computation of diluted earnings per share because the options’ exercise prices were lower than the average market price of the common shares during such period.
Equity Investments
UI is party to a 50-50 joint venture with NRG affiliates in GenConn, which operates two peaking generation plants in Connecticut.  UI’s investment in GenConn is being accounted for as an equity investment, the carrying value of which was $114.2 million and $118.2 million as of December 31, 2014 and 2013, respectively.  As of December 31, 2014, there was an immaterial amount of undistributed earnings from UI’s equity investment in GenConn.
UI’s pre-tax income from its equity investment in GenConn was $13.9 million, $15.3 million and $15.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.
Cash distributions from GenConn are reflected as either distributions of earnings or as returns of capital in the operating and investing sections of the Consolidated Statement of Cash Flows, respectively.  UI received cash distributions from GenConn of $17.9 million, $21.8 million and $21.5 million during the years ended December 31, 2014, 2013 and 2012, respectively.
Goodwill
UIL Holdings may be required to recognize an impairment of goodwill in the future due to market conditions or other factors related to its results of operations and performance. Those market events could include a decline in the forecasted results in the company business plan, significant adverse rate case results, changes in capital investment budgets or changes in interest rates that could impair the fair value of a reporting unit.  Recognition of impairments of a significant portion of goodwill would negatively affect reported results of operations and total capitalization, the effect of which could be material and could make it more difficult to maintain credit ratings, secure financing on attractive terms, maintain compliance with debt covenants and meet expectations of regulators.
A goodwill impairment test is performed each year and the test will be updated between annual tests if events or circumstances occur that may reduce the fair value of a reporting unit below its carrying value. The annual analysis of the potential impairment of goodwill is a two-step process.  Step one of the impairment test consists of comparing the fair values of reporting units with their aggregate carrying values, including goodwill.  The estimated fair values for the reporting units are determined by using the income approach and the market approach methodologies.
The income approach is based on discounted cash flows which are derived from internal forecasts and economic expectations.  Key assumptions used to determine fair value under the income approach include the cash flow period, terminal values based on a terminal growth rate, and the discount rate.  The discount rate represents the estimated cost of debt and equity financing weighted by the percentage of debt and equity in a company's target capital structure.
The market approach utilizes the guideline company method, which calculates valuation multiples based on operating and valuation metrics from publicly traded guideline companies in the regulated natural gas distribution industry.  Multiples derived from the guideline companies provide an indication of how much a knowledgeable investor in the marketplace would be willing to pay for an investment in a similar company.  These multiples are then applied to the appropriate operating metric to determine indications of fair value.
If the carrying amount of a reporting unit exceeds the reporting unit’s fair value, step two must be performed to determine the amount, if any, of the goodwill impairment loss.  If the carrying amount is less than fair value, further testing of goodwill impairment is not performed.
Step two of the goodwill impairment test consists of comparing the implied fair value of the reporting unit’s goodwill against the carrying value of the goodwill.  Determining the implied fair value of goodwill requires the valuation of a reporting unit’s identifiable tangible and intangible assets and liabilities as if the reporting unit had been acquired in a business combination on the testing date. The difference between the fair value of the entire reporting unit as determined in step one and the net fair value of all identifiable assets and liabilities represents the implied fair value of goodwill.  A goodwill impairment charge, if any, would be the difference between the carrying amount of goodwill and the implied fair value of goodwill upon the completion of step two.
As of October 1, 2014, the fair values of UIL Holdings’ applicable reporting units exceeded their carrying values and therefore Step two was not performed and no impairment was recognized.  No events or circumstances occurred subsequent to October 1, 2014 that would make it more likely than not that the fair value of the reporting units fell below their respective carrying values.
Impairment of Long‑Lived Assets and Investments
ASC 360 “Property, Plant, and Equipment” requires the recognition of impairment losses on long‑lived assets when the book value of an asset exceeds the sum of the expected future undiscounted cash flows that result from the use of the asset and its eventual disposition.  If impairment arises, then the amount of any impairment is measured based on discounted cash flows or estimated fair value.
ASC 360 also requires that rate‑regulated companies recognize an impairment loss when a regulator excludes all or part of a cost from rates, even if the regulator allows the company to earn a return on the remaining costs allowed.  Under this standard, the probability of recovery and the recognition of regulatory assets under the criteria of ASC 980 must be assessed on an ongoing basis.  As discussed in the description of ASC 980 in this Note (A) under “Regulatory Accounting,” determination that certain regulatory assets no longer qualify for accounting as such could have a material impact on the financial condition of UI, the Gas Companies and UIL Holdings.  As a result of UI’s 2013 distribution rate proceeding, a portion of UI’s deferred storm costs and capital costs related to UI’s recently constructed administrative and operations buildings were written off.  See “–
Note (C), Regulatory Proceedings, Electric Distribution and Transmission – Rates” for additional information.  In addition, as a result of PURA’s decision in a docket addressing UI’s semi-annual Generation Services Charge (GSC), bypassable federally mandated congestion charge and the nonbypassable federally mandated congestion charge reconciliations (NBFMCC), UI recorded a write-off during the fourth quarter of 2014.  See “– Note (C), Regulatory Proceedings, Electric Distribution and Transmission – Other Proceedings” for additional information.
ASC 323 “Investments” requires that a loss in the value of an investment that is other than a temporary decline should be recognized. In accordance with ASC 323, UIL Holdings reviews its investments accounted for by the equity method for impairment by identifying and measuring losses in the value based upon a comparison of fair value to carrying value.  At December 31, 2014, UIL Holdings did not have any equity investments that were impaired under this standard.
Income Taxes
In accordance with ASC 740 “Income Taxes,” UIL Holdings has provided deferred taxes for all temporary book‑tax differences using the liability method.  The liability method requires that deferred tax balances be adjusted to reflect enacted future tax rates that are anticipated to be in effect when the temporary differences reverse.  In accordance with generally accepted accounting principles for regulated industries, UIL Holdings’ regulated subsidiaries have established a regulatory asset for the net revenue requirements to be recovered from customers for the related future tax expense associated with certain of these temporary differences.  For ratemaking purposes, UIL Holdings’ regulated subsidiaries normalize all investment tax credits (ITCs) related to recoverable plant investments.
Under ASC 740, UIL Holdings may recognize the tax benefit of an uncertain tax position only if management believes it is more likely than not that the tax position will be sustained on examination by the taxing authority based upon the technical merits of the position.  The tax benefits recognized in the financial statements from such a position should be measured based upon the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement.  UIL Holdings’ policy is to recognize interest accrued and penalties associated with uncertain tax positions as a component of operating expense.  See – Note (E), Income Taxes for additional information.
UIL Holdings files a consolidated federal tax return which includes all of the activities of its subsidiaries.  Each subsidiary company is treated as a member of the consolidated group and each subsidiary company’s current and deferred tax expense or benefit is calculated based on the separate return method.
Pension and Other Postretirement Benefits
UIL Holdings accounts for pension plan costs and other postretirement benefits, consisting principally of health and life insurance, in accordance with the provisions of ASC 715 “Compensation - Retirement Benefits.”  See – Note (G), Pension and Other Benefits.
Property, Plant and Equipment
The cost of additions to property, plant and equipment and the cost of renewals and betterments are capitalized.  Cost consists of labor, materials, services and certain indirect construction costs, including AFUDC.  The costs of current repairs, major maintenance projects and minor replacements are charged to appropriate operating expense accounts as incurred.  The original cost of utility property, plant and equipment retired or otherwise disposed of and the cost of removal, less salvage, are charged to the accumulated provision for depreciation.
UI and the Gas Companies accrue for estimated costs of removal for certain of their plant-in-service.  Such removal costs are included in the approved rates used to depreciate these assets.  At the end of the service life of the applicable assets, the accumulated depreciation in excess of the historical cost of the asset provides for the estimated cost of removal.  In accordance with ASC 980 “Regulated Operations,” the accrued costs of removal have been recorded as a regulatory liability.
UIL Holdings’ property, plant and equipment as of December 31, 2014 and 2013 were comprised as follows:
		2014			2013
		(In Thousands)
Electric distribution plant		$	1,135,317		$	979,526
Electric transmission plant			646,826			630,834
Gas distribution plant			1,526,961			1,444,837
Software			195,864			144,494
Building and improvements			245,959			235,002
Land			65,201			64,848
Other plant			239,719			192,219
Total property, plant & equipment			4,055,847			3,691,760
Less accumulated depreciation			1,032,065			944,399
			3,023,782			2,747,361
Construction work in progress			268,908			321,319
Net property, plant & equipment		$	3,292,690		$	3,068,680
Regulatory Accounting
Generally accepted accounting principles for regulated entities in the United States of America allow UIL Holdings’ regulated subsidiaries to give accounting recognition to the actions of regulatory authorities in accordance with the provisions of Accounting Standards Codification (ASC) 980 “Regulated Operations.”  In accordance with ASC 980, UIL Holdings’ regulated utilities have deferred recognition of costs (a regulatory asset) or have recognized obligations (a regulatory liability) if it is probable that such costs will be recovered or obligations relieved in the future through the ratemaking process.  UIL Holdings’ regulated utilities are allowed to recover all such deferred costs through its regulated rates.  See Note (C), “Regulatory Proceedings,” for a discussion of the recovery of certain deferred costs, as well as a discussion of the regulatory decisions that provide for such recovery.
UI also has obligations under long‑term power contracts, the recovery of which is subject to regulation.  If UIL Holdings’ regulated utilities, or a portion of their assets or operations, were to cease meeting the criteria for application of these accounting rules, accounting standards for businesses in general would become applicable and immediate recognition of any previously deferred costs would be required in the year in which such criteria are no longer met (if such deferred costs are not recoverable in the portion of the business that continues to meet the criteria for application of ASC 980).  UIL Holdings expects its regulated utilities to continue to meet the criteria for application of ASC 980 for the foreseeable future.  If a change in accounting were to occur, it could have a material adverse effect on the earnings and retained earnings of the applicable regulated utility and UIL Holdings in that year and could also have a material adverse effect on the ongoing financial condition of the applicable regulated utility and UIL Holdings.
Unless otherwise stated below, all of UIL Holdings’ regulatory assets earn a return.  UIL Holdings’ regulatory assets and liabilities as of December 31, 2014 and 2013 included the following:
	Remaining		December 31,			December 31,
	Period		2014			2013
			(In Thousands)
Regulatory Assets:
Nuclear plant investments – above market	(a)		$	-		$	238,868
Unamortized redemption costs	7 to 19 years			10,499			11,301
Pension and other post-retirement benefit plans	(b)			402,700			316,076
Environmental remediation costs	7 years			13,197			14,953
Hardship programs	(c)			24,744			25,019
Debt premium	2 to 23 years			27,498			34,178
Deferred purchased gas	(d)			-			2,556
Income taxes due principally to book-tax differences	(m)			164,466			149,015
Unfunded future income taxes	(e)			14,859			32,517
Contracts for differences	(f)			64,276			142,743
Excess generation service charge	(g)			-			6,909
Deferred transmission expense	(h)			17,387			9,615
Storm Costs	(i)			-			14,752
Other	(j)			40,336			37,628
Total regulatory assets				779,962			1,036,130
Less current portion of regulatory assets				92,764			332,391
Regulatory Assets, Net			$	687,198		$	703,739
Regulatory Liabilities:
Accumulated deferred investment tax credits	29 years		$	4,319		$	4,465
Income taxes due principally to book-tax differences	(m)			-			200,673
Deferred gain on sale of property	(a)			-			37,933
Excess generation service charge	(g)			28,692			-
Middletown/Norwalk local transmission network service collections	35 years			20,828			21,402
Pension and other post-retirement benefit plans	(b)			9,536			27,686
Asset retirement obligation	(k)			7,248			5,593
Low income programs	(l)			19,065			25,300
Asset removal costs	(j)			336,028			319,530
Unfunded future income taxes	(e)			26,318			43,421
Contracts for differences	(f)			6,472			-
Deferred purchased gas	(d)			4,736			-
Non-firm margin sharing credits	10 years			8,933			-
Other	(j)			36,747			20,818
Total regulatory liabilities				508,922			706,821
Less current portion of regulatory liabilities				17,026			261,729
Regulatory Liabilities, Net			$	491,896		$	445,092
(a)	Asset/Liability relates to the Competitive Transition Assessment (CTA).  Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences.  Total CTA costs recovery and stranded cost
amortization are complete.  As a result of the outcome of UI’s 2013 distribution rate request, PURA approved UI’s proposed rate treatment to leave CTA rates unchanged until January 1, 2014 at which point the charge ended.  The remaining balances were eliminated. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Other Proceedings” for additional information.
(b)	Life is dependent upon timing of final pension plan distribution; balance, which is fully offset by a corresponding asset/liability, is recalculated each year in accordance with ASC 715 "Compensation-Retirement Benefits." See Note (G) “Pension and Other Benefits” for additional information.
(c)	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
(d)	Deferred purchase gas costs balances at the end of the rate year are normally recorded/returned in the next year.
(e)	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
(f)	Asset life is equal to delivery term of related contracts (which vary from approximately 5 - 12 years); balance fluctuates based upon quarterly market analysis performed on the related derivatives (Note K); amount, which does not earn a return, is fully offset by corresponding derivative asset/liability.  See “-Contracts for Differences” discussion above for additional information.
(g)	Regulatory asset or liability which defers generation-related and nonbypassable federally mandated congestion costs or revenues for future recovery from or return to customers.  Amount fluctuates based upon timing differences between revenues collected from rates and actual costs incurred.
(h)	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
(i)	Storm costs include accumulated costs for major storms occurring from January 2009 forward. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Rates” for a discussion of the recovery of these costs.
(j)	Amortization period and/or balance vary depending on the nature, cost of removal and/or remaining life of the underlying assets/liabilities; asset amount includes decoupling ($3.9 million) and certain other amounts that are not currently earning a return. See Note (C) “Regulatory Proceedings for a discussion of the decoupling recovery period.
(k)	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
(l)	Various hardship and payment plan programs approved for recovery.
(m)	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities; balances contain regulatory liabilities related to the CTA as well as regulatory assets not related to the CTA.  Due to the end of the CTA charge, the CTA regulatory liabilities are classified as current regulatory liabilities as of December 31, 2013 and the regulatory assets not related to the CTA are reclassified as long-term regulatory assets.
Restricted Cash
UIL Holdings’ restricted cash at December 31, 2014 and 2013 totaled $1.1 million and $2.0 million, respectively, which primarily relates to electric distribution and transmission capital projects, which have been withheld by UI and will remain in place until the verification of fulfillment of contractor obligations.
Revenues
Regulated utility revenues are based on authorized rates applied to each customer.  These retail rates are approved by regulatory bodies and can be changed only through formal proceedings.
UI utilizes a customer accounting software package integrated with the network meter reading system to estimate unbilled revenue on a customer-by-customer basis, utilizing actual daily meter readings at the end of each month to calculate consumption and pricing for each customer.  A significant portion of utility retail kilowatt-hour consumption is read through the network meter reading system.  For those customers still requiring manual meter readings, consumption is estimated based upon historical usage and actual pricing for each customer.
The Gas Companies’ unbilled revenues represent estimates of receivables for products and services provided but not yet billed. The estimates are determined based on various assumptions, such as current month energy load requirements, billing rates by customer classification and weather.
Stock-Based Compensation
Certain members of management have the opportunity to earn a pre-determined number of performance shares, the number of which is predicated upon the achievement of various pre-defined performance measures over a three-year period.  These performance shares are issued under the UIL Holdings Amended and Restated 2008 Stock and Incentive Compensation Plan (2008 Stock Plan).  Each award of performance shares vests at the end of a three-year cycle with the actual issuance of UIL Holdings’ common stock in respect of such performance shares following the end of each three-year cycle.  A new three-year cycle begins in January of each year.
UIL Holdings records compensation expense for these performance shares ratably over the three-year period, except in the case of retirement-eligible employees, for whom compensation expense is immediately recognized in accordance with ASC 718 “Compensation-Stock Compensation,” based on the value of the expected payout at the end of each year relative to the performance measures achieved.
Pursuant to the 2008 Stock Plan, target amounts of 123,940, 2,430, and 2,340 performance shares were granted to certain members of management in March 2014, May 2014 and August 2014, respectively; the averages of the high and low market prices on the grant dates, which approximate fair value, were $35.87 per share, $36.23 per share, and $34.90 per share respectively.
Also in March 2014, we granted a total of 2,196 shares of restricted stock to our President and Chief Executive Officer under the 2008 Stock Plan and in accordance with his employment agreement; the average of the high and low market price on the date of grant, which approximates fair value, was $35.87 per share.  Such shares vest in equal annual installments over a five-year period.
In May 2014, UIL Holdings granted a total of 25,160 shares of restricted stock to non-employee directors under the 2008 Stock Plan; the average of the high and low market price on the date of grant, which approximates fair value, was $35.90 per share.  Such shares vest in May 2015.
In June 2014, 9,540 shares of previously-granted performance shares and 2,177 shares of previously-granted restricted stock were forfeited.
As of December 31, 2014, the total number of shares authorized for stock-based compensation plans was 4,233,333.  Total stock-based compensation expense for the years ended December 31, 2014, 2013 and 2012 was $5.7 million, $5.3 million and $4.9 million, respectively.
Variable Interest Entities
We have identified GenConn as a variable interest entity (VIE), which is accounted for under the equity method.  UIL Holdings is not the primary beneficiary of GenConn, as defined in ASC 810 “Consolidation,” because it shares control of all significant activities of GenConn with its joint venturer, NRG affiliates.  As such, GenConn is not subject to consolidation.  GenConn recovers its costs through CfDs, which are cost of service-based and have been approved by PURA.  As a result, with the achievement of commercial operation by GenConn Devon and GenConn Middletown, our exposure to loss is primarily related to the potential for unrecovered GenConn operating or capital costs in a regulatory proceeding, the effect of which would be reflected in the carrying value of our 50% ownership position in GenConn and through “Income from Equity Investments” in UIL Holdings’ Consolidated Financial Statements.  Such exposure to loss cannot be determined at this time. For further discussion of GenConn, see “–Equity Investments” as well as Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Equity Investment in Peaking Generation.”
We have identified the selected capacity resources with which UI has CfDs as VIEs and have concluded that UI is not the primary beneficiary as UI does not have the power to direct any of the significant activities of these capacity resources.   As such, we have not consolidated the selected capacity resources.  UI’s maximum exposure to loss through these agreements is limited to the settlement amount under the CfDs as described in “–Derivatives – Contracts for Differences (CfDs)” above; however any such losses are fully recoverable through electric rates.  UI has no requirement to absorb additional losses nor has UI provided any financial or other support during the periods presented that were not previously contractually required.
We have identified the entities for which UI is required to enter into long-term contracts to purchase Renewable Energy Credits (RECs) as VIEs.  In assessing these contracts for VIE identification and reporting purposes, we have aggregated the contracts based on similar risk characteristics and significance to UI.  UI is not the primary beneficiary as UI does not have the power to direct any of the significant activities of these entities.  UI’s exposure to loss is primarily related to the purchase and resale of the RECs, but, any losses incurred are recoverable through electric rates.  For further discussion of RECs, see Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – New Renewable Source Generation.”
New Accounting Standards
In May 2014, the FASB issued Accounting Standards Update (ASU) 2014-09, which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition.  ASU 2014-09 requires entities to recognize revenue in a way that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services.  ASU 2014-09 is effective for interim and annual reporting periods beginning after December 15, 2016 and is to be applied retrospectively.  We are currently evaluating the effect that adopting this new accounting guidance will have on our consolidated financial statements.
In June 2014, the FASB issued updated guidance to ASC 718 “Compensation – Stock Compensation” which prescribes the accounting for share-based payments when the terms of an award provide that a performance target could be achieved after the requisite service period.  This guidance is effective during interim and annual periods beginning after December 15, 2015 and can be applied on a prospective basis to all awards granted or modified after the effective date or retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter.  This guidance is not expected to have a material impact on UIL Holdings’ consolidated financial statements.

CAPITALIZATION

CAPITALIZATION	12 Months Ended
	Dec. 31, 2014
CAPITALIZATION [Abstract]
CAPITALIZATION	(B)  CAPITALIZATION
	Common Stock
	UIL Holdings had 56,546,266 shares of its common stock, no par value, outstanding as of December 31, 2014 and 56,462,507 shares of its common stock, no par value, outstanding at December 31, 2013.  Not included in such shares were 308,193 and 276,845 shares of restricted stock as of December 31, 2014 and 2013, respectively.  These cumulative shares of restricted stock are, however, recognized as outstanding for purposes of calculating basic earnings per share because such shares represent the net of the amount of deferred vested restricted stock, less the amount of non-deferred unvested restricted stock.
	Restricted stock activity for 2014 is as follows:
			Number			Weighted Average
			of Shares			Grant Date
						Fair Value
	Nonvested Balance – December 31, 2013			30,920		$	38.9
	Granted			27,356		$	35.9
	Forfeited			(2,177	)	$	41.34
	Vested			(24,161	)	$	39.53
	Nonvested Balance – December 31, 2014			31,938		$	35.68
	As of December 31, 2014, total unrecognized costs for non-vested restricted stock awards were $0.5 million. The weighted-average period over which the restricted stock costs will be recognized is 8 months.
	Performance share activity for 2014 is as follows:
			Number			Weighted Average
			of Performance			Grant Date
			Shares			Fair Value
	Nonvested Balance – December 31, 2013			335,008		$	34.62
	Granted			146,792		$	35.24
	Forfeited			(9,540	)	$	38.81
	Vested			(131,020	)	$	30.8
	Nonvested Balance – December 31, 2014			341,240		$	36.23
	As of December 31, 2014, total unrecognized costs for performance shares were $1.8 million. The weighted-average period over which the performance-share costs will be recognized is 10 months.
	The weighted average grant date fair value of all restricted stock and performance shares granted during the year was $35.87, $39.21, and $34.33 for the years ended December 31, 2014, 2013, and 2012 respectively.
	Stock option transactions for 2014, 2013 and 2012 are as follows:
									Average
			Number			Option Price			Exercise
			of Options			per Share			Price
	Balance – December 31, 2011			98,220		$	21.68-$33.96		$	33.39
	Granted			-			N/	A		N/	A
	Forfeited			(38,000	)		N/	A		N/	A
	Exercised			(56,887	)	$	31.25-$33.96			N/	A
	Balance – December 31, 2012			3,333		$	21.68		$	21.68
	Granted			-			N/	A		N/	A
	Forfeited			-			N/	A		N/	A
	Exercised			(3,333	)	$	21.68			N/	A
	Balance – December 31, 2013			-			N/	A		N/	A
	Granted			-			N/	A		N/	A
	Forfeited			-			N/	A		N/	A
	Exercised			-			N/	A		N/	A
	Balance – December 31, 2014			-			N/	A		N/	A
	Exercisable at December 31, 2012			3,333		$	21.68		$	21.68
	Exercisable at December 31, 2013			-			N/	A		N/	A
	Exercisable at December 31, 2014			-			N/	A		N/	A
	There were no options outstanding as of December 31, 2014 and 2013.  As of December 31, 2012, the weighted-average remaining contractual lives for those options outstanding was 0.3 years.
	Cash received from options exercised under all share-based payment arrangements for the years ended December 31, 2013 and 2012 was $0.1 million and $1.9 million, respectively.  The actual tax benefit realized by UIL Holdings for the tax deductions from the exercises totaled $0.1 million for each of 2013 and 2012.
	The shares issued to non-employee directors as well as employee performance shares and options are drawn from the 2008 Stock Plan.
	Long-Term Debt
			December 31,
			2014			2013
			(In Thousands)
	UIL Holdings
	4.625% Unsecured Senior Notes, due 2020		$	450,000		$	450,000
	UI
	Pollution Control Revenue Bonds:
	4.50% 2010 Series, due 2027			27,500			27,500
	Auction Rate, 2003 Series, due 2033  (1)			64,460			64,460
	Senior Unsecured Notes:
	6.06% Senior Notes, Series A and B, due 2017			70,000			70,000
	2.98% Senior Notes, Series A due 2019			31,000			31,000
	3.61% Senior Notes, Series B and C and 6.26% Senior Notes, Series C and D, due 2022			162,500			162,500
	6.51% Senior Notes, Series E and F due 2037			28,000			28,000
	6.46% Senior Notes, Series A and 6.51%, Senior Notes, Series B, due 2018			100,000			100,000
	6.61% Senior Notes, Series C, due 2020			50,000			50,000
5.61% Senior Notes, due 2025			50,000			50,000
6.09% Senior Notes, due 2040			100,000			100,000
4.89% Senior Notes, Series D and E, due 2042			87,000			87,000
3.95% Senior Notes, Series F, due 2023			75,000			75,000
Gas Companies
Senior Secured Notes:
3.88% - 7.50% Senior Secured Medium Term Note IV, due 2018 - 2041			100,000			100,000
5.77%  - 6.38% Senior Secured Medium Term Notes III, due 2025 - 2037			85,000			85,000
6.88% - 7.95% Senior Secured Medium Term Notes I, due 2026 - 2028			29,000			29,000
10.06% First Mortgage Bond Series P, due 2019			10,000			10,000
Unsecured Notes:
4.76% - 9.60% Senior Unsecured Notes, due 2020 - 2021			18,180			19,635
6.85% - 9.10% Unsecured Medium Term Notes, Series A, due 2016 - 2017			30,000			30,000
8.12% - 8.49% Unsecured Medium Term Notes, Series B, due 2014 - 2024			-			10,000
5.63% - 6.66% Unsecured Medium Term Notes, Series C, due 2035 - 2037			65,000			65,000
4.30% - 5.23% Medium Term Note, Series D, due 2028 - 2043			45,000			45,000
5.33% Senior Notes, Series A, due 2043			15,000			15,000
Long-Term Debt			1,692,640			1,704,095
Less:  Current portion of long-term debt  (2)			6,526			11,834
Less:  Unamortized discount			2,263			2,597
Plus:  Unamortized premium			27,498			34,178
Net Long-Term Debt		$	1,711,349		$	1,723,842
-1	On December 31, 2014, the interest rate on the Bonds was 0.33%. The interest rate on these Bonds is reset through an auction held every 35 days.
-2	Includes the current portion of unamortized premium.
The amount of restricted net assets as of December 31, 2014 was approximately $570.1 million, of which approximately $114.2 million relates to UI’s equity investment in GenConn.  Substantially all of the respective utility’s properties are pledged as collateral for the applicable Senior Secured Medium Term Notes and First Mortgage Bonds.
The weighted-average remaining fixed rate period of outstanding long-term debt obligations of UIL Holdings and its subsidiaries as of December 31, 2014 was 10.8 years, at an average interest rate of 5.43%.
The fair value of UIL Holdings’ long-term debt was $1.9 billion and $1.8 billion as of December 31, 2014 and 2013, respectively, which was estimated by UIL Holdings based on market conditions.  The expenses to issue long‑term debt are deferred and amortized over the life of the respective debt issue or the fixed interest-rate period in the case of pollution control revenue bonds.
Information regarding maturities and mandatory redemptions/repayments are set forth below:
		2015			2016			2017			2018		2019 &		Total
													Thereafter
		(In Thousands)
Maturities:		$	1,455		$	11,455		$	91,455		$	151,455	$	1,436,820	$	1,692,640
In August 2014, CNG repaid, upon maturity, the outstanding balance of its 8.12% Medium Term Notes, Series B, in the aggregate amount of $5 million.  Also in August 2014, CNG redeemed all of its outstanding 8.49% Medium Term Notes, Series B, due 2024, for an aggregate of $5 million.
In October 2013, UI entered into a note purchase agreement with a group of institutional accredited investors providing for the sale to such investors on October 25, 2013 of senior unsecured 3.95% notes in the principal amount of $75 million, due on October 25, 2023.  UI used the net proceeds from this long-term debt issuance to repay short-term debt and for general corporate purposes.
In October 2013, CNG entered into a note purchase agreement with a group of qualified institutional buyers providing for the sale to such buyers on October 25, 2013 of senior unsecured 4.30% notes in the principal amount of $25 million, due on October 25, 2028 and 5.23% notes in the principal amount of $20 million, due on October 25, 2043.  CNG used the net proceeds of this long-term debt issuance to replenish cash that had been used to repay $ debt that matured in September 2013 and in December 2013.  CNG expects to use the remainder of the net proceeds for capital expenditures and general corporate purposes.
In October 2013, Berkshire entered into a note purchase agreement with a group of institutional accredited investors providing for the sale to such investors on December 10, 2013 of senior unsecured 5.33% notes in the principal amount of $15 million, due on December 10, 2043.  Berkshire used the net proceeds of this long‑term debt issuance for the repayment of short-term debt and expects to use the remaining net proceeds for general working capital, environmental expenditures and capital expenditures.

REGULATORY_PROCEEDINGS

REGULATORY PROCEEDINGS	12 Months Ended
	Dec. 31, 2014
REGULATORY PROCEEDINGS [Abstract]
REGULATORY PROCEEDINGS	(C)  REGULATORY PROCEEDINGS
	Electric Distribution and Transmission
	ISO-NE, an independent, not-for-profit corporation, is the Regional Transmission Organization (RTO) for New England.  ISO-NE is responsible for the reliable operation of the region’s bulk electric power system, which includes UI’s electric system, and administration of the region’s wholesale electricity marketplace.  ISO-NE also is responsible for the management of the comprehensive bulk electric power system and wholesale markets’ planning processes that address the region's electricity needs.
	Rates
	Utilities are entitled by Connecticut statutes to charge rates that are sufficient to allow them an opportunity to cover their reasonable operating and capital costs, to attract needed capital and to maintain their financial integrity, while also protecting relevant public interests.
	In August 2013, PURA approved new distribution rate schedules for UI for two years (the August Decision) which became effective at that time and which, among other things, increased the UI distribution and CTA allowed return on equity (ROE) from 8.75% to 9.15%, continued UI’s existing earnings sharing mechanism by which UI and customers share on a 50/50 basis all distribution earnings above the allowed ROE in a calendar year, continued the existing decoupling mechanism, and approved the establishment of the requested storm reserve.  Additionally, the August Decision disallowed approximately $22 million related to deferred storm costs and capital costs related to UI’s recently constructed administrative and operations buildings.  As a result of these disallowances and other adjustments related to the rate proceeding, we recorded a one-time pre-tax write off of $17.5 million related to UI in the third quarter of 2013.
	In December 2013, PURA issued a final decision on UI’s Petition for Reconsideration of the August Decision.  The final decision on the reconsideration restored approximately $6.8 million of deferred storm costs and approximately $2.7 million of capital costs related to UI’s recently constructed administrative and operations buildings which had been disallowed in the August Decision.  As a result, we recorded a one-time pre-tax adjustment of approximately $9.2 million in the fourth quarter of 2013 to reverse such amounts written off in the third quarter of 2013 as a result of the August Decision.  The resulting storm regulatory asset allowed for recovery totaled approximately $45 million.  As a result of PURA’s final decision in UI’s final CTA reconciliation proceeding, the remaining storm regulatory asset was offset against the remaining CTA and Connecticut Yankee DOE litigation regulatory liabilities. See Note “–Electric Distribution and Transmission – Other Proceedings” for additional information.
	Power Supply Arrangements
	Under Connecticut law, UI’s retail electricity customers are able to choose their electricity supplier while UI remains their electric distribution company.   UI purchases power for those of its customers under standard service rates who do not choose a retail electric supplier and have a maximum demand of less than 500 kilowatts and its customers under supplier of last resort service for those who are not eligible for standard service and who do not choose to purchase electric generation service from a retail electric supplier.  The cost of the power is a “pass-through” to those customers through the GSC charge on their bills.
	UI must procure the power to serve its standard service load pursuant to a procurement plan approved by PURA.  Under the procurement plan UI procures wholesale power for its standard service customers on a full requirements basis pursuant to contracts with a maximum duration of 12 months, with the delivery of such wholesale power to commence no later than six months from the applicable bid day.
	UI has wholesale power supply agreements in place for its entire standard service load for the first half of 2015, 80% of its standard service load for the second half of 2015 and for 20% of its standard service load for the first half of 2016.  Supplier of last resort service is procured on a quarterly basis, however, from time to time there are no bidders in the procurement process for supplier of last resort service and in such cases UI manages the load directly.  UI determined that its contracts for standard service and supplier of last resort service are derivatives under ASC 815 “Derivatives and Hedging” and elected the “normal purchase, normal sale” exception under ASC 815 “Derivatives and Hedging.”  UI regularly assesses the accounting treatment for its power supply contracts.  These wholesale power supply agreements contain default provisions that include required performance assurance, including certain collateral obligations, in the event that UI’s credit rating on senior debt were to fall below investment grade.  If UI’s credit rating were to decline one rating at Standard & Poor’s or two ratings at Moody’s and UI were to be placed on negative credit watch, monthly amounts due and payable to the power suppliers would be accelerated to semi-monthly payments. UI’s credit rating would have to decline two ratings at Standard & Poor’s and three ratings at Moody’s to fall below investment grade. If this were to occur, UI would have to deliver collateral security in an amount equal to the receivables due to the sellers for the thirty-day period immediately preceding the default notice. If such an event had occurred as of December 31, 2014, UI would have had to post an aggregate of approximately $20.6 million in collateral. UI would have been and remains able to provide that collateral.
	In addition, UI is authorized to seek long-term contracts for up to 20% of its standard service requirements and Connecticut Class I Renewable Energy Certificates (RECs) for UI’s standard service customers that will result in an economic benefit to ratepayers, both in terms of risk and cost mitigation.  UI continues to keep apprised of possible long-term contracts that could benefit customers, but has not executed any long-term contracts.
	New Renewable Source Generation
	Under Connecticut law (PA 11-80), Connecticut electric utilities are required to enter into long-term contracts to purchase RECs from renewable generators located on customer premises.  Under this program, UI is required to enter into contracts totaling approximately $200 million in commitments over an approximate 21-year period.  The obligations will phase in over a six-year solicitation period, and are expected to peak at an annual commitment level of about $13.6 million per year after all selected projects are online.  Upon purchase, UI accounts for the RECs as inventory.  UI expects to partially mitigate the cost of these contracts through the resale of the RECs.  PA 11-80 provides that the remaining costs (and any benefits) of these contracts, including any gain or loss resulting from the resale of the RECs, are fully recoverable from (or credited to) customers through electric rates.
	On October 23, 2013, PURA approved UI’s renewable connections program filed in accordance with PA 11-80, through which UI will develop up to 10 MW of renewable generation.  The costs for this program will be recovered on a cost of service basis.   PURA established a base ROE to be calculated as the greater of: (A) the current UI authorized distribution ROE (currently 9.15%) plus 25 basis points and (B) the current authorized distribution ROE for CL&P (currently 9.17%), less target equivalent market revenues (reflected as 25 basis points).  In addition, UI will retain a percentage of the market revenues from the project, which percentage is expected to equate to approximately 25 basis points on a levelized basis over the life of the project.  UI expects the cost of this program, a planned 2.8 MW fuel cell facility in New Haven, solar photovoltaic and fuel cell facilities totaling 5 MW in Bridgeport, and a 2.2 MW fuel cell facility in Woodbridge to be approximately $47 million.
	Pursuant to Connecticut law (PA 13-303), on September 19, 2013, at the direction of DEEP, UI entered into two contracts for energy and/or RECs from Class I renewable resources, totaling approximately 3.5% of UI’s distribution load, which were subsequently approved by PURA.  Costs of each of these agreements will be fully recoverable through electric rates.  On December 18, 2013, Allco Finance Limited, an unsuccessful bidder in the RFP, filed a complaint against DEEP in the United States District Court in Connecticut alleging that DEEP’s direction to UI and CL&P to enter into the contracts violated the Supremacy Clause of the U.S. Constitution and the Federal Power Act by setting wholesale electricity rates.  This complaint was dismissed in December 2014.
	Pursuant to Section 8 of Public Act 13-303, “An Act Concerning Connecticut’s Clean Energy Goals,” (PA 13-303), in January 2014, at DEEP’s direction, UI entered into three contracts for the purchase of RECs associated with an aggregate of 5.7 MW of energy production from biomass plants in New England. The costs of these agreements will be fully recoverable through electric rates.
	Transitional Standard Offer Incentive (TSO)
	State legislation significantly restructured the electric utility industry in Connecticut in 1998 and 2003.  As a result, PURA established an incentive plan for the procurement of long-term contracts for transitional standard offer service that compares UI’s actual average contract price to a regional average price for electricity, making adjustments as deemed appropriate by PURA. In a 2009 decision, PURA found that UI was not eligible for a procurement incentive for 2004. UI appealed PURA’s decision and in October 2012, UI, CL&P and the Connecticut Office of Consumer Counsel (OCC) filed with PURA a joint motion for approval of a settlement agreement by and among UI, CL&P, and the OCC. The settlement agreement, which was subsequently approved by PURA, provided that UI had met the statutory standard for receiving TSO incentives previously collected of approximately $2.7 million, which were recorded in the third quarter of 2012 and are included in “Other Income and (Deductions)” in UIL Holdings’ Consolidated Statement of Income. The settlement agreement also provides that no further amounts are due from UI to customers relating to the 2004 incentive.
	Transmission
	PURA decisions do not affect the revenue requirements determination for UI’s transmission business, including the applicable ROE, which are within the jurisdiction of the FERC.  The FERC has issued orders establishing allowable ROEs for transmission projects of transmission owners in New England, including UI.  The FERC established a base-level ROE of 11.14%, as well as a 50 basis point ROE adder on Pool Transmission Facilities (PTF) for participation in the RTO for New England and a 100 basis point ROE incentive for projects included in the ISO-NE Regional System Plan that were completed and on line as of December 31, 2008.
	UI’s overall transmission ROE is determined by the mix of UI’s transmission rate base between new and existing transmission assets, and whether such assets are PTF or non-PTF.  UI’s transmission assets are primarily PTF.  For 2014, UI’s overall allowed weighted-average ROE for its transmission business was 12.1%.  This includes the impact of the FERC order issued on October 16, 2014 and excludes any impacts of the reserve adjustment, both of which are discussed below.
	In September 2011, several New England governmental entities, including PURA, the Connecticut Attorney General and the OCC, filed a joint complaint (Initial Complaint) with the FERC against ISO-NE and several New England transmission owners, including UI, claiming that the current approved base ROE used in calculating formula rates for transmission service under the ISO-NE Open Access Transmission Tariff by the New England transmission owners  of 11.14% was not just and reasonable and seeking a reduction of the base ROE and a refund to customers for a refund period of October 1, 2011 through December 31, 2012 (refund period).
	Based on the August 6, 2013 initial decision of the presiding Administrative Law Judge finding that the existing base ROE was unjust and unreasonable we recorded a reserve for the refund period related to the Initial Complaint of $2.6 million pre-tax during the third quarter of 2013 based upon our assessment of the ultimate outcome of the proceeding.
	In December 2012, various additional parties filed a complaint with the FERC against several New England transmission owners, including UI, claiming that the current approved base ROE of 11.14% was not just and reasonable and seeking a reduction of the base ROE and a refund to customers for a refund period commencing December 27, 2012 (Second Complaint).
	On June 19, 2014, the FERC issued an order (June Order) in the Initial Complaint, tentatively finding that the just and reasonable base ROE for the New England transmission owners’ tariff is 10.57%.  In the June Order, the FERC adopted a new method for determining cost of equity, changing from a one-step discounted cash flow (DCF) methodology to a two-step DCF, which includes a long-term growth component.  The FERC also discontinued its past practice of adjusting the ROE to reflect changes in U.S. Treasury bond yields from the date of closing of the evidentiary record to the date of the FERC decision.
	The June Order applied the two-step DCF methodology, using an assumed long-term growth rate based on the Gross Domestic Product, to tentatively find that the zone of reasonableness for the New England transmission owners is 7.03% to 11.74%.  Within that tentative zone of reasonableness, the FERC found that, taking into account the unusual capital market conditions, the just and reasonable base ROE for the New England transmission owners’ tariff should be set halfway between the midpoint of the zone of reasonableness and the top of the zone of reasonableness, or 10.57%.   In connection with the application of the two-step DCF method, the FERC established a paper hearing process following which the FERC confirmed in its order on October 16, 2014 (October Order) that the Gross Domestic Product was the appropriate long-term growth rate to be used when calculating the base ROE and setting the New England transmission owners base ROE at 10.57% with a total or maximum ROE including incentives not to exceed 11.74%, for both the refund period and going forward effective on October 16, 2014.
	Also on June 19, 2014, the FERC announced it would institute hearing and settlement judge procedures in the Second Complaint.  The FERC determined there would be a 15-month refund period for the Second Complaint beginning December 27, 2012.  Settlement procedures were unsuccessful and we now expect this complaint to be litigated with a final FERC order likely being issued in 2016.
	On July 31, 2014, certain complainants in the Initial Complaint and the Second Complaint filed a similar additional complaint (Third Complaint) with the FERC against the New England transmission owners, alleging that the then current base ROE of 11.14% was not just and reasonable, and seeking a reduction in the base ROE and refunds to customers for a 15-month refund period beginning July 31, 2014.  The complainants in the Third Complaint also asked for a determination that the top of the zone of reasonableness caps the ROE for each individual project.
	On November 24, 2014, the FERC issued an order consolidating the Second Complaint and Third Complaint and stated a presiding judge decision should be rendered within twelve months of the commencement of hearing proceedings, or by November 30, 2015, with an expected decision by the FERC by September 2016.
	In 2014, we updated our assessment based upon the most recent information available.  Although we cannot predict the outcome of the proceedings involving the Second and Third Complaints, we recorded additional pre-tax reserves of $5.6 million relating to potential refunds to customers.  As of December 31, 2014, total pre-tax reserves relating to potential refunds to customers under all three claims were approximately $8.2 million.
	New England East-West Solution
	Pursuant to an agreement with CL&P (the Agreement), UI has the right to invest in, and own transmission assets associated with, the Connecticut portion of CL&P’s New England East West Solution (NEEWS) projects to improve regional energy reliability.  NEEWS consists of four inter-related transmission projects being developed by subsidiaries of Northeast Utilities (doing business as Eversource Energy), the parent company of CL&P, in collaboration with National Grid USA.  Three of the projects have portions located in Connecticut:  (1) the Greater Springfield Reliability Project (GSRP), which was fully energized in November 2013, (2) the Interstate Reliability Project (IRP), which is expected to be placed in service in the fourth quarter 2015 and (3) the Central Connecticut Reliability Project, which is being reassessed as part of the Greater Hartford Central Connecticut Study (GHCC). As CL&P places assets in service, it will transfer title to certain NEEWS transmission assets to UI in proportion to UI’s investments, but CL&P will continue to maintain these portions of the transmission system pursuant to an operating and maintenance agreement with UI.  Any termination of the Agreement pursuant to its terms would have no effect on the assets previously transferred to UI.
	Under the terms of the Agreement, UI has the option to make quarterly deposits to CL&P in exchange for ownership of specific NEEWS transmission assets as they are placed in service.  UI has the right to invest up to the greater of $60 million or an amount equal to 8.4% of CL&P’s costs for the originally proposed Connecticut portions of the NEEWS projects.  Based upon the current projected costs, UI’s investment rights in GSRP and IRP would be approximately $45 million.  In January 2015, ISO-NE issued a draft GHCC transmission solutions report to its Planning Advisory Committee.   UI is evaluating the draft report and awaiting the final ISO-NE GHCC transmission solution report, expected in the first quarter of 2015, to determine the impact on UI’s aggregate investment in NEEWS.
	Deposits associated with NEEWS are recorded as assets at the time the deposit is made and they are reported in the ‘Other’ line item within the Deferred Charges and Other Assets section of the consolidated balance sheet.   When title to the assets is transferred to UI, the amount of the corresponding deposit is reclassified from other assets to plant-in-service on the balance sheet and shown as a non-cash investing activity in the consolidated statement of cash flows.
	As of December 31, 2014, UI had made aggregate deposits of $43.5 million under the Agreement since its inception, with assets valued at approximately $24.6 million having been transferred to UI, as follows:  In September 2012, CL&P transferred approximately $6.2 million of transmission assets associated with the GSRP, and in February 2013, CL&P transferred approximately $18.4 million of transmission assets, representing the remaining portion of the GSRP.  UI earned pre-tax income on deposits, net of transferred assets, of approximately $1.7 million, $1.5 million and $1.6 million in the years ended December 31, 2014, 2013 and 2012, respectively.  On February 6, 2015, UI made an additional deposit of approximately $1.5 million.
	Approval for the Issuance of Debt
	Long-term debt issuances require regulatory authorization which is typically obtained for a specified amount of debt to be issued during a specified period of time.  On February 4, 2015, PURA approved UI’s application to issue long term debt in the aggregate amount of $400 million from time to time through 2017.  The proceeds from any issuances may be used by UI to   refinance existing maturing debt and its Pollution Control Revenue Bonds (PCRBs) and for general corporate purposes.  The debt authorized to be issued to refinance the PCRBs may be issued in either the taxable private placement market or bank market as an alternative to financing the bonds in the tax-exempt market.
	Other Proceedings
	UI generally has several regulatory proceedings open and pending at PURA at any given time.  Examples of such proceedings include an annual PURA review and reconciliation of Systems Benefits Charges (SBC) revenues and expenses, dockets to consider specific restructuring or electricity market issues, consideration of specific rate or customer issues, and review of conservation programs.
	UI files annual true-ups with PURA regarding Bypassable Federally Mandated Congestion Charges and Non-Bypassable Federally Mandated Congestion Charges.  These customer charges relate to “congestion costs” associated with not having adequate transmission infrastructure to move energy from the generating sources to the consumer and costs associated with ensuring adequate capacity on the electric system, such as peaking generation and capacity CfDs with generators.  These costs change from time to time and the annual reconciliation filing provides a mechanism for the electric distribution companies to adjust the charges to customers that allow the companies to recover the Federally Mandated Congestion Charges.
	UI makes a semi-annual transmission adjustment clause (TAC) filing with PURA setting forth its actual transmission revenues, projected transmission revenue requirement, and the required TAC charge or credit so that any under- or over-collections of transmission revenues from prior periods are reconciled along with the expected revenue requirements for the next six months from filing.  PURA holds an administrative proceeding to approve the TAC charge or credit and holds a hearing to determine the accuracy of customer billings under the TAC.  The TAC tariff and this semi-annual change of the TAC charge or credit facilitates the timely matching of transmission revenues and transmission revenue requirements.
	On November 12, 2014, PURA issued a decision in a docket addressing UI’s semi-annual GSC, bypassable federally mandated congestion charge and the NBFMCC reconciliations .  PURA’s decision allows for recovery of $7.7 million of the $11.3 million request included in UI’s filing for the reconciliation of certain revenues and expenses relating to the period from 2004 through 2013 and resulted in UI recording a pre-tax write-off of approximately $3.8 million during the fourth quarter of 2014 which included the disallowed portion of UI’s request as well as additional 2014 carrying charges.
	Also on November 12, 2014, PURA issued a final decision in UI’s final CTA reconciliation proceeding which extinguished all remaining CTA balances.  In addition, the final decision allowed for the application of an approximate $8.2 million remaining CTA regulatory liability, as well as an approximate $12.0 million regulatory liability related to the Connecticut Yankee DOE litigation, against the storm regulatory asset balance.  The final decision required that remaining regulatory liability balance be applied to the GSC “working capital allowance” and be returned to customers through the NBFMCC.
	Because the two decisions noted above do not conform to ratemaking principles, UI filed appeals with the State of Connecticut Superior Court in December 2014 for both the GSC/NBFMCC and the CTA final decisions.  On February 3, 2015, PURA filed a motion to dismiss UI’s appeal of the CTA final decision.
	Equity Investment in Peaking Generation
	UI is party to a 50-50 joint venture with NRG affiliates in GenConn, which operates two peaking generation plants in Connecticut.  The two peaking generation plants, GenConn Devon and GenConn Middletown, are both participating in the ISO-New England markets.  PURA has approved revenue requirements for the period from January 1, 2015 through December 31, 2015 of $29.5 million and $36.5 million for GenConn Devon and GenConn Middletown, respectively.  In addition, PURA has ruled that GenConn project costs incurred that were in excess of the proposed costs originally submitted in 2008 were prudently incurred and are recoverable.  Such costs are included in the determination of the 2015 approved revenue requirements.
	Gas Distribution
	Rates
	Utilities are entitled by Connecticut and Massachusetts statutes to charge rates that are sufficient to allow them an opportunity to cover their reasonable operating and capital costs, to attract needed capital and to maintain their financial integrity, while also protecting relevant public interests.
	The allowed returns on equity established by PURA are 9.18% and 9.36% for CNG and SCG, respectively.  Berkshire’s rates are established by the DPU.  Berkshire’s 10-year rate plan, which was approved by the DPU and included an approved ROE of 10.5%, expired on January 31, 2012.  Berkshire continues to charge the rates that were in effect at the end of the rate plan and currently anticipates that a base rate case would likely be filed in 2016, based on a calendar year 2015 test year, for rates to be effective in 2017.
	SCG and CNG each have purchased gas adjustment clauses and Berkshire has a cost of gas adjustment clause, approved by PURA and DPU, respectively, which enable them to pass their reasonably incurred cost of gas purchases through to customers.  These clauses allow utilities to recover costs associated with changes in the market price of purchased natural gas, substantially eliminating exposure to natural gas price risk.  Additionally, Berkshire’s mechanism allows for the recovery of the gas-cost portion of bad debt.
	On January 22, 2014, PURA approved new base delivery rates for CNG, with an effective date of January 10, 2014, which, among other things, approved an allowed ROE of 9.18%, a decoupling mechanism, and two separate ratemaking mechanisms that reconcile actual revenue requirements related to CNG’s cast iron and bare steel replacement program and system expansion.  Additionally, the final decision requires the establishment of an earnings sharing mechanism by which CNG and customers share on a 50/50 basis all earnings above the allowed ROE in a calendar year.  The decision also allows CNG, on a provisional basis, to reflect the increased rate base resulting from the accumulated deferred income tax (ADIT) impacts of the election of Section 338(h)(10) of the Internal Revenue Code upon its acquisition by UIL Holdings.   The decision requires CNG to seek a private letter ruling from the Internal Revenue Service with regard to the specific question of whether, after extinguishment of an ADIT balance, a directive by a public utility commission to institute a ratemaking mechanism to reflect a credit to ratepayers of ADIT benefits lost through a Section 338(h)(10) election would result in a normalization violation.  The decision states that in the event of a ruling from the Internal Revenue Service stating that imposing such a ratemaking mechanism would not create a normalization violation, PURA would adjust rates to offset the ratemaking impacts of the 338(h)(10) election on rate base.  We estimate the impact to be an approximate $2.5 to $3.5 million decrease in annual revenue requirements.  In March 2014, CNG filed a draft of its private letter ruling request with PURA for approval.  During the first quarter of 2014, the OCC appealed PURA’s decision to the Connecticut Superior Court with regard to the establishment of an adjustment mechanism for incremental cast iron and bare steel replacement as well as PURA’s directive to seek a private letter ruling with respect to the extinguishment of ADITs rather than ordering a rate credit to hold customers harmless from the ratemaking effect of extinguishing the ADITs. At the request of PURA, the OCC and CNG have been engaged in ongoing settlement discussions regarding the appeal, and PURA granted CNG an extension of time for submitting the private letter ruling request to the Internal Revenue Service.
	Other Proceedings
	On June 14, 2013, CNG, SCG and Yankee Gas Services Company, an unrelated regulated gas distribution company, filed a comprehensive joint 10-year natural gas expansion plan (“Expansion Plan”) with PURA and DEEP. The plan was in response to the gas expansion goals proposed in the Connecticut Governor’s Comprehensive Energy Strategy and Public Act 13-298.  The Expansion Plan included a set of recommendations designed to help meet the statewide goal of adding approximately 280,000 new customers (approximately 200,000 of which relate to CNG and SCG), including providing more flexibility to minimize a new customer’s contribution to the cost to serve them, providing tools to help fund natural gas conversion costs, establishing a process to extend natural gas service for interested customers who are further away from the main gas line, and  allowing utilities to secure additional pipeline capacity coming into Connecticut.  PURA issued its final Decision on November 22, 2013 approving new System Expansion (SE) rates exclusively for new on and off-main customers commencing service on or after January 1, 2014.  These rates include a 10% premium distribution component for on-main customers and a 30% premium for off-main customers.  The SE rates are complemented by new business rules that extend the Companies’ financial hurdle rate model from a 20-year to a 25-year time horizon, which will reduce the customer’s contributions to any construction costs, and allow the grouping of customers to help reduce or eliminate new customer contributions to system expansion.  A separate new business reconciliation mechanism was also approved that reconciles the actual new business revenue requirements each year with the revenues received from the new business customers.   As a result of the reconciliation, any shortfall or surplus in revenues will be charged or credited to existing firm customers.  This ensures the timely recovery of new business capital investments and any associated expenses.
	On June 11, 2014, PURA reopened the Expansion Plan Proceedings to modify the assignment of non-firm margin credits to comport with new statutory requirements that change the manner in which non-firm margin credits are allocated between existing customers and proposed gas expansion projects, and to consider a request made by CNG and SCG concerning the aggregating of potential customers when determining possible gas expansion projects.  SCG, CNG, Yankee Gas Services Company, the OCC and the Bureau of Energy & Technology Policy entered into a settlement agreement on these issues that was approved by PURA on January 14, 2015.  The settlement agreement specifically states how non-firm margin credits are to be allocated between existing customers and proposed gas expansion projects, streamlines reporting requirements for gas expansion projects, and among other issues, defines the methodology to be used for aggregating potential gas customers into possible gas expansion projects.
	Gas Supply Arrangements
	The Gas Companies satisfy their natural gas supply requirements through purchases from various producer/suppliers, withdrawals from natural gas storage, capacity contracts and winter peaking supplies and resources.  The Gas Companies operate diverse portfolios of gas supply, firm transportation capacity, gas storage and peaking resources.  Actual reasonable gas costs incurred by each of the Gas Companies are passed through to customers through state regulated purchased gas adjustment mechanisms, subject to regulatory review.
	The Gas Companies purchase the majority of their natural gas supply at market prices under seasonal, monthly or mid-term supply contracts and the remainder is acquired on the spot market.  The Gas Companies diversify their sources of supply by amount purchased and location and primarily acquire gas at various locations in the US Gulf of Mexico region, in the Appalachia region and in Canada.
	The Gas Companies acquire firm transportation capacity on interstate pipelines under long-term contracts and utilize that capacity to transport both natural gas supply purchased and natural gas withdrawn from storage to the local distribution system.  Collectively, the Gas Companies hold approximately 96 firm transportation contracts on 12 different pipelines.  Three of those pipelines, Tennessee Gas Pipeline, Algonquin Gas Transmission and Iroquois Gas Transmission, interconnect with one or more of the Gas Companies’ distribution system and the other pipelines provide indirect services upstream of the city gates.  The prices and terms and conditions of the long-term contracts for firm transportation capacity are regulated by the FERC.  The actual reasonable costs of such contracts are passed through to customers through state regulated purchased gas adjustment mechanisms.  The future obligations under these contracts as of December 31, 2014 are as follows:
		(In Thousands)
	2015		133,586
	2016		126,581
	2017		117,279
2018		82,238
2019		68,487
2020-after		450,763
	$	978,934
The Gas Companies acquire firm underground natural gas storage capacity using long-term contracts and fill the storage facilities with gas in the summer months for subsequent withdrawal in the winter months.  Collectively, the Gas Companies hold 24 gas storage contracts with seven different storage contractors.  The storage facilities are located in Pennsylvania, New York, West Virginia and Michigan.
Winter peaking resources are primarily attached to the local distribution systems and are either owned or are contracted for by the Gas Companies, each of which is a Local Distribution Company.  Each Gas Company owns or has rights to the natural gas stored in an LNG facility directly attached to its distribution system.

SHORTTERM_CREDIT_ARRANGEMENTS

SHORT-TERM CREDIT ARRANGEMENTS	12 Months Ended
	Dec. 31, 2014
SHORT-TERM CREDIT ARRANGEMENTS [Abstract]
SHORT-TERM CREDIT ARRANGEMENTS	(D)  SHORT‑TERM CREDIT ARRANGEMENTS
	UIL Holdings, UI, CNG, SCG, and Berkshire are parties to a revolving credit agreement with a group of banks that will expire on November 30, 2016 (the UIL Holdings Credit Facility).  The aggregate borrowing limit under the UIL Holdings Credit Facility is $400 million, all of which is available to UIL Holdings, $250 million of which is available to UI, $150 million of which is available to each of CNG and SCG, and $25 million of which is available to Berkshire, all subject to the aggregate limit of $400 million.  The UIL Holdings Credit Facility permits borrowings at fluctuating interest rates and also permits borrowings for fixed periods of time specified by each borrower at fixed interest rates determined by the Eurodollar interbank market in London (LIBOR).  The UIL Holdings Credit Facility also permits the issuance of letters of credit of up to $50 million.
	As of December 31, 2014, there was $89 million outstanding under the UIL Holdings Credit Facility.  UIL Holdings has outstanding standby letters of credit in the aggregate amount of $4.4 million, which expire on June 16, 2015 and January 31, 2016.  Available credit under the UIL Holdings Credit Facility at December 31, 2014 totaled $306.6 million for UIL Holdings and its subsidiaries in the aggregate.  We record borrowings under the UIL Holdings Credit Facility as short‑term debt, but the UIL Holdings Credit Facility provides for longer term commitments from banks allowing us to borrow and reborrow funds, at our option, until the facility’s expiration, thus affording us flexibility in managing our working capital requirements.
	In connection with the proposed acquisition, UIL Holdings, UI, CNG, SCG, and Berkshire entered into an Amendment No. 1 to the UIL Holdings Credit Facility with the banks on March 17, 2014.  The primary purpose of the Amendment No. 1 was to address provisions that would be impacted by the Acquisition. However, because we have terminated the Asset Purchase Agreement, these provisions of the Amendment No. 1 have no force or effect.
	On December 31, 2014, UIL Holdings’ 364-day Bridge Term Loan Agreement (Bridge Facility) entered into on March 28, 2014 with its subsidiary, WGP Acquisition LLC (WGP), and a group of banks and Morgan Stanley Senior Funding, Inc., as administrative agent, in an aggregate principal amount of up to $1.9 billion, terminated in accordance with its terms as a result of the termination of the Asset Purchase Agreement.  UIL Holdings had not drawn on commitments under the Bridge Facility and there were no amounts outstanding upon the Bridge Facility’s termination.
	In October 2012, UIL Holdings entered into a credit agreement with a borrowing limit of $100 million that expired on October 31, 2013 (the Credit Agreement).  The outstanding balance was repaid upon expiration.
	Information with respect to short-term borrowings is set forth below:
			2014			2013
			( In Thousands)
	UIL Holdings
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	111,000		$	202,000
	Average aggregate short-term borrowings outstanding during the year (1)		$	49,233		$	152,455
	Weighted average interest rate (1)			1.37	%		1.43	%
	Principal amounts outstanding at year-end		$	89,000		$	-
	UI
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	-		$	60,000
	Average aggregate short-term borrowings outstanding during the year (1)		$	-		$	13,510
	Weighted average interest rate (1)			N/	A		1.4	%
	Principal amounts outstanding at year-end		$	-		$	-
	Gas Companies
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	-		$	-
	Average aggregate short-term borrowings outstanding during the year (1)		$	-		$	-
	Weighted average interest rate (1)			N/	A		N/	A
	Principal amounts outstanding at year-end		$	-		$	-
	N/A – not applicable
		-1	Average short‑term borrowings represent the sum of daily borrowings outstanding, weighted for the number of days outstanding and divided by the number of days in the period.  The weighted average interest rate is determined by dividing interest expense by the amount of average borrowings.

INCOME_TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2014
INCOME TAXES [Abstract]
INCOME TAXES	(E) INCOME TAXES
		2014			2013			2012
		(In Thousands)
	Income tax expense consists of:
	Income tax provisions:
	Current
	Federal	$	-		$	(443	)	$	5,830
	State		1,798			(1,149	)		1,110
	Total current		1,798			(1,592	)		6,940
	Deferred
	Federal		54,407			64,931			61,510
	State		1,552			6,164			6,611
	Total deferred		55,959			71,095			68,121
	Investment tax credits		(195	)		(195	)		(195	)
	Total income tax expense	$	57,562		$	69,308		$	74,866
	Total income taxes differ from the amounts computed by applying the federal statutory tax rate to income before taxes.  The reasons for the differences are as follows:
		2014			2013			2012
		(In Thousands)
	Book income before income taxes	$	167,141		$	184,625		$	178,567
	Computed tax at federal statutory rate	$	58,499		$	64,619		$	62,499
	Increases (reductions) resulting from:
	Amortization of nuclear plant regulatory assets		-			6,867			9,334
	State income taxes, net of federal income tax benefits		2,177			3,259			5,018
	Allowance for equity funds used during construction		(3,064	)		(3,784	)		(2,749	)
	Investment tax credits		(195	)		(195	)		(195	)
	Other items, net		145			(1,458	)		959
	Total income tax expense	$	57,562		$	69,308		$	74,866
	Effective income tax rates		34.4	%		37.5	%		41.9	%
	The significant portion of UIL Holdings’ income tax expense, including deferred taxes, is recovered through its regulated subsidiaries’ utility rates. UIL Holdings’ annual income tax expense and associated effective tax rate is impacted by differences between the timing of deferred tax temporary difference activity and deferred tax recovery. UIL Holdings’ effective tax rate is also impacted by permanent differences between the book and tax treatment of certain costs.
	The decrease in UIL Holdings’ income tax expense and effective tax rate in 2014 compared to 2013 was primarily due to lower pre-tax earnings and the absence in 2014 of non-normalized CTA amortization.
	In 2012, UIL Holdings changed its cumulative treatment of the timing of deducting certain repair and maintenance costs to comply with Internal Revenue Service regulations. This change enabled UIL Holdings to fully reverse a reserve for an uncertain tax position and associated interest. As this underlying uncertainty was temporary in nature, its reversal did not impact overall income tax expense. As of December 31, 2014 and 2013, UIL Holdings does not believe it has taken a material uncertain tax position and, as a result, does not have any gross income tax reserves.
	In September 2013, the Internal Revenue Service issued final tangible property regulations that are meant to simplify, clarify and make more administrable previously issued guidance. UIL Holdings will comply with these regulations in a timely manner upon completing its evaluation of potential elections and the filing of its 2014 federal income tax return. Changes required and other changes under evaluation are not expected to have a significant impact on 2015 income tax expense, net balance sheet position or cash flows.
	UIL Holdings and its subsidiaries are subject to the United States federal income tax statutes administered by the IRS. UIL Holdings files a consolidated federal income tax return with its subsidiaries, all of which have joint and several liability for any potential assessments against the consolidated group. UIL Holdings and its subsidiaries are also subject to the income tax statutes of the State of Connecticut and the Commonwealth of Massachusetts.
	The 2014 change in the applicable Massachusetts statutory rate did not have a significant impact on UIL Holdings’ income tax expense. As of December 31, 2014, income tax years 2010 through 2014 are open and subject to federal, Connecticut, and Massachusetts audit.
	The following table summarizes UIL Holdings’ deferred income tax assets and liabilities as of December 31, 2014 and 2013.
		2014			2013
		(In Thousands)
	Deferred income tax assets:
	Post-retirement benefits	$	130,474		$	90,300
	Accrued removal obligation		134,175			119,904
	Net operating loss carry forward		49,772			42,818
	Other		64,929			104,467
		$	379,350		$	357,489
	Deferred income tax liabilities:
	Plant basis and accelerated depreciation timing differences	$	700,969		$	607,950
	Regulatory deferrals related to pension and other post-retirement benefits		149,158			110,980
	Investment in GenConn		53,378			53,350
	Other		64,946			104,009
		$	968,451		$	876,289
	The following table sets forth the carry forward balances for the years ended December 31, 2014 and 2013:
								Year
								Expiration
		2014			2013			Begins
		(In Thousands)
	Federal net operating loss	$	142,704		$	122,339			2032
	Alternative minimum tax credit		2,697			2,697			N/	A
	State tax credits		11,276			7,289			2017

SUPPLEMENTARY_INFORMATION

SUPPLEMENTARY INFORMATION	12 Months Ended
	Dec. 31, 2014
SUPPLEMENTARY INFORMATION [Abstract]
SUPPLEMENTARY INFORMATION	(F) SUPPLEMENTARY INFORMATION
		2014			2013			2012
		(In Thousands)
	Depreciation and Amortization
	Property, plant, and equipment depreciation	$	131,051		$	120,301		$	112,002
	Amortization of regulatory assets		20,506			69,555			69,346
	Total Depreciation and Amortization	$	151,557		$	189,856		$	181,348
	Taxes - Other than Income Taxes
	Operating:
	Connecticut gross earnings	$	73,429		$	75,330		$	65,753
	Local real estate and personal property		50,392			46,567			40,588
	Payroll taxes		13,050			8,005			7,274
	Other		1,400			556			422
	Total Taxes - Other than Income Taxes	$	138,271		$	130,458		$	114,037
	Other Income and (Deductions), net
	Interest income	$	2,573		$	2,733		$	2,631
	Allowance for funds used during construction - equity		8,814			10,811			7,480
	Allowance for funds used during construction - debt		5,157			7,170			6,979
	Weather insurance		(2,200	)		(70	)		3,488
	TSO incentives		-			-			2,745
	Other		3,676			(11	)		1,923
	Total Other Income and (Deductions), net	$	18,020		$	20,633		$	25,246

PENSION_AND_OTHER_BENEFITS

PENSION AND OTHER BENEFITS	12 Months Ended
	Dec. 31, 2014
PENSION AND OTHER BENEFITS [Abstract]
PENSION AND OTHER BENEFITS	(G)  PENSION AND OTHER BENEFITS
	Disclosures pertaining to UIL Holdings’ pension and other postretirement benefit plans (the Plans) are in accordance with ASC 715 “Compensation-Retirement Benefits.”  UIL Holdings has an investment policy addressing the oversight and management of pension assets and procedures for monitoring and control.  UIL Holdings has engaged State Street Bank and Bank of America as the trustees and investment managers to assist in areas of asset allocation and rebalancing, portfolio strategy implementation, and performance monitoring and evaluation.
	The goals of the asset investment strategy are to:
	·	Achieve long‑term capital growth while maintaining sufficient liquidity to provide for current benefit payments and UIL Holdings’ pension and other postretirement benefit plan operating expenses.
	·	Provide a total return that, over the long term, provides sufficient assets to fund UIL Holdings’ pension plan liabilities subject to an appropriate level of risk, contributions and pension and other postretirement benefit expenses.
	·	Optimize the return on assets, over the long term, by investing primarily in a diversified portfolio of equities and additional asset classes with differing rates of return, volatility and correlation.
	·	Diversify investments within asset classes to maximize preservation of principal and minimize over‑exposure to any one investment, thereby minimizing the impact of losses in single investments.
	The Plans comply with the Employee Retirement Income Security Act of 1974 (ERISA) as amended, and any applicable regulations and laws.
	The Retirement Benefits Plans Investment Committee of the Board of Directors oversees the investment of the Plans’ assets in conjunction with management and has conducted a review of the investment strategies and policies of the Plans.  This review included an analysis of the strategic asset allocation, including the relationship of Plan assets to Plan liabilities, and portfolio structure.  The 2015 target asset allocations, which may be revised by the Retirement Benefits Plans Investment Committee, are approximately as follows:  60% equity securities and 40% debt securities.  In the event that the relationship of Plan assets to Plan liabilities changes, the Retirement Benefits Plans Investment Committee will consider changes to the investment allocations.  The other postretirement employee benefit fund assets are invested in a balanced mutual fund and, accordingly, the asset allocation mix of the balanced mutual fund may differ from the target asset allocation mix from time to time.
	The funding policy for the Plans is to make annual contributions that satisfy the minimum funding requirements of ERISA, but that do not exceed the maximum deductible limits of the Internal Revenue Code.  These amounts are determined each year as a result of an actuarial valuation of the Plans.  UIL Holdings currently expects to make pension contributions of $15 million in 2015.  Such contribution levels will be adjusted, if necessary, based on actuarial calculations.
	UIL Holdings applies consistent estimation techniques regarding its actuarial assumptions, where appropriate, across the pension and postretirement plans of its operating subsidiaries.  The estimation technique utilized to develop the discount rate for its pension and postretirement benefit plans is based upon the yield of a portfolio of high quality corporate bonds that could be purchased as of December 31, 2014 to produce cash flows matching the expected plan disbursements within reasonable tolerances.  The expected return is based upon a combination of historical performance and anticipated future returns for a portfolio reflecting the mix of equity, debt and other investments included in plan assets.  Average wage increases are determined from projected annual pay increases, which are used to determine the wage base used to project employees’ pension benefits at retirement.  The health care cost trend rate is derived from projections of expected increases in health care costs.
	UIL Holdings is utilizing a discount rate of 4.30% as of December 31, 2014 for all of its qualified pension plans, compared to 5.20% in 2013.  The decrease in the discount rate, which was due to changes in long-term interest rates, resulted in an increase to the projected benefit obligation of approximately $112 million from 2013 to 2014.  The discount rate for non-qualified pension plans as of December 31, 2014 was 4.20% compared to 4.90% in 2013.
	The discount rate for UIL Holdings’ postretirement benefits plans reflects the differing plan requirements and expected future cash flows.  For the UI postretirement plan, the discount rate at December 31, 2014 was 4.30%, compared to 5.20% at December 31, 2013.  For the Gas Company postretirement plans, the December 31, 2014 discount rate was a composite rate of 4.20%, weighted by expected future cash outflows, compared to 4.85% for the previous year.
	The pension and other postretirement benefits plans assumptions may be revised over time as economic and market conditions change.  Changes in those assumptions could have a material impact on pension and other postretirement expenses.  For example, if there had been a 0.25% change in the discount rate assumed for the pension plans, the 2014 pension expense would have increased or decreased inversely by $3.2 million.  If there had been a 1% change in the expected return on assets assumed for the pension plans, the 2014 pension expense would have increased or decreased inversely by $7.2 million. If there had been a 0.25% change in the discount rate assumed for the other postretirement benefits plans, the 2014 other postretirement benefits plan expenses would have increased or decreased inversely by $0.4 million. If there had been a 1% change in the expected return on assets assumed for the other postretirement benefits plans, the 2014 other postretirement benefits plan expenses would have increased or decreased inversely by $0.4 million.
	During 2014, the Society of Actuaries issued its final updated mortality tables and projection scales.  UIL Holdings, in conjunction with its actuaries, performed an analysis to determine the appropriateness of adopting these tables and the related mortality projections.  As a result, the UIL Holdings pension and postretirement plan liabilities as of December 31, 2014 reflect updated mortality assumptions.   The Plans have adopted the Society of Actuaries’ new base table, with collar adjustments.  In addition, the Plans are using a projection scale more aligned and consistent with recent experience to estimate projected changes in future mortality.  The change in the mortality assumption increased the projected benefit obligations for the pension and other postretirement benefit plans as of December 31, 2014 by approximately $38 million and $7 million, respectively.  There was no impact on 2014 expense.
	Also in 2014, UIL Holdings, in conjunction with its actuaries, completed an experience study of its demographic assumptions.  Such studies are undertaken periodically and encompass other demographic assumptions, such as termination, retirement and disability.  The changes resulting from the experience study decreased the projected benefit obligations for pension and other postretirement plans as of December 31, 2014 by approximately $34 million and $16 million, respectively.  There was no impact on 2014 expense.
	Pension Plans
	The United Illuminating Company Pension Plan (the UI Pension Plan) covers the majority of employees of UIL Holdings Corporate and UI.  UI also has a non‑qualified supplemental pension plan for certain employees and a non‑qualified retiree‑only pension plan for certain early retirement benefits.
	The Gas Companies have multiple qualified pension plans covering substantially all of their union and management employees.  These entities also have non‑qualified supplemental pension plans for certain employees.  The qualified pension plans are traditional defined benefit plans or cash balance plans for those hired on or after specified dates.  In some cases, neither of these plans is offered to new employees and have been replaced with enhanced 401(k) plans for those hired on or after specified dates.
	UI has established a supplemental retirement benefit trust and, through this trust, purchased life insurance policies on certain officers of UIL Holdings and UI to fund the future liability under the non-qualified supplemental plan.  The cash surrender value of these policies is included in “Other investments” on the Consolidated Balance Sheet.
	In addition, regarding the non-qualified plans, UIL Holdings has several rabbi trusts that were established to provide a supplemental retirement benefit for certain officers and directors of the Gas Companies.
	Other Postretirement Benefits Plans
	In addition to providing pension benefits, UI also provides other postretirement benefits, consisting principally of health care and life insurance benefits, for retired employees and their dependents.  UI does not provide prescription drug benefits for Medicare-eligible employees in its other postretirement health care plans.  Non-union employees who are 55 years of age and whose sum of age and years of service at time of retirement is equal to or greater than 65 are eligible for benefits partially subsidized by UI.  The amount of benefits subsidized by UI is determined by age and years of service at retirement.  For funding purposes, UI established a 401(h) account in connection with the UI Pension Plan and Serial Voluntary Employee Benefit Association Trust (VEBA) accounts for the years 2007 through 2020 to fund other postretirement benefits for UI’s non‑union employees who retire on or after January 1, 1994. These VEBA accounts were approved by the IRS and UI contributed $4.5 million to fund the Serial VEBA accounts in 2007. UI does not expect to make a contribution in 2015 to fund OPEB for non-union employees.
	Union employees whose sum of age and years of service at the time of retirement is equal to or greater than 85 (or who are 62 with at least 20 years of service) are eligible for benefits partially subsidized by UI.  The amount of benefits subsidized by UI is determined by age and years of service at retirement.  For funding purposes, UI established a VEBA to fund other postretirement benefits for UI’s union employees.  The funding strategy for the VEBA is to select funds that most clearly mirror the pension allocation strategy.  Approximately 54% of UI’s employees are represented by Local 470‑1, Utility Workers Union of America, AFL‑CIO, for collective bargaining purposes.  Plan assets for the union VEBA consist primarily of equity and fixed‑income securities.  UI does not expect to make a contribution in 2015 to fund other postretirement benefits for union employees.
	SCG and CNG also have plans providing other postretirement benefits for substantially all of their employees.  These benefits consist primarily of health care, prescription drug and life insurance benefits, for retired employees and their dependents.  The eligibility for these benefits is determined by the employee’s date of hire, number of years of service, age and whether the employee belongs to a certain group, such as a union.  Dependents are also eligible at the employee’s date of retirement provided the retired participant pays the necessary contribution.  These plans are contributory with the level of participant’s contributions evaluated annually.  Benefits payments under these plans include annual caps for CNG participants hired after 1993 and SCG participants hired after 1996.  SCG non-union employees hired after November 1995 are not eligible for these benefits.  Union employees hired after April 1, 2010 and December 1, 2009 at SCG and CNG, respectively, are not eligible for these benefits.  As such, Gas Company OPEB liabilities are not especially sensitive to increases in the healthcare trend rate.  These plans are funded through a combination of 401(h) accounts and Voluntary Employee Benefit Association Trust (VEBA) accounts.  UIL Holdings did not make any contributions to these plans in 2014, nor does it currently plan to make a contribution in 2015.
	Other Accounting Matters
	ASC 715 requires an employer that sponsors one or more defined benefit pension or other postretirement plans to recognize an asset or liability for the overfunded or underfunded status of the plan.  For a pension plan, the asset or liability is the difference between the fair value of the plan’s assets and the projected benefit obligation.  For any other postretirement benefit plan, the asset or liability is the difference between the fair value of the plan’s assets and the accumulated postretirement benefit obligation.  UIL Holdings reflects all unrecognized prior service costs and credits and unrecognized actuarial gains and losses as regulatory assets rather than in accumulated other comprehensive income, as management believes it is probable that such items will be recoverable through the ratemaking process.  As of December 31, 2014 and 2013, UIL Holdings has recorded regulatory assets of $235.4 million and $124.2 million, respectively.
	In accordance with ASC 715, UIL Holdings utilizes an alternative method to amortize prior service costs and unrecognized gains and losses.  UIL Holdings amortizes prior service costs for both the pension and other postretirement benefits plans on a straight-line basis over the average remaining service period of participants expected to receive benefits.  UIL Holdings utilizes an alternative method to amortize unrecognized actuarial gains and losses related to the pension and other postretirement benefits plans over the lesser of the average remaining service period or 10 years.  For ASC 715 purposes, UIL Holdings does not recognize gains or losses until there is a variance in an amount equal to at least 5% of the greater of the projected benefit obligation or the market-related value of assets.  There is no such allowance for a variance in capturing the amortization of other postretirement benefits unrecognized gains and losses.
	The following table represents the change in benefit obligation, change in plan assets and the respective funded status of UIL Holdings’ pension and other postretirement plans as of December 31, 2014 and 2013.  Plan assets and obligations have been measured as of December 31, 2014 and 2013.
									Other Post-Retirement
			Pension Benefits						Benefits
			2014			2013			2014			2013
	Change in Benefit Obligation:		(In Thousands)
	Benefit obligation at beginning of year		$	859,263		$	950,609		$	119,702		$	136,687
	Service cost			11,581			14,783			1,618			1,923
	Interest cost			44,076			39,948			5,947			5,539
	Participant contributions			-			-			1,265			1,253
	Settlements (1)			-			(2,367	)		-			-
	Actuarial (gain) loss			122,309			(96,739	)		10,872			(13,893	)
	Benefits paid (including expenses)			(50,194	)		(46,971	)		(12,928	)		(11,807	)
	Benefit obligation at end of year		$	987,035		$	859,263		$	126,476		$	119,702
	Change in Plan Assets:
	Fair value of plan assets at beginning of year		$	688,410		$	625,061		$	41,163		$	38,540
	Actual return on plan assets			59,675			54,259			3,558			6,003
	Employer contributions			24,135			58,428			-			-
	Participant contributions			-			-			1,265			1,253
	Settlements (1)			-			(2,367	)		-			-
	Benefits paid (including expenses)			(50,194	)		(46,971	)		(5,287	)		(4,633	)
	Fair value of plan assets at end of year		$	722,026		$	688,410		$	40,699		$	41,163
	Funded Status at December 31:
	Projected benefits (less than) greater than plan assets		$	265,009		$	170,853		$	85,777		$	78,539
	Amounts Recognized in the Statement of Financial Position consist of:
	Non-current liabilities		$	265,009		$	170,853		$	85,777		$	78,539
	Amounts Recognized as a Regulatory Asset consist of:
	Prior service cost		$	790		$	365		$	1,163		$	1,447
	Net (gain) loss			227,004			123,178			6,407			(792	)
	Total recognized as a regulatory asset		$	227,794		$	123,543		$	7,570		$	655
	Information on Pension Plans with an Accumulated Benefit Obligation in excess of Plan Assets:
	Projected benefit obligation		$	987,035		$	859,263			N/	A		N/	A
	Accumulated benefit obligation		$	888,942		$	784,081			N/	A		N/	A
	Fair value of plan assets		$	722,026		$	688,410			N/	A		N/	A
	The following weighted average actuarial assumptions were used in calculating the benefit obligations at December 31:
	Discount rate (Qualified Plans)			4.3	%		5.2	%		N/	A		N/	A
	Discount rate (Non-Qualified Plans)			4.2	%		4.9	%		N/	A		N/	A
Discount rate (Other Post-Retirement Benefits)			N/	A		N/	A		4.20-4.30	%		4.85-5.20	%
Average wage increase			3.50-3.80	%		3.50-3.80	%		N/	A		N/	A
Health care trend rate (current year)			N/	A		N/	A		7	%		7	%
Health care trend rate (2019-2028 forward)			N/	A		N/	A		5	%		5	%
(1) Reflects settlement charges resulting from a distribution to a former employee upon retirement
N/A – not applicable
The components of net periodic benefit cost are:
		For the Year Ended December 31,
		Pension Benefits									Other Post-Retirement Benefits
		2014			2013			2012			2014			2013			2012
		(In Thousands)
Components of net periodic benefit cost:
Service cost		$	11,581		$	14,783		$	12,032		$	1,618		$	1,923		$	1,604
Interest cost			44,076			39,948			41,470			5,947			5,539			6,246
Expected return on plan assets			(54,243	)		(51,453	)		(44,874	)		(2,799	)		(2,590	)		(2,503	)
Amortization of:
Prior service costs			291			605			647			284			(50	)		(69	)
Transition obligation (asset)			-			-			-			-			-			392
Actuarial (gain) loss			12,386			20,829			13,173			(686	)		1,776			965
Settlements (1)			-			632			-			-			-			-
Net periodic benefit cost		$	14,091		$	25,344		$	22,448		$	4,364		$	6,598		$	6,635
Other Changes in Plan Assets and Benefit Obligations Recognized as a Regulatory Asset:
Net (gain) loss		$	116,211		$	(99,572	)	$	122,368		$	6,513		$	(17,257	)	$	10,760
Amortization of:
Current year prior service costs			716			111			-			-			1,352			-
Prior service costs			(291	)		(605	)		(647	)		(284	)		50			69
Transition obligation (asset)			-			-			-			-			-			(392	)
Settlements (1)			-			(632	)		-			-			-			-
Actuarial (gain) loss			(12,386	)		(20,829	)		(13,173	)		686			(1,776	)		(965	)
Total recognized as regulatory asset		$	104,250		$	(121,527	)	$	108,548		$	6,915		$	(17,631	)	$	9,472
Total recognized in net periodic benefit costs and regulatory asset		$	118,341		$	(96,183	)	$	130,996		$	11,279		$	(11,033	)	$	16,107
Estimated Amortizations from Regulatory Assets into Net Periodic Benefit Cost for the next 12 month period:
Amortization of prior service cost		$	190		$	291		$	605		$	299		$	284		$	(50	)
Amortization of net (gain) loss			19,378			12,386			20,808			706			(298	)		1,939
Total estimated amortizations		$	19,568		$	12,677		$	21,413		$	1,005		$	(14	)	$	1,889
The following actuarial weighted average assumptions were used in calculating net periodic benefit cost:
Discount rate			4.90-5.20	%		4.00-4.25	%		5.05-5.30	%		4.85-5.20	%		4.00-4.25	%		5.05-5.30	%
Average wage increase			3.50-3.80	%		3.50-3.80	%		3.50-3.80	%		N/	A		N/	A		N/	A
Return on plan assets			7.00-8.00	%		7.75-8.00	%		7.75-8.00	%		5.56-8.00	%		5.56-8.00	%		5.56-8.00	%
Health care trend rate (current year)			N/	A		N/	A		N/	A		7	%		7.5	%		8	%
Health care trend rate (2019 forward)			N/	A		N/	A		N/	A		5	%		5	%		5	%
(1) Reflects settlement charges resulting from a distribution to a former employee upon retirement
N/A – not applicable
A one percentage point change in the assumed health care cost trend rate would have the following effects:
		1% Increase			1% Decrease
		(In Thousands)
Aggregate service and interest cost components		$	849		$	(673	)
Accumulated post-retirement benefit obligation		$	12,526		$	(10,134	)
Estimated Future Benefit Payments
The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid:
Year					Other
					Postretirement
		Pension Benefits			Benefits
		(In Thousands)
2015		$	48,061		$	7,156
2016		$	52,476		$	7,096
2017		$	52,384		$	7,191
2018		$	54,271		$	7,170
2019		$	54,390		$	7,182
2020-2023		$	300,990		$	36,264
Defined Contribution Retirement Plans/401(k)
UIL Holdings has several 401(k) plans in which substantially all of its employees are eligible to participate.  Employees may defer a portion of the compensation and invest in various investment alternatives.  Matching contributions are made in the form of UIL Holdings’ common stock or cash and are dependent on the specific provisions of each of the plans.  The matching expense for 2014, 2013 and 2012 was $5.4 million, $5.2 million and $4.9 million.

RELATED_PARTY_TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2014
RELATED PARTY TRANSACTIONS [Abstract]
RELATED PARTY TRANSACTIONS	(H)  RELATED PARTY TRANSACTIONS
	During the years ended December 31, 2014 and 2013, UI received cash distributions from GenConn.  See Note (A) “Business Organization and Statement of Accounting Policies – Equity Investments.”
	A Director of UIL Holdings holds a beneficial interest in the building located at 157 Church Street, New Haven, Connecticut, where UIL Holdings leases office space.  UIL Holdings’ lease payments for this office space for the years ended December 31, 2014, 2013 and 2012 totaled $1.8 million, $1.5 million and $4.8 million, respectively.  The decrease in lease payments in 2013 as compared to 2012 is due to a reduction in office space utilized by UIL Holdings headquarters beginning in June 2012.

LEASE_OBLIGATIONS

LEASE OBLIGATIONS	12 Months Ended
	Dec. 31, 2014
LEASE OBLIGATIONS [Abstract]
LEASE OBLIGATIONS	(I)  LEASE OBLIGATIONS
	UIL Holdings and its wholly-owned direct and indirect subsidiaries have lease arrangements for office equipment, office space and land.
	Operating leases, for which the rental payments are charged to operating expense, consist principally of leases of office space and facilities, land and railroad rights of way.  The future minimum lease payments under these operating leases are estimated to be as follows:
		(In Thousands)
	2015	$	5,000
	2016		4,992
	2017		4,990
	2018		5,031
	2019		4,426
	2020-after		45,486
		$	69,925
	Rental payments charged to operating expenses in 2014, 2013 and 2012 were as follows:
		Year Ended December 31,
		2014		2013		2012
		(In Thousands)
	Rental payments	$	5,925	$	5,886	$	11,639
	Less: Sublease rental payments received		-		-		241
	Rental payments charged to operating expenses	$	5,925	$	5,886	$	11,398

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2014
COMMITMENTS AND CONTINGENCIES [Abstract]
COMMITMENTS AND CONTINGENCIES	(J)  COMMITMENTS AND CONTINGENCIES
	In the ordinary course of business, we are involved in various proceedings, including legal, tax, regulatory and environmental matters, which require management’s assessment to determine the probability of whether a loss will occur and, if probable, an estimate of probable loss.  When assessments indicate that it is probable that a liability has been incurred and an amount can be reasonably estimated, we accrue a reserve and disclose the reserve and related matter.  We disclose material matters when losses are probable but for which an estimate cannot be reasonably estimated or when losses are not probable but are reasonably possible.  Subsequent analysis is performed on a periodic basis to assess the impact of any changes in events or circumstances and any resulting need to adjust existing reserves or record additional reserves.  However, given the inherent unpredictability of these legal and regulatory proceedings, we cannot assure you that our assessment of such proceedings will reflect the ultimate outcome, and an adverse outcome in certain matters could have a material adverse effect on our results of operations or cash flows.
	Connecticut Yankee Atomic Power Company
	UI has a 9.5% stock ownership share in the Connecticut Yankee Atomic Power Company, an inactive nuclear generating company (Connecticut Yankee), the carrying value of which was $0.2 million as of December 31, 2014.  Connecticut Yankee has completed the physical decommissioning of its generation facilities and is now engaged primarily in the long-term storage of its spent nuclear fuel. Connecticut Yankee collects its costs through wholesale FERC-approved rates from UI and several other New England utilities.  UI recovers these costs from its customers through electric rates.
	In May 2013, Connecticut Yankee filed an application with FERC to, among other things, reduce its rates and eliminate future decommissioning funding requirements for its owners, using the United States Department of Energy (DOE) damage award, discussed below.  In June 2013, FERC issued a final decision which approved both the proposed rate reduction and the elimination of future decommissioning funding requirements.  As a result, UI’s obligation and corresponding regulatory asset were eliminated at that time.
	DOE Spent Fuel Litigation
	In 1998, Connecticut Yankee filed claims in the United States Court of Federal Claims seeking damages resulting from the breach of the 1983 spent fuel and high level waste disposal contract between Connecticut Yankee and the DOE.  In September 2010, the court issued its decision and awarded Connecticut Yankee damages of $39.7 million for its spent fuel-related costs through 2001, which was affirmed in May 2012.  Connecticut Yankee received payment of the damage award and, in light of its ownership share, in July 2013 UI received approximately $3.8 million of such award which was credited back to customers through the CTA.
	In December 2007, Connecticut Yankee filed a second set of complaints with the United States Court of Federal Claims against the DOE seeking damages incurred since January 1, 2002 for the DOE’s failure to remove Connecticut Yankee’s spent fuel.  In November 2013, the court issued a final judgment, which was not appealed, awarding Connecticut Yankee damages of $126.3 million.  In light of its ownership share, in June 2014, UI received approximately $12.0 million of such award which was applied, in part, against the remaining storm regulatory asset balance. The remaining regulatory liability balance was applied to the GSC “working capital allowance” and will be returned to customers through the nonbypassable federally mandated congestion charge. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Other Proceedings” for additional information.
	In August 2013, Connecticut Yankee filed a third set of complaints with the United States Court of Federal Claims against the DOE seeking an unspecified amount of damages incurred since January 1, 2009 for the DOE’s failure to remove Connecticut Yankee’s spent fuel.
	Environmental Matters
	In complying with existing environmental statutes and regulations and further developments in areas of environmental concern, including legislation and studies in the fields of water quality, hazardous waste handling and disposal, toxic substances, climate change and electric and magnetic fields, we may incur substantial capital expenditures for equipment modifications and additions, monitoring equipment and recording devices, as well as additional operating expenses.  The total amount of these expenditures is not now determinable.  Environmental damage claims may also arise from the operations of our subsidiaries.  Significant environmental issues known to us at this time are described below.
	Site Decontamination, Demolition and Remediation Costs
	In 2000, UI conveyed a former generation site on the Mill River in New Haven (English Station) to an unaffiliated entity, Quinnipiac Energy LLC (QE), reserving to UI permanent easements for the operation of its transmission facilities on the site.  At the time of the sale, approximately $1.9 million, an amount equal to the then-current estimate for remediation, was placed in escrow for purposes of bringing soil and groundwater on the English Station site into compliance with applicable environmental laws.  As of December 31, 2014, approximately $0.1 million of the escrow fund remained.  In 2006, QE sold the property to Evergreen Power, LLC (Evergreen Power) and Asnat Realty LLC (Asnat).  In January 2012, Evergreen Power and Asnat filed a lawsuit in federal district court in Connecticut against UI seeking, among other things: (i) an order directing UI to reimburse the plaintiffs for costs they have incurred and will incur for the testing, investigating and remediation of hazardous substances at the English Station site and (ii) an order directing UI to investigate and remediate the site.  In May 2012, UI filed an answer and counterclaims.  In July 2012, Evergreen Power and Asnat filed a motion for partial summary judgment with respect to UI’s liability under the federal Comprehensive Environmental Response, Compensation, and Liability Act, which was denied without prejudice.  In December 2013, Evergreen and Asnat filed a subsequent lawsuit in Connecticut state court seeking among other things: (i) remediation of the property; (ii) reimbursement of remediation costs; (iii) termination of UI’s easement rights; (iv) reimbursement for costs associated with securing the property; and (v) punitive damages.  UI believes the claims are without merit.  UI’s knowledge of the current conditions at the English Station site is insufficient for it to make a reliable update of the original $1.9 million remediation estimate.  Management cannot presently assess the potential financial impact, if any, of the suits, and thus has not recorded a liability related to it and no amount of loss, if any, can be reasonably estimated at this time.
	In April 2013, DEEP issued an administrative order addressed to UI, QE, Evergreen Power, Asnat and others, ordering the parties to take certain actions related to investigating and remediating the English Station site.  Mediation of the matter began in the fourth quarter of 2013 and is continuing.  At this time, management cannot predict the financial impact on UI of the DEEP order or other matters relating to this site and no amount of loss, if any, can be reasonably estimated at this time.
	UI owns transmission-related property adjacent to the New Haven Harbor Generating Station (formerly owned by UI), on which UI performed an environmental analysis that indicated remediation expenses would be approximately $3.2 million. UI has accrued these estimated expenses, which were recovered in transmission rates.
	The Gas Companies own or have previously owned properties where Manufactured Gas Plants (MGPs) had historically operated.  MGP operations have led to contamination of soil and groundwater with petroleum hydrocarbons, benzene and metals, among other things, at these properties, the regulation and cleanup of which is regulated by the federal Resource Conservation and Recovery Act as well as other federal and state statutes and regulations.  Each of the Gas Companies has or had an ownership interest in one or more such properties contaminated as a result of MGP-related activities.  Under the existing regulations, the cleanup of such sites requires state and at times, federal, regulators’ involvement and approval before cleanup can commence.  In certain cases, such contamination has been evaluated, characterized and remediated.  In other cases, the sites have been evaluated and characterized, but not yet remediated.  Finally, at some of these sites, the scope of the contamination has not yet been fully characterized; no liability was recorded in respect of these sites as of December 31, 2014 and no amount of loss, if any, can be reasonably estimated at this time.  In the past, the Gas Companies have received approval for the recovery of MGP-related remediation expenses from customers through rates and will seek recovery in rates for ongoing MGP-related remediation expenses for all of their MGP sites.
	SCG owns properties on Housatonic Avenue in Bridgeport, and on Chapel Street in New Haven, and CNG owns a property located on Columbus Boulevard in Hartford, all of which are former MGP sites.  Costs associated with the remediation of the sites could be significant and will be subject to a review by PURA as to whether these costs are recoverable in rates.  We cannot presently reasonably estimate the costs or range of costs of remediation or the likelihood of recoverability.  As a result, as of December 31, 2014, we have not recorded any liabilities related to these properties.
	Berkshire owns property on Mill Street in Greenfield, Massachusetts, a former MGP site.  We estimate that expenses associated with the remaining remedial activities, as well as the required ongoing monitoring and reporting to the Massachusetts Department of Environmental Protection will likely amount to approximately $0.9 million and have recorded a liability and offsetting regulatory asset for such expenses as of December 31, 2014.  Historically, Berkshire has received approval from the DPU for recovery of environmental expenses in its customer rates.
	Berkshire formerly owned a site on East Street (the East Street Site) in Pittsfield, Massachusetts, a former MGP site.  The East Street Site is part of a larger site known as the GE–Pittsfield/Housatonic River Site.  Berkshire sold the East Street Site to the General Electric Company (GE) in the 1970s and was named a potentially responsible party for the site by the EPA in 1990.  In December 2002, Berkshire reached a settlement with GE which provides, among other things, a framework for Berkshire and GE to allocate various monitoring and remediation costs at the East Street Site.  As of December 31, 2014, we had accrued approximately $3.2 million and established a regulatory asset for these and future costs incurred by GE in responding to releases of hazardous substances at the East Street Site.  Historically, Berkshire has received approval from the DPU for recovery of remediation expenses in its customer rates.
	Middletown/Norwalk Transmission Project
	The general contractor and two subcontractors responsible for civil construction work in connection with the installation of UI’s portion of the Middletown/Norwalk Transmission Project’s underground electric cable system filed lawsuits in Connecticut state court on September 22, 2009, March 23, 2009 and January 25, 2010, respectively.  The claims, as revised by the general contractor in October 2011, sought payment for change order requests of approximately $33.3 million, a 10% general contractor mark-up on any approved subcontractor change order claims (approximately $2.3 million), interest, costs, and attorneys' fees.  In December 2011, UI settled the claims brought by the two subcontractors and their respective lawsuits were dismissed, reducing UI’s estimate of the general contractor’s claims to approximately $7.7 million, exclusive of the contractor’s claims for interest, costs, and attorneys’ fees.    UI also pursued an indemnification claim against the general contractor for the payments made in settlement to the two subcontractors.
	On September 3, 2013, the court found for UI on all claims but one related to certain change orders, and ordered UI to pay the Contractor approximately $1.3 million, which has since been paid.  The court also found against UI on the indemnification claims. On October 22, 2013, the general contractor filed an appeal of the Court’s ruling. UI expects to recover any amounts paid to resolve the contractor and subcontractor claims through UI’s transmission revenue requirements.
	In April 2013, an affiliate of the general contractor for the Middletown/Norwalk Transmission Project, purporting to act as a shareholder on behalf of UIL Holdings, filed a complaint against the UIL Holdings Board of Directors alleging that the directors breached a fiduciary duty by failing to undertake an independent investigation in response to a letter from the affiliate asking for an investigation regarding alleged improper practices by UI in connection with the Middletown/Norwalk Transmission Project.  In October 2013, the court granted the defendants’ motion to dismiss the complaint.  In November 2013, the plaintiff filed an appeal of the court order in the Connecticut Appellate Court, which remains pending.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS [Abstract]
FAIR VALUE MEASUREMENTS	(K) FAIR VALUE MEASUREMENTS
	As required by ASC 820 “Fair Value Measurements and Disclosures,” financial assets and liabilities are classified in their entirety, based on the lowest level of input that is significant to the fair value measurement.  Our assessment of the significance of a particular input to the fair value measurement requires judgment, and may affect the valuation of the fair value of assets and liabilities and their placement within the fair value hierarchy levels.
	The following tables set forth the fair value of our financial assets and liabilities, other than pension benefits and other postretirement benefits, as of December 31, 2014 and December 31, 2013.
			Fair Value Measurements Using
			Quoted Prices in				Significant				Significant			Total
			Active Markets				Other				Unobservable
			for Identical				Observable				Inputs (Level 3)
			Assets (Level 1)				Inputs (Level 2)
	31-Dec-14		(In Thousands)
	Assets:
	Derivative assets		$	-			$	-			$	27,270		$	27,270
	Noncurrent investments			11,387				-				-			11,387
	Deferred Compensation Plan			3,624				-				-			3,624
	Supplemental retirement benefit trust life insurance policies			-				8,498				-			8,498
			$	15,011			$	8,498			$	27,270		$	50,779
	Liabilities:
	Derivative liabilities		$	-			$	-			$	85,074		$	85,074
	Long-term debt			-				1,941,711				-			1,941,711
			$	-			$	1,941,711			$	85,074		$	2,026,785
	Net fair value assets/(liabilities), December 31, 2014		$	15,011			$	(1,933,213	)		$	(57,804	)	$	(1,976,006	)
			Fair Value Measurements Using
			Quoted Prices in				Significant				Significant			Total
			Active Markets				Other				Unobservable
			for Identical				Observable				Inputs (Level 3)
			Assets (Level 1)				Inputs (Level 2)
	31-Dec-13		(In Thousands)
	Assets:
	Derivative assets		$	-			$	-			$	53,447		$	53,447
	Noncurrent investments			11,148				-				-			11,148
	Deferred Compensation Plan			3,775				-				-			3,775
	Supplemental retirement benefit trust life insurance policies			-				7,898				-			7,898
			$	14,923			$	7,898			$	53,447		$	76,268
	Liabilities:
	Derivative liabilities		$	-			$	-			$	196,233		$	196,233
	Long-term debt			-				1,846,867				-			1,846,867
			$	-			$	1,846,867			$	196,233		$	2,043,100
	Net fair value assets/(liabilities), December 31, 2013		$	14,923			$	(1,838,969	)		$	(142,786	)	$	(1,966,832	)
	Fair value measurements categorized in Level 3 of the fair value hierarchy are prepared by individuals with expertise in valuation techniques, pricing of energy and energy-related products, and accounting requirements.  The derivative assets consist primarily of CfDs.  The determination of fair value of the CfDs was based on a probability-based expected cash flow analysis that was discounted at the December 31, 2014 or December 31, 2013 risk-free interest rates, as applicable, and an adjustment for non-performance risk using credit default swap rates.  Certain management assumptions were required, including development of pricing that extended over the term of the contracts.  We believe this methodology provides the most reasonable estimates of the amount of future discounted cash flows associated with the CfDs.  Additionally, on a quarterly basis, we perform analytics to ensure that the fair value of the derivatives is consistent with changes, if any, in the various fair value model inputs.  Additional quantitative information about Level 3 fair value measurements is as follows:
		Unobservable Input		Range at				Range at
				31-Dec-14				31-Dec-13
	Contracts for differences	Risk of non-performance			0.00% - 0.66	%			0.00% - 0.62	%
		Discount rate			1.65% - 2.25	%			1.75% - 3.21	%
		Forward pricing ($ per MW)		$	3.15 - $14.59			$	1.40 - $9.83
	Significant isolated changes in the risk of non-performance, the discount rate or the contract term pricing would result in an inverse change in the fair value of the CfDs.
	The determination of the fair value of the supplemental retirement benefit trust life insurance policies was based on quoted prices as of December 31, 2014 and December 31, 2013 in the active markets for the various funds within which the assets are held.
	Long-term debt is carried at cost on the consolidated balance sheet.  The fair value of long-term debt as displayed in the table above is based on evaluated prices that reflect significant observable market information such as reported trades, actual trade information of similar securities, benchmark yields, broker/dealer quotes of new issue prices and relevant credit information.
	The following tables set forth a reconciliation of changes in the fair value of the assets and liabilities above that are classified as Level 3 in the fair value hierarchy for the twelve month periods ended December 31, 2014 and 2013.
			Year Ended
			31-Dec-14
			(In Thousands)
	Net derivative assets/(liabilities), December 31, 2013		$	(142,786	)
	Unrealized gains and (losses), net			84,982
	Net derivative assets/(liabilities), December 31, 2014		$	(57,804	)
	Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of December 31, 2014		$	84,982
			Year Ended
			31-Dec-13
			(In Thousands)
	Net derivative assets/(liabilities), December 31, 2012		$	(176,605	)
	Unrealized gains and (losses), net			33,819
	Net derivative assets/(liabilities), December 31, 2013		$	(142,786	)
	Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of December 31, 2013		$	33,819
	The following table sets forth a reconciliation of changes in the net regulatory asset/(liability) balances that were established to recover any unrealized gains/(losses) associated with the CfDs for the years ended December 31, 2014 and 2013.  The amounts offset the net CfDs liabilities included in the derivative liabilities detailed above.
			Year Ended
			31-Dec-14
		(In Thousands)
Net regulatory assets/(liabilities), December 31, 2013		$	142,786
Unrealized (gains) and losses, net			(84,982	)
Net regulatory assets/(liabilities), December 31, 2014		$	57,804
		Year Ended
		31-Dec-13
		(In Thousands)
Net regulatory assets/(liabilities), December 31, 2012		$	176,605
Unrealized (gains) and losses, net			(33,819	)
Net regulatory assets/(liabilities), December 31, 2013		$	142,786
The following tables set forth the fair values of UIL Holdings’ pension and OPEB assets as of December 31, 2014 and 2013.
		Fair Value Measurements Using
		Quoted Prices in				Significant				Significant			Total
		Active Markets for				Other				Unobservable
		Identical Assets				Observable				Inputs (Level 3)
		(Level 1)				Inputs (Level 2)
		(In Thousands)
31-Dec-14
Pension assets
Mutual funds		$	-			$	687,311			$	-		$	687,311
Hedge fund			-				-				34,715			34,715
			-				687,311				34,715			722,026
OPEB assets
Mutual funds			33,688				7,011				-			40,699
			33,688				7,011				-			40,699
Fair value of plan assets, December 31, 2014		$	33,688			$	694,322			$	34,715		$	762,725
31-Dec-13
Pension assets
Mutual funds		$	-			$	653,579			$	-		$	653,579
Hedge fund			-				-				34,831			34,831
			-				653,579				34,831			688,410
OPEB assets
Mutual funds			34,759				6,404				-			41,163
			34,759				6,404				-			41,163
Fair value of plan assets, December 31, 2013		$	34,759			$	659,983			$	34,831		$	729,573
The determination of fair values of the Level 2 co-mingled mutual funds and the Level 3 hedge fund were based on the Net Asset Value (NAV) provided by the managers of the underlying fund investments and the unrealized gains and losses.  The NAV provided by the managers typically reflect the fair value of each underlying fund investment.  Changes in the fair value of pension benefits and OPEB are accounted for in accordance with ASC 715 Compensation – Retirement Benefits as discussed in Note (G) “Pension and Other Benefits”.
The following tables set forth a reconciliation of changes in the fair value of the assets above that are classified as Level 3 in the fair value hierarchy for the twelve month periods ended December 31, 2014 and 2013.
		Year Ended
		31-Dec-14
		(In Thousands)
Pension assets-Level 3, December 31, 2013		$	34,831
Unrealized/Realized gains and (losses), net			(116	)
Pension assets-Level 3, December 31, 2014		$	34,715
		Year Ended
		31-Dec-13
		(In Thousands)
Pension assets-Level 3, December 31, 2012		$	27,683
Unrealized/Realized gains and (losses), net			2,035
Purchases			5,113
Pension assets-Level 3, December 31, 2013		$	34,831

QUARTERLY_FINANCIAL_DATA_UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2014
QUARTERLY FINANCIAL DATA (UNAUDITED) [Abstract]
QUARTERLY FINANCIAL DATA (UNAUDITED)	(L) QUARTERLY FINANCIAL DATA (UNAUDITED)
	Selected quarterly financial data for 2014 and 2013 are set forth below:
			1st		2nd		3rd		4th
			Quarter		Quarter		Quarter		Quarter
	(In Thousands, Except Per Share Amounts)
	2014
	Operating Revenues		$	571,162	$	334,794	$	293,026	$	432,961
	Operating Income		$	104,414	$	36,272	$	34,152	$	72,565
	Net Income		$	55,465	$	9,303	$	12,504	$	32,307
	Net Income attributable to UIL Holdings		$	55,452	$	9,343	$	12,498	$	32,300
	Earnings Per Share of Common Stock – Basic: (1)		$	0.98	$	0.16	$	0.22	$	0.57
	Earnings Per Share of Common Stock – Diluted: (1)		$	0.97	$	0.16	$	0.22	$	0.56
	2013
	Operating Revenues		$	548,039	$	319,074	$	316,478	$	435,125
	Operating Income		$	96,233	$	43,235	$	22,659	$	78,362
	Net Income		$	51,807	$	17,934	$	5,157	$	40,419
	Net Income attributable to UIL Holdings		$	51,791	$	17,924	$	5,144	$	40,406
	Earnings Per Share of Common Stock – Basic: (1)		$	1.02	$	0.35	$	0.1	$	0.71
	Earnings Per Share of Common Stock – Diluted: (1)		$	1.01	$	0.35	$	0.1	$	0.71
		-1	Based on weighted average number of shares outstanding each quarter.  Diluted earnings per share reflects the effect of restricted stock, performance shares and for 2013, dilutive stock options.  Quarterly per share amounts are not intended to be additive.

SEGMENT_INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2014
SEGMENT INFORMATION [Abstract]
SEGMENT INFORMATION	(M)  SEGMENT INFORMATION
	UIL Holdings is organized into Electric Distribution, Electric Transmission and Gas Distribution reporting segments based on several factors including, but not limited to, the nature of each segment’s products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates.  The following measures of segment profit and loss are utilized by management to make decisions about allocating resources to the segments and assessing performance.  The following table reconciles certain segment information with that provided in our Consolidated Financial Statements.  In the table, distribution includes all electric utility revenue and expenses except for transmission, which is provided in a separate column.  “Other” includes the information for the remainder of our non‑utility activities and unallocated corporate costs, including minority interest investments and administrative costs.  Revenues from inter‑segment transactions are not material.  All of our revenues are derived in the United States.
	(In Thousands)
			31-Dec-14
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	539,249	$	257,300	$	796,549	$	835,394		$	-		$	1,631,943
	Purchased power and gas			173,059		-		173,059		428,471			(2,092	)		599,438
	Operation and maintenance			180,931		54,517		235,448		179,553			(15,441	)		399,560
	Transmission wholesale			-		88,370		88,370		-			-			88,370
	Depreciation and amortization			51,213		16,197		67,410		73,232			10,915			151,557
	Taxes - other than income taxes			51,510		35,723		87,233		50,394			644			138,271
	Acquisition-related expenses			-		-		-		-			7,344			7,344
	Operating Income			82,536		62,493		145,029		103,744			(1,370	)		247,403
	Other Income and (Deductions), net			12,004		3,798		15,802		745			(14,322	)		2,225
	Interest Charges, net			33,276		12,922		46,198		27,946			22,236			96,380
	Income from Equity Investments			13,893		-		13,893		-			-			13,893
	Income (Loss) Before Income Taxes			75,157		53,369		128,526		76,543			(37,928	)		167,141
	Income Taxes			23,546		20,612		44,158		28,280			(14,876	)		57,562
	Net Income (Loss)			51,611		32,757		84,368		48,263			(23,052	)		109,579
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		(14	)		-			(14	)
	Net Income (Loss) attributable to UIL Holdings		$	51,611	$	32,757	$	84,368	$	48,277		$	(23,052	)	$	109,593
	Total Capital Expenditures (1)		$	-	$	-	$	142,179	$	131,919		$	38,055		$	312,153
			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total
	Total Assets at December 31, 2014		$	-	$	-	$	2,876,792	$	2,087,284		$	147,859		$	5,111,935
	-1	Capital expenditures are shown on a cash basis.  Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.
	-2	Information for segmenting total assets between Distribution and Transmission is not available.  Total Electric Distribution and Transmission assets are disclosed in the Total Electric Distribution and Transmission column.  Net plant in service is segregated by segment and, as of December 31, 2014, was $1,283.6 million and $659.4 million for Distribution and Transmission, respectively.
	-3	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2014.
	(In Thousands)
			31-Dec-13
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	560,877	$	242,681	$	803,558	$	815,023		$	135		$	1,618,716
	Purchased power and gas			139,135		-		139,135		438,189			-			577,324
	Operation and maintenance			189,378		45,540		234,918		154,418			(5,307	)		384,029
	Transmission wholesale			-		88,206		88,206		-			-			88,206
	Depreciation and amortization			91,670		16,353		108,023		77,890			3,943			189,856
	Taxes - other than income taxes			49,421		33,991		83,412		46,477			569			130,458
	Rate case disallowances			8,354		-		8,354		-			-			8,354
	Operating Income			82,919		58,591		141,510		98,049			930			240,489
	Other Income and (Deductions), net			13,335		4,874		18,209		(323	)		2,747			20,633
	Interest Charges, net			27,052		12,046		39,098		28,935			23,736			91,769
	Income from Equity Investments			15,272		-		15,272		-			-			15,272
	Income (Loss) Before Income Taxes			84,474		51,419		135,893		68,791			(20,059	)		184,625
	Income Taxes			37,816		17,784		55,600		23,309			(9,601	)		69,308
	Net Income (Loss)			46,658		33,635		80,293		45,482			(10,458	)		115,317
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		52			-			52
	Net Income (Loss) attributable to UIL Holdings		$	46,658	$	33,635	$	80,293	$	45,430		$	(10,458	)	$	115,265
	Total Capital Expenditures (1)		$	-	$	-	$	160,042	$	97,346		$	47,790		$	305,178
			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total (3)
	Total Assets at December 31, 2013		$	-	$	-	$	2,950,707	$	2,010,246		$	183,267		$	5,144,220
			31-Dec-12
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	561,148	$	222,314	$	783,462	$	702,887		$	152		$	1,486,501
	Purchased power and gas			154,546		-		154,546		370,234			-			524,780
	Operation and maintenance			178,862		43,185		222,047		137,707			(3,477	)		356,277
	Transmission wholesale			-		79,469		79,469		-			-			79,469
	Depreciation and amortization			88,672		14,890		103,562		75,205			2,581			181,348
	Taxes - other than income taxes			44,845		26,773		71,618		42,254			165			114,037
Operating Income (Loss)			94,223		57,997		152,220		77,487			883			230,590
Other Income and (Deductions), net			16,562		3,945		20,507		4,071			668			25,246
Interest Charges, net			28,308		12,941		41,249		28,001			23,292			92,542
Income from Equity Investments			15,273		-		15,273		-			-			15,273
Income (Loss) Before Income Taxes			97,750		49,001		146,751		53,557			(21,741	)		178,567
Income Taxes			45,091		17,025		62,116		21,305			(8,555	)		74,866
Net Income (Loss)			52,659		31,976		84,635		32,252			(13,186	)		103,701
Less:
Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		64			-			64
Net Income (Loss) attributable to UIL Holdings		$	52,659	$	31,976	$	84,635	$	32,188		$	(13,186	)	$	103,637
Total Capital Expenditures (1)		$	-	$	-	$	178,107	$	80,837		$	29,689		$	288,633
		Electric Distribution and Transmission (2)
		Distribution		Transmission		Total		Gas Distribution (3)			Other			Total (3)
Total Assets at December 31, 2012		$	-	$	-	$	2,935,562	$	1,993,560		$	90,042		$	5,019,164
-1	Capital expenditures are shown on a cash basis.  Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.
-2	Information for segmenting total assets between Distribution and Transmission is not available.  Total Electric Distribution and Transmission assets are disclosed in the Total Electric and Distribution and Transmission column.  Net plant in service is segregated by segment and, as of December 31, 2013, was $1,181.1 million and $656.0 million for Distribution and Transmission, respectively.  As of December 31, 2012, net plant in service was $1,114.2 million and $612.0 million for Distribution and Transmission, respectively.
-3	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2013 and 2012.

SUBSEQUENT_EVENT_PROPOSED_MERG

SUBSEQUENT EVENT - PROPOSED MERGER WITH IBERDROLA USA	12 Months Ended
	Dec. 31, 2014
SUBSEQUENT EVENT - PROPOSED MERGER WITH IBERDROLA USA [Abstract]
SUBSEQUENT EVENT - PROPOSED MERGER WITH IBERDROLA USA	(N) SUBSEQUENT EVENT – PROPOSED MERGER WITH IBERDROLA USA
	On February 25, 2015, we announced that UIL Holdings had entered into a definitive merger agreement with Iberdrola USA under which Iberdrola USA will acquire UIL Holdings and create a newly listed U.S. publicly-traded company. In connection with the merger, each issued and outstanding share of the common stock of UIL Holdings (other than the issued shares of UIL Holdings common stock that are owned by UIL Holdings, which will be automatically cancelled at the time the merger is consummated) will be converted into the right to receive one validly issued share of common stock of the newly listed company and $10.50 in cash. Immediately following the consummation of the merger, former holders of UIL Holdings’ common stock will own approximately 18.5% of the newly listed company. We currently expect that the transaction will close by the end of 2015. There are no assurances that the proposed merger with Iberdrola USA will be consummated on the currently expected timetable or at all. Unless stated otherwise, all forward-looking information contained in this report does not take into account or give any effect to the impact of our proposed merger with Iberdrola USA.
	Further information concerning the proposed merger will be included in a proxy statement/prospectus contained in a registration statement on Form S-4 to be filed by us with the SEC in connection with the proposed merger.

Schedule_I_Condensed_Financial

Schedule I - Condensed Financial Statements of Registrant	12 Months Ended
	Dec. 31, 2014
Schedule I - Condensed Financial Statements of Registrant
Schedule I - Condensed Financial Statements of Registrant	Schedule I – Condensed Financial Statements of Registrant
	UIL HOLDINGS CORPORATION (PARENT)
	CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	STATEMENTS OF INCOME
	FOR THE YEARS ENDED DECEMBER 31, 2014, 2013, AND 2012
	(In Thousands except per share amounts)
		2014			2013			2012
	Operating Revenues	$	18,441		$	6,209		$	4,193
	Operating Expenses
	Operation and maintenance		1,966			844			639
	Depreciation and amortization		10,494			3,842			2,530
	Taxes - other than income taxes		551			562			156
	Acquitistion-related expenses		7,344			-			-
	Total Operating Expenses		20,355			5,248			3,325
	Operating Income		(1,914	)		961			868
	Other Income and (Deductions), net
	Acquisition-related bridge facility fees		(15,795	)		2,552			351
	Other income and (deductions)		1,763			-			-
	Total Other Income and (Deductions), net		(14,032	)		2,552			351
	Interest Charges, net		22,239			23,735			23,292
	Equity in earnings of subsidiaries		132,783			125,871			117,083
	Income Before Income Taxes		94,598			105,649			95,010
	Income Taxes		(14,981	)		(9,668	)		(8,691	)
	Net Income		109,579			115,317			103,701
	Net Income Attributable to Noncontrolling Interest		(14	)		52			64
	Net Income Attributable to UIL Holdings	$	109,593		$	115,265		$	103,637
	Average Number of Common Shares Outstanding - Basic		56,834			52,415			50,831
	Average Number of Common Shares Outstanding - Diluted		57,136			52,711			51,108
	Earnings Per Share of Common Stock - Basic:	$	1.93		$	2.2		$	2.04
	Earnings Per Share of Common Stock - Diluted:	$	1.92		$	2.18		$	2.02
	UIL HOLDINGS CORPORATION (PARENT)
	CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	STATEMENTS OF COMPREHENSIVE INCOME
	FOR THE YEARS ENDED DECEMBER 31, 2014, 2013, AND 2012
	(In Thousands)
		2014			2013			2012
	Net Income	$	109,579		$	115,317		$	103,701
	Other Comprehensive Income (Loss), net of income taxes
	Changes in unrealized gains(losses) related to pension and other post-retirement benefit plans		(815	)		1,008			(90	)
	Other		3			(24	)		16
	Total Other Comprehensive Income (Loss), net of deferred income taxes		(812	)		984			(74	)
	Comprehensive Income		108,767			116,301			103,627
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests		(14	)		52			64
	Comprehensive Income Attributable to UIL Holdings	$	108,781		$	116,249		$	103,563
	UIL HOLDINGS CORPORATION (PARENT)
	CONDENSED FINANCIAL INFORMATION OF REGISTRANT
	BALANCE SHEET
	AS OF DECEMBER 31, 2014 AND 2013
	(In Thousands)
		December 31,			December 31,
		2014			2013
	ASSETS
	Current Assets
	Unrestricted cash and temporary cash investments	$	3,074		$	28,915
	Intercompany receivables		24,875			22,934
	Deferred income taxes		30,653			19,927
	Refundable taxes		8,107			13,337
	Other		6,170			5,720
	Total Current Assets		72,879			90,833
	Investments in Subsidiaries		1,769,034			1,669,052
	Net Property, Plant and Equipment		123,337			105,078
	Deferred income taxes		5,951			-
	Other Assets		7,624			6,520
Total Assets	$	1,978,825		$	1,871,483
LIABILITIES AND CAPITALIZATION
Current Liabilities
Line of credit borrowings	$	89,000		$	-
Accounts payable		21,409			15,780
Dividends payable		24,428			24,392
Other		19,956			23,500
Total Current Liabilities		154,793			63,672
Deferred income taxes		-			1,035
Other Liabilities		8,093			5,558
Capitalization
Long-term debt, net of unamortized discount and premium		447,737			447,403
Net Common Stock Equity		1,368,202			1,353,815
Total Capitalization		1,815,939			1,801,218
Total Liabilities and Capitalization	$	1,978,825		$	1,871,483
UIL HOLDINGS CORPORATION (PARENT)
CONDENSED FINANCIAL INFORMATION OF REGISTRANT
STATEMENTS OF CASH FLOWS
FOR THE YEARS ENDED DECEMBER 31, 2014, 2013, AND 2012
(In Thousands)
	2014			2013			2012
Net Cash provided by Operating Activities	$	104,150		$	122,285		$	89,875
Cash Flows from Investing Activities
Plant expenditures		(33,209	)		(47,790	)		(29,689	)
Capital contributions to subsidiaries		(96,000	)		-			(100,000	)
Intercompany loan receivable		8,000			(8,000	)		-
Other		-			-			304
Net Cash (used in) Investing Activities		(121,209	)		(55,790	)		(129,385	)
Cash Flows from Financing Activities
Issuance of common stock		-			206,516			1,943
Line of credit borrowings (repayments), net		89,000			(157,000	)		122,000
Payment of common stock dividend		(97,708	)		(87,602	)		(87,490	)
Other		(74	)		391			508
Net Cash provided by (used in) Financing Activities		(8,782	)		(37,695	)		36,961
Unrestricted Cash and Temporary Cash Investments:
Net change for the period		(25,841	)		28,800			(2,549	)
Balance at beginning of period		28,915			115			2,664
Balance at end of period	$	3,074		$	28,915		$	115
Note 1.  Basis of Presentation
The accompanying condensed financial statements of UIL Holdings Corporation (parent) should be read in conjunction with the consolidated financial statements and notes thereto of UIL Holdings Corporation and subsidiaries ("Registrant") included in Part II, Item 8 of this Form 10-K.  UIL Holdings Corporation’s (parent) significant accounting policies are consistent with those of the Registrant.
Dividends Paid
UIL Holdings Corporation received dividends from subsidiaries of $151.2 million, $140.5 million and $73.1 million in 2014, 2013 and 2012, respectively.
Note 2.  Capitalization and Short-Term Credit Arrangements
See Notes to Consolidated Financial Statements in this Form 10-K for disclosure of Parent’s capitalization information as described in Note B “Capitalization” and of line of credit borrowings as described in Note D “Short-Term Credit Arrangements.”
Information regarding maturities of long-term debt is set forth below:
	2015			2016			2017			2018		2019 &Thereafter
	(In Thousands)
Maturities:	$	-		$	-		$	-		$	-	$	450,000
Note 3.  Related Party Transactions
Operating Revenues in the accompanying statements of income consist of revenues from services provided to subsidiaries.  Accounts payable in the accompanying balance sheets includes intercompany accounts payable of $5.2 million and an immaterial amount at December 31, 2014 and 2013, respectively.
Note 4.  Contingencies
For a discussion of material contingencies see “Item 8.  Notes to Consolidating Financial Statements – Note J Commitments and Contingencies” in this Form 10-K.

Schedule_II_Valuation_and_Qual

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Schedule II-Valuation and Qualifying Accounts [Abstract]
Schedule II-Valuation and Qualifying Accounts	UIL Holdings Corporation
	Schedule II - Valuation and Qualifying Accounts
	For the Years Ended December 31, 2014, 2013 and 2012
	(Thousands of Dollars)
	Col. A.		Col. B.		Col. C.		Col. D.				Col. E.			Col. F.
							Additions
	Classification		Balance at		Acquired		Charged to		Charged to		Deductions			Balance at
			Beginning		Balance		Costs and		Other					End
			of Period				Expenses		Accounts					of Period
	RESERVE DEDUCTION FROM ASSETS TO WHICH IT APPLIES:
	Reserve for uncollectible accounts (consolidated):
	2014		$	12,021	$	-	$	45,659	$	-	$	48,799	(A)	$	8,881
	2013		$	11,867	$	-	$	33,476	$	-	$	33,322	(A)	$	12,021
	2012		$	10,939	$	-	$	36,850	$	-	$	35,922	(A)	$	11,867
	(A)	Accounts written off, net of recoveries

STATEMENT_OF_ACCOUNTING_POLICI1

STATEMENT OF ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2014
STATEMENT OF ACCOUNTING POLICIES [Abstract]
Basis of Presentation	Basis of Presentation
	The financial statements of UIL Holdings are prepared on a consolidated basis and therefore include the accounts of UIL Holdings’ majority-owned subsidiaries noted above.  Intercompany accounts and transactions have been eliminated in consolidation.
	The preparation of financial statements in conformity with GAAP requires management to use estimates and assumptions that affect (1) the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and (2) the reported amounts of revenues and expenses during the reporting period.  Actual results could differ from those estimates.
	Certain immaterial amounts that were reported as such in the Consolidated Financial Statements in previous periods have been reclassified to conform to the current presentation.
Philadelphia Gas Works	Philadelphia Gas Works
	On March 2, 2014, UIL Holdings entered into an Asset Purchase Agreement (the Asset Purchase Agreement) with the City of Philadelphia pursuant to which UIL Holdings, through a wholly-owned subsidiary, would acquire the operating assets and assume certain liabilities of Philadelphia Gas Works for an initial purchase price of $1.86 billion, subject to adjustment (Acquisition).
	The Acquisition was subject to the satisfaction or waiver of certain customary and other closing conditions for transactions of this type, including approval from the Philadelphia City Council.  On October 27, 2014, the City Council announced that it would not endorse the Acquisition.  In light of the City Council’s announcement, on December 4, 2014 we exercised our contractual right to terminate the Asset Purchase Agreement.
	As of December 31, 2014, UIL Holdings incurred pre-tax acquisition-related expenses of approximately $23.1 million, $7.3 million of which represents legal, investment banking, and due diligence costs that are included in operating expenses and $15.8 million of which are fees associated with a Bridge Term Loan Agreement (Bridge Facility) that is included in other income and (deductions) in the Consolidated Statement of Income.  See Note (D) “Short-Term Credit Arrangements” for additional information about the Bridge Facility.
Milford LNG Purchase	Milford LNG Purchase
	On July 31, 2014, United Resources, Inc., a wholly owned subsidiary of UIL Holdings, purchased from Iberdrola USA, Inc. and certain of its subsidiaries, all of the outstanding equity of certain entities (the Purchased Entities) owning (a) a 14.6 million gallon liquefied natural gas (LNG) storage tank operated by SCG and located on property owned by SCG in Milford, Connecticut (the Tank), (b) certain equipment, materials and supplies used in or useful for the operation of the Tank (together with the Tank, the Assets) and (c) the LNG inventory, for a cash purchase price of approximately $20.3 million.  The structure and the pricing of the transaction are intended to maintain the current regulatory structure of the Purchased Entities and the Assets, and have no impact on customers.  The Assets earn a rate of return equal to SCG’s allowed rate of return.
Allowance for Funds Used During Construction	Allowance for Funds Used During Construction
	In accordance with the uniform systems of accounts, the Company capitalizes allowance for funds used during construction (AFUDC), which represents the approximate cost of debt and equity capital devoted to plant under construction.  The portion of the allowance applicable to borrowed funds and the allowance applicable to equity funds are presented as other income in the Consolidated Statement of Income.  Although the allowance does not represent current cash income, it has been recoverable under the ratemaking process over the service lives of the related properties.  Weighted-average AFUDC rates for 2014, 2013 and 2012 were 6.12%, 9.63% and 5.61%, respectively.
Asset Retirement Obligations	Asset Retirement Obligations
	The fair value of the liability for an asset retirement obligation (ARO) and/or a conditional ARO is recorded in the period in which it is incurred and the cost is capitalized by increasing the carrying amount of the related long-lived asset.  The liability is adjusted to its present value periodically over time, and the capitalized cost is depreciated over the useful
	life of the related asset.  Upon settlement, the obligation is settled either at its recorded amount or a gain or a loss is incurred.  Any timing differences between rate recovery and depreciation expense are deferred as either a regulatory asset or a regulatory liability.
	The term conditional ARO refers to an entity's legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within the control of the entity.  If an entity has sufficient information to reasonably estimate the fair value of the liability for a conditional ARO, it must recognize that liability at the time the liability is incurred.
	As of December 31, 2014 and 2013, UIL Holdings’ ARO, including estimated conditional AROs, was $18.7 million and $18.5 million, respectively, and consisted primarily of obligations related to the removal or retirement of asbestos, polychlorinated biphenyl (PCB)-contaminated equipment, gas pipeline and cast iron gas mains.  The long-lived assets associated with the AROs are gas storage property, distribution property and other property.  UIL Holdings’ ARO is carried on the balance sheet as other long-term liabilities.
	ARO activity for 2014 and 2013 is as follows:
			2014			2013
			(In Thousands)
	Balance as of December 31		$	18,510		$	18,289
	Liabilities incurred during the year			-			-
	Liabilities settled during the year			(762	)		(740	)
	Accretion			971			961
	Balance as of December 31		$	18,719		$	18,510
Cash and Temporary Cash Investments	Cash and Temporary Cash Investments
	UIL Holdings considers all of its highly liquid debt instruments with an original maturity of three months or less at the date of purchase to be cash and temporary cash investments.
Depreciation	Depreciation
	Provisions for depreciation on utility plant for book purposes are computed on a straight‑line basis, using estimated service lives.  For utility plant other than software, service lives are determined by independent engineers and subject to review and approval by PURA and DPU.  Software service life is based upon management’s estimate of useful life.  The aggregate annual provisions for depreciation for the years 2014, 2013 and 2012 were approximately 3.2%, 3.4%, and 3.5%, respectively, of the original cost of depreciable property.
Derivatives	Derivatives
	UIL Holdings’ regulated subsidiaries are parties to contracts, and involved in transactions, that are derivatives.
	Contracts for Differences (CfDs)
	Pursuant to Connecticut’s 2005 Energy Independence Act, the Connecticut Public Utilities Regulatory Authority (PURA) solicited bids to create new or incremental capacity resources in order to reduce federally mandated congestion charges, and selected four new capacity resources.  To facilitate the transactions between the selected capacity resources and Connecticut electric customers, and provide the commitment necessary for owners of these resources to obtain necessary financing, PURA required that UI and The Connecticut Light and Power Company (CL&P) execute long-term contracts with the selected resources.  In August 2007, PURA approved four CfDs, each of which specifies a capacity quantity and a monthly settlement that reflects the difference between a forward market price and the contract price.  UI executed two of the contracts and CL&P executed the other two contracts.  The costs or benefits of each contract will be paid by or allocated to customers and will be subject to a cost-sharing agreement between UI and CL&P pursuant to which approximately 20% of the cost or benefit is borne by or allocated to UI customers and approximately 80% is borne by or allocated to CL&P customers.
	PURA has determined that costs associated with these CfDs will be fully recoverable by UI and CL&P through electric rates, and in accordance with ASC 980 “Regulated Operations,” UI has deferred recognition of costs (a regulatory asset) or obligations (a regulatory liability).  The CfDs are marked-to-market in accordance with ASC 815 “Derivatives and Hedging.”  For those CfDs signed by CL&P, UI records its approximate 20% portion pursuant to the cost-sharing agreement noted above.  As of December 31, 2014, UI has recorded a gross derivative asset of $27.3 million ($6.6 million of which is related to UI’s portion of the CfD signed by CL&P), a regulatory asset of $64.3 million, a gross derivative liability of $85.1 million ($59.2 million of which is related to UI’s portion of the CfD signed by CL&P) and a regulatory liability of $6.5 million.  See Note (K) “Fair Value of Financial Instruments” for additional CfD information.
	The gross derivative assets and liabilities as of December 31, 2014 and 2013 were as follows:
			December 31,			December 31,
			2014			2013
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,849		$	9,098
	Deferred Charges and Other Assets		$	20,421		$	44,349
	Gross derivative liabilties:
	Current Liabilities		$	23,308		$	26,976
	Noncurrent Liabilities		$	61,766		$	169,327
	The unrealized gains and losses from fair value adjustments to these derivatives, which are recorded in regulatory assets or regulatory liabilities, for years ended December 31, 2014 and 2013 were as follows:
			Year Ended
			December 31,
			2014			2013
			(In Thousands)
	Regulatory Assets - Derivative liabilities		$	(78,510	)	$	(33,819	)
	Regulatory Liabilities - Derivative assets		$	(6,472	)	$	-
	The fluctuations in the balances of the derivatives as well as the related unrealized gains in the year ended December 31, 2014 compared to 2013 are primarily due to increases in forward prices for capacity and reserves as a result of ISO New England market rule changes.
	Weather Insurance Contracts
	On an annual basis, SCG and Berkshire each assess the need for weather insurance contracts for the upcoming heating season in order to provide financial protection from significant weather fluctuations.  According to the terms of such contracts, if temperatures are warmer than normal at a prescribed level for the contract period, a payment is received by the gas company; in addition, under certain of the contracts, if temperatures are colder than normal at a prescribed level for the contract period, the gas company is required to make a payment.  The premiums paid are amortized over the terms of the contracts.  The intrinsic value of the contracts is carried on the balance sheet with changes in value recorded in the income statement as Other Income and (Deductions).  As a result of PURA’s approval of a decoupling mechanism for CNG which went into effect in January 2014, CNG does not enter into weather insurance contracts.
Earnings per share	Earnings per Share
	The following table presents a reconciliation of the basic and diluted earnings per share calculations for the years 2014, 2013 and 2012:
			Year Ended December 31,
			2014			2013			2012
			(In Thousands, except per share amounts)
	Numerator:
	Net income attributable to UIL Holdings		$	109,593		$	115,265		$	103,637
	Less:  Net income allocated to unvested units			63			117			184
	Net income attributable to common shareholders		$	109,530		$	115,148		$	103,453
	Denominator:
	Basic average number of shares outstanding			56,834			52,415			50,831
	Effect of dilutive securities			302			296			277
	Diluted average number of shares outstanding			57,136			52,711			51,108
	Earnings per share:
	Basic		$	1.93		$	2.2		$	2.04
	Diluted		$	1.92		$	2.18		$	2.02
	All outstanding options to purchase shares of common stock during 2013 and 2012 were included in the computation of diluted earnings per share because the options’ exercise prices were lower than the average market price of the common shares during such period.
Equity Investments	Equity Investments
	UI is party to a 50-50 joint venture with NRG affiliates in GenConn, which operates two peaking generation plants in Connecticut.  UI’s investment in GenConn is being accounted for as an equity investment, the carrying value of which was $114.2 million and $118.2 million as of December 31, 2014 and 2013, respectively.  As of December 31, 2014, there was an immaterial amount of undistributed earnings from UI’s equity investment in GenConn.
	UI’s pre-tax income from its equity investment in GenConn was $13.9 million, $15.3 million and $15.3 million for the years ended December 31, 2014, 2013 and 2012, respectively.
	Cash distributions from GenConn are reflected as either distributions of earnings or as returns of capital in the operating and investing sections of the Consolidated Statement of Cash Flows, respectively.  UI received cash distributions from GenConn of $17.9 million, $21.8 million and $21.5 million during the years ended December 31, 2014, 2013 and 2012, respectively.
Goodwill	Goodwill
	UIL Holdings may be required to recognize an impairment of goodwill in the future due to market conditions or other factors related to its results of operations and performance. Those market events could include a decline in the forecasted results in the company business plan, significant adverse rate case results, changes in capital investment budgets or changes in interest rates that could impair the fair value of a reporting unit.  Recognition of impairments of a significant portion of goodwill would negatively affect reported results of operations and total capitalization, the effect of which could be material and could make it more difficult to maintain credit ratings, secure financing on attractive terms, maintain compliance with debt covenants and meet expectations of regulators.
	A goodwill impairment test is performed each year and the test will be updated between annual tests if events or circumstances occur that may reduce the fair value of a reporting unit below its carrying value. The annual analysis of the potential impairment of goodwill is a two-step process.  Step one of the impairment test consists of comparing the fair values of reporting units with their aggregate carrying values, including goodwill.  The estimated fair values for the reporting units are determined by using the income approach and the market approach methodologies.
	The income approach is based on discounted cash flows which are derived from internal forecasts and economic expectations.  Key assumptions used to determine fair value under the income approach include the cash flow period, terminal values based on a terminal growth rate, and the discount rate.  The discount rate represents the estimated cost of debt and equity financing weighted by the percentage of debt and equity in a company's target capital structure.
	The market approach utilizes the guideline company method, which calculates valuation multiples based on operating and valuation metrics from publicly traded guideline companies in the regulated natural gas distribution industry.  Multiples derived from the guideline companies provide an indication of how much a knowledgeable investor in the marketplace would be willing to pay for an investment in a similar company.  These multiples are then applied to the appropriate operating metric to determine indications of fair value.
	If the carrying amount of a reporting unit exceeds the reporting unit’s fair value, step two must be performed to determine the amount, if any, of the goodwill impairment loss.  If the carrying amount is less than fair value, further testing of goodwill impairment is not performed.
	Step two of the goodwill impairment test consists of comparing the implied fair value of the reporting unit’s goodwill against the carrying value of the goodwill.  Determining the implied fair value of goodwill requires the valuation of a reporting unit’s identifiable tangible and intangible assets and liabilities as if the reporting unit had been acquired in a business combination on the testing date. The difference between the fair value of the entire reporting unit as determined in step one and the net fair value of all identifiable assets and liabilities represents the implied fair value of goodwill.  A goodwill impairment charge, if any, would be the difference between the carrying amount of goodwill and the implied fair value of goodwill upon the completion of step two.
	As of October 1, 2014, the fair values of UIL Holdings’ applicable reporting units exceeded their carrying values and therefore Step two was not performed and no impairment was recognized.  No events or circumstances occurred subsequent to October 1, 2014 that would make it more likely than not that the fair value of the reporting units fell below their respective carrying values.
Impairment of Long-Lived Assets and Investments	Impairment of Long‑Lived Assets and Investments
	ASC 360 “Property, Plant, and Equipment” requires the recognition of impairment losses on long‑lived assets when the book value of an asset exceeds the sum of the expected future undiscounted cash flows that result from the use of the asset and its eventual disposition.  If impairment arises, then the amount of any impairment is measured based on discounted cash flows or estimated fair value.
	ASC 360 also requires that rate‑regulated companies recognize an impairment loss when a regulator excludes all or part of a cost from rates, even if the regulator allows the company to earn a return on the remaining costs allowed.  Under this standard, the probability of recovery and the recognition of regulatory assets under the criteria of ASC 980 must be assessed on an ongoing basis.  As discussed in the description of ASC 980 in this Note (A) under “Regulatory Accounting,” determination that certain regulatory assets no longer qualify for accounting as such could have a material impact on the financial condition of UI, the Gas Companies and UIL Holdings.  As a result of UI’s 2013 distribution rate proceeding, a portion of UI’s deferred storm costs and capital costs related to UI’s recently constructed administrative and operations buildings were written off.  See “–
	Note (C), Regulatory Proceedings, Electric Distribution and Transmission – Rates” for additional information.  In addition, as a result of PURA’s decision in a docket addressing UI’s semi-annual Generation Services Charge (GSC), bypassable federally mandated congestion charge and the nonbypassable federally mandated congestion charge reconciliations (NBFMCC), UI recorded a write-off during the fourth quarter of 2014.  See “– Note (C), Regulatory Proceedings, Electric Distribution and Transmission – Other Proceedings” for additional information.
	ASC 323 “Investments” requires that a loss in the value of an investment that is other than a temporary decline should be recognized. In accordance with ASC 323, UIL Holdings reviews its investments accounted for by the equity method for impairment by identifying and measuring losses in the value based upon a comparison of fair value to carrying value.  At December 31, 2014, UIL Holdings did not have any equity investments that were impaired under this standard.
Income Taxes	Income Taxes
	In accordance with ASC 740 “Income Taxes,” UIL Holdings has provided deferred taxes for all temporary book‑tax differences using the liability method.  The liability method requires that deferred tax balances be adjusted to reflect enacted future tax rates that are anticipated to be in effect when the temporary differences reverse.  In accordance with generally accepted accounting principles for regulated industries, UIL Holdings’ regulated subsidiaries have established a regulatory asset for the net revenue requirements to be recovered from customers for the related future tax expense associated with certain of these temporary differences.  For ratemaking purposes, UIL Holdings’ regulated subsidiaries normalize all investment tax credits (ITCs) related to recoverable plant investments.
	Under ASC 740, UIL Holdings may recognize the tax benefit of an uncertain tax position only if management believes it is more likely than not that the tax position will be sustained on examination by the taxing authority based upon the technical merits of the position.  The tax benefits recognized in the financial statements from such a position should be measured based upon the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement.  UIL Holdings’ policy is to recognize interest accrued and penalties associated with uncertain tax positions as a component of operating expense.  See – Note (E), Income Taxes for additional information.
	UIL Holdings files a consolidated federal tax return which includes all of the activities of its subsidiaries.  Each subsidiary company is treated as a member of the consolidated group and each subsidiary company’s current and deferred tax expense or benefit is calculated based on the separate return method.
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits
	UIL Holdings accounts for pension plan costs and other postretirement benefits, consisting principally of health and life insurance, in accordance with the provisions of ASC 715 “Compensation - Retirement Benefits.”  See – Note (G), Pension and Other Benefits.
Property, Plant and Equipment	Property, Plant and Equipment
	The cost of additions to property, plant and equipment and the cost of renewals and betterments are capitalized.  Cost consists of labor, materials, services and certain indirect construction costs, including AFUDC.  The costs of current repairs, major maintenance projects and minor replacements are charged to appropriate operating expense accounts as incurred.  The original cost of utility property, plant and equipment retired or otherwise disposed of and the cost of removal, less salvage, are charged to the accumulated provision for depreciation.
	UI and the Gas Companies accrue for estimated costs of removal for certain of their plant-in-service.  Such removal costs are included in the approved rates used to depreciate these assets.  At the end of the service life of the applicable assets, the accumulated depreciation in excess of the historical cost of the asset provides for the estimated cost of removal.  In accordance with ASC 980 “Regulated Operations,” the accrued costs of removal have been recorded as a regulatory liability.
	UIL Holdings’ property, plant and equipment as of December 31, 2014 and 2013 were comprised as follows:
			2014			2013
			(In Thousands)
	Electric distribution plant		$	1,135,317		$	979,526
	Electric transmission plant			646,826			630,834
	Gas distribution plant			1,526,961			1,444,837
	Software			195,864			144,494
	Building and improvements			245,959			235,002
	Land			65,201			64,848
	Other plant			239,719			192,219
	Total property, plant & equipment			4,055,847			3,691,760
	Less accumulated depreciation			1,032,065			944,399
				3,023,782			2,747,361
	Construction work in progress			268,908			321,319
	Net property, plant & equipment		$	3,292,690		$	3,068,680
Regulatory Accounting	Regulatory Accounting
	Generally accepted accounting principles for regulated entities in the United States of America allow UIL Holdings’ regulated subsidiaries to give accounting recognition to the actions of regulatory authorities in accordance with the provisions of Accounting Standards Codification (ASC) 980 “Regulated Operations.”  In accordance with ASC 980, UIL Holdings’ regulated utilities have deferred recognition of costs (a regulatory asset) or have recognized obligations (a regulatory liability) if it is probable that such costs will be recovered or obligations relieved in the future through the ratemaking process.  UIL Holdings’ regulated utilities are allowed to recover all such deferred costs through its regulated rates.  See Note (C), “Regulatory Proceedings,” for a discussion of the recovery of certain deferred costs, as well as a discussion of the regulatory decisions that provide for such recovery.
	UI also has obligations under long‑term power contracts, the recovery of which is subject to regulation.  If UIL Holdings’ regulated utilities, or a portion of their assets or operations, were to cease meeting the criteria for application of these accounting rules, accounting standards for businesses in general would become applicable and immediate recognition of any previously deferred costs would be required in the year in which such criteria are no longer met (if such deferred costs are not recoverable in the portion of the business that continues to meet the criteria for application of ASC 980).  UIL Holdings expects its regulated utilities to continue to meet the criteria for application of ASC 980 for the foreseeable future.  If a change in accounting were to occur, it could have a material adverse effect on the earnings and retained earnings of the applicable regulated utility and UIL Holdings in that year and could also have a material adverse effect on the ongoing financial condition of the applicable regulated utility and UIL Holdings.
	Unless otherwise stated below, all of UIL Holdings’ regulatory assets earn a return.  UIL Holdings’ regulatory assets and liabilities as of December 31, 2014 and 2013 included the following:
		Remaining		December 31,			December 31,
		Period		2014			2013
				(In Thousands)
	Regulatory Assets:
	Nuclear plant investments – above market	(a)		$	-		$	238,868
	Unamortized redemption costs	7 to 19 years			10,499			11,301
	Pension and other post-retirement benefit plans	(b)			402,700			316,076
	Environmental remediation costs	7 years			13,197			14,953
	Hardship programs	(c)			24,744			25,019
	Debt premium	2 to 23 years			27,498			34,178
	Deferred purchased gas	(d)			-			2,556
	Income taxes due principally to book-tax differences	(m)			164,466			149,015
	Unfunded future income taxes	(e)			14,859			32,517
	Contracts for differences	(f)			64,276			142,743
	Excess generation service charge	(g)			-			6,909
	Deferred transmission expense	(h)			17,387			9,615
	Storm Costs	(i)			-			14,752
	Other	(j)			40,336			37,628
	Total regulatory assets				779,962			1,036,130
	Less current portion of regulatory assets				92,764			332,391
	Regulatory Assets, Net			$	687,198		$	703,739
	Regulatory Liabilities:
	Accumulated deferred investment tax credits	29 years		$	4,319		$	4,465
	Income taxes due principally to book-tax differences	(m)			-			200,673
	Deferred gain on sale of property	(a)			-			37,933
	Excess generation service charge	(g)			28,692			-
	Middletown/Norwalk local transmission network service collections	35 years			20,828			21,402
	Pension and other post-retirement benefit plans	(b)			9,536			27,686
	Asset retirement obligation	(k)			7,248			5,593
	Low income programs	(l)			19,065			25,300
	Asset removal costs	(j)			336,028			319,530
	Unfunded future income taxes	(e)			26,318			43,421
	Contracts for differences	(f)			6,472			-
	Deferred purchased gas	(d)			4,736			-
	Non-firm margin sharing credits	10 years			8,933			-
	Other	(j)			36,747			20,818
	Total regulatory liabilities				508,922			706,821
	Less current portion of regulatory liabilities				17,026			261,729
	Regulatory Liabilities, Net			$	491,896		$	445,092
	(a)	Asset/Liability relates to the Competitive Transition Assessment (CTA).  Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences.  Total CTA costs recovery and stranded cost
	amortization are complete.  As a result of the outcome of UI’s 2013 distribution rate request, PURA approved UI’s proposed rate treatment to leave CTA rates unchanged until January 1, 2014 at which point the charge ended.  The remaining balances were eliminated. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Other Proceedings” for additional information.
	(b)	Life is dependent upon timing of final pension plan distribution; balance, which is fully offset by a corresponding asset/liability, is recalculated each year in accordance with ASC 715 "Compensation-Retirement Benefits." See Note (G) “Pension and Other Benefits” for additional information.
	(c)	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
	(d)	Deferred purchase gas costs balances at the end of the rate year are normally recorded/returned in the next year.
	(e)	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
	(f)	Asset life is equal to delivery term of related contracts (which vary from approximately 5 - 12 years); balance fluctuates based upon quarterly market analysis performed on the related derivatives (Note K); amount, which does not earn a return, is fully offset by corresponding derivative asset/liability.  See “-Contracts for Differences” discussion above for additional information.
	(g)	Regulatory asset or liability which defers generation-related and nonbypassable federally mandated congestion costs or revenues for future recovery from or return to customers.  Amount fluctuates based upon timing differences between revenues collected from rates and actual costs incurred.
	(h)	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
	(i)	Storm costs include accumulated costs for major storms occurring from January 2009 forward. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Rates” for a discussion of the recovery of these costs.
	(j)	Amortization period and/or balance vary depending on the nature, cost of removal and/or remaining life of the underlying assets/liabilities; asset amount includes decoupling ($3.9 million) and certain other amounts that are not currently earning a return. See Note (C) “Regulatory Proceedings for a discussion of the decoupling recovery period.
	(k)	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
	(l)	Various hardship and payment plan programs approved for recovery.
	(m)	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities; balances contain regulatory liabilities related to the CTA as well as regulatory assets not related to the CTA.  Due to the end of the CTA charge, the CTA regulatory liabilities are classified as current regulatory liabilities as of December 31, 2013 and the regulatory assets not related to the CTA are reclassified as long-term regulatory assets.
Restricted Cash	Restricted Cash
	UIL Holdings’ restricted cash at December 31, 2014 and 2013 totaled $1.1 million and $2.0 million, respectively, which primarily relates to electric distribution and transmission capital projects, which have been withheld by UI and will remain in place until the verification of fulfillment of contractor obligations.
Revenues	Revenues
	Regulated utility revenues are based on authorized rates applied to each customer.  These retail rates are approved by regulatory bodies and can be changed only through formal proceedings.
	UI utilizes a customer accounting software package integrated with the network meter reading system to estimate unbilled revenue on a customer-by-customer basis, utilizing actual daily meter readings at the end of each month to calculate consumption and pricing for each customer.  A significant portion of utility retail kilowatt-hour consumption is read through the network meter reading system.  For those customers still requiring manual meter readings, consumption is estimated based upon historical usage and actual pricing for each customer.
	The Gas Companies’ unbilled revenues represent estimates of receivables for products and services provided but not yet billed. The estimates are determined based on various assumptions, such as current month energy load requirements, billing rates by customer classification and weather.
Stock-Based Compensation	Stock-Based Compensation
	Certain members of management have the opportunity to earn a pre-determined number of performance shares, the number of which is predicated upon the achievement of various pre-defined performance measures over a three-year period.  These performance shares are issued under the UIL Holdings Amended and Restated 2008 Stock and Incentive Compensation Plan (2008 Stock Plan).  Each award of performance shares vests at the end of a three-year cycle with the actual issuance of UIL Holdings’ common stock in respect of such performance shares following the end of each three-year cycle.  A new three-year cycle begins in January of each year.
	UIL Holdings records compensation expense for these performance shares ratably over the three-year period, except in the case of retirement-eligible employees, for whom compensation expense is immediately recognized in accordance with ASC 718 “Compensation-Stock Compensation,” based on the value of the expected payout at the end of each year relative to the performance measures achieved.
	Pursuant to the 2008 Stock Plan, target amounts of 123,940, 2,430, and 2,340 performance shares were granted to certain members of management in March 2014, May 2014 and August 2014, respectively; the averages of the high and low market prices on the grant dates, which approximate fair value, were $35.87 per share, $36.23 per share, and $34.90 per share respectively.
	Also in March 2014, we granted a total of 2,196 shares of restricted stock to our President and Chief Executive Officer under the 2008 Stock Plan and in accordance with his employment agreement; the average of the high and low market price on the date of grant, which approximates fair value, was $35.87 per share.  Such shares vest in equal annual installments over a five-year period.
	In May 2014, UIL Holdings granted a total of 25,160 shares of restricted stock to non-employee directors under the 2008 Stock Plan; the average of the high and low market price on the date of grant, which approximates fair value, was $35.90 per share.  Such shares vest in May 2015.
	In June 2014, 9,540 shares of previously-granted performance shares and 2,177 shares of previously-granted restricted stock were forfeited.
	As of December 31, 2014, the total number of shares authorized for stock-based compensation plans was 4,233,333.  Total stock-based compensation expense for the years ended December 31, 2014, 2013 and 2012 was $5.7 million, $5.3 million and $4.9 million, respectively.
Variable Interest Entities	Variable Interest Entities
	We have identified GenConn as a variable interest entity (VIE), which is accounted for under the equity method.  UIL Holdings is not the primary beneficiary of GenConn, as defined in ASC 810 “Consolidation,” because it shares control of all significant activities of GenConn with its joint venturer, NRG affiliates.  As such, GenConn is not subject to consolidation.  GenConn recovers its costs through CfDs, which are cost of service-based and have been approved by PURA.  As a result, with the achievement of commercial operation by GenConn Devon and GenConn Middletown, our exposure to loss is primarily related to the potential for unrecovered GenConn operating or capital costs in a regulatory proceeding, the effect of which would be reflected in the carrying value of our 50% ownership position in GenConn and through “Income from Equity Investments” in UIL Holdings’ Consolidated Financial Statements.  Such exposure to loss cannot be determined at this time. For further discussion of GenConn, see “–Equity Investments” as well as Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Equity Investment in Peaking Generation.”
	We have identified the selected capacity resources with which UI has CfDs as VIEs and have concluded that UI is not the primary beneficiary as UI does not have the power to direct any of the significant activities of these capacity resources.   As such, we have not consolidated the selected capacity resources.  UI’s maximum exposure to loss through these agreements is limited to the settlement amount under the CfDs as described in “–Derivatives – Contracts for Differences (CfDs)” above; however any such losses are fully recoverable through electric rates.  UI has no requirement to absorb additional losses nor has UI provided any financial or other support during the periods presented that were not previously contractually required.
	We have identified the entities for which UI is required to enter into long-term contracts to purchase Renewable Energy Credits (RECs) as VIEs.  In assessing these contracts for VIE identification and reporting purposes, we have aggregated the contracts based on similar risk characteristics and significance to UI.  UI is not the primary beneficiary as UI does not have the power to direct any of the significant activities of these entities.  UI’s exposure to loss is primarily related to the purchase and resale of the RECs, but, any losses incurred are recoverable through electric rates.  For further discussion of RECs, see Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – New Renewable Source Generation.”
New Accounting Standards	New Accounting Standards
	In May 2014, the FASB issued Accounting Standards Update (ASU) 2014-09, which supersedes the revenue recognition requirements in ASC 605, Revenue Recognition.  ASU 2014-09 requires entities to recognize revenue in a way that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services.  ASU 2014-09 is effective for interim and annual reporting periods beginning after December 15, 2016 and is to be applied retrospectively.  We are currently evaluating the effect that adopting this new accounting guidance will have on our consolidated financial statements.
	In June 2014, the FASB issued updated guidance to ASC 718 “Compensation – Stock Compensation” which prescribes the accounting for share-based payments when the terms of an award provide that a performance target could be achieved after the requisite service period.  This guidance is effective during interim and annual periods beginning after December 15, 2015 and can be applied on a prospective basis to all awards granted or modified after the effective date or retrospectively to all awards with performance targets that are outstanding as of the beginning of the earliest annual period presented in the financial statements and to all new or modified awards thereafter.  This guidance is not expected to have a material impact on UIL Holdings’ consolidated financial statements.

STATEMENT_OF_ACCOUNTING_POLICI2

STATEMENT OF ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2014
STATEMENT OF ACCOUNTING POLICIES [Abstract]
ARO Activity for 2014 and 2013	ARO activity for 2014 and 2013 is as follows:
			2014			2013
			(In Thousands)
	Balance as of December 31		$	18,510		$	18,289
	Liabilities incurred during the year			-			-
	Liabilities settled during the year			(762	)		(740	)
	Accretion			971			961
	Balance as of December 31		$	18,719		$	18,510
Value of Gross Derivative Assets and Liabilities	The gross derivative assets and liabilities as of December 31, 2014 and 2013 were as follows:
			December 31,			December 31,
			2014			2013
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,849		$	9,098
	Deferred Charges and Other Assets		$	20,421		$	44,349
	Gross derivative liabilties:
	Current Liabilities		$	23,308		$	26,976
	Noncurrent Liabilities		$	61,766		$	169,327
Unrealized Gains and Losses From Mark-To-Market Adjustments	The unrealized gains and losses from fair value adjustments to these derivatives, which are recorded in regulatory assets or regulatory liabilities, for years ended December 31, 2014 and 2013 were as follows:
			Year Ended
			December 31,
			2014			2013
			(In Thousands)
	Regulatory Assets - Derivative liabilities		$	(78,510	)	$	(33,819	)
	Regulatory Liabilities - Derivative assets		$	(6,472	)	$	-
Reconciliation of Basic and Diluted Earnings Per Share	The following table presents a reconciliation of the basic and diluted earnings per share calculations for the years 2014, 2013 and 2012:
			Year Ended December 31,
			2014			2013			2012
			(In Thousands, except per share amounts)
	Numerator:
	Net income attributable to UIL Holdings		$	109,593		$	115,265		$	103,637
	Less:  Net income allocated to unvested units			63			117			184
	Net income attributable to common shareholders		$	109,530		$	115,148		$	103,453
	Denominator:
	Basic average number of shares outstanding			56,834			52,415			50,831
	Effect of dilutive securities			302			296			277
	Diluted average number of shares outstanding			57,136			52,711			51,108
	Earnings per share:
	Basic		$	1.93		$	2.2		$	2.04
	Diluted		$	1.92		$	2.18		$	2.02
Net Property, Plant and Equipment			2014			2013
			(In Thousands)
	Electric distribution plant		$	1,135,317		$	979,526
	Electric transmission plant			646,826			630,834
	Gas distribution plant			1,526,961			1,444,837
	Software			195,864			144,494
	Building and improvements			245,959			235,002
	Land			65,201			64,848
	Other plant			239,719			192,219
	Total property, plant & equipment			4,055,847			3,691,760
	Less accumulated depreciation			1,032,065			944,399
				3,023,782			2,747,361
	Construction work in progress			268,908			321,319
	Net property, plant & equipment		$	3,292,690		$	3,068,680
Regulatory Assets and Liabilities	Unless otherwise stated below, all of UIL Holdings’ regulatory assets earn a return.  UIL Holdings’ regulatory assets and liabilities as of December 31, 2014 and 2013 included the following:
		Remaining		December 31,			December 31,
		Period		2014			2013
				(In Thousands)
	Regulatory Assets:
	Nuclear plant investments – above market	(a)		$	-		$	238,868
	Unamortized redemption costs	7 to 19 years			10,499			11,301
	Pension and other post-retirement benefit plans	(b)			402,700			316,076
	Environmental remediation costs	7 years			13,197			14,953
	Hardship programs	(c)			24,744			25,019
	Debt premium	2 to 23 years			27,498			34,178
	Deferred purchased gas	(d)			-			2,556
	Income taxes due principally to book-tax differences	(m)			164,466			149,015
	Unfunded future income taxes	(e)			14,859			32,517
	Contracts for differences	(f)			64,276			142,743
	Excess generation service charge	(g)			-			6,909
	Deferred transmission expense	(h)			17,387			9,615
	Storm Costs	(i)			-			14,752
	Other	(j)			40,336			37,628
	Total regulatory assets				779,962			1,036,130
	Less current portion of regulatory assets				92,764			332,391
	Regulatory Assets, Net			$	687,198		$	703,739
	Regulatory Liabilities:
	Accumulated deferred investment tax credits	29 years		$	4,319		$	4,465
	Income taxes due principally to book-tax differences	(m)			-			200,673
	Deferred gain on sale of property	(a)			-			37,933
	Excess generation service charge	(g)			28,692			-
	Middletown/Norwalk local transmission network service collections	35 years			20,828			21,402
	Pension and other post-retirement benefit plans	(b)			9,536			27,686
	Asset retirement obligation	(k)			7,248			5,593
	Low income programs	(l)			19,065			25,300
	Asset removal costs	(j)			336,028			319,530
	Unfunded future income taxes	(e)			26,318			43,421
	Contracts for differences	(f)			6,472			-
	Deferred purchased gas	(d)			4,736			-
	Non-firm margin sharing credits	10 years			8,933			-
	Other	(j)			36,747			20,818
	Total regulatory liabilities				508,922			706,821
	Less current portion of regulatory liabilities				17,026			261,729
	Regulatory Liabilities, Net			$	491,896		$	445,092
	(a)	Asset/Liability relates to the Competitive Transition Assessment (CTA).  Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences.  Total CTA costs recovery and stranded cost

CAPITALIZATION_Tables

CAPITALIZATION (Tables)	12 Months Ended
	Dec. 31, 2014
CAPITALIZATION [Abstract]
Restricted stock activity	Restricted stock activity for 2014 is as follows:
			Number			Weighted Average
			of Shares			Grant Date
						Fair Value
	Nonvested Balance – December 31, 2013			30,920		$	38.9
	Granted			27,356		$	35.9
	Forfeited			(2,177	)	$	41.34
	Vested			(24,161	)	$	39.53
	Nonvested Balance – December 31, 2014			31,938		$	35.68
Performance share activity	Performance share activity for 2014 is as follows:
			Number			Weighted Average
			of Performance			Grant Date
			Shares			Fair Value
	Nonvested Balance – December 31, 2013			335,008		$	34.62
	Granted			146,792		$	35.24
	Forfeited			(9,540	)	$	38.81
	Vested			(131,020	)	$	30.8
	Nonvested Balance – December 31, 2014			341,240		$	36.23
Stock option transactions	Stock option transactions for 2014, 2013 and 2012 are as follows:
									Average
			Number			Option Price			Exercise
			of Options			per Share			Price
	Balance – December 31, 2011			98,220		$	21.68-$33.96		$	33.39
	Granted			-			N/	A		N/	A
	Forfeited			(38,000	)		N/	A		N/	A
	Exercised			(56,887	)	$	31.25-$33.96			N/	A
	Balance – December 31, 2012			3,333		$	21.68		$	21.68
	Granted			-			N/	A		N/	A
	Forfeited			-			N/	A		N/	A
	Exercised			(3,333	)	$	21.68			N/	A
	Balance – December 31, 2013			-			N/	A		N/	A
	Granted			-			N/	A		N/	A
	Forfeited			-			N/	A		N/	A
	Exercised			-			N/	A		N/	A
	Balance – December 31, 2014			-			N/	A		N/	A
	Exercisable at December 31, 2012			3,333		$	21.68		$	21.68
	Exercisable at December 31, 2013			-			N/	A		N/	A
	Exercisable at December 31, 2014			-			N/	A		N/	A
Long-term debt	Long-Term Debt
			December 31,
			2014			2013
			(In Thousands)
	UIL Holdings
	4.625% Unsecured Senior Notes, due 2020		$	450,000		$	450,000
	UI
	Pollution Control Revenue Bonds:
	4.50% 2010 Series, due 2027			27,500			27,500
	Auction Rate, 2003 Series, due 2033  (1)			64,460			64,460
	Senior Unsecured Notes:
	6.06% Senior Notes, Series A and B, due 2017			70,000			70,000
	2.98% Senior Notes, Series A due 2019			31,000			31,000
	3.61% Senior Notes, Series B and C and 6.26% Senior Notes, Series C and D, due 2022			162,500			162,500
	6.51% Senior Notes, Series E and F due 2037			28,000			28,000
	6.46% Senior Notes, Series A and 6.51%, Senior Notes, Series B, due 2018			100,000			100,000
	6.61% Senior Notes, Series C, due 2020			50,000			50,000
	5.61% Senior Notes, due 2025			50,000			50,000
	6.09% Senior Notes, due 2040			100,000			100,000
	4.89% Senior Notes, Series D and E, due 2042			87,000			87,000
	3.95% Senior Notes, Series F, due 2023			75,000			75,000
	Gas Companies
	Senior Secured Notes:
	3.88% - 7.50% Senior Secured Medium Term Note IV, due 2018 - 2041			100,000			100,000
	5.77%  - 6.38% Senior Secured Medium Term Notes III, due 2025 - 2037			85,000			85,000
	6.88% - 7.95% Senior Secured Medium Term Notes I, due 2026 - 2028			29,000			29,000
	10.06% First Mortgage Bond Series P, due 2019			10,000			10,000
	Unsecured Notes:
	4.76% - 9.60% Senior Unsecured Notes, due 2020 - 2021			18,180			19,635
	6.85% - 9.10% Unsecured Medium Term Notes, Series A, due 2016 - 2017			30,000			30,000
	8.12% - 8.49% Unsecured Medium Term Notes, Series B, due 2014 - 2024			-			10,000
	5.63% - 6.66% Unsecured Medium Term Notes, Series C, due 2035 - 2037			65,000			65,000
	4.30% - 5.23% Medium Term Note, Series D, due 2028 - 2043			45,000			45,000
	5.33% Senior Notes, Series A, due 2043			15,000			15,000
	Long-Term Debt			1,692,640			1,704,095
	Less:  Current portion of long-term debt  (2)			6,526			11,834
	Less:  Unamortized discount			2,263			2,597
	Plus:  Unamortized premium			27,498			34,178
	Net Long-Term Debt		$	1,711,349		$	1,723,842
	-1	On December 31, 2014, the interest rate on the Bonds was 0.33%. The interest rate on these Bonds is reset through an auction held every 35 days.
	-2	Includes the current portion of unamortized premium.
Maturities and mandatory redemptions and repayments	Information regarding maturities and mandatory redemptions/repayments are set forth below:
			2015			2016			2017			2018		2019 &		Total
														Thereafter
			(In Thousands)
	Maturities:		$	1,455		$	11,455		$	91,455		$	151,455	$	1,436,820	$	1,692,640

REGULATORY_PROCEEDINGS_Tables

REGULATORY PROCEEDINGS (Tables)	12 Months Ended
	Dec. 31, 2014
REGULATORY PROCEEDINGS [Abstract]
Long-term Supply Commitment	The Gas Companies acquire firm transportation capacity on interstate pipelines under long-term contracts and utilize that capacity to transport both natural gas supply purchased and natural gas withdrawn from storage to the local distribution system.  Collectively, the Gas Companies hold approximately 96 firm transportation contracts on 12 different pipelines.  Three of those pipelines, Tennessee Gas Pipeline, Algonquin Gas Transmission and Iroquois Gas Transmission, interconnect with one or more of the Gas Companies’ distribution system and the other pipelines provide indirect services upstream of the city gates.  The prices and terms and conditions of the long-term contracts for firm transportation capacity are regulated by the FERC.  The actual reasonable costs of such contracts are passed through to customers through state regulated purchased gas adjustment mechanisms.  The future obligations under these contracts as of December 31, 2014 are as follows:
		(In Thousands)
	2015		133,586
	2016		126,581
	2017		117,279
	2018		82,238
	2019		68,487
	2020-after		450,763
		$	978,934

SHORTTERM_CREDIT_ARRANGEMENTS_

SHORT-TERM CREDIT ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2014
SHORT-TERM CREDIT ARRANGEMENTS [Abstract]
Short-term borrowings	Information with respect to short-term borrowings is set forth below:
			2014			2013
			( In Thousands)
	UIL Holdings
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	111,000		$	202,000
	Average aggregate short-term borrowings outstanding during the year (1)		$	49,233		$	152,455
	Weighted average interest rate (1)			1.37	%		1.43	%
	Principal amounts outstanding at year-end		$	89,000		$	-
	UI
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	-		$	60,000
	Average aggregate short-term borrowings outstanding during the year (1)		$	-		$	13,510
	Weighted average interest rate (1)			N/	A		1.4	%
	Principal amounts outstanding at year-end		$	-		$	-
	Gas Companies
	Maximum aggregate principal amount of short-term borrowing outstanding at any month-end		$	-		$	-
	Average aggregate short-term borrowings outstanding during the year (1)		$	-		$	-
	Weighted average interest rate (1)			N/	A		N/	A
	Principal amounts outstanding at year-end		$	-		$	-
	N/A – not applicable
		-1	Average short‑term borrowings represent the sum of daily borrowings outstanding, weighted for the number of days outstanding and divided by the number of days in the period.  The weighted average interest rate is determined by dividing interest expense by the amount of average borrowings.

INCOME_TAXES_Tables

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2014
INCOME TAXES [Abstract]
Components of income tax		2014			2013			2012
		(In Thousands)
	Income tax expense consists of:
	Income tax provisions:
	Current
	Federal	$	-		$	(443	)	$	5,830
	State		1,798			(1,149	)		1,110
	Total current		1,798			(1,592	)		6,940
	Deferred
	Federal		54,407			64,931			61,510
	State		1,552			6,164			6,611
	Total deferred		55,959			71,095			68,121
	Investment tax credits		(195	)		(195	)		(195	)
	Total income tax expense	$	57,562		$	69,308		$	74,866
Reconciliation of statutory federal tax rate to effective tax rate	Total income taxes differ from the amounts computed by applying the federal statutory tax rate to income before taxes.  The reasons for the differences are as follows:
		2014			2013			2012
		(In Thousands)
	Book income before income taxes	$	167,141		$	184,625		$	178,567
	Computed tax at federal statutory rate	$	58,499		$	64,619		$	62,499
	Increases (reductions) resulting from:
	Amortization of nuclear plant regulatory assets		-			6,867			9,334
	State income taxes, net of federal income tax benefits		2,177			3,259			5,018
	Allowance for equity funds used during construction		(3,064	)		(3,784	)		(2,749	)
	Investment tax credits		(195	)		(195	)		(195	)
	Other items, net		145			(1,458	)		959
	Total income tax expense	$	57,562		$	69,308		$	74,866
	Effective income tax rates		34.4	%		37.5	%		41.9	%
Deferred tax assets and liabilities	The following table summarizes UIL Holdings’ deferred income tax assets and liabilities as of December 31, 2014 and 2013.
		2014			2013
		(In Thousands)
	Deferred income tax assets:
	Post-retirement benefits	$	130,474		$	90,300
	Accrued removal obligation		134,175			119,904
	Net operating loss carry forward		49,772			42,818
	Other		64,929			104,467
		$	379,350		$	357,489
	Deferred income tax liabilities:
	Plant basis and accelerated depreciation timing differences	$	700,969		$	607,950
	Regulatory deferrals related to pension and other post-retirement benefits		149,158			110,980
	Investment in GenConn		53,378			53,350
	Other		64,946			104,009
		$	968,451		$	876,289
Schedule of carry forward balances	The following table sets forth the carry forward balances for the years ended December 31, 2014 and 2013:
								Year
								Expiration
		2014			2013			Begins
		(In Thousands)
	Federal net operating loss	$	142,704		$	122,339			2032
	Alternative minimum tax credit		2,697			2,697			N/	A
	State tax credits		11,276			7,289			2017

SUPPLEMENTARY_INFORMATION_Tabl

SUPPLEMENTARY INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2014
SUPPLEMENTARY INFORMATION [Abstract]
Supplementary Information		2014			2013			2012
		(In Thousands)
	Depreciation and Amortization
	Property, plant, and equipment depreciation	$	131,051		$	120,301		$	112,002
	Amortization of regulatory assets		20,506			69,555			69,346
	Total Depreciation and Amortization	$	151,557		$	189,856		$	181,348
	Taxes - Other than Income Taxes
	Operating:
	Connecticut gross earnings	$	73,429		$	75,330		$	65,753
	Local real estate and personal property		50,392			46,567			40,588
	Payroll taxes		13,050			8,005			7,274
	Other		1,400			556			422
	Total Taxes - Other than Income Taxes	$	138,271		$	130,458		$	114,037
	Other Income and (Deductions), net
	Interest income	$	2,573		$	2,733		$	2,631
	Allowance for funds used during construction - equity		8,814			10,811			7,480
	Allowance for funds used during construction - debt		5,157			7,170			6,979
	Weather insurance		(2,200	)		(70	)		3,488
	TSO incentives		-			-			2,745
	Other		3,676			(11	)		1,923
	Total Other Income and (Deductions), net	$	18,020		$	20,633		$	25,246

PENSION_AND_OTHER_BENEFITS_Tab

PENSION AND OTHER BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2014
PENSION AND OTHER BENEFITS [Abstract]
Changes in Benefit Obligation	The following table represents the change in benefit obligation, change in plan assets and the respective funded status of UIL Holdings’ pension and other postretirement plans as of December 31, 2014 and 2013.  Plan assets and obligations have been measured as of December 31, 2014 and 2013.
								Other Post-Retirement
		Pension Benefits						Benefits
		2014			2013			2014			2013
	Change in Benefit Obligation:	(In Thousands)
	Benefit obligation at beginning of year	$	859,263		$	950,609		$	119,702		$	136,687
	Service cost		11,581			14,783			1,618			1,923
	Interest cost		44,076			39,948			5,947			5,539
	Participant contributions		-			-			1,265			1,253
	Settlements (1)		-			(2,367	)		-			-
	Actuarial (gain) loss		122,309			(96,739	)		10,872			(13,893	)
	Benefits paid (including expenses)		(50,194	)		(46,971	)		(12,928	)		(11,807	)
	Benefit obligation at end of year	$	987,035		$	859,263		$	126,476		$	119,702
	Change in Plan Assets:
	Fair value of plan assets at beginning of year	$	688,410		$	625,061		$	41,163		$	38,540
	Actual return on plan assets		59,675			54,259			3,558			6,003
	Employer contributions		24,135			58,428			-			-
	Participant contributions		-			-			1,265			1,253
	Settlements (1)		-			(2,367	)		-			-
	Benefits paid (including expenses)		(50,194	)		(46,971	)		(5,287	)		(4,633	)
	Fair value of plan assets at end of year	$	722,026		$	688,410		$	40,699		$	41,163
	Funded Status at December 31:
	Projected benefits (less than) greater than plan assets	$	265,009		$	170,853		$	85,777		$	78,539
	Amounts Recognized in the Statement of Financial Position consist of:
	Non-current liabilities	$	265,009		$	170,853		$	85,777		$	78,539
	Amounts Recognized as a Regulatory Asset consist of:
	Prior service cost	$	790		$	365		$	1,163		$	1,447
	Net (gain) loss		227,004			123,178			6,407			(792	)
	Total recognized as a regulatory asset	$	227,794		$	123,543		$	7,570		$	655
	Information on Pension Plans with an Accumulated Benefit Obligation in excess of Plan Assets:
	Projected benefit obligation	$	987,035		$	859,263			N/	A		N/	A
	Accumulated benefit obligation	$	888,942		$	784,081			N/	A		N/	A
	Fair value of plan assets	$	722,026		$	688,410			N/	A		N/	A
	The following weighted average actuarial assumptions were used in calculating the benefit obligations at December 31:
	Discount rate (Qualified Plans)		4.3	%		5.2	%		N/	A		N/	A
	Discount rate (Non-Qualified Plans)		4.2	%		4.9	%		N/	A		N/	A
	Discount rate (Other Post-Retirement Benefits)		N/	A		N/	A		4.20-4.30	%		4.85-5.20	%
	Average wage increase		3.50-3.80	%		3.50-3.80	%		N/	A		N/	A
	Health care trend rate (current year)		N/	A		N/	A		7	%		7	%
	Health care trend rate (2019-2028 forward)		N/	A		N/	A		5	%		5	%
	(1) Reflects settlement charges resulting from a distribution to a former employee upon retirement
	N/A – not applicable
Components of net Periodic Benefit Cost for Pension and Other Postretirement Benefits (OPEB)	The components of net periodic benefit cost are:
		For the Year Ended December 31,
		Pension Benefits									Other Post-Retirement Benefits
		2014			2013			2012			2014			2013			2012
		(In Thousands)
	Components of net periodic benefit cost:
	Service cost	$	11,581		$	14,783		$	12,032		$	1,618		$	1,923		$	1,604
	Interest cost		44,076			39,948			41,470			5,947			5,539			6,246
	Expected return on plan assets		(54,243	)		(51,453	)		(44,874	)		(2,799	)		(2,590	)		(2,503	)
	Amortization of:
	Prior service costs		291			605			647			284			(50	)		(69	)
	Transition obligation (asset)		-			-			-			-			-			392
	Actuarial (gain) loss		12,386			20,829			13,173			(686	)		1,776			965
	Settlements (1)		-			632			-			-			-			-
	Net periodic benefit cost	$	14,091		$	25,344		$	22,448		$	4,364		$	6,598		$	6,635
	Other Changes in Plan Assets and Benefit Obligations Recognized as a Regulatory Asset:
	Net (gain) loss	$	116,211		$	(99,572	)	$	122,368		$	6,513		$	(17,257	)	$	10,760
	Amortization of:
	Current year prior service costs		716			111			-			-			1,352			-
	Prior service costs		(291	)		(605	)		(647	)		(284	)		50			69
	Transition obligation (asset)		-			-			-			-			-			(392	)
	Settlements (1)		-			(632	)		-			-			-			-
	Actuarial (gain) loss		(12,386	)		(20,829	)		(13,173	)		686			(1,776	)		(965	)
	Total recognized as regulatory asset	$	104,250		$	(121,527	)	$	108,548		$	6,915		$	(17,631	)	$	9,472
	Total recognized in net periodic benefit costs and regulatory asset	$	118,341		$	(96,183	)	$	130,996		$	11,279		$	(11,033	)	$	16,107
	Estimated Amortizations from Regulatory Assets into Net Periodic Benefit Cost for the next 12 month period:
	Amortization of prior service cost	$	190		$	291		$	605		$	299		$	284		$	(50	)
	Amortization of net (gain) loss		19,378			12,386			20,808			706			(298	)		1,939
	Total estimated amortizations	$	19,568		$	12,677		$	21,413		$	1,005		$	(14	)	$	1,889
	The following actuarial weighted average assumptions were used in calculating net periodic benefit cost:
	Discount rate		4.90-5.20	%		4.00-4.25	%		5.05-5.30	%		4.85-5.20	%		4.00-4.25	%		5.05-5.30	%
	Average wage increase		3.50-3.80	%		3.50-3.80	%		3.50-3.80	%		N/	A		N/	A		N/	A
	Return on plan assets		7.00-8.00	%		7.75-8.00	%		7.75-8.00	%		5.56-8.00	%		5.56-8.00	%		5.56-8.00	%
	Health care trend rate (current year)		N/	A		N/	A		N/	A		7	%		7.5	%		8	%
	Health care trend rate (2019 forward)		N/	A		N/	A		N/	A		5	%		5	%		5	%
	(1) Reflects settlement charges resulting from a distribution to a former employee upon retirement
	N/A – not applicable
Effect of one percentage change in assumed health care cost trend rate	A one percentage point change in the assumed health care cost trend rate would have the following effects:
		1% Increase			1% Decrease
		(In Thousands)
	Aggregate service and interest cost components	$	849		$	(673	)
	Accumulated post-retirement benefit obligation	$	12,526		$	(10,134	)
Expected future benefit payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid:
	Year				Other
					Postretirement
		Pension Benefits			Benefits
		(In Thousands)
	2015	$	48,061		$	7,156
	2016	$	52,476		$	7,096
	2017	$	52,384		$	7,191
	2018	$	54,271		$	7,170
	2019	$	54,390		$	7,182
	2020-2023	$	300,990		$	36,264

LEASE_OBLIGATIONS_Tables

LEASE OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2014
LEASE OBLIGATIONS [Abstract]
Future minimum payments	Operating leases, for which the rental payments are charged to operating expense, consist principally of leases of office space and facilities, land and railroad rights of way.  The future minimum lease payments under these operating leases are estimated to be as follows:
		(In Thousands)
	2015	$	5,000
	2016		4,992
	2017		4,990
	2018		5,031
	2019		4,426
	2020-after		45,486
		$	69,925
Schedule of rental payments charged to operating expenses
	Rental payments charged to operating expenses in 2014, 2013 and 2012 were as follows:
		Year Ended December 31,
		2014		2013		2012
		(In Thousands)
	Rental payments	$	5,925	$	5,886	$	11,639
	Less: Sublease rental payments received		-		-		241
	Rental payments charged to operating expenses	$	5,925	$	5,886	$	11,398

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2014
FAIR VALUE MEASUREMENTS [Abstract]
Fair Value of Financial Assets and Liabilities	The following tables set forth the fair value of our financial assets and liabilities, other than pension benefits and other postretirement benefits, as of December 31, 2014 and December 31, 2013.
			Fair Value Measurements Using
			Quoted Prices in				Significant				Significant			Total
			Active Markets				Other				Unobservable
			for Identical				Observable				Inputs (Level 3)
			Assets (Level 1)				Inputs (Level 2)
	31-Dec-14		(In Thousands)
	Assets:
	Derivative assets		$	-			$	-			$	27,270		$	27,270
	Noncurrent investments			11,387				-				-			11,387
	Deferred Compensation Plan			3,624				-				-			3,624
	Supplemental retirement benefit trust life insurance policies			-				8,498				-			8,498
			$	15,011			$	8,498			$	27,270		$	50,779
	Liabilities:
	Derivative liabilities		$	-			$	-			$	85,074		$	85,074
	Long-term debt			-				1,941,711				-			1,941,711
			$	-			$	1,941,711			$	85,074		$	2,026,785
	Net fair value assets/(liabilities), December 31, 2014		$	15,011			$	(1,933,213	)		$	(57,804	)	$	(1,976,006	)
			Fair Value Measurements Using
			Quoted Prices in				Significant				Significant			Total
			Active Markets				Other				Unobservable
			for Identical				Observable				Inputs (Level 3)
			Assets (Level 1)				Inputs (Level 2)
	31-Dec-13		(In Thousands)
	Assets:
	Derivative assets		$	-			$	-			$	53,447		$	53,447
	Noncurrent investments			11,148				-				-			11,148
	Deferred Compensation Plan			3,775				-				-			3,775
	Supplemental retirement benefit trust life insurance policies			-				7,898				-			7,898
			$	14,923			$	7,898			$	53,447		$	76,268
	Liabilities:
	Derivative liabilities		$	-			$	-			$	196,233		$	196,233
	Long-term debt			-				1,846,867				-			1,846,867
			$	-			$	1,846,867			$	196,233		$	2,043,100
	Net fair value assets/(liabilities), December 31, 2013		$	14,923			$	(1,838,969	)		$	(142,786	)	$	(1,966,832	)
Additional Quantitative Information about Level 3 Fair Value Measurements	Fair value measurements categorized in Level 3 of the fair value hierarchy are prepared by individuals with expertise in valuation techniques, pricing of energy and energy-related products, and accounting requirements.  The derivative assets consist primarily of CfDs.  The determination of fair value of the CfDs was based on a probability-based expected cash flow analysis that was discounted at the December 31, 2014 or December 31, 2013 risk-free interest rates, as applicable, and an adjustment for non-performance risk using credit default swap rates.  Certain management assumptions were required, including development of pricing that extended over the term of the contracts.  We believe this methodology provides the most reasonable estimates of the amount of future discounted cash flows associated with the CfDs.  Additionally, on a quarterly basis, we perform analytics to ensure that the fair value of the derivatives is consistent with changes, if any, in the various fair value model inputs.  Additional quantitative information about Level 3 fair value measurements is as follows:
		Unobservable Input		Range at				Range at
				31-Dec-14				31-Dec-13
	Contracts for differences	Risk of non-performance			0.00% - 0.66	%			0.00% - 0.62	%
		Discount rate			1.65% - 2.25	%			1.75% - 3.21	%
		Forward pricing ($ per MW)		$	3.15 - $14.59			$	1.40 - $9.83
Changes in Fair Value of Assets and Liabilities Classified as level 3	The following tables set forth a reconciliation of changes in the fair value of the assets and liabilities above that are classified as Level 3 in the fair value hierarchy for the twelve month periods ended December 31, 2014 and 2013.
			Year Ended
			31-Dec-14
			(In Thousands)
	Net derivative assets/(liabilities), December 31, 2013		$	(142,786	)
	Unrealized gains and (losses), net			84,982
	Net derivative assets/(liabilities), December 31, 2014		$	(57,804	)
	Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of December 31, 2014		$	84,982
			Year Ended
			31-Dec-13
			(In Thousands)
	Net derivative assets/(liabilities), December 31, 2012		$	(176,605	)
	Unrealized gains and (losses), net			33,819
	Net derivative assets/(liabilities), December 31, 2013		$	(142,786	)
	Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of December 31, 2013		$	33,819
Change in Regulatory Asset/(Liability) Balance	The following table sets forth a reconciliation of changes in the net regulatory asset/(liability) balances that were established to recover any unrealized gains/(losses) associated with the CfDs for the years ended December 31, 2014 and 2013.  The amounts offset the net CfDs liabilities included in the derivative liabilities detailed above.
			Year Ended
			31-Dec-14
			(In Thousands)
	Net regulatory assets/(liabilities), December 31, 2013		$	142,786
	Unrealized (gains) and losses, net			(84,982	)
	Net regulatory assets/(liabilities), December 31, 2014		$	57,804
			Year Ended
			31-Dec-13
			(In Thousands)
	Net regulatory assets/(liabilities), December 31, 2012		$	176,605
	Unrealized (gains) and losses, net			(33,819	)
	Net regulatory assets/(liabilities), December 31, 2013		$	142,786
Fair Value of Pension and OPEB Assets	The following tables set forth the fair values of UIL Holdings’ pension and OPEB assets as of December 31, 2014 and 2013.
			Fair Value Measurements Using
			Quoted Prices in				Significant				Significant			Total
			Active Markets for				Other				Unobservable
			Identical Assets				Observable				Inputs (Level 3)
			(Level 1)				Inputs (Level 2)
			(In Thousands)
	31-Dec-14
	Pension assets
	Mutual funds		$	-			$	687,311			$	-		$	687,311
	Hedge fund			-				-				34,715			34,715
				-				687,311				34,715			722,026
	OPEB assets
	Mutual funds			33,688				7,011				-			40,699
				33,688				7,011				-			40,699
	Fair value of plan assets, December 31, 2014		$	33,688			$	694,322			$	34,715		$	762,725
	31-Dec-13
	Pension assets
	Mutual funds		$	-			$	653,579			$	-		$	653,579
	Hedge fund			-				-				34,831			34,831
				-				653,579				34,831			688,410
	OPEB assets
	Mutual funds			34,759				6,404				-			41,163
				34,759				6,404				-			41,163
	Fair value of plan assets, December 31, 2013		$	34,759			$	659,983			$	34,831		$	729,573
Schedule of Changes in Fair Value of Level 3 Plan Assets	The following tables set forth a reconciliation of changes in the fair value of the assets above that are classified as Level 3 in the fair value hierarchy for the twelve month periods ended December 31, 2014 and 2013.
			Year Ended
			31-Dec-14
			(In Thousands)
	Pension assets-Level 3, December 31, 2013		$	34,831
	Unrealized/Realized gains and (losses), net			(116	)
	Pension assets-Level 3, December 31, 2014		$	34,715
			Year Ended
			31-Dec-13
			(In Thousands)
	Pension assets-Level 3, December 31, 2012		$	27,683
	Unrealized/Realized gains and (losses), net			2,035
	Purchases			5,113
	Pension assets-Level 3, December 31, 2013		$	34,831

QUARTERLY_FINANCIAL_DATA_UNAUD1

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2014
QUARTERLY FINANCIAL DATA (UNAUDITED) [Abstract]
Schedule of Quarterly Financial Data	Selected quarterly financial data for 2014 and 2013 are set forth below:
			1st		2nd		3rd		4th
			Quarter		Quarter		Quarter		Quarter
	(In Thousands, Except Per Share Amounts)
	2014
	Operating Revenues		$	571,162	$	334,794	$	293,026	$	432,961
	Operating Income		$	104,414	$	36,272	$	34,152	$	72,565
	Net Income		$	55,465	$	9,303	$	12,504	$	32,307
	Net Income attributable to UIL Holdings		$	55,452	$	9,343	$	12,498	$	32,300
	Earnings Per Share of Common Stock – Basic: (1)		$	0.98	$	0.16	$	0.22	$	0.57
	Earnings Per Share of Common Stock – Diluted: (1)		$	0.97	$	0.16	$	0.22	$	0.56
	2013
	Operating Revenues		$	548,039	$	319,074	$	316,478	$	435,125
	Operating Income		$	96,233	$	43,235	$	22,659	$	78,362
	Net Income		$	51,807	$	17,934	$	5,157	$	40,419
	Net Income attributable to UIL Holdings		$	51,791	$	17,924	$	5,144	$	40,406
	Earnings Per Share of Common Stock – Basic: (1)		$	1.02	$	0.35	$	0.1	$	0.71
	Earnings Per Share of Common Stock – Diluted: (1)		$	1.01	$	0.35	$	0.1	$	0.71
		-1	Based on weighted average number of shares outstanding each quarter.  Diluted earnings per share reflects the effect of restricted stock, performance shares and for 2013, dilutive stock options.  Quarterly per share amounts are not intended to be additive.

SEGMENT_INFORMATION_Tables

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2014
SEGMENT INFORMATION [Abstract]
Reconciliation of Operating Profit (Loss) From Segments to Consolidated Financial Statements	UIL Holdings is organized into Electric Distribution, Electric Transmission and Gas Distribution reporting segments based on several factors including, but not limited to, the nature of each segment’s products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates.  The following measures of segment profit and loss are utilized by management to make decisions about allocating resources to the segments and assessing performance.  The following table reconciles certain segment information with that provided in our Consolidated Financial Statements.  In the table, distribution includes all electric utility revenue and expenses except for transmission, which is provided in a separate column.  “Other” includes the information for the remainder of our non‑utility activities and unallocated corporate costs, including minority interest investments and administrative costs.  Revenues from inter‑segment transactions are not material.  All of our revenues are derived in the United States.
	(In Thousands)
			31-Dec-14
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	539,249	$	257,300	$	796,549	$	835,394		$	-		$	1,631,943
	Purchased power and gas			173,059		-		173,059		428,471			(2,092	)		599,438
	Operation and maintenance			180,931		54,517		235,448		179,553			(15,441	)		399,560
	Transmission wholesale			-		88,370		88,370		-			-			88,370
	Depreciation and amortization			51,213		16,197		67,410		73,232			10,915			151,557
	Taxes - other than income taxes			51,510		35,723		87,233		50,394			644			138,271
	Acquisition-related expenses			-		-		-		-			7,344			7,344
	Operating Income			82,536		62,493		145,029		103,744			(1,370	)		247,403
	Other Income and (Deductions), net			12,004		3,798		15,802		745			(14,322	)		2,225
	Interest Charges, net			33,276		12,922		46,198		27,946			22,236			96,380
	Income from Equity Investments			13,893		-		13,893		-			-			13,893
	Income (Loss) Before Income Taxes			75,157		53,369		128,526		76,543			(37,928	)		167,141
	Income Taxes			23,546		20,612		44,158		28,280			(14,876	)		57,562
	Net Income (Loss)			51,611		32,757		84,368		48,263			(23,052	)		109,579
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		(14	)		-			(14	)
	Net Income (Loss) attributable to UIL Holdings		$	51,611	$	32,757	$	84,368	$	48,277		$	(23,052	)	$	109,593
	Total Capital Expenditures (1)		$	-	$	-	$	142,179	$	131,919		$	38,055		$	312,153
	(In Thousands)
			31-Dec-13
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	560,877	$	242,681	$	803,558	$	815,023		$	135		$	1,618,716
	Purchased power and gas			139,135		-		139,135		438,189			-			577,324
	Operation and maintenance			189,378		45,540		234,918		154,418			(5,307	)		384,029
	Transmission wholesale			-		88,206		88,206		-			-			88,206
	Depreciation and amortization			91,670		16,353		108,023		77,890			3,943			189,856
	Taxes - other than income taxes			49,421		33,991		83,412		46,477			569			130,458
	Rate case disallowances			8,354		-		8,354		-			-			8,354
	Operating Income			82,919		58,591		141,510		98,049			930			240,489
	Other Income and (Deductions), net			13,335		4,874		18,209		(323	)		2,747			20,633
	Interest Charges, net			27,052		12,046		39,098		28,935			23,736			91,769
	Income from Equity Investments			15,272		-		15,272		-			-			15,272
	Income (Loss) Before Income Taxes			84,474		51,419		135,893		68,791			(20,059	)		184,625
	Income Taxes			37,816		17,784		55,600		23,309			(9,601	)		69,308
	Net Income (Loss)			46,658		33,635		80,293		45,482			(10,458	)		115,317
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		52			-			52
	Net Income (Loss) attributable to UIL Holdings		$	46,658	$	33,635	$	80,293	$	45,430		$	(10,458	)	$	115,265
	Total Capital Expenditures (1)		$	-	$	-	$	160,042	$	97,346		$	47,790		$	305,178
			31-Dec-12
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	561,148	$	222,314	$	783,462	$	702,887		$	152		$	1,486,501
	Purchased power and gas			154,546		-		154,546		370,234			-			524,780
	Operation and maintenance			178,862		43,185		222,047		137,707			(3,477	)		356,277
	Transmission wholesale			-		79,469		79,469		-			-			79,469
	Depreciation and amortization			88,672		14,890		103,562		75,205			2,581			181,348
	Taxes - other than income taxes			44,845		26,773		71,618		42,254			165			114,037
	Operating Income (Loss)			94,223		57,997		152,220		77,487			883			230,590
	Other Income and (Deductions), net			16,562		3,945		20,507		4,071			668			25,246
	Interest Charges, net			28,308		12,941		41,249		28,001			23,292			92,542
	Income from Equity Investments			15,273		-		15,273		-			-			15,273
	Income (Loss) Before Income Taxes			97,750		49,001		146,751		53,557			(21,741	)		178,567
	Income Taxes			45,091		17,025		62,116		21,305			(8,555	)		74,866
	Net Income (Loss)			52,659		31,976		84,635		32,252			(13,186	)		103,701
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		64			-			64
	Net Income (Loss) attributable to UIL Holdings		$	52,659	$	31,976	$	84,635	$	32,188		$	(13,186	)	$	103,637
Total Capital Expenditures (1)		$	-	$	-	$	178,107	$	80,837		$	29,689		$	288,633
Reconciliation of Total Assets from Segments to Consolidated Financial Statements
			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total
	Total Assets at December 31, 2014		$	-	$	-	$	2,876,792	$	2,087,284		$	147,859		$	5,111,935
	-1	Capital expenditures are shown on a cash basis.  Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.
	-2	Information for segmenting total assets between Distribution and Transmission is not available.  Total Electric Distribution and Transmission assets are disclosed in the Total Electric Distribution and Transmission column.  Net plant in service is segregated by segment and, as of December 31, 2014, was $1,283.6 million and $659.4 million for Distribution and Transmission, respectively.
	-3	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2014.
			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total (3)
	Total Assets at December 31, 2013		$	-	$	-	$	2,950,707	$	2,010,246		$	183,267		$	5,144,220
			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total (3)
	Total Assets at December 31, 2012		$	-	$	-	$	2,935,562	$	1,993,560		$	90,042		$	5,019,164
	-1	Capital expenditures are shown on a cash basis.  Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.
	-2	Information for segmenting total assets between Distribution and Transmission is not available.  Total Electric Distribution and Transmission assets are disclosed in the Total Electric and Distribution and Transmission column.  Net plant in service is segregated by segment and, as of December 31, 2013, was $1,181.1 million and $656.0 million for Distribution and Transmission, respectively.  As of December 31, 2012, net plant in service was $1,114.2 million and $612.0 million for Distribution and Transmission, respectively.
	-3	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2013 and 2012.

STATEMENT_OF_ACCOUNTING_POLICI3

STATEMENT OF ACCOUNTING POLICIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 02, 2014
Ownership percentage in GenConn [Abstract]
Ownership percentage in joint venture (in hundredths)	50.00%
Allowance for Funds Used During Construction [Abstract]
Weighted-average allowance for funds used during construction (in hundredths)	6.12%	9.63%	5.61%
Depreciation [Abstract]
Annual depreciation rate (in hundredths)	3.20%	3.40%	3.50%
Asset Retirement Obligations Activity [Abstract]
Beginning Balance	$18,510,000	$18,289,000
Liabilities incurred during the year	0	0
Liabilities settled during the year	-762,000	-740,000
Accretion	971,000	961,000
Ending Balance	18,719,000	18,510,000	18,289,000
Business Acquisition [Line Items]
Acquisition related expenses	7,344,000	0	0
Inventory acquired for cash purchase price	20,321,000	0	0
Philadelphia Gas Works [Member]
Business Acquisition [Line Items]
Initial purchase price				1,860,000,000
Acquisition related expenses	23,100,000
Philadelphia Gas Works [Member] | Bridge Facility [Member]
Business Acquisition [Line Items]
Acquisition related expenses	15,800,000
Philadelphia Gas Works [Member] | Operating Expense [Member]
Business Acquisition [Line Items]
Acquisition related expenses	7,300,000
Milford LNG [Member]
Business Acquisition [Line Items]
Capacity of storage tank acquired	14,600,000
Inventory acquired for cash purchase price	$20,300,000

STATEMENT_OF_ACCOUNTING_POLICI4

STATEMENT OF ACCOUNTING POLICIES, DERIVATIVES, EARNINGS PER SHARE (Details) (USD $)	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	CapacityResources																CapacityResources
Derivative [Line Items]
Gross derivative asset	$27,300,000																$27,300,000
Regulatory asset	64,300,000																64,300,000
Gross derivative asset, UIL's portion of entity	6,600,000																6,600,000
Gross derivative liability	85,100,000																85,100,000
Gross derivative liability, UIL's portion of entity	59,200,000																59,200,000
Regulatory liabilities	6,500,000																6,500,000
Derivatives [Abstract]
Number of new capacity resources selected	4																4
Number of Contracts for Differences (CfDs) approved by Public Utility Regulatory Authority (PURA)	4																4
Number of Contracts for Differences (CfDs) executed by UI	2																2
Number of Contracts for Differences (CfDs) executed by CL&P	2																2
Percentage of cost or benefit borne by or allocated to UI customers for CFDs (in hundredths)																	20.00%
Percentage of cost or benefit borne by or allocated to CL&P customers (in hundredths)																	80.00%
Unrealized gain and losses from mark-to-market adjustments [Abstract]
Regulatory Assets - Derivative liabilities																	-78,510,000	-33,819,000
Regulatory Liabilities - Derivative assets																	-6,472,000	0
Numerator [Abstract]
Net income attributable to UIL Holdings	32,300,000		12,498,000		9,343,000		55,452,000		40,406,000		5,144,000		17,924,000		51,791,000		109,593,000	115,265,000	103,637,000
Less: Net income allocated to unvested units																	63,000	117,000	184,000
Net income attributable to common shareholders																	109,530,000	115,148,000	103,453,000
Denominator [Abstract]
Basic average number of shares outstanding (in shares)																	56,834,000	52,415,000	50,831,000
Effect of dilutive securities (in shares)																	302,000	296,000	277,000
Diluted average number of shares outstanding (in shares)																	57,136,000	52,711,000	51,108,000
Earnings per share [Abstract]
Basic (in dollars per share)	$0.57	[1]	$0.22	[1]	$0.16	[1]	$0.98	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.02	[1]	$1.93	$2.20	$2.04
Diluted (in dollars per share)	$0.56	[1]	$0.22	[1]	$0.16	[1]	$0.97	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.01	[1]	$1.92	$2.18	$2.02
Current Assets [Member]
Derivative [Line Items]
Gross derivative asset	6,849,000								9,098,000								6,849,000	9,098,000
Deferred Charges and Other Assets [Member]
Derivative [Line Items]
Gross derivative asset	20,421,000								44,349,000								20,421,000	44,349,000
Current Liabilities [Member]
Derivative [Line Items]
Gross derivative liability	23,308,000								26,976,000								23,308,000	26,976,000
Noncurrent Liabilities [Member]
Derivative [Line Items]
Gross derivative liability	$61,766,000								$169,327,000								$61,766,000	$169,327,000
[1]	Based on weighted average number of shares outstanding each quarter. Diluted earnings per share reflects the effect of restricted stock, performance shares and for 2013, dilutive stock options. Quarterly per share amounts are not intended to be additive.

STATEMENT_OF_ACCOUNTING_POLICI5

STATEMENT OF ACCOUNTING POLICIES, PROPERTY, PLANT AND EQUIPMENT, EQUITY INVESTMENTS (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity Investments [Abstract]
Carrying value of joint venture	$114,195,000	$118,241,000
Income (loss) from equity investment	13,893,000	15,272,000	15,273,000
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	4,055,847,000	3,691,760,000
Less accumulated depreciation	1,032,065,000	944,399,000
Total	3,023,782,000	2,747,361,000
Construction work in progress	268,908,000	321,319,000
Net Property, Plant and Equipment	3,292,690,000	3,068,680,000
Electric Distribution Plant [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	1,135,317,000	979,526,000
Electric Transmission Plant [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	646,826,000	630,834,000
Gas Distribution Plant [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	1,526,961,000	1,444,837,000
Software [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	195,864,000	144,494,000
Building Improvements [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	245,959,000	235,002,000
Land [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	65,201,000	64,848,000
Other Plant [Member]
Property, plant and equipment [Abstract]
Gross property, plant, & equipment	239,719,000	192,219,000
GenConn [Member]
Equity Investments [Abstract]
Carrying value of joint venture	114,200,000	118,200,000
Income (loss) from equity investment	13,900,000	15,300,000	15,300,000
Distributions received from joint venture	17,900,000	21,800,000	21,500,000
Undistributed earnings in equity method investment	$0
Number of peaking generation plants	2

STATEMENT_OF_ACCOUNTING_POLICI6

STATEMENT OF ACCOUNTING POLICIES, REGULATORY ASSETS (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Regulatory Assets [Line Items]
Total Regulatory Assets	$779,962,000		$1,036,130,000
Asset decoupling amount	3,900,000
Less current portion of regulatory assets	92,764,000		332,391,000
Regulatory Assets, Net	687,198,000		703,739,000
Nuclear Plant Investments - Above Market [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	[1]	238,868,000	[1]
Unamortized Redemption Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	10,499,000		11,301,000
Remaining period, minimum	7 years
Remaining period, maximum	19 years
Pension and Other Post-Retirement Benefit Plans [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	402,700,000	[2]	316,076,000	[2]
Environmental Remediation Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	13,197,000		14,953,000
Remaining period	7 years
Hardship Programs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	24,744,000	[3]	25,019,000	[3]
Debt Premium [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	27,498,000		34,178,000
Remaining period, minimum	2 years
Remaining period, maximum	23 years
Deferred Purchased Gas [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	[4]	2,556,000	[4]
Income Taxes Due Principally to Book-tax Differences [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	164,466,000	[5]	149,015,000	[5]
Unfunded Future Income Taxes [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	14,859,000	[6]	32,517,000	[6]
Contracts For Differences [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	64,276,000	[7]	142,743,000	[7]
Term of contract minimum	5 years
Term of contract maximum	12 years
Excess Generation Service Charge [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	[8]	6,909,000	[8]
Deferred Transmission Expense [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	17,387,000	[9]	9,615,000	[9]
Storm Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	[10]	14,752,000	[10]
Other Regulatory Asset [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	$40,336,000	[11]	$37,628,000	[11]
[1]	Asset/Liability relates to the Competitive Transition Assessment (CTA). Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences. Total CTA costs recovery and stranded cost amortization are complete. As a result of the outcome of UI's 2013 distribution rate request, PURA approved UI's proposed rate treatment to leave CTA rates unchanged until January 1, 2014 at which point the charge ended. The remaining balances were eliminated. See Note (C) "Regulatory Proceedings - Electric Distribution and Transmission - Other Proceedings" for additional information.
[2]	Life is dependent upon timing of final pension plan distribution; balance, which is fully offset by a corresponding asset/liability, is recalculated each year in accordance with ASC 715 "Compensation-Retirement Benefits." See Note (G) "Pension and Other Benefits" for additional information.
[3]	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
[4]	Deferred purchase gas costs balances at the end of the rate year are normally recorded/returned in the next year.
[5]	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities; balances contain regulatory liabilities related to the CTA as well as regulatory assets not related to the CTA. Due to the end of the CTA charge, the CTA regulatory liabilities are classified as current regulatory liabilities as of December 31, 2013 and the regulatory assets not related to the CTA are reclassified as long-term regulatory assets.
[6]	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
[7]	Asset life is equal to delivery term of related contracts (which vary from approximately 5 - 12 years); balance fluctuates based upon quarterly market analysis performed on the related derivatives (Note K); amount, which does not earn a return, is fully offset by corresponding derivative asset/liability. See "-Contracts for Differences" discussion above for additional information.
[8]	Regulatory asset or liability which defers generation-related and nonbypassable federally mandated congestion costs or revenues for future recovery from or return to customers. Amount fluctuates based upon timing differences between revenues collected from rates and actual costs incurred.
[9]	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
[10]	Storm costs include accumulated costs for major storms occurring from January 2009 forward. See Note (C) "Regulatory Proceedings - Electric Distribution and Transmission - Rates" for a discussion of the recovery of these costs.
[11]	Amortization period and/or balance vary depending on the nature, cost of removal and/or remaining life of the underlying assets/liabilities; asset amount includes decoupling ($3.9 million) and certain other amounts that are not currently earning a return. See Note (C) "Regulatory Proceedings for a discussion of the decoupling recovery period.

STATEMENT_OF_ACCOUNTING_POLICI7

STATEMENT OF ACCOUNTING POLICIES, REGULATORY LIABILITIES (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$508,922		$706,821
Less current portion of regulatory liabilities	17,026		261,729
Regulatory Liabilities, Net	491,896		445,092
Accumulated Deferred Investment Tax Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,319		4,465
Remaining period	29 years
Income Taxes Due Principally To Book Tax Differences Liabilities [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	0	[1]	200,673	[1]
Deferred Gain on Sale of Property [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	0	[2]	37,933	[2]
Excess Generation Service Charge [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	28,692	[3]	0	[3]
Middletown/Norwalk Local Transmission Network Service Collections [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	20,828		21,402
Remaining period	35 years
Pension And Other Post-Retirement Benefit Plans [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	9,536	[4]	27,686	[4]
Asset Retirement Obligation [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	7,248	[5]	5,593	[5]
Low Income Program [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	19,065	[6]	25,300	[6]
Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	336,028	[7]	319,530	[7]
Unfunded Future Income Taxes [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	26,318	[8]	43,421	[8]
Contracts For Differences [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	6,472	[9]	0	[9]
Deferred Purchased Gas [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,736	[10]	0	[10]
Non-Firm Margin Sharing Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	8,933		0
Remaining period	10 years
Other Regulatory Liability [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$36,747	[7]	$20,818	[7]
[1]	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities; balances contain regulatory liabilities related to the CTA as well as regulatory assets not related to the CTA. Due to the end of the CTA charge, the CTA regulatory liabilities are classified as current regulatory liabilities as of December 31, 2013 and the regulatory assets not related to the CTA are reclassified as long-term regulatory assets.
[2]	Asset/Liability relates to the Competitive Transition Assessment (CTA). Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences. Total CTA costs recovery and stranded cost amortization are complete. As a result of the outcome of UI's 2013 distribution rate request, PURA approved UI's proposed rate treatment to leave CTA rates unchanged until January 1, 2014 at which point the charge ended. The remaining balances were eliminated. See Note (C) "Regulatory Proceedings - Electric Distribution and Transmission - Other Proceedings" for additional information.
[3]	Regulatory asset or liability which defers generation-related and nonbypassable federally mandated congestion costs or revenues for future recovery from or return to customers. Amount fluctuates based upon timing differences between revenues collected from rates and actual costs incurred.
[4]	Life is dependent upon timing of final pension plan distribution; balance, which is fully offset by a corresponding asset/liability, is recalculated each year in accordance with ASC 715 "Compensation-Retirement Benefits." See Note (G) "Pension and Other Benefits" for additional information.
[5]	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
[6]	Various hardship and payment plan programs approved for recovery.
[7]	Amortization period and/or balance vary depending on the nature, cost of removal and/or remaining life of the underlying assets/liabilities; asset amount includes decoupling ($3.9 million) and certain other amounts that are not currently earning a return. See Note (C) "Regulatory Proceedings for a discussion of the decoupling recovery period.
[8]	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
[9]	Asset life is equal to delivery term of related contracts (which vary from approximately 5 - 12 years); balance fluctuates based upon quarterly market analysis performed on the related derivatives (Note K); amount, which does not earn a return, is fully offset by corresponding derivative asset/liability. See "-Contracts for Differences" discussion above for additional information.
[10]	Deferred purchase gas costs balances at the end of the rate year are normally recorded/returned in the next year.

STATEMENT_OF_ACCOUNTING_POLICI8

STATEMENT OF ACCOUNTING POLICIES, STOCK-BASED COMPENSATION (Details) (USD $)	12 Months Ended			1 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Aug. 31, 2014	31-May-14	Mar. 31, 2014
Restricted cash [Abstract]
Restricted cash	$1.10	$2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares authorized for stock-based compensation (in shares)	4,233,333
Total stock-based compensation expense	$5.70	$5.30	$4.90
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)	27,356
Weighted average grant date fair value (in dollars per share)	$35.90
Number of shares forfeited (in shares)				2,177
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance measurement period	3 years
Vesting period	3 years
Number of shares granted (in shares)	146,792
Weighted average grant date fair value (in dollars per share)	$35.24
Number of shares forfeited (in shares)				9,540
Management [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)					2,340	2,430	123,940
Weighted average grant date fair value (in dollars per share)					$34.90	$36.23	$35.87
President and Chief Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
Number of shares granted (in shares)							2,196
Weighted average grant date fair value (in dollars per share)							$35.87
Vesting rights	equal annual installments over a five year period
Non-Employee Directors [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)						25,160
Weighted average grant date fair value (in dollars per share)						$35.90

CAPITALIZATION_Details

CAPITALIZATION (Details) (Common Stock [Member], USD $)	Dec. 31, 2014	Dec. 31, 2013
Common Stock [Member]
Equity [Line Items]
Common stock outstanding (in shares)	56,546,266	56,462,507
Common stock par value (in dollars per share)	$0	$0

CAPITALIZATION_Sharebased_Comp

CAPITALIZATION, Share-based Compensation (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Weighted average grant date fair value [Abstract]
Weighted average grant date fair value (in dollars per share)	$35.87	$39.21	$34.33
Average exercise price [Abstract]
Weighted-average remaining contractual life			0 years 3 months 18 days
Restricted Stock [Member]
Number of shares [Abstract]
Beginning Balance (in shares)	30,920
Granted (in shares)	27,356
Forfeited (in shares)	-2,177
Vested (in shares)	-24,161
Ending Balance (in shares)	31,938
Weighted average grant date fair value [Abstract]
Beginning Balance (in dollars per share)	$38.90
Granted (in dollars per share)	$35.90
Forfeited (in dollars per share)	$41.34
Vested (in dollars per share)	$39.53
Ending Balance (in dollars per share)	$35.68
Restricted stock [Abstract]
Restricted stock (in shares)	308,193	276,845
Average exercise price [Abstract]
Unrecognized costs for stock awards	$0.50
Weighted-average period for cost recognition	8 months
Performance Shares [Member]
Number of shares [Abstract]
Beginning Balance (in shares)	335,008
Granted (in shares)	146,792
Forfeited (in shares)	-9,540
Vested (in shares)	-131,020
Ending Balance (in shares)	341,240
Weighted average grant date fair value [Abstract]
Beginning Balance (in dollars per share)	$34.62
Granted (in dollars per share)	$35.24
Forfeited (in dollars per share)	$38.81
Vested (in dollars per share)	$30.80
Ending Balance (in dollars per share)	$36.23
Average exercise price [Abstract]
Unrecognized costs for stock awards	1.8
Weighted-average period for cost recognition	10 months
Stock Options [Member]
Number of options [Roll Forward]
Beginning balance (in shares)	0	3,333	98,220
Granted (in shares)	0	0	0
Forfeited (in shares)	0	0	-38,000
Exercised (in shares)	0	-3,333	-56,887
Ending balance (in shares)	0	0	3,333
Option price per share [Abstract]
Beginning balance, minimum (in dollars per share)		$21.68	$21.68
Beginning balance, maximum (in dollars per share)		$21.68	$33.96
Exercised, minimum (in dollars per share)		$21.68	$31.25
Exercised, maximum (in dollars per share)		$21.68	$33.96
Ending balance, minimum (in dollars per share)			$21.68
Ending balance, maximum (in dollars per share)			$21.68
Average exercise price [Abstract]
Beginning balance (in dollars per share)		$21.68	$33.39
Ending balance (in dollars per share)			$21.68
Number of exercisable stock options (in shares)	0	0	3,333
Option price per share, minimum (in dollars per share)			$21.68
Option price per share, maximum (in dollars per share)			$21.68
Average exercisable at end of period (in dollars per share)			$21.68
Cash received from options exercised under all share-based payment arrangements		0.1	1.9
Tax benefit realized for the tax deductions from the option exercises		$0.10	$0.10

CAPITALIZATION_Longterm_Debt_D

CAPITALIZATION, Long-term Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Long-term debt [Abstract]
Long-term debt	$1,692,640,000		$1,704,095,000
Less: Current portion of long-term debt	6,526,000	[1]	11,834,000	[1]
Less: Unamortized discount	2,263,000		2,597,000
Plus: Unamortized premium	27,498,000		34,178,000
Net Long-Term Debt	1,711,349,000		1,723,842,000
Interest rate on tax-exempt bond (in hundredths)	0.33%
Restricted net assets	570,100,000
Auction rate interest rate reset period	35 days
Fair value long-term debt	1,900,000,000		1,800,000,000
Weighted average maturity term of long-term debt	10 years 9 months 18 days
Long term debt average interest (in hundredths)	5.43%
Maturities [Abstract]
2015	1,455,000
2016	11,455,000
2017	91,455,000
2018	151,455,000
2019 & thereafter	1,436,820,000
Total	1,692,640,000		1,704,095,000
United Illuminating Company (UI) [Member]
Long-term debt [Abstract]
Restricted net assets, UI equity investment	114,200,000
United Illuminating Company (UI) [Member] | Series A Senior Notes Due 2018 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Interest rate (in hundredths)	6.46%
Due date	31-Dec-18
United Illuminating Company (UI) [Member] | Series A Senior Notes Due 2019 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	31,000,000		31,000,000
Interest rate (in hundredths)	2.98%
Due date	31-Dec-19
United Illuminating Company (UI) [Member] | Series A and B Senior Notes Due 2018 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	100,000,000		100,000,000
United Illuminating Company (UI) [Member] | Series B Senior Notes Due 2018 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Interest rate (in hundredths)	6.51%
Due date	31-Dec-18
United Illuminating Company (UI) [Member] | 2010 Series Due 2027 [Member] | Pollution Control Revenue Bonds [Member]
Long-term debt [Abstract]
Long-term debt payable	27,500,000		27,500,000
Interest rate (in hundredths)	4.50%
Due date	31-Dec-27
United Illuminating Company (UI) [Member] | 2003 Series Due 2033 [Member] | Pollution Control Revenue Bonds [Member]
Long-term debt [Abstract]
Long-term debt payable	64,460,000	[2]	64,460,000	[2]
Interest rate, other	Auction Rate
Due date	31-Dec-33
United Illuminating Company (UI) [Member] | Series A and B Senior Notes Due 2017 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	70,000,000		70,000,000
Interest rate (in hundredths)	6.06%
Due date	31-Dec-17
United Illuminating Company (UI) [Member] | Series C and D Senior Notes Due 2022 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Interest rate (in hundredths)	6.26%
Due date	31-Dec-22
United Illuminating Company (UI) [Member] | Series E and F Senior Notes Due 2037 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	28,000,000		28,000,000
Interest rate (in hundredths)	6.51%
Due date	31-Dec-37
United Illuminating Company (UI) [Member] | Series C Senior Notes Due 2020 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	50,000,000		50,000,000
Interest rate (in hundredths)	6.61%
Due date	31-Dec-20
United Illuminating Company (UI) [Member] | Senior Notes Due 2040 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	100,000,000		100,000,000
Interest rate (in hundredths)	6.09%
Due date	31-Dec-40
United Illuminating Company (UI) [Member] | Series D and E Senior Notes Due 2042 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	87,000,000		87,000,000
Interest rate (in hundredths)	4.89%
Due date	31-Dec-42
United Illuminating Company (UI) [Member] | Series B and C Senior Notes [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Interest rate (in hundredths)	3.61%
Due date	31-Dec-22
United Illuminating Company (UI) [Member] | Series B, C and D Senior Notes Due 2022 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	162,500,000		162,500,000
United Illuminating Company (UI) [Member] | Senior Notes Due 2025 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	50,000,000		50,000,000
Interest rate (in hundredths)	5.61%
Due date	31-Dec-25
United Illuminating Company (UI) [Member] | Series F Senior Note Due 2023 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	75,000,000		75,000,000
Interest rate (in hundredths)	3.95%
Due date	31-Dec-23
UIL Holdings [Member] | Unsecured Senior Notes Due 2020 [Member]
Long-term debt [Abstract]
Long-term debt payable	450,000,000		450,000,000
Interest rate (in hundredths)	4.63%
Due date	31-Dec-20
Gas Companies [Member] | Senior Unsecured Notes Due 2020 - 2021 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	18,180,000		19,635,000
Interest rate, minimum (in hundredths)	4.76%
Interest rate, maximum (in hundredths)	9.60%
Due date, minimum	31-Dec-20
Due date, maximum	31-Dec-21
Gas Companies [Member] | Secured Medium Term Note IV, Due 2018-2041 [Member] | Secured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	100,000,000		100,000,000
Interest rate, minimum (in hundredths)	3.88%
Interest rate, maximum (in hundredths)	7.50%
Due date, minimum	31-Dec-18
Due date, maximum	31-Dec-41
Gas Companies [Member] | Secured Medium Term Notes III, Due 2025-2037 [Member] | Secured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	85,000,000		85,000,000
Interest rate, minimum (in hundredths)	5.77%
Interest rate, maximum (in hundredths)	6.38%
Due date, minimum	31-Dec-25
Due date, maximum	31-Dec-37
Gas Companies [Member] | Secured Medium Term Notes I, Due 2026-2028 [Member] | Secured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	29,000,000		29,000,000
Interest rate, minimum (in hundredths)	6.88%
Interest rate, maximum (in hundredths)	7.95%
Due date, minimum	31-Dec-26
Due date, maximum	31-Dec-28
Gas Companies [Member] | First Mortgage Bond Series P Due 2019 [Member] | Secured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	10,000,000		10,000,000
Interest rate (in hundredths)	10.06%
Due date	31-Dec-19
Gas Companies [Member] | Series A Unsecured Medium Term Notes Due 2016-2017 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	30,000,000		30,000,000
Interest rate, minimum (in hundredths)	6.85%
Interest rate, maximum (in hundredths)	9.10%
Due date, minimum	31-Dec-16
Due date, maximum	31-Dec-17
Gas Companies [Member] | Series B Unsecured Medium Term Notes Due 2014-2024 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	0		10,000,000
Interest rate, minimum (in hundredths)	8.12%
Interest rate, maximum (in hundredths)	8.49%
Due date, minimum	31-Dec-14
Due date, maximum	31-Dec-24
Gas Companies [Member] | Series C Unsecured Medium Term Notes Due 2035-2037 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	65,000,000		65,000,000
Interest rate, minimum (in hundredths)	5.63%
Interest rate, maximum (in hundredths)	6.66%
Due date, minimum	31-Dec-35
Due date, maximum	31-Dec-37
Gas Companies [Member] | Series D Medium Term Note Due 2028 - 2043 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	45,000,000		45,000,000
Interest rate, minimum (in hundredths)	4.30%
Interest rate, maximum (in hundredths)	5.23%
Due date, minimum	31-Dec-28
Due date, maximum	31-Dec-43
Gas Companies [Member] | Series A Senior Note Due 2043 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable	15,000,000		15,000,000
Interest rate (in hundredths)	5.33%
Due date	31-Dec-43
CNG [Member] | Senior Unsecured Note Due 2028 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable			25,000,000
Interest rate (in hundredths)			4.30%
Due date			25-Oct-28
CNG [Member] | Senior Unsecured Note Due 2043 [Member] | Unsecured Notes [Member]
Long-term debt [Abstract]
Long-term debt payable			$20,000,000
Interest rate (in hundredths)			5.23%
Due date			25-Oct-43
[1]	Includes the current portion of unamortized premium.
[2]	On December 31, 2014, the interest rate on the Bonds was 0.33%. The interest rate on these Bonds is reset through an auction held every 35 days.

REGULATORY_PROCEEDINGS_Details

REGULATORY PROCEEDINGS (Details) (USD $)

0 Months Ended

1 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

Nov. 12, 2014

Dec. 31, 2013

Aug. 31, 2013

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Jun. 19, 2014

Oct. 16, 2014

Jun. 14, 2013

Jan. 22, 2014

Feb. 28, 2013

Sep. 30, 2012

Feb. 02, 2015

MW

Customer

Mechanism

Contract

kW

Project

Plant

Gas Supply Arrangements [Member]

Future Supply Commitments [Line Items]

Number of firm transportation contracts

96

Number of pipelines

12

Number of pipelines interconnect

3

Number of gas storage contracts

24

Number of different storage contractors

7

Future obligations under gas supply arrangements [Abstract]

2015

$133,586,000

2016

126,581,000

2017

117,279,000

2018

82,238,000

2019

68,487,000

2020-after

450,763,000

Supply obligation total

978,934,000

Electric Distribution and Transmission [Member]

Approval for issuance of Debt [Abstract]

Principal Amount Of Debt Securities PURA Approved For Issuance

400,000,000

Electric Distribution and Transmission [Member] | United Illuminating Company (UI) [Member]

Rates [Abstract]

Length of time for approved new distribution rate

2 years

Allowed distribution return on equity (in hundredths)

8.75%

9.15%

Allowed distribution return on equity per 2013 decision (in hundredths)

9.15%

Earnings share split of profit

50/50

Disallowance of deferred storm costs and capital costs per PURA final decision in rate case

22,000,000

Pre-tax write-off

3,800,000

17,500,000

Reversal of write-off related to deferred storm costs and capital costs per PURA final reconsideration decision

9,200,000

Restoration of disallowed deferred storm costs per PURA final decision rate case

6,800,000

Restoration of disallowed capital costs per PURA final decision rate case

2,700,000

Allowed recovery of storm costs, per PURA final decision rate case

45,000,000

45,000,000

45,000,000

Power Supply Arrangements [Abstract]

Maximum kilowatt allowed for UI to provide power

500

Maximum duration of contracts

12 months

Maximum number of months to commence delivery of such wholesale power

6 months

Percentage of standard service customers with wholesale power supply agreements in place for the second half of 2015 (in hundredths)

80.00%

Percentage of standard service customers with wholesale power supply agreements in place for the first half of 2016 (in hundredths)

20.00%

Collateral required to be posted if the entity's credit rating declined two ratings to fall below investment grade

20,600,000

Percentage of standard service requirements for which long term contracts which can be sought (in hundredths)

20.00%

New Renewable Source Generation [Abstract]

Maximum amount of commitment to purchase Renewable Energy Credits (RECs) from new facilities behind distribution customer meters

200,000,000

Period of commitment to purchase Renewable Energy Credits (RECs)

21 years

Solicitation period obligations will phase-in

6 years

Maximum annual commitment level obligation after year six

13,600,000

Number of megawatts of grid connected renewable energy allowed to be developed by UI (in MW)

10

Basis point added to return on equity (in hundredths)

0.25%

Current authorized distribution ROE for CL&P (in hundredths)

9.17%

Megawatts of project planned in New Haven (in MW)

2.8

Megawatts of project planned in Bridgeport (in MW)

5

Megawatts of project planned in Woodbridge (in MW)

2.2

Cost of renewable connections program

47,000,000

Percentage of UI's distribution load represented by quantity of energy and RECs to be purchased (in hundredths)

3.50%

Number of contract for energy and/or RECs

2

Number of long term contracts to purchase RECs from existing biomass facilities

3

Number of megawatts energy to be produced by existing biomass facilities

5.7

Transitional Standard Offer Incentive (TSO) [Abstract]

Amount of TSO incentives approved

2,700,000

Transmission Return of Equity (ROE) [Abstract]

Weighted average return on equity (in hundredths)

12.10%

Current approved base return on equity (in hundredths)

11.14%

ROE adder on pool transmission facilities in basis points

50

Roe incentive for projects included in the ISO-NE regional system plan in basis points

100

Reserve recorded by UI for refund

2,600,000

8,200,000

Additional Reserve recorded by UI for refund relating to second and third complaints

5,600,000

Refund period

15 months

New England East-West Solution [Abstract]

Number of inter related transmission projects

4

Number of inter-related transmission projects with portions sited in Connecticut

3

Minimum amount of entity's investment for ownership of specific transmission assets

60,000,000

Threshold percentage of CL&P's costs for the Connecticut portions of projects (in hundredths)

8.40%

Expected amount of investment

45,000,000

Amount of transmission assets

24,600,000

18,400,000

6,200,000

Cumulative amount of deposits

43,500,000

Pre-tax income earned on deposits in NEEWS project.

1,700,000

1,500,000

1,600,000

Other Proceedings [Abstract]

Amount approved for recovery

7,700,000

Total estimated loss

11,300,000

Pre-tax write-off

3,800,000

17,500,000

Remaining CTA regulatory liability

8,200,000

Regulatory liability related to CT Yankee DOE litigation

12,000,000

Equity Investment in Peaking Generation [Abstract]

Ratio of equity investment in peaking generation for joint venture

50-50

Number of peaking generation plants

2

Electric Distribution and Transmission [Member] | United Illuminating Company (UI) [Member] | Subsequent Event [Member]

New England East-West Solution [Abstract]

Additional amount of deposits

1,500,000

Electric Distribution and Transmission [Member] | GenConn Devon [Member]

Equity Investment in Peaking Generation [Abstract]

Revenue requirements for equity investment in peaking generation

29,500,000

Electric Distribution and Transmission [Member] | GenConn Middletown [Member]

Equity Investment in Peaking Generation [Abstract]

Revenue requirements for equity investment in peaking generation

36,500,000

Electric Distribution and Transmission [Member] | New England Transmission Owners [Member] | June 2014 FERC Order [Member]

Transmission Return of Equity (ROE) [Abstract]

Reasonable Base Return on equity (in hundredths)

10.57%

Electric Distribution and Transmission [Member] | New England Transmission Owners [Member] | October 2014 FERC Order [Member]

Transmission Return of Equity (ROE) [Abstract]

Reasonable Base Return on equity (in hundredths)

10.57%

Electric Distribution and Transmission [Member] | New England Transmission Owners [Member] | Maximum [Member] | June 2014 FERC Order [Member]

Transmission Return of Equity (ROE) [Abstract]

Reasonable Base Return on equity (in hundredths)

11.74%

Electric Distribution and Transmission [Member] | New England Transmission Owners [Member] | Maximum [Member] | October 2014 FERC Order [Member]

Transmission Return of Equity (ROE) [Abstract]

Reasonable Base Return on equity (in hundredths)

11.74%

Electric Distribution and Transmission [Member] | New England Transmission Owners [Member] | Minimum [Member] | June 2014 FERC Order [Member]

Transmission Return of Equity (ROE) [Abstract]

Reasonable Base Return on equity (in hundredths)

7.03%

Gas Distribution [Member]

Other Proceedings [Abstract]

Duration of expansion plan

10 years

Initial time horizon for financial hurdle rate model

20 years

Duration to which financial hurdle rate model extended

25 years

Number of new customers to be added

280,000

Rate premium for distribution component of on-main customers (in hundredths)

10.00%

Rate premium for distribution component of off-main customers (in hundredths)

30.00%

Gas Distribution [Member] | Connecticut Natural Gas Corporation (CNG) [Member]

Rates [Abstract]

Approved return on equity (in hundredths)

9.18%

Number of rate making mechanisms

2

Earnings share mechanism ratio

50/50

Gas Distribution [Member] | Connecticut Natural Gas Corporation (CNG) [Member] | Maximum [Member]

Rates [Abstract]

Decrease in annual revenue requirements

3,500,000

Gas Distribution [Member] | Connecticut Natural Gas Corporation (CNG) [Member] | Minimum [Member]

Rates [Abstract]

Decrease in annual revenue requirements

$2,500,000

Gas Distribution [Member] | Connecticut Natural Gas Corporation (CNG) and Southern Connecticut Gas Company [Member]

Other Proceedings [Abstract]

Number of new customers to be added

200,000

Gas Distribution [Member] | The Southern Connecticut Gas Company (SCG) [Member]

Rates [Abstract]

Approved return on equity (in hundredths)

9.36%

Gas Distribution [Member] | The Berkshire Gas Company [Member]

Rates [Abstract]

Approved return on equity (in hundredths)

10.50%

Duration of approved rate plan

10 years

SHORTTERM_CREDIT_ARRANGEMENTS_1

SHORT-TERM CREDIT ARRANGEMENTS (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Oct. 31, 2012
Gas Companies [Member]
Short-term borrowings [Abstract]
Maximum aggregate principal amount of short-term borrowing outstanding at any month-end	$0		$0
Average aggregate short-term borrowings outstanding during the year	0	[1]	0	[1]
Weighted average interest rate (in hundredths)		[1]		[1]
Principal amounts outstanding at year-end	0		0
UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Number of days of loan term agreement	364 days
UIL [Member] | Non-gas Companies [Member]
Short-term borrowings [Abstract]
Maximum aggregate principal amount of short-term borrowing outstanding at any month-end	111,000,000		202,000,000
Average aggregate short-term borrowings outstanding during the year	49,233,000	[1]	152,455,000	[1]
Weighted average interest rate (in hundredths)	1.37%	[1]	1.43%	[1]
Principal amounts outstanding at year-end	89,000,000		0
UI [Member] | Non-gas Companies [Member]
Short-term borrowings [Abstract]
Maximum aggregate principal amount of short-term borrowing outstanding at any month-end	0		60,000,000
Average aggregate short-term borrowings outstanding during the year	0	[1]	13,510,000	[1]
Weighted average interest rate (in hundredths)		[1]	1.40%	[1]
Principal amounts outstanding at year-end	0		0
Standby Letter of Credit Due 2015 [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Amounts outstanding under the Credit Facility	89,000,000
Expiration date	16-Jun-15
Standby Letter Of Credit Due 2016 [Member]
Disclosure of short-term credit arrangements [Abstract]
Standby letter of credit outstanding	4,400,000
Expiration date	31-Jan-16
Revolving Credit Facility [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Available credit under the Credit Facility	306,600,000
Amounts outstanding under the Credit Facility	0
Expiration date	30-Nov-16
Maximum borrowing capacity	400,000,000
Issuance of letter of credit, maximum	50,000,000
Revolving Credit Facility [Member] | UI [Member]
Disclosure of short-term credit arrangements [Abstract]
Available credit under the Credit Facility	250,000,000
Revolving Credit Facility [Member] | CNG [Member]
Disclosure of short-term credit arrangements [Abstract]
Available credit under the Credit Facility	150,000,000
Revolving Credit Facility [Member] | SNG [Member]
Disclosure of short-term credit arrangements [Abstract]
Available credit under the Credit Facility	150,000,000
Revolving Credit Facility [Member] | Berkshire [Member]
Disclosure of short-term credit arrangements [Abstract]
Available credit under the Credit Facility	25,000,000
Credit Agreement [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Expiration date	31-Oct-13
Maximum borrowing capacity					100,000,000
Bridge Facility [Member] | UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Maximum borrowing capacity	$1,900,000
[1]	Average short-term borrowings represent the sum of daily borrowings outstanding, weighted for the number of days outstanding and divided by the number of days in the period. The weighted average interest rate is determined by dividing interest expense by the amount of average borrowings.

INCOME_TAXES_Details

INCOME TAXES (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current
Federal		($443)	$5,830
State	1,798	-1,149	1,110
Total current	1,798	-1,592	6,940
Deferred
Federal	54,407	64,931	61,510
State	1,552	6,164	6,611
Total deferred	55,959	71,095	68,121
Investment tax credits	-195	-195	-195
Total income tax expense	57,562	69,308	74,866
Reconciliation of federal statutory rate to effective tax rate
Book income before income taxes	167,141	184,625	178,567
Computed tax at federal statutory rate	58,499	64,619	62,499
Increases (reductions) resulting from:
Amortization of nuclear plant regulatory assets	0	6,867	9,334
State income taxes, net of federal income tax benefits	2,177	3,259	5,018
Allowance for equity funds used during construction	-3,064	-3,784	-2,749
Investment tax credits	-195	-195	-195
Other items, net	145	-1,458	959
Total income tax expense	57,562	69,308	74,866
Effective income tax rates (in hundredths)	34.40%	37.50%	41.90%
Deferred income tax assets:
Post-retirement benefits	130,474	90,300
Accrued removal obligation	134,175	119,904
Net operating loss carry forward	49,772	42,818
Other	64,929	104,467
Total deferred income tax assets	379,350	357,489
Deferred income tax liabilities:
Plant basis and accelerated depreciation timing differences	700,969	607,950
Regulatory deferrals related to pension and other post-retirement benefits	149,158	110,980
Investment in GenConn	53,378	53,350
Other	64,946	104,009
Total deferred income tax liabilities	968,451	876,289
Operating loss carryforwards balances [Abstract]
Federal net operating loss	142,704	122,339
Alternative minimum tax credit	2,697	2,697
State tax credits	$11,276	$7,289
Federal net operating loss, Year Expiration Begins	31-Dec-32
State tax credit, Year Expiration Begins	31-Dec-17

SUPPLEMENTARY_INFORMATION_Deta

SUPPLEMENTARY INFORMATION (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Depreciation and Amortization [Abstract]
Property, plant and equipment depreciation	$131,051	$120,301	$112,002
Amortization of regulatory assets	20,506	69,555	69,346
Total depreciation and amortization	151,557	189,856	181,348
Taxes - Other than Income Taxes - Operating [Abstract]
Connecticut gross earnings	73,429	75,330	65,753
Local real estate and personal property	50,392	46,567	40,588
Payroll taxes	13,050	8,005	7,274
Other	1,400	556	422
Total Taxes - Other than Income Taxes	138,271	130,458	114,037
Other Income and (Deductions), net [Abstract]
Interest income	2,573	2,733	2,631
Allowance for funds used during construction - equity	8,814	10,811	7,480
Allowance for funds used during construction - debt	5,157	7,170	6,979
Weather insurance	-2,200	-70	3,488
TSO incentives	0	0	2,745
Other	3,676	-11	1,923
Total Other Income and (Deductions), net	$18,020	$20,633	$25,246

PENSION_AND_OTHER_BENEFITS_Det

PENSION AND OTHER BENEFITS (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
PENSION AND OTHER BENEFITS [Abstract]
Potential funding requirement for 2015	$15,000,000
Effect of the change in the discount rate on Projected Benefit Obligation	112,000,000
Change in the discount rate assumed for pension expense (in hundredths)	0.25%
Effect of the change in the discount rate on pension expense	3,200,000
Change in the expected return on assets (in hundredths)	1.00%
Effect of the change in the expected return on assets on pension expenses	7,200,000
Change in the discount rate assumed, other postretirement plans (in hundredths)	0.25%
Effect of the change in the discount rate on other postretirement expense	400,000
Change in the expected return on assets, other postretirement plans (in hundredths)	1.00%
Effect of the change in the expected return on assets on other postretirement expense	400,000
Increase in projected benefit obligation for pension plan resulting from change in mortality assumption	38,000,000
Increase in projected benefit obligations for other post retirement plans resulting from change in mortality assumption	7,000,000
Decrease in projected benefit obligations for pension plans resulting from the experience study	34,000,000
Decrease in projected benefit obligations for other postretirement plans resulting from the experience study	16,000,000
Other Post Retirement Benefit Plans [Abstract]
Terms of other postretirement benefits plans - non union employees	Non-union employees who are 55 years of age and whose sum of age and years of service at time of retirement is equal to or greater than 65 are eligible for benefits partially subsidized by UI. The amount of benefits subsidized by UI is determined by age and years of service at retirement. For funding purposes, UI established a 401(h) account in connection with the UI Pension Plan and Serial Voluntary Employee Benefit Association Trust (VEBA) accounts for the years 2007 through 2020 to fund other postretirement benefits for UIbs non union employees who retire on or after January 1, 1994. These VEBA accounts were approved by the IRS and UI contributed $4.5 million to fund the Serial VEBA accounts in 2007. UI does not expect to make a contribution in 2015 to fund OPEB for non-union employees.
Terms of other postretirement benefit plans - union employees	Union employees whose sum of age and years of service at the time of retirement is equal to or greater than 85 (or who are 62 with at least 20 years of service) are eligible for benefits partially subsidized by UI. The amount of benefits subsidized by UI is determined by age and years of service at retirement. For funding purposes, UI established a VEBA to fund other postretirement benefits for UIbs union employees. The funding strategy for the VEBA is to select funds that most clearly mirror the pension allocation strategy. SCG and CNG also have plans providing other postretirement benefits for substantially all of their employees. These benefits consist primarily of health care, prescription drug and life insurance benefits, for retired employees and their dependents. The eligibility for these benefits is determined by the employeebs date of hire, number of years of service, age and whether the employee belongs to a certain group, such as a union. Dependents are also eligible at the employeebs date of retirement provided the retired participant pays the necessary contribution. These plans are contributory with the level of participantbs contributions evaluated annually. Benefits payments under these plans include annual caps for CNG participants hired after 1993 and SCG participants hired after 1996. SCG non-union employees hired after November 1995 are not eligible for these benefits. Union employees hired after April 1, 2010 and December 1, 2009 at SCG and CNG, respectively, are not eligible for these benefits. As such, Gas Company OPEB liabilities are not especially sensitive to increases in the healthcare trend rate.
Description of alternative method to amortize prior service costs and unrecognized actuarial gains and losses.	UIL Holdings utilizes an alternative method to amortize unrecognized actuarial gains and losses related to the pension and other postretirement benefits plans over the lesser of the average remaining service period or 10 years. For ASC 715 purposes, UIL Holdings does not recognize gains or losses until there is a variance in an amount equal to at least 5% of the greater of the projected benefit obligation or the market-related value of assets.
Change in Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	729,573,000
Fair value of plan assets at end of year	762,725,000		729,573,000
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Aggregate service and interest cost components, increase	849,000
Aggregate service and interest cost components, decrease	-673,000
Accumulated post-retirement benefit obligation, increase	12,526,000
Accumulated post-retirement benefit obligation, decrease	-10,134,000
Defined Contribution Retirement Plans/401(k) Disclosure [Abstract]
Matching contributions	5,400,000		5,200,000		4,900,000
Other Accounting Matters [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets of pension and other postretirement plans	235,400,000		124,200,000
Pension Benefits [Member]
Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	859,263,000		950,609,000
Service cost	11,581,000		14,783,000		12,032,000
Interest cost	44,076,000		39,948,000		41,470,000
Participant contributions	0		0
Settlements	0	[1]	-2,367,000	[1]
Actuarial (gain) loss	122,309,000		-96,739,000
Benefits paid (including expenses)	-50,194,000		-46,971,000
Benefit obligation at end of year	987,035,000		859,263,000		950,609,000
Change in Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	688,410,000		625,061,000
Actual return on plan assets	59,675,000		54,259,000
Employer contributions	24,135,000		58,428,000
Participant contributions	0		0
Settlements	0	[1]	-2,367,000	[1]
Benefits paid (including expenses)	-50,194,000		-46,971,000
Fair value of plan assets at end of year	722,026,000		688,410,000		625,061,000
Funded Status [Abstract]
Projected benefits (less than) greater than plan assets	265,009,000		170,853,000
Amounts Recognized in the Statement of Financial Position consist of [Abstract]
Non-current liabilities	265,009,000		170,853,000
Amounts Recognized as a Regulatory Asset consist of: [Abstract]
Prior service cost	790,000		365,000
Net (gain) loss	227,004,000		123,178,000
Total recognized as regulatory assets	227,794,000		123,543,000
Pension Plans with an Accumulated Benefit Obligations in excess of Plan Assets [Abstract]
Projected benefit obligation	987,035,000		859,263,000
Accumulated benefit obligation	888,942,000		784,081,000
Fair value of plan assets	722,026,000		688,410,000
Components of net periodic benefit cost:
Service cost	11,581,000		14,783,000		12,032,000
Interest cost	44,076,000		39,948,000		41,470,000
Expected return on plan assets	-54,243,000		-51,453,000		-44,874,000
Amortization of:
Prior service costs	291,000		605,000		647,000
Transition obligation (asset)	0		0		0
Actuarial (gain) loss	12,386,000		20,829,000		13,173,000
Settlements	0	[1]	632,000	[1]	0	[1]
Net periodic benefit cost	14,091,000		25,344,000		22,448,000
Estimated Future Benefit Payments [Abstract]
2015	48,061,000
2016	52,476,000
2017	52,384,000
2018	54,271,000
2019	54,390,000
2020-2023	300,990,000
Pension Benefits [Member] | Minimum [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Average wage increase (in hundredths)	3.50%		3.50%
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)	4.90%		4.00%		5.05%
Average wage increase (in hundredths)	3.50%		3.50%		3.50%
Return on plan assets (in hundredths)	7.00%		7.75%		7.75%
Pension Benefits [Member] | Maximum [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Average wage increase (in hundredths)	3.80%		3.80%
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)	5.20%		4.25%		5.30%
Average wage increase (in hundredths)	3.80%		3.80%		3.80%
Return on plan assets (in hundredths)	8.00%		8.00%		8.00%
Pension Benefits [Member] | Non Qualified Plans [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (in hundredths)	4.20%		4.90%
Pension Benefits [Member] | Qualified Plans [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (in hundredths)	4.30%		5.20%
Pension Benefits [Member] | Other Changes in Plans Assets and Benefit Obligations Recognized as a Regulatory Assets [Member]
Other Changes in Plan Assets and Benefit Obligations Recognized as Regulatory Asset [Abstract]
Net (gain) loss	116,211,000		-99,572,000		122,368,000
Amortization of:
Current year prior service costs	716,000		111,000		0
Prior service costs	-291,000		-605,000		-647,000
Transition obligation (asset)	0		0		0
Actuarial (gain) loss	-12,386,000		-20,829,000		-13,173,000
Settlements	0	[1]	-632,000	[1]	0	[1]
Total recognized as regulatory asset	104,250,000		-121,527,000		108,548,000
Total recognized in net periodic benefit costs and regulatory asset	118,341,000		-96,183,000		130,996,000
Pension Benefits [Member] | Estimated amortization from Regulatory Assets [Member]
Amortization of:
Prior service costs	190,000		291,000		605,000
Amortization of net (gain) loss	19,378,000		12,386,000		20,808,000
Total estimated amortizations	19,568,000		12,677,000		21,413,000
Other Post-Retirement Benefits [Member]
Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	119,702,000		136,687,000
Service cost	1,618,000		1,923,000		1,604,000
Interest cost	5,947,000		5,539,000		6,246,000
Participant contributions	1,265,000		1,253,000
Settlements	0	[1]	0	[1]
Actuarial (gain) loss	10,872,000		-13,893,000
Benefits paid (including expenses)	-12,928,000		-11,807,000
Benefit obligation at end of year	126,476,000		119,702,000		136,687,000
Change in Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	41,163,000		38,540,000
Actual return on plan assets	3,558,000		6,003,000
Employer contributions	0		0
Participant contributions	1,265,000		1,253,000
Settlements	0	[1]	0	[1]
Benefits paid (including expenses)	-5,287,000		-4,633,000
Fair value of plan assets at end of year	40,699,000		41,163,000		38,540,000
Funded Status [Abstract]
Projected benefits (less than) greater than plan assets	85,777,000		78,539,000
Amounts Recognized in the Statement of Financial Position consist of [Abstract]
Non-current liabilities	85,777,000		78,539,000
Amounts Recognized as a Regulatory Asset consist of: [Abstract]
Prior service cost	1,163,000		1,447,000
Net (gain) loss	6,407,000		-792,000
Total recognized as regulatory assets	7,570,000		655,000
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (in hundredths)	4.30%		5.20%
Health care trend rate (current year) (in hundredths)	7.00%		7.00%
Health care trend rate (2019-2028 forward)	5.00%		5.00%
Components of net periodic benefit cost:
Service cost	1,618,000		1,923,000		1,604,000
Interest cost	5,947,000		5,539,000		6,246,000
Expected return on plan assets	-2,799,000		-2,590,000		-2,503,000
Amortization of:
Prior service costs	284,000		-50,000		-69,000
Transition obligation (asset)	0		0		392,000
Actuarial (gain) loss	-686,000		1,776,000		965,000
Settlements	0	[1]	0	[1]	0	[1]
Net periodic benefit cost	4,364,000		6,598,000		6,635,000
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Composite health care trend rate (current year), (in hundredths)	7.00%		7.50%		8.00%
Composite health care trend rate (2019 forward), (in hundredths)	5.00%		5.00%		5.00%
Estimated Future Benefit Payments [Abstract]
2015	7,156,000
2016	7,096,000
2017	7,191,000
2018	7,170,000
2019	7,182,000
2020-2023	36,264,000
Other Post-Retirement Benefits [Member] | Minimum [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (in hundredths)	4.20%		4.85%
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)	4.85%		4.00%		5.05%
Return on plan assets (in hundredths)	5.56%		5.56%		5.56%
Other Post-Retirement Benefits [Member] | Maximum [Member]
Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (in hundredths)	4.30%		5.20%
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)	5.20%		4.25%		5.30%
Return on plan assets (in hundredths)	8.00%		8.00%		8.00%
Other Post-Retirement Benefits [Member] | Other Changes in Plans Assets and Benefit Obligations Recognized as a Regulatory Assets [Member]
Other Changes in Plan Assets and Benefit Obligations Recognized as Regulatory Asset [Abstract]
Net (gain) loss	6,513,000		-17,257,000		10,760,000
Amortization of:
Current year prior service costs	0		1,352,000		0
Prior service costs	-284,000		50,000		69,000
Transition obligation (asset)	0		0		-392,000
Actuarial (gain) loss	686,000		-1,776,000		-965,000
Settlements	0	[1]	0	[1]	0	[1]
Total recognized as regulatory asset	6,915,000		-17,631,000		9,472,000
Total recognized in net periodic benefit costs and regulatory asset	11,279,000		-11,033,000		16,107,000
Other Post-Retirement Benefits [Member] | Estimated amortization from Regulatory Assets [Member]
Amortization of:
Prior service costs	299,000		284,000		-50,000
Amortization of net (gain) loss	706,000		-298,000		1,939,000
Total estimated amortizations	1,005,000		-14,000		1,889,000
UI [Member]
Defined Benefit Plan Disclosure [Line Items]
Account contributions to fund Serial VEBA Accounts in 2007	$4,500,000
Percentage of employees represented by Local 470-1 Utility Workers Union of America (in hundredths)	54.00%
Equity Securities [Member]
Other Post Retirement Benefit Plans [Abstract]
Target allocation of equity securities for 2015 (in hundredths)	60.00%
Debt Securities [Member]
Other Post Retirement Benefit Plans [Abstract]
Target allocation of equity securities for 2015 (in hundredths)	40.00%
[1]	Reflects settlement charges resulting from a distribution to a former employee upon retirement.

RELATED_PARTY_TRANSACTIONS_Det

RELATED PARTY TRANSACTIONS (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
RELATED PARTY TRANSACTIONS [Abstract]
Lease payments for office space	$1.80	$1.50	$4.80

LEASE_OBLIGATIONS_Details

LEASE OBLIGATIONS (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Future minimum lease payments under non-cancelable operating leases [Abstract]
2015	$5,000
2016	4,992
2017	4,990
2018	5,031
2019	4,426
2020-after	45,486
Total	69,925
Rental payments charged to operating expenses [Abstract]
Rental payments	5,925	5,886	11,639
Less: Sublease rental payments received	0	0	241
Rental payments charged to operating expenses	$5,925	$5,886	$11,398

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2014
		Subcontractor
Connecticut Yankee Atomic Power Company [Member]
Site Contingency [Line Items]
Percentage stock ownership share in CT Yankee atomic power company (in hundredths)		9.50%
Carrying value of stock in CT Yankee atomic power company		$0.20
DOE spent fuel litigation [Abstract]
Damages awarded for spent fuel related costs		39.7
Entity's share of amount awarded to CT Yankee atomic power company	3.8
Actual second set of damages award		126.3
Entity's share of second set of damage claims		12
Mill River New Haven Connecticut Site [Member]
Site Decontamination, Demolition and Remediation Costs [Abstract]
Amount placed in escrow for estimated remediation		1.9
Remaining amount of escrow		0.1
New Haven Harbor Station Site [Member]
Site Decontamination, Demolition and Remediation Costs [Abstract]
Site contingency, liability accrued		3.2
Mill Street Greenfield Massachusetts Site [Member]
Site Decontamination, Demolition and Remediation Costs [Abstract]
Site contingency, liability accrued		0.9
East Street Site Pittsfield Massachusetts [Member]
Site Decontamination, Demolition and Remediation Costs [Abstract]
Site contingency, liability accrued		3.2
Middletown/Norwalk Transmission Projects [Member]
Middletown/Norwalk Transmission Project [Abstract]
Amount sought for change order requests		33.3
Percentage of general contractor mark-up on approved subcontractor change order claims (in hundredths)		10.00%
Amount of general contractor mark up on approved subcontractor change order claims		2.3
Subcontractors responsible for civil construction		2
Revised estimate for change order requests		7.7
Amount in Memorandum of Decision issued by the court for the company to pay to contractor		$1.30

FAIR_VALUE_MEASUREMENTS_Detail

FAIR VALUE MEASUREMENTS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities: [Abstract]
Long-term debt	$1,692,640	$1,704,095
Fair Value, Measurements, Recurring [Member]
Assets: [Abstract]
Derivative assets	27,270	53,447
Noncurrent investments	11,387	11,148
Deferred Compensation Plan	3,624	3,775
Supplemental retirement benefit trust life insurance policies	8,498	7,898
Total financial assets, fair value	50,779	76,268
Liabilities: [Abstract]
Derivative liabilities	85,074	196,233
Long-term debt	1,941,711	1,846,867
Total financial liabilities, fair value	2,026,785	2,043,100
Net fair value assets/(liabilities)	-1,976,006	-1,966,832
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets: [Abstract]
Derivative assets	0	0
Noncurrent investments	11,387	11,148
Deferred Compensation Plan	3,624	3,775
Supplemental retirement benefit trust life insurance policies	0	0
Total financial assets, fair value	15,011	14,923
Liabilities: [Abstract]
Derivative liabilities	0	0
Long-term debt	0	0
Total financial liabilities, fair value	0	0
Net fair value assets/(liabilities)	15,011	14,923
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets: [Abstract]
Derivative assets	0	0
Noncurrent investments	0	0
Deferred Compensation Plan	0	0
Supplemental retirement benefit trust life insurance policies	8,498	7,898
Total financial assets, fair value	8,498	7,898
Liabilities: [Abstract]
Derivative liabilities	0	0
Long-term debt	1,941,711	1,846,867
Total financial liabilities, fair value	1,941,711	1,846,867
Net fair value assets/(liabilities)	-1,933,213	-1,838,969
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets: [Abstract]
Derivative assets	27,270	53,447
Noncurrent investments	0	0
Deferred Compensation Plan	0	0
Supplemental retirement benefit trust life insurance policies	0	0
Total financial assets, fair value	27,270	53,447
Liabilities: [Abstract]
Derivative liabilities	85,074	196,233
Long-term debt	0	0
Total financial liabilities, fair value	85,074	196,233
Net fair value assets/(liabilities)	($57,804)	($142,786)

FAIR_VALUE_MEASUREMENTS_Unobse

FAIR VALUE MEASUREMENTS, Unobservable Input (Details) (Contract For Difference [Member], USD $)	Dec. 31, 2014	Dec. 31, 2013
Contract For Difference [Member]
Unobservable input [Abstract]
Risk of non-performance, lower range (in hundredths)	0.00%	0.00%
Risk of non-performance, upper range (in hundredths)	0.66%	0.62%
Discount rate, lower range (in hundredths)	1.65%	1.75%
Discount rate, upper range (in hundredths)	2.25%	3.21%
Forward pricing, lower range (in dollars per MW)	$3.15	$1.40
Forward pricing, upper range (in dollars per MW)	$14.59	$9.83

FAIR_VALUE_MEASUREMENTS_Assets

FAIR VALUE MEASUREMENTS, Assets and Liabilities Classified as Level 3 (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Changes in fair value of assets and liabilities classified as level 3 [Roll Forward]
Net derivative assets/(liabilities), Beginning balance	($142,786)	($176,605)
Unrealized gains and (losses), net	84,982	33,819
Net derivative assets/(liabilities), Ending balance	-57,804	-142,786
Change in unrealized gains (losses) net relating to net derivative assets/(liabilities)	$84,982	$33,819

FAIR_VALUE_MEASUREMENTS_Regula

FAIR VALUE MEASUREMENTS, Regulatory Assets and Liabilities (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Change in regulatory asset/liability balances [Roll Forward]
Net regulatory assets/(liabilities), Beginning balance	$142,786	$176,605
Unrealized (gains) and losses, net	-84,982	-33,819
Net regulatory assets/(liabilities), Ending balance	$57,804	$142,786

FAIR_VALUE_MEASUREMENTS_Define

FAIR VALUE MEASUREMENTS, Defined Benefit Pension Plan (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$762,725	$729,573
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,688	34,759
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	694,322	659,983
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,715	34,831
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	722,026	688,410	625,061
Pension [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	687,311	653,579
Pension [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,715	34,831
Pension [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	687,311	653,579
Pension [Member] | Mutual Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension [Member] | Mutual Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	687,311	653,579
Pension [Member] | Mutual Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,715	34,831
Pension [Member] | Hedge Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension [Member] | Hedge Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension [Member] | Hedge Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34,715	34,831
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,699	41,163
OPEB [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,688	34,759
OPEB [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,011	6,404
OPEB [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
OPEB [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,699	41,163
OPEB [Member] | Mutual Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33,688	34,759
OPEB [Member] | Mutual Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,011	6,404
OPEB [Member] | Mutual Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$0	$0

FAIR_VALUE_MEASUREMENTS_Pensio

FAIR VALUE MEASUREMENTS, Pension assets, level 3 fair value (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, beginning of period	$34,831	$27,683
Unrealized/Realized gains and (losses), net	-116	2,035
Purchases		5,113
Fair value of plan assets, end of period	$34,715	$34,831

QUARTERLY_FINANCIAL_DATA_UNAUD2

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
QUARTERLY FINANCIAL DATA (UNAUDITED) [Abstract]
Operating Revenues	$432,961		$293,026		$334,794		$571,162		$435,125		$316,478		$319,074		$548,039		$1,631,943	$1,618,716	$1,486,501
Operating Income	72,565		34,152		36,272		104,414		78,362		22,659		43,235		96,233		247,403	240,489	230,590
Net income	32,307		12,504		9,303		55,465		40,419		5,157		17,934		51,807		109,579	115,317	103,701
Net income attributable to UIL Holdings	$32,300		$12,498		$9,343		$55,452		$40,406		$5,144		$17,924		$51,791		$109,593	$115,265	$103,637
Earnings Per Share of Common Stock - Basic: (in dollars per share)	$0.57	[1]	$0.22	[1]	$0.16	[1]	$0.98	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.02	[1]	$1.93	$2.20	$2.04
Earnings Per Share of Common Stock - Diluted: (in dollars per share)	$0.56	[1]	$0.22	[1]	$0.16	[1]	$0.97	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.01	[1]	$1.92	$2.18	$2.02
[1]	Based on weighted average number of shares outstanding each quarter. Diluted earnings per share reflects the effect of restricted stock, performance shares and for 2013, dilutive stock options. Quarterly per share amounts are not intended to be additive.

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details) (USD $)	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenues	$432,961,000		$293,026,000	$334,794,000	$571,162,000	$435,125,000		$316,478,000	$319,074,000	$548,039,000	$1,631,943,000		$1,618,716,000		$1,486,501,000
Purchased power and gas											599,438,000		577,324,000		524,780,000
Operation and maintenance											399,560,000		384,029,000		356,277,000
Transmission wholesale											88,370,000		88,206,000		79,469,000
Depreciation and amortization											151,557,000		189,856,000		181,348,000
Taxes - other than income taxes											138,271,000		130,458,000		114,037,000
Acquisition-related expenses											7,344,000		0		0
Rate case disallowances											0		8,354,000		0
Operating Income	72,565,000		34,152,000	36,272,000	104,414,000	78,362,000		22,659,000	43,235,000	96,233,000	247,403,000		240,489,000		230,590,000
Other Income and (Deductions), net											2,225,000		20,633,000		25,246,000
Interest Charges, net											96,380,000		91,769,000		92,542,000
Income from Equity Investments											13,893,000		15,272,000		15,273,000
Income (Loss) Before Income Taxes											167,141,000		184,625,000		178,567,000
Income Taxes											57,562,000		69,308,000		74,866,000
Net Income (Loss)	32,307,000		12,504,000	9,303,000	55,465,000	40,419,000		5,157,000	17,934,000	51,807,000	109,579,000		115,317,000		103,701,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											-14,000		52,000		64,000
Net Income attributable to UIL Holdings	32,300,000		12,498,000	9,343,000	55,452,000	40,406,000		5,144,000	17,924,000	51,791,000	109,593,000		115,265,000		103,637,000
Total Capital Expenditure											312,153,000	[1]	305,178,000	[1]	288,633,000	[1]
Total Assets	5,111,935,000	[2]				5,144,220,000	[3]				5,111,935,000	[2]	5,144,220,000	[3]	5,019,164,000	[3]
Goodwill	266,205,000					266,205,000					266,205,000		266,205,000
Electric Distribution Reportable Segment [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues											539,249,000		560,877,000		561,148,000
Purchased power and gas											173,059,000		139,135,000		154,546,000
Operation and maintenance											180,931,000		189,378,000		178,862,000
Transmission wholesale											0		0		0
Depreciation and amortization											51,213,000		91,670,000		88,672,000
Taxes - other than income taxes											51,510,000		49,421,000		44,845,000
Acquisition-related expenses											0
Rate case disallowances													8,354,000
Operating Income											82,536,000		82,919,000		94,223,000
Other Income and (Deductions), net											12,004,000		13,335,000		16,562,000
Interest Charges, net											33,276,000		27,052,000		28,308,000
Income from Equity Investments											13,893,000		15,272,000		15,273,000
Income (Loss) Before Income Taxes											75,157,000		84,474,000		97,750,000
Income Taxes											23,546,000		37,816,000		45,091,000
Net Income (Loss)											51,611,000		46,658,000		52,659,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											0		0		0
Net Income attributable to UIL Holdings											51,611,000		46,658,000		52,659,000
Total Capital Expenditure											0	[1]	0	[1]	0	[1]
Total Assets	0	[4]				0	[5]				0	[4]	0	[5]	0	[5]
Electric Transmission Reportable Segment [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues											257,300,000		242,681,000		222,314,000
Purchased power and gas											0		0		0
Operation and maintenance											54,517,000		45,540,000		43,185,000
Transmission wholesale											88,370,000		88,206,000		79,469,000
Depreciation and amortization											16,197,000		16,353,000		14,890,000
Taxes - other than income taxes											35,723,000		33,991,000		26,773,000
Acquisition-related expenses											0
Rate case disallowances													0
Operating Income											62,493,000		58,591,000		57,997,000
Other Income and (Deductions), net											3,798,000		4,874,000		3,945,000
Interest Charges, net											12,922,000		12,046,000		12,941,000
Income from Equity Investments											0		0		0
Income (Loss) Before Income Taxes											53,369,000		51,419,000		49,001,000
Income Taxes											20,612,000		17,784,000		17,025,000
Net Income (Loss)											32,757,000		33,635,000		31,976,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											0		0		0
Net Income attributable to UIL Holdings											32,757,000		33,635,000		31,976,000
Total Capital Expenditure											0	[1]	0	[1]	0	[1]
Total Assets	0	[4]				0	[5]				0	[4]	0	[5]	0	[5]
Total Electric Reportable Segments [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues											796,549,000		803,558,000		783,462,000
Purchased power and gas											173,059,000		139,135,000		154,546,000
Operation and maintenance											235,448,000		234,918,000		222,047,000
Transmission wholesale											88,370,000		88,206,000		79,469,000
Depreciation and amortization											67,410,000		108,023,000		103,562,000
Taxes - other than income taxes											87,233,000		83,412,000		71,618,000
Acquisition-related expenses											0
Rate case disallowances													8,354,000
Operating Income											149,029,000		141,510,000		152,220,000
Other Income and (Deductions), net											15,802,000		18,209,000		20,507,000
Interest Charges, net											46,198,000		39,098,000		41,249,000
Income from Equity Investments											13,893,000		15,272,000		15,273,000
Income (Loss) Before Income Taxes											128,526,000		135,893,000		146,751,000
Income Taxes											44,158,000		55,600,000		62,116,000
Net Income (Loss)											84,368,000		80,293,000		84,635,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											0		0		0
Net Income attributable to UIL Holdings											84,368,000		80,293,000		84,635,000
Total Capital Expenditure											142,179,000	[1]	160,042,000	[1]	178,107,000	[1]
Total Assets	2,876,792,000	[4]				2,950,707,000	[5]				2,876,792,000	[4]	2,950,707,000	[5]	2,935,562,000	[5]
Gas Distribution Reportable Segment [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues											835,394,000		815,023,000		702,887,000
Purchased power and gas											428,471,000		438,189,000		370,234,000
Operation and maintenance											179,553,000		154,418,000		137,707,000
Transmission wholesale											0		0		0
Depreciation and amortization											73,232,000		77,890,000		75,205,000
Taxes - other than income taxes											50,394,000		46,477,000		42,254,000
Acquisition-related expenses											0
Rate case disallowances													0
Operating Income											103,744,000		98,049,000		77,487,000
Other Income and (Deductions), net											745,000		-323,000		4,071,000
Interest Charges, net											27,946,000		28,935,000		28,001,000
Income from Equity Investments											0		0		0
Income (Loss) Before Income Taxes											76,543,000		68,791,000		53,557,000
Income Taxes											28,280,000		23,309,000		21,305,000
Net Income (Loss)											48,263,000		45,482,000		32,252,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											-14,000		52,000		64,000
Net Income attributable to UIL Holdings											48,277,000		45,430,000		32,188,000
Total Capital Expenditure											131,919,000	[1]	97,346,000	[1]	80,837,000	[1]
Total Assets	2,087,284,000	[2]				2,010,246,000	[3]				2,087,284,000	[2]	2,010,246,000	[3]	1,993,560,000	[3]
Goodwill	266,200,000					266,200,000					266,200,000		266,200,000		266,200,000
Other [Member]
Segment Reporting Information [Line Items]
Operating Revenues											0		135,000		152,000
Purchased power and gas											-2,092,000		0		0
Operation and maintenance											-15,441,000		-5,307,000		-3,477,000
Transmission wholesale											0		0		0
Depreciation and amortization											10,915,000		3,943,000		2,581,000
Taxes - other than income taxes											644,000		569,000		165,000
Acquisition-related expenses											7,344,000
Rate case disallowances													0
Operating Income											-1,370,000		930,000		883,000
Other Income and (Deductions), net											-14,322,000		2,747,000		668,000
Interest Charges, net											22,236,000		23,736,000		23,292,000
Income from Equity Investments											0		0		0
Income (Loss) Before Income Taxes											-37,928,000		-20,059,000		-21,741,000
Income Taxes											-14,876,000		-9,601,000		-8,555,000
Net Income (Loss)											-23,052,000		-10,458,000		-13,186,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests											0		0		0
Net Income attributable to UIL Holdings											-23,052,000		-10,458,000		-13,186,000
Total Capital Expenditure											38,055,000	[1]	47,790,000	[1]	29,689,000	[1]
Total Assets	147,859,000					183,267,000					147,859,000		183,267,000		90,042,000
Distribution Segment [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Net plant in service	1,283,600,000					1,181,100,000					1,283,600,000		1,181,100,000		1,114,200,000
Transmission Segment [Member] | Reporting Segments [Member]
Segment Reporting Information [Line Items]
Net plant in service	$659,400,000					$656,000,000					$659,400,000		$656,000,000		$612,000,000
[1]	Capital expenditures are shown on a cash basis. Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.
[2]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2014.
[3]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2013 and 2012
[4]	Information for segmenting total assets between Distribution and Transmission is not available. Total Electric Distribution and Transmission assets are disclosed in the Total Electric Distribution and Transmission column. Net plant in service is segregated by $659.4 million for Distribution and Transmission, respectively. segment and, as of December 31, 2014, was $1,283.6 million and $659.4 million for Distribution and Transmission, respectively.
[5]	Information for segmenting total assets between Distribution and Transmission is not available. Total Electric Distribution and Transmission assets are disclosed in the Total Electric and Distribution and Transmission column. Net plant in service is segregated by segment and, as of December 31, 2013, was $1,181.1 million and $656.0 million for Distribution and Transmission, respectively. As of December 31, 2012, net plant in service was $1,114.2 million and $612.0 million for Distribution and Transmission, respectively.

SUBSEQUENT_EVENT_PROPOSED_MERG1

SUBSEQUENT EVENT - PROPOSED MERGER WITH IBERDROLA USA (Details) (Subsequent Event [Member], USD $)	Feb. 25, 2015
Subsequent Event [Member]
Subsequent Event [Line Items]
Cash consideration per share (in dollars per share)	$10.50
Former UIL Holdings stock holders, percent ownership of Iberdrola USA (in hundredths)	18.50%

Schedule_I_Condensed_Financial1

Schedule I - Condensed Financial Statements of Registrant, Statements of Income (Details) (USD $)	3 Months Ended																12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Expenses
Operation and maintenance																	$399,560	$384,029	$356,277
Depreciation and amortization																	151,557	189,856	181,348
Taxes - other than income taxes																	138,271	130,458	114,037
Acquisition-related expenses																	7,344	0	0
Total Operating Expenses																	1,384,540	1,378,227	1,255,911
Operating Income	72,565		34,152		36,272		104,414		78,362		22,659		43,235		96,233		247,403	240,489	230,590
Other Income and (Deductions), net
Acquisition-related bridge facility fees																	-15,795	0	0
Other income and (deductions)																	18,020	20,633	25,246
Total Other Income and (Deductions), net																	2,225	20,633	25,246
Interest Charges, net																	96,380	91,769	92,542
Income Taxes																	57,562	69,308	74,866
Net Income	32,307		12,504		9,303		55,465		40,419		5,157		17,934		51,807		109,579	115,317	103,701
Net Income attributable to UIL Holdings	32,300		12,498		9,343		55,452		40,406		5,144		17,924		51,791		109,593	115,265	103,637
Average Number of Common Shares Outstanding - Basic (in shares)																	56,834,000	52,415,000	50,831,000
Average Number of Common Shares Outstanding - Diluted (in shares)																	57,136,000	52,711,000	51,108,000
Earnings Per Share of Common Stock - Basic: (in dollars per share)	$0.57	[1]	$0.22	[1]	$0.16	[1]	$0.98	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.02	[1]	$1.93	$2.20	$2.04
Earnings Per Share of Common Stock - Diluted: (in dollars per share)	$0.56	[1]	$0.22	[1]	$0.16	[1]	$0.97	[1]	$0.71	[1]	$0.10	[1]	$0.35	[1]	$1.01	[1]	$1.92	$2.18	$2.02
UIL Holdings Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Operating Revenues																	18,441	6,209	4,193
Operating Expenses
Operation and maintenance																	1,966	844	639
Depreciation and amortization																	10,494	3,842	2,530
Taxes - other than income taxes																	551	562	156
Acquisition-related expenses																	7,344	0	0
Total Operating Expenses																	20,355	5,248	3,325
Operating Income																	-1,914	961	868
Other Income and (Deductions), net
Acquisition-related bridge facility fees																	-15,795	2,552	351
Other income and (deductions)																	1,763	0	0
Total Other Income and (Deductions), net																	-14,032	2,552	351
Interest Charges, net																	22,239	23,735	23,292
Equity in Earnings of Subsidiaries																	132,783	125,871	117,083
Income Before Income Taxes																	94,598	105,649	95,010
Income Taxes																	-14,981	-9,668	-8,691
Net Income																	109,579	115,317	103,701
Net Income Attributable to Noncontrolling Interest																	-14	52	64
Net Income attributable to UIL Holdings																	$109,593	$115,265	$103,637
Average Number of Common Shares Outstanding - Basic (in shares)																	56,834	52,415	50,831
Average Number of Common Shares Outstanding - Diluted (in shares)																	57,136	52,711	51,108
Earnings Per Share of Common Stock - Basic: (in dollars per share)																	$1.93	$2.20	$2.04
Earnings Per Share of Common Stock - Diluted: (in dollars per share)																	$1.92	$2.18	$2.02
[1]	Based on weighted average number of shares outstanding each quarter. Diluted earnings per share reflects the effect of restricted stock, performance shares and for 2013, dilutive stock options. Quarterly per share amounts are not intended to be additive.

Schedule_I_Condensed_Financial2

Schedule I - Condensed Financial Statements of Registrant, Statements of Comprehensive Income (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net Income	$32,307	$12,504	$9,303	$55,465	$40,419	$5,157	$17,934	$51,807	$109,579	$115,317	$103,701
Other Comprehensive Income (Loss), net of income taxes
Changes in unrealized gains (losses) related to pension and other post-retirement benefit plans									-815	1,008	-90
Other									3	-24	16
Total Other Comprehensive Income (Loss), net of income taxes									-812	984	-74
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests									-14	52	64
Comprehensive Income Attributable to UIL Holdings									108,781	116,249	103,563
UIL Holdings Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income									109,579	115,317	103,701
Other Comprehensive Income (Loss), net of income taxes
Changes in unrealized gains (losses) related to pension and other post-retirement benefit plans									-815	1,008	-90
Other									3	-24	16
Total Other Comprehensive Income (Loss), net of income taxes									-812	984	-74
Comprehensive Income									108,767	116,301	103,627
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests									-14	52	64
Comprehensive Income Attributable to UIL Holdings									$108,781	$116,249	$103,563

Schedule_I_Condensed_Financial3

Schedule I - Condensed Financial Statements of Registrant, Balance Sheet (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
In Thousands, unless otherwise specified
Current Assets
Unrestricted cash and temporary cash investments	$115,579		$69,153		$17,857		$30,999
Intercompany receivable	232,887		245,252
Deferred income taxes	0		21,742
Refundable taxes	15,211		8,244
Other	12,815		12,122
Total Current Assets	670,096		888,004
Net Property, Plant and Equipment	3,292,690		3,068,680
Other Assets	20,292		11,640
Total Assets	5,111,935	[1]	5,144,220	[2]	5,019,164	[2]
Current Liabilities
Line of credit borrowings	89,000		0
Accounts payable	217,700		164,416
Dividends payable	24,428		24,392
Total Current Liabilities	495,558		612,823
Deferred income taxes	585,335		540,542
Other Liabilities	46,924		49,047
Capitalization
Long-term debt, net of unamortized discount and premium	1,711,349		1,723,842
Net Common Stock Equity	1,368,202		1,353,815		1,116,553		1,094,361
Total Capitalization	3,079,670		3,077,997
Total Liabilities and Capitalization	5,111,935		5,144,220
UIL Holdings Corporation [Member]
Current Assets
Unrestricted cash and temporary cash investments	3,074		28,915		115		2,664
Intercompany receivable	24,875		22,934
Deferred income taxes	30,653		19,927
Refundable taxes	8,107		13,337
Other	6,170		5,720
Total Current Assets	72,879		90,833
Investments in Subsidiaries	1,769,034		1,669,052
Net Property, Plant and Equipment	123,337		105,078
Deferred income taxes	5,951		0
Other Assets	7,624		6,520
Total Assets	1,978,825		1,871,483
Current Liabilities
Line of credit borrowings	89,000		0
Accounts payable	21,409		15,780
Dividends payable	24,428		24,392
Other	19,956		23,500
Total Current Liabilities	154,793		63,672
Deferred income taxes	0		1,035
Other Liabilities	8,093		5,558
Capitalization
Long-term debt, net of unamortized discount and premium	447,737		447,403
Net Common Stock Equity	1,368,202		1,353,815
Total Capitalization	1,815,939		1,801,218
Total Liabilities and Capitalization	$1,978,825		$1,871,483
[1]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2014.
[2]	Includes $266.2 million of goodwill in the Gas Distribution segment as of December 31, 2013 and 2012

Schedule_I_Condensed_Financial4

Schedule I - Condensed Financial Statements of Registrant, Statements of Cash Flows (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net Cash provided by Operating Activities	$402,182		$325,208		$333,941
Cash Flows from Investing Activities
Plant expenditures	-312,153	[1]	-305,178	[1]	-288,633	[1]
Other	690		360		844
Net Cash provided by (used in) Investing Activities	-335,298		-299,201		-306,259
Cash Flows from Financing Activities
Issuance of common stock	0		206,516		1,943
Line of credit borrowings (repayments), net	89,000		-187,000		-48,000
Payment of common stock dividend	-97,708		-87,602		-87,490
Other	-295		-170		-822
Net Cash provided by (used in) Financing Activities	-20,458		25,289		-40,824
Unrestricted Cash and Temporary Cash Investments:
Net change for the period	46,426		51,296		-13,142
Balance at beginning of period	69,153		17,857		30,999
Balance at end of period	115,579		69,153		17,857
UIL Holdings Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net Cash provided by Operating Activities	104,150		122,285		89,875
Cash Flows from Investing Activities
Plant expenditures	-33,209		-47,790		-29,689
Capital contributions to subsidiaries	-96,000		0		-100,000
Intercompany loan receivable	8,000		-8,000		0
Other	0		0		304
Net Cash provided by (used in) Investing Activities	-121,209		-55,790		-129,385
Cash Flows from Financing Activities
Issuance of common stock	0		206,516		1,943
Line of credit borrowings (repayments), net	89,000		-157,000		122,000
Payment of common stock dividend	-97,708		-87,602		-87,490
Other	-74		391		508
Net Cash provided by (used in) Financing Activities	-8,782		-37,695		36,961
Unrestricted Cash and Temporary Cash Investments:
Net change for the period	-25,841		28,800		-2,549
Balance at beginning of period	28,915		115		2,664
Balance at end of period	$3,074		$28,915		$115
[1]	Capital expenditures are shown on a cash basis. Information for segmenting total capital expenditures between Distribution and Transmission is not available. Total Electric Distribution and Transmission capital expenditures are disclosed in the Total Electric Distribution and Transmission column.

Schedule_I_Condensed_Financial5

Schedule I - Condensed Financial Statements of Registrant, Notes (Details) (UIL Holdings Corporation [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
UIL Holdings Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends received from subsidiaries	$151,200,000	$140,500,000	$73,100,000
Information regarding maturities of long-term debt [Abstract]
2015	0
2016	0
2017	0
2018	0
2019 & thereafter	450,000,000
Due to Related Parties [Abstract]
Accounts payable to Related Parties	$5,200,000	$0

Schedule_II_Valuation_and_Qual1

Schedule II - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reserve for uncollectible accounts (consolidated): [Abstract]
Balance at beginning of period	$12,021		$11,867		$10,939
Acquired balance	0		0		0
Additions charged to costs and expenses	45,659		33,476		36,850
Additions charged to other accounts	0		0		0
Deductions	48,799	[1]	33,322	[1]	35,922	[1]
Balance at end of period	$8,881		$12,021		$11,867
[1]	Accounts written off, net of recoveries.