UIL (UIL) Inactive 10-Q30 Apr 152015 Q1 Quarterly reportFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2015	Apr. 27, 2015
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 Common Stock, Shares Outstanding		56,617,292
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15

CONSOLIDATED_STATEMENT_OF_INCO

CONSOLIDATED STATEMENT OF INCOME (Unaudited) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CONSOLIDATED STATEMENT OF INCOME (Unaudited) [Abstract]
Operating Revenues	$584,053	$571,162
Operation
Purchased power	97,102	53,130
Natural gas purchased	174,520	214,925
Operation and maintenance	101,347	92,877
Transmission wholesale	19,709	20,911
Depreciation and amortization (Note F)	43,284	40,318
Taxes - other than income taxes (Note F)	41,315	39,536
Merger and acquisition-related expenses (Note A)	6,702	5,051
Total Operating Expenses	483,979	466,748
Operating Income	100,074	104,414
Other Income and (Deductions), net
Acquisition-related bridge facility fees (Note A)	0	-6,413
Other income and (deductions) (Note F)	4,368	3,862
Total Other Income and (Deductions), net	4,368	-2,551
Interest Charges, net
Interest on long-term debt	22,225	22,452
Other interest, net	1,232	175
Interest charges, gross	23,457	22,627
Amortization of debt expense and redemption premiums	607	607
Total Interest Charges, net	24,064	23,234
Income from Equity Investments	2,936	3,386
Income Before Income Taxes	83,314	82,015
Income Taxes (Note E)	25,705	26,550
Net Income	57,609	55,465
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	7	13
Net Income attributable to UIL Holdings	$57,602	$55,452
Average Number of Common Shares Outstanding - Basic (in shares)	56,881	56,779
Average Number of Common Shares Outstanding - Diluted (in shares)	57,184	57,043
Earnings Per Share of Common Stock - Basic (Note A) (in dollars per share)	$1.01	$0.98
Earnings Per Share of Common Stock - Diluted (Note A) (in dollars per share)	$1.01	$0.97
Cash Dividends Declared per share of Common Stock (in dollars per share)	$0.43	$0.43

CONSOLIDATED_STATEMENT_OF_COMP

CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net Income	$57,609	$55,465
Other Comprehensive Income (Loss), net of income taxes
Changes in unrealized gains (losses) related to pension and other post-retirement benefit plans	273	61
Other	7	12
Total Other Comprehensive Income (Loss), net of income taxes	280	73
Comprehensive Income	57,889	55,538
Less:
Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	7	13
Comprehensive Income Attributable to UIL Holdings	$57,882	$55,525

CONSOLIDATED_BALANCE_SHEET_Una

CONSOLIDATED BALANCE SHEET (Unaudited) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Current Assets
Unrestricted cash and temporary cash investments	$80,120		$115,579
Restricted cash	910		1,051
Accounts receivable less allowance of $9,917 and $8,881, respectively	297,712		232,887
Unbilled revenues	91,112		95,816
Current regulatory assets (Note A)	87,071		92,764
Natural gas in storage, at average cost	31,437		86,428
Refundable taxes	17,612		15,211
Current portion of derivative assets (Note A)	6,847		6,849
Prepayments	22,510		10,696
Other	12,383		12,815
Total Current Assets	647,714		670,096
Other investments
Equity investment in GenConn (Note A)	111,709		114,195
Other	28,418		25,777
Total Other investments	140,127		139,972
Net Property, Plant and Equipment (Note A)	3,316,841		3,292,690
Regulatory Assets (Note A)	700,321		687,198
Deferred Charges and Other Assets
Unamortized debt issuance expenses	13,148		13,571
Other long-term receivable	1,489		1,490
Derivative assets (Note A)	19,583		20,421
Goodwill	266,205		266,205
Other	22,920		20,292
Total Deferred Charges and Other Assets	323,345		321,979
Total Assets	5,128,348	[1]	5,111,935	[1]
Current Liabilities
Line of credit borrowings	70,000		89,000
Current portion of long-term debt	6,527		6,526
Accounts payable	167,405		217,700
Dividends payable	24,459		24,428
Accrued liabilities	60,237		71,182
Current regulatory liabilities (Note A)	23,557		17,026
Taxes accrued	26,248		20,184
Interest accrued	25,558		22,437
Deferred income taxes	17,466		3,767
Current portion of derivative liabilities (Note A)	23,193		23,308
Total Current Liabilities	444,650		495,558
Deferred Income Taxes	604,160		585,335
Regulatory Liabilities (Note A)	491,155		491,896
Other Noncurrent Liabilities
Pension accrued	264,790		265,009
Other post-retirement benefits accrued	85,498		85,777
Derivative liabilities (Note A)	76,008		61,766
Other	48,278		46,924
Total Other Noncurrent Liabilities	474,574		459,476
Commitments and Contingencies (Note J)
Capitalization (Note B)
Long-term debt, net of unamortized discount and premium	1,710,168		1,711,349
Preferred Stock, not subject to mandatory redemption	119		119
Common Stock Equity
Common stock	1,153,251		1,149,985
Paid-in capital	20,218		21,587
Retained earnings	230,050		196,907
Accumulated other comprehensive income (loss)	3		-277
Net Common Stock Equity	1,403,522		1,368,202
Total Capitalization	3,113,809		3,079,670
Total Liabilities and Capitalization	$5,128,348		$5,111,935

[1]	I Includes $266.2 million of goodwill in the Gas Distribution segment as of March 31, 2015 and December 31, 2014.

CONSOLIDATED_BALANCE_SHEET_Una1

CONSOLIDATED BALANCE SHEET (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current Assets
Allowance for doubtful accounts receivable	$9,917	$8,881

CONSOLIDATED_STATEMENT_OF_CASH

CONSOLIDATED STATEMENT OF CASH FLOWS (Unaudited) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Cash Flows From Operating Activities
Net income	$57,609		$55,465
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	43,891		40,925
Deferred income taxes	27,556		22,854
Allowance for funds used during construction (AFUDC) - equity	-2,157		-2,550
Stock-based compensation expense (Note A)	3,673		2,471
Pension expense	9,258		7,835
Undistributed (earnings) losses in equity investments	-2,935		-3,388
Other regulatory activity, net	3,110		35,691
Other non-cash items, net	-1,365		2,875
Changes in:
Accounts receivable, net	-65,821		-60,398
Unbilled revenues	4,704		7,576
Natural gas in storage	54,991		47,086
Cash distributions from GenConn	2,839		3,271
Prepayments	-11,814		-6,282
Accounts payable	-31,028		9,478
Interest accrued	3,121		3,944
Taxes accrued/refundable, net	3,663		3,278
Accrued liabilities	-12,765		-12,768
Accrued pension	-8,049		-10,413
Accrued other post-employment benefits	-1,707		5,973
Other assets	-927		418
Other liabilities	1,506		3,047
Total Adjustments	19,744		100,923
Net Cash provided by Operating Activities	77,353		156,388
Cash Flows from Investing Activities
Plant expenditures including AFUDC debt	-70,648	[1]	-64,692	[1]
Cash distributions from GenConn	2,581		2,134
Changes in restricted cash	141		-133
Deposits in New England East West Solution (NEEWS) (Note C)	-1,451		-1,044
Net Cash provided by (used in) Investing Activities	-69,377		-63,735
Cash Flows from Financing Activities
Line of credit borrowings (repayments), net	-19,000		0
Payment of common stock dividend	-24,428		-24,421
Other	-7		-13
Net Cash provided by (used in) Financing Activities	-43,435		-24,434
Unrestricted Cash and Temporary Cash Investments:
Net change for the period	-35,459		68,219
Balance at beginning of period	115,579		69,153
Balance at end of period	80,120		137,372
Non-cash investing activity:
Plant expenditures included in ending accounts payable	$16,834		$11,285

[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.

BUSINESS_ORGANIZATION_AND_STAT

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES	3 Months Ended
BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES	Mar. 31, 2015
BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES [Abstract]
BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES	(A)	BUSINESS ORGANIZATION AND 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).

	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 year‑end balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (GAAP). Certain information and footnote disclosures, which are normally included in financial statements prepared in accordance with GAAP, have been condensed or omitted in accordance with Securities and Exchange Commission (SEC) rules and regulations. We believe that the disclosures made are adequate to make the information presented not misleading. The information presented in the Consolidated Financial Statements reflects all adjustments which, in our opinion, are necessary for a fair statement of the financial position and results of operations for the interim periods described herein. All such adjustments are of a normal and recurring nature. The results for the three-month period March 31, 2015 are not necessarily indicative of the results for the entire fiscal year ending December 31, 2015.

	Proposed Merger with Iberdrola USA

	On February 25, 2015, we announced that UIL Holdings had entered into a definitive merger agreement (the Agreement) with Iberdrola USA and its wholly-owned subsidiary, Green Merger Sub, Inc. (merger sub) under which Iberdrola USA will acquire UIL Holdings through a merger of UIL Holdings with and into merger sub and merger sub being the surviving corporation (the merger). Merger sub will change its name to UIL Holdings Corporation and remain a direct or indirect wholly-owned subsidiary of Iberdrola USA. Iberdrola USA will then become 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 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. The merger is subject to certain closing conditions, including the approval of the shareowners of UIL Holdings and approvals from the Connecticut Public Utilities Regulatory Authority (PURA), the Massachusetts Department of Public Utilities (DPU), the Federal Energy Regulatory Commission (FERC), the Committee on Foreign Investments in the United States and the expiration or early termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the HSR Act), which period was terminated on April 7, 2015. For further discussion of the regulatory approval process, see Note (C) “Regulatory Proceedings.”

	We currently expect that the merger will close promptly after satisfaction or waiver of all closing conditions, including receipt of shareowner approval and all regulatory approvals, and not later than December 31, 2015. There are no assurances that the merger 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 the proposed merger.

	For the three months ended March 31, 2015, UIL Holdings incurred pre-tax merger-related expenses of approximately $6.7 million which represented legal, investment banking, and other merger-related costs.

	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 with the SEC in the second quarter of 2015 in connection with the proposed merger.

	Philadelphia Gas Works

	In March 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, was to acquire the operating assets and assume certain liabilities of Philadelphia Gas Works. The proposed 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. In light of the City Council’s October 2014 announcement to not endorse the proposed acquisition, we exercised our contractual right to terminate the Asset Purchase Agreement in December 2014.

	For the three months ended March 31, 2014, UIL Holdings incurred pre-tax acquisition-related expenses of approximately $11.5 million, $5.1 million of which represented legal, investment banking, and due diligence costs that are included in operating expenses and $6.4 million of which is a fee associated with a Bridge Term Loan Agreement that is included in other income and (deductions) in the Consolidated Statement of Income.

	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, 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 March 31, 2015, UI has recorded a gross derivative asset of $26.4 million ($5.4 million of which is related to UI’s portion of the CfD signed by CL&P), a regulatory asset of $78.0 million, a gross derivative liability of $99.2 million ($72.9 million of which is related to UI’s portion of the CfD signed by CL&P) and a regulatory liability of $5.3 million. See Note (K) “Fair Value of Financial Instruments” for additional CfD information.

	The gross derivative assets and liabilities as of March 31, 2015 and December 31, 2014 were as follows:

			March 31,				December 31,
			2015				2014
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,847			$	6,849
	Deferred Charges and Other Assets		$	19,583			$	20,421

	Gross derivative liabilties:
	Current Liabilities		$	23,193			$	23,308
	Noncurrent Liabilities		$	76,008			$	61,766

	The unrealized gains and losses from fair value adjustments to these derivatives, which are recorded in regulatory assets or regulatory liabilities, for three-month periods ended March 31, 2015 and 2014 were as follows:

			Three Months Ended
			March 31,
			2015				2014
			(In Thousands)

	Regulatory Assets - Derivative liabilities		$	13,769			$	(71,619	)

	Regulatory Liabilities - Derivative assets		$	1,197			$	(2,942	)

	The fluctuations in the balances of the derivatives as well as the related unrealized gains in the three-month period ended March 31, 2015 compared to the three-month period ended March 31, 2014 are primarily due to fluctuations in forward prices for capacity and reserves.

	Earnings per Share

The following table presents a reconciliation of the basic and diluted earnings per share calculations for the three‑month periods ended March 31, 2015 and 2014:

		2015				2014
		(In Thousands, except per share amounts)

Numerator:
Net income attributable to UIL Holdings		$	57,602			$	55,452
Less: Net income allocated to unvested units			33				30
Net income attributable to common shareholders		$	57,569			$	55,422

Denominator:
Basic average number of shares outstanding			56,881				56,779
Effect of dilutive securities (1)			303				264
Diluted average number of shares outstanding			57,184				57,043

Earnings per share:
Basic		$	1.01			$	0.98
Diluted		$	1.01			$	0.97

	-1	Includes unvested restricted stock and performance shares.

Equity Investments

UI is party to a 50-50 joint venture with the 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 $111.7 million and $114.2 million as of March 31, 2015 and December 31, 2014, respectively. As of March 31, 2015, 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 $2.9 million and $3.4 million for the three-month periods ending March 31, 2015 and 2014, 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 $5.4 million in each of the three-month periods ending March 31, 2015 and 2014.

Regulatory Accounting

Unless otherwise stated below, all of our regulatory assets earn a return. Our regulatory assets and liabilities as of March 31, 2015 and December 31, 2014 included the following:

		Remaining		March 31,				December 31,
		Period		2015				2014
				(In Thousands)
Regulatory Assets:
Unamortized redemption costs		7 to 19 years			10,298				10,499
Pension and other post-retirement benefit plans		(a)			403,358				402,700
Environmental remediation costs		7 years			14,127				13,197
Hardship programs		(b)			19,661				24,744
Debt premium		2 to 23 years			26,229				27,498
Income taxes due principally to book-tax differences		(c)			166,039				164,466
Unfunded future income taxes		(d)			15,555				14,859
Contracts for differences		(e)			78,045				64,276
Deferred transmission expense		(f)			20,981				17,387
Other		(g)			33,099				40,336
Total regulatory assets					787,392				779,962
Less current portion of regulatory assets					87,071				92,764
Regulatory Assets, Net				$	700,321			$	687,198

Regulatory Liabilities:
Accumulated deferred investment tax credits		29 years		$	4,282			$	4,319
Excess generation service charge		(h)			16,825				28,692
Middletown/Norwalk local transmission network service collections		35 years			20,685				20,828
Pension and other post-retirement benefit plans		(a)			8,722				9,536
Asset retirement obligation		(i)			7,247				7,248
Low income programs		(j)			22,253				19,065
Asset removal costs		(i)			340,236				336,028
Unfunded future income taxes		(d)			26,848				26,318
Contracts for differences		(e)			5,274				6,472
Deferred purchased gas		(k)			6,511				4,736
Non-firm margin sharing credits		9 years			13,505				8,933
Other		(g)			42,324				36,747
Total regulatory liabilities					514,712				508,922
Less current portion of regulatory liabilities					23,557				17,026
Regulatory Liabilities, Net				$	491,155			$	491,896

(a)	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.
(b)	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
(c)	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities.
(d)	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
(e)	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.
(f)	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
(g)	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 certain amounts that are not currently earning a return; liability amount includes decoupling of $9.6 million.
(h)	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.
(i)	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
(j)	Various hardship and payment plan programs approved for recovery.
(k)	Deferred purchased gas costs balances at the end of the rate year are normally recorded/returned in the next year.

Stock-Based Compensation

Pursuant to the UIL Holdings 2008 Stock and Incentive Compensation Plan (2008 Stock Plan), 94,410 restricted stock units were granted to certain members of management in March 2015; the average of the high and low market prices on the grant date, which approximate fair value, was $49.72 per share.

Also in March 2015, we granted a total of 1,584 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 $49.72 per share. Such shares vest in equal annual installments over a five-year period.

Total stock-based compensation expense for the three-month periods ended March 31, 2015 and 2014 $3.7 million and $2.5 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 Pronouncements

In April 2015, the FASB issued Accounting Standards Update (ASU) 2015-03, “Interest—Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs” which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. ASU 2015-03 is effective for interim and annual reporting periods beginning after December 15, 2015 and is to be applied retrospectively. The effect that adopting this new accounting guidance will have on our consolidated financial statements will be reductions in both Deferred Charges and Other Assets and Long-term debt on the consolidated balance sheet. This effect is not expected to be material to UIL Holdings’ consolidated financial statements.

In April 2015, the FASB issued a proposal to defer by one year the effective date of ASU 2014-09 which 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. A final decision is expected in the second quarter of 2015. We are currently evaluating the effect that adopting this new accounting guidance will have on our consolidated financial statements.

CAPITALIZATION

CAPITALIZATION	3 Months Ended
	Mar. 31, 2015
CAPITALIZATION [Abstract]
CAPITALIZATION	(B)	CAPITALIZATION

	Common Stock

	UIL Holdings had 56,617,292 shares of its common stock, no par value, outstanding at March 31, 2015.

REGULATORY_PROCEEDINGS

REGULATORY PROCEEDINGS	3 Months Ended
	Mar. 31, 2015
REGULATORY PROCEEDINGS [Abstract]
REGULATORY PROCEEDINGS	(C)	REGULATORY PROCEEDINGS

	Proposed Merger with Iberdrola USA

	As discussed in Note A “Organization and Statement of Accounting Policies”, on February 25, 2015 we announced that UIL Holdings had entered into a the Agreement with Iberdrola USA and merger sub under which Iberdrola USA will acquire UIL Holdings through a merger of UIL Holdings with and into merger sub and merger sub being the surviving corporation. The merger is subject to certain closing conditions, including the approval of the shareowners of UIL Holdings and approvals from PURA, the DPU, FERC, and the Committee on Foreign Investments in the United States (CFIUS) and the expiration or early termination of the applicable waiting period under the HSR Act.

	On March 25, 2015, UIL Holdings and Iberdrola USA filed joint applications with PURA, the DPU and the FERC seeking the required approvals. In addition, UIL Holdings and Iberdrola USA each made its respective HSR Act filings on March 25, 2015, and the waiting period was terminated on April 7, 2015.

	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.

	UI’s allowed distribution return on equity established by PURA is 9.15%. UI is required to return 50% of any distribution earnings over the allowed twelve month level to customers by means of an earnings sharing mechanism.

	Power Supply Arrangements

	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 March 31 2015, UI would have had to post an aggregate of approximately $19.7 million in collateral. UI would have been and remains able to provide that collateral.

	New Renewable Source Generation

	Pursuant to Connecticut law (PA 13-303), on September 19, 2013, at the direction of the Connecticut Department of Energy and Environmental Protection, (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 for such contracts, 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. On January 2, 2015 Allco filed an appeal with the United States Court of Appeals for the Second Circuit.

	Transmission

	PURA decisions do not affect the revenue requirements determination for UI’s transmission business, including the applicable return on equity (ROE), which is within the jurisdiction of the FERC. For 2015, UI is estimating an overall allowed weighted-average ROE for its transmission business in the range of 11.3% to 11.4%. 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 Connecticut Office of Consumer Council (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 of 11.14% used in calculating formula rates for transmission service under the ISO-NE Open Access Transmission Tariff by the New England transmission owners 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 FERC Administrative Law Judge finding that the existing base ROE was unjust and unreasonable and our assessment of the ultimate outcome of the proceeding, we recorded a reserve for the refund period of $2.6 million pre-tax during the third quarter of 2013.

	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%. On October 16, 2014 the FERC issued an order (October Order) confirming 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.

	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. The FERC consolidated 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 December 31, 2015, with an expected decision by the FERC by October 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 under the Second and Third Complaint. We will continue to record additional reserves through the third refund period.

	On March 3, 2015, the FERC issued an Order on Rehearing in the First Complaint (the March Order) denying all rehearing requests from the complainants and the New England transmission owners. UI recorded additional pre-tax reserves of $3.4 million in the first quarter of 2015 relating to the Third Complaint and the March Order. As of March 31, 2015, cumulative pre-tax reserves relating to refunds and potential refunds to customers under all three claims were approximately $11.6 million, of which $2.9 million has already been refunded to customers.

	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 February 2015, ISO-NE issued its final GHCC transmission solutions report and, in March 2015, approved the proposed plan applications. UI and Eversource are evaluating the approved projects 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 March 31, 2015, UI had made aggregate deposits of $45 million under the Agreement since its inception, with assets associated with the GSRP valued at approximately $24.6 million having been transferred to UI. UI earned pre-tax income on deposits, net of transferred assets, of approximately $0.6 million and $0.3 million in the three‑month periods ended March 31, 2015 and 2014, respectively.

	Other Proceedings

	On November 12, 2014, PURA issued a decision in a docket addressing UI’s semi-annual Generation Services Charge (GSC), bypassable federally mandated congestion charge and the non-bypassable federally mandated congestion charge (NBFMCC) reconciliations. PURA’s decision allowed 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. This resulted in UI recording a pre-tax write-off of approximately $3.8 million during the fourth quarter of 2014, which amount 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 Competitive Transition Assessment (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 Atomic Power Company litigation against the U.S. Department of Energy (DOE), against UI’s 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.

	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. Based on existing tracking mechanisms in place for gas and other costs, discussions with the DPU, and precedence set by other utility companies, Berkshire believes that regulatory assets are recoverable and regulatory liabilities are fairly stated.

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 upon which PURA subsequently issued comments. 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 engaged in settlement discussions regarding the appeal. Settlement discussions have now terminated, and CNG has agreed to file a motion with PURA to extend the due date for CNG's response to PURA's comments on the private letter ruling request until June 24, 2015.

Other Proceedings

As discussed above, CNG’s 2013 rate proceeding provides for a decoupling mechanism as well as a rate making mechanism related to its cast iron and bare steel replacement program. Additionally, a comprehensive joint 10-year natural gas expansion plan (“Expansion Plan”) filed jointly by CNG, SCG and Yankee Gas Services Company in response to the gas expansion goals proposed in the Connecticut Governor’s Comprehensive Energy Strategy and Public Act 13-298 and approved by PURA includes a new business reconciliation mechanism that reconciles the actual new business revenue requirements each year with the revenues received from the new business customers. The initial filings for these mechanisms are discussed below.

On March 2, 2015, CNG filed its initial decoupling adjustment which includes a $10.8 million credit to customers, which will be credited on customers’ bills during the period of April 1, 2015 through March 31, 2016.

On March 20, 2015, SCG and CNG filed their initial System Expansion (SE) Rate reconciliation for 2014. The proposed SE rate was approved by PURA for implementation as of April 1, 2015, pending final PURA approval following a contested hearing.

On April 1, 2015, CNG filed its initial Distribution Integrity Management Program (DIMP) reconciliation filing, which reconciles actual revenue requirements related to CNG’s cast iron and bare steel replacement program. The proposed DIMP rate was approved by PURA for implementation as of May 1, 2015.

SHORTTERM_CREDIT_ARRANGEMENTS

SHORT-TERM CREDIT ARRANGEMENTS	3 Months Ended
	Mar. 31, 2015
SHORT-TERM CREDIT ARRANGEMENTS [Abstract]
SHORT-TERM CREDIT ARRANGEMENTS	(D)	SHORT-TERM CREDIT ARRANGEMENTS

	As of March 31, 2015, there was $70 million in borrowings outstanding under the existing revolving credit agreement among UIL Holdings, certain of its subsidiaries and a group of banks that expires on November 30, 2016 (the UIL Holdings Credit Facility). 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 March 31, 2015 totaled $325.6 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.

INCOME_TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2015
INCOME TAXES [Abstract]
INCOME TAXES	(E)	INCOME TAXES

	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 in the treatment of certain transactions for book and tax purposes and by differences between the timing of deferred tax temporary difference activity and deferred tax recovery. In accordance with ASC 740, we use an estimated annual effective tax rate approach to calculate interim period income tax expense for ordinary income. We also record separate income tax effects for significant unusual or infrequent items. The annualized effective income tax rates for the three-month periods ended March 31, 2015 and 2014 were 31.6% and 33.4%, respectively. The decrease in the effective rate was due primarily to changes in property related flow through impacts.

SUPPLEMENTARY_INFORMATION

SUPPLEMENTARY INFORMATION	3 Months Ended
SUPPLEMENTARY INFORMATION	Mar. 31, 2015
SUPPLEMENTARY INFORMATION [Abstract]
SUPPLEMENTARY INFORMATION	(F)	SUPPLEMENTARY INFORMATION

			Three Months Ended
			March 31,
			2015		2014
			(In Thousands)
	Depreciation and Amortization
	Property, plant, and equipment depreciation		$	34,741	$	31,988
	Amortization of regulatory assets			8,543		8,330
	Total Depreciation and Amortization		$	43,284	$	40,318

	Taxes - Other than Income Taxes
	Operating:
	Connecticut gross earnings		$	22,966	$	22,714
	Local real estate and personal property			12,990		11,964
	Payroll taxes			4,914		3,857
	Other			445		1,001
	Total Taxes - Other than Income Taxes		$	41,315	$	39,536

	Other Income and (Deductions), net
	Interest income		$	709	$	542
	Allowance for funds used during construction - equity			2,157		2,550
	Allowance for funds used during construction - debt			1,046		1,410
	Weather insurance			-		(1,906	)
	Other			456		1,266
	Total Other Income and (Deductions), net		$	4,368	$	3,862

PENSION_AND_OTHER_BENEFITS

PENSION AND OTHER BENEFITS	3 Months Ended
PENSION AND OTHER BENEFITS	Mar. 31, 2015
PENSION AND OTHER BENEFITS [Abstract]
PENSION AND OTHER BENEFITS	(G)	PENSION AND OTHER BENEFITS

	In April 2015, we made pension contributions of $5 million. Additional contributions during the remainder of 2015 are expected to aggregate $10 million.

	The following tables represent the components of net periodic benefit cost for pension and other postretirement benefits as well as the actuarial weighted-average assumptions used in calculating net periodic benefit cost for the three-month periods ended March 31, 2015 and 2014:

			Three Months Ended March 31,
			Pension Benefits						Other Postretirement Benefits
			2015			2014			2015			2014
			(In Thousands)
	Components of net periodic benefit cost:
	Service cost		$	3,605		$	2,896		$	393		$	404
	Interest cost			10,505			11,019			1,327			1,487
	Expected return on plan assets			(14,120	)		(13,560	)		(690	)		(700	)
	Amortization of:
	Prior service costs			48			73			75			71
	Actuarial loss			4,845			3,097			176			(172	)
	Net periodic benefit cost		$	4,883		$	3,525		$	1,281		$	1,090

	Discount rate			4.20%-4.30	%		4.90%-5.20	%		4.20%-4.30	%		4.85%-5.20	%
	Average wage increase			3.50%-3.80	%		3.50%-3.80	%		N/	A		N/	A
	Return on plan assets			7.75%-8.00	%		7.75%-8.00	%		5.56%-8.00	%		5.56%-8.00	%
	Composite health care trend rate (current year)			N/	A		N/	A		7	%		7	%
	Composite health care trend rate (2019 forward)			N/	A		N/	A		5	%		5	%

	N/A – not applicable

RELATED_PARTY_TRANSACTIONS

RELATED PARTY TRANSACTIONS	3 Months Ended
	Mar. 31, 2015
RELATED PARTY TRANSACTIONS [Abstract]
RELATED PARTY TRANSACTIONS	(H)	RELATED PARTY TRANSACTIONS

	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 each of the three‑month periods ended March 31, 2015 and 2014 totaled $0.4 million.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015.

	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.

	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 January 2012 Evergreen Power, LLC (Evergreen Power) and Asnat Realty LLC (Asnat), subsequent owners of a former generation site in New Haven (English Station) that UI sold in 2000, 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 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 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, 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 performed an environmental analysis on transmission-related property adjacent to the New Haven Harbor Generating Station 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 and are contaminated as a result of MGP-related activities. Under 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 March 31, 2015 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 March 31, 2015, 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 March 31, 2015. 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 which was sold to the General Electric Company (GE) in the 1970s. UI 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 March 31, 2015, 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 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 a lawsuit in Connecticut state court on September 22, 2009. 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. On October 22, 2013, the general contractor filed an appeal of the Court’s ruling, which remains pending. 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, which dismissal was affirmed by the Connecticut Appellate Court in March 2015.

FAIR_VALUE_MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
FAIR VALUE MEASUREMENTS	Mar. 31, 2015
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 March 31, 2015 and December 31, 2014.

			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-Mar-15		(In Thousands)
	Assets:
	Derivative assets		$	-		$	-			$	26,430		$	26,430
	Noncurrent investments			12,698			-				-			12,698
	Deferred Compensation Plan			3,667			-				-			3,667
	Supplemental retirement benefit trust life insurance policies			-			8,678				-			8,678
			$	16,365		$	8,678			$	26,430		$	51,473

	Liabilities:
	Derivative liabilities		$	-		$	-			$	99,201		$	99,201
	Long-term debt			-			1,985,013				-			1,985,013
			$	-		$	1,985,013			$	99,201		$	2,084,214

	Net fair value assets/(liabilities), March 31, 2015		$	16,365		$	(1,976,335	)		$	(72,771	)	$	(2,032,741	)

	31-Dec-14
	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 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 March 31, 2015 or December 31, 2014 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
			Unobservable Input		31-Mar-15				31-Dec-14

	Contracts for differences		Risk of non-performance			0.00% - 0.64	%			0.00% - 0.66	%
			Discount rate			1.37% - 2.03	%			1.65% - 2.25	%
			Forward pricing ($ per MW)		$	3.15 - $11.19			$	3.15 - $14.59

	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 fair value of the noncurrent investments is determined using quoted market prices in active markets for identical assets. The investments primarily consist of money market funds.

	Under the UIL Deferred Compensation Plan (DCP), directors, named executive officers and certain other executives may elect to defer certain elements of compensation. Participants in the DCP are permitted to direct investments of their elective deferral accounts into “deemed” investments consisting of mutual funds and UIL Holdings common stock equivalents, with the exception of long-term incentive plan deferrals which are required to be invested in UIL Holdings common stock equivalents. These investments, which are actively traded in sufficient frequency and volume to provide pricing information on an ongoing basis, are marked-to-market based upon such pricing information.

	The determination of the fair value of the supplemental retirement benefit trust life insurance policies was based on quoted prices as of March 31, 2015 and December 31, 2014 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 three-month period ended March 31, 2015.

			Three Months Ended
			31-Mar-15
		(In Thousands)

Net derivative assets/(liabilities), December 31, 2014		$	(57,804	)
Unrealized gains and (losses), net			(14,967	)
Net derivative assets/(liabilities), March 31, 2015		$	(72,771	)


Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of March 31, 2015		$	(14,967	)

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 three-month period ended March 31, 2015. The amounts offset the net CfDs liabilities included in the derivative liabilities detailed above.


		Three Months Ended
		31-Mar-15
		(In Thousands)

Net regulatory assets/(liabilities), December 31, 2014		$	57,804
Unrealized (gains) and losses, net			14,967
Net regulatory assets/(liabilities), March 31, 2015		$	72,771

SEGMENT_INFORMATION

SEGMENT INFORMATION	3 Months Ended
SEGMENT INFORMATION	Mar. 31, 2015
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)
			Three months ended March 31, 2015
			Electric Distribution and Transmission
			Distribution			Transmission			Total			Gas Distribution				Other				Total
	Operating Revenues		$	191,888		$	58,082		$	249,970		$	334,083			$	-			$	584,053
	Purchased power and gas			97,102			-			97,102			175,737				(1,217	)			271,622
	Operation and maintenance			47,304			13,488			60,792			45,847				(5,292	)			101,347
	Transmission wholesale			-			19,709			19,709			-				-				19,709
	Depreciation and amortization			14,133			4,196			18,329			21,777				3,178				43,284
	Taxes - other than income taxes			15,042			8,381			23,423			17,562				330				41,315
	Merger and acquisition-related expenses			-			-			-			-				6,702				6,702
	Operating Income			18,307			12,308			30,615			73,160				(3,701	)			100,074

	Other Income and (Deductions), net			1,941			1,485			3,426			459				483				4,368

	Interest Charges, net			8,039			3,471			11,510			6,707				5,847				24,064

	Income from Equity Investments			2,936			-			2,936			-				-				2,936

	Income (Loss) Before Income Taxes			15,145			10,322			25,467			66,912				(9,065	)			83,314

	Income Taxes			3,853			3,861			7,714			25,664				(7,673	)			25,705
	Net Income (Loss)			11,292			6,461			17,753			41,248				(1,392	)			57,609
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-			-			-			7				-				7
	Net Income (Loss) attributable to UIL Holdings		$	11,292		$	6,461		$	17,753		$	41,241			$	(1,392	)		$	57,602

	Total Capital Expenditures (1)		$	-		$	-		$	38,082		$	23,204			$	9,362			$	70,648

	-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.


	(In Thousands)
			Three months ended March 31, 2014
			Electric Distribution and Transmission
			Distribution			Transmission			Total			Gas Distribution				Other				Total
	Operating Revenues		$	145,189		$	58,788		$	203,977		$	367,185			$	-			$	571,162
	Purchased power and gas			53,130			-			53,130			214,925				-				268,055
	Operation and maintenance			45,817			10,581			56,398			39,656				(3,177	)			92,877
	Transmission wholesale			-			20,911			20,911			-				-				20,911
	Depreciation and amortization			12,063			4,225			16,288			21,748				2,282				40,318
	Taxes - other than income taxes			12,861			8,352			21,213			17,640				683				39,536
	Merger and acquisition-related expenses			-			-			-			-				5,051				5,051
	Operating Income			21,318			14,719			36,037			73,216				(4,839	)			104,414

	Other Income and (Deductions), net			3,186			983			4,169			(981	)			(5,739	)			(2,551	)

	Interest Charges, net			7,832			3,204			11,036			6,763				5,435				23,234

	Income from Equity Investments			3,386			-			3,386			-				-				3,386

	Income (Loss) Before Income Taxes			20,058			12,498			32,556			65,472				(16,013	)			82,015

	Income Taxes			6,102			3,852			9,954			26,417				(9,821	)			26,550
	Net Income (Loss)			13,956			8,646			22,602			39,055				(6,192	)			55,465
	Less:
	Preferred Stock Dividends of
	Subsidiary, Noncontrolling Interests			-			-			-			13				-				13
	Net Income (Loss) attributable to UIL Holdings		$	13,956		$	8,646		$	22,602		$	39,042			$	(6,192	)		$	55,452

Total Capital Expenditures (1)		$	-		$	-		$	33,787		$	19,859			$	11,046			$	64,692

		Electric Distribution and Transmission (2)
		Distribution			Transmission			Total			Gas Distribution (3)				Other				Total (3)
Total Assets at March 31, 2015		$	-		$	-		$	2,859,820		$	2,095,806			$	172,722			$	5,128,348

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 March 31, 2015, was $1,290.4 million and $665.8 million for Distribution and Transmission, respectively. Net plant in service 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 March 31, 2015 and December 31, 2014.

BUSINESS_ORGANIZATION_AND_STAT1

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2015
BUSINESS ORGANIZATION AND 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 year‑end balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (GAAP). Certain information and footnote disclosures, which are normally included in financial statements prepared in accordance with GAAP, have been condensed or omitted in accordance with Securities and Exchange Commission (SEC) rules and regulations. We believe that the disclosures made are adequate to make the information presented not misleading. The information presented in the Consolidated Financial Statements reflects all adjustments which, in our opinion, are necessary for a fair statement of the financial position and results of operations for the interim periods described herein. All such adjustments are of a normal and recurring nature. The results for the three-month period March 31, 2015 are not necessarily indicative of the results for the entire fiscal year ending December 31, 2015.
Business Combinations	Proposed Merger with Iberdrola USA

	On February 25, 2015, we announced that UIL Holdings had entered into a definitive merger agreement (the Agreement) with Iberdrola USA and its wholly-owned subsidiary, Green Merger Sub, Inc. (merger sub) under which Iberdrola USA will acquire UIL Holdings through a merger of UIL Holdings with and into merger sub and merger sub being the surviving corporation (the merger). Merger sub will change its name to UIL Holdings Corporation and remain a direct or indirect wholly-owned subsidiary of Iberdrola USA. Iberdrola USA will then become 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 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. The merger is subject to certain closing conditions, including the approval of the shareowners of UIL Holdings and approvals from the Connecticut Public Utilities Regulatory Authority (PURA), the Massachusetts Department of Public Utilities (DPU), the Federal Energy Regulatory Commission (FERC), the Committee on Foreign Investments in the United States and the expiration or early termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the HSR Act), which period was terminated on April 7, 2015. For further discussion of the regulatory approval process, see Note (C) “Regulatory Proceedings.”

	We currently expect that the merger will close promptly after satisfaction or waiver of all closing conditions, including receipt of shareowner approval and all regulatory approvals, and not later than December 31, 2015. There are no assurances that the merger 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 the proposed merger.

	For the three months ended March 31, 2015, UIL Holdings incurred pre-tax merger-related expenses of approximately $6.7 million which represented legal, investment banking, and other merger-related costs.

	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 with the SEC in the second quarter of 2015 in connection with the proposed merger.

	Philadelphia Gas Works

	In March 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, was to acquire the operating assets and assume certain liabilities of Philadelphia Gas Works. The proposed 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. In light of the City Council’s October 2014 announcement to not endorse the proposed acquisition, we exercised our contractual right to terminate the Asset Purchase Agreement in December 2014.

	For the three months ended March 31, 2014, UIL Holdings incurred pre-tax acquisition-related expenses of approximately $11.5 million, $5.1 million of which represented legal, investment banking, and due diligence costs that are included in operating expenses and $6.4 million of which is a fee associated with a Bridge Term Loan Agreement that is included in other income and (deductions) in the Consolidated Statement of Income.
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, 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 March 31, 2015, UI has recorded a gross derivative asset of $26.4 million ($5.4 million of which is related to UI’s portion of the CfD signed by CL&P), a regulatory asset of $78.0 million, a gross derivative liability of $99.2 million ($72.9 million of which is related to UI’s portion of the CfD signed by CL&P) and a regulatory liability of $5.3 million. See Note (K) “Fair Value of Financial Instruments” for additional CfD information.

	The gross derivative assets and liabilities as of March 31, 2015 and December 31, 2014 were as follows:

			March 31,				December 31,
			2015				2014
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,847			$	6,849
	Deferred Charges and Other Assets		$	19,583			$	20,421

	Gross derivative liabilties:
	Current Liabilities		$	23,193			$	23,308
	Noncurrent Liabilities		$	76,008			$	61,766

	The unrealized gains and losses from fair value adjustments to these derivatives, which are recorded in regulatory assets or regulatory liabilities, for three-month periods ended March 31, 2015 and 2014 were as follows:

			Three Months Ended
			March 31,
			2015				2014
			(In Thousands)

	Regulatory Assets - Derivative liabilities		$	13,769			$	(71,619	)

	Regulatory Liabilities - Derivative assets		$	1,197			$	(2,942	)

	The fluctuations in the balances of the derivatives as well as the related unrealized gains in the three-month period ended March 31, 2015 compared to the three-month period ended March 31, 2014 are primarily due to fluctuations in forward prices for capacity and reserves.
Earnings per Share	Earnings per Share

	The following table presents a reconciliation of the basic and diluted earnings per share calculations for the three‑month periods ended March 31, 2015 and 2014:

			2015				2014
			(In Thousands, except per share amounts)

	Numerator:
	Net income attributable to UIL Holdings		$	57,602			$	55,452
	Less: Net income allocated to unvested units			33				30
	Net income attributable to common shareholders		$	57,569			$	55,422

	Denominator:
	Basic average number of shares outstanding			56,881				56,779
	Effect of dilutive securities (1)			303				264
	Diluted average number of shares outstanding			57,184				57,043

	Earnings per share:
	Basic		$	1.01			$	0.98
	Diluted		$	1.01			$	0.97

		-1	Includes unvested restricted stock and performance shares.
Equity Investments	Equity Investments

	UI is party to a 50-50 joint venture with the 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 $111.7 million and $114.2 million as of March 31, 2015 and December 31, 2014, respectively. As of March 31, 2015, 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 $2.9 million and $3.4 million for the three-month periods ending March 31, 2015 and 2014, 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 $5.4 million in each of the three-month periods ending March 31, 2015 and 2014.
Regulatory Accounting	Regulatory Accounting

	Unless otherwise stated below, all of our regulatory assets earn a return. Our regulatory assets and liabilities as of March 31, 2015 and December 31, 2014 included the following:

			Remaining		March 31,				December 31,
			Period		2015				2014
					(In Thousands)
	Regulatory Assets:
	Unamortized redemption costs		7 to 19 years			10,298				10,499
	Pension and other post-retirement benefit plans		(a)			403,358				402,700
	Environmental remediation costs		7 years			14,127				13,197
	Hardship programs		(b)			19,661				24,744
	Debt premium		2 to 23 years			26,229				27,498
	Income taxes due principally to book-tax differences		(c)			166,039				164,466
	Unfunded future income taxes		(d)			15,555				14,859
	Contracts for differences		(e)			78,045				64,276
	Deferred transmission expense		(f)			20,981				17,387
	Other		(g)			33,099				40,336
	Total regulatory assets					787,392				779,962
	Less current portion of regulatory assets					87,071				92,764
	Regulatory Assets, Net				$	700,321			$	687,198

	Regulatory Liabilities:
	Accumulated deferred investment tax credits		29 years		$	4,282			$	4,319
	Excess generation service charge		(h)			16,825				28,692
	Middletown/Norwalk local transmission network service collections		35 years			20,685				20,828
	Pension and other post-retirement benefit plans		(a)			8,722				9,536
	Asset retirement obligation		(i)			7,247				7,248
	Low income programs		(j)			22,253				19,065
	Asset removal costs		(i)			340,236				336,028
	Unfunded future income taxes		(d)			26,848				26,318
	Contracts for differences		(e)			5,274				6,472
	Deferred purchased gas		(k)			6,511				4,736
	Non-firm margin sharing credits		9 years			13,505				8,933
	Other		(g)			42,324				36,747
	Total regulatory liabilities					514,712				508,922
	Less current portion of regulatory liabilities					23,557				17,026
	Regulatory Liabilities, Net				$	491,155			$	491,896

	(a)	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.
	(b)	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
	(c)	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities.
	(d)	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
	(e)	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.
	(f)	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
	(g)	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 certain amounts that are not currently earning a return; liability amount includes decoupling of $9.6 million.
	(h)	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.
	(i)	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
	(j)	Various hardship and payment plan programs approved for recovery.
	(k)	Deferred purchased gas costs balances at the end of the rate year are normally recorded/returned in the next year.
Stock-Based Compensation	Stock-Based Compensation

	Pursuant to the UIL Holdings 2008 Stock and Incentive Compensation Plan (2008 Stock Plan), 94,410 restricted stock units were granted to certain members of management in March 2015; the average of the high and low market prices on the grant date, which approximate fair value, was $49.72 per share.

	Also in March 2015, we granted a total of 1,584 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 $49.72 per share. Such shares vest in equal annual installments over a five-year period.

	Total stock-based compensation expense for the three-month periods ended March 31, 2015 and 2014 $3.7 million and $2.5 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 Pronouncements	New Accounting Pronouncements

	In April 2015, the FASB issued Accounting Standards Update (ASU) 2015-03, “Interest—Imputation of Interest: Simplifying the Presentation of Debt Issuance Costs” which requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. ASU 2015-03 is effective for interim and annual reporting periods beginning after December 15, 2015 and is to be applied retrospectively. The effect that adopting this new accounting guidance will have on our consolidated financial statements will be reductions in both Deferred Charges and Other Assets and Long-term debt on the consolidated balance sheet. This effect is not expected to be material to UIL Holdings’ consolidated financial statements.

	In April 2015, the FASB issued a proposal to defer by one year the effective date of ASU 2014-09 which 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. A final decision is expected in the second quarter of 2015. We are currently evaluating the effect that adopting this new accounting guidance will have on our consolidated financial statements.

BUSINESS_ORGANIZATION_AND_STAT2

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2015
BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES [Abstract]
Value of Gross Derivative Assets and Liabilities	The gross derivative assets and liabilities as of March 31, 2015 and December 31, 2014 were as follows:

			March 31,				December 31,
			2015				2014
			(In Thousands)
	Gross derivative assets:
	Current Assets		$	6,847			$	6,849
	Deferred Charges and Other Assets		$	19,583			$	20,421

	Gross derivative liabilties:
	Current Liabilities		$	23,193			$	23,308
	Noncurrent Liabilities		$	76,008			$	61,766
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 three-month periods ended March 31, 2015 and 2014 were as follows:

			Three Months Ended
			March 31,
			2015				2014
			(In Thousands)

	Regulatory Assets - Derivative liabilities		$	13,769			$	(71,619	)

	Regulatory Liabilities - Derivative assets		$	1,197			$	(2,942	)
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 three‑month periods ended March 31, 2015 and 2014:

			2015				2014
			(In Thousands, except per share amounts)

	Numerator:
	Net income attributable to UIL Holdings		$	57,602			$	55,452
	Less: Net income allocated to unvested units			33				30
	Net income attributable to common shareholders		$	57,569			$	55,422

	Denominator:
	Basic average number of shares outstanding			56,881				56,779
	Effect of dilutive securities (1)			303				264
	Diluted average number of shares outstanding			57,184				57,043

	Earnings per share:
	Basic		$	1.01			$	0.98
	Diluted		$	1.01			$	0.97

		-1	Includes unvested restricted stock and performance shares.
Regulatory Assets and Liabilities	Unless otherwise stated below, all of our regulatory assets earn a return. Our regulatory assets and liabilities as of March 31, 2015 and December 31, 2014 included the following:

			Remaining		March 31,				December 31,
			Period		2015				2014
					(In Thousands)
	Regulatory Assets:
	Unamortized redemption costs		7 to 19 years			10,298				10,499
	Pension and other post-retirement benefit plans		(a)			403,358				402,700
	Environmental remediation costs		7 years			14,127				13,197
	Hardship programs		(b)			19,661				24,744
	Debt premium		2 to 23 years			26,229				27,498
	Income taxes due principally to book-tax differences		(c)			166,039				164,466
	Unfunded future income taxes		(d)			15,555				14,859
	Contracts for differences		(e)			78,045				64,276
	Deferred transmission expense		(f)			20,981				17,387
	Other		(g)			33,099				40,336
	Total regulatory assets					787,392				779,962
	Less current portion of regulatory assets					87,071				92,764
	Regulatory Assets, Net				$	700,321			$	687,198

	Regulatory Liabilities:
	Accumulated deferred investment tax credits		29 years		$	4,282			$	4,319
	Excess generation service charge		(h)			16,825				28,692
	Middletown/Norwalk local transmission network service collections		35 years			20,685				20,828
	Pension and other post-retirement benefit plans		(a)			8,722				9,536
	Asset retirement obligation		(i)			7,247				7,248
	Low income programs		(j)			22,253				19,065
	Asset removal costs		(i)			340,236				336,028
	Unfunded future income taxes		(d)			26,848				26,318
	Contracts for differences		(e)			5,274				6,472
	Deferred purchased gas		(k)			6,511				4,736
	Non-firm margin sharing credits		9 years			13,505				8,933
	Other		(g)			42,324				36,747
	Total regulatory liabilities					514,712				508,922
	Less current portion of regulatory liabilities					23,557				17,026
	Regulatory Liabilities, Net				$	491,155			$	491,896

	(a)	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.
	(b)	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
	(c)	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities.
	(d)	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
	(e)	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.
	(f)	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
	(g)	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 certain amounts that are not currently earning a return; liability amount includes decoupling of $9.6 million.
	(h)	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.
	(i)	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
	(j)	Various hardship and payment plan programs approved for recovery.
	(k)	Deferred purchased gas costs balances at the end of the rate year are normally recorded/returned in the next year.

SUPPLEMENTARY_INFORMATION_Tabl

SUPPLEMENTARY INFORMATION (Tables)	3 Months Ended
SUPPLEMENTARY INFORMATION (Tables)	Mar. 31, 2015
SUPPLEMENTARY INFORMATION [Abstract]
Supplementary Information		Three Months Ended
		March 31,
		2015		2014
		(In Thousands)
	Depreciation and Amortization
	Property, plant, and equipment depreciation	$	34,741	$	31,988
	Amortization of regulatory assets		8,543		8,330
	Total Depreciation and Amortization	$	43,284	$	40,318

	Taxes - Other than Income Taxes
	Operating:
	Connecticut gross earnings	$	22,966	$	22,714
	Local real estate and personal property		12,990		11,964
	Payroll taxes		4,914		3,857
	Other		445		1,001
	Total Taxes - Other than Income Taxes	$	41,315	$	39,536

	Other Income and (Deductions), net
	Interest income	$	709	$	542
	Allowance for funds used during construction - equity		2,157		2,550
	Allowance for funds used during construction - debt		1,046		1,410
	Weather insurance		-		(1,906	)
	Other		456		1,266
	Total Other Income and (Deductions), net	$	4,368	$	3,862

PENSION_AND_OTHER_BENEFITS_Tab

PENSION AND OTHER BENEFITS (Tables)	3 Months Ended
PENSION AND OTHER BENEFITS (Tables)	Mar. 31, 2015
PENSION AND OTHER BENEFITS [Abstract]
Components of Net Periodic Benefit Cost for Pension and Other Postretirement Benefits	The following tables represent the components of net periodic benefit cost for pension and other postretirement benefits as well as the actuarial weighted-average assumptions used in calculating net periodic benefit cost for the three-month periods ended March 31, 2015 and 2014:

		Three Months Ended March 31,
		Pension Benefits						Other Postretirement Benefits
		2015			2014			2015			2014
		(In Thousands)
	Components of net periodic benefit cost:
	Service cost	$	3,605		$	2,896		$	393		$	404
	Interest cost		10,505			11,019			1,327			1,487
	Expected return on plan assets		(14,120	)		(13,560	)		(690	)		(700	)
	Amortization of:
	Prior service costs		48			73			75			71
	Actuarial loss		4,845			3,097			176			(172	)
	Net periodic benefit cost	$	4,883		$	3,525		$	1,281		$	1,090

	Discount rate		4.20%-4.30	%		4.90%-5.20	%		4.20%-4.30	%		4.85%-5.20	%
	Average wage increase		3.50%-3.80	%		3.50%-3.80	%		N/	A		N/	A
	Return on plan assets		7.75%-8.00	%		7.75%-8.00	%		5.56%-8.00	%		5.56%-8.00	%
	Composite health care trend rate (current year)		N/	A		N/	A		7	%		7	%
	Composite health care trend rate (2019 forward)		N/	A		N/	A		5	%		5	%

	N/A – not applicable
Weighted Average Actuarial Assumption used in Calculating Net Periodic Benefit Cost	The following tables represent the components of net periodic benefit cost for pension and other postretirement benefits as well as the actuarial weighted-average assumptions used in calculating net periodic benefit cost for the three-month periods ended March 31, 2015 and 2014:

		Three Months Ended March 31,
		Pension Benefits						Other Postretirement Benefits
		2015			2014			2015			2014
		(In Thousands)
	Components of net periodic benefit cost:
	Service cost	$	3,605		$	2,896		$	393		$	404
	Interest cost		10,505			11,019			1,327			1,487
	Expected return on plan assets		(14,120	)		(13,560	)		(690	)		(700	)
	Amortization of:
	Prior service costs		48			73			75			71
	Actuarial loss		4,845			3,097			176			(172	)
	Net periodic benefit cost	$	4,883		$	3,525		$	1,281		$	1,090

	Discount rate		4.20%-4.30	%		4.90%-5.20	%		4.20%-4.30	%		4.85%-5.20	%
	Average wage increase		3.50%-3.80	%		3.50%-3.80	%		N/	A		N/	A
	Return on plan assets		7.75%-8.00	%		7.75%-8.00	%		5.56%-8.00	%		5.56%-8.00	%
	Composite health care trend rate (current year)		N/	A		N/	A		7	%		7	%
	Composite health care trend rate (2019 forward)		N/	A		N/	A		5	%		5	%

	N/A – not applicable

FAIR_VALUE_MEASUREMENTS_Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
FAIR VALUE MEASUREMENTS (Tables)	Mar. 31, 2015
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 March 31, 2015 and December 31, 2014.

		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-Mar-15	(In Thousands)
	Assets:
	Derivative assets	$	-			$	-			$	26,430		$	26,430
	Noncurrent investments		12,698				-				-			12,698
	Deferred Compensation Plan		3,667				-				-			3,667
	Supplemental retirement benefit trust life insurance policies		-				8,678				-			8,678
		$	16,365			$	8,678			$	26,430		$	51,473

	Liabilities:
	Derivative liabilities	$	-			$	-			$	99,201		$	99,201
	Long-term debt		-				1,985,013				-			1,985,013
		$	-			$	1,985,013			$	99,201		$	2,084,214

	Net fair value assets/(liabilities), March 31, 2015	$	16,365			$	(1,976,335	)		$	(72,771	)	$	(2,032,741	)

	31-Dec-14
	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	)
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 March 31, 2015 or December 31, 2014 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
		Unobservable Input			31-Mar-15				31-Dec-14

	Contracts for differences	Risk of non-performance				0.00% - 0.64	%			0.00% - 0.66	%
		Discount rate				1.37% - 2.03	%			1.65% - 2.25	%
		Forward pricing ($ per MW)			$	3.15 - $11.19			$	3.15 - $14.59
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 three-month period ended March 31, 2015.

		Three Months Ended
		31-Mar-15
		(In Thousands)

	Net derivative assets/(liabilities), December 31, 2014	$	(57,804	)
	Unrealized gains and (losses), net		(14,967	)
	Net derivative assets/(liabilities), March 31, 2015	$	(72,771	)


	Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of March 31, 2015	$	(14,967	)
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 three-month period ended March 31, 2015. The amounts offset the net CfDs liabilities included in the derivative liabilities detailed above.


		Three Months Ended
		31-Mar-15
		(In Thousands)

	Net regulatory assets/(liabilities), December 31, 2014	$	57,804
	Unrealized (gains) and losses, net		14,967
	Net regulatory assets/(liabilities), March 31, 2015	$	72,771

SEGMENT_INFORMATION_Tables

SEGMENT INFORMATION (Tables)	3 Months Ended
SEGMENT INFORMATION (Tables)	Mar. 31, 2015
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)
			Three months ended March 31, 2015
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	191,888	$	58,082	$	249,970	$	334,083		$	-		$	584,053
	Purchased power and gas			97,102		-		97,102		175,737			(1,217	)		271,622
	Operation and maintenance			47,304		13,488		60,792		45,847			(5,292	)		101,347
	Transmission wholesale			-		19,709		19,709		-			-			19,709
	Depreciation and amortization			14,133		4,196		18,329		21,777			3,178			43,284
	Taxes - other than income taxes			15,042		8,381		23,423		17,562			330			41,315
	Merger and acquisition-related expenses			-		-		-		-			6,702			6,702
	Operating Income			18,307		12,308		30,615		73,160			(3,701	)		100,074

	Other Income and (Deductions), net			1,941		1,485		3,426		459			483			4,368

	Interest Charges, net			8,039		3,471		11,510		6,707			5,847			24,064

	Income from Equity Investments			2,936		-		2,936		-			-			2,936

	Income (Loss) Before Income Taxes			15,145		10,322		25,467		66,912			(9,065	)		83,314

	Income Taxes			3,853		3,861		7,714		25,664			(7,673	)		25,705
	Net Income (Loss)			11,292		6,461		17,753		41,248			(1,392	)		57,609
	Less:
	Preferred Stock Dividends of Subsidiary, Noncontrolling Interests			-		-		-		7			-			7
	Net Income (Loss) attributable to UIL Holdings		$	11,292	$	6,461	$	17,753	$	41,241		$	(1,392	)	$	57,602

	Total Capital Expenditures (1)		$	-	$	-	$	38,082	$	23,204		$	9,362		$	70,648

	(In Thousands)
			Three months ended March 31, 2014
			Electric Distribution and Transmission
			Distribution		Transmission		Total		Gas Distribution			Other			Total
	Operating Revenues		$	145,189	$	58,788	$	203,977	$	367,185		$	-		$	571,162
	Purchased power and gas			53,130		-		53,130		214,925			-			268,055
	Operation and maintenance			45,817		10,581		56,398		39,656			(3,177	)		92,877
	Transmission wholesale			-		20,911		20,911		-			-			20,911
	Depreciation and amortization			12,063		4,225		16,288		21,748			2,282			40,318
	Taxes - other than income taxes			12,861		8,352		21,213		17,640			683			39,536
	Merger and acquisition-related expenses			-		-		-		-			5,051			5,051
	Operating Income			21,318		14,719		36,037		73,216			(4,839	)		104,414

	Other Income and (Deductions), net			3,186		983		4,169		(981	)		(5,739	)		(2,551	)

	Interest Charges, net			7,832		3,204		11,036		6,763			5,435			23,234

	Income from Equity Investments			3,386		-		3,386		-			-			3,386

	Income (Loss) Before Income Taxes			20,058		12,498		32,556		65,472			(16,013	)		82,015

	Income Taxes			6,102		3,852		9,954		26,417			(9,821	)		26,550
	Net Income (Loss)			13,956		8,646		22,602		39,055			(6,192	)		55,465
	Less:
	Preferred Stock Dividends of
	Subsidiary, Noncontrolling Interests			-		-		-		13			-			13
	Net Income (Loss) attributable to UIL Holdings		$	13,956	$	8,646	$	22,602	$	39,042		$	(6,192	)	$	55,452

	Total Capital Expenditures (1)		$	-	$	-	$	33,787	$	19,859		$	11,046		$	64,692
Reconciliation of Total Assets from Segments to Consolidated Financial Statements			Electric Distribution and Transmission (2)
			Distribution		Transmission		Total		Gas Distribution (3)			Other			Total (3)
	Total Assets at March 31, 2015		$	-	$	-	$	2,859,820	$	2,095,806		$	172,722		$	5,128,348

	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 March 31, 2015, was $1,290.4 million and $665.8 million for Distribution and Transmission, respectively. Net plant in service 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 March 31, 2015 and December 31, 2014.

BUSINESS_ORGANIZATION_AND_STAT3

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Feb. 25, 2015
Ownership percentage in GenConn [Abstract]
Ownership percentage in joint venture (in hundredths)	50.00%
Business Acquisition [Line Items]
Merger and acquisition-related expenses	$6,702	$5,051
Philadelphia Gas Works [Member]
Business Acquisition [Line Items]
Merger and acquisition-related expenses		11,500
Philadelphia Gas Works [Member] \| Bridge Facility [Member]
Business Acquisition [Line Items]
Merger and acquisition-related expenses		6,400
Philadelphia Gas Works [Member] \| Operating Expense [Member]
Business Acquisition [Line Items]
Merger and acquisition-related expenses		5,100
Iberdrola USA [Member]
Business Acquisition [Line Items]
Cash consideration per share (in dollars per share)			$10.50
Percentage of ownership arise from merger (in hundredths)			18.50%
Merger and acquisition-related expenses	$6,700

BUSINESS_ORGANIZATION_AND_STAT4

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, DERIVATIVES, EARNINGS PER SHARE (Details) (USD $)	3 Months Ended
Share data in Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
	CapacityResource
	Contract
Derivative [Line Items]
Gross derivative asset	$26,400,000
Gross derivative liability	99,200,000
Regulatory asset	78,000,000
Gross derivative asset, UIL's portion of entity	5,400,000
Gross derivative liability, UIL's portion of entity	72,900,000
Regulatory liabilities	5,300,000
Derivatives [Abstract]
Number of new capacity resources selected	4
Number of Contracts for Differences (CfDs) approved by Public Utility Regulatory Authority (PURA)	4
Number of Contracts for Differences (CfDs) executed by UI	2
Number of Contracts for Differences (CfDs) executed by CL&P	2
Percentage of cost borne by UI customers for CFDs (in hundredths)	20.00%
Percentage of cost borne by CL&P customers (in hundredths)	80.00%
Unrealized gain and losses from mark-to-market adjustments [Abstract]
Regulatory Assets - Derivative liability	13,769,000		-71,619,000
Regulatory Liabilities - Derivative assets	1,197,000		-2,942,000
Numerator [Abstract]
Net income attributable to UIL Holdings	57,602,000		55,452,000
Less: Net income allocated to unvested units	33,000		30,000
Net income attributable to common shareholders	57,569,000		55,422,000
Denominator [Abstract]
Basic average number of shares outstanding (in shares)	56,881		56,779
Effect of dilutive securities (in shares)	303	[1]	264	[1]
Diluted average number of shares outstanding (in shares)	57,184		57,043
Earnings per share [Abstract]
Basic (in dollars per share)	$1.01		$0.98
Diluted (in dollars per share)	$1.01		$0.97
Current Assets [Member]
Derivative [Line Items]
Gross derivative asset	6,847,000				6,849,000
Deferred Charges and Other Assets [Member]
Derivative [Line Items]
Gross derivative asset	19,583,000				20,421,000
Current Liabilities [Member]
Derivative [Line Items]
Gross derivative liability	23,193,000				23,308,000
Noncurrent Liabilities [Member]
Derivative [Line Items]
Gross derivative liability	$76,008,000				$61,766,000

[1]	Includes unvested restricted stock and performance shares.

BUSINESS_ORGANIZATION_AND_STAT5

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, EQUITY INVESTMENTS (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Equity Investments [Abstract]
Carrying value of joint venture	$111,709,000		$114,195,000
Income (loss) from equity investment	2,936,000	3,386,000
GenConn [Member]
Equity Investments [Abstract]
Number of peaking generation plants	2
Carrying value of joint venture	111,700,000		114,200,000
Income (loss) from equity investment	2,900,000	3,400,000
Distributions received from joint venture	$5,400,000	$5,400,000

BUSINESS_ORGANIZATION_AND_STAT6

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, REGULATORY ASSETS (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Regulatory Assets [Line Items]
Total Regulatory Assets	$787,392		$779,962
Less current portion of regulatory assets	87,071		92,764
Regulatory Assets, Net	700,321		687,198
Unamortized Redemption Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	10,298		10,499
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	403,358	[1]	402,700	[1]
Environmental Remediation Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	14,127		13,197
Remaining period	7 years
Hardship Programs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	19,661	[2]	24,744	[2]
Debt Premium [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	26,229		27,498
Remaining period, minimum	2 years
Remaining period, maximum	23 years
Income Taxes Due Principally to Book Tax Differences Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	166,039	[3]	164,466	[3]
Contracts For Differences [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	78,045	[4]	64,276	[4]
Term of contract minimum	5 years
Term of contract maximum	12 years
Deferred Transmission Income/Expense [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	20,981	[5]	17,387	[5]
Other [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	33,099	[6]	40,336	[6]
Unfunded Future Income Taxes [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	$15,555	[7]	$14,859	[7]

[1]	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.
[2]	Hardship customer accounts deferred for future recovery to the extent they exceed the amount in rates.
[3]	Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities.
[4]	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.
[5]	Regulatory asset or liability which defers transmission income or expense and fluctuates based upon actual revenues and revenue requirements.
[6]	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 certain amounts that are not currently earning a return; liability amount includes decoupling of $9.6 million.
[7]	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.

BUSINESS_ORGANIZATION_AND_STAT7

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, REGULATORY LIABILITIES (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$514,712,000		$508,922,000
Less current portion of regulatory liabilities	23,557,000		17,026,000
Regulatory Liabilities, Net	491,155,000		491,896,000
Accumulated Deferred Investment Tax Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,282,000		4,319,000
Remaining period	29 years
Excess Generation Service Charge [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	16,825,000	[1]	28,692,000	[1]
Middletown/Norwalk Local Transmission Network Service Collections [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	20,685,000		20,828,000
Remaining period	35 years
Pension and Other Post-Retirement Benefit Plans [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	8,722,000	[2]	9,536,000	[2]
Asset Retirement Obligation [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	7,247,000	[3]	7,248,000	[3]
Low Income Programs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	22,253,000	[4]	19,065,000	[4]
Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	340,236,000	[3]	336,028,000	[3]
Unfunded Future Income Taxes [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	26,848,000	[5]	26,318,000	[5]
Contracts For Differences [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	5,274,000	[6]	6,472,000	[6]
Deferred Purchased Gas [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	6,511,000	[7]	4,736,000	[7]
Non-Firm Margin Sharing Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	13,505,000		8,933,000
Remaining period	9 years
Other [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	42,324,000	[8]	36,747,000	[8]
Decoupling Liability [Member]
Regulatory Liabilities [Line Items]
Liability decoupling amount	$9,600,000

[1]	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.
[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]	The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.
[4]	Various hardship and payment plan programs approved for recovery.
[5]	The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.
[6]	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.
[7]	Deferred purchased gas costs balances at the end of the rate year are normally recorded/returned in the next year.
[8]	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 certain amounts that are not currently earning a return; liability amount includes decoupling of $9.6 million.

BUSINESS_ORGANIZATION_AND_STAT8

BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, STOCK BASED COMPENSATION (Details) (USD $)	3 Months Ended		1 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$3.70	$2.50
Management [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)	94,410
Weighted average grant date fair value (in dollars per share)	$49.72
President and Chief Executive Officer [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted (in shares)			1,584
Weighted average grant date fair value (in dollars per share)			$49.72
Vesting period	5 years
Vesting rights	equal annual installments over a five year period

CAPITALIZATION_Details

CAPITALIZATION (Details) (Common Stock [Member], USD $)	Mar. 31, 2015
Common Stock [Member]
Temporary Equity [Line Items]
Common stock outstanding (in shares)	56,617,292
Common stock par value (in dollars per share)	$0

REGULATORY_PROCEEDINGS_Details

REGULATORY PROCEEDINGS (Details) (USD $)	0 Months Ended	3 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Nov. 12, 2014	Mar. 31, 2015	Mar. 31, 2014	Jun. 19, 2014	Oct. 16, 2014	Jan. 22, 2014	Dec. 31, 2014	Sep. 30, 2013	Mar. 02, 2015
		Contract				Mechanism
		Project
Electric Distribution and Transmission [Member] \| United Illuminating Company (UI) [Member]
Schedule of Regulatory Proceedings [Line Items]
Allowed distribution return on equity (in hundredths)		9.15%
Profit sharing percentage (in hundredths)		50.00%
Power Supply Arrangements [Abstract]
Percentage of standard service customers with wholesale power supply agreements in place for the first half of 2016 (in hundredths)		20.00%
Percentage of standard service customers with wholesale power supply agreements in place for the second half of 2015 (in hundredths)		80.00%
Collateral required to be posted if the entity's credit rating declined two ratings to fall below investment grade		$19.70
New Renewable Source Generation [Abstract]
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
Transmission [Abstract]
Current approved base return on equity (in hundredths)		11.14%
Reserve recorded by UI for refund		11.6						2.6
Refunded reserve		2.9
Additional Reserve recorded by UI for refund relating to second and third complaints							5.6
Additional Reserve recorded by UI for refund relating to third complaint		3.4
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
Threshold percentage of CL&P's costs for the Connecticut portions of projects (in hundredths)		8.40%
Expected amount of investment		45
Cumulative amount of deposits		45
Amount of transmission assets		24.6
Pre-tax income earned on each deposit in NEEWS project		0.6	0.3
Other Proceedings [Abstract]
Amount approved for recovery	7.7
Total estimated loss	11.3
Pre-tax write-off	3.8
Remaining CTA regulatory liability	8.2
Regulatory liability related to CT Yankee DOE litigation	12
Electric Distribution and Transmission [Member] \| United Illuminating Company (UI) [Member] \| Minimum [Member]
Transmission [Abstract]
Weighted average return on equity (in hundredths)		11.30%
Electric Distribution and Transmission [Member] \| United Illuminating Company (UI) [Member] \| Maximum [Member]
Transmission [Abstract]
Weighted average return on equity (in hundredths)		11.40%
Electric Distribution and Transmission [Member] \| New England Transmission Owners [Member] \| June 2014 FERC Order [Member]
Transmission [Abstract]
Reasonable base ROE (in hundredths)				10.57%
Electric Distribution and Transmission [Member] \| New England Transmission Owners [Member] \| October 2014 FERC Order [Member]
Transmission [Abstract]
Reasonable base ROE (in hundredths)					10.57%
Electric Distribution and Transmission [Member] \| New England Transmission Owners [Member] \| Maximum [Member] \| October 2014 FERC Order [Member]
Transmission [Abstract]
Reasonable base ROE (in hundredths)					11.74%
Gas Distribution [Member]
Other Proceedings [Abstract]
Duration of expansion plan		10 years
Credit to customer									10.8
Gas Distribution [Member] \| Connecticut Natural Gas Corporation (CNG) [Member]
Gas Distribution 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] \| Minimum [Member]
Gas Distribution Rates [Abstract]
Decrease in annual revenue requirements		2.5
Gas Distribution [Member] \| Connecticut Natural Gas Corporation (CNG) [Member] \| Maximum [Member]
Gas Distribution Rates [Abstract]
Decrease in annual revenue requirements		$3.50
Gas Distribution [Member] \| The Southern Connecticut Gas Company (SCG) [Member]
Gas Distribution Rates [Abstract]
Approved return on equity (in hundredths)		9.36%
Gas Distribution [Member] \| The Berkshire Gas Company [Member]
Gas Distribution Rates [Abstract]
Approved return on equity (in hundredths)		10.50%
Duration of approved rate plan		10 years

SHORTTERM_CREDIT_ARRANGEMENTS_

SHORT-TERM CREDIT ARRANGEMENTS (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015
Standby Letter of Credit Due 2015 [Member] \| UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Expiration date	16-Jun-15
Amounts outstanding under the Credit Facility	$70
Standby Letter Of Credit Due 2016 [Member]
Disclosure of short-term credit arrangements [Abstract]
Standby letters of credit outstanding	4.4
Expiration date	31-Jan-16
Revolving Credit Facility [Member] \| UIL [Member]
Disclosure of short-term credit arrangements [Abstract]
Expiration date	30-Nov-16
Available credit under the Credit Facility	$325.60

INCOME_TAXES_Details

INCOME TAXES (Details)	3 Months Ended
INCOME TAXES (Details)	Mar. 31, 2015	Mar. 31, 2014
INCOME TAXES [Abstract]
Effective book income tax rates (in hundredths)	31.60%	33.40%

SUPPLEMENTARY_INFORMATION_Deta

SUPPLEMENTARY INFORMATION (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Depreciation and Amortization [Abstract]
Property, plant and equipment depreciation	$34,741	$31,988
Amortization of regulatory assets	8,543	8,330
Total Depreciation and Amortization	43,284	40,318
Taxes - Other than Income Taxes - Operating [Abstract]
Connecticut gross earnings	22,966	22,714
Local real estate and personal property	12,990	11,964
Payroll taxes	4,914	3,857
Other	445	1,001
Total Taxes - Other than Income Taxes	41,315	39,536
Other Income and (Deductions), net [Abstract]
Interest income	709	542
Allowance for funds used during construction - equity	2,157	2,550
Allowance for funds used during construction - debt	1,046	1,410
Weather insurance	0	-1,906
Other	456	1,266
Total Other Income and (Deductions), net	$4,368	$3,862

PENSION_AND_OTHER_BENEFITS_Det

PENSION AND OTHER BENEFITS (Details) (USD $)	1 Months Ended	3 Months Ended
PENSION AND OTHER BENEFITS (Details) (USD $)	Apr. 30, 2015	Mar. 31, 2015	Mar. 31, 2014
Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions	$5,000,000
Additional contribution during remainder of 2015	10,000,000
Pension Benefit [Member]
Components of net periodic benefit cost [Abstract]
Service cost		3,605,000	2,896,000
Interest cost		10,505,000	11,019,000
Expected return on plan assets		-14,120,000	-13,560,000
Amortization of [Abstract]
Prior service costs		48,000	73,000
Actuarial loss		4,845,000	3,097,000
Net periodic benefit cost		4,883,000	3,525,000
Pension Benefit [Member] \| Minimum [Member]
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)		4.20%	4.90%
Average wage increase (in hundredths)		3.50%	3.50%
Return on plan assets (in hundredths)		7.75%	7.75%
Pension Benefit [Member] \| Maximum [Member]
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)		4.30%	5.20%
Average wage increase (in hundredths)		3.80%	3.80%
Return on plan assets (in hundredths)		8.00%	8.00%
Other Postretirement Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost		393,000	404,000
Interest cost		1,327,000	1,487,000
Expected return on plan assets		-690,000	-700,000
Amortization of [Abstract]
Prior service costs		75,000	71,000
Actuarial loss		176,000	-172,000
Net periodic benefit cost		$1,281,000	$1,090,000
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Composite health care trend rate (current year) (in hundredths)		7.00%	7.00%
Composite health care trend rate (2019 forward) (in hundredths)		5.00%	5.00%
Other Postretirement Benefits [Member] \| Minimum [Member]
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)		4.20%	4.85%
Return on plan assets (in hundredths)		5.56%	5.56%
Other Postretirement Benefits [Member] \| Maximum [Member]
Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (in hundredths)		4.30%	5.20%
Return on plan assets (in hundredths)		8.00%	8.00%

RELATED_PARTY_TRANSACTIONS_Det

RELATED PARTY TRANSACTIONS (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
RELATED PARTY TRANSACTIONS [Abstract]
Lease payments for office space	$0.40	$0.40

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Details) (USD $)	0 Months Ended
In Millions, unless otherwise specified	Jul. 31, 2013	Sep. 03, 2013	Mar. 31, 2015	Jun. 30, 2014	Nov. 30, 2013	31-May-10
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
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 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) (Fair Value, Measurements, Recurring [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets [Abstract]
Derivative assets	$26,430	$27,270
Noncurrent investments	12,698	11,387
Deferred Compensation Plan	3,667	3,624
Supplemental retirement benefit trust life insurance policies	8,678	8,498
Total financial assets, fair value	51,473	50,779
Liabilities [Abstract]
Derivative liabilities	99,201	85,074
Long-term debt	1,985,013	1,941,711
Total financial liabilities, fair value	2,084,214	2,026,785
Net fair value assets/(liabilities)	-2,032,741	-1,976,006
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Derivative assets	0	0
Noncurrent investments	12,698	11,387
Deferred Compensation Plan	3,667	3,624
Supplemental retirement benefit trust life insurance policies	0	0
Total financial assets, fair value	16,365	15,011
Liabilities [Abstract]
Derivative liabilities	0	0
Long-term debt	0	0
Total financial liabilities, fair value	0	0
Net fair value assets/(liabilities)	16,365	15,011
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	8,678	8,498
Total financial assets, fair value	8,678	8,498
Liabilities [Abstract]
Derivative liabilities	0	0
Long-term debt	1,985,013	1,941,711
Total financial liabilities, fair value	1,985,013	1,941,711
Net fair value assets/(liabilities)	-1,976,335	-1,933,213
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Derivative assets	26,430	27,270
Noncurrent investments	0	0
Deferred Compensation Plan	0	0
Supplemental retirement benefit trust life insurance policies	0	0
Total financial assets, fair value	26,430	27,270
Liabilities [Abstract]
Derivative liabilities	99,201	85,074
Long-term debt	0	0
Total financial liabilities, fair value	99,201	85,074
Net fair value assets/(liabilities)	($72,771)	($57,804)

FAIR_VALUE_MEASUREMENTS_Unobse

FAIR VALUE MEASUREMENTS, Unobservable Input Reconciliation (Details) (Contracts for Differences [Member], USD $)	Mar. 31, 2015	Dec. 31, 2014
Minimum [Member]
Unobservable Input [Abstract]
Risk of non-performance range (in hundredths)	0.00%	0.00%
Discount rate range (in hundredths)	1.37%	1.65%
Forward pricing range (in dollars per MW)	$3.15	$3.15
Maximum [Member]
Unobservable Input [Abstract]
Risk of non-performance range (in hundredths)	0.64%	0.66%
Discount rate range (in hundredths)	2.03%	2.25%
Forward pricing range (in dollars per MW)	$11.19	$14.59

FAIR_VALUE_MEASUREMENTS_Assets

FAIR VALUE MEASUREMENTS, Assets and Liabilities Classified as level 3 (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Changes in fair value of assets and liabilities classified as level 3 [Roll Forward]
Net derivative assets/(liabilities), Beginning balance	($57,804)
Unrealized gains and (losses), net	-14,967
Net derivative assets/(liabilities), Ending balance	-72,771
Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of March 31, 2015	($14,967)

FAIR_VALUE_MEASUREMENTS_Regula

FAIR VALUE MEASUREMENTS, Regulatory Assets and Liabilities (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Change in regulatory asset/liability balances [Roll Forward]
Net regulatory assets/(liabilities), Beginning balance	$57,804
Unrealized (gains) and losses, net	14,967
Net regulatory assets/(liabilities), Ending balance	$72,771

SEGMENT_INFORMATION_Details

SEGMENT INFORMATION (Details) (USD $)	3 Months Ended
SEGMENT INFORMATION (Details) (USD $)	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$584,053,000		$571,162,000
Purchased power and gas	271,622,000		268,055,000
Operation and maintenance	101,347,000		92,877,000
Transmission wholesale	19,709,000		20,911,000
Depreciation and amortization	43,284,000		40,318,000
Taxes - other than income taxes	41,315,000		39,536,000
Merger and acquisition-related expenses	6,702,000		5,051,000
Operating Income	100,074,000		104,414,000
Other Income and (Deductions), net	4,368,000		-2,551,000
Interest Charges, net	24,064,000		23,234,000
Income from Equity Investments	2,936,000		3,386,000
Income (Loss) Before Income Taxes	83,314,000		82,015,000
Income Taxes	25,705,000		26,550,000
Net Income (Loss)	57,609,000		55,465,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	7,000		13,000
Net Income (Loss) attributable to UIL Holdings	57,602,000		55,452,000
Total Capital Expenditure	70,648,000	[1]	64,692,000	[1]
Total Assets	5,128,348,000	[2]			5,111,935,000	[2]
Goodwill	266,205,000				266,205,000
Reporting Segments [Member] \| Electric Distribution Reportable Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	191,888,000		145,189,000
Purchased power and gas	97,102,000		53,130,000
Operation and maintenance	47,304,000		45,817,000
Transmission wholesale	0		0
Depreciation and amortization	14,133,000		12,063,000
Taxes - other than income taxes	15,042,000		12,861,000
Merger and acquisition-related expenses	0		0
Operating Income	18,307,000		21,318,000
Other Income and (Deductions), net	1,941,000		3,186,000
Interest Charges, net	8,039,000		7,832,000
Income from Equity Investments	2,936,000		3,386,000
Income (Loss) Before Income Taxes	15,145,000		20,058,000
Income Taxes	3,853,000		6,102,000
Net Income (Loss)	11,292,000		13,956,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	0		0
Net Income (Loss) attributable to UIL Holdings	11,292,000		13,956,000
Total Capital Expenditure	0	[1]	0	[1]
Total Assets	0	[3]			0	[3]
Net plant in service	1,290,400,000				1,283,600,000
Reporting Segments [Member] \| Electric Transmission Reportable Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	58,082,000		58,788,000
Purchased power and gas	0		0
Operation and maintenance	13,488,000		10,581,000
Transmission wholesale	19,709,000		20,911,000
Depreciation and amortization	4,196,000		4,225,000
Taxes - other than income taxes	8,381,000		8,352,000
Merger and acquisition-related expenses	0		0
Operating Income	12,308,000		14,719,000
Other Income and (Deductions), net	1,485,000		983,000
Interest Charges, net	3,471,000		3,204,000
Income from Equity Investments	0		0
Income (Loss) Before Income Taxes	10,322,000		12,498,000
Income Taxes	3,861,000		3,852,000
Net Income (Loss)	6,461,000		8,646,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	0		0
Net Income (Loss) attributable to UIL Holdings	6,461,000		8,646,000
Total Capital Expenditure	0	[1]	0	[1]
Total Assets	0	[3]			0	[3]
Net plant in service	665,800,000				659,400,000
Reporting Segments [Member] \| Total Electric Distribution and Transmission Reportable Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenues	249,970,000		203,977,000
Purchased power and gas	97,102,000		53,130,000
Operation and maintenance	60,792,000		56,398,000
Transmission wholesale	19,709,000		20,911,000
Depreciation and amortization	18,329,000		16,288,000
Taxes - other than income taxes	23,423,000		21,213,000
Merger and acquisition-related expenses	0		0
Operating Income	30,615,000		36,037,000
Other Income and (Deductions), net	3,426,000		4,169,000
Interest Charges, net	11,510,000		11,036,000
Income from Equity Investments	2,936,000		3,386,000
Income (Loss) Before Income Taxes	25,467,000		32,556,000
Income Taxes	7,714,000		9,954,000
Net Income (Loss)	17,753,000		22,602,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	0		0
Net Income (Loss) attributable to UIL Holdings	17,753,000		22,602,000
Total Capital Expenditure	38,082,000	[1]	33,787,000	[1]
Total Assets	2,859,820,000	[3]			2,876,792,000	[3]
Reporting Segments [Member] \| Gas Distribution Reportable Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	334,083,000		367,185,000
Purchased power and gas	175,737,000		214,925,000
Operation and maintenance	45,847,000		39,656,000
Transmission wholesale	0		0
Depreciation and amortization	21,777,000		21,748,000
Taxes - other than income taxes	17,562,000		17,640,000
Merger and acquisition-related expenses	0		0
Operating Income	73,160,000		73,216,000
Other Income and (Deductions), net	459,000		-981,000
Interest Charges, net	6,707,000		6,763,000
Income from Equity Investments	0		0
Income (Loss) Before Income Taxes	66,912,000		65,472,000
Income Taxes	25,664,000		26,417,000
Net Income (Loss)	41,248,000		39,055,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	7,000		13,000
Net Income (Loss) attributable to UIL Holdings	41,241,000		39,042,000
Total Capital Expenditure	23,204,000	[1]	19,859,000	[1]
Total Assets	2,095,806,000	[2]			2,087,284,000	[2]
Goodwill	266,200,000				266,200,000
Reporting Segments [Member] \| Other Reportable Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues	0		0
Purchased power and gas	-1,217,000		0
Operation and maintenance	-5,292,000		-3,177,000
Transmission wholesale	0		0
Depreciation and amortization	3,178,000		2,282,000
Taxes - other than income taxes	330,000		683,000
Merger and acquisition-related expenses	6,702,000		5,051,000
Operating Income	-3,701,000		-4,839,000
Other Income and (Deductions), net	483,000		-5,739,000
Interest Charges, net	5,847,000		5,435,000
Income from Equity Investments	0		0
Income (Loss) Before Income Taxes	-9,065,000		-16,013,000
Income Taxes	-7,673,000		-9,821,000
Net Income (Loss)	-1,392,000		-6,192,000
Less: Preferred Stock Dividends of Subsidiary, Noncontrolling Interests	0		0
Net Income (Loss) attributable to UIL Holdings	-1,392,000		-6,192,000
Total Capital Expenditure	9,362,000	[1]	11,046,000	[1]
Total Assets	$172,722,000				$147,859,000

[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]	I Includes $266.2 million of goodwill in the Gas Distribution segment as of March 31, 2015 and December 31, 2014.
[3]	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 March 31, 2015, was $1,290.4 million and $665.8 million for Distribution and Transmission, respectively. As of December 31, 2014, net plant in service was $1,283.6 million and $659.4 million for Distribution and Transmission, respectively.