BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, REGULATORY LIABILITIES (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 543,765		$ 706,821
Less current portion of regulatory liabilities	30,043		261,729
Regulatory Liabilities, Net	513,722		445,092
Accumulated Deferred Investment Tax Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,355		4,465
Remaining period	29 years
Income Taxes Due Principally to Book-Tax Differences [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	0	[1]	200,673	[1]
Deferred Gain on Sale of Property [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	0	[2]	37,933	[2]
Excess Generation Service Charge [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	25,296	[3]	0	[3]
Middletown/Norwalk Local Transmission Network Service Collections [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	20,972		21,402
Remaining period	35 years
Pension and Other Post-Retirement Benefit Plans [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	24,465		27,686
Remaining period	6 years
Asset Retirement Obligation [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	6,604	[4]	5,593	[4]
Low Income Programs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	30,158	[5]	25,300	[5]
Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	333,712	[6]	319,530	[6]
Deferred Income Taxes [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	26,247	[7]	43,421	[7]
Contracts For Differences [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	6,608	[8]	0	[8]
Deferred Purchased Gas [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	6,596	[9]	0	[9]
Non-Firm Margin Sharing Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	29,339		0
Remaining period	10 years
Other [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 29,413	[6]	$ 20,818	[6]

[1] Amortization period and/or balance vary depending on the nature and/or remaining life of the underlying assets/liabilities; balances contain regulatory liabilities related to the CTA as well as regulatory assets not related to the CTA. Due to the end of the CTA charge, the CTA regulatory liabilities are classified as current regulatory liabilities as of December 31, 2013 and the regulatory assets not related to the CTA are reclassified as long-term regulatory assets.

[2] Asset/Liability relates to the Competitive Transition Assessment (CTA). Balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences. Total CTA costs recovery and stranded cost amortization are complete. As a result of the outcome of UI's 2013 distribution rate request, PURA approved UI's proposed rate treatment to leave CTA rates unchanged until January 1, 2014 at which point the charge ended. The remaining balances were eliminated. See Note (C) "Regulatory Proceedings - Electric Distribution and Transmission - Other Proceedings" for additional information.

[3] Regulatory asset or liability which defers generation-related and nonbypassable federally mandated congestion costs or revenues for future recovery from or return to customers. Amount fluctuates based upon timing differences between revenues collected from rates and actual costs incurred.

[4] The liability will be extinguished simultaneous with the retirement of the assets and settlement of the corresponding asset retirement obligation.

[5] Various hardship and payment plan programs approved for recovery.

[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 decoupling ($5.5 million) and certain other amounts that are not currently earning a return. See Note (C) "Regulatory Proceedings" for a discussion of the decoupling recovery period.

[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.

[8] Asset life is equal to delivery term of related contracts (which vary from approximately 6 - 13 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.

[9] Deferred purchase gas costs balances at the end of the rate year are normally recorded/returned in the next year.