BUSINESS ORGANIZATION AND STATEMENT OF ACCOUNTING POLICIES, REGULATORY LIABILITIES (Details) (USD $)	9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 494,305,000		$ 466,440,000
Less current portion of regulatory liabilities	7,135,000		21,284,000
Regulatory Liabilities, Net	487,170,000		445,156,000
Decoupling of Asset	12,400,000
Accumulated Deferred Investment Tax Credits [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,502,000		4,612,000
Remaining period	30 years
Income Taxes Due Principally To Book Tax Differences [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	57,828,000	[1]	41,928,000	[1]
Deferred Gain on Sale of Property [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	37,933,000	[2]	37,933,000	[2]
Middletown/Norwalk Local Transmission Network Service Collections [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	21,545,000		21,975,000
Remaining period	36 years
Pension And Other Post-Retirement Benefit Plans [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	11,985,000		15,016,000
Remaining period, minimum	1 year
Remaining period, maximum	7 years
Deferred Income Taxes [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	44,522,000	[3]	41,816,000	[3]
Asset Retirement Obligation [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	4,254,000	[4]	4,995,000	[4]
Deferred Purchased Gas [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	11,893,000	[5]	0	[5]
Low Income Program [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	23,509,000	[6]	17,651,000	[6]
Asset Removal Costs [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	254,131,000	[1]	243,854,000	[1]
Other [Member]
Regulatory Liabilities [Line Items]
Total regulatory liabilities	$ 22,203,000	[1]	$ 36,660,000	[1]

[1] 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 ($12.4 million) and certain other amounts that are not currently earning a return. See Note (C) “Regulatory Proceedings – Electric Distribution and Transmission – Rates” for a discussion of the decoupling recovery period.

[2] Asset/Liability relates to the Competitive Transition Assessment (CTA). Total CTA costs recovery and stranded cost amortization were substantially completed in the third quarter of 2013. The remaining balances are fully offset by amounts primarily included in income taxes, due principally to book-tax differences. 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 will end and the remaining balances will be extinguished.

[3] The balance will be extinguished when the asset, which is fully offset by a corresponding liability, or liability has been realized or settled, respectively.

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

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

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