CAPITALIZATION (Details) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Schedule of Capitalization, Long-term Debt [Line Items]
Issuances of long term debt	$ 203,500,000	$ 1,050,000
Remaining amount of note purchase agreement	100,000,000
United Illuminating Company (UI) [Member] | Unsecured Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Amount of note purchase agreement	203,500,000
United Illuminating Company (UI) [Member] | Series B Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Principal amount of note outstanding	51,500,000
Interest rate (in hundredths)	3.61%
Maturity date	Jan. 31, 2022
United Illuminating Company (UI) [Member] | Series A Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Principal amount of note outstanding	31,000,000
Interest rate (in hundredths)	2.98%
Maturity date	Jan. 31, 2019
United Illuminating Company (UI) [Member] | Series C Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Principal amount of note outstanding	34,000,000
Interest rate (in hundredths)	3.61%
Maturity date	Jan. 31, 2022
United Illuminating Company (UI) [Member] | Series D Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Principal amount of note outstanding	52,000,000
Interest rate (in hundredths)	4.89%
Maturity date	Jan. 30, 2042
United Illuminating Company (UI) [Member] | Series E Senior Notes [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Principal amount of note outstanding	35,000,000
Interest rate (in hundredths)	4.89%
Maturity date	Jan. 30, 2042
United Illuminating Company (UI) [Member] | Pollution Controlled Revenue Bonds [Member]
Schedule of Capitalization, Long-term Debt [Line Items]
Bonds refinanced, aggregate principal amount outstanding	103,500,000
Issuances of long term debt	$ 103,500,000
Common Stock [Member]
Temporary Equity [Line Items]
Common stock outstanding (in shares)	50,665,114
Common stock par value (in dollars per share)	$ 0