PENSION AND OTHER BENEFITS (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
United Illuminating Company (UI) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions					$ 48,100,000
Additional contributions during the remainder of the fiscal year	4,100,000				4,100,000
Components of net periodic benefit cost:
Service cost	3,143,000		1,781,000		9,430,000		5,342,000
Interest cost	10,120,000		5,272,000		30,362,000		15,816,000
Expected return on plan assets	(10,647,000)		(4,767,000)		(31,941,000)		(14,300,000)
Amortization of:
Prior service costs	162,000		162,000		483,000		485,000
Transition obligation (asset)	0		0		0		0
Actuarial (gain) loss	3,507,000		3,078,000		10,523,000		9,232,000
Net periodic benefit cost	6,285,000		5,526,000		18,857,000		16,575,000
Weighted-average assumptions used in calculating net periodic benefit cost [Abstract]
Discount rate, minimum (in hundredths)	5.10%		5.65%		5.10%		5.65%
Discount rate, maximum (in hundredths)	5.35%		5.85%		5.35%		5.85%
Average wage increase (in hundredths)			3.80%				3.80%
Average wage increase, minimum (in hundredths)	3.50%				3.50%
Average wage increase, maximum (in hundredths)	3.80%				3.80%
Return on plan assets (in hundredths)			8.50%				8.50%
Return on plan assets, minimum (in hundredths)	8.25%				8.25%
Return on plan assets, maximum (in hundredths)	8.50%				8.50%
United Illuminating Company (UI) [Member] | Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	541,000		340,000		1,622,000		1,020,000
Interest cost	1,659,000		982,000		4,977,000		2,947,000
Expected return on plan assets	(740,000)		(438,000)		(2,222,000)		(1,315,000)
Amortization of:
Prior service costs	(25,000)		(26,000)		(76,000)		(77,000)
Transition obligation (asset)	255,000		265,000		765,000		794,000
Actuarial (gain) loss	502,000		488,000		1,506,000		1,463,000
Net periodic benefit cost	2,192,000		1,611,000		6,572,000		4,832,000
Weighted-average assumptions used in calculating net periodic benefit cost [Abstract]
Discount rate (in hundredths)			5.80%				5.80%
Discount rate, minimum (in hundredths)	5.15%				5.15%
Discount rate, maximum (in hundredths)	5.30%				5.30%
Return on plan assets (in hundredths)			8.50%				8.50%
Return on plan assets, minimum (in hundredths)	6.83%				6.83%
Return on plan assets, maximum (in hundredths)	8.25%				8.25%
Composite health care trend rate (current year) (in hundredths)			9.50%				9.50%
Composite health care trend rate (current year), minimum (in hundredths)	7.80%				7.80%
Composite health care trend rate (current year), maximum (in hundredths)	8.50%				8.50%
Health care trend rate ( 2018 forward) (in hundredths)			5.00%	[1]			5.00%	[1]
Health care trend rate ( 2018 forward) minimum (in hundredths)	4.50%	[1]			4.50%	[1]
Health care trend rate ( 2018 forward) maximum (in hundredths)	5.00%	[1]			5.00%	[1]
Gas Companies [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions					18,400,000
Additional contributions during the remainder of the fiscal year	$ 3,000,000				$ 3,000,000

[1] For the period ended September 30, 2010, the health care trend rate was applicable for 2019 forward.