PENSION AND OTHER BENEFITS (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
United Illuminating Company (UI) [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			$ 44,000,000
Additional contributions during the remainder of the fiscal year	8,200,000		8,200,000
Components of net periodic benefit cost:
Service cost	3,144,000	1,781,000	6,287,000	3,561,000
Interest cost	10,121,000	5,272,000	20,242,000	10,544,000
Expected return on plan assets	(10,647,000)	(4,766,000)	(21,294,000)	(9,533,000)
Amortization of:
Prior service costs	160,000	161,000	321,000	323,000
Transition obligation (asset)	0	0	0	0
Actuarial (gain) loss	3,509,000	3,076,000	7,016,000	6,154,000
Net periodic benefit cost	6,287,000	5,524,000	12,572,000	11,049,000
Weighted-average assumptions used in calculating net periodic benefit cost [Abstract]
Discount rate (in hundredths)				5.80%
Discount rate, minimum (in hundredths)	5.10%	5.65%	5.15%
Discount rate, maximum (in hundredths)	5.35%	5.85%	5.30%
Average wage increase (in hundredths)		3.80%
Average wage increase, minimum (in hundredths)	3.50%
Average wage increase, maximum (in hundredths)	3.80%
Return on plan assets (in hundredths)		8.50%		8.50%
Return on plan assets, minimum (in hundredths)	8.25%		6.83%
Return on plan assets, maximum (in hundredths)	8.50%		8.25%
Composite health care trend rate (current year) (in hundredths)				9.50%
Composite health care trend rate (current year), minimum (in hundredths)			7.80%
Composite health care trend rate (current year), maximum (in hundredths)			8.50%
Composite health care trend rate (2019 forward) (in hundredths)				5.00%
Composite health care trend rate (2019 forward), minimum (in hundredths)			4.50%
Composite health care trend rate (2019 forward), maximum (in hundredths)			5.00%
United Illuminating Company (UI) [Member] | Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	540,000	340,000	1,081,000	680,000
Interest cost	1,659,000	983,000	3,318,000	1,965,000
Expected return on plan assets	(741,000)	(439,000)	(1,482,000)	(877,000)
Amortization of:
Prior service costs	(26,000)	(25,000)	(51,000)	(51,000)
Transition obligation (asset)	255,000	264,000	510,000	529,000
Actuarial (gain) loss	502,000	487,000	1,004,000	975,000
Net periodic benefit cost	2,189,000	1,610,000	4,380,000	3,221,000
Gas Companies [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension contributions			15,300,000
Additional contributions during the remainder of the fiscal year	$ 6,000,000		$ 6,000,000