COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Shareholders' Equity, Beginning Balance			$ 3,811,176,000
Net Income	78,719,000	73,348,000	194,303,000	160,948,000
Net Income Attributable to Noncontrolling Interests	1,441,000	1,402,000	2,870,000	2,792,000
Other Comprehensive Income/ (Loss)	(4,600,000)	900,000	(2,400,000)	1,700,000
Shareholders' Equity, Ending Balance	3,915,106,000		3,915,106,000
Common Shareholders Equity Member
Shareholders' Equity, Beginning Balance	3,885,300,000	3,625,200,000	3,811,200,000	3,577,900,000
Net Income	78,700,000	73,300,000	194,300,000	160,900,000
Dividends on Common Shares	(48,900,000)	(45,400,000)	(97,700,000)	(90,900,000)
Dividends on Preferred Shares of CL&P	(1,400,000)	(1,400,000)	(2,800,000)	(2,800,000)
Issuance of Common Shares		200,000	4,200,000	5,400,000
Other Transcations, Net	6,000,000	6,100,000	8,300,000	6,700,000
Other Comprehensive Income/ (Loss)	(4,600,000)	900,000	(2,400,000)	1,700,000
Shareholders' Equity, Ending Balance	3,915,100,000	3,658,900,000	3,915,100,000	3,658,900,000
Noncontrolling Interest Member
Shareholders' Equity, Beginning Balance	1,500,000	0	1,500,000
Contributions To Northern Pass Trans	300,000	1,100,000	300,000	1,100,000
Shareholders' Equity, Ending Balance	1,800,000	1,100,000	1,800,000	1,100,000
Total Equity Member
Shareholders' Equity, Beginning Balance	3,886,800,000	3,625,200,000	3,812,700,000	3,577,900,000
Net Income	78,700,000	73,300,000	194,300,000	160,900,000
Dividends on Common Shares	(48,900,000)	(45,400,000)	(97,700,000)	(90,900,000)
Dividends on Preferred Shares of CL&P	(1,400,000)	(1,400,000)	(2,800,000)	(2,800,000)
Issuance of Common Shares		200,000	4,200,000	5,400,000
Contributions To Northern Pass Trans	300,000	1,100,000	300,000	1,100,000
Other Transcations, Net	6,000,000	6,100,000	8,300,000	6,700,000
Other Comprehensive Income/ (Loss)	(4,600,000)	900,000	(2,400,000)	1,700,000
Shareholders' Equity, Ending Balance	3,916,900,000	3,660,000,000	3,916,900,000	3,660,000,000
Preferred Stock Member
Shareholders' Equity, Beginning Balance	116,200,000	116,200,000	116,200,000	116,200,000
Dividends on Preferred Shares of CL&P	(1,400,000)	(1,400,000)	(2,800,000)	(2,800,000)
Net Income Attributable to Noncontrolling Interests	1,400,000	1,400,000	2,800,000	2,800,000
Shareholders' Equity, Ending Balance	$ 116,200,000	$ 116,200,000	$ 116,200,000	$ 116,200,000