Other Income, Net (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Public Utilities Allowance For Funds Used During Construction Additions	$ 6,600,000	$ 4,600,000	$ 18,400,000	$ 11,600,000
Other Income/(Loss), Net	1,430,000	10,118,000	19,077,000	19,726,000
The Connecticut Light and Power Company [Member]
Public Utilities Allowance For Funds Used During Construction Additions	1,400,000	1,200,000	4,100,000	3,700,000
Other Income/(Loss), Net	(2,356,000)	6,938,000	4,308,000	12,616,000
Public Service Company of New Hampshire [Member]
Public Utilities Allowance For Funds Used During Construction Additions	4,200,000	2,900,000	12,000,000	7,100,000
Other Income/(Loss), Net	3,293,000	3,667,000	12,112,000	5,882,000
Western Massachusetts Electric Company [Member]
Public Utilities Allowance For Funds Used During Construction Additions	200,000	200,000	500,000	400,000
Other Income/(Loss), Net	$ (722,000)	$ 747,000	$ 259,000	$ 1,512,000