COMMON SHARES (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 5
Common Stock Shares Authorized	225,000,000
Common Stock Shares Issued	195,976,708	195,781,740
Treasury Stock Shares	19,151,327	19,333,659
The Connecticut Light and Power Company [Member]
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 10
Common Stock Shares Authorized	24,500,000
Common Stock Shares Issued	6,035,205	6,035,205
Public Service Company of New Hampshire [Member]
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 1
Common Stock Shares Authorized	100,000,000
Common Stock Shares Issued	301	301
Western Massachusetts Electric Company [Member]
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 25
Common Stock Shares Authorized	1,072,471
Common Stock Shares Issued	434,653	434,653