COMMON SHARES (Details) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 5	$ 5
Common Stock Shares Authorized	225,000,000	225,000,000
Common Stock Shares Issued	196,010,807	195,781,740
Treasury Stock Shares	19,008,390	19,333,659
The Connecticut Light and Power Company [Member]
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 10	$ 10
Common Stock Shares Authorized	24,500,000	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	$ 1
Common Stock Shares Authorized	100,000,000	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	$ 25
Common Stock Shares Authorized	1,072,471	1,072,471
Common Stock Shares Issued	434,653	434,653