COMMON SHARES (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Class Of Stock Line Items
Common Stock Par Or Stated Value Per Share	$ 5
Common Stock Shares Authorized	380,000,000	225,000,000
Common Stock Shares Issued	196,052,770	195,781,740
Treasury Stock Shares	18,894,078	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	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	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	1,072,471
Common Stock Shares Issued	434,653	434,653