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Environmental Matters (Tablels)
9 Months Ended
Sep. 30, 2011
Notes To Consolidated Financial Statements [Abstract] 
Schedule Of Environmental Loss Contingencies By Site Text Block
 As of September 30, 2011 As of December 31, 2010
    Reserve    Reserve
 Number of Sites (in millions) Number of Sites (in millions)
NU   33 $ 26.0  33 $ 30.3
CL&P  6   0.9  6   0.8
PSNH  12   6.3  12   8.8
WMECO  8   0.2  8   0.2