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Environmental Matters (Tables)
3 Months Ended
Mar. 31, 2015
Notes To Consolidated Financial Statements [Abstract]  
Schedule Of Environmental Loss Contingencies By Site Text Block
 As of March 31, 2015  As of December 31, 2014
    Reserve     Reserve
 Number of Sites (in millions)  Number of Sites (in millions)
ES 65 $ 43.6    65 $ 43.3
CL&P 16   5.0    16   3.8
NSTAR Electric 14   1.7    13   1.1
PSNH 12   3.4    13   5.2
WMECO 4   0.6    4   0.5