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Other Retirement Benefits (Tables)
12 Months Ended
Dec. 31, 2011
Notes To Consolidated Financial Statements [Abstract]  
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits by Title of Individual and Type of Deferred Compensation [Table Text Block]
            
NU  For the Years Ended December 31,
(Millions of Dollars)2011 2010 2009
Actuarially-Determined Liability$52.8 $ 49.9 $ 47.9
Other Retirement Benefits Expense 4.7   4.2   3.9

   For the Years Ended December 31,
   2011 2010 2009
(Millions of Dollars)CL&P PSNH WMECO CL&P PSNH WMECO CL&P PSNH WMECO
Actuarially-Determined Liability$1.2 $2.5 $0.2 $ 0.4 $ 2.4 $ 0.2 $ 0.4 $ 2.4 $ 0.2
Other Retirement Benefits Expense 2.6  1.0  0.5   2.3   0.9   0.4   2.2   0.9   0.4