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DOCUMENT AND ENTITY INFORMATION (USD $)
9 Months Ended
Sep. 30, 2013
Oct. 31, 2013
Document And Entity [Line Items]    
Entity Registrant Name NORTHEAST UTILITIES  
Document Period End Date Sep. 30, 2013  
Document Type 10-Q  
Entity Central Index Key 0000072741  
Current Fiscal Year End Date --12-31  
Entity Common Stock, Shares Outstanding   315,094,075
Entity Public Float $ 13,224,337,788  
Entity Filer Category Large Accelerated Filer  
Entity Current Reporting Status Yes  
Entity Voluntary Filers No  
Entity Well-known Seasoned Issuer Yes  
Document Fiscal Year Focus 2013  
Document Fiscal Period Focus FY  
Amendment Flag false  
The Connecticut Light And Power Company [Member]
   
Document And Entity [Line Items]    
Entity Registrant Name The Connecticut Light and Power Company  
Entity Central Index Key 0000023426  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Public Service Company Of New Hampshire [Member]
   
Document And Entity [Line Items]    
Entity Registrant Name Public Service Company of New Hampshire  
Entity Central Index Key 0000315256  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Western Massachusetts Electric Company [Member]
   
Document And Entity [Line Items]    
Entity Registrant Name Western Massachusetts Electric Company  
Entity Central Index Key 0000106170  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
NSTAR Electric Company [Member]
   
Document And Entity [Line Items]    
Entity Registrant Name NSTAR Electric Company  
Entity Central Index Key 0000013372  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer