MERGER OF NU AND NSTAR (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended
	Apr. 09, 2012	Sep. 30, 2013	Dec. 31, 2012
Business Combination Consideration Transferred [Abstract]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	136,000,000
Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Less Noncontrolling Interest [Abstract]
Goodwill		$ 3,519,401	$ 3,519,401
Goodwill Roll Forward [Abstract]
Goodwill, Beginning Balance		3,519,401	3,519,401
Goodwill, Ending Balance		$ 3,519,401	$ 3,519,401