SUBSEQUENT EVENTS (Details)	3 Months Ended
	Mar. 31, 2012
Subsequent Event [Line Items]
Subsequent Event, Description	On April 2, 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. Given the long-term nature of the remarketing, the $62 million has been classified as Long-Term Debt on the accompanying unaudited condensed consolidated balance sheets as of March 31, 2012. The PCRBs, which mature on May 1, 2031, carry a coupon rate of 1.55 percent during the current three-year fixed-rate period and are subject to mandatory tender for purchase on April 1, 2015. On April 2, 2012, NU repaid the NU parent $263 million 7.25 percent Series A Senior Notes that matured on April 1, 2012 with the proceeds from the issuance of the floating rate Series D Senior Notes issued on March 22, 2012. On April 10, 2012, NU acquired 100 percent of the outstanding common stock of NSTAR and NSTAR (through a successor, NSTAR LLC) became a direct wholly-owned subsidiary of NU. Refer to Note 2, "Merger of NU and NSTAR," for further information.