LONG-TERM DEBT (Details)	6 Months Ended
Jun. 30, 2012
Debt Instrument Line Items
Long-term Debt, Description	8. LONG-TERM DEBT (NU, CL&P) On March 22, 2012, NU parent issued $300 million of floating rate Series D Senior Notes with a maturity date of September 20, 2013. The notes have a coupon rate based on the three-month LIBOR rate plus a credit spread of 0.75 percent and will reset quarterly. The notes had an interest rate of 1.22 percent as of June 30, 2012. The proceeds, net of issuance expenses, were used to repay at maturity the NU parent $263 million Series A Senior Notes that matured on April 1, 2012, to repay short-term borrowings outstanding under the NU parent Credit Agreement and for other general corporate purposes. The indenture under which the bonds were issued requires NU to comply with certain covenants as are customarily included in such indentures. On April 2, 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. 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 parent repaid its $263 million 7.25 percent Series A Senior Notes that matured on April 1, 2012 with the proceeds from the issuance of floating rate Series D Senior Notes issued on March 22, 2012. In addition, as a result of consolidating CYAPC and YAEC, NU has consolidated $179 million in additional spent nuclear fuel obligations. The spent nuclear fuel obligation is payable to the DOE at any time prior to the first delivery to the DOE of spent nuclear fuel and radio-active waste used to generate electricity prior to April 7, 1983. Until payment is made to the DOE, the outstanding liability will continue to accrue interest at the 3-month Treasury bill yield rate. NU, including CL&P, NSTAR Electric, PSNH and WMECO, was in compliance with all its debt covenants as of June 30, 2012.
The Connecticut Light And Power Company [Member]
Debt Instrument Line Items
Long-term Debt, Description	On April 2, 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. 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.

LONG-TERM DEBT (Details)

6 Months Ended

Jun. 30, 2012

8. LONG-TERM DEBT (NU, CL&P) On March 22, 2012, NU parent issued $300 million of floating rate Series D Senior Notes with a maturity date of September 20, 2013. The notes have a coupon rate based on the three-month LIBOR rate plus a credit spread of 0.75 percent and will reset quarterly. The notes had an interest rate of 1.22 percent as of June 30, 2012. The proceeds, net of issuance expenses, were used to repay at maturity the NU parent $263 million Series A Senior Notes that matured on April 1, 2012, to repay short-term borrowings outstanding under the NU parent Credit Agreement and for other general corporate purposes. The indenture under which the bonds were issued requires NU to comply with certain covenants as are customarily included in such indentures. On April 2, 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. 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 parent repaid its $263 million 7.25 percent Series A Senior Notes that matured on April 1, 2012 with the proceeds from the issuance of floating rate Series D Senior Notes issued on March 22, 2012. In addition, as a result of consolidating CYAPC and YAEC, NU has consolidated $179 million in additional spent nuclear fuel obligations. The spent nuclear fuel obligation is payable to the DOE at any time prior to the first delivery to the DOE of spent nuclear fuel and radio-active waste used to generate electricity prior to April 7, 1983. Until payment is made to the DOE, the outstanding liability will continue to accrue interest at the 3-month Treasury bill yield rate. NU, including CL&P, NSTAR Electric, PSNH and WMECO, was in compliance with all its debt covenants as of June 30, 2012.

The Connecticut Light And Power Company [Member]

Debt Instrument Line Items

Long-term Debt, Description

On April 2, 2012, CL&P remarketed $62 million of tax-exempt PCRBs for a three-year period. 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.

- Definition

Description of long-term debt arrangements, which are debt arrangements that originally require full repayment more than twelve months after issuance or greater than the normal operating cycle of the company, if longer, and disclosures pertaining to the underlying arrangements, including repayment terms, conversion features, interest rates, restrictions on assets and activities, debt covenants, and other matters important to users of the financial statements. Types of long-term debt arrangements include borrowing under notes payable, bonds payable, debentures, term loans, and other contractual obligations for payment.

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