Contractual Obligations with Yankee Companies (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Loss Contingency, Information about Litigation Matters [Abstract]
Court of Federal Claims Ruling To CYAPC			$ 126.3
Court Of Federal Claims Ruling To YAEC			73.3
Court Of Federal Claims Ruling To MYAPC			35.8
Connecticut Yankee Proceeds Received	90.0	36.3
Yankee Atomic Proceeds Received	73.3
Maine Yankee Proceeds Received	$ 35.8
Refund Obligation To Customers	As of September 30, 2014, CL&P's refund obligation to customers of $65.4 million was recorded as an offset to the deferred storm restoration costs regulatory asset, as directed by PURA. NSTAR Electric's, PSNH's and WMECO's refund obligation to customers of $29.1 million, $13.1 million and $18.1 million, respectively, was recorded as a regulatory liability in each company's respective regulatory tracker mechanisms. Refunds to customers for these DOE proceeds began in the third quarter of 2014. For further information, see Note 2, "Regulatory Accounting," to the financial statements.
MYAPC Phase One Damages Proceeds To Member Companies	DOE Phase I Damages - Proceeds Received – On September 17, 2014, in accordance with the MYAPC refund plan, MYAPC returned a portion of the DOE Phase I Damages proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, in the amount of $3.2 million, $1.1 million, $1.4 million and $0.8 million, respectively. These amounts reduced receivables at CL&P, NSTAR Electric, PSNH and WMECO.