DIVIDEND RESTRICTIONS (Details)	12 Months Ended
Dec. 31, 2015
Line of Credit Facility, Dividend Restrictions	CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends from retained earnings for lawful and legitimate business purposes. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict the payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of Eversource, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and to the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter. As of December 31, 2015, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.8 billion for Eversource, $1.2 billion for CL&P, $1.6 billion for NSTAR Electric, $494.9 million for PSNH and $198.1 million for WMECO as of December 31, 2015. As of December 31, 2015, Eversource, CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends.
Public Service Company Of New Hampshire [Member]
Statutory Dividend Payment Restrictions Disclosure	PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2015, $13.4 million of PSNH's Retained Earnings was subject to restriction under its FERC hydroelectric license conditions and PSNH was in compliance with this provision.

DIVIDEND RESTRICTIONS (Details)

12 Months Ended

Dec. 31, 2015

Line of Credit Facility, Dividend Restrictions

CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends from retained earnings for lawful and legitimate business purposes. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict the payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of Eversource, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and to the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter. As of December 31, 2015, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.8 billion for Eversource, $1.2 billion for CL&P, $1.6 billion for NSTAR Electric, $494.9 million for PSNH and $198.1 million for WMECO as of December 31, 2015. As of December 31, 2015, Eversource, CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends.

Public Service Company Of New Hampshire [Member]

Statutory Dividend Payment Restrictions Disclosure

PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2015, $13.4 million of PSNH's Retained Earnings was subject to restriction under its FERC hydroelectric license conditions and PSNH was in compliance with this provision.