CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended					12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended									12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended												12 Months Ended				12 Months Ended								12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended								12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Dec. 31, 2010 Common Stock [Member]	Dec. 31, 2013 Additional Paid-in Capital [Member]	Dec. 31, 2012 Additional Paid-in Capital [Member]	Dec. 31, 2011 Additional Paid-in Capital [Member]	Dec. 31, 2010 Additional Paid-in Capital [Member]	Dec. 31, 2013 Retained Earnings [Member]	Dec. 31, 2012 Retained Earnings [Member]	Dec. 31, 2011 Retained Earnings [Member]	Dec. 31, 2010 Retained Earnings [Member]	Dec. 31, 2013 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2011 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2010 Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2013 Treasury Stock [Member]	Dec. 31, 2012 Treasury Stock [Member]	Dec. 31, 2011 Treasury Stock [Member]	Dec. 31, 2010 Treasury Stock [Member]	Dec. 31, 2012 Stockholders Equity Total Member	Dec. 31, 2013 Common Shareholders Equity [Member]	Dec. 31, 2012 Common Shareholders Equity [Member]	Dec. 31, 2011 Common Shareholders Equity [Member]	Dec. 31, 2010 Common Shareholders Equity [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member] Common Stock [Member]	Dec. 31, 2012 The Connecticut Light And Power Company [Member] Common Stock [Member]	Dec. 31, 2011 The Connecticut Light And Power Company [Member] Common Stock [Member]	Dec. 31, 2010 The Connecticut Light And Power Company [Member] Common Stock [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2012 The Connecticut Light And Power Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2011 The Connecticut Light And Power Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2010 The Connecticut Light And Power Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member] Retained Earnings [Member]	Dec. 31, 2012 The Connecticut Light And Power Company [Member] Retained Earnings [Member]	Dec. 31, 2011 The Connecticut Light And Power Company [Member] Retained Earnings [Member]	Dec. 31, 2010 The Connecticut Light And Power Company [Member] Retained Earnings [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 The Connecticut Light And Power Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2011 The Connecticut Light And Power Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2010 The Connecticut Light And Power Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2013 The Connecticut Light And Power Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2012 The Connecticut Light And Power Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2011 The Connecticut Light And Power Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2010 The Connecticut Light And Power Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2013 NSTAR Electric Company [Member] Common Stock [Member]	Dec. 31, 2012 NSTAR Electric Company [Member] Common Stock [Member]	Dec. 31, 2011 NSTAR Electric Company [Member] Common Stock [Member]	Dec. 31, 2010 NSTAR Electric Company [Member] Common Stock [Member]	Dec. 31, 2013 NSTAR Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2012 NSTAR Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2011 NSTAR Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2010 NSTAR Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2013 NSTAR Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2012 NSTAR Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2011 NSTAR Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2010 NSTAR Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2013 NSTAR Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2012 NSTAR Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2011 NSTAR Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2010 NSTAR Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member] Common Stock [Member]	Dec. 31, 2012 Public Service Company Of New Hampshire [Member] Common Stock [Member]	Dec. 31, 2011 Public Service Company Of New Hampshire [Member] Common Stock [Member]	Dec. 31, 2010 Public Service Company Of New Hampshire [Member] Common Stock [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member] Additional Paid-in Capital [Member]	Dec. 31, 2012 Public Service Company Of New Hampshire [Member] Additional Paid-in Capital [Member]	Dec. 31, 2011 Public Service Company Of New Hampshire [Member] Additional Paid-in Capital [Member]	Dec. 31, 2010 Public Service Company Of New Hampshire [Member] Additional Paid-in Capital [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member] Retained Earnings [Member]	Dec. 31, 2012 Public Service Company Of New Hampshire [Member] Retained Earnings [Member]	Dec. 31, 2011 Public Service Company Of New Hampshire [Member] Retained Earnings [Member]	Dec. 31, 2010 Public Service Company Of New Hampshire [Member] Retained Earnings [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 Public Service Company Of New Hampshire [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2011 Public Service Company Of New Hampshire [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2010 Public Service Company Of New Hampshire [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2013 Public Service Company Of New Hampshire [Member] Common Shareholders Equity [Member]	Dec. 31, 2012 Public Service Company Of New Hampshire [Member] Common Shareholders Equity [Member]	Dec. 31, 2011 Public Service Company Of New Hampshire [Member] Common Shareholders Equity [Member]	Dec. 31, 2010 Public Service Company Of New Hampshire [Member] Common Shareholders Equity [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member] Common Stock [Member]	Dec. 31, 2012 Western Massachusetts Electric Company [Member] Common Stock [Member]	Dec. 31, 2011 Western Massachusetts Electric Company [Member] Common Stock [Member]	Dec. 31, 2010 Western Massachusetts Electric Company [Member] Common Stock [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2012 Western Massachusetts Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2011 Western Massachusetts Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2010 Western Massachusetts Electric Company [Member] Additional Paid-in Capital [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2012 Western Massachusetts Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2011 Western Massachusetts Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2010 Western Massachusetts Electric Company [Member] Retained Earnings [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2012 Western Massachusetts Electric Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2011 Western Massachusetts Electric Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2010 Western Massachusetts Electric Company [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Dec. 31, 2013 Western Massachusetts Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2012 Western Massachusetts Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2011 Western Massachusetts Electric Company [Member] Common Shareholders Equity [Member]	Dec. 31, 2010 Western Massachusetts Electric Company [Member] Common Shareholders Equity [Member]
Common Stock, Shares, Outstanding		315,273,559	314,053,634	177,158,692	176,448,081																						6,035,205	6,035,205	6,035,205	6,035,205																	100	100	100	100													301	301	301	301																	434,653	434,653	434,653	434,653
Common Stock, Value, Outstanding		$ 1,665,351	$ 1,662,547	$ 980,264	$ 978,909	$ 6,192,765	$ 6,183,267	$ 1,797,884	$ 1,777,592	$ 2,125,980	$ 1,802,714	$ 1,651,875	$ 1,452,777	$ (46,031)	$ (72,854)	$ (70,686)	$ (43,370)	$ (326,537)	$ (338,624)	$ (346,667)	$ (354,732)		$ 9,611,528	$ 9,237,050	$ 4,012,670	$ 3,811,176	$ 60,352	$ 60,352	$ 60,352	$ 60,352	$ 1,682,047	$ 1,640,149	$ 1,613,503	$ 1,605,275	$ 961,482	$ 839,628	$ 735,948	$ 734,561	$ (1,387)	$ (1,800)	$ (2,251)	$ (2,713)	$ 2,702,494	$ 2,538,329	$ 2,407,552	$ 2,397,475	$ 0	$ 0	$ 0	$ 0	$ 992,625	$ 992,625	$ 992,625	$ 992,625	$ 1,420,828	$ 1,210,405	$ 1,239,123	$ 1,158,489	$ 2,413,453	$ 2,203,030	$ 2,231,748	$ 2,151,114	$ 0	$ 0	$ 0	$ 0	$ 701,911	$ 701,052	$ 700,285	$ 579,577	$ 438,515	$ 395,118	$ 388,910	$ 347,471	$ (8,550)	$ (9,655)	$ (10,832)	$ (601)	$ 1,131,876	$ 1,086,515	$ 1,078,363	$ 926,447	$ 10,866	$ 10,866	$ 10,866	$ 10,866	$ 390,743	$ 390,412	$ 340,115	$ 248,044	$ 181,014	$ 160,577	$ 115,506	$ 98,757	$ (3,517)	$ (3,846)	$ (4,186)	$ (83)	$ 579,106	$ 558,009	$ 462,301	$ 357,584
Net Income	533,077									793,689	533,077	400,513											793,689	533,077	400,513										279,412	209,725	250,164						279,412	209,725	250,164										268,546	190,242	252,494		268,546	190,242	252,494										111,397	96,882	100,267						111,397	96,882	100,267										60,438	54,503	43,054						60,438	54,503	43,054
Dividends on Common Shares										(462,741)	(375,527)	(195,595)											(462,741)	(375,527)	(195,595)										(151,999)	(100,486)	(243,218)						(151,999)	(100,486)	(243,218)										(56,000)	(217,000)	(169,900)		(56,000)	(217,000)	(169,900)										(68,000)	(90,674)	(58,828)						(68,000)	(90,674)	(58,828)										(40,001)	(9,432)	(26,305)						(40,001)	(9,432)	(26,305)
Issuance of Common Shares		2,804	2,040	1,355		8,274	11,287	4,496															11,078	13,327	5,851
Stock Issued During Period, Shares, New Issues		560,848	408,018	271,030
Dividends, Preferred Stock										(7,682)	(7,029)	(5,559)											(7,682)	(7,029)	(5,559)										(5,559)	(5,559)	(5,559)						(5,559)	(5,559)	(5,559)										(2,123)	(1,960)	(1,960)		(2,123)	(1,960)	(1,960)
Stock Issued During Period, Value, Employee Stock Ownership Plan																															1,847	1,595	1,429										1,847	1,595	1,429																						859	767	678										859	767	678						331	297	259										331	297	259
Long-Term Incentive Plan Activity						(10,748)	(3,897)	7,359															(10,748)	(3,897)	7,359
Other Comprehensive Income (Loss), Net of Tax	(2,168)													26,823	(2,168)	(27,316)							26,823	(2,168)	(27,316)														413	451	462		413	451	462																														1,105	1,177	(10,231)		1,105	1,177	(10,231)														329	340	(4,103)		329	340	(4,103)
Stock Issued During Period, Value, Treasury Stock Reissued						17,381	8,454	7,048										12,087	8,043	8,065			29,468	16,497	15,113
Stock Issued During Period, Shares, Treasury Stock Reissued		659,077	438,329	439,581
Payments of Stock Issuance Costs																															51	51	51										51	51	51
Net Income Attributable to Noncontrolling Interests	7,132										(103)	(261)												(103)	(261)
Capital Contributions from NU Parent																															40,000	25,000	6,748										40,000	25,000	6,748																								120,030												120,030							50,000	91,812											50,000	91,812
SharesIssuedInConnectionWithNstarMerger	136,048,595
SharesIssuedValueInConectionWithNstarMerger	680,243						4,358,027															5,038,270
OtherChangesInShareholdersEquity						(5,409)	8,574	1,389															(5,409)	8,574	1,389
OtherEquityImpactsOfMergerWithNstar							$ 2,938				$ 421											$ 3,359