CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Income	$ 209,387	$ 129,247	$ 464,520	$ 367,083
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	509	510	1,018	1,019
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(1,248)	218	(1,116)	458
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,120	2,086	2,074	3,047
Other Comprehensive Income (Loss), Net of Tax, Total	381	2,814	1,976	4,524
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(3,759)	(3,759)
Comprehensive Income	207,888	130,181	462,737	367,848
The Connecticut Light And Power Company [Member]
Net Income	78,770	37,385	148,004	116,684
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	111	111	222	222
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(43)	7	(39)	15
Other Comprehensive Income (Loss), Net of Tax, Total	68	118	183	237
Comprehensive Income	78,838	37,503	148,187	116,921
NSTAR Electric Company [Member]
Net Income	81,963	60,129	165,523	118,216
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(2)		(182)
Other Comprehensive Income (Loss), Net of Tax, Total	(2)		(182)
Comprehensive Income	81,961	60,129	165,341	118,216
Public Service Company Of New Hampshire [Member]
Net Income	27,945	24,080	59,990	56,718
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	290	291	581	581
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(75)	12	(67)	26
Other Comprehensive Income (Loss), Net of Tax, Total	215	303	514	607
Comprehensive Income	28,160	24,383	60,504	57,325
Western Massachusetts Electric Company [Member]
Net Income	14,195	7,018	27,439	25,120
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	84	84	169	169
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(12)	2	(11)	4
Other Comprehensive Income (Loss), Net of Tax, Total	72	86	158	173
Comprehensive Income	$ 14,267	$ 7,104	$ 27,597	$ 25,293