CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Income	$ 205,529	$ 209,387	$ 451,562	$ 464,520
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	534	509	1,068	1,018
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	1,061	(1,248)	1,325	(1,116)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(1,784)	1,120	(913)	2,074
Other Comprehensive Income (Loss), Net of Tax, Total	(189)	381	1,480	1,976
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(3,759)	(3,759)
Comprehensive Income	203,460	207,888	449,283	462,737
The Connecticut Light And Power Company [Member]
Net Income	82,875	78,770	169,921	148,004
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	36	(43)	45	(39)
Other Comprehensive Income (Loss), Net of Tax, Total	147	68	267	183
Comprehensive Income	83,022	78,838	170,188	148,187
NSTAR Electric Company [Member]
Net Income	68,167	81,963	122,661	165,523
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	(11)	(2)	(21)	(182)
Other Comprehensive Income (Loss), Net of Tax, Total	(11)	(2)	(21)	(182)
Comprehensive Income	68,156	81,961	122,640	165,341
Public Service Company Of New Hampshire [Member]
Net Income	31,255	27,945	67,313	59,990
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	291	290	581	581
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	63	(75)	79	(67)
Other Comprehensive Income (Loss), Net of Tax, Total	354	215	660	514
Comprehensive Income	31,609	28,160	67,973	60,504
Western Massachusetts Electric Company [Member]
Net Income	13,265	14,195	30,092	27,439
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	110	84	219	169
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	10	(12)	13	(11)
Other Comprehensive Income (Loss), Net of Tax, Total	120	72	232	158
Comprehensive Income	$ 13,385	$ 14,267	$ 30,324	$ 27,597