CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income	$ 886,004	$ 827,065	$ 793,689
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,079	2,037	2,049
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,588)	315	(940)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	7,674	(30,330)	25,714
Other Comprehensive Income (Loss), Net of Tax, Total	7,165	(27,978)	26,823
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,682)
Comprehensive Income	885,650	791,568	812,830
The Connecticut Light And Power Company [Member]
Net Income	299,360	287,754	279,412
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	444	444	444
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(89)	12	(31)
Other Comprehensive Income (Loss), Net of Tax, Total	355	456	413
Comprehensive Income	299,715	288,210	279,825
NSTAR Electric Company [Member]
Net Income	344,542	303,088	268,546
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	103	442
Other Comprehensive Income (Loss), Net of Tax, Total	103	442
Comprehensive Income	344,645	303,530	268,546
Public Service Company Of New Hampshire [Member]
Net Income	114,442	113,944	111,397
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	1,162	1,162	1,162
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(154)	19	(54)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	0	(3)
Other Comprehensive Income (Loss), Net of Tax, Total	1,008	1,181	1,105
Comprehensive Income	115,450	115,125	112,502
Western Massachusetts Electric Company [Member]
Net Income	56,506	57,819	60,438
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	379	338	338
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(25)	3	(9)
Other Comprehensive Income (Loss), Net of Tax, Total	354	341	329
Comprehensive Income	56,860	58,160	60,767
Eversource Parent [Member]
Net Income	878,485	819,546	786,007
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,079	2,037	2,049
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,588)	315	(940)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	7,674	(30,330)	25,714
Other Comprehensive Income (Loss), Net of Tax, Total	7,165	(27,978)	26,823
Comprehensive Income	$ 885,650	$ 791,568	$ 812,830