CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income	$ 949,821	$ 886,004	$ 827,065
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	2,137	2,079	2,037
Changes in Unrealized Gains/(Losses) on Marketable Securities	2,294	(2,588)	315
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(2,869)	7,674	(30,330)
Other Comprehensive Income/(Loss), Net of Tax	1,562	7,165	(27,978)
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Comprehensive Income	943,864	885,650	791,568
The Connecticut Light And Power Company [Member]
Net Income	334,254	299,360	287,754
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	444	444	444
Changes in Unrealized Gains/(Losses) on Marketable Securities	79	(89)	12
Other Comprehensive Income/(Loss), Net of Tax	523	355	456
Comprehensive Income	334,777	299,715	288,210
NSTAR Electric Company [Member]
Net Income	292,705	344,542	303,088
Other Comprehensive Income/(Loss), Net of Tax:
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(177)	103	442
Other Comprehensive Income/(Loss), Net of Tax	(177)	103	442
Comprehensive Income	292,528	344,645	303,530
Public Service Company Of New Hampshire [Member]
Net Income	131,985	114,442	113,944
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	1,162	1,162	1,162
Changes in Unrealized Gains/(Losses) on Marketable Securities	136	(154)	19
Other Comprehensive Income/(Loss), Net of Tax	1,298	1,008	1,181
Comprehensive Income	133,283	115,450	115,125
Western Massachusetts Electric Company [Member]
Net Income	58,072	56,506	57,819
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	438	379	338
Changes in Unrealized Gains/(Losses) on Marketable Securities	22	(25)	3
Other Comprehensive Income/(Loss), Net of Tax	460	354	341
Comprehensive Income	$ 58,532	$ 56,860	$ 58,160