CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Income	$ 232,629	$ 205,529	$ 493,966	$ 451,562
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	514	534	1,048	1,068
Changes in Unrealized Gains/(Losses) on Marketable Securities	960	1,061	2,605	1,325
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(2,268)	(1,784)	(1,306)	(913)
Net OCI	(794)	(189)	2,347	1,480
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(3,759)	(3,759)
Comprehensive Income Attributable to Common Shareholders	229,955	203,460	492,554	449,283
The Connecticut Light And Power Company [Member]
Net Income	91,293	82,875	181,501	169,921
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	91	111	202	222
Changes in Unrealized Gains/(Losses) on Marketable Securities	33	36	89	45
Net OCI	124	147	291	267
Comprehensive Income Attributable to Common Shareholders	91,417	83,022	181,792	170,188
NSTAR Electric Company [Member]
Net Income	77,363	68,167	143,525	122,661
Other Comprehensive (Loss)/Income, Net of Tax:
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(4)	(11)	(8)	(21)
Net OCI	(4)	(11)	(8)	(21)
Comprehensive Income Attributable to Common Shareholders	77,359	68,156	143,517	122,640
Public Service Company Of New Hampshire [Member]
Net Income	31,591	31,255	65,903	67,313
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	290	291	581	581
Changes in Unrealized Gains/(Losses) on Marketable Securities	58	63	155	79
Net OCI	348	354	736	660
Comprehensive Income Attributable to Common Shareholders	31,939	31,609	66,639	67,973
Western Massachusetts Electric Company [Member]
Net Income	17,621	13,265	34,839	30,092
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	110	110	219	219
Changes in Unrealized Gains/(Losses) on Marketable Securities	9	10	25	13
Net OCI	119	120	244	232
Comprehensive Income Attributable to Common Shareholders	$ 17,740	$ 13,385	$ 35,083	$ 30,324