CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Revenues	$ 1,762,811	$ 1,767,184	$ 3,867,946	$ 3,822,819
Operating Expenses:
Purchased Power, Fuel and Transmission	549,704	581,260	1,303,353	1,336,119
Operations and Maintenance	302,714	320,714	632,979	640,850
Depreciation	189,881	176,507	376,686	350,492
Amortization of Regulatory (Liabilities)/Assets, Net	(7,807)	(8,716)	16,210	12,281
Energy Efficiency Programs	116,398	119,667	262,556	256,842
Taxes Other Than Income Taxes	156,234	154,330	311,455	314,277
Total Operating Expenses	1,307,124	1,343,762	2,903,239	2,910,861
Operating Income	455,687	423,422	964,707	911,958
Interest Expense	107,329	100,492	210,758	198,703
Other Income/(Loss), Net	21,543	8,038	35,120	10,049
Income Before Income Tax Expense	369,901	330,968	789,069	723,304
Income Tax Expense	137,272	125,439	295,103	271,742
Net Income	232,629	205,529	493,966	451,562
Net Income Attributable to Noncontrolling Interests	1,880	1,880	3,759	3,759
Net Income Attributable to Common Shareholders	$ 230,749	$ 203,649	$ 490,207	$ 447,803
Basic and Diluted Earnings Per Common Share (in dollars per share)	$ 0.72	$ 0.64	$ 1.54	$ 1.41
Dividends Declared Per Common Share (in dollars per share)	$ 0.48	$ 0.45	$ 0.95	$ 0.89
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,391,365	317,785,495	317,427,258	317,651,319
Diluted (in shares)	317,947,194	318,476,699	318,035,864	318,478,876
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 666,558	$ 679,787	$ 1,398,867	$ 1,415,103
Operating Expenses:
Purchased Power, Fuel and Transmission	207,211	234,504	452,149	507,104
Operations and Maintenance	108,501	122,532	236,727	233,375
Depreciation	60,797	57,532	120,549	114,500
Amortization of Regulatory (Liabilities)/Assets, Net	11,422	(2,988)	24,225	6,891
Energy Efficiency Programs	32,153	35,498	68,744	73,589
Taxes Other Than Income Taxes	70,437	70,568	144,414	146,030
Total Operating Expenses	490,521	517,646	1,046,808	1,081,489
Operating Income	176,037	162,141	352,059	333,614
Interest Expense	35,299	35,978	70,264	72,477
Other Income/(Loss), Net	3,804	6,275	6,561	7,211
Income Before Income Tax Expense	144,542	132,438	288,356	268,348
Income Tax Expense	53,249	49,563	106,855	98,427
Net Income	91,293	82,875	181,501	169,921
NSTAR Electric Company [Member]
Operating Revenues	584,069	591,301	1,187,848	1,205,517
Operating Expenses:
Purchased Power, Fuel and Transmission	197,291	219,189	430,384	473,525
Operations and Maintenance	85,281	88,954	173,632	183,650
Depreciation	56,181	52,571	111,397	104,457
Amortization of Regulatory (Liabilities)/Assets, Net	2,984	3,971	7,961	8,654
Energy Efficiency Programs	59,876	61,922	127,188	128,165
Taxes Other Than Income Taxes	34,648	34,194	62,041	66,750
Total Operating Expenses	436,261	460,801	912,603	965,201
Operating Income	147,808	130,500	275,245	240,316
Interest Expense	23,445	20,216	45,473	41,104
Other Income/(Loss), Net	2,029	2,836	5,277	2,502
Income Before Income Tax Expense	126,392	113,120	235,049	201,714
Income Tax Expense	49,029	44,953	91,524	79,053
Net Income	77,363	68,167	143,525	122,661
Public Service Company Of New Hampshire [Member]
Operating Revenues	230,383	218,517	483,541	460,807
Operating Expenses:
Purchased Power, Fuel and Transmission	60,442	45,653	122,189	95,867
Operations and Maintenance	65,134	63,788	127,484	123,001
Depreciation	32,447	28,644	63,182	56,879
Amortization of Regulatory (Liabilities)/Assets, Net	(18,937)	(8,186)	(13,492)	332
Energy Efficiency Programs	3,287	3,259	7,032	6,879
Taxes Other Than Income Taxes	23,118	22,287	44,001	44,082
Total Operating Expenses	165,491	155,445	350,396	327,040
Operating Income	64,892	63,072	133,145	133,767
Interest Expense	12,970	12,526	25,780	24,987
Other Income/(Loss), Net	456	282	1,654	432
Income Before Income Tax Expense	52,378	50,828	109,019	109,212
Income Tax Expense	20,787	19,573	43,116	41,899
Net Income	31,591	31,255	65,903	67,313
Western Massachusetts Electric Company [Member]
Operating Revenues	120,744	116,396	250,879	244,491
Operating Expenses:
Purchased Power, Fuel and Transmission	33,858	32,665	74,724	72,228
Operations and Maintenance	21,743	22,088	44,242	43,893
Depreciation	12,296	11,476	24,298	22,847
Amortization of Regulatory (Liabilities)/Assets, Net	(361)	992	(849)	2,203
Energy Efficiency Programs	8,079	10,347	18,743	21,203
Taxes Other Than Income Taxes	10,197	9,600	20,624	19,833
Total Operating Expenses	85,812	87,168	181,782	182,207
Operating Income	34,932	29,228	69,097	62,284
Interest Expense	6,182	6,072	12,431	12,075
Other Income/(Loss), Net	272	104	349	(46)
Income Before Income Tax Expense	29,022	23,260	57,015	50,163
Income Tax Expense	11,401	9,995	22,176	20,071
Net Income	$ 17,621	$ 13,265	$ 34,839	$ 30,092