CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating Revenues	$ 1,767,184	$ 1,817,061	$ 3,822,819	$ 4,330,491
Operating Expenses:
Purchased Power and Transmission	581,260	685,118	1,336,119	1,847,167
Operations and Maintenance	320,714	316,641	640,850	650,024
Depreciation	176,507	163,668	350,492	327,505
Amortization of Regulatory Assets/(Liabilities), Net	(8,716)	(1,166)	12,281	59,438
Energy Efficiency Programs	119,667	101,850	256,842	248,452
Taxes Other Than Income Taxes	154,330	138,935	314,277	288,415
Total Operating Expenses	1,343,762	1,405,046	2,910,861	3,421,001
Operating Income	423,422	412,015	911,958	909,490
Interest Expense:
Total Interest Expense	100,492	92,259	198,703	187,102
Other Income [Abstract]
Other Income/(Loss), Net	8,038	12,899	10,049	18,626
Income Before Income Tax Expense	330,968	332,655	723,304	741,014
Income Tax Expense	125,439	123,268	271,742	276,494
Net Income	205,529	209,387	451,562	464,520
Net Income Attributable to Noncontrolling Interests	1,880	1,880	3,759	3,759
Net Income Attributable to Controlling Interests	$ 203,649	$ 207,507	$ 447,803	$ 460,761
Earnings Per Share Basic And Diluted	$ 0.64	$ 0.65	$ 1.41	$ 1.45
Common Stock Dividends Per Share Declared	$ 0.45	$ 0.42	$ 0.89	$ 0.84
Weighted Average Common Shares Outstanding:
Basic	317,785,495	317,613,166	317,651,319	317,352,004
Diluted	318,476,699	318,559,568	318,478,876	318,525,378
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 679,787	$ 666,554	$ 1,415,103	$ 1,471,471
Operating Expenses:
Purchased Power and Transmission	234,504	253,180	507,104	586,799
Operations and Maintenance	122,532	118,687	233,375	236,044
Depreciation	57,532	52,191	114,500	105,094
Amortization of Regulatory Assets/(Liabilities), Net	(2,988)	(7,530)	6,891	40,776
Energy Efficiency Programs	35,498	33,963	73,589	76,770
Taxes Other Than Income Taxes	70,568	62,102	146,030	130,181
Total Operating Expenses	517,646	512,593	1,081,489	1,175,664
Operating Income	162,141	153,961	333,614	295,807
Interest Expense:
Total Interest Expense	35,978	36,124	72,477	72,748
Other Income [Abstract]
Other Income/(Loss), Net	6,275	4,062	7,211	6,221
Income Before Income Tax Expense	132,438	121,899	268,348	229,280
Income Tax Expense	49,563	43,129	98,427	81,276
Net Income	82,875	78,770	169,921	148,004
NSTAR Electric Company [Member]
Operating Revenues	591,301	617,196	1,205,517	1,384,004
Operating Expenses:
Purchased Power and Transmission	219,189	283,129	473,525	684,995
Operations and Maintenance	88,954	69,430	183,650	145,254
Depreciation	52,571	48,949	104,457	97,716
Amortization of Regulatory Assets/(Liabilities), Net	3,971	(7,336)	8,654	(12,901)
Energy Efficiency Programs	61,922	41,733	128,165	97,150
Taxes Other Than Income Taxes	34,194	29,876	66,750	60,841
Total Operating Expenses	460,801	465,781	965,201	1,073,055
Operating Income	130,500	151,415	240,316	310,949
Interest Expense:
Total Interest Expense	20,216	17,781	41,104	38,227
Other Income [Abstract]
Other Income/(Loss), Net	2,836	2,533	2,502	3,136
Income Before Income Tax Expense	113,120	136,167	201,714	275,858
Income Tax Expense	44,953	54,204	79,053	110,335
Net Income	68,167	81,963	122,661	165,523
Public Service Company Of New Hampshire [Member]
Operating Revenues	218,517	241,875	460,807	526,722
Operating Expenses:
Purchased Power and Transmission	45,653	47,938	95,867	147,516
Operations and Maintenance	63,788	76,468	123,001	134,895
Depreciation	28,644	25,751	56,879	51,397
Amortization of Regulatory Assets/(Liabilities), Net	(8,186)	12,050	332	27,181
Energy Efficiency Programs	3,259	3,356	6,879	7,128
Taxes Other Than Income Taxes	22,287	22,249	44,082	41,331
Total Operating Expenses	155,445	187,812	327,040	409,448
Operating Income	63,072	54,063	133,767	117,274
Interest Expense:
Total Interest Expense	12,526	11,662	24,987	22,935
Other Income [Abstract]
Other Income/(Loss), Net	282	1,245	432	1,628
Income Before Income Tax Expense	50,828	43,646	109,212	95,967
Income Tax Expense	19,573	15,701	41,899	35,977
Net Income	31,255	27,945	67,313	59,990
Western Massachusetts Electric Company [Member]
Operating Revenues	116,396	125,194	244,491	278,058
Operating Expenses:
Purchased Power and Transmission	32,665	43,055	72,228	112,716
Operations and Maintenance	22,088	20,104	43,893	39,889
Depreciation	11,476	10,848	22,847	21,223
Amortization of Regulatory Assets/(Liabilities), Net	992	3,336	2,203	7,264
Energy Efficiency Programs	10,347	9,519	21,203	20,594
Taxes Other Than Income Taxes	9,600	9,398	19,833	18,833
Total Operating Expenses	87,168	96,260	182,207	220,519
Operating Income	29,228	28,934	62,284	57,539
Interest Expense:
Total Interest Expense	6,072	6,291	12,075	13,112
Other Income [Abstract]
Other Income/(Loss), Net	104	1,245	(46)	1,819
Income Before Income Tax Expense	23,260	23,888	50,163	46,246
Income Tax Expense	9,995	9,693	20,071	18,807
Net Income	$ 13,265	$ 14,195	$ 30,092	$ 27,439