CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Operating Revenues	$ 2,039,706	$ 1,933,105	$ 5,862,525	$ 6,263,597
Operating Expenses:
Purchased Power, Fuel and Transmission	665,810	702,640	2,001,929	2,549,807
Operations and Maintenance	324,734	327,283	965,584	977,306
Depreciation	181,288	167,884	531,781	495,389
Amortization of Regulatory Assets/(Liabilities), Net	43,942	(16,851)	56,223	42,587
Energy Efficiency Programs	149,121	132,107	405,962	380,559
Taxes Other Than Income Taxes	164,942	150,804	479,219	439,221
Total Operating Expenses	1,529,837	1,463,867	4,440,698	4,884,869
Operating Income/(Loss)	509,869	469,238	1,421,827	1,378,728
Interest Expense	99,865	92,534	298,568	279,635
Other Income, Net	13,641	5,241	23,689	23,866
Income Before Income Tax Expense	423,645	381,945	1,146,948	1,122,959
Income Tax Expense	156,446	144,146	428,186	420,640
Net Income	267,199	237,799	718,762	702,319
Net Income Attributable to Noncontrolling Interests	1,880	1,879	5,639	5,639
Net Income Attributable to Common Shareholders	$ 265,319	$ 235,920	$ 713,123	$ 696,680
Basic Earnings Per Common Share (in dollars per share)	$ 0.83	$ 0.74	$ 2.24	$ 2.20
Diluted Earnings Per Common Share (in dollars per share)	0.83	0.74	2.24	2.19
Dividends Declared Per Common Share (in dollars per share)	$ 0.45	$ 0.42	$ 1.34	$ 1.25
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,787,836	317,452,212	317,696,823	317,296,107
Diluted (in shares)	318,577,079	318,405,269	318,511,609	318,396,042
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 760,037	$ 704,262	$ 2,175,141	$ 2,175,733
Operating Expenses:
Purchased Power, Fuel and Transmission	253,509	274,762	760,613	861,562
Operations and Maintenance	123,034	122,280	356,409	358,324
Depreciation	57,675	54,809	172,175	159,903
Amortization of Regulatory Assets/(Liabilities), Net	23,418	(22,859)	30,308	17,917
Energy Efficiency Programs	44,381	42,590	117,969	119,360
Taxes Other Than Income Taxes	81,948	71,563	227,981	201,743
Total Operating Expenses	583,965	543,145	1,665,455	1,718,809
Operating Income/(Loss)	176,072	161,117	509,686	456,924
Interest Expense	36,083	36,716	108,561	109,463
Other Income, Net	3,669	2,356	10,881	8,576
Income Before Income Tax Expense	143,658	126,757	412,006	356,037
Income Tax Expense	57,026	46,569	155,453	127,845
Net Income	86,632	80,188	256,553	228,192
NSTAR Electric Company [Member]
Operating Revenues	780,462	750,724	1,985,979	2,134,728
Operating Expenses:
Purchased Power, Fuel and Transmission	291,382	299,040	764,907	984,035
Operations and Maintenance	96,282	83,486	279,932	228,740
Depreciation	54,695	49,101	159,151	146,818
Amortization of Regulatory Assets/(Liabilities), Net	9,621	2,257	18,275	(10,643)
Energy Efficiency Programs	84,717	67,693	212,882	164,843
Taxes Other Than Income Taxes	35,050	34,982	101,800	95,821
Total Operating Expenses	571,747	536,559	1,536,947	1,609,614
Operating Income/(Loss)	208,715	214,165	449,032	525,114
Interest Expense	21,101	18,992	62,206	57,218
Other Income, Net	5,022	513	7,524	3,649
Income Before Income Tax Expense	192,636	195,686	394,350	471,545
Income Tax Expense	75,440	77,062	154,493	187,397
Net Income	117,196	118,624	239,857	284,148
Public Service Company Of New Hampshire [Member]
Operating Revenues	266,946	234,364	727,753	761,086
Operating Expenses:
Purchased Power, Fuel and Transmission	59,833	53,017	155,700	200,533
Operations and Maintenance	64,183	65,190	187,184	200,085
Depreciation	29,646	26,592	86,524	77,989
Amortization of Regulatory Assets/(Liabilities), Net	14,158	1,967	14,490	29,148
Energy Efficiency Programs	3,983	3,873	10,862	11,001
Taxes Other Than Income Taxes	20,460	20,104	64,543	61,435
Total Operating Expenses	192,263	170,743	519,303	580,191
Operating Income/(Loss)	74,683	63,621	208,450	180,895
Interest Expense	12,397	11,647	37,386	34,582
Other Income, Net	574	685	1,007	2,313
Income Before Income Tax Expense	62,860	52,659	172,071	148,626
Income Tax Expense	24,345	20,158	66,242	56,135
Net Income	38,515	32,501	105,829	92,491
Western Massachusetts Electric Company [Member]
Operating Revenues	124,042	125,093	368,533	403,151
Operating Expenses:
Purchased Power, Fuel and Transmission	32,178	36,465	104,406	149,182
Operations and Maintenance	24,125	21,762	68,018	61,651
Depreciation	11,567	11,196	34,414	32,420
Amortization of Regulatory Assets/(Liabilities), Net	1,102	3,930	3,305	11,194
Energy Efficiency Programs	12,389	12,107	33,593	32,701
Taxes Other Than Income Taxes	10,609	9,599	30,440	28,430
Total Operating Expenses	91,970	95,059	274,176	315,578
Operating Income/(Loss)	32,072	30,034	94,357	87,573
Interest Expense	6,222	5,901	18,298	19,014
Other Income, Net	179	587	133	2,406
Income Before Income Tax Expense	26,029	24,720	76,192	70,965
Income Tax Expense	10,018	9,749	30,089	28,555
Net Income	$ 16,011	$ 14,971	$ 46,103	$ 42,410