CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Revenues	$ 7,954,827	$ 7,741,856	$ 7,301,204
Operating Expenses:
Purchased Power and Transmission	3,086,905	3,021,550	2,482,954
Operations and Maintenance	1,329,289	1,427,589	1,514,986
Depreciation	665,856	614,657	610,777
Amortization of Regulatory Assets/(Liabilities), Net	22,339	10,704	206,322
Amortization of Rate Reduction Bonds	0	0	42,581
Energy Efficiency Programs	495,701	473,127	401,919
Taxes Other Than Income Taxes	590,573	561,380	512,230
Total Operating Expenses	6,190,663	6,109,007	5,771,769
Operating Income	1,764,164	1,632,849	1,529,435
Interest Expense:
Total Interest Expense	372,420	362,106	338,699
Other Income [Abstract]
Other Income/(Loss), Net	34,227	24,619	29,894
Income Before Income Tax Expense	1,425,971	1,295,362	1,220,630
Income Tax Expense	539,967	468,297	426,941
Net Income	886,004	827,065	793,689
Net Income Attributable to Noncontrolling Interests	7,519	7,519	7,682
Net Income Attributable to Controlling Interests	$ 878,485	$ 819,546	$ 786,007
Basic Earnings Per Common Share	$ 2.77	$ 2.59	$ 2.49
Diluted Earnings Per Common Share	$ 2.76	$ 2.58	$ 2.49
Weighted Average Common Shares Outstanding:
Basic	317,336,881	316,136,748	315,311,387
Diluted	318,432,687	317,417,414	316,211,160
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 2,802,675	$ 2,692,582	$ 2,442,341
Operating Expenses:
Purchased Power and Transmission	1,054,313	982,876	872,769
Operations and Maintenance	487,281	494,578	523,247
Depreciation	215,289	188,837	177,603
Amortization of Regulatory Assets/(Liabilities), Net	12,318	59,336	4,870
Energy Efficiency Programs	153,725	156,335	89,858
Taxes Other Than Income Taxes	268,688	255,370	234,418
Total Operating Expenses	2,191,614	2,137,332	1,902,765
Operating Income	611,061	555,250	539,576
Interest Expense:
Total Interest Expense	145,795	147,421	133,650
Other Income [Abstract]
Other Income/(Loss), Net	11,490	13,376	15,149
Income Before Income Tax Expense	476,756	421,205	421,075
Income Tax Expense	177,396	133,451	141,663
Net Income	299,360	287,754	279,412
NSTAR Electric Company [Member]
Operating Revenues	2,681,342	2,536,677	2,493,479
Operating Expenses:
Purchased Power and Transmission	1,190,191	1,122,298	849,149
Operations and Maintenance	306,528	326,972	376,360
Depreciation	196,770	188,693	180,298
Amortization of Regulatory Assets/(Liabilities), Net	(12,989)	(6,330)	230,148
Amortization of Rate Reduction Bonds	0	0	15,054
Energy Efficiency Programs	224,755	193,516	206,536
Taxes Other Than Income Taxes	133,260	133,072	127,778
Total Operating Expenses	2,038,515	1,958,221	1,985,323
Operating Income	642,827	578,456	508,156
Interest Expense:
Total Interest Expense	75,347	77,878	70,383
Other Income [Abstract]
Other Income/(Loss), Net	5,106	4,491	3,639
Income Before Income Tax Expense	572,586	505,069	441,412
Income Tax Expense	228,044	201,981	172,866
Net Income	344,542	303,088	268,546
Public Service Company Of New Hampshire [Member]
Operating Revenues	972,203	959,500	935,402
Operating Expenses:
Purchased Power and Transmission	247,721	313,732	269,754
Operations and Maintenance	276,554	261,848	267,797
Depreciation	105,372	98,436	91,581
Amortization of Regulatory Assets/(Liabilities), Net	16,276	(29,602)	(20,387)
Amortization of Rate Reduction Bonds	0	0	19,748
Energy Efficiency Programs	14,324	14,286	14,494
Taxes Other Than Income Taxes	81,779	71,417	67,196
Total Operating Expenses	742,026	730,117	710,183
Operating Income	230,177	229,383	225,219
Interest Expense:
Total Interest Expense	45,990	45,349	46,176
Other Income [Abstract]
Other Income/(Loss), Net	3,315	2,045	3,455
Income Before Income Tax Expense	187,502	186,079	182,498
Income Tax Expense	73,060	72,135	71,101
Net Income	114,442	113,944	111,397
Western Massachusetts Electric Company [Member]
Operating Revenues	518,128	493,423	472,724
Operating Expenses:
Purchased Power and Transmission	177,172	172,876	147,059
Operations and Maintenance	86,360	89,406	96,194
Depreciation	43,362	41,886	37,568
Amortization of Regulatory Assets/(Liabilities), Net	14,545	(6,228)	(3,206)
Amortization of Rate Reduction Bonds	0	0	7,780
Energy Efficiency Programs	42,867	42,937	39,524
Taxes Other Than Income Taxes	38,302	34,907	28,458
Total Operating Expenses	402,608	375,784	353,377
Operating Income	115,520	117,639	119,347
Interest Expense:
Total Interest Expense	24,792	24,931	24,851
Other Income [Abstract]
Other Income/(Loss), Net	2,748	2,379	3,310
Income Before Income Tax Expense	93,476	95,087	97,806
Income Tax Expense	36,970	37,268	37,368
Net Income	56,506	57,819	60,438
Eversource Parent [Member]
Operating Revenues	0	0	8
Operating Expenses:
Operations and Maintenance	9,315	29,598	12,766
Operating Income	(9,315)	(29,598)	(12,758)
Interest Expense:
Total Interest Expense	45,130	33,168	31,639
Other Income [Abstract]
Equity In Earnings Of Subsidiaries	900,824	848,435	785,650
Other, Net	6,602	1,830	5,062
Other Income/(Loss), Net	907,426	850,265	790,712
Income Before Income Tax Expense	852,981	787,499	746,315
Income Tax Expense	(25,504)	(32,047)	(39,692)
Net Income	$ 878,485	$ 819,546	$ 786,007
Basic Earnings Per Common Share	$ 2.77	$ 2.59	$ 2.49
Diluted Earnings Per Common Share	$ 2.76	$ 2.58	$ 2.49
Weighted Average Common Shares Outstanding:
Basic	317,336,881	316,136,748	315,311,387
Diluted	318,432,687	317,417,414	316,211,160