NSTAR Electric (NSARO) 10-K 26 Feb 16 2015 FY Annual report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2015	Jan. 31, 2016	Jun. 30, 2015
Document And Entity [Line Items]
Entity Registrant Name	EVERSOURCE ENERGY
Document Period End Date	Dec. 31, 2015
Document Type	10-K
Entity Central Index Key	72,741
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		317,191,249
Entity Public Float			$ 14,345,789,335
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light And Power Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	The Connecticut Light and Power Company
Entity Central Index Key	23,426
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Public Service Company Of New Hampshire [Member]
Document And Entity [Line Items]
Entity Registrant Name	Public Service Company of New Hampshire
Entity Central Index Key	315,256
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Western Massachusetts Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	Western Massachusetts Electric Company
Entity Central Index Key	106,170
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	NSTAR Electric Company
Entity Central Index Key	13,372
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current Assets:
Cash	$ 23,947	$ 38,703
Receivables, Net	775,480	856,346
Unbilled Revenues	202,647	211,758
Taxes Receivable	305,359	337,307
Fuel, Materials and Supplies	336,476	349,664
Regulatory Assets Current	845,843	672,493
Prepayments and Other Current Assets	129,034	226,194
Total Current Assets	2,618,786	2,692,465
Property, Plant and Equipment, Net	19,892,441	18,647,041
Deferred Debits and Other Assets:
Regulatory Assets Long Term	3,737,960	4,054,086
Goodwill	3,519,401	3,519,401
Marketable Securities	516,478	515,025
Other Long-Term Assets	295,243	312,369
Total Deferred Debits and Other Assets	8,069,082	8,400,881
Total Assets	30,580,309	29,740,387
Current Liabilities:
Notes Payable	1,160,953	956,825
Long-Term Debt - Current Portion	228,883	245,583
Accounts Payable - Current	813,646	868,231
Regulatory Liability Current	107,759	235,022
Deferred Tax Liabilities Current		160,288
Other Liabilities - Current	678,549	668,432
Total Current Liabilities	2,989,790	3,134,381
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	5,147,678	4,467,473
Regulatory Liabilities Long-Term	513,595	515,144
Long-Term Derivative Liabilities	337,102	409,632
Accrued Pension, SERP and PBOP	1,407,288	1,638,558
Other Long-Term Liabilities	871,499	874,387
Total Deferred Credits and Other Liabilities	8,277,162	7,905,194
Capitalization:
Long-Term Debt	8,805,574	8,568,429
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,568	155,568
Common Shareholders' Equity:
Common Stock	1,669,313	1,666,796
Capital Surplus, Paid In	6,262,368	6,235,834
Retained Earnings	2,797,355	2,448,661
Accumulated Other Comprehensive Loss	(66,844)	(74,009)
Treasury Stock	(309,977)	(300,467)
Common Shareholders' Equity	10,352,215	9,976,815
Total Capitalization	19,313,357	18,700,812
Total Liabilities and Capitalization	30,580,309	29,740,387
The Connecticut Light And Power Company [Member]
Current Assets:
Cash	1,057	2,356
Receivables, Net	352,536	355,140
Accounts Receivable from Affiliated Companies	21,214	16,757
Unbilled Revenues	99,879	102,137
Taxes Receivable	137,643	116,148
Regulatory Assets Current	268,318	220,344
Materials and Supplies	43,124	46,664
Prepayments and Other Current Assets	32,234	37,822
Total Current Assets	956,005	897,368
Property, Plant and Equipment, Net	7,156,809	6,809,664
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,369,028	1,475,508
Other Long-Term Assets	111,115	161,860
Total Deferred Debits and Other Assets	1,480,143	1,637,368
Total Assets	9,592,957	9,344,400
Current Liabilities:
Notes Payable To Affiliated Companies	277,400	133,400
Long-Term Debt - Current Portion	0	162,000
Accounts Payable - Current	267,764	272,971
Accounts Payable to Affiliated Companies	66,456	65,594
Obligations to Third Party Suppliers	60,746	73,624
Regulatory Liability Current	61,155	124,722
Deferred Tax Liabilities Current		34,100
Derivative Liabilities - Current	91,820	88,459
Other Liabilities - Current	110,631	153,420
Total Current Liabilities	935,972	1,074,190
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,820,865	1,642,805
Regulatory Liabilities Long-Term	74,830	81,298
Long-Term Derivative Liabilities	336,189	406,199
Accrued Pension, SERP and PBOP	271,056	273,854
Other Long-Term Liabilities	133,446	148,844
Total Deferred Credits and Other Liabilities	2,636,386	2,553,000
Capitalization:
Long-Term Debt	2,763,682	2,664,243
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
Common Shareholders' Equity:
Common Stock	60,352	60,352
Capital Surplus, Paid In	1,910,663	1,804,869
Retained Earnings	1,170,278	1,072,477
Accumulated Other Comprehensive Loss	(576)	(931)
Common Shareholders' Equity	3,140,717	2,936,767
Total Capitalization	6,020,599	5,717,210
Total Liabilities and Capitalization	9,592,957	9,344,400
NSTAR Electric Company [Member]
Current Assets:
Cash	3,346	12,773
Receivables, Net	229,936	234,481
Accounts Receivable from Affiliated Companies	4,034	40,353
Unbilled Revenues	29,464	29,741
Taxes Receivable	70,236	144,601
Regulatory Assets Current	348,408	198,710
Materials and Supplies	75,487	74,179
Prepayments and Other Current Assets	11,448	10,815
Total Current Assets	772,359	745,653
Property, Plant and Equipment, Net	5,655,458	5,335,436
Deferred Debits and Other Assets:
Regulatory Assets Long Term	1,112,977	1,179,100
Other Long-Term Assets	62,467	61,880
Total Deferred Debits and Other Assets	1,175,444	1,240,980
Total Assets	7,603,261	7,322,069
Current Liabilities:
Notes Payable	62,500	302,000
Long-Term Debt - Current Portion	200,000	4,700
Accounts Payable - Current	228,250	217,311
Accounts Payable to Affiliated Companies	38,648	63,517
Obligations to Third Party Suppliers	56,718	34,824
Renewable Portfolio Standards Compliance Obligation	104,847	60,750
Regulatory Liability Current	3,281	49,611
Deferred Tax Liabilities Current	0	55,136
Other Liabilities - Current	72,007	90,939
Total Current Liabilities	766,251	878,788
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,760,339	1,527,667
Regulatory Liabilities Long-Term	264,352	262,738
Accrued Pension, SERP and PBOP	209,153	235,529
Other Long-Term Liabilities	120,939	129,279
Total Deferred Credits and Other Liabilities	2,354,783	2,155,213
Capitalization:
Long-Term Debt	1,829,766	1,781,541
Noncontrolling Interest in Consolidated Subsidiary:
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	995,378	994,130
Retained Earnings	1,613,538	1,468,955
Accumulated Other Comprehensive Loss	545	442
Common Shareholders' Equity	2,609,461	2,463,527
Total Capitalization	4,482,227	4,288,068
Total Liabilities and Capitalization	7,603,261	7,322,069
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash	1,733	489
Receivables, Net	77,546	80,151
Accounts Receivable from Affiliated Companies	2,352	3,194
Unbilled Revenues	38,207	40,181
Taxes Receivable	43,128	14,571
Fuel, Materials and Supplies	156,868	148,139
Regulatory Assets Current	104,971	111,705
Prepayments and Other Current Assets	24,302	27,821
Total Current Assets	449,107	426,251
Property, Plant and Equipment, Net	2,855,363	2,635,844
Deferred Debits and Other Assets:
Regulatory Assets Long Term	257,873	293,115
Other Long-Term Assets	34,176	32,963
Total Deferred Debits and Other Assets	292,049	326,078
Total Assets	3,596,519	3,388,173
Current Liabilities:
Notes Payable To Affiliated Companies	231,300	90,500
Accounts Payable - Current	87,925	93,349
Accounts Payable to Affiliated Companies	24,214	33,734
Regulatory Liability Current	6,898	16,044
Deferred Tax Liabilities Current	0	36,164
Other Liabilities - Current	43,921	38,969
Total Current Liabilities	394,258	308,760
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	705,894	587,292
Regulatory Liabilities Long-Term	47,851	51,372
Accrued Pension, SERP and PBOP	89,579	93,243
Other Long-Term Liabilities	50,746	50,155
Total Deferred Credits and Other Liabilities	894,070	782,062
Capitalization:
Long-Term Debt	1,071,017	1,070,021
Common Shareholders' Equity:
Common Stock	0	0
Capital Surplus, Paid In	748,634	748,240
Retained Earnings	494,901	486,459
Accumulated Other Comprehensive Loss	(6,361)	(7,369)
Common Shareholders' Equity	1,237,174	1,227,330
Total Capitalization	2,308,191	2,297,351
Total Liabilities and Capitalization	3,596,519	3,388,173
Western Massachusetts Electric Company [Member]
Current Assets:
Cash	834
Receivables, Net	50,912	51,066
Accounts Receivable from Affiliated Companies	18,633	7,851
Unbilled Revenues	15,065	15,146
Taxes Receivable	33,407	18,126
Regulatory Assets Current	56,166	51,923
Marketable Securities - Current	0	28,658
Prepayments and Other Current Assets	7,882	7,607
Total Current Assets	182,899	180,377
Property, Plant and Equipment, Net	1,575,306	1,461,321
Deferred Debits and Other Assets:
Regulatory Assets Long Term	135,010	146,307
Marketable Securities	0	29,452
Other Long-Term Assets	24,875	18,731
Total Deferred Debits and Other Assets	159,885	194,490
Total Assets	1,918,090	1,836,188
Current Liabilities:
Notes Payable To Affiliated Companies	143,400	21,400
Long-Term Debt - Current Portion	0	50,000
Accounts Payable - Current	58,364	53,732
Accounts Payable to Affiliated Companies	19,896	14,328
Regulatory Liability Current	13,122	22,486
Deferred Tax Liabilities Current	0	18,089
Other Liabilities - Current	29,927	24,080
Total Current Liabilities	264,709	204,115
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	470,539	416,822
Regulatory Liabilities Long-Term	11,597	10,835
Other Postretirement Benefit Plan Liability		17,705
Accrued Pension, SERP and PBOP	19,515
Other Long-Term Liabilities	36,819	33,747
Total Deferred Credits and Other Liabilities	538,470	479,109
Capitalization:
Long-Term Debt	517,329	575,184
Common Shareholders' Equity:
Common Stock	10,866	10,866
Capital Surplus, Paid In	391,398	391,256
Retained Earnings	198,140	178,834
Accumulated Other Comprehensive Loss	(2,822)	(3,176)
Common Shareholders' Equity	597,582	577,780
Total Capitalization	1,114,911	1,152,964
Total Liabilities and Capitalization	1,918,090	1,836,188
Eversource Parent [Member]
Current Assets:
Cash	67	138
Accounts Receivable from Affiliated Companies	23,689	6,725
Notes Receivable from Affiliated Companies	850,300	741,150
Prepayments and Other Current Assets	41,254	41,366
Total Current Assets	915,310	789,379
Deferred Debits and Other Assets:
Equity Method Investments	8,915,178	8,387,976
Notes Receivable, Related Parties, Noncurrent	128,800	106,300
Deferred Tax Assets, Net, Noncurrent	143,054	177,908
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	48,314	34,483
Total Deferred Debits and Other Assets	12,467,157	11,938,478
Total Assets	13,382,467	12,727,857
Current Liabilities:
Notes Payable	1,098,453	654,825
Long-Term Debt - Current Portion	28,883	28,883
Accounts Payable - Current	78	141
Accounts Payable to Affiliated Companies	15,601	150,268
Other Liabilities - Current	60,999	71,778
Total Current Liabilities	1,204,014	905,895
Deferred Credits and Other Liabilities:
Other Long-Term Liabilities	134,908	125,608
Total Deferred Credits and Other Liabilities	134,908	125,608
Capitalization:
Long-Term Debt	1,691,330	1,719,539
Common Shareholders' Equity:
Common Stock	1,669,313	1,666,796
Capital Surplus, Paid In	6,262,368	6,235,834
Retained Earnings	2,797,355	2,448,661
Accumulated Other Comprehensive Loss	(66,844)	(74,009)
Treasury Stock	(309,977)	(300,467)
Common Shareholders' Equity	10,352,215	9,976,815
Total Capitalization	12,043,545	11,696,354
Total Liabilities and Capitalization	$ 13,382,467	$ 12,727,857

CONSOLIDATED STATEMENTS OF INCO

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

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income	$ 886,004	$ 827,065	$ 793,689
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,079	2,037	2,049
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,588)	315	(940)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	7,674	(30,330)	25,714
Other Comprehensive Income (Loss), Net of Tax, Total	7,165	(27,978)	26,823
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,682)
Comprehensive Income	885,650	791,568	812,830
The Connecticut Light And Power Company [Member]
Net Income	299,360	287,754	279,412
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	444	444	444
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(89)	12	(31)
Other Comprehensive Income (Loss), Net of Tax, Total	355	456	413
Comprehensive Income	299,715	288,210	279,825
NSTAR Electric Company [Member]
Net Income	344,542	303,088	268,546
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	103	442
Other Comprehensive Income (Loss), Net of Tax, Total	103	442
Comprehensive Income	344,645	303,530	268,546
Public Service Company Of New Hampshire [Member]
Net Income	114,442	113,944	111,397
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	1,162	1,162	1,162
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(154)	19	(54)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	0	(3)
Other Comprehensive Income (Loss), Net of Tax, Total	1,008	1,181	1,105
Comprehensive Income	115,450	115,125	112,502
Western Massachusetts Electric Company [Member]
Net Income	56,506	57,819	60,438
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	379	338	338
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(25)	3	(9)
Other Comprehensive Income (Loss), Net of Tax, Total	354	341	329
Comprehensive Income	56,860	58,160	60,767
Eversource Parent [Member]
Net Income	878,485	819,546	786,007
Other Comprehensive Income Loss Net Of Tax Period Increase Decrease Abstract
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	2,079	2,037	2,049
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,588)	315	(940)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	7,674	(30,330)	25,714
Other Comprehensive Income (Loss), Net of Tax, Total	7,165	(27,978)	26,823
Comprehensive Income	$ 885,650	$ 791,568	$ 812,830

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Common Shareholders Equity [Member]	The Connecticut Light And Power Company [Member]	The Connecticut Light And Power Company [Member]Common Stock [Member]	The Connecticut Light And Power Company [Member]Additional Paid-in Capital [Member]	The Connecticut Light And Power Company [Member]Retained Earnings [Member]	The Connecticut Light And Power Company [Member]Accumulated Other Comprehensive Income (Loss) [Member]	The Connecticut Light And Power Company [Member]Common Shareholders Equity [Member]	NSTAR Electric Company [Member]	NSTAR Electric Company [Member]Common Stock [Member]	NSTAR Electric Company [Member]Additional Paid-in Capital [Member]	NSTAR Electric Company [Member]Retained Earnings [Member]	NSTAR Electric Company [Member]Accumulated Other Comprehensive Income (Loss) [Member]	NSTAR Electric Company [Member]Stockholders Equity Total Member	NSTAR Electric Company [Member]Common Shareholders Equity [Member]	Public Service Company Of New Hampshire [Member]	Public Service Company Of New Hampshire [Member]Common Stock [Member]	Public Service Company Of New Hampshire [Member]Additional Paid-in Capital [Member]	Public Service Company Of New Hampshire [Member]Retained Earnings [Member]	Public Service Company Of New Hampshire [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Public Service Company Of New Hampshire [Member]Common Shareholders Equity [Member]	Western Massachusetts Electric Company [Member]	Western Massachusetts Electric Company [Member]Common Stock [Member]	Western Massachusetts Electric Company [Member]Additional Paid-in Capital [Member]	Western Massachusetts Electric Company [Member]Retained Earnings [Member]	Western Massachusetts Electric Company [Member]Accumulated Other Comprehensive Income (Loss) [Member]	Western Massachusetts Electric Company [Member]Common Shareholders Equity [Member]
Common Stock, Shares, Outstanding		314,053,634							6,035,205						100							301						434,653
Common Stock, Value, Outstanding		$ 1,662,547	$ 6,183,267	$ 1,802,714	$ (72,854)	$ (338,624)	$ 9,237,050		$ 60,352	$ 1,640,149	$ 839,628	$ (1,800)	$ 2,538,329		$ 0	$ 992,625	$ 1,210,405			$ 2,203,030		$ 0	$ 701,052	$ 395,118	$ (9,655)	$ 1,086,515		$ 10,866	$ 390,412	$ 160,577	$ (3,846)	$ 558,009
Net Income	$ 793,689							$ 279,412			279,412		279,412	$ 268,546			268,546			268,546	$ 111,397			111,397		111,397	$ 60,438			60,438		60,438
Dividends on Common Shares				(462,741)			(462,741)				(151,999)		(151,999)				(56,000)			(56,000)				(68,000)		(68,000)				(40,001)		(40,001)
Issuance of Common Shares		$ 2,804	8,274				11,078
Stock Issued During Period, Shares, New Issues		560,848
Dividends on Preferred Stock				(7,682)			(7,682)				(5,559)		(5,559)				(2,123)			(2,123)
Stock Issued During Period, Value, Employee Stock Ownership Plan										1,847			1,847										859			859			331			331
Long-Term Incentive Plan Activity			(10,748)				(10,748)
Other Comprehensive Income (Loss), Net of Tax	26,823				26,823		26,823	413				413									1,105				1,105	1,105	329				329	329
Stock Issued During Period, Value, Treasury Stock Reissued			17,381			12,087	29,468
Stock Issued During Period, Shares, Treasury Stock Reissued		659,077
Payments of Stock Issuance Costs										51			51
Net Income Attributable to Noncontrolling Interests	7,682
Capital Contributions from NU Parent								40,000		40,000			40,000								0
OtherChangesInShareholdersEquity			(5,409)				(5,409)
Common Stock, Shares, Outstanding		315,273,559							6,035,205						100							301						434,653
Common Stock, Value, Outstanding		$ 1,665,351	6,192,765	2,125,980	(46,031)	(326,537)	9,611,528		$ 60,352	1,682,047	961,482	(1,387)	2,702,494		$ 0	992,625	1,420,828			2,413,453		$ 0	701,911	438,515	(8,550)	1,131,876		$ 10,866	390,743	181,014	(3,517)	579,106
Net Income	827,065			827,065			827,065	287,754			287,754		287,754	303,088			303,088			303,088	113,944			113,944		113,944	57,819			57,819		57,819
Dividends on Common Shares				(496,524)			(496,524)				(171,200)		(171,200)				(253,000)			(253,000)				(66,000)		(66,000)				(59,999)		(59,999)
Issuance of Common Shares		$ 1,445	37,817				6,609
Stock Issued During Period, Shares, New Issues		288,941,000
Dividends on Preferred Stock				(7,519)			(7,519)				(5,559)		(5,559)				(1,961)			(1,961)
Stock Issued During Period, Value, Employee Stock Ownership Plan										2,771			2,771										1,329			1,329			$ 513			513
Long-Term Incentive Plan Activity			$ 9,657				(9,569)
Other Comprehensive Income (Loss), Net of Tax	(27,978)				(27,978)		(27,978)	456				456	456	442							1,181				1,181	1,181	341
Stock Issued During Period, Value, Treasury Stock Reissued						26,070	63,887
Stock Issued During Period, Shares, Treasury Stock Reissued		1,420,837,000
Payments of Stock Issuance Costs										51			51
Net Income Attributable to Noncontrolling Interests	$ 7,519
Capital Contributions from NU Parent								120,000		120,000			120,000								45,000											341
SharesIssuedInConnectionWithNstarMerger
SharesIssuedValueInConectionWithNstarMerger
OtherChangesInShareholdersEquity							9,316									1,505
Common Stock, Shares, Outstanding	316,983,337	316,983,337							6,035,205						100							301						434,653
Common Stock, Value, Outstanding		$ 1,666,796	$ 6,235,834	2,448,661	(74,009)	(300,467)	9,976,815		$ 60,352	1,804,869	1,072,477	(931)	2,936,767		$ 0	994,130	1,468,955			2,463,527		$ 0	748,240	486,459	(7,369)	1,227,330		$ 10,866	$ 391,256	178,834	(3,176)	577,780
OtherEquityImpactsOfMergerWithNstar
Net Income	$ 886,004			886,004			886,004	299,360			299,360		299,360	344,542			344,542			344,542	114,442			114,442		114,442	56,506			56,506		56,506
Dividends on Common Shares				(529,791)			(529,791)				(196,000)		(196,000)				(197,999)			(197,999)				(106,000)		(106,000)				(37,200)		(37,200)
Issuance of Common Shares		$ 2,517	$ 6,951				9,468
Stock Issued During Period, Shares, New Issues		503,443
Dividends on Preferred Stock				(7,519)			(7,519)				(5,559)		(5,559)				(1,960)			(1,960)
Stock Issued During Period, Value, Employee Stock Ownership Plan										743			743										394			394			142			142
Long-Term Incentive Plan Activity			(6,140)				(6,140)
Other Comprehensive Income (Loss), Net of Tax	7,165				7,165		7,165	355				355	355	$ 103				$ 103	$ 103		1,008				1,008	1,008	$ 354				354	354
Stock Issued During Period, Shares, Treasury Stock Reissued		(295,531)
Payments of Stock Issuance Costs										51			51
Net Income Attributable to Noncontrolling Interests	$ 7,519
Capital Contributions from NU Parent								$ 105,000		105,000			105,000								$ 0
OtherChangesInShareholdersEquity			3,653				3,653										1,248
IncreaseInTreasuryShares			22,070			(9,510)	12,560
Common Stock, Shares, Outstanding	317,191,249	317,191,249							6,035,205						100							301						434,653
Common Stock, Value, Outstanding		$ 1,669,313	$ 6,262,368	$ 2,797,355	$ (66,844)	$ (309,977)	$ 10,352,215		$ 60,352	$ 1,910,663	$ 1,170,278	$ (576)	$ 3,140,717		$ 0	$ 995,378	$ 1,613,538			$ 2,609,461		$ 0	$ 748,634	$ 494,901	$ (6,361)	$ 1,237,174		$ 10,866	$ 391,398	$ 198,140	$ (2,822)	$ 597,582

CONSOLIDATED STATEMENT OF CASH

CONSOLIDATED STATEMENT OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Operating Activities:
Net Income	$ 886,004	$ 827,065	$ 793,689
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	665,856	614,657	610,777
Deferred Income Tax Expense (Benefit)	491,736	443,259	431,413
Pension, SERP and PBOP Expense	96,017	99,056	195,698
Pension and PBOP Contributions	(162,452)	(211,649)	(342,184)
Regulatory Over/(Under) Recoveries, Net	(163,287)	6,853	(24,276)
Amortization of Regulatory Assets/(Liabilities), Net	22,339	10,704	206,322
Amortization of Rate Reduction Bonds	0	0	42,581
Other	(91,945)	39,523	56,071
(Payments)/Refunds Related to Spent Nuclear Fuel	(297,253)	132,138
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(39,797)	(122,139)	(163,549)
Increase Decrease in Fuel, Materials and Supplies	34,112	(41,310)	(14,811)
Taxes Receivable/(Accrued)	30,282	(323,224)	(50,950)
Accounts Payable	(91,618)	144,743	(54,619)
Other Current Assets and Liabilities, Net	44,031	15,797	(22,623)
Net Cash Flows Provided by Operating Activities	1,424,025	1,635,473	1,663,539
Investing Activities:
Investments in Property, Plant and Equipment	(1,724,139)	(1,603,744)	(1,456,787)
Proceeds from Sales of Marketable Securities	799,165	488,789	627,532
Purchases of Marketable Securities	(717,114)	(491,220)	(679,784)
Other Investing Activities	(17,062)	14,380	67,816
Net Cash Flows Used in Investing Activities	(1,659,150)	(1,591,795)	(1,441,223)
Financing Activities:
Cash Dividends on Common Stock	(529,791)	(475,227)	(462,741)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,682)
Increase/(Decrease) in Short-Term Debt	(242,122)	285,075	(397,000)
Issuance of Long-Term Debt	1,225,000	725,000	1,680,000
Retirements of Long-Term Debt	(216,700)	(576,551)	(929,885)
Retirements of Rate Reduction Bonds	0	0	(82,139)
Other Financing Activities	(8,499)	883	(25,253)
Net Cash Flows Provided by/(Used in) Financing Activities	220,369	(48,339)	(224,700)
Net Increase/(Decrease) in Cash	(14,756)	(4,661)	(2,384)
Cash - Beginning of Year	38,703	43,364	45,748
Cash - End of Year	23,947	38,703	43,364
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	299,360	287,754	279,412
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	215,289	188,837	177,603
Deferred Income Tax Expense (Benefit)	135,994	130,949	130,038
Pension, SERP and PBOP Expense	14,091	14,992	24,416
Regulatory Over/(Under) Recoveries, Net	(53,781)	(20,502)	28,298
Amortization of Regulatory Assets/(Liabilities), Net	12,318	59,336	4,870
Other	(36,385)	(1,342)	(3,478)
(Payments)/Refunds Related to Spent Nuclear Fuel	(242,231)	68,610
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(29,195)	(78,631)	(56,593)
Increase Decrease in Fuel, Materials and Supplies	22,810	13,063	9,997
Taxes Receivable/(Accrued)	(13,517)	(126,376)	(41,594)
Accounts Payable	(16,910)	68,891	(66,225)
Other Current Assets and Liabilities, Net	(9,514)	6,838	8,513
Net Cash Flows Provided by Operating Activities	298,329	612,419	495,257
Investing Activities:
Investments in Property, Plant and Equipment	(523,849)	(515,710)	(434,934)
Other Investing Activities	(716)	12,653	2,650
Net Cash Flows Used in Investing Activities	(524,565)	(503,057)	(432,284)
Financing Activities:
Cash Dividends on Common Stock	(196,000)	(171,200)	(151,999)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Increase/(Decrease) in Short-Term Debt	0	0	(89,000)
Issuance of Long-Term Debt	350,000	250,000	400,000
Increase/(Decrease) in Notes Payable to Affiliate	144,000	(153,900)	(117,800)
Retirements of Long-Term Debt	(162,000)	(150,000)	(125,000)
Capital Contributions from NU Parent	105,000	120,000	40,000
Other Financing Activities	(10,504)	(3,584)	(6,379)
Net Cash Flows Provided by/(Used in) Financing Activities	224,937	(114,243)	(55,737)
Net Increase/(Decrease) in Cash	(1,299)	(4,881)	7,236
Cash - Beginning of Year	2,356	7,237	1
Cash - End of Year	1,057	2,356	7,237
NSTAR Electric Company [Member]
Operating Activities:
Net Income	344,542	303,088	268,546
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	196,770	188,693	180,298
Deferred Income Tax Expense (Benefit)	173,155	108,133	48,808
Pension, SERP and PBOP Expense	10,786	6,760	35,731
Pension Contribution	(9,886)	(120,306)	(82,000)
Regulatory Over/(Under) Recoveries, Net	(124,323)	57,696	(119,433)
Amortization of Regulatory Assets/(Liabilities), Net	(12,989)	(6,330)	230,148
Amortization of Rate Reduction Bonds	0	0	15,054
Bad Debt Expense	14,228	24,740	28,108
Other	(56,063)	(51,478)	4,428
(Payments)/Refunds Related to Spent Nuclear Fuel	783	30,193
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(35,525)	(18,853)	(45,405)
Increase Decrease in Fuel, Materials and Supplies	406	(29,943)	3,227
Taxes Receivable/(Accrued)	77,429	(122,746)	(38,003)
Accounts Payable	21,961	9,753	31,875
Accounts Payable Related Parties	11,450	115,092	(44,491)
Other Current Assets and Liabilities, Net	44,302	38,535	(6,468)
Net Cash Flows Provided by Operating Activities	657,026	533,027	510,423
Investing Activities:
Investments in Property, Plant and Equipment	(469,466)	(465,028)	(476,600)
Decrease in Restricted Cash	0	0	37,604
Other Investing Activities	0	0	400
Net Cash Flows Used in Investing Activities	(469,466)	(465,028)	(438,596)
Financing Activities:
Cash Dividends on Common Stock	(197,999)	(253,000)	(56,000)
Cash Dividends on Preferred Stock	(1,960)	(1,961)	(2,123)
Increase/(Decrease) in Short-Term Debt	(239,500)	198,500	(172,500)
Issuance of Long-Term Debt	250,000	300,000	200,000
Retirements of Long-Term Debt	(4,700)	(301,650)	(1,650)
Retirements of Rate Reduction Bonds	0	0	(43,493)
Other Financing Activities	(2,828)	(5,136)	(1,735)
Net Cash Flows Provided by/(Used in) Financing Activities	(196,987)	(63,247)	(77,501)
Net Increase/(Decrease) in Cash	(9,427)	4,752	(5,674)
Cash - Beginning of Year	12,773	8,021	13,695
Cash - End of Year	3,346	12,773	8,021
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	114,442	113,944	111,397
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	105,372	98,436	91,581
Deferred Income Tax Expense (Benefit)	83,776	94,813	75,693
Pension, SERP and PBOP Expense	4,580	7,197	26,846
Pension and PBOP Contributions	(982)	(2,482)	(112,964)
Regulatory Over/(Under) Recoveries, Net	41	(11,875)	(8,481)
Amortization of Regulatory Assets/(Liabilities), Net	16,276	(29,602)	(20,387)
Amortization of Rate Reduction Bonds	0	0	19,748
Other	8,677	10,095	16,079
(Payments)/Refunds Related to Spent Nuclear Fuel	979	14,453
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(4,750)	(15,576)	2,412
Increase Decrease in Fuel, Materials and Supplies	(8,729)	(19,403)	(33,391)
Taxes Receivable/(Accrued)	(23,909)	(23,857)	26,462
Accounts Payable	(22,203)	17,796	2,632
Other Current Assets and Liabilities, Net	953	(5,972)	(9,520)
Net Cash Flows Provided by Operating Activities	274,523	247,967	188,107
Investing Activities:
Investments in Property, Plant and Equipment	(308,036)	(256,159)	(186,009)
Decrease in Restricted Cash	0	(1,013)	22,040
Other Investing Activities	306	(139)	(88)
Net Cash Flows Used in Investing Activities	(307,730)	(257,311)	(164,057)
Financing Activities:
Cash Dividends on Common Stock	(106,000)	(66,000)	(68,000)
Increase/(Decrease) in Short-Term Debt	0	4,000	23,200
Issuance of Long-Term Debt	0	75,000	250,000
Increase/(Decrease) in Notes Payable to Affiliate	140,800	0	0
Retirements of Long-Term Debt	0	(50,000)	(198,235)
Retirements of Rate Reduction Bonds	0	0	(29,294)
Capital Contributions from NU Parent	0	45,000	0
Other Financing Activities	(349)	1,703	(4,084)
Net Cash Flows Provided by/(Used in) Financing Activities	34,451	9,703	(26,413)
Net Increase/(Decrease) in Cash	1,244	359	(2,363)
Cash - Beginning of Year	489	130	2,493
Cash - End of Year	1,733	489	130
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	56,506	57,819	60,438
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	43,362	41,886	37,568
Deferred Income Tax Expense (Benefit)	39,428	34,108	87,028
Regulatory Over/(Under) Recoveries, Net	(17,501)	1,925	8,458
Amortization of Regulatory Assets/(Liabilities), Net	14,545	(6,228)	(3,206)
Amortization of Rate Reduction Bonds	0	0	7,780
Other	(6,421)	(2,005)	3,381
(Payments)/Refunds Related to Spent Nuclear Fuel	(56,784)	18,883
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(17,822)	39,872	(53,292)
Taxes Receivable/(Accrued)	(15,281)	(22,454)	19,840
Accounts Payable	(2,602)	1,269	7,456
Other Current Assets and Liabilities, Net	5,594	(11,796)	3,356
Net Cash Flows Provided by Operating Activities	43,024	153,279	178,807
Investing Activities:
Investments in Property, Plant and Equipment	(134,551)	(116,205)	(128,786)
Proceeds from Sales of Marketable Securities	186,444	73,198	70,778
Purchases of Marketable Securities	(128,861)	(73,888)	(71,390)
Other Investing Activities	0	3,200	7,401
Net Cash Flows Used in Investing Activities	(76,968)	(113,695)	(121,997)
Financing Activities:
Cash Dividends on Common Stock	(37,200)	(59,999)	(40,001)
Issuance of Long-Term Debt	0	0	80,000
Increase/(Decrease) in Notes Payable to Affiliate	122,000	21,400	(31,900)
Retirements of Long-Term Debt	(50,000)	0	(55,000)
Retirements of Rate Reduction Bonds	0	0	(9,352)
Other Financing Activities	(22)	(985)	(558)
Net Cash Flows Provided by/(Used in) Financing Activities	34,778	(39,584)	(56,811)
Net Increase/(Decrease) in Cash	834	0	(1)
Cash - Beginning of Year		0	1
Cash - End of Year	834		0
Eversource Parent [Member]
Operating Activities:
Net Income	878,485	819,546	786,007
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity In Earnings Of Subsidiaries	900,824	848,435	785,650
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries	602,300	609,800	407,837
Deferred Income Tax Expense (Benefit)	16,880	7,956	15,159
Other	(22,864)	9,409	29,169
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(16,980)	88,800	14,704
Taxes Receivable/(Accrued)	(14,426)	23,178	13,295
Accounts Payable Related Parties	(134,730)	5,942	(7,058)
Other Current Assets and Liabilities, Net	6,832	14,484	(1,411)
Net Cash Flows Provided by Operating Activities	414,673	730,680	472,052
Investing Activities:
Capital Contributions To Subsidiaries	(218,500)	(437,553)	(65,400)
(Increase) Decrease In Notes Receivable From Affiliated Company	(131,650)	86,100	5,475
Other Investing Activities	12,000	0	(1,862)
Net Cash Flows Used in Investing Activities	(338,150)	(351,453)	(61,787)
Financing Activities:
Cash Dividends on Common Stock	(529,791)	(475,227)	(462,741)
Increase/(Decrease) in Short-Term Debt	(2,622)	86,575	(135,500)
Issuance of Long-Term Debt	450,000	0	750,000
Retirements of Long-Term Debt	0	0	(550,000)
Other Financing Activities	5,819	9,528	(12,418)
Net Cash Flows Provided by/(Used in) Financing Activities	(76,594)	(379,124)	(410,659)
Net Increase/(Decrease) in Cash	(71)	103	(394)
Cash - Beginning of Year	138	429
Cash - End of Year	$ 67	$ 138	$ 429

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Significant Accounting Policies [Text Block]	EVERSOURCE ENERGY AND SUBSIDIARIES THE CONN ECTICUT LIGHT AND POWER COMPANY NSTAR E LECTRIC COMPANY AND SUBSIDIARY PUBLIC SERVICE COMPANY O F NEW HAMPSHIRE AND SUBSIDIARY WESTERN MASSACHUSETTS ELECTRIC COMPANY COMBINED NOTES TO FINANCIAL STATEMENTS Refer to the Glossary of Terms included in this combined Annual Report on Form 10-K for abbreviations and acronyms used throughout the co mbined notes to the financial statements. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES A. About Eversource , CL&P, NSTAR Electric, PSNH and WMECO Eversource Energy : Eversource Energy is a public utility holding company primarily engaged , through its wholly owned regulated utility subsidiaries , in the energy delivery business. Eversource Energy 's wholly owned regulated utility subsidiaries consist of CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas. Eversource provides energy delivery service to approximately 3. 6 million electric and natural gas customers through these six regulated utilities in Connecticut, Massachusetts and New Hampshire . On April 30 , 2015, the Company's legal name was changed from Northeast Utilities to Eversource Energy. CL&P, NSTAR Electric, PSNH and WMECO are each doing business as Eversource Energy. Eversource , CL&P, NSTAR Electric, PSNH and WMECO are reporting companies under the Securities Exchange Act of 1934. Eversource Energy is a public utility holding company under the Public Utility Holding Company Act of 2005. Arrangements among the regulated electric companies and other Eversource companies, outside agencies and other utilities covering interconnections, interchange of electric power and sales of utility property are subject to regulation by the FERC. The Regulated companies are subject to regulation of rates, accounting and other matters by the FERC and/or applicable state regulatory commissions (the PURA for CL&P and Yankee Gas, the DPU for NSTAR Electric, WMECO and NSTAR Gas, and the NHPUC for PSNH). Regulated Companies: CL&P, NSTAR Electric, PSNH and WMECO furnish franchised retail electric service in Connecticut, Massachusetts and New Hampshire. Yankee Gas and NSTAR Gas are engaged in the distribution and sale of natural gas to c ustomers within Connecticut and Massachusetts, respectively. CL&P, NSTAR Electric, PSNH and WMECO's results include the operations of their respective distribution and transmission businesses. PSNH and WMECO's distribution results include the operations of their respective generation businesses. Eversource also has a regulated subsidiary, NPT, which was formed to construct, own and operate the Northern Pass line, a HVDC transmission line from Québec to New Hampshire under development that will interconnect with a new HVDC transmission line being developed by a transmission subsidiary of HQ. Other: Eversource S ervice , Eversource 's service company, Rocky River Realty Company, a wholly-owned real estate subsidiary of Eversource , Renewable Properties, Inc., an indirect, wholly-owned subsidiary of Eversource , and Properties, Inc., a wholly-owned subsidiary of PSNH, provide support services to Eversource , including its R egulated companies. Eversource Gas Transmission LLC, a n indirect, wholly-owned subsidiary of Eversource, holds an equity interest in the Access Northeast project. B. Basis of Presentation The consolidated financial statements of Eversource , NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource , NSTAR Electric and PSNH and the financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements." The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership interest in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements . Eversource's utility subsidiaries' distribution (including generation ) and transmission businesses are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information. Certain r eclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation and as a result of the adoption of new accounting guidance . See Note 1C, "Summary of Significant Accounting Policies – Accounting Standards," for further information. In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource . The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on t he balance sheets of Eversource , CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Board s of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric. As of December 31, 201 5 and 201 4 , Eversource 's carrying amount of goodwill was approximately $3.5 billion. Eversource performs an assessment for possible impairment of its goodwill at least annually. Eversource completed its annual goodwill impairment test for each of its reporting units as of October 1, 201 5 and determined that no impairment exists. See Note 2 1 , "Goodwill , " for further information. C. Accounting Standards Accounting Standards Issued but not Yet Effective : In May 2014, the Financial Accounting Standards Board (FASB) issued an Accounting Standards Update (ASU) 2014-09, Revenue from Contracts with Customers , which amends existing revenue recognition guidance and is required to be applied retrospectively (either to each reporting period presented or cumulatively at the date of initial application). In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers – Deferral of the Effective Date , which defers the effective date of ASU 2014-09 to the first quarter of 2018, with 2017 application permitted. The Company is reviewing the requirements of ASU 2014-09 and will implement the standard in the first quarter of 2018. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. In January 2016, the FASB issued ASU 2016-01, Financial Ins truments-Overall: Recognition and Measurement of Financial Assets and Liabilities , which is required to be implemented in the first quarter of 2018. The Company is reviewin g the requirements of the ASU. The ASU will remove the available-for-sale designation for equity securities, whereby changes in fair value are recorded in other comprehensive income in shareholders' equity, and will require changes in fair value of all equity securities to be recorded in earnings beginning on January 1, 2018, with the unrealized gain or loss on available-for-sale equity securities as of that date reclassified to retained earnings as a cumulative effect of adoption. T he fair value of available-for-sale equity securities subject to this guidance as of December 31, 2015 w as approximately $ 52 million. The remaining available-for-sale equity securities included in marketable securities on the balance sheet are held in nuclear decommissioning trusts and are subject to regulatory accounting treatment and will not be impacted by this guidance. Implementation of the ASU for other financial instruments is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. On February 25, 2016, the FASB issued ASU 2016-02, Leases , which changes existing lease accounting guidance and is required to be applied in the first quarter of 2019, with earlier application permitted. The ASU is required to be implemented for leases beginning on the date of initial application. For prior periods presented, leases are required to be recognized and measured using a modified retrospective approach. The Company is reviewing the requirements of ASU 2016-02. Recently Adopted Accounting Standards: In April 2015, the FASB issued ASU 2015-03, Simplifying the Presentation of Debt Issuance Costs , that change d the balance sheet presentation of debt issuance costs. Un der the ASU , issuance costs related to debt are presented on the balance sheet as a direct deduction from the carrying amount of the debt liability rather than as a deferred cost. The new accounting guidance is effective for interim and annual periods beginning in the first quarter of 2016 with early adoption permitted and is required to be applied retrospectively . On December 31, 2015, the Company adopted the new accounting guidance and applied it retrospectively to all prior periods presented in the financial statements. The adoption of this ASU did not have a material effect on the balance sheets and had no impact on the results of operations or cash flows of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. See Note 8, "Long-Term Debt," for the prior year amounts that have been retrospectively adjusted. On November 20, 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes, that required all deferred tax liabilities and assets , along with any related valuation allowance, be classified as noncurrent on the balance sheet. This new accounting guidance is effective for interim and annual periods beginning in the first quarter of 2017 with early adoption permitted and may be applied either prospectively or retrospectively. On Dece mber 31, 2015, the Company adopted the new accounting guidance and applied it prospectively . The adoption of this ASU did not have a material effect on the balance sheets and had no impact on the results of operations or cash flows of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. The current portion of Accumulated Deferred Income Taxes as of December 31, 2 014, which was included in Total Current Liabilities on the balance sheets, was $160.3 million for Eversource, $ 34.1 million for CL&P, $55.1 million for NSTAR Electric, $36.2 million for PSNH, and $18.1 million for WMECO. D. Cash and Cash Equivalents Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets. E. Provision for Uncollectible Accounts Eversource , including CL&P, NSTAR Electric, PSNH and WMECO, presents its receivables at estimated net realizable value by maintaining a provision for uncollectible accounts. This provision is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. The estimate is based upon historical collection and write-off experience and man agement's assessment of collecta bility from customers. Management co ntinuously assesses the collecta bility of r eceivables and adjusts collecta bility estimates based on actual experience. Receivable balances are written off against the provision for uncollectible accounts when the customer accounts are terminated and these balances are deemed to be uncollectible . The PURA allows CL&P and Yankee Gas to accelerate the recovery of accounts receivable balances attributable to qualified customers under financial or medical duress (uncollectible hardship accounts receivable) outstanding for greater than 180 days and 90 days , respectively . The DPU allows WMECO and NSTAR Gas to also recover in rates amounts associated with certain uncollectible hardship accounts receivable. Certain of NSTAR Electric's uncollectible hardsh ip accounts receivable are expected to be recovered in future rates , similar to WMECO and NSTAR Gas. Uncollectible customer account balances, which are expected to be recovered in rates, are included in Regulatory Assets or Other Long-Term Assets on the balance sheets . The total provision for uncollectible accounts and for uncollectible hardship accounts , which is included in the total provision, are included in Receivables, Net on the balance sheets, and w ere as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2015 2014 2015 2014 Eversource $ 190.7 $ 175.3 $ 118.5 $ 91.5 CL&P 79.5 84.3 68.1 74.0 NSTAR Electric 52.6 40.7 25.3 - PSNH 8.7 7.7 - - WMECO 14.0 9.9 7.4 6.2 F. Fuel, Materials and Supplies and Allowance Inventory Fuel, Materials and Supplies include natural gas, coal, biomass and oil inventories a s well as materials purchased primarily for construction or operation and maintenance purposes. Natural gas, coal , biomass and oil inventories are valued at their respective weighted average cost. Materials and supplies are valued at the lower of average cost or market. Fuel, Materials and Supplies also include Renewable Energy Certificates (RECs) , which are purchased from suppliers of renewable sources of generation. RECs are used to meet state mandated Renewable Portfolio Standards requirements. PSNH is subject to federal and state laws and regulations that regulate emissions of air pollutants, including SO 2 , CO 2 , and NO x related to its regulated generation units, and uses SO 2 , CO 2 , and NO x emissions allowances. At the end of each compliance period, PSNH is required to relinquish SO 2 , CO 2 , and NO x emissions allowances corresponding to the actual respective emissions emitted by its generating units over the compliance period. SO 2 and NO x emissions allowances are obtained through an annual allocation from the federal and state regulators that are granted at no cost and through purchases from third parties. CO 2 emissions allowances are obtained through an annual allocation from the state regulator that are granted at no cost and are acquired through auctions and through purchases from third parties. SO 2 , CO 2 , and NO x emissions allowances are charged to expense based on their weighted average cost as they are utilized against emissions volumes at PSNH's generating units. SO 2 , CO 2 , and NO x emissions allowances are recorded within Fuel, Materials and Supplies on the balance sheet and are classified as short-term or long-term depending on the period in which they are expected to be utilized against act ual emi ssions. Current SO 2 and CO 2 emissions allowances were classified as Fuel, Materials and Supplies on the balance sheets and long-term SO 2 and CO 2 emissions allowances were classified as Other Long-Term Assets on the balance sheets. The carry ing amount of fuel, materials and supplies , RECs , and emission allowances were as follows: As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) Eversource Electric PSNH Eversource Electric PSNH Current: Fuel $ 152.5 $ - $ 103.4 $ 164.3 $ - $ 95.1 Materials and Supplies 131.2 32.2 44.6 159.5 49.1 52.2 RECs 50.9 43.3 7.0 25.8 25.1 0.7 Emission Allowances 1.9 - 1.9 0.1 - 0.1 Long-Term: Emission Allowances 17.5 - 17.5 20.1 - 20.1 G . Deposits As of December 31, 201 5 , Eversource , CL&P , NS TAR Electric and PSNH had $ 17.1 million , $ 0.7 million , $ 8.5 million and $ 1.5 million , respectively, of cash collateral posted not subject to master netting agreements, with ISO-NE related to energy purchase transactions , which was included in Prepayments and Other Current Assets on the balance sheets. As of December 31, 201 4 , these amounts were $ 9.9 million , $ 1.2 million and $ 2.5 million for Eversource, CL&P and PSNH , respectively. H . Fair Value Measurements Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans , the nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs, and the estimate d fair value of preferred stock and long-term debt. Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below: Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Determination of Fair Value: The valuation techniques and inputs used in Eversource 's fair value meas urements are described in Note 4 , " Der ivative Instruments, " Note 5 , " Marketable Securities, " Note 6 , " Asset Retirement Obligations, " Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pensions," and Note 13 , " Fair Value of Financial Instru ments " to the financial statements. I . Derivative Accounting M any of the Regulated companies' cont racts for the purchase and sale of ene rgy or energy- related products are derivatives . The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts, as contract settlements are recovered from, or refunded to, customers in future rates. The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts . All of these judgments can have a signif icant impact on the financial statements. The judgmen t applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal and accrual accounting is terminated , and fair value accounting is applied prospectively. The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. All c hanges in the fair value of derivative contracts are recorded as regulatory asset s or liabilities and do not impact net income. For further information regarding derivative contracts , see Note 4 , " Derivative I nstruments, " to the financial statements. J. Equity Method Investments Equity investments are included in Other Long-Term Assets on the balance sheets and net earnings related to these equity investments are included in Other Income, Net on the statements of income. Regional Decommissioned Nuclear Companies : CL&P, NSTAR Electric, PSNH and WMECO own common stock in three regional nuclear generation companies (CYAPC, YAEC and MYAPC, collectively referred to as the Yankee Companies), each of which owned a single nuclear generating facility that has been decom missioned. For CL&P, NSTAR Electric, PSNH and WME CO, the respective investments in CYAPC, YAEC and MYAPC are accounted for under the equity method. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership int erest in each of these entities is greater than 50 percent. I ntercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements . CL&P's, NSTAR Electric's, PSNH's and WMECO's o wnership interests in the Yankee C ompanies and the total carrying values, which were included in Other Long-Term Assets on their respective balance sheets , were as follows: Ownership Interests (percent) Carrying Amount (in millions) As of December 31, 2015 and 2014 As of December 31, CYAPC YAEC MYAPC 2015 2014 CL&P 34.5 % 24.5 % 12.0 % $ 1.2 $ 1.2 NSTAR Electric 14.0 14.0 4.0 0.5 0.5 PSNH 5.0 7.0 5.0 0.3 0.3 WMECO 9.5 7.0 3.0 0.3 0.3 For further information on the Yankee Companies, see Note 1 1 C, " Commitmen ts and Contingencies - Contractual Obligations - Yankee Companies , " to the financial statements. Infrastructure and Other Investments : As of December 31, 201 5 and 201 4 , Eversource ha d an equity ownership interest in an energy investment fund of $ 30.3 million and $ 17 .8 million, respectively . Eversource had a 40 percent equity ownership interest in the Algonquin Gas Transmission, LLC ( legal entity that owns Access Northeast assets) of $ 10.7 million as of December 31, 2015. K. Revenues Regulated Companies ' Retail Revenues : The Regulated companies' retail revenues are based on rates approved by the ir respective state regulatory commissions. In general, rates can only be changed through formal proceedings with the state regulatory commissions. The Regulated companies' rates are designed to recover the costs to provide service to their customers, and include a return on investment . The Regulated companies also utilize regulatory commission-approved tracking mechanisms to recover certain costs on a fully-reconciling basis. These tracking mechanisms require ra tes to be changed periodically to ensure recovery of actual costs incurred . CL&P ( effective December 1, 2014), WMECO , and NSTAR Gas (effective January 1, 2016) , each have a regulatory commission approv ed revenue decoupling mechanism . Distribution r evenues are decoupled from customer sales volumes, which breaks the relationship between sales volumes and revenues recognized. CL&P and WMECO reconcile their annual base distribution rate recovery to pre-established levels of baseline distribution delivery service revenues. Any difference between the allowed level of distribution revenue and the actual amount incurred during a 12-month period is adjusted through rates in the following period. A significant portion of the Regulated companies' retail revenues relate to the recovery of costs incurred for the sale of electricity and natural gas purchased on behalf of customers. These energy supply costs are recovered from customer s in rates through cost tracking mechanisms. Energy purchases are re corded in Purchased Power, Fuel and Transmission, and the sale s of energy associated with these purchases are recorded in Operating Revenues . Regulated Companies' Unbilled Revenues: Because customers are billed throughout the month based on pre-determined cycles rather than on a calendar month basis, an estimate of electricity or natural gas delivered to customers for which the customers have not yet been billed is calculated as of the balance sheet date. Unbilled revenues are included in Operating Revenues on the statements of income and in Current A ssets on the balance sheets. Actual amounts billed to customers when meter readings become available may vary from the estimated amount. The Regulated companies estimate unbilled sales monthly using the daily load cycle method. The daily load cycle method allocates billed sales to the current calendar month based on the daily load for each billing cycle. The billed sales are subtracted from total month load, net of delivery losses, to estimate unbilled sales. Unbilled revenues are estimated by first allocating unbilled sales to the respective customer classes, then applying an estimated rate by customer class to those sales. The estimate of unbilled revenues can significantly impact the amount of revenues recorded at NSTAR Electric and PSNH because they do not have a revenue decoupling mechanism. CL&P and WMECO record a regulatory deferral to reflect the actual allowed amount of revenue for decoupling . Regulated Companies' Transmission Revenues - Wholesale Rates: Wholesale transmission revenues are recovered through FERC approved formula rates. Wholesale transmission revenues for CL&P, NSTAR Electric, PSNH, and WMECO are collected through a combination of regional and local rates, both of which are under the ISO New England Transmission, Markets and Services Tariff (ISO-NE Tariff). The ISO-NE Tariff includes Reg ional Network Service (RNS), Schedule 21 – E S rate schedules , which recover the costs of transmission and other transmission-related services for CL&P, PSNH and WMECO , and Schedule 21 - NSTAR rate schedules , which recover costs of transmission and other transmission-related services for NSTAR Electric. The RNS rate, administered by ISO-NE and billed to all New England transmission load , including CL&P, NSTAR Electri c, PSNH and WMECO's distribution businesses, is reset on June 1 st of each year and recovers the revenue requirements associated with Pool Transmission F acilities ( PTF) that benefit the entire New England region. The Schedule 21 – ES rate and Schedule 21 - NSTAR rate are administered by Eversource and recover any PTF costs not recovered under RNS rates, as well as the cost of transmission facilities associated with the respective utility's local system. The Schedule 21 - ES rate is reset on January 1 st and June 1 st of each year, while the Schedule 21 - NSTAR rate is reset on June 1 st of each year. The Schedule 21 – ES rate and Schedule 21 - NSTAR rate calculations recover total transmission revenue requirements net of revenues received from other sources (i.e., RNS, rentals, etc.), thereby ensuring that Eversource recovers all of CL&P's, NSTAR Electric's, PSNH's and WMECO's regional and local transmission revenue requirements in accordance with the ISO-NE Tariff. The RNS, Schedule 21 – ES rate and Schedule 21 - NSTAR rate provide for the annual reconciliation and recovery or refund of estimated costs to actual costs. The financial impacts of differences between actual and estimated costs are deferred for future recovery from, or refunded to, transmission customers. See Note 11E, "Commitment s and Contingencies – FERC ROE Complaints," for complaints filed at the FERC relating to Eversource 's ROE. Regulated Companies' Transmission Revenues - Retail Rates: A significant portion of the Eversource transmission segment revenue comes from ISO-NE charges to the distribution businesses of CL&P, NSTAR Electric, PSNH and WMECO, each of which recovers these costs through rates charged to their retail customers. CL&P, NSTAR Electric, PSNH and WMECO each have a retail transmission cost tracking mechanism as part of their rates, which allows the electric distribution companies to charge their retail customers for transmission costs on a timely basis. L. Operating Expenses Costs related to fuel and natural gas included in Purc hased Power, Fuel and Transmission on the statements of income were as follows: For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Eversource - Natural Gas and Fuel $ 516.7 $ 599.4 $ 466.5 PSNH - Fuel 85.4 113.4 104.8 M. Allowance for Funds Used During Construction AFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the Regulated companies' utility plant on the balance sheet . The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Other Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income . AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense . The Regulated companies' average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings and capitalization (preferred stock, long-term debt and common equity) , as appropriate . The average rate is applied to average eligible CWIP amounts to calculate AFUDC. AFUDC costs and the weighted-average AFUDC rates were as follows : Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2015 2014 2013 Borrowed Funds $ 7.2 $ 5.8 $ 4.1 Equity Funds 18.8 13.7 7.1 Total AFUDC $ 26.0 $ 19.5 $ 11.2 Average AFUDC Rate 3.9% 3.4% 2.7% For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars, NSTAR NSTAR NSTAR except percentages) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Borrowed Funds $ 2.6 $ 2.0 $ 1.0 $ 1.0 $ 1.9 $ 2.0 $ 0.6 $ 0.9 $ 2.2 $ 0.5 $ 0.5 $ 0.5 Equity Funds 5.2 4.3 1.2 1.7 2.9 3.8 0.6 1.7 2.9 - 0.2 1.0 Total AFUDC $ 7.8 $ 6.3 $ 2.2 $ 2.7 $ 4.8 $ 5.8 $ 1.2 $ 2.6 $ 5.1 $ 0.5 $ 0.7 $ 1.5 Average AFUDC Rate 5.5% 3.2% 1.8% 4.4% 3.4% 2.5% 1.8% 5.6% 3.7% 0.5% 1.1% 6.1% N. Other Income, Net Items included within Other Income, Net on the statements of income primarily consist of investment income /( loss), interest income, AFUDC related to equity funds, and equity in earnings of equity method investees . Investment income /( loss) primarily relate s to debt and equity securities held in trust . For further information, see Note 5 , "Marketable Securities," to the financial statements. For further information on AFUDC related to equity funds, see Note 1M, "Summary of Significant Accounting Policies – Allowance for Funds Used During Construction," to the financial statements. O. Other Taxes Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respe

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Public Utilities Disclosure [Text Block]	2 . REGULATORY ACCOUNTING Eversource's Regulated companies are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for rate-regulated operations, which consider s the effect of regulation on the timing of the recognition of certain revenues and expenses. The Regulated companies' financial statements reflect the effects of the rate-making process. The rates charged to the customers of Eversource's Regulated companies are designed to collect each company's costs to provide service, including a return on investment. Management believes it is probable that each of the Regulated companies will recover their respective investments in long-lived assets, including regulatory assets. If management were to determine that it could no longer apply the accounting guidance applicable to rate-regulated enterprises to any of the Regulate d companies' operations, or if management could not conclude it is probable that costs would be recovered from customers in future rates, the costs would be charged to net income in the period in which the determination is made. Regulatory Assets: The c omponents of regulatory assets we re as follows: Eversource As of December 31, (Millions of Dollars) 2015 2014 Benefit Costs $ 1,828.2 $ 2,016.0 Derivative Liabilities 388.0 425.5 Income Taxes, Net 650.9 635.3 Storm Restoration Costs 436.9 502.8 Goodwill-related 484.9 505.4 Regulatory Tracker Mechanisms 526.5 350.5 Contractual Obligations - Yankee Companies 134.4 123.8 Other Regulatory Assets 134.0 167.3 Total Regulatory Assets 4,583.8 4,726.6 Less: Current Portion 845.8 672.5 Total Long-Term Regulatory Assets $ 3,738.0 $ 4,054.1 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Benefit Costs $ 413.6 $ 479.9 $ 164.2 $ 84.9 $ 445.4 $ 515.9 $ 174.3 $ 85.0 Derivative Liabilities 380.8 1.3 - - 410.9 4.5 - - Income Taxes, Net 444.4 85.7 34.5 31.8 437.7 83.7 38.0 35.5 Storm Restoration Costs 271.4 110.9 31.5 23.1 319.6 103.7 47.7 31.8 Goodwill-related - 416.3 - - - 433.9 - - Regulatory Tracker Mechanisms 45.1 311.0 101.2 40.1 16.1 141.4 103.5 33.0 Other Regulatory Assets 82.0 56.3 31.5 11.3 66.1 94.7 41.3 12.9 Total Regulatory Assets 1,637.3 1,461.4 362.9 191.2 1,695.8 1,377.8 404.8 198.2 Less: Current Portion 268.3 348.4 105.0 56.2 220.3 198.7 111.7 51.9 Total Long-Term Regulatory Assets $ 1,369.0 $ 1,113.0 $ 257.9 $ 135.0 $ 1,475.5 $ 1,179.1 $ 293.1 $ 146.3 Benefit Costs: Eversource's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other PBOP plans. The liability recorded by the Regulated companies to recognize the funded status of their retiree benefit plans is offset by a regulatory asset in lieu of a charge to Accumulated Other Comprehensive Income/(Loss), reflecting ultimate recovery from customers through rates. The regulatory asset is amortized as the actuarial gains and losses and prior service cost are amortized to net periodic benefit cost for the pension and PBOP plans. All amounts are remeasured annually . Regulatory accounting is als o applied to the portions of Eversource's service company costs that support the Regulated companies, as these amounts are also recoverable. As these regulatory assets do not represent a cash outlay for the Regulated companies, no carrying charge is recovered from customers. CL&P, NSTAR Electric, PSNH and WMECO recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric and WMECO each recover their quali fied pension and PBOP expenses related to distribution operations through rate reconciling mechanism s that fully track the change in net pension and PBOP expenses each y ear . Derivative Liabilities: R egulatory assets are recorded as an offset to derivative liabilities and relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates . These assets are excluded from rate base and are being recovered as the actual settlement s occur over the duration of the contracts. See Note 4 , "Derivative Instruments," to the financial statements for further information on these contracts . Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. The amortization period of these assets varies depending on the nature and/or remainin g life of the underlying assets and liabilities. For further information regarding income taxes, see Note 1 0 , "Income Taxes," to the financial statements. Storm Restoration Costs: The storm restoration cost deferrals relate to costs incurred for major storm events at CL&P, NSTAR Electric, PSNH and WMECO that each company expects to recover from customers. A storm must meet certain criteria to qualify as a major storm with the criteria specific to each state jurisdiction and utility company . Once a storm qualifies as a major storm , all qualifying expenses incurred during storm restoration efforts are deferred and recovered from customers . In addition to storm restoration costs, CL&P and PSNH are each allowed to recover pre-staging storm costs . Of the total deferred storm restoration costs, $197 million is pending regulatory approval (including $106 million at NSTAR Electric, $61 million at PSNH, and $30 million at WMECO). Management believes the storm restoration costs were prudent and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire , and that recovery from customers is probable through the applicable regulatory recovery process. Each electric utility has sought, or is seeking , recovery of its deferred storm restoration costs through its applicable regulatory recovery process. Each electric utility company earns a return on its deferred storm restoration cost regulatory asset balance. Goodwill-related: The goodwill regulatory asset originated from a 1 999 merger transaction and the DPU allowed its recovery in NSTAR Electric and NSTAR Gas rates . This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40-year period , and , as of December 31, 201 5 , there were 2 4 years of amortization remaining. Regulatory Tracker Mechanisms: T he Regulated companies' approved rates are designed to recover their costs incurred to provide service to customers. The Regul ated companies recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The difference s between the costs incurred (or the rate recovery all owed) and the actual revenues are recorded as regulatory assets (for undercollections) or as regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recorded on all material regulatory tracker mechanisms. CL&P, NSTAR Electric, PSNH and WMECO each recover , on a fully reconciling basis, the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs (including LBR at NSTAR Electric) , low income assistance programs, certain uncollectible accounts receivable for hardship customers, and restructuring and stranded costs as a result of deregulati on . Energy procurement costs at PSNH include the costs related to its generating stations and at WMECO include the costs related to its solar generation . CL& P (effective December 1, 2014) and WMECO each have a regulatory commission approved revenue decoupling mechanism. Distribution r evenues are decoupled from customer sales volumes, which breaks the relationship between sales volumes and revenues recognized. CL&P and WMECO reconcile their annual base distribution rate recovery to pre-established levels of baseline distribution delivery service revenues. Any difference between the allowed level of distribution revenu e and the actual amount received during a 12-month period is adjusted through rates in the following period. CL&P and WMECO's revenue decoupling mechanisms permit recovery of an annual base amount of distribution revenues of $1.059 billion and $ 132.4 million, respectively. Contractual Obligations - Yankee Companies: CL&P, NSTAR Electric, PSNH and WMECO are responsible for their proportionate share of the remaining costs of the CYAPC, YAEC and MYAPC nuclear facilities, including nuclear fuel storage . A portion of these cos ts was recorded as a regulatory asset. Amounts for CL&P are earning a return and are being recovered through the CTA. Amounts for NSTAR Electric and WMECO are being recovered without a return through the transition charge. Amounts for PSNH were fully recovered in 2006. As a result of Eversource's consolidation of CYAPC and YAEC, Eversource's regulatory asset balance also includes the regulatory assets of CYAPC and YAEC, which total ed $ 110.9 million and $ 97.8 million as of December 31, 201 5 and 201 4 , respectively. I ntercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements. Other Regulatory Assets: Other Regulatory Assets primarily include asset retirement obligations, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt , purchase power contract termination costs and various other item s. Regulatory Costs in Other Long-Term Assets: The Regulated companies had $ 75.3 million ( including $ 3.1 million for CL&P, $ 35.4 million for NSTAR Electric, $ 4.8 million for PSNH and $ 16.7 million for WMECO) and $ 60.5 million ( including $ 1.3 million for CL&P, $ 33.2 million for NSTAR Electric, $0.9 million for PSNH, and $ 11 million for WMECO) of additional regulatory costs as of December 31, 201 5 and 201 4 , respectively, that were included in Other Long-Term Assets on the balance sheets. These amounts represent incurred costs for which recovery has not yet been specifically approved by the applicable regulatory agency. However, based on regulatory policies or past precedent on similar costs, management believes it is probable that these costs will ultimately be approved and recovered from customers in rates. The NSTAR Electric balance as of December 31 , 2015 and 2014 primarily related to the deferral of certain bad debt costs expected to be recovered in future rates . Equity Return on Regulatory Assets: For rate-making purposes, the Regulated companies recover the carrying cost s related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $ 1.5 million and $ 1.7 million for CL&P as of December 31, 2015 and 2014, respectively. These carrying costs will be recovered from customers in future rates. As of December 31, 2015 and 2014, this equity return , which is not recorded on the balance sheets , totaled $ 48.3 million and $ 43.3 million , respectively, for PSNH. These amounts include $25 million of equity return on the Clean Air Project costs that PSNH has agreed not to bill customers pending NHPUC approval of a generation divestiture settlem ent agreement . For further information on the divestiture, see Note 11H, "Commitments and Contingencies – PSNH Generation Restructuring." Regulatory Liabilities: The compon ents of regulatory liabilities wer e as follows: Eversource As of December 31, (Millions of Dollars) 2015 2014 Cost of Removal $ 437.1 $ 439.9 Regulatory Tracker Mechanisms 99.7 192.3 AFUDC - Transmission 66.1 67.1 Other Regulatory Liabilities 18.5 50.8 Total Regulatory Liabilities 621.4 750.1 Less: Current Portion 107.8 235.0 Total Long-Term Regulatory Liabilities $ 513.6 $ 515.1 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Cost of Removal $ 24.1 $ 257.4 $ 47.2 $ 2.8 $ 19.7 $ 258.3 $ 50.3 $ 1.1 Regulatory Tracker Mechanisms 56.2 3.3 3.4 12.9 122.6 20.7 14.2 22.3 AFUDC - Transmission 51.5 5.7 - 8.9 53.6 4.4 - 9.1 Other Regulatory Liabilities 4.2 1.3 4.2 0.1 10.1 28.9 2.9 0.8 Total Regulatory Liabilities 136.0 267.7 54.8 24.7 206.0 312.3 67.4 33.3 Less: Current Portion 61.2 3.3 6.9 13.1 124.7 49.6 16.0 22.5 Total Long-Term Regulatory Liabilities $ 74.8 $ 264.4 $ 47.9 $ 11.6 $ 81.3 $ 262.7 $ 51.4 $ 10.8 Cost of Removal: Eversource's Regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense and the cumulative amount collected from customers but not yet expended is recognized as a regulatory liability . Expended costs that exceed amounts collected from customers are recognized as regulatory assets, as they are probabl e of recovery in future rates. AFUDC - Transmission: Regulatory liabilities were recorded by CL&P and WMECO for AFUDC accrued on certain reliability-related transmission projects to reflect local rate base recovery as a result of a FERC-approv ed transmission tariff . A r egulatory liability was recorded by NSTAR Electric for AFUDC accrued on certain reliability-related transmission projects through December 31, 2015 to reflect local rate base recovery. The se regulatory liabilities for CL&P, NSTAR Electric and WMECO will be amortized over the depreciable life of the related transmission assets. 2015 Regulatory Developments: FERC ROE Complaints: As a result of the actions taken by the FERC and other developments in the pending ROE complaint proceedings described in Note 11 E , "Commitments and Contingencies – FERC ROE Complaints ," Eversource recorded reserves for the first and second ROE complaints , which were recorded as a regulatory liability and as a reduction to operating revenues. T he cumulative pre-tax reserves (excluding interest) as of December 31, 2015 , which include the impact of refunds given to customers, totaled $ 39.1 million for Eversource (including $21.4 million for CL&P, $8.5 million for NSTAR Electric, $3.1 million for PSNH, and $6.1 million for WMECO). NS TAR Electric and NSTAR Gas Comprehensive Settlement Agreement : On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the " Settlement " ) as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric ' s energy efficiency programs for 2009 through 2011 (11 dockets in total). In 2015, as a result of the DPU order, NSTA R Electric and NSTAR Gas commenced refunding a combined $44.7 million to customers, which was recorded as a regulatory liability . Refunds to customers will continue through December 2016 . As a result of the Settlement, NSTAR Electric increased its operating revenues and decreased its amortization expense in 2015, resulting in the recognition of a $21.7 million pre-tax benefit in 2015. NSTAR Electric Basic Service Bad Debt Adder : On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had removed energy-related bad debt costs from base distribution rates effective January 1, 2006. As a result of the DPU order, in the first quarter of 2015, NSTAR Electric increased its regulatory assets and reduced its operations and maintenance expense by an under recovered amount of $24.2 million for energy-related bad debt costs through 2014, resulting in a pre-tax benefit in 2015 . NSTAR Electric filed for recovery of the energy-related bad debt costs regulatory asset from customers and on November 20, 2015 the DPU approved NSTAR Electric's proposed rate increase to recover these costs over a 12-month period, effective January 1, 2016. CL&P Distribution Rates : On July 2, 2015, PURA issued a final order that approved a settlement agreement filed on May 19, 2015, which allows for an increase to rate base of approximately $163 million associated with ADIT, including a regulatory asset to recover the incremental revenue requirement for the period December 1, 2014 through November 30, 2015 over a subsequent 24-month period. The rate base increase provided an increase to total allowed annual revenue requirements of $18.4 million beginning December 1, 2014 . As part of the settlement agreement , the $18.4 million for the period December 1, 2014 through November 30, 2015 was recorded as a regulatory asset with a corresponding increase in Operating Revenues , and is being collected from customers in rates over a 24-month period beginning December 1, 2015. NSTAR Gas Distribution Rates : On October 30, 2015, the DPU issued its order in the NSTAR Gas distribution rate case, which approved an annualized base rate increase of $15.8 million , plus other increases of approximately $11.5 million, mostly relating to recovery of pension and PBOP expenses and the Hopkinton GSA, effective January 1, 2016. In the order, the DPU also approved an authorized regulatory ROE of 9.8 percent, the establishment of a revenue decoupling mechanism, the recovery of certain bad debt expenses, and a 52.1 percent equity component of its capital structure. On November 19, 2015, NSTAR Gas filed a motion for reconsideration of the order with the DPU seeking the correction of mathematical errors and other plant and cost of service items. As a result of this order, Eversource recorded regulatory deferrals for costs that have been approved for recovery or are expected to be approved for recovery in future rate proceedings, which resulted in the recognition of a $17.2 million pre-tax benefit in 2015. Included in this amount is a $10.5 million pre-tax benefit recorded at NSTAR Electric for certain uncollectible hardship accounts receivable that are expected to be recovered in future rates given the allowed recoveries of uncollectible hardship accounts receivable by WMECO and NSTAR Gas.

PROPERTY, PLANT AND ACCUMULATED

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Property Plant And Equipment Disclosure [Text Block]	3. PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION Utility property, plant and equipment is recorded at original cost. Original cost includes materials , labor, con struction overhead and AFUDC for regulated property. The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operating Expenses as incurred. The following tables summarize the investments in utility property, plant and equipment by asset category : Eversource As of December 31, (Millions of Dollars) 2015 2014 Distribution - Electric $ 13,054.8 $ 12,495.2 Distribution - Natural Gas 2,727.2 2,595.4 Transmission - Electric 7,691.9 6,930.7 Generation 1,194.1 1,170.9 Electric and Natural Gas Utility 24,668.0 23,192.2 Other (1) 558.6 551.3 Property, Plant and Equipment, Gross 25,226.6 23,743.5 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,141.1) (5,777.8) Other (255.6) (231.8) Total Accumulated Depreciation (6,396.7) (6,009.6) Property, Plant and Equipment, Net 18,829.9 17,733.9 Construction Work in Progress 1,062.5 913.1 Total Property, Plant and Equipment, Net $ 19,892.4 $ 18,647.0 (1) These assets are primarily comprised of building improvements , computer software , hardware and equipment at Eversource Service . As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Distribution $ 5,377.2 $ 5,100.5 $ 1,804.8 $ 812.3 $ 5,158.8 $ 4,895.5 $ 1,696.7 $ 784.2 Transmission 3,618.0 2,131.3 928.2 964.9 3,274.0 1,928.5 789.7 891.0 Generation - - 1,158.1 36.0 - - 1,136.5 34.4 Property, Plant and Equipment, Gross 8,995.2 7,231.8 3,891.1 1,813.2 8,432.8 6,824.0 3,622.9 1,709.6 Less: Accumulated Depreciation (2,041.9) (1,886.8) (1,171.0) (307.0) (1,928.0) (1,761.4) (1,090.0) (297.4) Property, Plant and Equipment, Net 6,953.3 5,345.0 2,720.1 1,506.2 6,504.8 5,062.6 2,532.9 1,412.2 Construction Work in Progress 203.5 310.5 135.3 69.1 304.9 272.8 102.9 49.1 Total Property, Plant and Equipment, Net $ 7,156.8 $ 5,655.5 $ 2,855.4 $ 1,575.3 $ 6,809.7 $ 5,335.4 $ 2,635.8 $ 1,461.3 As o f December 31, 2015, PSNH had $1.2 billion in gross generation utility plant assets and related Accumulated Depreciation of $ 522.4 million. These generation assets are the subject of a divestiture agreement entered into on June 10, 2015 between Eversource, PSNH and key New Hampshire officials whereby, among other reso lutions, PSNH has agreed to divest these generation assets upon NHPUC approval . Upon completi on of the divestiture process, remaining costs not recovered by the sale of these assets (stranded costs) will be recovered via bonds that will be secured by a non- bypassable charge or other recovery mechanisms in rates billed to PSNH's customers. See Note 11H , “Commitments and Contingencies – PSNH Generation Restructuring,” for further information. Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution) . The composite rates , which are subject to approval by the appropriate state regulatory agency , include a cost of removal component (other than PSNH Generation) , which is collected f rom customers over the lives of the plant assets and is recognized as a regulatory liability . Depreciation rates are applied to property from the time it is placed in service. Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability. The depreciation rates for the various classes of utility property , plant and equipment aggregate to composite rates as follows: (Percent) 2015 2014 2013 Eversource 2.9 % 3.0 % 2.8 % CL&P 2.7 % 2.7 % 2.5 % NSTAR Electric 3.0 % 3.0 % 2.9 % PSNH 3.2 % 3.0 % 3.0 % WMECO 2.7 % 3.3 % 2.9 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2015 (Years) Eversource CL&P NSTAR Electric PSNH WMECO Distribution 34.8 37.3 31.9 31.3 30.5 Transmission 41.6 38.7 43.8 41.6 50.0 Generation 30.7 - - 30.9 25.0 Other 14.1 - - - -

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	4 . DERIVATIVE INSTRUMENTS The Regulated companies purchase and procure energy and energy-related products, which are subject to price volatility, for their customers. The costs associated with supplying energy to customers are recoverable from customers in future rates. The Regulated companies manage the risks associated with the price volatility of energy and energy-related products through the use of derivative and nonderivative contracts. Many of the derivative contracts meet the definition of, and are designated as, normal and qualify for accrual accounting under the applicable accounting guidance. The costs and benefits of derivative contracts that meet the definition of normal are recognized in Operating Expenses or Operating Revenues on the statements of income, as applicable, as electricity or natural gas is delivered. Derivative contracts that are not designated as normal are recorded at fair value as current or long-term Derivative Assets or Derivative Liabilities on the balance sheets. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivatives, as contract settlement amounts are recovered from, or refunded to, customers in their respective energy supply rates. The gross fair values of derivative assets and liabilities with the same counterparty are offset and reported as net Derivative Assets or Derivative Liabilities, with current and long-term portions, on the balance sheets. The following table presents the gross fair values of contracts , categorized by risk type , and the net amount s recorded as current or long-term derivative asset s or liabilities : As of December 31, 2015 2014 Commodity Supply Net Amount Commodity Supply Net Amount and Price Risk Recorded as and Price Risk Recorded as (Millions of Dollars) Management Netting (1) a Derivative Management Netting (1) a Derivative Current Derivative Assets: Level 3: Eversource $ 16.7 $ (10.9) $ 5.8 $ 16.2 $ (6.6) $ 9.6 CL&P 16.7 (10.9) 5.8 16.1 (6.6) 9.5 NSTAR Electric - - - 0.1 - 0.1 Long-Term Derivative Assets: Level 2: Eversource $ 0.1 $ - $ 0.1 $ - $ - $ - Level 3: Eversource 62.0 (19.3) 42.7 93.5 (19.2) 74.3 CL&P 60.7 (19.3) 41.4 93.5 (19.2) 74.3 NSTAR Electric 1.3 - 1.3 - - - Current Derivative Liabilities: Level 2: Eversource $ (5.8) $ - $ (5.8) $ (9.8) $ - $ (9.8) Level 3: Eversource (92.3) - (92.3) (90.0) - (90.0) CL&P (91.8) - (91.8) (88.5) - (88.5) NSTAR Electric (0.5) - (0.5) (1.5) - (1.5) Long-Term Derivative Liabilities: Level 2: Eversource $ - $ - $ - $ (0.3) $ - $ (0.3) Level 3: Eversource (337.1) - (337.1) (409.3) - (409.3) CL&P (336.2) - (336.2) (406.2) - (406.2) NSTAR Electric (0.9) - (0.9) (3.1) - (3.1) (1) Amounts represent derivative assets and liabilities that Eversource elected to record net on the balance sheets. These amounts are subject to master netting agreements or similar agreements for which the right of offset exists . The business activities that result in the recognition of derivative assets also create e xposure to various counterparties. As of December 31, 201 5 , Eversource 's and CL&P's derivative assets were exposed to counterparty credit risk. Of Eversource 's and CL&P's derivative assets , approximately $ 47 million was contracted with inve stment grade entities. For further information on the fair value of d erivative contracts, see Note 1 H , "Summary of Significant Accounting Policies - Fair Value Measurements ," and Note 1 I , "Summary of Significant Accounting Policies - Derivative Accounting ," to the financial statements. Derivative Contracts At Fair Value with Offsetting Regulatory Amounts Commodity Supply and Price Risk Management : As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of the costs or benefits of each contract borne by or allocated to CL&P and 20 percent borne by or allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020. NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019. As of December 31, 2015 and 2014 , Eversource had NYMEX financial contracts for natural gas futures in order to reduce variability associated with the purchase price of approximately 9.1 million and 8.8 million MMBtu of natural gas, respectively. For the years ended December 31, 2015, 2014 and 2013, there were losses of $60.2 million and gains of $134.4 million and $160.6 million, respectively, deferred as regulatory c osts, which reflect the change in fair value associated with Eversource's derivative contracts. Credit Risk Certain of Eversource's derivative contracts contain credit risk contingent provisions. These provisions require Eversource to maintain investment grade credit ratings from the major rating agencies and to post collateral for contracts in a net liability position over specified credit limits. As of December 31, 2015 and 2014, E versource had $ 5.8 million and $ 10 million, respectively, of derivative contracts in a net liability position that were subject to credit risk contingent provisions and would have been required to post additional c ollateral of $ 5.8 million and $ 10 million, respectively, if Eversource parent's unsecured debt credit ratings had been downgraded to below investment grade. Fair Value Measurements of Derivative Instruments Derivative contracts classified as Level 2 in the fair value hierarchy relate to the financial contracts for natural gas futures. Prices are obtained from broker quotes and are based on actual market activity. The contracts are valued using NYMEX natural gas prices. Valuations of these contracts also incorporate discount rates using the yield curve approach. The fair value of derivative contracts classified as Level 3 utilizes significant unobservable inputs. The fair value is modeled using income techniques, such as discounted cash flow valuations adjusted for assumptions relating to exit price. Significant observable inputs for valuations of these contracts include energy and energy-related product prices in future years for which quoted prices in an active market exist. Fair value measurements categorized in Level 3 of the fair value hierarchy are prepared by individuals with expertise in valuation techniques, pricing of energy and energy-related products, and accounting requirements. The future power and capacity prices for periods that are not quoted in an active market or established at auction are based on available market data and are escalated based on estimates of inflation in order to address the full time period of the contract. Valuations of derivative contracts using a discounted cash flow methodology include assumptions regarding the timing and likelihood of scheduled payments and also reflect non-performance risk, including credit, using the default probability approach based on the counterparty's credit rating for assets and the Company's credit rating for liabilities. Valuations incorporate estimates of premiums or discounts that would be required by a market participant to arrive at an exit price, using historical market transactions adjusted for the terms of the contract. The following is a summary of Eversource's , including CL&P's and NSTAR Electric's, Level 3 derivative contracts and the range of the significant unobservable inputs utilized in the ir respective valuations over the duration of the contracts: As of December 31, 2015 2014 Range Period Covered Range Period Covered Capacity Prices: Eversource $ 10.81 - 15.82 per kW-Month 2016 - 2026 $ 5.30 - 12.98 per kW-Month 2016 - 2026 CL&P $ 10.81 - 12.60 per kW-Month 2019 - 2026 $ 11.08 - 12.98 per kW-Month 2018 - 2026 NSTAR Electric $ 10.81 - 15.82 per kW-Month 2016 - 2019 $ 5.30 - 11.10 per kW-Month 2016 - 2019 Forward Reserve: Eversource, CL&P $ 2.00 per kW-Month 2016 - 2024 $ 5.80 - 9.50 per kW-Month 2015 - 2024 REC Prices: Eversource, NSTAR Electric $ 45 - 51 per REC 2016 - 2018 $ 38 - 56 per REC 2015 - 2018 Exit price premiums of 5 percent to 22 percent are also applied on these contracts and reflect the uncertainty and illiquidity premiums that would be required based on the most recent market activity available for similar type contracts . Valuations using significant unobservable inputs: The following table presents changes in the Level 3 category of derivative assets and derivative liabilities measured at fair value on a recurring basis. The derivative assets and liabilities are presented on a net basis. (Millions of Dollars) Eversource CL&P NSTAR Electric Derivatives, Net: Fair Value as of January 1, 2014 $ (635.2) $ (630.6) $ (7.3) Net Realized/Unrealized Gains Included in Regulatory Assets and Liabilities 141.3 139.7 4.3 Settlements 78.5 80.0 (1.5) Fair Value as of December 31, 2014 $ (415.4) $ (410.9) $ (4.5) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (52.1) (51.3) (0.8) Settlements 86.6 81.4 5.2 Fair Value as of December 31, 2015 $ (380.9) $ (380.8) $ (0.1) Significant increases or decreases in future energy or capacity prices in isolation would decrease or increase, respectively, the fair value of the derivative l iability. Any increases in risk premiums would increase the fair value of the derivative liabili t y . Changes in these fair values are recorded as a regulato ry asset or liability and do not impact net income.

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Marketable Securities [Text Block]	5 . MARKETABLE SECURITIES Eversource maintains trusts that hold marketable securities to fund certain non-qualified executive benefits. These trusts are not subject to regulatory oversight by state or federal agencies. CYAPC and YAEC maintain legally restricted trusts, each of which holds marketable securities, to fund the decommissioning and spent nuclear fuel removal obligations of their nuclear fuel storage facilities. WMECO maintained a spent nuclear fuel trust to fund WMECO's pre-1983 spent nuclear fuel obligation . In late 2015, this trust was liquidated to satisfy the spent nuclear fuel obligation with the DOE . For further information, see Note 8, "Long-Term Debt." Trading Securities: Eversource has elected to record certain equity securities as trading securities, with the changes in fair values recorded in Other Income, Net on the statements of income. As of December 31, 2015 and 2014, these securities were classified as Level 1 in the fair value hierarchy and totaled $ 14.2 million and $85.1 mil lion, respectively. For the years ended December 31, 2015, 2014 and 2013, net gains on these securities of $ 2 million , $1.9 million and $10.2 million , respectively, were recorded in Other Income, Net on the statements of income. Dividend income is recorded in Other Income, Net when dividends are declared. In 2015, certain of the securities classified as trading securities were sold and the proceeds were re-invested in equity securities designated as available-for-sale securities. Available-for-Sale Securities: The following is a summary of available-for-sale securities , which are recorded at fair value and are included in current and long-term Marketable Securities on the balance sheets. As of December 31, 2015 2014 Pre-Tax Pre-Tax Pre-Tax Pre-Tax Amortized Unrealized Unrealized Amortized Unrealized Unrealized (Millions of Dollars) Cost Gains Losses Fair Value Cost Gains Losses Fair Value Eversource Debt Securities (1) (2) $ 256.5 $ 4.5 $ (0.6) $ 260.4 $ 313.0 $ 7.5 $ (0.3) $ 320.2 Equity Securities (1) 215.3 59.2 (3.4) 271.1 160.6 73.3 - 233.9 WMECO Debt Securities (2) - - - - 58.2 - (0.1) 58.1 Amounts include CYAPC's and YAEC's marketable securities held in nuclea r decommissioning trusts of $436.9 million and $450.8 million as of December 31, 2015 and 2014, respectively. Unrealized gains and losses for the nuclear decommissioning trusts are recorded in Marketable Securities with the corresponding offset to Oth er Long-Term Liabilities on the balance sheets, with no impact on the statements of income. Unrealized gains and losses on debt securities held by WMECO were recorded in Marketable Securities with the corresponding offset to Other Long-Term Assets on the balance sheets. Unrealized Losses and Other-than-Temporary Impairment: There have been no significant unrealized losses, other-than-temporary i mpairments or credit losses in 2015 or 2014 . Factors considered in determining whether a credit loss exists include the duration and severity of the impairment, adverse conditions specifically affecting the issuer, and the payment history, ratings and rating changes of the security. For asset-backed debt securities, underlying collateral and expected future cash flows are also evaluated. Realized Gains and Losses: Realized gains and losses on available-for-sale securities a re recorded in Other Income, Net for Eversource ' s benefit trust and a re offset in Other Long-Term Liabilities for CYAPC and YAEC. Eversource utilizes the specific identification basis method for the Eversource benefit trust and the average cost basis method for the CYAPC and YAEC nuclear decommissioning trusts to compute the realized gains and losses on the sale of a vailable-for-sale securities. Contractual Maturities : As of December 31 , 201 5 , the contractual maturities of available-for-sale debt securities were as follows: Eversource Amortized Fair (Millions of Dollars) Cost Value Less than one year (1) $ 33.3 $ 33.2 One to five years 50.2 50.7 Six to ten years 56.6 57.2 Greater than ten years 116.4 119.3 Total Debt Securities $ 256.5 $ 260.4 (1) Amounts in the Less than one year category include securities in the CYAPC and YAEC nuclear decommissioning trusts, which are restricted and are classified in long-term Marketable Securities on the balance sheet s . Fair Value Measurements: The following table presents the marketable securities recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy : Eversource As of December 31, (Millions of Dollars) 2015 2014 Level 1: Mutual Funds and Equities $ 285.3 $ 319.0 Money Market Funds 26.9 24.9 Total Level 1 $ 312.2 $ 343.9 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 46.6 $ 51.3 Corporate Debt Securities 43.9 49.1 Asset-Backed Debt Securities 20.0 54.1 Municipal Bonds 111.4 116.3 Other Fixed Income Securities 11.6 24.5 Total Level 2 $ 233.5 $ 295.3 Total Marketable Securities $ 545.7 $ 639.2 As of December 31, 2014, the WMECO spent nuclear fuel trust included investments in money market funds of $ 4.3 million classified as Level 1 in the fair value hierarchy, and $ 14.7 million of corporate debt securities, $14.5 million of a sset-backed debt securities, $13 million of municipal bonds and $11.6 million of other fixed income securities classified as Level 2 in the fair value hierarchy . The trust was liquidated in late 2015. U.S. government issued debt securities are valued using market approaches that incorporate transactions for the same or similar bonds and adjustments for yields and maturity dates. Corporate debt securities are valued using a market approach, utilizing recent trades of the same or similar instrument and also incorporating yield curves, credit spreads and specific bond terms and conditions. Asset-backed debt securities include collateralized mortgage obligations, commercial mortgage backed securities, and securities collateralized by auto loans, credit card loans or receivables. Asset-backed debt securities are valued using recent trades of similar instruments, prepayment assumptions, yield curves, issuance and maturity dates, and tranche information. Municipal bonds are valued using a market approach that incorporates reported trades and benchmark yields. Other fixed income securities are valued using pricing models, quoted prices of securities with similar characteristics, and discounted cash flows.

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Asset Retirement Obligation Disclosure [Text Block]	6. ASSET RETIREMENT OBLIGATIONS Eversource , including CL&P, NSTAR Electric, PSNH and WMECO, recognizes a liability for the fair value of an ARO on the obligation date if the liability's fair value can be reasonably estimated and is conditional on a future event. Settlement dates and future costs are reasonably estimated when sufficient information becomes available. Management has identified various categories of AROs, primarily certain assets containing asbestos and hazardous contamination , and has performed fair value calculation s reflecting expected probabilities for settlement scenarios . The fair value of an ARO is recorded as a liability in Other Long -Term Liabilities with a corresponding amount included in Property, Plant and Equipment, Net on the balance sheets. The ARO assets are depreciated, and the ARO liabilities are accreted over the estimated life of the obligation with corresponding credits recorded as accumulated depreciation and ARO liabilities, respectively. As the Regulated companies are rate-regulated on a cost-of-service basis, these companies apply regulatory accounting guidance and both the depreciation and accretion costs associated with the Regulated companies' AROs are recorded as increases to Regulatory Assets on the balance sheets . A reconciliation of the beginning and ending carrying amounts of ARO liabilities are as follows: Eversource As of December 31, (Millions of Dollars) 2015 2014 Balance as of Beginning of Year $ 426.3 $ 424.9 Liabilities Incurred During the Year 6.6 1.3 Liabilities Settled During the Year (18.2) (19.5) Accretion 26.5 25.1 Revisions in Estimated Cash Flows (11.1) (5.5) Balance as of End of Year $ 430.1 $ 426.3 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Balance as of Beginning of Year $ 35.3 $ 34.3 $ 20.6 $ 5.9 $ 35.0 $ 32.8 $ 19.5 $ 4.5 Liabilities Incurred During the Year - 6.2 0.4 - - - - 1.1 Liabilities Settled During the Year - (1.5) - (0.1) (1.1) - - - Accretion 2.2 1.8 1.3 0.4 1.9 1.5 1.1 0.3 Revisions in Estimated Cash Flows (3.7) (5.5) (0.7) (0.5) (0.5) - - - Balance as of End of Year $ 33.8 $ 35.3 $ 21.6 $ 5.7 $ 35.3 $ 34.3 $ 20.6 $ 5.9 Eversource 's amounts include CYAPC and YAEC's AROs of $ 319.1 million and $ 317.3 million as of December 31, 2015 and 2014 , respectively. The fair value of the ARO for CY APC and YAEC include s uncertainties of the fuel off- load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste. The incremental asset recorded as an offset to the ARO liability was fully depreciated since the plants have no remaining useful life. Any changes in the assumptions used to calculate the fair value of the ARO liability are recorded with a corresponding of fset to the related regulatory a sset. The assets held in the CYAPC and YAEC nuclear decommissioning trust s are restricted for sett l ing the ARO and all other decommissioning obligations. For further information on the assets held in the nuclear decommissioning trust s , see Note 5 , " Marketable Securities, " to the financial statements .

SHORT TERM DEBT

SHORT TERM DEBT	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Short Term Debt Text Block	7. SHORT-TERM DEBT Short-Term Borrowing Limits: The amount of short-term borrowings that may be incurred by CL&P , NSTAR Electric and WMECO is subject to periodic approval by the FERC. As a result of the NHPUC having jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings. On June 16, 2015, t he FERC granted authorization that allow s CL&P and WMECO to incur total short-term borrowings up to a maximum of $600 million and $300 million, respectively, effective January 1, 2016 through December 31, 2017 . On June 11, 2014 , the FERC granted authorization to allow NSTAR Electric to issue total short-term debt securities in an aggregate principal amount not to exceed $655 million outstanding at an y one time, effective October 24, 2014 through October 23, 201 6 . PSNH is authorized by regulation of the NHPUC to incur short-term borrowings up to 10 percent of net fixed plant plus an additional $60 million until further ordered by the NHPUC . As of December 31, 201 5 , PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled approximately $ 325 million. CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. As of December 31, 201 5 , CL&P had $ 327.3 million of unsecured debt capacity available under this authorization. Yankee Gas and NSTAR Gas are not required to obtain approval from any state or federal authority to incur short-term debt. Credit Agreements and Commercial Paper Programs: Eversource parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year $1.45 billion revolving credit facility. On October 26, 2015, this revolving credit facility was amended and restated and the termination date was extended to September 4, 2020. Under the revolving credit facility, CL&P has a borrowing sublimit of $600 million, and PSNH and WMECO each have borrowing sublimits of $300 million. The revolving credit facility serves to backstop Eversource parent's $1.45 billion commercial paper program. The commercial paper program allows Eversource parent to issue commercial paper as a form of short-term debt. As of December 31, 2015 and 2014, Eversource parent had approximately $1.1 billion in short-term borrowings outstanding on each date under the Eversource parent comm ercial paper program, leaving $351.5 million and $348.9 million of available borrowing capac ity as of December 31, 2015 and 2014, respectively. The weighted-average interest rate on these borrowings as of December 31, 2015 and 2014 was 0.72 percent and 0.4 3 percent, respectively. As of December 31, 2015, there were intercompany loans from Eversource parent of $277.4 million to CL&P , $ 231.3 million to PSNH and $ 143.4 million to WMECO. As of December 31, 2014, there were intercompany loans from Eversource parent of $133.4 million to CL&P, $90.5 million to PSNH and $21.4 million to WMECO. NSTAR Electric has a five-year $450 million revolving credit facility. On October 26, 2015, this revolving credit facility was amended and restated and the termination date was extended to September 4, 2020. The facility serves to backstop NSTAR Electric's $450 million commercial paper program. As of December 31, 2015 and 2014 , NSTAR Electric had $ 62.5 million and $ 302 million, respectively, in short-term borrowings outstanding under its commercial paper program, leaving $ 387.5 million and $148 million of available borrowing capacity as of December 31, 201 5 and 201 4 , respectively. The weighted-average interest rate on these bo rrowings as of December 31, 2015 and 2014 was 0. 4 0 percent and 0. 27 percent, respectively. Except as described below, a mounts outstanding under the commercial paper programs are included in Notes Payable for Eversource and NSTAR Electric and are classified in current liabilities on the balance sheets as all borrowings are outstanding for no more than 364 days at one time. Intercompany loans from Eversource parent to CL&P, PSNH and WMECO are included in Notes Payable to Eversource Parent and are classified in current liabilities on the ir respective balance sheets. Intercompany loans from Eversource to CL&P, PSNH and WMECO are eliminated in consolidation o n Eversource 's balance sheets. On January 15 , 2015, Eversource p arent is sued $ 150 million of 1.60 percent Series G Senior Not es due to mature in 2018 and $300 million of 3.15 percent Series H Senior Notes, due to mature in 2025 . The proceeds, net of issuance costs, were used to re pay short-term borrowings outstanding under the Eversource parent commercial paper program. As the debt proceeds, net of issuance costs, refinanced short-term debt , the short-term debt was classified as Long-Term Debt as of December 31, 2014. See Note 8 , "Long-Term Debt , " for further information on these debt issuances. Under the credit facilities described above , Eversource and its subsidiaries must comply with certain financial and non-financial coven ants, including a consolidated debt to total capitalization rati o. As of December 31, 201 5 and 201 4 , Eversource and its subsidiaries were in compliance with these covenants. If Eversource or its subsidiaries were not in compliance with these covenants, an event of default would occur requiring all outstanding borrowings by such borrower to be repaid and additional borrowings by such borrower w ould not be permitted under its respective credit facility.

LONG-TERM DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Long-term Debt [Text Block]	8. LONG-TERM DEBT Details of long-term debt outstanding are as follows : CL&P As of December 31, (Millions of Dollars) 2015 2014 First Mortgage Bonds: 7.875% 1994 Series D due 2024 $ 139.8 $ 139.8 5.750% 2004 Series B due 2034 130.0 130.0 5.000% 2005 Series A due 2015 - 100.0 5.625% 2005 Series B due 2035 100.0 100.0 6.350% 2006 Series A due 2036 250.0 250.0 5.375% 2007 Series A due 2017 150.0 150.0 5.750% 2007 Series B due 2037 150.0 150.0 5.750% 2007 Series C due 2017 100.0 100.0 6.375% 2007 Series D due 2037 100.0 100.0 5.650% 2008 Series A due 2018 300.0 300.0 5.500% 2009 Series A due 2019 250.0 250.0 2.500% 2013 Series A due 2023 400.0 400.0 4.300% 2014 Series A due 2044 250.0 250.0 4.150% 2015 Series A due 2045 350.0 - Total First Mortgage Bonds 2,669.8 2,419.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 1.550% Fixed Rate Tax Exempt due 2031 - 62.0 Total Pollution Control Revenue Bonds 120.5 182.5 Pre-1983 Spent Nuclear Fuel Obligation - 244.5 Less Amounts due Within One Year - (162.0) Unamortized Premiums and Discounts, Net (10.7) (4.8) Unamortized Debt Issuance Costs (1) (15.9) (15.8) CL&P Long-Term Debt (1) $ 2,763.7 $ 2,664.2 NSTAR Electric As of December 31, (Millions of Dollars) 2015 2014 Debentures: 5.750% due 2036 $ 200.0 $ 200.0 5.625% due 2017 400.0 400.0 5.500% due 2040 300.0 300.0 2.375% due 2022 400.0 400.0 Variable Rate due 2016 (0.6036% and 0.4721% as of December 31, 2015 and 2014) 200.0 200.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 - Total Debentures 2,050.0 1,800.0 Bonds: 7.375% Tax Exempt Sewage Facility Revenue Bonds, due 2015 - 4.7 Less Amounts due Within One Year (200.0) (4.7) Unamortized Premiums and Discounts, Net (8.5) (7.3) Unamortized Debt Issuance Costs (1) (11.7) (11.2) NSTAR Electric Long-Term Debt (1) $ 1,829.8 $ 1,781.5 PSNH As of December 31, (Millions of Dollars) 2015 2014 First Mortgage Bonds: 5.60% Series M due 2035 $ 50.0 $ 50.0 6.15% Series N due 2017 70.0 70.0 6.00% Series O due 2018 110.0 110.0 4.50% Series P due 2019 150.0 150.0 4.05% Series Q due 2021 122.0 122.0 3.20% Series R due 2021 160.0 160.0 3.50% Series S due 2023 325.0 325.0 Total First Mortgage Bonds 987.0 987.0 Pollution Control Revenue Bonds: Adjustable Rate Tax Exempt Series A due 2021 (0.193% and 0.175% as of December 31, 2015 and 2014) 89.3 89.3 Unamortized Premiums and Discounts, Net 0.1 - Unamortized Debt Issuance Costs (1) (5.4) (6.3) PSNH Long-Term Debt (1) $ 1,071.0 $ 1,070.0 WMECO As of December 31, (Millions of Dollars) 2015 2014 Notes: 5.90% Senior Notes Series B, due 2034 $ 50.0 $ 50.0 5.24% Senior Notes Series C, due 2015 - 50.0 6.70% Senior Notes Series D, due 2037 40.0 40.0 5.10% Senior Notes Series E, due 2020 95.0 95.0 3.50% Senior Notes Series F, due 2021 250.0 250.0 3.88% Senior Notes Series G, due 2023 80.0 80.0 Total Notes 515.0 565.0 Pre-1983 Spent Nuclear Fuel Obligation - 57.4 Less Amounts due Within One Year - (50.0) Unamortized Premiums and Discounts, Net 5.2 6.1 Unamortized Debt Issuance Costs (1) (2.9) (3.3) WMECO Long-Term Debt (1) $ 517.3 $ 575.2 OTHER As of December 31, (Millions of Dollars) 2015 2014 Yankee Gas - First Mortgage Bonds: 8.48% Series B due 2022 $ 20.0 $ 20.0 5.26% Series H due 2019 50.0 50.0 5.35% Series I due 2035 50.0 50.0 6.90% Series J due 2018 100.0 100.0 4.87% Series K due 2020 50.0 50.0 4.82% Series L due 2044 100.0 100.0 3.35% Series M due 2025 75.0 - Total First Mortgage Bonds 445.0 370.0 Unamortized Premium 0.4 0.6 Unamortized Debt Issuance Costs (1) (1.7) (1.5) Yankee Gas Long-Term Debt (1) 443.7 369.1 NSTAR Gas - First Mortgage Bonds: 9.95% Series J due 2020 25.0 25.0 7.11% Series K due 2033 35.0 35.0 7.04% Series M due 2017 25.0 25.0 4.46% Series N due 2020 125.0 125.0 4.35% Series O due 2045 100.0 - Total First Mortgage Bonds 310.0 210.0 Unamortized Debt Issuance Costs (1) (0.8) (0.6) NSTAR Gas Long-Term Debt (1) 309.2 209.4 Eversource Parent - Notes and Debentures: 4.50% Debentures due 2019 350.0 350.0 1.45% Senior Notes Series E due 2018 300.0 300.0 2.80% Senior Notes Series F due 2023 450.0 450.0 1.60% Senior Notes Series G due 2018 150.0 - 3.15% Senior Notes Series H due 2025 300.0 - Eversource Parent Commercial Paper Borrowings - 446.3 Total Eversource Parent Notes and Debentures 1,550.0 1,546.3 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 179.5 179.4 Fair Value Adjustment (2) 173.5 202.3 Less Fair Value Adjustment - Current Portion (2) (28.9) (28.9) Unamortized Premiums and Discounts, Net (1.3) (1.2) Unamortized Debt Issuance Costs (1) (1.9) 1.1 Total Other Long-Term Debt (1) $ 2,623.8 $ 2,477.5 Total Eversource Long-Term Debt (1) $ 8,805.6 $ 8,568.4 (1) Effective December 31, 2015, t he carrying amount of Long-Term Debt includes unamortized debt issuance costs presented as a direct reduction from the carrying amount of the debt liability, in accordance with new accounting guidance. The December 31, 2014 carrying amount of Long-Term Debt was retrospectively adjusted to conform to the current year presentation. See Note 1 C , "Summary of Significant Accounting Policies – Accounting Standards," for further information. (2) The fair value adjustment amount is the purchase price adjustment , net of amortization, required to record the NSTAR long-term debt at fair value on the date of the merger. Long-Term Debt Issuances : On January 1 5, 2015, Eversource p arent issued $150 million of 1.60 percent Series G Senior Notes , due to mature in 2018 , and $300 million of 3.15 percent Series H Senior Notes, due to mature in 2025. As the debt proceeds, net of issuance costs, refinanced short-term debt, the short-term debt was classified as Long-Term Debt as of December 31, 2014. On May 20, 2015 and Dec ember 1 , 2015, CL&P issued $300 million and $50 million, respectively, of 4.15 percent 2015 Series A First and Refunding Mortgage Bonds due to mature in 2045. On September 10, 2015, Yankee Gas issued $75 million of 3.35 percent 2015 Series M First Mortgage Bonds due to mature in 2025 . On November 18, 2015, NSTAR Electric issued $250 million of 3.25 percent debentures, due to mature in 2025. On December 8, 2015, NSTAR Gas issued $100 million of 4.35 percent Series O First Mortgage Bonds due to mature in 2045. The proceeds of all debt issuances, net of issuance costs, were used to repay short-term borrowings and fund capital expenditures and working capital . Long-Term Debt Repayments : On April 1, 2015, CL&P repaid at maturity the $100 million 5.00 percent 2005 Series A First and Refunding Mortgage Bonds and also redeemed the $62 million 1996A Series 1.55 percent PCRBs that were subject to mandatory tender using short-term borrowings. On August 3, 2015, WMECO repaid at maturity the $50 million 5.24 percent Series C Senior Notes, using short-term borrowings. Long-Term Debt Issuance Authorizations: On November 25, 2015, PURA approved Yankee Gas' request to extend the authorization period for issuance of up to $125 million in long-term debt from December 31, 2015 to December 31, 2016. On December 4, 2015, the DPU authorized WMECO to issue up to $100 million in long-term debt for the period through December 31, 2016. On December 4, 2015, the DPU approved NSTAR Electric's request to extend the authorization period for issuance of up to $250 million in long-term debt from December 31, 2015 to December 31, 2016. Long-Term Debt Provisions : The utility plant of CL&P, PSNH, Yankee Gas and NSTAR Gas is subject to the lien of each company's respective first mortgage bond indenture. The Eversource parent, NSTAR Electric and WMECO debt is unsecured. Additionally, t he long-term debt agreements provide that Eversource and certain of its subsidiaries must comply with certain covenants as are customarily included in such agreements, including a minimum equity requirement for NSTAR Gas. Under the minimum equity requirement, the outstanding long-term debt of NSTAR Gas must not exceed equity. CL&P's obligation to repay the PCRBs is secured by first mortgage bonds. The first mortgage bonds contain similar terms and provisions as the applicable series of PCRBs. If CL&P fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. CL&P's $120.5 million tax-exempt PCRBs will be subject to redemption at par on or after September 1, 2021. All other long-term debt securities are subject to make-whole provisions. PSNH's obligation to repay the PCRBs is secured by first mortgage bonds and bond insurance. The first mortgage bonds contain similar terms and provisions as the PCRBs. If PSNH fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. The PSNH Series A tax-exempt PCRBs are currently callable at 100 percent of par. The PCRBs bear interest at a rate that is periodically set pursuant to auctions. PSNH is not obligated to purchase these PCRBs, which mature in 2021, from the remarketing agent. Yankee Gas has certain long-term debt agreements that contain cross-default provisions . No other debt issuances contain cross-default provisions as of December 31, 201 5 . Pr e-1983 Spent Nuclear Fuel Obligation: Under the Nuclear Waste Policy Act of 1982, CL&P and WMECO were obligated to pay the D OE for the costs of disposal of pre-1983 spent nuclear fuel and high-level radioactive waste for the period prior to the sale of their ownership shares in the Millstone nuclear power stations , which were sold in March 2001 . The DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. After the sale of the Millstone nuclear power stations in March 2001 , CL&P and WMECO remained responsible for th eir share of the disposal costs for nuclear fuel used to generate electricity prior to April 7, 1983 ( pre-1983 Spent Nuclear Fuel) and recorded an accrual for the full liability thereof to the DOE . This liability accrued i nterest costs at the 3- month Treasury bill yield rate. As of December 31, 2014, CL&P and WMECO's p re-1983 Spent Nuclear Fuel obligation was $244.5 million and $57.4 million, respectively, which included accumulated interest costs of $178 million for CL&P and $41.8 million for WMECO. In late 2015, CL&P and WMECO made payments of $ 244.6 million and $ 57.4 million , respectively, to fully satisfy the ir pre-1983 Spent Nuclear Fuel obligation s to the DOE , which included accumulated interest of $ 178 million and $ 41.8 million, respectively. CL&P issued debt to fund its payment while WMECO liquidated its spent nuclear fuel trust. In addition, as a result of consolidating CYAPC, Eversource has consolidated $ 179.5 million and $179.4 million , respectively, in additional pre-1983 spent nuclear fuel obligations to the DOE , which include accumulated interest costs of $ 130.7 million and $ 130.6 million as of December 31, 2015 and 2014 , respectively . CYAPC maintain s a trust to fund amounts due to the DOE for the disposal of pre-1983 spent nuclear fuel. For further information, see Note 5 , "Marketable Securities," to the financial statements. Long-Term Debt Maturities: Long-term debt maturities on debt outstanding for the years 2016 through 2020 and thereafter are shown below. These amounts exclud e the CYAPC pre-1983 spent nuclear fue l obligation , net unamortized premiums, discounts and debt issuance costs , and other fair value adjustments as of December 31, 2015 : (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 200.0 $ - $ 200.0 $ - $ - 2017 745.0 250.0 400.0 70.0 - 2018 960.0 300.0 - 110.0 - 2019 800.0 250.0 - 150.0 - 2020 295.0 - - - 95.0 Thereafter 5,736.6 1,990.3 1,450.0 746.3 420.0 Total $ 8,736.6 $ 2,790.3 $ 2,050.0 $ 1,076.3 $ 515.0

PENSION BENEFITS AND POSTRETIRE

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	9 . EMPLOYEE BENEFITS A. Pension Benefits and Postretirement Benefits Other Than Pensions As of December 31, 2014, Eversource Service sponsored two defined benefit retirement plans that covered eligible employees, including , among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the se two pension plans were merged into one plan, sponsored by Eversource Service (Pension Plan). The Pension P lan is subject to the provisions of ERISA, as amended by the PPA of 2006. Eversource 's policy is to annually fund the Pension Plan in an amount at least equal to an amount that will satisfy all federal funding requirements. In addition to the Pension Plan , Eversource maintains non-qualified defined benefit retirement plans sponsored by Eversource Service (herein collectively referred to as the SERP Plans), which provide benefits in excess of Internal Revenue Code limitations to eligible current and retired participants. As of December 31, 2014, Eversource Service also sponsored defined benefit postretirement plans that provide d certain retiree benefits, primarily medical, dental and life insurance , to retired employees that me t certain age and service eligibility requirements, including , among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the se postretirement plans were merged into one plan, sponsored by Eversource Service (PBOP Plan). Under certain circumstances, eligible retirees are required to contribute to the costs of postretirement benefits. The benefits provided under the PBOP Plan are not vested and the Company has the right to modify any benefit provision subject to applicable laws at that time. Eversource annually funds postretirement costs through tax deductible contributions to external trusts. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of recording an adjustment to Accumulated Other Comprehensive Income/(Loss) for the funded status of the Pension, SERP and PBOP Plans . Regulatory accounting is also applied to the portions of the Eversource Service costs that support the Regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP Plans funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income /( Loss). For further information , see Note 2 , "Regulatory Accounting," and Note 1 4 , " Accumulated Other Comprehensive Income/(Loss), " to the financial statements. For the year ended December 31, 2015, the difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans are reflected as a component of unrecognized actuarial gains or losses , which are recorded in Regulatory Assets or Accumulated Other Comprehensive Income/(Loss) . Unrecognized actuarial gains or losses a re amort ized as a component of p ension and PBOP expense over the estimated average future employee service period . Pension and SERP Plans : On January 1, 2014, NSTAR Electric & Gas was merged into Eversource Service (service company merger) and, concurrently, all employees were transferred to the company they p redominantly provide services for: Eversource Service , NSTAR Electric or NSTAR Gas . As a result of the se employee transfers, the pension and SERP assets and liabilities of NSTAR Electric & Gas were attributed by participant a nd transferred to the applicable operating company's balance sheets. This change had no impact on the income statement or net assets of NSTAR Electric or Eversource . The Pension and SERP P lans are a ccounted for under the multiple- employer approach, with each operating company's balance sheet reflecting its share of the funded stat us of the plans . Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, s ee Note 5 , "Marketable Securities," to the financial statements. The following tables provide information on the P ension and SERP P lan benefit obligations, fair values of Pension P lan assets, and funded status : Pension and SERP Eversource As of December 31, (Millions of Dollars) 2015 2014 Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (5,486.2) $ (4,676.5) Service Cost (91.4) (79.9) Interest Cost (227.0) (225.7) Actuarial Gain/(Loss) 331.5 (739.6) Benefits Paid - Pension 238.5 230.3 Benefits Paid - Lump Sum 149.5 - Benefits Paid - SERP 5.0 5.2 Benefit Obligation as of End of Year $ (5,080.1) $ (5,486.2) Change in Pension Plan Assets Fair Value of Pension Plan Assets as of Beginning of Year $ 4,126.5 $ 3,985.9 Employer Contributions 154.6 171.6 Actual Return on Pension Plan Assets 12.3 199.3 Benefits Paid (238.5) (230.3) Benefits Paid - Lump Sum (149.5) - Fair Value of Pension Plan Assets as of End of Year $ 3,905.4 $ 4,126.5 Funded Status as of December 31 st $ (1,174.7) $ (1,359.7) Pension and SERP As of December 31, 2015 As of December 31, 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (1,230.1) $ (982.6) $ (580.7) $ (249.4) $ (1,083.4) $ (1,353.3) $ (529.0) $ (223.9) Change due to transfer of employees (4.6) 6.2 (1.9) (1.3) 26.4 479.9 32.2 6.2 Service Cost (24.7) (14.9) (12.1) (4.3) (20.2) (13.6) (9.7) (3.5) Interest Cost (51.1) (40.2) (24.3) (10.4) (50.5) (41.3) (23.8) (10.3) Actuarial Gain/(Loss) 77.8 34.1 38.9 12.6 (161.0) (107.0) (73.3) (29.8) Benefits Paid - Pension 60.2 47.6 23.2 12.7 58.3 52.4 22.8 11.9 Benefits Paid - Lump Sum 14.5 - 9.1 2.5 - - - - Benefits Paid - SERP 0.4 0.1 0.2 - 0.3 0.3 0.1 - Benefit Obligation as of End of Year $ (1,157.6) $ (949.7) $ (547.6) $ (237.6) $ (1,230.1) $ (982.6) $ (580.7) $ (249.4) Change in Pension Plan Assets Fair Value of Pension Plan Assets as of Beginning of Year $ 980.8 $ 879.0 $ 498.4 $ 234.0 $ 1,016.3 $ 1,235.3 $ 528.6 $ 240.4 Change due to transfer of employees 4.6 (6.2) 1.9 1.3 (26.4) (441.4) (32.2) (6.2) Employer Contributions - 5.0 1.0 - - 101.0 - - Actual Return on Pension Plan Assets 2.8 2.7 1.5 0.7 49.2 36.5 24.8 11.7 Benefits Paid (60.2) (47.6) (23.2) (12.7) (58.3) (52.4) (22.8) (11.9) Benefits Paid - Lump Sum (14.5) - (9.1) (2.5) - - - - Fair Value of Pension Plan Assets as of End of Year $ 913.5 $ 832.9 $ 470.5 $ 220.8 $ 980.8 $ 879.0 $ 498.4 $ 234.0 Funded Status as of December 31 st $ (244.1) $ (116.8) $ (77.1) $ (16.8) $ (249.3) $ (103.6) $ (82.3) $ (15.4) In August 2015, Eversource made a total lump-sum payout of $149.5 million, which reduced the projected benefit obligation and Pension Plan assets by a corresponding amount. Therefore, the lump-sum payment had no impact on the net Accrued Pension Liability reflected on the Eversource, CL&P, PSNH and WMECO b alance sheets as of December 31 , 2015. During 2014, the Society of Actuaries released a series of updated mortal ity tables resulting from studies that measured mortality rates for various groups of individuals . The updated mortality tables released in 2014 increas ed the life expec tancy of plan participants by three to five years and had the effect of increasing the estimate d benefits to be provided to plan participants. The impact of adopting the updated mortality tables on Eversource 's liability as of December 31, 2014 was an increase of approximately $340 million. In 2015 , a revised scale for the mortality table was released having the effect of decreasing the estimate of benefits to be provided to plan participants. The impact of the adoption of the new mortality scale resulted in a decrease of $48 million on Eversource's liability as of December 31, 2015. The increase in the discount rate used to calculate the funded status resulted in a decrease on Eversource's l iability of approximately $267 million as of December 31, 2015. D ecrease s in the discount rate s resulted in an increase on Eversource 's liability of approximately $53 0 million as of December 31, 2014 . The p ension and SERP Plans' funded status includes the current portion of the SERP liability, which is included in Other Current Liabilities on the accompanying balance sheets. As of December 31, 2015 and 2014, the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2015 $ 4,733.2 $ 1,062.7 $ 888.8 $ 506.4 $ 222.3 2014 5,000.1 1,101.4 910.4 524.5 226.4 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2015 2014 Discount Rate 4.21 % - 4.60 % 4.20 % Compensation/Progression Rate 3.50% 3.50 % Pension and SERP Expense: Eversource charges net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the year ended December 31, 2013 (prior to the service company merger ) , the net periodic pension expense recorded at NSTAR Electric represent ed the full cost of the plan with a portion of the costs allocated to affiliated companies based on participant demographic data. The components of net periodic benefit expense for the Pension and SERP Plans are shown below. The net periodic benefit expense and the intercompany allocations less the capitalized portion of pension and SERP amounts are included in Operations and Maintenance expense on the statements of income. Capitalized pension amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net on the balance sheets . Pension and SERP expense reflected in the statements of cash flows for CL&P, NSTAR Electric, PSNH and WMECO does not include the intercompany allocations or the corresponding capitalized portion , as these amounts are cash settled on a short-term basis . Pension and SERP For the Year Ended December 31, 2015 NSTAR (Millions of Dollars) Eversource (1) CL&P Electric PSNH (1) WMECO Service Cost $ 91.4 $ 24.7 $ 14.9 $ 12.1 $ 4.3 Interest Cost 227.0 51.1 40.2 24.3 10.4 Expected Return on Pension Plan Assets (335.9) (78.9) (70.0) (40.4) (18.9) Actuarial Loss 148.5 32.2 35.8 11.6 6.4 Prior Service Cost/(Credit) 3.7 1.5 (0.1) 0.5 0.3 Total Net Periodic Benefit Expense $ 134.7 $ 30.6 $ 20.8 $ 8.1 $ 2.5 Intercompany Allocations N/A $ 22.5 $ 13.6 $ 6.7 $ 4.4 Capitalized Pension Expense $ 41.0 $ 18.8 $ 11.4 $ 3.5 $ 1.9 Pension and SERP For the Year Ended December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 79.9 $ 20.2 $ 13.6 $ 9.7 $ 3.5 Interest Cost 225.7 50.5 41.3 23.8 10.3 Expected Return on Pension Plan Assets (310.8) (75.4) (63.0) (38.1) (17.9) Actuarial Loss 128.4 33.7 23.5 11.6 6.9 Prior Service Cost 4.4 1.8 - 0.7 0.4 Total Net Periodic Benefit Expense $ 127.6 $ 30.8 $ 15.4 $ 7.7 $ 3.2 Intercompany Allocations N/A $ 26.7 $ 10.4 $ 7.6 $ 5.1 Capitalized Pension Expense $ 35.2 $ 17.6 $ 7.9 $ 3.0 $ 2.4 Pension and SERP For the Year Ended December 31, 2013 NSTAR (Millions of Dollars) Eversource CL&P Electric (2) PSNH WMECO Service Cost $ 102.3 $ 24.9 $ 33.1 $ 13.1 $ 4.7 Interest Cost 206.7 48.3 58.0 23.6 10.0 Expected Return on Pension Plan Assets (278.1) (73.8) (84.4) (35.4) (17.4) Actuarial Loss 210.5 55.9 58.1 21.6 11.8 Prior Service Cost/(Credit) 4.0 1.8 (0.3) 0.7 0.4 Total Net Periodic Benefit Expense $ 245.4 $ 57.1 $ 64.5 $ 23.6 $ 9.5 Intercompany Allocations N/A $ 44.9 $ (8.4) $ 10.5 $ 8.0 Capitalized Pension Expense $ 73.2 $ 28.0 $ 28.9 $ 7.3 $ 5.2 Amounts exclude $ 3.2 million for the year ended December 31, 2015 that represent amounts included in other deferred debits. NSTAR E lectric's allocated expense associated with the NSTAR SERP was $3.2 million for the year ended December 31, 2013 and was not included in the NSTA R Electric amounts in the table above. For the year s ended December 31, 2015 and 2014, the SERP amount is now allocated to NSTAR Electric due to the service company merger. The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2015 2014 2013 Discount Rate 4.20% 4.85 % - 5.03 % 4.13 % - 4.24 % Expected Long-Term Rate of Return 8.25 % 8.25 % 8.25% Compensation/Progression Rate 3.50 % 3.50 % - 4.00 % 3.50 % - 4.00 % The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income (OCI) as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented: Regulatory Assets OCI For the Years Ended December 31, (Millions of Dollars) 2015 2014 2015 2014 Actuarial (Gains)/Losses Arising During the Year $ (2.0) $ 797.3 $ (6.2) $ 55.9 Actuarial Losses Reclassified as Net Periodic Benefit Expense (142.3) (122.8) (6.2) (5.6) Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.5) (4.2) (0.2) (0.2) The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2015 and 2014, as well as the amounts that are expected to be recognized as components in 2016: Regulatory Assets as of Expected AOCI as of Expected December 31, 2016 December 31, 2016 (Millions of Dollars) 2015 2014 Expense 2015 2014 Expense Actuarial Loss $ 1,667.6 $ 1,811.9 $ 120.6 $ 81.1 $ 93.5 $ 5.4 Prior Service Cost 9.7 13.2 3.4 0.6 0.8 0.2 PBOP Plan : On January 1, 2014, concurrent with the service company merger, the PBOP assets and liabilities of NSTAR Electric & Gas were attributed by participant and transferred to the applicable operating company's balance sheets. This change had no impact on the income statement s or ne t assets of NSTAR Electric or Eversource . The PBOP Plan is accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plan. The following tables provide information on the PBOP Plan benefit obligations , fair values of plan assets, and funded status : PBOP Eversource As of December 31, (Millions of Dollars) 2015 2014 Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (1,147.9) $ (1,038.0) Service Cost (16.3) (12.5) Interest Cost (47.2) (49.5) Actuarial Gain/(Loss) 106.0 (95.5) Benefits Paid 54.0 47.6 Benefit Obligation as of End of Year $ (1,051.4) $ (1,147.9) Change in Plan Assets Fair Value of Plan Assets as of Beginning of Year $ 862.6 $ 826.5 Actual Return on Plan Assets (4.3) 43.7 Employer Contributions 7.9 40.0 Benefits Paid (54.0) (47.6) Fair Value of Plan Assets as of End of Year $ 812.2 $ 862.6 Funded Status as of December 31 st $ (239.2) $ (285.3) PBOP As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (173.9) $ (468.7) $ (91.8) $ (36.6) $ (180.4) $ - $ (93.5) $ (38.7) Change due to transfer of employees 0.1 2.3 (0.3) - 3.7 (395.5) 4.3 1.0 Service Cost (2.1) (5.4) (1.4) (0.4) (2.2) (3.1) (1.3) (0.4) Interest Cost (7.2) (19.0) (3.9) (1.5) (8.1) (19.4) (4.3) (1.7) Actuarial Gain/(Loss) 7.2 59.1 3.6 1.5 3.5 (68.6) (1.1) 1.3 Benefits Paid 11.9 18.9 5.3 2.6 9.6 17.9 4.1 1.9 Benefit Obligation as of End of Year $ (164.0) $ (412.8) $ (88.5) $ (34.4) $ (173.9) $ (468.7) $ (91.8) $ (36.6) Change in Plan Assets Fair Value of Plan Assets as of Beginning of Year $ 149.0 $ 336.5 $ 80.9 $ 34.4 $ 151.3 $ - $ 81.8 $ 35.3 Change due to transfer of employees - 0.6 0.2 - (3.2) 316.7 (3.1) (1.0) Actual Return on Plan Assets (0.4) (2.8) - (0.1) 6.3 18.4 3.8 1.6 Employer Contributions - 4.9 - - 4.2 19.3 2.5 0.4 Benefits Paid (11.9) (18.9) (5.3) (2.6) (9.6) (17.9) (4.1) (1.9) Fair Value of Plan Assets as of End of Year $ 136.7 $ 320.3 $ 75.8 $ 31.7 $ 149.0 $ 336.5 $ 80.9 $ 34.4 Funded Status as of December 31 st $ (27.3) $ (92.5) $ (12.7) $ (2.7) $ (24.9) $ (132.2) $ (10.9) $ (2.2) During 201 4, the Society of Actuaries released a series of updated mortal ity tables resulting from studies that measured mortality rates for various groups of individuals . The updated mortality tables released in 2014 increased the life expec tancy of plan participants by three to five years and had the effect of increasing the estimate d benefits to be provided to plan participants. The impact of adopting the updated mortality tables on Eversource's liability as of December 31, 2014 was an increase of approximately $ 82 million. In 2015, a revised scale for the mortality table was released having the effect of decreasing the estimate of benefits to be provided to plan participants. The impact of the adoption of the new mortality scale resulted in a decrease of $ 23 millio n on Eversource's liability as of December 31, 2015. The increase in the discount rate used to calculate the funded status resulted in a decrease on Eversource's liability of approximately $ 60 million as of December 31, 2015. D ecreases in the discount rate s resulted in an increa se on Eversource's liability of approximately $110 million as of December 31, 2014 . The following actuarial assumptions were used in calculating the PBOP Plan's year end funded status: PBOP As of December 31, 2015 2014 Discount Rate 4.62 % 4.22 % Health Care Cost Trend Rate 6.25 % 6.50 % PBOP Expense: Eversource charges net periodic postre tire ment benefits expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the year ended December 31, 2013 (prior to the service company merger), t he net periodic postretirement expense of the NSTAR PBOP Plan allocated to NS T AR Electric was $ 4.6 million . The components of net periodic be nefit expense for the PBOP Plan are shown below. The net periodic benefit expense and the intercompany allocations less the capitalized portion of PBOP are included in Operations and Maintenance on the statements of income. Capitalized PBOP amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net on the balance sheets . PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric, PSNH and WMECO does not include the intercompany allocations or the corresponding capitalized portion, as these amounts are cash settled on a short-term basis. PBOP For the Year Ended December 31, 2015 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 16.3 $ 2.1 $ 5.4 $ 1.4 $ 0.4 Interest Cost 47.2 7.2 19.0 3.9 1.5 Expected Return on Plan Assets (67.4) (11.1) (27.3) (6.0) (2.5) Actuarial Loss 6.8 0.7 2.3 0.5 - Prior Service Credit (0.5) - (0.2) - - Total Net Periodic Benefit Expense/(Income) $ 2.4 $ (1.1) $ (0.8) $ (0.2) $ (0.6) Intercompany Allocations N/A $ 1.9 $ 0.8 $ 0.4 $ 0.3 Capitalized PBOP Expense/(Income) $ 0.1 $ (0.2) $ (0.2) $ 0.2 $ (0.2) PBOP For the Year Ended December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 12.5 $ 2.2 $ 3.1 $ 1.3 $ 0.4 Interest Cost 49.5 8.1 19.4 4.3 1.7 Expected Return on Plan Assets (63.3) (10.5) (25.9) (5.4) (2.3) Actuarial Loss/(Gain) 12.2 4.2 (0.5) 2.2 0.5 Prior Service Credit (2.8) - (1.9) - - Total Net Periodic Benefit Expense/(Income) $ 8.1 $ 4.0 $ (5.8) $ 2.4 $ 0.3 Intercompany Allocations N/A $ 3.8 $ 0.8 $ 1.0 $ 0.7 Capitalized PBOP Expense/(Income) $ 1.4 $ 1.8 $ (2.3) $ 0.8 $ 0.2 PBOP For the Year Ended December 31, 2013 (Millions of Dollars) Eversource CL&P PSNH WMECO Service Cost $ 16.9 $ 3.4 $ 2.3 $ 0.7 Interest Cost 47.2 7.9 4.0 1.7 Expected Return on Plan Assets (55.4) (10.1) (5.2) (2.3) Actuarial Loss 26.0 7.4 3.6 1.1 Prior Service Credit (2.1) - - - Total Net Periodic Benefit Expense $ 32.6 $ 8.6 $ 4.7 $ 1.2 Intercompany Allocations N/A $ 7.1 $ 1.6 $ 1.3 Capitalized PBOP Expense $ 8.8 $ 3.9 $ 1.3 $ 0.6 The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2015 2014 2013 Discount Rate 4.22 % 4.78 % - 5.10 % 4.04 % - 4.35 % Expected Long-Term Rate of Return 8.25 % 8.25 % 8.25% As of December 31, 201 5 and 201 4 , the health care cost trend rate assumption s used to determine the PBOP Plan ' s funded st atus was 6.25 percent and 6.5 percent, respectively, subsequently decreasing to an ultimate rate of 4.5 percent in 2023 . The health care cost trend rate assum ption used to calculate the PBOP expense amount was 6.5 percent for the year ended December 31, 201 5 . Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. The effect of changing the assumed health care cost trend rate by one percentage point for the year ended December 31, 201 5 would have the following effects : One Percentage One Percentage (Millions of Dollars) Point Increase Point Decrease Effect on PBOP Obligation $ 115.3 $ (90.8) Effect on Total Service and Interest Cost Components 8.5 (6.3) The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts recognized in Regulatory Assets and OCI that were reclassified as net periodic benefit (expense)/income during the years presented: Regulatory Assets OCI For the Years Ended December 31, (Millions of Dollars) 2015 2014 2015 2014 Actuarial (Gains)/Losses Arising During the Year $ (34.1) $ 115.1 $ 0.7 $ 0.4 Actuarial Losses Reclassified as Net Periodic Benefit Expense (6.4) (11.6) (0.4) (0.6) Prior Service Credit Reclassified as Net Periodic Benefit Income 0.5 2.8 - - The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2015 and 2014, as well as the amounts that are expected to be recognized as components in 2016: Regulatory Assets as of Expected AOCI as of Expected December 31, 2016 December 31, 2016 (Millions of Dollars) 2015 2014 Expense 2015 2014 Expense Actuarial Loss $ 152.2 $ 192.7 $ 4.0 $ 6.3 $ 6.0 $ 0.4 Prior Service Credit (1.3) (1.8) (0.2) - - - Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans: (Millions of Dollars) 2016 2017 2018 2019 2020 2021-2025 Pension and SERP $ 253.5 $ 272.9 $ 273.9 $ 283.7 $ 292.7 $ 1,604.3 PBOP 60.8 61.2 61.4 61.8 62.4 315.4 Eversource Contributions: Eversource contributed $ 154.6 million to the Pension P lan in 201 5 , of which $ 5 million was contributed by NSTAR Electric , $1 million by PSNH and the remainder by other Eversource subsidiarie s, primarily Eversource Service . Based on the current status of the P ension Plan and federal pension funding requirements , although not required to make a minimum pension contribution in 2016 , Eversource currently expects to make contribution s of approximately $ 146 million in 201 6 , of which $ 21 million will be contributed by NSTAR Electric and $ 17 million by PSNH . The remaining $ 108 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service . Eversource contributed $ 7.9 million to the PBOP P lan in 2015 , of which $4.9 million was contributed by NSTAR Electric . Eversource expects to make approximately $ 9.5 million in contri butions in 2016 . Fair Value of Pension and PBOP Plan Assets: Pension and PBOP funds are held in external trusts. Trust assets, including accumulated earnings , must be used exclusively for P ension and PBOP payments. Eversource 's investment strategy for its Pension and PBOP Plans is to maximize the long-term rates of return on these plans' assets within an acceptable level of risk. The investment strategy for each asset category includes a diversificati on of asset types, fund strategies and fund managers and it establishes target asset allocations that are routinely reviewed and periodically rebalanced. PBOP assets are comprised of assets held in the PBOP Plan as well as specific assets within the defined benefit pension plan trust (401(h) assets) . The investment policy and strategy of the 401(h) assets is consistent with that of t he defined benefit pension plan . Eversource 's expected long-term rates of return on Pension and PBOP Plan assets are based on target asset allocation assumptions and related expected long-term rates of return. In developing its expected long-term rate of return assumptions for the Pension and PBOP Plans, Eversource evaluated input from consultants , as well as long-term inflation assumptions and historical returns. For the year ended December 31, 201 5 , management has assumed long-term rates of return of 8.25 percent for the Pension and PBOP Plan assets . These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows: As of December 31, 2015 As of December 31, 2014 Pension Plan and Tax-Exempt Assets Within PBOP Plan Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Target Asset Allocation Assumed Rate of Return Equity Securities: United States 22% 8.5% 24% 9% International 13% 8.5% 10% 9% Emerging Markets 5% 10% 6% 10% Private Equity 12% 12% 10% 13% Debt Securities: Fixed Income 12% 4.5% 15% 5% High Yield Fixed Income 13% 8.5% 9% 7.5% Emerging Markets Debt 5% 7.5% 6% 7.5% Real Estate and Other Assets 10% 7.5% 9% 7.5% Hedge Funds 8% 7% 11% 7% The t axable assets within the PBOP P lan have a target asset allocation of 70 percent equity securities and 30 percent fixed income securities . The following table presents, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Pension Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2015 2014 Asset Category: Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equity Securities (1) $ 396.5 $ 985.7 $ 305.2 $ 1,687.4 $ 414.7 $ 1,035.0 $ 292.2 $ 1,741.9 Private Equity 7.6 - 464.7 472.3 18.8 - 367.9 386.7 Fixed Income (2) - 432.0 784.8 1,216.8 10.2 561.4 722.0 1,293.6 Real Estate and Other Assets - 117.5 260.3 377.8 - 132.0 265.8 397.8 Hedge Funds - 49.7 290.8 340.5 - 20.0 475.0 495.0 Total $ 404.1 $ 1,584.9 $ 2,105.8 $ 4,094.8 $ 443.7 $ 1,748.4 $ 2,122.9 $ 4,315.0 Less: 401(h) PBOP Assets (3) (189.4) (188.5) Total Pension Assets $ 3,905.4 $ 4,126.5 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2015 2014 Asset Category: Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equity Securities (1) $ 109.7 $ 121.6 $ 77.8 $ 309.1 $ 104.1 $ 172.8 $ 75.1 $ 352.0 Private Equity - - 32.9 32.9 - - 24.9 24.9 Fixed Income (2) 9.7 99.9 81.6 191.2 16.1 110.0 78.3 204.4 Real Estate and Other Assets - 17.0 20.4 37.4 - 19.4 15.0 34.4 Hedge Funds - - 52.2 52.2 - - 58.4 58.4 Total $ 119.4 $ 238.5 $ 264.9 $ 622.8 $ 120.2 $ 302.2 $ 251.7 $ 674.1 Add: 401(h) PBOP Assets (3) 189.4 188.5 Total PBOP Assets $ 812.2 $ 862.6 United States, International and Emerging Market s equity securities classified as Level 2 include investments in commingled funds . Level 3 investments include hedge funds that are overlayed with equity index swaps and futures contracts and funds invested in equities that have redemption restrictions . Fixed Income investments classified as L evel 3 investments include fixed income funds that invest in a variety of opportunistic fixed income strategies , and hedge funds that are overlayed with fixed income futures . The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretireme nt benefits under the PBOP Plan . The Company values assets based on observable inputs when available. Equity securities , exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Commingled funds included in Level 2 equity securities are recorded at the net asset value provided by the asset manager, which is based on the market prices of the underlying equity securities. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Fixed income securities , such as government issued securities, corporate bonds and high yield bond funds , are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Hedge funds and investments in opportunistic fixed income funds are recorded at net asset value based on the values of the underlying assets. The assets in the hedge funds and opportunistic fixed income funds are valued using observable inputs and are classified as Level 3 within the fair value hierarchy due to redemption restrictions. Private Equity investments and Real Estate and Other Assets are valued using the net asset value provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments. These investments are classified as Level 3 due to redemption restrictions. Fair Value Measurements Using Significant Unobservable Inputs (Level 3): The foll owing tables present changes in the Level 3 category of Eversource's Pension and PBOP Plan assets for the years ended December 31, 201 5 and 201 4 : Pension Plan Equity Private Fixed Real Estate and Hedge (Millions of Dollars) Securities Equity Income Other Assets Funds Total Balance as of January 1, 2014 $ 255.5 $ 300.3 $ 589.5 $ 288.5 $ 416.9 $ 1,850.7 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End (2.3) 14.0 45.2 (3.6) 23.5 76.8 Relating to Assets Distributed During the Year - 13.9 (6.2) 28.3 (15.2) 20.8 Purchases, Sales and Settlements 39.0 39.7 93.5 (47.4) 49.8 174.6 Balance as of December 31, 2014 $ 292.2 $ 367.9 $ 722.0 $ 265.8 $ 475.0 $ 2,122.9 Transfer Between Categories 76.5 - - - (76.5) - Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End 5.3 24.4 (6.7) (7.1) - 15.9 Relating to Assets Distributed During the Year - 27.3 17.0 24.8 (0.9) 68.2 Purchases, Sales and Settlements (68.8) 45.1 52.5 (23.2) (106.8) (101.2) Balance as of December 31, 2015 $ 305.2 $ 464.7 $ 784.8 $ 260.3 $ 290.8 $ 2,105.8 PBOP Plan Equity Private Fixed Real Estate and Hedge (Millions of Dollars) Securities Equity Income Other Assets Funds Total Balance as of January 1, 2014 $ 69.1 $ 17.9 $ 51.5 $ 33.9 $ 57.0 $ 229.4 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End 6.0 1.3 1.9 (2.8) 1.4 7.8 Relating to Assets Distributed During the Year - 0.1 - (2.2) - (2.1) Purchases, Sales and Settlements - 5.6 24.9 (13.9) - 16.6 Balance as of December 31, 2014 $ 75.1 $ 24.9 $ 78.3 $ 15.0 $ 58.4 $ 251.7 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End (2.0) 2.6 2.1 0.3 (1.5) 1.5 Relating to Assets Distributed During the Year - - (0.3) - - (0.3) Purchases, Sales and Settlements 4.7 5.4 1.5 5.1 (4.7) 12.0 Balance as of December 31, 2015 $ 77.8 $ 32.9 $ 81.6 $ 20.4 $ 52.2 $ 264.9

DEFINED CONTRIBUTION PLANS

DEFINED CONTRIBUTION PLANS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Compensation and Employee Benefit Plans [Text Block]	B. Defined Contribution Plans Effective January 1, 2014, Eversource maintains one defined contribution plan on behalf of eligible participants, the Eversource 401k Plan. The Eversource 401k Plan provides for employee and employer contributions up to statutory limits. For eligible employees, the Eversource 401k Plan provides employer matching contributions of either 100 percent up to a maximum of three percent of eligible compensation or 50 percent up to a maximum of eight percent of eligible compensation. Beginning in 2014 f or newly hired employees, the Eversource 401k Plan provides employer matching contributions of 100 percent up to a maximum of three percent of eligible compensation . The Eversource 401k Plan also contains a K-Vantage feature for the benefit of eligible participants , which provides an additional annual employer contribution based on age and years of service. K-Vantage participants are not eligible to actively participate in the Eversource Pension P lan . The total defined Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2015 $ 30.4 $ 4.8 $ 6.3 $ 3.4 $ 1.0 2014 29.7 5.0 6.3 3.2 1.0 2013 37.0 5.1 8.5 3.3 1.0 Allocations of Eversource common shares were made from Eversource treasury shares to satisfy a portion of the Eversource 4 01k Plan obligation , which provides 100 percent of the matching contribution in Eversource common shares. For treasury shares used to satisfy the Eversource 401k Plan employer matching contributions, compensation expense is recognized equal to the fair value of shares that have been allocated to participants. Any difference between the fair value and the average cost of the allocated treasury shares is charged or credited to Capital Surplus, Paid In on the balance sheet . For the years ended December 31, 201 5 , 201 4 and 201 3 , Eversource recognized $ 7 million, $22 million and $9.1 million, respectively, of compensa tion expense related to treasury shares used to satisfy the matching contribution .

SHARE-BASED PAYMENTS

SHARE-BASED PAYMENTS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Shareholders' Equity and Share-based Payments [Text Block]	C . Share-Based Payments Share-based compensation awa rds are recorded using a fair- value-based method at the date of grant. Eversource , CL&P, NSTAR Electric, PSNH and WMECO record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as for the allocation of costs associated with shares issued or sold to Eversource 's service company employees and officers that support CL&P, NSTAR Electric, PSNH and WMECO. Eversource Incentive Plan s : Eversource maintains long-term equity-based incentive plans in which Eversource , CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are e ligible to participate. The incentive p lan s authorize Eversource to grant up to 8,0 00,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 201 5 and 201 4 , Eversource had 3,005,010 and 3,112,020 common shares, respectively, available for issuance under the se p lan s . Eversource accounts for its various share-based plans as follows: RSUs - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of Eversource 's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares. P erformance S hares - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. V esting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the total shareholder return as compared to the Edison Electric Institute (EEI) Index during the requisite service period . The fair value of performance shares is determined at the date of g rant using a lattice model. Stock Options - Stock options currently outstanding are fully vested. ESPP Shares - For shares sold under the ESPP, no compensation expense was recorded as the ESPP qualified as a non-compensatory plan. The ESPP ended as of February 1, 2016. RSUs: Eversource granted RSUs under the annual long-t erm incentive programs that are subject to three-year graded vesting schedules for employees, and one-year graded vesting schedules , or immediate vesting , for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes , subsequent to vesting. A summary of RSU transactions is as follows: Weighted Average RSUs Grant-Date (Units) Fair Value Outstanding as of December 31, 2014 1,380,747 $ 35.67 Granted 266,230 $ 54.57 Shares issued (888,495) $ 33.94 Forfeited (29,174) $ 46.68 Outstanding as of December 31, 2015 729,308 $ 43.45 The weighted average grant-date fair value of RSU s granted for the years ended December 31, 201 5 , 201 4 and 201 3 was $ 54.57 , $ 42.27 and $39. 56 , respectively. As of December 31, 201 5 and 201 4 , the number and weighted average grant-date fair value of unvested RSUs was 469,772 and $ 48 . 58 per share, and 1, 0 2 4 , 729 and $38 .14 per share , respectively. During 2015, there were 784,376 RSUs at a weighted average grant-date fair value of $ 37.21 per share that vested and were either paid or deferred . As of December 31, 201 5 , 259,536 RSUs were fully vest ed and deferred and an additional 446,283 are expected to vest. Performance Shares: Eversource granted performa nce shares under the annual long-term i ncentive programs that vest based upon the extent to which Company goals are achieved at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows: Performance Weighted Average Shares Grant-Date (Units) Fair Value Outstanding as of December 31, 2014 375,644 $ 42.20 Granted 172,543 $ 55.04 Shares issued (4,604) $ 42.23 Forfeited (15,155) $ 45.33 Outstanding as of December 31, 2015 528,428 $ 46.30 The weighted average grant-date fair value of Performance Share s granted for the years ended December 31, 201 5 , 201 4 and 201 3 was $ 55.04 , $ 43.4 0 and $ 40.96 , respectively. As of December 31, 2015, all outstanding performance shares are unvested. The total compensation expense and associated future income tax benefit s recognized by Eversource , CL&P, NSTAR Electric, PSNH and WMECO for sha re-based compensation awards we re as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Compensation Expense $ 23.1 $ 24.6 $ 27.0 Future Income Tax Benefit 9.4 10.3 10.7 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Compensation Expense $ 9.3 $ 5.8 $ 3.2 $ 1.7 $ 8.1 $ 7.4 $ 3.0 $ 1.3 $ 6.8 $ 7.5 $ 2.3 $ 1.3 Future Income Tax Benefit 3.8 2.4 1.3 0.7 3.4 3.1 1.3 0.5 2.7 3.0 0.9 0.5 As of December 31, 201 5 , there was $ 14.9 million of total unrecognized compensation expense related to nonvested share-based awards for Eversource , including $ 6.1 million for CL&P, $ 3.8 million for NSTAR Electric, $ 2.2 m illion for PSNH and $ 1.2 million for WMECO. This cost is expected to be recognized ratably over a weighted-average period of 1.74 years for Eversource , and 1.7 3 years for each CL&P, NSTAR Electric, PSNH and WMECO. For each of the years ended December 31, 201 5 and 201 4 , changes in excess tax benefits totaling $ 9.5 million increased cash flows from financing activities. For the year ended December 31, 2013 , changes in excess tax benefits totaling $5.5 million decreased cash flows from financing activities . Stock Options: Stock options currently outstanding were granted under the NSTAR Incentive P lan , expire ten years from the date of grant and are fully vested. The weighted average remaining contractual lives for the options outstanding as of December 31, 201 5 is 2.6 years. A summary of stock option transactions is as follows: Weighted Average Intrinsic Value Options Exercise Price (Millions) Outstanding and Exercisable - December 31, 2014 351,616 $ 26.69 $ 9.4 Exercised (179,744) $ 26.90 $ 4.4 Outstanding and Exercisable - December 31, 2015 171,872 $ 26.47 $ 4.2 Cash received for options exercised during the year ended December 31, 201 5 totaled $ 4.8 million. The tax benefit realized from stock options exercised totaled $ 1.9 million for the year ended December 31, 201 5 . Employee Share Purchase Plan: Eversource maintained an ESPP for eligible employees, which allowed for Eversource common shares to be purchased by employees at the end of successive six-month offering periods at 95 percent of the closing market price on the last day of each six-month period. Employees were permitted to purchase shares having a value not exceeding 25 percent of their compensation as of the beginning of the offering period up to a specified limit . The ESPP qualified as a non-compensatory plan under accounting guidance for share-based payments, and no compensation expense was recorded for ESPP purchases. During 201 5 , employees purchased 33,715 shares at discounted prices of $ 52.80 and $ 47.23 . Employees purchased 40,779 shares in 201 4 at discounted prices of $ 41.61 and $ 41.71 . As of December 31, 201 5 and 201 4 , 743,260 and 776,975 shares, respectively, remained available for future issuance under the ESPP. The ESPP ended as of February 1, 2016. An income tax rate of 40 percent is used to estimate the tax effect on total share-based payments determined under the fair value-based method for all awards. The Company generally settles stock option exercises and fully vested RSUs and performance shares with the issuance of common shares purchased in the open market .

OTHER RETIREMENT BENEFITS

OTHER RETIREMENT BENEFITS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Compensation Related Costs, General [Text Block]	D . Other Retirement Benefits Eversource provides retirement and other benefits for certain current and past company officers . These benefits are accounted for on an accrual basis and expensed over a period equal to the service lives of the employees. The actuarially-determined liability for these benefits, which is included in Other Long-Term Liabilities on the balance sheets, as well as the related expense included in Operations and Maintenance on the income statements , are as follows: Eversource As of and For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Actuarially-Determined Liability $ 55.2 $ 57.5 $ 51.3 Other Retirement Benefits Expense 3.9 4.5 4.4 As of and For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P PSNH WMECO Actuarially-Determined Liability $ 0.4 $ - $ 2.4 $ 0.2 $ 0.4 $ - $ 2.6 $ 0.2 $ 0.4 $ 2.3 $ 0.1 Other Retirement Benefits Expense 1.5 1.0 0.7 0.3 2.1 0.3 0.9 0.4 2.5 1.0 0.5

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Income Tax Disclosure [Text Block]	10. INCOME TAXES The components of income tax expense are as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Current Income Taxes: Federal $ 6.2 $ 4.4 $ 8.8 State 45.7 24.5 (9.4) Total Current 51.9 28.9 (0.6) Deferred Income Taxes, Net: Federal 436.1 406.8 386.2 State 55.6 36.5 45.4 Total Deferred 491.7 443.3 431.6 Investment Tax Credits, Net (3.6) (3.9) (4.1) Income Tax Expense $ 540.0 $ 468.3 $ 426.9 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Current Income Taxes: Federal $ 26.9 $ 36.3 $ (16.7) $ (3.5) $ (0.2) $ 75.0 $ (22.6) $ 1.9 $ 20.1 $ 95.8 $ (8.2) $ (53.4) State 15.8 19.8 6.0 1.6 4.3 20.2 (0.1) 1.8 (6.7) 29.6 3.6 4.2 Total Current 42.7 56.1 (10.7) (1.9) 4.1 95.2 (22.7) 3.7 13.4 125.4 (4.6) (49.2) Deferred Income Taxes, Net: Federal 135.8 147.5 74.5 33.4 138.0 88.0 79.6 28.1 114.9 49.8 64.5 84.7 State 0.2 25.7 9.3 6.0 (7.1) 20.1 15.2 6.0 15.1 (1.0) 11.2 2.3 Total Deferred 136.0 173.2 83.8 39.4 130.9 108.1 94.8 34.1 130.0 48.8 75.7 87.0 Investment Tax Credits, Net (1.3) (1.3) - (0.5) (1.5) (1.3) - (0.5) (1.7) (1.3) - (0.4) Income Tax Expense $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 $ 141.7 $ 172.9 $ 71.1 $ 37.4 A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2015 2014 2013 Income Before Income Tax Expense $ 1,425.9 $ 1,295.4 $ 1,220.6 Statutory Federal Income Tax Expense at 35% 499.1 453.4 427.2 Tax Effect of Differences: Depreciation (4.6) (5.6) (7.4) Investment Tax Credit Amortization (3.6) (3.9) (4.1) Other Federal Tax Credits (3.8) (3.5) (3.7) State Income Taxes, Net of Federal Impact 61.1 42.5 27.6 Dividends on ESOP (8.1) (8.0) (8.0) Tax Asset Valuation Allowance/Reserve Adjustments 4.7 (2.9) (4.3) Other, Net (4.8) (3.7) (0.4) Income Tax Expense $ 540.0 $ 468.3 $ 426.9 Effective Tax Rate 37.9% 36.2% 35.0% For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars, NSTAR NSTAR NSTAR except percentages) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Income Before Income Tax Expense $ 476.8 $ 572.6 $ 187.5 $ 93.5 $ 421.2 $ 505.1 $ 186.1 $ 95.1 $ 421.1 $ 441.4 $ 182.5 $ 97.8 Statutory Federal Income Tax Expense at 35% 166.9 200.4 65.6 32.7 147.4 176.8 65.1 33.3 147.4 154.5 63.9 34.2 Tax Effect of Differences: Depreciation (1.7) (1.4) 0.5 (0.3) (3.6) (1.3) 0.3 (0.2) (7.0) 0.1 0.6 - Investment Tax Credit Amortization (1.3) (1.3) - (0.5) (1.5) (1.3) - (0.5) (1.7) (1.3) - (0.4) Other Federal Tax Credits - - (3.8) - - - (3.5) - - - (3.7) - State Income Taxes, Net of Federal Impact 9.2 29.6 9.9 4.9 4.4 26.2 9.8 5.0 5.0 18.6 9.6 4.2 Tax Asset Valuation Allowance/ Reserve Adjustments 1.2 - - - (6.3) - - - 0.4 - - - Other, Net 3.1 0.7 0.9 0.2 (6.9) 1.6 0.4 (0.3) (2.4) 1.0 0.7 (0.6) Income Tax Expense $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 $ 141.7 $ 172.9 $ 71.1 $ 37.4 Effective Tax Rate 37.2% 39.8% 39.0% 39.6% 31.7% 40.0% 38.7% 39.2% 33.6% 39.2% 39.0% 38.2% Eversource , CL&P, NSTAR Electric, PSNH and WMECO file a consolidated federal income tax return and unitary, combined and separate state income tax returns. These entities are also parties to a tax allocation agreement under which taxable subsidiaries do not pay any more taxes than they would have otherwise paid had they filed a separate company tax return, and subsidiaries generating tax losses, if any, are paid for their losses when utilized. Deferred tax assets and liabilities are recognized for the future tax effects of temporary differences between the carrying amounts and the tax basis of assets and liabilities. The tax effect of temporary differences is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and relevant accounting authoritative literature . The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows: Eversource As of December 31, (Millions of Dollars) 2015 2014 Deferred Tax Assets: Employee Benefits $ 637.5 $ 632.2 Derivative Liabilities 172.7 199.6 Regulatory Deferrals - Liabilities 243.5 366.7 Allowance for Uncollectible Accounts 60.5 60.5 Tax Effect - Tax Regulatory Liabilities 9.7 10.0 Federal Net Operating Loss Carryforwards 5.4 59.1 Purchase Accounting Adjustment 119.3 126.2 Other 197.1 198.7 Total Deferred Tax Assets 1,445.7 1,653.0 Less: Valuation Allowance 3.7 5.1 Net Deferred Tax Assets $ 1,442.0 $ 1,647.9 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 4,602.6 $ 4,215.9 Property Tax Accruals 76.7 109.6 Regulatory Amounts: Regulatory Deferrals - Assets 1,289.1 1,277.9 Tax Effect - Tax Regulatory Assets 249.3 240.2 Goodwill Regulatory Asset - 1999 Merger 194.9 203.2 Derivative Assets 17.7 32.6 Other 159.4 196.3 Total Deferred Tax Liabilities $ 6,589.7 $ 6,275.7 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Deferred Tax Assets: Employee Benefits $ 126.1 $ 91.3 $ 37.1 $ 10.0 $ 129.0 $ 39.9 $ 46.8 $ 9.2 Derivative Liabilities 165.7 0.6 - - 193.0 1.8 - - Regulatory Deferrals - Liabilities 36.0 109.4 42.1 6.1 73.9 181.3 46.5 11.4 Allowance for Uncollectible Accounts 30.4 8.5 3.6 4.5 32.3 13.8 3.2 3.8 Tax Effect - Tax Regulatory Liabilities 3.1 1.5 2.3 2.4 3.1 1.8 2.1 2.5 Federal Net Operating Loss Carryforwards - - 2.4 0.4 - - 32.1 4.5 Other 55.5 3.4 61.1 5.0 53.8 19.9 48.9 4.9 Total Deferred Tax Assets 416.8 214.7 148.6 28.4 485.1 258.5 179.6 36.3 Less: Valuation Allowance 3.1 - - - 4.0 - - - Net Deferred Tax Assets $ 413.7 $ 214.7 $ 148.6 $ 28.4 $ 481.1 $ 258.5 $ 179.6 $ 36.3 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 1,545.6 $ 1,387.1 $ 655.3 $ 416.1 $ 1,378.6 $ 1,296.9 $ 596.6 $ 385.8 Property Tax Accruals 27.3 22.8 7.3 10.6 58.1 25.0 7.4 12.8 Regulatory Amounts: Regulatory Deferrals - Assets 456.8 339.7 137.9 60.5 502.3 276.0 147.6 60.4 Tax Effect - Tax Regulatory Assets 168.7 36.0 15.4 9.0 166.9 35.5 15.9 9.3 Goodwill Regulatory Asset - 1999 Merger - 167.4 - - - 174.4 - - Derivative Assets 17.7 - - - 32.6 - - - Other 18.5 22.0 38.6 2.7 19.4 33.5 35.6 2.8 Total Deferred Tax Liabilities $ 2,234.6 $ 1,975.0 $ 854.5 $ 498.9 $ 2,157.9 $ 1,841.3 $ 803.1 $ 471.1 Carryforwards: The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards: As of December 31, 2015 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Expiration Range Federal Net Operating Loss $ 15.5 $ - $ - $ 7.0 $ 1.0 2032 Federal Tax Credit 26.1 0.1 0.2 15.0 - 2031 - 2035 Federal Charitable Contribution 14.9 - - - - 2016 - 2018 State Tax Credit 101.2 73.8 - - - 2015 - 2020 State Charitable Contribution 3.0 - - - - 2015 - 2019 As of December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Expiration Range Federal Net Operating Loss $ 168.8 $ - $ - $ 91.8 $ 12.7 2031 - 2032 Federal Tax Credit 16.3 0.1 0.2 11.1 - 2031 - 2034 Federal Charitable Contribution 19.4 - - - - 2016 - 2018 State Tax Credit 99.7 71.0 - - - 2014 - 2019 State Loss Carryforwards 40.6 - - - - 2014 - 2034 State Charitable Contribution 2.1 - - - - 2015 - 2018 In 2015, the Company decreased its valuation allowance reserve for state credits and state loss carryforwards by $1.3 million (CL&P $0.9 million), net of tax, to reflect an update for expired state tax credits and loss carryforwards . In 2014, the Company recorded a reduction to its state credit carryforwards of $11 million (CL&P $ 10.1 million), net of tax, as a result of an update to reflect the amounts expired. Further, the Company decreased its valuation allowance reserve for state credits by $19.2 million at CL&P, net of tax, to reflect an update for expired state credits and latest estimate of usage. For 2015 and 2014, state credit and state loss carryforwards have been partially reserved b y a valuation allowance of $3.1 million and $4.4 million (net of tax) , respectively . Unrecognized Tax Benefits : A reconciliation of the activity in unrecognized t ax benefits , all of which woul d impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2013 $ 83.1 $ 49.0 Gross Increases - Current Year 8.2 2.1 Gross Decreases - Prior Year (1.1) (0.3) Settlements (49.8) (39.4) Lapse of Statute of Limitations (2.2) - Balance as of December 31, 2013 38.2 11.4 Gross Increases - Current Year 9.3 2.7 Gross Increases - Prior Year 0.3 0.2 Lapse of Statute of Limitations (1.6) - Balance as of December 31, 2014 46.2 14.3 Gross Increases - Current Year 9.9 2.6 Gross Increases - Prior Year 0.1 - Lapse of Statute of Limitations (8.2) (3.4) Balance as of December 31, 2015 $ 48.0 $ 13.5 Interest and Penalties: Interest on uncertain tax positions is recorded and generally classified as a component of Other Interest Expense on the statements of income . However, when resolution of uncertainties results in the Company receiving interest income, any related interest benefit is recorded in Other Income, Net on the statements of income. No penalties have been recorded. The amount of interest expense/(income) on uncertain tax positions recognized and the related accrued interest payable/(receivable) are as follows: Other Interest Expense/(Income) Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2015 2014 2013 2015 2014 Eversource $ 0.1 $ 0.4 $ (8.6) $ 2.0 $ 1.9 CL&P 0 - (4.0) - - Tax Positions: During 2015 and 2014, Eversource did not resolve any of its uncertain tax positions . Open Tax Years: The following table summarizes Eversource , CL&P, NSTAR Electric, PSNH and WMECO's tax years that remain subject to examination by major tax jurisdictions as of December 31, 201 5 : Description Tax Years Federal 2015 Connecticut 2012 - 2015 Massachusetts 2012 - 2015 New Hampshire 2012 - 2015 Eversource estimates that during the next twelve months, differences of a non-timing nature could be resolved, resulting in a zero to $ 2.3 million decrease in unrecognized tax benefits by Eversource . These estimated changes are not expected to have a material impact on the earnings of Eversource . Other companies' impacts are not expected to be material. 201 5 Federal Legislation: On December 18, 2015, the "Protecting Americans from Tax Hikes" Act became law, which extended the accelerated deduction of depreciation to businesses from 2015 through 2019. This extended stimulus provides Eversource with cash flow benefits in 2016 of approximately $ 275 mil lion ( including appro ximately $105 million for CL&P, $7 2 million for NSTAR Electric, $46 million for PSNH, and $25 million for WMECO ) due to a refund of taxes paid in 2015 and lower expected tax payments in 2016 of approximately $300 million. 201 5 Connecticut Legislation : In 2015, the state of Connecticut enacted several changes to its corporate tax laws. Among the changes, commencing as of January 1, 2015, is the reduction in the amount of tax credits that corporations can utilize against its tax liability in a year and a continuation of the corporate income tax surcharge through 2018, which effectively increases the state corporate tax rate to 9 percent for the years 2016 and 2017 and 8.25 percent for 2018. Also, effective January 1, 2016, all Connecticut companies have a mandatory unitary tax filing requirement. Management continues to review the tax law changes and their impact on the effective tax rates of Eversource and CL& P . 2014 Federal Legislation: On December 19, 2014, the "Tax Increase Prevention Act of 2014" became law, which extended the accelerated deduction of depreciation to businesses through 2014. This extended stimulus provide d Eversource with cash flow benefits of approximately $ 250 million (approximately $ 86 million at CL&P, $ 64 million at NSTAR Electric, $ 44 million at PSNH, and $ 2 1 million at WMECO) in 2015.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Commitments and Contingencies Disclosure [Text Block]	11 . COMMITMENTS AND CONTINGENCIES A. Environmental Matters General: Eversource , CL&P, NSTAR Electric, PSNH and WMECO are subject to environmental laws and regulations intended to mitigate or remove the effect of past operations and improve or maintain the quality of the environment. These laws and regulations require the removal or the remedy of the effect on the environment of the disposal or release of certain specified hazardous substances at current and former operating sites. Eversource , CL&P, NSTAR Electric , PSNH and WMECO have an active environmental auditing and training program and believe that they are substantially in compliance with all enacted laws and regulations. Environmental reserves are accrue d when assessments indicate it is probable that a liability has been incurred and an amount can be reasonably estimated. The approach used estimates the liability based on the most likely action plan from a variety of available remediation options, including no action required or several different remedies ranging from establishing institutional controls to full site remediation and monitoring. These liabilities are estimated on an undiscounted basis and do not assume that the amounts are recoverable from insurance companies or other third parties. The environmental reserves include sites at different stages of discovery and remediation and do not include any unasserted claims. These estimates are subjective in nature as they take into consideration several different remediation options at each specific site. The reliability and precision of these estimates can be affected by several factors, including new information concerning either the level of contamination at the site, the extent of Eversource , CL&P, NSTAR Electric, PSNH and WMECO's responsibility for remediation or the extent of remediation required, recently en acted laws and regulations or change s in cost estimates due to certain economic factors. It is possible that new information or future developments could require a reassessment of the potential exposure to related environmental matters. As this information becomes available, management will continue to assess the potential exposure and adjust the reserves accordingly. The amounts recorded as environmental reserves included in Other Current Liabilities and Other Long-Term Liabilities on the balance sheets represent management's best estimate of the liability for environmental costs, and take into co nsideration site assessment, remediation and long-term monitoring costs . The environmental reserves also tak e into account recurring costs of managing hazardous substances and pollutants, mandated expenditures to remediate previously contaminated sites and any other inf requent and non-recurring clean- up costs. A reconciliation of the activity in the environmental reserves is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Balance as of January 1, 2014 $ 35.4 $ 3.4 $ 1.2 $ 5.4 $ 0.4 Additions 12.7 1.0 - 0.1 0.2 Payments/Reductions (4.8) (0.6) (0.1) (0.3) (0.1) Balance as of December 31, 2014 43.3 3.8 1.1 5.2 0.5 Additions 13.5 1.3 2.0 2.3 0.2 Payments/Reductions (5.7) (0.5) (0.7) (3.0) (0.1) Balance as of December 31, 2015 $ 51.1 $ 4.6 $ 2.4 $ 4.5 $ 0.6 The number of related env ironmental sites and reserves for which remediation or long- term monitoring , preliminary site work or site assessment is being performed are as follow s: As of December 31, 2015 As of December 31, 2014 Reserve Reserve Number of Sites (in millions) Number of Sites (in millions) Eversource 64 $ 51.1 65 $ 43.3 CL&P 14 4.6 16 3.8 NSTAR Electric 15 2.4 13 1.1 PSNH 12 4.5 13 5.2 WMECO 4 0.6 4 0.5 Included in the Eversource number of sites and reserve amounts above are former MGP sites that were operated several decades ago and manufactured gas from coal and other processes, which resulted in certain by-products remaining in the environment that may pose a potential risk to human health and the environment , for which Eversource may have potential liability . The reserve balance s related to these former MGP sites w ere $ 45.5 mi llion and $38.8 million as of December 31, 201 5 and 201 4 , respectively, and related primarily to the natural gas business segment. As o f December 31, 2015 , for 9 environmental sites ( 3 for CL&P , 1 for WMECO) that are included in the Company's reserve for environmental costs, the information known and the nature of the remediation options allow for the Company to estimate the range of losses for environmental costs. As of December 31, 201 5 , $ 24.7 million ( including $ 1.7 million for CL&P and $ 0.3 million for WMECO ) had been accrued as a liability for these sites, which represent s the low end of the range of the liabilities for environmental costs. Management believes that a dditional losses of up to approximately $ 33.9 million (approximately $ 1.4 million for CL&P, and $ 0. 1 million for WMECO) may be incurred in remediating these sites . As of D ecember 31, 2015 , for 12 environmental sites ( 3 for CL&P and 2 for NSTAR Electric ) that are included in the Company's reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to und ertake. As of December 31, 201 5 , $ 13.7 million ( including $ 2 million for CL&P ) had been accrued as a liability for these sites. As of December 31, 20 1 5 , for the remaining 43 environmental sites ( including 8 for CL&P, 13 for NSTAR Electric, 12 for PSNH, and 3 for WMECO) that are included in the Company's reserve for environmental costs, the $ 12.7 million accrual ( including $ 0.9 million for CL&P, $ 2.4 million for NSTAR Electric, $ 4.5 million for PSNH, and $ 0.3 million for WMECO) represents management's best estimate of the potential liability and no additional loss is anticipated at this time. CERCLA: Of the total environmental sites , nine sites ( four for NSTAR Electric and three for PSNH ) are superfund sites under t he federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) and its amendments or state equivalents for which the Company has been notified that it is a potentially responsible party but for which the site assessment and remediation are not being managed by the C ompany. As of December 31, 201 5 , a liability of $ 0. 8 mi llion accrued on these sites represents management's best estimate of its potential remediation costs with respect to these superfund sites. Environmental Rate Recovery: PSNH, NSTAR Gas and Yankee Gas have rate recovery mechanisms for MGP related environmental costs , therefore, changes in their respective environmental reserves do not impact Net Income . CL&P recovers a certain level of environmental costs currently in rates . CL&P, NSTAR Electric and WMECO do not have a separate environmental cost recovery regulatory mechanism . B. Long-Term Contractual Arrangements Estimated Future Annual Costs: The estimated future annual costs of significant long-term contractual arrangements as of December 31, 2015 are as follows: Eversource (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 177.4 $ 110.1 $ 81.5 $ 51.1 $ 34.9 $ 80.6 $ 535.6 Renewable Energy 246.6 273.3 238.3 237.4 237.0 2,174.7 3,407.3 Peaker CfDs 55.8 41.1 20.4 7.8 4.0 3.6 132.7 Natural Gas Procurement 137.9 123.8 78.4 57.8 46.9 99.7 544.5 Coal, Wood and Other 45.4 23.3 3.4 1.9 1.9 13.1 89.0 Transmission Support Commitments 21.4 19.0 20.3 20.2 20.2 - 101.1 Total $ 684.5 $ 590.6 $ 442.3 $ 376.2 $ 344.9 $ 2,371.7 $ 4,810.2 CL&P (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 145.0 $ 87.2 $ 58.2 $ 38.0 $ 29.3 $ 47.6 $ 405.3 Renewable Energy 70.1 71.7 72.1 72.3 72.4 649.7 1,008.3 Peaker CfDs 55.8 41.1 20.4 7.8 4.0 3.6 132.7 Transmission Support Commitments 8.4 7.5 8.0 8.0 8.0 - 39.9 Yankee Companies Billings 0.1 0.4 0.8 0.8 0.8 10.7 13.6 Total $ 279.4 $ 207.9 $ 159.5 $ 126.9 $ 114.5 $ 711.6 $ 1,599.8 NSTAR Electric (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 14.1 $ 4.8 $ 5.5 $ 5.5 $ 3.1 $ 28.1 $ 61.1 Renewable Energy 99.0 117.0 80.4 78.5 76.6 489.8 941.3 Transmission Support Commitments 6.6 5.9 6.3 6.2 6.2 - 31.2 Yankee Companies Billings 0.1 0.2 0.3 0.3 0.3 3.6 4.8 Total $ 119.8 $ 127.9 $ 92.5 $ 90.5 $ 86.2 $ 521.5 $ 1,038.4 PSNH (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 18.3 $ 18.1 $ 17.8 $ 7.6 $ 2.5 $ 4.9 $ 69.2 Renewable Energy 67.9 69.0 70.1 70.7 72.0 860.4 1,210.1 Coal, Wood and Other 45.4 23.3 3.4 1.9 1.9 13.1 89.0 Transmission Support Commitments 4.6 4.0 4.3 4.3 4.3 - 21.5 Yankee Companies Billings 0.1 0.2 0.3 0.3 0.3 4.2 5.4 Total $ 136.3 $ 114.6 $ 95.9 $ 84.8 $ 81.0 $ 882.6 $ 1,395.2 WMECO (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Renewable Energy $ 9.6 $ 15.6 $ 15.7 $ 15.9 $ 16.0 $ 174.8 $ 247.6 Transmission Support Commitments 1.8 1.6 1.7 1.7 1.7 - 8.5 Yankee Companies Billings - 0.1 0.2 0.2 0.2 2.7 3.4 Total $ 11.4 $ 17.3 $ 17.6 $ 17.8 $ 17.9 $ 177.5 $ 259.5 Supply and Stranded Cost: CL&P, NSTAR Electric and PSNH have various IPP contracts or purchase obligations for electricity, including payment obligations resulting from the buydown of electricity purchase contracts. Such contracts extend throug h 202 4 for CL&P , 203 1 for NSTAR Electric and 2023 for PSNH . In addition, CL&P , along with UI , has four capacity CfDs for a total of approximately 787 MW of capacity consisting of three generation projects and one demand response project. The capacity CfDs extend through 2026 a nd obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set contractual capacity price and the capacity market prices received by the generation facilities in the ISO-NE capacity markets. CL&P has a sharing agreement with UI, whereby UI will share 20 percent of the costs and benefits of these contracts. CL&P's portion of the costs and benefits of these contracts will be paid by or refunded to CL&P's customers . The contractual obligations table above does not include CL&P's, NSTAR Electric's or WMECO's default service contracts, the amounts of which vary with customers' energy needs. The contractual obligations table also does not include PSNH's short-term power supply management. Renewable Energy: Renewable energy contracts include non-cancellable commitments under contracts of CL&P, NSTAR Electric, PS NH, and WMECO for the purchase of energy and capacity from renewable energy facilities. Such contracts extend throug h 2035 fo r CL&P, 2031 for NSTAR Electric, 203 3 for PSNH and 2031 for WMECO. The contractual obligations table above does not include long-term commitments signed by CL&P, NSTAR Electric and WMECO, as required by the PURA and DPU, for the purchase of renewable energy and related products that are contingent on the future construction of energy facilities. Peaker CfDs : In 2008, CL&P entered into three CfDs with developers of peaking g eneration units approved by PURA ( Peaker CfDs ). These units have a total of approximately 500 MW of peakin g capacity. As directed by P URA , CL&P and UI have entered into a sharing agreement, whereby CL&P is responsible for 80 percent and UI for 20 percent of the net costs or benefits of these CfDs . The Peaker CfDs pay the generation facility owner the difference between capacity, forward reserve and energy market revenues and a cost-of-service payment stream for 30 years. The ultimate cost or benefit to CL&P under these contracts will depend on the costs of plant operation and the prices that the projects receive for capacity and other products in the ISO-NE markets. CL&P's portion of the amounts paid or received under the Peaker CfDs will be recoverable from or refunded to CL&P's customers. Natural Gas Procurement : In the normal course of business, Eversource 's natural g as distribution business es have long-term contracts for the purchase , transportation and storage of natural gas as part of its portfolio of supplies. The se contracts extend through 2029 . Coal , Wood and Other : PSNH has entered into various arrang ements for the purchase of coal , wood and the transportation services for fuel supply for i ts electric generating assets. Also included in the contractual obligations table above is a contract for capacity on the Portland Natural Gas Transmission System (PNGTS) pipeline that extends through 201 8 . The costs of this contract of $ 4.5 million are not recoverable from customers. Transmission Support Commitments: Along with other New England utilities, CL&P, NSTAR Electric, PSNH and WMECO entered into agreements in 1985 to support transmission and terminal facilities that were built to import electricity from the Hydro-Québec system in Canada. CL&P, NSTAR Electric, PSNH and WMECO are obligated to pay, over a 30-year period ending in 2020, their proportionate shares of the annual operation and maintenance expenses and capital costs of those facilities. Yankee Companies Billings : CL&P , NSTAR Electric , PSNH and WMECO have decommissioning and plant closure cost obligations to the Yankee Companies, which have each completed the physical decommissioning of their respective nuclear facilities and are now engaged in the long-term storage of their spent fuel. For further information on the Yankee Companies, see Note 11C, "Commitments and Contingencies - Contractual Obligations - Yankee Companies," to the financial statements. The total cost s incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Supply and Stranded Cost $ 147.6 $ 99.2 $ 141.0 Renewable Energy 144.3 114.4 91.3 Peaker CfDs 42.7 18.1 51.9 Natural Gas Procurement 428.6 482.5 349.8 Coal, Wood and Other 95.9 120.5 112.6 Transmission Support Commitments 25.3 25.0 24.9 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Supply and Stranded Cost $ 120.3 $ 6.5 $ 20.8 $ - $ 63.0 $ 7.0 $ 26.0 $ 3.2 $ 77.6 $ 32.4 $ 29.0 $ 2.0 Renewable Energy 20.0 86.7 37.2 0.4 0.7 87.4 26.3 - - 84.9 6.4 - Peaker CfDs 42.7 - - - 18.1 - - - 51.9 - - - Coal, Wood and Other - - 95.9 - - - 120.5 - - - 112.6 - Transmission Support Commitments 10.0 7.8 5.4 2.1 9.9 7.7 5.3 2.1 9.8 7.7 5.3 2.1 C . Contractual Obligations - Yankee Companies CL&P, NSTAR Electric, PSNH and WMECO have plant closure and fuel storage cost obligations to the Yankee Companies, which have each completed the physical decommissioning of their respective nuclear facilities and are now engaged in the long-term storage of their spent fuel. The Yankee Companies collect these costs through wholesale, FERC-approved rates charged under power purchase agreements with several New England utilities, including CL&P, NSTAR Electric, PSNH and WMECO. These companies in turn recover these costs from their customers through state regulatory commission-app roved retail rates. The Yankee Companies have collected or are currently collecting amounts that management believes are adequate to recover the remaining plant closure and fuel storage cost estimates for the respective plants. Management believes CL&P, NSTAR Electric and WMECO will recover their shares of these obligations from their customers. PSNH has recovered its total share of these costs from its customers. CL&P, NSTAR Electric, PSNH and WMECO's percentage share of the obligations to support the Yankee Companies under FERC-approved rate tariffs is the same as their respective ownership percentages in the Yankee Companies. For further information on the ownership percentages, see Note 1J, "Summary of Significant Accounting Policies - Equity Method Investments," to the financial statements. Spent Nuclear Fuel Litigation: DOE Phase I Damages – In 2013 , CYAPC, YAEC and MYAPC received proceeds of $39.6 million, $38.3 million , and $81.7 million , respectively, based on a final court judgment awarding damages for separate complaints filed by the Yankee Companies in 1998 against the DOE seeking monetary damages resulting from the DOE's failure to begin accepting spent nuclear fuel for disposal pursuant to the terms of the 1983 spent fuel and high level waste disposal contracts between the Yankee Companies and the DOE (DOE Phase I Damages). Phase I covered damages for the period 1998 through 2002. In 2013 , CYAPC, YAEC and MYAPC reduce d rates in their wholesale power contracts through the application of the DOE proceeds for the benefit of customers. CL&P, NSTAR Electric, PSNH and WMECO began receiving the benefit of the Phase I DOE proceeds in 2013 , and the benefits are being passed on to customers. In accordance with MYAPC 's three-year ref und plan of the DOE Phase I Damages proceeds , in September 2014, MYAPC returned the second portion of the proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, in the amount of $3.2 million, $1.1 million, $1.4 million and $0.8 million, respectively. On September 28, 2015, MYAPC returned the remaining DOE Phase I Damages proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, in the amount of $ 2.3 million, $ 0.8 million, $ 1 million and $ 0.6 million, respectively. These amounts reduced receivables at CL&P, NSTAR Electric, PSNH and WMECO . DOE Phase II Damages - In 2014, CYAPC, YAEC and MYAPC received proceeds of $126.3 million, $73.3 million and $35.8 million, respectively, based on a final court judgment awarding damages for separate lawsuits filed by the Yankee Companies in 2007 against the DOE seeking recovery of actual damages incurred related to the alleged failure of the DOE to provide for a permanent facility to store spent nuclear fuel generated in years 2001 through 2008 for CYAPC and YAEC, and from 2002 through 2008 for MYAPC (DOE Phase II Damages). The Yankee Companies returned the DOE Phase II Damages proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, for the benefit of their respective customers in June 2014. As of December 31 , 2014, CL&P's refund obligation to customers of $65.4 million was recorded as an offset to the deferred storm restoration costs regulatory asset, as directed by PURA. NSTAR Electric's, PSNH's and WMECO's refund obligation to customers of $29.1 million, $13.1 million and $18.1 million, respectively, was recorded as a regulatory liability in each company's respective regulatory tracker mechanisms. Refunds to customers for these Phase II DOE proceeds were completed in 2015 . DOE Phase III Damages – I n August 2013, the Yankee Companies each filed subsequent lawsuits against the DOE seeking recovery of actual damages incurred in the years 2009 through 2012. The DOE Phase III trial concluded on July 1, 2 015, with a post-trial briefing that concluded on October 14, 2015. The parties are a waiting a decision from the court. D . Guarantees and Indemnifications I n the normal course of business , Eversource parent provides credit assurances on behalf of its subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, in the form of guarantees. Eversource parent issued a declining balance guaranty on behalf of a wholly-owned subsidiary to guarantee the payment of the subsidiary's capital contributions for its investment in the Access Northeast project. The guarantee will not exceed $206 million and will decrease as capital contributions are made . The guaranty will expire upon the earlier of the full performance of the guaranteed obligations or December 31, 2021. Eversource parent issued a guaranty on behalf of its subsidiary, NPT, under which, beginning at the time the Northern Pass Transmission line goes into commercial operation, E versource parent will guarantee the financial obligations of NPT under the TSA with HQ in an amount not to exceed $25 million. E versource parent 's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations. E versource parent has also guarantee d certain indemnification and other obligations as a result of the sale s of former unregulated subsidiar ies and the termination of an unregulated business , with maximum exposure s either not specified or not material. Management does not anticipate a material impact to Net Income as a result of these various guarantees and indemnifications. T he following table summarizes Eversource parent 's exposure to guarantees and indemnifications of its subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, and guarantees to external parties, as of December 31, 2015 : Maximum Exposure Company Description (in millions) Expiration Dates On behalf of subsidiaries: Various Surety Bonds (1) $ 32.7 2016 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate $ 11.4 2019 and 2024 On behalf of external parties: Algonquin Gas Transmission, LLC Access Northeast project (owner of Access Northeast assets) capital contributions guarantee $ 204.8 2021 (1) Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended. Certain surety bonds contain credit rating s triggers that would require Eversource parent to post collateral in the event that the unsecured debt credit ratings of Eversource are downgraded. E . FERC ROE Complaint s Three separate complaints have been filed at FERC by combinations of New England state attorneys general, state regulatory commissions, consumer advocates, consumer groups, municipal parties and other parties (the "Complainants"). In the first complaint, filed in 2011, the Complainants alleged that the NETOs' base ROE that had been utilized since 2006 was unjust and unreasonable, asserted that the rate was excessive due to changes in the capital markets, and sought an order to reduce it prospectively from the date of the final FERC order and for the 15-month period beginning October 1, 2011 to December 31, 2012. In the second and third complaints, filed in 2012 and 2014, the Complainants challenged the NETOs' base ROE and sought refunds for the respective 15-month periods beginning December 27, 2012 and July 31, 2014. As a result of the actions taken by the FERC and ot her developments in the first complaint matter, the Company recorded additional reserves at its electric subsidiaries in 2015 and 2014. In 2015, Eversource recognized a pre-tax charge to earnings (excluding interest) of $20 million, of which $12.5 million was recorded at CL&P, $2.4 million at NSTAR Electric, $1 million at PSNH, and $4.1 million at WMECO. The pre-tax charge was recorded as a regulatory liability and as a reduction to Operating Revenues. In 2014, the net aggregate pre-tax charge to earni ngs (excluding interest) totaled $37 million, of which $20.7 million was recorded at CL&P, $7.9 million at NSTAR Electric, $2.8 million at PSNH and $5.6 million at WMECO . In 2013, the net aggregate pre-tax charge to earnings (excluding interest) totaled $23.7 million, of which $12.8 million was recorded at CL&P, $5.7 million at NSTAR Electric, $2.3 million at PSNH and $2.9 million at WMECO. The second and third complaint proceedings are ongoing and a final FERC order is expected in late 2016 or early 2017. Although management is uncertain on the final outcome of the second and third complaints regarding the ROE, management believes the current reserves established are appropriate to reflect probable and reasonably estimable refunds. F. N STAR Electric and NSTAR Gas Comprehensive Settlement Agreement On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the " Settlement " ) as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric ' s energy efficiency programs for 2009 through 2011 (11 dockets in total). In the first quarter of 2015, as a result of the DPU order, NSTAR Electric and NSTAR Gas commenced refunding a combined $44.7 million to customers, which was recorded as a regulatory liability. Refunds to customers will continue through December 2016. As a result of the Settlement, NSTAR Electric increased its operating revenues and decreased its amortization expense in 2015, resulting in the recognition of a $21.7 million pre-tax benefit in 2015. G. NSTAR Electric Basic Service Bad Debt Adder On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had removed energy-related bad debt costs from base distribution rates effective January 1, 2006. As a result of the DPU order, in the first quarter of 2015, NSTAR Electric increased its regulatory assets and reduced its operations and maintenance expense by an under recovered amount of $24.2 million for energy-related bad debt costs through 2014, resulting in a pre-tax benefit in 2015 . NSTAR Electric filed for recovery of the energy-related bad debt costs regulatory asset from customers and on November 20, 2015 the DPU approved NSTAR Electric's proposed rate increase, to recover these costs over a 12-month period, effective January 1, 2016. H . PSNH Generation Restructuring On June 10, 2015, Eversource and PSNH entered into the 2015 Public Service Company of New Hampshire Restructuring and Rate Stabilization Agreement (the Agreement) with the New Hampshire Office of Energy and Planning, certain members of the NHPUC staff, the Office of Consumer Advocate, two State Senators, and several other parties. The Agreement was filed with the NHPUC on the same day. Under the terms of the Agreement, PSNH has agreed to divest its generation assets upon NHPUC approval. The Agreement is designed to provide a resolution of issues pertaining to PSNH's generation a ssets in pending regulatory proceedings before the NHPUC. The Agreement provided for the Clean Air Project prudence proceeding to be resolved and all remaining Clean Air Project costs to be included in rates effective January 1, 2016. As part of the Agreement, PSNH has agreed to forego recovery of $25 million of the deferred equity return related to the Clean Air Project. In addition, PSNH will not seek a general distribution rate increase effective before July 1, 2017 and will contribute $5 million to create a clean energy fund, which will not be recoverable from its customers. In 2015, PSNH recorded the $5 million contribution as a long-term liability and an increase to Operations and Maintenance expense on the statements of income. Upon completion of the divestiture process, all remaining stranded costs will be recovered via bonds that will be secured by a non- bypassable charge or through other recoveries in rates billed to PSNH customers. On January 26, 2016, Advisory Staff of the NHPUC and the parties to the Agreement filed a stipulation with the NHPUC agreeing that near-term divestiture of PSNH's generation was in the public interest and that the Agreement should be approved. Implementation of the Agreement is subject to NHPUC approval, which is expected in early 2016. If the NHPUC approves the settlements and the sale of the plants, then management expect s to sell the plants in the first half of 2017. The sales price of the generating assets could be less than the carrying value, but we believe that full recovery of PSNH's generation assets is probable through a combination of cash flows during the remaining operating period, sales proceeds upon divestiture, and recovery of stranded costs in future rates. I . Litigation and Legal Proceedings Eversource , including CL&P, NSTAR Electric, PSNH and WMECO, are involved in legal, tax and regulatory proceedings regarding matters arising in the ordinary course of business, which involve management's assessment to determine the probability of whether a loss will occur and, if probable, its best estimate of probable loss. The Company records and discloses losses when these losses are pro bable and reasonably estimable, and discloses matters when losses are probable but not estimable or when losses are reasonably possible . L egal costs related to the defense of loss contingencies are expensed as incurred.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Leases of Lessee Disclosure [Text Block]	LEASES Eversource , including CL&P, NSTAR Electric, PSNH and WMECO, has entered into lease agreements, some of which are capital leases, for the use of data processing and office equipment, vehicles , service centers, and office space. In addition, CL&P , NSTAR Electric, PSNH and WMECO incur costs associated with leas es ent ered into by Eversource Service and Rocky River Realty Company , which are included below in their respective operating lease rental expenses and future minimum rental payments . These intercompany lease amounts are eliminated on an Eversource consolidated basis. The provisions of the Eversource , CL&P, NSTAR Electric, PSNH, and WMECO lease agreements generally contain renewal options. Certain lease agreements contain payments impacted by the commercial paper rate plus a credit spread or the consumer price index. Operating lease rental payments charged to expense are as follows: NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2015 $ 12.1 $ 12.5 $ 9.6 $ 2.8 $ 2.2 2014 14.3 6.0 7.8 1.5 1.2 2013 16.3 8.1 6.7 1.7 2.9 The 2015 rental payments above for CL&P, NSTAR Electric, PSNH, and WMECO include an intercompany rate of return , property tax and o perational expense component paid to Rocky River Realty Company. Future minimum rental payments , excluding executory costs, such as property taxes, state use taxes, insurance, and maintenance, under long-term noncancelable leases, as of December 31, 201 5 are as follows: Operating Leases NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2016 $ 16.4 $ 2.9 $ 9.7 $ 0.8 $ 0.8 2017 13.8 2.0 8.5 0.7 0.7 2018 10.4 1.3 6.5 0.5 0.6 2019 8.5 1.0 5.3 0.4 0.5 2020 6.8 0.7 4.3 0.3 0.5 Thereafter 15.4 1.7 9.0 0.7 1.8 Future minimum lease payments $ 71.3 $ 9.6 $ 43.3 $ 3.4 $ 4.9 Capital Leases (Millions of Dollars) Eversource CL&P PSNH 2016 $ 2.2 $ 1.9 $ 0.3 2017 2.1 1.9 0.2 2018 2.1 2.0 0.1 2019 2.0 2.0 0.0 2020 2.0 2.0 0.0 Thereafter 1.4 1.4 0.0 Future minimum lease payments 11.8 11.2 0.6 Less amount representing interest 3.6 3.6 0.0 Present value of future minimum lease payments $ 8.2 $ 7.6 $ 0.6 CL&P entered into certain contracts for the purchase of energy that qualify as leases. These contracts do not have minimum lease payments and therefore are not included in the tables above . However, such contracts have been included in the contractual obligations tabl e in N ote 1 1 B , "Commitments and Contingencies - Long-Term Contractual Arrangements," to the financial statements.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Fair Value Disclosures [Text Block]	13 . FAIR VALUE OF FINANCIAL INSTRUMENTS The following methods and assumptions were used to estimate the fair value of each of the following financial instruments: Preferred Stock and Long-Term Debt: The fair value of CL& P's and NSTAR Electric' s preferred stock is based upon pricing models that incorporate interest rates and other market factors, valuations or trades of similar securities and cash flow project ions. The fair value of long-term debt securities is based upon pricing models that incorporate quoted market prices for those issues or similar issues adjusted for market conditions, credit ratings of the respective companies and treasury benchmark yields. The fair values provided in the tables below are classified as Level 2 within the fair value hierarchy. Carrying amounts and estimated fair values are as follows : As of December 31, 2015 2014 Eversource Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 157.9 $ 155.6 $ 153.6 Long-Term Debt 9,034.5 9,425.9 8,814.0 9,451.2 As of December 31, 2015 CL&P NSTAR Electric PSNH WMECO Carrying Fair Carrying Fair Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 114.9 $ 43.0 $ 43.0 $ - $ - $ - $ - Long-Term Debt 2,763.7 3,031.6 2,029.8 2,182.4 1,071.0 1,121.2 517.3 551.8 As of December 31, 2014 CL&P NSTAR Electric PSNH WMECO Carrying Fair Carrying Fair Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 112.0 $ 43.0 $ 41.6 $ - $ - $ - $ - Long-Term Debt 2,826.2 3,214.5 1,786.2 1,993.5 1,070.0 1,137.9 625.2 689.4 Effective December 31, 2015, t he carrying amount of Long-Term Debt includes unamortized debt issuance costs presented as a direct reduction from the carrying amount of the debt liability, in accordance with new accounting guidance. The December 31, 2014 carrying amount of Long-Term Debt was retrospectively adjusted to conform to the current year presentation. See Note 1 C , "Summary of Significant Accounting Policies – Accounting Standards," for further information. Derivative Instruments: Derivative instruments are carried at fair value. For further information, see Note 4 , "Derivative In struments," to the financial statements. Other Financial Instruments: Investments in marketable securities are carried a t fair value . For further information, see Note 5 , "Marketable S ecurities," to the financial statements. The carrying value of other financial instruments included in current assets and current liabilities on the balance sheets , including cash and cash equivalents and special deposits, approximates their fair value due to the ir short-term nature . See Not e 1H , "Summary of Significant Accounting Policies - Fair Value Measurements," for the fair value measurement policy and the fair value hierarchy .

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Comprehensive Income Note [Text Block]	14. ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) The changes in accumulated other comprehensive income /( loss) by co mponent , net of tax effect , is as follows: For the Year Ended December 31, 2015 For the Year Ended December 31, 2014 Qualified Unrealized Qualified Unrealized Cash Flow Gains/(Losses) Defined Cash Flow Gains on Defined Eversource Hedging on Marketable Benefit Hedging Marketable Benefit (Millions of Dollars) Instruments Securities Plans Total Instruments Securities Plans Total Balance as of January 1 st $ (12.4) $ 0.7 $ (62.3) $ (74.0) $ (14.4) $ 0.4 $ (32.0) $ (46.0) OCI Before Reclassifications - (2.6) 3.5 0.9 - 0.3 (34.2) (33.9) Amounts Reclassified from AOCI 2.1 - 4.2 6.3 2.0 - 3.9 5.9 Net OCI 2.1 (2.6) 7.7 7.2 2.0 0.3 (30.3) (28.0) Balance as of December 31 st $ (10.3) $ (1.9) $ (54.6) $ (66.8) $ (12.4) $ 0.7 $ (62.3) $ (74.0) Eversource 's qualified cash flow hedging instruments represent interest rate swap agreements on debt issuances that were settled in prior years. The settlement amount was recorded in AOCI and is being amortized into Net Income over the term of the underlying debt instrument. CL&P, PSNH and WMECO continue to amortize interest rate swaps settled in prior years from AOCI into Interest Expense over the remaining life of the associated long-term debt . Such interest rate swaps are not material to their respective financial statements. The amortization expense of actuarial gains and losses and prior service cost on the defined benefit plans is amortized from AOCI into Operations and Maintenance over the average future employee service period, and is reflected in amounts reclassified from AOCI. Defined b enefit p lan OCI amounts before reclassifications relate to actuarial gains and losses that arose during the year and were recognized in AOCI . T he related tax effects recognized in AOCI during 2015 and 2013 were net deferred tax liabilities of $ 2 million in 2015 and $11.4 million in 201 3 , respectively, and net deferred tax assets of $22.3 million in 2014 . The follow ing table sets forth the amount s reclassified from AOCI by component and the impacted line item on the statements of income : Amounts Reclassified from AOCI Eversource For the Years Ended December 31, Statements of Income (Millions of Dollars) 2015 2014 2013 Line Item Impacted Qualified Cash Flow Hedging Instruments $ (3.5) $ (3.4) $ (3.4) Interest Expense Tax Effect 1.4 1.4 1.4 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (2.1) $ (2.0) $ (2.0) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (6.6) $ (6.2) $ (10.5) Operations and Maintenance (1) Amortization of Prior Service Cost (0.2) (0.2) (0.2) Operations and Maintenance (1) Total Defined Benefit Plan Costs (6.8) (6.4) (10.7) Tax Effect 2.6 2.5 4.3 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (4.2) $ (3.9) $ (6.4) Total Amounts Reclassified from AOCI, Net of Tax $ (6.3) $ (5.9) $ (8.4) (1) T hese amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 9 A, "Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pensions," for further information. As of December 31, 201 5 , it wa s estimated that a pre-tax amount of $3. 6 million ( including $0.7 million for CL &P, $2 million for PSNH and $0. 7 million for WMECO) will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of the interest rate swap agreements which have been settled. In addition, it is estimated that a pre-tax amount of $ 6 million will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of Pension, SERP and PBOP costs.

DIVIDEND RESTRICTIONS

DIVIDEND RESTRICTIONS	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Dividend Payment Restrictions [Table Text Block]	15. DIVIDEND RESTRICTIONS E versource parent's ability to pay dividends may be affected by certain state statutes, the ability of its subsidiaries to pay common dividends and the leverage restriction tied to its consolidated total debt to total capitalization ratio requirement in its revolving credit agreement. CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends from retained earnings for lawful and legitimate business purposes. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas . Such state law restrictions do not restrict the payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of Eversource , CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and to the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter . As of December 31, 201 5 , all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $ 2.8 billion for Eversource , $ 1.2 b illion for CL&P, $ 1.6 b illion for NSTAR Electric, $ 494.9 million for PSNH and $ 198.1 million for WMECO as of December 31, 201 5 . As of December 31, 201 5 , Eversource , CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends. PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 201 5 , $ 13.4 million of PSNH's Retained Earnings was subject to restriction under its FERC hy droelectric license conditions and PSNH was in compliance with this provision .

COMMON SHARES

COMMON SHARES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Stock by Class [Text Block]	16 . COMMON SHARES The following table sets forth the Eversource parent common shares and those of CL&P, NSTAR Electric , PSNH and WMECO that were authorized and issued as well as the respective per share par values : Shares Authorized Issued Per Share as of December 31, as of December 31, Par Value 2015 and 2014 2015 2014 Eversource $ 5 380,000,000 333,862,615 333,359,172 CL&P $ 10 24,500,000 6,035,205 6,035,205 NSTAR Electric $ 1 100,000,000 100 100 PSNH $ 1 100,000,000 301 301 WMECO $ 25 1,072,471 434,653 434,653 As of December 31, 201 5 and 201 4 , there were 16,671,366 and 16,375,835 Eversource common shares held as treasury shares , respectively . As of December 31, 201 5 and 201 4 , Eversource common shares outstanding were 317,191,249 and 316,983,337 , respectively. In May 2015, the Comp any repurchased 532,521 Eversource common shares at a share price of $47.94. Such shares are included in Treasury Stock on the consolidated balance sheet at their weighted average original average cost of $26.02 per share.

PREFFERED STOCK NOT SUBJECT TO

PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Preferred Stock Text Block	17. PREFERRED STOCK NOT SUBJE CT TO MANDATORY REDEMPTION The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in Eversource 's financial statements. CL&P is authorized to issue up to 9,000,000 shares of preferred stock, par value $50 per share, and NSTAR Electric is authorized to issue 2,890,000 shares of preferred stock, par value $100 per share. Holders of preferred stock of CL&P and NSTAR Electric are entitled to receive cumulative dividends in preference to any payment of dividends on the common stock. Upon liquidation, holders of preferred stock of CL&P and NSTAR Electric are entitled to receive a liquidation preference before any distribution to holders of common stock in an amount equal to the par value of the preferred stock plus accrued and unpaid dividends. If the net assets were to be insufficient to pay the liquidation preference in full, then the net assets would be distributed ratably to all holders of preferred stock. The preferred stock of CL&P and NSTAR Electric is subject to optional redemption by the CL&P and NSTAR Electric Board of Directors at any time. Details of preferred stock not subject to mandatory redemption are as follows (in millions except in redemption price and share s): Redemption Price Shares Outstanding as of As of December 31, Series Per Share December 31, 2015 and 2014 2015 2014 CL&P $ 1.90 Series of 1947 $ 52.50 163,912 $ 8.2 $ 8.2 $ 2.00 Series of 1947 $ 54.00 336,088 16.8 16.8 $ 2.04 Series of 1949 $ 52.00 100,000 5.0 5.0 $ 2.20 Series of 1949 $ 52.50 200,000 10.0 10.0 3.90 % Series of 1949 $ 50.50 160,000 8.0 8.0 $ 2.06 Series E of 1954 $ 51.00 200,000 10.0 10.0 $ 2.09 Series F of 1955 $ 51.00 100,000 5.0 5.0 4.50 % Series of 1956 $ 50.75 104,000 5.2 5.2 4.96 % Series of 1958 $ 50.50 100,000 5.0 5.0 4.50 % Series of 1963 $ 50.50 160,000 8.0 8.0 5.28 % Series of 1967 $ 51.43 200,000 10.0 10.0 $ 3.24 Series G of 1968 $ 51.84 300,000 15.0 15.0 6.56 % Series of 1968 $ 51.44 200,000 10.0 10.0 Total CL&P 2,324,000 $ 116.2 $ 116.2 NSTAR Electric 4.25 % Series $ 103.625 180,000 $ 18.0 $ 18.0 4.78 % Series $ 102.80 250,000 25.0 25.0 Total NSTAR Electric 430,000 $ 43.0 $ 43.0 Fair Value Adjustment due to Merger with NSTAR (3.6) (3.6) Total Eversource - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

COMMON SHARESHOLDERS' EQUITY AN

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	18. COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $ 7.5 million, $7.5 million and $7.7 million for the years ended December 31, 2015, 2014 and 2013. These dividends were presented as Net Income Attributable to Noncontrolling Interests on the Eversource statements of income. Noncontrolling Interest – Preferred Stock of Subsidiaries on the Eversource balance sheets totaled $ 155.6 million as of December 31, 2015 and 2014. Common Shareholders' Equity was fully attributable to the parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest on the Eversource balance sheets. For the years ended December 31, 201 5 , 201 4 and 201 3 , there was no change in ownership of the common equity of CL&P and NSTAR Electric.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Earnings Per Share [Text Block]	19 . EARNINGS PER SHARE Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is compu ted on the basis of the weighted average number of common shares outstanding during each period plus the potential dilut ive effect o f certain share-based compensation awards as if they were converted into common shares . For the year s ended December 31, 201 5 , 201 4 and 201 3 , there were 1,474 , 3,643 and 1,575 antidilutive share awards excluded from the computation of diluted EPS , respectively . The following table sets forth the components of basic and diluted EPS: Eversource For the Years Ended December 31, (Millions of Dollars, except share information) 2015 2014 2013 Net Income Attributable to Common Shareholders $ 878.5 $ 819.5 $ 786.0 Weighted Average Common Shares Outstanding: Basic 317,336,881 316,136,748 315,311,387 Dilutive Effect 1,095,806 1,280,666 899,773 Diluted 318,432,687 317,417,414 316,211,160 Basic EPS $ 2.77 $ 2.59 $ 2.49 Diluted EPS $ 2.76 $ 2.58 $ 2.49 RSU and performance share awards are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unve sted RSU and performance share awards is calculated using the treasury stock method. Assumed proceeds of the se awards under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the awards (the difference between the market value of the average awards outstanding for the period, using the average market price during the period, and the grant date market value). The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Segment Reporting Disclosure [Text Block]	20 . SEGMENT INFORMATION Presentation: Eversource is organized between the Electric Distribution, Electric Transmission and Natural Gas Distribution reportable segments and Other based on a combination of factors, including the characteristics of each segments' products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates. These reportable segments represent substantially all of Eversource's total consolidated revenues. Revenues from the sale of electricity and natural gas primarily are derived from residential, commercial and industrial customers and are not dependent on any single customer. The Electric Distribution reportable segment includes the generation activities of PSNH and WMECO. The remainder of Eversource's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of Eversource parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of Eversource parent, 2) the revenues and expenses of Eversource Service, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, 4) the results of Eversource Gas Transmission LLC and 5) the results of other unregulated subsidiaries, which ar e not part of its core business. Cash flows used for investments in plant included in the segment information below are cash capital expenditures that do not include amounts incurred but not paid, cost of removal, AFUDC related to equity funds, and the capitalized portions of pension expense. Eversource's reportable segments are determined based upon the level at which Eversource's chief operating decision maker assesses performance and makes decisions about the allocation of company resources. Each of Eversource's subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, has one reportable segment. Eversource's operating segments and reporting units are consistent with its reportable business segments. Eversou rce's segment information is as follows: For the Year Ended December 31, 2015 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,903.6 $ 995.5 $ 1,069.1 $ 863.6 $ (877.0) $ 7,954.8 Depreciation and Amortization (425.2) (70.5) (165.6) (29.0) 2.1 (688.2) Other Operating Expenses (4,470.2) (776.7) (314.9) (817.9) 877.3 (5,502.4) Operating Income 1,008.2 148.3 588.6 16.7 2.4 1,764.2 Interest Expense (186.3) (36.9) (105.8) (48.0) 4.6 (372.4) Interest Income 5.7 0.1 1.6 4.4 (5.1) 6.7 Other Income, Net 7.2 0.8 14.5 977.8 (972.8) 27.5 Income Tax (Expense)/Benefit (322.8) (40.1) (191.6) 14.5 - (540.0) Net Income 512.0 72.2 307.3 965.4 (970.9) 886.0 Net Income Attributable to Noncontrolling Interests (4.7) - (2.8) - - (7.5) Net Income Attributable to Common Shareholders $ 507.3 $ 72.2 $ 304.5 $ 965.4 $ (970.9) $ 878.5 Total Assets (as of) $ 17,981.3 $ 3,104.5 $ 8,019.3 $ 13,256.7 $ (11,781.5) $ 30,580.3 Cash Flows Used for Investments in Plant $ 718.9 $ 182.2 $ 749.1 $ 73.9 $ - $ 1,724.1 For the Year Ended December 31, 2014 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,663.4 $ 1,007.3 $ 1,018.2 $ 790.9 $ (737.9) $ 7,741.9 Depreciation and Amortization (384.6) (68.1) (150.5) (42.1) 19.9 (625.4) Other Operating Expenses (4,366.2) (786.7) (302.1) (748.0) 719.3 (5,483.7) Operating Income 912.6 152.5 565.6 0.8 1.3 1,632.8 Interest Expense (191.6) (34.0) (104.1) (36.6) 4.2 (362.1) Interest Income 5.1 - 0.9 3.6 (3.6) 6.0 Other Income, Net 10.7 0.2 10.3 916.0 (918.6) 18.6 Income Tax (Expense)/Benefit (269.7) (46.4) (174.5) 22.3 - (468.3) Net Income 467.1 72.3 298.2 906.1 (916.7) 827.0 Net Income Attributable to Noncontrolling Interests (4.7) - (2.8) - - (7.5) Net Income Attributable to Common Shareholders $ 462.4 $ 72.3 $ 295.4 $ 906.1 $ (916.7) $ 819.5 Total Assets (as of) $ 17,536.9 $ 3,029.3 $ 7,615.6 $ 12,664.9 $ (11,106.3) $ 29,740.4 Cash Flows Used for Investments in Plant $ 645.2 $ 176.7 $ 731.6 $ 50.2 $ - $ 1,603.7 For the Year Ended December 31, 2013 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,362.3 $ 855.8 $ 978.7 $ 777.5 $ (673.1) $ 7,301.2 Depreciation and Amortization (604.8) (66.7) (136.2) (62.2) 10.2 (859.7) Other Operating Expenses (3,927.7) (659.4) (281.8) (715.0) 671.8 (4,912.1) Operating Income 829.8 129.7 560.7 0.3 8.9 1,529.4 Interest Expense (175.0) (33.1) (100.3) (35.5) 5.2 (338.7) Interest Income 4.1 - 0.7 5.4 (5.6) 4.6 Other Income, Net 12.9 0.8 10.9 858.9 (858.2) 25.3 Income Tax (Expense)/Benefit (240.0) (36.5) (182.1) 31.9 (0.2) (426.9) Net Income 431.8 60.9 289.9 861.0 (849.9) 793.7 Net Income Attributable to Noncontrolling Interests (4.8) - (2.9) - - (7.7) Net Income Attributable to Common Shareholders $ 427.0 $ 60.9 $ 287.0 $ 861.0 $ (849.9) $ 786.0 Cash Flows Used for Investments in Plant $ 639.0 $ 168.1 $ 618.5 $ 31.2 $ - $ 1,456.8

GOODWILL

GOODWILL	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Goodwill Disclosure [Text Block]	21 . GOODWILL Eversource recorded approximately $ 3.2 billion of goodwill in connection with the 2012 merger with NSTAR and $0.3 billion of goodwill related to the acquisition of the parent of Yankee Gas in 2000 . G oodwill is not subject to amortization , h owever is subject to a fair value based assessment for impairment at least annually and whenever facts or circumstances indicate that there may be an impairment . A resulting write-down, if any, would be charged to O perating E xpense s . Eversource's reporting units for the purpose of testing goodwill for impairment are Electric Distribution, Electric Transmission and Natural Gas Distribution. These reporting units are consistent with the operating segments underlying the reportable segments identified in Note 2 0 , "Segment Information," to the financial statements. The annual goodwill assessment included an evaluation of the Company's share price and credit ratings, analyst reports, financial performance, cost and risk factors, long-term strategy, growth and future projections, as well as macroeconomic, industry and market conditions. Eversource completed its annual goodwill impairment test for each of its reporting units as of October 1, 201 5 and dete rmined that no impairment existed . There were no events subsequent to October 1, 2015 that indicated impairment of goodwill. There were no changes to the goodwill balance or the allocation of goodwill as of December 31, 2015 or 2014. The following table presents goodwill by reportable segmen t: As of December 31, 2015 and 2014 Electric Electric Natural Gas (Billions of Dollars) Distribution Transmission Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 3.5

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Variable Interest Entities Text Block	22 . VARIABLE INTEREST ENTITIES The Company's variable interests outside of the consolidated group are not material and consist of contracts that are required by regulation and provide for regulatory recovery of contract costs and benefits through customer rates. Eversource , CL&P and NSTAR Electric hold variable interests in variable interest entities ( VIEs ) through agreements with certain entities that own single renewable energy or peaking generation power plants and with other independent power producers. Eversource , CL&P and NSTAR Electric do not control the activities that are economically significant to these VIEs or provide financial or other support to these VIEs. Therefore, Eversource , CL&P and NSTAR Electric do not consolidate any power plant VIEs.

QUARTERLY FINANCIAL DATA (Unaud

QUARTERLY FINANCIAL DATA (Unaudited)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Quarterly Financial Information [Text Block]	QUARTERLY FINANCIAL DATA (UNAUDITED) 23. Eversource Quarter Ended (Millions of Dollars, except per share information) 2015 2014 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,513.4 $ 1,817.1 $ 1,933.1 $ 1,691.2 $ 2,290.6 $ 1,677.6 $ 1,892.5 $ 1,881.2 Operating Income 497.5 412.0 469.2 385.5 467.7 294.0 440.9 430.2 Net Income 255.1 209.4 237.8 183.7 237.8 129.2 236.5 223.6 Net Income Attributable to Common Shareholders 253.3 207.5 235.9 181.8 236.0 127.4 234.6 221.5 Basic EPS (a) $ 0.80 $ 0.65 $ 0.74 $ 0.57 $ 0.75 $ 0.40 $ 0.74 $ 0.69 Diluted EPS (a) $ 0.80 $ 0.65 $ 0.74 $ 0.57 $ 0.74 $ 0.40 $ 0.74 $ 0.69 (a) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2015 2014 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 804.9 $ 666.6 $ 704.3 $ 626.9 $ 734.6 $ 587.3 $ 695.6 $ 675.1 Operating Income 141.8 154.0 161.1 154.2 158.0 92.1 146.2 159.0 Net Income 69.2 78.8 80.2 71.2 79.3 37.4 83.9 87.2 NSTAR Electric Operating Revenues $ 766.8 $ 617.2 $ 750.7 $ 546.6 $ 666.2 $ 561.5 $ 727.9 $ 581.1 Operating Income 159.5 151.4 214.2 117.7 118.4 121.5 206.6 132.0 Net Income 83.6 82.0 118.6 60.3 58.1 60.1 115.6 69.3 PSNH Operating Revenues $ 284.8 $ 241.9 $ 234.4 $ 211.1 $ 299.8 $ 211.6 $ 223.7 $ 224.4 Operating Income 63.2 54.1 63.6 49.3 64.0 49.0 56.4 60.0 Net Income 32.0 27.9 32.5 22.0 32.6 24.1 28.2 29.0 WMECO Operating Revenues $ 152.9 $ 125.2 $ 125.1 $ 114.9 $ 137.4 $ 108.3 $ 118.1 $ 129.6 Operating Income 28.6 28.9 30.0 28.0 34.7 17.7 31.2 34.0 Net Income 13.2 14.2 15.0 14.1 18.1 7.0 14.7 18.0

SIGNIFCANT ACCOUNTING POLICIES

SIGNIFCANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Organization Consolidation And Presentation Of Financial Statements Disclosure Text Block	The consolidated financial statements of Eversource , NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource , NSTAR Electric and PSNH and the financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements." The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's, PSNH's and WMECO's combined ownership interest in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements . Eversource's utility subsidiaries' distribution (including generation ) and transmission businesses are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for entities with rate-regulated operations, which considers the effect of regulation on the differences in the timing of the recognition of certain revenues and expenses from those of other businesses and industries. See Note 2, "Regulatory Accounting," for further information. Certain r eclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation and as a result of the adoption of new accounting guidance . See Note 1C, "Summary of Significant Accounting Policies – Accounting Standards," for further information. In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource . The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on t he balance sheets of Eversource , CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Board s of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric. As of December 31, 201 5 and 201 4 , Eversource 's carrying amount of goodwill was approximately $3.5 billion. Eversource performs an assessment for possible impairment of its goodwill at least annually. Eversource completed its annual goodwill impairment test for each of its reporting units as of October 1, 201 5 and determined that no impairment exists. See Note 2 1 , "Goodwill , " for further information.
Fair Value Of Financial Instruments Policy	H . Fair Value Measurements Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases or normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans , the nonrecurring fair value measurements of nonfinancial assets such as goodwill and AROs, and the estimate d fair value of preferred stock and long-term debt. Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below: Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Determination of Fair Value: The valuation techniques and inputs used in Eversource 's fair value meas urements are described in Note 4 , " Der ivative Instruments, " Note 5 , " Marketable Securities, " Note 6 , " Asset Retirement Obligations, " Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pensions," and Note 13 , " Fair Value of Financial Instru ments " to the financial statements. Eversource , including CL&P, NSTAR Electric, PSNH and WMECO, recognizes a liability for the fair value of an ARO on the obligation date if the liability's fair value can be reasonably estimated and is conditional on a future event. Settlement dates and future costs are reasonably estimated when sufficient information becomes available. Management has identified various categories of AROs, primarily certain assets containing asbestos and hazardous contamination , and has performed fair value calculation s reflecting expected probabilities for settlement scenarios . The fair value of an ARO is recorded as a liability in Other Long -Term Liabilities with a corresponding amount included in Property, Plant and Equipment, Net on the balance sheets. The ARO assets are depreciated, and the ARO liabilities are accreted over the estimated life of the obligation with corresponding credits recorded as accumulated depreciation and ARO liabilities, respectively. As the Regulated companies are rate-regulated on a cost-of-service basis, these companies apply regulatory accounting guidance and both the depreciation and accretion costs associated with the Regulated companies' AROs are recorded as increases to Regulatory Assets on the balance sheets . The Company values assets based on observable inputs when available. Equity securities , exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Commingled funds included in Level 2 equity securities are recorded at the net asset value provided by the asset manager, which is based on the market prices of the underlying equity securities. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Fixed income securities , such as government issued securities, corporate bonds and high yield bond funds , are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Hedge funds and investments in opportunistic fixed income funds are recorded at net asset value based on the values of the underlying assets. The assets in the hedge funds and opportunistic fixed income funds are valued using observable inputs and are classified as Level 3 within the fair value hierarchy due to redemption restrictions. Private Equity investments and Real Estate and Other Assets are valued using the net asset value provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments. These investments are classified as Level 3 due to redemption restrictions. The following methods and assumptions were used to estimate the fair value of each of the following financial instruments:
Allowance For Funds Used During Construction Policy	M. Allowance for Funds Used During Construction AFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the Regulated companies' utility plant on the balance sheet . The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Other Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income . AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense . The Regulated companies' average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings and capitalization (preferred stock, long-term debt and common equity) , as appropriate . The average rate is applied to average eligible CWIP amounts to calculate AFUDC.
Other Taxes Policy	As agents for state and local governments, Eversource's companies that serve customers in Connecticut and Massachusetts collect certain sales taxes that are recorded on a net basis with no impact on the statements of income.
Public Utilities Policy Text Block	Eversource's Regulated companies are subject to rate-regulation that is based on cost recovery and meets the criteria for application of accounting guidance for rate-regulated operations, which consider s the effect of regulation on the timing of the recognition of certain revenues and expenses. The Regulated companies' financial statements reflect the effects of the rate-making process. The rates charged to the customers of Eversource's Regulated companies are designed to collect each company's costs to provide service, including a return on investment. Management believes it is probable that each of the Regulated companies will recover their respective investments in long-lived assets, including regulatory assets. If management were to determine that it could no longer apply the accounting guidance applicable to rate-regulated enterprises to any of the Regulate d companies' operations, or if management could not conclude it is probable that costs would be recovered from customers in future rates, the costs would be charged to net income in the period in which the determination is made.
Derivatives Policy Text Block	I . Derivative Accounting M any of the Regulated companies' cont racts for the purchase and sale of ene rgy or energy- related products are derivatives . The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the Regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts, as contract settlements are recovered from, or refunded to, customers in future rates. The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts . All of these judgments can have a signif icant impact on the financial statements. The judgmen t applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal and accrual accounting is terminated , and fair value accounting is applied prospectively. The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. All c hanges in the fair value of derivative contracts are recorded as regulatory asset s or liabilities and do not impact net income. For further information regarding derivative contracts , see Note 4 , " Derivative I nstruments, " to the financial statements.
Environmental Costs Policy	Environmental Matters General: Eversource , CL&P, NSTAR Electric, PSNH and WMECO are subject to environmental laws and regulations intended to mitigate or remove the effect of past operations and improve or maintain the quality of the environment. These laws and regulations require the removal or the remedy of the effect on the environment of the disposal or release of certain specified hazardous substances at current and former operating sites. Eversource , CL&P, NSTAR Electric , PSNH and WMECO have an active environmental auditing and training program and believe that they are substantially in compliance with all enacted laws and regulations.
Earnings Per Share Policy Text Block	RSU and performance share awards are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. The dilutive effect of unve sted RSU and performance share awards is calculated using the treasury stock method. Assumed proceeds of the se awards under the treasury stock method consist of the remaining compensation cost to be recognized and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the awards (the difference between the market value of the average awards outstanding for the period, using the average market price during the period, and the grant date market value). The dilutive effect of stock options to purchase common shares is also calculated using the treasury stock method. Assumed proceeds for stock options consist of cash proceeds that would be received upon exercise, and a theoretical tax benefit. The theoretical tax benefit is calculated as the tax impact of the intrinsic value of the stock options (the difference between the market value of the average stock options outstanding for the period, using the average market price during the period, and the exercise price).
Segment Reporting Policy Policy Text Block	SEGMENT INFORMATION Presentation: Eversource is organized between the Electric Distribution, Electric Transmission and Natural Gas Distribution reportable segments and Other based on a combination of factors, including the characteristics of each segments' products and services, the sources of operating revenues and expenses and the regulatory environment in which each segment operates. These reportable segments represent substantially all of Eversource's total consolidated revenues. Revenues from the sale of electricity and natural gas primarily are derived from residential, commercial and industrial customers and are not dependent on any single customer. The Electric Distribution reportable segment includes the generation activities of PSNH and WMECO. The remainder of Eversource's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of Eversource parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of Eversource parent, 2) the revenues and expenses of Eversource Service, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, 4) the results of Eversource Gas Transmission LLC and 5) the results of other unregulated subsidiaries, which ar e not part of its core business. Cash flows used for investments in plant included in the segment information below are cash capital expenditures that do not include amounts incurred but not paid, cost of removal, AFUDC related to equity funds, and the capitalized portions of pension expense. Eversource's reportable segments are determined based upon the level at which Eversource's chief operating decision maker assesses performance and makes decisions about the allocation of company resources. Each of Eversource's subsidiaries, including CL&P, NSTAR Electric, PSNH and WMECO, has one reportable segment. Eversource's operating segments and reporting units are consistent with its reportable business segments. Eversou rce's segment information is as follows:
Consolidation Variable Interest Entity Policy	VARIABLE INTEREST ENTITIES The Company's variable interests outside of the consolidated group are not material and consist of contracts that are required by regulation and provide for regulatory recovery of contract costs and benefits through customer rates. Eversource , CL&P and NSTAR Electric hold variable interests in variable interest entities ( VIEs ) through agreements with certain entities that own single renewable energy or peaking generation power plants and with other independent power producers. Eversource , CL&P and NSTAR Electric do not control the activities that are economically significant to these VIEs or provide financial or other support to these VIEs. Therefore, Eversource , CL&P and NSTAR Electric do not consolidate any power plant VIEs.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets.
Asset Retirement Obligations, Policy [Policy Text Block]	Eversource 's amounts include CYAPC and YAEC's AROs of $ 319.1 million and $ 317.3 million as of December 31, 2015 and 2014 , respectively. The fair value of the ARO for CY APC and YAEC include s uncertainties of the fuel off- load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste. The incremental asset recorded as an offset to the ARO liability was fully depreciated since the plants have no remaining useful life. Any changes in the assumptions used to calculate the fair value of the ARO liability are recorded with a corresponding of fset to the related regulatory a sset. The assets held in the CYAPC and YAEC nuclear decommissioning trust s are restricted for sett l ing the ARO and all other decommissioning obligations. For further information on the assets held in the nuclear decommissioning trust s , see Note 5 , " Marketable Securities, " to the financial statements .
Pension And Other Postretirement Plans Policy	A. Pension Benefits and Postretirement Benefits Other Than Pensions As of December 31, 2014, Eversource Service sponsored two defined benefit retirement plans that covered eligible employees, including , among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the se two pension plans were merged into one plan, sponsored by Eversource Service (Pension Plan). The Pension P lan is subject to the provisions of ERISA, as amended by the PPA of 2006. Eversource 's policy is to annually fund the Pension Plan in an amount at least equal to an amount that will satisfy all federal funding requirements. In addition to the Pension Plan , Eversource maintains non-qualified defined benefit retirement plans sponsored by Eversource Service (herein collectively referred to as the SERP Plans), which provide benefits in excess of Internal Revenue Code limitations to eligible current and retired participants. As of December 31, 2014, Eversource Service also sponsored defined benefit postretirement plans that provide d certain retiree benefits, primarily medical, dental and life insurance , to retired employees that me t certain age and service eligibility requirements, including , among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. Effective January 1, 2015, the se postretirement plans were merged into one plan, sponsored by Eversource Service (PBOP Plan). Under certain circumstances, eligible retirees are required to contribute to the costs of postretirement benefits. The benefits provided under the PBOP Plan are not vested and the Company has the right to modify any benefit provision subject to applicable laws at that time. Eversource annually funds postretirement costs through tax deductible contributions to external trusts. Because the Regulated companies recover the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of recording an adjustment to Accumulated Other Comprehensive Income/(Loss) for the funded status of the Pension, SERP and PBOP Plans . Regulatory accounting is also applied to the portions of the Eversource Service costs that support the Regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP Plans funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income /( Loss). For further information , see Note 2 , "Regulatory Accounting," and Note 1 4 , " Accumulated Other Comprehensive Income/(Loss), " to the financial statements. For the year ended December 31, 2015, the difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans are reflected as a component of unrecognized actuarial gains or losses , which are recorded in Regulatory Assets or Accumulated Other Comprehensive Income/(Loss) . Unrecognized actuarial gains or losses a re amort ized as a component of p ension and PBOP expense over the estimated average future employee service period . Pension and SERP Plans : On January 1, 2014, NSTAR Electric & Gas was merged into Eversource Service (service company merger) and, concurrently, all employees were transferred to the company they p redominantly provide services for: Eversource Service , NSTAR Electric or NSTAR Gas . As a result of the se employee transfers, the pension and SERP assets and liabilities of NSTAR Electric & Gas were attributed by participant a nd transferred to the applicable operating company's balance sheets. This change had no impact on the income statement or net assets of NSTAR Electric or Eversource . Pension and SERP Expense: Eversource charges net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the year ended December 31, 2013 (prior to the service company merger ) , the net periodic pension expense recorded at NSTAR Electric represent ed the full cost of the plan with a portion of the costs allocated to affiliated companies based on participant demographic data. PBOP Expense: Eversource charges net periodic postre tire ment benefits expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. For the year ended December 31, 2013 (prior to the service company merger),
Property, Plant and Equipment, Depreciation Methods	Utility property, plant and equipment is recorded at original cost. Original cost includes materials, labor, construction overhead and AFUDC for regulated property. The cost of repairs and maintenance, including planned major maintenance activities, is charged to Operating Expenses as incurred. As of December 31, 2015, PSNH had $1.2 billion in gross generation utility plant assets and related Accumulated Depreciation of $522.4 million. These generation assets are the subject of a divestiture agreement entered into on June 10, 2015 between Eversource, PSNH and key New Hampshire officials whereby, among other resolutions, PSNH has agreed to divest these generation assets upon NHPUC approval. Upon completion of the divestiture process, remaining costs not recovered by the sale of these assets (stranded costs) will be recovered via bonds that will be secured by a non-bypassable charge or other recovery mechanisms in rates billed to PSNH’s customers. See Note 11H, “Commitments and Contingencies – PSNH Generation Restructuring,” for further information. Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution). The composite rates, which are subject to approval by the appropriate state regulatory agency, include a cost of removal component (other than PSNH Generation), which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability. Depreciation rates are applied to property from the time it is placed in service. Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability.
Income Tax, Policy [Policy Text Block]	10. INCOME TAXES Deferred tax assets and liabilities are recognized for the future tax effects of temporary differences between the carrying amounts and the tax basis of assets and liabilities. The tax effect of temporary differences is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and relevant accounting authoritative literature . Interest and Penalties: Interest on uncertain tax positions is recorded and generally classified as a component of Other Interest Expense on the statements of income . However, when resolution of uncertainties results in the Company receiving interest income, any related interest benefit is recorded in Other Income, Net on the statements of income. No penalties have been recorded.
Member of Group Filing Consolidated Return, Policy [Policy Text Block]	Eversource , CL&P, NSTAR Electric, PSNH and WMECO file a consolidated federal income tax return and unitary, combined and separate state income tax returns. These entities are also parties to a tax allocation agreement under which taxable subsidiaries do not pay any more taxes than they would have otherwise paid had they filed a separate company tax return, and subsidiaries generating tax losses, if any, are paid for their losses when utilized.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	C . Share-Based Payments Share-based compensation awa rds are recorded using a fair- value-based method at the date of grant. Eversource , CL&P, NSTAR Electric, PSNH and WMECO record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as for the allocation of costs associated with shares issued or sold to Eversource 's service company employees and officers that support CL&P, NSTAR Electric, PSNH and WMECO. Eversource Incentive Plan s : Eversource maintains long-term equity-based incentive plans in which Eversource , CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are e ligible to participate. The incentive p lan s authorize Eversource to grant up to 8,0 00,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. Eversource accounts for its various share-based plans as follows: RSUs - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of Eversource 's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares. P erformance S hares - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. V esting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the total shareholder return as compared to the Edison Electric Institute (EEI) Index during the requisite service period . The fair value of performance shares is determined at the date of g rant using a lattice model. Stock Options - Stock options currently outstanding are fully vested. ESPP Shares - For shares sold under the ESPP, no compensation expense was recorded as the ESPP qualified as a non-compensatory plan. The ESPP ended as of February 1, 2016. RSUs: Eversource granted RSUs under the annual long-t erm incentive programs that are subject to three-year graded vesting schedules for employees, and one-year graded vesting schedules , or immediate vesting , for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes , subsequent to vesting. The weighted average grant-date fair value of RSU s granted for the years ended December 31, 201 5 , 201 4 and 201 3 was $ 54.57 , $ 42.27 and $39. 56 , respectively. As of December 31, 201 5 and 201 4 , the number and weighted average grant-date fair value of unvested RSUs was 469,772 and $ 48 . 58 per share, and 1, 0 2 4 , 729 and $38 .14 per share , respectively. During 2015, there were 784,376 RSUs at a weighted average grant-date fair value of $ 37.21 per share that vested and were either paid or deferred . As of December 31, 201 5 , 259,536 RSUs were fully vest ed and deferred and an additional 446,283 are expected to vest. Performance Shares: Eversource granted performa nce shares under the annual long-term i ncentive programs that vest based upon the extent to which Company goals are achieved at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows: Stock Options: Stock options currently outstanding were granted under the NSTAR Incentive P lan , expire ten years from the date of grant and are fully vested. The weighted average remaining contractual lives for the options outstanding as of December 31, 201 5 is 2.6 years. A summary of stock option transactions is as follows: Employee Share Purchase Plan: Eversource maintained an ESPP for eligible employees, which allowed for Eversource common shares to be purchased by employees at the end of successive six-month offering periods at 95 percent of the closing market price on the last day of each six-month period. Employees were permitted to purchase shares having a value not exceeding 25 percent of their compensation as of the beginning of the offering period up to a specified limit . The ESPP qualified as a non-compensatory plan under accounting guidance for share-based payments, and no compensation expense was recorded for ESPP purchases. D . Other Retirement Benefits Eversource provides retirement and other benefits for certain current and past company officers . These benefits are accounted for on an accrual basis and expensed over a period equal to the service lives of the employees. The actuarially-determined liability for these benefits, which is included in Other Long-Term Liabilities on the balance sheets, as well as the related expense included in Operations and Maintenance on the income statements , are as follows:

Provision for Uncollectible Acc

Provision for Uncollectible Accounts (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Accounts Notes Loans And Financing Receivable Text Block	Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2015 2014 2015 2014 Eversource $ 190.7 $ 175.3 $ 118.5 $ 91.5 CL&P 79.5 84.3 68.1 74.0 NSTAR Electric 52.6 40.7 25.3 - PSNH 8.7 7.7 - - WMECO 14.0 9.9 7.4 6.2

Fuel Materials and Supplies and

Fuel Materials and Supplies and Allowance Inventory (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Utility Inventory [Table Text Block]	As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) Eversource Electric PSNH Eversource Electric PSNH Current: Fuel $ 152.5 $ - $ 103.4 $ 164.3 $ - $ 95.1 Materials and Supplies 131.2 32.2 44.6 159.5 49.1 52.2 RECs 50.9 43.3 7.0 25.8 25.1 0.7 Emission Allowances 1.9 - 1.9 0.1 - 0.1 Long-Term: Emission Allowances 17.5 - 17.5 20.1 - 20.1

Equity Method Investments (Tabl

Equity Method Investments (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Equity Method Investments [Table Text Block]	Ownership Interests (percent) Carrying Amount (in millions) As of December 31, 2015 and 2014 As of December 31, CYAPC YAEC MYAPC 2015 2014 CL&P 34.5 % 24.5 % 12.0 % $ 1.2 $ 1.2 NSTAR Electric 14.0 14.0 4.0 0.5 0.5 PSNH 5.0 7.0 5.0 0.3 0.3 WMECO 9.5 7.0 3.0 0.3 0.3

Operating Expenses (Tables)

Operating Expenses (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Fuel Costs [Table Text Block]	For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Eversource - Natural Gas and Fuel $ 516.7 $ 599.4 $ 466.5 PSNH - Fuel 85.4 113.4 104.8

Allowance for Funds Used During

Allowance for Funds Used During Construction (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Allowance For Funds Used During Construction [Table Text Block]	Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2015 2014 2013 Borrowed Funds $ 7.2 $ 5.8 $ 4.1 Equity Funds 18.8 13.7 7.1 Total AFUDC $ 26.0 $ 19.5 $ 11.2 Average AFUDC Rate 3.9% 3.4% 2.7% For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars, NSTAR NSTAR NSTAR except percentages) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Borrowed Funds $ 2.6 $ 2.0 $ 1.0 $ 1.0 $ 1.9 $ 2.0 $ 0.6 $ 0.9 $ 2.2 $ 0.5 $ 0.5 $ 0.5 Equity Funds 5.2 4.3 1.2 1.7 2.9 3.8 0.6 1.7 2.9 - 0.2 1.0 Total AFUDC $ 7.8 $ 6.3 $ 2.2 $ 2.7 $ 4.8 $ 5.8 $ 1.2 $ 2.6 $ 5.1 $ 0.5 $ 0.7 $ 1.5 Average AFUDC Rate 5.5% 3.2% 1.8% 4.4% 3.4% 2.5% 1.8% 5.6% 3.7% 0.5% 1.1% 6.1%

Other Taxes (Tables)

Other Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
State Of Connecticut Gross Earnings Taxes [Table Text Block]	For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Eversource $ 147.2 $ 148.2 $ 144.1 CL&P 128.5 127.9 128.2

Supplemental Cash Flow Informat

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	P. Supplemental Cash Flow Information Eversource As of and For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Cash Paid During the Year for: Interest, Net of Amounts Capitalized $ 365.9 $ 349.6 $ 343.3 Income Taxes 10.3 334.2 50.0 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 216.6 181.9 193.1 As of and For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 144.4 $ 75.7 $ 42.3 $ 26.7 $ 144.1 $ 75.3 $ 41.1 $ 25.9 $ 131.6 $ 75.8 $ 43.3 $ 25.8 Income Taxes 55.2 (19.8) 14.4 14.7 135.4 217.1 2.3 25.1 55.0 163.4 (30.1) (69.0) Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 76.0 23.5 46.5 27.0 63.5 34.6 39.3 14.2 51.4 57.0 34.9 19.5

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Regulatory Assets Text Block	Eversource As of December 31, (Millions of Dollars) 2015 2014 Benefit Costs $ 1,828.2 $ 2,016.0 Derivative Liabilities 388.0 425.5 Income Taxes, Net 650.9 635.3 Storm Restoration Costs 436.9 502.8 Goodwill-related 484.9 505.4 Regulatory Tracker Mechanisms 526.5 350.5 Contractual Obligations - Yankee Companies 134.4 123.8 Other Regulatory Assets 134.0 167.3 Total Regulatory Assets 4,583.8 4,726.6 Less: Current Portion 845.8 672.5 Total Long-Term Regulatory Assets $ 3,738.0 $ 4,054.1 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Benefit Costs $ 413.6 $ 479.9 $ 164.2 $ 84.9 $ 445.4 $ 515.9 $ 174.3 $ 85.0 Derivative Liabilities 380.8 1.3 - - 410.9 4.5 - - Income Taxes, Net 444.4 85.7 34.5 31.8 437.7 83.7 38.0 35.5 Storm Restoration Costs 271.4 110.9 31.5 23.1 319.6 103.7 47.7 31.8 Goodwill-related - 416.3 - - - 433.9 - - Regulatory Tracker Mechanisms 45.1 311.0 101.2 40.1 16.1 141.4 103.5 33.0 Other Regulatory Assets 82.0 56.3 31.5 11.3 66.1 94.7 41.3 12.9 Total Regulatory Assets 1,637.3 1,461.4 362.9 191.2 1,695.8 1,377.8 404.8 198.2 Less: Current Portion 268.3 348.4 105.0 56.2 220.3 198.7 111.7 51.9 Total Long-Term Regulatory Assets $ 1,369.0 $ 1,113.0 $ 257.9 $ 135.0 $ 1,475.5 $ 1,179.1 $ 293.1 $ 146.3
Schedule Of Regulatory Liabilities Text Block	Eversource As of December 31, (Millions of Dollars) 2015 2014 Cost of Removal $ 437.1 $ 439.9 Regulatory Tracker Mechanisms 99.7 192.3 AFUDC - Transmission 66.1 67.1 Other Regulatory Liabilities 18.5 50.8 Total Regulatory Liabilities 621.4 750.1 Less: Current Portion 107.8 235.0 Total Long-Term Regulatory Liabilities $ 513.6 $ 515.1 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Cost of Removal $ 24.1 $ 257.4 $ 47.2 $ 2.8 $ 19.7 $ 258.3 $ 50.3 $ 1.1 Regulatory Tracker Mechanisms 56.2 3.3 3.4 12.9 122.6 20.7 14.2 22.3 AFUDC - Transmission 51.5 5.7 - 8.9 53.6 4.4 - 9.1 Other Regulatory Liabilities 4.2 1.3 4.2 0.1 10.1 28.9 2.9 0.8 Total Regulatory Liabilities 136.0 267.7 54.8 24.7 206.0 312.3 67.4 33.3 Less: Current Portion 61.2 3.3 6.9 13.1 124.7 49.6 16.0 22.5 Total Long-Term Regulatory Liabilities $ 74.8 $ 264.4 $ 47.9 $ 11.6 $ 81.3 $ 262.7 $ 51.4 $ 10.8

PROPERTY, PLANT AND ACCUMULAT42

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Public Utility Property, Plant, and Equipment [Text Block]	Eversource As of December 31, (Millions of Dollars) 2015 2014 Distribution - Electric $ 13,054.8 $ 12,495.2 Distribution - Natural Gas 2,727.2 2,595.4 Transmission - Electric 7,691.9 6,930.7 Generation 1,194.1 1,170.9 Electric and Natural Gas Utility 24,668.0 23,192.2 Other (1) 558.6 551.3 Property, Plant and Equipment, Gross 25,226.6 23,743.5 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,141.1) (5,777.8) Other (255.6) (231.8) Total Accumulated Depreciation (6,396.7) (6,009.6) Property, Plant and Equipment, Net 18,829.9 17,733.9 Construction Work in Progress 1,062.5 913.1 Total Property, Plant and Equipment, Net $ 19,892.4 $ 18,647.0 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Distribution $ 5,377.2 $ 5,100.5 $ 1,804.8 $ 812.3 $ 5,158.8 $ 4,895.5 $ 1,696.7 $ 784.2 Transmission 3,618.0 2,131.3 928.2 964.9 3,274.0 1,928.5 789.7 891.0 Generation - - 1,158.1 36.0 - - 1,136.5 34.4 Property, Plant and Equipment, Gross 8,995.2 7,231.8 3,891.1 1,813.2 8,432.8 6,824.0 3,622.9 1,709.6 Less: Accumulated Depreciation (2,041.9) (1,886.8) (1,171.0) (307.0) (1,928.0) (1,761.4) (1,090.0) (297.4) Property, Plant and Equipment, Net 6,953.3 5,345.0 2,720.1 1,506.2 6,504.8 5,062.6 2,532.9 1,412.2 Construction Work in Progress 203.5 310.5 135.3 69.1 304.9 272.8 102.9 49.1 Total Property, Plant and Equipment, Net $ 7,156.8 $ 5,655.5 $ 2,855.4 $ 1,575.3 $ 6,809.7 $ 5,335.4 $ 2,635.8 $ 1,461.3 (Percent) 2015 2014 2013 Eversource 2.9 % 3.0 % 2.8 % CL&P 2.7 % 2.7 % 2.5 % NSTAR Electric 3.0 % 3.0 % 2.9 % PSNH 3.2 % 3.0 % 3.0 % WMECO 2.7 % 3.3 % 2.9 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2015 (Years) Eversource CL&P NSTAR Electric PSNH WMECO Distribution 34.8 37.3 31.9 31.3 30.5 Transmission 41.6 38.7 43.8 41.6 50.0 Generation 30.7 - - 30.9 25.0 Other 14.1 - - - -

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Derivative Instruments In Statement Of Financial Position Fair Value Text Block	As of December 31, 2015 2014 Commodity Supply Net Amount Commodity Supply Net Amount and Price Risk Recorded as and Price Risk Recorded as (Millions of Dollars) Management Netting (1) a Derivative Management Netting (1) a Derivative Current Derivative Assets: Level 3: Eversource $ 16.7 $ (10.9) $ 5.8 $ 16.2 $ (6.6) $ 9.6 CL&P 16.7 (10.9) 5.8 16.1 (6.6) 9.5 NSTAR Electric - - - 0.1 - 0.1 Long-Term Derivative Assets: Level 2: Eversource $ 0.1 $ - $ 0.1 $ - $ - $ - Level 3: Eversource 62.0 (19.3) 42.7 93.5 (19.2) 74.3 CL&P 60.7 (19.3) 41.4 93.5 (19.2) 74.3 NSTAR Electric 1.3 - 1.3 - - - Current Derivative Liabilities: Level 2: Eversource $ (5.8) $ - $ (5.8) $ (9.8) $ - $ (9.8) Level 3: Eversource (92.3) - (92.3) (90.0) - (90.0) CL&P (91.8) - (91.8) (88.5) - (88.5) NSTAR Electric (0.5) - (0.5) (1.5) - (1.5) Long-Term Derivative Liabilities: Level 2: Eversource $ - $ - $ - $ (0.3) $ - $ (0.3) Level 3: Eversource (337.1) - (337.1) (409.3) - (409.3) CL&P (336.2) - (336.2) (406.2) - (406.2) NSTAR Electric (0.9) - (0.9) (3.1) - (3.1)
Schedule Of Derivative Instruments Gain Loss In Statement Of Financial Performance Text Block
Fairvalueinputsliabilitiesquantitativeinformationtabletextblock	As of December 31, 2015 2014 Range Period Covered Range Period Covered Capacity Prices: Eversource $ 10.81 - 15.82 per kW-Month 2016 - 2026 $ 5.30 - 12.98 per kW-Month 2016 - 2026 CL&P $ 10.81 - 12.60 per kW-Month 2019 - 2026 $ 11.08 - 12.98 per kW-Month 2018 - 2026 NSTAR Electric $ 10.81 - 15.82 per kW-Month 2016 - 2019 $ 5.30 - 11.10 per kW-Month 2016 - 2019 Forward Reserve: Eversource, CL&P $ 2.00 per kW-Month 2016 - 2024 $ 5.80 - 9.50 per kW-Month 2015 - 2024 REC Prices: Eversource, NSTAR Electric $ 45 - 51 per REC 2016 - 2018 $ 38 - 56 per REC 2015 - 2018
FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTableTextBlock	(Millions of Dollars) Eversource CL&P NSTAR Electric Derivatives, Net: Fair Value as of January 1, 2014 $ (635.2) $ (630.6) $ (7.3) Net Realized/Unrealized Gains Included in Regulatory Assets and Liabilities 141.3 139.7 4.3 Settlements 78.5 80.0 (1.5) Fair Value as of December 31, 2014 $ (415.4) $ (410.9) $ (4.5) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (52.1) (51.3) (0.8) Settlements 86.6 81.4 5.2 Fair Value as of December 31, 2015 $ (380.9) $ (380.8) $ (0.1)

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Available For Sale Securities Reconciliation [Table TextBlock]	As of December 31, 2015 2014 Pre-Tax Pre-Tax Pre-Tax Pre-Tax Amortized Unrealized Unrealized Amortized Unrealized Unrealized (Millions of Dollars) Cost Gains Losses Fair Value Cost Gains Losses Fair Value Eversource Debt Securities (1) (2) $ 256.5 $ 4.5 $ (0.6) $ 260.4 $ 313.0 $ 7.5 $ (0.3) $ 320.2 Equity Securities (1) 215.3 59.2 (3.4) 271.1 160.6 73.3 - 233.9 WMECO Debt Securities (2) - - - - 58.2 - (0.1) 58.1
Investments Classified by Contractual Maturity Date [Table Text Block]	Eversource Amortized Fair (Millions of Dollars) Cost Value Less than one year (1) $ 33.3 $ 33.2 One to five years 50.2 50.7 Six to ten years 56.6 57.2 Greater than ten years 116.4 119.3 Total Debt Securities $ 256.5 $ 260.4
Fair Value Heirarchy [Table Text Block]	Eversource As of December 31, (Millions of Dollars) 2015 2014 Level 1: Mutual Funds and Equities $ 285.3 $ 319.0 Money Market Funds 26.9 24.9 Total Level 1 $ 312.2 $ 343.9 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 46.6 $ 51.3 Corporate Debt Securities 43.9 49.1 Asset-Backed Debt Securities 20.0 54.1 Municipal Bonds 111.4 116.3 Other Fixed Income Securities 11.6 24.5 Total Level 2 $ 233.5 $ 295.3 Total Marketable Securities $ 545.7 $ 639.2

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (TABLE)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Change in Asset Retirement Obligation [Table Text Block]	Eversource As of December 31, (Millions of Dollars) 2015 2014 Balance as of Beginning of Year $ 426.3 $ 424.9 Liabilities Incurred During the Year 6.6 1.3 Liabilities Settled During the Year (18.2) (19.5) Accretion 26.5 25.1 Revisions in Estimated Cash Flows (11.1) (5.5) Balance as of End of Year $ 430.1 $ 426.3 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Balance as of Beginning of Year $ 35.3 $ 34.3 $ 20.6 $ 5.9 $ 35.0 $ 32.8 $ 19.5 $ 4.5 Liabilities Incurred During the Year - 6.2 0.4 - - - - 1.1 Liabilities Settled During the Year - (1.5) - (0.1) (1.1) - - - Accretion 2.2 1.8 1.3 0.4 1.9 1.5 1.1 0.3 Revisions in Estimated Cash Flows (3.7) (5.5) (0.7) (0.5) (0.5) - - - Balance as of End of Year $ 33.8 $ 35.3 $ 21.6 $ 5.7 $ 35.3 $ 34.3 $ 20.6 $ 5.9

LONG-TERM DEBT (TABLES)

LONG-TERM DEBT (TABLES)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Maturities of Long-term Debt [Table Text Block]	(Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 200.0 $ - $ 200.0 $ - $ - 2017 745.0 250.0 400.0 70.0 - 2018 960.0 300.0 - 110.0 - 2019 800.0 250.0 - 150.0 - 2020 295.0 - - - 95.0 Thereafter 5,736.6 1,990.3 1,450.0 746.3 420.0 Total $ 8,736.6 $ 2,790.3 $ 2,050.0 $ 1,076.3 $ 515.0
Schedule of Long-term Debt Instruments [Table Text Block]	CL&P As of December 31, (Millions of Dollars) 2015 2014 First Mortgage Bonds: 7.875% 1994 Series D due 2024 $ 139.8 $ 139.8 5.750% 2004 Series B due 2034 130.0 130.0 5.000% 2005 Series A due 2015 - 100.0 5.625% 2005 Series B due 2035 100.0 100.0 6.350% 2006 Series A due 2036 250.0 250.0 5.375% 2007 Series A due 2017 150.0 150.0 5.750% 2007 Series B due 2037 150.0 150.0 5.750% 2007 Series C due 2017 100.0 100.0 6.375% 2007 Series D due 2037 100.0 100.0 5.650% 2008 Series A due 2018 300.0 300.0 5.500% 2009 Series A due 2019 250.0 250.0 2.500% 2013 Series A due 2023 400.0 400.0 4.300% 2014 Series A due 2044 250.0 250.0 4.150% 2015 Series A due 2045 350.0 - Total First Mortgage Bonds 2,669.8 2,419.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 1.550% Fixed Rate Tax Exempt due 2031 - 62.0 Total Pollution Control Revenue Bonds 120.5 182.5 Pre-1983 Spent Nuclear Fuel Obligation - 244.5 Less Amounts due Within One Year - (162.0) Unamortized Premiums and Discounts, Net (10.7) (4.8) Unamortized Debt Issuance Costs (1) (15.9) (15.8) CL&P Long-Term Debt (1) $ 2,763.7 $ 2,664.2 NSTAR Electric As of December 31, (Millions of Dollars) 2015 2014 Debentures: 5.750% due 2036 $ 200.0 $ 200.0 5.625% due 2017 400.0 400.0 5.500% due 2040 300.0 300.0 2.375% due 2022 400.0 400.0 Variable Rate due 2016 (0.6036% and 0.4721% as of December 31, 2015 and 2014) 200.0 200.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 - Total Debentures 2,050.0 1,800.0 Bonds: 7.375% Tax Exempt Sewage Facility Revenue Bonds, due 2015 - 4.7 Less Amounts due Within One Year (200.0) (4.7) Unamortized Premiums and Discounts, Net (8.5) (7.3) Unamortized Debt Issuance Costs (1) (11.7) (11.2) NSTAR Electric Long-Term Debt (1) $ 1,829.8 $ 1,781.5 PSNH As of December 31, (Millions of Dollars) 2015 2014 First Mortgage Bonds: 5.60% Series M due 2035 $ 50.0 $ 50.0 6.15% Series N due 2017 70.0 70.0 6.00% Series O due 2018 110.0 110.0 4.50% Series P due 2019 150.0 150.0 4.05% Series Q due 2021 122.0 122.0 3.20% Series R due 2021 160.0 160.0 3.50% Series S due 2023 325.0 325.0 Total First Mortgage Bonds 987.0 987.0 Pollution Control Revenue Bonds: Adjustable Rate Tax Exempt Series A due 2021 (0.193% and 0.175% as of December 31, 2015 and 2014) 89.3 89.3 Unamortized Premiums and Discounts, Net 0.1 - Unamortized Debt Issuance Costs (1) (5.4) (6.3) PSNH Long-Term Debt (1) $ 1,071.0 $ 1,070.0 WMECO As of December 31, (Millions of Dollars) 2015 2014 Notes: 5.90% Senior Notes Series B, due 2034 $ 50.0 $ 50.0 5.24% Senior Notes Series C, due 2015 - 50.0 6.70% Senior Notes Series D, due 2037 40.0 40.0 5.10% Senior Notes Series E, due 2020 95.0 95.0 3.50% Senior Notes Series F, due 2021 250.0 250.0 3.88% Senior Notes Series G, due 2023 80.0 80.0 Total Notes 515.0 565.0 Pre-1983 Spent Nuclear Fuel Obligation - 57.4 Less Amounts due Within One Year - (50.0) Unamortized Premiums and Discounts, Net 5.2 6.1 Unamortized Debt Issuance Costs (1) (2.9) (3.3) WMECO Long-Term Debt (1) $ 517.3 $ 575.2 OTHER As of December 31, (Millions of Dollars) 2015 2014 Yankee Gas - First Mortgage Bonds: 8.48% Series B due 2022 $ 20.0 $ 20.0 5.26% Series H due 2019 50.0 50.0 5.35% Series I due 2035 50.0 50.0 6.90% Series J due 2018 100.0 100.0 4.87% Series K due 2020 50.0 50.0 4.82% Series L due 2044 100.0 100.0 3.35% Series M due 2025 75.0 - Total First Mortgage Bonds 445.0 370.0 Unamortized Premium 0.4 0.6 Unamortized Debt Issuance Costs (1) (1.7) (1.5) Yankee Gas Long-Term Debt (1) 443.7 369.1 NSTAR Gas - First Mortgage Bonds: 9.95% Series J due 2020 25.0 25.0 7.11% Series K due 2033 35.0 35.0 7.04% Series M due 2017 25.0 25.0 4.46% Series N due 2020 125.0 125.0 4.35% Series O due 2045 100.0 - Total First Mortgage Bonds 310.0 210.0 Unamortized Debt Issuance Costs (1) (0.8) (0.6) NSTAR Gas Long-Term Debt (1) 309.2 209.4 Eversource Parent - Notes and Debentures: 4.50% Debentures due 2019 350.0 350.0 1.45% Senior Notes Series E due 2018 300.0 300.0 2.80% Senior Notes Series F due 2023 450.0 450.0 1.60% Senior Notes Series G due 2018 150.0 - 3.15% Senior Notes Series H due 2025 300.0 - Eversource Parent Commercial Paper Borrowings - 446.3 Total Eversource Parent Notes and Debentures 1,550.0 1,546.3 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 179.5 179.4 Fair Value Adjustment (2) 173.5 202.3 Less Fair Value Adjustment - Current Portion (2) (28.9) (28.9) Unamortized Premiums and Discounts, Net (1.3) (1.2) Unamortized Debt Issuance Costs (1) (1.9) 1.1 Total Other Long-Term Debt (1) $ 2,623.8 $ 2,477.5 Total Eversource Long-Term Debt (1) $ 8,805.6 $ 8,568.4

Pension Benefits and Postreti47

Pension Benefits and Postretirement Benefits Other Than Pensions (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Net Benefit Costs [Table Text Block]	Pension and SERP For the Year Ended December 31, 2015 NSTAR (Millions of Dollars) Eversource (1) CL&P Electric PSNH (1) WMECO Service Cost $ 91.4 $ 24.7 $ 14.9 $ 12.1 $ 4.3 Interest Cost 227.0 51.1 40.2 24.3 10.4 Expected Return on Pension Plan Assets (335.9) (78.9) (70.0) (40.4) (18.9) Actuarial Loss 148.5 32.2 35.8 11.6 6.4 Prior Service Cost/(Credit) 3.7 1.5 (0.1) 0.5 0.3 Total Net Periodic Benefit Expense $ 134.7 $ 30.6 $ 20.8 $ 8.1 $ 2.5 Intercompany Allocations N/A $ 22.5 $ 13.6 $ 6.7 $ 4.4 Capitalized Pension Expense $ 41.0 $ 18.8 $ 11.4 $ 3.5 $ 1.9 Pension and SERP For the Year Ended December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 79.9 $ 20.2 $ 13.6 $ 9.7 $ 3.5 Interest Cost 225.7 50.5 41.3 23.8 10.3 Expected Return on Pension Plan Assets (310.8) (75.4) (63.0) (38.1) (17.9) Actuarial Loss 128.4 33.7 23.5 11.6 6.9 Prior Service Cost 4.4 1.8 - 0.7 0.4 Total Net Periodic Benefit Expense $ 127.6 $ 30.8 $ 15.4 $ 7.7 $ 3.2 Intercompany Allocations N/A $ 26.7 $ 10.4 $ 7.6 $ 5.1 Capitalized Pension Expense $ 35.2 $ 17.6 $ 7.9 $ 3.0 $ 2.4 Pension and SERP For the Year Ended December 31, 2013 NSTAR (Millions of Dollars) Eversource CL&P Electric (2) PSNH WMECO Service Cost $ 102.3 $ 24.9 $ 33.1 $ 13.1 $ 4.7 Interest Cost 206.7 48.3 58.0 23.6 10.0 Expected Return on Pension Plan Assets (278.1) (73.8) (84.4) (35.4) (17.4) Actuarial Loss 210.5 55.9 58.1 21.6 11.8 Prior Service Cost/(Credit) 4.0 1.8 (0.3) 0.7 0.4 Total Net Periodic Benefit Expense $ 245.4 $ 57.1 $ 64.5 $ 23.6 $ 9.5 Intercompany Allocations N/A $ 44.9 $ (8.4) $ 10.5 $ 8.0 Capitalized Pension Expense $ 73.2 $ 28.0 $ 28.9 $ 7.3 $ 5.2 PBOP For the Year Ended December 31, 2015 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 16.3 $ 2.1 $ 5.4 $ 1.4 $ 0.4 Interest Cost 47.2 7.2 19.0 3.9 1.5 Expected Return on Plan Assets (67.4) (11.1) (27.3) (6.0) (2.5) Actuarial Loss 6.8 0.7 2.3 0.5 - Prior Service Credit (0.5) - (0.2) - - Total Net Periodic Benefit Expense/(Income) $ 2.4 $ (1.1) $ (0.8) $ (0.2) $ (0.6) Intercompany Allocations N/A $ 1.9 $ 0.8 $ 0.4 $ 0.3 Capitalized PBOP Expense/(Income) $ 0.1 $ (0.2) $ (0.2) $ 0.2 $ (0.2) PBOP For the Year Ended December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Service Cost $ 12.5 $ 2.2 $ 3.1 $ 1.3 $ 0.4 Interest Cost 49.5 8.1 19.4 4.3 1.7 Expected Return on Plan Assets (63.3) (10.5) (25.9) (5.4) (2.3) Actuarial Loss/(Gain) 12.2 4.2 (0.5) 2.2 0.5 Prior Service Credit (2.8) - (1.9) - - Total Net Periodic Benefit Expense/(Income) $ 8.1 $ 4.0 $ (5.8) $ 2.4 $ 0.3 Intercompany Allocations N/A $ 3.8 $ 0.8 $ 1.0 $ 0.7 Capitalized PBOP Expense/(Income) $ 1.4 $ 1.8 $ (2.3) $ 0.8 $ 0.2 PBOP For the Year Ended December 31, 2013 (Millions of Dollars) Eversource CL&P PSNH WMECO Service Cost $ 16.9 $ 3.4 $ 2.3 $ 0.7 Interest Cost 47.2 7.9 4.0 1.7 Expected Return on Plan Assets (55.4) (10.1) (5.2) (2.3) Actuarial Loss 26.0 7.4 3.6 1.1 Prior Service Credit (2.1) - - - Total Net Periodic Benefit Expense $ 32.6 $ 8.6 $ 4.7 $ 1.2 Intercompany Allocations N/A $ 7.1 $ 1.6 $ 1.3 Capitalized PBOP Expense $ 8.8 $ 3.9 $ 1.3 $ 0.6
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	As of December 31, 2015 and 2014, the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2015 $ 4,733.2 $ 1,062.7 $ 888.8 $ 506.4 $ 222.3 2014 5,000.1 1,101.4 910.4 524.5 226.4 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status:
Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]	The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income (OCI) as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented: Regulatory Assets OCI For the Years Ended December 31, (Millions of Dollars) 2015 2014 2015 2014 Actuarial (Gains)/Losses Arising During the Year $ (2.0) $ 797.3 $ (6.2) $ 55.9 Actuarial Losses Reclassified as Net Periodic Benefit Expense (142.3) (122.8) (6.2) (5.6) Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.5) (4.2) (0.2) (0.2) The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2015 and 2014, as well as the amounts that are expected to be recognized as components in 2016: Regulatory Assets as of Expected AOCI as of Expected December 31, 2016 December 31, 2016 (Millions of Dollars) 2015 2014 Expense 2015 2014 Expense Actuarial Loss $ 1,667.6 $ 1,811.9 $ 120.6 $ 81.1 $ 93.5 $ 5.4 Prior Service Cost 9.7 13.2 3.4 0.6 0.8 0.2 The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts recognized in Regulatory Assets and OCI that were reclassified as net periodic benefit (expense)/income during the years presented: Regulatory Assets OCI For the Years Ended December 31, (Millions of Dollars) 2015 2014 2015 2014 Actuarial (Gains)/Losses Arising During the Year $ (34.1) $ 115.1 $ 0.7 $ 0.4 Actuarial Losses Reclassified as Net Periodic Benefit Expense (6.4) (11.6) (0.4) (0.6) Prior Service Credit Reclassified as Net Periodic Benefit Income 0.5 2.8 - - The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Loss amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2015 and 2014, as well as the amounts that are expected to be recognized as components in 2016: Regulatory Assets as of Expected AOCI as of Expected December 31, 2016 December 31, 2016 (Millions of Dollars) 2015 2014 Expense 2015 2014 Expense Actuarial Loss $ 152.2 $ 192.7 $ 4.0 $ 6.3 $ 6.0 $ 0.4 Prior Service Credit (1.3) (1.8) (0.2) - - -
Schedule of Assumptions Used [Table Text Block]	Pension and SERP As of December 31, 2015 2014 Discount Rate 4.21 % - 4.60 % 4.20 % Compensation/Progression Rate 3.50% 3.50 % The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2015 2014 2013 Discount Rate 4.20% 4.85 % - 5.03 % 4.13 % - 4.24 % Expected Long-Term Rate of Return 8.25 % 8.25 % 8.25% Compensation/Progression Rate 3.50 % 3.50 % - 4.00 % 3.50 % - 4.00 % The following actuarial assumptions were used in calculating the PBOP Plan's year end funded status: PBOP As of December 31, 2015 2014 Discount Rate 4.62 % 4.22 % Health Care Cost Trend Rate 6.25 % 6.50 % The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2015 2014 2013 Discount Rate 4.22 % 4.78 % - 5.10 % 4.04 % - 4.35 % Expected Long-Term Rate of Return 8.25 % 8.25 % 8.25%
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	One Percentage One Percentage (Millions of Dollars) Point Increase Point Decrease Effect on PBOP Obligation $ 115.3 $ (90.8) Effect on Total Service and Interest Cost Components 8.5 (6.3)
Schedule of Expected Benefit Payments [Table Text Block]	Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans: (Millions of Dollars) 2016 2017 2018 2019 2020 2021-2025 Pension and SERP $ 253.5 $ 272.9 $ 273.9 $ 283.7 $ 292.7 $ 1,604.3 PBOP 60.8 61.2 61.4 61.8 62.4 315.4
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block]	Pension and SERP Eversource As of December 31, (Millions of Dollars) 2015 2014 Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (5,486.2) $ (4,676.5) Service Cost (91.4) (79.9) Interest Cost (227.0) (225.7) Actuarial Gain/(Loss) 331.5 (739.6) Benefits Paid - Pension 238.5 230.3 Benefits Paid - Lump Sum 149.5 - Benefits Paid - SERP 5.0 5.2 Benefit Obligation as of End of Year $ (5,080.1) $ (5,486.2) Change in Pension Plan Assets Fair Value of Pension Plan Assets as of Beginning of Year $ 4,126.5 $ 3,985.9 Employer Contributions 154.6 171.6 Actual Return on Pension Plan Assets 12.3 199.3 Benefits Paid (238.5) (230.3) Benefits Paid - Lump Sum (149.5) - Fair Value of Pension Plan Assets as of End of Year $ 3,905.4 $ 4,126.5 Funded Status as of December 31 st $ (1,174.7) $ (1,359.7) Pension and SERP As of December 31, 2015 As of December 31, 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (1,230.1) $ (982.6) $ (580.7) $ (249.4) $ (1,083.4) $ (1,353.3) $ (529.0) $ (223.9) Change due to transfer of employees (4.6) 6.2 (1.9) (1.3) 26.4 479.9 32.2 6.2 Service Cost (24.7) (14.9) (12.1) (4.3) (20.2) (13.6) (9.7) (3.5) Interest Cost (51.1) (40.2) (24.3) (10.4) (50.5) (41.3) (23.8) (10.3) Actuarial Gain/(Loss) 77.8 34.1 38.9 12.6 (161.0) (107.0) (73.3) (29.8) Benefits Paid - Pension 60.2 47.6 23.2 12.7 58.3 52.4 22.8 11.9 Benefits Paid - Lump Sum 14.5 - 9.1 2.5 - - - - Benefits Paid - SERP 0.4 0.1 0.2 - 0.3 0.3 0.1 - Benefit Obligation as of End of Year $ (1,157.6) $ (949.7) $ (547.6) $ (237.6) $ (1,230.1) $ (982.6) $ (580.7) $ (249.4) Change in Pension Plan Assets Fair Value of Pension Plan Assets as of Beginning of Year $ 980.8 $ 879.0 $ 498.4 $ 234.0 $ 1,016.3 $ 1,235.3 $ 528.6 $ 240.4 Change due to transfer of employees 4.6 (6.2) 1.9 1.3 (26.4) (441.4) (32.2) (6.2) Employer Contributions - 5.0 1.0 - - 101.0 - - Actual Return on Pension Plan Assets 2.8 2.7 1.5 0.7 49.2 36.5 24.8 11.7 Benefits Paid (60.2) (47.6) (23.2) (12.7) (58.3) (52.4) (22.8) (11.9) Benefits Paid - Lump Sum (14.5) - (9.1) (2.5) - - - - Fair Value of Pension Plan Assets as of End of Year $ 913.5 $ 832.9 $ 470.5 $ 220.8 $ 980.8 $ 879.0 $ 498.4 $ 234.0 Funded Status as of December 31 st $ (244.1) $ (116.8) $ (77.1) $ (16.8) $ (249.3) $ (103.6) $ (82.3) $ (15.4) PBOP Eversource As of December 31, (Millions of Dollars) 2015 2014 Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (1,147.9) $ (1,038.0) Service Cost (16.3) (12.5) Interest Cost (47.2) (49.5) Actuarial Gain/(Loss) 106.0 (95.5) Benefits Paid 54.0 47.6 Benefit Obligation as of End of Year $ (1,051.4) $ (1,147.9) Change in Plan Assets Fair Value of Plan Assets as of Beginning of Year $ 862.6 $ 826.5 Actual Return on Plan Assets (4.3) 43.7 Employer Contributions 7.9 40.0 Benefits Paid (54.0) (47.6) Fair Value of Plan Assets as of End of Year $ 812.2 $ 862.6 Funded Status as of December 31 st $ (239.2) $ (285.3) PBOP As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Change in Benefit Obligation Benefit Obligation as of Beginning of Year $ (173.9) $ (468.7) $ (91.8) $ (36.6) $ (180.4) $ - $ (93.5) $ (38.7) Change due to transfer of employees 0.1 2.3 (0.3) - 3.7 (395.5) 4.3 1.0 Service Cost (2.1) (5.4) (1.4) (0.4) (2.2) (3.1) (1.3) (0.4) Interest Cost (7.2) (19.0) (3.9) (1.5) (8.1) (19.4) (4.3) (1.7) Actuarial Gain/(Loss) 7.2 59.1 3.6 1.5 3.5 (68.6) (1.1) 1.3 Benefits Paid 11.9 18.9 5.3 2.6 9.6 17.9 4.1 1.9 Benefit Obligation as of End of Year $ (164.0) $ (412.8) $ (88.5) $ (34.4) $ (173.9) $ (468.7) $ (91.8) $ (36.6) Change in Plan Assets Fair Value of Plan Assets as of Beginning of Year $ 149.0 $ 336.5 $ 80.9 $ 34.4 $ 151.3 $ - $ 81.8 $ 35.3 Change due to transfer of employees - 0.6 0.2 - (3.2) 316.7 (3.1) (1.0) Actual Return on Plan Assets (0.4) (2.8) - (0.1) 6.3 18.4 3.8 1.6 Employer Contributions - 4.9 - - 4.2 19.3 2.5 0.4 Benefits Paid (11.9) (18.9) (5.3) (2.6) (9.6) (17.9) (4.1) (1.9) Fair Value of Plan Assets as of End of Year $ 136.7 $ 320.3 $ 75.8 $ 31.7 $ 149.0 $ 336.5 $ 80.9 $ 34.4 Funded Status as of December 31 st $ (27.3) $ (92.5) $ (12.7) $ (2.7) $ (24.9) $ (132.2) $ (10.9) $ (2.2)
Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]	Pension Plan Equity Private Fixed Real Estate and Hedge (Millions of Dollars) Securities Equity Income Other Assets Funds Total Balance as of January 1, 2014 $ 255.5 $ 300.3 $ 589.5 $ 288.5 $ 416.9 $ 1,850.7 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End (2.3) 14.0 45.2 (3.6) 23.5 76.8 Relating to Assets Distributed During the Year - 13.9 (6.2) 28.3 (15.2) 20.8 Purchases, Sales and Settlements 39.0 39.7 93.5 (47.4) 49.8 174.6 Balance as of December 31, 2014 $ 292.2 $ 367.9 $ 722.0 $ 265.8 $ 475.0 $ 2,122.9 Transfer Between Categories 76.5 - - - (76.5) - Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End 5.3 24.4 (6.7) (7.1) - 15.9 Relating to Assets Distributed During the Year - 27.3 17.0 24.8 (0.9) 68.2 Purchases, Sales and Settlements (68.8) 45.1 52.5 (23.2) (106.8) (101.2) Balance as of December 31, 2015 $ 305.2 $ 464.7 $ 784.8 $ 260.3 $ 290.8 $ 2,105.8 PBOP Plan Equity Private Fixed Real Estate and Hedge (Millions of Dollars) Securities Equity Income Other Assets Funds Total Balance as of January 1, 2014 $ 69.1 $ 17.9 $ 51.5 $ 33.9 $ 57.0 $ 229.4 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End 6.0 1.3 1.9 (2.8) 1.4 7.8 Relating to Assets Distributed During the Year - 0.1 - (2.2) - (2.1) Purchases, Sales and Settlements - 5.6 24.9 (13.9) - 16.6 Balance as of December 31, 2014 $ 75.1 $ 24.9 $ 78.3 $ 15.0 $ 58.4 $ 251.7 Actual Return/(Loss) on Plan Assets: Relating to Assets Still Held as of Year End (2.0) 2.6 2.1 0.3 (1.5) 1.5 Relating to Assets Distributed During the Year - - (0.3) - - (0.3) Purchases, Sales and Settlements 4.7 5.4 1.5 5.1 (4.7) 12.0 Balance as of December 31, 2015 $ 77.8 $ 32.9 $ 81.6 $ 20.4 $ 52.2 $ 264.9
Schedule of Allocation of Plan Assets [Table Text Block]	As of December 31, 2015 As of December 31, 2014 Pension Plan and Tax-Exempt Assets Within PBOP Plan Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Target Asset Allocation Assumed Rate of Return Equity Securities: United States 22% 8.5% 24% 9% International 13% 8.5% 10% 9% Emerging Markets 5% 10% 6% 10% Private Equity 12% 12% 10% 13% Debt Securities: Fixed Income 12% 4.5% 15% 5% High Yield Fixed Income 13% 8.5% 9% 7.5% Emerging Markets Debt 5% 7.5% 6% 7.5% Real Estate and Other Assets 10% 7.5% 9% 7.5% Hedge Funds 8% 7% 11% 7% Pension Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2015 2014 Asset Category: Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equity Securities (1) $ 396.5 $ 985.7 $ 305.2 $ 1,687.4 $ 414.7 $ 1,035.0 $ 292.2 $ 1,741.9 Private Equity 7.6 - 464.7 472.3 18.8 - 367.9 386.7 Fixed Income (2) - 432.0 784.8 1,216.8 10.2 561.4 722.0 1,293.6 Real Estate and Other Assets - 117.5 260.3 377.8 - 132.0 265.8 397.8 Hedge Funds - 49.7 290.8 340.5 - 20.0 475.0 495.0 Total $ 404.1 $ 1,584.9 $ 2,105.8 $ 4,094.8 $ 443.7 $ 1,748.4 $ 2,122.9 $ 4,315.0 Less: 401(h) PBOP Assets (3) (189.4) (188.5) Total Pension Assets $ 3,905.4 $ 4,126.5 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2015 2014 Asset Category: Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Equity Securities (1) $ 109.7 $ 121.6 $ 77.8 $ 309.1 $ 104.1 $ 172.8 $ 75.1 $ 352.0 Private Equity - - 32.9 32.9 - - 24.9 24.9 Fixed Income (2) 9.7 99.9 81.6 191.2 16.1 110.0 78.3 204.4 Real Estate and Other Assets - 17.0 20.4 37.4 - 19.4 15.0 34.4 Hedge Funds - - 52.2 52.2 - - 58.4 58.4 Total $ 119.4 $ 238.5 $ 264.9 $ 622.8 $ 120.2 $ 302.2 $ 251.7 $ 674.1 Add: 401(h) PBOP Assets (3) 189.4 188.5 Total PBOP Assets $ 812.2 $ 862.6

DEFINED CONTRIBUTION PLANS (TAB

DEFINED CONTRIBUTION PLANS (TABLES)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Defined Contribution Plans 401k [Table Text Block]	NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2015 $ 30.4 $ 4.8 $ 6.3 $ 3.4 $ 1.0 2014 29.7 5.0 6.3 3.2 1.0 2013 37.0 5.1 8.5 3.3 1.0

Share-Based Payments (Tables)

Share-Based Payments (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	Weighted Average RSUs Grant-Date (Units) Fair Value Outstanding as of December 31, 2014 1,380,747 $ 35.67 Granted 266,230 $ 54.57 Shares issued (888,495) $ 33.94 Forfeited (29,174) $ 46.68 Outstanding as of December 31, 2015 729,308 $ 43.45 Performance Weighted Average Shares Grant-Date (Units) Fair Value Outstanding as of December 31, 2014 375,644 $ 42.20 Granted 172,543 $ 55.04 Shares issued (4,604) $ 42.23 Forfeited (15,155) $ 45.33 Outstanding as of December 31, 2015 528,428 $ 46.30 Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Compensation Expense $ 23.1 $ 24.6 $ 27.0 Future Income Tax Benefit 9.4 10.3 10.7 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Compensation Expense $ 9.3 $ 5.8 $ 3.2 $ 1.7 $ 8.1 $ 7.4 $ 3.0 $ 1.3 $ 6.8 $ 7.5 $ 2.3 $ 1.3 Future Income Tax Benefit 3.8 2.4 1.3 0.7 3.4 3.1 1.3 0.5 2.7 3.0 0.9 0.5 Weighted Average Intrinsic Value Options Exercise Price (Millions) Outstanding and Exercisable - December 31, 2014 351,616 $ 26.69 $ 9.4 Exercised (179,744) $ 26.90 $ 4.4 Outstanding and Exercisable - December 31, 2015 171,872 $ 26.47 $ 4.2

Other Retirement Benefits (Tabl

Other Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits by Title of Individual and Type of Deferred Compensation [Table Text Block]	Eversource As of and For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Actuarially-Determined Liability $ 55.2 $ 57.5 $ 51.3 Other Retirement Benefits Expense 3.9 4.5 4.4 As of and For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P PSNH WMECO Actuarially-Determined Liability $ 0.4 $ - $ 2.4 $ 0.2 $ 0.4 $ - $ 2.6 $ 0.2 $ 0.4 $ 2.3 $ 0.1 Other Retirement Benefits Expense 1.5 1.0 0.7 0.3 2.1 0.3 0.9 0.4 2.5 1.0 0.5

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Current Income Taxes: Federal $ 6.2 $ 4.4 $ 8.8 State 45.7 24.5 (9.4) Total Current 51.9 28.9 (0.6) Deferred Income Taxes, Net: Federal 436.1 406.8 386.2 State 55.6 36.5 45.4 Total Deferred 491.7 443.3 431.6 Investment Tax Credits, Net (3.6) (3.9) (4.1) Income Tax Expense $ 540.0 $ 468.3 $ 426.9 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Current Income Taxes: Federal $ 26.9 $ 36.3 $ (16.7) $ (3.5) $ (0.2) $ 75.0 $ (22.6) $ 1.9 $ 20.1 $ 95.8 $ (8.2) $ (53.4) State 15.8 19.8 6.0 1.6 4.3 20.2 (0.1) 1.8 (6.7) 29.6 3.6 4.2 Total Current 42.7 56.1 (10.7) (1.9) 4.1 95.2 (22.7) 3.7 13.4 125.4 (4.6) (49.2) Deferred Income Taxes, Net: Federal 135.8 147.5 74.5 33.4 138.0 88.0 79.6 28.1 114.9 49.8 64.5 84.7 State 0.2 25.7 9.3 6.0 (7.1) 20.1 15.2 6.0 15.1 (1.0) 11.2 2.3 Total Deferred 136.0 173.2 83.8 39.4 130.9 108.1 94.8 34.1 130.0 48.8 75.7 87.0 Investment Tax Credits, Net (1.3) (1.3) - (0.5) (1.5) (1.3) - (0.5) (1.7) (1.3) - (0.4) Income Tax Expense $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 $ 141.7 $ 172.9 $ 71.1 $ 37.4
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2015 2014 2013 Income Before Income Tax Expense $ 1,425.9 $ 1,295.4 $ 1,220.6 Statutory Federal Income Tax Expense at 35% 499.1 453.4 427.2 Tax Effect of Differences: Depreciation (4.6) (5.6) (7.4) Investment Tax Credit Amortization (3.6) (3.9) (4.1) Other Federal Tax Credits (3.8) (3.5) (3.7) State Income Taxes, Net of Federal Impact 61.1 42.5 27.6 Dividends on ESOP (8.1) (8.0) (8.0) Tax Asset Valuation Allowance/Reserve Adjustments 4.7 (2.9) (4.3) Other, Net (4.8) (3.7) (0.4) Income Tax Expense $ 540.0 $ 468.3 $ 426.9 Effective Tax Rate 37.9% 36.2% 35.0% For the Years Ended December 31, 2015 2014 2013 (Millions of Dollars, NSTAR NSTAR NSTAR except percentages) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Income Before Income Tax Expense $ 476.8 $ 572.6 $ 187.5 $ 93.5 $ 421.2 $ 505.1 $ 186.1 $ 95.1 $ 421.1 $ 441.4 $ 182.5 $ 97.8 Statutory Federal Income Tax Expense at 35% 166.9 200.4 65.6 32.7 147.4 176.8 65.1 33.3 147.4 154.5 63.9 34.2 Tax Effect of Differences: Depreciation (1.7) (1.4) 0.5 (0.3) (3.6) (1.3) 0.3 (0.2) (7.0) 0.1 0.6 - Investment Tax Credit Amortization (1.3) (1.3) - (0.5) (1.5) (1.3) - (0.5) (1.7) (1.3) - (0.4) Other Federal Tax Credits - - (3.8) - - - (3.5) - - - (3.7) - State Income Taxes, Net of Federal Impact 9.2 29.6 9.9 4.9 4.4 26.2 9.8 5.0 5.0 18.6 9.6 4.2 Tax Asset Valuation Allowance/ Reserve Adjustments 1.2 - - - (6.3) - - - 0.4 - - - Other, Net 3.1 0.7 0.9 0.2 (6.9) 1.6 0.4 (0.3) (2.4) 1.0 0.7 (0.6) Income Tax Expense $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 $ 141.7 $ 172.9 $ 71.1 $ 37.4 Effective Tax Rate 37.2% 39.8% 39.0% 39.6% 31.7% 40.0% 38.7% 39.2% 33.6% 39.2% 39.0% 38.2%
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	Eversource As of December 31, (Millions of Dollars) 2015 2014 Deferred Tax Assets: Employee Benefits $ 637.5 $ 632.2 Derivative Liabilities 172.7 199.6 Regulatory Deferrals - Liabilities 243.5 366.7 Allowance for Uncollectible Accounts 60.5 60.5 Tax Effect - Tax Regulatory Liabilities 9.7 10.0 Federal Net Operating Loss Carryforwards 5.4 59.1 Purchase Accounting Adjustment 119.3 126.2 Other 197.1 198.7 Total Deferred Tax Assets 1,445.7 1,653.0 Less: Valuation Allowance 3.7 5.1 Net Deferred Tax Assets $ 1,442.0 $ 1,647.9 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 4,602.6 $ 4,215.9 Property Tax Accruals 76.7 109.6 Regulatory Amounts: Regulatory Deferrals - Assets 1,289.1 1,277.9 Tax Effect - Tax Regulatory Assets 249.3 240.2 Goodwill Regulatory Asset - 1999 Merger 194.9 203.2 Derivative Assets 17.7 32.6 Other 159.4 196.3 Total Deferred Tax Liabilities $ 6,589.7 $ 6,275.7 As of December 31, 2015 2014 NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Deferred Tax Assets: Employee Benefits $ 126.1 $ 91.3 $ 37.1 $ 10.0 $ 129.0 $ 39.9 $ 46.8 $ 9.2 Derivative Liabilities 165.7 0.6 - - 193.0 1.8 - - Regulatory Deferrals - Liabilities 36.0 109.4 42.1 6.1 73.9 181.3 46.5 11.4 Allowance for Uncollectible Accounts 30.4 8.5 3.6 4.5 32.3 13.8 3.2 3.8 Tax Effect - Tax Regulatory Liabilities 3.1 1.5 2.3 2.4 3.1 1.8 2.1 2.5 Federal Net Operating Loss Carryforwards - - 2.4 0.4 - - 32.1 4.5 Other 55.5 3.4 61.1 5.0 53.8 19.9 48.9 4.9 Total Deferred Tax Assets 416.8 214.7 148.6 28.4 485.1 258.5 179.6 36.3 Less: Valuation Allowance 3.1 - - - 4.0 - - - Net Deferred Tax Assets $ 413.7 $ 214.7 $ 148.6 $ 28.4 $ 481.1 $ 258.5 $ 179.6 $ 36.3 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 1,545.6 $ 1,387.1 $ 655.3 $ 416.1 $ 1,378.6 $ 1,296.9 $ 596.6 $ 385.8 Property Tax Accruals 27.3 22.8 7.3 10.6 58.1 25.0 7.4 12.8 Regulatory Amounts: Regulatory Deferrals - Assets 456.8 339.7 137.9 60.5 502.3 276.0 147.6 60.4 Tax Effect - Tax Regulatory Assets 168.7 36.0 15.4 9.0 166.9 35.5 15.9 9.3 Goodwill Regulatory Asset - 1999 Merger - 167.4 - - - 174.4 - - Derivative Assets 17.7 - - - 32.6 - - - Other 18.5 22.0 38.6 2.7 19.4 33.5 35.6 2.8 Total Deferred Tax Liabilities $ 2,234.6 $ 1,975.0 $ 854.5 $ 498.9 $ 2,157.9 $ 1,841.3 $ 803.1 $ 471.1
Summary of Operating Loss Carryforwards [Table Text Block]	Carryforwards: The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards: As of December 31, 2015 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Expiration Range Federal Net Operating Loss $ 15.5 $ - $ - $ 7.0 $ 1.0 2032 Federal Tax Credit 26.1 0.1 0.2 15.0 - 2031 - 2035 Federal Charitable Contribution 14.9 - - - - 2016 - 2018 State Tax Credit 101.2 73.8 - - - 2015 - 2020 State Charitable Contribution 3.0 - - - - 2015 - 2019 As of December 31, 2014 NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO Expiration Range Federal Net Operating Loss $ 168.8 $ - $ - $ 91.8 $ 12.7 2031 - 2032 Federal Tax Credit 16.3 0.1 0.2 11.1 - 2031 - 2034 Federal Charitable Contribution 19.4 - - - - 2016 - 2018 State Tax Credit 99.7 71.0 - - - 2014 - 2019 State Loss Carryforwards 40.6 - - - - 2014 - 2034 State Charitable Contribution 2.1 - - - - 2015 - 2018
Summary of Income Tax Contingencies [Table Text Block]	(Millions of Dollars) Eversource CL&P Balance as of January 1, 2013 $ 83.1 $ 49.0 Gross Increases - Current Year 8.2 2.1 Gross Decreases - Prior Year (1.1) (0.3) Settlements (49.8) (39.4) Lapse of Statute of Limitations (2.2) - Balance as of December 31, 2013 38.2 11.4 Gross Increases - Current Year 9.3 2.7 Gross Increases - Prior Year 0.3 0.2 Lapse of Statute of Limitations (1.6) - Balance as of December 31, 2014 46.2 14.3 Gross Increases - Current Year 9.9 2.6 Gross Increases - Prior Year 0.1 - Lapse of Statute of Limitations (8.2) (3.4) Balance as of December 31, 2015 $ 48.0 $ 13.5 Other Interest Expense/(Income) Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2015 2014 2013 2015 2014 Eversource $ 0.1 $ 0.4 $ (8.6) $ 2.0 $ 1.9 CL&P 0 - (4.0) - -
Summary of Income Tax Examination [Table Text Block]	Description Tax Years Federal 2015 Connecticut 2012 - 2015 Massachusetts 2012 - 2015 New Hampshire 2012 - 2015

Environmental Matters (Tables)

Environmental Matters (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Environmental Loss Contingencies By Site Text Block	(Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Balance as of January 1, 2014 $ 35.4 $ 3.4 $ 1.2 $ 5.4 $ 0.4 Additions 12.7 1.0 - 0.1 0.2 Payments/Reductions (4.8) (0.6) (0.1) (0.3) (0.1) Balance as of December 31, 2014 43.3 3.8 1.1 5.2 0.5 Additions 13.5 1.3 2.0 2.3 0.2 Payments/Reductions (5.7) (0.5) (0.7) (3.0) (0.1) Balance as of December 31, 2015 $ 51.1 $ 4.6 $ 2.4 $ 4.5 $ 0.6 As of December 31, 2015 As of December 31, 2014 Reserve Reserve Number of Sites (in millions) Number of Sites (in millions) Eversource 64 $ 51.1 65 $ 43.3 CL&P 14 4.6 16 3.8 NSTAR Electric 15 2.4 13 1.1 PSNH 12 4.5 13 5.2 WMECO 4 0.6 4 0.5

Long-Term Contractual Arrangeme

Long-Term Contractual Arrangements (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Long-term Purchase Commitment [Table Text Block]	B. Long-Term Contractual Arrangements Estimated Future Annual Costs: The estimated future annual costs of significant long-term contractual arrangements as of December 31, 2015 are as follows: Eversource (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 177.4 $ 110.1 $ 81.5 $ 51.1 $ 34.9 $ 80.6 $ 535.6 Renewable Energy 246.6 273.3 238.3 237.4 237.0 2,174.7 3,407.3 Peaker CfDs 55.8 41.1 20.4 7.8 4.0 3.6 132.7 Natural Gas Procurement 137.9 123.8 78.4 57.8 46.9 99.7 544.5 Coal, Wood and Other 45.4 23.3 3.4 1.9 1.9 13.1 89.0 Transmission Support Commitments 21.4 19.0 20.3 20.2 20.2 - 101.1 Total $ 684.5 $ 590.6 $ 442.3 $ 376.2 $ 344.9 $ 2,371.7 $ 4,810.2 CL&P (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 145.0 $ 87.2 $ 58.2 $ 38.0 $ 29.3 $ 47.6 $ 405.3 Renewable Energy 70.1 71.7 72.1 72.3 72.4 649.7 1,008.3 Peaker CfDs 55.8 41.1 20.4 7.8 4.0 3.6 132.7 Transmission Support Commitments 8.4 7.5 8.0 8.0 8.0 - 39.9 Yankee Companies Billings 0.1 0.4 0.8 0.8 0.8 10.7 13.6 Total $ 279.4 $ 207.9 $ 159.5 $ 126.9 $ 114.5 $ 711.6 $ 1,599.8 NSTAR Electric (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 14.1 $ 4.8 $ 5.5 $ 5.5 $ 3.1 $ 28.1 $ 61.1 Renewable Energy 99.0 117.0 80.4 78.5 76.6 489.8 941.3 Transmission Support Commitments 6.6 5.9 6.3 6.2 6.2 - 31.2 Yankee Companies Billings 0.1 0.2 0.3 0.3 0.3 3.6 4.8 Total $ 119.8 $ 127.9 $ 92.5 $ 90.5 $ 86.2 $ 521.5 $ 1,038.4 PSNH (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Supply and Stranded Cost $ 18.3 $ 18.1 $ 17.8 $ 7.6 $ 2.5 $ 4.9 $ 69.2 Renewable Energy 67.9 69.0 70.1 70.7 72.0 860.4 1,210.1 Coal, Wood and Other 45.4 23.3 3.4 1.9 1.9 13.1 89.0 Transmission Support Commitments 4.6 4.0 4.3 4.3 4.3 - 21.5 Yankee Companies Billings 0.1 0.2 0.3 0.3 0.3 4.2 5.4 Total $ 136.3 $ 114.6 $ 95.9 $ 84.8 $ 81.0 $ 882.6 $ 1,395.2 WMECO (Millions of Dollars) 2016 2017 2018 2019 2020 Thereafter Total Renewable Energy $ 9.6 $ 15.6 $ 15.7 $ 15.9 $ 16.0 $ 174.8 $ 247.6 Transmission Support Commitments 1.8 1.6 1.7 1.7 1.7 - 8.5 Yankee Companies Billings - 0.1 0.2 0.2 0.2 2.7 3.4 Total $ 11.4 $ 17.3 $ 17.6 $ 17.8 $ 17.9 $ 177.5 $ 259.5 Eversource For the Years Ended December 31, (Millions of Dollars) 2015 2014 2013 Supply and Stranded Cost $ 147.6 $ 99.2 $ 141.0 Renewable Energy 144.3 114.4 91.3 Peaker CfDs 42.7 18.1 51.9 Natural Gas Procurement 428.6 482.5 349.8 Coal, Wood and Other 95.9 120.5 112.6 Transmission Support Commitments 25.3 25.0 24.9 For the Years Ended December 31, 2015 2014 2013 NSTAR NSTAR NSTAR (Millions of Dollars) CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO CL&P Electric PSNH WMECO Supply and Stranded Cost $ 120.3 $ 6.5 $ 20.8 $ - $ 63.0 $ 7.0 $ 26.0 $ 3.2 $ 77.6 $ 32.4 $ 29.0 $ 2.0 Renewable Energy 20.0 86.7 37.2 0.4 0.7 87.4 26.3 - - 84.9 6.4 - Peaker CfDs 42.7 - - - 18.1 - - - 51.9 - - - Coal, Wood and Other - - 95.9 - - - 120.5 - - - 112.6 - Transmission Support Commitments 10.0 7.8 5.4 2.1 9.9 7.7 5.3 2.1 9.8 7.7 5.3 2.1

Guarantees and Indemnifications

Guarantees and Indemnifications (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Guarantee Obligations Text Block	Maximum Exposure Company Description (in millions) Expiration Dates On behalf of subsidiaries: Various Surety Bonds (1) $ 32.7 2016 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate $ 11.4 2019 and 2024 On behalf of external parties: Algonquin Gas Transmission, LLC Access Northeast project (owner of Access Northeast assets) capital contributions guarantee $ 204.8 2021

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Rent Expense [Table Text Block]	NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2015 $ 12.1 $ 12.5 $ 9.6 $ 2.8 $ 2.2 2014 14.3 6.0 7.8 1.5 1.2 2013 16.3 8.1 6.7 1.7 2.9
Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block]	Capital Leases (Millions of Dollars) Eversource CL&P PSNH 2016 $ 2.2 $ 1.9 $ 0.3 2017 2.1 1.9 0.2 2018 2.1 2.0 0.1 2019 2.0 2.0 0.0 2020 2.0 2.0 0.0 Thereafter 1.4 1.4 0.0 Future minimum lease payments 11.8 11.2 0.6 Less amount representing interest 3.6 3.6 0.0 Present value of future minimum lease payments $ 8.2 $ 7.6 $ 0.6
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Operating Leases NSTAR (Millions of Dollars) Eversource CL&P Electric PSNH WMECO 2016 $ 16.4 $ 2.9 $ 9.7 $ 0.8 $ 0.8 2017 13.8 2.0 8.5 0.7 0.7 2018 10.4 1.3 6.5 0.5 0.6 2019 8.5 1.0 5.3 0.4 0.5 2020 6.8 0.7 4.3 0.3 0.5 Thereafter 15.4 1.7 9.0 0.7 1.8 Future minimum lease payments $ 71.3 $ 9.6 $ 43.3 $ 3.4 $ 4.9

FAIR VALUE OF FINANCIAL INSTR56

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Fair Value By Balance Sheet Grouping Text Block	As of December 31, 2015 2014 Eversource Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 157.9 $ 155.6 $ 153.6 Long-Term Debt 9,034.5 9,425.9 8,814.0 9,451.2 As of December 31, 2015 CL&P NSTAR Electric PSNH WMECO Carrying Fair Carrying Fair Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 114.9 $ 43.0 $ 43.0 $ - $ - $ - $ - Long-Term Debt 2,763.7 3,031.6 2,029.8 2,182.4 1,071.0 1,121.2 517.3 551.8 As of December 31, 2014 CL&P NSTAR Electric PSNH WMECO Carrying Fair Carrying Fair Carrying Fair Carrying Fair (Millions of Dollars) Amount Value Amount Value Amount Value Amount Value Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 112.0 $ 43.0 $ 41.6 $ - $ - $ - $ - Long-Term Debt 2,826.2 3,214.5 1,786.2 1,993.5 1,070.0 1,137.9 625.2 689.4

ACCUMULATED OTHER COMPREHENSI57

ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Accumulated Other Comprehensive Income Loss Table Text Block	For the Year Ended December 31, 2015 For the Year Ended December 31, 2014 Qualified Unrealized Qualified Unrealized Cash Flow Gains/(Losses) Defined Cash Flow Gains on Defined Eversource Hedging on Marketable Benefit Hedging Marketable Benefit (Millions of Dollars) Instruments Securities Plans Total Instruments Securities Plans Total Balance as of January 1 st $ (12.4) $ 0.7 $ (62.3) $ (74.0) $ (14.4) $ 0.4 $ (32.0) $ (46.0) OCI Before Reclassifications - (2.6) 3.5 0.9 - 0.3 (34.2) (33.9) Amounts Reclassified from AOCI 2.1 - 4.2 6.3 2.0 - 3.9 5.9 Net OCI 2.1 (2.6) 7.7 7.2 2.0 0.3 (30.3) (28.0) Balance as of December 31 st $ (10.3) $ (1.9) $ (54.6) $ (66.8) $ (12.4) $ 0.7 $ (62.3) $ (74.0)
Schedule Of Comprehensive Income Loss [Table Text Block]	Amounts Reclassified from AOCI Eversource For the Years Ended December 31, Statements of Income (Millions of Dollars) 2015 2014 2013 Line Item Impacted Qualified Cash Flow Hedging Instruments $ (3.5) $ (3.4) $ (3.4) Interest Expense Tax Effect 1.4 1.4 1.4 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (2.1) $ (2.0) $ (2.0) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (6.6) $ (6.2) $ (10.5) Operations and Maintenance (1) Amortization of Prior Service Cost (0.2) (0.2) (0.2) Operations and Maintenance (1) Total Defined Benefit Plan Costs (6.8) (6.4) (10.7) Tax Effect 2.6 2.5 4.3 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (4.2) $ (3.9) $ (6.4) Total Amounts Reclassified from AOCI, Net of Tax $ (6.3) $ (5.9) $ (8.4)

COMMON SHARES (Tables)

COMMON SHARES (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Stock by Class [Text Block]	16 . COMMON SHARES The following table sets forth the Eversource parent common shares and those of CL&P, NSTAR Electric , PSNH and WMECO that were authorized and issued as well as the respective per share par values : Shares Authorized Issued Per Share as of December 31, as of December 31, Par Value 2015 and 2014 2015 2014 Eversource $ 5 380,000,000 333,862,615 333,359,172 CL&P $ 10 24,500,000 6,035,205 6,035,205 NSTAR Electric $ 1 100,000,000 100 100 PSNH $ 1 100,000,000 301 301 WMECO $ 25 1,072,471 434,653 434,653 As of December 31, 201 5 and 201 4 , there were 16,671,366 and 16,375,835 Eversource common shares held as treasury shares , respectively . As of December 31, 201 5 and 201 4 , Eversource common shares outstanding were 317,191,249 and 316,983,337 , respectively. In May 2015, the Comp any repurchased 532,521 Eversource common shares at a share price of $47.94. Such shares are included in Treasury Stock on the consolidated balance sheet at their weighted average original average cost of $26.02 per share.

PREFFERED STOCK (TABLES)

PREFFERED STOCK (TABLES)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule of Preferred Stock [Text Block]	Redemption Price Shares Outstanding as of As of December 31, Series Per Share December 31, 2015 and 2014 2015 2014 CL&P $ 1.90 Series of 1947 $ 52.50 163,912 $ 8.2 $ 8.2 $ 2.00 Series of 1947 $ 54.00 336,088 16.8 16.8 $ 2.04 Series of 1949 $ 52.00 100,000 5.0 5.0 $ 2.20 Series of 1949 $ 52.50 200,000 10.0 10.0 3.90 % Series of 1949 $ 50.50 160,000 8.0 8.0 $ 2.06 Series E of 1954 $ 51.00 200,000 10.0 10.0 $ 2.09 Series F of 1955 $ 51.00 100,000 5.0 5.0 4.50 % Series of 1956 $ 50.75 104,000 5.2 5.2 4.96 % Series of 1958 $ 50.50 100,000 5.0 5.0 4.50 % Series of 1963 $ 50.50 160,000 8.0 8.0 5.28 % Series of 1967 $ 51.43 200,000 10.0 10.0 $ 3.24 Series G of 1968 $ 51.84 300,000 15.0 15.0 6.56 % Series of 1968 $ 51.44 200,000 10.0 10.0 Total CL&P 2,324,000 $ 116.2 $ 116.2 NSTAR Electric 4.25 % Series $ 103.625 180,000 $ 18.0 $ 18.0 4.78 % Series $ 102.80 250,000 25.0 25.0 Total NSTAR Electric 430,000 $ 43.0 $ 43.0 Fair Value Adjustment due to Merger with NSTAR (3.6) (3.6) Total Eversource - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

COMMON SHARESHOLDERS' EQUITY 60

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (NU) (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Minority Interest Disclosure Text Block

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Earnings Per Share Basic And Diluted [Table Text Block]	Eversource For the Years Ended December 31, (Millions of Dollars, except share information) 2015 2014 2013 Net Income Attributable to Common Shareholders $ 878.5 $ 819.5 $ 786.0 Weighted Average Common Shares Outstanding: Basic 317,336,881 316,136,748 315,311,387 Dilutive Effect 1,095,806 1,280,666 899,773 Diluted 318,432,687 317,417,414 316,211,160 Basic EPS $ 2.77 $ 2.59 $ 2.49 Diluted EPS $ 2.76 $ 2.58 $ 2.49

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting Information [Line Items]
Schedule Of Segment Reporting Information By Segment Text Block	For the Year Ended December 31, 2015 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,903.6 $ 995.5 $ 1,069.1 $ 863.6 $ (877.0) $ 7,954.8 Depreciation and Amortization (425.2) (70.5) (165.6) (29.0) 2.1 (688.2) Other Operating Expenses (4,470.2) (776.7) (314.9) (817.9) 877.3 (5,502.4) Operating Income 1,008.2 148.3 588.6 16.7 2.4 1,764.2 Interest Expense (186.3) (36.9) (105.8) (48.0) 4.6 (372.4) Interest Income 5.7 0.1 1.6 4.4 (5.1) 6.7 Other Income, Net 7.2 0.8 14.5 977.8 (972.8) 27.5 Income Tax (Expense)/Benefit (322.8) (40.1) (191.6) 14.5 - (540.0) Net Income 512.0 72.2 307.3 965.4 (970.9) 886.0 Net Income Attributable to Noncontrolling Interests (4.7) - (2.8) - - (7.5) Net Income Attributable to Common Shareholders $ 507.3 $ 72.2 $ 304.5 $ 965.4 $ (970.9) $ 878.5 Total Assets (as of) $ 17,981.3 $ 3,104.5 $ 8,019.3 $ 13,256.7 $ (11,781.5) $ 30,580.3 Cash Flows Used for Investments in Plant $ 718.9 $ 182.2 $ 749.1 $ 73.9 $ - $ 1,724.1 For the Year Ended December 31, 2014 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,663.4 $ 1,007.3 $ 1,018.2 $ 790.9 $ (737.9) $ 7,741.9 Depreciation and Amortization (384.6) (68.1) (150.5) (42.1) 19.9 (625.4) Other Operating Expenses (4,366.2) (786.7) (302.1) (748.0) 719.3 (5,483.7) Operating Income 912.6 152.5 565.6 0.8 1.3 1,632.8 Interest Expense (191.6) (34.0) (104.1) (36.6) 4.2 (362.1) Interest Income 5.1 - 0.9 3.6 (3.6) 6.0 Other Income, Net 10.7 0.2 10.3 916.0 (918.6) 18.6 Income Tax (Expense)/Benefit (269.7) (46.4) (174.5) 22.3 - (468.3) Net Income 467.1 72.3 298.2 906.1 (916.7) 827.0 Net Income Attributable to Noncontrolling Interests (4.7) - (2.8) - - (7.5) Net Income Attributable to Common Shareholders $ 462.4 $ 72.3 $ 295.4 $ 906.1 $ (916.7) $ 819.5 Total Assets (as of) $ 17,536.9 $ 3,029.3 $ 7,615.6 $ 12,664.9 $ (11,106.3) $ 29,740.4 Cash Flows Used for Investments in Plant $ 645.2 $ 176.7 $ 731.6 $ 50.2 $ - $ 1,603.7 For the Year Ended December 31, 2013 Eversource Electric Natural Gas Electric (Millions of Dollars) Distribution Distribution Transmission Other Eliminations Total Operating Revenues $ 5,362.3 $ 855.8 $ 978.7 $ 777.5 $ (673.1) $ 7,301.2 Depreciation and Amortization (604.8) (66.7) (136.2) (62.2) 10.2 (859.7) Other Operating Expenses (3,927.7) (659.4) (281.8) (715.0) 671.8 (4,912.1) Operating Income 829.8 129.7 560.7 0.3 8.9 1,529.4 Interest Expense (175.0) (33.1) (100.3) (35.5) 5.2 (338.7) Interest Income 4.1 - 0.7 5.4 (5.6) 4.6 Other Income, Net 12.9 0.8 10.9 858.9 (858.2) 25.3 Income Tax (Expense)/Benefit (240.0) (36.5) (182.1) 31.9 (0.2) (426.9) Net Income 431.8 60.9 289.9 861.0 (849.9) 793.7 Net Income Attributable to Noncontrolling Interests (4.8) - (2.9) - - (7.7) Net Income Attributable to Common Shareholders $ 427.0 $ 60.9 $ 287.0 $ 861.0 $ (849.9) $ 786.0 Cash Flows Used for Investments in Plant $ 639.0 $ 168.1 $ 618.5 $ 31.2 $ - $ 1,456.8

GOODWILL (Tables)

GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2015
Notes To Consolidated Financial Statements [Abstract]
Schedule Of Goodwill Text Block	As of December 31, 2015 and 2014 Electric Electric Natural Gas (Billions of Dollars) Distribution Transmission Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 3.5

QUARTERLY FINANCIAL DATA (Una64

QUARTERLY FINANCIAL DATA (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	Eversource Quarter Ended (Millions of Dollars, except per share information) 2015 2014 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,513.4 $ 1,817.1 $ 1,933.1 $ 1,691.2 $ 2,290.6 $ 1,677.6 $ 1,892.5 $ 1,881.2 Operating Income 497.5 412.0 469.2 385.5 467.7 294.0 440.9 430.2 Net Income 255.1 209.4 237.8 183.7 237.8 129.2 236.5 223.6 Net Income Attributable to Common Shareholders 253.3 207.5 235.9 181.8 236.0 127.4 234.6 221.5 Basic EPS (a) $ 0.80 $ 0.65 $ 0.74 $ 0.57 $ 0.75 $ 0.40 $ 0.74 $ 0.69 Diluted EPS (a) $ 0.80 $ 0.65 $ 0.74 $ 0.57 $ 0.74 $ 0.40 $ 0.74 $ 0.69 (a) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2015 2014 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 804.9 $ 666.6 $ 704.3 $ 626.9 $ 734.6 $ 587.3 $ 695.6 $ 675.1 Operating Income 141.8 154.0 161.1 154.2 158.0 92.1 146.2 159.0 Net Income 69.2 78.8 80.2 71.2 79.3 37.4 83.9 87.2 NSTAR Electric Operating Revenues $ 766.8 $ 617.2 $ 750.7 $ 546.6 $ 666.2 $ 561.5 $ 727.9 $ 581.1 Operating Income 159.5 151.4 214.2 117.7 118.4 121.5 206.6 132.0 Net Income 83.6 82.0 118.6 60.3 58.1 60.1 115.6 69.3 PSNH Operating Revenues $ 284.8 $ 241.9 $ 234.4 $ 211.1 $ 299.8 $ 211.6 $ 223.7 $ 224.4 Operating Income 63.2 54.1 63.6 49.3 64.0 49.0 56.4 60.0 Net Income 32.0 27.9 32.5 22.0 32.6 24.1 28.2 29.0 WMECO Operating Revenues $ 152.9 $ 125.2 $ 125.1 $ 114.9 $ 137.4 $ 108.3 $ 118.1 $ 129.6 Operating Income 28.6 28.9 30.0 28.0 34.7 17.7 31.2 34.0 Net Income 13.2 14.2 15.0 14.1 18.1 7.0 14.7 18.0

ACCOUNTING STANDARDS (Details)

ACCOUNTING STANDARDS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Liabilities Current		$ 160,288
Available for sale securities subject to new accounting guidance	$ 52,000
The Connecticut Light And Power Company [Member]
Deferred Tax Liabilities Current		34,100
NSTAR Electric Company [Member]
Deferred Tax Liabilities Current	0	55,136
Public Service Company Of New Hampshire [Member]
Deferred Tax Liabilities Current	0	36,164
Western Massachusetts Electric Company [Member]
Deferred Tax Liabilities Current	$ 0	$ 18,089

Provision for Uncollectible A66

Provision for Uncollectible Accounts (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	$ 190.7	$ 175.3
Uncollectible Hardship Accounts Receivable Reserve	118.5	91.5
The Connecticut Light And Power Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	79.5	84.3
Uncollectible Hardship Accounts Receivable Reserve	68.1	74
NSTAR Electric Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	52.6	40.7
Uncollectible Hardship Accounts Receivable Reserve	25.3
Public Service Company Of New Hampshire [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	8.7	7.7
Western Massachusetts Electric Company [Member]
Accounts Notes And Loans Receivable [Line Items]
Allowance For Doubtful Accounts Receivable Current	14	9.9
Uncollectible Hardship Accounts Receivable Reserve	$ 7.4	$ 6.2

Fuel, Materials and Supplies an

Fuel, Materials and Supplies and Allowance Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Public Utilities Inventory Fuel [Member]
Other Inventory, Current	$ 152,500	$ 164,300
Public Utilities Inventory Supplies [Member]
Other Inventory, Current	131,200	159,500
Emission Allowances [Member]
Other Inventory, Current	1,900	100
Other Inventory, Noncurrent	17,500	20,100
RECs [Member]
Other Inventory, Current	50,900	25,800
NSTAR Electric Company [Member]
Materials and Supplies	75,487	74,179
NSTAR Electric Company [Member] | Public Utilities Inventory Supplies [Member]
Other Inventory, Current	32,200	49,100
NSTAR Electric Company [Member] | RECs [Member]
Other Inventory, Current	43,300	25,100
Public Service Company Of New Hampshire [Member] | Public Utilities Inventory Fuel [Member]
Other Inventory, Current	103,400	95,100
Public Service Company Of New Hampshire [Member] | Public Utilities Inventory Supplies [Member]
Other Inventory, Current	44,600	52,200
Public Service Company Of New Hampshire [Member] | Emission Allowances [Member]
Other Inventory, Current	1,900	100
Other Inventory, Noncurrent	17,500	20,100
Public Service Company Of New Hampshire [Member] | RECs [Member]
Other Inventory, Current	$ 7,000	$ 700

Deposits (Details)

Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Special Deposits [Line Items]
Cash Collateral Deposited	$ 17.1	$ 9.9
The Connecticut Light And Power Company [Member]
Special Deposits [Line Items]
Cash Collateral Deposited	0.7	1.2
NSTAR Electric Company [Member]
Special Deposits [Line Items]
Cash Collateral Deposited	8.5
Public Service Company Of New Hampshire [Member]
Special Deposits [Line Items]
Cash Collateral Deposited	$ 1.5	$ 2.5

Equity Method Investments (Deta

Equity Method Investments (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
CYAPC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	34.50%
CYAPC [Member] | NSTAR Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	14.00%
CYAPC [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	5.00%
CYAPC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	9.50%
YAEC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	24.50%
YAEC [Member] | NSTAR Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	14.00%
YAEC [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	7.00%
YAEC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	7.00%
MYAPC [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	12.00%
MYAPC [Member] | NSTAR Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	4.00%
MYAPC [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	5.00%
MYAPC [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	3.00%
Yankee Companies [Member] | The Connecticut Light And Power Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 1.2	$ 1.2
Yankee Companies [Member] | NSTAR Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	0.5	0.5
Yankee Companies [Member] | Public Service Company Of New Hampshire [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	0.3	0.3
Yankee Companies [Member] | Western Massachusetts Electric Company [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	0.3	0.3
Energy Investment Fund [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	30.3	$ 17.8
Algonquin Gas Tansmsission LLC - Access Northeast [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	$ 10.7

Operating Expenses (Details)

Operating Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fuel [Line Items]
Fuel Power Costs	$ 516.7	$ 599.4	$ 466.5
Public Service Company Of New Hampshire [Member]
Fuel [Line Items]
Fuel Power Costs	$ 85.4	$ 113.4	$ 104.8

Allowance for Funds Used Duri71

Allowance for Funds Used During Construction (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance For Funds Used During Construction [Line Items]
AFUDC Borrowed Funds	$ 7.2	$ 5.8	$ 4.1
AFUDC Equity Funds	18.8	13.7	7.1
Total AFUDC	$ 26	$ 19.5	$ 11.2
Average AFUDC Rate	3.90%	3.40%	2.70%
The Connecticut Light And Power Company [Member]
Allowance For Funds Used During Construction [Line Items]
AFUDC Borrowed Funds	$ 2.6	$ 1.9	$ 2.2
AFUDC Equity Funds	5.2	2.9	2.9
Total AFUDC	$ 7.8	$ 4.8	$ 5.1
Average AFUDC Rate	5.50%	3.40%	3.70%
NSTAR Electric Company [Member]
Allowance For Funds Used During Construction [Line Items]
AFUDC Borrowed Funds	$ 2	$ 2	$ 0.5
AFUDC Equity Funds	4.3	3.8
Total AFUDC	$ 6.3	$ 5.8	$ 0.5
Average AFUDC Rate	3.20%	2.50%	0.50%
Public Service Company Of New Hampshire [Member]
Allowance For Funds Used During Construction [Line Items]
AFUDC Borrowed Funds	$ 1	$ 0.6	$ 0.5
AFUDC Equity Funds	1.2	0.6	0.2
Total AFUDC	$ 2.2	$ 1.2	$ 0.7
Average AFUDC Rate	1.80%	1.80%	1.10%
Western Massachusetts Electric Company [Member]
Allowance For Funds Used During Construction [Line Items]
AFUDC Borrowed Funds	$ 1	$ 0.9	$ 0.5
AFUDC Equity Funds	1.7	1.7	1
Total AFUDC	$ 2.7	$ 2.6	$ 1.5
Average AFUDC Rate	4.40%	5.60%	6.10%

Other Income, Net (Details)

Other Income, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Component Of Other Income Nonoperating [Line Items]
AFUDC Equity Funds	$ 18.8	$ 13.7	$ 7.1
The Connecticut Light And Power Company [Member]
Component Of Other Income Nonoperating [Line Items]
AFUDC Equity Funds	5.2	2.9	2.9
Public Service Company Of New Hampshire [Member]
Component Of Other Income Nonoperating [Line Items]
AFUDC Equity Funds	1.2	0.6	0.2
Western Massachusetts Electric Company [Member]
Component Of Other Income Nonoperating [Line Items]
AFUDC Equity Funds	$ 1.7	$ 1.7	$ 1

Other Taxes (Details)

Other Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Excise And Sales Taxes	$ 147.2	$ 148.2	$ 144.1
The Connecticut Light And Power Company [Member]
Excise And Sales Taxes	$ 128.5	$ 127.9	$ 128.2

Supplemental Cash Flow Inform74

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capital Expenditures Incurred But Not Yet Paid	$ 216.6	$ 181.9	$ 193.1
Interest Paid, Net of Amounts Capitalized	365.9	349.6	343.3
Income Taxes Paid	10.3	334.2	50
The Connecticut Light And Power Company [Member]
Capital Expenditures Incurred But Not Yet Paid	76	63.5	51.4
Interest Paid, Net of Amounts Capitalized	144.4	144.1	131.6
Income Taxes Paid	55.2	135.4	55
NSTAR Electric Company [Member]
Capital Expenditures Incurred But Not Yet Paid	23.5	34.6	57
Interest Paid, Net of Amounts Capitalized	75.7	75.3	75.8
Income Taxes Paid	(19.8)	217.1	163.4
Public Service Company Of New Hampshire [Member]
Capital Expenditures Incurred But Not Yet Paid	46.5	39.3	34.9
Interest Paid, Net of Amounts Capitalized	42.3	41.1	43.3
Income Taxes Paid	14.4	2.3	(30.1)
Western Massachusetts Electric Company [Member]
Capital Expenditures Incurred But Not Yet Paid	27	14.2	19.5
Interest Paid, Net of Amounts Capitalized	26.7	25.9	25.8
Income Taxes Paid	$ 14.7	$ 25.1	$ (69)

Severance Benefits (Details)

Severance Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]
Description Of Postemployment Benefits	For the years ended December 31, 2015, 2014 and 2013, Eversource recorded severance benefit expense of $4.7 million, $15 million and $9.7 million, respectively, in connection with organizational and cost saving initiatives, and, in 2014, the partial outsourcing of information technology functions. As of December 31, 2015 and 2014, the severance accrual totaled $9.3 million and $10.4 million, respectively, and was included in Other Current Liabilities on the balance sheets.
Postemployment Benefits Period Expense	$ 4.7	$ 15	$ 9.7
Postemployment Benefits Liability Current	$ 9.3	$ 10.4

Related Parties (Details)

Related Parties (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
The Connecticut Light And Power Company [Member]
Related Party Transaction [Line Items]
Long Term Receivable From Nusco	$ 25	$ 25
Public Service Company Of New Hampshire [Member]
Related Party Transaction [Line Items]
Long Term Receivable From Nusco	3.8	3.8
Western Massachusetts Electric Company [Member]
Related Party Transaction [Line Items]
Long Term Receivable From Nusco	$ 5.5	$ 5.5

REGULATORY ACCOUNTING (Details)

REGULATORY ACCOUNTING (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Regulatory Asset [Line Items]
Regulatory Assets, Total	$ 4,583,800	$ 4,726,600
Regulatory Assets Current	845,843	672,493
Regulatory Assets Long Term	3,737,960	4,054,086
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	$ 75,300	60,500
Description of Regulatory Assets and Liabilities	Benefit Costs: Eversource's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other PBOP plans. The liability recorded by the Regulated companies to recognize the funded status of their retiree benefit plans is offset by a regulatory asset in lieu of a charge to Accumulated Other Comprehensive Income/(Loss), reflecting ultimate recovery from customers through rates. The regulatory asset is amortized as the actuarial gains and losses and prior service cost are amortized to net periodic benefit cost for the pension and PBOP plans.  All amounts are remeasured annually. Regulatory accounting is also applied to the portions of Eversource's service company costs that support the Regulated companies, as these amounts are also recoverable. As these regulatory assets do not represent a cash outlay for the Regulated companies, no carrying charge is recovered from customers. CL&P, NSTAR Electric, PSNH and WMECO recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric and WMECO each recover their qualified pension and PBOP expenses related to distribution operations through rate reconciling mechanisms that fully track the change in net pension and PBOP expenses each year. Derivative Liabilities: Regulatory assets are recorded as an offset to derivative liabilities and relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates. These assets are excluded from rate base and are being recovered as the actual settlements occur over the duration of the contracts. See Note 4, "Derivative Instruments," to the financial statements for further information on these contracts. Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. The amortization period of these assets varies depending on the nature and/or remaining life of the underlying assets and liabilities.  For further information regarding income taxes, see Note 10, "Income Taxes," to the financial statements. Storm Restoration Costs: The storm restoration cost deferrals relate to costs incurred for major storm events at CL&P, NSTAR Electric, PSNH and WMECO that each company expects to recover from customers. A storm must meet certain criteria to qualify as a major storm with the criteria specific to each state jurisdiction and utility company. Once a storm qualifies as a major storm, all qualifying expenses incurred during storm restoration efforts are deferred and recovered from customers. In addition to storm restoration costs, CL&P and PSNH are each allowed to recover pre-staging storm costs. Of the total deferred storm restoration costs, $197 million is pending regulatory approval (including $106 million at NSTAR Electric, $61 million at PSNH, and $30 million at WMECO). Management believes the storm restoration costs were prudent and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire, and that recovery from customers is probable through the applicable regulatory recovery process. Each electric utility has sought, or is seeking, recovery of its deferred storm restoration costs through its applicable regulatory recovery process. Each electric utility company earns a return on its deferred storm restoration cost regulatory asset balance. Goodwill-related: The goodwill regulatory asset originated from a 1999 merger transaction and the DPU allowed its recovery in NSTAR Electric and NSTAR Gas rates. This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40-year period, and, as of December 31, 2015, there were 24 years of amortization remaining. Regulatory Tracker Mechanisms: The Regulated companies’ approved rates are designed to recover their costs incurred to provide service to customers. The Regulated companies recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The differences between the costs incurred (or the rate recovery allowed) and the actual revenues are recorded as regulatory assets (for undercollections) or as regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recorded on all material regulatory tracker mechanisms. CL&P, NSTAR Electric, PSNH and WMECO each recover, on a fully reconciling basis, the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs (including LBR at NSTAR Electric), low income assistance programs, certain uncollectible accounts receivable for hardship customers, and restructuring and stranded costs as a result of deregulation. Energy procurement costs at PSNH include the costs related to its generating stations and at WMECO include the costs related to its solar generation. CL&P (effective December 1, 2014) and WMECO each have a regulatory commission approved revenue decoupling mechanism. Distribution revenues are decoupled from customer sales volumes, which breaks the relationship between sales volumes and revenues recognized. CL&P and WMECO reconcile their annual base distribution rate recovery to pre-established levels of baseline distribution delivery service revenues. Any difference between the allowed level of distribution revenue and the actual amount received during a 12-month period is adjusted through rates in the following period. CL&P and WMECO's revenue decoupling mechanisms permit recovery of an annual base amount of distribution revenues of $1.059 billion and $132.4 million, respectively. Contractual Obligations - Yankee Companies: CL&P, NSTAR Electric, PSNH and WMECO are responsible for their proportionate share of the remaining costs of the CYAPC, YAEC and MYAPC nuclear facilities, including nuclear fuel storage. A portion of these costs was recorded as a regulatory asset. Amounts for CL&P are earning a return and are being recovered through the CTA. Amounts for NSTAR Electric and WMECO are being recovered without a return through the transition charge. Amounts for PSNH were fully recovered in 2006. As a result of Eversource's consolidation of CYAPC and YAEC, Eversource's regulatory asset balance also includes the regulatory assets of CYAPC and YAEC, which totaled $110.9 million and $97.8 million as of December 31, 2015 and 2014, respectively. Intercompany transactions between CL&P, NSTAR Electric, PSNH and WMECO and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements. Other Regulatory Assets: Other Regulatory Assets primarily include asset retirement obligations, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt, purchase power contract termination costs and various other items. Regulatory Costs in Other Long-Term Assets: The Regulated companies had $75.3 million (including $3.1 million for CL&P, $35.4 million for NSTAR Electric, $4.8 million for PSNH and $16.7 million for WMECO) and $60.5 million (including $1.3 million for CL&P, $33.2 million for NSTAR Electric, $0.9 million for PSNH, and $11 million for WMECO) of additional regulatory costs as of December 31, 2015 and 2014, respectively, that were included in Other Long-Term Assets on the balance sheets. These amounts represent incurred costs for which recovery has not yet been specifically approved by the applicable regulatory agency. However, based on regulatory policies or past precedent on similar costs, management believes it is probable that these costs will ultimately be approved and recovered from customers in rates. The NSTAR Electric balance as of December 31, 2015 and 2014 primarily related to the deferral of certain bad debt costs expected to be recovered in future rates. Equity Return on Regulatory Assets: For rate-making purposes, the Regulated companies recover the carrying costs related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $1.5 million and $1.7 million for CL&P as of December 31, 2015 and 2014, respectively. These carrying costs will be recovered from customers in future rates. As of December 31, 2015 and 2014, this equity return, which is not recorded on the balance sheets, totaled $48.3 million and $43.3 million, respectively, for PSNH. These amounts include $25 million of equity return on the Clean Air Project costs that PSNH has agreed not to bill customers pending NHPUC approval of a generation divestiture settlement agreement. For further information on the divestiture, see Note 11H, "Commitments and Contingencies – PSNH Generation Restructuring." Regulatory Liabilities: The components of regulatory liabilities were as follows: Cost of Removal: Eversource's Regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense and the cumulative amount collected from customers but not yet expended is recognized as a regulatory liability. Expended costs that exceed amounts collected from customers are recognized as regulatory assets, as they are probable of recovery in future rates. AFUDC - Transmission: Regulatory liabilities were recorded by CL&P and WMECO for AFUDC accrued on certain reliability-related transmission projects to reflect local rate base recovery as a result of a FERC-approved transmission tariff. A regulatory liability was recorded by NSTAR Electric for AFUDC accrued on certain reliability-related transmission projects through December 31, 2015 to reflect local rate base recovery. These regulatory liabilities for CL&P, NSTAR Electric and WMECO will be amortized over the depreciable life of the related transmission assets.
Public Utilities Disclosure Of Regulatory Matters	2015 Regulatory Developments: FERC ROE Complaints: As a result of the actions taken by the FERC and other developments in the pending ROE complaint proceedings described in Note 11E, "Commitments and Contingencies – FERC ROE Complaints," Eversource recorded reserves for the first and second ROE complaints, which were recorded as a regulatory liability and as a reduction to operating revenues. The cumulative pre-tax reserves (excluding interest) as of December 31, 2015, which include the impact of refunds given to customers, totaled $39.1 million for Eversource (including $21.4 million for CL&P, $8.5 million for NSTAR Electric, $3.1 million for PSNH, and $6.1 million for WMECO). NSTAR Electric and NSTAR Gas Comprehensive Settlement Agreement: On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2009 through 2011 (11 dockets in total). In 2015, as a result of the DPU order, NSTAR Electric and NSTAR Gas commenced refunding a combined $44.7 million to customers, which was recorded as a regulatory liability. Refunds to customers will continue through December 2016. As a result of the Settlement, NSTAR Electric increased its operating revenues and decreased its amortization expense in 2015, resulting in the recognition of a $21.7 million pre-tax benefit in 2015. NSTAR Electric Basic Service Bad Debt Adder: On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had removed energy-related bad debt costs from base distribution rates effective January 1, 2006. As a result of the DPU order, in the first quarter of 2015, NSTAR Electric increased its regulatory assets and reduced its operations and maintenance expense by an under recovered amount of $24.2 million for energy-related bad debt costs through 2014, resulting in a pre-tax benefit in 2015. NSTAR Electric filed for recovery of the energy-related bad debt costs regulatory asset from customers and on November 20, 2015 the DPU approved NSTAR Electric’s proposed rate increase to recover these costs over a 12-month period, effective January 1, 2016. CL&P Distribution Rates: On July 2, 2015, PURA issued a final order that approved a settlement agreement filed on May 19, 2015, which allows for an increase to rate base of approximately $163 million associated with ADIT, including a regulatory asset to recover the incremental revenue requirement for the period December 1, 2014 through November 30, 2015 over a subsequent 24-month period. The rate base increase provided an increase to total allowed annual revenue requirements of $18.4 million beginning December 1, 2014. As part of the settlement agreement, the $18.4 million for the period December 1, 2014 through November 30, 2015 was recorded as a regulatory asset with a corresponding increase in Operating Revenues, and is being collected from customers in rates over a 24-month period beginning December 1, 2015. NSTAR Gas Distribution Rates: On October 30, 2015, the DPU issued its order in the NSTAR Gas distribution rate case, which approved an annualized base rate increase of $15.8 million, plus other increases of approximately $11.5 million, mostly relating to recovery of pension and PBOP expenses and the Hopkinton GSA, effective January 1, 2016. In the order, the DPU also approved an authorized regulatory ROE of 9.8 percent, the establishment of a revenue decoupling mechanism, the recovery of certain bad debt expenses, and a 52.1 percent equity component of its capital structure. On November 19, 2015, NSTAR Gas filed a motion for reconsideration of the order with the DPU seeking the correction of mathematical errors and other plant and cost of service items. As a result of this order, Eversource recorded regulatory deferrals for costs that have been approved for recovery or are expected to be approved for recovery in future rate proceedings, which resulted in the recognition of a $17.2 million pre-tax benefit in 2015. Included in this amount is a $10.5 million pre-tax benefit recorded at NSTAR Electric for certain uncollectible hardship accounts receivable that are expected to be recovered in future rates given the allowed recoveries of uncollectible hardship accounts receivable by WMECO and NSTAR Gas.
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	$ 621,400	750,100
Regulatory Liability Current	107,759	235,022
Regulatory Liabilities Long-Term	513,595	515,144
The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,637,300	1,695,800
Regulatory Assets Current	268,318	220,344
Regulatory Assets Long Term	1,369,028	1,475,508
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	3,100	1,300
Public Utilities Amount Of Allowance For Earnings On Equity Capitalized For Rate Making Purposes	1,500	1,700
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	136,000	206,000
Regulatory Liability Current	61,155	124,722
Regulatory Liabilities Long-Term	74,830	81,298
NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,461,400	1,377,800
Regulatory Assets Current	348,408	198,710
Regulatory Assets Long Term	1,112,977	1,179,100
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	35,400	33,200
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	267,700	312,300
Regulatory Liability Current	3,281	49,611
Regulatory Liabilities Long-Term	264,352	262,738
Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	362,900	404,800
Regulatory Assets Current	104,971	111,705
Regulatory Assets Long Term	257,873	293,115
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	4,800	900
Public Utilities Amount Of Allowance For Earnings On Equity Capitalized For Rate Making Purposes	48,300	43,300
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	54,800	67,400
Regulatory Liability Current	6,898	16,044
Regulatory Liabilities Long-Term	47,851	51,372
Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	191,200	198,200
Regulatory Assets Current	56,166	51,923
Regulatory Assets Long Term	135,010	146,307
Regulatory Assets And Liabilities Other Disclosures Abstract
Amount of Regulatory Costs Not yet Approved	16,700	11,000
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	24,700	33,300
Regulatory Liability Current	13,122	22,486
Regulatory Liabilities Long-Term	11,597	10,835
CYAPC and YAEC [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	110,900	97,800
Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	437,100	439,900
Cost Of Removal [Member] | The Connecticut Light And Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	24,100	19,700
Cost Of Removal [Member] | NSTAR Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	257,400	258,300
Cost Of Removal [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	47,200	50,300
Cost Of Removal [Member] | Western Massachusetts Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	2,800	1,100
Regulatory Tracker Deferrals Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	99,700	192,300
Regulatory Tracker Deferrals Regulatory Liabilities [Member] | The Connecticut Light And Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	56,200	122,600
Regulatory Tracker Deferrals Regulatory Liabilities [Member] | NSTAR Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	3,300	20,700
Regulatory Tracker Deferrals Regulatory Liabilities [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	3,400	14,200
Regulatory Tracker Deferrals Regulatory Liabilities [Member] | Western Massachusetts Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	12,900	22,300
AFUDC Transmission Incentive [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	66,100	67,100
AFUDC Transmission Incentive [Member] | The Connecticut Light And Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	51,500	53,600
AFUDC Transmission Incentive [Member] | NSTAR Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	5,700	4,400
AFUDC Transmission Incentive [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	0	0
AFUDC Transmission Incentive [Member] | Western Massachusetts Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	8,900	9,100
Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	18,500	50,800
Other Regulatory Liabilities [Member] | The Connecticut Light And Power Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	4,200	10,100
Other Regulatory Liabilities [Member] | NSTAR Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	1,300	28,900
Other Regulatory Liabilities [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	4,200	2,900
Other Regulatory Liabilities [Member] | Western Massachusetts Electric Company [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities, Total	100	800
Benefit Costs [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,828,200	2,016,000
Benefit Costs [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	413,600	445,400
Benefit Costs [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	479,900	515,900
Benefit Costs [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	164,200	174,300
Benefit Costs [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	84,900	85,000
Regulatory Assets Offsetting Derivative Liabilities [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	388,000	425,500
Regulatory Assets Offsetting Derivative Liabilities [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	380,800	410,900
Regulatory Assets Offsetting Derivative Liabilities [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	1,300	4,500
Regulatory Assets Offsetting Derivative Liabilities [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	0	0
Regulatory Assets Offsetting Derivative Liabilities [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	0	0
Deferred Income Tax Charges Member
Regulatory Asset [Line Items]
Regulatory Assets, Total	650,900	635,300
Deferred Income Tax Charges Member | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	444,400	437,700
Deferred Income Tax Charges Member | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	85,700	83,700
Deferred Income Tax Charges Member | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	34,500	38,000
Deferred Income Tax Charges Member | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	31,800	35,500
Storm Restoration Costs [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	436,900	502,800
Storm Restoration Costs [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	271,400	319,600
Storm Restoration Costs [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	110,900	103,700
Storm Restoration Costs [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	31,500	47,700
Storm Restoration Costs [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	23,100	31,800
Goodwill Regulatory Asset [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	484,900	505,400
Goodwill Regulatory Asset [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	416,300	433,900
Regulatory Tracker Deferrals Regulatory Assets [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	526,500	350,500
Regulatory Tracker Deferrals Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	45,100	16,100
Regulatory Tracker Deferrals Regulatory Assets [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	311,000	141,400
Regulatory Tracker Deferrals Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	101,200	103,500
Regulatory Tracker Deferrals Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	40,100	33,000
Unrecovered Contractual Obligations [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	134,400	123,800
Other Regulatory Assets [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	134,000	167,300
Other Regulatory Assets [Member] | The Connecticut Light And Power Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	82,000	66,100
Other Regulatory Assets [Member] | NSTAR Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	56,300	94,700
Other Regulatory Assets [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	31,500	41,300
Other Regulatory Assets [Member] | Western Massachusetts Electric Company [Member]
Regulatory Asset [Line Items]
Regulatory Assets, Total	$ 11,300	$ 12,900

PROPERTY, PLANT AND ACCUMULAT78

PROPERTY, PLANT AND ACCUMULATED DEPRECIATION (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	$ 13,054,800	$ 12,495,200
Public Utilities Property Plant And Equipment Distribution Natural Gas	2,727,200	2,595,400
Public Utilities Property Plant And Equipment Transmission	7,691,900	6,930,700
Public Utilities Property Plant And Equipment Generation Or Processing	1,194,100	1,170,900
Public Utilities Property Plant And Equipment Electric And Natural Gas Utility Total	24,668,000	23,192,200
Public Utilities Property Plant And Equipment Other Property Plant And Equipment	558,600	551,300
Public Utilities Property Plant And Equipment Plant In Service	25,226,600	23,743,500
Less Accumulated Depreciation [Abstract]
Electric And Natural Gas Utility Accumulated Depreciation	(6,141,100)	(5,777,800)
Other Accumulated Depreciation	(255,600)	(231,800)
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(6,396,700)	(6,009,600)
Property Plant And Equipment Net Excluding Construction Work In Progress	18,829,900	17,733,900
Public Utilities Property Plant And Equipment Construction Work In Progress	1,062,500	913,100
Property, Plant and Equipment, Net	$ 19,892,441	$ 18,647,041
Public Utilities Property Plant and Equipment Depreciation Rates	2.90%	3.00%	2.80%
Useful Lives [Abstract]
Distribution Assets Average Useful Life	34.8
Transmission Assets Average Useful Life	41.6
Generation Assets Average Useful Life	30.7
Other Assets Average Useful Life	14.1
The Connecticut Light And Power Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	$ 5,377,200	$ 5,158,800
Public Utilities Property Plant And Equipment Transmission	3,618,000	3,274,000
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	8,995,200	8,432,800
Less Accumulated Depreciation [Abstract]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(2,041,900)	(1,928,000)
Property Plant And Equipment Net Excluding Construction Work In Progress	6,953,300	6,504,800
Public Utilities Property Plant And Equipment Construction Work In Progress	203,500	304,900
Property, Plant and Equipment, Net	$ 7,156,809	$ 6,809,664
Public Utilities Property Plant and Equipment Depreciation Rates	2.70%	2.70%	2.50%
Useful Lives [Abstract]
Distribution Assets Average Useful Life	37.3
Transmission Assets Average Useful Life	38.7
Generation Assets Average Useful Life	0
Other Assets Average Useful Life	0
NSTAR Electric Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	$ 5,100,500	$ 4,895,500
Public Utilities Property Plant And Equipment Transmission	2,131,300	1,928,500
Public Utilities Property Plant And Equipment Generation Or Processing	0	0
Public Utilities Property Plant And Equipment Plant In Service	7,231,800	6,824,000
Less Accumulated Depreciation [Abstract]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(1,886,800)	(1,761,400)
Property Plant And Equipment Net Excluding Construction Work In Progress	5,345,000	5,062,600
Public Utilities Property Plant And Equipment Construction Work In Progress	310,500	272,800
Property, Plant and Equipment, Net	$ 5,655,458	$ 5,335,436
Public Utilities Property Plant and Equipment Depreciation Rates	3.00%	3.00%	2.90%
Useful Lives [Abstract]
Distribution Assets Average Useful Life	31.9
Transmission Assets Average Useful Life	43.8
Generation Assets Average Useful Life	0
Other Assets Average Useful Life	0
Public Service Company Of New Hampshire [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	$ 1,804,800	$ 1,696,700
Public Utilities Property Plant And Equipment Transmission	928,200	789,700
Public Utilities Property Plant And Equipment Generation Or Processing	1,158,100	1,136,500
Public Utilities Property Plant And Equipment Plant In Service	3,891,100	3,622,900
Less Accumulated Depreciation [Abstract]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(1,171,000)	(1,090,000)
Property Plant And Equipment Net Excluding Construction Work In Progress	2,720,100	2,532,900
Public Utilities Property Plant And Equipment Construction Work In Progress	135,300	102,900
Property, Plant and Equipment, Net	$ 2,855,363	$ 2,635,844
Public Utilities Property Plant and Equipment Depreciation Rates	3.20%	3.00%	3.00%
Useful Lives [Abstract]
Distribution Assets Average Useful Life	31.3
Transmission Assets Average Useful Life	41.6
Generation Assets Average Useful Life	30.9
Other Assets Average Useful Life	0
Public Service Company Of New Hampshire [Member] | Generation Plant [Member]
Less Accumulated Depreciation [Abstract]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	$ (522,400)
Western Massachusetts Electric Company [Member]
Public Utility Property Plant And Equipment [Line Items]
Public Utilities Property Plant And Equipment Distribution	812,300	$ 784,200
Public Utilities Property Plant And Equipment Transmission	964,900	891,000
Public Utilities Property Plant And Equipment Generation Or Processing	36,000	34,400
Public Utilities Property Plant And Equipment Plant In Service	1,813,200	1,709,600
Less Accumulated Depreciation [Abstract]
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation	(307,000)	(297,400)
Property Plant And Equipment Net Excluding Construction Work In Progress	1,506,200	1,412,200
Public Utilities Property Plant And Equipment Construction Work In Progress	69,100	49,100
Property, Plant and Equipment, Net	$ 1,575,306	$ 1,461,321
Public Utilities Property Plant and Equipment Depreciation Rates	2.70%	3.30%	2.90%
Useful Lives [Abstract]
Distribution Assets Average Useful Life	30.5
Transmission Assets Average Useful Life	50
Generation Assets Average Useful Life	25
Other Assets Average Useful Life	0

DERIVATIVE INSTURMENTS (Details

DERIVATIVE INSTURMENTS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)$ / KWmo$ / REC	Dec. 31, 2014USD ($)$ / KWmo$ / REC$ / MWh	Dec. 31, 2013USD ($)
Derivative Instrument Detail Abstract
Derivative Liabilities, Noncurrent	$ (337,102)	$ (409,632)
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	Commodity Supply and Price Risk Management: As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of the costs or benefits of each contract borne by or allocated to CL&P and 20 percent borne by or allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020. NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019. As of December 31, 2015 and 2014, Eversource had NYMEX financial contracts for natural gas futures in order to reduce variability associated with the purchase price of approximately 9.1 million and 8.8 million MMBtu of natural gas, respectively.
Derivative Credit Risk Related Contingent Features Abstract
Derivative Net Liability Position Aggregate Fair Value	$ (5,800)	(10,000)
Additional Collateral Aggregate Fair Value	$ 5,800	10,000
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsExitPricePremium	Exit price premiums of 5 percent to 22 percent are also applied on these contracts and reflect the uncertainty and illiquidity premiums that would be required based on the most recent market activity available for similar type contracts
The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	$ (91,820)	(88,459)
Derivative Liabilities, Noncurrent	(336,189)	(406,199)
Derivative Assets Subject to Credit Risk with investment grade counterparty	$ 47,000
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	Commodity Supply and Price Risk Management: As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of the costs or benefits of each contract borne by or allocated to CL&P and 20 percent borne by or allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020.
Fair Value Inputs Level 2 [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	$ (5,800)	(9,800)
Derivative Liabilities, Noncurrent	0	(300)
Derivative Assets Noncurrent	100	0
Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	5,800	9,600
Derivative Liabilities - Current		(90,000)
Derivative Liabilities, Noncurrent	(337,100)	(409,300)
Derivative Assets Noncurrent	42,700	$ 74,300
Consolidated Current Derivative Liabilities	$ (92,300)
Fair Value Inputs Level 3 [Member] | Minimum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices | $ / KWmo	10.81	5.30
FairValueInputsRenewableEnergyCreditPrices | $ / REC	45	38
FairValueInputsForwardReserve | $ / KWmo		5.80
Fair Value Inputs Level 3 [Member] | Maximum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	15.82	12.98
FairValueInputsRenewableEnergyCreditPrices | $ / REC	51	56
FairValueInputsForwardReserve | $ / KWmo		9.50
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	$ 5,800	$ 9,500
Derivative Liabilities - Current	(91,800)	(88,500)
Derivative Liabilities, Noncurrent	(336,200)	(406,200)
Derivative Assets Noncurrent	$ 41,400	$ 74,300
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | Minimum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	10.81	11.08
FairValueInputsForwardReserve | $ / KWmo		5.80
Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member] | Maximum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	12.60	12.98
FairValueInputsForwardReserve | $ / KWmo		9.50
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	$ 0	$ 100
Derivative Liabilities - Current	(500)	(1,500)
Derivative Liabilities, Noncurrent	(900)	$ (3,100)
Derivative Assets Noncurrent	$ 1,300
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | Minimum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	10.81	5.30
Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member] | Maximum [Member]
FairValueInputsQuantitativeInformation[Abstract]
FairValueInputsCapacityPrices	15.82	11.10
Amount Offset Against Derivatives [Member] | NSTAR Electric Company [Member]
Other Derivatives Not Designated As Hedging Instruments At Fair Value Net Total Abstract
Description of Derivative Activity Volume	NSTAR Electric has a renewable energy contract to purchase 0.1 million MWh of energy per year through 2018 and a capacity-related contract to purchase up to 35 MW per year through 2019.
Amount Offset Against Derivatives [Member] | Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	$ (10,900)	$ (6,600)
Derivative Assets Noncurrent	(19,300)	(19,200)
Amount Offset Against Derivatives [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	(10,900)	(6,600)
Derivative Liabilities, Noncurrent	0
Derivative Assets Noncurrent	(19,300)	(19,200)
Commodity [Member]
Derivative Instruments Not Designated As Hedging Instruments Gain Loss Net Abstract
Derivative Gain Loss On Derivative Net	0	0
Derivative Instruments Gain Loss Recognized In Regulatory Asset Liability	60,200	134,400	$ 160,600
Commodity [Member] | Fair Value Inputs Level 2 [Member]
Derivative Instrument Detail Abstract
Derivative Liabilities - Current	(5,800)	(9,800)
Derivative Liabilities, Noncurrent	0	(300)
Derivative Assets Noncurrent	100	0
Commodity [Member] | Fair Value Inputs Level 3 [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	16,700	16,200
Derivative Liabilities - Current	(92,300)	(90,000)
Derivative Liabilities, Noncurrent	(337,100)	(409,300)
Derivative Assets Noncurrent	62,000	93,500
Commodity [Member] | Fair Value Inputs Level 3 [Member] | The Connecticut Light And Power Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	16,700	16,100
Derivative Liabilities - Current	(91,800)	(88,500)
Derivative Liabilities, Noncurrent	(336,200)	(406,200)
Derivative Assets Noncurrent	60,700	93,500
Commodity [Member] | Fair Value Inputs Level 3 [Member] | NSTAR Electric Company [Member]
Derivative Instrument Detail Abstract
Derivative Assets - Current	0	100
Derivative Liabilities - Current	(500)	(1,500)
Derivative Liabilities, Noncurrent	(900)	$ (3,100)
Derivative Assets Noncurrent	$ 1,300

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ (415.4)	$ (635.2)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	(52.1)	141.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	86.6	78.5
Ending Balance	(380.9)	(415.4)
The Connecticut Light And Power Company [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	(410.9)	(630.6)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	(51.3)	139.7
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	81.4	80
Ending Balance	(380.8)	(410.9)
NSTAR Electric Company [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	(4.5)	(7.3)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Reg Asset Liability	(0.8)	4.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	5.2	(1.5)
Ending Balance	$ (0.1)	$ (4.5)

MARKETABLE SECURITIES (Details)

MARKETABLE SECURITIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Fair Value Of Securities Under Fair Value Option	$ 14.2	$ 85.1
Fair Value, Option, Changes in Fair Value, Gain (Loss)	2	1.9	$ 10.2
Investments, Debt and Equity Securities [Abstract]
Marketable Securities, Restricted	436.9	450.8
Available For Sale Securities Debt Maturities Fair Value Abstract
Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value	57.2
Available For Sale Securities Debt Maturities After Ten Years Fair Value	119.3
Available For Sale Securities Debt Maturities After One Year Through Five Years Fair Value	50.7
Available For Sale Securities Debt Maturities Within One Year Fair Value	33.2
Available For Sale Securities Debt Maturities Fair Value	260.4
Available For Sale Securities Debt Maturities Amortized Cost Abstract
Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost	50.2
Available For Sale Securities Debt Maturities Within One Year Amortized Cost	33.3
Available For Sale Securities Debt Maturities After Ten Years Amortized Cost	116.4
Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost	56.6
Available For Sale Securities Debt Maturities Amortized Cost	256.5
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	545.7	639.2
Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	58.1
Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	312.2	343.9
Fair Value Inputs Level 1 Member | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	4.3
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	233.5	295.3
Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	53.8
US Government Debt Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	46.6	51.3
US Government Debt Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	0
Corporate Bond Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	43.9	49.1
Corporate Bond Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	14.7
Asset Backed Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	20	54.1
Asset Backed Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	14.5
Municipal Bonds Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	111.4	116.3
Municipal Bonds Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	13
Other Debt Securities Member | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	11.6	24.5
Other Debt Securities Member | Fair Value Inputs Level 2 [Member] | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	11.6
Cash And Cash Equivalents Member | Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	26.9	24.9
Cash And Cash Equivalents Member | Fair Value Inputs Level 1 Member | Western Massachusetts Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	0	4.3
Mutual Funds [Member] | Fair Value Inputs Level 1 Member
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Investments Fair Value Disclosure	285.3	319
Debt Securities
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	260.4	320.2
Available-for-sale Securities, Gross Unrealized Gains	4.5	7.5
AvailableForSaleSecuritiesGrossUnrealizedLoss	0.6	0.3
Available For Sale Securities Amortized Cost	256.5	313
Debt Securities | Western Massachusetts Electric Company [Member]
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	0	58.1
Available-for-sale Securities, Gross Unrealized Gains	0	0
AvailableForSaleSecuritiesGrossUnrealizedLoss	0	0.1
Available For Sale Securities Amortized Cost	0	58.2
Equity Securities
Investments, Debt and Equity Securities [Abstract]
Available For Sale Securities Fair Value Disclosure	271.1	233.9
Available-for-sale Securities, Gross Unrealized Gains	59.2	73.3
AvailableForSaleSecuritiesGrossUnrealizedLoss	3.4	0
Available For Sale Securities Amortized Cost	$ 215.3	$ 160.6

ASSET RETIREMENT OBLIGATIONS (D

ASSET RETIREMENT OBLIGATIONS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	$ 426.3	$ 424.9
Asset Retirement Obligation, Liabilities Incurred	6.6	1.3
Asset Retirement Obligation, Liabilities Settled	(18.2)	(19.5)
Asset Retirement Obligation, Accretion Expense	26.5	25.1
Asset Retirement Obligation, Revision of Estimate	(11.1)	(5.5)
Asset Retirement Obligation, Ending Balance	430.1	426.3
The Connecticut Light And Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	35.3	35
Asset Retirement Obligation, Liabilities Settled	0	(1.1)
Asset Retirement Obligation, Accretion Expense	2.2	1.9
Asset Retirement Obligation, Revision of Estimate	(3.7)	(0.5)
Asset Retirement Obligation, Ending Balance	33.8	35.3
NSTAR Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	34.3	32.8
Asset Retirement Obligation, Liabilities Incurred	6.2
Asset Retirement Obligation, Liabilities Settled	(1.5)	0
Asset Retirement Obligation, Accretion Expense	1.8	1.5
Asset Retirement Obligation, Revision of Estimate	(5.5)	0
Asset Retirement Obligation, Ending Balance	35.3	34.3
Public Service Company Of New Hampshire [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	20.6	19.5
Asset Retirement Obligation, Liabilities Incurred	0.4	0
Asset Retirement Obligation, Accretion Expense	1.3	1.1
Asset Retirement Obligation, Revision of Estimate	(0.7)
Asset Retirement Obligation, Ending Balance	21.6	20.6
Western Massachusetts Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	5.9	4.5
Asset Retirement Obligation, Liabilities Incurred	0	1.1
Asset Retirement Obligation, Liabilities Settled	(0.1)
Asset Retirement Obligation, Accretion Expense	0.4	0.3
Asset Retirement Obligation, Revision of Estimate	(0.5)
Asset Retirement Obligation, Ending Balance	5.7	5.9
CYAPC and YAEC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Beginning Balance	317.3
Asset Retirement Obligation, Ending Balance	$ 319.1	$ 317.3

SHORT-TERM DEBT (Details)

SHORT-TERM DEBT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Line of Credit Facility, Description	Credit Agreements and Commercial Paper Programs: Eversource parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five-year $1.45 billion revolving credit facility. On October 26, 2015, this revolving credit facility was amended and restated and the termination date was extended to September 4, 2020. Under the revolving credit facility, CL&P has a borrowing sublimit of $600 million, and PSNH and WMECO each have borrowing sublimits of $300 million. The revolving credit facility serves to backstop Eversource parent's $1.45 billion commercial paper program. The commercial paper program allows Eversource parent to issue commercial paper as a form of short-term debt. As of December 31, 2015 and 2014, Eversource parent had approximately $1.1 billion in short-term borrowings outstanding on each date under the Eversource parent commercial paper program, leaving $351.5 million and $348.9 million of available borrowing capacity as of December 31, 2015 and 2014, respectively. The weighted-average interest rate on these borrowings as of December 31, 2015 and 2014 was 0.72 percent and 0.43 percent, respectively. As of December 31, 2015, there were intercompany loans from Eversource parent of $277.4 million to CL&P, $231.3 million to PSNH and $143.4 million to WMECO. As of December 31, 2014, there were intercompany loans from Eversource parent of $133.4 million to CL&P, $90.5 million to PSNH and $21.4 million to WMECO. NSTAR Electric has a five-year $450 million revolving credit facility. On October 26, 2015, this revolving credit facility was amended and restated and the termination date was extended to September 4, 2020. The facility serves to backstop NSTAR Electric's $450 million commercial paper program. As of December 31, 2015 and 2014, NSTAR Electric had $62.5 million and $302 million, respectively, in short-term borrowings outstanding under its commercial paper program, leaving $387.5 million and $148 million of available borrowing capacity as of December 31, 2015 and 2014, respectively. The weighted-average interest rate on these borrowings as of December 31, 2015 and 2014 was 0.40 percent and 0.27 percent, respectively.
Short Term Debt Regulatory Limits	The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric and WMECO is subject to periodic approval by the FERC. As a result of the NHPUC having jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings. On June 16, 2015, the FERC granted authorization that allows CL&P and WMECO to incur total short-term borrowings up to a maximum of $600 million and $300 million, respectively, effective January 1, 2016 through December 31, 2017. On June 11, 2014, the FERC granted authorization to allow NSTAR Electric to issue total short-term debt securities in an aggregate principal amount not to exceed $655 million outstanding at any one time, effective October 24, 2014 through October 23, 2016. CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. As of December 31, 2015, CL&P had $327.3 million of unsecured debt capacity available under this authorization. PSNH is authorized by regulation of the NHPUC to incur short-term borrowings up to 10 percent of net fixed plant plus an additional $60 million until further ordered by the NHPUC. As of December 31, 2015, PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled approximately $325 million.
Description of ST debt reclassified to LT	On January 15, 2015, Eversource parent issued $150 million of 1.60 percent Series G Senior Notes due to mature in 2018 and $300 million of 3.15 percent Series H Senior Notes, due to mature in 2025. The proceeds, net of issuance costs, were used to repay short-term borrowings outstanding under the Eversource parent commercial paper program. As the debt proceeds, net of issuance costs, refinanced short-term debt, the short-term debt was classified as Long-Term Debt as of December 31, 2014.
Notes Payable	$ 1,160,953	$ 956,825
The Connecticut Light And Power Company [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	277,400	133,400
NSTAR Electric Company [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	$ 387,500	$ 148,000
WeightedAverageDiscountRatePercent	0.40%	0.27%
Notes Payable	$ 62,500	$ 302,000
Public Service Company Of New Hampshire [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	231,300	90,500
Western Massachusetts Electric Company [Member]
Line of Credit Facility [Line Items]
Notes Payable To Affiliated Companies	143,400	21,400
Eversource Parent [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Remaining Borrowing Capacity	351,100	348,900
CommercialPaper	$ 1,100,000	$ 1,100,000
WeightedAverageDiscountRatePercent	0.72%	0.43%
Notes Payable	$ 1,098,453	$ 654,825

LONG-TERM DEBT (Details)

LONG-TERM DEBT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-Term Debt - Current Portion	$ 228,883	$ 245,583
Long-Term Debt	8,805,574	8,568,429
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	200,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	745,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	960,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	800,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	295,000
Long-term Debt, Maturities, Repayments of Principal after Year Five	5,736,600
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	8,736,600
The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
Long-Term Debt - Current Portion	0	162,000
Long-Term Debt	2,763,682	2,664,243
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	250,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	300,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	250,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,990,300
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	$ 2,790,300
Long-term Debt, Description	On May 20, 2015 and December 1, 2015, CL&P issued $300 million and $50 million, respectively, of 4.15 percent 2015 Series A First and Refunding Mortgage Bonds due to mature in 2045. : On April 1, 2015, CL&P repaid at maturity the $100 million 5.00 percent 2005 Series A First and Refunding Mortgage Bonds and also redeemed the $62 million 1996A Series 1.55 percent PCRBs that were subject to mandatory tender using short-term borrowings.
Repayment of spent nuclear fuel	$ 244,600
Interest included in payment to settle spent nuclear fuel obligation	178,000
The Connecticut Light And Power Company [Member] | Series D 1994 Due 2024 7.875 % [Member]
Debt Instrument [Line Items]
Long-Term Debt	139,800	139,800
The Connecticut Light And Power Company [Member] | Series B 2004 Due 2034 5.750% [Member]
Debt Instrument [Line Items]
Long-Term Debt	130,000	130,000
The Connecticut Light And Power Company [Member] | Series A 2005 Due 2015 5.000% [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	100,000
The Connecticut Light And Power Company [Member] | Series B 2005 Due 2035 5.625% [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000	100,000
The Connecticut Light And Power Company [Member] | Series A 2006 Due 2036 6.350% [Member]
Debt Instrument [Line Items]
Long-Term Debt	250,000	250,000
The Connecticut Light And Power Company [Member] | Series A 2007 Due 2017 5.375% [Member]
Debt Instrument [Line Items]
Long-Term Debt	150,000	150,000
The Connecticut Light And Power Company [Member] | Series B 2007 Due 2037 5.750% [Member]
Debt Instrument [Line Items]
Long-Term Debt	150,000	150,000
The Connecticut Light And Power Company [Member] | Series D 2007 Due 2037 6.375% [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000	100,000
The Connecticut Light And Power Company [Member] | Series A 2008 Due 2018 5.650% [Member]
Debt Instrument [Line Items]
Long-Term Debt	300,000	300,000
The Connecticut Light And Power Company [Member] | Series A 2009 Due 2019 5.500% [Member]
Debt Instrument [Line Items]
Long-Term Debt	250,000	250,000
The Connecticut Light And Power Company [Member] | One-Year Fixed Rate Tax Exempt Due 2031 [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	62,000
The Connecticut Light And Power Company [Member] | Fees And Interest Due For Spent Nuclear Fuel Disposal Costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	244,500
The Connecticut Light And Power Company [Member] | Total First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-Term Debt	2,669,800	2,419,800
The Connecticut Light And Power Company [Member] | Total Pollution Control Bonds [Member]
Debt Instrument [Line Items]
Long-Term Debt	120,500	182,500
The Connecticut Light And Power Company [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	(10,700)	(4,800)
The Connecticut Light And Power Company [Member] | Serires C 2007 5.750% Due 2017 [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000	100,000
The Connecticut Light And Power Company [Member] | Fixed Rate 4.375% due 2028 [Member]
Debt Instrument [Line Items]
Long-Term Debt	120,500	120,500
The Connecticut Light And Power Company [Member] | Series A Due 2023 2.5 percent [Member]
Debt Instrument [Line Items]
Long-Term Debt	400,000	400,000
The Connecticut Light And Power Company [Member] | Series A 2014 Due 2044 4.30% [Member]
Debt Instrument [Line Items]
Long-Term Debt	250,000	250,000
The Connecticut Light And Power Company [Member] | Series O First Mortgage Bonds due 2045 4.35% [Member]
Debt Instrument [Line Items]
Long-Term Debt	350,000
The Connecticut Light And Power Company [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(15,900)	(15,800)
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
Long-Term Debt - Current Portion	200,000	4,700
Long-Term Debt	1,829,766	1,781,541
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	200,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	400,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	1,450,000
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	$ 2,050,000
Long-term Debt, Description	. On November 18, 2015, NSTAR Electric issued $250 million of 3.25 percent debentures, due to mature in 2025.
NSTAR Electric Company [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	$ (8,500)	(7,300)
NSTAR Electric Company [Member] | Total Other [Member]
Debt Instrument [Line Items]
Long-Term Debt	2,050,000	1,800,000
NSTAR Electric Company [Member] | Due 2022 2.375% [Member]
Debt Instrument [Line Items]
Long-Term Debt	400,000	400,000
NSTAR Electric Company [Member] | Due 2017 5.625% [Member]
Debt Instrument [Line Items]
Long-Term Debt	400,000	400,000
NSTAR Electric Company [Member] | Due 2036 5.75% [Member]
Debt Instrument [Line Items]
Long-Term Debt	200,000	200,000
NSTAR Electric Company [Member] | Due 2040 5.5% [Member]
Debt Instrument [Line Items]
Long-Term Debt	300,000	300,000
NSTAR Electric Company [Member] | TaxExempt Sewage Facility Revenue Bonds Due 2015 [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	4,700
NSTAR Electric Company [Member] | Variable Due 2016 [Member]
Debt Instrument [Line Items]
Long-Term Debt	200,000	200,000
NSTAR Electric Company [Member] | Debentures 2014 Due 2044 4.40% [Member]
Debt Instrument [Line Items]
Long-Term Debt	300,000	300,000
NSTAR Electric Company [Member] | Debentures Due 2025 3.25% [Member]
Debt Instrument [Line Items]
Long-Term Debt	250,000
NSTAR Electric Company [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(11,700)	(11,200)
Public Service Company Of New Hampshire [Member]
Debt Instrument [Line Items]
Long-Term Debt	1,071,017	1,070,021
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	70,000
Long-term Debt, Maturities, Repayments of Principal in Year Three	110,000
Long-term Debt, Maturities, Repayments of Principal in Year Four	150,000
Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Long-term Debt, Maturities, Repayments of Principal after Year Five	746,300
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	1,076,300
Public Service Company Of New Hampshire [Member] | Series M 2005 Due 2035 5.60% [Member]
Debt Instrument [Line Items]
Long-Term Debt	50,000	50,000
Public Service Company Of New Hampshire [Member] | Series N 2007 Due 2017 6.15% [Member]
Debt Instrument [Line Items]
Long-Term Debt	70,000	70,000
Public Service Company Of New Hampshire [Member] | Series O 2008 Due 2018 6.00% [Member]
Debt Instrument [Line Items]
Long-Term Debt	110,000	110,000
Public Service Company Of New Hampshire [Member] | Series P 2009 Due 2019 4.50% [Member]
Debt Instrument [Line Items]
Long-Term Debt	150,000	150,000
Public Service Company Of New Hampshire [Member] | Adjustablerateseriesadue 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt	89,300	89,300
Public Service Company Of New Hampshire [Member] | Total First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-Term Debt	987,000	987,000
Public Service Company Of New Hampshire [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	100	0
Public Service Company Of New Hampshire [Member] | Series Q 4.05% 2011 Due 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt	122,000	122,000
Public Service Company Of New Hampshire [Member] | Series R 2011 3.30% due 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt	160,000	160,000
Public Service Company Of New Hampshire [Member] | Series2013due2023member [Member]
Debt Instrument [Line Items]
Long-Term Debt	325,000	325,000
Public Service Company Of New Hampshire [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(5,400)	(6,300)
Western Massachusetts Electric Company [Member]
Debt Instrument [Line Items]
Long-Term Debt - Current Portion	0	50,000
Long-Term Debt	517,329	575,184
Maturities of Long-term Debt [Abstract]
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Long-term Debt, Maturities, Repayments of Principal in Year Five	95,000
Long-term Debt, Maturities, Repayments of Principal after Year Five	420,000
LongTermDebtMaturitiesRepaymentsOfPrincipalTotal	$ 515,000
Long-term Debt, Description	On August 3, 2015, WMECO repaid at maturity the $50 million 5.24 percent Series C Senior Notes, using short-term borrowings.
Repayment of spent nuclear fuel	$ 57,400
Interest included in payment to settle spent nuclear fuel obligation	41,800
Western Massachusetts Electric Company [Member] | Senior Notes Series B 5.90% Due 2034 [Member]
Debt Instrument [Line Items]
Long-Term Debt	50,000	50,000
Western Massachusetts Electric Company [Member] | Senior Notes Series C 5.24% Due 2015 [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	50,000
Western Massachusetts Electric Company [Member] | Senior Notes Series D 6.70% Due 2037 [Member]
Debt Instrument [Line Items]
Long-Term Debt	40,000	40,000
Western Massachusetts Electric Company [Member] | Senior Notes Series E 5.10% Due 2020 [Member]
Debt Instrument [Line Items]
Long-Term Debt	95,000	95,000
Western Massachusetts Electric Company [Member] | Fees And Interest Due For Spent Nuclear Fuel Disposal Costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	57,400
Western Massachusetts Electric Company [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	5,200	6,100
Western Massachusetts Electric Company [Member] | Senior Notes Series F 3.50% due 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt	250,000	250,000
Western Massachusetts Electric Company [Member] | Total Pollution Control Notes and Other Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt	515,000	565,000
Western Massachusetts Electric Company [Member] | Series g 2013 due 2023 member [Member]
Debt Instrument [Line Items]
Long-Term Debt	80,000	80,000
Western Massachusetts Electric Company [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(2,900)	(3,300)
Yankee Gas Services Company [Member]
Debt Instrument [Line Items]
Long-Term Debt	443,700	369,100
Yankee Gas Services Company [Member] | Total First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-Term Debt	445,000	370,000
Yankee Gas Services Company [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	400	600
Yankee Gas Services Company [Member] | Series B due 2022 8.48% [Member]
Debt Instrument [Line Items]
Long-Term Debt	20,000	20,000
Yankee Gas Services Company [Member] | Series H due 2019 5.26% [Member]
Debt Instrument [Line Items]
Long-Term Debt	50,000	50,000
Yankee Gas Services Company [Member] | Series I due 2035 5.35% [Member]
Debt Instrument [Line Items]
Long-Term Debt	50,000	50,000
Yankee Gas Services Company [Member] | Series J due 2018 6.90% [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000	100,000
Yankee Gas Services Company [Member] | Series K due 2020 4.87% [Member]
Debt Instrument [Line Items]
Long-Term Debt	50,000	50,000
Yankee Gas Services Company [Member] | Series L 2014 Due 2044 4.82 % [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000	100,000
Yankee Gas Services Company [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(1,700)	(1,500)
Yankee Gas Services Company [Member] | Series M 2015 due 2025 3.35% [Member]
Debt Instrument [Line Items]
Long-Term Debt	75,000
NSTAR Gas Company [Member]
Debt Instrument [Line Items]
Long-Term Debt	309,200	209,400
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-Term Debt	310,000	210,000
NSTAR Gas Company [Member] | Series J Due 202 9.95% [Member]
Debt Instrument [Line Items]
Long-Term Debt	25,000	25,000
NSTAR Gas Company [Member] | Series K Due 2033 7.11% [Member]
Debt Instrument [Line Items]
Long-Term Debt	35,000	35,000
NSTAR Gas Company [Member] | Series M Due 2017 7.04% [Member]
Debt Instrument [Line Items]
Long-Term Debt	25,000	25,000
NSTAR Gas Company [Member] | Series N Due 2020 4.46% [Member]
Debt Instrument [Line Items]
Long-Term Debt	125,000	125,000
NSTAR Gas Company [Member] | Series O First Mortgage Bonds due 2045 4.35% [Member]
Debt Instrument [Line Items]
Long-Term Debt	100,000
NSTAR Gas Company [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(800)	(600)
Subsidiaries [Member] | Unamortized Premiums and Discounts, Net [Member]
Debt Instrument [Line Items]
Long-Term Debt	(1,300)	(1,200)
Subsidiaries [Member] | Fair Value Adjustment [Member]
Debt Instrument [Line Items]
Long-Term Debt	173,500	202,300
Subsidiaries [Member] | Total Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Long-Term Debt	2,623,800	2,477,500
Subsidiaries [Member] | Total Other [Member]
Debt Instrument [Line Items]
Long-Term Debt	1,550,000	1,546,300
Subsidiaries [Member] | Commerical Paper and Revolver Borrowings [Member]
Debt Instrument [Line Items]
Long-Term Debt	0	446,300
Subsidiaries [Member] | Debentures Due 2019 4.50% [Member]
Debt Instrument [Line Items]
Long-Term Debt	350,000	350,000
Subsidiaries [Member] | Spent Nuclear Fuel Obilgation CY [Member]
Debt Instrument [Line Items]
Long-Term Debt	179,500	179,400
Subsidiaries [Member] | FairValueAdjustmentMemberCurrentPortion [Member]
Debt Instrument [Line Items]
Long-Term Debt	28,900	28,900
Subsidiaries [Member] | Series F Due 2023 2.8% [Member]
Debt Instrument [Line Items]
Long-Term Debt	450,000	450,000
Subsidiaries [Member] | Series E Due 2018 1.45% [Member]
Debt Instrument [Line Items]
Long-Term Debt	300,000	300,000
Subsidiaries [Member] | Unamortized Debt issuance costs [Member]
Debt Instrument [Line Items]
Long-Term Debt	(1,900)	1,100
Subsidiaries [Member] | Senior Notes Series G 1.6% due 2018 [Member]
Debt Instrument [Line Items]
Long-Term Debt	150,000
Subsidiaries [Member] | Senior Notes Series H 3.15% due 2025 [Member]
Debt Instrument [Line Items]
Long-Term Debt	300,000
Subsidiaries [Member] | Interest Included in Spent Nuclear Fuel Obligation [Member]
Debt Instrument [Line Items]
Long-Term Debt	$ 130,700	$ 130,600

PENSION BENEFITS AND POSTRETI85

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, SERP and PBOP	$ 1,407,288	$ 1,638,558
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year, Description	Eversource currently expects to make contributions of approximately $146 million in 2016, of which $21 million will be contributed by NSTAR Electric and $17 million by PSNH. The remaining $108 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource contributed $7.9 million to the PBOP Plan in 2015, of which $4.9 million was contributed by NSTAR Electric. Eversource expects to make approximately $9.5 million in contributions in 2016.
Amount That Represents Deferred Regulatory Assets	$ 3,200
United States Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	8.50%	9.00%
Target Allocation	22.00%	24.00%
International Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	8.50%	9.00%
Target Allocation	13.00%	10.00%
Emergining Markets Equity Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	10.00%	10.00%
Target Allocation	5.00%	6.00%
Private Equity Funds [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	12.00%	13.00%
Target Allocation	12.00%	10.00%
Fixed Income Debt Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	4.50%	5.00%
Target Allocation	12.00%	15.00%
High Yield Fixed Income Debt Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	8.50%	7.50%
Target Allocation	13.00%	9.00%
Emerging Markets Debt Securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	7.50%	7.50%
Target Allocation	5.00%	6.00%
Hedge Funds [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	7.00%	7.00%
Target Allocation	8.00%	11.00%
Real Estate [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	7.50%	7.50%
Target Allocation	10.00%	9.00%
Pension Plans Defined Benefit Member
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	$ (5,486,200)	$ (4,676,500)
Defined Benefit Plan Service Cost	(91,400)	(79,900)	$ (102,300)
Defined Benefit Plan Interest Cost	(227,000)	(225,700)	(206,700)
Defined Benefit Plan, Actuarial Net (Gains) Losses	331,500	(739,600)
Defined Benefit Plan, Benefits Paid	238,500	230,300
Defined Benefit Plan, Payments SERP	5,000	5,200
Defined Benefit Plan Benefits Paid Lump Sum	149,500
Benefit Obligation Ending Balance	(5,080,100)	(5,486,200)	(4,676,500)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	91,400	79,900	102,300
Defined Benefit Plan Interest Cost	227,000	225,700	206,700
Defined Benefit Plan, Expected Return on Plan Assets	(335,900)	(310,800)	(278,100)
Defined Benefit Plan, Amortization of Gains (Losses)	148,500	128,400	210,500
Defined Benefit Plan Amortization Of Prior Service Cost Credit	3,700	4,400	4,000
Defined Benefit Plan Net Periodic Benefit Cost	134,700	127,600	245,400
Amount Capitalized Defined Benefit Expense	41,000	35,200	73,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	4,126,500	3,985,900
Defined Benefit Plan, Actual Return on Plan Assets	12,300	199,300
Defined Benefit Plan, Contributions by Employer	154,600	171,600
Defined Benefit Plan, Benefits Paid	(238,500)	(230,300)
Defined Benefit Plan Benefits Paid Lump Sum	(149,500)
Fair Value of Plan Assets Ending Balance	3,905,400	4,126,500	$ 3,985,900
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(1,174,700)	(1,359,700)
Defined Benefit Plan, Accumulated Benefit Obligation	$ 4,733,200	$ 5,000,100
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.20%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.50%	3.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	8.25%	8.25%
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	$ 4,126,500	$ 3,985,900
Fair Value of Plan Assets Ending Balance	3,905,400	4,126,500	$ 3,985,900
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	(6,200)	55,900
OCI Reclassification Adjustment for Net Actuarial Gain (Loss), before Tax	(6,200)	(5,600)
OCI Reclassification Adjustment for Amortization of Prior Service Cost, before tax	(200)	(200)
Gain Loss Arising During Year Regulatory	(2,000)	797,300
Losses Reclassifed From RegAsset PreTax	(142,300)	(122,800)
AmortizationPriorServiceCostfromRegAsset	(3,500)	(4,200)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Gains Losses included in AOCI, Pre Tax	81,100	93,500
Prior Service Cost balance in AOCI	600	800
RegulatoryAsset Gains Losses Before Tax	1,667,600	1,811,900
Regulatory Asset Prior Service Cost	9,700	$ 13,200
Defined Benefit Amounts to be Reclassified from AOCI in next fiscal year
Future Amortization Of Gain Loss.	5,400
Future Amortization of Prior Service cost	200
Regulatory Asset Amortization Of Net Gains Losses	120,600
Regulatory Asset Defined Benefit Plan Amortization Of Net Prior ServiceCost	$ 3,400
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Assumed Rate of Return on Defined Benefit Plan Assets	8.25%
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 253,500
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	272,900
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	273,900
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	283,700
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	292,700
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 1,604,300
Impact of change in mortality assumption	During 2014, the Society of Actuaries released a series of updated mortality tables resulting from studies that measured mortality rates for various groups of individuals. The updated mortality tables released in 2014 increased the life expectancy of plan participants by three to five years and had the effect of increasing the estimated benefits to be provided to plan participants. The impact of adopting the updated mortality tables on Eversource's liability as of December 31, 2014 was an increase of approximately $340 million. In 2015, a revised scale for the mortality table was released having the effect of decreasing the estimate of benefits to be provided to plan participants. The impact of the adoption of the new mortality scale resulted in a decrease of $48 million on Eversource's liability as of December 31, 2015.
Impact of Decrease in Discount Rate	The increase in the discount rate used to calculate the funded status resulted in a decrease on Eversource's liability of approximately $267 million as of December 31, 2015. Decreases in the discount rates resulted in an increase on Eversource's liability of approximately $530 million as of December 31, 2014.
Pension Plans Defined Benefit Member | Minimum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.21%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.85%	4.13%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		3.50%	3.50%
Pension Plans Defined Benefit Member | Maximum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.60%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		5.03%	4.24%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		4.00%	4.00%
Pension Plans Defined Benefit Member | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	$ 443,700
Fair Value of Plan Assets Ending Balance	404,100	$ 443,700
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	443,700
Fair Value of Plan Assets Ending Balance	404,100	443,700
Pension Plans Defined Benefit Member | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	1,748,400
Fair Value of Plan Assets Ending Balance	1,584,900	1,748,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	1,748,400
Fair Value of Plan Assets Ending Balance	1,584,900	1,748,400
Pension Plans Defined Benefit Member | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	2,122,900	1,850,700
Fair Value of Plan Assets Ending Balance	2,105,800	2,122,900	$ 1,850,700
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	2,122,900	1,850,700
Defined Benefit Plan, Actual Return on Plan Assets Still Held	15,900	76,800
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	68,200	20,800
Defined Benefit Plan, Purchases, Sales, and Settlements	(101,200)	174,600
Fair Value of Plan Assets Ending Balance	2,105,800	2,122,900	1,850,700
Pension Plans Defined Benefit Member | Private Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	386,700
Fair Value of Plan Assets Ending Balance	472,300	386,700
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	386,700
Fair Value of Plan Assets Ending Balance	472,300	386,700
Pension Plans Defined Benefit Member | Private Equity Funds [Member] | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	18,800
Fair Value of Plan Assets Ending Balance	7,600	18,800
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	18,800
Fair Value of Plan Assets Ending Balance	7,600	18,800
Pension Plans Defined Benefit Member | Private Equity Funds [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	367,900	300,300
Fair Value of Plan Assets Ending Balance	464,700	367,900	300,300
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	367,900	300,300
Defined Benefit Plan, Actual Return on Plan Assets Still Held	24,400	14,000
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	27,300	13,900
Defined Benefit Plan, Purchases, Sales, and Settlements	45,100	39,700
Fair Value of Plan Assets Ending Balance	464,700	367,900	300,300
Pension Plans Defined Benefit Member | Fixed Income Debt Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	1,293,600
Fair Value of Plan Assets Ending Balance	1,216,800	1,293,600
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	1,293,600
Fair Value of Plan Assets Ending Balance	1,216,800	1,293,600
Pension Plans Defined Benefit Member | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	10,200
Fair Value of Plan Assets Ending Balance	0	10,200
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	10,200
Fair Value of Plan Assets Ending Balance	0	10,200
Pension Plans Defined Benefit Member | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	561,400
Fair Value of Plan Assets Ending Balance	432,000	561,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	561,400
Fair Value of Plan Assets Ending Balance	432,000	561,400
Pension Plans Defined Benefit Member | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	722,000	589,500
Fair Value of Plan Assets Ending Balance	784,800	722,000	589,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	722,000	589,500
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(6,700)	45,200
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	17,000	(6,200)
Defined Benefit Plan, Purchases, Sales, and Settlements	52,500	93,500
Fair Value of Plan Assets Ending Balance	784,800	722,000	589,500
Pension Plans Defined Benefit Member | Hedge Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	495,000
Fair Value of Plan Assets Ending Balance	340,500	495,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	495,000
Fair Value of Plan Assets Ending Balance	340,500	495,000
Pension Plans Defined Benefit Member | Hedge Funds [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	20,000
Fair Value of Plan Assets Ending Balance	49,700	20,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	20,000
Fair Value of Plan Assets Ending Balance	49,700	20,000
Pension Plans Defined Benefit Member | Hedge Funds [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	475,000	416,900
Fair Value of Plan Assets Ending Balance	290,800	475,000	416,900
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	475,000	416,900
Defined Benefit Plan, Actual Return on Plan Assets Still Held	0	23,500
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	(900)	(15,200)
Defined Benefit Plan, Purchases, Sales, and Settlements	(106,800)	49,800
Fair Value of Plan Assets Ending Balance	290,800	475,000	416,900
TransferBetweenCategories	(76,500)
Pension Plans Defined Benefit Member | Real Estate [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	397,800
Fair Value of Plan Assets Ending Balance	377,800	397,800
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	397,800
Fair Value of Plan Assets Ending Balance	377,800	397,800
Pension Plans Defined Benefit Member | Real Estate [Member] | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	0
Fair Value of Plan Assets Ending Balance	0	0
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	0
Fair Value of Plan Assets Ending Balance	0	0
Pension Plans Defined Benefit Member | Real Estate [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	132,000
Fair Value of Plan Assets Ending Balance	117,500	132,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	132,000
Fair Value of Plan Assets Ending Balance	117,500	132,000
Pension Plans Defined Benefit Member | Real Estate [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	265,800	288,500
Fair Value of Plan Assets Ending Balance	260,300	265,800	288,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	265,800	288,500
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(7,100)	(3,600)
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	24,800	28,300
Defined Benefit Plan, Purchases, Sales, and Settlements	(23,200)	(47,400)
Fair Value of Plan Assets Ending Balance	260,300	265,800	288,500
Pension Plans Defined Benefit Member | Assetsrelatedto401h [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	188,500
Fair Value of Plan Assets Ending Balance	189,400	188,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	188,500
Fair Value of Plan Assets Ending Balance	189,400	188,500
Pension Plans Defined Benefit Member | Equity Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	1,741,900
Fair Value of Plan Assets Ending Balance	1,687,400	1,741,900
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	1,741,900
Fair Value of Plan Assets Ending Balance	1,687,400	1,741,900
Pension Plans Defined Benefit Member | Equity Member | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	414,700
Fair Value of Plan Assets Ending Balance	396,500	414,700
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	414,700
Fair Value of Plan Assets Ending Balance	396,500	414,700
Pension Plans Defined Benefit Member | Equity Member | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	1,035,000
Fair Value of Plan Assets Ending Balance	985,700	1,035,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	1,035,000
Fair Value of Plan Assets Ending Balance	985,700	1,035,000
Pension Plans Defined Benefit Member | Equity Member | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	292,200	255,500
Fair Value of Plan Assets Ending Balance	305,200	292,200	255,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	292,200	255,500
Defined Benefit Plan, Actual Return on Plan Assets Still Held	5,300	(2,300)
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	(68,800)	39,000
Fair Value of Plan Assets Ending Balance	305,200	292,200	255,500
TransferBetweenCategories	76,500
PBOP Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(1,147,900)	(1,038,000)
Defined Benefit Plan Service Cost	(16,300)	(12,500)	(16,900)
Defined Benefit Plan Interest Cost	(47,200)	(49,500)	(47,200)
Defined Benefit Plan, Actuarial Net (Gains) Losses	106,000	(95,500)
Defined Benefit Plan, Benefits Paid	54,000	47,600
Benefit Obligation Ending Balance	(1,051,400)	(1,147,900)	(1,038,000)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	16,300	12,500	16,900
Defined Benefit Plan Interest Cost	47,200	49,500	47,200
Defined Benefit Plan, Expected Return on Plan Assets	(67,400)	(63,300)	(55,400)
Defined Benefit Plan, Amortization of Gains (Losses)	6,800	12,200	26,000
Defined Benefit Plan Amortization Of Prior Service Cost Credit	(500)	(2,800)	(2,100)
Defined Benefit Plan Net Periodic Benefit Cost	2,400	8,100	32,600
Amount Capitalized Defined Benefit Expense	100	1,400	8,800
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	862,600	826,500
Defined Benefit Plan, Actual Return on Plan Assets	(4,300)	43,700
Defined Benefit Plan, Contributions by Employer	7,900	40,000
Defined Benefit Plan, Benefits Paid	(54,000)	(47,600)
Fair Value of Plan Assets Ending Balance	812,200	862,600	$ 826,500
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	$ (239,200)	$ (285,300)
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Description of Direction and Pattern of Change for Assumed Health Care Cost Trend Rate	As of December 31, 2015 and 2014, the health care cost trend rate assumptions used to determine the PBOP Plan's funded status was 6.25 percent and 6.5 percent, respectively, subsequently decreasing to an ultimate rate of 4.5 percent in 2023.
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.22%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.25%	8.25%	8.25%
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	$ 115,300
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	(90,800)
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	8,500
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	(6,300)
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	862,600	$ 826,500
Fair Value of Plan Assets Ending Balance	812,200	862,600	$ 826,500
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	700	400
OCI Reclassification Adjustment for Net Actuarial Gain (Loss), before Tax	(400)	(600)
Gain Loss Arising During Year Regulatory	(34,100)	115,100
Losses Reclassifed From RegAsset PreTax	(6,400)	(11,600)
AmortizationPriorServiceCostfromRegAsset	500	2,800
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Gains Losses included in AOCI, Pre Tax	6,300	6,000
RegulatoryAsset Gains Losses Before Tax	152,200	192,700
Regulatory Asset Prior Service Cost	(1,300)	$ (1,800)
Defined Benefit Amounts to be Reclassified from AOCI in next fiscal year
Future Amortization Of Gain Loss.	400
Regulatory Asset Amortization Of Net Gains Losses	4,000
Regulatory Asset Defined Benefit Plan Amortization Of Net Prior ServiceCost	(200)
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	60,800
Defined Benefit Plan, Expected Future Benefit Payments in Year Two	61,200
Defined Benefit Plan, Expected Future Benefit Payments in Year Three	61,400
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	61,800
Defined Benefit Plan, Expected Future Benefit Payments in Year Five	62,400
Defined Benefit Plan, Expected Future Benefit Payments in Five Fiscal Years Thereafter	$ 315,400
Impact of change in mortality assumption	During 2014, the Society of Actuaries released a series of updated mortality tables resulting from studies that measured mortality rates for various groups of individuals. The updated mortality tables released in 2014 increased the life expectancy of plan participants by three to five years and had the effect of increasing the estimated benefits to be provided to plan participants. The impact of adopting the updated mortality tables on Eversource's liability as of December 31, 2014 was an increase of approximately $82 million. In 2015, a revised scale for the mortality table was released having the effect of decreasing the estimate of benefits to be provided to plan participants. The impact of the adoption of the new mortality scale resulted in a decrease of $23 million on Eversource's liability as of December 31, 2015.
Impact of Decrease in Discount Rate	The increase in the discount rate used to calculate the funded status resulted in a decrease on Eversource's liability of approximately $60 million as of December 31, 2015. Decreases in the discount rates resulted in an increase on Eversource's liability of approximately $110 million as of December 31, 2014.
PBOP Plan | Minimum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.62%	4.22%
Health Care Trend Assumption Used In Funded Status	6.25%	6.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.78%	4.04%
PBOP Plan | Maximum [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		5.10%	4.35%
PBOP Plan | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	$ 120,200
Fair Value of Plan Assets Ending Balance	119,400	$ 120,200
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	120,200
Fair Value of Plan Assets Ending Balance	119,400	120,200
PBOP Plan | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	302,200
Fair Value of Plan Assets Ending Balance	238,500	302,200
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	302,200
Fair Value of Plan Assets Ending Balance	238,500	302,200
PBOP Plan | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	251,700	229,400
Fair Value of Plan Assets Ending Balance	264,900	251,700	$ 229,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	251,700	229,400
Defined Benefit Plan, Actual Return on Plan Assets Still Held	1,500	7,800
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	(300)	(2,100)
Defined Benefit Plan, Purchases, Sales, and Settlements	12,000	16,600
Fair Value of Plan Assets Ending Balance	264,900	251,700	229,400
PBOP Plan | Private Equity Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	24,900
Fair Value of Plan Assets Ending Balance	32,900	24,900
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	24,900
Fair Value of Plan Assets Ending Balance	32,900	24,900
PBOP Plan | Private Equity Funds [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	24,900	17,900
Fair Value of Plan Assets Ending Balance	32,900	24,900	17,900
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	24,900	17,900
Defined Benefit Plan, Actual Return on Plan Assets Still Held	2,600	1,300
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	100
Defined Benefit Plan, Purchases, Sales, and Settlements	5,400	5,600
Fair Value of Plan Assets Ending Balance	32,900	24,900	17,900
PBOP Plan | Fixed Income Debt Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	204,400
Fair Value of Plan Assets Ending Balance	191,200	204,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	204,400
Fair Value of Plan Assets Ending Balance	191,200	204,400
PBOP Plan | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	16,100
Fair Value of Plan Assets Ending Balance	9,700	16,100
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	16,100
Fair Value of Plan Assets Ending Balance	9,700	16,100
PBOP Plan | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	110,000
Fair Value of Plan Assets Ending Balance	99,900	110,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	110,000
Fair Value of Plan Assets Ending Balance	99,900	110,000
PBOP Plan | Fixed Income Debt Securities [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	78,300	51,500
Fair Value of Plan Assets Ending Balance	81,600	78,300	51,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	78,300	51,500
Defined Benefit Plan, Actual Return on Plan Assets Still Held	2,100	1,900
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	(300)
Defined Benefit Plan, Purchases, Sales, and Settlements	1,500	24,900
Fair Value of Plan Assets Ending Balance	81,600	78,300	51,500
PBOP Plan | Hedge Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	58,400
Fair Value of Plan Assets Ending Balance	52,200	58,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	58,400
Fair Value of Plan Assets Ending Balance	52,200	58,400
PBOP Plan | Hedge Funds [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	58,400	57,000
Fair Value of Plan Assets Ending Balance	52,200	58,400	57,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	58,400	57,000
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(1,500)	1,400
Defined Benefit Plan, Purchases, Sales, and Settlements	(4,700)	0
Fair Value of Plan Assets Ending Balance	52,200	58,400	57,000
PBOP Plan | Real Estate [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	34,400
Fair Value of Plan Assets Ending Balance	37,400	34,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	34,400
Fair Value of Plan Assets Ending Balance	37,400	34,400
PBOP Plan | Real Estate [Member] | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	19,400
Fair Value of Plan Assets Ending Balance	17,000	19,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	19,400
Fair Value of Plan Assets Ending Balance	17,000	19,400
PBOP Plan | Real Estate [Member] | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	15,000	33,900
Fair Value of Plan Assets Ending Balance	20,400	15,000	33,900
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	15,000	33,900
Defined Benefit Plan, Actual Return on Plan Assets Still Held	300	(2,800)
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	(2,200)
Defined Benefit Plan, Purchases, Sales, and Settlements	5,100	(13,900)
Fair Value of Plan Assets Ending Balance	20,400	15,000	33,900
PBOP Plan | Assetsrelatedto401h [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	188,500
Fair Value of Plan Assets Ending Balance	189,400	188,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	188,500
Fair Value of Plan Assets Ending Balance	189,400	188,500
PBOP Plan | Equity Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	352,000
Fair Value of Plan Assets Ending Balance	309,100	352,000
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	352,000
Fair Value of Plan Assets Ending Balance	309,100	352,000
PBOP Plan | Equity Member | Fair Value Inputs Level 1 Member
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	104,100
Fair Value of Plan Assets Ending Balance	109,700	104,100
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	104,100
Fair Value of Plan Assets Ending Balance	109,700	104,100
PBOP Plan | Equity Member | Fair Value Inputs Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	172,800
Fair Value of Plan Assets Ending Balance	121,600	172,800
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	172,800
Fair Value of Plan Assets Ending Balance	121,600	172,800
PBOP Plan | Equity Member | Fair Value Inputs Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	75,100	69,100
Fair Value of Plan Assets Ending Balance	77,800	75,100	69,100
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	75,100	69,100
Defined Benefit Plan, Actual Return on Plan Assets Still Held	(2,000)	6,000
Defined Benefit Plan, Purchases, Sales, and Settlements	4,700	0
Fair Value of Plan Assets Ending Balance	77,800	75,100	69,100
The Connecticut Light And Power Company [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, SERP and PBOP	271,056	273,854
The Connecticut Light And Power Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(1,230,100)	(1,083,400)
ChangeInLiabilityDueToTransferOfEmployees	(4,600)	26,400
Defined Benefit Plan Service Cost	(24,700)	(20,200)	(24,900)
Defined Benefit Plan Interest Cost	(51,100)	(50,500)	(48,300)
Defined Benefit Plan, Actuarial Net (Gains) Losses	77,800	(161,000)
Defined Benefit Plan, Benefits Paid	60,200	58,300
Defined Benefit Plan, Payments SERP	400	300
Defined Benefit Plan Benefits Paid Lump Sum	14,500
Benefit Obligation Ending Balance	(1,157,600)	(1,230,100)	(1,083,400)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	24,700	20,200	24,900
Defined Benefit Plan Interest Cost	51,100	50,500	48,300
Defined Benefit Plan, Expected Return on Plan Assets	(78,900)	(75,400)	(73,800)
Defined Benefit Plan, Amortization of Gains (Losses)	32,200	33,700	55,900
Defined Benefit Plan Amortization Of Prior Service Cost Credit	1,500	1,800	1,800
Defined Benefit Plan Net Periodic Benefit Cost	30,600	30,800	57,100
Related Intercompany Allocationsof Defined Benefit Expense	22,500	26,700	44,900
Amount Capitalized Defined Benefit Expense	18,800	17,600	28,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	980,800	1,016,300
Defined Benefit Plan, Actual Return on Plan Assets	2,800	49,200
Defined Benefit Plan, Contributions by Employer		0
Defined Benefit Plan, Benefits Paid	(60,200)	(58,300)
Defined Benefit Plan Benefits Paid Lump Sum	(14,500)
Fair Value of Plan Assets Ending Balance	913,500	980,800	1,016,300
ChangeInAssetsDueToTransferOfEmployees	4,600	(26,400)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(244,100)	(249,300)
Defined Benefit Plan, Accumulated Benefit Obligation	1,062,700	1,101,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	980,800	1,016,300
Fair Value of Plan Assets Ending Balance	913,500	980,800	1,016,300
The Connecticut Light And Power Company [Member] | PBOP Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(173,900)	(180,400)
ChangeInLiabilityDueToTransferOfEmployees	100	3,700
Defined Benefit Plan Service Cost	(2,100)	(2,200)	(3,400)
Defined Benefit Plan Interest Cost	(7,200)	(8,100)	(7,900)
Defined Benefit Plan, Actuarial Net (Gains) Losses	7,200	3,500
Defined Benefit Plan, Benefits Paid	11,900	9,600
Benefit Obligation Ending Balance	(164,000)	(173,900)	(180,400)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	2,100	2,200	3,400
Defined Benefit Plan Interest Cost	7,200	8,100	7,900
Defined Benefit Plan, Expected Return on Plan Assets	(11,100)	(10,500)	(10,100)
Defined Benefit Plan, Amortization of Gains (Losses)	700	4,200	7,400
Defined Benefit Plan Amortization Of Prior Service Cost Credit		0	0
Defined Benefit Plan Net Periodic Benefit Cost	(1,100)	4,000	8,600
Related Intercompany Allocationsof Defined Benefit Expense	1,900	3,800	7,100
Amount Capitalized Defined Benefit Expense	(200)	1,800	3,900
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	149,000	151,300
Defined Benefit Plan, Actual Return on Plan Assets	(400)	6,300
Defined Benefit Plan, Contributions by Employer	0	4,200
Defined Benefit Plan, Benefits Paid	(11,900)	(9,600)
Fair Value of Plan Assets Ending Balance	136,700	149,000	151,300
ChangeInAssetsDueToTransferOfEmployees	0	(3,200)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(27,300)	(24,900)
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	149,000	151,300
Fair Value of Plan Assets Ending Balance	136,700	149,000	151,300
NSTAR Electric Company [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, SERP and PBOP	209,153	235,529
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Pension Contribution	9,886	120,306	82,000
NSTAR Electric Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(982,600)	(1,353,300)
ChangeInLiabilityDueToTransferOfEmployees	6,200	479,900
Defined Benefit Plan Service Cost	(14,900)	(13,600)	(33,100)
Defined Benefit Plan Interest Cost	(40,200)	(41,300)	(58,000)
Defined Benefit Plan, Actuarial Net (Gains) Losses	34,100	(107,000)
Defined Benefit Plan, Benefits Paid	47,600	52,400
Defined Benefit Plan, Payments SERP	100
Benefit Obligation Ending Balance	(949,700)	(982,600)	(1,353,300)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	14,900	13,600	33,100
Defined Benefit Plan Interest Cost	40,200	41,300	58,000
Defined Benefit Plan, Expected Return on Plan Assets	(70,000)	(63,000)	(84,400)
Defined Benefit Plan, Amortization of Gains (Losses)	35,800	23,500	58,100
Defined Benefit Plan Amortization Of Prior Service Cost Credit	(100)	0	(300)
Defined Benefit Plan Net Periodic Benefit Cost	20,800	15,400	64,500
Related Intercompany Allocationsof Defined Benefit Expense	13,600	10,400	(8,400)
Amount Capitalized Defined Benefit Expense	11,400	7,900	28,900
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	879,000	1,235,300
Defined Benefit Plan, Actual Return on Plan Assets	2,700	36,500
Defined Benefit Plan, Contributions by Employer	5,000	101,000
Defined Benefit Plan, Benefits Paid	(47,600)	(52,400)
Fair Value of Plan Assets Ending Balance	832,900	879,000	1,235,300
ChangeInAssetsDueToTransferOfEmployees	(6,200)	(441,400)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(116,800)	(103,600)
Defined Benefit Plan, Accumulated Benefit Obligation	888,800	910,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	879,000	1,235,300
Fair Value of Plan Assets Ending Balance	832,900	879,000	1,235,300
NSTAR Electric Company [Member] | PBOP Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(468,700)	0
ChangeInLiabilityDueToTransferOfEmployees	2,300	(395,500)
Defined Benefit Plan Service Cost	(5,400)	(3,100)
Defined Benefit Plan Interest Cost	(19,000)	(19,400)
Defined Benefit Plan, Actuarial Net (Gains) Losses	59,100	(68,600)
Defined Benefit Plan, Benefits Paid	18,900	17,900
Benefit Obligation Ending Balance	(412,800)	(468,700)	0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	5,400	3,100
Defined Benefit Plan Interest Cost	19,000	19,400
Defined Benefit Plan, Expected Return on Plan Assets	(27,300)	(25,900)
Defined Benefit Plan, Amortization of Gains (Losses)	2,300	(500)
Defined Benefit Plan Amortization Of Prior Service Cost Credit	(200)	(1,900)
Defined Benefit Plan Net Periodic Benefit Cost	(800)	(5,800)	4,600
Related Intercompany Allocationsof Defined Benefit Expense	800	800
Amount Capitalized Defined Benefit Expense	(200)	(2,300)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	336,500	0
Defined Benefit Plan, Actual Return on Plan Assets	(2,800)	18,400
Defined Benefit Plan, Contributions by Employer	4,900	19,300
Defined Benefit Plan, Benefits Paid	(18,900)	(17,900)
Fair Value of Plan Assets Ending Balance	320,300	336,500	0
ChangeInAssetsDueToTransferOfEmployees	600	316,700
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(92,500)	(132,200)
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	336,500	0
Fair Value of Plan Assets Ending Balance	320,300	336,500	$ 0
NSTAR Electric Company [Member] | Supplemental Employee Retirement Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Net Periodic Benefit Cost		3,200
Public Service Company Of New Hampshire [Member]
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, SERP and PBOP	89,579	93,243
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Amount That Represents Deferred Regulatory Assets	3,200
Public Service Company Of New Hampshire [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(580,700)	(529,000)
ChangeInLiabilityDueToTransferOfEmployees	(1,900)	32,200
Defined Benefit Plan Service Cost	(12,100)	(9,700)	$ (13,100)
Defined Benefit Plan Interest Cost	(24,300)	(23,800)	(23,600)
Defined Benefit Plan, Actuarial Net (Gains) Losses	38,900	(73,300)
Defined Benefit Plan, Benefits Paid	23,200	22,800
Defined Benefit Plan, Payments SERP	200	100
Defined Benefit Plan Benefits Paid Lump Sum	9,100
Benefit Obligation Ending Balance	(547,600)	(580,700)	(529,000)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	12,100	9,700	13,100
Defined Benefit Plan Interest Cost	24,300	23,800	23,600
Defined Benefit Plan, Expected Return on Plan Assets	(40,400)	(38,100)	(35,400)
Defined Benefit Plan, Amortization of Gains (Losses)	11,600	11,600	21,600
Defined Benefit Plan Amortization Of Prior Service Cost Credit	500	700	700
Defined Benefit Plan Net Periodic Benefit Cost	8,100	7,700	23,600
Related Intercompany Allocationsof Defined Benefit Expense	6,700	7,600	10,500
Amount Capitalized Defined Benefit Expense	3,500	3,000	7,300
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	498,400	528,600
Defined Benefit Plan, Actual Return on Plan Assets	1,500	24,800
Defined Benefit Plan, Contributions by Employer	1,000	0
Defined Benefit Plan, Benefits Paid	(23,200)	(22,800)
Defined Benefit Plan Benefits Paid Lump Sum	(9,100)
Fair Value of Plan Assets Ending Balance	470,500	498,400	528,600
ChangeInAssetsDueToTransferOfEmployees	1,900	(32,200)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(77,100)	(82,300)
Defined Benefit Plan, Accumulated Benefit Obligation	506,400	524,500
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	498,400	528,600
Fair Value of Plan Assets Ending Balance	470,500	498,400	528,600
Public Service Company Of New Hampshire [Member] | PBOP Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(91,800)	(93,500)
ChangeInLiabilityDueToTransferOfEmployees	(300)	4,300
Defined Benefit Plan Service Cost	(1,400)	(1,300)	(2,300)
Defined Benefit Plan Interest Cost	(3,900)	(4,300)	(4,000)
Defined Benefit Plan, Actuarial Net (Gains) Losses	3,600	(1,100)
Defined Benefit Plan, Benefits Paid	5,300	4,100
Benefit Obligation Ending Balance	(88,500)	(91,800)	(93,500)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	1,400	1,300	2,300
Defined Benefit Plan Interest Cost	3,900	4,300	4,000
Defined Benefit Plan, Expected Return on Plan Assets	(6,000)	(5,400)	(5,200)
Defined Benefit Plan, Amortization of Gains (Losses)	500	2,200	3,600
Defined Benefit Plan Amortization Of Prior Service Cost Credit		0	0
Defined Benefit Plan Net Periodic Benefit Cost	(200)	2,400	4,700
Related Intercompany Allocationsof Defined Benefit Expense	400	1,000	1,600
Amount Capitalized Defined Benefit Expense	200	800	1,300
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	80,900	81,800
Defined Benefit Plan, Actual Return on Plan Assets	0	3,800
Defined Benefit Plan, Contributions by Employer	0	2,500
Defined Benefit Plan, Benefits Paid	(5,300)	(4,100)
Fair Value of Plan Assets Ending Balance	75,800	80,900	81,800
ChangeInAssetsDueToTransferOfEmployees	200	(3,100)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(12,700)	(10,900)
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	80,900	81,800
Fair Value of Plan Assets Ending Balance	75,800	80,900	81,800
Western Massachusetts Electric Company [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan Benefits Paid Lump Sum	2,500
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan Benefits Paid Lump Sum	(2,500)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Accrued Pension, SERP and PBOP	19,515
Western Massachusetts Electric Company [Member] | Pension Plans Defined Benefit Member
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(249,400)	(223,900)
ChangeInLiabilityDueToTransferOfEmployees	(1,300)	6,200
Defined Benefit Plan Service Cost	(4,300)	(3,500)	(4,700)
Defined Benefit Plan Interest Cost	(10,400)	(10,300)	(10,000)
Defined Benefit Plan, Actuarial Net (Gains) Losses	12,600	(29,800)
Defined Benefit Plan, Benefits Paid	12,700	11,900
Defined Benefit Plan, Payments SERP	0
Benefit Obligation Ending Balance	(237,600)	(249,400)	(223,900)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	4,300	3,500	4,700
Defined Benefit Plan Interest Cost	10,400	10,300	10,000
Defined Benefit Plan, Expected Return on Plan Assets	(18,900)	(17,900)	(17,400)
Defined Benefit Plan, Amortization of Gains (Losses)	6,400	6,900	11,800
Defined Benefit Plan Amortization Of Prior Service Cost Credit	300	400	400
Defined Benefit Plan Net Periodic Benefit Cost	2,500	3,200	9,500
Related Intercompany Allocationsof Defined Benefit Expense	4,400	5,100	8,000
Amount Capitalized Defined Benefit Expense	1,900	2,400	5,200
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	234,000	240,400
Defined Benefit Plan, Actual Return on Plan Assets	700	11,700
Defined Benefit Plan, Contributions by Employer	0
Defined Benefit Plan, Benefits Paid	(12,700)	(11,900)
Fair Value of Plan Assets Ending Balance	220,800	234,000	240,400
ChangeInAssetsDueToTransferOfEmployees	1,300	(6,200)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(16,800)	(15,400)
Defined Benefit Plan, Accumulated Benefit Obligation	222,300	226,400
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	234,000	240,400
Fair Value of Plan Assets Ending Balance	220,800	234,000	240,400
Western Massachusetts Electric Company [Member] | PBOP Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation Beginning Balance	(36,600)	(38,700)
ChangeInLiabilityDueToTransferOfEmployees	0	1,000
Defined Benefit Plan Service Cost	(400)	(400)	(700)
Defined Benefit Plan Interest Cost	(1,500)	(1,700)	(1,700)
Defined Benefit Plan, Actuarial Net (Gains) Losses	1,500	1,300
Defined Benefit Plan, Benefits Paid	2,600	1,900
Benefit Obligation Ending Balance	(34,400)	(36,600)	(38,700)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Defined Benefit Plan Service Cost	400	400	700
Defined Benefit Plan Interest Cost	1,500	1,700	1,700
Defined Benefit Plan, Expected Return on Plan Assets	(2,500)	(2,300)	(2,300)
Defined Benefit Plan, Amortization of Gains (Losses)	0	500	1,100
Defined Benefit Plan Amortization Of Prior Service Cost Credit			0
Defined Benefit Plan Net Periodic Benefit Cost	(600)	300	1,200
Related Intercompany Allocationsof Defined Benefit Expense	300	700	1,300
Amount Capitalized Defined Benefit Expense	(200)	200	600
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets Beginning Balance	34,400	35,300
Defined Benefit Plan, Actual Return on Plan Assets	(100)	1,600
Defined Benefit Plan, Contributions by Employer	0	400
Defined Benefit Plan, Benefits Paid	(2,600)	(1,900)
Fair Value of Plan Assets Ending Balance	31,700	34,400	35,300
ChangeInAssetsDueToTransferOfEmployees	0	(1,000)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Defined Benefit Plan, Funded Status of Plan	(2,700)	(2,200)
Level 3 Rollforwards
Fair Value of Plan Assets Beginning Balance	34,400	35,300
Fair Value of Plan Assets Ending Balance	$ 31,700	$ 34,400	$ 35,300

Defined Contribution Plans (Det

Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Contribution Plan, Cost Recognized	$ 30.4	$ 29.7	$ 37
The Connecticut Light And Power Company [Member]
Defined Contribution Plan, Cost Recognized	4.8	5	5.1
NSTAR Electric Company [Member]
Defined Contribution Plan, Cost Recognized	6.3	6.3	8.5
Western Massachusetts Electric Company [Member]
Defined Contribution Plan, Cost Recognized	1	1	1
Public Service Company Of New Hampshire [Member]
Defined Contribution Plan, Cost Recognized	$ 3.4	$ 3.2	$ 3.3

Employee Stock Ownership Plan (

Employee Stock Ownership Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]
Employee Stock Ownership Plan (ESOP), Compensation Expense	$ 7	$ 22	$ 9.1

Share-Based Payments (Details)

Share-Based Payments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	8,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	3,005,010	3,112,020
AllocatedShareBasedCompensationExpense	$ 23,100,000	$ 24,600,000	$ 27,000,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	9,400,000	$ 10,300,000	10,700,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 14,900,000
Description Of Compensation Cost Not Yet Recognized Period For Recognition	This cost is expected to be recognized ratably over a weighted-average period of 1.74 years for Eversource, and 1.73 years for each CL&P, NSTAR Electric, PSNH and WMECO.
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	469,772	1,024,729
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 48.58	$ 38.14
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	784,376
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 37.21
Share Based Compensation Arrangement By Share Based Payment Award Vested Outstanding Number	259,536
Share Based Compensation Arrangement By Share Based Payment Award Expected To Vest	446,283
Employee Service Share Based Compensation Stock Option Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	171,872	351,616
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(179,744)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 26.47	$ 26.69
ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	$ 26.90
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 4,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	4,200,000	$ 9,400,000
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	4,800,000
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	$ 1,900,000
Employee Service Share Based Compensation E S P P Disclosures [Abstract]
Stock Issued During Period, Shares, Employee Stock Purchase Plans	33,715	40,779
Employee Stock Purchase Plan Shares Remaining For Future Issuance	743,260	776,975
ESPP Discounted Purchase Price First Six Months	$ 52.8	$ 41.61
ESPP Discounted Purchase Price Second Six Months	47.23	41.71
Deferred Compensation Liability, Classified, Noncurrent [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	55,200,000	57,500,000	51,300,000
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	3,900,000	4,500,000	4,400,000
The Connecticut Light And Power Company [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
AllocatedShareBasedCompensationExpense	9,300,000	8,100,000	6,800,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	3,800,000	3,400,000	2,700,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	6,100,000
Deferred Compensation Liability, Classified, Noncurrent [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	400,000	400,000	400,000
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	1,500,000	2,100,000	2,500,000
NSTAR Electric Company [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
AllocatedShareBasedCompensationExpense	5,800,000	7,400,000	7,500,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	2,400,000	3,100,000	3,000,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	3,800,000
Deferred Compensation Liability, Classified, Noncurrent [Abstract]
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	1,000,000	300,000
Public Service Company Of New Hampshire [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
AllocatedShareBasedCompensationExpense	3,200,000	3,000,000	2,300,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	1,300,000	1,300,000	900,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	2,200,000
Deferred Compensation Liability, Classified, Noncurrent [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	2,400,000	2,600,000	2,300,000
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	700,000	900,000	1,000,000
Western Massachusetts Electric Company [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
AllocatedShareBasedCompensationExpense	1,700,000	1,300,000	1,300,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	700,000	500,000	500,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	1,200,000
Deferred Compensation Liability, Classified, Noncurrent [Abstract]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent	200,000	200,000	100,000
Deferred Compensation Cash-based Arrangements, Expense Pertaining to Deferred Benefits	$ 300,000	$ 400,000	$ 500,000
Restricted Stock Units (RSUs) [Member]
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	266,230
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	(888,495)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(29,174)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Ending Balance	729,308	1,380,747
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Weighted Average Grant Date Fair Value Beginning Balance		$ 35.67
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 54.57	$ 42.27	$ 39.56
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Issued In Period Weighted Average Grant Date Fair Value	33.94
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	46.68
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Weighted Average Grant Date Fair Value Ending Balance	$ 43.45
Performance Shares [Member]
Employee Service Share Based Compensation Awards Other Than Options Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	172,543
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	(4,604)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(15,155)
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Ending Balance	528,428	375,644
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 55.04	$ 43.40	$ 40.96
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Issued In Period Weighted Average Grant Date Fair Value	42.23
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	45.33
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Weighted Average Grant Date Fair Value Ending Balance	$ 46.30	$ 42.20

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	$ 6,200	$ 4,400	$ 8,800
Current State and Local Tax Expense (Benefit)	45,700	24,500	(9,400)
Total Current Income Tax Expense (Benefit)	51,900	28,900	(600)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	436,100	406,800	386,200
Deferred State and Local Income Tax Expense (Benefit)	55,600	36,500	45,400
Total Deferred Income Taxes	491,736	443,259	431,413
Investment Tax Credit	(3,600)	(3,900)	(4,100)
Income Tax Expense	539,967	468,297	426,941
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	1,425,971	1,295,362	1,220,630
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	499,100	453,400	427,200
Tax Effect Of Differences [Abstract]
Income Tax Reconciliation, Nondeductible Expense, Depreciation	(4,600)	(5,600)	(7,400)
Investment Tax Credit	(3,600)	(3,900)	(4,100)
Income Tax Reconciliation, Tax Credits, Other	(3,800)	(3,500)	(3,700)
Income Tax Reconciliation, State and Local Income Taxes	61,100	42,500	27,600
Income Tax Rate Reconciliation Deductions Employee Stock Ownership Plan Dividends	(8,100)	(8,000)	(8,000)
Tax Asset Valuation Allowance / Reserve Adjustments	4,700	(2,900)	(4,300)
Income Tax Reconciliation, Other Adjustments	(4,800)	(3,700)	(400)
Income Tax Expense	$ 539,967	$ 468,297	$ 426,941
Effective Income Tax Rate, Continuing Operations	37.90%	36.20%	35.00%
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets Employee Benefits	$ 637,500	$ 632,200
Deferred Tax Assets, Derivative Instruments	172,700	199,600
Deferred Tax Assets, Regulatory Assets and Liabilities	243,500	366,700
Deferred Tax Assets, Allowance for Doubtful Accounts	60,500	60,500
Deferred Tax Assets Tax Effect Tax Regulatory Liabilities	9,700	10,000
Deferred Tax Assets, Operating Loss Carryforwards	5,400	59,100
Purchase Accounting Deferred Tax Asset	119,300	126,200
Deferred Tax Assets, Other	197,100	198,700
Deferred Tax Assets, Gross	1,445,700	1,653,000
Deferred Tax Assets, Valuation Allowance	3,700	5,100
Deferred Tax Assets, Net	1,442,000	1,647,900
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	4,602,600	4,215,900
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	76,700	109,600
Deferred Tax Liabilities, Regulatory Amounts [Abstract]
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	1,289,100	1,277,900
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	249,300	240,200
Deferred Tax Liabilities Goodwill Regulatory Asset	194,900	203,200
Deferred Tax Liabilities Regulatory Assets Derivative Assets	17,700	32,600
Deferred Tax Liabilities, Other	159,400	196,300
Deferred Tax Liabilities, Total	$ 6,589,700	6,275,700
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Tax Credit Carryforward Description	In 2015, the Company decreased its valuation allowance reserve for state credits and state loss carryforwards by $1.3 million (CL&P $0.9 million), net of tax, to reflect an update for expired state tax credits and loss carryforwards. In 2014, the Company recorded a reduction to its state credit carryforwards of $11 million (CL&P $10.1 million), net of tax, as a result of an update to reflect the amounts expired. Further, the Company decreased its valuation allowance reserve for state credits by $19.2 million at CL&P, net of tax, to reflect an update for expired state credits and latest estimate of usage.
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	$ 46,200	38,200	$ 83,100
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	9,900	9,300	8,200
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions	100	300
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions			(1,100)
Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities			(49,800)
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	(8,200)	(1,600)	(2,200)
Unrecognized Tax Benefits, Ending Balance	48,000	46,200	38,200
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]
Unrecognized Tax Benefits, Interest on Income Taxes Expense	100	400	(8,600)
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ 2,000	$ 1,900
Income Tax Uncertainties [Abstract]
Income Tax Examination Description	Tax Positions: During 2015 and 2014, Eversource did not resolve any of its uncertain tax positions.
Tax Years [Abstract]
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Other Information	Eversource estimates that during the next twelve months, differences of a non-timing nature could be resolved, resulting in a zero to $2.3 million decrease in unrecognized tax benefits by Eversource. These estimated changes are not expected to have a material impact on the earnings of Eversource. Other companies' impacts are not expected to be material.
Other Tax Disclosures [Abstract]
Other Information Pertaining To Income Taxes	2015 Federal Legislation: On December 18, 2015, the "Protecting Americans from Tax Hikes" Act became law, which extended the accelerated deduction of depreciation to businesses from 2015 through 2019. This extended stimulus provides Eversource with cash flow benefits in 2016 of approximately $275 million (including approximately $105 million for CL&P, $72 million for NSTAR Electric, $46 million for PSNH, and $25 million for WMECO) due to a refund of taxes paid in 2015 and lower expected tax payments in 2016 of approximately $300 million. 2015 Connecticut Legislation: In 2015, the state of Connecticut enacted several changes to its corporate tax laws. Among the changes, commencing as of January 1, 2015, is the reduction in the amount of tax credits that corporations can utilize against its tax liability in a year and a continuation of the corporate income tax surcharge through 2018, which effectively increases the state corporate tax rate to 9 percent for the years 2016 and 2017 and 8.25 percent for 2018. Also, effective January 1, 2016, all Connecticut companies have a mandatory unitary tax filing requirement. Management continues to review the tax law changes and their impact on the effective tax rates of Eversource and CL&P.	2014 Federal Legislation: On December 19, 2014, the "Tax Increase Prevention Act of 2014" became law, which extended the accelerated deduction of depreciation to businesses through 2014. This extended stimulus provided Eversource with cash flow benefits of approximately $250 million (approximately $86 million at CL&P, $64 million at NSTAR Electric, $44 million at PSNH, and $21 million at WMECO) in 2015.
Maximum [Member]
Tax Years [Abstract]
Decrease In Unrecognized Tax Benefits Is Reasonably Possible	$ 2,300
Minimum [Member]
Tax Years [Abstract]
Decrease In Unrecognized Tax Benefits Is Reasonably Possible	0
Federal [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards	15,500	$ 168,800
Tax Credit Carryforward, Amount	26,100	16,300
Charitable Contribution	14,900	19,400
State and Local Jurisdiction [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards		40,600
Tax Credit Carryforward, Amount	101,200	99,700
Charitable Contribution	3,000	2,100
Tax Credit and Operating Loss Carryforward Valuation Allowance	3,100	4,400
The Connecticut Light And Power Company [Member]
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	26,900	(200)	20,100
Current State and Local Tax Expense (Benefit)	15,800	4,300	(6,700)
Total Current Income Tax Expense (Benefit)	42,700	4,100	13,400
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	135,800	138,000	114,900
Deferred State and Local Income Tax Expense (Benefit)	200	(7,100)	15,100
Total Deferred Income Taxes	135,994	130,949	130,038
Investment Tax Credit	(1,300)	(1,500)	(1,700)
Income Tax Expense	177,396	133,451	141,663
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	476,756	421,205	421,075
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	166,900	147,400	147,400
Tax Effect Of Differences [Abstract]
Income Tax Reconciliation, Nondeductible Expense, Depreciation	(1,700)	(3,600)	(7,000)
Investment Tax Credit	(1,300)	(1,500)	(1,700)
Income Tax Reconciliation, Tax Credits, Other	0	0	0
Income Tax Reconciliation, State and Local Income Taxes	9,200	4,400	5,000
Tax Asset Valuation Allowance / Reserve Adjustments	1,200	(6,300)	400
Income Tax Reconciliation, Other Adjustments	3,100	(6,900)	(2,400)
Income Tax Expense	$ 177,396	$ 133,451	$ 141,663
Effective Income Tax Rate, Continuing Operations	37.20%	31.70%	33.60%
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets Employee Benefits	$ 126,100	$ 129,000
Deferred Tax Assets, Derivative Instruments	165,700	193,000
Deferred Tax Assets, Regulatory Assets and Liabilities	36,000	73,900
Deferred Tax Assets, Allowance for Doubtful Accounts	30,400	32,300
Deferred Tax Assets Tax Effect Tax Regulatory Liabilities	3,100	3,100
Deferred Tax Assets, Operating Loss Carryforwards	0	0
Deferred Tax Assets, Other	55,500	53,800
Deferred Tax Assets, Gross	416,800	485,100
Deferred Tax Assets, Valuation Allowance	3,100	4,000
Deferred Tax Assets, Net	413,700	481,100
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	1,545,600	1,378,600
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	27,300	58,100
Deferred Tax Liabilities, Regulatory Amounts [Abstract]
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	456,800	502,300
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	168,700	166,900
Deferred Tax Liabilities Regulatory Assets Derivative Assets	17,700	32,600
Deferred Tax Liabilities, Other	18,500	19,400
Deferred Tax Liabilities, Total	$ 2,234,600	2,157,900
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Tax Credit Carryforward Description	In 2015, the Company decreased its valuation allowance reserve for state credits and state loss carryforwards by $1.3 million (CL&P $0.9 million), net of tax, to reflect an update for expired state tax credits and loss carryforwards. In 2014, the Company recorded a reduction to its state credit carryforwards of $11 million (CL&P $10.1 million), net of tax, as a result of an update to reflect the amounts expired. Further, the Company decreased its valuation allowance reserve for state credits by $19.2 million at CL&P, net of tax, to reflect an update for expired state credits and latest estimate of usage.
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	$ 14,300	11,400	$ 49,000
Unrecognized Tax Benefits, Increases Resulting from Current Period Tax Positions	2,600	2,700	2,100
Unrecognized Tax Benefits, Increases Resulting from Prior Period Tax Positions		200
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions			(300)
Unrecognized Tax Benefits, Decreases Resulting from Settlements with Taxing Authorities			(39,400)
Unrecognized Tax Benefits, Reductions Resulting from Lapse of Applicable Statute of Limitations	(3,400)
Unrecognized Tax Benefits, Ending Balance	13,500	14,300	11,400
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense and Accrued Interest [Abstract]
Unrecognized Tax Benefits, Interest on Income Taxes Expense			(4,000)
The Connecticut Light And Power Company [Member] | Federal [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards	0	0
Tax Credit Carryforward, Amount	100	100
The Connecticut Light And Power Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards		0
Tax Credit Carryforward, Amount	73,800	71,000
NSTAR Electric Company [Member]
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	36,300	75,000	95,800
Current State and Local Tax Expense (Benefit)	19,800	20,200	29,600
Total Current Income Tax Expense (Benefit)	56,100	95,200	125,400
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	147,500	88,000	49,800
Deferred State and Local Income Tax Expense (Benefit)	25,700	20,100	(1,000)
Total Deferred Income Taxes	173,155	108,133	48,808
Investment Tax Credit	(1,300)	(1,300)	(1,300)
Income Tax Expense	228,044	201,981	172,866
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	572,586	505,069	441,412
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	200,400	176,800	154,500
Tax Effect Of Differences [Abstract]
Income Tax Reconciliation, Nondeductible Expense, Depreciation	(1,400)	(1,300)	100
Investment Tax Credit	(1,300)	(1,300)	(1,300)
Income Tax Reconciliation, Tax Credits, Other	0	0	0
Income Tax Reconciliation, State and Local Income Taxes	29,600	26,200	18,600
Income Tax Reconciliation, Other Adjustments	700	1,600	1,000
Income Tax Expense	$ 228,044	$ 201,981	$ 172,866
Effective Income Tax Rate, Continuing Operations	39.80%	40.00%	39.20%
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets Employee Benefits	$ 91,300	$ 39,900
Deferred Tax Assets, Derivative Instruments	600	1,800
Deferred Tax Assets, Regulatory Assets and Liabilities	109,400	181,300
Deferred Tax Assets, Allowance for Doubtful Accounts	8,500	13,800
Deferred Tax Assets Tax Effect Tax Regulatory Liabilities	1,500	1,800
Deferred Tax Assets, Operating Loss Carryforwards	0	0
Deferred Tax Assets, Other	3,400	19,900
Deferred Tax Assets, Gross	214,700	258,500
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	1,387,100	1,296,900
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	22,800	25,000
Deferred Tax Liabilities, Regulatory Amounts [Abstract]
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	339,700	276,000
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	36,000	35,500
Deferred Tax Liabilities Goodwill Regulatory Asset	167,400	174,400
Deferred Tax Liabilities Regulatory Assets Derivative Assets	0	0
Deferred Tax Liabilities, Other	22,000	33,500
Deferred Tax Liabilities, Total	1,975,000	1,841,300
NSTAR Electric Company [Member] | Federal [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards	0	0
Tax Credit Carryforward, Amount	200	200
NSTAR Electric Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards		0
Tax Credit Carryforward, Amount	0	0
Public Service Company Of New Hampshire [Member]
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	(16,700)	(22,600)	$ (8,200)
Current State and Local Tax Expense (Benefit)	6,000	(100)	3,600
Total Current Income Tax Expense (Benefit)	(10,700)	(22,700)	(4,600)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	74,500	79,600	64,500
Deferred State and Local Income Tax Expense (Benefit)	9,300	15,200	11,200
Total Deferred Income Taxes	83,776	94,813	75,693
Investment Tax Credit	0	0	0
Income Tax Expense	73,060	72,135	71,101
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	187,502	186,079	182,498
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	65,600	65,100	63,900
Tax Effect Of Differences [Abstract]
Income Tax Reconciliation, Nondeductible Expense, Depreciation	500	300	600
Investment Tax Credit	0	0	0
Income Tax Reconciliation, Tax Credits, Other	(3,800)	(3,500)	(3,700)
Income Tax Reconciliation, State and Local Income Taxes	9,900	9,800	9,600
Income Tax Reconciliation, Other Adjustments	900	400	700
Income Tax Expense	$ 73,060	$ 72,135	$ 71,101
Effective Income Tax Rate, Continuing Operations	39.00%	38.70%	39.00%
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets Employee Benefits	$ 37,100	$ 46,800
Deferred Tax Assets, Derivative Instruments	0	0
Deferred Tax Assets, Regulatory Assets and Liabilities	42,100	46,500
Deferred Tax Assets, Allowance for Doubtful Accounts	3,600	3,200
Deferred Tax Assets Tax Effect Tax Regulatory Liabilities	2,300	2,100
Deferred Tax Assets, Operating Loss Carryforwards	2,400	32,100
Deferred Tax Assets, Other	61,100	48,900
Deferred Tax Assets, Gross	148,600	179,600
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	655,300	596,600
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	7,300	7,400
Deferred Tax Liabilities, Regulatory Amounts [Abstract]
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	137,900	147,600
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	15,400	15,900
Deferred Tax Liabilities Regulatory Assets Derivative Assets	0	0
Deferred Tax Liabilities, Other	38,600	35,600
Deferred Tax Liabilities, Total	854,500	803,100
Public Service Company Of New Hampshire [Member] | Federal [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards	7,000	91,800
Tax Credit Carryforward, Amount	15,000	11,100
Public Service Company Of New Hampshire [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards		0
Tax Credit Carryforward, Amount	0	0
Western Massachusetts Electric Company [Member]
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	(3,500)	1,900	$ (53,400)
Current State and Local Tax Expense (Benefit)	1,600	1,800	4,200
Total Current Income Tax Expense (Benefit)	(1,900)	3,700	(49,200)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	33,400	28,100	84,700
Deferred State and Local Income Tax Expense (Benefit)	6,000	6,000	2,300
Total Deferred Income Taxes	39,428	34,108	87,028
Investment Tax Credit	(500)	(500)	(400)
Income Tax Expense	36,970	37,268	37,368
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income Before Income Tax Expense	93,476	95,087	97,806
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	32,700	33,300	34,200
Tax Effect Of Differences [Abstract]
Income Tax Reconciliation, Nondeductible Expense, Depreciation	(300)	(200)	0
Investment Tax Credit	(500)	(500)	(400)
Income Tax Reconciliation, Tax Credits, Other	0	0	0
Income Tax Reconciliation, State and Local Income Taxes	4,900	5,000	4,200
Income Tax Reconciliation, Other Adjustments	200	(300)	(600)
Income Tax Expense	$ 36,970	$ 37,268	$ 37,368
Effective Income Tax Rate, Continuing Operations	39.60%	39.20%	38.20%
Deferred Tax Assets, Net [Abstract]
Deferred Tax Assets Employee Benefits	$ 10,000	$ 9,200
Deferred Tax Assets, Derivative Instruments	0	0
Deferred Tax Assets, Regulatory Assets and Liabilities	6,100	11,400
Deferred Tax Assets, Allowance for Doubtful Accounts	4,500	3,800
Deferred Tax Assets Tax Effect Tax Regulatory Liabilities	2,400	2,500
Deferred Tax Assets, Operating Loss Carryforwards	400	4,500
Deferred Tax Assets, Other	5,000	4,900
Deferred Tax Assets, Gross	28,400	36,300
Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Property, Plant and Equipment	416,100	385,800
Deferred Tax Liabilities Resulting From Property Tax Accruals And Other	10,600	12,800
Deferred Tax Liabilities, Regulatory Amounts [Abstract]
Deferred Tax Liabilities Regulatory Assets Other Regulatory Deferrals	60,500	60,400
Deferred Tax Liabilities Regulatory Assets Tax Effect Tax Regulatory Assets	9,000	9,300
Deferred Tax Liabilities Regulatory Assets Derivative Assets	0	0
Deferred Tax Liabilities, Other	2,700	2,800
Deferred Tax Liabilities, Total	498,900	471,100
Western Massachusetts Electric Company [Member] | Federal [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards	1,000	12,700
Tax Credit Carryforward, Amount	0	0
Western Massachusetts Electric Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards and Tax Credit Carryforwards [Abstract]
Operating Loss Carryforwards		0
Tax Credit Carryforward, Amount	$ 0	$ 0

Environmental Matters (Details)

Environmental Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Site Contingency [Line Items]
Environmental Site Quantity	64	65
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 43.3	$ 35.4
Accrual For Environmental Loss Contingencies Provision For New Losses	13.5	12.7
Accrual for Environmental Loss Contingencies, Payments	(5.7)	(4.8)
Ending Balance	$ 51.1	43.3
Site Contingency [Abstract]
Information on range of possible loss and superfunds	CERCLA: Of the total environmental sites, nine sites (four for NSTAR Electric and three for PSNH) are superfund sites under the federal Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) and its amendments or state equivalents for which the Company has been notified that it is a potentially responsible party but for which the site assessment and remediation are not being managed by the Company.  As of December 31, 2015, a liability of $0.8 million accrued on these sites represents management's best estimate of its potential remediation costs with respect to these superfund sites. Included in the Eversource number of sites and reserve amounts above are former MGP sites that were operated several decades ago and manufactured gas from coal and other processes, which resulted in certain by-products remaining in the environment that may pose a potential risk to human health and the environment, for which Eversource may have potential liability. The reserve balances related to these former MGP sites were $45.5 million and $38.8 million as of December 31, 2015 and 2014, respectively, and related primarily to the natural gas business segment. As of December 31, 2015, for 9 environmental sites (3 for CL&P, 1 for WMECO) that are included in the Company's reserve for environmental costs, the information known and the nature of the remediation options allow for the Company to estimate the range of losses for environmental costs. As of December 31, 2015, $24.7 million (including $1.7 million for CL&P and $0.3 million for WMECO) had been accrued as a liability for these sites, which represents the low end of the range of the liabilities for environmental costs. Management believes that additional losses of up to approximately $33.9 million (approximately $1.4 million for CL&P, and $0.1 million for WMECO) may be incurred in remediating these sites. As of December 31, 2015, for 12 environmental sites (3 for CL&P and 2 for NSTAR Electric) that are included in the Company’s reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2015, $13.7 million (including $2 million for CL&P) had been accrued as a liability for these sites. As of December 31, 2015, for the remaining 43 environmental sites (including 8 for CL&P, 13 for NSTAR Electric, 12 for PSNH, and 3 for WMECO) that are included in the Company’s reserve for environmental costs, the $12.7 million accrual (including $0.9 million for CL&P, $2.4 million for NSTAR Electric, $4.5 million for PSNH, and $0.3 million for WMECO) represents management’s best estimate of the potential liability and no additional loss is anticipated at this time.
MGP Site accrual [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual For Environmental Loss Contingencies Component Amount	$ 45.5	$ 38.8
The Connecticut Light And Power Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	14	16
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 3.8	$ 3.4
Accrual For Environmental Loss Contingencies Provision For New Losses	1.3	1
Accrual for Environmental Loss Contingencies, Payments	(0.5)	(0.6)
Ending Balance	$ 4.6	$ 3.8
NSTAR Electric Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	15	13
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 1.1	$ 1.2
Accrual For Environmental Loss Contingencies Provision For New Losses	2	0
Accrual for Environmental Loss Contingencies, Payments	(0.7)	(0.1)
Ending Balance	$ 2.4	$ 1.1
Public Service Company Of New Hampshire [Member]
Site Contingency [Line Items]
Environmental Site Quantity	12	13
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 5.2	$ 5.4
Accrual For Environmental Loss Contingencies Provision For New Losses	2.3	0.1
Accrual for Environmental Loss Contingencies, Payments	(3)	(0.3)
Ending Balance	$ 4.5	$ 5.2
Western Massachusetts Electric Company [Member]
Site Contingency [Line Items]
Environmental Site Quantity	4	4
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning Balance	$ 0.5	$ 0.4
Accrual For Environmental Loss Contingencies Provision For New Losses	0.2	0.2
Accrual for Environmental Loss Contingencies, Payments	(0.1)	(0.1)
Ending Balance	$ 0.6	$ 0.5

Long-Term Contractual Arrange91

Long-Term Contractual Arrangements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	$ 684.5
Unrecorded Unconditional Purchase Obligation, Due within Two Years	590.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	442.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	376.2
Unrecorded Unconditional Purchase Obligation, Due within Five Years	344.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,371.7
Unrecorded Unconditional Purchase Obligation, Total	4,810.2
Supply And Stranded Costs Obligations Incurred	147.6	$ 99.2	$ 141
Natural Gas Procurement Costs Incurred	428.6	482.5	349.8
Fuel Costs Incurred	95.9	120.5	112.6
Transmission Support Commitment Costs Incurred	25.3	25	24.9
Peaker CfD Expense Incurred	42.7	18.1	51.9
Renewable Energy Costs Incurred	144.3	114.4	91.3
Supply And Stranded Cost Obligations [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	177.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	110.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	81.5
Unrecorded Unconditional Purchase Obligation, Due within Four Years	51.1
Unrecorded Unconditional Purchase Obligation, Due within Five Years	34.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	80.6
Unrecorded Unconditional Purchase Obligation, Total	535.6
Renewable Energy Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	246.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	273.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	238.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	237.4
Unrecorded Unconditional Purchase Obligation, Due within Five Years	237
Unrecorded Unconditional Purchase Obligation, Due after Five Years	2,174.7
Unrecorded Unconditional Purchase Obligation, Total	3,407.3
Peaker Contracts For Differences [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	55.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	41.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	20.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	7.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	3.6
Unrecorded Unconditional Purchase Obligation, Total	132.7
Natural Gas Procurement Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	137.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	123.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	78.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	57.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	46.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	99.7
Unrecorded Unconditional Purchase Obligation, Total	544.5
Wood, Coal And Transporation Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	45.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	23.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	3.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	1.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	1.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	13.1
Unrecorded Unconditional Purchase Obligation, Total	89
Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	21.4
Recorded Unconditional Purchase Obligation Due in Second Year	19
Recorded Unconditional Purchase Obligation Due in Third Year	20.3
Recorded Unconditional Purchase Obligation Due in Fourth Year	20.2
Recorded Unconditional Purchase Obligation Due in Fifth Year	20.2
Recorded Unconditional Purchase Obligation Due after Fifth Year	0
Recorded Unconditional Purchase Obligation, Total	101.1
The Connecticut Light And Power Company [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	279.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	207.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	159.5
Unrecorded Unconditional Purchase Obligation, Due within Four Years	126.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	114.5
Unrecorded Unconditional Purchase Obligation, Due after Five Years	711.6
Unrecorded Unconditional Purchase Obligation, Total	1,599.8
Supply And Stranded Costs Obligations Incurred	120.3	63	77.6
Transmission Support Commitment Costs Incurred	10	9.9	9.8
Peaker CfD Expense Incurred	42.7	18.1	51.9
Renewable Energy Costs Incurred	20	0.7
The Connecticut Light And Power Company [Member] | Supply And Stranded Cost Obligations [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	145
Unrecorded Unconditional Purchase Obligation, Due within Two Years	87.2
Unrecorded Unconditional Purchase Obligation, Due within Three Years	58.2
Unrecorded Unconditional Purchase Obligation, Due within Four Years	38
Unrecorded Unconditional Purchase Obligation, Due within Five Years	29.3
Unrecorded Unconditional Purchase Obligation, Due after Five Years	47.6
Unrecorded Unconditional Purchase Obligation, Total	405.3
The Connecticut Light And Power Company [Member] | Renewable Energy Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	70.1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	71.7
Unrecorded Unconditional Purchase Obligation, Due within Three Years	72.1
Unrecorded Unconditional Purchase Obligation, Due within Four Years	72.3
Unrecorded Unconditional Purchase Obligation, Due within Five Years	72.4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	649.7
Unrecorded Unconditional Purchase Obligation, Total	1,008.3
The Connecticut Light And Power Company [Member] | Peaker Contracts For Differences [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	55.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	41.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	20.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	7.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	4
Unrecorded Unconditional Purchase Obligation, Due after Five Years	3.6
Unrecorded Unconditional Purchase Obligation, Total	132.7
The Connecticut Light And Power Company [Member] | Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	8.4
Recorded Unconditional Purchase Obligation Due in Second Year	7.5
Recorded Unconditional Purchase Obligation Due in Third Year	8
Recorded Unconditional Purchase Obligation Due in Fourth Year	8
Recorded Unconditional Purchase Obligation Due in Fifth Year	8
Recorded Unconditional Purchase Obligation Due after Fifth Year	0
Recorded Unconditional Purchase Obligation, Total	39.9
The Connecticut Light And Power Company [Member] | Yankee Companies Billings [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	0.1
Recorded Unconditional Purchase Obligation Due in Second Year	0.4
Recorded Unconditional Purchase Obligation Due in Third Year	0.8
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.8
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.8
Recorded Unconditional Purchase Obligation Due after Fifth Year	10.7
Recorded Unconditional Purchase Obligation, Total	13.6
NSTAR Electric Company [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	119.8
Unrecorded Unconditional Purchase Obligation, Due within Two Years	127.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	92.5
Unrecorded Unconditional Purchase Obligation, Due within Four Years	90.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	86.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	521.5
Unrecorded Unconditional Purchase Obligation, Total	1,038.4
Supply And Stranded Costs Obligations Incurred	6.5	7	32.4
Transmission Support Commitment Costs Incurred	7.8	7.7	7.7
Renewable Energy Costs Incurred	86.7	87.4	84.9
NSTAR Electric Company [Member] | Supply And Stranded Cost Obligations [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	14.1
Unrecorded Unconditional Purchase Obligation, Due within Two Years	4.8
Unrecorded Unconditional Purchase Obligation, Due within Three Years	5.5
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	3.1
Unrecorded Unconditional Purchase Obligation, Due after Five Years	28.1
Unrecorded Unconditional Purchase Obligation, Total	61.1
NSTAR Electric Company [Member] | Renewable Energy Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	99
Unrecorded Unconditional Purchase Obligation, Due within Two Years	117
Unrecorded Unconditional Purchase Obligation, Due within Three Years	80.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	78.5
Unrecorded Unconditional Purchase Obligation, Due within Five Years	76.6
Unrecorded Unconditional Purchase Obligation, Due after Five Years	489.8
Unrecorded Unconditional Purchase Obligation, Total	941.3
NSTAR Electric Company [Member] | Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	6.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	5.9
Unrecorded Unconditional Purchase Obligation, Due within Three Years	6.3
Unrecorded Unconditional Purchase Obligation, Due within Four Years	6.2
Unrecorded Unconditional Purchase Obligation, Due within Five Years	6.2
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation, Total	31.2
NSTAR Electric Company [Member] | Yankee Companies Billings [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	0.1
Recorded Unconditional Purchase Obligation Due in Second Year	0.2
Recorded Unconditional Purchase Obligation Due in Third Year	0.3
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.3
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.3
Recorded Unconditional Purchase Obligation Due after Fifth Year	3.6
Recorded Unconditional Purchase Obligation, Total	4.8
Public Service Company Of New Hampshire [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	136.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	114.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	95.9
Unrecorded Unconditional Purchase Obligation, Due within Four Years	84.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	81
Unrecorded Unconditional Purchase Obligation, Due after Five Years	882.6
Unrecorded Unconditional Purchase Obligation, Total	1,395.2
Supply And Stranded Costs Obligations Incurred	20.8	26	29
Fuel Costs Incurred	95.9	120.5	112.6
Transmission Support Commitment Costs Incurred	5.4	5.3	5.3
Renewable Energy Costs Incurred	37.2	26.3	6.4
Public Service Company Of New Hampshire [Member] | Supply And Stranded Cost Obligations [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	18.3
Unrecorded Unconditional Purchase Obligation, Due within Two Years	18.1
Unrecorded Unconditional Purchase Obligation, Due within Three Years	17.8
Unrecorded Unconditional Purchase Obligation, Due within Four Years	7.6
Unrecorded Unconditional Purchase Obligation, Due within Five Years	2.5
Unrecorded Unconditional Purchase Obligation, Due after Five Years	4.9
Unrecorded Unconditional Purchase Obligation, Total	69.2
Public Service Company Of New Hampshire [Member] | Renewable Energy Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	67.9
Unrecorded Unconditional Purchase Obligation, Due within Two Years	69
Unrecorded Unconditional Purchase Obligation, Due within Three Years	70.1
Unrecorded Unconditional Purchase Obligation, Due within Four Years	70.7
Unrecorded Unconditional Purchase Obligation, Due within Five Years	72
Unrecorded Unconditional Purchase Obligation, Due after Five Years	860.4
Unrecorded Unconditional Purchase Obligation, Total	1,210.1
Public Service Company Of New Hampshire [Member] | Wood, Coal And Transporation Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	45.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	23.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	3.4
Unrecorded Unconditional Purchase Obligation, Due within Four Years	1.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	1.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	13.1
Unrecorded Unconditional Purchase Obligation, Total	89
Public Service Company Of New Hampshire [Member] | Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	4.6
Recorded Unconditional Purchase Obligation Due in Second Year	4
Recorded Unconditional Purchase Obligation Due in Third Year	4.3
Recorded Unconditional Purchase Obligation Due in Fourth Year	4.3
Recorded Unconditional Purchase Obligation Due in Fifth Year	4.3
Recorded Unconditional Purchase Obligation Due after Fifth Year	0
Recorded Unconditional Purchase Obligation, Total	21.5
Public Service Company Of New Hampshire [Member] | Yankee Companies Billings [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	0.1
Recorded Unconditional Purchase Obligation Due in Second Year	0.2
Recorded Unconditional Purchase Obligation Due in Third Year	0.3
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.3
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.3
Recorded Unconditional Purchase Obligation Due after Fifth Year	4.2
Recorded Unconditional Purchase Obligation, Total	5.4
Western Massachusetts Electric Company [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	11.4
Unrecorded Unconditional Purchase Obligation, Due within Two Years	17.3
Unrecorded Unconditional Purchase Obligation, Due within Three Years	17.6
Unrecorded Unconditional Purchase Obligation, Due within Four Years	17.8
Unrecorded Unconditional Purchase Obligation, Due within Five Years	17.9
Unrecorded Unconditional Purchase Obligation, Due after Five Years	177.5
Unrecorded Unconditional Purchase Obligation, Total	259.5
Supply And Stranded Costs Obligations Incurred		3.2	2
Transmission Support Commitment Costs Incurred	2.1	$ 2.1	$ 2.1
Renewable Energy Costs Incurred	0.4
Western Massachusetts Electric Company [Member] | Renewable Energy Contracts [Member]
Long-term Purchase Commitment [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	9.6
Unrecorded Unconditional Purchase Obligation, Due within Two Years	15.6
Unrecorded Unconditional Purchase Obligation, Due within Three Years	15.7
Unrecorded Unconditional Purchase Obligation, Due within Four Years	15.9
Unrecorded Unconditional Purchase Obligation, Due within Five Years	16
Unrecorded Unconditional Purchase Obligation, Due after Five Years	174.8
Unrecorded Unconditional Purchase Obligation, Total	247.6
Western Massachusetts Electric Company [Member] | Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	1.8
Recorded Unconditional Purchase Obligation Due in Second Year	1.6
Recorded Unconditional Purchase Obligation Due in Third Year	1.7
Recorded Unconditional Purchase Obligation Due in Fourth Year	1.7
Recorded Unconditional Purchase Obligation Due in Fifth Year	1.7
Recorded Unconditional Purchase Obligation Due after Fifth Year	0
Recorded Unconditional Purchase Obligation, Total	8.5
Western Massachusetts Electric Company [Member] | Yankee Companies Billings [Member]
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation Due within One Year	0
Recorded Unconditional Purchase Obligation Due in Second Year	0.1
Recorded Unconditional Purchase Obligation Due in Third Year	0.2
Recorded Unconditional Purchase Obligation Due in Fourth Year	0.2
Recorded Unconditional Purchase Obligation Due in Fifth Year	0.2
Recorded Unconditional Purchase Obligation Due after Fifth Year	2.7
Recorded Unconditional Purchase Obligation, Total	$ 3.4

Contractual Obligations with Ya

Contractual Obligations with Yankee Companies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain Contingency [Line Items]
Refund Obligation To Customers		As of December 31, 2014, CL&P's refund obligation to customers of $65.4 million was recorded as an offset to the deferred storm restoration costs regulatory asset, as directed by PURA. NSTAR Electric's, PSNH's and WMECO's refund obligation to customers of $29.1 million, $13.1 million and $18.1 million, respectively, was recorded as a regulatory liability in each company's respective regulatory tracker mechanisms. Refunds to customers for these Phase II DOE proceeds were completed in 2015.
MYAPC Phase One Damages Proceeds To Member Companies	In accordance with MYAPC's three-year refund plan of the DOE Phase I Damages proceeds, in September 2014, MYAPC returned the second portion of the proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, in the amount of $3.2 million, $1.1 million, $1.4 million and $0.8 million, respectively. On September 28, 2015, MYAPC returned the remaining DOE Phase I Damages proceeds to the member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, in the amount of $2.3 million, $0.8 million, $1 million and $0.6 million, respectively. These amounts reduced receivables at CL&P, NSTAR Electric, PSNH and WMECO.
CYAPC [Member] | DOE Phase I Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation			$ 39.6
CYAPC [Member] | DOE Phase II Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation		$ 126.3
YAEC [Member] | DOE Phase I Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation			38.3
YAEC [Member] | DOE Phase II Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation		73.3
MYAPC [Member] | DOE Phase I Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation			$ 81.7
MYAPC [Member] | DOE Phase II Damages [Member]
Gain Contingency [Line Items]
Awards Received from Litigation		$ 35.8

Guarantees and Indemnificatio93

Guarantees and Indemnifications (Details) $ in Millions	Dec. 31, 2015USD ($)
Guarantee Of Financial Obligations Of Npt [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$ 25
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2016 And 2018 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	32.7
Guarantee Of Rocky River Reality And Nusco Lease Payments For Real Estate And Vehicles Expiring 2019 Through 2024 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	11.4
Access Northeast Project Capital Contributions Guarantee Expiring In 2021 [Member]
Guarantee Obligations [Line Items]
Guarantee Obligations Maximum Exposure	$ 204.8

Other Contingencies (Details)

Other Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss Contingencies [Line Items]
Loss Contingency, Description	E.         FERC ROE Complaints E.         FERC ROE Complaints Three separate complaints have been filed at FERC by combinations of New England state attorneys general, state regulatory commissions, consumer advocates, consumer groups, municipal parties and other parties (the "Complainants"). In the first complaint, filed in 2011, the Complainants alleged that the NETOs' base ROE that had been utilized since 2006 was unjust and unreasonable, asserted that the rate was excessive due to changes in the capital markets, and sought an order to reduce it prospectively from the date of the final FERC order and for the 15-month period beginning October 1, 2011 to December 31, 2012. In the second and third complaints, filed in 2012 and 2014, the Complainants challenged the NETOs' base ROE and sought refunds for the respective 15-month periods beginning December 27, 2012 and July 31, 2014. As a result of the actions taken by the FERC and other developments in the first complaint matter, the Company recorded additional reserves at its electric subsidiaries in 2015 and 2014. In 2015, Eversource recognized a pre-tax charge to earnings (excluding interest) of $20 million, of which $12.5 million was recorded at CL&P, $2.4 million at NSTAR Electric, $1 million at PSNH, and $4.1 million at WMECO. The pre-tax charge was recorded as a regulatory liability and as a reduction to Operating Revenues. In 2014, the net aggregate pre-tax charge to earnings (excluding interest) totaled $37 million, of which $20.7 million was recorded at CL&P, $7.9 million at NSTAR Electric, $2.8 million at PSNH and $5.6 million at WMECO. In 2013, the net aggregate pre-tax charge to earnings (excluding interest) totaled $23.7 million, of which $12.8 million was recorded at CL&P, $5.7 million at NSTAR Electric, $2.3 million at PSNH and $2.9 million at WMECO. The second and third complaint proceedings are ongoing and a final FERC order is expected in late 2016 or early 2017. Although management is uncertain on the final outcome of the second and third complaints regarding the ROE, management believes the current reserves established are appropriate to reflect probable and reasonably estimable refunds. F.        NSTAR Electric and NSTAR Gas Comprehensive Settlement Agreement On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2009 through 2011 (11 dockets in total). In the first quarter of 2015, as a result of the DPU order, NSTAR Electric and NSTAR Gas commenced refunding a combined $44.7 million to customers, which was recorded as a regulatory liability. Refunds to customers will continue through December 2016. As a result of the Settlement, NSTAR Electric increased its operating revenues and decreased its amortization expense in 2015, resulting in the recognition of a $21.7 million pre-tax benefit in 2015. G.        NSTAR Electric Basic Service Bad Debt Adder On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had removed energy-related bad debt costs from base distribution rates effective January 1, 2006. As a result of the DPU order, in the first quarter of 2015, NSTAR Electric increased its regulatory assets and reduced its operations and maintenance expense by an under recovered amount of $24.2 million for energy-related bad debt costs through 2014, resulting in a pre-tax benefit in 2015. NSTAR Electric filed for recovery of the energy-related bad debt costs regulatory asset from customers and on November 20, 2015the DPU approved NSTAR Electric’s proposed rate increase, to recover these costs over a 12-month period, effective January 1, 2016. H.        PSNH Generation Restructuring On June 10, 2015, Eversource and PSNH entered into the 2015 Public Service Company of New Hampshire Restructuring and Rate Stabilization Agreement (the Agreement) with the New Hampshire Office of Energy and Planning, certain members of the NHPUC staff, the Office of Consumer Advocate, two State Senators, and several other parties. The Agreement was filed with the NHPUC on the same day. Under the terms of the Agreement, PSNH has agreed to divest its generation assets upon NHPUC approval. The Agreement is designed to provide a resolution of issues pertaining to PSNH's generation assets in pending regulatory proceedings before the NHPUC. The Agreement provided for the Clean Air Project prudence proceeding to be resolved and all remaining Clean Air Project costs to be included in rates effective January 1, 2016. As part of the Agreement, PSNH has agreed to forego recovery of $25 million of the deferred equity return related to the Clean Air Project. In addition, PSNH will not seek a general distribution rate increase effective before July 1, 2017 and will contribute $5 million to create a clean energy fund, which will not be recoverable from its customers. In 2015, PSNH recorded the $5 million contribution as a long-term liability and an increase to Operations and Maintenance expense on the statements of income. Upon completion of the divestiture process, all remaining stranded costs will be recovered via bonds that will be secured by a non-bypassable charge or through other recoveries in rates billed to PSNH customers. On January 26, 2016, Advisory Staff of the NHPUC and the parties to the Agreement filed a stipulation with the NHPUC agreeing that near-term divestiture of PSNH’s generation was in the public interest and that the Agreement should be approved. Implementation of the Agreement is subject to NHPUC approval, which is expected in early 2016. If the NHPUC approves the settlements and the sale of the plants, then management expects to sell the plants in the first half of 2017. The sales price of the generating assets could be less than the carrying value, but we believe that full recovery of PSNH's generation assets is probable through a combination of cash flows during the remaining operating period, sales proceeds upon divestiture, and recovery of stranded costs in future rates. I.        Litigation and Legal Proceedings Eversource, including CL&P, NSTAR Electric, PSNH and WMECO, are involved in legal, tax and regulatory proceedings regarding matters arising in the ordinary course of business, which involve management's assessment to determine the probability of whether a loss will occur and, if probable, its best estimate of probable loss. The Company records and discloses losses when these losses are probable and reasonably estimable, and discloses matters when losses are probable but not estimable or when losses are reasonably possible. Legal costs related to the defense of loss contingencies are expensed as incurred.
Public Utilities Disclosure Of Regulatory Matters	2015 Regulatory Developments: FERC ROE Complaints: As a result of the actions taken by the FERC and other developments in the pending ROE complaint proceedings described in Note 11E, "Commitments and Contingencies – FERC ROE Complaints," Eversource recorded reserves for the first and second ROE complaints, which were recorded as a regulatory liability and as a reduction to operating revenues. The cumulative pre-tax reserves (excluding interest) as of December 31, 2015, which include the impact of refunds given to customers, totaled $39.1 million for Eversource (including $21.4 million for CL&P, $8.5 million for NSTAR Electric, $3.1 million for PSNH, and $6.1 million for WMECO). NSTAR Electric and NSTAR Gas Comprehensive Settlement Agreement: On March 2, 2015, the DPU approved the comprehensive settlement agreement between NSTAR Electric, NSTAR Gas and the Massachusetts Attorney General (the "Settlement") as filed with the DPU on December 31, 2014. The Settlement resolved the outstanding NSTAR Electric CPSL program filings for 2006 through 2011, the NSTAR Electric and NSTAR Gas PAM and energy efficiency-related customer billing adjustments reported in 2012, and the recovery of LBR related to NSTAR Electric's energy efficiency programs for 2009 through 2011 (11 dockets in total). In 2015, as a result of the DPU order, NSTAR Electric and NSTAR Gas commenced refunding a combined $44.7 million to customers, which was recorded as a regulatory liability. Refunds to customers will continue through December 2016. As a result of the Settlement, NSTAR Electric increased its operating revenues and decreased its amortization expense in 2015, resulting in the recognition of a $21.7 million pre-tax benefit in 2015. NSTAR Electric Basic Service Bad Debt Adder: On January 7, 2015, the DPU issued an order concluding that NSTAR Electric had removed energy-related bad debt costs from base distribution rates effective January 1, 2006. As a result of the DPU order, in the first quarter of 2015, NSTAR Electric increased its regulatory assets and reduced its operations and maintenance expense by an under recovered amount of $24.2 million for energy-related bad debt costs through 2014, resulting in a pre-tax benefit in 2015. NSTAR Electric filed for recovery of the energy-related bad debt costs regulatory asset from customers and on November 20, 2015 the DPU approved NSTAR Electric’s proposed rate increase to recover these costs over a 12-month period, effective January 1, 2016. CL&P Distribution Rates: On July 2, 2015, PURA issued a final order that approved a settlement agreement filed on May 19, 2015, which allows for an increase to rate base of approximately $163 million associated with ADIT, including a regulatory asset to recover the incremental revenue requirement for the period December 1, 2014 through November 30, 2015 over a subsequent 24-month period. The rate base increase provided an increase to total allowed annual revenue requirements of $18.4 million beginning December 1, 2014. As part of the settlement agreement, the $18.4 million for the period December 1, 2014 through November 30, 2015 was recorded as a regulatory asset with a corresponding increase in Operating Revenues, and is being collected from customers in rates over a 24-month period beginning December 1, 2015. NSTAR Gas Distribution Rates: On October 30, 2015, the DPU issued its order in the NSTAR Gas distribution rate case, which approved an annualized base rate increase of $15.8 million, plus other increases of approximately $11.5 million, mostly relating to recovery of pension and PBOP expenses and the Hopkinton GSA, effective January 1, 2016. In the order, the DPU also approved an authorized regulatory ROE of 9.8 percent, the establishment of a revenue decoupling mechanism, the recovery of certain bad debt expenses, and a 52.1 percent equity component of its capital structure. On November 19, 2015, NSTAR Gas filed a motion for reconsideration of the order with the DPU seeking the correction of mathematical errors and other plant and cost of service items. As a result of this order, Eversource recorded regulatory deferrals for costs that have been approved for recovery or are expected to be approved for recovery in future rate proceedings, which resulted in the recognition of a $17.2 million pre-tax benefit in 2015. Included in this amount is a $10.5 million pre-tax benefit recorded at NSTAR Electric for certain uncollectible hardship accounts receivable that are expected to be recovered in future rates given the allowed recoveries of uncollectible hardship accounts receivable by WMECO and NSTAR Gas.
FERC ROE Reserve - Cumulative - Pre Tax Charge [Member]
Loss Contingencies [Line Items]
Loss Contingency Loss in Period	$ 20	$ 37	$ 23.7
FERC ROE Reserve - Cumulative - Pre Tax Charge [Member] | The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Loss Contingency Loss in Period	12.5	20.7	12.8
FERC ROE Reserve - Cumulative - Pre Tax Charge [Member] | NSTAR Electric Company [Member]
Loss Contingencies [Line Items]
Loss Contingency Loss in Period	2.4	7.9	5.7
FERC ROE Reserve - Cumulative - Pre Tax Charge [Member] | Public Service Company Of New Hampshire [Member]
Loss Contingencies [Line Items]
Loss Contingency Loss in Period	1	2.8	2.3
FERC ROE Reserve - Cumulative - Pre Tax Charge [Member] | Western Massachusetts Electric Company [Member]
Loss Contingencies [Line Items]
Loss Contingency Loss in Period	$ 4.1	$ 5.6	$ 2.9

LEASES (Details)

LEASES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Capital Leases, Future Minimum Payments Due in Two Years	$ 2.2
Capital Leases, Future Minimum Payments Due in Three Years	2.1
Capital Leases, Future Minimum Payments Due in Four Years	2.1
Capital Leases, Future Minimum Payments Due in Five Years	2
Capital Leases, Future Minimum Payments Due Thereafter	1.4
Capital Leases, Future Minimum Payments Due	11.8
Capital Leases, Future Minimum Payments, Interest Included in Payments	3.6
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	8.2
Operating Leases, Rent Expense	16.3
Operating Leases, Future Minimum Payments, Due in Two Years	16.4
Operating Leases, Future Minimum Payments, Due in Three Years	13.8
Operating Leases, Future Minimum Payments, Due in Four Years	10.4
Operating Leases, Future Minimum Payments, Due in Five Years	8.5
Operating Leases, Future Minimum Payments, Due Thereafter	15.4
Operating Leases, Future Minimum Payments Due	71.3
The Connecticut Light And Power Company [Member]
Operating Leased Assets [Line Items]
Capital Leases, Future Minimum Payments Due in Two Years	1.9
Capital Leases, Future Minimum Payments Due in Three Years	1.9
Capital Leases, Future Minimum Payments Due in Four Years	2
Capital Leases, Future Minimum Payments Due in Five Years	2
Capital Leases, Future Minimum Payments Due Thereafter	1.4
Capital Leases, Future Minimum Payments Due	11.2
Capital Leases, Future Minimum Payments, Interest Included in Payments	3.6
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	7.6
Operating Leases, Rent Expense	8.1
Operating Leases, Future Minimum Payments, Due in Two Years	2.9
Operating Leases, Future Minimum Payments, Due in Three Years	2
Operating Leases, Future Minimum Payments, Due in Four Years	1.3
Operating Leases, Future Minimum Payments, Due in Five Years	1
Operating Leases, Future Minimum Payments, Due Thereafter	1.7
Operating Leases, Future Minimum Payments Due	9.6
NSTAR Electric Company [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	7.8	$ 6.7
Operating Leases, Future Minimum Payments, Due in Two Years	9.7
Operating Leases, Future Minimum Payments, Due in Three Years	8.5
Operating Leases, Future Minimum Payments, Due in Four Years	6.5
Operating Leases, Future Minimum Payments, Due in Five Years	5.3
Operating Leases, Future Minimum Payments, Due Thereafter	9
Operating Leases, Future Minimum Payments Due	43.3
Public Service Company Of New Hampshire [Member]
Operating Leased Assets [Line Items]
Capital Leases, Future Minimum Payments Due in Two Years	0.3
Capital Leases, Future Minimum Payments Due in Three Years	0.2
Capital Leases, Future Minimum Payments Due in Four Years	0.1
Capital Leases, Future Minimum Payments Due in Five Years	0
Capital Leases, Future Minimum Payments Due Thereafter	0
Capital Leases, Future Minimum Payments Due	0.6
Capital Leases, Future Minimum Payments, Interest Included in Payments	0
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	0.6
Operating Leases, Rent Expense	1.7
Operating Leases, Future Minimum Payments, Due in Two Years	0.8
Operating Leases, Future Minimum Payments, Due in Three Years	0.7
Operating Leases, Future Minimum Payments, Due in Four Years	0.5
Operating Leases, Future Minimum Payments, Due in Five Years	0.4
Operating Leases, Future Minimum Payments, Due Thereafter	0.7
Operating Leases, Future Minimum Payments Due	3.4
Western Massachusetts Electric Company [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	1.2	$ 2.9
Operating Leases, Future Minimum Payments, Due in Two Years	0.8
Operating Leases, Future Minimum Payments, Due in Three Years	0.7
Operating Leases, Future Minimum Payments, Due in Four Years	0.6
Operating Leases, Future Minimum Payments, Due in Five Years	0.5
Operating Leases, Future Minimum Payments, Due Thereafter	1.8
Operating Leases, Future Minimum Payments Due	$ 4.9

FAIR VALUE OF FINANCIAL INSTR96

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	$ 155,568	$ 155,568
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	155,600	155,600
Other Long Term Debt	9,034,500	8,814,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	157,900	153,600
Other Long Term Debt	9,425,900	9,451,200
The Connecticut Light And Power Company [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
The Connecticut Light And Power Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	116,200	116,200
Other Long Term Debt	2,763,700	2,826,200
The Connecticut Light And Power Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	114,900	112,000
Other Long Term Debt	3,031,600	3,214,500
NSTAR Electric Company [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
NSTAR Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	43,000
Other Long Term Debt	2,029,800	1,786,200
NSTAR Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Temporary Equity, Carrying Amount, Attributable to Noncontrolling Interest	43,000	41,600
Other Long Term Debt	2,182,400	1,993,500
Public Service Company Of New Hampshire [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	1,071,000	1,070,000
Public Service Company Of New Hampshire [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	1,121,200	1,137,900
Western Massachusetts Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	517,300	625,200
Western Massachusetts Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other Long Term Debt	$ 551,800	$ 689,400

ACCUMULATED OTHER COMPREHENSI97

ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				$ (74,009)				$ (46,000)	$ (74,009)	$ (46,000)
Other Comprehensive Income Before Reclassifications, Net of Tax									900	(33,900)
Reclassification From OCI, Net Of Tax									6,300	5,900
Other Comprehensive Income (Loss), Net of Tax, Total									7,165	(27,978)	$ 26,823
AOCI Ending Balance	$ (66,844)				$ (74,009)				(66,844)	(74,009)	(46,000)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense									(372,420)	(362,106)	(338,699)
Income Tax Expense									(539,967)	(468,297)	(426,941)
Net Income Attributable to Controlling Interests	181,800	$ 235,900	$ 207,500	253,300	221,500	$ 234,600	$ 127,400	236,000	878,485	819,546	786,007
OCI Benefit Plans Before Reclassification Adjustments, Tax [Abstract]
OCI Benefit Plans Before Reclassification Adjustments TAX Effect									2,000	(22,300)	11,400
Future AOCI Reclassification Amounts [Abstract]
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months									3,500
Pension SERP And PBOP Gain Loss To Be Reclassified Within Twelve Months									6,900
The Connecticut Light And Power Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				(931)					(931)
Other Comprehensive Income (Loss), Net of Tax, Total									355	456	413
AOCI Ending Balance	(576)				(931)				(576)	(931)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense									(145,795)	(147,421)	(133,650)
Income Tax Expense									(177,396)	(133,451)	(141,663)
Future AOCI Reclassification Amounts [Abstract]
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months									700
Public Service Company Of New Hampshire [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				(7,369)					(7,369)
Other Comprehensive Income (Loss), Net of Tax, Total									1,008	1,181	1,105
AOCI Ending Balance	(6,361)				(7,369)				(6,361)	(7,369)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense									(45,990)	(45,349)	(46,176)
Income Tax Expense									(73,060)	(72,135)	(71,101)
Future AOCI Reclassification Amounts [Abstract]
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months									2,000
Western Massachusetts Electric Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				(3,176)					(3,176)
Other Comprehensive Income (Loss), Net of Tax, Total									354	341	329
AOCI Ending Balance	(2,822)				(3,176)				(2,822)	(3,176)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense									(24,792)	(24,931)	(24,851)
Income Tax Expense									(36,970)	(37,268)	(37,368)
Future AOCI Reclassification Amounts [Abstract]
Cash Flow Hedge Loss To Be Reclassified Within Twelve Months									600
Qualified Cash Flow Hedging Instruments [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				(12,400)				(14,400)	(12,400)	(14,400)
Other Comprehensive Income Before Reclassifications, Net of Tax									0
Reclassification From OCI, Net Of Tax									2,100	2,000
Other Comprehensive Income (Loss), Net of Tax, Total									2,100	2,000
AOCI Ending Balance	(10,300)				(12,400)				(10,300)	(12,400)	(14,400)
Unrealized Gains Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				700				400	700	400
Other Comprehensive Income Before Reclassifications, Net of Tax									(2,600)	300
Other Comprehensive Income (Loss), Net of Tax, Total									(2,600)	300
AOCI Ending Balance	(1,900)				700				(1,900)	700	400
Pension, SERP and PBOP Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance				$ (62,300)				$ (32,000)	(62,300)	(32,000)
Other Comprehensive Income Before Reclassifications, Net of Tax									3,500	(34,200)
Reclassification From OCI, Net Of Tax									4,200	3,900
Other Comprehensive Income (Loss), Net of Tax, Total									7,700	(30,300)
AOCI Ending Balance	$ (54,600)				$ (62,300)				(54,600)	(62,300)	(32,000)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Net Income Attributable to Controlling Interests									(6,300)	(5,900)	(8,400)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Qualified Cash Flow Hedging Instruments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense									(3,500)	(3,400)	(3,400)
Income Tax Expense									1,400	1,400	1,400
Net Income Attributable to Controlling Interests									(2,100)	(2,000)	(2,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension, SERP and PBOP Benefit Plans [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
OCI Reclassification Adjustment for Net Actuarial Gain (Loss), before Tax									(6,600)	(6,200)	(10,500)
OCI Reclassification Adjustment for Amortization of Prior Service Cost, before tax									(200)	(200)	(200)
OCI Reclassification Adjustment for Pension, SERP and PBOP Plans, before Tax									(6,800)	(6,400)	(10,700)
Income Tax Expense									2,600	2,500	4,300
Net Income Attributable to Controlling Interests									$ (4,200)	$ (3,900)	$ (6,400)

DIVIDEND RESTRICTIONS (Details)

DIVIDEND RESTRICTIONS (Details)	12 Months Ended
	Dec. 31, 2015
Line of Credit Facility, Dividend Restrictions	CL&P, NSTAR Electric, PSNH and WMECO are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric, PSNH and WMECO, would not be construed or applied by the FERC to prohibit the payment of dividends from retained earnings for lawful and legitimate business purposes. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict the payment of dividends from retained earnings or net income. Pursuant to the joint revolving credit agreement of Eversource, CL&P, PSNH, WMECO, Yankee Gas and NSTAR Gas, and to the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total debt to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter. As of December 31, 2015, all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $2.8 billion for Eversource, $1.2 billion for CL&P, $1.6 billion for NSTAR Electric, $494.9 million for PSNH and $198.1 million for WMECO as of December 31, 2015. As of December 31, 2015, Eversource, CL&P, NSTAR Electric, PSNH, WMECO, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends.
Public Service Company Of New Hampshire [Member]
Statutory Dividend Payment Restrictions Disclosure	PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2015, $13.4 million of PSNH's Retained Earnings was subject to restriction under its FERC hydroelectric license conditions and PSNH was in compliance with this provision.

COMMON SHARES (Details)

COMMON SHARES (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$ 5	$ 5
Common Stock Shares Authorized	380,000,000	380,000,000
Common Stock Shares Issued	333,862,615	333,359,172
Treasury Stock Shares	16,671,366	16,375,835
Common Stock, Shares, Outstanding	317,191,249	316,983,337
Treasury Stock Shares Acquired	532,521
Treasury Stock Acquired Average Cost Per Share	$ 26.02
The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$ 10	$ 10
Common Stock Shares Authorized	24,500,000	24,500,000
Common Stock Shares Issued	6,035,205	6,035,205
NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$ 1	$ 1
Common Stock Shares Authorized	100,000,000	100,000,000
Common Stock Shares Issued	100	100
Public Service Company Of New Hampshire [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$ 1	$ 1
Common Stock Shares Authorized	100,000,000	100,000,000
Common Stock Shares Issued	301	301
Western Massachusetts Electric Company [Member]
Class Of Stock [Line Items]
Common Stock Par Or Stated Value Per Share	$ 25	$ 25
Common Stock Shares Authorized	1,072,471	1,072,471
Common Stock Shares Issued	434,653	434,653

PREFFERED STOCK NOT SUBJECT 100

PREFFERED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (DETAILS) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class Of Stock [Line Items]
Preferred Stock, Value, Outstanding	$ 155,600	$ 155,600
Cash Dividends on Preferred Stock	$ 7,519	7,519	$ 7,682
The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	2,324,000
Preferred Stock, Value, Outstanding	$ 116,200	116,200
Cash Dividends on Preferred Stock	$ 5,559	5,559	5,559
Preferred Stock Authorized Description	The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in Eversource’s financial statements. CL&P is authorized to issue up to 9,000,000 shares of preferred stock, par value $50 per share, and NSTAR Electric is authorized to issue 2,890,000 shares of preferred stock, par value $100 per share. Holders of preferred stock of CL&P and NSTAR Electric are entitled to receive cumulative dividends in preference to any payment of dividends on the common stock. Upon liquidation, holders of preferred stock of CL&P and NSTAR Electric are entitled to receive a liquidation preference before any distribution to holders of common stock in an amount equal to the par value of the preferred stock plus accrued and unpaid dividends. If the net assets were to be insufficient to pay the liquidation preference in full, then the net assets would be distributed ratably to all holders of preferred stock. The preferred stock of CL&P and NSTAR Electric is subject to optional redemption by the CL&P and NSTAR Electric Board of Directors at any time.
NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	430,000
Preferred Stock, Value, Outstanding	$ 43,000	43,000
Cash Dividends on Preferred Stock	$ 1,960	1,961	$ 2,123
Series 1947 $1.90 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	163,912
Preferred Stock, Redemption Price Per Share	$ 52.50
Preferred Stock, Value, Outstanding	$ 8,200	8,200
Series 1947 $2.00 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	336,088
Preferred Stock, Redemption Price Per Share	$ 54
Preferred Stock, Value, Outstanding	$ 16,800	16,800
Series 1949 $2.04 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 52
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1949 $2.20 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 52.50
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series 1949 3.90% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	160,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 8,000	8,000
Series E 1954 $2.06 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series F 1955 $2.09 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 51
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1956 4.5% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	104,000
Preferred Stock, Redemption Price Per Share	$ 50.75
Preferred Stock, Value, Outstanding	$ 5,200	5,200
Series 1958 4.96% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	100,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 5,000	5,000
Series 1963 4.5% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	160,000
Preferred Stock, Redemption Price Per Share	$ 50.50
Preferred Stock, Value, Outstanding	$ 8,000	8,000
Series 1967 5.28% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51.43
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Series G of 1968 $3.24 [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	300,000
Preferred Stock, Redemption Price Per Share	$ 51.84
Preferred Stock, Value, Outstanding	$ 15,000	15,000
Series 1968 6.56% [Member] | The Connecticut Light And Power Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	200,000
Preferred Stock, Redemption Price Per Share	$ 51.44
Preferred Stock, Value, Outstanding	$ 10,000	10,000
Preferred Stock 4.25% [Member] | NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	180,000
Preferred Stock, Redemption Price Per Share	$ 103.625
Preferred Stock, Value, Outstanding	$ 18,000	18,000
Preferred Stock 4.78% [Member] | NSTAR Electric Company [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Outstanding	250,000
Preferred Stock, Redemption Price Per Share	$ 102.80
Preferred Stock, Value, Outstanding	$ 25,000	$ 25,000

COMMON SHAREHOLDER EQUIT AND NC

COMMON SHAREHOLDER EQUIT AND NCI (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shareholders' Equity, Beginning Balance				$ 9,976,815					$ 9,976,815
Net Income	$ 183,700	$ 237,800	$ 209,400	255,100	$ 223,600	$ 236,500	$ 129,200	$ 237,800	886,004	$ 827,065	$ 793,689
Net Income Attributable to Noncontrolling Interests									7,519	7,519	7,682
Other Comprehensive Income (Loss), Net of Tax									7,165	(27,978)	26,823
Shareholders' Equity, Ending Balance	10,352,215				9,976,815				10,352,215	9,976,815
Common Shareholders Equity [Member]
Shareholders' Equity, Beginning Balance											9,237,100
Net Income									886,004	827,065
Dividends on Common Shares									(529,791)	(496,524)	(462,741)
Dividends on Preferred Stock									(7,519)	(7,519)	(7,682)
Issuance of Common Shares									9,468	6,609	11,078
Other Transcations, Net									0	63,600	13,200
Other Comprehensive Income (Loss), Net of Tax									7,165	(27,978)	26,823
Preferred Stock Member
Shareholders' Equity, Beginning Balance				$ 155,600				$ 155,600	155,600	155,600	155,600
Dividends on Preferred Stock									0	(7,500)	(7,700)
Net Income Attributable to Noncontrolling Interests									0	7,500	7,700
Shareholders' Equity, Ending Balance	$ 155,600				$ 155,600				$ 155,600	$ 155,600	$ 155,600

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Notes To Consolidated Financial Statements [Abstract]
Net Income Attributable to Controlling Interests	$ 181,800	$ 235,900	$ 207,500	$ 253,300	$ 221,500	$ 234,600	$ 127,400	$ 236,000	$ 878,485	$ 819,546	$ 786,007
Basic									317,336,881	316,136,748	315,311,387
Weighted Average Number Diluted Shares Outstanding Adjustment									1,095,806	1,280,666	899,773
Diluted									318,432,687	317,417,414	316,211,160
Earnings Per Share Basic And Diluted	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 0.69	$ 0.74	$ 0.40	$ 0.75
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount									1,474	3,643	1,575
Basic Earnings Per Common Share									$ 2.77	$ 2.59	$ 2.49
Diluted Earnings Per Common Share									$ 2.76	$ 2.58	$ 2.49

SEGMENT INFORMATION (Details)

SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,691,200	$ 1,933,100	$ 1,817,100	$ 2,513,400	$ 1,881,200	$ 1,892,500	$ 1,677,600	$ 2,290,600	$ 7,954,827	$ 7,741,856	$ 7,301,204
Operating Income	385,500	469,200	412,000	497,500	430,200	440,900	294,000	467,700	1,764,164	1,632,849	1,529,435
Total Interest Expense									(372,420)	(362,106)	(338,699)
Other Income/(Loss), Net									34,227	24,619	29,894
Income Tax Expense									(539,967)	(468,297)	(426,941)
Net Income	183,700	237,800	209,400	255,100	223,600	236,500	129,200	237,800	886,004	827,065	793,689
Net Income Attributable to Noncontrolling Interests									(7,519)	(7,519)	(7,682)
Net Income Attributable to Controlling Interests	181,800	$ 235,900	$ 207,500	$ 253,300	221,500	$ 234,600	$ 127,400	$ 236,000	878,485	819,546	786,007
Total Assets	30,580,309				29,740,387				30,580,309	29,740,387
Investments in Property, Plant and Equipment									1,724,139	1,603,744	1,456,787
Electric Distribution Member
Segment Reporting Information [Line Items]
Operating Revenues									5,903,600	5,663,400	5,362,300
Depreciation And Amortization									(425,200)	(384,600)	(604,800)
Operating Expenses, Other									(4,470,200)	(4,366,200)	(3,927,700)
Operating Income									1,008,200	912,600	829,800
Total Interest Expense									(186,300)	(191,600)	(175,000)
Interest Income									5,700	5,100	4,100
Other Income/(Loss) Excluding Interest Income									7,200	10,700	12,900
Income Tax Expense									(322,800)	(269,700)	(240,000)
Net Income									512,000	467,100	431,800
Net Income Attributable to Noncontrolling Interests									(4,700)	(4,700)	(4,800)
Net Income Attributable to Controlling Interests									507,300	462,400	427,000
Total Assets	17,981,300				17,536,900				17,981,300	17,536,900
Investments in Property, Plant and Equipment									718,900	645,200	639,000
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues									995,500	1,007,300	855,800
Depreciation And Amortization									(70,500)	(68,100)	(66,700)
Operating Expenses, Other									(776,700)	(786,700)	(659,400)
Operating Income									148,300	152,500	129,700
Total Interest Expense									(36,900)	(34,000)	(33,100)
Interest Income									100	0	0
Other Income/(Loss) Excluding Interest Income									800	200	800
Income Tax Expense									(40,100)	(46,400)	(36,500)
Net Income									72,200	72,300	60,900
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									72,200	72,300	60,900
Total Assets	3,104,500				3,029,300				3,104,500	3,029,300
Investments in Property, Plant and Equipment									182,200	176,700	168,100
Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues									1,069,100	1,018,200	978,700
Depreciation And Amortization									(165,600)	(150,500)	(136,200)
Operating Expenses, Other									(314,900)	(302,100)	(281,800)
Operating Income									588,600	565,600	560,700
Total Interest Expense									(105,800)	(104,100)	(100,300)
Interest Income									1,600	900	700
Other Income/(Loss) Excluding Interest Income									14,500	10,300	10,900
Income Tax Expense									(191,600)	(174,500)	(182,100)
Net Income									307,300	298,200	289,900
Net Income Attributable to Noncontrolling Interests									(2,800)	(2,800)	(2,900)
Net Income Attributable to Controlling Interests									304,500	295,400	287,000
Total Assets	8,019,300				7,615,600				8,019,300	7,615,600
Investments in Property, Plant and Equipment									749,100	731,600	618,500
Other Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues									863,600	790,900	777,500
Depreciation And Amortization									(29,000)	(42,100)	(62,200)
Operating Expenses, Other									(817,900)	(748,000)	(715,000)
Operating Income									16,700	800	300
Total Interest Expense									(48,000)	(36,600)	(35,500)
Interest Income									4,400	3,600	5,400
Other Income/(Loss) Excluding Interest Income									977,800	916,000	858,900
Income Tax Expense									14,500	22,300	31,900
Net Income									965,400	906,100	861,000
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									965,400	906,100	861,000
Total Assets	13,256,700				12,664,900				13,256,700	12,664,900
Investments in Property, Plant and Equipment									73,900	50,200	31,200
Eliminations Segment [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(877,000)	(737,900)	(673,100)
Depreciation And Amortization									2,100	19,900	10,200
Operating Expenses, Other									877,300	719,300	671,800
Operating Income									2,400	1,300	8,900
Total Interest Expense									4,600	4,200	5,200
Interest Income									(5,100)	(3,600)	(5,600)
Other Income/(Loss) Excluding Interest Income									(972,800)	(918,600)	(858,200)
Income Tax Expense									0	0	(200)
Net Income									(970,900)	(916,700)	(849,900)
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income Attributable to Controlling Interests									(970,900)	(916,700)	(849,900)
Total Assets	(11,781,500)				(11,106,300)				(11,781,500)	(11,106,300)
Investments in Property, Plant and Equipment									0	0	0
Total [Member]
Segment Reporting Information [Line Items]
Operating Revenues									7,954,800	7,741,900	7,301,200
Depreciation And Amortization									(688,200)	(625,400)	(859,700)
Operating Expenses, Other									(5,502,400)	(5,483,700)	(4,912,100)
Operating Income									1,764,200	1,632,800	1,529,400
Total Interest Expense									(372,400)	(362,100)	(338,700)
Interest Income									6,700	6,000	4,600
Other Income/(Loss) Excluding Interest Income									27,500	18,600	25,300
Income Tax Expense									(540,000)	(468,300)	(426,900)
Net Income									886,000	827,000	793,700
Net Income Attributable to Noncontrolling Interests									(7,500)	(7,500)	(7,700)
Net Income Attributable to Controlling Interests									878,500	819,500	786,000
Total Assets	$ 30,580,300				$ 29,740,400				30,580,300	29,740,400
Investments in Property, Plant and Equipment									$ 1,724,100	$ 1,603,700	$ 1,456,800

GOODWILL (Details)

GOODWILL (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line item]
Goodwill Acquired During Period	$ 3,200,000
Goodwill		$ 3,519,401	$ 3,519,401
Yankee Gas Services Company [Member]
Goodwill [Line item]
Goodwill		300,000	300,000
Electric Distribution Member
Goodwill [Line item]
Goodwill		2,500,000	2,500,000
Electric Transmission [Member]
Goodwill [Line item]
Goodwill		600,000	600,000
Natural Gas Distribution [Member]
Goodwill [Line item]
Goodwill		$ 400,000	$ 400,000

QUARTERLY FINANCIAL DATA (UN105

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Revenues	$ 1,691,200	$ 1,933,100	$ 1,817,100	$ 2,513,400	$ 1,881,200	$ 1,892,500	$ 1,677,600	$ 2,290,600	$ 7,954,827	$ 7,741,856	$ 7,301,204
Operating Income	385,500	469,200	412,000	497,500	430,200	440,900	294,000	467,700	1,764,164	1,632,849	1,529,435
Net Income	183,700	237,800	209,400	255,100	223,600	236,500	129,200	237,800	886,004	827,065	793,689
Net Income Attributable to Controlling Interests	$ 181,800	$ 235,900	$ 207,500	$ 253,300	$ 221,500	$ 234,600	$ 127,400	$ 236,000	$ 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
Earnings Per Share Basic And Diluted	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 0.69	$ 0.74	$ 0.40	$ 0.75
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 626,900	$ 704,300	$ 666,600	$ 804,900	$ 675,100	$ 695,600	$ 587,300	$ 734,600	$ 2,802,675	$ 2,692,582	$ 2,442,341
Operating Income	154,200	161,100	154,000	141,800	159,000	146,200	92,100	158,000	611,061	555,250	539,576
Net Income	71,200	80,200	78,800	69,200	87,200	83,900	37,400	79,300	299,360	287,754	279,412
NSTAR Electric Company [Member]
Operating Revenues	546,600	750,700	617,200	766,800	581,100	727,900	561,500	666,200	2,681,342	2,536,677	2,493,479
Operating Income	117,700	214,200	151,400	159,500	132,000	206,600	121,500	118,400	642,827	578,456	508,156
Net Income	60,300	118,600	82,000	83,600	69,300	115,600	60,100	58,100	344,542	303,088	268,546
Public Service Company Of New Hampshire [Member]
Operating Revenues	211,100	234,400	241,900	284,800	224,400	223,700	211,600	299,800	972,203	959,500	935,402
Operating Income	49,300	63,600	54,100	63,200	60,000	56,400	49,000	64,000	230,177	229,383	225,219
Net Income	22,000	32,500	27,900	32,000	29,000	28,200	24,100	32,600	114,442	113,944	111,397
Western Massachusetts Electric Company [Member]
Operating Revenues	114,900	125,100	125,200	152,900	129,600	118,100	108,300	137,400	518,128	493,423	472,724
Operating Income	28,000	30,000	28,900	28,600	34,000	31,200	17,700	34,700	115,520	117,639	119,347
Net Income	$ 14,100	$ 15,000	$ 14,200	$ 13,200	$ 18,000	$ 14,700	$ 7,000	$ 18,100	$ 56,506	$ 57,819	$ 60,438

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	$ 175,317	$ 171,251	$ 165,549
Valuation Allowances and Reserves, Charged to Cost and Expense	51,077	55,657	55,465
Valuation Allowances and Reserves, Charged to Other Accounts	79,622	51,227	37,744
Valuation Allowances and Reserves, Deductions	115,336	102,818	87,507
Valuation Allowances and Reserves, Ending Balance	190,680	175,317	$ 171,251
Uncollectible Hardship Accounts Receivable Reserves
The Connecticut Light And Power Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	84,287	81,995	$ 77,571
Valuation Allowances and Reserves, Charged to Cost and Expense	10,105	6,598	3,947
Valuation Allowances and Reserves, Charged to Other Accounts	30,592	39,706	27,258
Valuation Allowances and Reserves, Deductions	45,505	44,012	26,781
Valuation Allowances and Reserves, Ending Balance	79,479	84,287	81,995
NSTAR Electric Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	40,670	41,679	44,115
Valuation Allowances and Reserves, Charged to Cost and Expense	14,228	24,740	28,108
Valuation Allowances and Reserves, Charged to Other Accounts	29,559	627	0
Valuation Allowances and Reserves, Deductions	31,829	26,376	30,544
Valuation Allowances and Reserves, Ending Balance	52,628	40,670	41,679
Public Service Company Of New Hampshire [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	7,663	7,364	6,760
Valuation Allowances and Reserves, Charged to Cost and Expense	8,889	6,815	6,608
Valuation Allowances and Reserves, Charged to Other Accounts	841	797	779
Valuation Allowances and Reserves, Deductions	8,660	7,313	6,783
Valuation Allowances and Reserves, Ending Balance	8,733	7,663	7,364
Western Massachusetts Electric Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Beginning Balance	9,880	9,984	8,501
Valuation Allowances and Reserves, Charged to Cost and Expense	4,940	2,415	2,580
Valuation Allowances and Reserves, Charged to Other Accounts	7,418	3,608	4,299
Valuation Allowances and Reserves, Deductions	8,190	6,127	5,396
Valuation Allowances and Reserves, Ending Balance	$ 14,048	$ 9,880	$ 9,984
Uncollectible Hardship Accounts Receivable Reserves
Yankee Gas Services Company [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Uncollectible Hardship Accounts Receivable Reserves