Western Massachusetts Electric 10-K 23 Feb 17 2016 FY Annual report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2017	Jun. 30, 2016
Document And Entity [Line Items]
Entity Registrant Name	EVERSOURCE ENERGY
Document Period End Date	Dec. 31, 2016
Document Type	10-K
Entity Central Index Key	72,741
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		316,885,808
Entity Public Float			$ 18,939,770,997
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	2,016
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light And Power Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	CONNECTICUT LIGHT & POWER CO
Entity Central Index Key	23,426
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Entity Filer Category	Non-accelerated Filer
Public Service Company Of New Hampshire [Member]
Document And Entity [Line Items]
Entity Registrant Name	PUBLIC SERVICE CO OF NEW HAMPSHIRE
Entity Central Index Key	315,256
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		301
Entity Filer Category	Non-accelerated Filer
Western Massachusetts Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	WESTERN MASSACHUSETTS ELECTRIC CO
Entity Central Index Key	106,170
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		434,653
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	NSTAR ELECTRIC CO
Entity Central Index Key	13,372
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		100
Entity Filer Category	Non-accelerated Filer

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash and Cash Equivalents	$ 30,251	$ 23,947
Receivables, Net	847,301	775,480
Unbilled Revenues	168,490	202,647
Taxes Receivable	80,471	305,359
Fuel, Materials, Supplies and Inventory	328,721	336,476
Regulatory Assets	887,625	845,843
Prepayments and Other Current Assets	134,813	129,034
Total Current Assets	2,477,672	2,618,786
Property, Plant and Equipment, Net	21,350,510	19,892,441
Deferred Debits and Other Assets:
Regulatory Assets	3,638,688	3,737,960
Goodwill	3,519,401	3,519,401
Marketable Securities	544,642	516,478
Other Long-Term Assets	522,260	295,243
Total Deferred Debits and Other Assets	8,224,991	8,069,082
Total Assets	32,053,173	30,580,309
Current Liabilities:
Notes Payable	1,148,500	1,160,953
Long-Term Debt – Current Portion	773,883	228,883
Accounts Payable	884,521	813,646
Regulatory Liabilities	146,787	107,759
Other Current Liabilities	684,914	678,549
Total Current Liabilities	3,638,605	2,989,790
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	5,607,207	5,147,678
Regulatory Liabilities	702,255	513,595
Derivative Liabilities	413,676	337,102
Accrued Pension, SERP and PBOP	1,141,514	1,407,288
Other Long-Term Liabilities	853,260	871,499
Total Deferred Credits and Other Liabilities	8,717,912	8,277,162
Capitalization:
Long-Term Debt	8,829,354	8,805,574
Noncontrolling Interest - Preferred Stock of Subsidiaries	155,568	155,568
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,313
Capital Surplus, Paid In	6,250,224	6,262,368
Retained Earnings	3,175,171	2,797,355
Accumulated Other Comprehensive Loss	(65,282)	(66,844)
Treasury Stock	(317,771)	(309,977)
Common Shareholders' Equity	10,711,734	10,352,215
Total Capitalization	19,696,656	19,313,357
Commitments and Contingencies (Note 11)
Total Liabilities and Capitalization	32,053,173	30,580,309
The Connecticut Light And Power Company [Member]
Current Assets:
Cash and Cash Equivalents	6,579	1,057
Receivables, Net	359,132	352,536
Accounts Receivable from Affiliated Companies	16,851	21,214
Unbilled Revenues	50,373	99,879
Taxes Receivable	19,700	137,643
Materials, Supplies and Inventory	52,050	43,124
Regulatory Assets	335,526	268,318
Prepayments and Other Current Assets	32,970	32,234
Total Current Assets	873,181	956,005
Property, Plant and Equipment, Net	7,632,392	7,156,809
Deferred Debits and Other Assets:
Regulatory Assets	1,391,564	1,369,028
Other Long-Term Assets	137,907	111,115
Total Deferred Debits and Other Assets	1,529,471	1,480,143
Total Assets	10,035,044	9,592,957
Current Liabilities:
Notes Payable to Eversource Parent	80,100	277,400
Long-Term Debt – Current Portion	250,000	0
Accounts Payable	289,532	267,764
Accounts Payable to Affiliated Companies	88,075	66,456
Obligations to Third Party Suppliers	55,520	60,746
Regulatory Liabilities	47,055	61,155
Derivative Liabilities	77,765	91,820
Other Current Liabilities	120,399	110,631
Total Current Liabilities	1,008,446	935,972
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,987,661	1,820,865
Regulatory Liabilities	100,138	74,830
Derivative Liabilities	412,750	336,189
Accrued Pension, SERP and PBOP	300,208	271,056
Other Long-Term Liabilities	123,244	133,446
Total Deferred Credits and Other Liabilities	2,924,001	2,636,386
Capitalization:
Long-Term Debt	2,516,010	2,763,682
Noncontrolling Interest - Preferred Stock of Subsidiaries	116,200	116,200
Common Shareholders' Equity:
Common Shares	60,352	60,352
Capital Surplus, Paid In	2,110,714	1,910,663
Retained Earnings	1,299,374	1,170,278
Accumulated Other Comprehensive Loss	(53)	(576)
Common Shareholders' Equity	3,470,387	3,140,717
Total Capitalization	6,102,597	6,020,599
Commitments and Contingencies (Note 11)
Total Liabilities and Capitalization	10,035,044	9,592,957
NSTAR Electric Company [Member]
Current Assets:
Cash and Cash Equivalents	3,494	3,346
Receivables, Net	257,557	229,936
Accounts Receivable from Affiliated Companies	8,581	4,034
Unbilled Revenues	31,632	29,464
Taxes Receivable	39,738	70,236
Materials, Supplies and Inventory	62,288	75,487
Regulatory Assets	289,400	348,408
Prepayments and Other Current Assets	14,906	11,448
Total Current Assets	707,596	772,359
Property, Plant and Equipment, Net	6,051,835	5,655,458
Deferred Debits and Other Assets:
Regulatory Assets	1,057,746	1,112,977
Prepaid PBOP	95,073	0
Other Long-Term Assets	60,572	62,467
Total Deferred Debits and Other Assets	1,213,391	1,175,444
Total Assets	7,972,822	7,603,261
Current Liabilities:
Notes Payable	126,500	62,500
Long-Term Debt – Current Portion	400,000	200,000
Accounts Payable	232,599	228,250
Accounts Payable to Affiliated Companies	91,532	38,648
Obligations to Third Party Suppliers	55,863	56,718
Renewable Portfolio Standards Compliance Obligations	75,571	104,847
Regulatory Liabilities	63,653	3,281
Other Current Liabilities	71,122	72,007
Total Current Liabilities	1,116,840	766,251
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,836,292	1,760,339
Regulatory Liabilities	391,823	264,352
Accrued Pension, SERP and PBOP	111,827	209,153
Other Long-Term Liabilities	123,194	120,939
Total Deferred Credits and Other Liabilities	2,463,136	2,354,783
Capitalization:
Long-Term Debt	1,678,116	1,829,766
Noncontrolling Interest - Preferred Stock of Subsidiaries	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,045,378	995,378
Retained Earnings	1,625,984	1,613,538
Accumulated Other Comprehensive Loss	368	545
Common Shareholders' Equity	2,671,730	2,609,461
Total Capitalization	4,392,846	4,482,227
Commitments and Contingencies (Note 11)
Total Liabilities and Capitalization	7,972,822	7,603,261
Public Service Company Of New Hampshire [Member]
Current Assets:
Cash and Cash Equivalents	4,646	1,733
Receivables, Net	84,450	77,546
Accounts Receivable from Affiliated Companies	4,185	2,352
Unbilled Revenues	41,004	38,207
Taxes Receivable	6,177	43,128
Fuel, Materials, Supplies and Inventory	162,354	156,868
Regulatory Assets	117,240	104,971
Prepayments and Other Current Assets	22,731	24,302
Total Current Assets	442,787	449,107
Property, Plant and Equipment, Net	3,039,313	2,855,363
Deferred Debits and Other Assets:
Regulatory Assets	245,525	257,873
Other Long-Term Assets	37,720	34,176
Total Deferred Debits and Other Assets	283,245	292,049
Total Assets	3,765,345	3,596,519
Current Liabilities:
Notes Payable to Eversource Parent	160,900	231,300
Long-Term Debt – Current Portion	70,000	0
Accounts Payable	85,716	87,925
Accounts Payable to Affiliated Companies	29,154	24,214
Regulatory Liabilities	12,659	6,898
Other Current Liabilities	43,253	43,921
Total Current Liabilities	401,682	394,258
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	785,385	705,894
Regulatory Liabilities	44,779	47,851
Accrued Pension, SERP and PBOP	94,652	89,579
Other Long-Term Liabilities	49,442	50,746
Total Deferred Credits and Other Liabilities	974,258	894,070
Capitalization:
Long-Term Debt	1,002,048	1,071,017
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	843,134	748,634
Retained Earnings	549,286	494,901
Accumulated Other Comprehensive Loss	(5,063)	(6,361)
Common Shareholders' Equity	1,387,357	1,237,174
Total Capitalization	2,389,405	2,308,191
Commitments and Contingencies (Note 11)
Total Liabilities and Capitalization	3,765,345	3,596,519
Western Massachusetts Electric Company [Member]
Current Assets:
Cash and Cash Equivalents	0	834
Receivables, Net	54,940	50,912
Accounts Receivable from Affiliated Companies	14,425	18,633
Unbilled Revenues	15,329	15,065
Taxes Receivable	1,067	33,407
Materials, Supplies and Inventory	8,618	5,992
Regulatory Assets	64,123	56,166
Prepayments and Other Current Assets	1,528	1,890
Total Current Assets	160,030	182,899
Property, Plant and Equipment, Net	1,678,262	1,575,306
Deferred Debits and Other Assets:
Regulatory Assets	127,291	135,010
Other Long-Term Assets	29,062	24,875
Total Deferred Debits and Other Assets	156,353	159,885
Total Assets	1,994,645	1,918,090
Current Liabilities:
Notes Payable to Eversource Parent	51,000	143,400
Accounts Payable	56,036	58,364
Accounts Payable to Affiliated Companies	19,478	19,896
Obligations to Third Party Suppliers	10,508	9,654
Renewable Portfolio Standards Compliance Obligations	20,383	6,395
Regulatory Liabilities	14,888	13,122
Other Current Liabilities	14,984	13,878
Total Current Liabilities	187,277	264,709
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	490,793	470,539
Regulatory Liabilities	17,227	11,597
Accrued Pension, SERP and PBOP	20,390	19,515
Other Long-Term Liabilities	41,308	36,819
Total Deferred Credits and Other Liabilities	569,718	538,470
Capitalization:
Long-Term Debt	566,536	517,329
Common Shareholders' Equity:
Common Shares	10,866	10,866
Capital Surplus, Paid In	444,398	391,398
Retained Earnings	218,212	198,140
Accumulated Other Comprehensive Loss	(2,362)	(2,822)
Common Shareholders' Equity	671,114	597,582
Total Capitalization	1,237,650	1,114,911
Commitments and Contingencies (Note 11)
Total Liabilities and Capitalization	$ 1,994,645	$ 1,918,090

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Revenues	$ 7,639,129	$ 7,954,827	$ 7,741,856
Operating Expenses:
Purchased Power, Fuel and Transmission	2,500,828	3,086,905	3,021,550
Operations and Maintenance	1,323,549	1,329,289	1,427,589
Depreciation	715,466	665,856	614,657
Amortization of Regulatory Assets, Net	71,696	22,339	10,704
Energy Efficiency Programs	533,659	495,701	473,127
Taxes Other Than Income Taxes	634,072	590,573	561,380
Total Operating Expenses	5,779,270	6,190,663	6,109,007
Operating Income	1,859,859	1,764,164	1,632,849
Interest Expense	400,961	372,420	362,106
Other Income, Net	45,920	34,227	24,619
Income Before Income Tax Expense	1,504,818	1,425,971	1,295,362
Income Tax Expense	554,997	539,967	468,297
Net Income	949,821	886,004	827,065
Net Income Attributable to Noncontrolling Interests	7,519	7,519	7,519
Net Income Attributable to Common Shareholders	$ 942,302	$ 878,485	$ 819,546
Basic Earnings Per Common Share (in dollars per share)	$ 2.97	$ 2.77	$ 2.59
Diluted Earnings Per Common Share (in dollars per share)	$ 2.96	$ 2.76	$ 2.58
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,650,180	317,336,881	316,136,748
Diluted (in shares)	318,454,239	318,432,687	317,417,414
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 2,805,955	$ 2,802,675	$ 2,692,582
Operating Expenses:
Purchased Power, Fuel and Transmission	919,723	1,054,313	982,876
Operations and Maintenance	490,069	487,281	494,578
Depreciation	230,489	215,289	188,837
Amortization of Regulatory Assets, Net	38,765	12,318	59,336
Energy Efficiency Programs	154,015	153,725	156,335
Taxes Other Than Income Taxes	299,719	268,688	255,370
Total Operating Expenses	2,132,780	2,191,614	2,137,332
Operating Income	673,175	611,061	555,250
Interest Expense	144,110	145,795	147,421
Other Income, Net	13,497	11,490	13,376
Income Before Income Tax Expense	542,562	476,756	421,205
Income Tax Expense	208,308	177,396	133,451
Net Income	334,254	299,360	287,754
NSTAR Electric Company [Member]
Operating Revenues	2,557,878	2,681,342	2,536,677
Operating Expenses:
Purchased Power, Fuel and Transmission	953,356	1,190,191	1,122,298
Operations and Maintenance	393,170	306,528	326,972
Depreciation	213,115	196,770	188,693
Amortization of Regulatory Assets/(Liabilities), Net	30,083	(12,989)	(6,330)
Energy Efficiency Programs	277,608	224,755	193,516
Taxes Other Than Income Taxes	136,759	133,260	133,072
Total Operating Expenses	2,004,091	2,038,515	1,958,221
Operating Income	553,787	642,827	578,456
Interest Expense	84,005	75,347	77,878
Other Income, Net	10,690	5,106	4,491
Income Before Income Tax Expense	480,472	572,586	505,069
Income Tax Expense	187,767	228,044	201,981
Net Income	292,705	344,542	303,088
Public Service Company Of New Hampshire [Member]
Operating Revenues	959,482	972,203	959,500
Operating Expenses:
Purchased Power, Fuel and Transmission	210,786	247,721	313,732
Operations and Maintenance	260,779	276,554	261,848
Depreciation	116,519	105,372	98,436
Amortization of Regulatory Assets/(Liabilities), Net	11,170	16,276	(29,602)
Energy Efficiency Programs	14,204	14,324	14,286
Taxes Other Than Income Taxes	82,964	81,779	71,417
Total Operating Expenses	696,422	742,026	730,117
Operating Income	263,060	230,177	229,383
Interest Expense	50,040	45,990	45,349
Other Income, Net	1,329	3,315	2,045
Income Before Income Tax Expense	214,349	187,502	186,079
Income Tax Expense	82,364	73,060	72,135
Net Income	131,985	114,442	113,944
Western Massachusetts Electric Company [Member]
Operating Revenues	484,192	518,128	493,423
Operating Expenses:
Purchased Power, Fuel and Transmission	131,449	177,172	172,876
Operations and Maintenance	96,712	86,360	89,406
Depreciation	46,147	43,362	41,886
Amortization of Regulatory Assets/(Liabilities), Net	4,249	14,545	(6,228)
Energy Efficiency Programs	44,179	42,867	42,937
Taxes Other Than Income Taxes	41,079	38,302	34,907
Total Operating Expenses	363,815	402,608	375,784
Operating Income	120,377	115,520	117,639
Interest Expense	24,425	24,792	24,931
Other Income, Net	142	2,748	2,379
Income Before Income Tax Expense	96,094	93,476	95,087
Income Tax Expense	38,022	36,970	37,268
Net Income	$ 58,072	$ 56,506	$ 57,819

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income	$ 949,821	$ 886,004	$ 827,065
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	2,137	2,079	2,037
Changes in Unrealized Gains/(Losses) on Marketable Securities	2,294	(2,588)	315
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(2,869)	7,674	(30,330)
Other Comprehensive Income/(Loss), Net of Tax	1,562	7,165	(27,978)
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Comprehensive Income	943,864	885,650	791,568
The Connecticut Light And Power Company [Member]
Net Income	334,254	299,360	287,754
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	444	444	444
Changes in Unrealized Gains/(Losses) on Marketable Securities	79	(89)	12
Other Comprehensive Income/(Loss), Net of Tax	523	355	456
Comprehensive Income	334,777	299,715	288,210
NSTAR Electric Company [Member]
Net Income	292,705	344,542	303,088
Other Comprehensive Income/(Loss), Net of Tax:
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(177)	103	442
Other Comprehensive Income/(Loss), Net of Tax	(177)	103	442
Comprehensive Income	292,528	344,645	303,530
Public Service Company Of New Hampshire [Member]
Net Income	131,985	114,442	113,944
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	1,162	1,162	1,162
Changes in Unrealized Gains/(Losses) on Marketable Securities	136	(154)	19
Other Comprehensive Income/(Loss), Net of Tax	1,298	1,008	1,181
Comprehensive Income	133,283	115,450	115,125
Western Massachusetts Electric Company [Member]
Net Income	58,072	56,506	57,819
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	438	379	338
Changes in Unrealized Gains/(Losses) on Marketable Securities	22	(25)	3
Other Comprehensive Income/(Loss), Net of Tax	460	354	341
Comprehensive Income	$ 58,532	$ 56,860	$ 58,160

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares [Member]	Capital Surplus, Paid In [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]	The Connecticut Light And Power Company [Member]	The Connecticut Light And Power Company [Member]Common Shares [Member]	The Connecticut Light And Power Company [Member]Capital Surplus, Paid In [Member]	The Connecticut Light And Power Company [Member]Retained Earnings [Member]	The Connecticut Light And Power Company [Member]Accumulated Other Comprehensive Loss [Member]	NSTAR Electric Company [Member]	NSTAR Electric Company [Member]Common Shares [Member]	NSTAR Electric Company [Member]Capital Surplus, Paid In [Member]	NSTAR Electric Company [Member]Retained Earnings [Member]	NSTAR Electric Company [Member]Accumulated Other Comprehensive Loss [Member]	Public Service Company Of New Hampshire [Member]	Public Service Company Of New Hampshire [Member]Common Shares [Member]	Public Service Company Of New Hampshire [Member]Capital Surplus, Paid In [Member]	Public Service Company Of New Hampshire [Member]Retained Earnings [Member]	Public Service Company Of New Hampshire [Member]Accumulated Other Comprehensive Loss [Member]	Western Massachusetts Electric Company [Member]	Western Massachusetts Electric Company [Member]Common Shares [Member]	Western Massachusetts Electric Company [Member]Capital Surplus, Paid In [Member]	Western Massachusetts Electric Company [Member]Retained Earnings [Member]	Western Massachusetts Electric Company [Member]Accumulated Other Comprehensive Loss [Member]
Beginning Balance (in shares) at Dec. 31, 2013		315,273,559						6,035,205					100					301					434,653
Beginning balance at Dec. 31, 2013	$ 9,611,528	$ 1,665,351	$ 6,192,765	$ 2,125,980	$ (326,537)	$ (46,031)	$ 2,702,494	$ 60,352	$ 1,682,047	$ 961,482	$ (1,387)	$ 2,413,453	$ 0	$ 992,625	$ 1,420,828	$ 0	$ 1,131,876	$ 0	$ 701,911	$ 438,515	$ (8,550)	$ 579,106	$ 10,866	$ 390,743	$ 181,014	$ (3,517)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	827,065			827,065			287,754			287,754		303,088			303,088		113,944			113,944		57,819			57,819
Dividends on Common Stock	(496,524)			(496,524)			(171,200)			(171,200)		(253,000)			(253,000)		(66,000)			(66,000)		(59,999)			(59,999)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,961)			(1,961)
Allocation of Benefits - ESOP							2,771		2,771								1,329		1,329			513		513
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent							120,000		120,000								45,000		45,000
Issuance of Common Shares (in shares)		288,941
Issuance of Common Shares	6,609	$ 1,445	5,164
Long-Term Incentive Plan Activity	(9,569)		(9,569)
Increase in Treasury Shares (in shares)		1,420,837
Increase in Treasury Shares	63,887		37,817		26,070
Other Changes in Shareholders' Equity	9,316		9,657	(341)								1,505		1,505
Other Comprehensive Income (Loss)	(27,978)					(27,978)	456				456	442				442	1,181				1,181	341				341
Ending Balance (in shares) at Dec. 31, 2014		316,983,337						6,035,205					100					301					434,653
Ending balance at Dec. 31, 2014	9,976,815	$ 1,666,796	6,235,834	2,448,661	(300,467)	(74,009)	2,936,767	$ 60,352	1,804,869	1,072,477	(931)	2,463,527	$ 0	994,130	1,468,955	442	1,227,330	$ 0	748,240	486,459	(7,369)	577,780	$ 10,866	391,256	178,834	(3,176)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	886,004			886,004			299,360			299,360		344,542			344,542		114,442			114,442		56,506			56,506
Dividends on Common Stock	(529,791)			(529,791)			(196,000)			(196,000)		(197,999)			(197,999)		(106,000)			(106,000)		(37,200)			(37,200)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Allocation of Benefits - ESOP							743		743								394		394			142		142
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent							105,000		105,000
Issuance of Common Shares (in shares)		503,443
Issuance of Common Shares	9,468	$ 2,517	6,951
Long-Term Incentive Plan Activity	(6,140)		(6,140)
Increase in Treasury Shares (in shares)		(295,531)
Increase in Treasury Shares	12,560		22,070		(9,510)
Other Changes in Shareholders' Equity	3,653		3,653									1,248		1,248
Other Comprehensive Income (Loss)	7,165					7,165	355				355	103				103	1,008				1,008	354
Ending Balance (in shares) at Dec. 31, 2015		317,191,249						6,035,205					100					301					434,653
Ending balance at Dec. 31, 2015	10,352,215	$ 1,669,313	6,262,368	2,797,355	(309,977)	(66,844)	3,140,717	$ 60,352	1,910,663	1,170,278	(576)	2,609,461	$ 0	995,378	1,613,538	545	1,237,174	$ 0	748,634	494,901	(6,361)	597,582	$ 10,866	391,398	198,140	(2,822)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	949,821			949,821			334,254					292,705					131,985					58,072
Dividends on Common Stock	(564,486)			(564,486)			(199,599)			(199,599)		(278,299)			(278,299)		(77,600)			(77,600)		(38,000)			(38,000)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent							200,000		200,000			50,000		50,000			94,500		94,500			53,000		53,000
Issuance of Common Shares (in shares)		15,787
Issuance of Common Shares	(5,560)	$ 79	(5,639)
Long-Term Incentive Plan Activity	(6,056)		(6,056)
Increase in Treasury Shares (in shares)		(321,228)
Increase in Treasury Shares	(7,794)				(7,794)
Other Changes in Shareholders' Equity	(449)		(449)
Other Comprehensive Income (Loss)	1,562					1,562	523				523	(177)				(177)	1,298				1,298	460				460
Ending Balance (in shares) at Dec. 31, 2016		316,885,808						6,035,205					100					301					434,653
Ending balance at Dec. 31, 2016	$ 10,711,734	$ 1,669,392	$ 6,250,224	$ 3,175,171	$ (317,771)	$ (65,282)	$ 3,470,387	$ 60,352	$ 2,110,714	$ 1,299,374	$ (53)	$ 2,671,730	$ 0	$ 1,045,378	$ 1,625,984	$ 368	$ 1,387,357	$ 0	$ 843,134	$ 549,286	$ (5,063)	$ 671,114	$ 10,866	$ 444,398	$ 218,212	$ (2,362)

CONSOLIDATED STATEMENTS OF COM6

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Stockholders' Equity [Abstract]
Dividends on Common Shares (in dollars per share)	$ 1.78	$ 1.67	$ 1.57
Per Share Par Value (in dollars per share)	$ 5	$ 5	$ 5

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities:
Net Income	$ 949,821	$ 886,004	$ 827,065
Provided by Operating Activities:
Depreciation	715,466	665,856	614,657
Deferred Income Taxes	466,463	491,736	443,259
Pension, SERP and PBOP Expense	39,912	96,017	99,056
Pension and PBOP Contributions	(158,741)	(162,452)	(211,649)
Regulatory Over/(Under) Recoveries, Net	13,340	(163,287)	6,853
Amortization of Regulatory Assets, Net	71,696	22,339	10,704
Refunds/(Payments) Related to Spent Nuclear Fuel, Net	59,804	(297,253)	132,138
Other	(77,294)	(82,219)	56,026
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(142,699)	(39,797)	(122,139)
Fuel, Materials, Supplies and Inventory	7,755	34,112	(41,310)
Taxes Receivable/Accrued, Net	234,543	30,282	(323,224)
Accounts Payable	(14,126)	(91,618)	144,743
Other Current Assets and Liabilities, Net	9,112	44,031	15,797
Net Cash Flows Provided by Operating Activities	2,175,052	1,433,751	1,651,976
Investing Activities:
Investments in Property, Plant and Equipment	(1,976,867)	(1,724,139)	(1,603,744)
Proceeds from Sales of Marketable Securities	659,338	799,165	488,789
Purchases of Marketable Securities	(681,272)	(717,114)	(491,220)
Payments to Acquire Investments	(188,958)	(23,353)	(9,779)
Other Investing Activities	36,951	6,291	24,159
Net Cash Flows Used in Investing Activities	(2,150,808)	(1,659,150)	(1,591,795)
Financing Activities:
Cash Dividends on Common Shares	(564,486)	(529,791)	(475,227)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,519)
Increase/(Decrease) in Short-Term Debt	(12,453)	(242,122)	285,075
Issuance of Long-Term Debt	800,000	1,225,000	725,000
Retirements of Long-Term Debt	(200,000)	(216,700)	(576,551)
Other Financing Activities	(33,482)	(18,225)	(15,620)
Net Cash Flows (Used in)/Provided by Financing Activities	(17,940)	210,643	(64,842)
Net Increase/(Decrease) in Cash and Cash Equivalents	6,304	(14,756)	(4,661)
Cash and Cash Equivalents - Beginning of Year	23,947	38,703	43,364
Cash and Cash Equivalents - End of Year	30,251	23,947	38,703
The Connecticut Light And Power Company [Member]
Operating Activities:
Net Income	334,254	299,360	287,754
Provided by Operating Activities:
Depreciation	230,489	215,289	188,837
Deferred Income Taxes	168,919	135,994	130,949
Pension, SERP and PBOP Expense	6,948	14,091	14,992
Regulatory Over/(Under) Recoveries, Net	(68,730)	(53,781)	(20,502)
Amortization of Regulatory Assets, Net	38,765	12,318	59,336
Refunds/(Payments) Related to Spent Nuclear Fuel, Net	13,568	(242,231)	68,610
Other	(32,212)	(36,385)	(1,342)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	3,229	(29,195)	(78,631)
Fuel, Materials, Supplies and Inventory	(8,926)	22,810	13,063
Taxes Receivable/Accrued, Net	123,692	(13,517)	(126,376)
Accounts Payable	3,252	(16,910)	68,891
Other Current Assets and Liabilities, Net	(1,770)	(9,514)	6,838
Net Cash Flows Provided by Operating Activities	811,478	298,329	612,419
Investing Activities:
Investments in Property, Plant and Equipment	(611,984)	(523,849)	(515,710)
Proceeds from the Sale of Property, Plant and Equipment	9,047	0	4,918
Other Investing Activities	296	(716)	7,735
Net Cash Flows Used in Investing Activities	(602,641)	(524,565)	(503,057)
Financing Activities:
Cash Dividends on Common Shares	(199,599)	(196,000)	(171,200)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
(Decrease)/Increase in Notes Payable to Eversource Parent	(197,300)	144,000	(153,900)
Issuance of Long-Term Debt	0	350,000	250,000
Retirements of Long-Term Debt	0	(162,000)	(150,000)
Capital Contributions from Eversource Parent	200,000	105,000	120,000
Other Financing Activities	(857)	(10,504)	(3,584)
Net Cash Flows (Used in)/Provided by Financing Activities	(203,315)	224,937	(114,243)
Net Increase/(Decrease) in Cash and Cash Equivalents	5,522	(1,299)	(4,881)
Cash and Cash Equivalents - Beginning of Year	1,057	2,356	7,237
Cash and Cash Equivalents - End of Year	6,579	1,057	2,356
NSTAR Electric Company [Member]
Operating Activities:
Net Income	292,705	344,542	303,088
Provided by Operating Activities:
Depreciation	213,115	196,770	188,693
Deferred Income Taxes	80,200	173,155	108,133
Pension, SERP and PBOP Expense	(327)	10,786	6,760
Pension and PBOP Contributions	(37,305)	(9,886)	(120,306)
Regulatory Over/(Under) Recoveries, Net	117,795	(124,323)	57,696
Amortization of Regulatory Assets/(Liabilities), Net	30,083	(12,989)	(6,330)
Bad Debt Expense	27,978	14,228	24,740
Refunds/(Payments) Related to Spent Nuclear Fuel, Net	4,983	783	30,193
Other	(52,326)	(56,063)	(51,478)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(58,591)	(35,525)	(18,853)
Fuel, Materials, Supplies and Inventory	13,198	406	(29,943)
Taxes Receivable/Accrued, Net	27,434	77,429	(122,746)
Accounts Payable	(32,969)	21,961	9,753
Accounts Receivable from/Payable to Affiliates, Net	48,337	11,450	115,092
Other Current Assets and Liabilities, Net	(32,920)	44,302	38,535
Net Cash Flows Provided by Operating Activities	641,390	657,026	533,027
Investing Activities:
Investments in Property, Plant and Equipment	(524,306)	(469,466)	(465,028)
Net Cash Flows Used in Investing Activities	(524,306)	(469,466)	(465,028)
Financing Activities:
Cash Dividends on Common Shares	(278,299)	(197,999)	(253,000)
Cash Dividends on Preferred Stock	(1,960)	(1,960)	(1,961)
Increase/(Decrease) in Short-Term Debt	64,000	(239,500)	198,500
Issuance of Long-Term Debt	250,000	250,000	300,000
Retirements of Long-Term Debt	(200,000)	(4,700)	(301,650)
Capital Contributions from Eversource Parent	50,000	0	0
Other Financing Activities	(677)	(2,828)	(5,136)
Net Cash Flows (Used in)/Provided by Financing Activities	(116,936)	(196,987)	(63,247)
Net Increase/(Decrease) in Cash and Cash Equivalents	148	(9,427)	4,752
Cash and Cash Equivalents - Beginning of Year	3,346	12,773	8,021
Cash and Cash Equivalents - End of Year	3,494	3,346	12,773
Public Service Company Of New Hampshire [Member]
Operating Activities:
Net Income	131,985	114,442	113,944
Provided by Operating Activities:
Depreciation	116,519	105,372	98,436
Deferred Income Taxes	87,345	83,776	94,813
Pension, SERP and PBOP Expense	875	4,580	7,197
Pension and PBOP Contributions	(17,078)	(982)	(2,482)
Regulatory Over/(Under) Recoveries, Net	(4,491)	41	(11,875)
Amortization of Regulatory Assets/(Liabilities), Net	11,170	16,276	(29,602)
Refunds/(Payments) Related to Spent Nuclear Fuel, Net	3,926	979	14,453
Other	6,521	8,677	10,095
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(18,822)	(4,750)	(15,576)
Fuel, Materials, Supplies and Inventory	(5,485)	(8,729)	(19,403)
Taxes Receivable/Accrued, Net	32,303	(23,909)	(23,857)
Accounts Payable	11,353	(22,203)	17,796
Other Current Assets and Liabilities, Net	5,651	953	(5,972)
Net Cash Flows Provided by Operating Activities	361,772	274,523	247,967
Investing Activities:
Investments in Property, Plant and Equipment	(305,430)	(308,036)	(256,159)
Other Investing Activities	326	306	(1,152)
Net Cash Flows Used in Investing Activities	(305,104)	(307,730)	(257,311)
Financing Activities:
Cash Dividends on Common Shares	(77,600)	(106,000)	(66,000)
(Decrease)/Increase in Notes Payable to Eversource Parent	(70,400)	140,800	4,000
Issuance of Long-Term Debt	0	0	75,000
Retirements of Long-Term Debt	0	0	(50,000)
Capital Contributions from Eversource Parent	94,500	0	45,000
Other Financing Activities	(255)	(349)	1,703
Net Cash Flows (Used in)/Provided by Financing Activities	(53,755)	34,451	9,703
Net Increase/(Decrease) in Cash and Cash Equivalents	2,913	1,244	359
Cash and Cash Equivalents - Beginning of Year	1,733	489	130
Cash and Cash Equivalents - End of Year	4,646	1,733	489
Western Massachusetts Electric Company [Member]
Operating Activities:
Net Income	58,072	56,506	57,819
Provided by Operating Activities:
Depreciation	46,147	43,362	41,886
Deferred Income Taxes	21,498	39,428	34,108
Regulatory Over/(Under) Recoveries, Net	590	(17,501)	1,925
Amortization of Regulatory Assets/(Liabilities), Net	4,249	14,545	(6,228)
Refunds/(Payments) Related to Spent Nuclear Fuel, Net	3,553	(56,784)	18,883
Other	(3,726)	(6,421)	(2,005)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(7,164)	(17,822)	39,872
Taxes Receivable/Accrued, Net	33,340	(15,281)	(22,454)
Accounts Payable	(1,915)	(2,602)	1,269
Other Current Assets and Liabilities, Net	12,686	5,594	(11,796)
Net Cash Flows Provided by Operating Activities	167,330	43,024	153,279
Investing Activities:
Investments in Property, Plant and Equipment	(140,626)	(134,551)	(116,205)
Proceeds from Sales of Marketable Securities	2,479	186,444	73,198
Purchases of Marketable Securities	(2,426)	(128,861)	(73,888)
Other Investing Activities	0	0	3,200
Net Cash Flows Used in Investing Activities	(140,573)	(76,968)	(113,695)
Financing Activities:
Cash Dividends on Common Shares	(38,000)	(37,200)	(59,999)
(Decrease)/Increase in Notes Payable to Eversource Parent	(92,400)	122,000	21,400
Issuance of Long-Term Debt	50,000	0	0
Retirements of Long-Term Debt	0	(50,000)	0
Capital Contributions from Eversource Parent	53,000
Other Financing Activities	(191)	(22)	(985)
Net Cash Flows (Used in)/Provided by Financing Activities	(27,591)	34,778	(39,584)
Net Increase/(Decrease) in Cash and Cash Equivalents	(834)	834	0
Cash and Cash Equivalents - Beginning of Year	834	0	0
Cash and Cash Equivalents - End of Year	$ 0	$ 834	$ 0

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	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 3.7 million electric and natural gas customers through these six regulated utilities in Connecticut, Massachusetts and New Hampshire. 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 customers 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 their respective generation operations. 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 Service, Eversource's service company, and several wholly-owned real estate subsidiaries of Eversource, provide support services to Eversource, including its Regulated companies. Eversource holds several equity ownership interests, which are accounted for under the equity method. Eversource also consolidates the operations of CYAPC and YAEC, both of which are inactive regional nuclear generation companies engaged in the long-term storage of their spent nuclear fuel. 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 assets) 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 reclassifications 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 the 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 Boards 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, 2016 and 2015 , 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, 2016 and determined that no impairment exists. See Note 22, "Goodwill," for further information. C. Accounting Standards A ccounting 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). The Company is evaluating the requirements and potential impacts of ASU 2014-09 and will implement the standard in the first quarter of 2018 cumulatively at the date of initial application. The guidance continues to be interpreted on an industry specific level, including the timing of recognizing revenues from billings to protected customers that may not meet the collectibility threshold for revenue recognition. Therefore, while the effects of implementing the ASU on results of operations are not expected to be material, there may be changes in the timing of revenue recognition on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH and WMECO. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Liabilities , which is required to be implemented in the first quarter of 2018. The ASU will remove the available-for-sale designation for equity securities, whereby changes in fair value are recorded in accumulated other comprehensive income within 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. The fair value of available-for-sale equity securities subject to this guidance as of December 31, 2016 was approximately $48 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 and WMECO. In February 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, including balance sheet recognition of leases previously deemed operating leases, and expects to implement the ASU in the first quarter of 2019. Recently Adopted Accounting Standards In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation: Improvements to Employee Share-Based Payment Accounting to simplify some aspects of the accounting for share-based payment transactions. The Company implemented this guidance in the first quarter of 2016, as permitted. Beginning in the first quarter of 2016, the excess tax benefits associated with the distribution of stock compensation awards, previously recognized in Capital Surplus, Paid In within Common Shareholders' Equity on the balance sheet, are recognized in income tax expense in the income statement. The impact of this ASU reduced income tax expense by $19.1 million for the year ended December 31, 2016 . Also, in the statement of cash flows, the excess tax benefits are presented as an operating activity rather than a financing activity beginning in 2016, and cash paid to satisfy the statutory income tax withholding obligation previously reflected within operating activities in 2015 and 2014 was retrospectively adjusted and is now treated as a financing activity. The cash payments to satisfy this obligation for the years ended December 31, 2016 , 2015 and 2014 were $26.6 million , $9.7 million and $16.5 million , respectively, and are included in Other Financing Activities on the statements of cash flows. 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 management's assessment of collectability from customers. Management continuously assesses the collectability of receivables and adjusts collectability 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 also to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. Certain of NSTAR Electric's uncollectible hardship accounts receivable are expected to be recovered in future rates, similar to WMECO and NSTAR Gas. These uncollectible customer account balances 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 were as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2016 2015 2016 2015 Eversource $ 200.6 $ 190.7 $ 119.9 $ 118.5 CL&P 86.4 79.5 67.7 68.1 NSTAR Electric 54.8 52.6 26.2 25.3 PSNH 9.9 8.7 — — WMECO 15.5 14.0 9.9 7.4 F. Fuel, Materials, Supplies and Inventory Fuel, Materials, Supplies and Inventory include natural gas, coal, biomass and oil inventories, materials and supplies purchased primarily for construction or operation and maintenance purposes, RECs and emission allowances. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and 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 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, Supplies and Inventory on the balance sheet and are classified as current or long-term depending on the period in which they are expected to be utilized against actual emissions. The carrying amounts of fuel, materials and supplies, RECs, and emission allowances were as follows: As of December 31, 2016 2015 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Eversource CL&P NSTAR Electric PSNH WMECO Current: Fuel $ 135.7 $ — $ — $ 99.9 $ — $ 152.5 $ — $ — $ 103.4 $ — Materials and Supplies 142.7 48.2 34.5 47.3 5.2 131.2 43.1 32.2 44.6 5.4 RECs 47.9 3.9 27.8 12.8 3.4 50.9 — 43.3 7.0 0.6 Emission Allowances 2.4 — — 2.4 — 1.9 — — 1.9 — Long-Term: Emission Allowances 17.5 — — 17.5 — 17.5 — — 17.5 — Deposits As of December 31, 2016 , Eversource, CL&P, NSTAR Electric and PSNH had $21.7 million , $1.4 million , $11.8 million and $0.5 million , respectively, of cash collateral posted not subject to master netting agreements, with ISO-NE related to energy transactions, which was included in Prepayments and Other Current Assets on the balance sheets. As of December 31, 2015 , these amounts were $17.1 million , $0.7 million , $8.5 million and $1.5 million for Eversource, CL&P, NSTAR Electric 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 estimated 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 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. Certain investments held in the Pension and PBOP plans have been valued using net asset value ("NAV") as a practical expedient. These investments are not traded on an exchange and are typically structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. They include commingled funds, private equity funds, real estate funds and hedge funds. In 2016, Eversource retrospectively adopted new accounting guidance that requires investments for which fair value is measured using the NAV practical expedient no longer be classified within the fair value hierarchy. Investments valued using the NAV practical expedient are included separately in fair value disclosures and are not classified within any of the fair value hierarchy levels. Prior to the adoption of this guidance, these investments were reported within Level 2 or Level 3 of the fair value hierarchy. The adoption of this guidance changes fair value disclosures, but does not impact the methodology for valuing these investments, or the financial statement results. See Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other than Pensions" for the fair value disclosures of the Pension and PBOP plan assets. Determination of Fair Value: The valuation techniques and inputs used in Eversource's fair value measurements are described in Note 4, "Derivative Instruments," Note 5, "Marketable Securities," Note 6, "Asset Retirement Obligations," Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pensions," and Note 14, "Fair Value of Financial Instruments" to the financial statements. I. Derivative Accounting Many of the Regulated companies' contracts for the purchase and sale of energy 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 significant impact on the financial statements. The judgment 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 changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income. For further information regarding derivative contracts, see Note 4, "Derivative Instruments," to the financial statements. J. Investments Investments are included in Other Long-Term Assets on the balance sheets and earnings impacts from equity investments are included in Other Income, Net on the statements of income. Strategic, Infrastructure and Other Investments: As of December 31, 2016 and 2015 , Eversource had investments totaling $236.9 million and $48.0 million , respectively. As of December 31, 2016, Eversource had a 15 percent ownership interest in a FERC-regulated transmission business of $154.6 million . As of December 31, 2016 and 2015 , Eversource's investments included a 40 percent ownership interest in Access Northeast of $30.9 million and $10.7 million , respectively, a 37.2 percent ( 14.5 percent of which related to NSTAR Electric) ownership interest in two companies that transmit electricity imported from the Hydro-Quebec system in Canada of $7.7 million and $7.0 million , respectively, and other investments totaling $43.7 million and $30.3 million , respectively. NSTAR Electric's investments totaled $3.0 million and $2.7 million , respectively, as of December 31, 2016 and 2015 . 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 decommissioned. For CL&P, NSTAR Electric, PSNH and WMECO, the respective investments in CYAPC, YAEC and MYAPC are accounted for under the equity method and are included in Other Long-Term Assets on their respective balance sheets. 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. For further information on the Yankee Companies, see Note 11C, "Commitments and Contingencies – Spent Nuclear Fuel Obligations – Yankee Companies," to the financial statements. K. Revenues Regulated Companies' Retail Revenues: The Regulated companies' retail revenues are based on rates approved by their 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 rates to be changed periodically to ensure recovery of actual costs incurred. CL&P, WMECO and NSTAR Gas each have a regulatory commission approved revenue decoupling mechanism. NSTAR Gas' decoupling mechanism was effective January 1, 2016. Distribution revenues are decoupled from customer sales volumes, where applicable, which breaks the relationship between sales volumes and revenues recognized. CL&P, WMECO and NSTAR Gas 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 is adjusted through rates in a subsequent 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 customers in rates through cost tracking mechanisms. Energy purchases are recorded in Purchased Power, Fuel and Transmission, and the sales of energy associated with these purchases are recorded in Operating Revenues on the statements of income. 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 Assets 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 volumes monthly by first allocating billed sales volumes to the current calendar month based on the daily load (for electric distribution companies) or the daily send-out (for natural gas distribution companies) for each billing cycle. The billed sales volumes are then subtracted from total month load or send-out, net of delivery losses, to estimate unbilled sales volumes. Unbilled revenues are estimated by first allocating unbilled sales volumes to the respective customer classes, then applying an estimated rate by customer class to those sales volumes. The estimate of unbilled revenues can significantly impact the amount of revenues recorded at NSTAR Electric, PSNH and Yankee Gas because they do not have a revenue decoupling mechanism. CL&P, WMECO and NSTAR Gas record a regulatory deferral to reflect the actual allowed amount of revenue associated with their respective decoupled distribution rate design. Regulated Companies' Transmission Revenues - Wholesale Rates: The Eversource transmission owning companies have a combination of FERC-approved regional and local formula rates that work in tandem to recover all their transmission costs. These rates are part of the ISO-NE Tariff. Regional rates recover the costs of higher voltage transmission facilities that benefit the region, and are collected from all New England transmission customers, including the Eversource distribution businesses. Eversource has two sets of local rates, one for the combined transmission revenue requirements of CL&P, PSNH and WMECO, and the other for NSTAR Electric. These local rates recover the companies' total transmission revenue requirements, less revenues received from regional rates and other sources, and are collected from Eversource's distribution businesses and other transmission customers. The distribution businesses of Eversource, in turn, recover the FERC approved charges from retail customers through annual or semiannual tracking mechanisms. The transmission formula rates 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, "Commitments 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 Purchased Power, Fuel and Transmission on the statements of income were as follows: For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Eversource - Natural Gas and Fuel $ 372.2 $ 516.7 $ 599.4 PSNH - Fuel 45.0 85.4 113.4 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 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) 2016 2015 2014 Borrowed Funds $ 10.8 $ 7.2 $ 5.8 Equity Funds 26.2 18.8 13.7 Total AFUDC $ 37.0 $ 26.0 $ 19.5 Average AFUDC Rate 4.4 % 3.9 % 3.4 % For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars, except percentages) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Borrowed Funds $ 3.3 $ 4.6 $ 0.8 $ 0.6 $ 2.6 $ 2.0 $ 1.0 $ 1.0 $ 1.9 $ 2.0 $ 0.6 $ 0.9 Equity Funds 6.3 10.2 0.3 — 5.2 4.3 1.2 1.7 2.9 3.8 0.6 1.7 Total AFUDC $ 9.6 $ 14.8 $ 1.1 $ 0.6 $ 7.8 $ 6.3 $ 2.2 $ 2.7 $ 4.8 $ 5.8 $ 1.2 $ 2.6 Average AFUDC Rate 4.7 % 3.9 % 1.0 % 0.8 % 5.5 % 3.2 % 1.8 % 4.4 % 3.4 % 2.5 % 1.8 % 5.6 % 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 income/(loss) related to equity method investees. Investment income/(loss) primarily relates to debt and equity securities held in trust. For further information on gains/(losses) related to debt and equity securities, 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 respective customers. These gross receipts taxes are shown separately with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the statements of income as follows: For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Eversource $ 162.7 $ 147.2 $ 148.2 CL&P 145.2 128.5 127.9 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. P. Supplemental Cash Flow Information Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2016 2015 2014 Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 398.1 $ 365.9 $ 349.6 Income Taxes (135.5 ) 10.3 334.2 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 301.5 216.6 181.9 As of and For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 143.3 $ 88.2 $ 46.5 $ 24.7 $ 144.

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
REGULATORY ACCOUNTING	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 considers 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 its 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 Regulated 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 components of regulatory assets were as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Benefit Costs $ 1,817.8 $ 1,828.2 Derivative Liabilities 423.3 388.0 Income Taxes, Net 644.5 650.9 Storm Restoration Costs 385.3 436.9 Goodwill-related 464.4 484.9 Regulatory Tracker Mechanisms 576.6 526.5 Contractual Obligations - Yankee Companies 84.9 134.4 Other Regulatory Assets 129.5 134.0 Total Regulatory Assets 4,526.3 4,583.8 Less: Current Portion 887.6 845.8 Total Long-Term Regulatory Assets $ 3,638.7 $ 3,738.0 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR PSNH WMECO Benefit Costs $ 429.3 $ 438.6 $ 184.2 $ 86.7 $ 413.6 $ 479.9 $ 164.2 $ 84.9 Derivative Liabilities 420.5 2.8 — — 380.8 1.3 — — Income Taxes, Net 437.0 89.7 24.2 30.8 444.4 85.7 34.5 31.8 Storm Restoration Costs 239.8 112.5 17.1 15.9 271.4 110.9 31.5 23.1 Goodwill-related — 398.7 — — — 416.3 — — Regulatory Tracker Mechanisms 123.9 257.3 104.5 46.7 45.1 311.0 101.2 40.1 Other Regulatory Assets 76.6 47.5 32.7 11.3 82.0 56.3 31.5 11.3 Total Regulatory Assets 1,727.1 1,347.1 362.7 191.4 1,637.3 1,461.4 362.9 191.2 Less: Current Portion 335.5 289.4 117.2 64.1 268.3 348.4 105.0 56.2 Total Long-Term Regulatory Assets $ 1,391.6 $ 1,057.7 $ 245.5 $ 127.3 $ 1,369.0 $ 1,113.0 $ 257.9 $ 135.0 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 (or asset) recorded by the Regulated companies to recognize the funded status of their retiree benefit plans is offset by a regulatory asset (or offset by a regulatory liability in the case of a benefit plan asset) in lieu of a charge to Accumulated Other Comprehensive Income/(Loss), reflecting ultimate recovery from customers through rates. The regulatory asset (or regulatory liability) 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 or regulatory liabilities 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, $239 million is pending regulatory approval (including $33 million at CL&P, $124 million at NSTAR Electric, $78 million at PSNH, and $4 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 either records a carrying charge on its deferred storm restoration cost regulatory asset balance or the regulatory asset balance is included in rate base. Goodwill-related: The goodwill regulatory asset originated from a 1999 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, 2016 , there were 23 years of amortization remaining. Regulatory Tracker Mechanisms: The Regulated companies' approved rates are designed to recover 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, WMECO and NSTAR Gas each have a regulatory commission approved revenue decoupling mechanism. NSTAR Gas' decoupling mechanism was effective January 1, 2016. Distribution revenues are decoupled from customer sales volumes, where applicable, which breaks the relationship between sales volumes and revenues recognized. CL&P, WMECO and NSTAR Gas 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 is adjusted through rates in a subsequent period. CL&P's 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, including nuclear fuel storage, of the CYAPC, YAEC and MYAPC nuclear facilities. 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 $70.9 million and $110.9 million as of December 31, 2016 and 2015 , 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, and various other items. Regulatory Costs in Other Long-Term Assets: Eversource's Regulated companies had $86.3 million (including $5.9 million for CL&P, $35.0 million for NSTAR Electric, $8.2 million for PSNH and $20.1 million for WMECO) and $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) of additional regulatory costs as of December 31, 2016 and 2015 , 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. 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 $1.2 million and $1.5 million for CL&P as of December 31, 2016 and 2015 , respectively. These carrying costs will be recovered from customers in future rates. As of December 31, 2016 and 2015 , this equity return, which is not recorded on the balance sheets, totaled $44.9 million and $48.3 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 as part of a generation divestiture settlement agreement. Regulatory Liabilities: The components of regulatory liabilities were as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Cost of Removal $ 459.7 $ 437.1 Regulatory Tracker Mechanisms 145.3 99.7 Benefit Costs 136.2 — AFUDC - Transmission 65.8 66.1 Other Regulatory Liabilities 42.1 18.5 Total Regulatory Liabilities 849.1 621.4 Less: Current Portion 146.8 107.8 Total Long-Term Regulatory Liabilities $ 702.3 $ 513.6 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cost of Removal $ 38.8 $ 271.6 $ 44.1 $ 8.6 $ 24.1 $ 257.4 $ 47.2 $ 2.8 Benefit Costs — 113.1 — — — — — — Regulatory Tracker Mechanisms 37.2 63.7 10.7 14.7 56.2 3.3 3.4 12.9 AFUDC - Transmission 50.2 6.9 — 8.7 51.5 5.7 — 8.9 Other Regulatory Liabilities 21.0 0.2 2.7 0.1 4.2 1.3 4.2 0.1 Total Regulatory Liabilities 147.2 455.5 57.5 32.1 136.0 267.7 54.8 24.7 Less: Current Portion 47.1 63.7 12.7 14.9 61.2 3.3 6.9 13.1 Total Long-Term Regulatory Liabilities $ 100.1 $ 391.8 $ 44.8 $ 17.2 $ 74.8 $ 264.4 $ 47.9 $ 11.6 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 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. 2016 Regulatory Developments: FERC ROE Complaints: As of December 31, 2016 , Eversource has a reserve established for the first and second ROE complaints in the pending FERC ROE complaint proceedings, which was recorded as a regulatory liability. The cumulative pre-tax reserve (excluding interest) as of December 31, 2016 , which includes 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). See Note 11E, "Commitments and Contingencies – FERC ROE Complaints," for further information on developments in the pending ROE complaint proceedings. Transmission Merger Cost Recovery Filing: On January 31, 2017, FERC issued an order accepting a settlement agreement filed by Eversource Service on November 22, 2016, which included the recovery through transmission rates of $27.5 million of costs, over the period June 1, 2016 through May 31, 2017, associated with the merger of Northeast Utilities and NSTAR. Eversource recorded the $27.5 million as a regulatory asset ( $13.2 million at CL&P, $7.8 million at NSTAR Electric, $3.0 million at PSNH and $3.5 million at WMECO) and as a reduction to Operations and Maintenance expense on the Eversource statements of income in 2016. The remaining regulatory asset, after amortization, as of December 31, 2016 was $11.5 million at Eversource ( $5.5 million at CL&P, $3.2 million at NSTAR Electric, $1.3 million at PSNH and $1.5 million at WMECO). Spent Nuclear Fuel Litigation - Yankee Companies: As a result of damages awarded to the Yankee Companies for spent nuclear fuel lawsuits against the DOE described in Note 11C, "Commitments and Contingencies - Spent Nuclear Fuel Obligations - Yankee Companies," the Yankee Companies returned a portion of the DOE Phase III Damages proceeds to Eversource's utility subsidiaries, for the benefit of their respective customers, and MYAPC also refunded an additional amount from its spent nuclear fuel trust to Eversource's utility subsidiaries. Proceeds received from the Yankee Companies to CL&P, NSTAR Electric, PSNH and WMECO were $13.6 million , $5.0 million , $3.9 million and $3.6 million , respectively, and the corresponding refund obligation to customers was recorded as a regulatory liability. CL&P 2016 Unbilled Revenues Order: Pursuant to an order received in 2016, unbilled revenues associated with CL&P's retail transmission and by-passable FMCC regulatory tracker reconciliation deferrals will be recovered in rates in 2017 and are therefore classified within current regulatory assets.

PROPERTY, PLANT AND EQUIPMENT A

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION 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 Operations and Maintenance expense 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) 2016 2015 Distribution - Electric $ 13,716.9 $ 13,054.8 Distribution - Natural Gas 3,010.4 2,727.2 Transmission - Electric 8,517.4 7,691.9 Generation 1,224.2 1,194.1 Electric and Natural Gas Utility 26,468.9 24,668.0 Other (1) 591.6 558.6 Property, Plant and Equipment, Gross 27,060.5 25,226.6 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,480.4 ) (6,141.1 ) Other (242.0 ) (255.6 ) Total Accumulated Depreciation (6,722.4 ) (6,396.7 ) Property, Plant and Equipment, Net 20,338.1 18,829.9 Construction Work in Progress 1,012.4 1,062.5 Total Property, Plant and Equipment, Net $ 21,350.5 $ 19,892.4 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Distribution $ 5,562.9 $ 5,402.3 $ 1,949.8 $ 841.9 $ 5,377.2 $ 5,100.5 $ 1,804.8 $ 812.3 Transmission 3,912.9 2,435.8 1,059.3 1,061.1 3,618.0 2,131.3 928.2 964.9 Generation — — 1,188.2 36.0 — — 1,158.1 36.0 Property, Plant and Equipment, Gross 9,475.8 7,838.1 4,197.3 1,939.0 8,995.2 7,231.8 3,891.1 1,813.2 Less: Accumulated Depreciation (2,082.4 ) (2,025.4 ) (1,254.7 ) (338.8 ) (2,041.9 ) (1,886.8 ) (1,171.0 ) (307.0 ) Property, Plant and Equipment, Net 7,393.4 5,812.7 2,942.6 1,600.2 6,953.3 5,345.0 2,720.1 1,506.2 Construction Work in Progress 239.0 239.1 96.7 78.1 203.5 310.5 135.3 69.1 Total Property, Plant and Equipment, Net $ 7,632.4 $ 6,051.8 $ 3,039.3 $ 1,678.3 $ 7,156.8 $ 5,655.5 $ 2,855.4 $ 1,575.3 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. The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows: (Percent) 2016 2015 2014 Eversource 3.0 % 2.9 % 3.0 % CL&P 2.7 % 2.7 % 2.7 % NSTAR Electric 3.0 % 3.0 % 3.0 % PSNH 3.1 % 3.2 % 3.0 % WMECO 2.7 % 2.7 % 3.3 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2016 (Years) Eversource CL&P NSTAR Electric PSNH WMECO Distribution 35.1 37.7 32.0 31.3 30.7 Transmission 41.5 38.0 43.8 43.5 49.7 Generation 29.0 — — 29.1 25.0 Other 11.0 — — — —

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS	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 non-derivative 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 amounts recorded as current or long-term derivative assets or liabilities: As of December 31, 2016 2015 (Millions of Dollars) Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: Level 2: Eversource $ 6.0 $ — $ 6.0 $ — $ — $ — Level 3: Eversource, CL&P 13.9 (9.4 ) 4.5 16.7 (10.9 ) 5.8 Long-Term Derivative Assets: Level 2: Eversource $ 0.3 $ (0.1 ) $ 0.2 $ 0.1 $ — $ 0.1 Level 3: Eversource 77.3 (11.7 ) 65.6 62.0 (19.3 ) 42.7 CL&P 77.3 (11.7 ) 65.6 60.7 (19.3 ) 41.4 NSTAR Electric — — — 1.3 — 1.3 Current Derivative Liabilities: Level 2: Eversource $ — $ — $ — $ (5.8 ) $ — $ (5.8 ) Level 3: Eversource (79.7 ) — (79.7 ) (92.3 ) — (92.3 ) CL&P (77.8 ) — (77.8 ) (91.8 ) — (91.8 ) NSTAR Electric (1.9 ) — (1.9 ) (0.5 ) — (0.5 ) Long-Term Derivative Liabilities : Level 3: Eversource $ (413.7 ) $ — $ (413.7 ) $ (337.1 ) $ — $ (337.1 ) CL&P (412.8 ) — (412.8 ) (336.2 ) — (336.2 ) NSTAR Electric (0.9 ) — (0.9 ) (0.9 ) — (0.9 ) (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 exposure to various counterparties. As of December 31, 2016 , Eversource's and CL&P's derivative assets were exposed to counterparty credit risk. Of Eversource's and CL&P's derivative assets, $76.2 million and $70.0 million , respectively, were contracted with investment grade entities. For further information on the fair value of derivative contracts, see Note 1H, "Summary of Significant Accounting Policies – Fair Value Measurements," and Note 1I, "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, 2016 and 2015 , Eversource had NYMEX financial contracts for natural gas futures in order to reduce variability associated with the purchase price of 9.2 million and 9.1 million MMBtu of natural gas, respectively. For the years ended December 31, 2016 , 2015 and 2014 , there were losses of $125.5 million and $60.2 million and gains of $134.4 million , respectively, deferred as regulatory costs, 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 , Eversource had $5.8 million of derivative contracts in a net liability position that were subject to credit risk contingent provisions and would have been required to post additional collateral of $5.8 million if Eversource's unsecured debt credit ratings had been downgraded to below investment grade. As of December 31, 2016 , Eversource had no derivative contracts in a net liability position that were subject to credit risk contingent provisions. 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 valuations over the duration of the contracts: As of December 31, 2016 2015 Range Period Covered Range Period Covered Capacity Prices: Eversource $ 5.50 — 8.70 per kW-Month 2020 - 2026 $ 10.81 — 15.82 per kW-Month 2016 - 2026 CL&P 5.50 — 8.70 per kW-Month 2020 - 2026 10.81 — 12.60 per kW-Month 2019 - 2026 Forward Reserve: Eversource, CL&P $ 1.40 — 2.00 per kW-Month 2017 - 2024 $2.00 per kW-Month 2016 - 2024 REC Prices: Eversource, NSTAR Electric $ 24 — 29 per REC 2017 - 2018 $ 45 — 51 per REC 2016 - 2018 Exit price premiums of 3 percent through 20 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, 2015 $ (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 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (130.7 ) (122.7 ) (8.0 ) Settlements 88.3 83.0 5.3 Fair Value as of December 31, 2016 $ (423.3 ) $ (420.5 ) $ (2.8 ) Significant increases or decreases in future energy or capacity prices in isolation would decrease or increase, respectively, the fair value of the derivative liability. Any increases in risk premiums would increase the fair value of the derivative liability. Changes in these fair values are recorded as a regulatory asset or liability and do not impact net income.

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
MARKETABLE SECURITIES	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 spent nuclear fuel removal obligations of their nuclear fuel storage facilities. 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, 2016 and 2015 , these securities were classified as Level 1 in the fair value hierarchy and totaled $9.6 million and $14.2 million , respectively. For the years ended December 31, 2016 , 2015 and 2014 , net gains on these securities of $0.6 million , $2.0 million and $1.9 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. 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, 2016 2015 (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Eversource Debt Securities $ 296.2 $ 1.1 $ (2.1 ) $ 295.2 $ 256.5 $ 4.5 $ (0.6 ) $ 260.4 Equity Securities 203.3 62.3 (1.2 ) 264.4 215.3 59.2 (3.4 ) 271.1 Eversource's debt and equity securities include CYAPC's and YAEC's marketable securities held in nuclear decommissioning trusts of $466.7 million and $436.9 million as of December 31, 2016 and 2015 , respectively. Unrealized gains and losses for these nuclear decommissioning trusts are recorded in Marketable Securities with the corresponding offset to Other Long-Term Liabilities on the balance sheets, with no impact on the statements of income. Unrealized Losses and Other-than-Temporary Impairment: There have been no significant unrealized losses, other-than-temporary impairments or credit losses in 2016 or 2015 . 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 are recorded in Other Income, Net for Eversource's benefit trust and are 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 available-for-sale securities. Contractual Maturities : As of December 31, 2016 , the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Cost Fair Value Less than one year (1) $ 60.5 $ 60.3 One to five years 45.4 45.8 Six to ten years 59.7 58.3 Greater than ten years 130.6 130.8 Total Debt Securities $ 296.2 $ 295.2 (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 sheets. 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 (Millions of Dollars) As of December 31, 2016 2015 Level 1: Mutual Funds and Equities $ 274.0 $ 285.3 Money Market Funds 54.8 26.9 Total Level 1 $ 328.8 $ 312.2 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 63.0 $ 46.6 Corporate Debt Securities 41.1 43.9 Asset-Backed Debt Securities 18.5 20.0 Municipal Bonds 107.5 111.4 Other Fixed Income Securities 10.3 11.6 Total Level 2 $ 240.4 $ 233.5 Total Marketable Securities $ 569.2 $ 545.7 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, 2016
Asset Retirement Obligation Disclosure [Abstract]
ASSET RETIREMENT OBLIGATIONS	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 calculations 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 and the corresponding credits are 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 (Millions of Dollars) As of December 31, 2016 2015 Balance as of Beginning of Year $ 430.1 $ 426.3 Liabilities Incurred During the Year 1.3 6.6 Liabilities Settled During the Year (19.0 ) (18.2 ) Accretion 22.9 26.5 Revisions in Estimated Cash Flows (8.9 ) (11.1 ) Balance as of End of Year $ 426.4 $ 430.1 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Balance as of Beginning of Year $ 33.8 $ 35.3 $ 21.6 $ 5.7 $ 35.3 $ 34.3 $ 20.6 $ 5.9 Liabilities Incurred During the Year — — 0.5 — — 6.2 0.4 — Liabilities Settled During the Year — (0.3 ) — (0.1 ) — (1.5 ) — (0.1 ) Accretion 2.2 1.7 1.4 0.3 2.2 1.8 1.3 0.4 Revisions in Estimated Cash Flows — — — — (3.7 ) (5.5 ) (0.7 ) (0.5 ) Balance as of End of Year $ 36.0 $ 36.7 $ 23.5 $ 5.9 $ 33.8 $ 35.3 $ 21.6 $ 5.7 Eversource's amounts include CYAPC and YAEC's AROs of $308.6 million and $319.1 million as of December 31, 2016 and 2015 , respectively. The fair value of the ARO for CYAPC and YAEC includes 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 offset to the related regulatory asset. The assets held in the CYAPC and YAEC nuclear decommissioning trusts are restricted for settling the ARO and all other decommissioning obligations. For further information on the assets held in the nuclear decommissioning trusts, see Note 5, "Marketable Securities," to the financial statements.

SHORT-TERM DEBT

SHORT-TERM DEBT	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
SHORT-TERM DEBT	SHORT-TERM DEBT Short-Term Debt Borrowing Limits: The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric, WMECO and NPT 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, through December 31, 2017. On August 8, 2016, 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, through October 23, 2018. On November 3, 2016, FERC authorized NPT to issue up to an aggregate of $800 million in short-term debt and long-term debt through December 31, 2018. 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, 2016 , PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled approximately $349 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, 2016 , CL&P had $557.6 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. Commercial Paper Programs and Credit Agreements : Eversource parent has a $1.45 billion commercial paper program allowing Eversource parent to issue commercial paper as a form of short-term debt. As of December 31, 2016 and 2015 , Eversource parent had approximately $1.0 billion and approximately $1.1 billion , respectively, in short-term borrowings outstanding under the Eversource parent commercial paper program, leaving $428.0 million and $351.5 million of available borrowing capacity as of December 31, 2016 and 2015 , respectively. The weighted-average interest rate on these borrowings as of December 31, 2016 and 2015 was 0.88 percent and 0.72 percent, respectively. As of December 31, 2016 , there were intercompany loans from Eversource parent of $80.1 million to CL&P, $160.9 million to PSNH, and $51.0 million to WMECO. 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. Eversource parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five -year $1.45 billion revolving credit facility. Effective September 26, 2016, the revolving credit facility's termination date was extended for one additional year to September 4, 2021. The revolving credit facility serves to backstop Eversource parent's $1.45 billion commercial paper program. There were no borrowings outstanding on the revolving credit facility as of December 31, 2016 or 2015 . NSTAR Electric has a $450 million commercial paper program allowing NSTAR Electric to issue commercial paper as a form of short-term debt. As of December 31, 2016 and 2015 , NSTAR Electric had $126.5 million and $62.5 million , respectively, in short-term borrowings outstanding under its commercial paper program, leaving $323.5 million and $387.5 million of available borrowing capacity as of December 31, 2016 and 2015 , respectively. The weighted-average interest rate on these borrowings as of December 31, 2016 and 2015 was 0.71 percent and 0.40 percent, respectively. NSTAR Electric is a party to a five -year $450 million revolving credit facility. Effective September 26, 2016, the revolving credit facility's termination date was extended for one additional year to September 4, 2021. The revolving credit facility serves to backstop NSTAR Electric's $450 million commercial paper program. There were no borrowings outstanding on the revolving credit facility as of December 31, 2016 or 2015 . Amounts 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 their respective balance sheets. Intercompany loans from Eversource to CL&P, PSNH and WMECO are eliminated in consolidation on Eversource's balance sheets. Under the credit facilities described above, Eversource and its subsidiaries must comply with certain financial and non-financial covenants, including a consolidated debt to total capitalization ratio. As of December 31, 2016 and 2015 , 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 would not be permitted under its respective credit facility.

LONG-TERM DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2016 2015 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 5.625% 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 350.0 350.0 Total First Mortgage Bonds 2,669.8 2,669.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year (250.0 ) — Unamortized Premiums and Discounts, Net (10.0 ) (10.7 ) Unamortized Debt Issuance Costs (14.3 ) (15.9 ) CL&P Long-Term Debt $ 2,516.0 $ 2,763.7 NSTAR Electric (Millions of Dollars) As of December 31, 2016 2015 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% as of December 31, 2015) — 200.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 250.0 2.700% due 2026 250.0 — Total Debentures 2,100.0 2,050.0 Less Amounts due Within One Year (400.0 ) (200.0 ) Unamortized Premiums and Discounts, Net (9.1 ) (8.5 ) Unamortized Debt Issuance Costs (12.8 ) (11.7 ) NSTAR Electric Long-Term Debt $ 1,678.1 $ 1,829.8 PSNH (Millions of Dollars) As of December 31, 2016 2015 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 6.150% Series N due 2017 70.0 70.0 6.000% Series O due 2018 110.0 110.0 4.500% Series P due 2019 150.0 150.0 4.050% Series Q due 2021 122.0 122.0 3.200% Series R due 2021 160.0 160.0 3.500% 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 (1.138% and 0.193% as of December 31, 2016 and 2015, respectively) 89.3 89.3 Less Amounts due Within One Year (70.0 ) — Unamortized Premiums and Discounts, Net 0.1 0.1 Unamortized Debt Issuance Costs (4.4 ) (5.4 ) PSNH Long-Term Debt $ 1,002.0 $ 1,071.0 WMECO (Millions of Dollars) As of December 31, 2016 2015 Notes: 5.900% Senior Notes Series B due 2034 $ 50.0 $ 50.0 6.700% Senior Notes Series D due 2037 40.0 40.0 5.100% Senior Notes Series E due 2020 95.0 95.0 3.500% Senior Notes Series F due 2021 250.0 250.0 3.880% Senior Notes Series G due 2023 80.0 80.0 2.750% Senior Notes Series H due 2026 50.0 — Total Notes 565.0 515.0 Unamortized Premiums and Discounts, Net 4.2 5.2 Unamortized Debt Issuance Costs (2.7 ) (2.9 ) WMECO Long-Term Debt $ 566.5 $ 517.3 OTHER (Millions of Dollars) As of December 31, 2016 2015 Yankee Gas - First Mortgage Bonds: 8.480% Series B due 2022 $ 20.0 $ 20.0 5.260% Series H due 2019 50.0 50.0 5.350% Series I due 2035 50.0 50.0 6.900% Series J due 2018 100.0 100.0 4.870% Series K due 2020 50.0 50.0 4.820% Series L due 2044 100.0 100.0 3.350% Series M due 2025 75.0 75.0 Total First Mortgage Bonds 445.0 445.0 Unamortized Premium 0.4 0.4 Unamortized Debt Issuance Costs (1.5 ) (1.7 ) Yankee Gas Long-Term Debt 443.9 443.7 NSTAR Gas - First Mortgage Bonds: 9.950% Series J due 2020 25.0 25.0 7.110% Series K due 2033 35.0 35.0 7.040% Series M due 2017 25.0 25.0 4.460% Series N due 2020 125.0 125.0 4.350% Series O due 2045 100.0 100.0 Total First Mortgage Bonds 310.0 310.0 Less Amounts due Within One Year (25.0 ) — Unamortized Debt Issuance Costs (0.7 ) (0.8 ) NSTAR Gas Long-Term Debt 284.3 309.2 Eversource Parent - Notes and Debentures: 4.500% Debentures due 2019 350.0 350.0 1.450% Senior Notes Series E due 2018 300.0 300.0 2.800% Senior Notes Series F due 2023 450.0 450.0 1.600% Senior Notes Series G due 2018 150.0 150.0 3.150% Senior Notes Series H due 2025 300.0 300.0 2.500% Senior Notes Series I due 2021 250.0 — 3.350% Senior Notes Series J due 2026 250.0 — Total Eversource Parent Notes and Debentures 2,050.0 1,550.0 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 180.0 179.5 Fair Value Adjustment (1) 144.6 173.5 Less Fair Value Adjustment - Current Portion (1) (28.9 ) (28.9 ) Unamortized Premiums and Discounts, Net (2.2 ) (1.3 ) Unamortized Debt Issuance Costs (4.9 ) (1.9 ) Total Other Long-Term Debt $ 3,066.8 $ 2,623.8 Total Eversource Long-Term Debt $ 8,829.4 $ 8,805.6 (1) 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 2012 merger. Long-Term Debt Issuances: In March 2016, Eversource parent issued $250 million of 2.50 percent Series I Senior Notes due to mature in 2021 and $250 million of 3.35 percent Series J Senior Notes due to mature in 2026. The proceeds, net of issuance costs, were used to repay short-term borrowings under the Eversource parent commercial paper program. In May 2016, NSTAR Electric issued $250 million of 2.70 percent debentures, due to mature in 2026. The proceeds, net of issuance costs, were used to repay short-term borrowings under the NSTAR Electric commercial paper program and fund capital expenditures and working capital. In June 2016, WMECO issued $50 million of 2.75 percent Series H Senior Notes, due to mature in 2026. The proceeds, net of issuance costs, were used to repay short-term borrowings. Long-Term Debt Repayments: In May 2016, NSTAR Electric repaid at maturity $200 million variable rate debentures, using short term borrowings. Debt Issuance Authorizations: On November 3, 2016, FERC authorized NPT to issue up to an aggregate of $800 million in short-term debt and long-term debt through December 31, 2018. On December 28, 2016, PURA approved Yankee Gas' request to extend the authorization period for issuance of up to $125 million in long-term debt from December 31, 2016 to December 31, 2017. On January 4, 2017, PURA approved CL&P's request for authorization up to $1.325 billion in long-term debt through December 31, 2020. 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, the 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 equity requirements for WMECO and NSTAR Gas. Under the equity requirements, WMECO must maintain a certain consolidated indebtedness to capitalization ratio as of the end of any fiscal quarter and NSTAR Gas' outstanding long-term debt 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 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. WMECO and Yankee Gas have certain long-term debt agreements that contain cross-default provisions. No other debt issuances contain cross-default provisions as of December 31, 2016 . Pre-1983 Spent Nuclear Fuel Obligation: Under the Nuclear Waste Policy Act of 1982, the DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. CYAPC is obligated to pay the DOE for the costs to dispose of spent nuclear fuel and high-level radioactive waste generated prior to April 7, 1983 (pre-1983 Spent Nuclear Fuel) and recorded an accrual for the full liability thereof to the DOE. This liability accrues interest costs at the 3-month Treasury bill yield rate. For nuclear fuel used to generate electricity prior to April 7, 1983, payment may be made any time prior to the first delivery of spent fuel to the DOE. Fees for disposal of nuclear fuel burned on or after April 7, 1983 were billed to member companies and paid to the DOE. As a result of consolidating CYAPC, Eversource has consolidated $ 180.0 million and $ 179.5 million , respectively, in pre-1983 spent nuclear fuel obligations to the DOE, which include accumulated interest costs of $131.2 million and $130.7 million as of December 31, 2016 and 2015, respectively. CYAPC maintains 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 2017 through 2021 and thereafter are shown below. These amounts exclude the CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2016 : (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 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 2021 871.3 — — 371.3 250.0 Thereafter 5,665.3 1,990.3 1,700.0 375.0 220.0 Total $ 9,336.6 $ 2,790.3 $ 2,100.0 $ 1,076.3 $ 565.0

EMPLOYEE BENEFITS

EMPLOYEE BENEFITS	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
EMPLOYEE BENEFITS	EMPLOYEE BENEFITS A. Pension Benefits and Postretirement Benefits Other Than Pensions Eversource Service sponsors a defined benefit retirement plan (the "Pension Plan") that covers eligible employees, including, among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. The Pension Plan 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 SERP Plans, sponsored by Eversource Service, which provide benefits in excess of Internal Revenue Code limitations to eligible participants consisting of current and retired employees. Eversource Service also sponsored a defined benefit postretirement plan (PBOP) that provided certain benefits, primarily medical, dental and life insurance to eligible employees that met certain age and service eligibility requirements. In August 2016, the Company amended its PBOP Plan, which standardized separate benefit structures that existed within the plan and made other benefit changes. The new plan provides life insurance and a health reimbursement arrangement created for the purpose of reimbursing retirees and dependents for health insurance premiums and certain medical expenses. 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 15, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans is 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 are amortized as a component of pension and PBOP expense over the estimated average future employee service period. Pension and SERP Plans: The Pension and SERP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, see Note 5, "Marketable Securities," to the financial statements. The following tables provide information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP Eversource As of December 31, (Millions of Dollars) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,080.1 ) $ (5,486.2 ) Plan Amendment (9.0 ) — Service Cost (75.0 ) (91.4 ) Interest Cost (185.5 ) (227.0 ) Actuarial Gain/(Loss) (151.8 ) 331.5 Benefits Paid - Pension 254.0 238.5 Benefits Paid - Lump Sum — 149.5 Benefits Paid - SERP 5.1 5.0 Benefit Obligation as of End of Year $ (5,242.3 ) $ (5,080.1 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 3,905.4 $ 4,126.5 Employer Contributions 146.2 154.6 Actual Return on Pension Plan Assets 278.4 12.3 Benefits Paid (254.0 ) (238.5 ) Benefits Paid - Lump Sum — (149.5 ) Fair Value of Pension Plan Assets as of End of Year $ 4,076.0 $ 3,905.4 Funded Status as of December 31st $ (1,166.3 ) $ (1,174.7 ) Pension and SERP As of December 31, 2016 As of December 31, 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) $ (1,230.1 ) $ (982.6 ) $ (580.7 ) $ (249.4 ) Plan Amendment — (2.8 ) — — — — — — Change due to transfer of employees 8.8 (0.6 ) 2.4 1.9 (4.6 ) 6.2 (1.9 ) (1.3 ) Service Cost (18.8 ) (13.2 ) (9.9 ) (3.1 ) (24.7 ) (14.9 ) (12.1 ) (4.3 ) Interest Cost (41.6 ) (33.8 ) (20.7 ) (8.4 ) (51.1 ) (40.2 ) (24.3 ) (10.4 ) Actuarial Gain/(Loss) (23.9 ) (33.3 ) (21.5 ) (3.9 ) 77.8 34.1 38.9 12.6 Benefits Paid - Pension 62.6 53.8 24.9 13.2 60.2 47.6 23.2 12.7 Benefits Paid - Lump Sum — — — — 14.5 — 9.1 2.5 Benefits Paid - SERP 0.3 0.2 0.2 — 0.4 0.1 0.2 — Benefit Obligation as of End of Year $ (1,170.2 ) $ (979.4 ) $ (572.2 ) $ (237.9 ) $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 913.5 $ 832.9 $ 470.5 $ 220.8 $ 980.8 $ 879.0 $ 498.4 $ 234.0 Change due to transfer of employees (8.8 ) 0.6 (2.4 ) (1.9 ) 4.6 (6.2 ) 1.9 1.3 Employer Contributions 0.4 28.4 17.1 — — 5.0 1.0 — Actual Return on Pension Plan Assets 63.0 59.2 33.7 15.3 2.8 2.7 1.5 0.7 Benefits Paid (62.6 ) (53.8 ) (24.9 ) (13.2 ) (60.2 ) (47.6 ) (23.2 ) (12.7 ) Benefits Paid - Lump Sum — — — — (14.5 ) — (9.1 ) (2.5 ) Fair Value of Pension Plan Assets as of End of Year $ 905.5 $ 867.3 $ 494.0 $ 221.0 $ 913.5 $ 832.9 $ 470.5 $ 220.8 Funded Status as of December 31st $ (264.7 ) $ (112.1 ) $ (78.2 ) $ (16.9 ) $ (244.1 ) $ (116.8 ) $ (77.1 ) $ (16.8 ) In 2016, there was a decrease in the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in an increase to Eversource's pension liability of approximately $177 million , partially offset by a revised scale for the mortality table resulting in a decrease to Eversource's pension liability of approximately $32 million as of December 31, 2016. In December 2016, Eversource amended its pension plan to adjust the calculation of lump sum payments or annuity payments for certain employees. This amendment resulted in an increase to the liability of $9 million as of December 31, 2016. In 2015, there was an increase in the discount rate used to calculate the funded status and a revised scale for the mortality table for the Eversource pension liability, resulting in a decrease of the estimated benefits to be provided to plan participants and a decrease to Eversource's liability of approximately $267 million and $48 million , respectively, as of December 31, 2015. 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. The lump-sum payment had no impact on the net Accrued Pension Liability reflected on the Eversource, CL&P, PSNH and WMECO balance sheets as of December 31, 2015. The pension and SERP Plans' funded status includes the current portion of the SERP liability totaling $24.8 million and $6.6 million as of December 31, 2016 and 2015, respectively, which is included in Other Current Liabilities on the accompanying balance sheets. As of December 31, 2016 and 2015 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 4,829.6 $ 1,065.2 $ 904.8 $ 518.9 $ 220.0 2015 4,733.2 1,062.7 888.8 506.4 222.3 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2016 2015 Discount Rate 4.01% — 4.33% 4.21% — 4.60% 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. Effective January 1, 2016, the Company refined its method of estimating the discount rate for the service and interest cost components of Pension expense from the yield-curve approach to the spot rate methodology, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. Historically, these components were estimated using the same weighted-average discount rate as for the funded status. The total pre-tax benefit of this change on Pension expense, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, for the year ended December 31, 2016 was approximately $46 million . 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 75.0 $ 18.8 $ 13.2 $ 9.9 $ 3.1 Interest Cost 185.5 41.6 33.8 20.7 8.4 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (67.6 ) (38.6 ) (17.5 ) Actuarial Loss 125.7 25.4 34.4 9.9 5.5 Prior Service Cost 3.6 1.5 — 0.5 0.3 Total Net Periodic Benefit Expense/(Income) $ 71.9 $ 15.2 $ 13.8 $ 2.4 $ (0.2 ) Intercompany Allocations N/A $ 13.8 $ 8.9 $ 4.0 $ 2.5 Capitalized Pension Expense $ 22.1 $ 9.3 $ 7.6 $ 1.4 $ 0.4 Pension and SERP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource (1) CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 (1) Amounts exclude $3.2 million for the year ended December 31, 2015 that represent amounts included in other deferred debits. The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2016 2015 2014 Discount Rate 3.27 % — 4.89 % 4.20% 4.85 % — 5.03 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 184.6 $ (2.0 ) $ 6.8 $ (6.2 ) Actuarial Losses Reclassified as Net Periodic Benefit Expense (119.9 ) (142.3 ) (5.8 ) (6.2 ) Prior Service Cost Arising During the Year 7.1 — 1.9 — Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.4 ) (3.5 ) (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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 1,732.3 $ 1,667.6 $ 128.5 $ 82.1 $ 81.1 $ 5.8 Prior Service Cost 13.4 9.7 4.1 2.3 0.6 0.2 PBOP Plan: 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) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,051.4 ) $ (1,147.9 ) Plan Amendment 244.0 — Service Cost (12.2 ) (16.3 ) Interest Cost (32.9 ) (47.2 ) Actuarial Gain/(Loss) (17.7 ) 106.0 Benefits Paid 60.2 54.0 Benefit Obligation as of End of Year $ (810.0 ) $ (1,051.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 812.2 $ 862.6 Actual Return on Plan Assets 51.3 (4.3 ) Employer Contributions 12.5 7.9 Benefits Paid (60.2 ) (54.0 ) Fair Value of Plan Assets as of End of Year $ 815.8 $ 812.2 Funded Status as of December 31st $ 5.8 $ (239.2 ) PBOP As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) $ (173.9 ) $ (468.7 ) $ (91.8 ) $ (36.6 ) Plan Amendment (12.5 ) 195.3 (6.7 ) (1.7 ) — — — — Change due to transfer of employees 1.3 0.3 0.3 0.2 0.1 2.3 (0.3 ) — Service Cost (2.0 ) (3.0 ) (1.3 ) (0.4 ) (2.1 ) (5.4 ) (1.4 ) (0.4 ) Interest Cost (5.3 ) (12.2 ) (2.9 ) (1.1 ) (7.2 ) (19.0 ) (3.9 ) (1.5 ) Actuarial Gain/(Loss) 3.6 (24.6 ) 3.6 1.1 7.2 59.1 3.6 1.5 Benefits Paid 13.9 20.3 5.8 3.0 11.9 18.9 5.3 2.6 Benefit Obligation as of End of Year $ (165.0 ) $ (236.7 ) $ (89.7 ) $ (33.3 ) $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 136.7 $ 320.3 $ 75.8 $ 31.7 $ 149.0 $ 336.5 $ 80.9 $ 34.4 Change due to transfer of employees (0.8 ) (0.3 ) (0.2 ) (0.3 ) — 0.6 0.2 — Actual Return on Plan Assets 7.2 23.2 3.4 1.4 (0.4 ) (2.8 ) — (0.1 ) Employer Contributions — 8.9 — — — 4.9 — — Benefits Paid (13.9 ) (20.3 ) (5.8 ) (3.0 ) (11.9 ) (18.9 ) (5.3 ) (2.6 ) Fair Value of Plan Assets as of End of Year $ 129.2 $ 331.8 $ 73.2 $ 29.8 $ 136.7 $ 320.3 $ 75.8 $ 31.7 Funded Status as of December 31st $ (35.8 ) $ 95.1 $ (16.5 ) $ (3.5 ) $ (27.3 ) $ (92.5 ) $ (12.7 ) $ (2.7 ) The August 2016 PBOP plan amendment resulted in a reduction to Eversource's accumulated benefit liability of approximately $244 million . As of December 31, 2016, there was a decrease in the discount rate used to calculate the funded status, as compared to the discount rate as of December 31, 2015, resulting in an increase to the Eversource liability of approximately $75 million , which was partially offset by a decrease of approximately $52 million from changes in mortality and other assumptions. In 2015, there was an increase in the discount rate used to calculate the funded status of the Eversource PBOP liability and a revised scale for the mortality table resulting in a decrease of the estimated benefits to be provided to plan participants, both of which resulted in a decrease to Eversource's liability of approximately $60 million and $23 million , respectively, as of December 31, 2015. The following actuarial assumptions were used in calculating the PBOP Plan's year end funded status: PBOP As of December 31, 2016 2015 Discount Rate 4.21 % 4.62 % Health Care Cost Trend Rate N/A 6.25 % Effective with the plan amendment that standardized plan designs and made benefit changes in August 2016, the health care cost trend rate is no longer applicable. PBOP Expense: Eversource charges net periodic postretirement 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. Effective January 1, 2016, the Company refined its method of estimating the discount rate for the service and interest cost components of PBOP expense from the yield-curve methodology to the spot rate methodology, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. Historically these components were estimated using the same weighted-average discount rate as for the funded status. The total pre-tax benefit of this change on PBOP expense, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, for the year ended December 31, 2016 was approximately $10 million . The August 2016 PBOP Plan amendment resulted in a remeasurement of the benefit obligation and annual expense using assumptions at that point in time, including updated discount rates and asset values. The remeasurement resulted in a decrease in net periodic benefit costs for PBOP benefits, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, of approximately $10 million , which was recorded in 2016, and most of this amount will be deferred for future refund to customers. The components of net periodic benefit 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 expense 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 12.2 $ 2.0 $ 3.0 $ 1.3 $ 0.4 Interest Cost 32.9 5.3 12.2 2.9 1.1 Expected Return on Plan Assets (62.9 ) (10.1 ) (25.7 ) (5.5 ) (2.4 ) Actuarial Loss 9.0 1.5 3.2 0.7 0.1 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.2 ) 0.2 0.1 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (14.5 ) $ (0.4 ) $ (0.7 ) Intercompany Allocations N/A $ 0.3 $ (0.2 ) $ (0.1 ) $ 0.1 Capitalized PBOP Expense/(Income) $ (8.0 ) $ (0.5 ) $ (6.4 ) $ 0.1 $ (0.3 ) PBOP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2016 2015 2014 Discount Rate 2.88% — 4.09% 4.22% 4.78 % — 5.10 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% The health care cost trend rate assumption used to calculate the PBOP expense amount was 6.25 percent and 6.5 percent for the years ended December 31, 2016 and 2015, respectively. The effect of increasing the assumed health care cost trend rate by one percentage point for the year ended December 31, 2016 would have increased service and interest cost components of PBOP expense by a total of $4.4 million . A decrease of one percentage point in the assumed health care cost trend rate would have decreased the service and interest cost components of PBOP expense by a total of $3.4 million . Effective January 1, 2017, the health care trend rate no longer has an impact on the PBOP expense due to the benefit design changes effective with the plan amendment. 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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 32.4 $ (34.1 ) $ (2.0 ) $ 0.7 Actuarial (Losses)/Gains Reclassified as Net Periodic Benefit (Expense)/Income (9.2 ) (6.4 ) 0.2 (0.4 ) Prior Service (Credit)/Cost Arising During the Year (247.9 ) — 4.0 — Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 9.7 0.5 (0.6 ) — 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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 175.4 $ 152.2 $ 7.9 $ 4.5 $ 6.3 $ 0.4 Prior Service (Credit)/Cost (239.5 ) (1.3 ) (21.7 ) 3.4 — 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) 2017 2018 2019 2020 2021 2022-2026 Pension and SERP $ 284.5 $ 277.0 $ 284.3 $ 290.4 $ 298.9 $ 1,562.9 PBOP 54.8 55.0 55.1 55.4 55.4 270.7 Eversource Contributions: Based on the current status of the Pension Plan and federal pension funding requirements, Eversource currently expects to make contributions of approximately $175 million in 2017 , of which approximately $2 million and $25 million , will be contributed by CL&P, and NSTAR Electric, respectively. The remaining $148 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource expects to make $7.6 million in contributions to the PBOP Plan in 2017 , of which approximately $5 million will be contributed by NSTAR Electric. 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 Pension 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 diversification 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 Pension Plan trust (401(h) assets). The investment policy and strategy of the 401(h) assets is consistent with that of the 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, 2016 , 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, 2016 and 2015 Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Equity Securities: United States 22.0 % 8.5 % International 13.0 % 8.5 % Emerging Markets 5.0 % 10.0 % Private Equity 12.0 % 12.0 % Debt Securities: Fixed Income 12.0 % 4.5 % High Yield Fixed Income 13.0 % 8.5 % Emerging Markets Debt 5.0 % 7.5 % Real Estate and Other Assets 10.0 % 7.5 % Hedge Funds 8.0 % 7.0 % The taxable assets within the PBOP Plan 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) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 455.5 $ — $ 1,279.7 $ 1,735.2 $ 396.5 $ 62.2 $ 1,228.7 $ 1,687.4 Private Equity 6.0 — 518.4 524.4 7.6 — 464.7 472.3 Fixed Income (2) — 183.0 1,099.4 1,282.4 — 208.6 1,008.2 1,216.8 Real Estate and Other Assets 77.2 — 325.9 403.1 — 85.9 291.9 377.8 Hedge Funds — — 335.0 335.0 — — 340.5 340.5 Total $ 538.7 $ 183.0 $ 3,558.4 $ 4,280.1 $ 404.1 $ 356.7 $ 3,334.0 $ 4,094.8 Less: 401(h) PBOP Assets (3) (204.1 ) (189.4 ) Total Pension Assets $ 4,076.0 $ 3,905.4 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 88.6 $ — $ 214.1 $ 302.7 $ 109.7 $ — $ 199.4 $ 309.1 Private Equity — — 32.2 32.2 — — 32.9 32.9 Fixed Income (2) 9.5 44.8 132.3 186.6 9.7 50.5 131.0 191.2 Real Estate and Other Assets 15.5 — 27.5 43.0 — 6.6 30.8 37.4 Hedge Funds — — 47.2 47.2 — — 52.2 52.2 Total $ 113.6 $ 44.8 $ 453.3 $ 611.7 $ 119.4 $ 57.1 $ 446.3 $ 622.8 Add: 401(h) PBOP Assets (3) 204.1 189.4 Total PBOP Assets $ 815.8 $ 812.2 (1) United States, International and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include fixed income funds that invest in a variety of opportunistic fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement 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. 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. 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. Certain investments, such as commingled funds, private equity investments, real estate funds and hedge funds are valued using the NAV as a practical expedient. These investments are structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. Commingled funds are recorded at NAV provided by the asset manager, which is based on the market prices of the underlying equity securities. Hedge funds are recorded at NAV based on the values of the underlying assets. Private Equity investments, fixed income partnership funds and Real Estate and Other Assets are valued using the NAV 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. The Company has retrospectively adopted new accounting guidance that eliminates the requirement to classify assets valued at NAV, as a practical expedient, within the fair value hierarchy. Prior to the adoption of this guidance, these investments were classified as Level 2 or Level 3 in the fair value hierarchy. The adoption of this guidance changes fair value measurement disclosures, but does not impact the methodology for valuing the investments or financial statement results. Defined Contribution Plan 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 for 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 Plan. The total defined Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR PSNH WMECO 2016 $ 31.8 $ 4.5 $ 7.0 $ 3.4 $ 1.1 2015 30.4 4.8 6.3 3.4 1.0 2014 29.7 5.0 6.3 3.2 1.0 Share-Based Payments Share-based compensation awards 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 Plans: Eversource maintains long-term equity-based incentive plans in which Eversource, CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are eligible to participate. The incentive plans authorize Eversource to grant up to 8,000,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2016 and 2015 , Eversource had 2,692,350 and 3,005,010 common shares, respectively, available for issuance under these plans. 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 b

SHARE-BASED PAYMENTS

SHARE-BASED PAYMENTS	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED PAYMENTS	EMPLOYEE BENEFITS A. Pension Benefits and Postretirement Benefits Other Than Pensions Eversource Service sponsors a defined benefit retirement plan (the "Pension Plan") that covers eligible employees, including, among others, employees of CL&P, NSTAR Electric, PSNH and WMECO. The Pension Plan 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 SERP Plans, sponsored by Eversource Service, which provide benefits in excess of Internal Revenue Code limitations to eligible participants consisting of current and retired employees. Eversource Service also sponsored a defined benefit postretirement plan (PBOP) that provided certain benefits, primarily medical, dental and life insurance to eligible employees that met certain age and service eligibility requirements. In August 2016, the Company amended its PBOP Plan, which standardized separate benefit structures that existed within the plan and made other benefit changes. The new plan provides life insurance and a health reimbursement arrangement created for the purpose of reimbursing retirees and dependents for health insurance premiums and certain medical expenses. 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 15, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans is 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 are amortized as a component of pension and PBOP expense over the estimated average future employee service period. Pension and SERP Plans: The Pension and SERP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, see Note 5, "Marketable Securities," to the financial statements. The following tables provide information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP Eversource As of December 31, (Millions of Dollars) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,080.1 ) $ (5,486.2 ) Plan Amendment (9.0 ) — Service Cost (75.0 ) (91.4 ) Interest Cost (185.5 ) (227.0 ) Actuarial Gain/(Loss) (151.8 ) 331.5 Benefits Paid - Pension 254.0 238.5 Benefits Paid - Lump Sum — 149.5 Benefits Paid - SERP 5.1 5.0 Benefit Obligation as of End of Year $ (5,242.3 ) $ (5,080.1 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 3,905.4 $ 4,126.5 Employer Contributions 146.2 154.6 Actual Return on Pension Plan Assets 278.4 12.3 Benefits Paid (254.0 ) (238.5 ) Benefits Paid - Lump Sum — (149.5 ) Fair Value of Pension Plan Assets as of End of Year $ 4,076.0 $ 3,905.4 Funded Status as of December 31st $ (1,166.3 ) $ (1,174.7 ) Pension and SERP As of December 31, 2016 As of December 31, 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) $ (1,230.1 ) $ (982.6 ) $ (580.7 ) $ (249.4 ) Plan Amendment — (2.8 ) — — — — — — Change due to transfer of employees 8.8 (0.6 ) 2.4 1.9 (4.6 ) 6.2 (1.9 ) (1.3 ) Service Cost (18.8 ) (13.2 ) (9.9 ) (3.1 ) (24.7 ) (14.9 ) (12.1 ) (4.3 ) Interest Cost (41.6 ) (33.8 ) (20.7 ) (8.4 ) (51.1 ) (40.2 ) (24.3 ) (10.4 ) Actuarial Gain/(Loss) (23.9 ) (33.3 ) (21.5 ) (3.9 ) 77.8 34.1 38.9 12.6 Benefits Paid - Pension 62.6 53.8 24.9 13.2 60.2 47.6 23.2 12.7 Benefits Paid - Lump Sum — — — — 14.5 — 9.1 2.5 Benefits Paid - SERP 0.3 0.2 0.2 — 0.4 0.1 0.2 — Benefit Obligation as of End of Year $ (1,170.2 ) $ (979.4 ) $ (572.2 ) $ (237.9 ) $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 913.5 $ 832.9 $ 470.5 $ 220.8 $ 980.8 $ 879.0 $ 498.4 $ 234.0 Change due to transfer of employees (8.8 ) 0.6 (2.4 ) (1.9 ) 4.6 (6.2 ) 1.9 1.3 Employer Contributions 0.4 28.4 17.1 — — 5.0 1.0 — Actual Return on Pension Plan Assets 63.0 59.2 33.7 15.3 2.8 2.7 1.5 0.7 Benefits Paid (62.6 ) (53.8 ) (24.9 ) (13.2 ) (60.2 ) (47.6 ) (23.2 ) (12.7 ) Benefits Paid - Lump Sum — — — — (14.5 ) — (9.1 ) (2.5 ) Fair Value of Pension Plan Assets as of End of Year $ 905.5 $ 867.3 $ 494.0 $ 221.0 $ 913.5 $ 832.9 $ 470.5 $ 220.8 Funded Status as of December 31st $ (264.7 ) $ (112.1 ) $ (78.2 ) $ (16.9 ) $ (244.1 ) $ (116.8 ) $ (77.1 ) $ (16.8 ) In 2016, there was a decrease in the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in an increase to Eversource's pension liability of approximately $177 million , partially offset by a revised scale for the mortality table resulting in a decrease to Eversource's pension liability of approximately $32 million as of December 31, 2016. In December 2016, Eversource amended its pension plan to adjust the calculation of lump sum payments or annuity payments for certain employees. This amendment resulted in an increase to the liability of $9 million as of December 31, 2016. In 2015, there was an increase in the discount rate used to calculate the funded status and a revised scale for the mortality table for the Eversource pension liability, resulting in a decrease of the estimated benefits to be provided to plan participants and a decrease to Eversource's liability of approximately $267 million and $48 million , respectively, as of December 31, 2015. 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. The lump-sum payment had no impact on the net Accrued Pension Liability reflected on the Eversource, CL&P, PSNH and WMECO balance sheets as of December 31, 2015. The pension and SERP Plans' funded status includes the current portion of the SERP liability totaling $24.8 million and $6.6 million as of December 31, 2016 and 2015, respectively, which is included in Other Current Liabilities on the accompanying balance sheets. As of December 31, 2016 and 2015 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 4,829.6 $ 1,065.2 $ 904.8 $ 518.9 $ 220.0 2015 4,733.2 1,062.7 888.8 506.4 222.3 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2016 2015 Discount Rate 4.01% — 4.33% 4.21% — 4.60% 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. Effective January 1, 2016, the Company refined its method of estimating the discount rate for the service and interest cost components of Pension expense from the yield-curve approach to the spot rate methodology, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. Historically, these components were estimated using the same weighted-average discount rate as for the funded status. The total pre-tax benefit of this change on Pension expense, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, for the year ended December 31, 2016 was approximately $46 million . 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 75.0 $ 18.8 $ 13.2 $ 9.9 $ 3.1 Interest Cost 185.5 41.6 33.8 20.7 8.4 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (67.6 ) (38.6 ) (17.5 ) Actuarial Loss 125.7 25.4 34.4 9.9 5.5 Prior Service Cost 3.6 1.5 — 0.5 0.3 Total Net Periodic Benefit Expense/(Income) $ 71.9 $ 15.2 $ 13.8 $ 2.4 $ (0.2 ) Intercompany Allocations N/A $ 13.8 $ 8.9 $ 4.0 $ 2.5 Capitalized Pension Expense $ 22.1 $ 9.3 $ 7.6 $ 1.4 $ 0.4 Pension and SERP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource (1) CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 (1) Amounts exclude $3.2 million for the year ended December 31, 2015 that represent amounts included in other deferred debits. The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2016 2015 2014 Discount Rate 3.27 % — 4.89 % 4.20% 4.85 % — 5.03 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 184.6 $ (2.0 ) $ 6.8 $ (6.2 ) Actuarial Losses Reclassified as Net Periodic Benefit Expense (119.9 ) (142.3 ) (5.8 ) (6.2 ) Prior Service Cost Arising During the Year 7.1 — 1.9 — Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.4 ) (3.5 ) (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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 1,732.3 $ 1,667.6 $ 128.5 $ 82.1 $ 81.1 $ 5.8 Prior Service Cost 13.4 9.7 4.1 2.3 0.6 0.2 PBOP Plan: 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) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,051.4 ) $ (1,147.9 ) Plan Amendment 244.0 — Service Cost (12.2 ) (16.3 ) Interest Cost (32.9 ) (47.2 ) Actuarial Gain/(Loss) (17.7 ) 106.0 Benefits Paid 60.2 54.0 Benefit Obligation as of End of Year $ (810.0 ) $ (1,051.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 812.2 $ 862.6 Actual Return on Plan Assets 51.3 (4.3 ) Employer Contributions 12.5 7.9 Benefits Paid (60.2 ) (54.0 ) Fair Value of Plan Assets as of End of Year $ 815.8 $ 812.2 Funded Status as of December 31st $ 5.8 $ (239.2 ) PBOP As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) $ (173.9 ) $ (468.7 ) $ (91.8 ) $ (36.6 ) Plan Amendment (12.5 ) 195.3 (6.7 ) (1.7 ) — — — — Change due to transfer of employees 1.3 0.3 0.3 0.2 0.1 2.3 (0.3 ) — Service Cost (2.0 ) (3.0 ) (1.3 ) (0.4 ) (2.1 ) (5.4 ) (1.4 ) (0.4 ) Interest Cost (5.3 ) (12.2 ) (2.9 ) (1.1 ) (7.2 ) (19.0 ) (3.9 ) (1.5 ) Actuarial Gain/(Loss) 3.6 (24.6 ) 3.6 1.1 7.2 59.1 3.6 1.5 Benefits Paid 13.9 20.3 5.8 3.0 11.9 18.9 5.3 2.6 Benefit Obligation as of End of Year $ (165.0 ) $ (236.7 ) $ (89.7 ) $ (33.3 ) $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 136.7 $ 320.3 $ 75.8 $ 31.7 $ 149.0 $ 336.5 $ 80.9 $ 34.4 Change due to transfer of employees (0.8 ) (0.3 ) (0.2 ) (0.3 ) — 0.6 0.2 — Actual Return on Plan Assets 7.2 23.2 3.4 1.4 (0.4 ) (2.8 ) — (0.1 ) Employer Contributions — 8.9 — — — 4.9 — — Benefits Paid (13.9 ) (20.3 ) (5.8 ) (3.0 ) (11.9 ) (18.9 ) (5.3 ) (2.6 ) Fair Value of Plan Assets as of End of Year $ 129.2 $ 331.8 $ 73.2 $ 29.8 $ 136.7 $ 320.3 $ 75.8 $ 31.7 Funded Status as of December 31st $ (35.8 ) $ 95.1 $ (16.5 ) $ (3.5 ) $ (27.3 ) $ (92.5 ) $ (12.7 ) $ (2.7 ) The August 2016 PBOP plan amendment resulted in a reduction to Eversource's accumulated benefit liability of approximately $244 million . As of December 31, 2016, there was a decrease in the discount rate used to calculate the funded status, as compared to the discount rate as of December 31, 2015, resulting in an increase to the Eversource liability of approximately $75 million , which was partially offset by a decrease of approximately $52 million from changes in mortality and other assumptions. In 2015, there was an increase in the discount rate used to calculate the funded status of the Eversource PBOP liability and a revised scale for the mortality table resulting in a decrease of the estimated benefits to be provided to plan participants, both of which resulted in a decrease to Eversource's liability of approximately $60 million and $23 million , respectively, as of December 31, 2015. The following actuarial assumptions were used in calculating the PBOP Plan's year end funded status: PBOP As of December 31, 2016 2015 Discount Rate 4.21 % 4.62 % Health Care Cost Trend Rate N/A 6.25 % Effective with the plan amendment that standardized plan designs and made benefit changes in August 2016, the health care cost trend rate is no longer applicable. PBOP Expense: Eversource charges net periodic postretirement 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. Effective January 1, 2016, the Company refined its method of estimating the discount rate for the service and interest cost components of PBOP expense from the yield-curve methodology to the spot rate methodology, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. Historically these components were estimated using the same weighted-average discount rate as for the funded status. The total pre-tax benefit of this change on PBOP expense, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, for the year ended December 31, 2016 was approximately $10 million . The August 2016 PBOP Plan amendment resulted in a remeasurement of the benefit obligation and annual expense using assumptions at that point in time, including updated discount rates and asset values. The remeasurement resulted in a decrease in net periodic benefit costs for PBOP benefits, prior to the capitalized portion and amounts deferred and recovered through rate reconciliation mechanisms, of approximately $10 million , which was recorded in 2016, and most of this amount will be deferred for future refund to customers. The components of net periodic benefit 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 expense 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 12.2 $ 2.0 $ 3.0 $ 1.3 $ 0.4 Interest Cost 32.9 5.3 12.2 2.9 1.1 Expected Return on Plan Assets (62.9 ) (10.1 ) (25.7 ) (5.5 ) (2.4 ) Actuarial Loss 9.0 1.5 3.2 0.7 0.1 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.2 ) 0.2 0.1 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (14.5 ) $ (0.4 ) $ (0.7 ) Intercompany Allocations N/A $ 0.3 $ (0.2 ) $ (0.1 ) $ 0.1 Capitalized PBOP Expense/(Income) $ (8.0 ) $ (0.5 ) $ (6.4 ) $ 0.1 $ (0.3 ) PBOP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2016 2015 2014 Discount Rate 2.88% — 4.09% 4.22% 4.78 % — 5.10 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% The health care cost trend rate assumption used to calculate the PBOP expense amount was 6.25 percent and 6.5 percent for the years ended December 31, 2016 and 2015, respectively. The effect of increasing the assumed health care cost trend rate by one percentage point for the year ended December 31, 2016 would have increased service and interest cost components of PBOP expense by a total of $4.4 million . A decrease of one percentage point in the assumed health care cost trend rate would have decreased the service and interest cost components of PBOP expense by a total of $3.4 million . Effective January 1, 2017, the health care trend rate no longer has an impact on the PBOP expense due to the benefit design changes effective with the plan amendment. 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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 32.4 $ (34.1 ) $ (2.0 ) $ 0.7 Actuarial (Losses)/Gains Reclassified as Net Periodic Benefit (Expense)/Income (9.2 ) (6.4 ) 0.2 (0.4 ) Prior Service (Credit)/Cost Arising During the Year (247.9 ) — 4.0 — Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 9.7 0.5 (0.6 ) — 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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 175.4 $ 152.2 $ 7.9 $ 4.5 $ 6.3 $ 0.4 Prior Service (Credit)/Cost (239.5 ) (1.3 ) (21.7 ) 3.4 — 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) 2017 2018 2019 2020 2021 2022-2026 Pension and SERP $ 284.5 $ 277.0 $ 284.3 $ 290.4 $ 298.9 $ 1,562.9 PBOP 54.8 55.0 55.1 55.4 55.4 270.7 Eversource Contributions: Based on the current status of the Pension Plan and federal pension funding requirements, Eversource currently expects to make contributions of approximately $175 million in 2017 , of which approximately $2 million and $25 million , will be contributed by CL&P, and NSTAR Electric, respectively. The remaining $148 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource expects to make $7.6 million in contributions to the PBOP Plan in 2017 , of which approximately $5 million will be contributed by NSTAR Electric. 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 Pension 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 diversification 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 Pension Plan trust (401(h) assets). The investment policy and strategy of the 401(h) assets is consistent with that of the 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, 2016 , 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, 2016 and 2015 Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Equity Securities: United States 22.0 % 8.5 % International 13.0 % 8.5 % Emerging Markets 5.0 % 10.0 % Private Equity 12.0 % 12.0 % Debt Securities: Fixed Income 12.0 % 4.5 % High Yield Fixed Income 13.0 % 8.5 % Emerging Markets Debt 5.0 % 7.5 % Real Estate and Other Assets 10.0 % 7.5 % Hedge Funds 8.0 % 7.0 % The taxable assets within the PBOP Plan 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) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 455.5 $ — $ 1,279.7 $ 1,735.2 $ 396.5 $ 62.2 $ 1,228.7 $ 1,687.4 Private Equity 6.0 — 518.4 524.4 7.6 — 464.7 472.3 Fixed Income (2) — 183.0 1,099.4 1,282.4 — 208.6 1,008.2 1,216.8 Real Estate and Other Assets 77.2 — 325.9 403.1 — 85.9 291.9 377.8 Hedge Funds — — 335.0 335.0 — — 340.5 340.5 Total $ 538.7 $ 183.0 $ 3,558.4 $ 4,280.1 $ 404.1 $ 356.7 $ 3,334.0 $ 4,094.8 Less: 401(h) PBOP Assets (3) (204.1 ) (189.4 ) Total Pension Assets $ 4,076.0 $ 3,905.4 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 88.6 $ — $ 214.1 $ 302.7 $ 109.7 $ — $ 199.4 $ 309.1 Private Equity — — 32.2 32.2 — — 32.9 32.9 Fixed Income (2) 9.5 44.8 132.3 186.6 9.7 50.5 131.0 191.2 Real Estate and Other Assets 15.5 — 27.5 43.0 — 6.6 30.8 37.4 Hedge Funds — — 47.2 47.2 — — 52.2 52.2 Total $ 113.6 $ 44.8 $ 453.3 $ 611.7 $ 119.4 $ 57.1 $ 446.3 $ 622.8 Add: 401(h) PBOP Assets (3) 204.1 189.4 Total PBOP Assets $ 815.8 $ 812.2 (1) United States, International and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include fixed income funds that invest in a variety of opportunistic fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement 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. 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. 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. Certain investments, such as commingled funds, private equity investments, real estate funds and hedge funds are valued using the NAV as a practical expedient. These investments are structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. Commingled funds are recorded at NAV provided by the asset manager, which is based on the market prices of the underlying equity securities. Hedge funds are recorded at NAV based on the values of the underlying assets. Private Equity investments, fixed income partnership funds and Real Estate and Other Assets are valued using the NAV 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. The Company has retrospectively adopted new accounting guidance that eliminates the requirement to classify assets valued at NAV, as a practical expedient, within the fair value hierarchy. Prior to the adoption of this guidance, these investments were classified as Level 2 or Level 3 in the fair value hierarchy. The adoption of this guidance changes fair value measurement disclosures, but does not impact the methodology for valuing the investments or financial statement results. Defined Contribution Plan 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 for 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 Plan. The total defined Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR PSNH WMECO 2016 $ 31.8 $ 4.5 $ 7.0 $ 3.4 $ 1.1 2015 30.4 4.8 6.3 3.4 1.0 2014 29.7 5.0 6.3 3.2 1.0 Share-Based Payments Share-based compensation awards 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 Plans: Eversource maintains long-term equity-based incentive plans in which Eversource, CL&P, NSTAR Electric, PSNH and WMECO employees, officers and board members are eligible to participate. The incentive plans authorize Eversource to grant up to 8,000,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2016 and 2015 , Eversource had 2,692,350 and 3,005,010 common shares, respectively, available for issuance under these plans. 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 b

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The components of income tax expense are as follows: Eversource (Millions of Dollars) For the Years Ended December 31, 2016 2015 2014 Current Income Taxes: Federal $ 38.9 $ 6.2 $ 4.4 State 53.0 45.7 24.5 Total Current 91.9 51.9 28.9 Deferred Income Taxes, Net: Federal 427.9 436.1 406.8 State 38.6 55.6 36.5 Total Deferred 466.5 491.7 443.3 Investment Tax Credits, Net (3.4 ) (3.6 ) (3.9 ) Income Tax Expense $ 555.0 $ 540.0 $ 468.3 For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Current Income Taxes: Federal $ 27.3 $ 73.9 $ (13.7 ) $ 12.5 $ 26.9 $ 36.3 $ (16.7 ) $ (3.5 ) $ (0.2 ) $ 75.0 $ (22.6 ) $ 1.9 State 13.3 35.0 8.8 4.5 15.8 19.8 6.0 1.6 4.3 20.2 (0.1 ) 1.8 Total Current 40.6 108.9 (4.9 ) 17.0 42.7 56.1 (10.7 ) (1.9 ) 4.1 95.2 (22.7 ) 3.7 Deferred Income Taxes, Net: Federal 157.6 78.3 79.5 18.3 135.8 147.5 74.5 33.4 138.0 88.0 79.6 28.1 State 11.3 1.9 7.8 3.2 0.2 25.7 9.3 6.0 (7.1 ) 20.1 15.2 6.0 Total Deferred 168.9 80.2 87.3 21.5 136.0 173.2 83.8 39.4 130.9 108.1 94.8 34.1 Investment Tax Credits, Net (1.2 ) (1.3 ) — (0.5 ) (1.3 ) (1.3 ) — (0.5 ) (1.5 ) (1.3 ) — (0.5 ) Income Tax Expense $ 208.3 $ 187.8 $ 82.4 $ 38.0 $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource (Millions of Dollars, except percentages) For the Years Ended December 31, 2016 2015 2014 Income Before Income Tax Expense $ 1,504.8 $ 1,425.9 $ 1,295.4 Statutory Federal Income Tax Expense at 35% 526.7 499.1 453.4 Tax Effect of Differences: Depreciation (3.4 ) (4.6 ) (5.6 ) Investment Tax Credit Amortization (3.4 ) (3.6 ) (3.9 ) Other Federal Tax Credits (3.5 ) (3.8 ) (3.5 ) State Income Taxes, Net of Federal Impact 56.2 61.1 42.5 Dividends on ESOP (8.4 ) (8.1 ) (8.0 ) Tax Asset Valuation Allowance/Reserve Adjustments 3.3 4.7 (2.9 ) Excess Stock Benefit (1) (19.1 ) — — Other, Net 6.6 (4.8 ) (3.7 ) Income Tax Expense $ 555.0 $ 540.0 $ 468.3 Effective Tax Rate 36.9 % 37.9 % 36.2 % For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars, except percentages) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Income Before Income Tax Expense $ 542.6 $ 480.5 $ 214.3 $ 96.1 $ 476.8 $ 572.6 $ 187.5 $ 93.5 $ 421.2 $ 505.1 $ 186.1 $ 95.1 Statutory Federal Income Tax Expense at 35% 189.9 168.2 75.0 33.6 166.9 200.4 65.6 32.7 147.4 176.8 65.1 33.3 Tax Effect of Differences: Depreciation 1.6 (3.4 ) 1.0 0.3 (1.7 ) (1.4 ) 0.5 (0.3 ) (3.6 ) (1.3 ) 0.3 (0.2 ) Investment Tax Credit Amortization (1.2 ) (1.3 ) — (0.5 ) (1.3 ) (1.3 ) — (0.5 ) (1.5 ) (1.3 ) — (0.5 ) Other Federal Tax Credits — — (3.5 ) — — — (3.8 ) — — — (3.5 ) — State Income Taxes, Net of Federal Impact 14.5 24.0 10.8 5.0 9.2 29.6 9.9 4.9 4.4 26.2 9.8 5.0 Tax Asset Valuation Allowance/Reserve Adjustments 1.5 — — — 1.2 — — — (6.3 ) — — — Excess Stock Benefit (1) (0.9 ) (1.0 ) (0.4 ) (0.2 ) — — — — — — — — Other, Net 2.9 1.3 (0.5 ) (0.2 ) 3.1 0.7 0.9 0.2 (6.9 ) 1.6 0.4 (0.3 ) Income Tax Expense $ 208.3 $ 187.8 $ 82.4 $ 38.0 $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 Effective Tax Rate 38.4 % 39.1 % 38.4 % 39.6 % 37.2 % 39.8 % 39.0 % 39.6 % 31.7 % 40.0 % 38.7 % 39.2 % (1) In 2016, the Company adopted new accounting guidance, which prospectively changed the accounting for excess tax benefits associated with the distribution of stock compensation awards, previously recognized in Capital Surplus, Paid In within Common Shareholders' Equity on the balance sheet, to recognition within income tax expense in the income statement. See Note 1C, "Summary of Significant Accounting Policies - Accounting Standards," for further information. 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 (Millions of Dollars) As of December 31, 2016 2015 Deferred Tax Assets: Employee Benefits $ 640.6 $ 637.5 Derivative Liabilities 192.6 172.7 Regulatory Deferrals - Liabilities 290.9 243.5 Allowance for Uncollectible Accounts 76.6 60.5 Tax Effect - Tax Regulatory Liabilities 11.8 9.7 Federal Net Operating Loss Carryforwards — 5.4 Purchase Accounting Adjustment 112.2 119.3 Other 170.5 197.1 Total Deferred Tax Assets 1,495.2 1,445.7 Less: Valuation Allowance 5.1 3.7 Net Deferred Tax Assets $ 1,490.1 $ 1,442.0 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 5,001.2 $ 4,602.6 Property Tax Accruals 81.9 76.7 Regulatory Amounts: Regulatory Deferrals - Assets 1,321.8 1,289.1 Tax Effect - Tax Regulatory Assets 252.6 249.3 Goodwill Regulatory Asset - 1999 Merger 186.7 194.9 Derivative Assets 29.5 17.7 Other 223.6 159.4 Total Deferred Tax Liabilities $ 7,097.3 $ 6,589.7 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Deferred Tax Assets: Employee Benefits $ 138.8 $ 58.4 $ 46.5 $ 11.1 $ 126.1 $ 91.3 $ 37.1 $ 10.0 Derivative Liabilities 191.5 1.1 — — 165.7 0.6 — — Regulatory Deferrals - Liabilities 6.3 186.4 36.7 8.5 36.0 109.4 42.1 6.1 Allowance for Uncollectible Accounts 33.0 20.0 4.1 5.7 30.4 8.5 3.6 4.5 Tax Effect - Tax Regulatory Liabilities 4.9 1.1 2.6 2.2 3.1 1.5 2.3 2.4 Federal Net Operating Loss Carryforwards — — — — — — 2.4 0.4 Other 59.4 2.2 56.4 4.4 55.5 3.4 61.1 5.0 Total Deferred Tax Assets 433.9 269.2 146.3 31.9 416.8 214.7 148.6 28.4 Less: Valuation Allowance 4.5 — — — 3.1 — — — Net Deferred Tax Assets $ 429.4 $ 269.2 $ 146.3 $ 31.9 $ 413.7 $ 214.7 $ 148.6 $ 28.4 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 1,700.3 $ 1,463.5 $ 726.3 $ 438.4 $ 1,545.6 $ 1,387.1 $ 655.3 $ 416.1 Property Tax Accruals 29.7 25.6 8.0 11.2 27.3 22.8 7.3 10.6 Regulatory Amounts: Regulatory Deferrals - Assets 473.4 322.3 142.1 59.4 456.8 339.7 137.9 60.5 Tax Effect - Tax Regulatory Assets 170.4 36.1 12.2 8.7 168.7 36.0 15.4 9.0 Goodwill Regulatory Asset - 1999 Merger — 160.3 — — — 167.4 — — Derivative Assets 27.0 — — — 17.7 — — — Other 16.3 97.7 43.1 5.0 18.5 22.0 38.6 2.7 Total Deferred Tax Liabilities $ 2,417.1 $ 2,105.5 $ 931.7 $ 522.7 $ 2,234.6 $ 1,975.0 $ 854.5 $ 498.9 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR PSNH WMECO Expiration Range Federal Tax Credit $ 8.6 $ — $ — $ — $ — — Federal Charitable Contribution 27.8 — — — — 2016 - 2019 State Tax Credit 111.1 80.5 — — — 2016 - 2021 State Charitable Contribution 36.5 — — — — 2016 - 2020 As of December 31, 2015 (Millions of Dollars) Eversource CL&P NSTAR 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 In 2016, the Company increased its valuation allowance reserve for state credits by $1.3 million ( $1.3 million for CL&P), net of tax, to reflect an update for expired tax credits. In 2015, the Company decreased its valuation allowance reserve for state credits and state loss carryforwards by $1.3 million ( $0.9 million for CL&P), net of tax, to reflect an update for expired state tax credits and loss carryforwards. For 2016 and 2015, state credit and state loss carryforwards have been partially reserved by a valuation allowance of $4.5 million and $3.1 million (net of tax), respectively. Unrecognized Tax Benefits: A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2014 $ 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 Gross Increases - Current Year 9.9 3.9 Gross Increases - Prior Year 0.2 0.2 Lapse of Statute of Limitations (9.7 ) (2.3 ) Balance as of December 31, 2016 $ 48.4 $ 15.3 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) 2016 2015 2014 2016 2015 Eversource $ (0.2 ) $ 0.1 $ 0.4 $ 1.8 $ 2.0 Tax Positions: During 2016 and 2015, 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, 2016 : Description Tax Years Federal 2016 Connecticut 2013 - 2016 Massachusetts 2013 - 2016 New Hampshire 2014 - 2016 Eversource estimates that during the next twelve months, differences of a non-timing nature could be resolved, resulting in a zero to $1.6 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. 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 provided 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 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.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	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 each believes it is substantially in compliance with all enacted laws and regulations. Environmental reserves are accrued 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 reserve 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's, CL&P's, NSTAR Electric's, PSNH's and WMECO's responsibility for remediation or the extent of remediation required, recently enacted laws and regulations or changes 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 are included in Other Current Liabilities and Other Long-Term Liabilities on the balance sheets and represent management's best estimate of the liability for environmental costs, and take into consideration site assessment, remediation and long-term monitoring costs. The environmental reserves also take into account recurring costs of managing hazardous substances and pollutants, mandated expenditures to remediate contaminated sites and any other infrequent 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, 2015 $ 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 Additions 20.6 0.6 1.7 1.2 0.1 Payments/Reductions (5.9 ) (0.3 ) (0.9 ) (0.4 ) (0.1 ) Balance as of December 31, 2016 $ 65.8 $ 4.9 $ 3.2 $ 5.3 $ 0.6 The number of environmental sites and related reserves for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: As of December 31, 2016 As of December 31, 2015 Number of Sites Reserve (in millions) Number of Sites Reserve (in millions) Eversource 61 $ 65.8 64 $ 51.1 CL&P 14 4.9 14 4.6 NSTAR Electric 13 3.2 15 2.4 PSNH 11 5.3 12 4.5 WMECO 4 0.6 4 0.6 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 $59.0 million and $45.5 million as of December 31, 2016 and 2015, respectively, and related primarily to the natural gas business segment. The increase in the reserve balance is due to the completion of site assessments and revised estimates for certain MGP sites. As of December 31, 2016 , for 8 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, 2016 , $35.6 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 $16 million (approximately $1 million for CL&P) may be incurred in executing current remediation plans for these sites. As of December 31, 2016 , for 10 environmental sites ( 3 for CL&P ) 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, 2016 , $13.4 million (including $2.1 million for CL&P) had been accrued as a liability for these sites. As of December 31, 2016 , for the remaining 43 environmental sites (including 8 for CL&P, 13 for NSTAR Electric, 11 for PSNH, and 3 for WMECO) that are included in the Company's reserve for environmental costs, the $16.8 million accrual (including $1.1 million for CL&P, $3.2 million for NSTAR Electric, $5.3 million for PSNH, and $0.3 million for WMECO) represents management's best estimate of the probable 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 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, 2016 , a liability of $0.7 million 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. Long-Term Contractual Arrangements Estimated Future Annual Costs: The estimated future annual costs of significant long-term contractual arrangements as of December 31, 2016 are as follows: Eversource (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 115.8 $ 81.6 $ 69.4 $ 74.2 $ 58.4 $ 189.8 589.2 Renewable Energy 275.4 242.6 240.9 238.8 218.9 1,864.1 3,080.7 Peaker CfDs 42.3 21.5 21.7 31.1 27.6 54.2 198.4 Natural Gas Procurement 197.0 185.5 142.3 115.0 104.9 190.2 934.9 Coal, Wood and Other 15.5 3.9 1.9 1.9 1.9 11.3 36.4 Transmission Support Commitments 21.8 22.0 22.2 22.2 22.2 22.2 132.6 Total $ 667.8 $ 557.1 $ 498.4 $ 483.2 $ 433.9 $ 2,331.8 $ 4,972.2 CL&P (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 93.4 $ 58.7 $ 56.6 $ 68.8 $ 53.0 $ 162.3 $ 492.8 Renewable Energy 77.9 80.4 80.3 80.3 80.6 684.4 1,083.9 Peaker CfDs 42.3 21.5 21.7 31.1 27.6 54.2 198.4 Transmission Support Commitments 8.6 8.7 8.8 8.8 8.8 8.8 52.5 Total $ 222.2 $ 169.3 $ 167.4 $ 189.0 $ 170.0 $ 909.7 $ 1,827.6 NSTAR Electric (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 4.8 $ 5.5 $ 5.5 $ 3.1 $ 3.1 $ 25.0 $ 47.0 Renewable Energy 116.8 80.4 78.5 76.6 72.1 416.7 841.1 Transmission Support Commitments 6.8 6.8 6.9 6.9 6.9 6.9 41.2 Total $ 128.4 $ 92.7 $ 90.9 $ 86.6 $ 82.1 $ 448.6 $ 929.3 PSNH (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 17.6 $ 17.4 $ 7.3 $ 2.3 $ 2.3 $ 2.5 $ 49.4 Renewable Energy 65.2 66.1 66.3 65.9 50.1 601.9 915.5 Coal, Wood and Other 15.5 3.9 1.9 1.9 1.9 11.3 36.4 Transmission Support Commitments 4.6 4.7 4.7 4.7 4.7 4.7 28.1 Total $ 102.9 $ 92.1 $ 80.2 $ 74.8 $ 59.0 $ 620.4 $ 1,029.4 WMECO (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Renewable Energy $ 15.5 $ 15.7 $ 15.8 $ 16.0 $ 16.1 $ 161.1 $ 240.2 Transmission Support Commitments 1.8 1.8 1.8 1.8 1.8 1.8 10.8 Total $ 17.3 $ 17.5 $ 17.6 $ 17.8 $ 17.9 $ 162.9 $ 251.0 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 through 2024 for CL&P, 2031 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 units and one demand response project. The capacity CfDs 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 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 shares 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, PSNH, and WMECO for the purchase of energy and capacity from renewable energy facilities. Such contracts extend through 2037 for CL&P, 2031 for NSTAR Electric, 2033 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 generation units approved by PURA (Peaker CfDs). These units have a total of approximately 500 MW of peaking capacity. As directed by PURA, 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 gas distribution businesses have long-term contracts for the purchase, transportation and storage of natural gas as part of its portfolio of supplies. These contracts extend through 2031. Coal, Wood and Other: PSNH has entered into various arrangements for the purchase of coal, wood and the transportation services for fuel supply for its 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 2018. The costs of this contract of $2.0 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. The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Supply and Stranded Cost $ 152.5 $ 147.6 $ 99.2 Renewable Energy 210.9 144.3 114.4 Peaker CfDs 47.7 42.7 18.1 Natural Gas Procurement 323.9 428.6 482.5 Coal, Wood and Other 55.7 95.9 120.5 Transmission Support Commitments 15.9 25.3 25.0 For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Supply and Stranded Cost $ 132.7 $ 0.7 $ 19.1 $ — $ 120.3 $ 6.5 $ 20.8 $ — $ 63.0 $ 7.0 $ 26.0 $ 3.2 Renewable Energy 42.1 93.6 67.7 7.5 20.0 86.7 37.2 0.4 0.7 87.4 26.3 — Peaker CfDs 47.7 — — — 42.7 — — — 18.1 — — — Coal, Wood and Other — — 55.7 — — — 95.9 — — — 120.5 — Transmission Support Commitments 6.3 4.9 3.4 1.3 10.0 7.8 5.4 2.1 9.9 7.7 5.3 2.1 Spent Nuclear Fuel 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-approved 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. Spent Nuclear Fuel Litigation: The Yankee Companies have filed complaints against the DOE in the Court of Federal Claims seeking monetary damages resulting from the DOE's failure to provide for a permanent facility to store spent nuclear fuel pursuant to the terms of the 1983 spent fuel and high level waste disposal contracts between the Yankee Companies and the DOE. The court had previously awarded the Yankee Companies damages for Phase I and Phase II of litigation resulting from the DOE's failure to meet its contractual obligations. Phase I covered damages incurred in the years 1998 through 2002 and Phase II covered damages incurred in the years 2001 through 2008 for CYAPC and YAEC and from 2002 through 2008 for MYAPC. DOE Phase III Damages - In August 2013, the Yankee Companies each filed subsequent lawsuits against the DOE seeking recovery of actual damages incurred in the years 2009 through 2012 ("DOE Phase III"). The DOE Phase III trial concluded on July 1, 2015, followed by a post-trial briefing that concluded on October 14, 2015. On March 25, 2016, the court issued its decision and awarded CYAPC, YAEC and MYAPC damages of $32.6 million , $19.6 million and $24.6 million , respectively. In total, the Yankee Companies were awarded $76.8 million of the $77.9 million in damages sought in DOE Phase III. The decision became final on July 18, 2016, and the Yankee Companies received the awards from the DOE on October 14, 2016. The Yankee Companies received FERC approval of their proposed distribution of certain amounts of the awarded damages proceeds to member companies, including CL&P, NSTAR Electric, PSNH, and WMECO, which CYAPC and MYAPC made in December 2016. MYAPC also refunded $56.5 million from its spent nuclear fuel trust, a portion of which was also refunded to the Eversource utility subsidiaries. In total, Eversource received $26.1 million , of which CL&P, NSTAR Electric, PSNH and WMECO received $13.6 million , $5.0 million , $3.9 million , and $3.6 million , respectively. These amounts will be refunded to the customers of the respective Eversource utility subsidiaries. Guarantees and Indemnifications In 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 Eversource Gas Transmission LLC, a wholly-owned subsidiary, to guarantee the payment of the subsidiary's capital contributions for its investment in the Access Northeast project. The guaranty will not exceed $206 million and decreases 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, Eversource parent will guarantee the financial obligations of NPT under the TSA with HQ in an amount not to exceed $25 million . Eversource parent's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations. Eversource parent has also entered into a guaranty on behalf of NPT under which Eversource parent would guarantee NPT's obligations under a letter of credit facility with a financial institution that NPT may request in an aggregate amount of up to approximately $14 million . Eversource parent has also guaranteed certain indemnification and other obligations as a result of the sales of former unregulated subsidiaries and the termination of an unregulated business, with maximum exposures 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. The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries to external parties, as of December 31, 2016 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty $ 185.4 2021 Various Surety Bonds (1) $ 38.2 2017 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate $ 9.2 2019 - 2024 (1) Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended. Certain surety bonds contain credit ratings triggers that would require Eversource parent to post collateral in the event that the unsecured debt credit ratings of Eversource parent are downgraded. FERC ROE Complaints Four separate complaints have been filed at the FERC by combinations of New England state attorneys general, state regulatory commissions, consumer advocates, consumer groups, municipal parties and other parties (collectively the "Complainants"). In the first three complaints, the Complainants challenged the NETOs' base ROE of 11.14 percent that had been utilized since 2006 and sought an order to reduce it prospectively from the date of the final FERC order and for the 15 -month complaint periods stipulated in the separate complaints. The FERC ordered a 10.57 percent base ROE for the first complaint period and prospectively from October 16, 2014, and that a utility's total or maximum ROE for any incentive project shall not exceed the top of the new zone of reasonableness, which was set at 11.74 percent. In late 2014, the NETOs made a compliance filing, and CL&P, NSTAR Electric, PSNH and WMECO have refunded all amounts associated with the first complaint period. The NETOs and Complainants have appealed the decision in the first complaint to the D.C. Circuit Court of Appeals. A court decision is expected in 2017. In 2015, the Company recognized a pre-tax charge to earnings (excluding interest) of $20.0 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. In 2014, the net aggregate pre-tax charge to earnings (excluding interest) totaled $37.0 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. The pre-tax charges were recorded as a regulatory liability and as a reduction to Operating Revenues. For the second and third complaints, the state parties, municipal utilities and FERC trial staff each believe that the base ROE should be reduced to an amount lower than 11.14 percent. FERC's determination to set these cases for hearing was appealed to the D.C. Circuit Court of Appeals, and is being held in abeyance pending a final FERC order. On March 22, 2016, the FERC ALJ issued an initial decision on the second and third complaints. For the second complaint period, the FERC ALJ recommended a zone of reasonableness of 7.12 percent to 10.42 percent and a base ROE of 9.59 percent. For the third complaint period, the FERC ALJ recommended a zone of reasonableness of 7.04 percent to 12.19 percent and a base ROE of 10.90 percent. The FERC ALJ also found that the maximum ROE for transmission incentive projects should be the top of the zone of reasonableness. The parties filed briefs on April 21, 2016 and May 11, 2016, in which they requested changes to the FERC ALJ's recommendations. The final FERC order will determine both the base ROE and the maximum ROE for transmission incentive projects for the two complaint periods. The Company believes that the range of potential loss for the second complaint period (the 15 -month period beginning December 27, 2012) is from a base ROE of 10.57 percent to a base ROE of 9.59 percent. As the FERC ALJ initial decision on the third complaint recommended a base ROE of 10.90 percent, the Company concluded there is currently no range of potential loss for that complaint period (the 15 -month period beginning July 31, 2014). Given the differences between the recommended base ROEs in the FERC ALJ's initial decision on the second and third complaints, as well as other factors, the Company is unable to predict the outcome of the final FERC order on these two complaints. The Company does not believe any base ROE outcome within the 10.57 percent to 9.59 percent range is more likely than the base ROEs used to record the current revenues and reserves, and therefore the Company believes that the current reserves for the second complaint period are appropriate at this time. The impact of a 10 basis point change to a base ROE of 10.57 percent would affect Eversource's after-tax earnings by approximately $3 million for each of the historic 15 -month second and third complaint periods. If the Company adjusted its reserves based on the recommendations in the FERC ALJ initial decision (for both the base ROE and maximum ROE for transmission incentive projects), then it would result in an after-tax loss of approximately $34 million for the second complaint and an after-tax gain of approximately $8 million for the third complaint. For the fourth complaint, filed April 29, 2016 and covering a 15 -month period through July 30, 2017, certain municipal utilities claimed the current base ROE of 10.57 percent and the incentive cap of 11.74 percent are unjust and unreasonable. The NETOs answered on June 3, 2016 and requested that FERC dismiss the complaint. On September 20, 2016, the FERC issued an order establishing hearing and settlement judge procedures. The case has been set for trial proceedings concurrently with settlement proceedings. On February 1, 2017, the Complainants' filed their direct testimony. The NETO's answering testimony is due March 23, 2017. Trial is scheduled for August 2017, and a FERC ALJ initial decision could be received late in 2017. A final FERC order will determine both the base ROE and the maximum ROE for transmission incentive projects for the fourth complaint period and prospectively from the date the final FERC order is issued. Management cannot at this time predict the ultimate outcome of this proceeding or the estimated impacts on the financial position, results of operations or cash flows of Eversource, CL&P, NSTAR Electric, PSNH and WMECO. F. Eversource and NSTAR Electric Boston Harbor Civil Action On July 15, 2016, the United States Army Corps of Engineers filed a civil action in the United States District Court for the District of Massachusetts under provisions of the Rivers and Harbors Act of 1899 and the Clean Water Act against NSTAR Electric, Harbor Electric Energy Company, a wholly-owned subsidiary of NSTAR Electric ("HEEC"), and the Massachusetts Water Resources Authority (together with NSTAR Electric and HEEC, the "Defendants"). The action alleges that the Defendants failed to comply with certain permitting requirements relating to the placement of the HEEC-owned electric distribution cable beneath Boston Harbor. The action seeks an order to force HEEC to comply with cable depth requirements in the U.S. Army Corps of Engineers' permit or alternatively to remove the electric distribution cable and cease unauthorized work in U.S. waterways. The action also seeks civil penalties and other costs. Management believes there are valid defenses to the claims and is defending NSTAR Electric and HEEC vigorously. Concurrently, NSTAR Electric and HEEC are seeking to work collaboratively with all parties for a mutually beneficial resolution. At this time, management is unable to predict the outcome of this action or the impact on Eversource's and NSTAR Electric's financial position, results of operations, or cash flows. G. 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.

PSNH GENERATION ASSET SALE

PSNH GENERATION ASSET SALE	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
PSNH GENERATION ASSET SALE	PSNH GENERATION ASSET SALE 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. Under the terms of the Agreement, PSNH agreed to divest its generation assets, subject to NHPUC approval. The Agreement provided for 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 agreed to forego recovery of $25 million of the 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. On July 1, 2016, the NHPUC approved the Agreement in an order that, among other things, instructs PSNH to begin the process to divest its generation assets. The NHPUC selected an auction adviser to assist with the divestiture, and a final plan and auction process was approved by the NHPUC in November 2016. In December 2016, certain intervenors asked the NHPUC to reconsider certain aspects of its divestiture plan; the NHPUC rejected that request on December 23, 2016. On January 10, 2017, these intervenors appealed the NHPUC's decision to the New Hampshire Supreme Court, alleging procedural deficiencies, and complaining that the auction schedule and process were unreasonable. PSNH and the New Hampshire Attorney General's office acting on behalf of the NHPUC requested the court to reject this appeal. On February 10, 2017, the New Hampshire Supreme Court issued an order declining to accept the appeal. Management continues to believe the assets will be sold by the end of 2017. The sales price of the generation assets could be less than the carrying value, but the Company believes 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 via bonds that will be secured by a non-bypassable charge or through recoveries in future rates billed to PSNH's customers. As of December 31, 2016 , PSNH's generation assets were as follows: (Millions of Dollars) Gross Plant $ 1,192.1 Accumulated Depreciation (556.0 ) Net Plant 636.1 Fuel 99.9 Materials and Supplies 42.7 Emission Allowances 19.9 Total Generation Assets $ 798.6 As of December 31, 2016 , current and long-term liabilities associated with PSNH's generation assets included Accounts Payable of $40.5 million , Other Current Liabilities of $16.1 million , AROs of $20 million , and Accrued Pension, SERP and PBOP of $24.3 million .

LEASES

LEASES	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
LEASES	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 leases entered into by other Eversource subsidiaries, which include Eversource Service and Rocky River Realty Company, and 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: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 12.1 $ 12.5 $ 9.3 $ 2.9 $ 2.1 2015 12.1 12.5 9.6 2.8 2.2 2014 14.3 6.0 7.8 1.5 1.2 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, 2016 are as follows: Operating Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2017 $ 14.1 $ 2.0 $ 9.0 $ 0.9 $ 0.5 2018 10.6 1.3 7.0 0.6 0.3 2019 8.7 1.0 5.8 0.5 0.3 2020 7.0 0.7 4.8 0.4 0.2 2021 6.0 0.6 4.2 0.3 0.2 Thereafter 10.4 1.4 6.7 0.8 0.4 Future minimum lease payments $ 56.8 $ 7.0 $ 37.5 $ 3.5 $ 1.9 Capital Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2017 $ 2.3 $ 1.9 $ 0.2 $ 0.2 2018 2.3 2.0 0.2 0.1 2019 2.2 2.0 0.2 — 2020 2.2 2.0 0.2 — 2021 1.7 1.4 0.3 — Thereafter 1.1 — 1.1 — Future minimum lease payments 11.8 9.3 2.2 0.3 Less amount representing interest 2.9 2.5 0.4 — Present value of future minimum lease payments $ 8.9 $ 6.8 $ 1.8 $ 0.3 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 table in Note 11B, "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, 2016
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	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 projections. 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, 2016 2015 Eversource (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 158.3 $ 155.6 $ 157.9 Long-Term Debt 9,603.2 9,980.5 9,034.5 9,425.9 CL&P NSTAR Electric PSNH WMECO (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value As of December 31, 2016: Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 114.7 $ 43.0 $ 43.6 $ — $ — $ — $ — Long-Term Debt 2,766.0 3,049.6 2,078.1 2,201.6 1,072.0 1,109.7 566.5 589.0 As of December 31, 2015: 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 Derivative Instruments and Marketable Securities: Derivative instruments and investments in marketable securities are carried at fair value. For further information, see Note 4, "Derivative Instruments," and Note 5, "Marketable Securities," to the financial statements. See Note 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/(LOSS)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) The changes in accumulated other comprehensive income/(loss) by component, net of tax, is as follows: For the Year Ended December 31, 2016 For the Year Ended December 31, 2015 Eversource (Millions of Dollars) Qualified Cash Flow Hedging Instruments Unrealized Gains/(Losses) on Marketable Securities Defined Benefit Plans Total Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Balance as of January 1st $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 ) $ (12.4 ) $ 0.7 $ (62.3 ) $ (74.0 ) OCI Before Reclassifications — 2.3 (6.8 ) (4.5 ) — (2.6 ) 3.5 0.9 Amounts Reclassified from AOCL 2.1 — 3.9 6.0 2.1 — 4.2 6.3 Net OCI 2.1 2.3 (2.9 ) 1.5 2.1 (2.6 ) 7.7 7.2 Balance as of December 31st $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 ) 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 AOCL 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 AOCL 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. Defined benefit plan OCI amounts before reclassifications relate to actuarial gains and losses and prior service costs that arose during the year and were recognized in AOCL. The related tax effects recognized in AOCL were net deferred tax assets of $4.0 million and $ 22.3 million in 2016 and 2014, respectively, and were net deferred tax liabilities of $2.0 million in 2015. The unamortized actuarial gains and losses and prior service costs on the defined benefit plans are amortized from AOCL into Operations and Maintenance expense over the average future employee service period, and are reflected in amounts reclassified from AOCL. The following table sets forth the amounts reclassified from AOCL by component and the impacted line item on the statements of income: Amounts Reclassified from AOCL Eversource (Millions of Dollars) For the Years Ended December 31, Statements of Income Line Item Impacted 2016 2015 2014 Qualified Cash Flow Hedging Instruments $ (3.5 ) $ (3.5 ) $ (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 ) $ (2.1 ) $ (2.0 ) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (5.6 ) $ (6.6 ) $ (6.2 ) Operations and Maintenance Expense (1) Amortization of Prior Service Cost (0.8 ) (0.2 ) (0.2 ) Operations and Maintenance Expense (1) Total Defined Benefit Plan Costs (6.4 ) (6.8 ) (6.4 ) Tax Effect 2.5 2.6 2.5 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (3.9 ) $ (4.2 ) $ (3.9 ) Total Amounts Reclassified from AOCL, Net of Tax $ (6.0 ) $ (6.3 ) $ (5.9 ) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pensions," for further information. As of December 31, 2016 , it is estimated that a pre-tax amount of $3.4 million (including $0.6 million for CL&P, $2 million for PSNH and $0.7 million for WMECO) will be reclassified from AOCL 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 $6.6 million will be reclassified from AOCL 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, 2016
Equity [Abstract]
DIVIDEND RESTRICTIONS	DIVIDEND RESTRICTIONS Eversource 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 indebtedness to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter. As of December 31, 2016 , all companies were in compliance with such covenant. The Retained Earnings balances subject to these restrictions were $3.2 billion for Eversource, $1.3 billion for CL&P, $1.6 billion for NSTAR Electric, $549.3 million for PSNH and $218.2 million for WMECO as of December 31, 2016 . 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 as of December 31, 2016 . PSNH is further required to reserve an additional amount under its FERC hydroelectric license conditions. As of December 31, 2016 , $13.8 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

COMMON SHARES	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
SHARE-BASED PAYMENTS	COMMON SHARES The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2016 and 2015 Issued as of December 31, 2016 2015 Eversource $ 5 380,000,000 333,878,402 333,862,615 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, 2016 and 2015 , there were 16,992,594 and 16,671,366 Eversource common shares held as treasury shares, respectively. As of December 31, 2016 and 2015 , Eversource common shares outstanding were 316,885,808 and 317,191,249 , respectively. In 2016 and 2015, the Company repurchased 321,228 and 532,521 Eversource common shares, respectively, at a share price of $52.56 and $47.94 , respectively. Such shares are included in Treasury Stock on the consolidated balance sheets at their weighted average original average cost of $24.26 and $26.02 per share, respectively. COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $7.5 million for each of the years ended December 31, 2016 , 2015 and 2014 . 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, 2016 and 2015 . On the Eversource balance sheets, Common Shareholders' Equity was fully attributable to the parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest. For the years ended December 31, 2016 , 2015 and 2014 , there was no change in ownership of the common equity of CL&P and NSTAR Electric.

PREFERRED STOCK NOT SUBJECT TO

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	PREFERRED STOCK NOT SUBJECT 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. 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 shares): Redemption Price Per Share Shares Outstanding as of December 31, 2016 and 2015 As of December 31, Series 2016 2015 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 of 1956 $ 103.625 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 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	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	COMMON SHARES The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2016 and 2015 Issued as of December 31, 2016 2015 Eversource $ 5 380,000,000 333,878,402 333,862,615 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, 2016 and 2015 , there were 16,992,594 and 16,671,366 Eversource common shares held as treasury shares, respectively. As of December 31, 2016 and 2015 , Eversource common shares outstanding were 316,885,808 and 317,191,249 , respectively. In 2016 and 2015, the Company repurchased 321,228 and 532,521 Eversource common shares, respectively, at a share price of $52.56 and $47.94 , respectively. Such shares are included in Treasury Stock on the consolidated balance sheets at their weighted average original average cost of $24.26 and $26.02 per share, respectively. COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $7.5 million for each of the years ended December 31, 2016 , 2015 and 2014 . 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, 2016 and 2015 . On the Eversource balance sheets, Common Shareholders' Equity was fully attributable to the parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest. For the years ended December 31, 2016 , 2015 and 2014 , 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, 2016
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Basic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into common shares. The dilutive effect of unvested RSU and performance share awards and unexercised stock options is calculated using the treasury stock method. 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. For the year ended December 31, 2016 , there were no antidilutive share awards excluded from the diluted EPS computation. For the years ended December 31, 2015 and 2014 , there were 1,474 and 3,643 antidilutive share awards excluded from the computation of diluted EPS, respectively. The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Years Ended December 31, 2016 2015 2014 Net Income Attributable to Common Shareholders $ 942.3 $ 878.5 $ 819.5 Weighted Average Common Shares Outstanding: Basic 317,650,180 317,336,881 316,136,748 Dilutive Effect 804,059 1,095,806 1,280,666 Diluted 318,454,239 318,432,687 317,417,414 Basic EPS $ 2.97 $ 2.77 $ 2.59 Diluted EPS $ 2.96 $ 2.76 $ 2.58

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
SEGMENT INFORMATION	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' 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's equity method investments and 5) the results of other unregulated subsidiaries, which are 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. The Electric Transmission segment includes a reduction to Operations and Maintenance expense of $27.5 million in 2016 for costs incurred in previous years that will be recovered in transmission rates over the period June 1, 2016 through May 31, 2017. These costs were associated with the merger of Northeast Utilities and NSTAR. Eversource's segment information is as follows: For the Year Ended December 31, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 5,594.3 $ 857.7 $ 1,210.0 $ 870.4 $ (893.3 ) $ 7,639.1 Depreciation and Amortization (504.7 ) (65.3 ) (185.8 ) (33.5 ) 2.2 (787.1 ) Other Operating Expenses (4,155.1 ) (628.9 ) (321.8 ) (778.1 ) 891.8 (4,992.1 ) Operating Income 934.5 163.5 702.4 58.8 0.7 1,859.9 Interest Expense (193.1 ) (41.3 ) (110.0 ) (63.5 ) 6.9 (401.0 ) Interest Income 10.0 0.1 1.2 7.0 (7.3 ) 11.0 Other Income, Net 4.8 0.6 18.3 1,020.1 (1,008.9 ) 34.9 Income Tax (Expense)/Benefit (288.8 ) (45.2 ) (238.2 ) 16.5 0.7 (555.0 ) Net Income 467.4 77.7 373.7 1,038.9 (1,007.9 ) 949.8 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — (7.5 ) Net Income Attributable to Common Shareholders $ 462.8 $ 77.7 $ 370.8 $ 1,038.9 $ (1,007.9 ) $ 942.3 Total Assets (as of) $ 18,367.5 $ 3,303.8 $ 8,751.5 $ 14,493.1 $ (12,862.7 ) $ 32,053.2 Cash Flows Used for Investments in Plant $ 812.6 $ 255.3 $ 801.0 $ 108.0 $ — $ 1,976.9 For the Year Ended December 31, 2015 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric 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 (Millions of Dollars) Electric Natural Gas Electric 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 Cash Flows Used for Investments in Plant $ 645.2 $ 176.7 $ 731.6 $ 50.2 $ — $ 1,603.7

GOODWILL

GOODWILL	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL	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. Goodwill is not subject to amortization, however 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 Operating Expenses. 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 21, "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. This evaluation required the consideration of several factors that impact the fair value of the reporting units, including conditions and assumptions that affect the future cash flows of the reporting units. Key considerations include discount rates, utility sector market performance and merger transaction multiples, and internal estimates of future cash flows and net income. Eversource completed its annual goodwill impairment test for each of its reporting units as of October 1, 2016 and determined that no impairment existed. There were no events subsequent to October 1, 2016 that indicated impairment of goodwill. There were no changes to the goodwill balance or the allocation of goodwill as of December 31, 2016 or 2015 . The following table presents goodwill by reportable segment: As of December 31, 2016 and 2015 (Billions of Dollars) Electric Distribution Electric Transmission Natural Gas Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 3.5

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
VARIABLE INTEREST ENTITIES	VARIABLE INTEREST ENTITIES The Company's variable interests outside of the consolidated group include 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, with other independent power producers and with transmission businesses. 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 these VIEs.

QUARTERLY FINANCIAL DATA (UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Data [Abstract]
QUARTERLY FINANCIAL DATA (UNAUDITED)	QUARTERLY FINANCIAL DATA (UNAUDITED) Quarter Ended Eversource (Millions of Dollars, except per share information) 2016 2015 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,055.6 $ 1,767.2 $ 2,039.7 $ 1,776.6 $ 2,513.4 $ 1,817.1 $ 1,933.1 $ 1,691.2 Operating Income 488.5 423.4 509.9 438.1 497.5 412.0 469.2 385.5 Net Income 246.0 205.5 267.2 231.1 255.1 209.4 237.8 183.7 Net Income Attributable to Common Shareholders 244.2 203.6 265.3 229.2 253.3 207.5 235.9 181.8 Basic EPS (1) $ 0.77 $ 0.64 $ 0.83 $ 0.72 $ 0.80 $ 0.65 $ 0.74 $ 0.57 Diluted EPS (1) $ 0.77 $ 0.64 $ 0.83 $ 0.72 $ 0.80 $ 0.65 $ 0.74 $ 0.57 (1) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2016 2015 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 735.3 $ 679.8 $ 760.0 $ 630.9 $ 804.9 $ 666.6 $ 704.3 $ 626.9 Operating Income 171.5 162.1 176.1 163.5 141.8 154.0 161.1 154.2 Net Income 87.0 82.9 86.6 77.8 69.2 78.8 80.2 71.2 NSTAR Electric Operating Revenues $ 614.2 $ 591.3 $ 780.5 $ 571.9 $ 766.8 $ 617.2 $ 750.7 $ 546.6 Operating Income 109.8 130.5 208.7 104.8 159.5 151.4 214.2 117.7 Net Income 54.5 68.2 117.2 52.8 83.6 82.0 118.6 60.3 PSNH Operating Revenues $ 242.3 $ 218.5 $ 266.9 $ 231.8 $ 284.8 $ 241.9 $ 234.4 $ 211.1 Operating Income 70.7 63.1 74.7 54.6 63.2 54.1 63.6 49.3 Net Income 36.1 31.3 38.5 26.1 32.0 27.9 32.5 22.0 WMECO Operating Revenues $ 128.1 $ 116.4 $ 124.0 $ 115.7 $ 152.9 $ 125.2 $ 125.1 $ 114.9 Operating Income 33.1 29.2 32.1 26.0 28.6 28.9 30.0 28.0 Net Income 16.8 13.3 16.0 12.0 13.2 14.2 15.0 14.1

SCHEDULE I - FINANCIAL INFORMAT

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT	SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT BALANCE SHEETS AS OF DECEMBER 31, 2016 AND 2015 (Thousands of Dollars) 2016 2015 ASSETS Current Assets: Cash $ 93 $ 67 Accounts Receivable from Subsidiaries 32,864 23,689 Notes Receivable from Subsidiaries 740,300 850,300 Prepayments and Other Current Assets 23,122 41,254 Total Current Assets 796,379 915,310 Deferred Debits and Other Assets: Investments in Subsidiary Companies, at Equity 9,703,287 8,915,178 Notes Receivable from Subsidiaries 224,290 128,800 Accumulated Deferred Income Taxes 126,091 143,054 Goodwill 3,231,811 3,231,811 Other Long-Term Assets 44,020 48,314 Total Deferred Debits and Other Assets 13,329,499 12,467,157 Total Assets $ 14,125,878 $ 13,382,467 LIABILITIES AND CAPITALIZATION Current Liabilities: Notes Payable $ 1,022,000 $ 1,098,453 Long-Term Debt - Current Portion 28,883 28,883 Accounts Payable — 78 Accounts Payable to Subsidiaries 8,771 15,601 Other Current Liabilities 47,215 60,999 Total Current Liabilities 1,106,869 1,204,014 Deferred Credits and Other Liabilities 148,756 134,908 Capitalization: Long-Term Debt 2,158,519 1,691,330 Equity: Common Shareholders' Equity: Common Shares 1,669,392 1,669,313 Capital Surplus, Paid in 6,250,224 6,262,368 Retained Earnings 3,175,171 2,797,355 Accumulated Other Comprehensive Loss (65,282 ) (66,844 ) Treasury Stock (317,771 ) (309,977 ) Common Shareholders' Equity 10,711,734 10,352,215 Total Capitalization 12,870,253 12,043,545 Total Liabilities and Capitalization $ 14,125,878 $ 13,382,467 See the Combined Notes to Consolidated Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 17, "Common Shares," material obligations and guarantees as described in Note 11, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF INCOME FOR THE YEARS ENDED DECEMBER 31, 2016 , 2015 AND 2014 (Thousands of Dollars, Except Share Information) 2016 2015 2014 Operating Revenues $ — $ — $ — Operating Expenses: Other (39,453 ) 9,315 29,598 Operating Income/(Loss) 39,453 (9,315 ) (29,598 ) Interest Expense 59,420 45,130 33,168 Other Income, Net: Equity in Earnings of Subsidiaries 922,321 900,824 848,435 Other, Net 4,267 6,602 1,830 Other Income, Net 926,588 907,426 850,265 Income Before Income Tax Benefit 906,621 852,981 787,499 Income Tax Benefit (35,681 ) (25,504 ) (32,047 ) Net Income $ 942,302 $ 878,485 $ 819,546 Basic Earnings per Common Share $ 2.97 $ 2.77 $ 2.59 Diluted Earnings per Common Share $ 2.96 $ 2.76 $ 2.58 Weighted Average Common Shares Outstanding: Basic 317,650,180 317,336,881 316,136,748 Diluted 318,454,239 318,432,687 317,417,414 STATEMENTS OF COMPREHENSIVE INCOME 2016 2015 2014 Net Income $ 942,302 $ 878,485 $ 819,546 Other Comprehensive Income/(Loss), Net of Tax: Qualified Cash Flow Hedging Instruments 2,137 2,079 2,037 Changes in Unrealized Gains/(Losses) on Marketable Securities 2,294 (2,588 ) 315 Change in Funded Status of Pension, SERP and PBOP Benefit Plans (2,869 ) 7,674 (30,330 ) Other Comprehensive Income/(Loss), Net of Tax 1,562 7,165 (27,978 ) Comprehensive Income $ 943,864 $ 885,650 $ 791,568 See the Combined Notes to Consolidated Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 17, "Common Shares," material obligations and guarantees as described in Note 11, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF CASH FLOWS FOR THE YEARS ENDED DECEMBER 31, 2016, 2015 and 2014 (Thousands of Dollars) 2016 2015 2014 Operating Activities: Net Income $ 942,302 $ 878,485 $ 819,546 Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities: Equity in Earnings of Subsidiaries (922,321 ) (900,824 ) (848,435 ) Cash Dividends Received from Subsidiaries 724,877 602,300 609,800 Deferred Income Taxes 19,008 16,880 7,956 Other (27,963 ) (22,864 ) 9,409 Changes in Current Assets and Liabilities: Accounts Receivables from Subsidiaries (9,173 ) (16,980 ) 88,800 Taxes Receivable/Accrued, Net 8,050 (14,426 ) 23,178 Accounts Payable, Including Affiliate Payables (6,908 ) (134,730 ) 5,942 Other Current Assets and Liabilities, Net (7,433 ) 6,832 14,484 Net Cash Flows Provided by Operating Activities 720,439 414,673 730,680 Investing Activities: Capital Contributions to Subsidiaries (589,500 ) (218,500 ) (437,553 ) Decrease/(Increase) in Notes Receivable from Subsidiaries 14,510 (131,650 ) 86,100 Other Investing Activities — 12,000 — Net Cash Flows Used in Investing Activities (574,990 ) (338,150 ) (351,453 ) Financing Activities: Cash Dividends on Common Shares (564,486 ) (529,791 ) (475,227 ) Issuance of Long-Term Debt 500,000 450,000 — (Decrease)/Increase in Short-Term Debt (76,453 ) (2,622 ) 86,575 Other Financing Activities (4,484 ) 5,819 9,528 Net Cash Flows (Used in)/Provided by Financing Activities (145,423 ) (76,594 ) (379,124 ) Net Increase/(Decrease) in Cash 26 (71 ) 103 Cash - Beginning of Year 67 138 35 Cash - End of Year $ 93 $ 67 $ 138 Supplemental Cash Flow Information: Cash Paid/(Received) During the Year for: Interest $ 58,018 $ 43,024 $ 36,208 Income Taxes $ (65,531 ) $ (34,680 ) $ (86,804 ) See the Combined Notes to Consolidated Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 17, "Common Shares," material obligations and guarantees as described in Note 11, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt."

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	12 Months Ended
	Dec. 31, 2016
Valuation and Qualifying Accounts [Abstract]
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	SCHEDULE II EVERSOURCE ENERGY AND SUBSIDIARIES VALUATION AND QUALIFYING ACCOUNTS AND RESERVES FOR THE YEARS ENDED DECEMBER 31, 2016 , 2015 AND 2014 (Thousands of Dollars) Column A Column B Column C Column D Column E Additions (1) (2) Charged Charged to Balance as to Costs Other Deductions - Balance of Beginning and Accounts - Describe as of Description: of Year Expenses Describe (a) (b) End of Year Eversource : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2016 $ 190,680 $ 69,466 $ 45,452 $ 104,968 $ 200,630 2015 175,317 51,077 79,622 115,336 190,680 2014 171,251 55,657 51,227 102,818 175,317 CL&P: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2016 $ 79,479 $ 17,572 $ 28,801 $ 39,461 $ 86,391 2015 84,287 10,105 30,592 45,505 79,479 2014 81,995 6,598 39,706 44,012 84,287 NSTAR Electric: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2016 $ 52,628 $ 27,978 $ 4,050 $ 29,884 $ 54,772 2015 40,670 14,228 29,559 31,829 52,628 2014 41,679 24,740 627 26,376 40,670 PSNH : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2016 $ 8,733 $ 7,288 $ 498 $ 6,578 $ 9,941 2015 7,663 8,889 841 8,660 8,733 2014 7,364 6,815 797 7,313 7,663 WMECO : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2016 $ 14,048 $ 3,750 $ 7,203 $ 9,489 $ 15,512 2015 9,880 4,940 7,418 8,190 14,048 2014 9,984 2,415 3,608 6,127 9,880 (a) Amounts relate to uncollectible accounts receivables reserved for that are not charged to bad debt expense. 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 hardship accounts receivable are expected to be recovered in future rates, similar to WMECO and NSTAR Gas. (b) Amounts written off, net of recoveries.

SUMMARY OF SIGNIFICANT ACCOUN35

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	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 assets) 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 reclassifications 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 the 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 Boards 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.
Accounting Standards	Accounting Standards A ccounting 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). The Company is evaluating the requirements and potential impacts of ASU 2014-09 and will implement the standard in the first quarter of 2018 cumulatively at the date of initial application. The guidance continues to be interpreted on an industry specific level, including the timing of recognizing revenues from billings to protected customers that may not meet the collectibility threshold for revenue recognition. Therefore, while the effects of implementing the ASU on results of operations are not expected to be material, there may be changes in the timing of revenue recognition on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH and WMECO. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Liabilities , which is required to be implemented in the first quarter of 2018. The ASU will remove the available-for-sale designation for equity securities, whereby changes in fair value are recorded in accumulated other comprehensive income within 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. The fair value of available-for-sale equity securities subject to this guidance as of December 31, 2016 was approximately $48 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 and WMECO. In February 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, including balance sheet recognition of leases previously deemed operating leases, and expects to implement the ASU in the first quarter of 2019. Recently Adopted Accounting Standards In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation: Improvements to Employee Share-Based Payment Accounting to simplify some aspects of the accounting for share-based payment transactions. The Company implemented this guidance in the first quarter of 2016, as permitted. Beginning in the first quarter of 2016, the excess tax benefits associated with the distribution of stock compensation awards, previously recognized in Capital Surplus, Paid In within Common Shareholders' Equity on the balance sheet, are recognized in income tax expense in the income statement. The impact of this ASU reduced income tax expense by $19.1 million for the year ended December 31, 2016 . Also, in the statement of cash flows, the excess tax benefits are presented as an operating activity rather than a financing activity beginning in 2016, and cash paid to satisfy the statutory income tax withholding obligation previously reflected within operating activities in 2015 and 2014 was retrospectively adjusted and is now treated as a financing activity. The cash payments to satisfy this obligation for the years ended December 31, 2016 , 2015 and 2014 were $26.6 million , $9.7 million and $16.5 million , respectively, and are included in Other Financing Activities on the statements of cash flows.
Cash and Cash Equivalents	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.
Provision for Uncollectible Accounts	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 management's assessment of collectability from customers. Management continuously assesses the collectability of receivables and adjusts collectability 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 also to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. Certain of NSTAR Electric's uncollectible hardship accounts receivable are expected to be recovered in future rates, similar to WMECO and NSTAR Gas. These uncollectible customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets.
Fuel, Materials and Supplies, and Allowance Inventory, and REC inventory	Fuel, Materials, Supplies and Inventory Fuel, Materials, Supplies and Inventory include natural gas, coal, biomass and oil inventories, materials and supplies purchased primarily for construction or operation and maintenance purposes, RECs and emission allowances. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and 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 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, Supplies and Inventory on the balance sheet and are classified as current or long-term depending on the period in which they are expected to be utilized against actual emissions.
Deposits	Deposits As of December 31, 2016 , Eversource, CL&P, NSTAR Electric and PSNH had $21.7 million , $1.4 million , $11.8 million and $0.5 million , respectively, of cash collateral posted not subject to master netting agreements, with ISO-NE related to energy transactions, which was included in Prepayments and Other Current Assets on the balance sheets.
Fair Value Measurements	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 estimated 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 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. Certain investments held in the Pension and PBOP plans have been valued using net asset value ("NAV") as a practical expedient. These investments are not traded on an exchange and are typically structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. They include commingled funds, private equity funds, real estate funds and hedge funds. In 2016, Eversource retrospectively adopted new accounting guidance that requires investments for which fair value is measured using the NAV practical expedient no longer be classified within the fair value hierarchy. Investments valued using the NAV practical expedient are included separately in fair value disclosures and are not classified within any of the fair value hierarchy levels. Prior to the adoption of this guidance, these investments were reported within Level 2 or Level 3 of the fair value hierarchy. The adoption of this guidance changes fair value disclosures, but does not impact the methodology for valuing these investments, or the financial statement results.
Derivative Accounting	Derivative Accounting Many of the Regulated companies' contracts for the purchase and sale of energy 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 significant impact on the financial statements. The judgment 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 changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.
Equity Method Investments	Investments Investments are included in Other Long-Term Assets on the balance sheets and earnings impacts from equity investments are included in Other Income, Net on the statements of income.
Revenues	Revenues Regulated Companies' Retail Revenues: The Regulated companies' retail revenues are based on rates approved by their 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 rates to be changed periodically to ensure recovery of actual costs incurred. CL&P, WMECO and NSTAR Gas each have a regulatory commission approved revenue decoupling mechanism. NSTAR Gas' decoupling mechanism was effective January 1, 2016. Distribution revenues are decoupled from customer sales volumes, where applicable, which breaks the relationship between sales volumes and revenues recognized. CL&P, WMECO and NSTAR Gas 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 is adjusted through rates in a subsequent 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 customers in rates through cost tracking mechanisms. Energy purchases are recorded in Purchased Power, Fuel and Transmission, and the sales of energy associated with these purchases are recorded in Operating Revenues on the statements of income. 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 Assets 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 volumes monthly by first allocating billed sales volumes to the current calendar month based on the daily load (for electric distribution companies) or the daily send-out (for natural gas distribution companies) for each billing cycle. The billed sales volumes are then subtracted from total month load or send-out, net of delivery losses, to estimate unbilled sales volumes. Unbilled revenues are estimated by first allocating unbilled sales volumes to the respective customer classes, then applying an estimated rate by customer class to those sales volumes. The estimate of unbilled revenues can significantly impact the amount of revenues recorded at NSTAR Electric, PSNH and Yankee Gas because they do not have a revenue decoupling mechanism. CL&P, WMECO and NSTAR Gas record a regulatory deferral to reflect the actual allowed amount of revenue associated with their respective decoupled distribution rate design. Regulated Companies' Transmission Revenues - Wholesale Rates: The Eversource transmission owning companies have a combination of FERC-approved regional and local formula rates that work in tandem to recover all their transmission costs. These rates are part of the ISO-NE Tariff. Regional rates recover the costs of higher voltage transmission facilities that benefit the region, and are collected from all New England transmission customers, including the Eversource distribution businesses. Eversource has two sets of local rates, one for the combined transmission revenue requirements of CL&P, PSNH and WMECO, and the other for NSTAR Electric. These local rates recover the companies' total transmission revenue requirements, less revenues received from regional rates and other sources, and are collected from Eversource's distribution businesses and other transmission customers. The distribution businesses of Eversource, in turn, recover the FERC approved charges from retail customers through annual or semiannual tracking mechanisms. The transmission formula rates 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, "Commitments 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.
Allowance for Funds Used During Construction	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 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 Income, Net	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 income/(loss) related to equity method investees. Investment income/(loss) primarily relates to debt and equity securities held in trust.
Other Taxes	Other Taxes Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers.
Related Parties	Related Parties Eversource Service, Eversource's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, and other services to Eversource's companies. The Rocky River Realty Company, Renewable Properties, Inc. and Properties, Inc., three other Eversource subsidiaries, construct, acquire or lease some of the property and facilities used by Eversource's companies.

SUMMARY OF SIGNIFICANT ACCOUN36

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Accounts, Notes, Loans and Financing Receivable	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 were as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2016 2015 2016 2015 Eversource $ 200.6 $ 190.7 $ 119.9 $ 118.5 CL&P 86.4 79.5 67.7 68.1 NSTAR Electric 54.8 52.6 26.2 25.3 PSNH 9.9 8.7 — — WMECO 15.5 14.0 9.9 7.4
Schedule of Utility Inventory	The carrying amounts of fuel, materials and supplies, RECs, and emission allowances were as follows: As of December 31, 2016 2015 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Eversource CL&P NSTAR Electric PSNH WMECO Current: Fuel $ 135.7 $ — $ — $ 99.9 $ — $ 152.5 $ — $ — $ 103.4 $ — Materials and Supplies 142.7 48.2 34.5 47.3 5.2 131.2 43.1 32.2 44.6 5.4 RECs 47.9 3.9 27.8 12.8 3.4 50.9 — 43.3 7.0 0.6 Emission Allowances 2.4 — — 2.4 — 1.9 — — 1.9 — Long-Term: Emission Allowances 17.5 — — 17.5 — 17.5 — — 17.5 —
Schedule of Fuel Costs	Costs related to fuel and natural gas included in Purchased Power, Fuel and Transmission on the statements of income were as follows: For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Eversource - Natural Gas and Fuel $ 372.2 $ 516.7 $ 599.4 PSNH - Fuel 45.0 85.4 113.4
Schedule of Allowance For Funds Used During Construction	AFUDC costs and the weighted-average AFUDC rates were as follows: Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2016 2015 2014 Borrowed Funds $ 10.8 $ 7.2 $ 5.8 Equity Funds 26.2 18.8 13.7 Total AFUDC $ 37.0 $ 26.0 $ 19.5 Average AFUDC Rate 4.4 % 3.9 % 3.4 % For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars, except percentages) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Borrowed Funds $ 3.3 $ 4.6 $ 0.8 $ 0.6 $ 2.6 $ 2.0 $ 1.0 $ 1.0 $ 1.9 $ 2.0 $ 0.6 $ 0.9 Equity Funds 6.3 10.2 0.3 — 5.2 4.3 1.2 1.7 2.9 3.8 0.6 1.7 Total AFUDC $ 9.6 $ 14.8 $ 1.1 $ 0.6 $ 7.8 $ 6.3 $ 2.2 $ 2.7 $ 4.8 $ 5.8 $ 1.2 $ 2.6 Average AFUDC Rate 4.7 % 3.9 % 1.0 % 0.8 % 5.5 % 3.2 % 1.8 % 4.4 % 3.4 % 2.5 % 1.8 % 5.6 %
Schedule of Gross Earnings Taxes	These gross receipts taxes are shown separately with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the statements of income as follows: For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Eversource $ 162.7 $ 147.2 $ 148.2 CL&P 145.2 128.5 127.9
Schedule of Supplemental Cash Flow Information	Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2016 2015 2014 Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 398.1 $ 365.9 $ 349.6 Income Taxes (135.5 ) 10.3 334.2 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 301.5 216.6 181.9 As of and For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 143.3 $ 88.2 $ 46.5 $ 24.7 $ 144.4 $ 75.7 $ 42.3 $ 26.7 $ 144.1 $ 75.3 $ 41.1 $ 25.9 Income Taxes (73.9 ) 80.7 (36.0 ) (14.7 ) 55.2 (19.8 ) 14.4 14.7 135.4 217.1 2.3 25.1 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 116.2 60.9 37.9 26.1 76.0 23.5 46.5 27.0 63.5 34.6 39.3 14.2

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
Schedule of Regulatory Assets	The components of regulatory assets were as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Benefit Costs $ 1,817.8 $ 1,828.2 Derivative Liabilities 423.3 388.0 Income Taxes, Net 644.5 650.9 Storm Restoration Costs 385.3 436.9 Goodwill-related 464.4 484.9 Regulatory Tracker Mechanisms 576.6 526.5 Contractual Obligations - Yankee Companies 84.9 134.4 Other Regulatory Assets 129.5 134.0 Total Regulatory Assets 4,526.3 4,583.8 Less: Current Portion 887.6 845.8 Total Long-Term Regulatory Assets $ 3,638.7 $ 3,738.0 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR PSNH WMECO Benefit Costs $ 429.3 $ 438.6 $ 184.2 $ 86.7 $ 413.6 $ 479.9 $ 164.2 $ 84.9 Derivative Liabilities 420.5 2.8 — — 380.8 1.3 — — Income Taxes, Net 437.0 89.7 24.2 30.8 444.4 85.7 34.5 31.8 Storm Restoration Costs 239.8 112.5 17.1 15.9 271.4 110.9 31.5 23.1 Goodwill-related — 398.7 — — — 416.3 — — Regulatory Tracker Mechanisms 123.9 257.3 104.5 46.7 45.1 311.0 101.2 40.1 Other Regulatory Assets 76.6 47.5 32.7 11.3 82.0 56.3 31.5 11.3 Total Regulatory Assets 1,727.1 1,347.1 362.7 191.4 1,637.3 1,461.4 362.9 191.2 Less: Current Portion 335.5 289.4 117.2 64.1 268.3 348.4 105.0 56.2 Total Long-Term Regulatory Assets $ 1,391.6 $ 1,057.7 $ 245.5 $ 127.3 $ 1,369.0 $ 1,113.0 $ 257.9 $ 135.0
Schedule of Regulatory Liabilities	The components of regulatory liabilities were as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Cost of Removal $ 459.7 $ 437.1 Regulatory Tracker Mechanisms 145.3 99.7 Benefit Costs 136.2 — AFUDC - Transmission 65.8 66.1 Other Regulatory Liabilities 42.1 18.5 Total Regulatory Liabilities 849.1 621.4 Less: Current Portion 146.8 107.8 Total Long-Term Regulatory Liabilities $ 702.3 $ 513.6 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cost of Removal $ 38.8 $ 271.6 $ 44.1 $ 8.6 $ 24.1 $ 257.4 $ 47.2 $ 2.8 Benefit Costs — 113.1 — — — — — — Regulatory Tracker Mechanisms 37.2 63.7 10.7 14.7 56.2 3.3 3.4 12.9 AFUDC - Transmission 50.2 6.9 — 8.7 51.5 5.7 — 8.9 Other Regulatory Liabilities 21.0 0.2 2.7 0.1 4.2 1.3 4.2 0.1 Total Regulatory Liabilities 147.2 455.5 57.5 32.1 136.0 267.7 54.8 24.7 Less: Current Portion 47.1 63.7 12.7 14.9 61.2 3.3 6.9 13.1 Total Long-Term Regulatory Liabilities $ 100.1 $ 391.8 $ 44.8 $ 17.2 $ 74.8 $ 264.4 $ 47.9 $ 11.6

PROPERTY, PLANT AND EQUIPMENT38

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Schedule of Utility Property, Plant and Equipment	The following tables summarize the investments in utility property, plant and equipment by asset category: Eversource As of December 31, (Millions of Dollars) 2016 2015 Distribution - Electric $ 13,716.9 $ 13,054.8 Distribution - Natural Gas 3,010.4 2,727.2 Transmission - Electric 8,517.4 7,691.9 Generation 1,224.2 1,194.1 Electric and Natural Gas Utility 26,468.9 24,668.0 Other (1) 591.6 558.6 Property, Plant and Equipment, Gross 27,060.5 25,226.6 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,480.4 ) (6,141.1 ) Other (242.0 ) (255.6 ) Total Accumulated Depreciation (6,722.4 ) (6,396.7 ) Property, Plant and Equipment, Net 20,338.1 18,829.9 Construction Work in Progress 1,012.4 1,062.5 Total Property, Plant and Equipment, Net $ 21,350.5 $ 19,892.4 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Distribution $ 5,562.9 $ 5,402.3 $ 1,949.8 $ 841.9 $ 5,377.2 $ 5,100.5 $ 1,804.8 $ 812.3 Transmission 3,912.9 2,435.8 1,059.3 1,061.1 3,618.0 2,131.3 928.2 964.9 Generation — — 1,188.2 36.0 — — 1,158.1 36.0 Property, Plant and Equipment, Gross 9,475.8 7,838.1 4,197.3 1,939.0 8,995.2 7,231.8 3,891.1 1,813.2 Less: Accumulated Depreciation (2,082.4 ) (2,025.4 ) (1,254.7 ) (338.8 ) (2,041.9 ) (1,886.8 ) (1,171.0 ) (307.0 ) Property, Plant and Equipment, Net 7,393.4 5,812.7 2,942.6 1,600.2 6,953.3 5,345.0 2,720.1 1,506.2 Construction Work in Progress 239.0 239.1 96.7 78.1 203.5 310.5 135.3 69.1 Total Property, Plant and Equipment, Net $ 7,632.4 $ 6,051.8 $ 3,039.3 $ 1,678.3 $ 7,156.8 $ 5,655.5 $ 2,855.4 $ 1,575.3 The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2016 (Years) Eversource CL&P NSTAR Electric PSNH WMECO Distribution 35.1 37.7 32.0 31.3 30.7 Transmission 41.5 38.0 43.8 43.5 49.7 Generation 29.0 — — 29.1 25.0 Other 11.0 — — — — The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows: (Percent) 2016 2015 2014 Eversource 3.0 % 2.9 % 3.0 % CL&P 2.7 % 2.7 % 2.7 % NSTAR Electric 3.0 % 3.0 % 3.0 % PSNH 3.1 % 3.2 % 3.0 % WMECO 2.7 % 2.7 % 3.3 %

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The following table presents the gross fair values of contracts, categorized by risk type, and the net amounts recorded as current or long-term derivative assets or liabilities: As of December 31, 2016 2015 (Millions of Dollars) Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: Level 2: Eversource $ 6.0 $ — $ 6.0 $ — $ — $ — Level 3: Eversource, CL&P 13.9 (9.4 ) 4.5 16.7 (10.9 ) 5.8 Long-Term Derivative Assets: Level 2: Eversource $ 0.3 $ (0.1 ) $ 0.2 $ 0.1 $ — $ 0.1 Level 3: Eversource 77.3 (11.7 ) 65.6 62.0 (19.3 ) 42.7 CL&P 77.3 (11.7 ) 65.6 60.7 (19.3 ) 41.4 NSTAR Electric — — — 1.3 — 1.3 Current Derivative Liabilities: Level 2: Eversource $ — $ — $ — $ (5.8 ) $ — $ (5.8 ) Level 3: Eversource (79.7 ) — (79.7 ) (92.3 ) — (92.3 ) CL&P (77.8 ) — (77.8 ) (91.8 ) — (91.8 ) NSTAR Electric (1.9 ) — (1.9 ) (0.5 ) — (0.5 ) Long-Term Derivative Liabilities : Level 3: Eversource $ (413.7 ) $ — $ (413.7 ) $ (337.1 ) $ — $ (337.1 ) CL&P (412.8 ) — (412.8 ) (336.2 ) — (336.2 ) NSTAR Electric (0.9 ) — (0.9 ) (0.9 ) — (0.9 ) (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.
Fair Value Inputs, Liabilities, Quantitative Information	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 valuations over the duration of the contracts: As of December 31, 2016 2015 Range Period Covered Range Period Covered Capacity Prices: Eversource $ 5.50 — 8.70 per kW-Month 2020 - 2026 $ 10.81 — 15.82 per kW-Month 2016 - 2026 CL&P 5.50 — 8.70 per kW-Month 2020 - 2026 10.81 — 12.60 per kW-Month 2019 - 2026 Forward Reserve: Eversource, CL&P $ 1.40 — 2.00 per kW-Month 2017 - 2024 $2.00 per kW-Month 2016 - 2024 REC Prices: Eversource, NSTAR Electric $ 24 — 29 per REC 2017 - 2018 $ 45 — 51 per REC 2016 - 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation	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, 2015 $ (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 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (130.7 ) (122.7 ) (8.0 ) Settlements 88.3 83.0 5.3 Fair Value as of December 31, 2016 $ (423.3 ) $ (420.5 ) $ (2.8 )

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities Reconciliation	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, 2016 2015 (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Eversource Debt Securities $ 296.2 $ 1.1 $ (2.1 ) $ 295.2 $ 256.5 $ 4.5 $ (0.6 ) $ 260.4 Equity Securities 203.3 62.3 (1.2 ) 264.4 215.3 59.2 (3.4 ) 271.1
Investments Classified by Contractual Maturity Date	As of December 31, 2016 , the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Cost Fair Value Less than one year (1) $ 60.5 $ 60.3 One to five years 45.4 45.8 Six to ten years 59.7 58.3 Greater than ten years 130.6 130.8 Total Debt Securities $ 296.2 $ 295.2 (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 sheets.
Marketable Securities Recorded at Fair Value	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 (Millions of Dollars) As of December 31, 2016 2015 Level 1: Mutual Funds and Equities $ 274.0 $ 285.3 Money Market Funds 54.8 26.9 Total Level 1 $ 328.8 $ 312.2 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 63.0 $ 46.6 Corporate Debt Securities 41.1 43.9 Asset-Backed Debt Securities 18.5 20.0 Municipal Bonds 107.5 111.4 Other Fixed Income Securities 10.3 11.6 Total Level 2 $ 240.4 $ 233.5 Total Marketable Securities $ 569.2 $ 545.7

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Change in Asset Retirement Obligation	A reconciliation of the beginning and ending carrying amounts of ARO liabilities are as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Balance as of Beginning of Year $ 430.1 $ 426.3 Liabilities Incurred During the Year 1.3 6.6 Liabilities Settled During the Year (19.0 ) (18.2 ) Accretion 22.9 26.5 Revisions in Estimated Cash Flows (8.9 ) (11.1 ) Balance as of End of Year $ 426.4 $ 430.1 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Balance as of Beginning of Year $ 33.8 $ 35.3 $ 21.6 $ 5.7 $ 35.3 $ 34.3 $ 20.6 $ 5.9 Liabilities Incurred During the Year — — 0.5 — — 6.2 0.4 — Liabilities Settled During the Year — (0.3 ) — (0.1 ) — (1.5 ) — (0.1 ) Accretion 2.2 1.7 1.4 0.3 2.2 1.8 1.3 0.4 Revisions in Estimated Cash Flows — — — — (3.7 ) (5.5 ) (0.7 ) (0.5 ) Balance as of End of Year $ 36.0 $ 36.7 $ 23.5 $ 5.9 $ 33.8 $ 35.3 $ 21.6 $ 5.7

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2016 2015 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 5.625% 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 350.0 350.0 Total First Mortgage Bonds 2,669.8 2,669.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year (250.0 ) — Unamortized Premiums and Discounts, Net (10.0 ) (10.7 ) Unamortized Debt Issuance Costs (14.3 ) (15.9 ) CL&P Long-Term Debt $ 2,516.0 $ 2,763.7 NSTAR Electric (Millions of Dollars) As of December 31, 2016 2015 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% as of December 31, 2015) — 200.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 250.0 2.700% due 2026 250.0 — Total Debentures 2,100.0 2,050.0 Less Amounts due Within One Year (400.0 ) (200.0 ) Unamortized Premiums and Discounts, Net (9.1 ) (8.5 ) Unamortized Debt Issuance Costs (12.8 ) (11.7 ) NSTAR Electric Long-Term Debt $ 1,678.1 $ 1,829.8 PSNH (Millions of Dollars) As of December 31, 2016 2015 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 6.150% Series N due 2017 70.0 70.0 6.000% Series O due 2018 110.0 110.0 4.500% Series P due 2019 150.0 150.0 4.050% Series Q due 2021 122.0 122.0 3.200% Series R due 2021 160.0 160.0 3.500% 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 (1.138% and 0.193% as of December 31, 2016 and 2015, respectively) 89.3 89.3 Less Amounts due Within One Year (70.0 ) — Unamortized Premiums and Discounts, Net 0.1 0.1 Unamortized Debt Issuance Costs (4.4 ) (5.4 ) PSNH Long-Term Debt $ 1,002.0 $ 1,071.0 WMECO (Millions of Dollars) As of December 31, 2016 2015 Notes: 5.900% Senior Notes Series B due 2034 $ 50.0 $ 50.0 6.700% Senior Notes Series D due 2037 40.0 40.0 5.100% Senior Notes Series E due 2020 95.0 95.0 3.500% Senior Notes Series F due 2021 250.0 250.0 3.880% Senior Notes Series G due 2023 80.0 80.0 2.750% Senior Notes Series H due 2026 50.0 — Total Notes 565.0 515.0 Unamortized Premiums and Discounts, Net 4.2 5.2 Unamortized Debt Issuance Costs (2.7 ) (2.9 ) WMECO Long-Term Debt $ 566.5 $ 517.3 OTHER (Millions of Dollars) As of December 31, 2016 2015 Yankee Gas - First Mortgage Bonds: 8.480% Series B due 2022 $ 20.0 $ 20.0 5.260% Series H due 2019 50.0 50.0 5.350% Series I due 2035 50.0 50.0 6.900% Series J due 2018 100.0 100.0 4.870% Series K due 2020 50.0 50.0 4.820% Series L due 2044 100.0 100.0 3.350% Series M due 2025 75.0 75.0 Total First Mortgage Bonds 445.0 445.0 Unamortized Premium 0.4 0.4 Unamortized Debt Issuance Costs (1.5 ) (1.7 ) Yankee Gas Long-Term Debt 443.9 443.7 NSTAR Gas - First Mortgage Bonds: 9.950% Series J due 2020 25.0 25.0 7.110% Series K due 2033 35.0 35.0 7.040% Series M due 2017 25.0 25.0 4.460% Series N due 2020 125.0 125.0 4.350% Series O due 2045 100.0 100.0 Total First Mortgage Bonds 310.0 310.0 Less Amounts due Within One Year (25.0 ) — Unamortized Debt Issuance Costs (0.7 ) (0.8 ) NSTAR Gas Long-Term Debt 284.3 309.2 Eversource Parent - Notes and Debentures: 4.500% Debentures due 2019 350.0 350.0 1.450% Senior Notes Series E due 2018 300.0 300.0 2.800% Senior Notes Series F due 2023 450.0 450.0 1.600% Senior Notes Series G due 2018 150.0 150.0 3.150% Senior Notes Series H due 2025 300.0 300.0 2.500% Senior Notes Series I due 2021 250.0 — 3.350% Senior Notes Series J due 2026 250.0 — Total Eversource Parent Notes and Debentures 2,050.0 1,550.0 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 180.0 179.5 Fair Value Adjustment (1) 144.6 173.5 Less Fair Value Adjustment - Current Portion (1) (28.9 ) (28.9 ) Unamortized Premiums and Discounts, Net (2.2 ) (1.3 ) Unamortized Debt Issuance Costs (4.9 ) (1.9 ) Total Other Long-Term Debt $ 3,066.8 $ 2,623.8 Total Eversource Long-Term Debt $ 8,829.4 $ 8,805.6 (1) 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 2012 merger.
Schedule of Long-term Debt Instruments	Long-term debt maturities on debt outstanding for the years 2017 through 2021 and thereafter are shown below. These amounts exclude the CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2016 : (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 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 2021 871.3 — — 371.3 250.0 Thereafter 5,665.3 1,990.3 1,700.0 375.0 220.0 Total $ 9,336.6 $ 2,790.3 $ 2,100.0 $ 1,076.3 $ 565.0

EMPLOYEE BENEFITS (Tables)

EMPLOYEE BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	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) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,051.4 ) $ (1,147.9 ) Plan Amendment 244.0 — Service Cost (12.2 ) (16.3 ) Interest Cost (32.9 ) (47.2 ) Actuarial Gain/(Loss) (17.7 ) 106.0 Benefits Paid 60.2 54.0 Benefit Obligation as of End of Year $ (810.0 ) $ (1,051.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 812.2 $ 862.6 Actual Return on Plan Assets 51.3 (4.3 ) Employer Contributions 12.5 7.9 Benefits Paid (60.2 ) (54.0 ) Fair Value of Plan Assets as of End of Year $ 815.8 $ 812.2 Funded Status as of December 31st $ 5.8 $ (239.2 ) PBOP As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) $ (173.9 ) $ (468.7 ) $ (91.8 ) $ (36.6 ) Plan Amendment (12.5 ) 195.3 (6.7 ) (1.7 ) — — — — Change due to transfer of employees 1.3 0.3 0.3 0.2 0.1 2.3 (0.3 ) — Service Cost (2.0 ) (3.0 ) (1.3 ) (0.4 ) (2.1 ) (5.4 ) (1.4 ) (0.4 ) Interest Cost (5.3 ) (12.2 ) (2.9 ) (1.1 ) (7.2 ) (19.0 ) (3.9 ) (1.5 ) Actuarial Gain/(Loss) 3.6 (24.6 ) 3.6 1.1 7.2 59.1 3.6 1.5 Benefits Paid 13.9 20.3 5.8 3.0 11.9 18.9 5.3 2.6 Benefit Obligation as of End of Year $ (165.0 ) $ (236.7 ) $ (89.7 ) $ (33.3 ) $ (164.0 ) $ (412.8 ) $ (88.5 ) $ (34.4 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 136.7 $ 320.3 $ 75.8 $ 31.7 $ 149.0 $ 336.5 $ 80.9 $ 34.4 Change due to transfer of employees (0.8 ) (0.3 ) (0.2 ) (0.3 ) — 0.6 0.2 — Actual Return on Plan Assets 7.2 23.2 3.4 1.4 (0.4 ) (2.8 ) — (0.1 ) Employer Contributions — 8.9 — — — 4.9 — — Benefits Paid (13.9 ) (20.3 ) (5.8 ) (3.0 ) (11.9 ) (18.9 ) (5.3 ) (2.6 ) Fair Value of Plan Assets as of End of Year $ 129.2 $ 331.8 $ 73.2 $ 29.8 $ 136.7 $ 320.3 $ 75.8 $ 31.7 Funded Status as of December 31st $ (35.8 ) $ 95.1 $ (16.5 ) $ (3.5 ) $ (27.3 ) $ (92.5 ) $ (12.7 ) $ (2.7 ) The following tables provide information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP Eversource As of December 31, (Millions of Dollars) 2016 2015 Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,080.1 ) $ (5,486.2 ) Plan Amendment (9.0 ) — Service Cost (75.0 ) (91.4 ) Interest Cost (185.5 ) (227.0 ) Actuarial Gain/(Loss) (151.8 ) 331.5 Benefits Paid - Pension 254.0 238.5 Benefits Paid - Lump Sum — 149.5 Benefits Paid - SERP 5.1 5.0 Benefit Obligation as of End of Year $ (5,242.3 ) $ (5,080.1 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 3,905.4 $ 4,126.5 Employer Contributions 146.2 154.6 Actual Return on Pension Plan Assets 278.4 12.3 Benefits Paid (254.0 ) (238.5 ) Benefits Paid - Lump Sum — (149.5 ) Fair Value of Pension Plan Assets as of End of Year $ 4,076.0 $ 3,905.4 Funded Status as of December 31st $ (1,166.3 ) $ (1,174.7 ) Pension and SERP As of December 31, 2016 As of December 31, 2015 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) $ (1,230.1 ) $ (982.6 ) $ (580.7 ) $ (249.4 ) Plan Amendment — (2.8 ) — — — — — — Change due to transfer of employees 8.8 (0.6 ) 2.4 1.9 (4.6 ) 6.2 (1.9 ) (1.3 ) Service Cost (18.8 ) (13.2 ) (9.9 ) (3.1 ) (24.7 ) (14.9 ) (12.1 ) (4.3 ) Interest Cost (41.6 ) (33.8 ) (20.7 ) (8.4 ) (51.1 ) (40.2 ) (24.3 ) (10.4 ) Actuarial Gain/(Loss) (23.9 ) (33.3 ) (21.5 ) (3.9 ) 77.8 34.1 38.9 12.6 Benefits Paid - Pension 62.6 53.8 24.9 13.2 60.2 47.6 23.2 12.7 Benefits Paid - Lump Sum — — — — 14.5 — 9.1 2.5 Benefits Paid - SERP 0.3 0.2 0.2 — 0.4 0.1 0.2 — Benefit Obligation as of End of Year $ (1,170.2 ) $ (979.4 ) $ (572.2 ) $ (237.9 ) $ (1,157.6 ) $ (949.7 ) $ (547.6 ) $ (237.6 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 913.5 $ 832.9 $ 470.5 $ 220.8 $ 980.8 $ 879.0 $ 498.4 $ 234.0 Change due to transfer of employees (8.8 ) 0.6 (2.4 ) (1.9 ) 4.6 (6.2 ) 1.9 1.3 Employer Contributions 0.4 28.4 17.1 — — 5.0 1.0 — Actual Return on Pension Plan Assets 63.0 59.2 33.7 15.3 2.8 2.7 1.5 0.7 Benefits Paid (62.6 ) (53.8 ) (24.9 ) (13.2 ) (60.2 ) (47.6 ) (23.2 ) (12.7 ) Benefits Paid - Lump Sum — — — — (14.5 ) — (9.1 ) (2.5 ) Fair Value of Pension Plan Assets as of End of Year $ 905.5 $ 867.3 $ 494.0 $ 221.0 $ 913.5 $ 832.9 $ 470.5 $ 220.8 Funded Status as of December 31st $ (264.7 ) $ (112.1 ) $ (78.2 ) $ (16.9 ) $ (244.1 ) $ (116.8 ) $ (77.1 ) $ (16.8 )
Schedule of Defined Benefit Plans Disclosures	The components of net periodic benefit 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 expense 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 12.2 $ 2.0 $ 3.0 $ 1.3 $ 0.4 Interest Cost 32.9 5.3 12.2 2.9 1.1 Expected Return on Plan Assets (62.9 ) (10.1 ) (25.7 ) (5.5 ) (2.4 ) Actuarial Loss 9.0 1.5 3.2 0.7 0.1 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.2 ) 0.2 0.1 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (14.5 ) $ (0.4 ) $ (0.7 ) Intercompany Allocations N/A $ 0.3 $ (0.2 ) $ (0.1 ) $ 0.1 Capitalized PBOP Expense/(Income) $ (8.0 ) $ (0.5 ) $ (6.4 ) $ 0.1 $ (0.3 ) PBOP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 As of December 31, 2016 and 2015 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 4,829.6 $ 1,065.2 $ 904.8 $ 518.9 $ 220.0 2015 4,733.2 1,062.7 888.8 506.4 222.3 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status:
Schedule of Assumptions Used	The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2016 2015 Discount Rate 4.01% — 4.33% 4.21% — 4.60% Compensation/Progression Rate 3.50% 3.50% The following actuarial assumptions were used in calculating the PBOP Plan's year end funded status: PBOP As of December 31, 2016 2015 Discount Rate 4.21 % 4.62 % Health Care Cost Trend Rate N/A 6.25 % The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2016 2015 2014 Discount Rate 2.88% — 4.09% 4.22% 4.78 % — 5.10 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2016 2015 2014 Discount Rate 3.27 % — 4.89 % 4.20% 4.85 % — 5.03 % Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 3.50 % — 4.00 %
Schedule of Net Benefit Costs	Pension and SERP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO Service Cost $ 75.0 $ 18.8 $ 13.2 $ 9.9 $ 3.1 Interest Cost 185.5 41.6 33.8 20.7 8.4 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (67.6 ) (38.6 ) (17.5 ) Actuarial Loss 125.7 25.4 34.4 9.9 5.5 Prior Service Cost 3.6 1.5 — 0.5 0.3 Total Net Periodic Benefit Expense/(Income) $ 71.9 $ 15.2 $ 13.8 $ 2.4 $ (0.2 ) Intercompany Allocations N/A $ 13.8 $ 8.9 $ 4.0 $ 2.5 Capitalized Pension Expense $ 22.1 $ 9.3 $ 7.6 $ 1.4 $ 0.4 Pension and SERP For the Year Ended December 31, 2015 (Millions of Dollars) Eversource (1) CL&P NSTAR 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 (Millions of Dollars) Eversource CL&P NSTAR 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 (1) Amounts exclude $3.2 million for the year ended December 31, 2015 that represent amounts included in other deferred debits.
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 184.6 $ (2.0 ) $ 6.8 $ (6.2 ) Actuarial Losses Reclassified as Net Periodic Benefit Expense (119.9 ) (142.3 ) (5.8 ) (6.2 ) Prior Service Cost Arising During the Year 7.1 — 1.9 — Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.4 ) (3.5 ) (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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 1,732.3 $ 1,667.6 $ 128.5 $ 82.1 $ 81.1 $ 5.8 Prior Service Cost 13.4 9.7 4.1 2.3 0.6 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) 2016 2015 2016 2015 Actuarial Losses/(Gains) Arising During the Year $ 32.4 $ (34.1 ) $ (2.0 ) $ 0.7 Actuarial (Losses)/Gains Reclassified as Net Periodic Benefit (Expense)/Income (9.2 ) (6.4 ) 0.2 (0.4 ) Prior Service (Credit)/Cost Arising During the Year (247.9 ) — 4.0 — Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 9.7 0.5 (0.6 ) — 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, 2016 and 2015 , as well as the amounts that are expected to be recognized as components in 2017 : Regulatory Assets as of December 31, Expected 2017 Expense AOCL as of December 31, Expected 2017 Expense (Millions of Dollars) 2016 2015 2016 2015 Actuarial Loss $ 175.4 $ 152.2 $ 7.9 $ 4.5 $ 6.3 $ 0.4 Prior Service (Credit)/Cost (239.5 ) (1.3 ) (21.7 ) 3.4 — 0.2
Schedule of Expected 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) 2017 2018 2019 2020 2021 2022-2026 Pension and SERP $ 284.5 $ 277.0 $ 284.3 $ 290.4 $ 298.9 $ 1,562.9 PBOP 54.8 55.0 55.1 55.4 55.4 270.7
Schedule of Allocation of Plan Assets	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) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 455.5 $ — $ 1,279.7 $ 1,735.2 $ 396.5 $ 62.2 $ 1,228.7 $ 1,687.4 Private Equity 6.0 — 518.4 524.4 7.6 — 464.7 472.3 Fixed Income (2) — 183.0 1,099.4 1,282.4 — 208.6 1,008.2 1,216.8 Real Estate and Other Assets 77.2 — 325.9 403.1 — 85.9 291.9 377.8 Hedge Funds — — 335.0 335.0 — — 340.5 340.5 Total $ 538.7 $ 183.0 $ 3,558.4 $ 4,280.1 $ 404.1 $ 356.7 $ 3,334.0 $ 4,094.8 Less: 401(h) PBOP Assets (3) (204.1 ) (189.4 ) Total Pension Assets $ 4,076.0 $ 3,905.4 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2016 2015 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 88.6 $ — $ 214.1 $ 302.7 $ 109.7 $ — $ 199.4 $ 309.1 Private Equity — — 32.2 32.2 — — 32.9 32.9 Fixed Income (2) 9.5 44.8 132.3 186.6 9.7 50.5 131.0 191.2 Real Estate and Other Assets 15.5 — 27.5 43.0 — 6.6 30.8 37.4 Hedge Funds — — 47.2 47.2 — — 52.2 52.2 Total $ 113.6 $ 44.8 $ 453.3 $ 611.7 $ 119.4 $ 57.1 $ 446.3 $ 622.8 Add: 401(h) PBOP Assets (3) 204.1 189.4 Total PBOP Assets $ 815.8 $ 812.2 (1) United States, International and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include fixed income funds that invest in a variety of opportunistic fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plan. 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, 2016 and 2015 Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Equity Securities: United States 22.0 % 8.5 % International 13.0 % 8.5 % Emerging Markets 5.0 % 10.0 % Private Equity 12.0 % 12.0 % Debt Securities: Fixed Income 12.0 % 4.5 % High Yield Fixed Income 13.0 % 8.5 % Emerging Markets Debt 5.0 % 7.5 % Real Estate and Other Assets 10.0 % 7.5 % Hedge Funds 8.0 % 7.0 %
Schedule of Defined Contribution Plans	The total defined Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR PSNH WMECO 2016 $ 31.8 $ 4.5 $ 7.0 $ 3.4 $ 1.1 2015 30.4 4.8 6.3 3.4 1.0 2014 29.7 5.0 6.3 3.2 1.0
Schedule of Other Retirement Benefits	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 Expense on the income statements, are as follows: Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2016 2015 2014 Actuarially-Determined Liability $ 54.2 $ 55.2 $ 57.5 Other Retirement Benefits Expense 2.9 3.9 4.5 As of and For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Actuarially-Determined Liability $ 0.3 $ — $ 2.0 $ 0.1 $ 0.4 $ — $ 2.4 $ 0.2 $ 0.4 $ — $ 2.6 $ 0.2 Other Retirement Benefits Expense 1.1 0.7 0.6 0.2 1.5 1.0 0.7 0.3 2.1 0.3 0.9 0.4

SHARE-BASED PAYMENTS (Tables)

SHARE-BASED PAYMENTS (Tables)	12 Months Ended
	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Disclosure of Share-based Compensation Arrangements by Share-based Payment	The total compensation expense and associated future income tax benefits recognized by Eversource, CL&P, NSTAR Electric, PSNH and WMECO for share-based compensation awards were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Compensation Expense $ 23.6 $ 23.1 $ 24.6 Future Income Tax Benefit 9.6 9.4 10.3 For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Compensation Expense $ 9.1 $ 6.5 $ 3.5 $ 1.7 $ 9.3 $ 5.8 $ 3.2 $ 1.7 $ 8.1 $ 7.4 $ 3.0 $ 1.3 Future Income Tax Benefit 3.7 2.6 1.4 0.7 3.8 2.4 1.3 0.7 3.4 3.1 1.3 0.5
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Share Transactions	A summary of RSU transactions is as follows: RSUs (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2015 729,308 $ 43.45 Granted 305,340 $ 54.67 Shares Issued (270,060 ) $ 44.94 Forfeited (40,318 ) $ 53.99 Outstanding as of December 31, 2016 724,270 $ 47.86
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Share Transactions	A summary of performance share transactions is as follows: Performance Shares (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2015 528,428 $ 46.30 Granted 222,139 $ 53.64 Shares Issued (201,826 ) $ 40.93 Forfeited (25,807 ) $ 54.48 Outstanding as of December 31, 2016 522,934 $ 51.09
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Share Transactions	A summary of stock option transactions is as follows: Options Weighted Average Exercise Price Intrinsic Value (Millions) Outstanding and Exercisable - December 31, 2015 171,872 $ 26.47 $ 4.2 Exercised (47,232 ) $ 28.12 $ 1.3 Outstanding and Exercisable - December 31, 2016 124,640 $ 25.84 $ 3.7

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of income tax expense are as follows: Eversource (Millions of Dollars) For the Years Ended December 31, 2016 2015 2014 Current Income Taxes: Federal $ 38.9 $ 6.2 $ 4.4 State 53.0 45.7 24.5 Total Current 91.9 51.9 28.9 Deferred Income Taxes, Net: Federal 427.9 436.1 406.8 State 38.6 55.6 36.5 Total Deferred 466.5 491.7 443.3 Investment Tax Credits, Net (3.4 ) (3.6 ) (3.9 ) Income Tax Expense $ 555.0 $ 540.0 $ 468.3 For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Current Income Taxes: Federal $ 27.3 $ 73.9 $ (13.7 ) $ 12.5 $ 26.9 $ 36.3 $ (16.7 ) $ (3.5 ) $ (0.2 ) $ 75.0 $ (22.6 ) $ 1.9 State 13.3 35.0 8.8 4.5 15.8 19.8 6.0 1.6 4.3 20.2 (0.1 ) 1.8 Total Current 40.6 108.9 (4.9 ) 17.0 42.7 56.1 (10.7 ) (1.9 ) 4.1 95.2 (22.7 ) 3.7 Deferred Income Taxes, Net: Federal 157.6 78.3 79.5 18.3 135.8 147.5 74.5 33.4 138.0 88.0 79.6 28.1 State 11.3 1.9 7.8 3.2 0.2 25.7 9.3 6.0 (7.1 ) 20.1 15.2 6.0 Total Deferred 168.9 80.2 87.3 21.5 136.0 173.2 83.8 39.4 130.9 108.1 94.8 34.1 Investment Tax Credits, Net (1.2 ) (1.3 ) — (0.5 ) (1.3 ) (1.3 ) — (0.5 ) (1.5 ) (1.3 ) — (0.5 ) Income Tax Expense $ 208.3 $ 187.8 $ 82.4 $ 38.0 $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource (Millions of Dollars, except percentages) For the Years Ended December 31, 2016 2015 2014 Income Before Income Tax Expense $ 1,504.8 $ 1,425.9 $ 1,295.4 Statutory Federal Income Tax Expense at 35% 526.7 499.1 453.4 Tax Effect of Differences: Depreciation (3.4 ) (4.6 ) (5.6 ) Investment Tax Credit Amortization (3.4 ) (3.6 ) (3.9 ) Other Federal Tax Credits (3.5 ) (3.8 ) (3.5 ) State Income Taxes, Net of Federal Impact 56.2 61.1 42.5 Dividends on ESOP (8.4 ) (8.1 ) (8.0 ) Tax Asset Valuation Allowance/Reserve Adjustments 3.3 4.7 (2.9 ) Excess Stock Benefit (1) (19.1 ) — — Other, Net 6.6 (4.8 ) (3.7 ) Income Tax Expense $ 555.0 $ 540.0 $ 468.3 Effective Tax Rate 36.9 % 37.9 % 36.2 % For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars, except percentages) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Income Before Income Tax Expense $ 542.6 $ 480.5 $ 214.3 $ 96.1 $ 476.8 $ 572.6 $ 187.5 $ 93.5 $ 421.2 $ 505.1 $ 186.1 $ 95.1 Statutory Federal Income Tax Expense at 35% 189.9 168.2 75.0 33.6 166.9 200.4 65.6 32.7 147.4 176.8 65.1 33.3 Tax Effect of Differences: Depreciation 1.6 (3.4 ) 1.0 0.3 (1.7 ) (1.4 ) 0.5 (0.3 ) (3.6 ) (1.3 ) 0.3 (0.2 ) Investment Tax Credit Amortization (1.2 ) (1.3 ) — (0.5 ) (1.3 ) (1.3 ) — (0.5 ) (1.5 ) (1.3 ) — (0.5 ) Other Federal Tax Credits — — (3.5 ) — — — (3.8 ) — — — (3.5 ) — State Income Taxes, Net of Federal Impact 14.5 24.0 10.8 5.0 9.2 29.6 9.9 4.9 4.4 26.2 9.8 5.0 Tax Asset Valuation Allowance/Reserve Adjustments 1.5 — — — 1.2 — — — (6.3 ) — — — Excess Stock Benefit (1) (0.9 ) (1.0 ) (0.4 ) (0.2 ) — — — — — — — — Other, Net 2.9 1.3 (0.5 ) (0.2 ) 3.1 0.7 0.9 0.2 (6.9 ) 1.6 0.4 (0.3 ) Income Tax Expense $ 208.3 $ 187.8 $ 82.4 $ 38.0 $ 177.4 $ 228.0 $ 73.1 $ 37.0 $ 133.5 $ 202.0 $ 72.1 $ 37.3 Effective Tax Rate 38.4 % 39.1 % 38.4 % 39.6 % 37.2 % 39.8 % 39.0 % 39.6 % 31.7 % 40.0 % 38.7 % 39.2 %
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows: Eversource (Millions of Dollars) As of December 31, 2016 2015 Deferred Tax Assets: Employee Benefits $ 640.6 $ 637.5 Derivative Liabilities 192.6 172.7 Regulatory Deferrals - Liabilities 290.9 243.5 Allowance for Uncollectible Accounts 76.6 60.5 Tax Effect - Tax Regulatory Liabilities 11.8 9.7 Federal Net Operating Loss Carryforwards — 5.4 Purchase Accounting Adjustment 112.2 119.3 Other 170.5 197.1 Total Deferred Tax Assets 1,495.2 1,445.7 Less: Valuation Allowance 5.1 3.7 Net Deferred Tax Assets $ 1,490.1 $ 1,442.0 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 5,001.2 $ 4,602.6 Property Tax Accruals 81.9 76.7 Regulatory Amounts: Regulatory Deferrals - Assets 1,321.8 1,289.1 Tax Effect - Tax Regulatory Assets 252.6 249.3 Goodwill Regulatory Asset - 1999 Merger 186.7 194.9 Derivative Assets 29.5 17.7 Other 223.6 159.4 Total Deferred Tax Liabilities $ 7,097.3 $ 6,589.7 As of December 31, 2016 2015 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Deferred Tax Assets: Employee Benefits $ 138.8 $ 58.4 $ 46.5 $ 11.1 $ 126.1 $ 91.3 $ 37.1 $ 10.0 Derivative Liabilities 191.5 1.1 — — 165.7 0.6 — — Regulatory Deferrals - Liabilities 6.3 186.4 36.7 8.5 36.0 109.4 42.1 6.1 Allowance for Uncollectible Accounts 33.0 20.0 4.1 5.7 30.4 8.5 3.6 4.5 Tax Effect - Tax Regulatory Liabilities 4.9 1.1 2.6 2.2 3.1 1.5 2.3 2.4 Federal Net Operating Loss Carryforwards — — — — — — 2.4 0.4 Other 59.4 2.2 56.4 4.4 55.5 3.4 61.1 5.0 Total Deferred Tax Assets 433.9 269.2 146.3 31.9 416.8 214.7 148.6 28.4 Less: Valuation Allowance 4.5 — — — 3.1 — — — Net Deferred Tax Assets $ 429.4 $ 269.2 $ 146.3 $ 31.9 $ 413.7 $ 214.7 $ 148.6 $ 28.4 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 1,700.3 $ 1,463.5 $ 726.3 $ 438.4 $ 1,545.6 $ 1,387.1 $ 655.3 $ 416.1 Property Tax Accruals 29.7 25.6 8.0 11.2 27.3 22.8 7.3 10.6 Regulatory Amounts: Regulatory Deferrals - Assets 473.4 322.3 142.1 59.4 456.8 339.7 137.9 60.5 Tax Effect - Tax Regulatory Assets 170.4 36.1 12.2 8.7 168.7 36.0 15.4 9.0 Goodwill Regulatory Asset - 1999 Merger — 160.3 — — — 167.4 — — Derivative Assets 27.0 — — — 17.7 — — — Other 16.3 97.7 43.1 5.0 18.5 22.0 38.6 2.7 Total Deferred Tax Liabilities $ 2,417.1 $ 2,105.5 $ 931.7 $ 522.7 $ 2,234.6 $ 1,975.0 $ 854.5 $ 498.9
Summary of Operating Loss 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, 2016 (Millions of Dollars) Eversource CL&P NSTAR PSNH WMECO Expiration Range Federal Tax Credit $ 8.6 $ — $ — $ — $ — — Federal Charitable Contribution 27.8 — — — — 2016 - 2019 State Tax Credit 111.1 80.5 — — — 2016 - 2021 State Charitable Contribution 36.5 — — — — 2016 - 2020 As of December 31, 2015 (Millions of Dollars) Eversource CL&P NSTAR 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
Summary of Income Tax Contingencies	A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2014 $ 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 Gross Increases - Current Year 9.9 3.9 Gross Increases - Prior Year 0.2 0.2 Lapse of Statute of Limitations (9.7 ) (2.3 ) Balance as of December 31, 2016 $ 48.4 $ 15.3 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) 2016 2015 2014 2016 2015 Eversource $ (0.2 ) $ 0.1 $ 0.4 $ 1.8 $ 2.0
Summary of Income Tax Examinations	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, 2016 : Description Tax Years Federal 2016 Connecticut 2013 - 2016 Massachusetts 2013 - 2016 New Hampshire 2014 - 2016

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Environmental Loss Contingencies by Site	The number of environmental sites and related reserves for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: As of December 31, 2016 As of December 31, 2015 Number of Sites Reserve (in millions) Number of Sites Reserve (in millions) Eversource 61 $ 65.8 64 $ 51.1 CL&P 14 4.9 14 4.6 NSTAR Electric 13 3.2 15 2.4 PSNH 11 5.3 12 4.5 WMECO 4 0.6 4 0.6 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, 2015 $ 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 Additions 20.6 0.6 1.7 1.2 0.1 Payments/Reductions (5.9 ) (0.3 ) (0.9 ) (0.4 ) (0.1 ) Balance as of December 31, 2016 $ 65.8 $ 4.9 $ 3.2 $ 5.3 $ 0.6
Long-term Purchase Commitment	The estimated future annual costs of significant long-term contractual arrangements as of December 31, 2016 are as follows: Eversource (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 115.8 $ 81.6 $ 69.4 $ 74.2 $ 58.4 $ 189.8 589.2 Renewable Energy 275.4 242.6 240.9 238.8 218.9 1,864.1 3,080.7 Peaker CfDs 42.3 21.5 21.7 31.1 27.6 54.2 198.4 Natural Gas Procurement 197.0 185.5 142.3 115.0 104.9 190.2 934.9 Coal, Wood and Other 15.5 3.9 1.9 1.9 1.9 11.3 36.4 Transmission Support Commitments 21.8 22.0 22.2 22.2 22.2 22.2 132.6 Total $ 667.8 $ 557.1 $ 498.4 $ 483.2 $ 433.9 $ 2,331.8 $ 4,972.2 CL&P (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 93.4 $ 58.7 $ 56.6 $ 68.8 $ 53.0 $ 162.3 $ 492.8 Renewable Energy 77.9 80.4 80.3 80.3 80.6 684.4 1,083.9 Peaker CfDs 42.3 21.5 21.7 31.1 27.6 54.2 198.4 Transmission Support Commitments 8.6 8.7 8.8 8.8 8.8 8.8 52.5 Total $ 222.2 $ 169.3 $ 167.4 $ 189.0 $ 170.0 $ 909.7 $ 1,827.6 NSTAR Electric (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 4.8 $ 5.5 $ 5.5 $ 3.1 $ 3.1 $ 25.0 $ 47.0 Renewable Energy 116.8 80.4 78.5 76.6 72.1 416.7 841.1 Transmission Support Commitments 6.8 6.8 6.9 6.9 6.9 6.9 41.2 Total $ 128.4 $ 92.7 $ 90.9 $ 86.6 $ 82.1 $ 448.6 $ 929.3 PSNH (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Supply and Stranded Cost $ 17.6 $ 17.4 $ 7.3 $ 2.3 $ 2.3 $ 2.5 $ 49.4 Renewable Energy 65.2 66.1 66.3 65.9 50.1 601.9 915.5 Coal, Wood and Other 15.5 3.9 1.9 1.9 1.9 11.3 36.4 Transmission Support Commitments 4.6 4.7 4.7 4.7 4.7 4.7 28.1 Total $ 102.9 $ 92.1 $ 80.2 $ 74.8 $ 59.0 $ 620.4 $ 1,029.4 WMECO (Millions of Dollars) 2017 2018 2019 2020 2021 Thereafter Total Renewable Energy $ 15.5 $ 15.7 $ 15.8 $ 16.0 $ 16.1 $ 161.1 $ 240.2 Transmission Support Commitments 1.8 1.8 1.8 1.8 1.8 1.8 10.8 Total $ 17.3 $ 17.5 $ 17.6 $ 17.8 $ 17.9 $ 162.9 $ 251.0 The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2016 2015 2014 Supply and Stranded Cost $ 152.5 $ 147.6 $ 99.2 Renewable Energy 210.9 144.3 114.4 Peaker CfDs 47.7 42.7 18.1 Natural Gas Procurement 323.9 428.6 482.5 Coal, Wood and Other 55.7 95.9 120.5 Transmission Support Commitments 15.9 25.3 25.0 For the Years Ended December 31, 2016 2015 2014 (Millions of Dollars) CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO CL&P NSTAR PSNH WMECO Supply and Stranded Cost $ 132.7 $ 0.7 $ 19.1 $ — $ 120.3 $ 6.5 $ 20.8 $ — $ 63.0 $ 7.0 $ 26.0 $ 3.2 Renewable Energy 42.1 93.6 67.7 7.5 20.0 86.7 37.2 0.4 0.7 87.4 26.3 — Peaker CfDs 47.7 — — — 42.7 — — — 18.1 — — — Coal, Wood and Other — — 55.7 — — — 95.9 — — — 120.5 — Transmission Support Commitments 6.3 4.9 3.4 1.3 10.0 7.8 5.4 2.1 9.9 7.7 5.3 2.1
Schedule of Guarantor Obligations	The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries to external parties, as of December 31, 2016 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty $ 185.4 2021 Various Surety Bonds (1) $ 38.2 2017 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate $ 9.2 2019 - 2024 (1) Surety bond expiration dates reflect termination dates, the majority of which will be renewed or extended. Certain surety bonds contain credit ratings triggers that would require Eversource parent to post collateral in the event that the unsecured debt credit ratings of Eversource parent are downgraded.

PSNH GENERATION ASSET SALE (Tab

PSNH GENERATION ASSET SALE (Tables)	12 Months Ended
	Dec. 31, 2016
Regulated Operations [Abstract]
Schedule of Generation Assets and Liabilities	As of December 31, 2016 , PSNH's generation assets were as follows: (Millions of Dollars) Gross Plant $ 1,192.1 Accumulated Depreciation (556.0 ) Net Plant 636.1 Fuel 99.9 Materials and Supplies 42.7 Emission Allowances 19.9 Total Generation Assets $ 798.6 As of December 31, 2016 , current and long-term liabilities associated with PSNH's generation assets included Accounts Payable of $40.5 million , Other Current Liabilities of $16.1 million , AROs of $20 million , and Accrued Pension, SERP and PBOP of $24.3 million .

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
Schedule of Rent Expense	Operating lease rental payments charged to expense are as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2016 $ 12.1 $ 12.5 $ 9.3 $ 2.9 $ 2.1 2015 12.1 12.5 9.6 2.8 2.2 2014 14.3 6.0 7.8 1.5 1.2
Schedule of Future Minimum Lease Payments for Capital Leases	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, 2016 are as follows: Operating Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH WMECO 2017 $ 14.1 $ 2.0 $ 9.0 $ 0.9 $ 0.5 2018 10.6 1.3 7.0 0.6 0.3 2019 8.7 1.0 5.8 0.5 0.3 2020 7.0 0.7 4.8 0.4 0.2 2021 6.0 0.6 4.2 0.3 0.2 Thereafter 10.4 1.4 6.7 0.8 0.4 Future minimum lease payments $ 56.8 $ 7.0 $ 37.5 $ 3.5 $ 1.9
Schedule of Future Minimum Rental Payments for Operating Leases	Capital Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2017 $ 2.3 $ 1.9 $ 0.2 $ 0.2 2018 2.3 2.0 0.2 0.1 2019 2.2 2.0 0.2 — 2020 2.2 2.0 0.2 — 2021 1.7 1.4 0.3 — Thereafter 1.1 — 1.1 — Future minimum lease payments 11.8 9.3 2.2 0.3 Less amount representing interest 2.9 2.5 0.4 — Present value of future minimum lease payments $ 8.9 $ 6.8 $ 1.8 $ 0.3

FAIR VALUE OF FINANCIAL INSTR49

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping	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, 2016 2015 Eversource (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 158.3 $ 155.6 $ 157.9 Long-Term Debt 9,603.2 9,980.5 9,034.5 9,425.9 CL&P NSTAR Electric PSNH WMECO (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value As of December 31, 2016: Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 114.7 $ 43.0 $ 43.6 $ — $ — $ — $ — Long-Term Debt 2,766.0 3,049.6 2,078.1 2,201.6 1,072.0 1,109.7 566.5 589.0 As of December 31, 2015: 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

ACCUMULATED OTHER COMPREHENSI50

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes in accumulated other comprehensive income/(loss) by component, net of tax, is as follows: For the Year Ended December 31, 2016 For the Year Ended December 31, 2015 Eversource (Millions of Dollars) Qualified Cash Flow Hedging Instruments Unrealized Gains/(Losses) on Marketable Securities Defined Benefit Plans Total Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Balance as of January 1st $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 ) $ (12.4 ) $ 0.7 $ (62.3 ) $ (74.0 ) OCI Before Reclassifications — 2.3 (6.8 ) (4.5 ) — (2.6 ) 3.5 0.9 Amounts Reclassified from AOCL 2.1 — 3.9 6.0 2.1 — 4.2 6.3 Net OCI 2.1 2.3 (2.9 ) 1.5 2.1 (2.6 ) 7.7 7.2 Balance as of December 31st $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 )
Schedule of Comprehensive Income (Loss)	The following table sets forth the amounts reclassified from AOCL by component and the impacted line item on the statements of income: Amounts Reclassified from AOCL Eversource (Millions of Dollars) For the Years Ended December 31, Statements of Income Line Item Impacted 2016 2015 2014 Qualified Cash Flow Hedging Instruments $ (3.5 ) $ (3.5 ) $ (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 ) $ (2.1 ) $ (2.0 ) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (5.6 ) $ (6.6 ) $ (6.2 ) Operations and Maintenance Expense (1) Amortization of Prior Service Cost (0.8 ) (0.2 ) (0.2 ) Operations and Maintenance Expense (1) Total Defined Benefit Plan Costs (6.4 ) (6.8 ) (6.4 ) Tax Effect 2.5 2.6 2.5 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (3.9 ) $ (4.2 ) $ (3.9 ) Total Amounts Reclassified from AOCL, Net of Tax $ (6.0 ) $ (6.3 ) $ (5.9 ) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 9A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pensions," for further information.

COMMON SHARES (Tables)

COMMON SHARES (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Stock by Class	The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2016 and 2015 Issued as of December 31, 2016 2015 Eversource $ 5 380,000,000 333,878,402 333,862,615 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, 2016 and 2015 , there were 16,992,594 and 16,671,366 Eversource common shares held as treasury shares, respectively. As of December 31, 2016 and 2015 , Eversource common shares outstanding were 316,885,808 and 317,191,249 , respectively. In 2016 and 2015, the Company repurchased 321,228 and 532,521 Eversource common shares, respectively, at a share price of $52.56 and $47.94 , respectively. Such shares are included in Treasury Stock on the consolidated balance sheets at their weighted average original average cost of $24.26 and $26.02 per share, respectively. Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Per Share Shares Outstanding as of December 31, 2016 and 2015 As of December 31, Series 2016 2015 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 of 1956 $ 103.625 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 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

PREFERRED STOCK NOT SUBJECT T52

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Preferred Stock	The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric, PSNH and WMECO that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2016 and 2015 Issued as of December 31, 2016 2015 Eversource $ 5 380,000,000 333,878,402 333,862,615 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, 2016 and 2015 , there were 16,992,594 and 16,671,366 Eversource common shares held as treasury shares, respectively. As of December 31, 2016 and 2015 , Eversource common shares outstanding were 316,885,808 and 317,191,249 , respectively. In 2016 and 2015, the Company repurchased 321,228 and 532,521 Eversource common shares, respectively, at a share price of $52.56 and $47.94 , respectively. Such shares are included in Treasury Stock on the consolidated balance sheets at their weighted average original average cost of $24.26 and $26.02 per share, respectively. Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Per Share Shares Outstanding as of December 31, 2016 and 2015 As of December 31, Series 2016 2015 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 of 1956 $ 103.625 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 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

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Years Ended December 31, 2016 2015 2014 Net Income Attributable to Common Shareholders $ 942.3 $ 878.5 $ 819.5 Weighted Average Common Shares Outstanding: Basic 317,650,180 317,336,881 316,136,748 Dilutive Effect 804,059 1,095,806 1,280,666 Diluted 318,454,239 318,432,687 317,417,414 Basic EPS $ 2.97 $ 2.77 $ 2.59 Diluted EPS $ 2.96 $ 2.76 $ 2.58

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Eversource's segment information is as follows: For the Year Ended December 31, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 5,594.3 $ 857.7 $ 1,210.0 $ 870.4 $ (893.3 ) $ 7,639.1 Depreciation and Amortization (504.7 ) (65.3 ) (185.8 ) (33.5 ) 2.2 (787.1 ) Other Operating Expenses (4,155.1 ) (628.9 ) (321.8 ) (778.1 ) 891.8 (4,992.1 ) Operating Income 934.5 163.5 702.4 58.8 0.7 1,859.9 Interest Expense (193.1 ) (41.3 ) (110.0 ) (63.5 ) 6.9 (401.0 ) Interest Income 10.0 0.1 1.2 7.0 (7.3 ) 11.0 Other Income, Net 4.8 0.6 18.3 1,020.1 (1,008.9 ) 34.9 Income Tax (Expense)/Benefit (288.8 ) (45.2 ) (238.2 ) 16.5 0.7 (555.0 ) Net Income 467.4 77.7 373.7 1,038.9 (1,007.9 ) 949.8 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — (7.5 ) Net Income Attributable to Common Shareholders $ 462.8 $ 77.7 $ 370.8 $ 1,038.9 $ (1,007.9 ) $ 942.3 Total Assets (as of) $ 18,367.5 $ 3,303.8 $ 8,751.5 $ 14,493.1 $ (12,862.7 ) $ 32,053.2 Cash Flows Used for Investments in Plant $ 812.6 $ 255.3 $ 801.0 $ 108.0 $ — $ 1,976.9 For the Year Ended December 31, 2015 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric 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 (Millions of Dollars) Electric Natural Gas Electric 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 Cash Flows Used for Investments in Plant $ 645.2 $ 176.7 $ 731.6 $ 50.2 $ — $ 1,603.7

GOODWILL (Tables)

GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The following table presents goodwill by reportable segment: As of December 31, 2016 and 2015 (Billions of Dollars) Electric Distribution Electric Transmission Natural Gas Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 3.5

QUARTERLY FINANCIAL DATA (UNA56

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information	Quarter Ended Eversource (Millions of Dollars, except per share information) 2016 2015 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,055.6 $ 1,767.2 $ 2,039.7 $ 1,776.6 $ 2,513.4 $ 1,817.1 $ 1,933.1 $ 1,691.2 Operating Income 488.5 423.4 509.9 438.1 497.5 412.0 469.2 385.5 Net Income 246.0 205.5 267.2 231.1 255.1 209.4 237.8 183.7 Net Income Attributable to Common Shareholders 244.2 203.6 265.3 229.2 253.3 207.5 235.9 181.8 Basic EPS (1) $ 0.77 $ 0.64 $ 0.83 $ 0.72 $ 0.80 $ 0.65 $ 0.74 $ 0.57 Diluted EPS (1) $ 0.77 $ 0.64 $ 0.83 $ 0.72 $ 0.80 $ 0.65 $ 0.74 $ 0.57 (1) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2016 2015 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 735.3 $ 679.8 $ 760.0 $ 630.9 $ 804.9 $ 666.6 $ 704.3 $ 626.9 Operating Income 171.5 162.1 176.1 163.5 141.8 154.0 161.1 154.2 Net Income 87.0 82.9 86.6 77.8 69.2 78.8 80.2 71.2 NSTAR Electric Operating Revenues $ 614.2 $ 591.3 $ 780.5 $ 571.9 $ 766.8 $ 617.2 $ 750.7 $ 546.6 Operating Income 109.8 130.5 208.7 104.8 159.5 151.4 214.2 117.7 Net Income 54.5 68.2 117.2 52.8 83.6 82.0 118.6 60.3 PSNH Operating Revenues $ 242.3 $ 218.5 $ 266.9 $ 231.8 $ 284.8 $ 241.9 $ 234.4 $ 211.1 Operating Income 70.7 63.1 74.7 54.6 63.2 54.1 63.6 49.3 Net Income 36.1 31.3 38.5 26.1 32.0 27.9 32.5 22.0 WMECO Operating Revenues $ 128.1 $ 116.4 $ 124.0 $ 115.7 $ 152.9 $ 125.2 $ 125.1 $ 114.9 Operating Income 33.1 29.2 32.1 26.0 28.6 28.9 30.0 28.0 Net Income 16.8 13.3 16.0 12.0 13.2 14.2 15.0 14.1

SUMMARY OF SIGNIFICANT ACCOUN57

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands, customer in Millions	Mar. 25, 2016USD ($)	Dec. 31, 2016USD ($)companiesutilitycustomer	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer		3.7
Goodwill		$ 3,519,401	$ 3,519,401
Available for sale securities subject to new accounting guidance		48,000
Impact of share based compensation accounting guidance on income tax		19,100
Impact of new accounting standard on cash flow statement		26,600	9,700	$ 16,500
Equity method investment		$ 236,900	48,000
Number of companies that transmit electricity imported from hydro-quebec system | companies		2
Number of nuclear generation companies | companies		3
Regulatory assets		$ 4,526,300	4,583,800
Eversource [Member]
Summary of Accounting Policies [Line Items]
Goodwill		3,231,811	3,231,811
Cash collateral deposited		21,700	17,100
Equity method investment		9,703,287	8,915,178
The Connecticut Light And Power Company [Member]
Summary of Accounting Policies [Line Items]
Cash collateral deposited		1,400	700
Damages paid			244,600
Accumulated interest from damages awarded			178,000
Long term receivable		25,000
Regulatory assets		1,727,100	1,637,300
NSTAR Electric Company [Member]
Summary of Accounting Policies [Line Items]
Cash collateral deposited		11,800	8,500
Regulatory assets		1,347,100	1,461,400
Public Service Company Of New Hampshire [Member]
Summary of Accounting Policies [Line Items]
Cash collateral deposited		500	1,500
Long term receivable		3,800
Regulatory assets		362,700	362,900
Western Massachusetts Electric Company [Member]
Summary of Accounting Policies [Line Items]
Damages paid			57,400
Accumulated interest from damages awarded			41,800
Long term receivable		5,500
Regulatory assets		$ 191,400	191,200
Connecticut, Massachusetts and New Hampshire [Member]
Summary of Accounting Policies [Line Items]
Number of regulated utilities | utility		6
Algonquin Gas Tansmsission LLC - Access Northeast [Member]
Summary of Accounting Policies [Line Items]
Equity method investment		$ 30,900	$ 10,700
Equity method investment, ownership percentage		40.00%	40.00%
FERC Regulated Transmission Business [Member]
Summary of Accounting Policies [Line Items]
Equity method investment		$ 154,600
Equity method investment, ownership percentage		15.00%
Hydro-Quebec System [Member]
Summary of Accounting Policies [Line Items]
Equity method investment		$ 7,700	$ 7,000
Equity method investment, ownership percentage		37.20%	37.20%
Hydro-Quebec System [Member] | NSTAR Electric Company [Member]
Summary of Accounting Policies [Line Items]
Equity method investment		$ 3,000	$ 2,700
Equity method investment, ownership percentage		14.50%	14.50%
Yankee Companies [Member]
Summary of Accounting Policies [Line Items]
Net of damages awarded		$ 52,200
CYAPC and YAEC [Member]
Summary of Accounting Policies [Line Items]
Net of damages awarded	$ 32,600
Total amount of damages awarded		6,800
MYAPC [Member]
Summary of Accounting Policies [Line Items]
Net of damages awarded	$ 24,600	$ 14,400
Maximum [Member]
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		180 days
Minimum [Member]
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		90 days
Other Equity Method Investments [Member]
Summary of Accounting Policies [Line Items]
Equity method investment		$ 43,700	$ 30,300

SUMMARY OF SIGNIFICANT ACCOUN58

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	$ 200.6	$ 190.7
Uncollectible Hardship	119.9	118.5
The Connecticut Light And Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	86.4	79.5
Uncollectible Hardship	67.7	68.1
NSTAR Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	54.8	52.6
Uncollectible Hardship	26.2	25.3
Public Service Company Of New Hampshire [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	9.9	8.7
Uncollectible Hardship	0	0
Western Massachusetts Electric Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	15.5	14
Uncollectible Hardship	$ 9.9	$ 7.4

SUMMARY OF SIGNIFICANT ACCOUN59

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fuel, Materials, Supplies and Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fuel [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	$ 135.7	$ 152.5
Materials and Supplies [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	142.7	131.2
RECs [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	47.9	50.9
Emission Allowances [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	2.4	1.9
Other inventory, noncurrent	17.5	17.5
The Connecticut Light And Power Company [Member] | Fuel [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
The Connecticut Light And Power Company [Member] | Materials and Supplies [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	48.2	43.1
The Connecticut Light And Power Company [Member] | RECs [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	3.9	0
The Connecticut Light And Power Company [Member] | Emission Allowances [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
Other inventory, noncurrent	0	0
NSTAR Electric Company [Member] | Fuel [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
NSTAR Electric Company [Member] | Materials and Supplies [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	34.5	32.2
NSTAR Electric Company [Member] | RECs [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	27.8	43.3
NSTAR Electric Company [Member] | Emission Allowances [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
Other inventory, noncurrent	0	0
Public Service Company Of New Hampshire [Member] | Fuel [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	99.9	103.4
Public Service Company Of New Hampshire [Member] | Materials and Supplies [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	47.3	44.6
Public Service Company Of New Hampshire [Member] | RECs [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	12.8	7
Public Service Company Of New Hampshire [Member] | Emission Allowances [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	2.4	1.9
Other inventory, noncurrent	17.5	17.5
Western Massachusetts Electric Company [Member] | Fuel [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
Western Massachusetts Electric Company [Member] | Materials and Supplies [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	5.2	5.4
Western Massachusetts Electric Company [Member] | RECs [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0.6
Western Massachusetts Electric Company [Member] | Emission Allowances [Member]
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
Other inventory, noncurrent	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOUN60

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Accounting Policies [Line Items]
Fuel power costs	$ 372.2	$ 516.7	$ 599.4
Public Service Company Of New Hampshire [Member]
Summary of Accounting Policies [Line Items]
Fuel power costs	$ 45	$ 85.4	$ 113.4

SUMMARY OF SIGNIFICANT ACCOUN61

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 10.8	$ 7.2	$ 5.8
Equity Funds	26.2	18.8	13.7
Total AFUDC	$ 37	$ 26	$ 19.5
Average AFUDC Rate	4.40%	3.90%	3.40%
The Connecticut Light And Power Company [Member]
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 3.3	$ 2.6	$ 1.9
Equity Funds	6.3	5.2	2.9
Total AFUDC	$ 9.6	$ 7.8	$ 4.8
Average AFUDC Rate	4.70%	5.50%	3.40%
NSTAR Electric Company [Member]
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 4.6	$ 2	$ 2
Equity Funds	10.2	4.3	3.8
Total AFUDC	$ 14.8	$ 6.3	$ 5.8
Average AFUDC Rate	3.90%	3.20%	2.50%
Public Service Company Of New Hampshire [Member]
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 0.8	$ 1	$ 0.6
Equity Funds	0.3	1.2	0.6
Total AFUDC	$ 1.1	$ 2.2	$ 1.2
Average AFUDC Rate	1.00%	1.80%	1.80%
Western Massachusetts Electric Company [Member]
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 0.6	$ 1	$ 0.9
Equity Funds	0	1.7	1.7
Total AFUDC	$ 0.6	$ 2.7	$ 2.6
Average AFUDC Rate	0.80%	4.40%	5.60%

SUMMARY OF SIGNIFICANT ACCOUN62

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 162.7	$ 147.2	$ 148.2
The Connecticut Light And Power Company [Member]
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 145.2	$ 128.5	$ 127.9

SUMMARY OF SIGNIFICANT ACCOUN63

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	$ 398.1	$ 365.9	$ 349.6
Income Taxes	(135.5)	10.3	334.2
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	301.5	216.6	181.9
The Connecticut Light And Power Company [Member]
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	143.3	144.4	144.1
Income Taxes	(73.9)	55.2	135.4
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	116.2	76	63.5
NSTAR Electric Company [Member]
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	88.2	75.7	75.3
Income Taxes	80.7	(19.8)	217.1
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	60.9	23.5	34.6
Public Service Company Of New Hampshire [Member]
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	46.5	42.3	41.1
Income Taxes	(36)	14.4	2.3
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	37.9	46.5	39.3
Western Massachusetts Electric Company [Member]
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	24.7	26.7	25.9
Income Taxes	(14.7)	14.7	25.1
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	$ 26.1	$ 27	$ 14.2

REGULATORY ACCOUNTING - Compone

REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 4,526,300	$ 4,583,800
Less: Current Portion	887,625	845,843
Total Long-Term Regulatory Assets	3,638,688	3,737,960
Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	1,817,800	1,828,200
Derivative Liabilities [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	423,300	388,000
Income Taxes, Net [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	644,500	650,900
Storm Restoration Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	385,300	436,900
Goodwill-related [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	464,400	484,900
Regulatory Tracker Mechanisms [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	576,600	526,500
Contractual Obligations - Yankee Companies [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	84,900	134,400
Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	129,500	134,000
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	1,727,100	1,637,300
Less: Current Portion	335,526	268,318
Total Long-Term Regulatory Assets	1,391,564	1,369,028
The Connecticut Light And Power Company [Member] | Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	429,300	413,600
The Connecticut Light And Power Company [Member] | Derivative Liabilities [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	420,500	380,800
The Connecticut Light And Power Company [Member] | Income Taxes, Net [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	437,000	444,400
The Connecticut Light And Power Company [Member] | Storm Restoration Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	239,800	271,400
The Connecticut Light And Power Company [Member] | Goodwill-related [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light And Power Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	123,900	45,100
The Connecticut Light And Power Company [Member] | Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	76,600	82,000
NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	1,347,100	1,461,400
Less: Current Portion	289,400	348,408
Total Long-Term Regulatory Assets	1,057,746	1,112,977
NSTAR Electric Company [Member] | Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	438,600	479,900
NSTAR Electric Company [Member] | Derivative Liabilities [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	2,800	1,300
NSTAR Electric Company [Member] | Income Taxes, Net [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	89,700	85,700
NSTAR Electric Company [Member] | Storm Restoration Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	112,500	110,900
NSTAR Electric Company [Member] | Goodwill-related [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	398,700	416,300
NSTAR Electric Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	257,300	311,000
NSTAR Electric Company [Member] | Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	47,500	56,300
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	362,700	362,900
Less: Current Portion	117,240	104,971
Total Long-Term Regulatory Assets	245,525	257,873
Public Service Company Of New Hampshire [Member] | Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	184,200	164,200
Public Service Company Of New Hampshire [Member] | Derivative Liabilities [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire [Member] | Income Taxes, Net [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	24,200	34,500
Public Service Company Of New Hampshire [Member] | Storm Restoration Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	17,100	31,500
Public Service Company Of New Hampshire [Member] | Goodwill-related [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	104,500	101,200
Public Service Company Of New Hampshire [Member] | Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	32,700	31,500
Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	191,400	191,200
Less: Current Portion	64,123	56,166
Total Long-Term Regulatory Assets	127,291	135,010
Western Massachusetts Electric Company [Member] | Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	86,700	84,900
Western Massachusetts Electric Company [Member] | Derivative Liabilities [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Western Massachusetts Electric Company [Member] | Income Taxes, Net [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	30,800	31,800
Western Massachusetts Electric Company [Member] | Storm Restoration Costs [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	15,900	23,100
Western Massachusetts Electric Company [Member] | Goodwill-related [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Western Massachusetts Electric Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	46,700	40,100
Western Massachusetts Electric Company [Member] | Other Regulatory Assets [Member]
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 11,300	$ 11,300

REGULATORY ACCOUNTING - Storm R

REGULATORY ACCOUNTING - Storm Restoration Costs (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory assets	$ 4,526.3	$ 4,583.8
Storm Restoration Costs Pending Approval [Member]
Regulatory Assets [Line Items]
Regulatory assets	239
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,727.1	1,637.3
The Connecticut Light And Power Company [Member] | Storm Restoration Costs Pending Approval [Member]
Regulatory Assets [Line Items]
Regulatory assets	33
NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,347.1	1,461.4
NSTAR Electric Company [Member] | Storm Restoration Costs Pending Approval [Member]
Regulatory Assets [Line Items]
Regulatory assets	124
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Regulatory assets	362.7	362.9
Public Service Company Of New Hampshire [Member] | Storm Restoration Costs Pending Approval [Member]
Regulatory Assets [Line Items]
Regulatory assets	78
Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	191.4	$ 191.2
Western Massachusetts Electric Company [Member] | Storm Restoration Costs Pending Approval [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 4

REGULATORY ACCOUNTING - Goodwil

REGULATORY ACCOUNTING - Goodwill-related (Details) - NSTAR Electric and NSTAR Gas [Member] - Goodwill-related [Member]	12 Months Ended
	Dec. 31, 2016
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	40 years
Regulatory Asset, Amortization Period Remaining	23 years

REGULATORY ACCOUNTING - Regulat

REGULATORY ACCOUNTING - Regulatory Tracker Mechanisms (Details) - Regulatory Tracker Deferrals Regulatory Assets [Member] $ in Millions	Dec. 31, 2016USD ($)
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Decoupling mechanisms permitted in recovery of an annual base amount	$ 1,059
Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Decoupling mechanisms permitted in recovery of an annual base amount	$ 132.4

REGULATORY ACCOUNTING - Contrac

REGULATORY ACCOUNTING - Contractual Obligations - Yankee Companies (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory assets	$ 4,526.3	$ 4,583.8
CYAPC and YAEC [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 70.9	$ 110.9

REGULATORY ACCOUNTING - Regul69

REGULATORY ACCOUNTING - Regulatory Costs in Other Long-Term Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 86.3	$ 75.3
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	5.9	3.1
NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	35	35.4
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	8.2	4.8
Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 20.1	$ 16.7

REGULATORY ACCOUNTING - Equity

REGULATORY ACCOUNTING - Equity Return on Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet	$ 1.2	$ 1.5
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet	44.9	$ 48.3
Clean Air Project [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet	$ 25

REGULATORY ACCOUNTING - Compo71

REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 849,100	$ 621,400
Less: Current Portion	146,787	107,759
Total Long-Term Regulatory Liabilities	702,255	513,595
Cost of Removal [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	459,700	437,100
Regulatory Tracker Mechanisms [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	145,300	99,700
Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	136,200	0
AFUDC - Transmission [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	65,800	66,100
Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	42,100	18,500
The Connecticut Light And Power Company [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	147,200	136,000
Less: Current Portion	47,055	61,155
Total Long-Term Regulatory Liabilities	100,138	74,830
The Connecticut Light And Power Company [Member] | Cost of Removal [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	38,800	24,100
The Connecticut Light And Power Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	37,200	56,200
The Connecticut Light And Power Company [Member] | Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
The Connecticut Light And Power Company [Member] | AFUDC - Transmission [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	50,200	51,500
The Connecticut Light And Power Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	21,000	4,200
NSTAR Electric Company [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	455,500	267,700
Less: Current Portion	63,653	3,281
Total Long-Term Regulatory Liabilities	391,823	264,352
NSTAR Electric Company [Member] | Cost of Removal [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	271,600	257,400
NSTAR Electric Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	63,700	3,300
NSTAR Electric Company [Member] | Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	113,100	0
NSTAR Electric Company [Member] | AFUDC - Transmission [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	6,900	5,700
NSTAR Electric Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	200	1,300
Public Service Company Of New Hampshire [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	57,500	54,800
Less: Current Portion	12,659	6,898
Total Long-Term Regulatory Liabilities	44,779	47,851
Public Service Company Of New Hampshire [Member] | Cost of Removal [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	44,100	47,200
Public Service Company Of New Hampshire [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	10,700	3,400
Public Service Company Of New Hampshire [Member] | Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company Of New Hampshire [Member] | AFUDC - Transmission [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company Of New Hampshire [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,700	4,200
Western Massachusetts Electric Company [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	32,100	24,700
Less: Current Portion	14,888	13,122
Total Long-Term Regulatory Liabilities	17,227	11,597
Western Massachusetts Electric Company [Member] | Cost of Removal [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,600	2,800
Western Massachusetts Electric Company [Member] | Regulatory Tracker Mechanisms [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	14,700	12,900
Western Massachusetts Electric Company [Member] | Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0
Western Massachusetts Electric Company [Member] | AFUDC - Transmission [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,700	8,900
Western Massachusetts Electric Company [Member] | Other Regulatory Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 100	$ 100

REGULATORY ACCOUNTING - Regul72

REGULATORY ACCOUNTING - Regulatory Developments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Nov. 22, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Regulatory assets	$ 4,526.3		$ 4,583.8
Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	11.5
The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,727.1		1,637.3
The Connecticut Light And Power Company [Member] | Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	5.5
NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,347.1		1,461.4
NSTAR Electric Company [Member] | Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	3.2
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Regulatory assets	362.7		362.9
Public Service Company Of New Hampshire [Member] | Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	1.3
Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets	191.4		$ 191.2
Western Massachusetts Electric Company [Member] | Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	1.5
FERC ROE First and Second Complaints [Member]
Regulatory Assets [Line Items]
Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers	39.1
FERC ROE First and Second Complaints [Member] | The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers	21.4
FERC ROE First and Second Complaints [Member] | NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers	8.5
FERC ROE First and Second Complaints [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers	3.1
FERC ROE First and Second Complaints [Member] | Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Loss Contingency, Cumulative Pre-Tax Reserves Which Include Impact of Refunds Given to Customers	6.1
Transmission Merger Cost Recovery [Member]
Regulatory Assets [Line Items]
Amount of recovery through transmission rates	27.5
Regulatory assets		$ 27.5
Transmission Merger Cost Recovery [Member] | The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Regulatory assets		13.2
Transmission Merger Cost Recovery [Member] | NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets		7.8
Transmission Merger Cost Recovery [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Regulatory assets		3
Transmission Merger Cost Recovery [Member] | Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Regulatory assets		$ 3.5
Yankee Companies [Member] | The Connecticut Light And Power Company [Member]
Regulatory Assets [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company	13.6
Yankee Companies [Member] | NSTAR Electric Company [Member]
Regulatory Assets [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company	5
Yankee Companies [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company	3.9
Yankee Companies [Member] | Western Massachusetts Electric Company [Member]
Regulatory Assets [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company	$ 3.6

PROPERTY, PLANT AND EQUIPMENT73

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 13,716,900	$ 13,054,800
Distribution - Natural Gas	3,010,400	2,727,200
Transmission - Electric	8,517,400	7,691,900
Generation	1,224,200	1,194,100
Electric and Natural Gas Utility	26,468,900	24,668,000
Other	591,600	558,600
Property, Plant and Equipment, Gross	27,060,500	25,226,600
Less: Accumulated Depreciation
Electric and Natural Gas Utility	(6,480,400)	(6,141,100)
Other	(242,000)	(255,600)
Total Accumulated Depreciation	(6,722,400)	(6,396,700)
Property, Plant and Equipment, Net	20,338,100	18,829,900
Construction Work in Progress	1,012,400	1,062,500
Total Property, Plant and Equipment, Net	21,350,510	19,892,441
The Connecticut Light And Power Company [Member]
Property, Plant and Equipment [Line Items]
Distribution - Electric	5,562,900	5,377,200
Transmission - Electric	3,912,900	3,618,000
Generation	0	0
Property, Plant and Equipment, Gross	9,475,800	8,995,200
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,082,400)	(2,041,900)
Property, Plant and Equipment, Net	7,393,400	6,953,300
Construction Work in Progress	239,000	203,500
Total Property, Plant and Equipment, Net	7,632,392	7,156,809
NSTAR Electric Company [Member]
Property, Plant and Equipment [Line Items]
Distribution - Electric	5,402,300	5,100,500
Transmission - Electric	2,435,800	2,131,300
Generation	0	0
Property, Plant and Equipment, Gross	7,838,100	7,231,800
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,025,400)	(1,886,800)
Property, Plant and Equipment, Net	5,812,700	5,345,000
Construction Work in Progress	239,100	310,500
Total Property, Plant and Equipment, Net	6,051,835	5,655,458
Public Service Company Of New Hampshire [Member]
Property, Plant and Equipment [Line Items]
Distribution - Electric	1,949,800	1,804,800
Transmission - Electric	1,059,300	928,200
Generation	1,188,200	1,158,100
Property, Plant and Equipment, Gross	4,197,300	3,891,100
Less: Accumulated Depreciation
Total Accumulated Depreciation	(1,254,700)	(1,171,000)
Property, Plant and Equipment, Net	2,942,600	2,720,100
Construction Work in Progress	96,700	135,300
Total Property, Plant and Equipment, Net	3,039,313	2,855,363
Western Massachusetts Electric Company [Member]
Property, Plant and Equipment [Line Items]
Distribution - Electric	841,900	812,300
Transmission - Electric	1,061,100	964,900
Generation	36,000	36,000
Property, Plant and Equipment, Gross	1,939,000	1,813,200
Less: Accumulated Depreciation
Total Accumulated Depreciation	(338,800)	(307,000)
Property, Plant and Equipment, Net	1,600,200	1,506,200
Construction Work in Progress	78,100	69,100
Total Property, Plant and Equipment, Net	$ 1,678,262	$ 1,575,306

PROPERTY, PLANT AND EQUIPMENT74

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	3.00%	2.90%	3.00%
The Connecticut Light And Power Company [Member]
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.70%	2.70%	2.70%
NSTAR Electric Company [Member]
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	3.00%	3.00%	3.00%
Public Service Company Of New Hampshire [Member]
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	3.10%	3.20%	3.00%
Western Massachusetts Electric Company [Member]
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.70%	2.70%	3.30%

PROPERTY, PLANT AND EQUIPMENT75

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Distribution	35 years 1 month 6 days
Transmission	41 years 6 months
Generation	29 years
Other	11 years
The Connecticut Light And Power Company [Member]
Property, Plant and Equipment [Line Items]
Distribution	37 years 8 months 12 days
Transmission	38 years
NSTAR Electric Company [Member]
Property, Plant and Equipment [Line Items]
Distribution	32 years
Transmission	43 years 9 months 18 days
Public Service Company Of New Hampshire [Member]
Property, Plant and Equipment [Line Items]
Distribution	31 years 3 months 18 days
Transmission	43 years 6 months
Generation	29 years 1 month 6 days
Western Massachusetts Electric Company [Member]
Property, Plant and Equipment [Line Items]
Distribution	30 years 8 months 12 days
Transmission	49 years 8 months 12 days
Generation	25 years

DERIVATIVE INSTRUMENTS - Schedu

DERIVATIVE INSTRUMENTS - Schedule of Gross Fair Value of Contracts (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Inputs, Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	$ 13.9	$ 16.7
Netting	(9.4)	(10.9)
Net Amount Recorded as a Derivative	4.5	5.8
Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	77.3	62
Netting	(11.7)	(19.3)
Net Amount Recorded as a Derivative	65.6	42.7
Fair Value, Inputs, Level 3 [Member] | Other Current Liabilities [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(79.7)	(92.3)
Netting	0	0
Net Amount Recorded as a Derivative	(79.7)	(92.3)
Fair Value, Inputs, Level 3 [Member] | Derivative Liabilities Non Current [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(413.7)	(337.1)
Netting	0	0
Net Amount Recorded as a Derivative	(413.7)	(337.1)
Fair Value, Inputs, Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	6	0
Netting	0	0
Net Amount Recorded as a Derivative	6	0
Fair Value, Inputs, Level 2 [Member] | Other Noncurrent Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	0.3	0.1
Netting	(0.1)	0
Net Amount Recorded as a Derivative	0.2	0.1
Fair Value, Inputs, Level 2 [Member] | Other Current Liabilities [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	0	(5.8)
Netting	0	0
Net Amount Recorded as a Derivative	0	(5.8)
The Connecticut Light And Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	77.3	60.7
Netting	(11.7)	(19.3)
Net Amount Recorded as a Derivative	65.6	41.4
The Connecticut Light And Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Current Liabilities [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(77.8)	(91.8)
Netting	0	0
Net Amount Recorded as a Derivative	(77.8)	(91.8)
The Connecticut Light And Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative Liabilities Non Current [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(412.8)	(336.2)
Netting	0	0
Net Amount Recorded as a Derivative	(412.8)	(336.2)
NSTAR Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Noncurrent Assets [Member]
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	0	1.3
Netting	0	0
Net Amount Recorded as a Derivative	0	1.3
NSTAR Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Other Current Liabilities [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(1.9)	(0.5)
Netting	0	0
Net Amount Recorded as a Derivative	(1.9)	(0.5)
NSTAR Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative Liabilities Non Current [Member]
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(0.9)	(0.9)
Netting	0	0
Net Amount Recorded as a Derivative	$ (0.9)	$ (0.9)

DERIVATIVE INSTRUMENTS - Gross

DERIVATIVE INSTRUMENTS - Gross Fair Value of Contracts Narrative (Details) $ in Millions	Dec. 31, 2016USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets subject to credit risk with investment grade counterparty	$ 76.2
The Connecticut Light And Power Company [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets subject to credit risk with investment grade counterparty	$ 70

DERIVATIVE INSTRUMENTS - Deriva

DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details) MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)MMBTUMWhMW	Dec. 31, 2015USD ($)MMBTU	Dec. 31, 2014USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company (as a percentage)	20.00%
Amount of power to be purchased under capacity-related contract (up to for 35 mw) (in mw) | MW	787
Amount of natural gas to be purchased under futures contracts (in MMBtu) | MMBTU	9.2	9.1
Gain (loss) deferred as regulatory costs | $	$ 125.5	$ 60.2	$ (134.4)
The Connecticut Light And Power Company [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts (as a percentage)	80.00%
Amount of energy to be purchased under renewable energy contract (in mwh) | MWh	0.1
NSTAR Electric Company [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of power to be purchased under capacity-related contract (up to for 35 mw) (in mw) | MW	35
Amount of energy to be purchased under renewable energy contract (in mwh) | MWh	0.1

DERIVATIVE INSTRUMENTS - Credit

DERIVATIVE INSTRUMENTS - Credit Risk (Details) $ in Millions	Dec. 31, 2015USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative contracts in net liability position	$ 5.8
Additional collateral if unsecured credit ratings is downgraded	$ 5.8

DERIVATIVE INSTRUMENTS - Unobse

DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - Fair Value, Inputs, Level 3 [Member] - $ / KWmo	Dec. 31, 2016	Dec. 31, 2015
Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	5.5	10.81
Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	8.7	15.82
The Connecticut Light And Power Company [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	5.50	10.81
The Connecticut Light And Power Company [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	8.70	12.60
Eversource and The Connecticut Light And Power Company [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Forward Reserve (in USDPerKiloWattMonth)	1.40	2
Eversource and The Connecticut Light And Power Company [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Forward Reserve (in USDPerKiloWattMonth)	2	2
Eversource and NSTAR Electric Company [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	24	45
Eversource and NSTAR Electric Company [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	29	51

DERIVATIVE INSTRUMENTS - Unob81

DERIVATIVE INSTRUMENTS - Unobservable Inputs Narrative (Details) - Fair Value, Inputs, Level 3 [Member]	9 Months Ended
	Sep. 30, 2016
Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	3.00%
Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	20.00%

DERIVATIVE INSTRUMENTS - Variat

DERIVATIVE INSTRUMENTS - Variations Using Significant unobservable Inputs (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (380.9)	$ (415.4)
Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities	(130.7)	(52.1)
Settlements	88.3	86.6
Ending balance	(423.3)	(380.9)
The Connecticut Light And Power Company [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(380.8)	(410.9)
Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities	(122.7)	(51.3)
Settlements	83	81.4
Ending balance	(420.5)	(380.8)
NSTAR Electric Company [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	(0.1)	(4.5)
Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities	(8)	(0.8)
Settlements	5.3	5.2
Ending balance	$ (2.8)	$ (0.1)

MARKETABLE SECURITIES - Trading

MARKETABLE SECURITIES - Trading Securities (Details) - Fair Value, Inputs, Level 1 [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of securities under fair value option	$ 9.6	$ 14.2
Net gains on fair value option	$ 0.6	$ 2	$ 1.9

MARKETABLE SECURITIES - Schedul

MARKETABLE SECURITIES - Schedule of Available-for-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Marketable securities held in nuclear decommissioning plant	$ 466.7	$ 436.9
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	296.2	256.5
Pre-Tax Unrealized Gains	1.1	4.5
Pre-Tax Unrealized Losses	(2.1)	(0.6)
Fair Value	295.2	260.4
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	203.3	215.3
Pre-Tax Unrealized Gains	62.3	59.2
Pre-Tax Unrealized Losses	(1.2)	(3.4)
Fair Value	$ 264.4	$ 271.1

MARKETABLE SECURITIES - Contrac

MARKETABLE SECURITIES - Contractual Maturity (Details) $ in Millions	Dec. 31, 2016USD ($)
Amortized Cost
Less than one year	$ 60.5
One to five years	45.4
Six to ten years	59.7
Greater than ten years	130.6
Total Debt Securities	296.2
Fair Value
Less than one year	60.3
One to five years	45.8
Six to ten years	58.3
Greater than ten years	130.8
Total Debt Securities	$ 295.2

MARKETABLE SECURITIES - Fair Va

MARKETABLE SECURITIES - Fair Value Measurement (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	$ 569.2	$ 545.7
Fair Value, Inputs, Level 1 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	328.8	312.2
Fair Value, Inputs, Level 1 [Member] | Mutual Funds and Equities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	274	285.3
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	54.8	26.9
Fair Value, Inputs, Level 2 [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	240.4	233.5
Fair Value, Inputs, Level 2 [Member] | U.S. Government Issued Debt Securities (Agency and Treasury) [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	63	46.6
Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	41.1	43.9
Fair Value, Inputs, Level 2 [Member] | Asset-Backed Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	18.5	20
Fair Value, Inputs, Level 2 [Member] | Municipal Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	107.5	111.4
Fair Value, Inputs, Level 2 [Member] | Other Fixed Income Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total marketable securities	$ 10.3	$ 11.6

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	$ 430.1	$ 426.3
Liabilities Incurred During the Year	1.3	6.6
Liabilities Settled During the Year	(19)	(18.2)
Accretion	22.9	26.5
Revisions in Estimated Cash Flows	(8.9)	(11.1)
Balance as of End of Year	426.4	430.1
The Connecticut Light And Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	33.8	35.3
Liabilities Incurred During the Year	0	0
Liabilities Settled During the Year	0	0
Accretion	2.2	2.2
Revisions in Estimated Cash Flows	0	(3.7)
Balance as of End of Year	36	33.8
NSTAR Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	35.3	34.3
Liabilities Incurred During the Year	0	6.2
Liabilities Settled During the Year	(0.3)	(1.5)
Accretion	1.7	1.8
Revisions in Estimated Cash Flows	0	(5.5)
Balance as of End of Year	36.7	35.3
Public Service Company Of New Hampshire [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	21.6	20.6
Liabilities Incurred During the Year	0.5	0.4
Liabilities Settled During the Year	0	0
Accretion	1.4	1.3
Revisions in Estimated Cash Flows	0	(0.7)
Balance as of End of Year	23.5	21.6
Western Massachusetts Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	5.7	5.9
Liabilities Incurred During the Year	0	0
Liabilities Settled During the Year	(0.1)	(0.1)
Accretion	0.3	0.4
Revisions in Estimated Cash Flows	0	(0.5)
Balance as of End of Year	$ 5.9	$ 5.7

ASSET RETIREMENT OBLIGATIONS 88

ASSET RETIREMENT OBLIGATIONS - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligation	$ 426.4	$ 430.1	$ 426.3
CYAPC and YAEC [Member]
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligation	$ 308.6	$ 319.1

SHORT-TERM DEBT - Narrative (De

SHORT-TERM DEBT - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 28, 2016	Nov. 03, 2016	Aug. 08, 2016	Dec. 31, 2015	Jun. 16, 2015
Short-term Debt [Line Items]
Amount of debt authorized			$ 125,000,000
Notes payable	$ 1,148,500,000	$ 1,148,500,000				$ 1,160,953,000
The Connecticut Light And Power Company [Member]
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency							$ 600,000,000
Notes payable to related parties	80,100,000	80,100,000				277,400,000
Western Massachusetts Electric Company [Member]
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency							$ 300,000,000
Notes payable to related parties	51,000,000	51,000,000				143,400,000
NSTAR Electric Company [Member]
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency					$ 655,000,000
Notes payable	126,500,000	126,500,000				62,500,000
NSTAR Electric Company [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Amount of commercial paper program	450,000,000	450,000,000
Amount available for borrowing under credit facility	$ 323,500,000	$ 323,500,000				$ 387,500,000
Weighted average interest rate (as a percentage)	0.71%	0.71%				0.40%
Short-term borrowings outstanding under commercial paper program	$ 126,500,000	$ 126,500,000				$ 62,500,000
NSTAR Electric Company [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Amount of commercial paper program	$ 450,000,000	$ 450,000,000
Debt instrument term		5 years
Period of extension of termination date	1 year
Amount outstanding during period		$ 0
NPT [Member]
Short-term Debt [Line Items]
Amount of debt authorized				$ 800,000,000
Public Service Company Of New Hampshire [Member]
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency	$ 349,000,000	349,000,000
Notes payable to related parties	$ 160,900,000	$ 160,900,000				231,300,000
Public Service Company Of New Hampshire [Member] | Short Term Debt Authorization Calculation [Member]
Short-term Debt [Line Items]
Interest rate stated percentage (up to) (as a percentage)	10.00%	10.00%
Short-term debt borrowing calculation approved by regulatory agency	$ 60,000,000	$ 60,000,000
Eversource [Member]
Short-term Debt [Line Items]
Notes payable	1,022,000,000	1,022,000,000				1,098,453,000
Eversource [Member] | Commercial Paper [Member]
Short-term Debt [Line Items]
Amount of commercial paper program	1,450,000,000	1,450,000,000
Notes payable	1,000,000,000	1,000,000,000				1,100,000,000
Amount available for borrowing under credit facility	$ 428,000,000	$ 428,000,000				$ 351,500,000
Weighted average interest rate (as a percentage)	0.88%	0.88%				0.72%
Eversource [Member] | Line of Credit [Member]
Short-term Debt [Line Items]
Amount of commercial paper program	$ 1,450,000,000	$ 1,450,000,000
Debt instrument term		5 years
Period of extension of termination date	1 year
Amount outstanding during period		$ 0
Unsecured Debt [Member] | The Connecticut Light And Power Company [Member]
Short-term Debt [Line Items]
Period of maturity restricting provisions of debt		10 years
Total capitalization (as a percentage)		10.00%
Capacity available under preferred stock provisions	$ 557,600,000	$ 557,600,000

LONG-TERM DEBT - Schedule of Lo

LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Nov. 18, 2016	May 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt outstanding	$ 8,829,354				$ 8,805,574
Less Amounts due Within One Year	(773,883)				(228,883)
Senior Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt	8,829,400				8,805,600
The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	2,516,010				2,763,682
Less Amounts due Within One Year	(250,000)				0
The Connecticut Light And Power Company [Member] | Fixed rate Tax Exempt Due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	120,500				120,500
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	2,669,800				2,669,800
Unamortized Premiums and Discounts, Net	(10,000)				(10,700)
Unamortized Debt Issuance Costs	(14,300)				(15,900)
Long-Term Debt	$ 2,516,000				$ 2,763,700
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series D 1994 Notes Due 2024 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	7.875%				7.875%
Long-term debt outstanding	$ 139,800				$ 139,800
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series B 2004 Notes Due 2034 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.75%				5.75%
Long-term debt outstanding	$ 130,000				$ 130,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series B 2005 Notes Due 2035 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.625%				5.625%
Long-term debt outstanding	$ 100,000				$ 100,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2006 Notes Due 2036 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.35%				6.35%
Long-term debt outstanding	$ 250,000				$ 250,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2007 Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.375%				5.375%
Long-term debt outstanding	$ 150,000				$ 150,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series B 2007 Notes Due 2037 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.75%				5.75%
Long-term debt outstanding	$ 150,000				$ 150,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series C 2007 Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.75%				5.75%
Long-term debt outstanding	$ 100,000				$ 100,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series D 2007 Notes Due 2037 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.375%				6.375%
Long-term debt outstanding	$ 100,000				$ 100,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2008 Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.65%				5.65%
Long-term debt outstanding	$ 300,000				$ 300,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2009 Notes Due 2019 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.50%				5.50%
Long-term debt outstanding	$ 250,000				$ 250,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2013 Notes Due 2023 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.50%				2.50%
Long-term debt outstanding	$ 400,000				$ 400,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2014 Notes Due 2044 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.30%				4.30%
Long-term debt outstanding	$ 250,000				$ 250,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Series A 2015 Notes Due 2045 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.15%				4.15%
Long-term debt outstanding	$ 350,000				$ 350,000
The Connecticut Light And Power Company [Member] | First Mortgage Notes [Member] | Fixed rate Tax Exempt Due 2028 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.375%				4.375%
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	$ 1,678,116	$ 700,000			$ 1,829,766
Less Amounts due Within One Year	(400,000)				(200,000)
NSTAR Electric Company [Member] | Debentures [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	2,100,000				2,050,000
Less Amounts due Within One Year	(400,000)				(200,000)
Unamortized Premiums and Discounts, Net	(9,100)				(8,500)
Unamortized Debt Issuance Costs	(12,800)				(11,700)
Long-Term Debt	$ 1,678,100				$ 1,829,800
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2036 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.75%				5.75%
Long-term debt outstanding	$ 200,000				$ 200,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.625%				5.625%
Long-term debt outstanding	$ 400,000				$ 400,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2040 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.50%				5.50%
Long-term debt outstanding	$ 300,000				$ 300,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.375%				2.375%
Long-term debt outstanding	$ 400,000				$ 400,000
NSTAR Electric Company [Member] | Debentures [Member] | Variable Rate Due 2016 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)					0.6036%
Long-term debt outstanding	$ 0				$ 200,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2044 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.40%				4.40%
Long-term debt outstanding	$ 300,000				$ 300,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2025 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.25%				3.25%
Long-term debt outstanding	$ 250,000				$ 250,000
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.70%		2.70%		2.70%
Long-term debt outstanding	$ 250,000				$ 0
Public Service Company Of New Hampshire [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	1,002,048				1,071,017
Less Amounts due Within One Year	(70,000)				0
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	987,000				987,000
Less Amounts due Within One Year	(70,000)				0
Unamortized Premiums and Discounts, Net	100				100
Unamortized Debt Issuance Costs	(4,400)				(5,400)
Long-Term Debt	$ 1,002,000				$ 1,071,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series M Notes Due 2035 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.60%				5.60%
Long-term debt outstanding	$ 50,000				$ 50,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series N Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.15%				6.15%
Long-term debt outstanding	$ 70,000				$ 70,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series O Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.00%				6.00%
Long-term debt outstanding	$ 110,000				$ 110,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series P Notes Due 2019 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.50%				4.50%
Long-term debt outstanding	$ 150,000				$ 150,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series Q Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.05%				4.05%
Long-term debt outstanding	$ 122,000				$ 122,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series R Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.20%				3.20%
Long-term debt outstanding	$ 160,000				$ 160,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Series S Notes Due 2023 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.50%				3.50%
Long-term debt outstanding	$ 325,000				$ 325,000
Public Service Company Of New Hampshire [Member] | First Mortgage Notes [Member] | Adjustable Rate Tax Exempt Series A Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	1.138%				0.193%
Long-term debt outstanding	$ 89,300				$ 89,300
Western Massachusetts Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	566,536				517,329
Western Massachusetts Electric Company [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	565,000				515,000
Unamortized Premiums and Discounts, Net	4,200				5,200
Unamortized Debt Issuance Costs	(2,700)				(2,900)
Long-Term Debt	$ 566,500				$ 517,300
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series B Notes Due 2034 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.90%				5.90%
Long-term debt outstanding	$ 50,000				$ 50,000
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series D Notes Due 2037 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.70%				6.70%
Long-term debt outstanding	$ 40,000				$ 40,000
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series E Notes Due 2020 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.10%				5.10%
Long-term debt outstanding	$ 95,000				$ 95,000
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series F Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.50%				3.50%
Long-term debt outstanding	$ 250,000				$ 250,000
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series G Notes Due 2023 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.88%				3.88%
Long-term debt outstanding	$ 80,000				$ 80,000
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series H Notes Due 2026 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.75%				2.75%
Long-term debt outstanding	$ 50,000				$ 0
Yankee Gas Services Company [Member] | First Mortgage Notes [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	445,000				445,000
Unamortized Premiums and Discounts, Net	400				400
Unamortized Debt Issuance Costs	(1,500)				(1,700)
Long-Term Debt	$ 443,900				$ 443,700
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series B Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	8.48%				8.48%
Long-term debt outstanding	$ 20,000				$ 20,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series H Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.26%				5.26%
Long-term debt outstanding	$ 50,000				$ 50,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series I Senior Notes Due 2035 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	5.35%				5.35%
Long-term debt outstanding	$ 50,000				$ 50,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series J Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	6.90%				6.90%
Long-term debt outstanding	$ 100,000				$ 100,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series K Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.87%				4.87%
Long-term debt outstanding	$ 50,000				$ 50,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series L Senior Notes Due 2044 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.82%				4.82%
Long-term debt outstanding	$ 100,000				$ 100,000
Yankee Gas Services Company [Member] | First Mortgage Notes [Member] | Series M Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.35%				3.35%
Long-term debt outstanding	$ 75,000				$ 75,000
NSTAR Gas Company [Member] | First Mortgage Notes [Member]
Debt Instrument [Line Items]
Less Amounts due Within One Year	(25,000)				0
Unamortized Debt Issuance Costs	(700)				(800)
Long-Term Debt	284,300				309,200
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	$ 310,000				$ 310,000
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member] | Series J Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	9.95%				9.95%
Long-term debt outstanding	$ 25,000				$ 25,000
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member] | Series K Senior Notes Due 2033 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	7.11%				7.11%
Long-term debt outstanding	$ 35,000				$ 35,000
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member] | Series M Senior Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	7.04%				7.04%
Long-term debt outstanding	$ 25,000				$ 25,000
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member] | Series N Senior Notes Due 2020 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.46%				4.46%
Long-term debt outstanding	$ 125,000				$ 125,000
NSTAR Gas Company [Member] | Total First Mortgage Bonds [Member] | Series O Senior Notes Due 2045 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.35%				4.35%
Long-term debt outstanding	$ 100,000				$ 100,000
Eversource [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	2,158,519				1,691,330
Less Amounts due Within One Year	$ (28,883)				$ (28,883)
Eversource [Member] | Debentures [Member] | Unsecured Notes Due 2019 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	4.50%				4.50%
Long-term debt outstanding	$ 350,000				$ 350,000
Eversource [Member] | Debentures [Member] | Series E Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	1.45%				1.45%
Eversource [Member] | Debentures [Member] | Series F Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.80%				2.80%
Eversource [Member] | Debentures [Member] | Series G Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	1.60%				1.60%
Eversource [Member] | Debentures [Member] | Series H Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.15%				3.15%
Eversource [Member] | Debentures [Member] | Series I Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.50%				2.50%
Eversource [Member] | Debentures [Member] | Series J Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.35%				3.35%
Eversource [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	$ (2,200)				$ (1,300)
Unamortized Debt Issuance Costs	(4,900)				(1,900)
Eversource [Member] | Senior Notes [Member] | Series E Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	300,000				300,000
Eversource [Member] | Senior Notes [Member] | Series F Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	450,000				450,000
Eversource [Member] | Senior Notes [Member] | Series G Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	150,000				150,000
Eversource [Member] | Senior Notes [Member] | Series H Senior Notes Due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	300,000				300,000
Eversource [Member] | Senior Notes [Member] | Series I Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)				2.50%
Long-term debt outstanding	250,000				0
Eversource [Member] | Senior Notes [Member] | Series J Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)				3.35%
Long-term debt outstanding	250,000				0
Eversource [Member] | Senior Notes and Debentures [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	2,050,000				1,550,000
Eversource [Member] | Spent Nuclear Fuel Obilgation CY [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	180,000				179,500
Eversource [Member] | Fair Value Adjustment [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	144,600				173,500
Eversource [Member] | Fair Value Adjustment - Current Portion [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	(28,900)				(28,900)
Eversource [Member] | Total Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt outstanding	$ 3,066,800				$ 2,623,800

LONG-TERM DEBT - Long-Term Debt

LONG-TERM DEBT - Long-Term Debt Issuances (Details) - USD ($)	Dec. 31, 2016	Jun. 30, 2016	May 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Eversource [Member] | Senior Notes [Member] | Series I Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument face amount				$ 250,000,000
Interest rate stated percentage (as a percentage)				2.50%
Eversource [Member] | Senior Notes [Member] | Series J Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument face amount				$ 250,000,000
Interest rate stated percentage (as a percentage)				3.35%
Eversource [Member] | Debentures [Member] | Series I Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	2.50%				2.50%
Eversource [Member] | Debentures [Member] | Series J Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Interest rate stated percentage (as a percentage)	3.35%				3.35%
NSTAR Electric Company [Member] | Debentures [Member] | Unsecured Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument face amount			$ 250,000,000
Interest rate stated percentage (as a percentage)	2.70%		2.70%		2.70%
Western Massachusetts Electric Company [Member] | Senior Notes [Member] | Series H Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt instrument face amount		$ 50,000,000
Interest rate stated percentage (as a percentage)		2.75%

LONG-TERM DEBT - Long-Term De92

LONG-TERM DEBT - Long-Term Debt Repayment (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Repayments of debt		$ 200,000	$ 216,700	$ 576,551
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
Repayments of debt		$ 200,000	$ 4,700	$ 301,650
NSTAR Electric Company [Member] | Debentures [Member]
Debt Instrument [Line Items]
Repayments of debt	$ 200,000

LONG-TERM DEBT - Long-Term De93

LONG-TERM DEBT - Long-Term Debt Issuance Authorization (Details) - USD ($) $ in Thousands	Jan. 04, 2017	Dec. 31, 2016	Dec. 28, 2016	Nov. 18, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt outstanding		$ 8,829,354			$ 8,805,574
Amount of debt authorized			$ 125,000
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt outstanding		1,678,116		$ 700,000	1,829,766
The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
Long-term debt outstanding		$ 2,516,010			$ 2,763,682
Subsequent Event [Member] | The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
Amount of debt authorized	$ 1,325,000

LONG-TERN DEBT - Long-Term Debt

LONG-TERN DEBT - Long-Term Debt Provisions (Details)	12 Months Ended
	Dec. 31, 2016
Public Service Company Of New Hampshire [Member] | Senior Notes [Member] | Adjustable Rate Tax Exempt Series A Notes Due 2021 [Member]
Debt Instrument [Line Items]
Par value of stock (as a percentage)	100.00%

LONG-TERM DEBT - Pre-1983 Spent

LONG-TERM DEBT - Pre-1983 Spent Nuclear Fuel Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt outstanding	$ 8,829,354	$ 8,805,574
Interest included in payment to settle spent nuclear fuel obligation	$ 131,200	130,700
Fees And Interest Due For Spent Nuclear Fuel Disposal Costs [Member]
Debt Instrument [Line Items]
Long-term debt outstanding		$ 179,500

LONG-TERM DEBT - Schedule of 96

LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details) $ in Millions	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
2,017	$ 745
2,018	960
2,019	800
2,020	295
2,021	871.3
Thereafter	5,665.3
Total	9,336.6
The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
2,017	250
2,018	300
2,019	250
2,020	0
2,021	0
Thereafter	1,990.3
Total	2,790.3
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
2,017	400
2,018	0
2,019	0
2,020	0
2,021	0
Thereafter	1,700
Total	2,100
Public Service Company Of New Hampshire [Member]
Debt Instrument [Line Items]
2,017	70
2,018	110
2,019	150
2,020	0
2,021	371.3
Thereafter	375
Total	1,076.3
Western Massachusetts Electric Company [Member]
Debt Instrument [Line Items]
2,017	0
2,018	0
2,019	0
2,020	95
2,021	250
Thereafter	220
Total	$ 565

EMPLOYEE BENEFITS - Schedule of

EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	$ (5,080.1)	$ (5,486.2)
Plan Amendment	(9)	0
Service Cost	(75)	(91.4)	$ (79.9)
Interest Cost	(185.5)	(227)	(225.7)
Actuarial Gain/(Loss)	(151.8)	331.5
Benefits Paid - Pension	254	238.5
Benefits Paid - Lump Sum	0	149.5
Benefits Paid - SERP	5.1	5
Benefit Obligation as of End of Year	(5,242.3)	(5,080.1)	(5,486.2)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	3,905.4	4,126.5
Employer Contributions	146.2	154.6
Actual Return on Pension Plan Assets	278.4	12.3
Benefits Paid	(254)	(238.5)
Benefits Paid - Lump Sum	0	149.5
Fair Value of Pension Plan Assets as of End of Year	4,076	3,905.4	4,126.5
Funded Status as of December 31st	(1,166.3)	(1,174.7)
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,051.4)	(1,147.9)
Plan Amendment	244	0
Service Cost	(12.2)	(16.3)	(12.5)
Interest Cost	(32.9)	(47.2)	(49.5)
Actuarial Gain/(Loss)	(17.7)	106
Benefits Paid - Pension	60.2	54
Benefit Obligation as of End of Year	(810)	(1,051.4)	(1,147.9)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	812.2	862.6
Employer Contributions	12.5	7.9
Actual Return on Pension Plan Assets	51.3	(4.3)
Benefits Paid	(60.2)	(54)
Fair Value of Pension Plan Assets as of End of Year	815.8	812.2	862.6
Funded Status as of December 31st	5.8	(239.2)
The Connecticut Light And Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,157.6)	(1,230.1)
Plan Amendment	0	0
Change due to transfer of employees	8.8	(4.6)
Service Cost	(18.8)	(24.7)	(20.2)
Interest Cost	(41.6)	(51.1)	(50.5)
Actuarial Gain/(Loss)	(23.9)	77.8
Benefits Paid - Pension	62.6	60.2
Benefits Paid - Lump Sum	0	14.5
Benefits Paid - SERP	0.3	0.4
Benefit Obligation as of End of Year	(1,170.2)	(1,157.6)	(1,230.1)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	913.5	980.8
Change due to transfer of employees	(8.8)	4.6
Employer Contributions	0.4	0
Actual Return on Pension Plan Assets	63	2.8
Benefits Paid	(62.6)	(60.2)
Benefits Paid - Lump Sum	0	14.5
Fair Value of Pension Plan Assets as of End of Year	905.5	913.5	980.8
Funded Status as of December 31st	(264.7)	(244.1)
The Connecticut Light And Power Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(164)	(173.9)
Plan Amendment	(12.5)	0
Change due to transfer of employees	1.3	0.1
Service Cost	(2)	(2.1)	(2.2)
Interest Cost	(5.3)	(7.2)	(8.1)
Actuarial Gain/(Loss)	3.6	7.2
Benefits Paid - Pension	13.9	11.9
Benefit Obligation as of End of Year	(165)	(164)	(173.9)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	136.7	149
Change due to transfer of employees	(0.8)	0
Employer Contributions	0	0
Actual Return on Pension Plan Assets	7.2	(0.4)
Benefits Paid	(13.9)	(11.9)
Fair Value of Pension Plan Assets as of End of Year	129.2	136.7	149
Funded Status as of December 31st	(35.8)	(27.3)
NSTAR Electric Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(949.7)	(982.6)
Plan Amendment	(2.8)	0
Change due to transfer of employees	(0.6)	6.2
Service Cost	(13.2)	(14.9)	(13.6)
Interest Cost	(33.8)	(40.2)	(41.3)
Actuarial Gain/(Loss)	(33.3)	34.1
Benefits Paid - Pension	53.8	47.6
Benefits Paid - Lump Sum	0	0
Benefits Paid - SERP	0.2	0.1
Benefit Obligation as of End of Year	(979.4)	(949.7)	(982.6)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	832.9	879
Change due to transfer of employees	0.6	(6.2)
Employer Contributions	28.4	5
Actual Return on Pension Plan Assets	59.2	2.7
Benefits Paid	(53.8)	(47.6)
Benefits Paid - Lump Sum	0	0
Fair Value of Pension Plan Assets as of End of Year	867.3	832.9	879
Funded Status as of December 31st	(112.1)	(116.8)
NSTAR Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(412.8)	(468.7)
Plan Amendment	195.3	0
Change due to transfer of employees	0.3	2.3
Service Cost	(3)	(5.4)	(3.1)
Interest Cost	(12.2)	(19)	(19.4)
Actuarial Gain/(Loss)	(24.6)	59.1
Benefits Paid - Pension	20.3	18.9
Benefit Obligation as of End of Year	(236.7)	(412.8)	(468.7)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	320.3	336.5
Change due to transfer of employees	(0.3)	0.6
Employer Contributions	8.9	4.9
Actual Return on Pension Plan Assets	23.2	(2.8)
Benefits Paid	(20.3)	(18.9)
Fair Value of Pension Plan Assets as of End of Year	331.8	320.3	336.5
Funded Status as of December 31st	95.1	(92.5)
Public Service Company Of New Hampshire [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(547.6)	(580.7)
Plan Amendment	0	0
Change due to transfer of employees	2.4	(1.9)
Service Cost	(9.9)	(12.1)	(9.7)
Interest Cost	(20.7)	(24.3)	(23.8)
Actuarial Gain/(Loss)	(21.5)	38.9
Benefits Paid - Pension	24.9	23.2
Benefits Paid - Lump Sum	0	9.1
Benefits Paid - SERP	0.2	0.2
Benefit Obligation as of End of Year	(572.2)	(547.6)	(580.7)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	470.5	498.4
Change due to transfer of employees	(2.4)	1.9
Employer Contributions	17.1	1
Actual Return on Pension Plan Assets	33.7	1.5
Benefits Paid	(24.9)	(23.2)
Benefits Paid - Lump Sum	0	9.1
Fair Value of Pension Plan Assets as of End of Year	494	470.5	498.4
Funded Status as of December 31st	(78.2)	(77.1)
Public Service Company Of New Hampshire [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(88.5)	(91.8)
Plan Amendment	(6.7)	0
Change due to transfer of employees	0.3	(0.3)
Service Cost	(1.3)	(1.4)	(1.3)
Interest Cost	(2.9)	(3.9)	(4.3)
Actuarial Gain/(Loss)	3.6	3.6
Benefits Paid - Pension	5.8	5.3
Benefit Obligation as of End of Year	(89.7)	(88.5)	(91.8)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	75.8	80.9
Change due to transfer of employees	(0.2)	0.2
Employer Contributions	0	0
Actual Return on Pension Plan Assets	3.4	0
Benefits Paid	(5.8)	(5.3)
Fair Value of Pension Plan Assets as of End of Year	73.2	75.8	80.9
Funded Status as of December 31st	(16.5)	(12.7)
Western Massachusetts Electric Company [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefits Paid - Lump Sum	0
Change in Pension Plan Assets:
Benefits Paid - Lump Sum	0
Western Massachusetts Electric Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(237.6)	(249.4)
Plan Amendment	0	0
Change due to transfer of employees	1.9	(1.3)
Service Cost	(3.1)	(4.3)	(3.5)
Interest Cost	(8.4)	(10.4)	(10.3)
Actuarial Gain/(Loss)	(3.9)	12.6
Benefits Paid - Pension	13.2	12.7
Benefits Paid - Lump Sum		2.5
Benefits Paid - SERP	0	0
Benefit Obligation as of End of Year	(237.9)	(237.6)	(249.4)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	220.8	234
Change due to transfer of employees	(1.9)	1.3
Employer Contributions	0	0
Actual Return on Pension Plan Assets	15.3	0.7
Benefits Paid	(13.2)	(12.7)
Benefits Paid - Lump Sum		2.5
Fair Value of Pension Plan Assets as of End of Year	221	220.8	234
Funded Status as of December 31st	(16.9)	(16.8)
Western Massachusetts Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(34.4)	(36.6)
Plan Amendment	(1.7)	0
Change due to transfer of employees	0.2	0
Service Cost	(0.4)	(0.4)	(0.4)
Interest Cost	(1.1)	(1.5)	(1.7)
Actuarial Gain/(Loss)	1.1	1.5
Benefits Paid - Pension	3	2.6
Benefit Obligation as of End of Year	(33.3)	(34.4)	(36.6)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	31.7	34.4
Change due to transfer of employees	(0.3)	0
Employer Contributions	0	0
Actual Return on Pension Plan Assets	1.4	(0.1)
Benefits Paid	(3)	(2.6)
Fair Value of Pension Plan Assets as of End of Year	29.8	31.7	$ 34.4
Funded Status as of December 31st	$ (3.5)	$ (2.7)

EMPLOYEE BENEFITS - Pension Pla

EMPLOYEE BENEFITS - Pension Plan Narrative (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2016	Aug. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Decrease in liability due to change in discount rate			$ 177	$ 267
Change in liability due to change in mortality rate			32	48
Increase in liability due to amendment in pension plan			9
Lump sum payout		$ 149.5
Funded status of plan			(1,166.3)	(1,174.7)
Change in pension expense due to change in discount rate methodology for calculating interest and service costs			46
Employer contributions			146.2	154.6
Estimated future employer contributions in next fiscal year			175
Estimated future contributions in the next twelve months by other subsidiaries			$ 148
Assumed rate of return			8.25%
Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Amount resulting from revised mortality table and estimated benefits				23
Funded status of plan			$ 5.8	(239.2)
Change in pension expense due to change in discount rate methodology for calculating interest and service costs			10
Accumulated benefit obligation	$ 244
Increase in liability due to decrease in discount rate	$ 75
Change in mortality assumptions and other demographic assumptions			52
Defined Benefit Plan, Decrease in Liability Due to Decrease in Discount Rate				$ 60
Impact of plan amendment on annual expense			$ 10
Assumptions used in calculating net periodic benefit cost, health care cost rate (in percentage)			6.25%	6.50%
Increase in service and interest cost expense			$ 4.4
Decrease in service and interest cost			3.4
Employer contributions			12.5	$ 7.9
Estimated future employer contributions in next fiscal year			$ 7.6
Taxable assets in equity securities (in percentage)			70.00%
Taxable assets in fixed income securities			30.00%
The Connecticut Light And Power Company [Member] | Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			$ (264.7)	(244.1)
Employer contributions			0.4	0
Estimated future employer contributions in next fiscal year			2
The Connecticut Light And Power Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(35.8)	(27.3)
Employer contributions			0	0
NSTAR Electric Company [Member] | Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(112.1)	(116.8)
Employer contributions			28.4	5
Estimated future employer contributions in next fiscal year			25
NSTAR Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			95.1	(92.5)
Employer contributions			8.9	4.9
Estimated future employer contributions in next fiscal year			5
Public Service Company Of New Hampshire [Member] | Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(78.2)	(77.1)
Employer contributions			17.1	1
Public Service Company Of New Hampshire [Member] | Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(16.5)	(12.7)
Employer contributions			0	0
Western Massachusetts Electric Company [Member] | Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(16.9)	(16.8)
Employer contributions			0	0
Western Massachusetts Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			(3.5)	(2.7)
Employer contributions			0	0
Other Current Liabilities [Member]
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			$ 24.8	$ 6.6

EMPLOYEE BENEFITS - Schedule 99

EMPLOYEE BENEFITS - Schedule of Funded Status (Details) - Pension Plan [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 4,829.6	$ 4,733.2
The Connecticut Light And Power Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,065.2	1,062.7
NSTAR Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	904.8	888.8
Public Service Company Of New Hampshire [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	518.9	506.4
Western Massachusetts Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 220	$ 222.3

EMPLOYEE BENEFITS - Schedule100

EMPLOYEE BENEFITS - Schedule of Actuarial Assumptions (Details)	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.01%	4.21%
Compensation/Progression Rate	3.50%	3.50%
Pension Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.33%	4.60%
Compensation/Progression Rate	3.50%	3.50%
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.21%	4.62%
Health Care Cost Trend Rate		6.25%

EMPLOYEE BENEFITS - Schedule101

EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 75	$ 91.4	$ 79.9
Interest Cost	185.5	227	225.7
Expected Return on Pension Plan Assets	(317.9)	(335.9)	(310.8)
Actuarial Loss/(Gain)	125.7	148.5	128.4
Prior Service Cost	3.6	3.7	4.4
Total Net Periodic Benefit Expense/(Income)	71.9	134.7	127.6
Capitalized PBOP Expense/(Income)	(22.1)	(41)	(35.2)
Amount included in other deferred debits		3.2
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	12.2	16.3	12.5
Interest Cost	32.9	47.2	49.5
Expected Return on Pension Plan Assets	(62.9)	(67.4)	(63.3)
Actuarial Loss/(Gain)	9	6.8	12.2
Prior Service Cost	(9.1)	(0.5)	(2.8)
Total Net Periodic Benefit Expense/(Income)	(17.9)	2.4	8.1
Capitalized PBOP Expense/(Income)	(8)	0.1	(1.4)
The Connecticut Light And Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	18.8	24.7	20.2
Interest Cost	41.6	51.1	50.5
Expected Return on Pension Plan Assets	(72.1)	(78.9)	(75.4)
Actuarial Loss/(Gain)	25.4	32.2	33.7
Prior Service Cost	1.5	1.5	1.8
Total Net Periodic Benefit Expense/(Income)	15.2	30.6	30.8
Intercompany Allocations	13.8	22.5	26.7
Capitalized PBOP Expense/(Income)	(9.3)	(18.8)	(17.6)
The Connecticut Light And Power Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	2.1	2.2
Interest Cost	5.3	7.2	8.1
Expected Return on Pension Plan Assets	(10.1)	(11.1)	(10.5)
Actuarial Loss/(Gain)	1.5	0.7	4.2
Prior Service Cost	0.5	0	0
Total Net Periodic Benefit Expense/(Income)	(0.8)	(1.1)	4
Intercompany Allocations	0.3	1.9	3.8
Capitalized PBOP Expense/(Income)	(0.5)	(0.2)	(1.8)
NSTAR Electric Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	13.2	14.9	13.6
Interest Cost	33.8	40.2	41.3
Expected Return on Pension Plan Assets	(67.6)	(70)	(63)
Actuarial Loss/(Gain)	34.4	35.8	23.5
Prior Service Cost	0	(0.1)	0
Total Net Periodic Benefit Expense/(Income)	13.8	20.8	15.4
Intercompany Allocations	8.9	13.6	10.4
Capitalized PBOP Expense/(Income)	(7.6)	(11.4)	(7.9)
NSTAR Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3	5.4	3.1
Interest Cost	12.2	19	19.4
Expected Return on Pension Plan Assets	(25.7)	(27.3)	(25.9)
Actuarial Loss/(Gain)	3.2	2.3	(0.5)
Prior Service Cost	(7.2)	(0.2)	(1.9)
Total Net Periodic Benefit Expense/(Income)	(14.5)	(0.8)	(5.8)
Intercompany Allocations	(0.2)	0.8	0.8
Capitalized PBOP Expense/(Income)	(6.4)	(0.2)	2.3
Public Service Company Of New Hampshire [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	9.9	12.1	9.7
Interest Cost	20.7	24.3	23.8
Expected Return on Pension Plan Assets	(38.6)	(40.4)	(38.1)
Actuarial Loss/(Gain)	9.9	11.6	11.6
Prior Service Cost	0.5	0.5	0.7
Total Net Periodic Benefit Expense/(Income)	2.4	8.1	7.7
Intercompany Allocations	4	6.7	7.6
Capitalized PBOP Expense/(Income)	(1.4)	(3.5)	(3)
Public Service Company Of New Hampshire [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1.3	1.4	1.3
Interest Cost	2.9	3.9	4.3
Expected Return on Pension Plan Assets	(5.5)	(6)	(5.4)
Actuarial Loss/(Gain)	0.7	0.5	2.2
Prior Service Cost	0.2	0	0
Total Net Periodic Benefit Expense/(Income)	(0.4)	(0.2)	2.4
Intercompany Allocations	(0.1)	0.4	1
Capitalized PBOP Expense/(Income)	0.1	0.2	(0.8)
Western Massachusetts Electric Company [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3.1	4.3	3.5
Interest Cost	8.4	10.4	10.3
Expected Return on Pension Plan Assets	(17.5)	(18.9)	(17.9)
Actuarial Loss/(Gain)	5.5	6.4	6.9
Prior Service Cost	0.3	0.3	0.4
Total Net Periodic Benefit Expense/(Income)	(0.2)	2.5	3.2
Intercompany Allocations	2.5	4.4	5.1
Capitalized PBOP Expense/(Income)	(0.4)	(1.9)	(2.4)
Western Massachusetts Electric Company [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0.4	0.4	0.4
Interest Cost	1.1	1.5	1.7
Expected Return on Pension Plan Assets	(2.4)	(2.5)	(2.3)
Actuarial Loss/(Gain)	0.1	0	0.5
Prior Service Cost	0.1	0	0
Total Net Periodic Benefit Expense/(Income)	(0.7)	(0.6)	0.3
Intercompany Allocations	0.1	0.3	0.7
Capitalized PBOP Expense/(Income)	$ (0.3)	$ (0.2)	$ (0.2)

EMPLOYEE BENEFITS - Schedule102

EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)		4.20%
Expected Long-Term Rate of Return (in percentage)		8.25%
Compensation/Progression Rate (in percentage)		3.50%
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)		4.22%
Expected Long-Term Rate of Return (in percentage)		8.25%
Minimum [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.27%		4.85%
Expected Long-Term Rate of Return (in percentage)	8.25%		8.25%
Compensation/Progression Rate (in percentage)	3.50%		3.50%
Minimum [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	2.88%		4.78%
Expected Long-Term Rate of Return (in percentage)	8.25%		8.25%
Maximum [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	4.89%		5.03%
Expected Long-Term Rate of Return (in percentage)	8.25%		8.25%
Compensation/Progression Rate (in percentage)	3.50%		4.00%
Maximum [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	4.09%		5.10%
Expected Long-Term Rate of Return (in percentage)	8.25%		8.25%

EMPLOYEE BENEFITS - Summary of

EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Net Regulatory Assets [Abstract]
Actuarial Losses/(Gains) Arising During the Year	$ 184.6	$ (2)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(119.9)	(142.3)
Prior Service Cost Arising During the Year	7.1	0
Prior Service Cost Reclassified as Net Periodic Benefit Expense	(3.4)	(3.5)
Actuarial Loss	1,732.3	1,667.6
Expected Actuarial Loss Expense	128.5
Prior Service Cost	13.4	9.7
Expected Prior Service Cost Expense	4.1
OCI
Actuarial Losses/(Gains) Arising During the Year	6.8	(6.2)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(5.8)	(6.2)
Prior Service (Credit)/Cost Arising During the Year	1.9	0
Prior Service Cost Reclassified as Net Periodic Benefit Expense	(0.2)	(0.2)
Actuarial Loss	82.1	81.1
Expected Actuarial Loss Expense	5.8
Prior Service Cost	2.3	0.6
Expected Prior Service Cost Expense	0.2
Other Postretirement Benefit Plan [Member]
Net Regulatory Assets [Abstract]
Actuarial Losses/(Gains) Arising During the Year	32.4	(34.1)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(9.2)	(6.4)
Prior Service Cost Arising During the Year	(247.9)	0
Prior Service Cost Reclassified as Net Periodic Benefit Expense	9.7	0.5
Actuarial Loss	175.4	152.2
Expected Actuarial Loss Expense	7.9
Prior Service Cost	(239.5)	(1.3)
Expected Prior Service Cost Expense	(21.7)
OCI
Actuarial Losses/(Gains) Arising During the Year	(2)	0.7
Actuarial Losses Reclassified as Net Periodic Benefit Expense	0.2	(0.4)
Prior Service (Credit)/Cost Arising During the Year	4	0
Prior Service Cost Reclassified as Net Periodic Benefit Expense	(0.6)	0
Actuarial Loss	4.5	6.3
Expected Actuarial Loss Expense	0.4
Prior Service Cost	3.4	$ 0
Expected Prior Service Cost Expense	$ 0.2

EMPLOYEE BENEFITS - Schedule104

EMPLOYEE BENEFITS - Schedule of Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2016USD ($)
Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
2,017	$ 284.5
2,018	277
2,019	284.3
2,020	290.4
2,021	298.9
2022-2026	1,562.9
Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
2,017	54.8
2,018	55
2,019	55.1
2,020	55.4
2,021	55.4
2022-2026	$ 270.7

EMPLOYEE BENEFITS - Schedule105

EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)	12 Months Ended
	Dec. 31, 2016
United States [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	22.00%
Assumed Rate of Return	8.50%
International [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	13.00%
Assumed Rate of Return	8.50%
Emergining Markets [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	5.00%
Assumed Rate of Return	10.00%
Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	12.00%
Assumed Rate of Return	12.00%
Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	12.00%
Assumed Rate of Return	4.50%
High Yield Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	13.00%
Assumed Rate of Return	8.50%
Emerging Markets Debt [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	5.00%
Assumed Rate of Return	7.50%
Real Estate [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	10.00%
Assumed Rate of Return	7.50%
Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	8.00%
Assumed Rate of Return	7.00%

EMPLOYEE BENEFITS - Schedule106

EMPLOYEE BENEFITS - Schedule of Asset category (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 4,076	$ 3,905.4	$ 4,126.5
Uncategorized	3,558.4	3,334
Pension Plan [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,735.2	1,687.4
Uncategorized	1,279.7	1,228.7
Pension Plan [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	524.4	472.3
Uncategorized	518.4	464.7
Pension Plan [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,282.4	1,216.8
Uncategorized	1,099.4	1,008.2
Pension Plan [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	403.1	377.8
Uncategorized	325.9	291.9
Pension Plan [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	335	340.5
Uncategorized	335	340.5
Pension Plan [Member] | Total Assets Before 401 (h) [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	4,280.1	4,094.8
Pension Plan [Member] | 401(h) PBOP Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	204.1	189.4
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	538.7	404.1
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	455.5	396.5
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	6	7.6
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	77.2	0
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	183	356.7
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	62.2
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	183	208.6
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	85.9
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefit Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	815.8	812.2	$ 862.6
Uncategorized	453.3	446.3
Other Postretirement Benefit Plan [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	302.7	309.1
Uncategorized	214.1	199.4
Other Postretirement Benefit Plan [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	32.2	32.9
Uncategorized	32.2	32.9
Other Postretirement Benefit Plan [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	186.6	191.2
Uncategorized	132.3	131
Other Postretirement Benefit Plan [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	43	37.4
Uncategorized	27.5	30.8
Other Postretirement Benefit Plan [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	47.2	52.2
Uncategorized	47.2	52.2
Other Postretirement Benefit Plan [Member] | Total Assets Before 401 (h) [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	611.7	622.8
Other Postretirement Benefit Plan [Member] | 401(h) PBOP Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	204.1	189.4
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	113.6	119.4
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	88.6	109.7
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	9.5	9.7
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	15.5	0
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	44.8	57.1
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Private Equity [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Fixed Income [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	44.8	50.5
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Real Estate and Other Assets [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	6.6
Other Postretirement Benefit Plan [Member] | Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0	$ 0

EMPLOYEE BENEFITS - Defined Con

EMPLOYEE BENEFITS - Defined Contribution Plan Narrative (Details) - plan	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2014
Defined Contribution Plan, 401K [Member]
Defined Contribution Plan Disclosure [Line Items]
Number of plans held on behalf of eligible participants	1
Employer matching contribution (as a percentage)	100.00%	100.00%
Percentage of employees' pay (up to)	3.00%	3.00%
Defined Contribution Plan, Alternate Contribution 401K [Member]
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution (as a percentage)	50.00%
Percentage of employees' pay (up to)	8.00%

EMPLOYEE BENEFITS - Schedule108

EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 31.8	$ 30.4	$ 29.7
The Connecticut Light And Power Company [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	4.5	4.8	5
NSTAR Electric Company [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	7	6.3	6.3
Public Service Company Of New Hampshire [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	3.4	3.4	3.2
Western Massachusetts Electric Company [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 1.1	$ 1	$ 1

EMPLOYEE BENEFITS - Schedule109

EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	$ 54.2	$ 55.2	$ 57.5
Other Retirement Benefits Expense	2.9	3.9	4.5
The Connecticut Light And Power Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.3	0.4	0.4
Other Retirement Benefits Expense	1.1	1.5	2.1
NSTAR Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0	0	0
Other Retirement Benefits Expense	0.7	1	0.3
Public Service Company Of New Hampshire [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	2	2.4	2.6
Other Retirement Benefits Expense	0.6	0.7	0.9
Western Massachusetts Electric Company [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.1	0.2	0.2
Other Retirement Benefits Expense	$ 0.2	$ 0.3	$ 0.4

SHARE-BASED PAYMENTS - Narrativ

SHARE-BASED PAYMENTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in incentive plan (up to) (in shares)		8,000,000
Shares available for issuance under incentive plan (in shares)		2,692,350	3,005,010
Shares outstanding (in shares)		322,158
Weighted average grant date fair value of restricted stock units (in dollars per share)		$ 48.96
Total unrecognized compensation expense		$ 13.9
Period for recognition (in years)		1 year 9 months 4 days
Tax effect on total share-based payments (in percentage)		40.00%
Excess tax benefit		$ 19.1
Proceeds from excess tax benefit			$ 9.5	$ 9.5
Weighted average remaining contractual life		2 years
Cash received from stock options exercised		$ 1.3
Tax benefit realized from stock options		$ 0.5
Percentage of ESPP purchased by employees at the end of successive six-month offering period (in percentage)		95.00%
Number of shares purchased at discounted prices (in shares)		16,014	33,715
ESPP discounted purchase price for first six months (in dollars per share)		$ 51.11	$ 52.80
ESPP discounted purchase price for second six months (in dollars per share)			$ 47.23
Employee stock purchase plan available for future issuances (in shares)			743,260
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 42.27	54.67	$ 54.57
Shares outstanding (in shares)			469,772
Weighted average shares outstanding (in dollars per share)		$ 53.47	$ 48.58
Restricted stock units available (in shares)		402,263
Restricted stock unit fully vested (in shares)		402,112
Additional restricted stock unit expected to vest (in shares)		306,050
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)		$ 53.64	$ 55.04	$ 43.40
Shares outstanding (in shares)		301,363	528,428
Weighted average shares outstanding (in dollars per share)		$ 51.52	$ 46.30
Restricted stock units available (in shares)		423,025
Weighted average grant date fair value of restricted stock units (in dollars per share)		$ 45.94
Restricted stock unit fully vested (in shares)		221,571
The Connecticut Light And Power Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense		$ 5.1
Period for recognition (in years)		1 year 9 months 4 days
NSTAR Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense		$ 3.8
Period for recognition (in years)		1 year 9 months 4 days
Expiration period		10 years
Public Service Company Of New Hampshire [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense		$ 2
Period for recognition (in years)		1 year 9 months 4 days
Western Massachusetts Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense		$ 0.9
Period for recognition (in years)		1 year 9 months
Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program		3 years
Board Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program		1 year

SHARE-BASED PAYMENTS - Eversour

SHARE-BASED PAYMENTS - Eversource Incentve Plan (Details) - $ / shares	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)		729,308
Granted (in shares)		305,340
Shares issued (in shares)		(270,060)
Forfeited (in shares)		(40,318)
Ending balance (in shares)		724,270	729,308
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance (in dollars per share)		$ 43.45
Granted (in dollars per share)	$ 42.27	54.67	$ 54.57
Shares issued (in dollars per share)		44.94
Forfeited (in dollars per share)		53.99
Ending balance (in dollars per share)		$ 47.86	$ 43.45
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)		528,428
Granted (in shares)		222,139
Shares issued (in shares)		(201,826)
Forfeited (in shares)		(25,807)
Ending balance (in shares)		522,934	528,428
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance (in dollars per share)		$ 46.30
Granted (in dollars per share)		53.64	$ 55.04	$ 43.40
Shares issued (in dollars per share)		40.93
Forfeited (in dollars per share)		54.48
Ending balance (in dollars per share)		$ 51.09	$ 46.30

SHARE-BASED PAYMENTS - Schedule

SHARE-BASED PAYMENTS - Schedule of Compensation Expense and Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 23.6	$ 23.1	$ 24.6
Future Income Tax Benefit	9.6	9.4	10.3
The Connecticut Light And Power Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	9.1	9.3	8.1
Future Income Tax Benefit	3.7	3.8	3.4
NSTAR Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	6.5	5.8	7.4
Future Income Tax Benefit	2.6	2.4	3.1
Public Service Company Of New Hampshire [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	3.5	3.2	3
Future Income Tax Benefit	1.4	1.3	1.3
Western Massachusetts Electric Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	1.7	1.7	1.3
Future Income Tax Benefit	$ 0.7	$ 0.7	$ 0.5

SHARE-BASED PAYMENTS - Sched113

SHARE-BASED PAYMENTS - Schedule of Stock Options Outstanding (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (in shares) | shares	171,872
Exercised (in shares) | shares	(47,232)
Ending balance (in shares) | shares	124,640
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 26.47
Exercised (in dollars per share) | $ / shares	28.12
Ending balance (in dollars per share) | $ / shares	$ 25.84
Intrinsic Value (Millions)
Beginning balance | $	$ 4.2
Exercised | $	1.3
Ending balance | $	$ 3.7

INCOME TAXES - Components of In

INCOME TAXES - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current Income Taxes:
Federal	$ 38,900	$ 6,200	$ 4,400
State	53,000	45,700	24,500
Total Current	91,900	51,900	28,900
Deferred Income Taxes, Net:
Federal	427,900	436,100	406,800
State	38,600	55,600	36,500
Total Deferred	466,463	491,736	443,259
Investment Tax Credits, Net	(3,400)	(3,600)	(3,900)
Income Tax Expense	554,997	539,967	468,297
The Connecticut Light And Power Company [Member]
Current Income Taxes:
Federal	27,300	26,900	(200)
State	13,300	15,800	4,300
Total Current	40,600	42,700	4,100
Deferred Income Taxes, Net:
Federal	157,600	135,800	138,000
State	11,300	200	(7,100)
Total Deferred	168,919	135,994	130,949
Investment Tax Credits, Net	(1,200)	(1,300)	(1,500)
Income Tax Expense	208,308	177,396	133,451
NSTAR Electric Company [Member]
Current Income Taxes:
Federal	73,900	36,300	75,000
State	35,000	19,800	20,200
Total Current	108,900	56,100	95,200
Deferred Income Taxes, Net:
Federal	78,300	147,500	88,000
State	1,900	25,700	20,100
Total Deferred	80,200	173,155	108,133
Investment Tax Credits, Net	(1,300)	(1,300)	(1,300)
Income Tax Expense	187,767	228,044	201,981
Public Service Company Of New Hampshire [Member]
Current Income Taxes:
Federal	(13,700)	(16,700)	(22,600)
State	8,800	6,000	(100)
Total Current	(4,900)	(10,700)	(22,700)
Deferred Income Taxes, Net:
Federal	79,500	74,500	79,600
State	7,800	9,300	15,200
Total Deferred	87,345	83,776	94,813
Investment Tax Credits, Net	0	0	0
Income Tax Expense	82,364	73,060	72,135
Western Massachusetts Electric Company [Member]
Current Income Taxes:
Federal	12,500	(3,500)	1,900
State	4,500	1,600	1,800
Total Current	17,000	(1,900)	3,700
Deferred Income Taxes, Net:
Federal	18,300	33,400	28,100
State	3,200	6,000	6,000
Total Deferred	21,498	39,428	34,108
Investment Tax Credits, Net	(500)	(500)	(500)
Income Tax Expense	$ 38,022	$ 36,970	$ 37,268

INCOME TAXES - Reconciliation B

INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 1,504,818	$ 1,425,971	$ 1,295,362
Federal tax expense (in percentage)	35.00%	35.00%	35.00%
Statutory Federal Income Tax Expense at 35%	$ 526,700	$ 499,100	$ 453,400
Tax Effect of Differences:
Depreciation	(3,400)	(4,600)	(5,600)
Investment Tax Credit Amortization	(3,400)	(3,600)	(3,900)
Other Federal Tax Credits	(3,500)	(3,800)	(3,500)
State Income Taxes, Net of Federal Impact	56,200	61,100	42,500
Dividends on ESOP	(8,400)	(8,100)	(8,000)
Tax Asset Valuation Allowance/Reserve Adjustments	3,300	4,700	(2,900)
Excess Stock Benefit (1)	(19,100)	0	0
Other, Net	6,600	(4,800)	(3,700)
Income Tax Expense	$ 554,997	$ 539,967	$ 468,297
Effective Income Tax Rate Reconciliation, Percent	36.90%	37.90%	36.20%
The Connecticut Light And Power Company [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 542,562	$ 476,756	$ 421,205
Statutory Federal Income Tax Expense at 35%	189,900	166,900	147,400
Tax Effect of Differences:
Depreciation	1,600	(1,700)	(3,600)
Investment Tax Credit Amortization	(1,200)	(1,300)	(1,500)
Other Federal Tax Credits	0	0	0
State Income Taxes, Net of Federal Impact	14,500	9,200	4,400
Tax Asset Valuation Allowance/Reserve Adjustments	1,500	1,200	(6,300)
Excess Stock Benefit (1)	(900)	0	0
Other, Net	2,900	3,100	(6,900)
Income Tax Expense	$ 208,308	$ 177,396	$ 133,451
Effective Income Tax Rate Reconciliation, Percent	38.40%	37.20%	31.70%
NSTAR Electric Company [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 480,472	$ 572,586	$ 505,069
Statutory Federal Income Tax Expense at 35%	168,200	200,400	176,800
Tax Effect of Differences:
Depreciation	(3,400)	(1,400)	(1,300)
Investment Tax Credit Amortization	(1,300)	(1,300)	(1,300)
Other Federal Tax Credits	0	0	0
State Income Taxes, Net of Federal Impact	24,000	29,600	26,200
Tax Asset Valuation Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit (1)	(1,000)	0	0
Other, Net	1,300	700	1,600
Income Tax Expense	$ 187,767	$ 228,044	$ 201,981
Effective Income Tax Rate Reconciliation, Percent	39.10%	39.80%	40.00%
Public Service Company Of New Hampshire [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 214,349	$ 187,502	$ 186,079
Statutory Federal Income Tax Expense at 35%	75,000	65,600	65,100
Tax Effect of Differences:
Depreciation	1,000	500	300
Investment Tax Credit Amortization	0	0	0
Other Federal Tax Credits	(3,500)	(3,800)	(3,500)
State Income Taxes, Net of Federal Impact	10,800	9,900	9,800
Tax Asset Valuation Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit (1)	(400)	0	0
Other, Net	(500)	900	400
Income Tax Expense	$ 82,364	$ 73,060	$ 72,135
Effective Income Tax Rate Reconciliation, Percent	38.40%	39.00%	38.70%
Western Massachusetts Electric Company [Member]
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 96,094	$ 93,476	$ 95,087
Statutory Federal Income Tax Expense at 35%	33,600	32,700	33,300
Tax Effect of Differences:
Depreciation	300	(300)	(200)
Investment Tax Credit Amortization	(500)	(500)	(500)
Other Federal Tax Credits	0	0	0
State Income Taxes, Net of Federal Impact	5,000	4,900	5,000
Tax Asset Valuation Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit (1)	(200)	0	0
Other, Net	(200)	200	(300)
Income Tax Expense	$ 38,022	$ 36,970	$ 37,268
Effective Income Tax Rate Reconciliation, Percent	39.60%	39.60%	39.20%

INCOME TAXES - Temporary Differ

INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred Tax Assets:
Employee Benefits	$ 640.6	$ 637.5
Derivative Liabilities	192.6	172.7
Regulatory Deferrals - Liabilities	290.9	243.5
Allowance for Uncollectible Accounts	76.6	60.5
Tax Effect - Tax Regulatory Liabilities	11.8	9.7
Federal Net Operating Loss Carryforwards	0	5.4
Purchase Accounting Adjustment	112.2	119.3
Other	170.5	197.1
Total Deferred Tax Assets	1,495.2	1,445.7
Less: Valuation Allowance	5.1	3.7
Net Deferred Tax Assets	1,490.1	1,442
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	5,001.2	4,602.6
Property Tax Accruals	81.9	76.7
Regulatory Amounts:
Regulatory Deferrals - Assets	1,321.8	1,289.1
Tax Effect - Tax Regulatory Assets	252.6	249.3
Goodwill Regulatory Asset - 1999 Merger	186.7	194.9
Derivative Assets	29.5	17.7
Other	223.6	159.4
Total Deferred Tax Liabilities	7,097.3	6,589.7
The Connecticut Light And Power Company [Member]
Deferred Tax Assets:
Employee Benefits	138.8	126.1
Derivative Liabilities	191.5	165.7
Regulatory Deferrals - Liabilities	6.3	36
Allowance for Uncollectible Accounts	33	30.4
Tax Effect - Tax Regulatory Liabilities	4.9	3.1
Federal Net Operating Loss Carryforwards	0	0
Other	59.4	55.5
Total Deferred Tax Assets	433.9	416.8
Less: Valuation Allowance	4.5	3.1
Net Deferred Tax Assets	429.4	413.7
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	1,700.3	1,545.6
Property Tax Accruals	29.7	27.3
Regulatory Amounts:
Regulatory Deferrals - Assets	473.4	456.8
Tax Effect - Tax Regulatory Assets	170.4	168.7
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	27	17.7
Other	16.3	18.5
Total Deferred Tax Liabilities	2,417.1	2,234.6
NSTAR Electric Company [Member]
Deferred Tax Assets:
Employee Benefits	58.4	91.3
Derivative Liabilities	1.1	0.6
Regulatory Deferrals - Liabilities	186.4	109.4
Allowance for Uncollectible Accounts	20	8.5
Tax Effect - Tax Regulatory Liabilities	1.1	1.5
Federal Net Operating Loss Carryforwards	0	0
Other	2.2	3.4
Total Deferred Tax Assets	269.2	214.7
Less: Valuation Allowance	0	0
Net Deferred Tax Assets	269.2	214.7
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	1,463.5	1,387.1
Property Tax Accruals	25.6	22.8
Regulatory Amounts:
Regulatory Deferrals - Assets	322.3	339.7
Tax Effect - Tax Regulatory Assets	36.1	36
Goodwill Regulatory Asset - 1999 Merger	160.3	167.4
Derivative Assets	0	0
Other	97.7	22
Total Deferred Tax Liabilities	2,105.5	1,975
Public Service Company Of New Hampshire [Member]
Deferred Tax Assets:
Employee Benefits	46.5	37.1
Derivative Liabilities	0	0
Regulatory Deferrals - Liabilities	36.7	42.1
Allowance for Uncollectible Accounts	4.1	3.6
Tax Effect - Tax Regulatory Liabilities	2.6	2.3
Federal Net Operating Loss Carryforwards	0	2.4
Other	56.4	61.1
Total Deferred Tax Assets	146.3	148.6
Less: Valuation Allowance	0	0
Net Deferred Tax Assets	146.3	148.6
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	726.3	655.3
Property Tax Accruals	8	7.3
Regulatory Amounts:
Regulatory Deferrals - Assets	142.1	137.9
Tax Effect - Tax Regulatory Assets	12.2	15.4
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	0	0
Other	43.1	38.6
Total Deferred Tax Liabilities	931.7	854.5
Western Massachusetts Electric Company [Member]
Deferred Tax Assets:
Employee Benefits	11.1	10
Derivative Liabilities	0	0
Regulatory Deferrals - Liabilities	8.5	6.1
Allowance for Uncollectible Accounts	5.7	4.5
Tax Effect - Tax Regulatory Liabilities	2.2	2.4
Federal Net Operating Loss Carryforwards	0	0.4
Other	4.4	5
Total Deferred Tax Assets	31.9	28.4
Less: Valuation Allowance	0	0
Net Deferred Tax Assets	31.9	28.4
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	438.4	416.1
Property Tax Accruals	11.2	10.6
Regulatory Amounts:
Regulatory Deferrals - Assets	59.4	60.5
Tax Effect - Tax Regulatory Assets	8.7	9
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	0	0
Other	5	2.7
Total Deferred Tax Liabilities	$ 522.7	$ 498.9

INCOME TAXES - Tax Credits and

INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Federal Net Operating Loss		$ 15.5
Federal and State Tax Credit	$ 8.6	26.1
Federal and State Charitable Contribution	27.8	14.9
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	111.1	101.2
Federal and State Charitable Contribution	36.5	3
The Connecticut Light And Power Company [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Federal Net Operating Loss		0
Federal and State Tax Credit	0	0.1
Federal and State Charitable Contribution	0	0
The Connecticut Light And Power Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	80.5	73.8
Federal and State Charitable Contribution	0	0
NSTAR Electric Company [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Federal Net Operating Loss		0
Federal and State Tax Credit	0	0.2
Federal and State Charitable Contribution	0	0
NSTAR Electric Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Public Service Company Of New Hampshire [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Federal Net Operating Loss		7
Federal and State Tax Credit	0	15
Federal and State Charitable Contribution	0	0
Public Service Company Of New Hampshire [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Western Massachusetts Electric Company [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards [Line Items]
Federal Net Operating Loss		1
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Western Massachusetts Electric Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Proceeds from depreciation deduction due to income tax refunds	$ 275,000,000
Decrease in expected tax payments	300,000,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance for tax credit and operating loss carryforward	4,500,000	$ 3,100,000
Minimum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in unrecognized tax benefits	0
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Decrease in unrecognized tax benefits	1,600,000
Eversource [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	1,300,000	(1,300,000)
The Connecticut Light And Power Company [Member]
Operating Loss Carryforwards [Line Items]
Proceeds from depreciation deduction due to income tax refunds	105,000,000
The Connecticut Light And Power Company [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	1,300,000	$ (900,000)
NSTAR Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Proceeds from depreciation deduction due to income tax refunds	72,000,000
Public Service Company Of New Hampshire [Member]
Operating Loss Carryforwards [Line Items]
Proceeds from depreciation deduction due to income tax refunds	46,000,000
Western Massachusetts Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Proceeds from depreciation deduction due to income tax refunds	$ 25,000,000
Tax Year 2016 and 2017 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Increase in state corporate tax rate (in percentage)	9.00%
Tax Year 2018 [Member] | State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Increase in state corporate tax rate (in percentage)	8.25%

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	$ 48	$ 46.2	$ 38.2
Gross Increases - Current Year	9.9	9.9	9.3
Gross Increases - Prior Year	0.2	0.1	0.3
Lapse of Statute of Limitations	(9.7)	(8.2)	(1.6)
Ending Balance	48.4	48	46.2
The Connecticut Light And Power Company [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	13.5	14.3	11.4
Gross Increases - Current Year	3.9	2.6	2.7
Gross Increases - Prior Year	0.2	0	0.2
Lapse of Statute of Limitations	(2.3)	(3.4)	0
Ending Balance	$ 15.3	$ 13.5	$ 14.3

INCOME TAXES - Interest Expense

INCOME TAXES - Interest Expense and Accrued Interest Payable on Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Other Interest Expense/(Income)	$ (0.2)	$ 0.1	$ 0.4
Accrued Interest Expense	$ 1.8	$ 2

INCOME TAXES - Open Tax Year (D

INCOME TAXES - Open Tax Year (Details)	12 Months Ended
	Dec. 31, 2016
Federal [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,016
Maximum [Member] | Connecticut [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,016
Maximum [Member] | Massachusetts [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,016
Maximum [Member] | New Hampshire [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,016
Minimum [Member] | Connecticut [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,013
Minimum [Member] | Massachusetts [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,013
Minimum [Member] | New Hampshire [Member]
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,014

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	$ 51.1	$ 43.3
Additions	20.6	13.5
Payments/Reductions	(5.9)	(5.7)
Accrual for Environmental Loss Contingencies, Ending Balance	65.8	51.1
The Connecticut Light And Power Company [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	4.6	3.8
Additions	0.6	1.3
Payments/Reductions	(0.3)	(0.5)
Accrual for Environmental Loss Contingencies, Ending Balance	4.9	4.6
NSTAR Electric Company [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	2.4	1.1
Additions	1.7	2
Payments/Reductions	(0.9)	(0.7)
Accrual for Environmental Loss Contingencies, Ending Balance	3.2	2.4
Public Service Company Of New Hampshire [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	4.5	5.2
Additions	1.2	2.3
Payments/Reductions	(0.4)	(3)
Accrual for Environmental Loss Contingencies, Ending Balance	5.3	4.5
Western Massachusetts Electric Company [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	0.6	0.5
Additions	0.1	0.2
Payments/Reductions	(0.1)	(0.1)
Accrual for Environmental Loss Contingencies, Ending Balance	$ 0.6	$ 0.6

COMMITMENTS AND CONTINGENCIE123

COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)site	Dec. 31, 2015USD ($)site	Dec. 31, 2014USD ($)
Loss Contingencies [Line Items]
Number of Sites | site	61	64
Reserve | $	$ 65.8	$ 51.1	$ 43.3
The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Number of Sites | site	14	14
Reserve | $	$ 4.9	$ 4.6	3.8
NSTAR Electric Company [Member]
Loss Contingencies [Line Items]
Number of Sites | site	13	15
Reserve | $	$ 3.2	$ 2.4	1.1
Public Service Company Of New Hampshire [Member]
Loss Contingencies [Line Items]
Number of Sites | site	11	12
Reserve | $	$ 5.3	$ 4.5	5.2
Western Massachusetts Electric Company [Member]
Loss Contingencies [Line Items]
Number of Sites | site	4	4
Reserve | $	$ 0.6	$ 0.6	$ 0.5

COMMITMENTS AND CONTINGENCIE124

COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)site	Dec. 31, 2015USD ($)site	Dec. 31, 2014USD ($)
Loss Contingencies [Line Items]
Environmental site quantity | site	61	64
Reserve	$ 65.8	$ 51.1	$ 43.3
Number of environmental sites designated as superfund sites | site	9
The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	14	14
Reserve	$ 4.9	$ 4.6	3.8
Western Massachusetts Electric Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	4	4
Reserve	$ 0.6	$ 0.6	0.5
NSTAR Electric Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	13	15
Reserve	$ 3.2	$ 2.4	1.1
Number of environmental sites designated as superfund sites | site	4
Public Service Company Of New Hampshire [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	11	12
Reserve	$ 5.3	$ 4.5	$ 5.2
Number of environmental sites designated as superfund sites | site	3
MGP Site accrual [Member]
Loss Contingencies [Line Items]
Reserve balances related to former MGP sites	$ 59	$ 45.5
Environmental Sites for Which a Range of Loss Exists [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	8
Reserve	$ 35.6
Best estimate of potential remediation costs	$ 16
Environmental Sites for Which a Range of Loss Exists [Member] | The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	3
Reserve	$ 1.7
Best estimate of potential remediation costs	$ 1
Environmental Sites for Which a Range of Loss Exists [Member] | Western Massachusetts Electric Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	1
Reserve	$ 0.3
Environmental Site for Which a Range is Too Early to Determine [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	10
Reserve	$ 13.4
Environmental Site for Which a Range is Too Early to Determine [Member] | The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Environmental site quantity | site	3
Reserve	$ 2.1
Evironmental Sites with Best Estimate [Member]
Loss Contingencies [Line Items]
Reserve	$ 16.8
Environmental site quantity remaining | site	43
Evironmental Sites with Best Estimate [Member] | The Connecticut Light And Power Company [Member]
Loss Contingencies [Line Items]
Reserve	$ 1.1
Environmental site quantity remaining | site	8
Evironmental Sites with Best Estimate [Member] | Western Massachusetts Electric Company [Member]
Loss Contingencies [Line Items]
Reserve	$ 0.3
Environmental site quantity remaining | site	3
Evironmental Sites with Best Estimate [Member] | NSTAR Electric Company [Member]
Loss Contingencies [Line Items]
Reserve	$ 3.2
Environmental site quantity remaining | site	13
Evironmental Sites with Best Estimate [Member] | Public Service Company Of New Hampshire [Member]
Loss Contingencies [Line Items]
Reserve	$ 5.3
Environmental site quantity remaining | site	11
Superfund sites [Member]
Loss Contingencies [Line Items]
Best estimate of potential remediation costs	$ 0.7

COMMITMENTS AND CONTINGENCIE125

COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2016USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	$ 667.8
2,018	557.1
2,019	498.4
2,020	483.2
2,021	433.9
Thereafter	2,331.8
Total	4,972.2
Supply and Stranded Cost [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	115.8
2,018	81.6
2,019	69.4
2,020	74.2
2,021	58.4
Thereafter	189.8
Total	589.2
Renewable Energy [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	275.4
2,018	242.6
2,019	240.9
2,020	238.8
2,021	218.9
Thereafter	1,864.1
Total	3,080.7
Peaker CfDs [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	42.3
2,018	21.5
2,019	21.7
2,020	31.1
2,021	27.6
Thereafter	54.2
Total	198.4
Natural Gas Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	197
2,018	185.5
2,019	142.3
2,020	115
2,021	104.9
Thereafter	190.2
Total	934.9
Coal, Wood and Other [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	15.5
2,018	3.9
2,019	1.9
2,020	1.9
2,021	1.9
Thereafter	11.3
Total	36.4
Transmission Support Commitments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,017	21.8
2,018	22
2,019	22.2
2,020	22.2
2,021	22.2
Thereafter	22.2
Total	132.6
The Connecticut Light And Power Company [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	222.2
2,018	169.3
2,019	167.4
2,020	189
2,021	170
Thereafter	909.7
Total	1,827.6
The Connecticut Light And Power Company [Member] | Supply and Stranded Cost [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	93.4
2,018	58.7
2,019	56.6
2,020	68.8
2,021	53
Thereafter	162.3
Total	492.8
The Connecticut Light And Power Company [Member] | Renewable Energy [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	77.9
2,018	80.4
2,019	80.3
2,020	80.3
2,021	80.6
Thereafter	684.4
Total	1,083.9
The Connecticut Light And Power Company [Member] | Peaker CfDs [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	42.3
2,018	21.5
2,019	21.7
2,020	31.1
2,021	27.6
Thereafter	54.2
Total	198.4
The Connecticut Light And Power Company [Member] | Transmission Support Commitments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,017	8.6
2,018	8.7
2,019	8.8
2,020	8.8
2,021	8.8
Thereafter	8.8
Total	52.5
NSTAR Electric Company [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	128.4
2,018	92.7
2,019	90.9
2,020	86.6
2,021	82.1
Thereafter	448.6
Total	929.3
NSTAR Electric Company [Member] | Supply and Stranded Cost [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	4.8
2,018	5.5
2,019	5.5
2,020	3.1
2,021	3.1
Thereafter	25
Total	47
NSTAR Electric Company [Member] | Renewable Energy [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	116.8
2,018	80.4
2,019	78.5
2,020	76.6
2,021	72.1
Thereafter	416.7
Total	841.1
NSTAR Electric Company [Member] | Transmission Support Commitments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,017	6.8
2,018	6.8
2,019	6.9
2,020	6.9
2,021	6.9
Thereafter	6.9
Total	41.2
Public Service Company Of New Hampshire [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	102.9
2,018	92.1
2,019	80.2
2,020	74.8
2,021	59
Thereafter	620.4
Total	1,029.4
Public Service Company Of New Hampshire [Member] | Supply and Stranded Cost [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	17.6
2,018	17.4
2,019	7.3
2,020	2.3
2,021	2.3
Thereafter	2.5
Total	49.4
Public Service Company Of New Hampshire [Member] | Renewable Energy [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	65.2
2,018	66.1
2,019	66.3
2,020	65.9
2,021	50.1
Thereafter	601.9
Total	915.5
Public Service Company Of New Hampshire [Member] | Coal, Wood and Other [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	15.5
2,018	3.9
2,019	1.9
2,020	1.9
2,021	1.9
Thereafter	11.3
Total	36.4
Public Service Company Of New Hampshire [Member] | Transmission Support Commitments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,017	4.6
2,018	4.7
2,019	4.7
2,020	4.7
2,021	4.7
Thereafter	4.7
Total	28.1
Western Massachusetts Electric Company [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	17.3
2,018	17.5
2,019	17.6
2,020	17.8
2,021	17.9
Thereafter	162.9
Total	251
Western Massachusetts Electric Company [Member] | Renewable Energy [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,017	15.5
2,018	15.7
2,019	15.8
2,020	16
2,021	16.1
Thereafter	161.1
Total	240.2
Western Massachusetts Electric Company [Member] | Transmission Support Commitments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,017	1.8
2,018	1.8
2,019	1.8
2,020	1.8
2,021	1.8
Thereafter	1.8
Total	$ 10.8

COMMITMENTS AND CONTINGENCIE126

COMMITMENTS AND CONTINGENCIES - Long-Term Contractual Arrangement Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)contractprojectMW	Dec. 31, 2008contractMW
Long-term Purchase Commitment [Line Items]
Number of capacity contracts for differences between CL&P and United Illuminated Company | contract	4
Amount of capacity contracts for differences between CL&P and United Illuminated Company (in MW) | MW	787
Number of generation projects between CL&P and United Illuminated Company | project	3
Number of demand response projects between CL&P and United Illuminated Company | project	1
Percentage of costs and benefits borne by United Illuminated Company	20.00%
Peaker Contracts For Differences [Member]
Long-term Purchase Commitment [Line Items]
Percentage of costs and benefits borne by United Illuminated Company		20.00%
Period of payment to generation facility owner		30 years
The Connecticut Light And Power Company [Member] | Peaker Contracts For Differences [Member]
Long-term Purchase Commitment [Line Items]
Number of capacity contracts | contract		3
Amount of capacity contracts | MW		500
Percentage of costs and benefits borne		80.00%
Public Service Company Of New Hampshire [Member] | Coal, Wood and Other Contracts [Member]
Long-term Purchase Commitment [Line Items]
Costs unrecoverable from customers | $	$ 2
CL&P, NSTAR Electric, PSNH and WMECO [Member] | Transmission Support Commitments [Member]
Long-term Purchase Commitment [Line Items]
Period of payment of annual operation and maintenance expense	30 years

COMMITMENTS AND CONTINGENCIE127

COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Supply and Stranded Cost	$ 152.5	$ 147.6	$ 99.2
Renewable Energy	210.9	144.3	114.4
Peaker CfDs	47.7	42.7	18.1
Natural Gas Procurement	323.9	428.6	482.5
Coal, Wood and Other	55.7	95.9	120.5
Transmission Support Commitments	15.9	25.3	25
The Connecticut Light And Power Company [Member]
Long-term Purchase Commitment [Line Items]
Supply and Stranded Cost	132.7	120.3	63
Renewable Energy	42.1	20	0.7
Peaker CfDs	47.7	42.7	18.1
Coal, Wood and Other	0	0	0
Transmission Support Commitments	6.3	10	9.9
NSTAR Electric Company [Member]
Long-term Purchase Commitment [Line Items]
Supply and Stranded Cost	0.7	6.5	7
Renewable Energy	93.6	86.7	87.4
Peaker CfDs	0	0	0
Coal, Wood and Other	0	0	0
Transmission Support Commitments	4.9	7.8	7.7
Public Service Company Of New Hampshire [Member]
Long-term Purchase Commitment [Line Items]
Supply and Stranded Cost	19.1	20.8	26
Renewable Energy	67.7	37.2	26.3
Peaker CfDs	0	0	0
Coal, Wood and Other	55.7	95.9	120.5
Transmission Support Commitments	3.4	5.4	5.3
Western Massachusetts Electric Company [Member]
Long-term Purchase Commitment [Line Items]
Supply and Stranded Cost	0	0	3.2
Renewable Energy	7.5	0.4	0
Peaker CfDs	0	0	0
Coal, Wood and Other	0	0	0
Transmission Support Commitments	$ 1.3	$ 2.1	$ 2.1

COMMITMENTS AND CONTINGENCIE128

COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details) - USD ($) $ in Millions	Mar. 25, 2016	Dec. 31, 2016
CYAPC [Member]
Guarantor Obligations [Line Items]
Net of damages awarded	$ 32.6
YAEC [Member]
Guarantor Obligations [Line Items]
Net of damages awarded	19.6
MYAPC [Member]
Guarantor Obligations [Line Items]
Net of damages awarded	24.6	$ 14.4
Proceeds distributed from spent nuclear fuel trust		56.5
Yankee Companies [Member]
Guarantor Obligations [Line Items]
Net of damages awarded	76.8
Damages sought	$ 77.9
Eversource [Member] | Yankee Companies [Member]
Guarantor Obligations [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company		26.1
The Connecticut Light And Power Company [Member] | Yankee Companies [Member]
Guarantor Obligations [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company		13.6
NSTAR Electric Company [Member] | Yankee Companies [Member]
Guarantor Obligations [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company		5
Public Service Company Of New Hampshire [Member] | Yankee Companies [Member]
Guarantor Obligations [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company		3.9
Western Massachusetts Electric Company [Member] | Yankee Companies [Member]
Guarantor Obligations [Line Items]
Proceeds received from Yankee Companies to Eversource Utility Company		$ 3.6

COMMITMENTS AND CONTINGENCIE129

COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details) $ in Millions	Dec. 31, 2016USD ($)
Access Northeast [Member]
Loss Contingencies [Line Items]
Maximum exposure	$ 206
Guarantee Of Financial Obligations Of Npt [Member]
Loss Contingencies [Line Items]
Maximum exposure	25
Guarantee Of Npt Letters Of Credit [Member]
Loss Contingencies [Line Items]
Maximum exposure	$ 14

COMMITMENTS AND CONTINGENCIE130

COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details) $ in Millions	Dec. 31, 2016USD ($)
Access Northeast Project Capital Contributions Guarantee Expiring In 2021 [Member]
Guarantor Obligations [Line Items]
Maximum Exposure	$ 185.4
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2017 And 2018 [Member]
Guarantor Obligations [Line Items]
Maximum Exposure	38.2
Guarantee Of Rocky River Reality And Nusco Lease Payments For Real Estate And Vehicles Expiring 2019 Through 2024 [Member]
Guarantor Obligations [Line Items]
Maximum Exposure	$ 9.2

COMMITMENTS AND CONTINGENCIE131

COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints Narrative (Details) - USD ($) $ in Millions	Apr. 29, 2016	Mar. 22, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2017	Oct. 31, 2015	Mar. 27, 2014	Dec. 31, 2016
FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants			11.14%
Period of complaint			15 months
Loss contingency, loss in period				$ 20	$ 37
FERC ROE First Complaint [Member]
Loss Contingencies [Line Items]
Base ROE percentage of first complaint period									10.57%
FERC ROE First Complaint [Domain]
Loss Contingencies [Line Items]
Maximum percentage cap of ROE for incentive projects									11.74%
FERC ROE Second and Third Complaints [Member]
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants			11.14%
FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
Period of complaint			15 months					15 months
FERC ALJ recommended base ROE percentage		9.59%
Basis point change			0.10%
Loss contingency, estimate of possible earnings impact			$ 3						$ 3
FERC ROE Third Complaint [Member]
Loss Contingencies [Line Items]
Period of complaint			15 months				15 months
FERC ALJ recommended base ROE percentage		10.90%
Loss contingency, estimate of possible earnings impact			$ 3						3
FERC ROE Fourth Complaint [Member]
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants	10.57%
Maximum percentage cap of ROE for incentive projects	11.74%
The Connecticut Light And Power Company [Member] | FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Loss contingency, loss in period				12.5	20.7
NSTAR Electric Company [Member] | FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Loss contingency, loss in period				2.4	7.9
Public Service Company Of New Hampshire [Member] | FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Loss contingency, loss in period				1	2.8
Western Massachusetts Electric Company [Member] | FERC ROE Complaints [Member]
Loss Contingencies [Line Items]
Loss contingency, loss in period				$ 4.1	$ 5.6
Minimum [Member] | FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
FERC ALJ recommended zone of reasonableness FERC ROE percentage		7.12%
Potential loss from base ROE percentage			10.57%					10.57%
Minimum [Member] | FERC ROE Third Complaint [Member]
Loss Contingencies [Line Items]
FERC ALJ recommended zone of reasonableness FERC ROE percentage		7.04%
Maximum [Member] | FERC ROE Second Complaint [Member]
Loss Contingencies [Line Items]
FERC ALJ recommended zone of reasonableness FERC ROE percentage		10.42%
Potential loss from base ROE percentage								9.59%
Loss contingency, estimate of possible earnings impact			$ 34						34
Maximum [Member] | FERC ROE Third Complaint [Member]
Loss Contingencies [Line Items]
FERC ALJ recommended zone of reasonableness FERC ROE percentage		12.19%
Loss contingency, estimate of possible earnings impact			$ (8)						$ (8)
Subsequent Event [Member] | FERC ROE Fourth Complaint [Member]
Loss Contingencies [Line Items]
Period of complaint						15 months

PSNH GENERATION ASSET SALE - Na

PSNH GENERATION ASSET SALE - Narrative (Details) $ in Thousands	Jun. 10, 2015USD ($)senator	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2014USD ($)
Regulatory Assets [Line Items]
Equity return related to clean air project forgone	$ 25,000
Other current liabilities associated with PSNH's generation assets		$ 678,549	$ 684,914
Asset retirement obligation associated with PSNH's generation assets		430,100	426,400	$ 426,300
Accrued pension, SERP and PBOP associated with PSNH's generation assets		1,407,288	1,141,514
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Other current liabilities associated with PSNH's generation assets		43,921	43,253
Asset retirement obligation associated with PSNH's generation assets		21,600	23,500	$ 20,600
Accrued pension, SERP and PBOP associated with PSNH's generation assets		89,579	94,652
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Number of state senators | senator	2
Payments for restructuring	$ 5,000	$ 5,000
Accounts payable associated with PSNH's generation assets			40,500
Other current liabilities associated with PSNH's generation assets			16,100
Asset retirement obligation associated with PSNH's generation assets			20,000
Accrued pension, SERP and PBOP associated with PSNH's generation assets			$ 24,300

PSNH GENERATION ASSET SALE - PS

PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Gross Plant	$ 27,060,500	$ 25,226,600
Accumulated Depreciation	(6,722,400)	(6,396,700)
Total Property, Plant and Equipment, Net	21,350,510	19,892,441
Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	4,197,300	3,891,100
Accumulated Depreciation	(1,254,700)	(1,171,000)
Total Property, Plant and Equipment, Net	3,039,313	$ 2,855,363
Electricity Generation Plant, Non-Nuclear [Member] | Public Service Company Of New Hampshire [Member]
Regulatory Assets [Line Items]
Gross Plant	1,192,100
Accumulated Depreciation	(556,000)
Total Property, Plant and Equipment, Net	636,100
Fuel	99,900
Materials and Supplies	42,700
Emission Allowances	19,900
Total Generation Assets	$ 798,600

LEASES - Operating Leases Renta

LEASES - Operating Leases Rental Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 12.1	$ 12.1	$ 14.3
The Connecticut Light And Power Company [Member]
Operating Leased Assets [Line Items]
Operating leases, rent expense	12.5	12.5	6
NSTAR Electric Company [Member]
Operating Leased Assets [Line Items]
Operating leases, rent expense	9.3	9.6	7.8
Public Service Company Of New Hampshire [Member]
Operating Leased Assets [Line Items]
Operating leases, rent expense	2.9	2.8	1.5
Western Massachusetts Electric Company [Member]
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 2.1	$ 2.2	$ 1.2

LEASES - Future Minimum Rental

LEASES - Future Minimum Rental Payments, Operating and Capital Leases (Details) $ in Millions	Dec. 31, 2016USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	$ 14.1
2,018	10.6
2,019	8.7
2,020	7
2,021	6
Thereafter	10.4
Future minimum lease payments	56.8
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	2.3
2,018	2.3
2,019	2.2
2,020	2.2
2,021	1.7
Thereafter	1.1
Future minimum lease payments	11.8
Less amount representing interest	2.9
Present value of future minimum lease payments	8.9
The Connecticut Light And Power Company [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	2
2,018	1.3
2,019	1
2,020	0.7
2,021	0.6
Thereafter	1.4
Future minimum lease payments	7
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	1.9
2,018	2
2,019	2
2,020	2
2,021	1.4
Thereafter	0
Future minimum lease payments	9.3
Less amount representing interest	2.5
Present value of future minimum lease payments	6.8
NSTAR Electric Company [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	9
2,018	7
2,019	5.8
2,020	4.8
2,021	4.2
Thereafter	6.7
Future minimum lease payments	37.5
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	0.2
2,018	0.2
2,019	0.2
2,020	0.2
2,021	0.3
Thereafter	1.1
Future minimum lease payments	2.2
Less amount representing interest	0.4
Present value of future minimum lease payments	1.8
Public Service Company Of New Hampshire [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	0.9
2,018	0.6
2,019	0.5
2,020	0.4
2,021	0.3
Thereafter	0.8
Future minimum lease payments	3.5
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	0.2
2,018	0.1
2,019	0
2,020	0
2,021	0
Thereafter	0
Future minimum lease payments	0.3
Less amount representing interest	0
Present value of future minimum lease payments	0.3
Western Massachusetts Electric Company [Member]
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,017	0.5
2,018	0.3
2,019	0.3
2,020	0.2
2,021	0.2
Thereafter	0.4
Future minimum lease payments	$ 1.9

FAIR VALUE OF FINANCIAL INST136

FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	$ 155,568	$ 155,568
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	155,600	155,600
Long-Term Debt	9,603,200	9,034,500
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	158,300	157,900
Long-Term Debt	9,980,500	9,425,900
The Connecticut Light And Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
The Connecticut Light And Power Company [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Long-Term Debt	2,766,000	2,763,700
The Connecticut Light And Power Company [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	114,700	114,900
Long-Term Debt	3,049,600	3,031,600
NSTAR Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	43,000	43,000
NSTAR Electric Company [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	43,000	43,000
Long-Term Debt	2,078,100	2,029,800
NSTAR Electric Company [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	43,600	43,000
Long-Term Debt	2,201,600	2,182,400
Public Service Company Of New Hampshire [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	0	0
Long-Term Debt	1,072,000	1,071,000
Public Service Company Of New Hampshire [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	0	0
Long-Term Debt	1,109,700	1,121,200
Western Massachusetts Electric Company [Member] | Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	0	0
Long-Term Debt	566,500	517,300
Western Massachusetts Electric Company [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	0	0
Long-Term Debt	$ 589,000	$ 551,800

ACCUMULATED OTHER COMPREHENS137

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 10,352,215	$ 9,976,815
OCI Before Reclassifications		900
Amounts Reclassified from AOCL		6,300
Net OCI		7,200
Ending balance	10,711,734	10,352,215
AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(66,844)	(74,009)
OCI Before Reclassifications	(4,500)
Amounts Reclassified from AOCL	6,000
Net OCI	1,500
Ending balance	(65,282)	(66,844)
Qualified Cash Flow Hedging Instruments [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(10,300)	(12,400)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCL	2,100	2,100
Net OCI	2,100	2,100
Ending balance	(8,200)	(10,300)
Unrealized Gains/(Losses) on Marketable Securities [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,900)	700
OCI Before Reclassifications	2,300	(2,600)
Amounts Reclassified from AOCL	0	0
Net OCI	2,300	(2,600)
Ending balance	400	(1,900)
Defined Benefit Plans [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(54,600)	(62,300)
OCI Before Reclassifications	(6,800)	3,500
Amounts Reclassified from AOCL	3,900	4,200
Net OCI	(2,900)	7,700
Ending balance	$ (57,500)	$ (54,600)

ACCUMULATED OTHER COMPREHENS138

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Related tax effect recognized in AOCI	$ (2)	$ 4	$ 22.3
Pre-tax amount reclassified from AOCI as a decrease to net income		3.4
Pre-tax amount reclassified from AOCI as a decrease to net income as a result of amortization of Pension, SERP and PBOP costs		6.6
The Connecticut Light And Power Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income		0.6
Public Service Company Of New Hampshire [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income		2
Western Massachusetts Electric Company [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income		$ 0.7

ACCUMULATED OTHER COMPREHENS139

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pension SERP And PBOP Gain Loss To Be Reclassified Within Twelve Months									$ (6,600)
Tax Effect									(554,997)	$ (539,967)	$ (468,297)
Net Income Attributable to Common Shareholders	$ 229,200	$ 265,300	$ 203,600	$ 244,200	$ 181,800	$ 235,900	$ 207,500	$ 253,300	942,302	878,485	819,546
Defined Benefit Plan Costs:
Total Amounts Reclassified from AOCL, Net of Tax									(6,000)	(6,300)	(5,900)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									1,400	1,400	1,400
Qualified Cash Flow Hedging Instruments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income Attributable to Common Shareholders									(2,100)	(2,100)	(2,000)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									(5,600)	6,600	6,200
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									(800)	(200)	(200)
Defined Benefit Plans [Member]
Defined Benefit Plan Costs:
Amortization of Actuarial Losses									(6,400)	(6,800)	(6,400)
Tax Effect									2,500	2,600	2,500
Total Amounts Reclassified from AOCL, Net of Tax									(3,900)	(4,200)	(3,900)
Interest Rate Contract [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Qualified Cash Flow Hedging Instruments									$ (3,500)	$ (3,500)	$ (3,400)

DIVIDEND RESTRICTIONS - Narrati

DIVIDEND RESTRICTIONS - Narrative (Details) $ in Millions	Dec. 31, 2016USD ($)
Schedule of Restrictions on Retained Earnings [Line Items]
Consolidated total debt to total capital ratio (as a percentage)	0.65
Retained earnings subject to restrictions	$ 3,200
The Connecticut Light And Power Company [Member]
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	1,300
NSTAR Electric Company [Member]
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	1,600
Public Service Company Of New Hampshire [Member]
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	549.3
Retained earnings subject to FERC hydroelectric license conditions	13.8
Western Massachusetts Electric Company [Member]
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	$ 218.2

COMMON SHARES - Schedule of Com

COMMON SHARES - Schedule of Common Shares Authorized and Issued (Details) - $ / shares	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Per Share Par Value (in dollars per share)	$ 5	$ 5	$ 5
Authorized (in shares)	380,000,000	380,000,000
Issued (in shares)	333,878,402	333,862,615
The Connecticut Light And Power Company [Member]
Class of Stock [Line Items]
Per Share Par Value (in dollars per share)	$ 10	$ 10
Authorized (in shares)	24,500,000	24,500,000
Issued (in shares)	6,035,205	6,035,205
NSTAR Electric Company [Member]
Class of Stock [Line Items]
Per Share Par Value (in dollars per share)	$ 1	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	100	100
Public Service Company Of New Hampshire [Member]
Class of Stock [Line Items]
Per Share Par Value (in dollars per share)	$ 1	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	301	301
Western Massachusetts Electric Company [Member]
Class of Stock [Line Items]
Per Share Par Value (in dollars per share)	$ 25	$ 25
Authorized (in shares)	1,072,471	1,072,471
Issued (in shares)	434,653	434,653

PREFERRED STOCK NOT SUBJECT 142

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Narrative (Details)	Dec. 31, 2016$ / sharesshares
The Connecticut Light And Power Company [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares	9,000,000
Preferred stock par value per share (in dollars per share) | $ / shares	$ 50
NSTAR Electric Company [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares	2,890,000
Preferred stock par value per share (in dollars per share) | $ / shares	$ 100

COMMON SHARES - Narrative (Deta

COMMON SHARES - Narrative (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Common shares held as treasury shares (in shares)	16,992,594	16,671,366
Common shares repurchased (in shares)	321,228	532,521
Weighted average treasury stock (in dollars per share)	$ 24.26	$ 26.02
Treasury Stock [Member] | Eversource [Member]
Class of Stock [Line Items]
Share price of common shares repurchased (in dollars per share)	$ 52.56	$ 47.94

PREFERRED STOCK NOT SUBJECT 144

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Schedule of Preferred Stock by Class (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred stock value outstanding	$ 155.6	$ 155.6
The Connecticut Light And Power Company [Member]
Class of Stock [Line Items]
Shares outstanding (in shares)	2,324,000
Preferred stock value outstanding	$ 116.2	$ 116.2
The Connecticut Light And Power Company [Member] | Series of 1947 Preferred Stock at $1.90 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 1.90	$ 1.90
Redemption Price Per Share (in dollars per share)		$ 52.50
Shares outstanding (in shares)	163,912
Preferred stock value outstanding	$ 8.2	$ 8.2
The Connecticut Light And Power Company [Member] | Series of 1947 Preferred Stock at $2.00 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2	$ 2
Redemption Price Per Share (in dollars per share)		$ 54
Shares outstanding (in shares)	336,088
Preferred stock value outstanding	$ 16.8	$ 16.8
The Connecticut Light And Power Company [Member] | Series of 1949 Preferred Stock at $2.04 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.04	$ 2.04
Redemption Price Per Share (in dollars per share)		$ 52
Shares outstanding (in shares)	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company [Member] | Series of 1949 Preferred Stock at $2.20 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.20	$ 2.20
Redemption Price Per Share (in dollars per share)		$ 52.50
Shares outstanding (in shares)	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company [Member] | Series of 1949 Preferred Stock at 3.90% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	3.90%	3.90%
Redemption Price Per Share (in dollars per share)		$ 50.50
Shares outstanding (in shares)	160,000
Preferred stock value outstanding	$ 8	$ 8
The Connecticut Light And Power Company [Member] | Series E of 1954 Preferred Stock at $2.06 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.06	$ 2.06
Redemption Price Per Share (in dollars per share)		$ 51
Shares outstanding (in shares)	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company [Member] | Series F of 1955 Preferred Stock at $2.09 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.09	$ 2.09
Redemption Price Per Share (in dollars per share)		$ 51
Shares outstanding (in shares)	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company [Member] | Series of 1956 Preferred Stock at 4.5% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.50%	4.50%
Redemption Price Per Share (in dollars per share)		$ 50.75
Shares outstanding (in shares)	104,000
Preferred stock value outstanding	$ 5.2	$ 5.2
The Connecticut Light And Power Company [Member] | Series of 1958 Preferred Stock at 4.96% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.96%	4.96%
Redemption Price Per Share (in dollars per share)		$ 50.50
Shares outstanding (in shares)	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company [Member] | Series of 1963 Preferred Stock at 4.5% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.50%	4.50%
Redemption Price Per Share (in dollars per share)		$ 50.50
Shares outstanding (in shares)	160,000
Preferred stock value outstanding	$ 8	$ 8
The Connecticut Light And Power Company [Member] | Series of 1967 Preferred Stock at 5.28% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	5.28%	5.28%
Redemption Price Per Share (in dollars per share)		$ 51.43
Shares outstanding (in shares)	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company [Member] | Series G of 1968 Preferred Stock at $3.24 [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 3.24	$ 3.24
Redemption Price Per Share (in dollars per share)		$ 51.84
Shares outstanding (in shares)	300,000
Preferred stock value outstanding	$ 15	$ 15
The Connecticut Light And Power Company [Member] | Series of 1968 Preferred Stock at 6.56% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	6.56%	6.56%
Redemption Price Per Share (in dollars per share)		$ 51.44
Shares outstanding (in shares)	200,000
Preferred stock value outstanding	$ 10	$ 10
NSTAR Electric Company [Member]
Class of Stock [Line Items]
Shares outstanding (in shares)	430,000
Preferred stock value outstanding	$ 43	$ 43
NSTAR Electric Company [Member] | Preferred Stock 4.25% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.25%	4.25%
Redemption Price Per Share (in dollars per share)		$ 103.625
Shares outstanding (in shares)	180,000
Preferred stock value outstanding	$ 18	$ 18
NSTAR Electric Company [Member] | Preferred Stock 4.78% [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.78%	4.78%
Redemption Price Per Share (in dollars per share)		$ 102.80
Shares outstanding (in shares)	250,000
Preferred stock value outstanding	$ 25	$ 25
Fair Value Adjustment [Member] | NSTAR Electric Company [Member]
Class of Stock [Line Items]
Preferred stock value outstanding	$ 3.6	$ 3.6

COMMON SHARESHOLDERS' EQUITY145

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Dividends on preferred stock	$ 7,519	$ 7,519	$ 7,519
Noncontrolling Interest - Preferred Stock of Subsidiaries	155,568	155,568
Preferred stock value outstanding	$ 155,600	$ 155,600

EARNINGS PER SHARE - Narrative

EARNINGS PER SHARE - Narrative (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of dilted EPS (in shares)	0	1,474	3,643

EARNINGS PER SHARE - Components

EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 229,200	$ 265,300	$ 203,600	$ 244,200	$ 181,800	$ 235,900	$ 207,500	$ 253,300	$ 942,302	$ 878,485	$ 819,546
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,650,180	317,336,881	316,136,748
Dilutive Effect (in shares)									804,059	1,095,806	1,280,666
Diluted (in shares)									318,454,239	318,432,687	317,417,414
Basic EPS (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.97	$ 2.77	$ 2.59
Diluted EPS (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.96	$ 2.76	$ 2.58

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details)	12 Months Ended
	Dec. 31, 2016segment
The Connecticut Light And Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
Public Service Company Of New Hampshire [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
Western Massachusetts Electric Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1

SEGMENT INFORMATION - Schedule

SEGMENT INFORMATION - Schedule of Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,776,600	$ 2,039,700	$ 1,767,200	$ 2,055,600	$ 1,691,200	$ 1,933,100	$ 1,817,100	$ 2,513,400	$ 7,639,129	$ 7,954,827	$ 7,741,856
Depreciation and Amortization									(787,100)	(688,200)	(625,400)
Other Operating Expenses									(4,992,100)	(5,502,400)	(5,483,700)
Operating Income	438,100	509,900	423,400	488,500	385,500	469,200	412,000	497,500	1,859,859	1,764,164	1,632,849
Interest Expense									(400,961)	(372,420)	(362,106)
Interest Income									11,000	6,700	6,000
Other Income, Net									34,900	27,500	18,600
Tax Effect									(554,997)	(539,967)	(468,297)
Net Income	231,100	267,200	205,500	246,000	183,700	237,800	209,400	255,100	949,821	886,004	827,065
Net Income (Loss) Attributable to Noncontrolling Interest									(7,519)	(7,519)	(7,519)
Net Income Attributable to Common Shareholders	229,200	$ 265,300	$ 203,600	$ 244,200	181,800	$ 235,900	$ 207,500	$ 253,300	942,302	878,485	819,546
Total Assets (as of)	32,053,173				30,580,309				32,053,173	30,580,309
Cash Flows Used for Investments in Plant									1,976,867	1,724,139	1,603,744
Operating Segments [Member] | Electric Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues									5,594,300	5,903,600	5,663,400
Depreciation and Amortization									(504,700)	(425,200)	(384,600)
Other Operating Expenses									(4,155,100)	(4,470,200)	(4,366,200)
Operating Income									934,500	1,008,200	912,600
Interest Expense									(193,100)	(186,300)	(191,600)
Interest Income									10,000	5,700	5,100
Other Income, Net									4,800	7,200	10,700
Tax Effect									(288,800)	(322,800)	(269,700)
Net Income									467,400	512,000	467,100
Net Income (Loss) Attributable to Noncontrolling Interest									(4,600)	(4,700)	(4,700)
Net Income Attributable to Common Shareholders									462,800	507,300	462,400
Total Assets (as of)	18,367,500				17,981,300				18,367,500	17,981,300
Cash Flows Used for Investments in Plant									812,600	718,900	645,200
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Operating Revenues									857,700	995,500	1,007,300
Depreciation and Amortization									(65,300)	(70,500)	(68,100)
Other Operating Expenses									(628,900)	(776,700)	(786,700)
Operating Income									163,500	148,300	152,500
Interest Expense									(41,300)	(36,900)	(34,000)
Interest Income									100	100	0
Other Income, Net									600	800	200
Tax Effect									(45,200)	(40,100)	(46,400)
Net Income									77,700	72,200	72,300
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income Attributable to Common Shareholders									77,700	72,200	72,300
Total Assets (as of)	3,303,800				3,104,500				3,303,800	3,104,500
Cash Flows Used for Investments in Plant									255,300	182,200	176,700
Operating Segments [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating Revenues									1,210,000	1,069,100	1,018,200
Depreciation and Amortization									(185,800)	(165,600)	(150,500)
Other Operating Expenses									(321,800)	(314,900)	(302,100)
Operating Income									702,400	588,600	565,600
Interest Expense									(110,000)	(105,800)	(104,100)
Interest Income									1,200	1,600	900
Other Income, Net									18,300	14,500	10,300
Tax Effect									(238,200)	(191,600)	(174,500)
Net Income									373,700	307,300	298,200
Net Income (Loss) Attributable to Noncontrolling Interest									(2,900)	(2,800)	(2,800)
Net Income Attributable to Common Shareholders									370,800	304,500	295,400
Total Assets (as of)	8,751,500				8,019,300				8,751,500	8,019,300
Cash Flows Used for Investments in Plant									801,000	749,100	731,600
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating Revenues									870,400	863,600	790,900
Depreciation and Amortization									(33,500)	(29,000)	(42,100)
Other Operating Expenses									(778,100)	(817,900)	(748,000)
Operating Income									58,800	16,700	800
Interest Expense									(63,500)	(48,000)	(36,600)
Interest Income									7,000	4,400	3,600
Other Income, Net									1,020,100	977,800	916,000
Tax Effect									16,500	14,500	22,300
Net Income									1,038,900	965,400	906,100
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income Attributable to Common Shareholders									1,038,900	965,400	906,100
Total Assets (as of)	14,493,100				13,256,700				14,493,100	13,256,700
Cash Flows Used for Investments in Plant									108,000	73,900	50,200
Eliminations [Member]
Segment Reporting Information [Line Items]
Operating Revenues									(893,300)	(877,000)	(737,900)
Depreciation and Amortization									2,200	2,100	19,900
Other Operating Expenses									891,800	877,300	719,300
Operating Income									700	2,400	1,300
Interest Expense									6,900	4,600	4,200
Interest Income									(7,300)	(5,100)	(3,600)
Other Income, Net									(1,008,900)	(972,800)	(918,600)
Tax Effect									700	0	0
Net Income									(1,007,900)	(970,900)	(916,700)
Net Income (Loss) Attributable to Noncontrolling Interest									0	0	0
Net Income Attributable to Common Shareholders									(1,007,900)	(970,900)	(916,700)
Total Assets (as of)	$ (12,862,700)				$ (11,781,500)				(12,862,700)	(11,781,500)
Cash Flows Used for Investments in Plant									$ 0	$ 0	$ 0

GOODWILL - Narrative (Details)

GOODWILL - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2012	Dec. 31, 2000
Goodwill [Line Items]
Goodwill related to the acquisition of Yankee Gas	$ 3,519,401,000	$ 3,519,401,000	$ 3,519,401,000
Goodwill impairment	$ 0
Changes in goodwill balance		$ 0	$ 0
NSTAR Electric Company [Member]
Goodwill [Line Items]
Goodwill acquired during period				$ 3,200,000,000
Yankee Gas Services Company [Member]
Goodwill [Line Items]
Goodwill related to the acquisition of Yankee Gas					$ 300,000,000

GOODWILL - Schedule of Goodwill

GOODWILL - Schedule of Goodwill by Reportable Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 3,519,401	$ 3,519,401
Electric Distribution [Member]
Goodwill [Line Items]
Goodwill	2,500,000	2,500,000
Electric Transmission [Member]
Goodwill [Line Items]
Goodwill	600,000	600,000
Natural Gas Distribution [Member]
Goodwill [Line Items]
Goodwill	$ 400,000	$ 400,000

QUARTERLY FINANCIAL DATA (UN152

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Revenues	$ 1,776,600	$ 2,039,700	$ 1,767,200	$ 2,055,600	$ 1,691,200	$ 1,933,100	$ 1,817,100	$ 2,513,400	$ 7,639,129	$ 7,954,827	$ 7,741,856
Operating Income	438,100	509,900	423,400	488,500	385,500	469,200	412,000	497,500	1,859,859	1,764,164	1,632,849
Net Income	231,100	267,200	205,500	246,000	183,700	237,800	209,400	255,100	949,821	886,004	827,065
Net Income Attributable to Common Shareholders	$ 229,200	$ 265,300	$ 203,600	$ 244,200	$ 181,800	$ 235,900	$ 207,500	$ 253,300	$ 942,302	$ 878,485	$ 819,546
Basic Earnings Per Common Share (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.97	$ 2.77	$ 2.59
Diluted Earnings Per Common Share (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.96	$ 2.76	$ 2.58
The Connecticut Light And Power Company [Member]
Operating Revenues	$ 630,900	$ 760,000	$ 679,800	$ 735,300	$ 626,900	$ 704,300	$ 666,600	$ 804,900	$ 2,805,955	$ 2,802,675	$ 2,692,582
Operating Income	163,500	176,100	162,100	171,500	154,200	161,100	154,000	141,800	673,175	611,061	555,250
Net Income	77,800	86,600	82,900	87,000	71,200	80,200	78,800	69,200	334,254	299,360	287,754
NSTAR Electric Company [Member]
Operating Revenues	571,900	780,500	591,300	614,200	546,600	750,700	617,200	766,800	2,557,878	2,681,342	2,536,677
Operating Income	104,800	208,700	130,500	109,800	117,700	214,200	151,400	159,500	553,787	642,827	578,456
Net Income	52,800	117,200	68,200	54,500	60,300	118,600	82,000	83,600	292,705	344,542	303,088
Public Service Company Of New Hampshire [Member]
Operating Revenues	231,800	266,900	218,500	242,300	211,100	234,400	241,900	284,800	959,482	972,203	959,500
Operating Income	54,600	74,700	63,100	70,700	49,300	63,600	54,100	63,200	263,060	230,177	229,383
Net Income	26,100	38,500	31,300	36,100	22,000	32,500	27,900	32,000	131,985	114,442	113,944
Western Massachusetts Electric Company [Member]
Operating Revenues	115,700	124,000	116,400	128,100	114,900	125,100	125,200	152,900	484,192	518,128	493,423
Operating Income	26,000	32,100	29,200	33,100	28,000	30,000	28,900	28,600	120,377	115,520	117,639
Net Income	$ 12,000	$ 16,000	$ 13,300	$ 16,800	$ 14,100	$ 15,000	$ 14,200	$ 13,200	$ 58,072	$ 56,506	$ 57,819

SCHEDULE I - FINANCIAL INFOR153

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Assets:
Cash	$ 30,251	$ 23,947	$ 38,703	$ 43,364
Prepayments and Other Current Assets	134,813	129,034
Total Current Assets	2,477,672	2,618,786
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	236,900	48,000
Goodwill	3,519,401	3,519,401
Other Long-Term Assets	522,260	295,243
Total Deferred Debits and Other Assets	8,224,991	8,069,082
Total Assets	32,053,173	30,580,309
Current Liabilities:
Notes Payable	1,148,500	1,160,953
Long-Term Debt – Current Portion	773,883	228,883
Accounts Payable	884,521	813,646
Other Current Liabilities	684,914	678,549
Total Current Liabilities	3,638,605	2,989,790
Total Deferred Credits and Other Liabilities	8,717,912	8,277,162
Capitalization:
Long-Term Debt	8,829,354	8,805,574
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,313
Capital Surplus, Paid In	6,250,224	6,262,368
Retained Earnings	3,175,171	2,797,355
Accumulated Other Comprehensive Loss	(65,282)	(66,844)
Treasury Stock	(317,771)	(309,977)
Common Shareholders' Equity	10,711,734	10,352,215	9,976,815	9,611,528
Total Capitalization	19,696,656	19,313,357
Total Liabilities and Capitalization	32,053,173	30,580,309
Eversource [Member]
Current Assets:
Cash	93	67	$ 138	$ 35
Accounts Receivable from Subsidiaries	32,864	23,689
Notes Receivable from Subsidiaries	740,300	850,300
Prepayments and Other Current Assets	23,122	41,254
Total Current Assets	796,379	915,310
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	9,703,287	8,915,178
Notes Receivable from Subsidiaries	224,290	128,800
Accumulated Deferred Income Taxes	126,091	143,054
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	44,020	48,314
Total Deferred Debits and Other Assets	13,329,499	12,467,157
Total Assets	14,125,878	13,382,467
Current Liabilities:
Notes Payable	1,022,000	1,098,453
Long-Term Debt – Current Portion	28,883	28,883
Accounts Payable	0	78
Accounts Payable to Subsidiaries	8,771	15,601
Other Current Liabilities	47,215	60,999
Total Current Liabilities	1,106,869	1,204,014
Total Deferred Credits and Other Liabilities	148,756	134,908
Capitalization:
Long-Term Debt	2,158,519	1,691,330
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,313
Capital Surplus, Paid In	6,250,224	6,262,368
Retained Earnings	3,175,171	2,797,355
Accumulated Other Comprehensive Loss	(65,282)	(66,844)
Treasury Stock	(317,771)	(309,977)
Common Shareholders' Equity	10,711,734	10,352,215
Total Capitalization	12,870,253	12,043,545
Total Liabilities and Capitalization	$ 14,125,878	$ 13,382,467

SCHEDULE I - FINANCIAL INFOR154

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF INCOME (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 1,776,600	$ 2,039,700	$ 1,767,200	$ 2,055,600	$ 1,691,200	$ 1,933,100	$ 1,817,100	$ 2,513,400	$ 7,639,129	$ 7,954,827	$ 7,741,856
Operating Expenses:
Other									1,323,549	1,329,289	1,427,589
Operating Income	438,100	509,900	423,400	488,500	385,500	469,200	412,000	497,500	1,859,859	1,764,164	1,632,849
Interest Expense									400,961	372,420	362,106
Other Income, Net:
Other Income, Net									45,920	34,227	24,619
Income Before Income Tax Expense									1,504,818	1,425,971	1,295,362
Income Tax Benefit									554,997	539,967	468,297
Net Income	$ 231,100	$ 267,200	$ 205,500	$ 246,000	$ 183,700	$ 237,800	$ 209,400	$ 255,100	$ 949,821	$ 886,004	$ 827,065
Basic Earnings Per Common Share (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.97	$ 2.77	$ 2.59
Diluted Earnings Per Common Share (in dollars per share)	$ 0.72	$ 0.83	$ 0.64	$ 0.77	$ 0.57	$ 0.74	$ 0.65	$ 0.80	$ 2.96	$ 2.76	$ 2.58
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,650,180	317,336,881	316,136,748
Diluted (in shares)									318,454,239	318,432,687	317,417,414
Eversource [Member]
Condensed Income Statements, Captions [Line Items]
Operating Revenues									$ 0	$ 0	$ 0
Operating Expenses:
Other									(39,453)	9,315	29,598
Operating Income									39,453	(9,315)	(29,598)
Interest Expense									59,420	45,130	33,168
Other Income, Net:
Equity in Earnings of Subsidiaries									922,321	900,824	848,435
Other, Net									4,267	6,602	1,830
Other Income, Net									926,588	907,426	850,265
Income Before Income Tax Expense									906,621	852,981	787,499
Income Tax Benefit									(35,681)	(25,504)	(32,047)
Net Income									$ 942,302	$ 878,485	$ 819,546

SCHEDULE I - FINANCIAL INFOR155

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Statement of Income Captions [Line Items]
Net Income	$ 231,100	$ 267,200	$ 205,500	$ 246,000	$ 183,700	$ 237,800	$ 209,400	$ 255,100	$ 949,821	$ 886,004	$ 827,065
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments									2,137	2,079	2,037
Changes in Unrealized Gains/(Losses) on Marketable Securities									2,294	(2,588)	315
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									(2,869)	7,674	(30,330)
Other Comprehensive Income/(Loss), Net of Tax									1,562	7,165	(27,978)
Comprehensive Income									943,864	885,650	791,568
Eversource [Member]
Condensed Statement of Income Captions [Line Items]
Net Income									942,302	878,485	819,546
Other Comprehensive Income/(Loss), Net of Tax:
Other Comprehensive Income/(Loss), Net of Tax									1,562	7,165	(27,978)
Comprehensive Income									$ 943,864	$ 885,650	$ 791,568

SCHEDULE I - FINANCIAL INFOR156

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities:
Net Income	$ 231,100	$ 267,200	$ 205,500	$ 246,000	$ 183,700	$ 237,800	$ 209,400	$ 255,100	$ 949,821	$ 886,004	$ 827,065
Flows Provided by Operating Activities:
Deferred Income Taxes									466,463	491,736	443,259
Other									(77,294)	(82,219)	56,026
Accounts Receivables from Subsidiaries									(142,699)	(39,797)	(122,139)
Taxes Receivable/Accrued, Net									234,543	30,282	(323,224)
Other Current Assets and Liabilities, Net									9,112	44,031	15,797
Net Cash Flows Provided by Operating Activities									2,175,052	1,433,751	1,651,976
Investing Activities:
Other Investing Activities									36,951	6,291	24,159
Net Cash Flows Used in Investing Activities									(2,150,808)	(1,659,150)	(1,591,795)
Financing Activities:
Cash Dividends on Common Shares									(564,486)	(529,791)	(475,227)
Issuance of Long-Term Debt									800,000	1,225,000	725,000
(Decrease)/Increase in Short-Term Debt									(12,453)	(242,122)	285,075
Other Financing Activities									(33,482)	(18,225)	(15,620)
Net Cash Flows (Used in)/Provided by Financing Activities									(17,940)	210,643	(64,842)
Net Increase/(Decrease) in Cash and Cash Equivalents									6,304	(14,756)	(4,661)
Cash and Cash Equivalents - Beginning of Year				23,947				38,703	23,947	38,703	43,364
Cash and Cash Equivalents - End of Year	30,251				23,947				30,251	23,947	38,703
Cash Paid/(Received) During the Year for:
Income Taxes									(135,500)	10,300	334,200
Eversource [Member]
Operating Activities:
Net Income									942,302	878,485	819,546
Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries									(922,321)	(900,824)	(848,435)
Cash Dividends Received from Subsidiaries									724,877	602,300	609,800
Deferred Income Taxes									19,008	16,880	7,956
Other									(27,963)	(22,864)	9,409
Accounts Receivables from Subsidiaries									(9,173)	(16,980)	88,800
Taxes Receivable/Accrued, Net									8,050	(14,426)	23,178
Accounts Payable, Including Affiliate Payables									(6,908)	(134,730)	5,942
Other Current Assets and Liabilities, Net									(7,433)	6,832	14,484
Net Cash Flows Provided by Operating Activities									720,439	414,673	730,680
Investing Activities:
Capital Contributions to Subsidiaries									(589,500)	(218,500)	(437,553)
Decrease/(Increase) in Notes Receivable from Subsidiaries									14,510	(131,650)	86,100
Other Investing Activities									0	12,000	0
Net Cash Flows Used in Investing Activities									(574,990)	(338,150)	(351,453)
Financing Activities:
Cash Dividends on Common Shares									(564,486)	(529,791)	(475,227)
Issuance of Long-Term Debt									500,000	450,000	0
(Decrease)/Increase in Short-Term Debt									(76,453)	(2,622)	86,575
Other Financing Activities									(4,484)	5,819	9,528
Net Cash Flows (Used in)/Provided by Financing Activities									(145,423)	(76,594)	(379,124)
Net Increase/(Decrease) in Cash and Cash Equivalents									26	(71)	103
Cash and Cash Equivalents - Beginning of Year				$ 67				$ 138	67	138	35
Cash and Cash Equivalents - End of Year	$ 93				$ 67				93	67	138
Cash Paid/(Received) During the Year for:
Interest									58,018	43,024	36,208
Income Taxes									$ (65,531)	$ (34,680)	$ (86,804)

SCHEDULE II - VALUATION AND 157

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 190,680	$ 175,317	$ 171,251
Additions, Charged to Costs and Expense	69,466	51,077	55,657
Additions, Charged to Other Accounts	45,452	79,622	51,227
Deductions	104,968	115,336	102,818
Balance at end of period	200,630	190,680	175,317
Allowance for Doubtful Accounts [Member] | The Connecticut Light And Power Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	79,479	84,287	81,995
Additions, Charged to Costs and Expense	17,572	10,105	6,598
Additions, Charged to Other Accounts	28,801	30,592	39,706
Deductions	39,461	45,505	44,012
Balance at end of period	86,391	79,479	84,287
Allowance for Doubtful Accounts [Member] | NSTAR Electric Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	52,628	40,670	41,679
Additions, Charged to Costs and Expense	27,978	14,228	24,740
Additions, Charged to Other Accounts	4,050	29,559	627
Deductions	29,884	31,829	26,376
Balance at end of period	54,772	52,628	40,670
Allowance for Doubtful Accounts [Member] | Public Service Company Of New Hampshire [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	8,733	7,663	7,364
Additions, Charged to Costs and Expense	7,288	8,889	6,815
Additions, Charged to Other Accounts	498	841	797
Deductions	6,578	8,660	7,313
Balance at end of period	9,941	8,733	7,663
Allowance for Doubtful Accounts [Member] | Western Massachusetts Electric Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	14,048	9,880	9,984
Additions, Charged to Costs and Expense	3,750	4,940	2,415
Additions, Charged to Other Accounts	7,203	7,418	3,608
Deductions	9,489	8,190	6,127
Balance at end of period	$ 15,512	$ 14,048	$ 9,880
Maximum [Member] | CL&P and Yankee Gas [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Period of uncollectible hardship accounts receivable Reserves	180 days
Minimum [Member] | CL&P and Yankee Gas [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Period of uncollectible hardship accounts receivable Reserves	90 days