The Connecticut Light and Power Company (CNLTN) 10-Q3 Nov 172017 Q3 Quarterly reportFinancial data

Company Profile

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - shares	9 Months Ended
DOCUMENT AND ENTITY INFORMATION - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity [Line Items]
Entity Registrant Name	Eversource Energy
Entity Central Index Key	72,741
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Trading Symbol	ES
Entity Common Stock, Shares Outstanding (in shares)		316,885,808
The Connecticut Light And Power Company
Document And Entity [Line Items]
Entity Registrant Name	The Connecticut Light and Power Company
Entity Central Index Key	23,426
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Public Service Company Of New Hampshire
Document And Entity [Line Items]
Entity Registrant Name	Public Service Company of New Hampshire
Entity Central Index Key	315,256
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		301
Western Massachusetts Electric Company
Document And Entity [Line Items]
Entity Registrant Name	Western Massachusetts Electric Company
Entity Central Index Key	106,170
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		434,653
NSTAR Electric Company
Document And Entity [Line Items]
Entity Registrant Name	NSTAR Electric Company
Entity Central Index Key	13,372
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		100

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current Assets:
Cash and Cash Equivalents	$ 125,761	$ 30,251
Receivables, Net	919,959	847,301
Unbilled Revenues	146,634	168,490
Fuel, Materials, Supplies and Inventory	305,035	328,721
Regulatory Assets	746,142	887,625
Prepayments and Other Current Assets	159,939	215,284
Total Current Assets	2,403,470	2,477,672
Property, Plant and Equipment, Net	22,537,304	21,350,510
Deferred Debits and Other Assets:
Regulatory Assets	3,505,901	3,638,688
Goodwill	3,519,401	3,519,401
Marketable Securities	570,255	544,642
Other Long-Term Assets	627,289	522,260
Total Deferred Debits and Other Assets	8,222,846	8,224,991
Total Assets	33,163,620	32,053,173
Current Liabilities:
Notes Payable	18,238	1,148,500
Long-Term Debt – Current Portion	957,697	773,883
Accounts Payable	794,195	884,521
Obligations to Third Party Suppliers	149,789	122,806
Regulatory Liabilities	170,215	146,787
Other Current Liabilities	530,297	562,108
Total Current Liabilities	2,620,431	3,638,605
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	6,001,589	5,607,207
Regulatory Liabilities	700,207	702,255
Derivative Liabilities	391,910	413,676
Accrued Pension and SERP	946,629	1,141,514
Other Long-Term Liabilities	881,056	853,260
Total Deferred Credits and Other Liabilities	8,921,391	8,717,912
Capitalization:
Long-Term Debt	10,468,193	8,829,354
Noncontrolling Interest – Preferred Stock of Subsidiaries	155,568	155,568
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid In	6,235,846	6,250,224
Retained Earnings	3,474,185	3,175,171
Accumulated Other Comprehensive Loss	(63,615)	(65,282)
Treasury Stock	(317,771)	(317,771)
Common Stockholder's Equity	10,998,037	10,711,734
Total Capitalization	21,621,798	19,696,656
Total Liabilities and Capitalization	33,163,620	32,053,173
The Connecticut Light And Power Company
Current Assets:
Cash and Cash Equivalents	9,364	6,579
Receivables, Net	404,065	359,132
Accounts Receivable from Affiliated Companies	29,287	16,851
Unbilled Revenues	48,625	50,373
Materials, Supplies and Inventory	44,516	52,050
Regulatory Assets	274,982	335,526
Prepaid Property Taxes	55,375	19,678
Prepayments and Other Current Assets	13,832	32,992
Total Current Assets	880,046	873,181
Property, Plant and Equipment, Net	8,107,957	7,632,392
Deferred Debits and Other Assets:
Regulatory Assets	1,312,191	1,391,564
Other Long-Term Assets	145,246	137,907
Total Deferred Debits and Other Assets	1,457,437	1,529,471
Total Assets	10,445,440	10,035,044
Current Liabilities:
Notes Payable to Eversource Parent	0	80,100
Long-Term Debt – Current Portion	300,000	250,000
Accounts Payable	292,234	289,532
Accounts Payable to Affiliated Companies	80,899	88,075
Obligations to Third Party Suppliers	52,865	55,520
Accrued Taxes	64,332	16,090
Regulatory Liabilities	69,296	47,055
Derivative Liabilities	59,895	77,765
Other Current Liabilities	99,467	104,309
Total Current Liabilities	1,018,988	1,008,446
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	2,089,480	1,987,661
Regulatory Liabilities	98,777	100,138
Derivative Liabilities	391,758	412,750
Accrued Pension and SERP	297,492	300,208
Other Long-Term Liabilities	134,870	123,244
Total Deferred Credits and Other Liabilities	3,012,377	2,924,001
Capitalization:
Long-Term Debt	2,758,851	2,516,010
Noncontrolling Interest – Preferred Stock of Subsidiaries	116,200	116,200
Common Shareholders' Equity:
Common Shares	60,352	60,352
Capital Surplus, Paid In	2,110,752	2,110,714
Retained Earnings	1,367,650	1,299,374
Accumulated Other Comprehensive Loss	270	(53)
Common Stockholder's Equity	3,539,024	3,470,387
Total Capitalization	6,414,075	6,102,597
Total Liabilities and Capitalization	10,445,440	10,035,044
NSTAR Electric Company
Current Assets:
Cash and Cash Equivalents	89,915	3,494
Receivables, Net	322,193	257,557
Accounts Receivable from Affiliated Companies	13,632	8,581
Unbilled Revenues	39,160	31,632
Taxes Receivable	0	39,738
Fuel, Materials, Supplies and Inventory	53,203	62,288
Regulatory Assets	230,620	289,400
Prepayments and Other Current Assets	16,550	14,906
Total Current Assets	765,273	707,596
Property, Plant and Equipment, Net	6,268,689	6,051,835
Deferred Debits and Other Assets:
Regulatory Assets	1,049,324	1,057,746
Prepaid PBOP	115,367	95,073
Other Long-Term Assets	79,653	60,572
Total Deferred Debits and Other Assets	1,244,344	1,213,391
Total Assets	8,278,306	7,972,822
Current Liabilities:
Notes Payable	0	126,500
Long-Term Debt – Current Portion	43,814	400,000
Accounts Payable	198,251	232,599
Accounts Payable to Affiliated Companies	81,953	91,532
Obligations to Third Party Suppliers	86,346	55,863
Accrued Taxes	32,021	3,922
Renewable Portfolio Standards Compliance Obligations	69,527	75,571
Regulatory Liabilities	65,520	63,653
Other Current Liabilities	58,628	67,200
Total Current Liabilities	636,060	1,116,840
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,910,328	1,836,292
Regulatory Liabilities	392,851	391,823
Accrued Pension and SERP	39,830	111,827
Other Long-Term Liabilities	135,613	123,194
Total Deferred Credits and Other Liabilities	2,478,622	2,463,136
Capitalization:
Long-Term Debt	2,382,392	1,678,116
Noncontrolling Interest – Preferred Stock of Subsidiaries	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,047,678	1,045,378
Retained Earnings	1,690,198	1,625,984
Accumulated Other Comprehensive Loss	356	368
Common Stockholder's Equity	2,738,232	2,671,730
Total Capitalization	5,163,624	4,392,846
Total Liabilities and Capitalization	8,278,306	7,972,822
Public Service Company Of New Hampshire
Current Assets:
Cash and Cash Equivalents	597	4,646
Receivables, Net	93,299	84,450
Accounts Receivable from Affiliated Companies	24,331	4,185
Unbilled Revenues	37,133	41,004
Fuel, Materials, Supplies and Inventory	158,091	162,354
Regulatory Assets	112,465	117,240
Prepayments and Other Current Assets	3,797	28,908
Total Current Assets	429,713	442,787
Property, Plant and Equipment, Net	3,167,905	3,039,313
Deferred Debits and Other Assets:
Regulatory Assets	244,561	245,525
Other Long-Term Assets	51,740	37,720
Total Deferred Debits and Other Assets	296,301	283,245
Total Assets	3,893,919	3,765,345
Current Liabilities:
Notes Payable to Eversource Parent	202,300	160,900
Long-Term Debt – Current Portion	110,000	70,000
Accounts Payable	92,201	85,716
Accounts Payable to Affiliated Companies	42,788	29,154
Regulatory Liabilities	7,923	12,659
Other Current Liabilities	61,210	43,253
Total Current Liabilities	516,422	401,682
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	827,412	785,385
Regulatory Liabilities	40,822	44,779
Accrued Pension and SERP	98,553	94,652
Other Long-Term Liabilities	54,131	49,442
Total Deferred Credits and Other Liabilities	1,020,918	974,258
Capitalization:
Long-Term Debt	892,581	1,002,048
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	843,134	843,134
Retained Earnings	625,012	549,286
Accumulated Other Comprehensive Loss	(4,148)	(5,063)
Common Stockholder's Equity	1,463,998	1,387,357
Total Capitalization	2,356,579	2,389,405
Total Liabilities and Capitalization	3,893,919	3,765,345
Western Massachusetts Electric Company
Current Assets:
Cash and Cash Equivalents	0	0
Receivables, Net	58,034	54,940
Accounts Receivable from Affiliated Companies	23,440	14,425
Unbilled Revenues	15,000	15,329
Fuel, Materials, Supplies and Inventory	6,221	8,618
Regulatory Assets	60,606	64,123
Prepayments and Other Current Assets	1,297	2,595
Total Current Assets	164,598	160,030
Property, Plant and Equipment, Net	1,769,566	1,678,262
Deferred Debits and Other Assets:
Regulatory Assets	121,796	127,291
Other Long-Term Assets	38,934	29,062
Total Deferred Debits and Other Assets	160,730	156,353
Total Assets	2,094,894	1,994,645
Current Liabilities:
Notes Payable to Eversource Parent	96,900	51,000
Accounts Payable	58,518	56,036
Accounts Payable to Affiliated Companies	22,181	19,478
Obligations to Third Party Suppliers	9,736	10,508
Renewable Portfolio Standards Compliance Obligations	16,144	20,383
Regulatory Liabilities	10,236	14,888
Other Current Liabilities	13,020	14,984
Total Current Liabilities	226,735	187,277
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	519,998	490,793
Regulatory Liabilities	22,726	17,227
Accrued Pension and SERP	18,038	20,390
Other Long-Term Liabilities	45,831	41,308
Total Deferred Credits and Other Liabilities	606,593	569,718
Capitalization:
Long-Term Debt	566,172	566,536
Common Shareholders' Equity:
Common Shares	10,866	10,866
Capital Surplus, Paid In	444,398	444,398
Retained Earnings	242,157	218,212
Accumulated Other Comprehensive Loss	(2,027)	(2,362)
Common Stockholder's Equity	695,394	671,114
Total Capitalization	1,261,566	1,237,650
Total Liabilities and Capitalization	$ 2,094,894	$ 1,994,645

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Revenues	$ 1,988,512	$ 2,039,706	$ 5,856,458	$ 5,862,525
Operating Expenses:
Purchased Power, Fuel and Transmission	651,776	665,810	1,955,129	2,001,929
Operations and Maintenance	300,421	324,734	933,400	965,584
Depreciation	194,466	181,288	571,152	531,781
Amortization of Regulatory Assets, Net	41,848	43,942	58,058	56,223
Energy Efficiency Programs	129,205	149,121	391,761	405,962
Taxes Other Than Income Taxes	168,193	164,942	479,648	479,219
Total Operating Expenses	1,485,909	1,529,837	4,389,148	4,440,698
Operating Income/(Loss)	502,603	509,869	1,467,310	1,421,827
Interest Expense	108,719	99,865	319,477	298,568
Other Income, Net	21,184	13,641	56,304	23,689
Income Before Income Tax Expense	415,068	423,645	1,204,137	1,146,948
Income Tax Expense	152,818	156,446	447,921	428,186
Net Income	262,250	267,199	756,216	718,762
Net Income Attributable to Noncontrolling Interests	1,880	1,880	5,639	5,639
Net Income Attributable to Common Shareholders	$ 260,370	$ 265,319	$ 750,577	$ 713,123
Basic and Diluted Earnings Per Common Share (in dollars per share)	$ 0.82	$ 0.83	$ 2.36	$ 2.24
Dividends Declared Per Common Share (in dollars per share)	$ 0.48	$ 0.45	$ 1.43	$ 1.34
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,393,029	317,787,836	317,415,848	317,696,823
Diluted (in shares)	317,949,396	318,577,079	318,007,042	318,511,609
The Connecticut Light And Power Company
Operating Revenues	$ 774,762	$ 760,037	$ 2,173,629	$ 2,175,141
Operating Expenses:
Purchased Power, Fuel and Transmission	259,005	253,509	711,154	760,613
Operations and Maintenance	123,107	123,034	359,834	356,409
Depreciation	63,727	57,675	184,275	172,175
Amortization of Regulatory Assets, Net	34,574	23,418	58,799	30,308
Energy Efficiency Programs	37,739	44,381	106,483	117,969
Taxes Other Than Income Taxes	79,067	81,948	223,482	227,981
Total Operating Expenses	597,219	583,965	1,644,027	1,665,455
Operating Income/(Loss)	177,543	176,072	529,602	509,686
Interest Expense	36,313	36,083	106,577	108,561
Other Income, Net	7,509	3,669	14,070	10,881
Income Before Income Tax Expense	148,739	143,658	437,095	412,006
Income Tax Expense	52,595	57,026	159,450	155,453
Net Income	96,144	86,632	277,645	256,553
NSTAR Electric Company
Operating Revenues	725,701	780,462	1,913,548	1,985,979
Operating Expenses:
Purchased Power, Fuel and Transmission	259,400	291,382	689,784	764,907
Operations and Maintenance	92,571	96,282	266,203	279,932
Depreciation	56,200	54,695	167,598	159,151
Amortization of Regulatory Assets, Net	9,845	9,621	17,806	18,275
Energy Efficiency Programs	71,615	84,717	198,803	212,882
Taxes Other Than Income Taxes	37,052	35,050	99,090	101,800
Total Operating Expenses	526,683	571,747	1,439,284	1,536,947
Operating Income/(Loss)	199,018	208,715	474,264	449,032
Interest Expense	24,488	21,101	69,962	62,206
Other Income, Net	3,426	5,022	8,703	7,524
Income Before Income Tax Expense	177,956	192,636	413,005	394,350
Income Tax Expense	69,796	75,440	161,320	154,493
Net Income	108,160	117,196	251,685	239,857
Public Service Company Of New Hampshire
Operating Revenues	250,032	266,946	733,572	727,753
Operating Expenses:
Purchased Power, Fuel and Transmission	57,099	59,833	179,289	155,700
Operations and Maintenance	63,669	64,183	191,153	187,184
Depreciation	32,084	29,646	95,266	86,524
Amortization of Regulatory Assets/(Liabilities), Net	2,835	14,158	(10,658)	14,490
Energy Efficiency Programs	4,007	3,983	11,040	10,862
Taxes Other Than Income Taxes	22,936	20,460	66,935	64,543
Total Operating Expenses	182,630	192,263	533,025	519,303
Operating Income/(Loss)	67,402	74,683	200,547	208,450
Interest Expense	12,896	12,397	38,676	37,386
Other Income, Net	1,229	574	2,883	1,007
Income Before Income Tax Expense	55,735	62,860	164,754	172,071
Income Tax Expense	22,012	24,345	65,128	66,242
Net Income	33,723	38,515	99,626	105,829
Western Massachusetts Electric Company
Operating Revenues	126,335	124,042	377,214	368,533
Operating Expenses:
Purchased Power, Fuel and Transmission	34,828	32,178	109,553	104,406
Operations and Maintenance	21,528	24,125	65,769	68,018
Depreciation	12,546	11,567	36,844	34,414
Amortization of Regulatory Assets/(Liabilities), Net	286	1,102	(563)	3,305
Energy Efficiency Programs	10,996	12,389	29,739	33,593
Taxes Other Than Income Taxes	10,779	10,609	31,403	30,440
Total Operating Expenses	90,963	91,970	272,745	274,176
Operating Income/(Loss)	35,372	32,072	104,469	94,357
Interest Expense	6,321	6,222	18,752	18,298
Other Income, Net	1,060	179	1,409	133
Income Before Income Tax Expense	30,111	26,029	87,126	76,192
Income Tax Expense	12,504	10,018	34,680	30,089
Net Income	$ 17,607	$ 16,011	$ 52,446	$ 46,103

CONDENSED CONSOLIDATED STATEME4

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net Income	$ 262,250	$ 267,199	$ 756,216	$ 718,762
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	519	534	1,567	1,602
Changes in Unrealized Gains/(Losses) on Marketable Securities	(1,872)	946	733	2,271
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	673	(1,733)	(633)	(2,646)
Net OCI	(680)	(253)	1,667	1,227
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(5,639)	(5,639)
Comprehensive Income Attributable to Common Shareholders	259,690	265,066	752,244	714,350
The Connecticut Light And Power Company
Net Income	96,144	86,632	277,645	256,553
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	96	111	298	333
Changes in Unrealized Gains/(Losses) on Marketable Securities	(64)	33	25	78
Net OCI	32	144	323	411
Comprehensive Income Attributable to Common Shareholders	96,176	86,776	277,968	256,964
NSTAR Electric Company
Net Income	108,160	117,196	251,685	239,857
Other Comprehensive (Loss)/Income, Net of Tax:
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(4)	(10)	(12)	(31)
Net OCI	(4)	(10)	(12)	(31)
Comprehensive Income Attributable to Common Shareholders	108,156	117,186	251,673	239,826
Public Service Company Of New Hampshire
Net Income	33,723	38,515	99,626	105,829
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	291	290	872	871
Changes in Unrealized Gains/(Losses) on Marketable Securities	(112)	56	43	135
Net OCI	179	346	915	1,006
Comprehensive Income Attributable to Common Shareholders	33,902	38,861	100,541	106,835
Western Massachusetts Electric Company
Net Income	17,607	16,011	52,446	46,103
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	109	109	328	328
Changes in Unrealized Gains/(Losses) on Marketable Securities	(18)	9	7	22
Net OCI	91	118	335	350
Comprehensive Income Attributable to Common Shareholders	$ 17,698	$ 16,129	$ 52,781	$ 46,453

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities:
Net Income	$ 756,216	$ 718,762
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	571,152	531,781
Deferred Income Taxes	374,863	301,413
Pension, SERP and PBOP Expense, Net	16,891	31,627
Pension and PBOP Contributions	(197,900)	(121,854)
Regulatory Overrecoveries, Net	185,952	152,808
Amortization of Regulatory Assets, Net	58,058	56,223
Other	(148,741)	(27,671)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(107,473)	(191,454)
Fuel, Materials, Supplies and Inventory	23,686	25,425
Taxes Receivable/Accrued, Net	88,856	347,898
Accounts Payable	(96,551)	(121,513)
Other Current Assets and Liabilities, Net	(32,874)	(53,077)
Net Cash Flows Provided by Operating Activities	1,492,135	1,650,368
Investing Activities:
Investments in Property, Plant and Equipment	(1,642,280)	(1,359,171)
Proceeds from Sales of Marketable Securities	520,664	444,209
Purchases of Marketable Securities	(506,302)	(437,197)
Other Investing Activities	(10,177)	(9,463)
Net Cash Flows Used in Investing Activities	(1,638,095)	(1,361,622)
Financing Activities:
Cash Dividends on Common Shares	(451,562)	(423,471)
Cash Dividends on Preferred Stock	(5,639)	(5,639)
Decrease in Notes Payable	(231,500)	(426,453)
Issuance of Long-Term Debt	1,250,000	800,000
Retirements of Long-Term Debt	(320,000)	(200,000)
Other Financing Activities	171	(17,074)
Net Cash Flows Provided by/(Used in) Financing Activities	241,470	(272,637)
Net Increase (decrease) in Cash and Cash Equivalents	95,510	16,109
Cash and Cash Equivalents - Beginning of Period	30,251	23,947
Cash and Cash Equivalents - End of Period	125,761	40,056
The Connecticut Light And Power Company
Operating Activities:
Net Income	277,645	256,553
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	184,275	172,175
Deferred Income Taxes	90,132	109,637
Pension, SERP and PBOP (Benefits)/Expense, Net	4,546	4,825
Regulatory Overrecoveries, Net	71,413	33,492
Amortization of Regulatory Assets, Net	58,799	30,308
Other	(22,113)	(14,873)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(70,936)	(100,074)
Taxes Receivable/Accrued, Net	69,335	197,422
Accounts Payable	(1,649)	(30,168)
Other Current Assets and Liabilities, Net	(38,111)	(44,908)
Net Cash Flows Provided by Operating Activities	623,336	614,389
Investing Activities:
Investments in Property, Plant and Equipment	(621,882)	(438,518)
Proceeds from the Sale of Property, Plant and Equipment	0	9,047
Other Investing Activities	185	310
Net Cash Flows Used in Investing Activities	(621,697)	(429,161)
Financing Activities:
Cash Dividends on Common Shares	(205,200)	(149,700)
Capital Contributions from Eversource Parent	0	145,700
Cash Dividends on Preferred Stock	(4,169)	(4,169)
Increase/(Decrease) in Notes Payable to Eversource Parent	(80,100)	(168,900)
Premium on Long-Term Debt Issuance	21,937	0
Issuance of Long-Term Debt	525,000	0
Retirements of Long-Term Debt	(250,000)	0
Other Financing Activities	(6,322)	(609)
Net Cash Flows Provided by/(Used in) Financing Activities	1,146	(177,678)
Net Increase (decrease) in Cash and Cash Equivalents	2,785	7,550
Cash and Cash Equivalents - Beginning of Period	6,579	1,057
Cash and Cash Equivalents - End of Period	9,364	8,607
NSTAR Electric Company
Operating Activities:
Net Income	251,685	239,857
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	167,598	159,151
Deferred Income Taxes	71,327	40,960
Pension and PBOP Contributions	(83,040)	(26,734)
Pension, SERP and PBOP (Benefits)/Expense, Net	(7,305)	1,370
Regulatory Overrecoveries, Net	61,356	131,774
Amortization of Regulatory Assets, Net	17,806	18,275
Other	(23,120)	(20,088)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(95,398)	(103,444)
Fuel, Materials, Supplies and Inventory	9,086	30,659
Taxes Receivable/Accrued, Net	67,501	141,379
Accounts Payable	(38,486)	(22,913)
Other Current Assets and Liabilities, Net	13,961	(25,942)
Net Cash Flows Provided by Operating Activities	412,971	564,304
Investing Activities:
Investments in Property, Plant and Equipment	(358,041)	(327,731)
Other Investing Activities	(3,617)	0
Net Cash Flows Used in Investing Activities	(361,658)	(327,731)
Financing Activities:
Cash Dividends on Common Shares	(186,000)	(278,300)
Capital Contributions from Eversource Parent	2,300	25,000
Cash Dividends on Preferred Stock	(1,470)	(1,470)
Decrease in Notes Payable	(126,500)	(26,500)
Issuance of Long-Term Debt	350,000	250,000
Retirements of Long-Term Debt	0	(200,000)
Other Financing Activities	(3,222)	(2,495)
Net Cash Flows Provided by/(Used in) Financing Activities	35,108	(233,765)
Net Increase (decrease) in Cash and Cash Equivalents	86,421	2,808
Cash and Cash Equivalents - Beginning of Period	3,494	3,346
Cash and Cash Equivalents - End of Period	89,915	6,154
Public Service Company Of New Hampshire
Operating Activities:
Net Income	99,626	105,829
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	95,266	86,524
Deferred Income Taxes	43,217	74,522
Regulatory Overrecoveries, Net	8,910	(4,289)
Amortization of Regulatory (Liabilities)/Assets, Net	(10,658)	14,490
Other	(7,792)	(12,660)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(30,276)	(28,754)
Fuel, Materials, Supplies and Inventory	4,263	(4,014)
Taxes Receivable/Accrued, Net	10,749	33,589
Accounts Payable	18,394	14,508
Other Current Assets and Liabilities, Net	32,296	26,207
Net Cash Flows Provided by Operating Activities	263,995	305,952
Investing Activities:
Investments in Property, Plant and Equipment	(215,470)	(215,804)
Other Investing Activities	113	272
Net Cash Flows Used in Investing Activities	(215,357)	(215,532)
Financing Activities:
Cash Dividends on Common Shares	(23,900)	(58,200)
Capital Contributions from Eversource Parent	0	94,500
Increase/(Decrease) in Notes Payable to Eversource Parent	41,400	(123,800)
Retirements of Long-Term Debt	(70,000)	0
Other Financing Activities	(187)	(217)
Net Cash Flows Provided by/(Used in) Financing Activities	(52,687)	(87,717)
Net Increase (decrease) in Cash and Cash Equivalents	(4,049)	2,703
Cash and Cash Equivalents - Beginning of Period	4,646	1,733
Cash and Cash Equivalents - End of Period	597	4,436
Western Massachusetts Electric Company
Operating Activities:
Net Income	52,446	46,103
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	36,844	34,414
Deferred Income Taxes	29,008	15,587
Regulatory Overrecoveries, Net	10,291	323
Amortization of Regulatory (Liabilities)/Assets, Net	(563)	3,305
Other	(10,182)	(2,532)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(16,818)	1,933
Taxes Receivable/Accrued, Net	4,203	36,658
Accounts Payable	(5,777)	(16,240)
Other Current Assets and Liabilities, Net	(7,482)	5,277
Net Cash Flows Provided by Operating Activities	91,970	124,828
Investing Activities:
Investments in Property, Plant and Equipment	(109,233)	(104,811)
Proceeds from Sales of Marketable Securities	1,641	1,934
Purchases of Marketable Securities	(1,590)	(1,894)
Net Cash Flows Used in Investing Activities	(109,182)	(104,771)
Financing Activities:
Cash Dividends on Common Shares	(28,500)	(28,500)
Capital Contributions from Eversource Parent	0	53,000
Increase/(Decrease) in Notes Payable to Eversource Parent	45,900	(95,200)
Issuance of Long-Term Debt	0	50,000
Other Financing Activities	(188)	(191)
Net Cash Flows Provided by/(Used in) Financing Activities	17,212	(20,891)
Net Increase (decrease) in Cash and Cash Equivalents	0	(834)
Cash and Cash Equivalents - Beginning of Period	0	834
Cash and Cash Equivalents - End of Period	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	Sep. 30, 2017
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES A. Basis of Presentation 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. On June 2, 2017, Eversource announced that it had entered into an agreement to acquire Aquarion from Macquarie Infrastructure Partners for $1.675 billion , consisting of approximately $880 million in cash and $795 million of assumed Aquarion debt. The transaction requires approval from PURA, the DPU, the NHPUC, the Maine PUC, and the Federal Communications Commission, and is also subject to a review under the Hart-Scott-Rodino Act. On June 29, 2017, Eversource and Aquarion filed joint applications with regulatory agencies in Connecticut, Massachusetts, New Hampshire and Maine requesting approval of the transaction. With the exception of Massachusetts, all state and federal regulatory agency approvals have been received and the related review period has expired. The transaction is expected to close by December 31, 2017. The unaudited condensed 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 unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements." The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the Combined Notes to Financial Statements included in Item 8, "Financial Statements and Supplementary Data," of the Eversource 2016 Form 10-K, which was filed with the SEC. 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. The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of September 30, 2017 and December 31, 2016 , the results of operations and comprehensive income for the three and nine months ended September 30, 2017 and 2016 , and the cash flows for the nine months ended September 30, 2017 and 2016 . The results of operations and comprehensive income for the three and nine months ended September 30, 2017 and 2016 and the cash flows for the nine months ended September 30, 2017 and 2016 are not necessarily indicative of the results expected for a full year. 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 period data were made in the accompanying financial statements to conform to the current period presentation. B. Accounting Standards Accounting Standards Issued but Not Yet Effective: In May 2014, the Financial Accounting Standards Board ("FASB") issued an Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers , which amends existing revenue recognition guidance and is required to be applied retrospectively (either to each reporting period presented or cumulatively at the date of initial application). The Company will implement the standard in the first quarter of 2018 cumulatively at the date of initial application. Implementation of the ASU is not expected to have a material effect on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or 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 September 30, 2017 was approximately $51 million with an unrealized gain of $1.7 million . The remaining available-for-sale equity securities included in marketable securities on the balance sheet are held in nuclear decommissioning trusts and are subject to regulatory accounting treatment and will not be impacted by this guidance. Implementation of the ASU for other financial instruments is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. 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 lease criteria are required to be applied to leases and lease renewals entered into effective January 1, 2019, and leases entered into before that date 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 to be operating leases, and expects to implement the ASU in the first quarter of 2019. In March 2017, the FASB issued ASU 2017-07, Compensation – Retirement Benefits: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost , required to be implemented in the first quarter of 2018. The ASU requires separate presentation of service cost from other components of net pen sion and PBOP costs, with the other components presented as non-operating income and not subject to capitalization. The ASU is required to be applied retrospectively for the separate presentation in the income statement of service costs and other components and prospectively in the balance sheet for the capitalization of only the service cost component. The implementation of the ASU will not have an impact on the net income of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. C. 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, is included in Receivables, Net on the balance sheets, and was as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship (Millions of Dollars) As of September 30, 2017 As of December 31, 2016 As of September 30, 2017 As of December 31, 2016 Eversource $ 196.8 $ 200.6 $ 126.3 $ 119.9 CL&P 77.6 86.4 64.6 67.7 NSTAR Electric 55.7 54.8 32.3 26.2 PSNH 10.6 9.9 — — WMECO 17.0 15.5 11.3 9.9 D. 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 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Determination of Fair Value: The valuation techniques and inputs used in Eversource's fair value measurements are described in Note 4, "Derivative Instruments," Note 5, "Marketable Securities," and Note 10, "Fair Value of Financial Instruments," to the financial statements. E. Other Income, Net Items included within Other Income, Net on the statements of income primarily consist of income/(loss) related to equity method investments, investment income/(loss), interest income and AFUDC related to equity funds. For the three and nine months ended September 30, 2017 , Eversource had equity in earnings of $5.1 million and $23.0 million , respectively, related to its equity method investments . For the three and nine months ended September 30, 2016 Eversource had equity in earnings of $0.9 million and losses of $2.0 million , respectively, related to its equity method investments. Investment income/(loss) primarily relates to debt and equity securities held in trust. For further information, see Note 5, "Marketable Securities," to the financial statements. F. 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 Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Eversource $ 40.3 $ 45.1 $ 118.2 $ 124.8 CL&P 37.8 42.6 103.5 112.2 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. G. Supplemental Cash Flow Information Non-cash investing activities include plant additions included in Accounts Payable as follows: (Millions of Dollars) As of September 30, 2017 As of September 30, 2016 Eversource $ 307.7 $ 203.6 CL&P 113.4 64.5 NSTAR Electric 55.4 39.4 PSNH 39.6 31.0 WMECO 37.1 17.6

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	9 Months Ended
REGULATORY ACCOUNTING	Sep. 30, 2017
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 As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Benefit Costs $ 1,793.8 $ 1,817.8 Derivative Liabilities 385.1 423.3 Income Taxes, Net 652.7 644.5 Storm Restoration Costs 330.1 385.3 Goodwill-related 449.0 464.4 Regulatory Tracker Mechanisms 470.7 576.6 Asset Retirement Obligations 104.8 99.3 Other Regulatory Assets 65.8 115.1 Total Regulatory Assets 4,252.0 4,526.3 Less: Current Portion 746.1 887.6 Total Long-Term Regulatory Assets $ 3,505.9 $ 3,638.7 As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Benefit Costs $ 415.8 $ 436.7 $ 183.2 $ 84.8 $ 429.3 $ 438.6 $ 184.2 $ 86.7 Derivative Liabilities 381.6 2.4 — — 420.5 2.8 — — Income Taxes, Net 441.1 92.4 22.3 30.5 437.0 89.7 24.2 30.8 Storm Restoration Costs 195.7 112.4 9.2 12.8 239.8 112.5 17.1 15.9 Goodwill-related — 385.5 — — — 398.7 — — Regulatory Tracker Mechanisms 87.9 201.1 108.0 44.4 123.9 257.3 104.5 46.7 Asset Retirement Obligations 35.1 33.9 16.8 4.5 33.2 31.9 16.2 4.2 Other Regulatory Assets 30.0 15.5 17.6 5.4 43.4 15.6 16.5 7.1 Total Regulatory Assets 1,587.2 1,279.9 357.1 182.4 1,727.1 1,347.1 362.7 191.4 Less: Current Portion 275.0 230.6 112.5 60.6 335.5 289.4 117.2 64.1 Total Long-Term Regulatory Assets $ 1,312.2 $ 1,049.3 $ 244.6 $ 121.8 $ 1,391.6 $ 1,057.7 $ 245.5 $ 127.3 Regulatory Costs in Other Long-Term Assets: Eversource's Regulated companies had $108.7 million (including $3.9 million for CL&P, $42.3 million for NSTAR Electric, $18.5 million for PSNH, and $25.7 million for WMECO) and $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) of additional regulatory costs as of September 30, 2017 and December 31, 2016 , 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. Regulatory Liabilities: The components of regulatory liabilities were as follows: Eversource As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Cost of Removal $ 470.3 $ 459.7 Benefit Costs 125.5 136.2 Regulatory Tracker Mechanisms 175.8 145.3 AFUDC - Transmission 65.4 65.8 Other Regulatory Liabilities 33.4 42.1 Total Regulatory Liabilities 870.4 849.1 Less: Current Portion 170.2 146.8 Total Long-Term Regulatory Liabilities $ 700.2 $ 702.3 As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cost of Removal $ 40.5 $ 278.8 $ 40.5 $ 11.7 $ 38.8 $ 271.6 $ 44.1 $ 8.6 Benefit Costs — 106.0 — — — 113.1 — — Regulatory Tracker Mechanisms 57.1 65.5 5.6 12.7 37.2 63.7 10.7 14.7 AFUDC - Transmission 49.2 7.7 — 8.5 50.2 6.9 — 8.7 Other Regulatory Liabilities 21.3 0.4 2.6 — 21.0 0.2 2.7 0.1 Total Regulatory Liabilities 168.1 458.4 48.7 32.9 147.2 455.5 57.5 32.1 Less: Current Portion 69.3 65.5 7.9 10.2 47.1 63.7 12.7 14.9 Total Long-Term Regulatory Liabilities $ 98.8 $ 392.9 $ 40.8 $ 22.7 $ 100.1 $ 391.8 $ 44.8 $ 17.2

PROPERTY, PLANT AND EQUIPMENT A

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	9 Months Ended
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION The following tables summarize property, plant and equipment by asset category: Eversource As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Distribution - Electric $ 14,217.3 $ 13,716.9 Distribution - Natural Gas 3,158.1 3,010.4 Transmission - Electric 8,918.2 8,517.4 Generation 1,215.8 1,224.2 Electric and Natural Gas Utility 27,509.4 26,468.9 Other (1) 679.9 591.6 Property, Plant and Equipment, Gross 28,189.3 27,060.5 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,838.5 ) (6,480.4 ) Other (274.4 ) (242.0 ) Total Accumulated Depreciation (7,112.9 ) (6,722.4 ) Property, Plant and Equipment, Net 21,076.4 20,338.1 Construction Work in Progress (2) 1,460.9 1,012.4 Total Property, Plant and Equipment, Net $ 22,537.3 $ 21,350.5 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. (2) As of September 30, 2017 , the total CWIP related to NPT was approximately $201 million . As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Distribution $ 5,797.6 $ 5,543.1 $ 2,048.8 $ 868.1 $ 5,562.9 $ 5,402.3 $ 1,949.8 $ 841.9 Transmission 4,061.2 2,545.0 1,115.7 1,147.9 3,912.9 2,435.8 1,059.3 1,061.1 Generation — — 1,179.8 36.0 — — 1,188.2 36.0 Property, Plant and Equipment, Gross 9,858.8 8,088.1 4,344.3 2,052.0 9,475.8 7,838.1 4,197.3 1,939.0 Less: Accumulated Depreciation (2,207.0 ) (2,143.8 ) (1,315.7 ) (356.5 ) (2,082.4 ) (2,025.4 ) (1,254.7 ) (338.8 ) Property, Plant and Equipment, Net 7,651.8 5,944.3 3,028.6 1,695.5 7,393.4 5,812.7 2,942.6 1,600.2 Construction Work in Progress 456.2 324.4 139.3 74.1 239.0 239.1 96.7 78.1 Total Property, Plant and Equipment, Net $ 8,108.0 $ 6,268.7 $ 3,167.9 $ 1,769.6 $ 7,632.4 $ 6,051.8 $ 3,039.3 $ 1,678.3

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	9 Months Ended
DERIVATIVE INSTRUMENTS	Sep. 30, 2017
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 September 30, 2017 As of December 31, 2016 (Millions of Dollars) Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: Level 2: Eversource $ — $ — $ — $ 6.0 $ — $ 6.0 Level 3: CL&P 10.4 (7.7 ) 2.7 13.9 (9.4 ) 4.5 Long-Term Derivative Assets: Level 2: Eversource $ — $ — $ — $ 0.3 $ (0.1 ) $ 0.2 Level 3: CL&P 74.3 (6.9 ) 67.4 77.3 (11.7 ) 65.6 Current Derivative Liabilities: Level 2: Eversource $ (1.5 ) $ 0.4 $ (1.1 ) $ — $ — $ — Level 3: Eversource (62.2 ) — (62.2 ) (79.7 ) — (79.7 ) CL&P (59.9 ) — (59.9 ) (77.8 ) — (77.8 ) NSTAR Electric (2.3 ) — (2.3 ) (1.9 ) — (1.9 ) Long-Term Derivative Liabilities: Level 3: Eversource $ (391.9 ) $ — $ (391.9 ) $ (413.7 ) $ — $ (413.7 ) CL&P (391.8 ) — (391.8 ) (412.8 ) — (412.8 ) NSTAR Electric (0.1 ) — (0.1 ) (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. For further information on the fair value of derivative contracts, see Note 1D, "Summary of Significant Accounting Policies - Fair Value Measurements," 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 September 30, 2017 and December 31, 2016 , Eversource had New York Mercantile Exchange ("NYMEX") financial contracts for natural gas futures in order to reduce variability associated with the purchase price of approximately 10.4 million and 9.2 million MMBtu of natural gas, respectively. For the three months ended September 30, 2017 and 2016 , there were gains of $0.6 million and losses of $53.4 million , respectively, deferred as regulatory costs, which reflect the change in fair value associated with Eversource's derivative contracts. For the nine months ended September 30, 2017 and 2016 , these losses were $30.3 million and $127.8 million , respectively. 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 term 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 September 30, 2017 As of December 31, 2016 Range Period Covered Range Period Covered Capacity Prices: CL&P $ 5.00 — 8.70 per kW-Month 2021 - 2026 $ 5.50 — 8.70 per kW-Month 2020 - 2026 Forward Reserve: CL&P $ 1.00 — 2.00 per kW-Month 2017 - 2024 $ 1.40 — 2.00 per kW-Month 2017 - 2024 REC Prices: NSTAR Electric $ 15.75 — 22.00 per REC 2017 - 2018 $ 24.00 — 29.00 per REC 2017 - 2018 Exit price premiums of 1 percent through 18 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. 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. 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. For the Three Months Ended September 30, 2017 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric Eversource CL&P NSTAR Derivatives, Net: Fair Value as of Beginning of Period $ (397.1 ) $ (394.8 ) $ (2.3 ) $ (412.6 ) $ (411.3 ) $ (1.3 ) Net Realized/Unrealized Gains/Losses Included in Regulatory Assets and Liabilities 0.5 (0.7 ) 1.2 (52.3 ) (49.8 ) (2.5 ) Settlements 12.6 13.9 (1.3 ) 21.2 20.1 1.1 Fair Value as of End of Period $ (384.0 ) $ (381.6 ) $ (2.4 ) $ (443.7 ) $ (441.0 ) $ (2.7 ) For the Nine Months Ended September 30, 2017 2016 (Millions of Dollars) Eversource CL&P NSTAR Eversource CL&P NSTAR Derivatives, Net: Fair Value as of Beginning of Period $ (423.3 ) $ (420.5 ) $ (2.8 ) $ (380.9 ) $ (380.8 ) $ (0.1 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (17.9 ) (15.9 ) (2.0 ) (128.9 ) (122.0 ) (6.9 ) Settlements 57.2 54.8 2.4 66.1 61.8 4.3 Fair Value as of End of Period $ (384.0 ) $ (381.6 ) $ (2.4 ) $ (443.7 ) $ (441.0 ) $ (2.7 )

MARKETABLE SECURITIES

MARKETABLE SECURITIES	9 Months Ended
MARKETABLE SECURITIES	Sep. 30, 2017
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 , these securities were classified as Level 1 in the fair value hierarchy and totaled $9.6 million . These securities were sold during the first quarter of 2017 and were no longer held as of September 30, 2017 . For the three and nine months ended September 30, 2016 , net gains on these securities of $0.1 million and $0.6 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 September 30, 2017 As of December 31, 2016 Eversource (Millions of Dollars) Amortized Cost Pre-Tax Unrealized Gains Pre-Tax Unrealized Losses Fair Value Amortized Cost Pre-Tax Unrealized Gains Pre-Tax Unrealized Losses Fair Value Debt Securities $ 286.5 $ 5.5 $ (0.5 ) $ 291.5 $ 296.2 $ 1.1 $ (2.1 ) $ 295.2 Equity Securities 210.7 81.5 — 292.2 203.3 62.3 (1.2 ) 264.4 Eversource's debt and equity securities include CYAPC's and YAEC's marketable securities held in nuclear decommissioning trusts in the amounts of $489.1 million and $466.7 million as of September 30, 2017 and December 31, 2016 , 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 for the three and nine months ended September 30, 2017 and 2016 . 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 non-qualified benefit trust and are offset in Other Long-Term Liabilities for CYAPC and YAEC. Eversource utilizes the specific identification basis method for the Eversource non-qualified 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 September 30, 2017 , 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) $ 40.2 $ 40.2 One to five years 56.7 57.6 Six to ten years 52.6 54.1 Greater than ten years 137.0 139.6 Total Debt Securities $ 286.5 $ 291.5 (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 September 30, 2017 As of December 31, 2016 Level 1: Mutual Funds and Equities $ 292.2 $ 274.0 Money Market Funds 21.8 54.8 Total Level 1 $ 314.0 $ 328.8 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 69.0 $ 63.0 Corporate Debt Securities 56.1 41.1 Asset-Backed Debt Securities 20.4 18.5 Municipal Bonds 113.6 107.5 Other Fixed Income Securities 10.6 10.3 Total Level 2 $ 269.7 $ 240.4 Total Marketable Securities $ 583.7 $ 569.2 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.

SHORT-TERM AND LONG-TERM DEBT

SHORT-TERM AND LONG-TERM DEBT	9 Months Ended
SHORT-TERM AND LONG-TERM DEBT	Sep. 30, 2017
Debt Disclosure [Abstract]
SHORT-TERM AND LONG-TERM DEBT	SHORT-TERM AND LONG-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 September 30, 2017 and December 31, 2016 , Eversource parent had $917.0 million and approximately $1.0 billion , respectively, in short-term borrowings outstanding under the Eversource parent commercial paper program, leaving $533.0 million and $428.0 million of available borrowing capacity as of September 30, 2017 and December 31, 2016 , respectively. The weighted-average interest rate on these borrowings as of September 30, 2017 and December 31, 2016 was 1.34 percent and 0.88 percent , respectively. As of September 30, 2017 , there were intercompany loans from Eversource parent of $202.3 million to PSNH and $96.9 million to WMECO. 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. Eversource parent, CL&P, PSNH, WMECO, NSTAR Gas and Yankee Gas are parties to a five -year $1.45 billion revolving credit facility. The revolving credit facility terminates on 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 September 30, 2017 and December 31, 2016 . Except as described below, 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 parent to CL&P, PSNH and WMECO are eliminated in consolidation on Eversource's balance sheets. As a result of the October 2017 Eversource parent long-term debt issuances, the net proceeds of which were used to repay short-term borrowings outstanding under the Eversource parent commercial paper program, $898.8 million of short-term debt was reclassified to Long-Term Debt as of September 30, 2017. 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 September 30, 2017 , NSTAR Electric had no short-term borrowings outstanding and as of December 31, 2016 , NSTAR Electric had $126.5 million in short-term borrowings outstanding under its commercial paper program, leaving $450.0 million and $323.5 million of available borrowing capacity as of September 30, 2017 and December 31, 2016 , respectively. The weighted-average interest rate on these borrowings as of December 31, 2016 was 0.71 percent . NSTAR Electric is a party to a five -year $450 million revolving credit facility. The revolving credit facility terminates on 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 September 30, 2017 and December 31, 2016 . Long-Term Debt Issuances: In March 2017, Eversource parent issued $300 million of 2.75 percent Series K Senior Notes due to mature in 2022. The proceeds, net of issuance costs, were used to repay short-term borrowings under the Eversource parent commercial paper program. In March 2017, CL&P issued $300 million of 3.20 percent 2017 Series A First and Refunding Mortgage Bonds due to mature in 2027. The proceeds, net of issuance costs, were used to repay short-term borrowings. In May 2017, NSTAR Electric issued $350 million of 3.20 percent Debentures due to mature in 2027. The proceeds, net of issuance costs, were used to repay short-term borrowings and fund capital expenditures and working capital . In August 2017, CL&P issued $225 million of 4.30 percent 2014 Series A First and Refunding Mortgage Bonds due to mature in 2044. These bonds are part of the same series of CL&P’s existing 4.30 percent bonds that were initially issued in 2014. The aggregate outstanding principal amount for these bonds is now $475 million . The proceeds, net of issuance costs, were used to refinance short-term debt and fund capital expenditures and working capital. In September 2017, Yankee Gas issued $75 million of 3.02 percent Series N First Mortgage Bonds due to mature in 2027. The proceeds, net of issuance costs, were used to repay short-term borrowings. In October 2017, Eversource parent issued $450 million 2.75 percent Series K Senior Notes due to mature in 2022. These senior notes are part of the same series of Eversource parent’s existing 2.75 percent Series K Senior Notes that were initially issued in March 2017. The aggregate outstanding principal amount for the Series K Senior Notes is now $750 million . In addition, Eversource parent issued $450 million of 2.90 percent 2017 Series L Senior Notes due to mature in 2024. The proceeds, net of issuance costs, were used to repay short-term borrowings. In October 2017, NSTAR Electric issued $350 million of 3.20 percent Debentures due to mature in 2027. The debentures are part of the same series of NSTAR Electric’s existing 3.20 percent Debentures that were initially issued in May 2017. The aggregate outstanding principal amount for the 3.20 percent Debentures is now $700 million . The proceeds, net of issuance costs, will be used to redeem long-term debt due to mature on November 15, 2017. As the debt issuance refinanced short-term debt, the amount was reclassified to Long-Term Debt on Eversource's and NSTAR Electric's balance sheets. Long-Term Debt Repayments: In March 2017, CL&P repaid at maturity the $150 million 5.375 percent 2007 Series A First and Refunding Mortgage Bonds. In September 2017, CL&P repaid at maturity $100 million of 5.75 percent 2007 Series C First Mortgage Bonds and PSNH repaid at maturity $70 million of 6.15 percent 2007 Series N First Mortgage Bonds. In October 2017, NSTAR Gas repaid at maturity $25 million of 7.04 percent Series M First Mortgage Bonds. Long-Term Debt Issuance Authorizations: On January 4, 2017, PURA approved CL&P's request for authorization to issue up to $1.325 billion in long-term debt through December 31, 2020. On March 30, 2017, the DPU approved NSTAR Electric's request for authorization to issue up to $700 million in long-term debt through December 31, 2018.

PENSION BENEFITS AND POSTRETIRE

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	9 Months Ended
	Sep. 30, 2017
Postemployment Benefits [Abstract]
PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS	PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS Eversource Service sponsors a defined benefit retirement plan ("Pension Plan") that covers eligible participants. In addition to the Pension Plan, Eversource maintains non-qualified defined benefit retirement plans sponsored by Eversource Service ("SERP Plans"), which provide benefits in excess of Internal Revenue Code limitations to eligible participants. Eversource Service also sponsors a defined benefit postretirement plan that 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, to eligible participants that meet certain age and service eligibility requirements ("PBOP Plan"). 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 remeasurement resulted in a prior service credit of $5.3 million and $16.1 million for the three and nine months ended September 30, 2017 , respectively, which was reflected as a reduction to net periodic benefit expense for PBOP benefits. The majority of this amount will be deferred for future refund to customers. The components of net periodic benefit expense for the Pension, SERP and PBOP Plans are shown below. The net periodic benefit expense and the intercompany allocations, less the capitalized portions of pension, SERP and PBOP amounts, are included in Operations and Maintenance expense on the statements of income. Capitalized amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net on the balance sheets. Pension, SERP and 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. Pension and SERP Eversource For the Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Service Cost $ 17.4 $ 18.6 $ 53.8 $ 56.6 Interest Cost 47.2 46.4 140.7 139.2 Expected Return on Pension Plan Assets (83.5 ) (79.4 ) (250.5 ) (238.5 ) Actuarial Loss 33.9 31.4 101.3 94.2 Prior Service Cost 1.2 0.9 3.4 2.6 Total Net Periodic Benefit Expense $ 16.2 $ 17.9 $ 48.7 $ 54.1 Capitalized Pension Expense $ 5.5 $ 5.4 $ 16.5 $ 16.8 PBOP Eversource For the Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Service Cost $ 2.4 $ 3.0 $ 7.1 $ 9.2 Interest Cost 6.8 7.5 20.3 26.5 Expected Return on Plan Assets (16.0 ) (15.9 ) (47.8 ) (47.3 ) Actuarial Loss 2.2 3.0 6.9 5.0 Prior Service Credit (5.3 ) (3.6 ) (16.1 ) (3.7 ) Total Net Periodic Benefit Income $ (9.9 ) $ (6.0 ) $ (29.6 ) $ (10.3 ) Capitalized PBOP Income $ (4.8 ) $ (2.6 ) $ (14.3 ) $ (4.6 ) Pension and SERP For the Three Months Ended September 30, 2017 For the Three Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 4.6 $ 3.1 $ 2.4 $ 0.7 $ 4.6 $ 3.3 $ 2.5 $ 0.8 Interest Cost 10.5 8.6 5.3 2.1 10.2 8.5 5.1 2.1 Expected Return on Pension Plan Assets (17.8 ) (17.5 ) (10.0 ) (4.4 ) (18.0 ) (16.9 ) (9.6 ) (4.4 ) Actuarial Loss 6.8 8.9 3.0 1.5 6.3 8.7 2.5 1.3 Prior Service Cost 0.4 0.1 0.1 0.1 0.4 — 0.1 0.1 Total Net Periodic Benefit Expense/(Income) $ 4.5 $ 3.2 $ 0.8 $ — $ 3.5 $ 3.6 $ 0.6 $ (0.1 ) Intercompany Allocations $ 2.4 $ 1.8 $ 0.8 $ 0.5 $ 3.5 $ 2.2 $ 1.0 $ 0.6 Capitalized Pension Expense $ 2.4 $ 1.9 $ 0.4 $ 0.1 $ 2.2 $ 2.0 $ 0.4 $ 0.1 Pension and SERP For the Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 13.9 $ 9.4 $ 7.3 $ 2.3 $ 14.3 $ 9.9 $ 7.5 $ 2.4 Interest Cost 31.3 25.6 15.9 6.3 31.2 25.3 15.4 6.3 Expected Return on Pension Plan Assets (53.9 ) (52.5 ) (29.9 ) (13.3 ) (54.2 ) (50.7 ) (28.9 ) (13.1 ) Actuarial Loss 20.7 26.4 8.7 4.5 19.2 25.8 7.5 4.1 Prior Service Cost 1.1 0.2 0.4 0.2 1.1 — 0.3 0.2 Total Net Periodic Benefit Expense/(Income) $ 13.1 $ 9.1 $ 2.4 $ — $ 11.6 $ 10.3 $ 1.8 $ (0.1 ) Intercompany Allocations $ 7.4 $ 5.5 $ 2.5 $ 1.4 $ 10.3 $ 6.7 $ 3.0 $ 1.9 Capitalized Pension Expense $ 7.3 $ 5.4 $ 1.1 $ 0.3 $ 7.1 $ 5.7 $ 1.0 $ 0.3 PBOP For the Three Months Ended September 30, 2017 For the Three Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 0.5 $ 0.3 $ 0.3 $ 0.1 $ 0.6 $ 0.6 $ 0.4 $ 0.1 Interest Cost 1.3 1.9 0.8 0.3 1.3 2.5 0.7 0.3 Expected Return on Plan Assets (2.4 ) (6.6 ) (1.4 ) (0.6 ) (2.5 ) (6.4 ) (1.4 ) (0.6 ) Actuarial Loss 0.2 0.9 0.1 — 0.5 1.2 0.2 — Prior Service Cost/(Credit) 0.3 (4.3 ) 0.2 — 0.2 (2.9 ) 0.1 — Total Net Periodic Benefit (Income)/Expense $ (0.1 ) $ (7.8 ) $ — $ (0.2 ) $ 0.1 $ (5.0 ) $ — $ (0.2 ) Intercompany Allocations $ (0.2 ) $ (0.2 ) $ (0.1 ) $ — $ — $ (0.1 ) $ — $ — Capitalized PBOP Income $ (0.1 ) $ (4.0 ) $ — $ (0.1 ) $ — $ (2.2 ) $ — $ (0.1 ) PBOP For the Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 1.5 $ 1.1 $ 1.0 $ 0.3 $ 1.4 $ 2.5 $ 0.9 $ 0.3 Interest Cost 4.0 5.7 2.3 0.8 4.0 10.3 2.2 0.8 Expected Return on Plan Assets (7.3 ) (19.9 ) (4.1 ) (1.7 ) (7.6 ) (19.2 ) (4.2 ) (1.7 ) Actuarial Loss 0.7 2.6 0.4 — 0.9 1.7 0.5 — Prior Service Cost/(Credit) 0.8 (12.9 ) 0.4 0.1 0.2 (2.9 ) 0.1 — Total Net Periodic Benefit Income $ (0.3 ) $ (23.4 ) $ — $ (0.5 ) $ (1.1 ) $ (7.6 ) $ (0.5 ) $ (0.6 ) Intercompany Allocations $ (0.5 ) $ (0.7 ) $ (0.3 ) $ (0.1 ) $ 0.3 $ — $ — $ — Capitalized PBOP Income $ (0.4 ) $ (11.9 ) $ — $ (0.2 ) $ (0.5 ) $ (3.3 ) $ — $ (0.3 )

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
COMMITMENTS AND CONTINGENCIES	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES A. Environmental Matters 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. 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 September 30, 2017 As of December 31, 2016 Number of Sites Reserve (in millions) Number of Sites Reserve (in millions) Eversource 58 $ 57.7 61 $ 65.8 CL&P 14 4.9 14 4.9 NSTAR Electric 10 2.0 13 3.2 PSNH 11 5.7 11 5.3 WMECO 4 0.8 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 $51.9 million and $59.0 million as of September 30, 2017 and December 31, 2016 , respectively, and related primarily to the natural gas business segment. The reduction in the reserve balance at the MGP sites in the first quarter of 2017 was primarily due to a change in cost estimates at one site where actual contamination was less than originally estimated. 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. B. 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 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 will guarantee NPT's obligations under a facility with a financial institution pursuant to which NPT may request letters of credit 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 or cash flows 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 September 30, 2017 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty (1) $ 185.1 2021 Various Surety Bonds (2) 40.1 2017 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate 8.2 2019 - 2024 (1) Eversource parent issued a declining balance guaranty on behalf of its subsidiary, Eversource Gas Transmission LLC, to guarantee the payment of the subsidiary's capital contributions for its investment in the Access Northeast project. The guaranty 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. (2) 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. C. 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, II, and III of litigation resulting from the DOE's failure to meet its contractual obligations. These Phases covered damages incurred in the years 1998 through 2012, and the awarded damages have been received by the Yankee Companies with certain amounts of the damages refunded to their customers. DOE Phase IV Damages - On May 22, 2017, each of the Yankee Companies filed subsequent lawsuits against the DOE in the Court of Federal Claims seeking damages totaling approximately $100 million for CYAPC, YAEC and MYAPC, covering the years from 2013 to 2016 (“DOE Phase IV”). The DOE Phase IV trial is expected to begin in 2018. For further discussion, see Part I, Item 3, “Legal Proceedings - Yankee Companies v. U.S. Department of Energy ” of our 2016 Form 10-K. D. 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 each of the first three complaints, the Complainants challenged the NETOs' base ROE of 11.14 percent that had been utilized since 2005 and sought an order to reduce it prospectively from the date of the final FERC order and for the separate 15 -month complaint periods. In the fourth complaint, filed April 29, 2016, the Complainants challenged the NETOs' base ROE of 10.57 percent and the maximum ROE for transmission incentive ("incentive cap") of 11.74 percent , asserting that these ROEs were unjust and unreasonable. In response to appeals of the FERC decision in the first complaint filed by the NETOs and the Complainants, the U.S. Court of Appeals for the D.C. Circuit (the "Court") issued a decision on April 14, 2017 vacating and remanding the FERC's decision. The Court found that the FERC failed to make an explicit finding that the 11.14 percent base ROE was unjust and unreasonable, as required under Section 206 of the Federal Power Act, before it set a new base ROE. The Court also found that the FERC did not provide a rational connection between the record evidence and its decision to select the midpoint of the upper half of the zone of reasonableness for the new base ROE. On May 26, 2017, the Chief Administrative Law Judge ("ALJ") issued an order that the fourth complaint will continue to trial in December 2017 with an ALJ initial decision expected in March of 2018. A summary of the four separate complaints and the base ROEs pertinent to those complaints are as follows: Complaint 15-Month Time Period of Complaint (Beginning as of Complaint Filing Date) Original Base ROE Authorized by FERC at Time of Complaint Filing Date (1) Base ROE Subsequently Authorized by FERC for First Complaint Period and also Effective from October 16, 2014 through April 14, 2017 (1) Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions) FERC ALJ Recommendation of Base ROE on Second and Third Complaints (Issued March 22, 2016) First 10/1/2011 - 12/31/2012 11.14% 10.57% $— (2) N/A Second 12/27/2012 - 3/26/2014 11.14% N/A 39.1 (3) 9.59% Third 7/31/2014 - 10/30/2015 11.14% 10.57% — 10.90% Fourth 4/29/2016 - 7/28/2017 10.57% 10.57% — N/A (1) The billed ROE (base plus incentives) between October 1, 2011 and October 15, 2014 was within a range of 11.14 percent to 13.1 percent . On October 16, 2014, the FERC set the incentive cap at 11.74 percent for the first complaint period and also effective from October 16, 2014 through April 14, 2017, the date on which the Court vacated this FERC order. (2) CL&P, NSTAR Electric, PSNH and WMECO have refunded all amounts associated with the first complaint period, totaling $38.9 million (pre-tax and excluding interest) at Eversource (consisting of $22.4 million at CL&P, $8.4 million at NSTAR Electric, $2.8 million at PSNH, and $5.3 million at WMECO), reflecting both the base ROE and incentive cap prescribed by the FERC order. (3) The reserve represents the difference between the ROEs billed during the second complaint period and a 10.57 percent base ROE and 11.74 percent incentive cap. The reserve consisted of $21.4 million for CL&P, $8.5 million for NSTAR Electric, $3.1 million for PSNH, and $6.1 million for WMECO as of September 30, 2017 . On June 5, 2017, the NETOs, including Eversource, submitted a filing to the FERC to reinstate the base ROE of 11.14 percent with an associated ROE incentive cap of 13.5 percent effective June 8, 2017, as these were the last ROEs lawfully in effect for transmission billing purposes prior to the FERC order vacated by the Court on April 14, 2017. On October 6, 2017, the FERC did not accept the NETOs filing, temporarily leaving in place the ROEs ( 10.57 percent base ROE with an 11.74 percent incentive cap ROE) set in the first complaint proceeding until the FERC addresses the Court’s decision. On October 5, 2017 the NETOs filed a series of motions, requesting that the FERC dismiss the four complaint proceedings. Alternatively, if the FERC does not dismiss the proceedings, the NETOs requested that the FERC consolidate all four complaint proceedings for expeditious resolution and/or stay the trial in the fourth complaint proceeding and resolve it based on the standards set in the April 14, 2017 Court decision. At this time, the Company cannot reasonably estimate a range of gain or loss for the complaint proceedings. The April 14, 2017 Court decision did not provide a reasonable basis for a change to the reserve balance of $39.1 million (pre-tax, excluding interest) for the second complaint period, and the Company has not changed its reserve or recognized ROEs for any of the complaint periods. Management cannot at this time predict the ultimate effect of the Court decision or future FERC action on any of the complaint periods or the estimated impacts on the financial position, results of operations or cash flows of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. The average impact of a 10 basis point change to the base ROE for each of the 15 -month complaint periods would affect Eversource's after-tax earnings by approximately $3 million . E. Eversource and NSTAR Electric Boston Harbor Civil Action On July 15, 2016, the United States Attorney on behalf of 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 alleged that the Defendants failed to comply with certain permitting requirements related to the placement of the HEEC-owned electric distribution cable beneath Boston Harbor. The action sought an order to compel HEEC to comply with cable depth requirements in the United States Army Corps of Engineers' permit or alternatively to remove the electric distribution cable and cease unauthorized work in U.S. waterways. The action also sought civil penalties and other costs. After substantial negotiations, the parties reached a settlement whereby HEEC will install a new 115 kV distribution cable across Boston Harbor to Deer Island, utilizing a different route, and will remove portions of the existing cable. Upon the installation and completion of the new cable and the removal of the portions of the existing cable, all issues surrounding the current permit from the United States Army Corps of Engineers are expected to be resolved, and such litigation is expected to be dismissed with prejudice. In 2017, as a result of the settlement, NSTAR Electric expensed $4.9 million (pre-tax) of previously incurred capitalized costs associated with engineering work performed on the existing cable that will no longer be used. In addition, NSTAR Electric agreed to provide a rate base credit of $17.5 million to the Massachusetts Water Resources Authority for the new cable. This negotiated credit will result in the initial $17.5 million of construction costs on the new cable to be expensed as incurred. Construction of the new cable is expected to be completed in 2019.

PSNH GENERATION ASSET SALE

PSNH GENERATION ASSET SALE	9 Months Ended
PSNH GENERATION ASSET SALE	Sep. 30, 2017
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. On July 1, 2016, the NHPUC approved the Agreement in an order that, among other things, instructed PSNH to begin the process of divesting its generation assets. The NHPUC selected an auction adviser to assist with the divestiture, and the final plan and auction process were approved by the NHPUC in November 2016. As of September 30, 2017 , PSNH's generation assets were as follows: (Millions of Dollars) Gross Plant $ 1,184.1 Accumulated Depreciation (573.3 ) Net Plant 610.8 Fuel 92.9 Materials and Supplies 44.0 Emission Allowances 19.4 Total Generation Assets $ 767.1 On October 11, 2017, PSNH entered into two Purchase and Sale Agreements ("Agreements") to sell its thermal and hydroelectric generation assets to private investors at purchase prices of $175 million and $83 million , respectively, subject to adjustments as set forth in each Agreement. On October 12, 2017, PSNH filed an application with the NHPUC requesting approval of the Agreements. We ex pect to receive approvals from the NHPUC and other necessary regulatory agencies by late December 2017 or early 2018, with the transactions to be completed shortly therea fter. The Company will classify these assets as held for sale upon NHPUC approval of the sale. Upon completion, full recovery of PSNH's generation assets will occur through a combination of cash flows during the remaining operating period, sales proceeds, 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.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	9 Months Ended
FAIR VALUE OF FINANCIAL INSTRUMENTS	Sep. 30, 2017
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 September 30, 2017 As of December 31, 2016 Eversource (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 160.3 $ 155.6 $ 158.3 Long-Term Debt 11,425.9 11,968.1 9,603.2 9,980.5 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 September 30, 2017: Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 115.9 $ 43.0 $ 44.4 $ — $ — $ — $ — Long-Term Debt 3,058.9 3,388.8 2,426.2 2,598.1 1,002.6 1,047.0 566.2 603.7 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 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 1D, "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)	9 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	Sep. 30, 2017
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 Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 Qualified Unrealized Qualified Unrealized Cash Flow Gains Cash Flow Gains/(Losses) Eversource (Millions of Dollars) Hedging on Marketable Defined Hedging on Marketable Defined Instruments Securities Benefit Plans Total Instruments Securities Benefit Plans Total Balance as of Beginning of Period $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 ) OCI Before Reclassifications — 0.7 (3.5 ) (2.8 ) — 2.3 (5.3 ) (3.0 ) Amounts Reclassified from AOCL 1.6 — 2.9 4.5 1.6 — 2.6 4.2 Net OCI 1.6 0.7 (0.6 ) 1.7 1.6 2.3 (2.7 ) 1.2 Balance as of End of Period $ (6.6 ) $ 1.1 $ (58.1 ) $ (63.6 ) $ (8.7 ) $ 0.4 $ (57.3 ) $ (65.6 ) 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 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. For further information, see Note 7, "Pension Benefits and Postretirement Benefits Other Than Pensions."

COMMON SHARES

COMMON SHARES	9 Months Ended
COMMON SHARES	Sep. 30, 2017
Equity [Abstract]
COMMON SHARES	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 Authorized as of September 30, 2017 and Issued as of Par Value December 31, 2016 September 30, 2017 December 31, 2016 Eversource $ 5 380,000,000 333,878,402 333,878,402 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 both September 30, 2017 and December 31, 2016 , there were 16,992,594 Eversource common shares held as treasury shares. As of both September 30, 2017 and December 31, 2016 , Eversource common shares outstanding were 316,885,808 . COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $1.9 million for both of the three months ended September 30, 2017 and 2016 , and $5.6 million for both of the nine months ended September 30, 2017 and 2016 . 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 September 30, 2017 and December 31, 2016 . 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.

COMMON SHAREHOLDERS' EQUITY AND

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	9 Months Ended
COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	Sep. 30, 2017
Equity [Abstract]
COMMON SHAREHOLDERS' 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 Authorized as of September 30, 2017 and Issued as of Par Value December 31, 2016 September 30, 2017 December 31, 2016 Eversource $ 5 380,000,000 333,878,402 333,878,402 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 both September 30, 2017 and December 31, 2016 , there were 16,992,594 Eversource common shares held as treasury shares. As of both September 30, 2017 and December 31, 2016 , Eversource common shares outstanding were 316,885,808 . COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $1.9 million for both of the three months ended September 30, 2017 and 2016 , and $5.6 million for both of the nine months ended September 30, 2017 and 2016 . 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 September 30, 2017 and December 31, 2016 . 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.

EARNINGS PER SHARE

EARNINGS PER SHARE	9 Months Ended
EARNINGS PER SHARE	Sep. 30, 2017
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 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 three and nine months ended September 30, 2017 and 2016 , there were no antidilutive share awards excluded from the computation of diluted EPS. The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Three Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Net Income Attributable to Common Shareholders $ 260.4 $ 265.3 $ 750.6 $ 713.1 Weighted Average Common Shares Outstanding: Basic 317,393,029 317,787,836 317,415,848 317,696,823 Dilutive Effect 556,367 789,243 591,194 814,786 Diluted 317,949,396 318,577,079 318,007,042 318,511,609 Basic and Diluted EPS $ 0.82 $ 0.83 $ 2.36 $ 2.24

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
SEGMENT INFORMATION	Sep. 30, 2017
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION Presentation: Eversource is organized among 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 NSTAR Electric, 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, and 4) the results of other unregulated subsidiaries, which are not part of its core business. In addition, Other in the tables below includes Eversource parent's equity ownership interests in certain natural gas pipeline projects owned by Enbridge, Inc., the Bay State Wind project, a renewable energy investment fund, and two companies that transmit hydroelectricity imported from the Hydro-Quebec system in Canada. In the ordinary course of business, Yankee Gas and NSTAR Gas purchase natural gas transmission services from the Enbridge, Inc. natural gas pipeline projects described above. These affiliate transaction costs total approximately $62.5 million annually and are classified as Purchased Power, Fuel and Transmission on the Eversource statements of income. 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. Eversource's segment information is as follows: For the Three Months Ended September 30, 2017 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 1,547.1 $ 109.2 $ 328.5 $ 224.2 $ (220.5 ) $ 1,988.5 Depreciation and Amortization (159.6 ) (15.2 ) (52.6 ) (9.5 ) 0.6 (236.3 ) Other Operating Expenses (1,088.7 ) (95.5 ) (95.5 ) (190.0 ) 220.1 (1,249.6 ) Operating Income/(Loss) $ 298.8 $ (1.5 ) $ 180.4 $ 24.7 $ 0.2 $ 502.6 Interest Expense $ (51.3 ) $ (10.8 ) $ (29.2 ) $ (21.8 ) $ 4.4 $ (108.7 ) Other Income, Net 7.7 0.3 8.5 267.5 (262.8 ) 21.2 Net Income/(Loss) Attributable to Common Shareholders 157.4 (6.2 ) 99.0 268.4 (258.2 ) 260.4 For the Nine Months Ended September 30, 2017 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 4,224.2 $ 698.8 $ 970.0 $ 677.5 $ (714.0 ) $ 5,856.5 Depreciation and Amortization (394.9 ) (54.8 ) (154.5 ) (26.7 ) 1.7 (629.2 ) Other Operating Expenses (3,056.0 ) (535.2 ) (280.4 ) (602.4 ) 714.0 (3,760.0 ) Operating Income $ 773.3 $ 108.8 $ 535.1 $ 48.4 $ 1.7 $ 1,467.3 Interest Expense $ (149.0 ) $ (32.3 ) $ (86.1 ) $ (63.1 ) $ 11.0 $ (319.5 ) Other Income, Net 15.2 0.8 20.1 853.9 (833.7 ) 56.3 Net Income Attributable to Common Shareholders 393.4 49.1 289.6 839.5 (821.0 ) 750.6 Cash Flows Used for Investments in Plant 752.4 209.8 575.6 104.5 — 1,642.3 For the Three Months Ended September 30, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 1,623.4 $ 99.2 $ 306.8 $ 211.5 $ (201.2 ) $ 2,039.7 Depreciation and Amortization (154.8 ) (15.2 ) (47.1 ) (8.6 ) 0.5 (225.2 ) Other Operating Expenses (1,146.8 ) (87.8 ) (90.2 ) (179.3 ) 199.5 (1,304.6 ) Operating Income/(Loss) $ 321.8 $ (3.8 ) $ 169.5 $ 23.6 $ (1.2 ) $ 509.9 Interest Expense $ (49.0 ) $ (10.2 ) $ (26.9 ) $ (15.1 ) $ 1.3 $ (99.9 ) Other Income, Net 5.3 0.6 6.3 256.9 (255.5 ) 13.6 Net Income/(Loss) Attributable to Common Shareholders 170.1 (7.0 ) 88.4 268.5 (254.7 ) 265.3 For the Nine Months Ended September 30, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 4,362.6 $ 622.3 $ 892.5 $ 636.8 $ (651.7 ) $ 5,862.5 Depreciation and Amortization (380.9 ) (47.9 ) (137.7 ) (23.1 ) 1.6 (588.0 ) Other Operating Expenses (3,230.1 ) (462.4 ) (245.7 ) (564.7 ) 650.2 (3,852.7 ) Operating Income $ 751.6 $ 112.0 $ 509.1 $ 49.0 $ 0.1 $ 1,421.8 Interest Expense $ (144.6 ) $ (30.8 ) $ (82.2 ) $ (45.8 ) $ 4.8 $ (298.6 ) Other Income, Net 11.6 0.5 14.2 781.4 (784.0 ) 23.7 Net Income Attributable to Common Shareholders 381.3 51.9 266.6 791.7 (778.4 ) 713.1 Cash Flows Used for Investments in Plant 570.9 170.3 536.2 81.8 — 1,359.2 The following table summarizes Eversource's segmented total assets: Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Other Eliminations Total As of September 30, 2017 $ 18,826.0 $ 3,432.6 $ 9,290.3 $ 14,939.4 $ (13,324.7 ) $ 33,163.6 As of December 31, 2016 18,367.5 3,303.8 8,751.5 14,493.1 (12,862.7 ) 32,053.2

SUMMARY OF SIGNIFICANT ACCOUN21

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation 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. On June 2, 2017, Eversource announced that it had entered into an agreement to acquire Aquarion from Macquarie Infrastructure Partners for $1.675 billion , consisting of approximately $880 million in cash and $795 million of assumed Aquarion debt. The transaction requires approval from PURA, the DPU, the NHPUC, the Maine PUC, and the Federal Communications Commission, and is also subject to a review under the Hart-Scott-Rodino Act. On June 29, 2017, Eversource and Aquarion filed joint applications with regulatory agencies in Connecticut, Massachusetts, New Hampshire and Maine requesting approval of the transaction. With the exception of Massachusetts, all state and federal regulatory agency approvals have been received and the related review period has expired. The transaction is expected to close by December 31, 2017. The unaudited condensed 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 unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P and WMECO are herein collectively referred to as the "financial statements." The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the Combined Notes to Financial Statements included in Item 8, "Financial Statements and Supplementary Data," of the Eversource 2016 Form 10-K, which was filed with the SEC. 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. The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's, PSNH's and WMECO's financial position as of September 30, 2017 and December 31, 2016 , the results of operations and comprehensive income for the three and nine months ended September 30, 2017 and 2016 , and the cash flows for the nine months ended September 30, 2017 and 2016 . The results of operations and comprehensive income for the three and nine months ended September 30, 2017 and 2016 and the cash flows for the nine months ended September 30, 2017 and 2016 are not necessarily indicative of the results expected for a full year. 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 period data were made in the accompanying financial statements to conform to the current period presentation.
Accounting Standards	Accounting Standards Accounting Standards Issued but Not Yet Effective: In May 2014, the Financial Accounting Standards Board ("FASB") issued an Accounting Standards Update ("ASU") 2014-09, Revenue from Contracts with Customers , which amends existing revenue recognition guidance and is required to be applied retrospectively (either to each reporting period presented or cumulatively at the date of initial application). The Company will implement the standard in the first quarter of 2018 cumulatively at the date of initial application. Implementation of the ASU is not expected to have a material effect on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or 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 September 30, 2017 was approximately $51 million with an unrealized gain of $1.7 million . The remaining available-for-sale equity securities included in marketable securities on the balance sheet are held in nuclear decommissioning trusts and are subject to regulatory accounting treatment and will not be impacted by this guidance. Implementation of the ASU for other financial instruments is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric, PSNH or WMECO. 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 lease criteria are required to be applied to leases and lease renewals entered into effective January 1, 2019, and leases entered into before that date 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 to be operating leases, and expects to implement the ASU in the first quarter of 2019. In March 2017, the FASB issued ASU 2017-07, Compensation – Retirement Benefits: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost , required to be implemented in the first quarter of 2018. The ASU requires separate presentation of service cost from other components of net pen sion and PBOP costs, with the other components presented as non-operating income and not subject to capitalization. The ASU is required to be applied retrospectively for the separate presentation in the income statement of service costs and other components and prospectively in the balance sheet for the capitalization of only the service cost component. The implementation of the ASU will not have an impact on the net income of Eversource, CL&P, NSTAR Electric, PSNH or WMECO.
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.
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 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products.
Other Income, Net	Other Income, Net Items included within Other Income, Net on the statements of income primarily consist of income/(loss) related to equity method investments, investment income/(loss), interest income and AFUDC related to equity funds.
Other Taxes	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. Other Taxes Gross receipts taxes levied by the state of Connecticut are collected by CL&P and Yankee Gas from their respective customers.

SUMMARY OF SIGNIFICANT ACCOUN22

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	Sep. 30, 2017
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, is included in Receivables, Net on the balance sheets, and was as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship (Millions of Dollars) As of September 30, 2017 As of December 31, 2016 As of September 30, 2017 As of December 31, 2016 Eversource $ 196.8 $ 200.6 $ 126.3 $ 119.9 CL&P 77.6 86.4 64.6 67.7 NSTAR Electric 55.7 54.8 32.3 26.2 PSNH 10.6 9.9 — — WMECO 17.0 15.5 11.3 9.9
State Of Connecticut 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 Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Eversource $ 40.3 $ 45.1 $ 118.2 $ 124.8 CL&P 37.8 42.6 103.5 112.2
Schedule of Supplemental Cash Flow Information	Non-cash investing activities include plant additions included in Accounts Payable as follows: (Millions of Dollars) As of September 30, 2017 As of September 30, 2016 Eversource $ 307.7 $ 203.6 CL&P 113.4 64.5 NSTAR Electric 55.4 39.4 PSNH 39.6 31.0 WMECO 37.1 17.6

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	9 Months Ended
REGULATORY ACCOUNTING (Tables)	Sep. 30, 2017
Regulated Operations [Abstract]
Schedule of Regulatory Assets	The components of regulatory assets were as follows: Eversource As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Benefit Costs $ 1,793.8 $ 1,817.8 Derivative Liabilities 385.1 423.3 Income Taxes, Net 652.7 644.5 Storm Restoration Costs 330.1 385.3 Goodwill-related 449.0 464.4 Regulatory Tracker Mechanisms 470.7 576.6 Asset Retirement Obligations 104.8 99.3 Other Regulatory Assets 65.8 115.1 Total Regulatory Assets 4,252.0 4,526.3 Less: Current Portion 746.1 887.6 Total Long-Term Regulatory Assets $ 3,505.9 $ 3,638.7 As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Benefit Costs $ 415.8 $ 436.7 $ 183.2 $ 84.8 $ 429.3 $ 438.6 $ 184.2 $ 86.7 Derivative Liabilities 381.6 2.4 — — 420.5 2.8 — — Income Taxes, Net 441.1 92.4 22.3 30.5 437.0 89.7 24.2 30.8 Storm Restoration Costs 195.7 112.4 9.2 12.8 239.8 112.5 17.1 15.9 Goodwill-related — 385.5 — — — 398.7 — — Regulatory Tracker Mechanisms 87.9 201.1 108.0 44.4 123.9 257.3 104.5 46.7 Asset Retirement Obligations 35.1 33.9 16.8 4.5 33.2 31.9 16.2 4.2 Other Regulatory Assets 30.0 15.5 17.6 5.4 43.4 15.6 16.5 7.1 Total Regulatory Assets 1,587.2 1,279.9 357.1 182.4 1,727.1 1,347.1 362.7 191.4 Less: Current Portion 275.0 230.6 112.5 60.6 335.5 289.4 117.2 64.1 Total Long-Term Regulatory Assets $ 1,312.2 $ 1,049.3 $ 244.6 $ 121.8 $ 1,391.6 $ 1,057.7 $ 245.5 $ 127.3
Schedule of Regulatory Liabilities	The components of regulatory liabilities were as follows: Eversource As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Cost of Removal $ 470.3 $ 459.7 Benefit Costs 125.5 136.2 Regulatory Tracker Mechanisms 175.8 145.3 AFUDC - Transmission 65.4 65.8 Other Regulatory Liabilities 33.4 42.1 Total Regulatory Liabilities 870.4 849.1 Less: Current Portion 170.2 146.8 Total Long-Term Regulatory Liabilities $ 700.2 $ 702.3 As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Cost of Removal $ 40.5 $ 278.8 $ 40.5 $ 11.7 $ 38.8 $ 271.6 $ 44.1 $ 8.6 Benefit Costs — 106.0 — — — 113.1 — — Regulatory Tracker Mechanisms 57.1 65.5 5.6 12.7 37.2 63.7 10.7 14.7 AFUDC - Transmission 49.2 7.7 — 8.5 50.2 6.9 — 8.7 Other Regulatory Liabilities 21.3 0.4 2.6 — 21.0 0.2 2.7 0.1 Total Regulatory Liabilities 168.1 458.4 48.7 32.9 147.2 455.5 57.5 32.1 Less: Current Portion 69.3 65.5 7.9 10.2 47.1 63.7 12.7 14.9 Total Long-Term Regulatory Liabilities $ 98.8 $ 392.9 $ 40.8 $ 22.7 $ 100.1 $ 391.8 $ 44.8 $ 17.2

PROPERTY, PLANT AND EQUIPMENT24

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)	9 Months Ended
	Sep. 30, 2017
Property, Plant and Equipment [Abstract]
Public Utility Property, Plant, and Equipment	The following tables summarize property, plant and equipment by asset category: Eversource As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) Distribution - Electric $ 14,217.3 $ 13,716.9 Distribution - Natural Gas 3,158.1 3,010.4 Transmission - Electric 8,918.2 8,517.4 Generation 1,215.8 1,224.2 Electric and Natural Gas Utility 27,509.4 26,468.9 Other (1) 679.9 591.6 Property, Plant and Equipment, Gross 28,189.3 27,060.5 Less: Accumulated Depreciation Electric and Natural Gas Utility (6,838.5 ) (6,480.4 ) Other (274.4 ) (242.0 ) Total Accumulated Depreciation (7,112.9 ) (6,722.4 ) Property, Plant and Equipment, Net 21,076.4 20,338.1 Construction Work in Progress (2) 1,460.9 1,012.4 Total Property, Plant and Equipment, Net $ 22,537.3 $ 21,350.5 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. (2) As of September 30, 2017 , the total CWIP related to NPT was approximately $201 million . As of September 30, 2017 As of December 31, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Distribution $ 5,797.6 $ 5,543.1 $ 2,048.8 $ 868.1 $ 5,562.9 $ 5,402.3 $ 1,949.8 $ 841.9 Transmission 4,061.2 2,545.0 1,115.7 1,147.9 3,912.9 2,435.8 1,059.3 1,061.1 Generation — — 1,179.8 36.0 — — 1,188.2 36.0 Property, Plant and Equipment, Gross 9,858.8 8,088.1 4,344.3 2,052.0 9,475.8 7,838.1 4,197.3 1,939.0 Less: Accumulated Depreciation (2,207.0 ) (2,143.8 ) (1,315.7 ) (356.5 ) (2,082.4 ) (2,025.4 ) (1,254.7 ) (338.8 ) Property, Plant and Equipment, Net 7,651.8 5,944.3 3,028.6 1,695.5 7,393.4 5,812.7 2,942.6 1,600.2 Construction Work in Progress 456.2 324.4 139.3 74.1 239.0 239.1 96.7 78.1 Total Property, Plant and Equipment, Net $ 8,108.0 $ 6,268.7 $ 3,167.9 $ 1,769.6 $ 7,632.4 $ 6,051.8 $ 3,039.3 $ 1,678.3

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	9 Months Ended
DERIVATIVE INSTRUMENTS (Tables)	Sep. 30, 2017
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 September 30, 2017 As of December 31, 2016 (Millions of Dollars) Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: Level 2: Eversource $ — $ — $ — $ 6.0 $ — $ 6.0 Level 3: CL&P 10.4 (7.7 ) 2.7 13.9 (9.4 ) 4.5 Long-Term Derivative Assets: Level 2: Eversource $ — $ — $ — $ 0.3 $ (0.1 ) $ 0.2 Level 3: CL&P 74.3 (6.9 ) 67.4 77.3 (11.7 ) 65.6 Current Derivative Liabilities: Level 2: Eversource $ (1.5 ) $ 0.4 $ (1.1 ) $ — $ — $ — Level 3: Eversource (62.2 ) — (62.2 ) (79.7 ) — (79.7 ) CL&P (59.9 ) — (59.9 ) (77.8 ) — (77.8 ) NSTAR Electric (2.3 ) — (2.3 ) (1.9 ) — (1.9 ) Long-Term Derivative Liabilities: Level 3: Eversource $ (391.9 ) $ — $ (391.9 ) $ (413.7 ) $ — $ (413.7 ) CL&P (391.8 ) — (391.8 ) (412.8 ) — (412.8 ) NSTAR Electric (0.1 ) — (0.1 ) (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 September 30, 2017 As of December 31, 2016 Range Period Covered Range Period Covered Capacity Prices: CL&P $ 5.00 — 8.70 per kW-Month 2021 - 2026 $ 5.50 — 8.70 per kW-Month 2020 - 2026 Forward Reserve: CL&P $ 1.00 — 2.00 per kW-Month 2017 - 2024 $ 1.40 — 2.00 per kW-Month 2017 - 2024 REC Prices: NSTAR Electric $ 15.75 — 22.00 per REC 2017 - 2018 $ 24.00 — 29.00 per REC 2017 - 2018
Rollforward Of Net Derivative Asset Liabilities Valued Using 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. For the Three Months Ended September 30, 2017 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric Eversource CL&P NSTAR Derivatives, Net: Fair Value as of Beginning of Period $ (397.1 ) $ (394.8 ) $ (2.3 ) $ (412.6 ) $ (411.3 ) $ (1.3 ) Net Realized/Unrealized Gains/Losses Included in Regulatory Assets and Liabilities 0.5 (0.7 ) 1.2 (52.3 ) (49.8 ) (2.5 ) Settlements 12.6 13.9 (1.3 ) 21.2 20.1 1.1 Fair Value as of End of Period $ (384.0 ) $ (381.6 ) $ (2.4 ) $ (443.7 ) $ (441.0 ) $ (2.7 ) For the Nine Months Ended September 30, 2017 2016 (Millions of Dollars) Eversource CL&P NSTAR Eversource CL&P NSTAR Derivatives, Net: Fair Value as of Beginning of Period $ (423.3 ) $ (420.5 ) $ (2.8 ) $ (380.9 ) $ (380.8 ) $ (0.1 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (17.9 ) (15.9 ) (2.0 ) (128.9 ) (122.0 ) (6.9 ) Settlements 57.2 54.8 2.4 66.1 61.8 4.3 Fair Value as of End of Period $ (384.0 ) $ (381.6 ) $ (2.4 ) $ (443.7 ) $ (441.0 ) $ (2.7 )

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	9 Months Ended
MARKETABLE SECURITIES (Tables)	Sep. 30, 2017
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 September 30, 2017 As of December 31, 2016 Eversource (Millions of Dollars) Amortized Cost Pre-Tax Unrealized Gains Pre-Tax Unrealized Losses Fair Value Amortized Cost Pre-Tax Unrealized Gains Pre-Tax Unrealized Losses Fair Value Debt Securities $ 286.5 $ 5.5 $ (0.5 ) $ 291.5 $ 296.2 $ 1.1 $ (2.1 ) $ 295.2 Equity Securities 210.7 81.5 — 292.2 203.3 62.3 (1.2 ) 264.4
Investments Classified by Contractual Maturity Date	As of September 30, 2017 , 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) $ 40.2 $ 40.2 One to five years 56.7 57.6 Six to ten years 52.6 54.1 Greater than ten years 137.0 139.6 Total Debt Securities $ 286.5 $ 291.5 (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 on a Recurring Basis	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 September 30, 2017 As of December 31, 2016 Level 1: Mutual Funds and Equities $ 292.2 $ 274.0 Money Market Funds 21.8 54.8 Total Level 1 $ 314.0 $ 328.8 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 69.0 $ 63.0 Corporate Debt Securities 56.1 41.1 Asset-Backed Debt Securities 20.4 18.5 Municipal Bonds 113.6 107.5 Other Fixed Income Securities 10.6 10.3 Total Level 2 $ 269.7 $ 240.4 Total Marketable Securities $ 583.7 $ 569.2

PENSION BENEFITS AND POSTRETI27

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS (Tables)	9 Months Ended
	Sep. 30, 2017
Postemployment Benefits [Abstract]
Schedule of Net Benefit Costs	The components of net periodic benefit expense for the Pension, SERP and PBOP Plans are shown below. The net periodic benefit expense and the intercompany allocations, less the capitalized portions of pension, SERP and PBOP amounts, are included in Operations and Maintenance expense on the statements of income. Capitalized amounts relate to employees working on capital projects and are included in Property, Plant and Equipment, Net on the balance sheets. Pension, SERP and 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. Pension and SERP Eversource For the Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Service Cost $ 17.4 $ 18.6 $ 53.8 $ 56.6 Interest Cost 47.2 46.4 140.7 139.2 Expected Return on Pension Plan Assets (83.5 ) (79.4 ) (250.5 ) (238.5 ) Actuarial Loss 33.9 31.4 101.3 94.2 Prior Service Cost 1.2 0.9 3.4 2.6 Total Net Periodic Benefit Expense $ 16.2 $ 17.9 $ 48.7 $ 54.1 Capitalized Pension Expense $ 5.5 $ 5.4 $ 16.5 $ 16.8 PBOP Eversource For the Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Service Cost $ 2.4 $ 3.0 $ 7.1 $ 9.2 Interest Cost 6.8 7.5 20.3 26.5 Expected Return on Plan Assets (16.0 ) (15.9 ) (47.8 ) (47.3 ) Actuarial Loss 2.2 3.0 6.9 5.0 Prior Service Credit (5.3 ) (3.6 ) (16.1 ) (3.7 ) Total Net Periodic Benefit Income $ (9.9 ) $ (6.0 ) $ (29.6 ) $ (10.3 ) Capitalized PBOP Income $ (4.8 ) $ (2.6 ) $ (14.3 ) $ (4.6 ) Pension and SERP For the Three Months Ended September 30, 2017 For the Three Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 4.6 $ 3.1 $ 2.4 $ 0.7 $ 4.6 $ 3.3 $ 2.5 $ 0.8 Interest Cost 10.5 8.6 5.3 2.1 10.2 8.5 5.1 2.1 Expected Return on Pension Plan Assets (17.8 ) (17.5 ) (10.0 ) (4.4 ) (18.0 ) (16.9 ) (9.6 ) (4.4 ) Actuarial Loss 6.8 8.9 3.0 1.5 6.3 8.7 2.5 1.3 Prior Service Cost 0.4 0.1 0.1 0.1 0.4 — 0.1 0.1 Total Net Periodic Benefit Expense/(Income) $ 4.5 $ 3.2 $ 0.8 $ — $ 3.5 $ 3.6 $ 0.6 $ (0.1 ) Intercompany Allocations $ 2.4 $ 1.8 $ 0.8 $ 0.5 $ 3.5 $ 2.2 $ 1.0 $ 0.6 Capitalized Pension Expense $ 2.4 $ 1.9 $ 0.4 $ 0.1 $ 2.2 $ 2.0 $ 0.4 $ 0.1 Pension and SERP For the Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 13.9 $ 9.4 $ 7.3 $ 2.3 $ 14.3 $ 9.9 $ 7.5 $ 2.4 Interest Cost 31.3 25.6 15.9 6.3 31.2 25.3 15.4 6.3 Expected Return on Pension Plan Assets (53.9 ) (52.5 ) (29.9 ) (13.3 ) (54.2 ) (50.7 ) (28.9 ) (13.1 ) Actuarial Loss 20.7 26.4 8.7 4.5 19.2 25.8 7.5 4.1 Prior Service Cost 1.1 0.2 0.4 0.2 1.1 — 0.3 0.2 Total Net Periodic Benefit Expense/(Income) $ 13.1 $ 9.1 $ 2.4 $ — $ 11.6 $ 10.3 $ 1.8 $ (0.1 ) Intercompany Allocations $ 7.4 $ 5.5 $ 2.5 $ 1.4 $ 10.3 $ 6.7 $ 3.0 $ 1.9 Capitalized Pension Expense $ 7.3 $ 5.4 $ 1.1 $ 0.3 $ 7.1 $ 5.7 $ 1.0 $ 0.3 PBOP For the Three Months Ended September 30, 2017 For the Three Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 0.5 $ 0.3 $ 0.3 $ 0.1 $ 0.6 $ 0.6 $ 0.4 $ 0.1 Interest Cost 1.3 1.9 0.8 0.3 1.3 2.5 0.7 0.3 Expected Return on Plan Assets (2.4 ) (6.6 ) (1.4 ) (0.6 ) (2.5 ) (6.4 ) (1.4 ) (0.6 ) Actuarial Loss 0.2 0.9 0.1 — 0.5 1.2 0.2 — Prior Service Cost/(Credit) 0.3 (4.3 ) 0.2 — 0.2 (2.9 ) 0.1 — Total Net Periodic Benefit (Income)/Expense $ (0.1 ) $ (7.8 ) $ — $ (0.2 ) $ 0.1 $ (5.0 ) $ — $ (0.2 ) Intercompany Allocations $ (0.2 ) $ (0.2 ) $ (0.1 ) $ — $ — $ (0.1 ) $ — $ — Capitalized PBOP Income $ (0.1 ) $ (4.0 ) $ — $ (0.1 ) $ — $ (2.2 ) $ — $ (0.1 ) PBOP For the Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH WMECO CL&P NSTAR Electric PSNH WMECO Service Cost $ 1.5 $ 1.1 $ 1.0 $ 0.3 $ 1.4 $ 2.5 $ 0.9 $ 0.3 Interest Cost 4.0 5.7 2.3 0.8 4.0 10.3 2.2 0.8 Expected Return on Plan Assets (7.3 ) (19.9 ) (4.1 ) (1.7 ) (7.6 ) (19.2 ) (4.2 ) (1.7 ) Actuarial Loss 0.7 2.6 0.4 — 0.9 1.7 0.5 — Prior Service Cost/(Credit) 0.8 (12.9 ) 0.4 0.1 0.2 (2.9 ) 0.1 — Total Net Periodic Benefit Income $ (0.3 ) $ (23.4 ) $ — $ (0.5 ) $ (1.1 ) $ (7.6 ) $ (0.5 ) $ (0.6 ) Intercompany Allocations $ (0.5 ) $ (0.7 ) $ (0.3 ) $ (0.1 ) $ 0.3 $ — $ — $ — Capitalized PBOP Income $ (0.4 ) $ (11.9 ) $ — $ (0.2 ) $ (0.5 ) $ (3.3 ) $ — $ (0.3 )

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
COMMITMENTS AND CONTINGENCIES (Tables)	Sep. 30, 2017
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 September 30, 2017 As of December 31, 2016 Number of Sites Reserve (in millions) Number of Sites Reserve (in millions) Eversource 58 $ 57.7 61 $ 65.8 CL&P 14 4.9 14 4.9 NSTAR Electric 10 2.0 13 3.2 PSNH 11 5.7 11 5.3 WMECO 4 0.8 4 0.6
Schedule of Guarantor Obligations	The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries to external parties, as of September 30, 2017 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty (1) $ 185.1 2021 Various Surety Bonds (2) 40.1 2017 - 2018 Eversource Service and Rocky River Realty Company Lease Payments for Vehicles and Real Estate 8.2 2019 - 2024 (1) Eversource parent issued a declining balance guaranty on behalf of its subsidiary, Eversource Gas Transmission LLC, to guarantee the payment of the subsidiary's capital contributions for its investment in the Access Northeast project. The guaranty 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. (2) 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.
Schedule of Complaints and Base ROE	A summary of the four separate complaints and the base ROEs pertinent to those complaints are as follows: Complaint 15-Month Time Period of Complaint (Beginning as of Complaint Filing Date) Original Base ROE Authorized by FERC at Time of Complaint Filing Date (1) Base ROE Subsequently Authorized by FERC for First Complaint Period and also Effective from October 16, 2014 through April 14, 2017 (1) Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions) FERC ALJ Recommendation of Base ROE on Second and Third Complaints (Issued March 22, 2016) First 10/1/2011 - 12/31/2012 11.14% 10.57% $— (2) N/A Second 12/27/2012 - 3/26/2014 11.14% N/A 39.1 (3) 9.59% Third 7/31/2014 - 10/30/2015 11.14% 10.57% — 10.90% Fourth 4/29/2016 - 7/28/2017 10.57% 10.57% — N/A (1) The billed ROE (base plus incentives) between October 1, 2011 and October 15, 2014 was within a range of 11.14 percent to 13.1 percent . On October 16, 2014, the FERC set the incentive cap at 11.74 percent for the first complaint period and also effective from October 16, 2014 through April 14, 2017, the date on which the Court vacated this FERC order. (2) CL&P, NSTAR Electric, PSNH and WMECO have refunded all amounts associated with the first complaint period, totaling $38.9 million (pre-tax and excluding interest) at Eversource (consisting of $22.4 million at CL&P, $8.4 million at NSTAR Electric, $2.8 million at PSNH, and $5.3 million at WMECO), reflecting both the base ROE and incentive cap prescribed by the FERC order. (3) The reserve represents the difference between the ROEs billed during the second complaint period and a 10.57 percent base ROE and 11.74 percent incentive cap. The reserve consisted of $21.4 million for CL&P, $8.5 million for NSTAR Electric, $3.1 million for PSNH, and $6.1 million for WMECO as of September 30, 2017 .

PSNH GENERATION ASSET SALE - (T

PSNH GENERATION ASSET SALE - (Tables)	9 Months Ended
PSNH GENERATION ASSET SALE - (Tables)	Sep. 30, 2017
Regulated Operations [Abstract]
Schedule of Generation Assets and Liabilities	As of September 30, 2017 , PSNH's generation assets were as follows: (Millions of Dollars) Gross Plant $ 1,184.1 Accumulated Depreciation (573.3 ) Net Plant 610.8 Fuel 92.9 Materials and Supplies 44.0 Emission Allowances 19.4 Total Generation Assets $ 767.1

FAIR VALUE OF FINANCIAL INSTR30

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping	Carrying amounts and estimated fair values are as follows: As of September 30, 2017 As of December 31, 2016 Eversource (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 160.3 $ 155.6 $ 158.3 Long-Term Debt 11,425.9 11,968.1 9,603.2 9,980.5 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 September 30, 2017: Preferred Stock Not Subject to Mandatory Redemption $ 116.2 $ 115.9 $ 43.0 $ 44.4 $ — $ — $ — $ — Long-Term Debt 3,058.9 3,388.8 2,426.2 2,598.1 1,002.6 1,047.0 566.2 603.7 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

ACCUMULATED OTHER COMPREHENSI31

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	9 Months Ended
ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	Sep. 30, 2017
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 Nine Months Ended September 30, 2017 For the Nine Months Ended September 30, 2016 Qualified Unrealized Qualified Unrealized Cash Flow Gains Cash Flow Gains/(Losses) Eversource (Millions of Dollars) Hedging on Marketable Defined Hedging on Marketable Defined Instruments Securities Benefit Plans Total Instruments Securities Benefit Plans Total Balance as of Beginning of Period $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) $ (10.3 ) $ (1.9 ) $ (54.6 ) $ (66.8 ) OCI Before Reclassifications — 0.7 (3.5 ) (2.8 ) — 2.3 (5.3 ) (3.0 ) Amounts Reclassified from AOCL 1.6 — 2.9 4.5 1.6 — 2.6 4.2 Net OCI 1.6 0.7 (0.6 ) 1.7 1.6 2.3 (2.7 ) 1.2 Balance as of End of Period $ (6.6 ) $ 1.1 $ (58.1 ) $ (63.6 ) $ (8.7 ) $ 0.4 $ (57.3 ) $ (65.6 )

COMMON SHARES (Tables)

COMMON SHARES (Tables)	9 Months Ended
COMMON SHARES (Tables)	Sep. 30, 2017
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 Authorized as of September 30, 2017 and Issued as of Par Value December 31, 2016 September 30, 2017 December 31, 2016 Eversource $ 5 380,000,000 333,878,402 333,878,402 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

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	9 Months Ended
EARNINGS PER SHARE (Tables)	Sep. 30, 2017
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 Three Months Ended For the Nine Months Ended September 30, 2017 September 30, 2016 September 30, 2017 September 30, 2016 Net Income Attributable to Common Shareholders $ 260.4 $ 265.3 $ 750.6 $ 713.1 Weighted Average Common Shares Outstanding: Basic 317,393,029 317,787,836 317,415,848 317,696,823 Dilutive Effect 556,367 789,243 591,194 814,786 Diluted 317,949,396 318,577,079 318,007,042 318,511,609 Basic and Diluted EPS $ 0.82 $ 0.83 $ 2.36 $ 2.24

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
SEGMENT INFORMATION (Tables)	Sep. 30, 2017
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Eversource's segment information is as follows: For the Three Months Ended September 30, 2017 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 1,547.1 $ 109.2 $ 328.5 $ 224.2 $ (220.5 ) $ 1,988.5 Depreciation and Amortization (159.6 ) (15.2 ) (52.6 ) (9.5 ) 0.6 (236.3 ) Other Operating Expenses (1,088.7 ) (95.5 ) (95.5 ) (190.0 ) 220.1 (1,249.6 ) Operating Income/(Loss) $ 298.8 $ (1.5 ) $ 180.4 $ 24.7 $ 0.2 $ 502.6 Interest Expense $ (51.3 ) $ (10.8 ) $ (29.2 ) $ (21.8 ) $ 4.4 $ (108.7 ) Other Income, Net 7.7 0.3 8.5 267.5 (262.8 ) 21.2 Net Income/(Loss) Attributable to Common Shareholders 157.4 (6.2 ) 99.0 268.4 (258.2 ) 260.4 For the Nine Months Ended September 30, 2017 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 4,224.2 $ 698.8 $ 970.0 $ 677.5 $ (714.0 ) $ 5,856.5 Depreciation and Amortization (394.9 ) (54.8 ) (154.5 ) (26.7 ) 1.7 (629.2 ) Other Operating Expenses (3,056.0 ) (535.2 ) (280.4 ) (602.4 ) 714.0 (3,760.0 ) Operating Income $ 773.3 $ 108.8 $ 535.1 $ 48.4 $ 1.7 $ 1,467.3 Interest Expense $ (149.0 ) $ (32.3 ) $ (86.1 ) $ (63.1 ) $ 11.0 $ (319.5 ) Other Income, Net 15.2 0.8 20.1 853.9 (833.7 ) 56.3 Net Income Attributable to Common Shareholders 393.4 49.1 289.6 839.5 (821.0 ) 750.6 Cash Flows Used for Investments in Plant 752.4 209.8 575.6 104.5 — 1,642.3 For the Three Months Ended September 30, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 1,623.4 $ 99.2 $ 306.8 $ 211.5 $ (201.2 ) $ 2,039.7 Depreciation and Amortization (154.8 ) (15.2 ) (47.1 ) (8.6 ) 0.5 (225.2 ) Other Operating Expenses (1,146.8 ) (87.8 ) (90.2 ) (179.3 ) 199.5 (1,304.6 ) Operating Income/(Loss) $ 321.8 $ (3.8 ) $ 169.5 $ 23.6 $ (1.2 ) $ 509.9 Interest Expense $ (49.0 ) $ (10.2 ) $ (26.9 ) $ (15.1 ) $ 1.3 $ (99.9 ) Other Income, Net 5.3 0.6 6.3 256.9 (255.5 ) 13.6 Net Income/(Loss) Attributable to Common Shareholders 170.1 (7.0 ) 88.4 268.5 (254.7 ) 265.3 For the Nine Months Ended September 30, 2016 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Other Eliminations Total Operating Revenues $ 4,362.6 $ 622.3 $ 892.5 $ 636.8 $ (651.7 ) $ 5,862.5 Depreciation and Amortization (380.9 ) (47.9 ) (137.7 ) (23.1 ) 1.6 (588.0 ) Other Operating Expenses (3,230.1 ) (462.4 ) (245.7 ) (564.7 ) 650.2 (3,852.7 ) Operating Income $ 751.6 $ 112.0 $ 509.1 $ 49.0 $ 0.1 $ 1,421.8 Interest Expense $ (144.6 ) $ (30.8 ) $ (82.2 ) $ (45.8 ) $ 4.8 $ (298.6 ) Other Income, Net 11.6 0.5 14.2 781.4 (784.0 ) 23.7 Net Income Attributable to Common Shareholders 381.3 51.9 266.6 791.7 (778.4 ) 713.1 Cash Flows Used for Investments in Plant 570.9 170.3 536.2 81.8 — 1,359.2 The following table summarizes Eversource's segmented total assets: Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Other Eliminations Total As of September 30, 2017 $ 18,826.0 $ 3,432.6 $ 9,290.3 $ 14,939.4 $ (13,324.7 ) $ 33,163.6 As of December 31, 2016 18,367.5 3,303.8 8,751.5 14,493.1 (12,862.7 ) 32,053.2

SUMMARY OF SIGNIFICANT ACCOUN35

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Basis of Presentation (Details) customer in Millions, $ in Millions	Jun. 02, 2017USD ($)	Sep. 30, 2017customerutility
Schedule of Equity Method Investments [Line Items]
Number of electric and natural gas customers \| customer		3.7
Connecticut, Massachusetts and New Hampshire
Schedule of Equity Method Investments [Line Items]
Number of regulated utilities \| utility		6
Aquarion Water Company
Schedule of Equity Method Investments [Line Items]
Amount involved in acquisition of Aquarion	$ 1,675
Cash paid to acquire Aquarion	880
Liability assumed in acquisition of Aquarion	$ 795

SUMMARY OF SIGNIFICANT ACCOUN36

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounting Standards (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017USD ($)
Accounting Policies [Abstract]
Available for sale securities subject to new accounting guidance	$ 51
Available-for-sale securities, gross unrealized gain	$ 1.7

SUMMARY OF SIGNIFICANT ACCOUN37

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts Narrative (Details)	9 Months Ended
	Sep. 30, 2017
Maximum \| The Connecticut Light And Power Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of accounts receivable recoverable under financial or medical duress	180 days
Minimum \| Yankee Gas Services Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of accounts receivable recoverable under financial or medical duress	90 days

SUMMARY OF SIGNIFICANT ACCOUN38

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	$ 196.8	$ 200.6
Uncollectible Hardship	126.3	119.9
The Connecticut Light And Power Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	77.6	86.4
Uncollectible Hardship	64.6	67.7
NSTAR Electric Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	55.7	54.8
Uncollectible Hardship	32.3	26.2
Public Service Company Of New Hampshire
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	10.6	9.9
Uncollectible Hardship	0	0
Western Massachusetts Electric Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	17	15.5
Uncollectible Hardship	$ 11.3	$ 9.9

SUMMARY OF SIGNIFICANT ACCOUN39

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income, Net Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other Income, Net [Line Items]
Other Income, Net	$ 21,184	$ 13,641	$ 56,304	$ 23,689
Equity Method Investments
Other Income, Net [Line Items]
Other Income, Net	$ 5,100	$ 900	$ 23,000	$ (2,000)

SUMMARY OF SIGNIFICANT ACCOUN40

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Gross Tax Receipts [Line Items]
Excise and sales taxes	$ 40.3	$ 45.1	$ 118.2	$ 124.8
The Connecticut Light And Power Company
Schedule of Gross Tax Receipts [Line Items]
Excise and sales taxes	$ 37.8	$ 42.6	$ 103.5	$ 112.2

SUMMARY OF SIGNIFICANT ACCOUN41

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Schedule of Supplemental Cash Flow [Line Items]
Capital expenditures incurred but not yet paid	$ 307.7	$ 203.6
The Connecticut Light And Power Company
Schedule of Supplemental Cash Flow [Line Items]
Capital expenditures incurred but not yet paid	113.4	64.5
NSTAR Electric Company
Schedule of Supplemental Cash Flow [Line Items]
Capital expenditures incurred but not yet paid	55.4	39.4
Public Service Company Of New Hampshire
Schedule of Supplemental Cash Flow [Line Items]
Capital expenditures incurred but not yet paid	39.6	31
Western Massachusetts Electric Company
Schedule of Supplemental Cash Flow [Line Items]
Capital expenditures incurred but not yet paid	$ 37.1	$ 17.6

REGULATORY ACCOUNTING - Compone

REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 4,252,000	$ 4,526,300
Less: Current Portion	746,142	887,625
Total Long-Term Regulatory Assets	3,505,901	3,638,688
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,793,800	1,817,800
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	385,100	423,300
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	652,700	644,500
Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	330,100	385,300
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	449,000	464,400
Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	470,700	576,600
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	104,800	99,300
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	65,800	115,100
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Total Regulatory Assets	1,587,200	1,727,100
Less: Current Portion	274,982	335,526
Total Long-Term Regulatory Assets	1,312,191	1,391,564
The Connecticut Light And Power Company \| Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	415,800	429,300
The Connecticut Light And Power Company \| Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	381,600	420,500
The Connecticut Light And Power Company \| Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	441,100	437,000
The Connecticut Light And Power Company \| Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	195,700	239,800
The Connecticut Light And Power Company \| Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light And Power Company \| Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	87,900	123,900
The Connecticut Light And Power Company \| Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	35,100	33,200
The Connecticut Light And Power Company \| Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	30,000	43,400
NSTAR Electric Company
Regulatory Assets [Line Items]
Total Regulatory Assets	1,279,900	1,347,100
Less: Current Portion	230,620	289,400
Total Long-Term Regulatory Assets	1,049,324	1,057,746
NSTAR Electric Company \| Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	436,700	438,600
NSTAR Electric Company \| Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	2,400	2,800
NSTAR Electric Company \| Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	92,400	89,700
NSTAR Electric Company \| Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	112,400	112,500
NSTAR Electric Company \| Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	385,500	398,700
NSTAR Electric Company \| Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	201,100	257,300
NSTAR Electric Company \| Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	33,900	31,900
NSTAR Electric Company \| Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	15,500	15,600
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Total Regulatory Assets	357,100	362,700
Less: Current Portion	112,465	117,240
Total Long-Term Regulatory Assets	244,561	245,525
Public Service Company Of New Hampshire \| Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	183,200	184,200
Public Service Company Of New Hampshire \| Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire \| Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	22,300	24,200
Public Service Company Of New Hampshire \| Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	9,200	17,100
Public Service Company Of New Hampshire \| Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire \| Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	108,000	104,500
Public Service Company Of New Hampshire \| Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	16,800	16,200
Public Service Company Of New Hampshire \| Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	17,600	16,500
Western Massachusetts Electric Company
Regulatory Assets [Line Items]
Total Regulatory Assets	182,400	191,400
Less: Current Portion	60,606	64,123
Total Long-Term Regulatory Assets	121,796	127,291
Western Massachusetts Electric Company \| Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	84,800	86,700
Western Massachusetts Electric Company \| Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Western Massachusetts Electric Company \| Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	30,500	30,800
Western Massachusetts Electric Company \| Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	12,800	15,900
Western Massachusetts Electric Company \| Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Western Massachusetts Electric Company \| Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	44,400	46,700
Western Massachusetts Electric Company \| Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	4,500	4,200
Western Massachusetts Electric Company \| Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,400	$ 7,100

REGULATORY ACCOUNTING - Regulat

REGULATORY ACCOUNTING - Regulatory Costs in Other Long-Term Assets (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 108.7	$ 86.3
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	3.9	5.9
NSTAR Electric Company
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	42.3	35
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	18.5	8.2
Western Massachusetts Electric Company
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 25.7	$ 20.1

REGULATORY ACCOUNTING - Compo44

REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 870,400	$ 849,100
Less: Current Portion	170,215	146,787
Total Long-Term Regulatory Liabilities	700,207	702,255
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	470,300	459,700
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	125,500	136,200
Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	175,800	145,300
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	65,400	65,800
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	33,400	42,100
The Connecticut Light And Power Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	168,100	147,200
Less: Current Portion	69,296	47,055
Total Long-Term Regulatory Liabilities	98,777	100,138
The Connecticut Light And Power Company \| Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	40,500	38,800
The Connecticut Light And Power Company \| Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
The Connecticut Light And Power Company \| Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	57,100	37,200
The Connecticut Light And Power Company \| AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	49,200	50,200
The Connecticut Light And Power Company \| Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	21,300	21,000
NSTAR Electric Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	458,400	455,500
Less: Current Portion	65,520	63,653
Total Long-Term Regulatory Liabilities	392,851	391,823
NSTAR Electric Company \| Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	278,800	271,600
NSTAR Electric Company \| Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	106,000	113,100
NSTAR Electric Company \| Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	65,500	63,700
NSTAR Electric Company \| AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	7,700	6,900
NSTAR Electric Company \| Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	400	200
Public Service Company Of New Hampshire
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	48,700	57,500
Less: Current Portion	7,923	12,659
Total Long-Term Regulatory Liabilities	40,822	44,779
Public Service Company Of New Hampshire \| Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	40,500	44,100
Public Service Company Of New Hampshire \| Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company Of New Hampshire \| Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	5,600	10,700
Public Service Company Of New Hampshire \| AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company Of New Hampshire \| Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,600	2,700
Western Massachusetts Electric Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	32,900	32,100
Less: Current Portion	10,236	14,888
Total Long-Term Regulatory Liabilities	22,726	17,227
Western Massachusetts Electric Company \| Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	11,700	8,600
Western Massachusetts Electric Company \| Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Western Massachusetts Electric Company \| Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	12,700	14,700
Western Massachusetts Electric Company \| AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,500	8,700
Western Massachusetts Electric Company \| Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 0	$ 100

PROPERTY, PLANT AND EQUIPMENT45

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, plant and equipment by asset (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 14,217,300	$ 13,716,900
Distribution - Natural Gas	3,158,100	3,010,400
Transmission	8,918,200	8,517,400
Generation	1,215,800	1,224,200
Electric and Natural Gas Utility	27,509,400	26,468,900
Other	679,900	591,600
Property, Plant and Equipment, Gross	28,189,300	27,060,500
Less: Accumulated Depreciation
Electric and Natural Gas Utility	(6,838,500)	(6,480,400)
Other	(274,400)	(242,000)
Total Accumulated Depreciation	(7,112,900)	(6,722,400)
Property, Plant and Equipment, Net	21,076,400	20,338,100
Construction Work in Progress	1,460,900	1,012,400
Net Plant	22,537,304	21,350,510
Construction work in progress related to NPT	201,000
The Connecticut Light And Power Company
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	5,797,600	5,562,900
Transmission	4,061,200	3,912,900
Generation	0	0
Property, Plant and Equipment, Gross	9,858,800	9,475,800
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,207,000)	(2,082,400)
Property, Plant and Equipment, Net	7,651,800	7,393,400
Construction Work in Progress	456,200	239,000
Net Plant	8,107,957	7,632,392
NSTAR Electric Company
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	5,543,100	5,402,300
Transmission	2,545,000	2,435,800
Generation	0	0
Property, Plant and Equipment, Gross	8,088,100	7,838,100
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,143,800)	(2,025,400)
Property, Plant and Equipment, Net	5,944,300	5,812,700
Construction Work in Progress	324,400	239,100
Net Plant	6,268,689	6,051,835
Public Service Company Of New Hampshire
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,048,800	1,949,800
Transmission	1,115,700	1,059,300
Generation	1,179,800	1,188,200
Property, Plant and Equipment, Gross	4,344,300	4,197,300
Less: Accumulated Depreciation
Total Accumulated Depreciation	(1,315,700)	(1,254,700)
Property, Plant and Equipment, Net	3,028,600	2,942,600
Construction Work in Progress	139,300	96,700
Net Plant	3,167,905	3,039,313
Western Massachusetts Electric Company
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	868,100	841,900
Transmission	1,147,900	1,061,100
Generation	36,000	36,000
Property, Plant and Equipment, Gross	2,052,000	1,939,000
Less: Accumulated Depreciation
Total Accumulated Depreciation	(356,500)	(338,800)
Property, Plant and Equipment, Net	1,695,500	1,600,200
Construction Work in Progress	74,100	78,100
Net Plant	$ 1,769,566	$ 1,678,262

DERIVATIVE INSTRUMENTS - Gross

DERIVATIVE INSTRUMENTS - Gross Fair Value of Contracts (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Current Derivative Assets \| Level 2
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	$ 0	$ 6
Netting	0	0
Net Amount Recorded as a Derivative	0	6
Current Derivative Assets \| The Connecticut Light And Power Company \| Level 3
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	10.4	13.9
Netting	(7.7)	(9.4)
Net Amount Recorded as a Derivative	2.7	4.5
Long-term Derivative Assets \| Level 2
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	0	0.3
Netting	0	(0.1)
Net Amount Recorded as a Derivative	0	0.2
Long-term Derivative Assets \| The Connecticut Light And Power Company \| Level 3
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	74.3	77.3
Netting	(6.9)	(11.7)
Net Amount Recorded as a Derivative	67.4	65.6
Current Derivative Liabilities \| Level 2
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(1.5)	0
Netting	0.4	0
Net Amount Recorded as a Derivative	(1.1)	0
Current Derivative Liabilities \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(62.2)	(79.7)
Netting	0	0
Net Amount Recorded as a Derivative	(62.2)	(79.7)
Current Derivative Liabilities \| The Connecticut Light And Power Company \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(59.9)	(77.8)
Netting	0	0
Net Amount Recorded as a Derivative	(59.9)	(77.8)
Current Derivative Liabilities \| NSTAR Electric Company \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(2.3)	(1.9)
Netting	0	0
Net Amount Recorded as a Derivative	(2.3)	(1.9)
Long-Term Derivative Liabilities \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(391.9)	(413.7)
Netting	0	0
Net Amount Recorded as a Derivative	(391.9)	(413.7)
Long-Term Derivative Liabilities \| The Connecticut Light And Power Company \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(391.8)	(412.8)
Netting	0	0
Net Amount Recorded as a Derivative	(391.8)	(412.8)
Long-Term Derivative Liabilities \| NSTAR Electric Company \| Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(0.1)	(0.9)
Netting	0	0
Net Amount Recorded as a Derivative	$ (0.1)	$ (0.9)

DERIVATIVE INSTRUMENTS - Deriva

DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details) MWh in Millions, MMBTU in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)MMBTUMWhMW	Sep. 30, 2016USD ($)	Dec. 31, 2016MMBTU
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company			20.00%
Amount of power to be purchased under capacity-related contract (up to) \| MW			787
Amount of natural gas to be purchased under futures contracts \| MMBTU			10.4		9.2
Gains (losses) on deferred as regulatory costs \| $	$ 0.6	$ (53.4)	$ (30.3)	$ (127.8)
The Connecticut Light And Power Company
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts			80.00%
Amount of energy to be purchased under renewable energy contract (in mwh) \| MWh			0.1
NSTAR Electric Company
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of power to be purchased under capacity-related contract (up to) \| MW			35
Amount of energy to be purchased under renewable energy contract (in mwh) \| MWh			0.1

DERIVATIVE INSTRUMENTS - Unobse

DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - Level 3 - $ / KWmo	Sep. 30, 2017	Dec. 31, 2016
The Connecticut Light And Power Company \| Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	5	5.50
Forward Reserve (in USDPerKiloWattMonth)	1	1.40
The Connecticut Light And Power Company \| Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	8.70	8.70
Forward Reserve (in USDPerKiloWattMonth)	2	2
NSTAR Electric \| Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	15.75	24
NSTAR Electric \| Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	22	29

DERIVATIVE INSTRUMENTS - Unob49

DERIVATIVE INSTRUMENTS - Unobservable Inputs Narrative (Details) - Level 3	9 Months Ended
	Sep. 30, 2017
Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	1.00%
Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	18.00%

DERIVATIVE INSTRUMENTS - Deri50

DERIVATIVE INSTRUMENTS - Derivative Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Net [Rollforward]
Fair Value as of Beginning of Period	$ (397.1)	$ (412.6)	$ (423.3)	$ (380.9)
Net Realized/Unrealized Gains/Losses Included in Regulatory Assets and Liabilities	0.5	(52.3)	(17.9)	(128.9)
Settlements	12.6	21.2	57.2	66.1
Fair Value as of End of Period	(384)	(443.7)	(384)	(443.7)
The Connecticut Light And Power Company
Derivatives, Net [Rollforward]
Fair Value as of Beginning of Period	(394.8)	(411.3)	(420.5)	(380.8)
Net Realized/Unrealized Gains/Losses Included in Regulatory Assets and Liabilities	(0.7)	(49.8)	(15.9)	(122)
Settlements	13.9	20.1	54.8	61.8
Fair Value as of End of Period	(381.6)	(441)	(381.6)	(441)
NSTAR Electric Company
Derivatives, Net [Rollforward]
Fair Value as of Beginning of Period	(2.3)	(1.3)	(2.8)	(0.1)
Net Realized/Unrealized Gains/Losses Included in Regulatory Assets and Liabilities	1.2	(2.5)	(2)	(6.9)
Settlements	(1.3)	1.1	2.4	4.3
Fair Value as of End of Period	$ (2.4)	$ (2.7)	$ (2.4)	$ (2.7)

MARKETABLE SECURITIES - Trading

MARKETABLE SECURITIES - Trading Securities (Details) - Level 1 - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value of securities under fair value option			$ 9.6
Other Income
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net gain (loss) under fair value option	$ 0.1	$ 0.6

MARKETABLE SECURITIES - Schedul

MARKETABLE SECURITIES - Schedule of Available for Sale Securities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 286.5	$ 296.2
Pre-Tax Unrealized Gains	5.5	1.1
Pre-Tax Unrealized Losses	(0.5)	(2.1)
Fair Value	291.5	295.2
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	210.7	203.3
Pre-Tax Unrealized Gains	81.5	62.3
Pre-Tax Unrealized Losses	0	(1.2)
Fair Value	$ 292.2	$ 264.4

MARKETABLE SECURITIES - Availab

MARKETABLE SECURITIES - Available for Sale Securities Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Debt, equity and marketable securities held in nuclear decommissioning trust	$ 489.1	$ 466.7

MARKETABLE SECURITIES - Sched54

MARKETABLE SECURITIES - Schedule of Contractual Maturities (Details) $ in Millions	Sep. 30, 2017USD ($)
Amortized Cost
Less than one year	$ 40.2
One to five years	56.7
Six to ten years	52.6
Greater than ten years	137
Total Debt Securities	286.5
Fair Value
Less than one year	40.2
One to five years	57.6
Six to ten years	54.1
Greater than ten years	139.6
Total Debt Securities	$ 291.5

MARKETABLE SECURITIES - Sched55

MARKETABLE SECURITIES - Schedule of Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 583.7	$ 569.2
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	314	328.8
Level 1 \| Mutual Funds and Equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	292.2	274
Level 1 \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	21.8	54.8
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	269.7	240.4
Level 2 \| U.S. Government Issued Debt Securities (Agency and Treasury)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	69	63
Level 2 \| Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	56.1	41.1
Level 2 \| Asset-Backed Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	20.4	18.5
Level 2 \| Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	113.6	107.5
Level 2 \| Other Fixed Income Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities recorded at fair value on a recurring basis	$ 10.6	$ 10.3

SHORT-TERM AND LONG-TERM DEBT -

SHORT-TERM AND LONG-TERM DEBT - Commercial Paper Programs and Credit Agreements (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Short-term debt reclassified to long-term debt	$ 898,800,000
Eversource Parent
Line of Credit Facility [Line Items]
Amount outstanding during period	0	$ 0
Eversource Parent \| Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity	1,450,000,000
Short-term borrowings outstanding	917,000,000	1,000,000,000
Remaining borrowing capacity	$ 533,000,000	$ 428,000,000
Weighted average interest rate (as a percentage)	1.34%	0.88%
Eversource Parent \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 1,450,000,000
Debt instrument term	5 years
The Connecticut Light And Power Company
Line of Credit Facility [Line Items]
Notes payable to Eversource Parent	$ 0	$ 80,100,000
Public Service Company Of New Hampshire
Line of Credit Facility [Line Items]
Notes payable to Eversource Parent	202,300,000	160,900,000
Western Massachusetts Electric Company
Line of Credit Facility [Line Items]
Notes payable to Eversource Parent	96,900,000	51,000,000
NSTAR Electric Company
Line of Credit Facility [Line Items]
Amount outstanding during period	0	0
NSTAR Electric Company \| Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity	450,000,000
Short-term borrowings outstanding	0	126,500,000
Remaining borrowing capacity	450,000,000	$ 323,500,000
Weighted average interest rate (as a percentage)		0.71%
NSTAR Electric Company \| Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 450,000,000
Debt instrument term	5 years

SHORT-TERM AND LONG-TERM DEBT57

SHORT-TERM AND LONG-TERM DEBT - Long-Term Debt Issuances (Details) - Senior Notes - USD ($)	1 Months Ended
	Oct. 31, 2017	Aug. 31, 2017	Sep. 30, 2017	May 31, 2017	Mar. 31, 2017
Series N First Mortgage Bonds Due 2027
Debt Instrument [Line Items]
Debt instrument, face amount			$ 75,000,000
Interest rate stated percentage			3.02%
Eversource Parent \| Series K Senior Notes Due 2022
Debt Instrument [Line Items]
Debt instrument, face amount					$ 300,000,000
Interest rate stated percentage					2.75%
The Connecticut Light And Power Company \| 2017 Series A First and Refunding Mortgage Bonds Due 2027
Debt Instrument [Line Items]
Debt instrument, face amount					$ 300,000,000
Interest rate stated percentage					3.20%
The Connecticut Light And Power Company \| 2014 Series A First and Refunding Mortgage Bonds Due in 2044
Debt Instrument [Line Items]
Debt instrument, face amount		$ 225,000,000
Interest rate stated percentage		4.30%
Outstanding principal amount		$ 475,000,000
NSTAR Electric Company \| Unsecured Notes Due 2027
Debt Instrument [Line Items]
Debt instrument, face amount				$ 350,000,000
Interest rate stated percentage				3.20%
Subsequent Event \| Eversource Parent \| Series K Senior Notes Due 2022
Debt Instrument [Line Items]
Debt instrument, face amount	$ 450,000,000
Interest rate stated percentage	2.75%
Outstanding principal amount	$ 750,000,000
Subsequent Event \| Eversource Parent \| 2017 Series L Senior Notes, Due in 2024
Debt Instrument [Line Items]
Debt instrument, face amount	$ 450,000,000
Interest rate stated percentage	2.90%
Subsequent Event \| NSTAR Electric Company \| Unsecured Notes Due 2027
Debt Instrument [Line Items]
Debt instrument, face amount	$ 350,000,000
Interest rate stated percentage	3.20%
Outstanding principal amount	$ 700,000,000

SHORT-TERM AND LONG-TERM DEBT58

SHORT-TERM AND LONG-TERM DEBT - Long-Term Debt Repayments (Details) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Repayments of debt			$ 320,000	$ 200,000
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Repayments of debt			250,000	0
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Repayments of debt			$ 70,000	$ 0
2007 Series A First and Refunding Mortgage Bonds \| Senior Notes \| The Connecticut Light And Power Company
Debt Instrument [Line Items]
Repayments of debt		$ 150,000
Interest rate stated percentage		5.375%
2007 Series C First and Refunding Mortgage Bonds \| Senior Notes \| The Connecticut Light And Power Company
Debt Instrument [Line Items]
Repayments of debt	$ 100,000
Interest rate stated percentage	5.75%		5.75%
2007 Series N First Mortgage Bonds \| Senior Notes \| Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Repayments of debt	$ 70,000
Interest rate stated percentage	6.15%		6.15%
Series M First Mortgage Bonds \| Senior Notes \| NSTAR Gas Company
Debt Instrument [Line Items]
Repayments of debt	$ 25,000
Interest rate stated percentage	7.04%		7.04%

SHORT-TERM AND LONG - Long-Term

SHORT-TERM AND LONG - Long-Term Debt Issuance Authorization (Details) - Senior Notes - USD ($) $ in Millions	Mar. 30, 2017	Jan. 04, 2017
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Amount of debt authorized (up to)		$ 1,325
NSTAR Electric Company
Debt Instrument [Line Items]
Amount of debt authorized (up to)	$ 700

PENSION BENEFITS AND POSTRETI60

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Pension Plan
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Prior service credit as a result of remeasurement	$ 5.3	$ 16.1

PENSION BENEFITS AND POSTRETI61

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSIONS - Components of Periodic Benefit Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 17.4	$ 18.6	$ 53.8	$ 56.6
Interest Cost	47.2	46.4	140.7	139.2
Expected Return on Pension Plan Assets	(83.5)	(79.4)	(250.5)	(238.5)
Actuarial Loss	33.9	31.4	101.3	94.2
Prior Service Cost/(Credit)	1.2	0.9	3.4	2.6
Total Net Periodic Benefit Income	16.2	17.9	48.7	54.1
Capitalized PBOP Income/ Pension Expense	5.5	5.4	16.5	16.8
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	2.4	3	7.1	9.2
Interest Cost	6.8	7.5	20.3	26.5
Expected Return on Pension Plan Assets	(16)	(15.9)	(47.8)	(47.3)
Actuarial Loss	2.2	3	6.9	5
Prior Service Cost/(Credit)	(5.3)	(3.6)	(16.1)	(3.7)
Total Net Periodic Benefit Income	(9.9)	(6)	(29.6)	(10.3)
Capitalized PBOP Income/ Pension Expense	(4.8)	(2.6)	(14.3)	(4.6)
The Connecticut Light And Power Company \| Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	4.6	4.6	13.9	14.3
Interest Cost	10.5	10.2	31.3	31.2
Expected Return on Pension Plan Assets	(17.8)	(18)	(53.9)	(54.2)
Actuarial Loss	6.8	6.3	20.7	19.2
Prior Service Cost/(Credit)	0.4	0.4	1.1	1.1
Total Net Periodic Benefit Income	4.5	3.5	13.1	11.6
Intercompany Allocations	2.4	3.5	7.4	10.3
Capitalized PBOP Income/ Pension Expense	2.4	2.2	7.3	7.1
The Connecticut Light And Power Company \| Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.5	0.6	1.5	1.4
Interest Cost	1.3	1.3	4	4
Expected Return on Pension Plan Assets	(2.4)	(2.5)	(7.3)	(7.6)
Actuarial Loss	0.2	0.5	0.7	0.9
Prior Service Cost/(Credit)	0.3	0.2	0.8	0.2
Total Net Periodic Benefit Income	(0.1)	0.1	(0.3)	(1.1)
Intercompany Allocations	(0.2)	0	(0.5)	0.3
Capitalized PBOP Income/ Pension Expense	(0.1)	0	(0.4)	(0.5)
NSTAR Electric Company \| Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	3.1	3.3	9.4	9.9
Interest Cost	8.6	8.5	25.6	25.3
Expected Return on Pension Plan Assets	(17.5)	(16.9)	(52.5)	(50.7)
Actuarial Loss	8.9	8.7	26.4	25.8
Prior Service Cost/(Credit)	0.1	0	0.2	0
Total Net Periodic Benefit Income	3.2	3.6	9.1	10.3
Intercompany Allocations	1.8	2.2	5.5	6.7
Capitalized PBOP Income/ Pension Expense	1.9	2	5.4	5.7
NSTAR Electric Company \| Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.3	0.6	1.1	2.5
Interest Cost	1.9	2.5	5.7	10.3
Expected Return on Pension Plan Assets	(6.6)	(6.4)	(19.9)	(19.2)
Actuarial Loss	0.9	1.2	2.6	1.7
Prior Service Cost/(Credit)	(4.3)	(2.9)	(12.9)	(2.9)
Total Net Periodic Benefit Income	(7.8)	(5)	(23.4)	(7.6)
Intercompany Allocations	(0.2)	(0.1)	(0.7)	0
Capitalized PBOP Income/ Pension Expense	(4)	(2.2)	(11.9)	(3.3)
Public Service Company Of New Hampshire \| Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	2.4	2.5	7.3	7.5
Interest Cost	5.3	5.1	15.9	15.4
Expected Return on Pension Plan Assets	(10)	(9.6)	(29.9)	(28.9)
Actuarial Loss	3	2.5	8.7	7.5
Prior Service Cost/(Credit)	0.1	0.1	0.4	0.3
Total Net Periodic Benefit Income	0.8	0.6	2.4	1.8
Intercompany Allocations	0.8	1	2.5	3
Capitalized PBOP Income/ Pension Expense	0.4	0.4	1.1	1
Public Service Company Of New Hampshire \| Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.3	0.4	1	0.9
Interest Cost	0.8	0.7	2.3	2.2
Expected Return on Pension Plan Assets	(1.4)	(1.4)	(4.1)	(4.2)
Actuarial Loss	0.1	0.2	0.4	0.5
Prior Service Cost/(Credit)	0.2	0.1	0.4	0.1
Total Net Periodic Benefit Income	0	0	0	(0.5)
Intercompany Allocations	(0.1)	0	(0.3)	0
Capitalized PBOP Income/ Pension Expense	0	0	0	0
Western Massachusetts Electric Company \| Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.7	0.8	2.3	2.4
Interest Cost	2.1	2.1	6.3	6.3
Expected Return on Pension Plan Assets	(4.4)	(4.4)	(13.3)	(13.1)
Actuarial Loss	1.5	1.3	4.5	4.1
Prior Service Cost/(Credit)	0.1	0.1	0.2	0.2
Total Net Periodic Benefit Income	0	(0.1)	0	(0.1)
Intercompany Allocations	0.5	0.6	1.4	1.9
Capitalized PBOP Income/ Pension Expense	0.1	0.1	0.3	0.3
Western Massachusetts Electric Company \| Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.1	0.1	0.3	0.3
Interest Cost	0.3	0.3	0.8	0.8
Expected Return on Pension Plan Assets	(0.6)	(0.6)	(1.7)	(1.7)
Actuarial Loss	0	0	0	0
Prior Service Cost/(Credit)	0	0	0.1	0
Total Net Periodic Benefit Income	(0.2)	(0.2)	(0.5)	(0.6)
Intercompany Allocations	0	0	(0.1)	0
Capitalized PBOP Income/ Pension Expense	$ (0.1)	$ (0.1)	$ (0.2)	$ (0.3)

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Environmental Matters (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017USD ($)site	Dec. 31, 2016USD ($)site
Site Contingency [Line Items]
Number of Sites \| site	58	61
Reserve \| $	$ 57.7	$ 65.8
The Connecticut Light And Power Company
Site Contingency [Line Items]
Number of Sites \| site	14	14
Reserve \| $	$ 4.9	$ 4.9
NSTAR Electric Company
Site Contingency [Line Items]
Number of Sites \| site	10	13
Reserve \| $	$ 2	$ 3.2
Public Service Company Of New Hampshire
Site Contingency [Line Items]
Number of Sites \| site	11	11
Reserve \| $	$ 5.7	$ 5.3
Western Massachusetts Electric Company
Site Contingency [Line Items]
Number of Sites \| site	4	4
Reserve \| $	$ 0.8	$ 0.6

COMMITMENTS AND CONTINGENCIES63

COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Site Contingency [Line Items]
Reserve	$ 57.7	$ 65.8
MGP Site accrual
Site Contingency [Line Items]
Reserve	$ 51.9	$ 59

COMMITMENTS AND CONTINGENCIES64

COMMITMENTS AND CONTINGENCIES - Guarantees and Indemnifications Narrative (Details) $ in Millions	Sep. 30, 2017USD ($)
Guarantee Of Financial Obligations Of Npt
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure (up to)	$ 25
Guarantee Of Npt Letters Of Credit
Guarantor Obligations [Line Items]
Guarantor obligations, maximum exposure (up to)	$ 14

COMMITMENTS AND CONTINGENCIES65

COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations , Yankee Companies (Details) $ in Millions	May 22, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Damages sought, value	$ 100

COMMITMENTS AND CONTINGENCIES66

COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details) $ in Millions	Sep. 30, 2017USD ($)
Eversource Gas Transmission LLC
Loss Contingencies [Line Items]
Maximum Exposure	$ 185.1
Various
Loss Contingencies [Line Items]
Maximum Exposure	40.1
Eversource Service and Rocky River Realty Company
Loss Contingencies [Line Items]
Maximum Exposure	$ 8.2

COMMITMENTS AND CONTINGENCIES67

COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details) - USD ($) $ in Millions	Jun. 08, 2017	Apr. 14, 2017	Apr. 29, 2016	Sep. 30, 2017	Mar. 26, 2014	Apr. 14, 2017
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants	11.14%			11.14%
Percentage of maximum ROE for any incentive project	13.50%
FERC ROE Complaints
Loss Contingencies [Line Items]
Period of complaint				15 months
Basis point change				10.00%
Estimate of possible loss for each 10 basis point change to base ROE				$ 3
FERC ROE Fourth Complaint
Loss Contingencies [Line Items]
Base ROE percentage of complaint period			10.57%
Maximum percentage cap of ROE for incentive projects			11.74%
Loss contingency, estimate of possible earnings impact				0
FERC ROE First Complaint
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants		11.14%
Percentage of maximum ROE for any incentive project						11.74%
Loss contingency, estimate of possible earnings impact				0
FERC ROE Second Complaint
Loss Contingencies [Line Items]
Base ROE percentage of complaint period					10.57%
Percentage of maximum ROE for any incentive project					11.74%
Loss contingency, estimate of possible earnings impact				39.1
The Connecticut Light And Power Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				21.4
NSTAR Electric Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				8.5
Public Service Company Of New Hampshire \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				3.1
Western Massachusetts Electric Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				$ 6.1

COMMITMENTS AND CONTINGENCIES68

COMMITMENTS AND CONTINGENCIES - Schedule of Complaints and Base ROEs (Details) - USD ($) $ in Millions	Oct. 06, 2017	Jun. 08, 2017	Sep. 30, 2017	Jul. 28, 2017	Mar. 26, 2014	Dec. 31, 2012	Oct. 30, 2015	Apr. 14, 2017	Oct. 15, 2014
FERC ROE First Complaint
Loss Contingencies [Line Items]
Original Base ROE Authorized by FERC at Time of Complaint (in percentage)						11.14%
Base ROE Subsequently Authorized by FERC for first complaint period and prospectively from October 16, 2014 (in percentage)						10.57%
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			$ 0
Percentage of maximum ROE for any incentive project								11.74%
Customer refund payments			38.9
FERC ROE Second Complaint
Loss Contingencies [Line Items]
Original Base ROE Authorized by FERC at Time of Complaint (in percentage)					11.14%
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			39.1
FERC ALJ Recommendation of base ROE on Second and Third Complaints (Issued March 22, 2016) (in percentage)					9.59%
Percentage of maximum ROE for any incentive project					11.74%
FERC ROE Third Complaint
Loss Contingencies [Line Items]
Original Base ROE Authorized by FERC at Time of Complaint (in percentage)							11.14%
Base ROE Subsequently Authorized by FERC for first complaint period and prospectively from October 16, 2014 (in percentage)							10.57%
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			0
FERC ALJ Recommendation of base ROE on Second and Third Complaints (Issued March 22, 2016) (in percentage)							10.90%
FERC ROE Fourth Complaint
Loss Contingencies [Line Items]
Original Base ROE Authorized by FERC at Time of Complaint (in percentage)				10.57%
Base ROE Subsequently Authorized by FERC for first complaint period and prospectively from October 16, 2014 (in percentage)				10.57%
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			0
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of maximum ROE for any incentive project		13.50%
The Connecticut Light And Power Company \| FERC ROE First Complaint
Loss Contingencies [Line Items]
Customer refund payments			22.4
The Connecticut Light And Power Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			21.4
NSTAR Electric Company \| FERC ROE First Complaint
Loss Contingencies [Line Items]
Customer refund payments			8.4
NSTAR Electric Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			8.5
Public Service Company Of New Hampshire \| FERC ROE First Complaint
Loss Contingencies [Line Items]
Customer refund payments			2.8
Public Service Company Of New Hampshire \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			3.1
Western Massachusetts Electric Company \| FERC ROE First Complaint
Loss Contingencies [Line Items]
Customer refund payments			5.3
Western Massachusetts Electric Company \| FERC ROE Second Complaint
Loss Contingencies [Line Items]
Reserve (Pre-Tax and Excluding Interest) as of September 30, 2017 (in millions)			$ 6.1
Minimum \| FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of maximum ROE for any incentive project									11.14%
Maximum \| FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of maximum ROE for any incentive project									13.10%
Subsequent Event \| FERC ROE Fourth Complaint
Loss Contingencies [Line Items]
Original Base ROE Authorized by FERC at Time of Complaint (in percentage)	11.74%
Percentage of maximum ROE for any incentive project	10.57%

COMMITMENTS AND CONTINGENCIES69

COMMITMENTS AND CONTINGENCIES - Harbor Civil Action (Details) $ in Millions	Jul. 15, 2016MW	Sep. 30, 2017USD ($)
Loss Contingencies [Line Items]
Amount of capacity required for installation of distribution cable (in volts) \| MW	0.115
NSTAR Electric Company
Loss Contingencies [Line Items]
Charge relating to assets previously recognized as capital		$ 4.9
Base rate credit for new cable		$ 17.5

PSNH GENERATION ASSET SALE - Na

PSNH GENERATION ASSET SALE - Narrative (Details) $ in Millions	Oct. 11, 2017USD ($)agreement	Jun. 10, 2015USD ($)senator
Regulatory Assets [Line Items]
Equity return related to clean air project forgone		$ 25
Electricity Generation Plant, Non-Nuclear \| Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Number of state senators \| senator		2
Subsequent Event
Regulatory Assets [Line Items]
Number of purchase sale agreements \| agreement	2
Thermal generation assets	$ 175
Hydroelectric assets	$ 83

PSNH GENERATION ASSET SALE - PS

PSNH GENERATION ASSET SALE - PSNH Generation Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Gross Plant	$ 28,189,300	$ 27,060,500
Accumulated Depreciation	(7,112,900)	(6,722,400)
Net Plant	22,537,304	21,350,510
Emission Allowances	305,035	328,721
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Gross Plant	4,344,300	4,197,300
Accumulated Depreciation	(1,315,700)	(1,254,700)
Net Plant	3,167,905	3,039,313
Emission Allowances	158,091	$ 162,354
Electricity Generation Plant, Non-Nuclear \| Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Gross Plant	1,184,100
Accumulated Depreciation	(573,300)
Net Plant	610,800
Fuel	92,900
Materials and Supplies	44,000
Emission Allowances	19,400
Total Generation Assets	$ 767,100

FAIR VALUE OF FINANCIAL INSTR72

FAIR VALUE OF FINANCIAL INSTRUMENTS - Carrying Amounts and Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
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 \| Level 2
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	11,425,900	9,603,200
Fair Value \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	160,300	158,300
Long-Term Debt	11,968,100	9,980,500
The Connecticut Light And Power Company
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 \| Carrying Amount \| Level 2
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	3,058,900	2,766,000
The Connecticut Light And Power Company \| Fair Value \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	115,900	114,700
Long-Term Debt	3,388,800	3,049,600
NSTAR Electric Company
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 \| Carrying Amount \| Level 2
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	2,426,200	2,078,100
NSTAR Electric Company \| Fair Value \| Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	44,400	43,600
Long-Term Debt	2,598,100	2,201,600
Public Service Company Of New Hampshire \| Carrying Amount \| Level 2
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	1,002,600	1,072,000
Public Service Company Of New Hampshire \| Fair Value \| Level 2
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	1,047,000	1,109,700
Western Massachusetts Electric Company \| Carrying Amount \| Level 2
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	566,200	566,500
Western Massachusetts Electric Company \| Fair Value \| Level 2
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	$ 603,700	$ 589,000

ACCUMULATED OTHER COMPREHENSI73

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Accumulated Other Comprehensive Income (loss) by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent [Roll Forward]
Beginning balance			$ 10,711,734
OCI Before Reclassifications				$ (3,000)
Amounts Reclassified from AOCL				4,200
Net OCI	$ (680)	$ (253)	1,667	1,227
Ending balance	10,998,037		10,998,037
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent [Roll Forward]
Beginning balance			(65,300)	(66,800)
OCI Before Reclassifications			(2,800)
Amounts Reclassified from AOCL			4,500
Net OCI			1,700
Ending balance	(63,600)	(65,600)	(63,600)	(65,600)
Qualified Cash Flow Hedging Instruments
AOCI Attributable to Parent [Roll Forward]
Beginning balance			(8,200)	(10,300)
OCI Before Reclassifications			0	0
Amounts Reclassified from AOCL			1,600	1,600
Net OCI			1,600	1,600
Ending balance	(6,600)	(8,700)	(6,600)	(8,700)
Unrealized Gains/(Losses) on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Beginning balance			400	(1,900)
OCI Before Reclassifications			700	2,300
Amounts Reclassified from AOCL			0	0
Net OCI			700	2,300
Ending balance	1,100	400	1,100	400
Defined Benefit Plans
AOCI Attributable to Parent [Roll Forward]
Beginning balance			(57,500)	(54,600)
OCI Before Reclassifications			(3,500)	(5,300)
Amounts Reclassified from AOCL			2,900	2,600
Net OCI			(600)	(2,700)
Ending balance	$ (58,100)	$ (57,300)	$ (58,100)	$ (57,300)

COMMON SHARES - Schedule of Com

COMMON SHARES - Schedule of Common Shares (Details) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Per Value (in dollars per share)	$ 5	$ 5
Authorized (in shares)	380,000,000	380,000,000
Issued (in shares)	333,878,402	333,878,402
The Connecticut Light And Power Company
Class of Stock [Line Items]
Per 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
Class of Stock [Line Items]
Per 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
Class of Stock [Line Items]
Per 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
Class of Stock [Line Items]
Per Value (in dollars per share)	$ 25	$ 25
Authorized (in shares)	1,072,471	1,072,471
Issued (in shares)	434,653	434,653

COMMON SHARES - Narrative (Deta

COMMON SHARES - Narrative (Details) - shares	Sep. 30, 2017	Dec. 31, 2016
Equity [Abstract]
Treasury stock (in shares)	16,992,594	16,992,594
Common stock outstanding (in shares)	316,885,808	316,885,808

COMMON SHAREHOLDERS' EQUITY A76

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Equity [Abstract]
Net income attributable to noncontrolling interests	$ 1,900	$ 1,900	$ 5,600	$ 5,600
Noncontrolling Interest – Preferred Stock of Subsidiaries	$ 155,568		$ 155,568		$ 155,568

EARNINGS PER SHARE - Narrative

EARNINGS PER SHARE - Narrative (Details) - shares	3 Months Ended		9 Months Ended
EARNINGS PER SHARE - Narrative (Details) - shares	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive share awards excluded from computation (in shares)	0	0	0	0

EARNINGS PER SHARE - Schedule o

EARNINGS PER SHARE - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 260,370	$ 265,319	$ 750,577	$ 713,123
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,393,029	317,787,836	317,415,848	317,696,823
Dilutive Effect (in shares)	556,367	789,243	591,194	814,786
Diluted (in shares)	317,949,396	318,577,079	318,007,042	318,511,609
Basic and Diluted EPS (in dollars per share)	$ 0.82	$ 0.83	$ 2.36	$ 2.24

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) $ in Millions	9 Months Ended
SEGMENT INFORMATION - Narrative (Details) $ in Millions	Sep. 30, 2017USD ($)segmentcompany
Segment Reporting Information [Line Items]
Number of companies that transmit hydro electricity imported from The Hydro-Quebec System in Canada \| company	2
Amount of natural gas transmission purchased from Enbridge by Yankee Gas and NSTAR Gas \| $	$ 62.5
The Connecticut Light And Power Company
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric Company
Segment Reporting Information [Line Items]
Number of reportable segments	1
Public Service Company Of New Hampshire
Segment Reporting Information [Line Items]
Number of reportable segments	1
Western Massachusetts Electric Company
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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenues	$ 1,988,512	$ 2,039,706	$ 5,856,458	$ 5,862,525
Depreciation and Amortization	(236,300)	(225,200)	(629,200)	(588,000)
Other Operating Expenses	(1,249,600)	(1,304,600)	(3,760,000)	(3,852,700)
Operating Income/(Loss)	502,603	509,869	1,467,310	1,421,827
Interest Expense	(108,719)	(99,865)	(319,477)	(298,568)
Other Income, Net	21,184	13,641	56,304	23,689
Net Income Attributable to Common Shareholders	260,370	265,319	750,577	713,123
Cash Flows Used for Investments in Plant			1,642,280	1,359,171
Assets	33,163,620		33,163,620		$ 32,053,173
Operating Segments \| Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	1,547,100	1,623,400	4,224,200	4,362,600
Depreciation and Amortization	(159,600)	(154,800)	(394,900)	(380,900)
Other Operating Expenses	(1,088,700)	(1,146,800)	(3,056,000)	(3,230,100)
Operating Income/(Loss)	298,800	321,800	773,300	751,600
Interest Expense	(51,300)	(49,000)	(149,000)	(144,600)
Other Income, Net	7,700	5,300	15,200	11,600
Net Income Attributable to Common Shareholders	157,400	170,100	393,400	381,300
Cash Flows Used for Investments in Plant			752,400	570,900
Assets	18,826,000		18,826,000		18,367,500
Operating Segments \| Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating Revenues	109,200	99,200	698,800	622,300
Depreciation and Amortization	(15,200)	(15,200)	(54,800)	(47,900)
Other Operating Expenses	(95,500)	(87,800)	(535,200)	(462,400)
Operating Income/(Loss)	(1,500)	(3,800)	108,800	112,000
Interest Expense	(10,800)	(10,200)	(32,300)	(30,800)
Other Income, Net	300	600	800	500
Net Income Attributable to Common Shareholders	(6,200)	(7,000)	49,100	51,900
Cash Flows Used for Investments in Plant			209,800	170,300
Assets	3,432,600		3,432,600		3,303,800
Operating Segments \| Electric Transmission
Segment Reporting Information [Line Items]
Operating Revenues	328,500	306,800	970,000	892,500
Depreciation and Amortization	(52,600)	(47,100)	(154,500)	(137,700)
Other Operating Expenses	(95,500)	(90,200)	(280,400)	(245,700)
Operating Income/(Loss)	180,400	169,500	535,100	509,100
Interest Expense	(29,200)	(26,900)	(86,100)	(82,200)
Other Income, Net	8,500	6,300	20,100	14,200
Net Income Attributable to Common Shareholders	99,000	88,400	289,600	266,600
Cash Flows Used for Investments in Plant			575,600	536,200
Assets	9,290,300		9,290,300		8,751,500
Operating Segments \| Other
Segment Reporting Information [Line Items]
Operating Revenues	224,200	211,500	677,500	636,800
Depreciation and Amortization	(9,500)	(8,600)	(26,700)	(23,100)
Other Operating Expenses	(190,000)	(179,300)	(602,400)	(564,700)
Operating Income/(Loss)	24,700	23,600	48,400	49,000
Interest Expense	(21,800)	(15,100)	(63,100)	(45,800)
Other Income, Net	267,500	256,900	853,900	781,400
Net Income Attributable to Common Shareholders	268,400	268,500	839,500	791,700
Cash Flows Used for Investments in Plant			104,500	81,800
Assets	14,939,400		14,939,400		14,493,100
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(220,500)	(201,200)	(714,000)	(651,700)
Depreciation and Amortization	600	500	1,700	1,600
Other Operating Expenses	220,100	199,500	714,000	650,200
Operating Income/(Loss)	200	(1,200)	1,700	100
Interest Expense	4,400	1,300	11,000	4,800
Other Income, Net	(262,800)	(255,500)	(833,700)	(784,000)
Net Income Attributable to Common Shareholders	(258,200)	$ (254,700)	(821,000)	(778,400)
Cash Flows Used for Investments in Plant			0	$ 0
Assets	$ (13,324,700)		$ (13,324,700)		$ (12,862,700)