The Connecticut Light and Power Company (CNLPM) 10-K 26 Feb 19 2018 FY Annual report Financial data

DOCUMENT AND ENTITY INFORMATION

DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document And Entity [Line Items]
Entity Registrant Name	EVERSOURCE ENERGY
Document Period End Date	Dec. 31, 2018
Document Type	10-K
Entity Central Index Key	72,741
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		316,981,088
Entity Public Float			$ 18,544,847,538
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light And Power Company
Document And Entity [Line Items]
Entity Registrant Name	CONNECTICUT LIGHT & POWER CO
Entity Central Index Key	23,426
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Entity Filer Category	Non-accelerated Filer
Public Service Company Of New Hampshire
Document And Entity [Line Items]
Entity Registrant Name	PUBLIC SERVICE CO OF NEW HAMPSHIRE
Entity Central Index Key	315,256
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		301
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company
Document And Entity [Line Items]
Entity Registrant Name	NSTAR ELECTRIC CO
Entity Central Index Key	13,372
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		200
Entity Filer Category	Non-accelerated Filer

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and Cash Equivalents	$ 108,068	$ 38,165
Receivables, Net	994,055	925,083
Unbilled Revenues	176,285	201,361
Fuel, Materials, Supplies and Inventory	238,042	223,063
Regulatory Assets	514,779	741,868
Prepayments and Other Current Assets	260,995	138,009
Assets Held for Sale	0	219,550
Total Current Assets	2,292,224	2,487,099
Property, Plant and Equipment, Net	25,610,428	23,617,463
Deferred Debits and Other Assets:
Regulatory Assets	4,631,137	4,497,447
Goodwill	4,427,266	4,427,266
Marketable Securities	417,508	585,419
Other Long-Term Assets	862,693	605,692
Total Deferred Debits and Other Assets	10,338,604	10,115,824
Total Assets	38,241,256	36,220,386
Current Liabilities:
Notes Payable	910,000	1,088,087
Long-Term Debt – Current Portion	837,319	549,631
Rate Reduction Bonds – Current Portion	52,332	0
Accounts Payable	1,119,995	1,085,034
Regulatory Liabilities	370,230	128,071
Other Current Liabilities	823,006	738,222
Total Current Liabilities	4,112,882	3,589,045
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	3,506,030	3,297,518
Regulatory Liabilities	3,609,475	3,637,273
Derivative Liabilities	379,562	377,257
Accrued Pension, SERP and PBOP	962,510	1,228,091
Other Long-Term Liabilities	1,196,336	1,073,501
Total Deferred Credits and Other Liabilities	9,653,913	9,613,640
Capitalization:
Long-Term Debt	12,248,743	11,775,889
Rate Reduction Bonds	583,331	0
Preferred Stock Not Subject to Mandatory Redemption	155,570	155,570
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid In	6,241,222	6,239,940
Retained Earnings	3,953,974	3,561,084
Accumulated Other Comprehensive Loss	(60,000)	(66,403)
Treasury Stock	(317,771)	(317,771)
Common Shareholders' Equity	11,486,817	11,086,242
Commitments and Contingencies (Note 12)
Total Liabilities and Capitalization	38,241,256	36,220,386
Public Service Company Of New Hampshire
Current Assets:
Cash and Cash Equivalents	1,439	900
Receivables, Net	104,854	92,774
Accounts Receivable from Affiliated Companies	8,444	5,297
Unbilled Revenues	47,145	49,448
Taxes Receivable	25,913	5,838
Fuel, Materials, Supplies and Inventory	37,504	40,285
Regulatory Assets	67,228	130,134
Special Deposits	47,498	728
Prepayments and Other Current Assets	17,564	22,365
Assets Held for Sale	0	219,550
Total Current Assets	357,589	567,319
Property, Plant and Equipment, Net	2,880,073	2,642,274
Deferred Debits and Other Assets:
Regulatory Assets	862,288	810,677
Other Long-Term Assets	27,406	42,391
Total Deferred Debits and Other Assets	889,694	853,068
Total Assets	4,127,356	4,062,661
Current Liabilities:
Notes Payable to Eversource Parent	57,000	262,900
Long-Term Debt – Current Portion	150,000	110,000
Rate Reduction Bonds – Current Portion	52,332	0
Accounts Payable	111,292	128,685
Accounts Payable to Affiliated Companies	26,029	24,676
Dividends Payable to Eversource Parent	0	150,000
Regulatory Liabilities	55,526	6,251
Other Current Liabilities	64,046	67,924
Total Current Liabilities	516,225	750,436
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	481,221	443,468
Regulatory Liabilities	428,069	444,397
Accrued Pension, SERP and PBOP	124,457	124,639
Other Long-Term Liabilities	36,339	56,689
Total Deferred Credits and Other Liabilities	1,070,086	1,069,193
Capitalization:
Long-Term Debt	655,173	892,438
Rate Reduction Bonds	583,331	0
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	678,134	843,134
Retained Earnings	627,258	511,382
Accumulated Other Comprehensive Loss	(2,851)	(3,922)
Common Shareholders' Equity	1,302,541	1,350,594
Commitments and Contingencies (Note 12)
Total Liabilities and Capitalization	4,127,356	4,062,661
NSTAR Electric Company
Current Assets:
Cash and Cash Equivalents	1,606	1,763
Receivables, Net	361,296	341,341
Accounts Receivable from Affiliated Companies	31,344	40,723
Unbilled Revenues	34,518	49,865
Materials, Supplies and Inventory	114,202	95,517
Regulatory Assets	241,747	333,882
Prepayments and Other Current Assets	51,960	24,499
Total Current Assets	836,673	887,590
Property, Plant and Equipment, Net	8,794,700	8,246,494
Deferred Debits and Other Assets:
Regulatory Assets	1,196,512	1,190,575
Prepaid PBOP	132,810	126,948
Other Long-Term Assets	109,764	84,766
Total Deferred Debits and Other Assets	1,439,086	1,402,289
Total Assets	11,070,459	10,536,373
Current Liabilities:
Notes Payable	278,500	234,000
Accounts Payable	384,398	340,115
Accounts Payable to Affiliated Companies	89,636	91,260
Obligations to Third Party Suppliers	109,547	88,721
Renewable Portfolio Standards Compliance Obligations	139,898	111,524
Regulatory Liabilities	190,620	79,562
Other Current Liabilities	74,872	79,916
Total Current Liabilities	1,267,471	1,025,098
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,294,467	1,275,814
Regulatory Liabilities	1,513,279	1,514,451
Accrued Pension, SERP and PBOP	14,145	89,995
Other Long-Term Liabilities	263,096	198,176
Total Deferred Credits and Other Liabilities	3,084,987	3,078,436
Capitalization:
Long-Term Debt	2,944,846	2,943,759
Preferred Stock Not Subject to Mandatory Redemption	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,633,442	1,502,942
Retained Earnings	2,098,091	1,944,961
Accumulated Other Comprehensive Loss	(1,378)	(1,823)
Common Shareholders' Equity	3,730,155	3,446,080
Commitments and Contingencies (Note 12)
Total Liabilities and Capitalization	11,070,459	10,536,373
The Connecticut Light And Power Company
Current Assets:
Cash and Cash Equivalents	87,721	6,028
Receivables, Net	397,026	370,676
Accounts Receivable from Affiliated Companies	23,082	28,181
Unbilled Revenues	56,971	54,154
Materials, Supplies and Inventory	44,529	48,438
Regulatory Assets	125,155	200,281
Prepayments and Other Current Assets	60,279	46,926
Total Current Assets	794,763	754,684
Property, Plant and Equipment, Net	8,909,701	8,271,030
Deferred Debits and Other Assets:
Regulatory Assets	1,505,488	1,444,935
Other Long-Term Assets	199,767	159,597
Total Deferred Debits and Other Assets	1,705,255	1,604,532
Total Assets	11,409,719	10,630,246
Current Liabilities:
Notes Payable to Eversource Parent	0	69,500
Long-Term Debt – Current Portion	250,000	300,000
Accounts Payable	324,983	367,605
Accounts Payable to Affiliated Companies	26,452	82,201
Obligations to Third Party Suppliers	56,248	52,860
Regulatory Liabilities	109,614	38,967
Derivative Liabilities	55,058	54,392
Other Current Liabilities	161,088	127,234
Total Current Liabilities	983,443	1,092,759
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,166,784	1,103,367
Regulatory Liabilities	1,122,157	1,112,136
Derivative Liabilities	379,536	376,918
Accrued Pension, SERP and PBOP	282,771	354,469
Other Long-Term Liabilities	155,495	128,135
Total Deferred Credits and Other Liabilities	3,106,743	3,075,025
Capitalization:
Long-Term Debt	3,004,016	2,759,135
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
Common Shareholders' Equity:
Common Shares	60,352	60,352
Capital Surplus, Paid In	2,410,765	2,110,765
Retained Earnings	1,727,899	1,415,741
Accumulated Other Comprehensive Loss	301	269
Common Shareholders' Equity	4,199,317	3,587,127
Commitments and Contingencies (Note 12)
Total Liabilities and Capitalization	$ 11,409,719	$ 10,630,246

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Revenues	$ 8,448,201	$ 7,751,952	$ 7,639,129
Operating Expenses:
Purchased Power, Fuel and Transmission	3,138,969	2,535,271	2,500,828
Operations and Maintenance	1,335,213	1,307,052	1,342,134
Depreciation	819,930	773,802	715,466
Amortization of Regulatory Assets/(Liabilities), Net	252,026	89,986	71,696
Energy Efficiency Programs	472,380	480,835	533,659
Taxes Other Than Income Taxes	729,753	676,757	634,072
Total Operating Expenses	6,748,271	5,863,703	5,797,855
Operating Income	1,699,930	1,888,249	1,841,274
Interest Expense	498,805	421,755	400,961
Other Income, Net	128,366	107,913	64,505
Income Before Income Tax Benefit	1,329,491	1,574,407	1,504,818
Income Tax Expense	288,972	578,892	554,997
Net Income	1,040,519	995,515	949,821
Net Income Attributable to Noncontrolling Interests	7,519	7,519	7,519
Net Income/(Loss) Attributable to Common Shareholders	$ 1,033,000	$ 987,996	$ 942,302
Basic Earnings Per Common Share (in dollars per share)	$ 3.25	$ 3.11	$ 2.97
Diluted Earnings Per Common Share (in dollars per share)	$ 3.25	$ 3.11	$ 2.96
Weighted Average Common Shares Outstanding:
Basic (in shares)	317,370,369	317,411,097	317,650,180
Diluted (in shares)	317,993,934	318,031,580	318,454,239
The Connecticut Light And Power Company
Operating Revenues	$ 3,096,174	$ 2,887,359	$ 2,805,955
Operating Expenses:
Purchased Power, Fuel and Transmission	1,095,187	930,780	919,723
Operations and Maintenance	506,448	502,107	490,810
Depreciation	278,557	249,352	230,489
Amortization of Regulatory Assets/(Liabilities), Net	129,021	83,166	38,765
Energy Efficiency Programs	93,977	114,713	154,015
Taxes Other Than Income Taxes	357,147	323,887	299,719
Total Operating Expenses	2,460,337	2,204,005	2,133,521
Operating Income	635,837	683,354	672,434
Interest Expense	151,727	142,973	144,110
Other Income, Net	22,663	22,991	14,238
Income Before Income Tax Benefit	506,773	563,372	542,562
Income Tax Expense	129,056	186,646	208,308
Net Income	377,717	376,726	334,254
NSTAR Electric Company
Operating Revenues	3,112,926	2,980,629	3,041,588
Operating Expenses:
Purchased Power, Fuel and Transmission	1,257,073	1,025,414	1,084,324
Operations and Maintenance	462,100	482,924	500,315
Depreciation	276,372	274,008	259,262
Amortization of Regulatory Assets/(Liabilities), Net	46,654	33,831	34,332
Energy Efficiency Programs	292,288	294,053	321,787
Taxes Other Than Income Taxes	194,316	181,959	177,837
Total Operating Expenses	2,528,803	2,292,189	2,377,857
Operating Income	584,123	688,440	663,731
Interest Expense	105,193	105,729	108,428
Other Income, Net	53,066	34,100	21,263
Income Before Income Tax Benefit	531,996	616,811	576,566
Income Tax Expense	148,906	242,085	225,789
Net Income	383,090	374,726	350,777
Public Service Company Of New Hampshire
Operating Revenues	1,047,619	981,624	959,482
Operating Expenses:
Purchased Power, Fuel and Transmission	370,246	237,478	210,786
Operations and Maintenance	210,541	263,110	267,013
Depreciation	92,055	128,192	116,519
Amortization of Regulatory Assets/(Liabilities), Net	80,978	(16,577)	11,170
Energy Efficiency Programs	20,105	13,788	14,204
Taxes Other Than Income Taxes	77,280	89,760	82,964
Total Operating Expenses	851,205	715,751	702,656
Operating Income	196,414	265,873	256,826
Interest Expense	60,634	51,007	50,040
Other Income, Net	27,672	9,805	7,563
Income Before Income Tax Benefit	163,452	224,671	214,349
Income Tax Expense	47,576	88,675	82,364
Net Income	$ 115,876	$ 135,996	$ 131,985

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income	$ 1,040,519	$ 995,515	$ 949,821
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	1,756	1,974	2,137
Changes in Unrealized (Losses)/Gains on Marketable Securities	(547)	(350)	2,294
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	5,194	(2,745)	(2,869)
Other Comprehensive Income/(Loss), Net of Tax	6,403	(1,121)	1,562
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Comprehensive Income	1,039,403	986,875	943,864
The Connecticut Light And Power Company
Net Income	377,717	376,726	334,254
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	51	334	444
Changes in Unrealized (Losses)/Gains on Marketable Securities	(19)	(12)	79
Other Comprehensive Income/(Loss), Net of Tax	32	322	523
Comprehensive Income	377,749	377,048	334,777
NSTAR Electric Company
Net Income	383,090	374,726	350,777
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	437	438	437
Changes in Unrealized (Losses)/Gains on Marketable Securities	(5)	(3)	22
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	13	(264)	(177)
Other Comprehensive Income/(Loss), Net of Tax	445	171	282
Comprehensive Income	383,535	374,897	351,059
Public Service Company Of New Hampshire
Net Income	115,876	135,996	131,985
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	1,104	1,162	1,162
Changes in Unrealized (Losses)/Gains on Marketable Securities	(33)	(21)	136
Other Comprehensive Income/(Loss), Net of Tax	1,071	1,141	1,298
Comprehensive Income	$ 116,947	$ 137,137	$ 133,283

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Capital Surplus, Paid In	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	The Connecticut Light And Power Company	The Connecticut Light And Power CompanyCommon Shares	The Connecticut Light And Power CompanyCapital Surplus, Paid In	The Connecticut Light And Power CompanyRetained Earnings	The Connecticut Light And Power CompanyAccumulated Other Comprehensive Loss	NSTAR Electric Company	NSTAR Electric CompanyCommon Shares	NSTAR Electric CompanyCapital Surplus, Paid In	NSTAR Electric CompanyRetained Earnings	NSTAR Electric CompanyAccumulated Other Comprehensive Loss	Public Service Company Of New Hampshire	Public Service Company Of New HampshireCommon Shares	Public Service Company Of New HampshireCapital Surplus, Paid In	Public Service Company Of New HampshireRetained Earnings	Public Service Company Of New HampshireAccumulated Other Comprehensive Loss
Beginning Balance (in shares) at Dec. 31, 2015		317,191,249						6,035,205					200					301
Beginning balance at Dec. 31, 2015	$ 10,352,215	$ 1,669,313	$ 6,262,368	$ 2,797,355	$ (66,844)	$ (309,977)	$ 3,140,717	$ 60,352	$ 1,910,663	$ 1,170,278	$ (576)	$ 3,207,044	$ 0	$ 1,397,642	$ 1,811,678	$ (2,276)	$ 1,237,174	$ 0	$ 748,634	$ 494,901	$ (6,361)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	949,821			949,821			334,254			334,254		350,777			350,777		131,985			131,985
Dividends on Common Stock	(564,486)			(564,486)			(199,599)			(199,599)		(316,300)			(316,300)		(77,600)			(77,600)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Contributions from Eversource Parent																	94,500		94,500
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent							200,000		200,000
Issuance of Common Shares (in shares)		15,787
Issuance of Common Shares	(5,560)	$ 79	(5,639)
Long-Term Incentive Plan Activity	(6,056)		(6,056)
Increase in Treasury Shares (in shares)		(321,228)
Increase in Treasury Shares	(7,794)					(7,794)
Other Changes in Shareholders' Equity	(449)		(449)									103,000		103,000
Other Comprehensive Income	1,562				1,562		523				523	282				282	1,298				1,298
Ending Balance (in shares) at Dec. 31, 2016		316,885,808						6,035,205					200					301
Ending balance at Dec. 31, 2016	10,711,734	$ 1,669,392	6,250,224	3,175,171	(65,282)	(317,771)	3,470,387	$ 60,352	2,110,714	1,299,374	(53)	3,342,843	$ 0	1,500,642	1,844,195	(1,994)	1,387,357	$ 0	843,134	549,286	(5,063)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	995,515			995,515			376,726			376,726		374,726			374,726		135,996			135,996
Dividends on Common Stock	(602,083)			(602,083)			(254,800)			(254,800)		(272,000)			(272,000)		(173,900)			(173,900)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent												2,300		2,300
Long-Term Incentive Plan Activity	(10,834)		(10,834)
Other Changes in Shareholders' Equity	550		550
Other Comprehensive Income	(1,121)				(1,121)		322				322	171				171	1,141				1,141
Ending Balance (in shares) at Dec. 31, 2017		316,885,808						6,035,205					200					301
Ending balance at Dec. 31, 2017	11,086,242	$ 1,669,392	6,239,940	3,561,084	(66,403)	(317,771)	3,587,127	$ 60,352	2,110,765	1,415,741	269	3,446,080	$ 0	1,502,942	1,944,961	(1,823)	1,350,594	$ 0	843,134	511,382	(3,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,040,519			1,040,519			377,717					383,090			383,090		115,876			115,876
Dividends on Common Stock	(640,110)			(640,110)			(60,000)			(60,000)		(228,000)			(228,000)		(530,000)		(530,000)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Contributions from Eversource Parent																			365,000
Capital Contributions from Eversource Parent							300,000		300,000
Long-Term Incentive Plan Activity	(543)		(543)
Other Changes in Shareholders' Equity	1,825		1,825									130,500		130,500
Other Comprehensive Income	6,403				6,403		32				32	445				445	1,071				1,071
Ending Balance (in shares) at Dec. 31, 2018		316,885,808						6,035,205					200					301
Ending balance at Dec. 31, 2018	$ 11,486,817	$ 1,669,392	$ 6,241,222	$ 3,953,974	$ (60,000)	$ (317,771)	$ 4,199,317	$ 60,352	$ 2,410,765	$ 1,727,899	$ 301	$ 3,730,155	$ 0	$ 1,633,442	$ 2,098,091	$ (1,378)	$ 1,302,541	$ 0	$ 678,134	$ 627,258	$ (2,851)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Dividends on common shares (in dollars per share)	$ 2.02	$ 1.90	$ 1.78
Per share par value (in dollars per share)	$ 5	$ 5	$ 5

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net Income	$ 1,040,519	$ 995,515	$ 949,821
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities
Depreciation	819,930	773,802	715,466
Deferred Income Taxes	174,812	491,630	466,463
Bad Debt Expense	61,337	44,453	69,466
Pension, SERP and PBOP Expense, Net	5,498	22,454	39,912
Pension and PBOP Contributions	(194,947)	(242,800)	(158,741)
Regulatory Over/(Under) Recoveries, Net	34,920	(47,935)	13,340
Amortization of Regulatory Assets, Net	(252,026)	(89,986)	(71,696)
(Payments)/Refunds Related to Spent Nuclear Fuel, Net	(145,000)	0	59,804
Other	(111,225)	(204,421)	(118,195)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(141,433)	(117,155)	(142,699)
Fuel, Materials, Supplies and Inventory	(831)	(9,223)	7,755
Taxes Receivable/Accrued, Net	(67,770)	52,284	234,543
Accounts Payable	(22,084)	56,067	(14,126)
Other Current Assets and Liabilities, Net	78,226	91,545	13,737
Net Cash Flows Provided by Operating Activities	1,783,978	1,996,202	2,208,242
Investing Activities:
Investments in Property, Plant and Equipment	(2,523,371)	(2,348,105)	(1,976,867)
Proceeds from Sales of Marketable Securities	900,749	832,903	659,338
Proceeds from Sales of Marketable Securities Used to Pay Spent Nuclear Fuel Obligation	145,000	0	0
Purchases of Marketable Securities	(908,387)	(810,507)	(681,272)
Acquisition of Aquarion	0	(877,652)	0
Payments to Acquire Investments	(205,150)	(32,634)	(188,958)
Proceeds from the Sale of PSNH Generation Assets	193,924	0	0
Other Investing Activities	6,754	5,479	36,211
Net Cash Flows Used in Investing Activities	(2,390,481)	(3,230,516)	(2,151,548)
Financing Activities:
Cash Dividends on Common Shares	(640,110)	(602,083)	(564,486)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,519)
Increase/(Decrease) in Short-Term Debt	(379,310)	72,810	(12,453)
Issuance of Rate Reduction Bonds	635,663	0	0
Issuance of Long-Term Debt	2,200,000	2,500,000	800,000
Retirements of Long-Term Debt	(1,050,330)	(745,000)	(200,000)
Other Financing Activities	(28,457)	(4,754)	(33,482)
Net Cash Flows Provided by/(Used in) Financing Activities	729,937	1,213,454	(17,940)
Net Increase/(Decrease) in Cash, Cash Equivalents and Restricted Cash	123,434	(20,860)	38,754
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	85,890	106,750	67,996
Cash and Restricted Cash - End of Year	209,324	85,890	106,750
The Connecticut Light And Power Company
Operating Activities:
Net Income	377,717	376,726	334,254
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities
Depreciation	278,557	249,352	230,489
Deferred Income Taxes	54,859	119,295	168,919
Bad Debt Expense	15,831	5,312	17,572
Pension, SERP and PBOP Expense, Net	8,943	9,909	7,328
Pension and PBOP Contributions	(41,150)	(2,500)	(380)
Regulatory Over/(Under) Recoveries, Net	(53,372)	(8,017)	(68,730)
Amortization of Regulatory Assets, Net	(129,021)	(83,166)	(38,765)
Other	(69,786)	(42,973)	(36,245)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(67,334)	(47,768)	3,229
Fuel, Materials, Supplies and Inventory	3,909	3,612	(8,926)
Taxes Receivable/Accrued, Net	8,954	(9,688)	123,692
Accounts Payable	(76,924)	48,032	3,252
Other Current Assets and Liabilities, Net	18,846	21,860	(1,065)
Net Cash Flows Provided by Operating Activities	588,071	806,318	812,154
Investing Activities:
Investments in Property, Plant and Equipment	(864,136)	(824,383)	(611,984)
Proceeds from the Sale of PSNH Generation Assets	0	0	9,047
Other Investing Activities	209	236	296
Net Cash Flows Used in Investing Activities	(863,927)	(824,147)	(602,641)
Financing Activities:
Cash Dividends on Common Shares	(60,000)	(254,800)	(199,599)
(Decrease)/Increase in Notes Payable to Eversource Parent	(69,500)	(10,600)	(197,300)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Issuance of Long-Term Debt	500,000	525,000	0
Retirements of Long-Term Debt	(300,000)	(250,000)	0
Capital Contributions from Eversource Parent	300,000	0	200,000
Other Financing Activities	(7,091)	15,004	(857)
Net Cash Flows Provided by/(Used in) Financing Activities	357,850	19,045	(203,315)
Net Increase/(Decrease) in Cash, Cash Equivalents and Restricted Cash	81,994	1,216	6,198
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	9,619	8,403	2,205
Cash and Restricted Cash - End of Year	91,613	9,619	8,403
NSTAR Electric Company
Operating Activities:
Net Income	383,090	374,726	350,777
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities
Depreciation	276,372	274,008	259,262
Deferred Income Taxes	41,438	110,499	101,698
Bad Debt Expense	22,279	21,252	31,728
Pension, SERP and PBOP Expense, Net	(21,521)	(9,509)	(771)
Pension and PBOP Contributions	(61,751)	(90,721)	(37,305)
Regulatory Over/(Under) Recoveries, Net	149,647	(20,009)	118,385
Amortization of Regulatory Assets, Net	(46,654)	(33,831)	(34,332)
Other	(65,523)	(24,872)	(50,831)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(26,403)	(50,896)	(70,302)
Fuel, Materials, Supplies and Inventory	(18,685)	(24,610)	10,571
Taxes Receivable/Accrued, Net	(33,900)	39,205	60,774
Accounts Payable	37,140	(20,421)	18,000
Other Current Assets and Liabilities, Net	51,674	26,849	(14,227)
Net Cash Flows Provided by Operating Activities	780,511	639,332	812,091
Investing Activities:
Investments in Property, Plant and Equipment	(725,766)	(719,623)	(664,932)
Other Investing Activities	58	(3,552)	53
Net Cash Flows Used in Investing Activities	(725,708)	(723,175)	(664,879)
Financing Activities:
Cash Dividends on Common Shares	(228,000)	(272,000)	(316,300)
Cash Dividends on Preferred Stock	(1,960)	(1,960)	(1,960)
Increase/(Decrease) in Short-Term Debt	44,500	56,500	(28,400)
Issuance of Long-Term Debt	0	700,000	300,000
Retirements of Long-Term Debt	0	(400,000)	(200,000)
Capital Contributions from Eversource Parent	130,500	2,300	103,000
Other Financing Activities	108	(1,796)	(866)
Net Cash Flows Provided by/(Used in) Financing Activities	(54,852)	83,044	(144,526)
Net Increase/(Decrease) in Cash, Cash Equivalents and Restricted Cash	(49)	(799)	2,686
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	14,708	15,507	12,821
Cash and Restricted Cash - End of Year	14,659	14,708	15,507
Public Service Company Of New Hampshire
Operating Activities:
Net Income	115,876	135,996	131,985
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities
Depreciation	92,055	128,192	116,519
Deferred Income Taxes	35,924	63,883	87,345
Bad Debt Expense	6,383	6,704	7,288
Pension, SERP and PBOP Expense, Net	754	1,368	875
Pension and PBOP Contributions	0	(800)	(17,078)
Regulatory Over/(Under) Recoveries, Net	(27,264)	(30,788)	(4,491)
Amortization of Regulatory Assets, Net	(80,978)	16,577	(11,170)
Other	(15,363)	(16,813)	3,108
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(19,307)	(22,055)	(18,822)
Fuel, Materials, Supplies and Inventory	16,928	5,519	(5,485)
Taxes Receivable/Accrued, Net	(19,970)	339	32,303
Accounts Payable	(56,712)	29,453	11,353
Other Current Assets and Liabilities, Net	3,028	16,463	4,654
Net Cash Flows Provided by Operating Activities	213,310	300,884	360,724
Investing Activities:
Investments in Property, Plant and Equipment	(277,345)	(312,720)	(305,430)
Proceeds from the Sale of PSNH Generation Assets	193,924	0	0
Proceeds from the Sale of Property	4,782	0	0
Other Investing Activities	437	199	326
Net Cash Flows Used in Investing Activities	(78,202)	(312,521)	(305,104)
Financing Activities:
Cash Dividends on Common Shares	(150,000)	(23,900)	(77,600)
(Decrease)/Increase in Notes Payable to Eversource Parent	(205,900)	102,000	(70,400)
Issuance of Rate Reduction Bonds	635,663	0	0
Return of Capital	(530,000)	0	0
Retirements of Long-Term Debt	(199,250)	(70,000)	0
Capital Contributions from Eversource Parent	365,000	0	94,500
Other Financing Activities	(89)	(225)	(255)
Net Cash Flows Provided by/(Used in) Financing Activities	(84,576)	7,875	(53,755)
Net Increase/(Decrease) in Cash, Cash Equivalents and Restricted Cash	50,532	(3,762)	1,865
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	2,191	5,953	4,088
Cash and Restricted Cash - End of Year	$ 52,723	$ 2,191	$ 5,953

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES A. About Eversource, CL&P, NSTAR Electric and PSNH 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 and PSNH (electric utilities), Yankee Gas and NSTAR Gas (natural gas utilities) and Aquarion (water utilities). Eversource provides energy delivery and/or water service to approximately four million electric, natural gas and water customers through eight regulated utilities in Connecticut, Massachusetts and New Hampshire. Eversource, CL&P, NSTAR Electric and PSNH are reporting companies under the Securities Exchange Act of 1934. Eversource Energy is a public utility holding company under the Public Utility Holding Company Act of 2005. Arrangements among the regulated electric companies and other Eversource companies, outside agencies and other utilities covering interconnections, interchange of electric power and sales of utility property are subject to regulation by the FERC. Eversource's regulated companies are subject to regulation of rates, accounting and other matters by the FERC and/or applicable state regulatory commissions (the PURA for CL&P, Yankee Gas and Aquarion, the DPU for NSTAR Electric, NSTAR Gas and Aquarion, and the NHPUC for PSNH and Aquarion). CL&P, NSTAR Electric and PSNH furnish franchised retail electric service in Connecticut, Massachusetts and New Hampshire. Yankee Gas and NSTAR Gas are engaged in the distribution and sale of natural gas to customers within Connecticut and Massachusetts, respectively. Aquarion is engaged in the collection, treatment and distribution of water in Connecticut, Massachusetts and New Hampshire. CL&P, NSTAR Electric and PSNH's results include the operations of their respective distribution and transmission businesses. The distribution business also includes the results of NSTAR Electric's solar power facilities and PSNH's generation facilities prior to sale in 2018. PSNH completed the sales of its thermal generation assets on January 10, 2018 and its hydroelectric generation assets on August 26, 2018. As of December 31, 2018, PSNH does not own any electric generation facilities. See Note 13, "Generation Asset Sale," for further information. Eversource also has a regulated subsidiary, NPT, which was formed to construct, own and operate the Northern Pass line, a HVDC transmission line from Québec to New Hampshire under development that will interconnect with a new HVDC transmission line being developed by a transmission subsidiary of HQ. Eversource Service, Eversource's service company, and several wholly-owned real estate subsidiaries of Eversource, provide support services to Eversource, including its regulated companies. Eversource holds several equity ownership interests, which are accounted for under the equity method. Eversource also consolidates the operations of CYAPC and YAEC, both of which are inactive regional nuclear generation companies engaged in the long-term storage of their spent nuclear fuel. B. Basis of Presentation The consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource, NSTAR Electric and PSNH and the financial statements of CL&P are herein collectively referred to as the "financial statements." The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements. Eversource's utility subsidiaries' electric, natural gas and water distribution 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. Eversource's consolidated financial information includes the results of Aquarion and its subsidiaries beginning from the date of the acquisition on December 4, 2017. Certain reclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation. In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of Eversource, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Boards of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric. As of both December 31, 2018 and 2017 , Eversource's carrying amount of goodwill was approximately $ 4.4 billion . Eversource performs an assessment for possible impairment of its goodwill at least annually. Eversource completed its annual goodwill impairment test for each of its reporting units as of October 1, 2018 and determined that no impairment exists. See Note 24B, "Acquisition of Aquarion and Goodwill - Goodwill," for further information. C. Accounting Standards Accounting Standards Issued but Not Yet Effective: In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) , which changes existing lease accounting guidance and is required to be applied in the first quarter of 2019. The requirements of the new leases standard include balance sheet recognition of leases deemed to be operating leases and additional disclosure requirements. The recognition, measurement and presentation of expenses and cash flows are not significantly changed. The Company implemented the new leases standard in the first quarter of 2019 and applied the Topic 842 lease criteria to new leases and lease renewals entered into effective on or after January 1, 2019. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) - Targeted Improvements , allowing a transition method to adopt the new leases standard on a prospective basis as of the adoption date, with prior periods presented in the financial statements continuing to follow existing lease accounting guidance under Topic 840 (Leases) in the accounting literature. The Company adopted the prospective transition method allowed in ASU 2018-11. The Company has decided to elect the practical expedient package whereby it does not need to reassess whether or not an existing contract is or contains a lease or whether a lease is an operating or capital lease, and it does not need to reassess initial direct costs for leases. The Company has also elected the practical expedient to not reevaluate land easements existing at adoption if they were not previously accounted for as leases. The Company determined the impact the ASUs will have on its financial statements by reviewing its lease population and identifying lease data needed for the disclosure requirements. The Company implemented a new lease accounting system in 2019 to ensure ongoing compliance with the ASU’s requirements. Eversource recognized approximately $60 million , which includes approximately $25 million at NSTAR Electric, approximately $1 million at CL&P and approximately $1 million at PSNH, of operating lease liabilities and right-of-use assets on their respective balance sheets upon transition at January 1, 2019. Implementation of the new guidance will not have an impact on each company’s results of operations and cash flows. Accounting Standards Recently Adopted: On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted ASU 2014-09, Revenue from Contracts with Customers , which amended existing revenue recognition guidance, using the modified retrospective method (cumulatively at the date of initial application) applying it only to contracts that were not complete at January 1, 2018. Under this method of adoption, prior year reported results were not restated. Implementation of the ASU did not have a material effect on the results of operations, financial position or cash flows of Eversource, CL&P, NSTAR Electric or PSNH. See Note 22, "Revenues," for further information . The Company identified an item that was accounted for differently under the new revenue guidance, as compared to the previously existing guidance. As a result of applying guidance on the unit of account under the new standard, purchases of power from and sales of power to ISO-New England are now accounted for net by the hour, rather than net by the month. This change increased Operating Revenues and Purchased Power, Fuel and Transmission by $22.8 million for the year ended December 31, 2018, with no impact on net income. On January 1, 2018, Eversource adopted ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Liabilities . The ASU removed the available-for-sale designation for equity securities, whereby changes in fair value were previously recorded in accumulated other comprehensive income within shareholders' equity, and required changes in fair value of all equity securities to be recorded in earnings effective January 1, 2018. There was no cumulative effect of adoption. Unrealized losses recorded in Other Income, Net were $4.3 million for the year ended December 31, 2018. For further information, see Note 5, "Marketable Securities," to the financial statements. On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted ASU 2017-07, Compensation – Retirement Benefits: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The ASU required separate presentation of service cost from other components of net pension, SERP and PBOP costs, with the other components presented as non-operating income and not subject to capitalization. The ASU has been 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. As of December 31, 2018 , the non-service cost components of net pension, SERP and PBOP costs that were not capitalized in plant were recorded as an increase to regulatory liabilities of $39.8 million , as these amounts continue to be included in rates. See Note 1N, "Summary of Significant Accounting Policies - Other Income, Net," to the financial statements for the portion of pension, SERP and PBOP costs that are presented as non-operating income for the years ended December 31, 2018, 2017 and 2016. For the year ended December 31, 2017, the amounts, which were previously presented within Operations and Maintenance expense on the statements of income, totaled $29.9 million at Eversource, $1.8 million at CL&P, $19.2 million at NSTAR Electric and $5.9 million at PSNH, and have been retrospectively presented within Other Income, Net. For the year ended December 31, 2016, these amounts were $18.6 million at Eversource, $0.7 million at CL&P, $10.5 million at NSTAR Electric and $6.2 million at PSNH. On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted two accounting standards relating to the statement of cash flows; ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments, and ASU 2016-18, Restricted Cash. As a result of implementing ASU 2016-15, dividends from equity method investments of $19.1 million , $20.0 million , and $0.7 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively, are presented in operating activities at Eversource, for which the 2017 and 2016 amounts were previously classified in investing activities. ASU 2016-18 required that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash and restricted cash equivalents. Both standards were applied retrospectively, as required, and neither had a material impact on Eversource's, CL&P's, NSTAR Electric's or PSNH's statements of cash flows. See Note 1P, "Summary of Significant Accounting Policies - Supplemental Cash Flow Information," to the financial statements for a reconciliation of cash and cash equivalents as reported on the balance sheet to the statement of cash flows, which includes amounts described as restricted cash and restricted cash equivalents. D. Northern Pass Northern Pass is Eversource's planned 1,090 MW HVDC transmission line that will interconnect from the Québec-New Hampshire border to Franklin, New Hampshire and an associated alternating current radial transmission line between Franklin and Deerfield, New Hampshire. As of December 31, 2018, our capitalized Northern Pass project costs were approximately $307 million . In March 2018, the New Hampshire Site Evaluation Committee ("NHSEC") issued a written decision denying Northern Pass’ siting application after which the Massachusetts EDCs terminated the selection of, and subsequent contract negotiations with, Northern Pass under the Massachusetts Clean Energy RFP. On April 27, 2018, NPT filed a motion for rehearing with the NHSEC, and on July 12, 2018, the NHSEC issued its written decision denying Northern Pass’ motion for rehearing. On August 10, 2018, NPT filed an appeal to the New Hampshire Supreme Court, alleging that the NHSEC failed to follow applicable law in its review of the project. On October 12, 2018, the New Hampshire Supreme Court accepted this appeal. Subsequently, the NHSEC transmitted the record of its proceedings to the New Hampshire Supreme Court on December 11, 2018. Briefing of the appeal began on February 4, 2019 . The New Hampshire Supreme Court has not set a date for oral argument. NPT intends to continue to pursue NHSEC approval to construct this project. The March 2018 NHSEC decision denying Northern Pass' siting application caused us to review the recoverability of our Northern Pass project costs in the first quarter of 2018. In this recoverability review, we estimated undiscounted expected project cash flows and compared the result to our estimated project costs to determine whether the recorded amount was recoverable. Our undiscounted cash flows were substantially in excess of our estimated project costs. We completed this analysis and concluded that our project costs were recoverable as of March 31, 2018, based on our expectation that the Northern Pass project remains probable of being placed in service. Consistent with Eversource’s and HQ’s long-term relationship to bring clean energy into New England, Eversource and HQ remain committed to Northern Pass and the many benefits this project will bring to our customers and the region. If as a result of future events and changes in circumstances a new recoverability review were to conclude that our project costs are not recoverable, then we would reduce Northern Pass' project costs to the estimated fair value, which could result in most of our $307 million of capitalized project costs being impaired. Such an impairment could have a material adverse effect on our financial position and results of operations. E. Cash and Cash Equivalents Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets. F. Provision for Uncollectible Accounts Eversource, including CL&P, NSTAR Electric and PSNH, 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 NSTAR Electric and NSTAR Gas to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. The total provision for both uncollectible accounts and for uncollectible hardship accounts (the uncollectible hardship balance is included in the total provision) is included in Receivables, Net on the balance sheets, and is as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2018 2017 2018 2017 Eversource $ 212.7 $ 195.7 $ 131.5 $ 122.5 CL&P 88.0 78.9 71.9 65.5 NSTAR Electric 74.5 69.7 42.5 40.3 PSNH 11.1 10.5 — — In accordance with new revenue accounting guidance, uncollectible expense associated with customers' accounts receivable included in Operations and Maintenance expense on the statements of income is as follows: For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Eversource $ 61.3 $ 44.5 $ 69.5 CL&P 15.8 5.3 17.6 NSTAR Electric 22.3 21.3 31.7 PSNH 6.4 6.7 7.3 G. CL&P Energy Efficiency Loans In December 2018, CL&P transferred $41.3 million of its energy efficiency customer loan portfolio to two outside lenders in order to make additional loans to customers. CL&P remains the servicer of the loans and will transmit customer payments to the lenders. Under a three-year agreement with the lenders, additional energy efficiency loans will also be transferred with a maximum amount outstanding under this program of $55 million . The transaction did not qualify as a sale for accounting purposes, and the amounts of the loans ( $18.5 million and $22.8 million as of December 31, 2018 in current and long-term, respectively), included in Accounts Receivable, Net and Other Long-Term Assets, are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet. H. Fuel, Materials, Supplies and Inventory Fuel, Materials, Supplies and Inventory include natural gas inventory, materials and supplies purchased primarily for construction or operation and maintenance purposes, and RECs. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and are used to meet state mandated Renewable Portfolio Standards requirements. The carrying amounts of fuel, materials and supplies, and RECs, which are included in Current Assets on the balance sheets, were as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Fuel $ 33.1 $ — $ — $ — $ 29.7 $ — $ — $ — Materials and Supplies 126.1 44.5 48.6 24.3 117.1 44.4 45.1 18.5 RECs 78.8 — 65.6 13.2 76.3 4.0 50.4 21.8 Total - Current $ 238.0 $ 44.5 $ 114.2 $ 37.5 $ 223.1 $ 48.4 $ 95.5 $ 40.3 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, long-term debt and RRBs. Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below: Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Uncategorized - Investments that are measured at net asset value are not categorized within the fair value hierarchy. Determination of Fair Value: The valuation techniques and inputs used in Eversource's fair value measurements are described in Note 4, "Derivative Instruments," Note 5, "Marketable Securities," Note 6, "Asset Retirement Obligations," Note 10A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," Note 15, "Fair Value of Financial Instruments" and Note 24B, "Acquisition of Aquarion and Goodwill - Goodwill" to the financial statements. J. Derivative Accounting Many of the electric and natural gas companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts related to energy and energy-related products, as contract settlements are recovered from, or refunded to, customers in future rates. The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements. The judgment applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal, accrual accounting is terminated, and fair value accounting is applied prospectively. The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. All changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income. For further information regarding derivative contracts, see Note 4, "Derivative Instruments," to the financial statements. K. Investments Investments are included in Other Long-Term Assets on the balance sheets and earnings impacts from these equity investments are included in Other Income, Net on the statements of income. Strategic, Infrastructure and Other Investments: As of December 31, 2018 and 2017 , Eversource had investments totaling $463.7 million and $277.6 million , respectively. As of December 31, 2018 and 2017 , Eversource's investments included a 50 percent ownership in Bay State Wind, an offshore wind project of $234.3 million and $30.2 million , respectively, a 15 percent ownership interest in a FERC-regulated natural gas transmission business of $155.0 million and $159.6 million , respectively, a 37.2 percent ( 14.5 percent of which related to NSTAR Electric) ownership interest in two companies that transmit hydro-electricity imported from the Hydro-Quebec system in Canada of $19.5 million and $17.7 million , respectively, other investments totaling $54.9 million and $38.8 million , respectively, and a 40 percent ownership interest in Access Northeast of $31.3 million as of December 31, 2017. NSTAR Electric's investments totaled $7.6 million and $6.9 million , respectively, as of December 31, 2018 and 2017 . Impairment of Access Northeast: Access Northeast is a natural gas pipeline and storage project jointly owned by Eversource, Enbridge, Inc. ("Enbridge") and National Grid plc ("National Grid"), through Algonquin Gas Transmission, LLC ("AGT"). Equity method investments are assessed for impairment when conditions exist that indicate that the fair value of the investment is less than book value. If the decline in value is considered to be other-than-temporary, the investment is written down to its estimated fair value, which establishes a new cost basis in the investment. Impairment evaluations involve a significant degree of judgment and estimation, including identifying circumstances that indicate an impairment may exist and developing undiscounted future cash flows. In 2015 and 2016, AGT sought to secure long-term natural gas pipeline capacity contracts with EDCs in Massachusetts, Connecticut, New Hampshire, Maine, and Rhode Island. Subsequently, in 2016, the Massachusetts Supreme Judicial Court and the NHPUC each ruled that state statutes precluded the state regulatory agencies from approving those contracts in Massachusetts and New Hampshire, respectively. The New Hampshire Supreme Court overruled the NHPUC decision in May 2018. Legislative changes are needed in Massachusetts to allow the DPU to approve natural gas pipeline capacity contracts. No such changes have occurred during any legislative session to date. In September 2018, a series of non-Eversource natural gas explosions in eastern Massachusetts resulted in widespread property and system damage, personal injuries, and a fatality. As a result of these events, compounded by the failure to secure Massachusetts legislation to date, we believe there is significant uncertainty around the future timing of, and ability to secure, needed legislative change affecting the natural gas industry and pipeline expansion, which may significantly delay the completion of the Access Northeast project. Eversource identified the September 2018 natural gas series of explosions, compounded by the adverse legislative environment, as negative evidence that indicated potential impairment. Our impairment assessment used a discounted cash flow approach, including consideration of the severity and duration of any decline in fair value of our investment in the project, and involved significant management judgment and estimation, including projections of the project’s discounted cash flows and assumptions about exit price. In the third quarter of 2018, management determined that the future cash flows of the Access Northeast project were uncertain and could no longer be reasonably estimated and that the book value of our equity method investment was not recoverable. As a result, Eversource recorded an other-than-temporary impairment of $32.9 million within Other Income, Net on our statement of income in 2018, which represented the full carrying value of our equity method investment. Regional Decommissioned Nuclear Companies : CL&P, NSTAR Electric and PSNH own common stock in three regional nuclear generation companies (CYAPC, YAEC and MYAPC, collectively referred to as the "Yankee Companies"), each of which owned a single nuclear generating facility that has been decommissioned. For CL&P, NSTAR Electric and PSNH, the respective investments in CYAPC, YAEC and MYAPC are accounted for under the equity method and are included in Other Long-Term Assets on their respective balance sheets. For CL&P, NSTAR Electric and PSNH, these investments totaled $1.3 million , $0.9 million and $0.3 million as of both December 31, 2018 and 2017 . Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. For further information on the Yankee Companies, see Note 12C, "Commitments and Contingencies – Spent Nuclear Fuel Obligations – Yankee Companies," to the financial statements. Equity in Earnings and Dividends from Equity Method Investments: For the years ended December 31, 2018 , 2017 and 2016 , Eversource had equity in earnings, net of impairment, of unconsolidated affiliates of $3.8 million , $27.4 million , and $0.2 million , respectively. Eversource received dividends from its equity method investees of $22.3 million , $20.0 million and $0.1 million , respectively, for the years ended December 31, 2018 , 2017 and 2016 . 2019 Investment - Revolution Wind and South Fork Wind: On February 8, 2019, Eversource and Ørsted entered into a 50-50 partnership for key offshore wind assets in the Northeast. Eversource paid approximately $ 225 million for a 50 percent interest in Ørsted’s Revolution Wind and South Fork Wind power projects, as well as the 257-square-mile tract off the coasts of Massachusetts and Rhode Island, owned by North East Offshore LLC. Upon execution of the transaction, Eversource parent issued a guaranty on behalf of its subsidiary, Eversource Investment LLC. Eversource parent will guarantee, as a primary obligor, the financial obligations, primarily all post-Closing payment obligations of Eversource Investment LLC, under the Sale and Purchase Agreement and an Irrevocable Equity Commitment Letter with Ørsted in an amount not to exceed $ 127.6 million . Eversource parent's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations. L. Operating Expenses Costs related to fuel and natural gas included in Purchased Power, Fuel and Transmission on the statements of income were as follows: For the Years Ended December 31, (Millions of Dollars) 2018

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
REGULATORY ACCOUNTING	REGULATORY ACCOUNTING Eversource's utility 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: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Benefit Costs $ 1,914.8 $ 424.7 $ 544.4 $ 169.6 $ 2,068.8 $ 469.2 $ 560.7 $ 212.3 Income Taxes, Net 728.6 454.4 105.9 8.3 768.9 453.8 113.2 21.7 Securitized Stranded Costs 608.4 — — 608.4 — — — — Deferred Costs from Generation Asset Sale — — — — 516.1 — — 516.1 Storm Restoration Costs, Net 576.0 302.6 212.9 60.5 404.8 216.7 146.6 41.5 Regulatory Tracker Mechanisms 316.0 33.2 169.1 67.3 509.9 85.3 273.0 116.4 Derivative Liabilities 356.5 356.5 — — 367.2 362.3 — — Goodwill-related 348.4 — 299.1 — 365.2 — 313.6 — Asset Retirement Obligations 89.2 32.3 42.2 3.3 101.0 30.3 39.0 17.0 Other Regulatory Assets 208.0 27.0 64.6 12.1 137.4 27.6 78.4 15.8 Total Regulatory Assets 5,145.9 1,630.7 1,438.2 929.5 5,239.3 1,645.2 1,524.5 940.8 Less: Current Portion 514.8 125.2 241.7 67.2 741.9 200.3 333.9 130.1 Total Long-Term Regulatory Assets $ 4,631.1 $ 1,505.5 $ 1,196.5 $ 862.3 $ 4,497.4 $ 1,444.9 $ 1,190.6 $ 810.7 Benefit Costs: Eversource's Pension, SERP and PBOP Plans are accounted for in accordance with accounting guidance on defined benefit pension and other PBOP plans. The liability (or asset) recorded by the regulated companies to recognize the funded status of their retiree benefit plans is offset by a regulatory asset (or offset by a regulatory liability in the case of a benefit plan asset) in lieu of a charge to Accumulated Other Comprehensive Income/(Loss), reflecting ultimate recovery from customers through rates. The regulatory asset (or regulatory liability) is amortized as the actuarial gains and losses and prior service cost are amortized to net periodic benefit cost for the pension and PBOP plans. All amounts are remeasured annually. Regulatory accounting is also applied to the portions of Eversource's service company costs that support the regulated companies, as these amounts are also recoverable. As these regulatory assets or regulatory liabilities do not represent a cash outlay for the regulated companies, no carrying charge is recovered from customers. The decrease in the regulatory asset balance at PSNH as of December 31, 2018 was due in part to the generation divestiture and the securitization of remaining generation costs. CL&P, NSTAR Electric and PSNH recover benefit costs related to their distribution and transmission operations from customers in rates as allowed by their applicable regulatory commissions. NSTAR Electric recovers qualified pension and PBOP expenses related to its distribution operations through a rate reconciling mechanism that fully tracks the change in net pension and PBOP expenses each year. Income Taxes, Net: The tax effect of temporary book-tax differences (differences between the periods in which transactions affect income in the financial statements and the periods in which they affect the determination of taxable income, including those differences relating to uncertain tax positions) is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and accounting guidance for income taxes. Differences in income taxes between the accounting guidance and the rate-making treatment of the applicable regulatory commissions are recorded as regulatory assets. As these assets are offset by deferred income tax liabilities, no carrying charge is collected. The amortization period of these assets varies depending on the nature and/or remaining life of the underlying assets and liabilities. For further information regarding income taxes, see Note 11, "Income Taxes," to the financial statements. Securitized Stranded Costs and Deferred Costs from Generation Asset Sale: On May 8, 2018, a subsidiary of PSNH issued $635.7 million of securitized RRBs to finance PSNH's unrecovered remaining costs associated with the divestiture of its generation assets. Securitized regulatory assets, which are not earning an equity return, are being recovered over the amortization period of the associated RRBs. The PSNH RRBs are expected to be repaid by February 1, 2033. The unrecovered costs related to the difference between the carrying value and the fair value less costs to sell PSNH's thermal generation assets, and were reflected as Deferred Costs from Generation Asset Sale in the table above as of December 31, 2017. As of December 31, 2018, these costs are reflected in the Securitized Stranded Costs balance. For further information, see Note 13, "Generation Asset Sale." Storm Restoration Costs, Net: The storm restoration cost deferrals relate to costs incurred for storm events at CL&P, NSTAR Electric and PSNH that each company expects to recover from customers. A storm must meet certain criteria to qualify for deferral and recovery with the criteria specific to each state jurisdiction and utility company. Once a storm qualifies for recovery, all qualifying expenses incurred during storm restoration efforts are deferred and recovered from customers. Costs for storms that do not meet the specific criteria are expensed as incurred. In addition to storm restoration costs, CL&P and PSNH are each allowed to recover pre-staging storm costs. Management believes storm restoration costs deferred were prudently incurred and meet the criteria for specific cost recovery in Connecticut, Massachusetts and New Hampshire, and that recovery from customers is probable through the applicable regulatory recovery processes. Each electric utility company either recovers a carrying charge on its deferred storm restoration cost regulatory asset balance or the regulatory asset balance is included in rate base. In 2018, several significant storms caused extensive damage to our electric distribution systems and significant customer outages across all three states. These storms resulted in deferred storm restoration costs of approximately $266 million ( $148 million for CL&P, $94 million for NSTAR Electric, and $24 million for PSNH), which were reflected in Storm Restoration Costs, Net in the table above as of December 31, 2018 . On September 17, 2018, the NHPUC approved the recovery of $49 million , plus carrying charges, in storm costs incurred from August 2011 through March 2013 and the transfer of funding from PSNH’s major storm reserve to offset those costs. The costs of these storms (excluding the equity return component of the carrying charges) were deferred as regulatory assets, and the funding reserve collected from customers was accrued as a regulatory liability. The storm cost deferral is separate from the major storm funding reserve that is being collected from customers. As a result of the duration of time between incurring storm costs in August 2011 through March 2013 and final approval from the NHPUC in 2018, PSNH recognized $8.7 million (pre-tax) for the equity return component of the carrying charges, which have been collected from customers, within Other Income, Net on our statement of income in 2018. Storm costs incurred from December 2013 through April 2016 have been audited by the NHPUC staff and are pending NHPUC approval. Regulatory Tracker Mechanisms: The regulated companies' approved rates are designed to recover costs incurred to provide service to customers. The regulated companies recover certain of their costs on a fully-reconciling basis through regulatory commission-approved tracking mechanisms. The differences between the costs incurred (or the rate recovery allowed) and the actual revenues are recorded as regulatory assets (for undercollections) or as regulatory liabilities (for overcollections) to be included in future customer rates each year. Carrying charges are recovered in rates on all material regulatory tracker mechanisms. CL&P, NSTAR Electric and PSNH each recover, on a fully reconciling basis, the costs associated with the procurement of energy, transmission related costs from FERC-approved transmission tariffs, energy efficiency programs, low income assistance programs, certain uncollectible accounts receivable for hardship customers, and restructuring and stranded costs as a result of deregulation, and additionally for the Massachusetts utilities, pension and PBOP benefits and net metering for distributed generation. Energy procurement costs at NSTAR Electric include the costs related to its solar power facilities. CL&P, NSTAR Electric (effective February 1, 2018 as a result of a DPU-approved rate case decision), Yankee Gas (effective November 15, 2018 as a result of a PURA-approved rate case settlement agreement) and NSTAR Gas each have a regulatory commission approved revenue decoupling mechanism. Distribution revenues are decoupled from customer sales volumes, where applicable, which breaks the relationship between sales volumes and revenues recognized. Each company reconciles its annual base distribution rate recovery amount to the pre-established levels of baseline distribution delivery service revenues. Any difference between the allowed level of distribution revenue and the actual amount realized during a 12-month period is adjusted through rates in the following period. Derivative Liabilities: Regulatory assets are recorded as an offset to derivative liabilities and relate to the fair value of contracts used to purchase energy and energy-related products that will be recovered from customers in future rates. These assets are excluded from rate base and are being recovered as the actual settlements occur over the duration of the contracts. See Note 4, "Derivative Instruments," to the financial statements for further information on these contracts. Goodwill-related: The goodwill regulatory asset originated from a 1999 transaction, and the DPU allowed its recovery in NSTAR Electric and NSTAR Gas rates. This regulatory asset is currently being amortized and recovered from customers in rates without a carrying charge over a 40 -year period, and as of December 31, 2018 , there were 21 years of amortization remaining. Asset Retirement Obligations: The costs associated with the depreciation of the regulated companies' ARO assets and accretion of the ARO liabilities are recorded as regulatory assets in accordance with regulatory accounting guidance. The regulated companies' ARO assets, regulatory assets and liabilities offset and are excluded from rate base. These costs are being recovered over the life of the underlying property, plant and equipment. Other Regulatory Assets: Other Regulatory Assets primarily include contractual obligations associated with the remaining nuclear fuel storage costs of the CYAPC, YAEC and MYAPC nuclear facilities, environmental remediation costs, losses associated with the reacquisition or redemption of long-term debt, certain uncollectible accounts receivable for hardship customers, certain merger-related costs allowed for recovery, water tank painting costs, and various other items. Regulatory Costs in Long-Term Assets: Eversource's regulated companies had $122.9 million (including $42.1 million for CL&P, $49.3 million for NSTAR Electric and $12.2 million for PSNH) and $105.8 million (including $18.2 million for CL&P, $42.7 million for NSTAR Electric and $27.2 million for PSNH) of additional regulatory costs as of December 31, 2018 and 2017 , respectively, that were included in long-term assets on the balance sheets. These amounts represent incurred costs for which recovery has not yet been specifically approved by the applicable regulatory agency. However, based on regulatory policies or past precedent on similar costs, management believes it is probable that these costs will ultimately be approved and recovered from customers in rates. Equity Return on Regulatory Assets: For rate-making purposes, the regulated companies recover the carrying costs related to their regulatory assets. For certain regulatory assets, the carrying cost recovered includes an equity return component. This equity return, which is not recorded on the balance sheets, totaled $0.7 million and $1.0 million for CL&P as of December 31, 2018 and 2017 , respectively. These carrying costs will be recovered from customers in future rates. As of December 31, 2018 and 2017 , this equity return, which is not recorded on the balance sheets, totaled $12.0 million and $42.0 million , respectively, for PSNH. The 2017 amount included $25 million of equity return on the Clean Air Project costs that PSNH had agreed not to bill customers as part of the generation divestiture settlement agreement. PSNH sold its generation assets in 2018. Regulatory Liabilities: The components of regulatory liabilities were as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH EDIT due to Tax Cuts and Jobs Act $ 2,883.0 $ 1,031.0 $ 1,103.7 $ 396.4 $ 2,882.0 $ 1,031.6 $ 1,087.9 $ 405.1 Cost of Removal 521.0 39.9 307.1 22.1 502.1 23.2 293.8 37.9 Benefit Costs 91.2 — 76.9 — 132.3 — 112.6 — Regulatory Tracker Mechanisms 309.0 89.5 163.7 48.3 136.7 34.6 77.8 5.0 AFUDC - Transmission 70.7 47.4 23.3 — 67.1 48.8 18.3 — Revenue Subject to Refund due to Tax Cuts and Jobs Act 24.6 — — 12.6 — — — — Other Regulatory Liabilities 80.2 24.0 29.2 4.2 45.2 12.9 3.7 2.7 Total Regulatory Liabilities 3,979.7 1,231.8 1,703.9 483.6 3,765.4 1,151.1 1,594.1 450.7 Less: Current Portion 370.2 109.6 190.6 55.5 128.1 39.0 79.6 6.3 Total Long-Term Regulatory Liabilities $ 3,609.5 $ 1,122.2 $ 1,513.3 $ 428.1 $ 3,637.3 $ 1,112.1 $ 1,514.5 $ 444.4 EDIT due to Tax Cuts and Jobs Act: Pursuant to the "Tax Cuts and Jobs Act" (the "Act"), which became law on December 22, 2017, Eversource remeasured its existing deferred federal income tax balances as of December 31, 2017 to reflect the decrease in the U.S. federal corporate income tax rate from 35 percent to 21 percent. The remeasurement resulted in provisional regulated excess accumulated deferred income tax (excess ADIT or EDIT) liabilities that will benefit our customers in future periods and were recognized as regulatory liabilities on the balance sheet. We estimate that approximately 85 percent of the provisional regulated EDIT liabilities relate to property, plant, and equipment with remaining useful lives estimated to be in excess of 35 years. These amounts are subject to IRS normalization rules and will be returned to customers using the same timing as the remaining useful lives of the underlying assets that gave rise to the ADIT liabilities. Eversource's regulated companies are in the process of, or will be, refunding the EDIT liabilities to customers based on orders issued by applicable state regulatory commissions. For CL&P, amounts related to the EDIT liabilities will be incorporated as refunds to customers in May 1, 2019 base distribution rates. For NSTAR Electric (effective January 1, 2019) and NSTAR Gas (effective February 1, 2019), refunds related to EDIT will occur in rates through a new reconciling factor. Effective November 15, 2018, Yankee Gas' distribution rates charged to customers began to reflect the refund of EDIT. For PSNH, EDIT refunds will be addressed as part of the next distribution rate case filing. The EDIT balance related to PSNH's divested generation assets has been included as a component of the securitization of the stranded generation assets and has started to be refunded to customers via the Stranded Cost Recovery Charge effective August 1, 2018. For our transmission companies, the refund of excess ADIT to customers will be made based on future guidance from FERC. Cost of Removal: Eversource's regulated companies currently recover amounts in rates for future costs of removal of plant assets over the lives of the assets. The estimated cost to remove utility assets from service is recognized as a component of depreciation expense, and the cumulative amount collected from customers but not yet expended is recognized as a regulatory liability. AFUDC - Transmission: Regulatory liabilities were recorded by CL&P and NSTAR Electric for AFUDC accrued on certain reliability-related transmission projects to reflect local rate base recovery. These regulatory liabilities will be amortized over the depreciable life of the related transmission assets. Revenue Subject to Refund due to Tax Cuts and Jobs Act: Eversource established a regulatory liability, recorded as a reduction to revenue, to reflect the difference between the 35 percent federal corporate income tax rate included in rates charged to customers and the 21 percent federal corporate income tax rate, effective January 1, 2018 as a result of the Tax Cuts and Jobs Act, until rates billed to customers reflect the lower federal tax rate. Effective May 1, 2018, CL&P adjusted rates billed to customers to reflect the lower federal income tax rate prospectively and, as of December 31, 2018, fully refunded its regulatory liability associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 through April 30, 2018. Effective November 15, 2018, Yankee Gas adjusted distribution rates to reflect the lower federal income tax rate prospectively and to refund its regulatory liability associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 through November 14, 2018. Although Yankee Gas' new rates were effective January 1, 2019, the provisions of the settlement agreement took effect November 15, 2018. For NSTAR Electric and NSTAR Gas, a December 2018 DPU order indicated that the DPU will not require a revision to base rates for any potential refunds associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 to the effective dates of each company's rate changes (effective February 1, 2018 for NSTAR Electric and July 1, 2018 for NSTAR Gas). PSNH and Aquarion will refund the overcollection in distribution rates from January 1, 2018 to customers in a future period. PSNH will adjust distribution rates to reflect the prospective lower federal income tax rate effective July 1, 2019, or earlier if a rate case is filed for rates effective prior to July 1, 2019. Effective January 1, 2018, local transmission service rates were updated to reflect the lower U.S. federal corporate income tax rate that resulted from the act. On June 28, 2018, FERC granted a one-time tariff waiver related to the federal corporate income tax rate so that effective June 1, 2018, the regional transmission service rates reflect the reduced federal corporate income tax rate at 21 percent. The refund of excess ADIT to customers will be made based on future guidance from FERC. FERC ROE Complaints : As of December 31, 2018 , Eversource has a reserve established for the second ROE complaint in the pending FERC ROE complaint proceedings, which was recorded as a regulatory liability and is reflected within Regulatory Tracker Mechanisms in the table above. The cumulative pre-tax reserve (excluding interest) as of December 31, 2018 totaled $39.1 million for Eversource (including $21.4 million for CL&P, $14.6 million for NSTAR Electric and $3.1 million for PSNH). See Note 12E, "Commitments and Contingencies – FERC ROE Complaints," for further information on developments in the pending ROE complaint proceedings.

PROPERTY, PLANT AND EQUIPMENT A

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION Utility property, plant and equipment is recorded at original cost. Original cost includes materials, labor, construction overheads and AFUDC for regulated property. The cost of repairs and maintenance is charged to Operations and Maintenance expense as incurred. The following tables summarize property, plant and equipment by asset category: Eversource As of December 31, (Millions of Dollars) 2018 2017 Distribution - Electric $ 15,071.1 $ 14,410.5 Distribution - Natural Gas 3,546.2 3,244.2 Transmission - Electric 10,153.9 9,270.9 Distribution - Water 1,639.8 1,558.4 Solar 164.1 36.2 Utility 30,575.1 28,520.2 Other (1) 778.6 693.7 Property, Plant and Equipment, Gross 31,353.7 29,213.9 Less: Accumulated Depreciation Utility (7,126.2 ) (6,846.9 ) Other (336.7 ) (286.9 ) Total Accumulated Depreciation (7,462.9 ) (7,133.8 ) Property, Plant and Equipment, Net 23,890.8 22,080.1 Construction Work in Progress 1,719.6 1,537.4 Total Property, Plant and Equipment, Net $ 25,610.4 $ 23,617.5 As of December 31, 2018 2017 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Distribution - Electric $ 6,176.4 $ 6,756.4 $ 2,178.6 $ 5,888.3 $ 6,479.0 $ 2,083.4 Transmission - Electric 4,700.5 4,065.9 1,338.7 4,239.9 3,821.2 1,161.3 Solar — 164.1 — — 36.2 — Property, Plant and Equipment, Gross 10,876.9 10,986.4 3,517.3 10,128.2 10,336.4 3,244.7 Less: Accumulated Depreciation (2,302.6 ) (2,702.0 ) (772.9 ) (2,239.0 ) (2,550.2 ) (751.8 ) Property, Plant and Equipment, Net 8,574.3 8,284.4 2,744.4 7,889.2 7,786.2 2,492.9 Construction Work in Progress 335.4 510.3 135.7 381.8 460.3 149.4 Total Property, Plant and Equipment, Net $ 8,909.7 $ 8,794.7 $ 2,880.1 $ 8,271.0 $ 8,246.5 $ 2,642.3 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. Depreciation of utility assets is calculated on a straight-line basis using composite rates based on the estimated remaining useful lives of the various classes of property (estimated useful life for PSNH distribution and the water utilities). The composite rates, which are subject to approval by the appropriate state regulatory agency, include a cost of removal component, which is collected from customers over the lives of the plant assets and is recognized as a regulatory liability. Depreciation rates are applied to property from the time it is placed in service. Upon retirement from service, the cost of the utility asset is charged to the accumulated provision for depreciation. The actual incurred removal costs are applied against the related regulatory liability. The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows: (Percent) 2018 2017 2016 Eversource 2.9 % 3.0 % 3.0 % CL&P 2.8 % 2.8 % 2.7 % NSTAR Electric 2.8 % 2.9 % 2.9 % PSNH 2.8 % 3.1 % 3.1 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2018 (Years) Eversource CL&P NSTAR Electric PSNH Distribution - Electric 34.1 35.4 33.7 32.3 Distribution - Natural Gas 43.8 — — — Transmission - Electric 41.3 38.0 45.3 42.9 Distribution - Water 33.3 — — — Solar 24.9 — 24.9 — Other 12.9 — — —

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE INSTRUMENTS	DERIVATIVE INSTRUMENTS The electric and natural gas 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. These 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 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 electric and natural gas companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivatives, as contract settlement amounts are recovered from, or refunded to, customers in their respective energy supply rates. The gross fair values of derivative assets and liabilities with the same counterparty are offset and reported as net Derivative Assets or Derivative Liabilities, with current and long-term portions, on the balance sheets. The following table presents the gross fair values of contracts, categorized by risk type, and the net amounts recorded as current or long-term derivative assets or liabilities: As of December 31, 2018 2017 (Millions of Dollars) Fair Value Hierarchy Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: CL&P Level 3 9.6 (3.4 ) 6.2 9.5 (7.1 ) 2.4 Other Level 2 $ 1.5 $ (0.9 ) $ 0.6 $ — $ — $ — Long-Term Derivative Assets: CL&P Level 3 74.2 (2.3 ) 71.9 71.9 (5.3 ) 66.6 Current Derivative Liabilities: CL&P Level 3 (55.1 ) — (55.1 ) (54.4 ) — (54.4 ) Other Level 2 — — — (4.5 ) — (4.5 ) Long-Term Derivative Liabilities : CL&P Level 3 (379.5 ) — (379.5 ) (376.9 ) — (376.9 ) Other Level 2 — — — (0.4 ) — (0.4 ) (1) Amounts represent derivative assets and liabilities that Eversource elected to record net on the balance sheets. These amounts are subject to master netting agreements or similar agreements for which the right of offset exists. The business activities that result in the recognition of derivative assets also create exposure to various counterparties. As of December 31, 2018 , Eversource's and CL&P's derivative assets were exposed to counterparty credit risk and contracted with investment grade entities. For further information on the fair value of derivative contracts, see Note 1I, "Summary of Significant Accounting Policies – Fair Value Measurements," and Note 1J, "Summary of Significant Accounting Policies – Derivative Accounting," to the financial statements. Derivative Contracts at Fair Value with Offsetting Regulatory Amounts Commodity Supply and Price Risk Management : As required by regulation, CL&P, along with UI, has capacity-related contracts with generation facilities. CL&P has a sharing agreement with UI, with 80 percent of the costs or benefits of each contract borne by or allocated to CL&P and 20 percent borne by or allocated to UI. The combined capacity of these contracts is 787 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. In addition, CL&P has a contract to purchase 0.1 million MWh of energy per year through 2020. As of December 31, 2018 and 2017 , Eversource had New York Mercantile Exchange ("NYMEX") financial contracts for natural gas futures in order to reduce variability associated with the price of 12.5 million and 9.5 million MMBtu of natural gas, respectively. For the years ended December 31, 2018 , 2017 and 2016 , there were losses of $25.0 million , $29.0 million and $125.5 million , respectively, deferred as regulatory costs, which reflect the change in fair value associated with Eversource's derivative contracts. 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 related 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 CL&P's Level 3 derivative contracts and the range of the significant unobservable inputs utilized in the valuations over the duration of the contracts: As of December 31, 2018 2017 CL&P Range Period Covered Range Period Covered Capacity Prices $ 4.30 — 7.44 per kW-Month 2022 - 2026 $ 5.00 — 8.70 per kW-Month 2021 - 2026 Forward Reserve 0.75 — 1.78 per kW-Month 2019 - 2024 1.00 — 2.00 per kW-Month 2018 - 2024 Exit price premiums of 4.2 percent through 15.7 percent are also applied to 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 capacity or forward reserve 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. CL&P (Millions of Dollars) For the Years Ended December 31, 2018 2017 Derivatives, Net: Fair Value as of Beginning of Period $ (362.3 ) $ (420.5 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (32.0 ) (9.5 ) Settlements 37.8 67.7 Fair Value as of End of Period $ (356.5 ) $ (362.3 )

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
MARKETABLE SECURITIES	MARKETABLE SECURITIES Eversource holds marketable securities that are primarily used to fund certain non-qualified executive benefits. The trusts that hold marketable securities 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. In December 2018, CYAPC paid $145 million from its trust to the DOE to partially settle the pre-1983 spent nuclear fuel obligation. Equity Securities: In accordance with new accounting guidance, unrealized gains and losses on equity securities are recorded in Other Income, Net on the statements of income. The fair value of equity securities subject to this guidance as of December 31, 2018 and 2017 was $ 44.0 million and $52.5 million , respectively. For the year ended December 31, 2018 , there were unrealized losses of $4.3 million recorded in Other Income, Net related to these equity securities. For the year ended December 31, 2017, the unrealized gains and losses on these equity securities were recorded in Accumulated Other Comprehensive Income on the balance sheet. Dividend income is recorded in Other Income, Net when dividends are declared. Eversource's equity securities also include CYAPC's and YAEC's marketable securities held in spent nuclear fuel trusts, which had fair values of $ 200.0 million and $261.3 million as of December 31, 2018 and 2017 , respectively. Unrealized gains and losses for these spent nuclear fuel trusts are subject to regulatory accounting treatment and 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. Available-for-Sale Debt Securities: The following is a summary of the available-for-sale debt securities, which are recorded at fair value and are included in current and long-term Marketable Securities on the balance sheets. As of December 31, 2018 2017 Eversource (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Debt Securities $ 190.0 $ 0.4 $ (4.0 ) $ 186.4 $ 284.9 $ 3.2 $ (1.1 ) $ 287.0 Eversource's debt securities include CYAPC's and YAEC's marketable securities held in spent nuclear fuel trusts in the amounts of $143.9 million and $242.3 million as of December 31, 2018 and 2017 , respectively. Unrealized gains and losses on available-for-sale debt securities held in Eversource's non-qualified benefit trust are recorded in Accumulated Other Comprehensive Income. There have been no significant unrealized losses, other-than-temporary impairments, or credit losses for the years ended December 31, 2018 or 2017 . 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. As of December 31, 2018 , 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) $ 30.5 $ 30.3 One to five years 29.2 28.9 Six to ten years 43.6 42.9 Greater than ten years 86.7 84.3 Total Debt Securities $ 190.0 $ 186.4 (1) Amounts in the Less than one year category include securities in the CYAPC and YAEC spent nuclear fuel trusts, which are restricted and are classified in long-term Marketable Securities on the balance sheets. Realized Gains and Losses: Realized gains and losses are recorded in Other Income, Net for Eversource's benefit trust and are offset in Other Long-Term Liabilities for CYAPC and YAEC. Eversource utilizes the specific identification basis method for the Eversource non-qualified benefit trust, and the average cost basis method for the CYAPC and YAEC spent nuclear fuel trusts to compute the realized gains and losses on the sale of marketable securities. For the year ended December 31, 2017, Eversource recognized net realized gains of $9.8 million on the sales of available-for-sale securities held in the benefit trust. The proceeds of the sales were re-invested in the Eversource benefit trust. There were no similar sales for the year ended December 31, 2018. Fair Value Measurements: The following table presents the marketable securities recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Eversource (Millions of Dollars) As of December 31, 2018 2017 Level 1: Mutual Funds and Equities $ 244.0 $ 313.8 Money Market Funds 25.9 23.3 Total Level 1 $ 269.9 $ 337.1 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 79.6 $ 70.2 Corporate Debt Securities 39.5 50.9 Asset-Backed Debt Securities 14.0 21.2 Municipal Bonds 19.2 110.7 Other Fixed Income Securities 8.2 10.7 Total Level 2 $ 160.5 $ 263.7 Total Marketable Securities $ 430.4 $ 600.8 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 instruments and also incorporating yield curves, credit spreads and specific bond terms and conditions. Asset-backed debt securities include collateralized mortgage obligations, commercial mortgage backed securities, and securities collateralized by auto loans, credit card loans or receivables. Asset-backed debt securities are valued using recent trades of similar instruments, prepayment assumptions, yield curves, issuance and maturity dates, and tranche information. Municipal bonds are valued using a market approach that incorporates reported trades and benchmark yields. Other fixed income securities are valued using pricing models, quoted prices of securities with similar characteristics, and discounted cash flows.

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
ASSET RETIREMENT OBLIGATIONS	ASSET RETIREMENT OBLIGATIONS Eversource, including CL&P, NSTAR Electric and PSNH, recognizes a liability for the fair value of an ARO on the obligation date if the liability's fair value can be reasonably estimated, even if it is conditional on a future event. Settlement dates and future costs are reasonably estimated when sufficient information becomes available. Management has identified various categories of AROs, primarily CYAPC's and YAEC's obligation to dispose of spent nuclear fuel and high level waste, and also certain assets containing asbestos and hazardous contamination. Management has performed fair value calculations reflecting expected probabilities for settlement scenarios. The fair value of an ARO is recorded as a liability in Other Long-Term Liabilities with a corresponding amount included in Property, Plant and Equipment, Net on the balance sheets. The ARO assets are depreciated, and the ARO liabilities are accreted over the estimated life of the obligation and the corresponding credits are recorded as accumulated depreciation and ARO liabilities, respectively. As the electric and natural gas companies are rate-regulated on a cost-of-service basis, these companies apply regulatory accounting guidance and both the depreciation and accretion costs associated with these companies' AROs are recorded as increases to Regulatory Assets on the balance sheets. A reconciliation of the beginning and ending carrying amounts of ARO liabilities is as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Balance as of Beginning of Year $ 419.1 $ 31.5 $ 44.6 $ 25.0 $ 426.4 $ 36.0 $ 42.6 $ 23.5 Liabilities Incurred During the Year 11.3 — 11.3 — 0.2 0.1 0.1 — Liabilities Settled During the Year (36.6 ) — — (21.5 ) (19.3 ) (1.0 ) (0.2 ) — Accretion 25.5 2.0 2.2 0.5 26.3 2.3 2.1 1.5 Revisions in Estimated Cash Flows 46.9 — 14.3 — (14.5 ) (5.9 ) — — Balance as of End of Year $ 466.2 $ 33.5 $ 72.4 $ 4.0 $ 419.1 $ 31.5 $ 44.6 $ 25.0 Eversource's amounts include CYAPC and YAEC's AROs of $339.9 million and $301.5 million as of December 31, 2018 and 2017 , respectively. The fair value of the ARO for CYAPC and YAEC includes uncertainties of the fuel off-load dates related to the DOE's timing of performance regarding its obligation to dispose of the spent nuclear fuel and high level waste and other assumptions, including discount rates. The incremental asset recorded as an offset to the ARO liability was fully depreciated since the plants have no remaining useful life. Any changes in the ARO liability are recorded with a corresponding offset to the related regulatory asset. The assets held in the CYAPC and YAEC spent nuclear fuel trusts are restricted for settling the ARO and all other nuclear fuel storage obligations. For further information on the assets held in the spent nuclear fuel trusts, see Note 5, "Marketable Securities," to the financial statements. The increase in the ARO balance at NSTAR Electric for the year ended December 31, 2018 was due to the recording of new liabilities associated with new solar sites placed into service and the replacement of certain distribution cables, and revised remediation costs for existing AROs related to asbestos and hazardous contamination. The decrease in the ARO balance at PSNH for the year ended December 31, 2018 was a result of the generation divestiture and the securitization of remaining generation costs. See Note 13, "Generation Asset Sale," to the financial statements for further information on the PSNH generation divestiture.

SHORT-TERM DEBT

SHORT-TERM DEBT	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
SHORT-TERM DEBT	SHORT-TERM DEBT Short-Term Debt Borrowing Limits: The amount of short-term borrowings that may be incurred by CL&P, NSTAR Electric and NPT is subject to periodic approval by the FERC. Because the NHPUC has jurisdiction over PSNH's short-term debt, PSNH is not currently required to obtain FERC approval for its short-term borrowings. On November 30, 2017, the FERC granted authorization that allows CL&P to issue total short-term borrowings in an aggregate principal amount not to exceed $600 million outstanding at any one time, through December 31, 2019. On November 30, 2017, the FERC granted authorization that allows NSTAR Electric to issue total short-term borrowings in an aggregate principal amount not to exceed $655 million outstanding at any one time, through December 30, 2019. On December 3, 2018, FERC authorized NPT to issue up to an aggregate of $800 million in short-term debt and long-term debt through December 31, 2020. PSNH is authorized by regulation of the NHPUC to incur short-term borrowings up to 10 percent of net fixed plant plus an additional $60 million until further ordered by the NHPUC. As of December 31, 2018 , PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled approximately $331 million . CL&P's certificate of incorporation contains preferred stock provisions restricting the amount of unsecured debt that CL&P may incur, including limiting unsecured indebtedness with a maturity of less than 10 years to 10 percent of total capitalization. As of December 31, 2018 , CL&P had $758.1 million of unsecured debt capacity available under this authorization. Yankee Gas and NSTAR Gas are not required to obtain approval from any state or federal authority to incur short-term debt. Commercial Paper Programs and Credit Agreements : Eversource parent has a $1.45 billion commercial paper program allowing Eversource parent to issue commercial paper as a form of short-term debt. Eversource parent, CL&P, PSNH, NSTAR Gas and Yankee Gas are also parties to a five -year $1.45 billion revolving credit facility. Effective December 10, 2018, the revolving credit facility's termination date was extended for one additional year to December 8, 2023. The revolving credit facility serves to backstop Eversource parent's $1.45 billion commercial paper program. NSTAR Electric has a $650 million commercial paper program allowing NSTAR Electric to issue commercial paper as a form of short-term debt. NSTAR Electric is also a party to a five -year $650 million revolving credit facility. Effective December 10, 2018, the revolving credit facility's termination date was extended for one additional year to December 8, 2023. The revolving credit facility serves to backstop NSTAR Electric's $650 million commercial paper program. The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding as of December 31, Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2018 2017 2018 2017 2018 2017 Eversource Parent Commercial Paper Program $ 631.5 $ 979.3 $ 818.5 $ 470.7 2.77 % 1.86 % NSTAR Electric Commercial Paper Program 278.5 234.0 371.5 416.0 2.50 % 1.55 % There were no borrowings outstanding on either the Eversource parent or NSTAR Electric revolving credit facilities as of December 31, 2018 or 2017 . Eversource's water distribution segment has a $100.0 million revolving credit facility, which expires on August 19, 2019, and there were no amounts outstanding as of December 31, 2018 and $76.0 million outstanding as of December 31, 2017 . Amounts outstanding under the commercial paper programs and revolving credit facility are included in Notes Payable and classified in current liabilities on the Eversource and NSTAR Electric balance sheets as all borrowings are outstanding for no more than 364 days at one time. As a result of the Eversource parent long-term debt issuances on January 8, 2018, the net proceeds of which were used to repay short-term borrowings outstanding under its commercial paper program, $201.2 million of commercial paper borrowings under the Eversource parent commercial paper program were reclassified as Long-Term Debt as of December 31, 2017. Under the credit facilities described above, Eversource and its subsidiaries must comply with certain financial and non-financial covenants, including a consolidated debt to total capitalization ratio. As of December 31, 2018 and 2017 , Eversource and its subsidiaries were in compliance with these covenants. If Eversource or its subsidiaries were not in compliance with these covenants, an event of default would occur requiring all outstanding borrowings by such borrower to be repaid, and additional borrowings by such borrower would not be permitted under its respective credit facility. We believe the future operating cash flows of Eversource, CL&P, NSTAR Electric and PSNH, along with our existing borrowing availability and access to financial markets for the issuance of new long-term debt, will be sufficient to meet any working capital and future operating requirements, and capital investment forecast opportunities. Intercompany Borrowings: Eversource parent uses its available capital resources to provide loans to its subsidiaries to assist in meeting their short-term borrowing needs. In addition, growth in Eversource's key business initiatives requires cash infusion to those subsidiaries. Eversource parent records intercompany interest income from its loans to subsidiaries, which is eliminated in consolidation. Intercompany loans from Eversource parent to its subsidiaries are eliminated in consolidation on Eversource's balance sheets. As of December 31, 2018 , there were intercompany loans from Eversource parent to PSNH of $57.0 million . As of December 31, 2017 , there were intercompany loans from Eversource parent of $69.5 million to CL&P and $262.9 million to PSNH. Intercompany loans from Eversource parent are included in Notes Payable to Eversource Parent and are classified in current liabilities on the respective subsidiary's balance sheets.

LONG-TERM DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 7.875% 1994 Series D due 2024 $ 139.8 $ 139.8 5.750% 2004 Series B due 2034 130.0 130.0 5.625% 2005 Series B due 2035 100.0 100.0 6.350% 2006 Series A due 2036 250.0 250.0 5.750% 2007 Series B due 2037 150.0 150.0 6.375% 2007 Series D due 2037 100.0 100.0 5.650% 2008 Series A due 2018 — 300.0 5.500% 2009 Series A due 2019 250.0 250.0 2.500% 2013 Series A due 2023 400.0 400.0 4.300% 2014 Series A due 2044 475.0 475.0 4.150% 2015 Series A due 2045 350.0 350.0 3.200% 2017 Series A due 2027 300.0 300.0 4.000% 2018 Series A due 2048 500.0 — Total First Mortgage Bonds 3,144.8 2,944.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year (250.0 ) (300.0 ) Unamortized Premiums and Discounts, Net 10.2 11.5 Unamortized Debt Issuance Costs (21.5 ) (17.7 ) CL&P Long-Term Debt $ 3,004.0 $ 2,759.1 NSTAR Electric (Millions of Dollars) As of December 31, 2018 2017 Debentures: 5.750% due 2036 $ 200.0 $ 200.0 5.500% due 2040 300.0 300.0 2.375% due 2022 400.0 400.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 250.0 2.700% due 2026 250.0 250.0 3.200% due 2027 700.0 700.0 Total Debentures 2,400.0 2,400.0 Notes: 5.900% Senior Notes Series B due 2034 50.0 50.0 6.700% Senior Notes Series D due 2037 40.0 40.0 5.100% Senior Notes Series E due 2020 95.0 95.0 3.500% Senior Notes Series F due 2021 250.0 250.0 3.880% Senior Notes Series G due 2023 80.0 80.0 2.750% Senior Notes Series H due 2026 50.0 50.0 Total Notes 565.0 565.0 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net (2.5 ) (1.8 ) Unamortized Debt Issuance Costs (17.7 ) (19.4 ) NSTAR Electric Long-Term Debt $ 2,944.8 $ 2,943.8 PSNH (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 6.000% Series O due 2018 — 110.0 4.500% Series P due 2019 150.0 150.0 4.050% Series Q due 2021 122.0 122.0 3.200% Series R due 2021 160.0 160.0 3.500% Series S due 2023 325.0 325.0 Total First Mortgage Bonds 807.0 917.0 Pollution Control Revenue Bonds: Adjustable Rate Tax Exempt Series A due 2021 — 89.3 Less Amounts due Within One Year (150.0 ) (110.0 ) Unamortized Premiums and Discounts, Net — 0.2 Unamortized Debt Issuance Costs (1.8 ) (4.1 ) PSNH Long-Term Debt $ 655.2 $ 892.4 OTHER (Millions of Dollars) As of December 31, 2018 2017 Yankee Gas - First Mortgage Bonds: 3.020% - 8.480% due 2019 - 2048 $ 470.0 $ 520.0 NSTAR Gas - First Mortgage Bonds: 4.09% - 9.950% due 2020 - 2048 385.0 285.0 Eversource Parent and Other - Notes and Debentures: 4.500% Debentures due 2019 350.0 350.0 2.500% - 4.250% Senior Notes due 2021 - 2029 4,360.0 3,260.0 Unsecured Notes 3.570% - 6.430% due 2021 - 2037 289.5 290.9 Secured Debt 4.100% - 9.640% due 2021 - 2035 70.7 70.4 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 39.5 181.4 Fair Value Adjustment (1) 144.7 172.6 Less Fair Value Adjustment - Current Portion (1) (36.2 ) (35.4 ) Less Amounts due in One Year (401.1 ) (104.2 ) Commercial Paper Classified as Long-Term Debt — 201.2 Unamortized Premiums and Discounts, Net (4.2 ) 1.5 Unamortized Debt Issuance Costs (23.2 ) (12.8 ) Total Other Long-Term Debt $ 5,644.7 $ 5,180.6 Total Eversource Long-Term Debt $ 12,248.7 $ 11,775.9 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record the NSTAR long-term debt at fair value on the date of the 2012 merger and to record the Aquarion long-term debt at fair value on the date of the 2017 acquisition. Long-Term Debt Issuances and Repayments: The following table summarizes long-term debt issuances and repayments: (Millions of Dollars) Issue Date Issuances/(Repayments) Maturity Date Use of Proceeds for Issuances/ CL&P: 4.00% 2018 Series A First Mortgage Bonds March 2018 $ 500.0 April 2048 Repaid long-term debt that matured in 2018 and repaid short-term borrowings 5.65% 2008 Series A First Mortgage Bonds May 2008 (300.0 ) May 2018 Repaid at maturity on May 1, 2018 PSNH: 6.00% 2008 Series O First Mortgage Bonds May 2008 (110.0 ) May 2018 Repaid at maturity on May 1, 2018 2001 Series A Pollution Control Revenue Bonds December 2001 (89.3 ) May 2021 Redeemed on November 28, 2018 at a redemption price of $89.3 million Other: Eversource Parent 2.50% Series I Senior Notes (1) January 2018 200.0 March 2021 Repaid short-term borrowings Eversource Parent 3.30% Series M Senior Notes January 2018 450.0 January 2028 Repaid long-term debt that matured in 2018 Eversource Parent 3.80% Series N Senior Notes December 2018 400.0 December 2023 Repaid short-term borrowings Eversource Parent 4.25% Series O Senior Notes December 2018 500.0 April 2029 Repaid short-term borrowings Eversource Parent 1.60% Series G Senior Notes January 2015 (150.0 ) January 2018 Repaid at maturity on January 15, 2018 Eversource Parent 1.45% Series E Senior Notes May 2013 (300.0 ) May 2018 Repaid at maturity on May 1, 2018 Yankee Gas 4.13% Series O First Mortgage Bonds September 2018 50.0 October 2048 Repaid long-term debt that matured in 2018 Yankee Gas 6.90% Series J First Mortgage Bonds October 2008 (100.0 ) October 2018 Repaid at maturity on October 1, 2018 NSTAR Gas 4.09% Series P First Mortgage Bonds September 2018 100.0 October 2048 Repaid short-term borrowings (1) These notes are part of the same series issued by Eversource parent in March 2016. The aggregate outstanding principal amount of these notes is now $450 million . As a result of the Eversource parent debt issuances in January 2018, $446.8 million of current portion of long-term debt related to two Eversource parent issuances maturing in 2018 and $201.2 million of commercial paper borrowings were reclassified to Long-Term Debt as of December 31, 2017. Long-Term Debt Issuance Authorizations: On August 1, 2018, the DPU approved NSTAR Gas’ request for authorization to issue up to $200 million in long-term debt through December 31, 2019. On December 3, 2018, FERC authorized NPT to issue up to an aggregate of $800 million in short-term debt and long-term debt through December 31, 2020. Long-Term Debt Provisions: The utility plant of CL&P, PSNH, Yankee Gas, NSTAR Gas and a portion of Aquarion is subject to the lien of each company's respective first mortgage bond indenture. The Eversource parent, NSTAR Electric and certain Aquarion debt is unsecured. Additionally, the long-term debt agreements provide that Eversource and certain of its subsidiaries must comply with certain covenants as are customarily included in such agreements, including equity requirements for NSTAR Electric and NSTAR Gas. Under the equity requirements, NSTAR Electric's and Aquarion's senior notes must maintain a certain consolidated indebtedness to capitalization ratio as of the end of any fiscal quarter and NSTAR Gas' outstanding long-term debt must not exceed equity. CL&P's obligation to repay the PCRBs is secured by first mortgage bonds. The first mortgage bonds contain similar terms and provisions as the applicable series of PCRBs. If CL&P fails to meet its obligations under the first mortgage bonds, then the holder of the first mortgage bonds (the issuer of the PCRBs) would have rights under the first mortgage bonds. CL&P's tax-exempt PCRBs will be subject to redemption at par on or after September 1, 2021. Certain secured and unsecured long-term debt securities are callable at redemption price or are subject to make-whole provisions. Eversource, NSTAR Electric, Yankee Gas and Aquarion have certain long-term debt agreements that contain cross-default provisions. No other debt issuances contain cross-default provisions as of December 31, 2018 . Pre-1983 Spent Nuclear Fuel Obligation: Under the Nuclear Waste Policy Act of 1982, the DOE is responsible for the selection and development of repositories for, and the disposal of, spent nuclear fuel and high-level radioactive waste. CYAPC is obligated to pay the DOE for the costs to dispose of spent nuclear fuel and high-level radioactive waste generated prior to April 7, 1983 (pre-1983 Spent Nuclear Fuel) and recorded an accrual for the full liability thereof to the DOE. This liability accrues interest costs at the 3-month Treasury bill yield rate. For nuclear fuel used to generate electricity prior to April 7, 1983, payment may be made any time prior to the first delivery of spent fuel to the DOE. Fees for disposal of nuclear fuel burned on or after April 7, 1983 were billed to member companies and paid to the DOE. As of December 31, 2018 and 2017 , as a result of consolidating CYAPC, Eversource has consolidated $ 39.5 million and $181.4 million , respectively, in pre-1983 spent nuclear fuel obligations to the DOE. In December 2018, CYAPC paid $145 million to the DOE to partially settle this obligation. The obligation includes accumulated interest costs of $29.0 million and $132.6 million as of December 31, 2018 and 2017 , respectively. CYAPC maintains a trust to fund amounts due to the DOE for the disposal of pre-1983 spent nuclear fuel. For further information, see Note 5, "Marketable Securities," to the financial statements. Long-Term Debt Maturities: Long-term debt maturities on debt outstanding for the years 2019 through 2023 and thereafter are shown below. These amounts exclude the CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2018 : (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 801.1 $ 250.0 $ — $ 150.0 2020 296.1 — 95.0 — 2021 1,033.5 — 250.0 282.0 2022 1,188.9 — 400.0 — 2023 1,665.2 400.0 80.0 325.0 Thereafter 7,977.7 2,615.3 2,140.0 50.0 Total $ 12,962.5 $ 3,265.3 $ 2,965.0 $ 807.0

RATE REDUCTION BONDS AND VARIAB

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES	12 Months Ended
	Dec. 31, 2018
Rate Reduction Bonds and Variable Interest Entity [Abstract]
RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES	RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES Rate Reduction Bonds: PSNH Funding LLC 3 (PSNH Funding) is a bankruptcy remote, special purpose, wholly-owned subsidiary of PSNH. PSNH Funding was formed solely to issue rate reduction bonds (RRBs) to finance PSNH’s unrecovered remaining costs associated with the divestiture of its generation assets. On May 8, 2018, PSNH Funding issued $635.7 million of securitized RRBs in multiple tranches with a weighted average interest rate of 3.66 percent , and final maturity dates ranging from 2026 to 2035. The RRBs are expected to be repaid by February 1, 2033. RRB payments consist of principal and interest and will be paid semi-annually, beginning on February 1, 2019. The RRBs were issued pursuant to a finance order issued by the NHPUC on January 30, 2018 to recover remaining costs resulting from the divestiture of PSNH’s generation assets. The proceeds were used by PSNH Funding to purchase PSNH’s stranded cost asset-recovery property, including its vested property right to bill, collect and adjust a non-bypassable stranded cost recovery charge from PSNH’s retail customers. The collections will be used to pay principal, interest and other costs in connection with the RRBs. The RRBs are secured by the stranded cost asset-recovery property. Cash collections from the stranded cost recovery charges and funds on deposit in trust accounts are the sole source of funds to satisfy the debt obligation. PSNH is not the owner of the RRBs, and PSNH Funding’s assets and revenues are not available to pay PSNH’s creditors. The RRBs are non-recourse senior secured obligations of PSNH Funding and are not insured or guaranteed by PSNH or Eversource Energy. PSNH Funding is considered a variable interest entity (VIE) primarily because the equity capitalization is insufficient to support its operations. PSNH has the power to direct the significant activities of the VIE and is most closely associated with the VIE as compared to other interest holders. Therefore, PSNH is considered the primary beneficiary and consolidates PSNH Funding in its consolidated financial statements. The following tables summarize the impact of PSNH Funding on PSNH's balance sheet and income statement: (Millions of Dollars) Balance Sheet: As of December 31, 2018 Restricted Cash - Current Portion (included in Prepayments and Other Current Assets) $ 47.5 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 3.2 Securitized Stranded Cost (included in Regulatory Assets) 608.4 Other Regulatory Liabilities (included in Regulatory Liabilities) 5.8 Accrued Interest (included in Other Current Liabilities) 14.4 Rate Reduction Bonds - Current Portion 52.3 Rate Reduction Bonds - Long-Term Portion 583.3 (Millions of Dollars) Income Statement: For the Year Ended December 31, 2018 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 27.3 Interest Expense on RRB Principal (included in Interest Expense) 14.4 Variable Interest Entities - Other: The Company's variable interests outside of the consolidated group include contracts that are required by regulation and provide for regulatory recovery of contract costs and benefits through customer rates. Eversource, CL&P and NSTAR Electric hold variable interests in VIEs through agreements with certain entities that own single renewable energy or peaking generation power plants, with other independent power producers and with transmission businesses. Eversource, CL&P and NSTAR Electric do not control the activities that are economically significant to these VIEs or provide financial or other support to these VIEs. Therefore, Eversource, CL&P and NSTAR Electric do not consolidate these VIEs.

EMPLOYEE BENEFITS

EMPLOYEE BENEFITS	12 Months Ended
	Dec. 31, 2018
Postemployment Benefits [Abstract]
EMPLOYEE BENEFITS	EMPLOYEE BENEFITS A. Pension Benefits and Postretirement Benefits Other Than Pension Eversource provides defined benefit retirement plans ("Pension Plans") that cover eligible employees and are subject to the provisions of ERISA, as amended by the PPA of 2006. Eversource's policy is to annually fund the Pension Plans in an amount at least equal to an amount that will satisfy all federal funding requirements. In addition to the Pension Plans, Eversource maintains non-qualified defined benefit retirement plans ("SERP Plans") which provide benefits in excess of Internal Revenue Code limitations to eligible participants consisting of current and retired employees. Eversource also provides defined benefit postretirement plans ("PBOP Plans") that provide 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 employees that met certain age and service eligibility requirements. The benefits provided under the PBOP Plans are not vested, and the Company has the right to modify any benefit provision subject to applicable laws at that time. Eversource annually funds postretirement costs through tax deductible contributions to external trusts. The Pension, SERP and PBOP Plans cover eligible employees, including, among others, employees of the regulated companies. Because the regulated companies recover retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of recording an adjustment to Accumulated Other Comprehensive Income/(Loss) for the funded status of the Pension, SERP and PBOP Plans. Regulatory accounting is also applied to the portions of the Eversource Service retiree benefit costs that support the regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP Plans funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income/(Loss). For further information, see Note 2, "Regulatory Accounting," and Note 16, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans is reflected as a component of unamortized actuarial gains or losses, which are recorded in Regulatory Assets or Accumulated Other Comprehensive Income/(Loss). Unamortized actuarial gains or losses are amortized as a component of pension and PBOP expense over the estimated average future employee service period. Pension and SERP Plans: The Pension and SERP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, see Note 5, "Marketable Securities," to the financial statements. The following table provides information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP As of December 31, 2018 As of December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) $ (5,242.3 ) $ (1,170.2 ) $ (1,217.3 ) $ (572.2 ) Service Cost (84.8 ) (21.4 ) (17.4 ) (11.2 ) (71.3 ) (18.5 ) (15.5 ) (9.7 ) Interest Cost (196.4 ) (41.8 ) (43.5 ) (22.0 ) (188.0 ) (41.6 ) (42.7 ) (21.2 ) Actuarial Gain/(Loss) 414.9 106.1 98.6 39.2 (548.7 ) (116.9 ) (143.5 ) (65.1 ) Benefits Paid - Pension 261.8 59.6 66.9 26.2 243.7 63.5 55.4 26.4 Benefits Paid - Lump Sum 14.2 — 7.1 — 18.4 — 6.8 — Benefits Paid - SERP 6.8 0.3 0.3 0.2 20.4 0.3 0.3 0.3 Employee Transfers — 12.0 2.5 (0.9 ) — 8.2 5.5 (0.7 ) Increase due to acquisition of Aquarion — — — — (168.7 ) — — — Benefit Obligation as of End of Year $ (5,520.0 ) $ (1,160.4 ) $ (1,236.5 ) $ (610.7 ) $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 $ 4,076.0 $ 905.5 $ 1,088.3 $ 494.0 Employer Contributions 185.6 41.2 56.5 — 235.2 2.5 85.4 0.8 Actual Return on Pension Plan Assets (75.2 ) (14.2 ) (18.7 ) (7.6 ) 589.7 126.7 154.8 70.4 Benefits Paid - Pension (261.8 ) (59.6 ) (66.9 ) (26.2 ) (243.7 ) (63.5 ) (55.4 ) (26.4 ) Benefits Paid - Lump Sum (14.2 ) — (7.1 ) — (18.4 ) — (6.8 ) — Employee Transfers — (12.0 ) (2.5 ) 0.9 — (8.2 ) (5.5 ) 0.7 Increase due to acquisition of Aquarion — — — — 100.7 — — — Fair Value of Pension Plan Assets as of End of Year $ 4,573.9 $ 918.4 $ 1,222.1 $ 506.6 $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 Funded Status as of December 31st $ (946.1 ) $ (242.0 ) $ (14.4 ) $ (104.1 ) $ (1,197.0 ) $ (312.2 ) $ (90.2 ) $ (102.7 ) In 2018, there was an increase to the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in a decrease to Eversource's pension liability of approximately $465 million as of December 31, 2018, which was partially offset by changes in actual plan experience and changes in other assumptions. In 2017, there was a decrease to the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in an increase to Eversource's pension liability of approximately $390 million as of December 31, 2017. The pension and SERP Plans' funded status includes the current portion of the SERP liability totaling $8.9 million and $8.4 million as of December 31, 2018 and 2017 , respectively, which is included in Other Current Liabilities on the balance sheets. As of December 31, 2018 and 2017 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 5,070.8 $ 1,031.0 $ 1,144.7 $ 543.1 2017 5,583.6 1,179.2 1,260.1 597.2 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2018 2017 Discount Rate 4.22% — 4.45% 3.43% — 3.75% Compensation/Progression Rate 3.50% 3.50% The compensation rate for the Aquarion Plans was 4 percent as of December 31, 2018 and 2017. Pension and SERP Expense: Eversource charges net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. The Company utilizes the spot rate methodology to estimate the discount rate for the service and interest cost components of pension expense, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. The components of net periodic benefit expense for the Pension and SERP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets for future recovery, are shown below. The service cost component of net periodic benefit expense and the intercompany allocations, less the capitalized portions, are included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit costs are included in Other Income, Net on the statements of income. Pension and SERP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include the intercompany allocations or the corresponding capitalized and deferred portion, as these amounts are cash settled on a short-term basis. Pension and SERP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 84.8 $ 21.4 $ 17.4 $ 11.2 Interest Cost 196.4 41.8 43.5 22.0 Expected Return on Pension Plan Assets (391.6 ) (79.1 ) (104.9 ) (43.6 ) Actuarial Loss 145.7 29.1 41.1 11.6 Prior Service Cost 4.3 1.1 0.2 0.4 Total Net Periodic Benefit Expense/(Income) $ 39.6 $ 14.3 $ (2.7 ) $ 1.6 Intercompany Allocations N/A $ 6.1 $ 6.5 $ 1.9 Pension and SERP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 71.3 $ 18.5 $ 15.5 $ 9.7 Interest Cost 188.0 41.6 42.7 21.2 Expected Return on Pension Plan Assets (334.1 ) (71.7 ) (87.6 ) (40.0 ) Actuarial Loss 135.2 27.7 41.1 11.6 Prior Service Cost 4.5 1.5 0.6 0.5 Total Net Periodic Benefit Expense $ 64.9 $ 17.6 $ 12.3 $ 3.0 Intercompany Allocations N/A $ 9.8 $ 9.1 $ 3.3 Pension and SERP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 75.0 $ 18.8 $ 16.3 $ 9.9 Interest Cost 185.5 41.6 42.2 20.7 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (85.1 ) (38.6 ) Actuarial Loss 125.7 25.4 39.9 9.9 Prior Service Cost 3.6 1.5 0.3 0.5 Total Net Periodic Benefit Expense $ 71.9 $ 15.2 $ 13.6 $ 2.4 Intercompany Allocations N/A $ 13.8 $ 11.4 $ 4.0 The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.85% — 4.62% 3.20% — 3.90% 3.27% — 4.89% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 3.50% For the Aquarion Plans, the long-term expected rate of return was 7 percent and the compensation rate was 4 percent for the year ended December 31, 2018. The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income ("OCI") as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses Arising During the Year $ 48.6 $ 333.0 $ 0.7 $ 9.3 Actuarial Losses Reclassified as Net Periodic Benefit Expense (140.1 ) (129.5 ) (5.6 ) (5.7 ) Actuarial Losses Securitized as Stranded Costs (1) (36.7 ) — — — Prior Service Cost/(Credit) Arising During the Year — 1.0 — (0.4 ) Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.9 ) (4.1 ) (0.4 ) (0.4 ) Prior Service Cost Securitized as Stranded Costs (1) (0.1 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 1,807.6 $ 1,935.8 $ 140.6 $ 80.8 $ 85.7 $ 5.6 Prior Service Cost 6.3 10.3 0.9 1.1 1.5 0.2 PBOP Plans: The PBOP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. The following table provides information on the PBOP Plan benefit obligations, fair values of plan assets, and funded status: PBOP As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) $ (810.0 ) $ (165.0 ) $ (270.0 ) $ (89.7 ) Service Cost (10.0 ) (1.9 ) (2.0 ) (1.1 ) (9.5 ) (1.9 ) (1.7 ) (1.3 ) Interest Cost (30.7 ) (5.8 ) (8.7 ) (3.4 ) (27.1 ) (5.3 ) (8.7 ) (3.0 ) Actuarial Gain/(Loss) 102.5 14.4 28.4 8.6 (81.8 ) (18.5 ) (13.2 ) (11.9 ) Benefits Paid 45.3 10.1 14.5 4.9 41.5 9.9 13.5 4.6 Employee Transfers — (0.1 ) 0.1 0.2 — 2.4 1.5 0.2 Increase due to acquisition of Aquarion — — — — (61.7 ) — — — Benefit Obligation as of End of Year $ (841.5 ) $ (161.7 ) $ (246.3 ) $ (91.9 ) $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 922.2 $ 135.9 $ 405.5 $ 79.0 $ 815.8 $ 129.2 $ 361.6 $ 73.2 Actual Return on Plan Assets (36.6 ) (5.2 ) (17.4 ) (2.9 ) 118.0 18.1 52.9 10.4 Employer Contributions 9.3 — 5.2 — 7.6 — 5.3 — Benefits Paid (45.3 ) (10.1 ) (14.5 ) (4.9 ) (41.5 ) (9.9 ) (13.5 ) (4.6 ) Employee Transfers — — 0.3 — — (1.5 ) (0.8 ) — Increase due to acquisition of Aquarion — — — — 22.3 — — — Fair Value of Plan Assets as of End of Year $ 849.6 $ 120.6 $ 379.1 $ 71.2 $ 922.2 $ 135.9 $ 405.5 $ 79.0 Funded Status as of December 31st $ 8.1 $ (41.1 ) $ 132.8 $ (20.7 ) $ (26.4 ) $ (42.5 ) $ 126.9 $ (22.1 ) The Eversource funded status includes prepaid assets of $33.4 million and $13.1 million recorded in Other Long-Term Assets and liabilities of $25.3 million and $39.5 million included in Accrued Pension, SERP and PBOP on the balance sheets as of December 31, 2018 and 2017, respectively. As of December 31, 2018, there was an increase in the discount rate used to calculate the funded status, resulting in a decrease in the Eversource PBOP liability of approximately $88 million . As of December 31, 2017, there was a decrease in the discount rate used to calculate the funded status, as compared to the discount rate as of December 31, 2016, resulting in an increase to the Eversource PBOP liability of approximately $64 million . The following actuarial assumptions were used in calculating the PBOP Plans' year end funded status: PBOP As of December 31, 2018 2017 Discount Rate 4.38% — 4.41% 3.55% — 3.70% For the Eversource Service PBOP Plan, effective with the plan amendment that standardized plan designs and made benefit changes in August 2016, the health care cost trend rate is no longer applicable. For the Aquarion PBOP Plan, the health care trend rate is a range of 3.5 percent to 6.75 percent, with an ultimate rate of 3.5 percent to 5 percent in 2019 and 2023, for post-65 and pre-65 retirees, respectively. PBOP Expense: Eversource charges net periodic postretirement benefits expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. The Company utilizes the spot rate methodology to estimate the discount rate for the service and interest cost components of PBOP expense, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. The components of net periodic benefit expense for the PBOP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets on the balance sheets, are shown below. The service cost component of net periodic benefit expense and the intercompany allocations, less the capitalized portions, are included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit costs are included in Other Income, Net on the statements of income. PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include the intercompany allocations or the corresponding capitalized portion, as these amounts are cash settled on a short-term basis. PBOP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 10.0 $ 1.9 $ 2.0 $ 1.1 Interest Cost 30.7 5.8 8.7 3.4 Expected Return on Plan Assets (72.4 ) (10.4 ) (32.5 ) (6.0 ) Actuarial Loss 10.3 1.6 2.3 0.7 Prior Service (Credit)/Cost (23.6 ) 1.1 (16.9 ) 0.5 Total Net Periodic Benefit Income $ (45.0 ) $ — $ (36.4 ) $ (0.3 ) Intercompany Allocations N/A $ (1.0 ) $ (1.3 ) $ (0.4 ) PBOP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 9.5 $ 1.9 $ 1.7 $ 1.3 Interest Cost 27.1 5.3 8.7 3.0 Expected Return on Plan Assets (63.7 ) (9.7 ) (28.6 ) (5.5 ) Actuarial Loss 9.1 1.0 3.4 0.6 Prior Service (Credit)/Cost (21.6 ) 1.1 (17.0 ) 0.6 Total Net Periodic Benefit Income $ (39.6 ) $ (0.4 ) $ (31.8 ) $ — Intercompany Allocations N/A $ (0.7 ) $ (1.1 ) $ (0.5 ) PBOP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 12.2 $ 2.0 $ 3.4 $ 1.3 Interest Cost 32.9 5.3 13.3 2.9 Expected Return on Plan Assets (62.9 ) (10.1 ) (28.1 ) (5.5 ) Actuarial Loss 9.0 1.5 3.3 0.7 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.1 ) 0.2 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (15.2 ) $ (0.4 ) Intercompany Allocations N/A $ 0.3 $ (0.1 ) $ (0.1 ) The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.28% — 3.94% 3.48% — 4.64% 2.88% — 4.09% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% For the Aquarion Plan, the expected long-term rate of return was 7 percent and the health care trend rate was 7 percent for the year ended December 31, 2018. The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts recognized in Regulatory Assets and OCI that were reclassified as net periodic benefit (expense)/income during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses/(Gains) Arising During the Year $ 6.4 $ 44.8 $ (1.2 ) $ 2.6 Actuarial Losses Reclassified as Net Periodic Benefit Expense (9.9 ) (8.6 ) (0.4 ) (0.5 ) Actuarial Losses Securitized as Stranded Costs (1) (0.8 ) — — — Prior Service (Credit)/Cost Arising During the Year 1.3 (4.0 ) — (0.1 ) Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 23.6 22.3 — (0.7 ) Prior Service Cost Securitized as Stranded Costs (1) (1.3 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 207.3 $ 211.6 $ 9.9 $ 5.0 $ 6.6 $ 0.3 Prior Service (Credit)/Cost (197.6 ) (221.2 ) (23.6 ) 2.6 2.6 0.2 Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans: (Millions of Dollars) 2019 2020 2021 2022 2023 2024 - 2028 Pension and SERP $ 308.5 $ 310.4 $ 318.8 $ 326.6 $ 335.6 $ 1,764.1 PBOP 58.4 58.5 58.6 58.3 57.8 277.4 Eversource Contributions: Based on the current status of the Pension Plans and federal pension funding requirements, Eversource currently expects to make contributions of approximately $112 million in 2019 , of which approximately $44 million and $10 million will be contributed by CL&P and PSNH, respectively. The remaining $46 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource expects to make approximately $11 million in contributions to the PBOP Plan in 2019 , of which approximately $6 million will be contributed by NSTAR Electric. Fair Value of Pension and PBOP Plan Assets: Pension and PBOP funds are held in external trusts. Trust assets, including accumulated earnings, must be used exclusively for Pension and PBOP payments. Eversource's investment strategy for its Pension and PBOP Plans is to maximize the long-term rates of return on these plans' assets within an acceptable level of risk. The investment strategy for each asset category includes a diversification of asset types, fund strategies and fund managers and it establishes target asset allocations that are routinely reviewed and periodically rebalanced. PBOP assets are comprised of assets held in the PBOP Plan trust, as well as specific assets within the Pension Plan trust (401(h) assets). The investment policy and strategy of the 401(h) assets is consistent with that of the defined benefit pension plan. Eversource's expected long-term rates of return on Pension and PBOP Plan assets are based on target asset allocation assumptions and related expected long-term rates of return. In developing its expected long-term rate of return assumptions for the Pension and PBOP Plans, Eversource evaluated input from consultants, as well as long-term inflation assumptions and historical returns. For the year ended December 31, 2018 , management has assumed long-term rates of return of 8.25 percent for the Eversource Service Pension and PBOP Plan assets. Management has assumed a 7 percent long-term rate of return for the Aquarion Plans. These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows: As of December 31, 2018 2017 Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Target Asset Allocation Assumed Rate of Return Equity Securities: United States 15.0 % 8.5 % 21.5 % 8.5 % Global 10.0 % 8.75 % — % — % Non-United States 8.0 % 8.5 % 11.0 % 8.5 % Emerging Markets 4.0 % 10.0 % 4.5 % 10.0 % Debt Securities: Fixed Income 13.0 % 4.0 % 11.0 % 4.0 % Public High Yield Fixed Income 4.0 % 6.5 % 4.0 % 6.5 % Private Debt 15.0 % 9.0 % 15.0 % 9.0 % Emerging Markets Debt — % — % 2.0 % 6.5 % Private Equity 15.0 % 12.0 % 15.0 % 12.0 % Real Assets 16.0 % 7.5 % 12.0 % 7.5 % Hedge Funds — % — % 4.0 % 6.0 % The taxable assets within the Eversource PBOP Plan have a target asset allocation of 70 percent equity securities and 30 percent fixed income securities. The target asset allocation for the Aquarion Pension Plans is 59 percent equity, 36 percent debt and 5 percent other. The target asset allocation for the Aquarion PBOP Plan is 59 percent equity and 41 percent debt. The following table presents, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Pension Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 443.4 $ — $ 1,377.8 $ 1,821.2 $ 535.4 $ — $ 1,653.3 $ 2,188.7 Fixed Income (2) 85.5 160.8 1,265.5 1,511.8 56.6 215.9 1,218.3 1,490.8 Private Equity 6.1 — 834.0 840.1 11.2 — 641.8 653.0 Real Assets (3) 62.9 — 569.1 632.0 101.6 — 539.9 641.5 Total $ 597.9 $ 160.8 $ 4,046.4 $ 4,805.1 $ 704.8 $ 215.9 $ 4,053.3 $ 4,974.0 Less: 401(h) PBOP Assets (4) (231.2 ) (234.5 ) Total Pension Assets $ 4,573.9 $ 4,739.5 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 91.9 $ — $ 210.5 $ 302.4 $ 115.3 $ — $ 241.9 $ 357.2 Fixed Income (2) 22.0 40.3 123.0 185.3 23.4 44.0 133.9 201.3 Private Equity — — 32.7 32.7 — — 31.3 31.3 Real Assets (3) 27.5 — 70.5 98.0 22.4 — 75.5 97.9 Total $ 141.4 $ 40.3 $ 436.7 $ 618.4 $ 161.1 $ 44.0 $ 482.6 $ 687.7 Add: 401(h) PBOP Assets (4) 231.2 234.5 Total PBOP Assets $ 849.6 $ 922.2 (1) United States, Global, Non-United States and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include investments in commingled funds, fixed income funds that invest in a variety of opportunistic and fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) Real assets include real estate funds and hedge funds. (4) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plan. The Company values assets based on observable inputs when available. Equity securities, exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Fixed income securities, such as government issued securities, corporate bonds and high yield bond funds, are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Certain investments, such as commingled funds, private equity investments, real estate funds and hedge funds are valued using the NAV as a practical expedient. These investments are structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. Commingled funds are recorded at NAV provided by the asset manager, which is based on the market prices of the underlying equity securities. Private Equity investments, Fixed Income partnership funds and Real Assets are valued using the NAV provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments, or the NAV of underlying assets held in hedge funds. Assets valued at NAV are uncategorized in the fair value hierarchy. Defined Contribution Plans Eversource maintains defined contribution plans on behalf of eligible participants. The Eversource 401k Plan provides for employee and employer contributions up to statutory limits. For eligible employees, the Eversource 401k Plan provides employer matching contributions of either 100 percent up to a maximum of three percent of eligible compensation or 50 percent up to a maximum of eight percent of eligible compensation. The Eversource 401k Plan also contains a K-Vantage feature for the benefit of eligible participants, which provides an additional annual employer contribution based on age and years of service. K-Vantage participants are not eligible to actively participate in the Eversource Pension Plan. The total Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 38.4 $ 5.0 $ 9.7 $ 3.3 2017 34.5 4.6 8.5 3.7 2016 31.8 4.5 8.1 3.4 Share-Based Payments Share-based compensation awards are recorded using a fair-value based method at the date of grant. Eversource, CL&P, NSTAR Electric and PSNH record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as for the allocation of costs associated with shares issued or sold to Eversource's service company employees and officers that support CL&P, NSTAR Electric and PSNH. Eversource Incentive Plans: Eversource maintains long-term equity-based incentive plans in which Eversource, CL&P, NSTAR Electric and PSNH employees, officers and board members are eligible to participate. The incentive plans authorize Eversource to grant up to 6,700,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2018 and 2017 , Eversource had 3,720,650 and 2,445,110 common shares, respectively, available for issuance under these plans. Eversource accounts for its various share-based plans as follows: • RSUs - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of Eversource's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares. • Performance Shares - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. Vesting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the total shareholder return as compared to the Edison Electric Institute ("EEI") Index during the requisite service period. The fair value of performance shares is determined at the date of grant using a lattice model. RSUs: Eversource granted RSUs under the annual long-term incentive programs that are subject to three -year graded vesting schedules for employees, and one -year graded vesting schedules, or immediate vesting, for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes, subsequent to vesting. A summary of RSU transactions is as follows: RSUs (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 717,039 $ 49.29 Granted 286,315 $ 56.69 Shares Issued (201,386 ) $ 55.35 Forfeited (19,603 ) $ 56.78 Outstanding as of December 31, 2018 782,365 $ 50.25 The weighted average grant-date fair value of RSUs granted for the years ended December 31, 2018 , 2017 and 2016 was $56.69 , $55.97 and $54.67 , respectively. As of December 31, 2018 and 2017 , the number and weighted average grant-date fair value of unvested RSUs was 424,119 and $56.57 per share, and 388,269 and $56.15 per share, respectively. During 2018 , there were 216,572 RSUs at a weighted average grant-date fair value of $56.72 per share that vested during the year and were either paid or deferred. As of December 31, 2018 , 358,246 RSUs were fully vested and deferred and an additional 402,913 are expected to vest. Performance Shares: Eversource granted performance shares under the annual long-term incentive programs that vest based upon the extent to which Company goals are achieved at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows: Performance Shares (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 510,565 $ 55.45 Granted 184,355 $ 56.77 Shares Issued (178,258 ) $ 54.98 Forfeited (17,098 ) $ 56.18 Outstanding as of December 31, 2018 499,564 $ 56.08 The weighted average grant-date fair value of performance shares granted for the years ended December 31, 2018 , 2017 and 2016 was $56.77 , $55.70 and $53.64 , respectively. As of December 31, 2018 and 2017 , the number and weighted average grant-date fair value of unvested performance shares was 366,995 and $56.17 per share, and 331,207 and $55.79 per share, respectively. During 2018 , there were 131,349 performance shares at a weighted average grant-date fair value of $56.08 per share that vested during the year and were either paid or deferred. As of December 31, 2018 , 132,569 performance shares were fully vested and deferred. Compensation Expense: The total compensation expense and associated future income tax benefits recognized by Eversource, CL&P, NSTAR Electric and PSNH for share-based compensation awards were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Compensation Expense $ 21.4 $ 19.7 $ 23.6 Future Income Tax Benefit 5.4 8.0 9.6 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Compensation Expense $ 7.8 $ 7.7 $ 2.9 $ 7.0 $ 7.0 $ 3.2 $ 9.1 $ 8.2 $ 3.5 Future Income Tax Benefit 2.0 1.9 0.7 2.9 2.8 1.3 3.7 3.3 1.4 As of December 31, 2018 , there was $22.3 million of total unrecognized compensation expense related to nonveste

SHARE-BASED PAYMENTS

SHARE-BASED PAYMENTS	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED PAYMENTS	EMPLOYEE BENEFITS A. Pension Benefits and Postretirement Benefits Other Than Pension Eversource provides defined benefit retirement plans ("Pension Plans") that cover eligible employees and are subject to the provisions of ERISA, as amended by the PPA of 2006. Eversource's policy is to annually fund the Pension Plans in an amount at least equal to an amount that will satisfy all federal funding requirements. In addition to the Pension Plans, Eversource maintains non-qualified defined benefit retirement plans ("SERP Plans") which provide benefits in excess of Internal Revenue Code limitations to eligible participants consisting of current and retired employees. Eversource also provides defined benefit postretirement plans ("PBOP Plans") that provide 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 employees that met certain age and service eligibility requirements. The benefits provided under the PBOP Plans are not vested, and the Company has the right to modify any benefit provision subject to applicable laws at that time. Eversource annually funds postretirement costs through tax deductible contributions to external trusts. The Pension, SERP and PBOP Plans cover eligible employees, including, among others, employees of the regulated companies. Because the regulated companies recover retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of recording an adjustment to Accumulated Other Comprehensive Income/(Loss) for the funded status of the Pension, SERP and PBOP Plans. Regulatory accounting is also applied to the portions of the Eversource Service retiree benefit costs that support the regulated companies, as these costs are also recovered from customers. Adjustments to the Pension and PBOP Plans funded status for the unregulated companies are recorded on an after-tax basis to Accumulated Other Comprehensive Income/(Loss). For further information, see Note 2, "Regulatory Accounting," and Note 16, "Accumulated Other Comprehensive Income/(Loss)," to the financial statements. The difference between the actual return and calculated expected return on plan assets for the Pension and PBOP Plans is reflected as a component of unamortized actuarial gains or losses, which are recorded in Regulatory Assets or Accumulated Other Comprehensive Income/(Loss). Unamortized actuarial gains or losses are amortized as a component of pension and PBOP expense over the estimated average future employee service period. Pension and SERP Plans: The Pension and SERP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, see Note 5, "Marketable Securities," to the financial statements. The following table provides information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP As of December 31, 2018 As of December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) $ (5,242.3 ) $ (1,170.2 ) $ (1,217.3 ) $ (572.2 ) Service Cost (84.8 ) (21.4 ) (17.4 ) (11.2 ) (71.3 ) (18.5 ) (15.5 ) (9.7 ) Interest Cost (196.4 ) (41.8 ) (43.5 ) (22.0 ) (188.0 ) (41.6 ) (42.7 ) (21.2 ) Actuarial Gain/(Loss) 414.9 106.1 98.6 39.2 (548.7 ) (116.9 ) (143.5 ) (65.1 ) Benefits Paid - Pension 261.8 59.6 66.9 26.2 243.7 63.5 55.4 26.4 Benefits Paid - Lump Sum 14.2 — 7.1 — 18.4 — 6.8 — Benefits Paid - SERP 6.8 0.3 0.3 0.2 20.4 0.3 0.3 0.3 Employee Transfers — 12.0 2.5 (0.9 ) — 8.2 5.5 (0.7 ) Increase due to acquisition of Aquarion — — — — (168.7 ) — — — Benefit Obligation as of End of Year $ (5,520.0 ) $ (1,160.4 ) $ (1,236.5 ) $ (610.7 ) $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 $ 4,076.0 $ 905.5 $ 1,088.3 $ 494.0 Employer Contributions 185.6 41.2 56.5 — 235.2 2.5 85.4 0.8 Actual Return on Pension Plan Assets (75.2 ) (14.2 ) (18.7 ) (7.6 ) 589.7 126.7 154.8 70.4 Benefits Paid - Pension (261.8 ) (59.6 ) (66.9 ) (26.2 ) (243.7 ) (63.5 ) (55.4 ) (26.4 ) Benefits Paid - Lump Sum (14.2 ) — (7.1 ) — (18.4 ) — (6.8 ) — Employee Transfers — (12.0 ) (2.5 ) 0.9 — (8.2 ) (5.5 ) 0.7 Increase due to acquisition of Aquarion — — — — 100.7 — — — Fair Value of Pension Plan Assets as of End of Year $ 4,573.9 $ 918.4 $ 1,222.1 $ 506.6 $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 Funded Status as of December 31st $ (946.1 ) $ (242.0 ) $ (14.4 ) $ (104.1 ) $ (1,197.0 ) $ (312.2 ) $ (90.2 ) $ (102.7 ) In 2018, there was an increase to the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in a decrease to Eversource's pension liability of approximately $465 million as of December 31, 2018, which was partially offset by changes in actual plan experience and changes in other assumptions. In 2017, there was a decrease to the discount rate used to calculate the funded status of the Eversource pension liability, which resulted in an increase to Eversource's pension liability of approximately $390 million as of December 31, 2017. The pension and SERP Plans' funded status includes the current portion of the SERP liability totaling $8.9 million and $8.4 million as of December 31, 2018 and 2017 , respectively, which is included in Other Current Liabilities on the balance sheets. As of December 31, 2018 and 2017 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 5,070.8 $ 1,031.0 $ 1,144.7 $ 543.1 2017 5,583.6 1,179.2 1,260.1 597.2 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2018 2017 Discount Rate 4.22% — 4.45% 3.43% — 3.75% Compensation/Progression Rate 3.50% 3.50% The compensation rate for the Aquarion Plans was 4 percent as of December 31, 2018 and 2017. Pension and SERP Expense: Eversource charges net periodic pension expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. The Company utilizes the spot rate methodology to estimate the discount rate for the service and interest cost components of pension expense, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. The components of net periodic benefit expense for the Pension and SERP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets for future recovery, are shown below. The service cost component of net periodic benefit expense and the intercompany allocations, less the capitalized portions, are included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit costs are included in Other Income, Net on the statements of income. Pension and SERP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include the intercompany allocations or the corresponding capitalized and deferred portion, as these amounts are cash settled on a short-term basis. Pension and SERP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 84.8 $ 21.4 $ 17.4 $ 11.2 Interest Cost 196.4 41.8 43.5 22.0 Expected Return on Pension Plan Assets (391.6 ) (79.1 ) (104.9 ) (43.6 ) Actuarial Loss 145.7 29.1 41.1 11.6 Prior Service Cost 4.3 1.1 0.2 0.4 Total Net Periodic Benefit Expense/(Income) $ 39.6 $ 14.3 $ (2.7 ) $ 1.6 Intercompany Allocations N/A $ 6.1 $ 6.5 $ 1.9 Pension and SERP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 71.3 $ 18.5 $ 15.5 $ 9.7 Interest Cost 188.0 41.6 42.7 21.2 Expected Return on Pension Plan Assets (334.1 ) (71.7 ) (87.6 ) (40.0 ) Actuarial Loss 135.2 27.7 41.1 11.6 Prior Service Cost 4.5 1.5 0.6 0.5 Total Net Periodic Benefit Expense $ 64.9 $ 17.6 $ 12.3 $ 3.0 Intercompany Allocations N/A $ 9.8 $ 9.1 $ 3.3 Pension and SERP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 75.0 $ 18.8 $ 16.3 $ 9.9 Interest Cost 185.5 41.6 42.2 20.7 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (85.1 ) (38.6 ) Actuarial Loss 125.7 25.4 39.9 9.9 Prior Service Cost 3.6 1.5 0.3 0.5 Total Net Periodic Benefit Expense $ 71.9 $ 15.2 $ 13.6 $ 2.4 Intercompany Allocations N/A $ 13.8 $ 11.4 $ 4.0 The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.85% — 4.62% 3.20% — 3.90% 3.27% — 4.89% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 3.50% For the Aquarion Plans, the long-term expected rate of return was 7 percent and the compensation rate was 4 percent for the year ended December 31, 2018. The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income ("OCI") as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses Arising During the Year $ 48.6 $ 333.0 $ 0.7 $ 9.3 Actuarial Losses Reclassified as Net Periodic Benefit Expense (140.1 ) (129.5 ) (5.6 ) (5.7 ) Actuarial Losses Securitized as Stranded Costs (1) (36.7 ) — — — Prior Service Cost/(Credit) Arising During the Year — 1.0 — (0.4 ) Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.9 ) (4.1 ) (0.4 ) (0.4 ) Prior Service Cost Securitized as Stranded Costs (1) (0.1 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 1,807.6 $ 1,935.8 $ 140.6 $ 80.8 $ 85.7 $ 5.6 Prior Service Cost 6.3 10.3 0.9 1.1 1.5 0.2 PBOP Plans: The PBOP Plans are accounted for under the multiple-employer approach, with each operating company's balance sheet reflecting its share of the funded status of the plans. The following table provides information on the PBOP Plan benefit obligations, fair values of plan assets, and funded status: PBOP As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) $ (810.0 ) $ (165.0 ) $ (270.0 ) $ (89.7 ) Service Cost (10.0 ) (1.9 ) (2.0 ) (1.1 ) (9.5 ) (1.9 ) (1.7 ) (1.3 ) Interest Cost (30.7 ) (5.8 ) (8.7 ) (3.4 ) (27.1 ) (5.3 ) (8.7 ) (3.0 ) Actuarial Gain/(Loss) 102.5 14.4 28.4 8.6 (81.8 ) (18.5 ) (13.2 ) (11.9 ) Benefits Paid 45.3 10.1 14.5 4.9 41.5 9.9 13.5 4.6 Employee Transfers — (0.1 ) 0.1 0.2 — 2.4 1.5 0.2 Increase due to acquisition of Aquarion — — — — (61.7 ) — — — Benefit Obligation as of End of Year $ (841.5 ) $ (161.7 ) $ (246.3 ) $ (91.9 ) $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 922.2 $ 135.9 $ 405.5 $ 79.0 $ 815.8 $ 129.2 $ 361.6 $ 73.2 Actual Return on Plan Assets (36.6 ) (5.2 ) (17.4 ) (2.9 ) 118.0 18.1 52.9 10.4 Employer Contributions 9.3 — 5.2 — 7.6 — 5.3 — Benefits Paid (45.3 ) (10.1 ) (14.5 ) (4.9 ) (41.5 ) (9.9 ) (13.5 ) (4.6 ) Employee Transfers — — 0.3 — — (1.5 ) (0.8 ) — Increase due to acquisition of Aquarion — — — — 22.3 — — — Fair Value of Plan Assets as of End of Year $ 849.6 $ 120.6 $ 379.1 $ 71.2 $ 922.2 $ 135.9 $ 405.5 $ 79.0 Funded Status as of December 31st $ 8.1 $ (41.1 ) $ 132.8 $ (20.7 ) $ (26.4 ) $ (42.5 ) $ 126.9 $ (22.1 ) The Eversource funded status includes prepaid assets of $33.4 million and $13.1 million recorded in Other Long-Term Assets and liabilities of $25.3 million and $39.5 million included in Accrued Pension, SERP and PBOP on the balance sheets as of December 31, 2018 and 2017, respectively. As of December 31, 2018, there was an increase in the discount rate used to calculate the funded status, resulting in a decrease in the Eversource PBOP liability of approximately $88 million . As of December 31, 2017, there was a decrease in the discount rate used to calculate the funded status, as compared to the discount rate as of December 31, 2016, resulting in an increase to the Eversource PBOP liability of approximately $64 million . The following actuarial assumptions were used in calculating the PBOP Plans' year end funded status: PBOP As of December 31, 2018 2017 Discount Rate 4.38% — 4.41% 3.55% — 3.70% For the Eversource Service PBOP Plan, effective with the plan amendment that standardized plan designs and made benefit changes in August 2016, the health care cost trend rate is no longer applicable. For the Aquarion PBOP Plan, the health care trend rate is a range of 3.5 percent to 6.75 percent, with an ultimate rate of 3.5 percent to 5 percent in 2019 and 2023, for post-65 and pre-65 retirees, respectively. PBOP Expense: Eversource charges net periodic postretirement benefits expense to its subsidiaries based on the actual participant demographic data for each subsidiary's participants. The actual investment return in the trust each year is allocated to each of the subsidiaries annually in proportion to the investment return expected to be earned during the year. The Company utilizes the spot rate methodology to estimate the discount rate for the service and interest cost components of PBOP expense, which provides a more precise measurement by matching projected cash flows to the corresponding spot rates on the yield curve. The components of net periodic benefit expense for the PBOP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets on the balance sheets, are shown below. The service cost component of net periodic benefit expense and the intercompany allocations, less the capitalized portions, are included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit costs are included in Other Income, Net on the statements of income. PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include the intercompany allocations or the corresponding capitalized portion, as these amounts are cash settled on a short-term basis. PBOP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 10.0 $ 1.9 $ 2.0 $ 1.1 Interest Cost 30.7 5.8 8.7 3.4 Expected Return on Plan Assets (72.4 ) (10.4 ) (32.5 ) (6.0 ) Actuarial Loss 10.3 1.6 2.3 0.7 Prior Service (Credit)/Cost (23.6 ) 1.1 (16.9 ) 0.5 Total Net Periodic Benefit Income $ (45.0 ) $ — $ (36.4 ) $ (0.3 ) Intercompany Allocations N/A $ (1.0 ) $ (1.3 ) $ (0.4 ) PBOP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 9.5 $ 1.9 $ 1.7 $ 1.3 Interest Cost 27.1 5.3 8.7 3.0 Expected Return on Plan Assets (63.7 ) (9.7 ) (28.6 ) (5.5 ) Actuarial Loss 9.1 1.0 3.4 0.6 Prior Service (Credit)/Cost (21.6 ) 1.1 (17.0 ) 0.6 Total Net Periodic Benefit Income $ (39.6 ) $ (0.4 ) $ (31.8 ) $ — Intercompany Allocations N/A $ (0.7 ) $ (1.1 ) $ (0.5 ) PBOP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 12.2 $ 2.0 $ 3.4 $ 1.3 Interest Cost 32.9 5.3 13.3 2.9 Expected Return on Plan Assets (62.9 ) (10.1 ) (28.1 ) (5.5 ) Actuarial Loss 9.0 1.5 3.3 0.7 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.1 ) 0.2 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (15.2 ) $ (0.4 ) Intercompany Allocations N/A $ 0.3 $ (0.1 ) $ (0.1 ) The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.28% — 3.94% 3.48% — 4.64% 2.88% — 4.09% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% For the Aquarion Plan, the expected long-term rate of return was 7 percent and the health care trend rate was 7 percent for the year ended December 31, 2018. The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts recognized in Regulatory Assets and OCI that were reclassified as net periodic benefit (expense)/income during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses/(Gains) Arising During the Year $ 6.4 $ 44.8 $ (1.2 ) $ 2.6 Actuarial Losses Reclassified as Net Periodic Benefit Expense (9.9 ) (8.6 ) (0.4 ) (0.5 ) Actuarial Losses Securitized as Stranded Costs (1) (0.8 ) — — — Prior Service (Credit)/Cost Arising During the Year 1.3 (4.0 ) — (0.1 ) Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 23.6 22.3 — (0.7 ) Prior Service Cost Securitized as Stranded Costs (1) (1.3 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 207.3 $ 211.6 $ 9.9 $ 5.0 $ 6.6 $ 0.3 Prior Service (Credit)/Cost (197.6 ) (221.2 ) (23.6 ) 2.6 2.6 0.2 Estimated Future Benefit Payments: The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans: (Millions of Dollars) 2019 2020 2021 2022 2023 2024 - 2028 Pension and SERP $ 308.5 $ 310.4 $ 318.8 $ 326.6 $ 335.6 $ 1,764.1 PBOP 58.4 58.5 58.6 58.3 57.8 277.4 Eversource Contributions: Based on the current status of the Pension Plans and federal pension funding requirements, Eversource currently expects to make contributions of approximately $112 million in 2019 , of which approximately $44 million and $10 million will be contributed by CL&P and PSNH, respectively. The remaining $46 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource expects to make approximately $11 million in contributions to the PBOP Plan in 2019 , of which approximately $6 million will be contributed by NSTAR Electric. Fair Value of Pension and PBOP Plan Assets: Pension and PBOP funds are held in external trusts. Trust assets, including accumulated earnings, must be used exclusively for Pension and PBOP payments. Eversource's investment strategy for its Pension and PBOP Plans is to maximize the long-term rates of return on these plans' assets within an acceptable level of risk. The investment strategy for each asset category includes a diversification of asset types, fund strategies and fund managers and it establishes target asset allocations that are routinely reviewed and periodically rebalanced. PBOP assets are comprised of assets held in the PBOP Plan trust, as well as specific assets within the Pension Plan trust (401(h) assets). The investment policy and strategy of the 401(h) assets is consistent with that of the defined benefit pension plan. Eversource's expected long-term rates of return on Pension and PBOP Plan assets are based on target asset allocation assumptions and related expected long-term rates of return. In developing its expected long-term rate of return assumptions for the Pension and PBOP Plans, Eversource evaluated input from consultants, as well as long-term inflation assumptions and historical returns. For the year ended December 31, 2018 , management has assumed long-term rates of return of 8.25 percent for the Eversource Service Pension and PBOP Plan assets. Management has assumed a 7 percent long-term rate of return for the Aquarion Plans. These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows: As of December 31, 2018 2017 Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Target Asset Allocation Assumed Rate of Return Equity Securities: United States 15.0 % 8.5 % 21.5 % 8.5 % Global 10.0 % 8.75 % — % — % Non-United States 8.0 % 8.5 % 11.0 % 8.5 % Emerging Markets 4.0 % 10.0 % 4.5 % 10.0 % Debt Securities: Fixed Income 13.0 % 4.0 % 11.0 % 4.0 % Public High Yield Fixed Income 4.0 % 6.5 % 4.0 % 6.5 % Private Debt 15.0 % 9.0 % 15.0 % 9.0 % Emerging Markets Debt — % — % 2.0 % 6.5 % Private Equity 15.0 % 12.0 % 15.0 % 12.0 % Real Assets 16.0 % 7.5 % 12.0 % 7.5 % Hedge Funds — % — % 4.0 % 6.0 % The taxable assets within the Eversource PBOP Plan have a target asset allocation of 70 percent equity securities and 30 percent fixed income securities. The target asset allocation for the Aquarion Pension Plans is 59 percent equity, 36 percent debt and 5 percent other. The target asset allocation for the Aquarion PBOP Plan is 59 percent equity and 41 percent debt. The following table presents, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Pension Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 443.4 $ — $ 1,377.8 $ 1,821.2 $ 535.4 $ — $ 1,653.3 $ 2,188.7 Fixed Income (2) 85.5 160.8 1,265.5 1,511.8 56.6 215.9 1,218.3 1,490.8 Private Equity 6.1 — 834.0 840.1 11.2 — 641.8 653.0 Real Assets (3) 62.9 — 569.1 632.0 101.6 — 539.9 641.5 Total $ 597.9 $ 160.8 $ 4,046.4 $ 4,805.1 $ 704.8 $ 215.9 $ 4,053.3 $ 4,974.0 Less: 401(h) PBOP Assets (4) (231.2 ) (234.5 ) Total Pension Assets $ 4,573.9 $ 4,739.5 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 91.9 $ — $ 210.5 $ 302.4 $ 115.3 $ — $ 241.9 $ 357.2 Fixed Income (2) 22.0 40.3 123.0 185.3 23.4 44.0 133.9 201.3 Private Equity — — 32.7 32.7 — — 31.3 31.3 Real Assets (3) 27.5 — 70.5 98.0 22.4 — 75.5 97.9 Total $ 141.4 $ 40.3 $ 436.7 $ 618.4 $ 161.1 $ 44.0 $ 482.6 $ 687.7 Add: 401(h) PBOP Assets (4) 231.2 234.5 Total PBOP Assets $ 849.6 $ 922.2 (1) United States, Global, Non-United States and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include investments in commingled funds, fixed income funds that invest in a variety of opportunistic and fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) Real assets include real estate funds and hedge funds. (4) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plan. The Company values assets based on observable inputs when available. Equity securities, exchange traded funds and futures contracts classified as Level 1 in the fair value hierarchy are priced based on the closing price on the primary exchange as of the balance sheet date. Fixed income securities, such as government issued securities, corporate bonds and high yield bond funds, are included in Level 2 and are valued using pricing models, quoted prices of securities with similar characteristics or discounted cash flows. The pricing models utilize observable inputs such as recent trades for the same or similar instruments, yield curves, discount margins and bond structures. Swaps are valued using pricing models that incorporate interest rates and equity and fixed income index closing prices to determine a net present value of the cash flows. Certain investments, such as commingled funds, private equity investments, real estate funds and hedge funds are valued using the NAV as a practical expedient. These investments are structured as investment companies offering shares or units to multiple investors for the purpose of providing a return. Commingled funds are recorded at NAV provided by the asset manager, which is based on the market prices of the underlying equity securities. Private Equity investments, Fixed Income partnership funds and Real Assets are valued using the NAV provided by the partnerships, which are based on discounted cash flows of the underlying investments, real estate appraisals or public market comparables of the underlying investments, or the NAV of underlying assets held in hedge funds. Assets valued at NAV are uncategorized in the fair value hierarchy. Defined Contribution Plans Eversource maintains defined contribution plans on behalf of eligible participants. The Eversource 401k Plan provides for employee and employer contributions up to statutory limits. For eligible employees, the Eversource 401k Plan provides employer matching contributions of either 100 percent up to a maximum of three percent of eligible compensation or 50 percent up to a maximum of eight percent of eligible compensation. The Eversource 401k Plan also contains a K-Vantage feature for the benefit of eligible participants, which provides an additional annual employer contribution based on age and years of service. K-Vantage participants are not eligible to actively participate in the Eversource Pension Plan. The total Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 38.4 $ 5.0 $ 9.7 $ 3.3 2017 34.5 4.6 8.5 3.7 2016 31.8 4.5 8.1 3.4 Share-Based Payments Share-based compensation awards are recorded using a fair-value based method at the date of grant. Eversource, CL&P, NSTAR Electric and PSNH record compensation expense related to these awards, as applicable, for shares issued or sold to their respective employees and officers, as well as for the allocation of costs associated with shares issued or sold to Eversource's service company employees and officers that support CL&P, NSTAR Electric and PSNH. Eversource Incentive Plans: Eversource maintains long-term equity-based incentive plans in which Eversource, CL&P, NSTAR Electric and PSNH employees, officers and board members are eligible to participate. The incentive plans authorize Eversource to grant up to 6,700,000 new shares for various types of awards, including RSUs and performance shares, to eligible employees, officers, and board members. As of December 31, 2018 and 2017 , Eversource had 3,720,650 and 2,445,110 common shares, respectively, available for issuance under these plans. Eversource accounts for its various share-based plans as follows: • RSUs - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period based upon the fair value of Eversource's common shares at the date of grant. The par value of RSUs is reclassified to Common Stock from APIC as RSUs become issued as common shares. • Performance Shares - Eversource records compensation expense, net of estimated forfeitures, on a straight-line basis over the requisite service period. Performance shares vest based upon the extent to which Company goals are achieved. Vesting of outstanding performance shares is based upon both the Company's EPS growth over the requisite service period and the total shareholder return as compared to the Edison Electric Institute ("EEI") Index during the requisite service period. The fair value of performance shares is determined at the date of grant using a lattice model. RSUs: Eversource granted RSUs under the annual long-term incentive programs that are subject to three -year graded vesting schedules for employees, and one -year graded vesting schedules, or immediate vesting, for board members. RSUs are paid in shares, reduced by amounts sufficient to satisfy withholdings for income taxes, subsequent to vesting. A summary of RSU transactions is as follows: RSUs (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 717,039 $ 49.29 Granted 286,315 $ 56.69 Shares Issued (201,386 ) $ 55.35 Forfeited (19,603 ) $ 56.78 Outstanding as of December 31, 2018 782,365 $ 50.25 The weighted average grant-date fair value of RSUs granted for the years ended December 31, 2018 , 2017 and 2016 was $56.69 , $55.97 and $54.67 , respectively. As of December 31, 2018 and 2017 , the number and weighted average grant-date fair value of unvested RSUs was 424,119 and $56.57 per share, and 388,269 and $56.15 per share, respectively. During 2018 , there were 216,572 RSUs at a weighted average grant-date fair value of $56.72 per share that vested during the year and were either paid or deferred. As of December 31, 2018 , 358,246 RSUs were fully vested and deferred and an additional 402,913 are expected to vest. Performance Shares: Eversource granted performance shares under the annual long-term incentive programs that vest based upon the extent to which Company goals are achieved at the end of three-year performance measurement periods. Performance shares are paid in shares, after the performance measurement period. A summary of performance share transactions is as follows: Performance Shares (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 510,565 $ 55.45 Granted 184,355 $ 56.77 Shares Issued (178,258 ) $ 54.98 Forfeited (17,098 ) $ 56.18 Outstanding as of December 31, 2018 499,564 $ 56.08 The weighted average grant-date fair value of performance shares granted for the years ended December 31, 2018 , 2017 and 2016 was $56.77 , $55.70 and $53.64 , respectively. As of December 31, 2018 and 2017 , the number and weighted average grant-date fair value of unvested performance shares was 366,995 and $56.17 per share, and 331,207 and $55.79 per share, respectively. During 2018 , there were 131,349 performance shares at a weighted average grant-date fair value of $56.08 per share that vested during the year and were either paid or deferred. As of December 31, 2018 , 132,569 performance shares were fully vested and deferred. Compensation Expense: The total compensation expense and associated future income tax benefits recognized by Eversource, CL&P, NSTAR Electric and PSNH for share-based compensation awards were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Compensation Expense $ 21.4 $ 19.7 $ 23.6 Future Income Tax Benefit 5.4 8.0 9.6 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Compensation Expense $ 7.8 $ 7.7 $ 2.9 $ 7.0 $ 7.0 $ 3.2 $ 9.1 $ 8.2 $ 3.5 Future Income Tax Benefit 2.0 1.9 0.7 2.9 2.8 1.3 3.7 3.3 1.4 As of December 31, 2018 , there was $22.3 million of total unrecognized compensation expense related to nonveste

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The components of income tax expense are as follows: Eversource (Millions of Dollars) For the Years Ended December 31, 2018 2017 2016 Current Income Taxes: Federal $ 106.5 $ 58.9 $ 38.9 State 10.6 31.6 53.0 Total Current 117.1 90.5 91.9 Deferred Income Taxes, Net: Federal 122.6 433.0 427.9 State 52.2 58.6 38.6 Total Deferred 174.8 491.6 466.5 Investment Tax Credits, Net (2.9 ) (3.2 ) (3.4 ) Income Tax Expense $ 289.0 $ 578.9 $ 555.0 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Current Income Taxes: Federal $ 54.2 $ 79.3 $ 12.2 $ 50.9 $ 107.8 $ 18.6 $ 27.3 $ 86.4 $ (13.7 ) State 20.9 30.0 (0.5 ) 17.4 25.6 6.2 13.3 39.5 8.8 Total Current 75.1 109.3 11.7 68.3 133.4 24.8 40.6 125.9 (4.9 ) Deferred Income Taxes, Net: Federal 48.5 27.9 15.4 123.9 88.1 52.7 157.6 96.6 79.5 State 6.4 13.5 20.5 (4.6 ) 22.4 11.2 11.3 5.1 7.8 Total Deferred 54.9 41.4 35.9 119.3 110.5 63.9 168.9 101.7 87.3 Investment Tax Credits, Net (0.9 ) (1.8 ) — (1.0 ) (1.8 ) — (1.2 ) (1.8 ) — Income Tax Expense $ 129.1 $ 148.9 $ 47.6 $ 186.6 $ 242.1 $ 88.7 $ 208.3 $ 225.8 $ 82.4 A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource (Millions of Dollars, except percentages) For the Years Ended December 31, 2018 2017 2016 Income Before Income Tax Expense $ 1,329.5 $ 1,574.4 $ 1,504.8 Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016 279.2 551.0 526.7 Tax Effect of Differences: Depreciation (30.8 ) (10.8 ) (3.4 ) Investment Tax Credit Amortization (2.9 ) (3.2 ) (3.4 ) Other Federal Tax Credits — — (3.5 ) State Income Taxes, Net of Federal Impact 44.4 47.7 56.2 Dividends on ESOP (5.1 ) (8.4 ) (8.4 ) Tax Asset Valuation Allowance/Reserve Adjustments 5.2 7.0 3.3 Excess Stock Benefit (1.5 ) (2.9 ) (19.1 ) Other, Net 0.5 (1.5 ) 6.6 Income Tax Expense $ 289.0 $ 578.9 $ 555.0 Effective Tax Rate 21.7 % 36.8 % 36.9 % For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars, except percentages) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Income Before Income Tax Expense $ 506.8 $ 532.0 $ 163.5 $ 563.4 $ 616.8 $ 224.7 $ 542.6 $ 576.6 $ 214.3 Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016 106.4 111.7 34.3 197.2 215.9 78.6 189.9 201.8 75.0 Tax Effect of Differences: Depreciation (1.2 ) (2.8 ) 0.1 (5.2 ) (3.0 ) 1.1 1.6 (3.1 ) 1.0 Investment Tax Credit Amortization (0.9 ) (1.8 ) — (1.0 ) (1.8 ) — (1.2 ) (1.8 ) — Other Federal Tax Credits — — — — — — — — (3.5 ) State Income Taxes, Net of Federal Impact 14.5 33.2 15.8 4.5 31.2 11.3 14.5 29.0 10.8 Tax Asset Valuation Allowance/Reserve Adjustments 7.1 1.2 — (9.5 ) — — 1.5 — — Excess Stock Benefit (0.1 ) (0.1 ) (0.1 ) (0.7 ) (0.7 ) (0.3 ) (0.9 ) (1.2 ) (0.4 ) Other, Net 3.3 7.5 (2.5 ) 1.3 0.5 (2.0 ) 2.9 1.1 (0.5 ) Income Tax Expense $ 129.1 $ 148.9 $ 47.6 $ 186.6 $ 242.1 $ 88.7 $ 208.3 $ 225.8 $ 82.4 Effective Tax Rate 25.5 % 28.0 % 29.1 % 33.1 % 39.2 % 39.5 % 38.4 % 39.2 % 38.4 % Eversource, CL&P, NSTAR Electric and PSNH file a consolidated federal income tax return and unitary, combined and separate state income tax returns. These entities are also parties to a tax allocation agreement under which taxable subsidiaries do not pay any more taxes than they would have otherwise paid had they filed a separate company tax return, and subsidiaries generating tax losses, if any, are paid for their losses when utilized. Deferred tax assets and liabilities are recognized for the future tax effects of temporary differences between the carrying amounts and the tax basis of assets and liabilities. The tax effect of temporary differences is accounted for in accordance with the rate-making treatment of the applicable regulatory commissions and relevant accounting authoritative literature. The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Deferred Tax Assets: Employee Benefits $ 388.2 $ 94.5 $ 35.0 $ 31.1 $ 442.1 $ 112.3 $ 34.0 $ 38.0 Derivative Liabilities 111.4 111.4 — — 111.8 110.5 0.3 — Regulatory Deferrals - Liabilities 299.3 38.6 195.5 16.1 205.6 12.0 139.8 17.9 Allowance for Uncollectible Accounts 54.0 23.1 17.8 3.0 50.1 20.6 17.3 2.9 Tax Effect - Tax Regulatory Liabilities 830.3 336.8 288.9 111.7 832.6 337.2 281.2 116.8 Net Operating Loss Carryforwards 28.5 — — 0.6 47.8 — — — Purchase Accounting Adjustment 64.2 — — — 69.9 — — — Other 166.2 81.1 15.6 33.4 149.5 70.7 4.9 49.6 Total Deferred Tax Assets 1,942.1 685.5 552.8 195.9 1,909.4 663.3 477.5 225.2 Less: Valuation Allowance 19.5 10.7 — — 14.6 6.3 — — Net Deferred Tax Assets $ 1,922.6 $ 674.8 $ 552.8 $ 195.9 $ 1,894.8 $ 657.0 $ 477.5 $ 225.2 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 3,724.2 $ 1,293.3 $ 1,342.4 $ 410.6 $ 3,562.0 $ 1,224.9 $ 1,229.2 $ 502.5 Property Tax Accruals 73.2 35.4 26.3 5.2 56.7 20.7 24.2 5.5 Regulatory Amounts: Regulatory Deferrals - Assets 1,025.9 320.1 277.4 213.8 924.9 310.6 267.1 103.6 Tax Effect - Tax Regulatory Assets 238.9 167.0 9.7 8.1 243.1 173.1 9.8 11.4 Goodwill Regulatory Asset - 1999 Merger 95.2 — 81.7 — 99.8 — 85.7 — Derivative Assets 20.1 19.9 — — 17.4 17.4 — — Other 251.1 5.9 109.8 39.4 288.4 13.7 137.3 45.7 Total Deferred Tax Liabilities $ 5,428.6 $ 1,841.6 $ 1,847.3 $ 677.1 $ 5,192.3 $ 1,760.4 $ 1,753.3 $ 668.7 2017 Federal Legislation: On December 22, 2017, the Tax Cuts and Jobs Act became law, which amended existing federal tax rules and included numerous provisions that impacted corporations. In particular, the act reduced the U.S. federal corporate income tax rate from 35 percent to 21 percent effective January 1, 2018. For our regulated companies, the most significant changes are (1) the benefit of incurring a lower federal income tax expense and (2) the reduction in ADIT liabilities (now excess ADIT or EDIT), which were estimated to be approximately $2.9 billion and included in regulatory liabilities as of December 31, 2018 . In 2018, Eversource refunded $ 5.0 million ($ 4.4 million at PSNH and $ 0.6 million at Yankee Gas) to customers. See Note 2, "Regulatory Accounting," to the financial statements for further information. The Company assessed the applicable provisions in the act and recorded the associated impacts as of December 31, 2017. The Company recorded the provisional income tax amounts as of December 31, 2017 in accordance with SEC Staff Accounting Bulletin No. 118 ("SAB 118") issued by the SEC in December 2017, for changes pursuant to the act because the impacts could not be finalized upon issuance of the financial statements, but for which reasonable estimates could be determined. The Company has completed its evaluation of the impacts of the act as of December 31, 2018. The ultimate outcome was not materially different from the provisional estimates recorded as of December 31, 2017. While the Company has recorded the impacts of the act based on interpretation of the provisions as enacted, it is expected the U.S. Department of Treasury and the IRS will issue additional interpretative guidance in the future that could result in changes to previously finalized provisions. At this time, some of the states in which the Company does business have issued guidance regarding the act and the impact was not material. Carryforwards: The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR PSNH Expiration Range Eversource CL&P NSTAR PSNH Expiration Range Federal Net $ 103.6 $ — $ — $ — 2033 - 2037 $ 197.3 $ — $ — $ — 2027 - 2037 Federal Charitable 2.2 — — — 2020 - 2022 18.7 — — — 2017 - 2022 State Net Operating Loss 80.7 — — — 2019 - 2038 82.8 — — — 2028 - 2037 State Tax Credit 148.9 107.0 — — 2018 - 2023 139.0 94.5 — — 2017 - 2022 State Charitable 9.6 — — — 2019 - 2023 31.4 — — — 2017 - 2022 In 2018, the company increased its valuation allowance reserve for state credits by $5.2 million ( $4.4 million for CL&P), net of tax, to reflect an update for expired tax credits. In 2017, the Company increased its valuation allowance reserve for state credits by $9.9 million ( $1.8 million for CL&P), net of tax, to reflect an update for expired tax credits. For 2018 and 2017, state credit and state loss carryforwards have been partially reserved by a valuation allowance of $19.5 million and $14.4 million (net of tax), respectively. Unrecognized Tax Benefits: A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2016 $ 48.0 $ 13.5 Gross Increases - Current Year 9.9 3.9 Gross Increases - Prior Year 0.2 0.2 Lapse of Statute of Limitations (9.7 ) (2.3 ) Balance as of December 31, 2016 48.4 15.3 Gross Increases - Current Year 11.4 4.7 Gross Decreases - Prior Year (0.9 ) (0.5 ) Lapse of Statute of Limitations (7.2 ) (1.4 ) Balance as of December 31, 2017 51.7 18.1 Gross Increases - Current Year 9.2 3.2 Gross Decreases - Prior Year (6.5 ) (0.9 ) Lapse of Statute of Limitations (8.5 ) (2.2 ) Balance as of December 31, 2018 $ 45.9 $ 18.2 Interest and Penalties: Interest on uncertain tax positions is recorded and generally classified as a component of Other Interest Expense on the statements of income. However, when resolution of uncertainties results in the Company receiving interest income, any related interest benefit is recorded in Other Income, Net on the statements of income. No penalties have been recorded. The amount of interest expense/(income) on uncertain tax positions recognized and the related accrued interest payable/(receivable) are as follows: Other Interest Expense/(Income) Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2018 2017 2016 2018 2017 Eversource $ (1.7 ) $ — $ (0.2 ) $ 0.1 $ 1.8 Tax Positions: During 2018 and 2017, Eversource did not resolve any of its uncertain tax positions. Open Tax Years: The following table summarizes Eversource, CL&P, NSTAR Electric and PSNH's tax years that remain subject to examination by major tax jurisdictions as of December 31, 2018 : Description Tax Years Federal 2018 Connecticut 2015 - 2018 Massachusetts 2015 - 2018 New Hampshire 2016 - 2018 Eversource does not estimate to have an earnings impact related to unrecognized tax benefits during the next twelve months.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES A. Environmental Matters General: Eversource, CL&P, NSTAR Electric and PSNH 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 and PSNH have an active environmental auditing and training program and each believes it is substantially in compliance with all enacted laws and regulations. Environmental reserves are accrued when assessments indicate it is probable that a liability has been incurred and an amount can be reasonably estimated. The approach used estimates the liability based on the most likely action plan from a variety of available remediation options, including no action required or several different remedies ranging from establishing institutional controls to full site remediation and monitoring. These liabilities are estimated on an undiscounted basis and do not assume that the amounts are recoverable from insurance companies or other third parties. The environmental reserves include sites at different stages of discovery and remediation and do not include any unasserted claims. These reserve estimates are subjective in nature as they take into consideration several different remediation options at each specific site. The reliability and precision of these estimates can be affected by several factors, including new information concerning either the level of contamination at the site, the extent of Eversource's, CL&P's, NSTAR Electric's and PSNH'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 required environmental remediation. As this information becomes available, management will continue to assess the potential exposure and adjust the reserves accordingly. The amounts recorded as environmental reserves are included in Other Current Liabilities and Other Long-Term Liabilities on the balance sheets and represent management's best estimate of the liability for environmental costs, and take into consideration site assessment, remediation and long-term monitoring costs. The environmental reserves also take into account recurring costs of managing hazardous substances and pollutants, mandated expenditures to remediate contaminated sites and any other infrequent and non-recurring clean-up costs. A reconciliation of the activity in the environmental reserves is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Balance as of January 1, 2017 $ 65.8 $ 4.9 $ 3.8 $ 5.3 Additions 6.2 0.5 1.8 1.0 Payments/Reductions (17.1 ) (0.7 ) (2.9 ) (0.6 ) Balance as of December 31, 2017 54.9 4.7 2.7 5.7 Additions 23.5 1.9 9.7 — Payments/Reductions (13.7 ) (1.2 ) (1.5 ) (0.3 ) Balance as of December 31, 2018 $ 64.7 $ 5.4 $ 10.9 $ 5.4 The number of environmental sites for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: Eversource CL&P NSTAR Electric PSNH 2018 60 15 16 9 2017 59 14 15 10 The increase in the reserve balance was due primarily to the addition of environmental sites at NSTAR Electric and changes in cost estimates at certain MGP sites at our natural gas companies under investigation for which additional remediation will be required. 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 $50.1 million and $49.0 million as of December 31, 2018 and 2017, respectively, and related primarily to the natural gas business segment. As of December 31, 2018 , for 7 environmental sites ( 2 for CL&P) that are included in the Company's reserve for environmental costs, the information known and the nature of the remediation options allow for the Company to estimate the range of losses for environmental costs. As of December 31, 2018 , $23.8 million (including $0.7 million for CL&P) had been accrued as a liability for these sites, which represents the low end of the range of the liabilities for environmental costs. Management believes that additional losses of up to approximately $20 million ( $1 million at CL&P) may be incurred in executing current remediation plans for these sites. As of December 31, 2018 , for 12 environmental sites ( 4 for CL&P and 3 for NSTAR Electric) that are included in the Company's reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2018 , $11.1 million (including $1.9 million for CL&P and $1.9 million for NSTAR Electric) had been accrued as a liability for these sites. As of December 31, 2018 , for the remaining 41 environmental sites (including 9 for CL&P, 13 for NSTAR Electric and 9 for PSNH) that are included in the Company's reserve for environmental costs, the $29.8 million accrual (including $2.8 million for CL&P, $9.0 million for NSTAR Electric and $5.4 million for PSNH) represents management's best estimate of the probable liability and no additional loss is anticipated at this time. Environmental Rate Recovery: PSNH, NSTAR Gas and Yankee Gas have rate recovery mechanisms for MGP related environmental costs, therefore, changes in their respective environmental reserves do not impact Net Income. Effective with the May 2018 distribution rate case settlement, CL&P is allowed to defer certain environmental costs for future recovery. NSTAR Electric does not have a separate environmental cost recovery regulatory mechanism. Long-Term Contractual Arrangements Estimated Future Annual Costs: The estimated future annual costs of significant executed, non-cancelable, long-term contractual arrangements in effect as of December 31, 2018 are as follows: Eversource (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 68.3 $ 73.5 $ 69.1 $ 72.9 $ 74.1 $ 142.9 $ 500.8 Renewable Energy 262.4 261.0 238.9 240.5 217.2 1,662.0 2,882.0 Peaker CfDs 11.9 22.6 21.9 15.3 17.5 43.5 132.7 Natural Gas Procurement 243.8 227.7 183.6 149.2 135.1 1,039.7 1,979.1 Transmission Support Commitments 22.8 23.1 15.2 16.2 17.8 17.8 112.9 Total $ 609.2 $ 607.9 $ 528.7 $ 494.1 $ 461.7 $ 2,905.9 $ 5,607.5 CL&P (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 57.0 $ 69.7 $ 65.3 $ 69.1 $ 70.4 $ 123.9 $ 455.4 Renewable Energy 102.0 103.8 104.0 104.9 105.5 785.3 1,305.5 Peaker CfDs 11.9 22.6 21.9 15.3 17.5 43.5 132.7 Transmission Support Commitments 9.0 9.1 6.0 6.4 7.0 7.0 44.5 Total $ 179.9 $ 205.2 $ 197.2 $ 195.7 $ 200.4 $ 959.7 $ 1,938.1 NSTAR Electric (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 5.5 $ 3.1 $ 3.1 $ 3.1 $ 3.0 $ 19.0 $ 36.8 Renewable Energy 94.7 93.1 88.6 88.8 63.9 435.1 864.2 Transmission Support Commitments 9.0 9.1 6.0 6.3 7.0 7.0 44.4 Total $ 109.2 $ 105.3 $ 97.7 $ 98.2 $ 73.9 $ 461.1 $ 945.4 PSNH (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 5.8 $ 0.7 $ 0.7 $ 0.7 $ 0.7 $ — $ 8.6 Renewable Energy 65.7 64.1 46.3 46.8 47.8 441.6 712.3 Transmission Support Commitments 4.8 4.9 3.2 3.5 3.8 3.8 24.0 Total $ 76.3 $ 69.7 $ 50.2 $ 51.0 $ 52.3 $ 445.4 $ 744.9 Purchased Power and Capacity: CL&P, NSTAR Electric and PSNH have various IPP contracts or purchase obligations for electricity. Such contracts extend through 2024 for CL&P, 2031 for NSTAR Electric and 2023 for PSNH. In addition, CL&P, along with UI, has four capacity CfDs for a total of approximately 787 MW of capacity consisting of three generation units and one demand response project. The capacity CfDs extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set contractual capacity price and the capacity market prices received by the generation facilities in the ISO-NE capacity markets. CL&P has a sharing agreement with UI, whereby UI shares 20 percent of the costs and benefits of these contracts. CL&P's portion of the costs and benefits of these contracts will be paid by, or refunded to, CL&P's customers. The contractual obligations table above does not include CL&P's, NSTAR Electric's or PSNH's standard/basic service contracts, the amounts of which vary with customers' energy needs. Renewable Energy: Renewable energy contracts include non-cancellable commitments under contracts of CL&P, NSTAR Electric and PSNH for the purchase of energy and capacity from renewable energy facilities. Such contracts extend through 2039 for CL&P, 2038 for NSTAR Electric and 2033 for PSNH. The contractual obligations table above does not include long-term commitments signed by CL&P and NSTAR Electric, as required by the PURA and DPU, respectively, for the purchase of renewable energy and related products that are contingent on the future construction of energy facilities. The table also excludes certain CL&P long-term commitments required by regulation that have not yet been executed such as the selection of certain nuclear power-generating facilities awarded under the Act Concerning Zero Carbon Solicitation and Procurement. Peaker CfDs: In 2008, CL&P entered into three CfDs with developers of peaking generation units approved by PURA (Peaker CfDs). These units have a total of approximately 500 MW of peaking capacity. As directed by PURA, CL&P and UI have entered into a sharing agreement, whereby CL&P is responsible for 80 percent and UI for 20 percent of the net costs or benefits of these CfDs. The Peaker CfDs pay the generation facility owner the difference between capacity, forward reserve and energy market revenues and a cost-of-service payment stream for 30 years. The ultimate cost or benefit to CL&P under these contracts will depend on the costs of plant operation and the prices that the projects receive for capacity and other products in the ISO-NE markets. CL&P's portion of the amounts paid or received under the Peaker CfDs will be recoverable from, or refunded to, CL&P's customers. Natural Gas Procurement: In the normal course of business, Eversource's natural gas distribution businesses have long-term contracts for the purchase, transportation and storage of natural gas as part of its portfolio of supplies. These contracts extend through 2034. Transmission Support Commitments: Along with other New England utilities, CL&P, NSTAR Electric and PSNH entered into agreements in 1985 to support transmission and terminal facilities that were built to import electricity from the Hydro-Québec system in Canada. CL&P, NSTAR Electric and PSNH are obligated to pay, over a 30 -year period ending in 2020, their proportionate shares of the annual operation and maintenance expenses and capital costs of those facilities. The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Purchased Power and Capacity $ 72.0 $ 103.9 $ 152.5 Renewable Energy 218.5 235.5 210.9 Peaker CfDs 20.9 38.7 47.7 Natural Gas Procurement 432.4 377.0 323.9 Transmission Support Commitments 23.4 19.8 15.9 Coal, Wood and Other (1) — 47.7 55.7 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Purchased Power and Capacity $ 49.4 $ 4.4 $ 18.2 $ 81.0 $ 4.0 $ 18.9 $ 132.7 $ 0.7 $ 19.1 Renewable Energy 63.2 89.8 65.5 51.0 123.7 60.8 42.1 101.1 67.7 Peaker CfDs 20.9 — — 38.7 — — 47.7 — — Transmission Support Commitments 9.2 9.2 5.0 7.8 7.8 4.2 6.3 6.2 3.4 Coal, Wood and Other (1) — — — — — 47.7 — — 55.7 (1) PSNH previously entered into various arrangements for the purchase of coal, wood and the transportation services for fuel supply for its electric generating assets. On January 10, 2018, Eversource and PSNH completed the sale of PSNH's thermal generation assets. On August 26, 2018, Eversource and PSNH completed the sale of PSNH's hydroelectric generation assets. Upon sale, the remaining future contractual obligations were transferred to the respective buyers. See Note 13, "Generation Asset Sale," for further information. Spent Nuclear Fuel Obligations - Yankee Companies CL&P, NSTAR Electric and PSNH 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 have collected these costs through wholesale, FERC-approved rates charged under power purchase agreements with several New England utilities, including CL&P, NSTAR Electric and PSNH. These companies in turn recover these costs from their customers through state regulatory commission-approved retail rates. The Yankee Companies have collected 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 and NSTAR Electric 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 III Damages - In August 2013, the Yankee Companies each filed subsequent lawsuits against the DOE seeking recovery of actual damages incurred in the years 2009 through 2012 ("DOE Phase III"). On March 25, 2016, the court issued its decision and awarded CYAPC, YAEC and MYAPC damages of $32.6 million , $19.6 million and $24.6 million , respectively. The decision became final on July 18, 2016, and the Yankee Companies received the awards from the DOE on October 14, 2016. The Yankee Companies received FERC approval of their proposed distribution of certain amounts of the awarded damages proceeds to member companies, including CL&P, NSTAR Electric and PSNH, which CYAPC and MYAPC made in December 2016. MYAPC also refunded $56.5 million from its spent nuclear fuel trust, a portion of which was also refunded to the Eversource utility subsidiaries. In total, Eversource received $26.1 million , of which CL&P, NSTAR Electric and PSNH received $13.6 million , $8.6 million and $3.9 million , respectively. These amounts have been refunded to the customers of the respective Eversource utility subsidiaries. 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 monetary damages totaling approximately $100 million for CYAPC, YAEC and MYAPC, resulting from the DOE's failure to begin accepting spent nuclear fuel for disposal covering the years from 2013 to 2016 (“DOE Phase IV”). On February 21, 2019, the Yankee Companies received a partial summary judgment and partial final judgment in their favor for the undisputed amount of monetary damages, which is the vast majority of the damages being sought. The DOE Phase IV trial for the remaining amount of damages is expected to begin in 2019. Guarantees and Indemnifications In the normal course of business, Eversource parent provides credit assurances on behalf of its subsidiaries, including CL&P, NSTAR Electric and PSNH, 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 . 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 December 31, 2018 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty (1) $ 184.9 2021 Various Surety Bonds (2) 41.9 2019 - 2021 Rocky River Realty Company and Eversource Service Lease Payments for Real Estate 6.3 2019 - 2024 Bay State Wind LLC Real Estate Purchase 2.5 2019 (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 authorized capital contributions for its investment in the Access Northeast project. The guaranty decreases as authorized 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. As described in Note 1K, "Investments," Eversource parent issued a guaranty on behalf of its subsidiary, Eversource Investment LLC. Eversource parent will guarantee, as a primary obligor, the financial obligations, primarily all post-Closing payment obligations of Eversource Investment LLC, under the Sale and Purchase Agreement and an Irrevocable Equity Commitment Letter with Ørsted in an amount not to exceed $ 127.6 million . Eversource parent's obligations under the guaranty expire upon the full, final and indefeasible payment of the guaranteed obligations. 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, filed on October 1, 2011, December 27, 2012, and July 31, 2014, respectively, 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 billed 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. The ROE originally billed during the period October 1, 2011 (beginning of the first complaint period) through October 15, 2014 consisted of a base ROE of 11.14 percent and incentives up to 13.1 percent . On October 16, 2014, the FERC set the base ROE at 10.57 percent and the incentive cap at 11.74 percent for the first complaint period. This was also effective for all prospective billings to customers beginning October 16, 2014. This FERC order was vacated on April 14, 2017 by the U.S. Court of Appeals for the D.C. Circuit (the "Court"). All amounts associated with the first complaint period have been refunded, which totaled $38.9 million (pre-tax and excluding interest) at Eversource and reflected both the base ROE and incentive cap prescribed by the FERC order. The refund consisted of $22.4 million for CL&P, $13.7 million for NSTAR Electric and $2.8 million for PSNH. Eversource has recorded a reserve of $39.1 million (pre-tax and excluding interest) for the second complaint period as of December 31, 2018 . This reserve represents the difference between the billed rates 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, $14.6 million for NSTAR Electric and $3.1 million for PSNH as of December 31, 2018 . On October 16, 2018, FERC issued an order on all four complaints describing how it intends to address the issues that were remanded by the Court. FERC proposed a new framework to determine (1) whether an existing ROE is unjust and unreasonable and, if so, (2) how to calculate a replacement ROE. The parties to these proceedings were directed to submit briefs on this new proposed framework and how they would apply the proposed framework in each of the four complaint proceedings. Initial briefs were filed by the NETOs, Complainants and FERC Trial Staff on January 11, 2019. The NETOs' brief was supportive of the overall ROE methodology determined in the October 16, 2018 order providing the FERC does not change the proposed methodology or alter its implementation in a manner that has a material impact on the results. Reply briefs will be filed on March 8, 2019. The FERC order included illustrative calculations for the first complaint using FERC's proposed frameworks with financial data from that complaint. Those preliminary calculations indicated that for the first complaint period, for the NETOs that FERC concludes are of average financial risk, (1) a preliminary range of presumptively just and reasonable base ROEs is 9.60 percent to 10.99 percent ; (2) the pre-existing base ROE of 11.14 percent is therefore unjust and unreasonable; (3) the preliminary just and reasonable base ROE is 10.41 percent ; and (4) the preliminary incentive cap on total ROE is 13.08 percent . If the results of these illustrative calculations were included in a final FERC order for each of the complaint periods, then a 10.41 percent base ROE and a 13.08 percent incentive cap would not have a significant impact on our financial statements for all of the complaint periods. Although the order provided illustrative calculations, FERC stated that these calculations are merely preliminary. The FERC's preliminary calculations are not binding and do not represent what we believe to be the most likely outcome of a final FERC order, as changes to the methodology by FERC are possible as a result of the parties' arguments and calculations in the briefing process. Until FERC issues a final decision on each of these four complaints, there is significant uncertainty, and at this time, the Company cannot reasonably estimate a range of gain or loss for any of the four complaint proceedings. The October 16, 2018 FERC order or the January 11, 2019 briefs did not provide a reasonable basis for a change to the reserve or recognized ROEs for any of the complaint periods. Eversource, CL&P, NSTAR Electric and PSNH currently record revenues at the 10.57 percent base ROE and incentive cap at 11.74 percent established in the October 16, 2014 FERC order. 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 . F. 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. The parties reached a settlement pursuant to which HEEC agreed to install a new 115kV distribution cable across Boston Harbor to Deer Island, utilizing a different route, and 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 resulted in the initial $17.5 million of construction costs on the new cable being expensed as incurred, all of which was fully expensed by the end of 2018. Construction of the new cable is underway and is expected to be completed in 2019. G. Litigation and Legal Proceedings Eversource, including CL&P, NSTAR Electric and PSNH, are involved in legal, tax and regulatory proceedings regarding matters arising in the ordinary course of business, which involve management's assessment to determine the probability of whether a loss will occur and, if probable, its best estimate of probable loss. The Company records and discloses losses when these losses are probable and reasonably estimable, and discloses matters when losses are probable but not estimable or when losses are reasonably possible. Legal costs related to the defense of loss contingencies are expensed as incurred.

GENERATION ASSET SALE

GENERATION ASSET SALE	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
GENERATION ASSET SALE	GENERATION ASSET SALE In June 2015, Eversource and PSNH entered into the 2015 Public Service Company of New Hampshire Restructuring and Rate Stabilization Agreement, pursuant to which PSNH agreed to divest its generation assets, subject to NHPUC approval. The NHPUC approved this agreement as well as the final divestiture plan and auction process in 2016. On October 11, 2017, PSNH entered into two Purchase and Sale Agreements with private investors, one to sell its thermal generation assets at a purchase price of $175 million , subject to adjustment, (the “Thermal Agreement”) and a second to sell its hydroelectric generation assets at a purchase price of $83 million , subject to adjustment (the “Hydro Agreement”). The NHPUC approved these agreements in late November 2017, at which time the Company classified these assets as held for sale. On January 10, 2018, PSNH completed the sale of its thermal generation assets pursuant to the Thermal Agreement. In accordance with the Thermal Agreement, the original purchase price of $175 million was adjusted to reflect working capital adjustments, closing date adjustments and proration of taxes and fees prior to closing, totaling $40.9 million . In the second quarter of 2018, the purchase price was further adjusted by $17.3 million relating to the valuation of certain allowances. As a result of these adjustments, net proceeds from the sale of the thermal assets totaled $116.8 million . On July 16, 2018, FERC issued its order approving the transfer of PSNH's six hydroelectric licenses to private investors. On August 26, 2018, PSNH completed the sale of its hydroelectric generation assets pursuant to the Hydro Agreement. In accordance with the Hydro Agreement, the original purchase price of $83 million was adjusted to reflect contractual adjustments totaling $5.8 million , resulting in net proceeds of $77.2 million . The difference between the carrying value of the hydroelectric generation assets and the sale proceeds resulted in a gain of $17.3 million . An estimated gain from the sale of these assets was included as an offset to the total remaining costs associated with the sale of generation assets that were securitized on May 8, 2018. On May 8, 2018, PSNH Funding issued $635.7 million of securitized RRBs to finance PSNH's unrecovered remaining costs associated with the divestiture of its generation assets, which included the deferred costs resulting from the sale of the thermal generation assets. These RRBs are secured by a non-bypassable charge recoverable from PSNH customers. As of December 31, 2018, unamortized securitized stranded costs totaled $608.4 million and are included in Regulatory Assets on the Eversource and PSNH balance sheets. As of December 31, 2017, the deferred costs resulting from the thermal generation asset sale of $516.1 million represented the difference between the carrying value and the fair value less cost to sell the thermal generation assets. For further information on the securitized RRB issuance, see Note 9, "Rate Reduction Bonds and Variable Interest Entities." For the year ended December 31, 2018, pre-tax income associated with the hydroelectric assets prior to the sale on August 26, 2018 was $9.9 million . For the years ended December 31, 2017 and 2016, pre-tax income associated with PSNH's generation assets was $60.0 million , and $65.3 million , respectively. As of December 31, 2018 , all generation assets had been sold and as a result, no generation assets were classified as held for sale. As of December 31, 2017, PSNH's generation assets held for sale, which were included in current assets on the Eversource and PSNH balance sheets, and were part of the Electric Distribution reportable segment, were as follows: (Millions of Dollars) As of December 31, 2017 Thermal Gross Plant $ 1,091.4 Hydroelectric Gross Plant 83.0 Accumulated Depreciation (575.4 ) Net Plant 599.0 Fuel and Inventory 87.7 Materials and Supplies 27.3 Emission Allowances 19.1 Other Assets 2.6 Deferred Costs from Thermal Generation Asset Sale (516.1 ) Total Generation Assets Held for Sale $ 219.6

LEASES

LEASES	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
LEASES	LEASES Eversource, including CL&P, NSTAR Electric and PSNH, has entered into lease agreements, some of which are capital leases, for the use of land, office space, service centers, vehicles, information technology, and office equipment. In addition, CL&P, NSTAR Electric and PSNH incur costs associated with leases entered into by affiliated Eversource subsidiaries, including Eversource Service and Rocky River Realty Company, and are included below in their respective operating lease rental expenses and future minimum rental payments. These intercompany lease amounts are eliminated on an Eversource consolidated basis. The provisions of the Eversource, CL&P, NSTAR Electric and PSNH lease agreements generally contain renewal options. One lease agreement contains payments impacted by the consumer price index. Operating lease rental payments charged to expense are as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 10.8 $ 10.9 $ 11.8 $ 2.5 2017 10.5 11.7 11.3 3.3 2016 12.1 12.5 11.4 2.9 Future minimum rental payments, excluding executory costs, such as property taxes, state use taxes, insurance, and maintenance, under long-term non-cancelable leases, as of December 31, 2018 are as follows: Operating Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 11.5 $ 1.5 $ 7.2 $ 0.5 2020 9.8 1.4 6.0 0.4 2021 8.7 1.2 5.3 0.4 2022 7.2 1.1 4.4 0.4 2023 4.7 0.5 3.1 0.2 Thereafter 32.7 0.2 29.5 0.3 Future minimum lease payments $ 74.6 $ 5.9 $ 55.5 $ 2.2 Capital Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 3.4 $ 2.0 $ 0.5 $ 0.1 2020 3.4 2.0 0.5 0.1 2021 2.9 1.5 0.5 0.1 2022 1.5 — 0.6 0.1 2023 0.7 — 0.6 0.1 Thereafter 13.9 — 13.4 0.5 Future minimum lease payments 25.8 5.5 16.1 1.0 Less amount to arrive at present value 13.8 1.0 12.4 0.1 Present value of future minimum lease payments $ 12.0 $ 4.5 $ 3.7 $ 0.9 CL&P and PSNH entered into certain contracts for the purchase of energy that qualify as leases. These contracts do not have minimum lease payments and therefore are not included in the tables above. However, such contracts and corresponding expense have been included in the contractual obligations tables in Note 12B, "Commitments and Contingencies - Long-Term Contractual Arrangements," to the financial statements.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2018
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, Long-Term Debt and Rate Reduction Bonds: 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 and RRB 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 table below are classified as Level 2 within the fair value hierarchy. Carrying amounts and estimated fair values are as follows: Eversource CL&P NSTAR Electric PSNH (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value As of December 31, 2018: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 156.8 $ 116.2 $ 113.8 $ 43.0 $ 43.0 $ — $ — Long-Term Debt 13,086.1 13,154.9 3,254.0 3,429.2 2,944.8 3,024.1 805.2 819.5 Rate Reduction Bonds 635.7 645.8 — — — — 635.7 645.8 As of December 31, 2017: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 160.8 $ 116.2 $ 116.5 $ 43.0 $ 44.3 $ — $ — Long-Term Debt 12,325.5 12,877.1 3,059.1 3,430.5 2,943.8 3,156.5 1,002.4 1,038.2 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 1I, "Summary of Significant Accounting Policies – Fair Value Measurements," for the fair value measurement policy and the fair value hierarchy.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	12 Months Ended
	Dec. 31, 2018
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, are as follows: For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 Eversource (Millions of Dollars) Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Balance as of January 1st $ (6.2 ) $ — $ (60.2 ) $ (66.4 ) $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) OCI Before Reclassifications — (0.5 ) 0.3 (0.2 ) — (0.4 ) (7.2 ) (7.6 ) Amounts Reclassified from AOCI 1.8 — 4.8 6.6 2.0 — 4.5 6.5 Net OCI 1.8 (0.5 ) 5.1 6.4 2.0 (0.4 ) (2.7 ) (1.1 ) Balance as of December 31st $ (4.4 ) $ (0.5 ) $ (55.1 ) $ (60.0 ) $ (6.2 ) $ — $ (60.2 ) $ (66.4 ) Eversource's qualified cash flow hedging instruments represent interest rate swap agreements on debt issuances that were settled in prior years. The settlement amount was recorded in AOCI and is being amortized into Net Income over the term of the underlying debt instrument. CL&P, NSTAR Electric and PSNH continue to amortize interest rate swaps settled in prior years from AOCI into Interest Expense over the remaining life of the associated long-term debt. Such interest rate swaps are not material to their respective financial statements. Defined benefit plan OCI amounts before reclassifications relate to actuarial gains and losses that arose during the year and were recognized in AOCI. The unamortized actuarial gains and losses and prior service costs on the defined benefit plans are amortized from AOCI into Other Income, Net over the average future employee service period, and are reflected in amounts reclassified from AOCI. The related tax effects recognized in AOCI were net deferred tax liabilities of $0.2 million in 2018, and deferred tax assets of $4.1 million and $ 4.0 million in 2017 and 2016, respectively. The following table sets forth the amounts reclassified from AOCI by component and the impacted line item on the statements of income: Amounts Reclassified from AOCI Eversource (Millions of Dollars) For the Years Ended December 31, Statements of Income Line Item Impacted 2018 2017 2016 Qualified Cash Flow Hedging Instruments $ (2.8 ) $ (3.3 ) $ (3.5 ) Interest Expense Tax Effect 1.0 1.3 1.4 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (1.8 ) $ (2.0 ) $ (2.1 ) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (6.0 ) $ (6.2 ) $ (5.6 ) Other Income, Net (1) Amortization of Prior Service Cost (0.4 ) (1.1 ) (0.8 ) Other Income, Net (1) Total Defined Benefit Plan Costs (6.4 ) (7.3 ) (6.4 ) Tax Effect 1.6 2.8 2.5 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (4.8 ) $ (4.5 ) $ (3.9 ) Total Amounts Reclassified from AOCI, Net of Tax $ (6.6 ) $ (6.5 ) $ (6.0 ) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 1N, "Summary of Significant Accounting Policies – Other Income, Net" and Note 10A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," for further information. As of December 31, 2018 , it is estimated that a pre-tax amount of $2.5 million ( $0.7 million for NSTAR Electric and $1.8 million for PSNH) will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of the interest rate swap agreements which have been settled. In addition, it is estimated that a pre-tax amount of $6.3 million will be reclassified from AOCI as a decrease to Net Income over the next 12 months as a result of the amortization of Pension, SERP and PBOP costs.

DIVIDEND RESTRICTIONS

DIVIDEND RESTRICTIONS	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
DIVIDEND RESTRICTIONS	DIVIDEND RESTRICTIONS Eversource parent's ability to pay dividends may be affected by certain state statutes, the ability of its subsidiaries to pay common dividends and the leverage restriction tied to its consolidated total debt to total capitalization ratio requirement in its revolving credit agreement. Pursuant to the joint revolving credit agreement of Eversource, CL&P, PSNH, Yankee Gas and NSTAR Gas, and to the NSTAR Electric revolving credit agreement, each company is required to maintain consolidated total indebtedness to total capitalization ratio of no greater than 65 percent at the end of each fiscal quarter. As of December 31, 2018 , all companies were in compliance with such covenant. Eversource, CL&P, NSTAR Electric, PSNH, Yankee Gas and NSTAR Gas were in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends as of December 31, 2018 . The Retained Earnings balances subject to dividend restrictions were $4.0 billion for Eversource, $1.7 billion for CL&P, $2.1 billion for NSTAR Electric and $627.3 million for PSNH as of December 31, 2018 . CL&P, NSTAR Electric and PSNH are subject to Section 305 of the Federal Power Act that makes it unlawful for a public utility to make or pay a dividend from any funds "properly included in its capital account." Management believes that this Federal Power Act restriction, as applied to CL&P, NSTAR Electric and PSNH, would not be construed or applied by the FERC to prohibit the payment of dividends from retained earnings for lawful and legitimate business purposes. In addition, certain state statutes may impose additional limitations on such companies and on Yankee Gas and NSTAR Gas. Such state law restrictions do not restrict the payment of dividends from retained earnings or net income.

COMMON SHARES

COMMON SHARES	12 Months Ended
	Dec. 31, 2018
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 and PSNH that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2018 and 2017 Issued as of December 31, 2018 2017 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 $ 1 100,000,000 200 200 PSNH $ 1 100,000,000 301 301 As of both December 31, 2018 and 2017 , there were 16,992,594 Eversource common shares held as treasury shares. As of both December 31, 2018 and 2017 , there were 316,885,808 Eversource common shares outstanding. COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $7.5 million for each of the years ended December 31, 2018 , 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 December 31, 2018 and 2017 . On the Eversource balance sheets, Common Shareholders' Equity was fully attributable to Eversource parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest. For the years ended December 31, 2018 , 2017 and 2016 , there was no change in ownership of the common equity of CL&P and NSTAR Electric.

PREFERRED STOCK NOT SUBJECT TO

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION The CL&P and NSTAR Electric preferred stock is not subject to mandatory redemption and is presented as a noncontrolling interest of a subsidiary in Eversource's financial statements. 9,000,000 shares of preferred stock, par value $50 per share, and NSTAR Electric is authorized to issue 2,890,000 shares of preferred stock, par value $100 per share. Holders of preferred stock of CL&P and NSTAR Electric are entitled to receive cumulative dividends in preference to any payment of dividends on the common stock. Upon liquidation, holders of preferred stock of CL&P and NSTAR Electric are entitled to receive a liquidation preference before any distribution to holders of common stock in an amount equal to the par value of the preferred stock plus accrued and unpaid dividends. If the net assets were to be insufficient to pay the liquidation preference in full, then the net assets would be distributed ratably to all holders of preferred stock. The preferred stock of CL&P and NSTAR Electric is subject to optional redemption by the CL&P and NSTAR Electric Board of Directors at any time. Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Per Share Shares Outstanding as of December 31, As of December 31, Series 2018 2017 2018 2017 CL&P $1.90 Series of 1947 $ 52.50 163,912 163,912 $ 8.2 $ 8.2 $2.00 Series of 1947 $ 54.00 336,088 336,088 16.8 16.8 $2.04 Series of 1949 $ 52.00 100,000 100,000 5.0 5.0 $2.20 Series of 1949 $ 52.50 200,000 200,000 10.0 10.0 3.90% Series of 1949 $ 50.50 160,000 160,000 8.0 8.0 $2.06 Series E of 1954 $ 51.00 200,000 200,000 10.0 10.0 $2.09 Series F of 1955 $ 51.00 100,000 100,000 5.0 5.0 4.50% Series of 1956 $ 50.75 104,000 104,000 5.2 5.2 4.96% Series of 1958 $ 50.50 100,000 100,000 5.0 5.0 4.50% Series of 1963 $ 50.50 160,000 160,000 8.0 8.0 5.28% Series of 1967 $ 51.43 200,000 200,000 10.0 10.0 $3.24 Series G of 1968 $ 51.84 300,000 300,000 15.0 15.0 6.56% Series of 1968 $ 51.44 200,000 200,000 10.0 10.0 Total CL&P 2,324,000 2,324,000 $ 116.2 $ 116.2 NSTAR Electric 4.25% Series of 1956 $ 103.625 180,000 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 102.80 250,000 250,000 25.0 25.0 Total NSTAR Electric 430,000 430,000 $ 43.0 $ 43.0 Fair Value Adjustment due to Merger with NSTAR (3.6 ) (3.6 ) Other 6.00% Series of 1958 $ 100.00 23 23 $ — $ — Total Eversource - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

COMMON SHARESHOLDERS' EQUITY AN

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	COMMON SHARES The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric and PSNH that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2018 and 2017 Issued as of December 31, 2018 2017 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 $ 1 100,000,000 200 200 PSNH $ 1 100,000,000 301 301 As of both December 31, 2018 and 2017 , there were 16,992,594 Eversource common shares held as treasury shares. As of both December 31, 2018 and 2017 , there were 316,885,808 Eversource common shares outstanding. COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS Dividends on the preferred stock of CL&P and NSTAR Electric totaled $7.5 million for each of the years ended December 31, 2018 , 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 December 31, 2018 and 2017 . On the Eversource balance sheets, Common Shareholders' Equity was fully attributable to Eversource parent and Noncontrolling Interest – Preferred Stock of Subsidiaries was fully attributable to the noncontrolling interest. For the years ended December 31, 2018 , 2017 and 2016 , there was no change in ownership of the common equity of CL&P and NSTAR Electric.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2018
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. The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Years Ended December 31, 2018 2017 2016 Net Income Attributable to Common Shareholders $ 1,033.0 $ 988.0 $ 942.3 Weighted Average Common Shares Outstanding: Basic 317,370,369 317,411,097 317,650,180 Dilutive Effect 623,565 620,483 804,059 Diluted 317,993,934 318,031,580 318,454,239 Basic EPS $ 3.25 $ 3.11 $ 2.97 Diluted EPS $ 3.25 $ 3.11 $ 2.96

REVENUES

REVENUES	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES On January 1, 2018, Eversource, including CL&P, NSTAR Electric and PSNH, adopted ASU 2014-09, “ Revenue from Contracts with Customers (Topic 606) ” using the modified retrospective approach. The core principle of this accounting guidance is that revenue is recognized when promised goods or services (referred to as performance obligations) are transferred to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new standard uses a five-step model for recognizing and measuring revenue from contracts with customers, which includes identifying the contract with the customer, identifying the performance obligations promised within the contract, determining the transaction price (the amount of consideration to which the company expects to be entitled), allocating the transaction price to the performance obligations and recognizing revenue when (or as) the performance obligation is satisfied. The following table presents operating revenues disaggregated by revenue source: For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Revenue from Contracts with Customers Retail Tariff Sales Residential $ 3,766.6 $ 542.5 $ — $ 130.7 $ — $ — $ 4,439.8 Commercial 2,634.7 334.8 — 63.3 — (4.5 ) 3,028.3 Industrial 351.9 96.0 — 4.4 — (10.0 ) 442.3 Total Retail Tariff Sales Revenue 6,753.2 973.3 — 198.4 — (14.5 ) 7,910.4 Wholesale Transmission Revenue — — 1,308.9 — 47.3 (1,092.2 ) 264.0 Wholesale Market Sales Revenue 179.5 57.5 — 4.1 — — 241.1 Other Revenue from Contracts with Customers 65.9 (2.2 ) 12.6 7.2 889.0 (891.0 ) 81.5 Reserve for Revenue Subject to Refund (12.3 ) (8.3 ) — (3.7 ) — — (24.3 ) Total Revenue from Contracts with Customers 6,986.3 1,020.3 1,321.5 206.0 936.3 (1,997.7 ) 8,472.7 Alternative Revenue Programs (47.0 ) (1.2 ) (35.2 ) 5.4 — 31.9 (46.1 ) Other Revenue 17.9 3.1 — 0.6 — — 21.6 Total Operating Revenues $ 6,957.2 $ 1,022.2 $ 1,286.3 $ 212.0 $ 936.3 $ (1,965.8 ) $ 8,448.2 For the Year Ended December 31, 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH Revenue from Contracts with Customers Retail Tariff Sales Residential $ 1,828.2 $ 1,380.9 $ 557.5 Commercial 928.1 1,391.5 316.9 Industrial 147.7 124.9 79.3 Total Retail Tariff Sales Revenue 2,904.0 2,897.3 953.7 Wholesale Transmission Revenue 620.6 488.8 199.5 Wholesale Market Sales Revenue 48.3 76.1 56.6 Other Revenue from Contracts with Customers 35.0 28.9 15.5 Reserve for Revenue Subject to Refund — — (12.3 ) Total Revenue from Contracts with Customers 3,607.9 3,491.1 1,213.0 Alternative Revenue Programs (65.9 ) 0.9 (17.3 ) Other Revenue 8.5 8.3 1.1 Eliminations (454.3 ) (387.4 ) (149.2 ) Total Operating Revenues $ 3,096.2 $ 3,112.9 $ 1,047.6 Retail Tariff Sales: Regulated utilities provide products and services to their regulated customers under rates, pricing, payment terms and conditions of service, regulated by each state regulatory agency. The arrangement whereby a utility provides commodity service to a customer for a price approved by the respective state regulatory commission is referred to as a tariff sale contract, and the tariff governs all aspects of the provision of regulated services by utilities. The majority of revenue for Eversource, CL&P, NSTAR Electric and PSNH is derived from regulated retail tariff sales for the sale and distribution of electricity, natural gas and water to residential, commercial and industrial retail customers. The utility's performance obligation for the regulated tariff sales is to provide electricity, natural gas or water to the customer as demanded. The promise to provide the commodity represents a single performance obligation, as it is a promise to transfer a series of distinct goods or services that are substantially the same and that have the same pattern of transfer to the customer. Revenue is recognized over time as the customer simultaneously receives and consumes the benefits provided by the utility, and the utility satisfies its performance obligation. Revenue is recognized based on the output method as there is a directly observable output to the customer (electricity, natural gas or water units delivered to the customer and immediately consumed). Each Eversource utility is entitled to be compensated for performance completed to date (service taken by the customer) until service is terminated. In regulated tariff sales, the transaction prices are the rates approved by the respective state regulatory commissions. In general, rates can only be changed through formal proceedings with the state regulatory commissions. These rates are designed to recover the costs to provide service to customers and include a return on investment. Regulatory commission-approved tracking mechanisms are included in these rates and are also used to recover, on a fully-reconciling basis, certain costs, such as the procurement of energy supply, retail transmission charges, energy efficiency program costs, net metering for distributed generation, and restructuring and stranded costs. These tracking mechanisms result in rates being changed periodically to ensure recovery of actual costs incurred. Customers may elect to purchase electricity from each Eversource electric utility or may contract separately with a competitive third party supplier. Revenue is not recorded for the sale of the electricity commodity to customers who have contracted separately with these suppliers, only the delivery to a customer, as the utility is acting as an agent on behalf of the third party supplier. Wholesale Transmission Revenues: The Eversource electric transmission-owning companies (CL&P, NSTAR Electric and PSNH) each own and maintain transmission facilities that are part of an interstate power transmission grid over which electricity is transmitted throughout New England. CL&P, NSTAR Electric and PSNH, as well as most other New England utilities, are parties to a series of agreements that provide for coordinated planning and operation of the region's transmission facilities and the rules by which they acquire transmission services. The Eversource electric transmission-owning companies have a combination of FERC-approved regional and local formula rates that work in tandem to recover all their transmission costs. These rates are part of the ISO-NE Tariff. Regional rates recover the costs of higher voltage transmission facilities that benefit the region and are collected from all New England transmission customers, including the Eversource distribution businesses. Eversource's local rates recover the companies' total transmission revenue requirements, less revenues received from regional rates and other sources, and are collected from Eversource's distribution businesses and other transmission customers. The distribution businesses of Eversource, in turn, recover the FERC approved charges from retail customers through annual or semiannual tracking mechanisms, which are retail tariff sales. The utility's performance obligation for regulated wholesale transmission sales is to provide transmission services to the customer as demanded. The promise to provide transmission service represents a single performance obligation. The transaction prices are the transmission rate formulas as defined by the ISO-NE Tariff and are regulated and established by FERC. Wholesale transmission revenue is recognized over time as the performance obligation is completed, which occurs as transmission services are provided to customers. The revenue is recognized based on the output method. Each Eversource utility is entitled to be compensated for performance completed to date (e.g., use of the transmission system by the customer). Wholesale Market Sales Revenues: Wholesale market sales transactions include sales of energy and energy-related products into the ISO-NE wholesale electricity market, sales of natural gas to third party marketers, and also the sale of RECs to various counterparties. ISO-NE oversees the region's wholesale electricity market and administers the transactions and terms and conditions, including payment terms, which are established in the ISO-NE tariff, between the buyers and sellers in the market. Pricing is set by the wholesale market. The wholesale transactions in the ISO-NE market occur on a day-ahead basis or a real-time basis (daily) and are, therefore, short-term. Transactions are tracked and reported by ISO-NE net by the hour, which is the net hourly position of energy sales and purchases by each market participant. Beginning in the first quarter of 2018, the performance obligation for ISO-NE energy transactions is defined to be the net by hour transaction. Revenue is recognized when the performance obligation for these energy sales transactions is satisfied, when the sale occurs and the energy is transferred to the customer. For sales of natural gas, transportation, and natural gas pipeline capacity to third party marketers, revenue is recognized when the performance obligation is satisfied at the point in time the sale occurs and the natural gas or related product is transferred to the marketer. RECs are sold to various counterparties, and revenue is recognized when the performance obligation is satisfied upon transfer of title to the customer through the New England Power Pool Generation Information System. Other Revenue from Contracts with Customers: Other revenue from contracts with customers primarily includes property rentals that are not deemed leases. These revenues are generally recognized on a straight-line basis over time as the service is provided to the customer. Reserve for Revenue Subject to Refund: Current base rates include an estimate of income taxes, which was based on the U.S. federal corporate income tax rate in effect at the time of the rate proceeding. Eversource established a regulatory liability, recorded as a reduction to revenue, to reflect the difference between the 35 percent federal corporate income tax rate included in rates charged to customers and the 21 percent federal corporate income tax rate, effective January 1, 2018 as a result of the Tax Cuts and Jobs Act, until rates billed to customers reflect the lower federal tax rate. Effective May 1, 2018, CL&P adjusted rates billed to customers to reflect the lower federal income tax rate prospectively and, as of December 31, 2018, fully refunded its regulatory liability associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 through April 30, 2018. Effective November 15, 2018, Yankee Gas adjusted distribution rates to reflect the lower federal income tax rate prospectively and to refund its regulatory liability associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 through November 14, 2018. Although Yankee Gas' new rates were effective January 1, 2019, the provisions of the settlement agreement took effect November 15, 2018. For NSTAR Electric and NSTAR Gas, a December 2018 DPU order indicated that the DPU will not require a revision to base rates for any potential refunds associated with the higher federal corporate income tax rate billed to customers in the period between January 1, 2018 to the effective dates of each company's rate changes (effective February 1, 2018 for NSTAR Electric and July 1, 2018 for NSTAR Gas). PSNH and Aquarion will refund the overcollection in distribution rates from January 1, 2018 to customers in a future period. PSNH will adjust distribution rates to reflect the prospective lower federal income tax rate effective July 1, 2019, or earlier if a rate case is filed for rates effective prior to July 1, 2019. Alternative Revenue Programs: In accordance with accounting guidance for rate-regulated operations, certain of Eversource's utilities' rate making mechanisms qualify as alternative revenue programs ("ARPs") if they meet specified criteria, in which case revenues may be recognized prior to billing based on allowed levels of collection in rates. Eversource's utility companies recognize revenue and record a regulatory asset or liability once the condition or event allowing for the automatic adjustment of future rates occurs. ARP revenues include both the recognition of the deferral adjustment to ARP revenues, when the regulator-specified condition or event allowing for additional billing or refund has occurred, and an equal and offsetting reversal of the ARP deferral to revenues as those amounts are reflected in the price of service in subsequent periods. Eversource’s ARPs include the revenue decoupling mechanism and the annual reconciliation adjustment to transmission formula rates, described below. • Certain Eversource electric, natural gas and water companies, including CL&P and NSTAR Electric, have revenue decoupling mechanisms approved by a regulatory commission ("decoupled companies"). Decoupled companies’ distribution revenues are not directly based on sales volumes. The decoupled companies reconcile their annual base distribution rate recovery to pre-established levels of baseline distribution delivery service revenues, with any difference between the allowed level of distribution revenue and the actual amount realized adjusted through subsequent rates. • The transmission formula rates provide for the annual reconciliation and recovery or refund of estimated costs to actual costs. The financial impacts of differences between actual and estimated costs are deferred for future recovery from, or refund to, transmission customers. This transmission deferral reconciles billed transmission revenues to the revenue requirement for our transmission businesses. Other Revenues: Other Revenues include certain fees charged to customers and lease revenue that are not considered revenue from contracts with customers. Intercompany Eliminations: Intercompany eliminations are primarily related to the Eversource electric transmission revenues that are derived from ISO-NE regional transmission charges to the distribution businesses of CL&P, NSTAR Electric and PSNH that recover the costs of the wholesale transmission business, and revenues from Eversource's service company. Intercompany revenues and expenses between the Eversource wholesale transmission businesses and the Eversource distribution businesses and from Eversource's service company are eliminated in consolidation and included in "Eliminations" in the table above. Receivables: Receivables, Net on the balance sheet include trade receivables from our retail customers and receivables arising from ISO-NE billing related to wholesale transmission contracts and wholesale market transactions, sales of natural gas and capacity to marketers, sales of RECs, and property rentals. In general, retail tariff customers and wholesale transmission customers are billed monthly and the payment terms are generally due and payable upon receipt of the bill. Unbilled Revenues: Unbilled Revenues on the balance sheet represent estimated amounts due from retail customers for electricity, natural gas or water delivered to customers but not yet billed. The utility company has satisfied its performance obligation and the customer has received and consumed the commodity as of the balance sheet date, and therefore, the utility company records revenue for those services in the period the services were provided. Only the passage of time is required before the company is entitled to payment for the satisfaction of the performance obligation. Payment from customers is due monthly as services are rendered and amounts are billed. Actual amounts billed to customers when meter readings become available may vary from the estimated amount. Unbilled revenues are recognized by allocating estimated unbilled sales volumes to the respective customer classes, and then applying an estimated rate by customer class to those sales volumes. Unbilled revenue estimates reflect seasonality, weather, customer usage patterns, customer rates in effect for customer classes, and the timing of customer billing. The companies that have a decoupling mechanism record a regulatory deferral to reflect the actual allowed amount of revenue associated with their respective decoupled distribution rate design. Practical Expedients: Eversource has elected practical expedients in the accounting guidance that allow the company to record revenue in the amount that the company has a right to invoice, if that amount corresponds directly with the value to the customer of the company's performance to date, and not to disclose related unsatisfied performance obligations. Retail and wholesale transmission tariff sales fall into this category, as these sales are recognized as revenue in the period the utility provides the service and completes the performance obligation, which is the same as the monthly amount billed to customers. There are no other material revenue streams for which Eversource has unsatisfied performance obligations.

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION Eversource is organized among the Electric Distribution, Electric Transmission, Natural Gas Distribution and Water 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, natural gas and water primarily are derived from residential, commercial and industrial customers and are not dependent on any single customer. The Electric Distribution reportable segment includes the results of PSNH's generation facilities prior to sales in January and August 2018, and NSTAR Electric's solar power facilities. 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. On December 4, 2017, Eversource acquired Aquarion, which was considered to be a new operating segment, Water Distribution. Though the water distribution segment does not meet quantitative thresholds under the segment reporting accounting guidance, based on qualitative factors including the nature of the water distribution business, Water Distribution was deemed a reportable segment beginning in 2018. The remainder of Eversource's operations is presented as Other in the tables below and primarily consists of 1) the equity in earnings of Eversource parent from its subsidiaries and intercompany interest income, both of which are eliminated in consolidation, and interest expense related to the debt of Eversource parent, 2) the revenues and expenses of Eversource Service, most of which are eliminated in consolidation, 3) the operations of CYAPC and YAEC, 4) Eversource Water Ventures, Inc., parent company of Aquarion, and 5) 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. Each of Eversource's subsidiaries, including CL&P, NSTAR Electric and PSNH, has one reportable segment. The Electric Transmission segment includes a reduction to Operations and Maintenance expense of $27.5 million in 2016 for costs incurred in previous years that was recovered in transmission rates over the period June 1, 2016 through May 31, 2017. These costs were associated with the merger of Northeast Utilities and NSTAR. 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 and PBOP expense. Eversource's segment information is as follows: For the Year Ended December 31, 2018 (1) Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 6,957.2 $ 1,022.2 $ 1,286.3 $ 212.0 $ 936.3 $ (1,965.8 ) $ 8,448.2 Depreciation and Amortization (671.8 ) (75.0 ) (231.8 ) (46.5 ) (49.1 ) 2.2 (1,072.0 ) Other Operating Expenses (5,548.6 ) (787.6 ) (375.5 ) (99.8 ) (831.5 ) 1,966.7 (5,676.3 ) Operating Income 736.8 159.6 679.0 65.7 55.7 3.1 1,699.9 Interest Expense (202.8 ) (44.1 ) (120.6 ) (34.3 ) (129.3 ) 32.3 (498.8 ) Interest Income 18.7 — 2.4 — 30.3 (33.3 ) 18.1 Other Income/(Loss), Net 67.5 7.1 31.1 (0.4 ) 1,185.3 (1,180.3 ) 110.3 Income Tax (Expense)/Benefit (160.2 ) (29.4 ) (161.8 ) (0.1 ) 62.5 — (289.0 ) Net Income 460.0 93.2 430.1 30.9 1,204.5 (1,178.2 ) 1,040.5 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income Attributable to Common Shareholders $ 455.4 $ 93.2 $ 427.2 $ 30.9 $ 1,204.5 $ (1,178.2 ) $ 1,033.0 Total Assets (as of) $ 21,389.1 $ 3,904.9 $ 10,285.0 $ 2,253.0 $ 17,874.2 $ (17,464.9 ) $ 38,241.3 Cash Flows Used for Investments in Plant $ 961.3 $ 351.5 $ 929.7 $ 102.3 $ 178.6 $ — $ 2,523.4 For the Year Ended December 31, 2017 (2) Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution (3) Other Eliminations Total Operating Revenues $ 5,542.9 $ 947.3 $ 1,301.7 $ 15.9 $ 931.0 $ (986.8 ) $ 7,752.0 Depreciation and Amortization (542.6 ) (72.9 ) (209.4 ) (3.7 ) (37.4 ) 2.2 (863.8 ) Other Operating Expenses (4,072.6 ) (716.4 ) (382.8 ) (8.3 ) (806.6 ) 986.7 (5,000.0 ) Operating Income 927.7 158.0 709.5 3.9 87.0 2.1 1,888.2 Interest Expense (186.3 ) (43.1 ) (115.1 ) (3.1 ) (90.0 ) 15.8 (421.8 ) Interest Income 7.3 0.1 1.8 0.1 15.7 (16.7 ) 8.3 Other Income/(Loss), Net 41.6 3.8 27.3 — 1,113.0 (1,086.0 ) 99.7 Income Tax Expense (288.3 ) (44.2 ) (228.7 ) (2.1 ) (15.5 ) (0.1 ) (578.9 ) Net Income/(Loss) 502.0 74.6 394.8 (1.2 ) 1,110.2 (1,084.9 ) 995.5 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income/(Loss) Attributable to Common Shareholders $ 497.4 $ 74.6 $ 391.9 $ (1.2 ) $ 1,110.2 $ (1,084.9 ) $ 988.0 Total Assets (as of) $ 19,250.4 $ 3,595.2 $ 9,401.2 $ 2,182.9 $ 16,220.9 $ (14,430.2 ) $ 36,220.4 Cash Flows Used for Investments in Plant $ 1,020.7 $ 298.2 $ 867.6 $ 16.0 $ 145.6 $ — $ 2,348.1 For the Year Ended December 31, 2016 (2) Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Operating Revenues $ 5,594.3 $ 857.7 $ 1,210.0 $ — $ 870.4 $ (893.3 ) $ 7,639.1 Depreciation and Amortization (504.7 ) (65.3 ) (185.8 ) — (33.5 ) 2.2 (787.1 ) Other Operating Expenses (4,173.0 ) (629.0 ) (321.3 ) — (779.2 ) 891.8 (5,010.7 ) Operating Income 916.6 163.4 702.9 — 57.7 0.7 1,841.3 Interest Expense (193.1 ) (41.3 ) (110.0 ) — (63.5 ) 6.9 (401.0 ) Interest Income 10.0 0.1 1.2 — 7.0 (7.3 ) 11.0 Other Income, Net 22.7 0.7 17.8 — 1,021.2 (1,008.9 ) 53.5 Income Tax (Expense)/Benefit (288.8 ) (45.2 ) (238.2 ) — 16.5 0.7 (555.0 ) Net Income 467.4 77.7 373.7 — 1,038.9 (1,007.9 ) 949.8 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income Attributable to Common Shareholders $ 462.8 $ 77.7 $ 370.8 $ — $ 1,038.9 $ (1,007.9 ) $ 942.3 Cash Flows Used for Investments in Plant $ 812.6 $ 255.3 $ 801.0 $ — $ 108.0 $ — $ 1,976.9 (1) Effective January 1, 2018, upon implementation of the new revenue accounting guidance, the electric distribution segment is presented gross and intercompany transmission billings are presented in the eliminations column, as Eversource believes that the electric distribution segment acts as a principal, rather than an agent, in its contracts with retail customers. Retail customers contract directly with the electric distribution utility and do not differentiate between distribution and transmission services. Therefore, the electric distribution segment revenues, which are derived from retail customer billings, are presented gross of the eliminations. Prior to 2018, the electric distribution segment presented intercompany electric transmission billings net, based on indicators of net presentation prior to the new revenue guidance. See Note 22 "Revenues," to the financial statements regarding accounting for revenues. (2) As a result of the adoption of new accounting guidance, the non-service related components of pension, SERP and PBOP benefit costs are presented as non-operating income and recorded in Other Income, Net on the statements of income. The 2017 and 2016 amounts, which were previously presented within Operations and Maintenance expense on the statements of income, have been retrospectively presented within Other Income, Net for the years ended December 31, 2017 and 2016. See Note 1C, "Summary of Significant Accounting Policies - Accounting Standards" and Note 1N, "Summary of Significant Accounting Policies - Other Income, Net," to the financial statements for further information. (3) The water distribution business was determined to be a reportable segment beginning in 2018. The 2017 segment information has been recast to conform to the current segment reporting structure.

ACQUISITION OF AQUARION AND GOO

ACQUISITION OF AQUARION AND GOODWILL	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
ACQUISITION OF AQUARION AND GOODWILL	ACQUISITION OF AQUARION AND GOODWILL A. Acquisition of Aquarion On December 4, 2017, Eversource acquired Aquarion for a purchase price of $1.675 billion , consisting of approximately $880 million in cash and $795 million of assumed Aquarion debt. Aquarion is a holding company that owns three separate regulated water utility subsidiaries engaged in the water collection, treatment and distribution business that operate in Connecticut, Massachusetts and New Hampshire. These regulated utilities collect, treat and distribute water to residential, commercial and industrial customers, to other utilities for resale, and for private and municipal fire protection. Aquarion and its subsidiaries became wholly-owned subsidiaries of Eversource, and Eversource's consolidated financial information includes Aquarion and its subsidiaries' activity beginning December 4, 2017. The approximate $880 million cash purchase price included the $745 million equity purchase price plus a $135 million shareholder loan that was repaid at closing. Purchase Price Allocation : The purchase price allocation reflects a measurement period adjustment recorded in the first quarter of 2018 to revise the fair value of Aquarion's regulated debt. The $7.9 million increase to the fair value of Long-Term Debt (including the current portion) and corresponding increase to Regulatory Assets, included within Other Noncurrent Assets, excluding Goodwill in the table below, will be amortized over the life of the related debt. The allocation of the cash purchase price was as follows: (Millions of Dollars) Current Assets $ 41.2 PP&E 1,034.9 Goodwill 907.9 Other Noncurrent Assets, excluding Goodwill 215.5 Current Liabilities (121.9 ) Noncurrent Liabilities (421.6 ) Long-Term Debt (778.3 ) Total Cash Purchase Price $ 877.7 Pro Forma Financial Information: The following unaudited pro forma financial information reflects the pro forma combined results of operations of Eversource and Aquarion and reflects the amortization of purchase price adjustments assuming the acquisition had taken place on January 1, 2016. The unaudited pro forma financial information has been presented for illustrative purposes only and is not necessarily indicative of the consolidated results of operations that would have been achieved or the future consolidated results of operations of Eversource. For the Years Ended December 31, (Pro forma amounts in millions, except share amounts) 2017 2016 Operating Revenues $ 7,947.7 $ 7,849.0 Net Income Attributable to Common Shareholders 1,019.1 969.3 Basic EPS 3.21 3.05 Diluted EPS 3.20 3.04 Aquarion Revenues and Pre-Tax Income: The impact of Aquarion on Eversource's accompanying consolidated statement of income included operating revenues of $15.9 million and pre-tax income of $1.1 million for the year ended December 31, 2017. B. Goodwill In a business combination, the excess of the purchase price over the estimated fair values of the assets acquired and liabilities assumed is recognized as goodwill. Goodwill is evaluated for impairment at least annually and more frequently if indicators of impairment arise. In accordance with the accounting standards, if the fair value of a reporting unit is less than its carrying value (including goodwill), the goodwill is tested for impairment. Goodwill is not subject to amortization, however is subject to a fair value based assessment for impairment at least annually and whenever facts or circumstances indicate that there may be an impairment. A resulting write-down, if any, would be charged to Operating Expenses. Eversource completed the acquisition of Aquarion on December 4, 2017, resulting in the addition of $0.9 billion of goodwill. Upon completion of the acquisition, Eversource determined that the reporting units for the purpose of testing goodwill are Electric Distribution, Electric Transmission, Natural Gas Distribution and Water Distribution. The goodwill resulting from the Aquarion acquisition has been entirely allocated to the Water Distribution reporting unit. These reporting units are consistent with the operating segments underlying the reportable segments identified in Note 23, "Segment Information," to the financial statements. Eversource completed its annual goodwill impairment test for Electric Distribution, Electric Transmission, Natural Gas Distribution and Water Distribution reporting units as of October 1, 2018 and determined that no impairment existed. There were no events subsequent to October 1, 2018 that indicated impairment of goodwill. The annual goodwill assessment included an evaluation of the Company's share price and credit ratings, analyst reports, financial performance, cost and risk factors, long-term strategy, growth and future projections, as well as macroeconomic, industry and market conditions. This evaluation required the consideration of several factors that impact the fair value of the reporting units, including conditions and assumptions that affect the future cash flows of the reporting units. Key considerations include discount rates, utility sector market performance and merger transaction multiples, and internal estimates of future cash flows and net income. The following table presents goodwill by reportable segment as of December 31, 2018 and 2017: (Billions of Dollars) Electric Distribution Electric Transmission Natural Gas Distribution Water Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 0.9 $ 4.4

QUARTERLY FINANCIAL DATA (UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
QUARTERLY FINANCIAL DATA (UNAUDITED)	QUARTERLY FINANCIAL DATA (UNAUDITED) Quarter Ended Eversource (Millions of Dollars, except per share information) 2018 2017 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,288.0 $ 1,853.9 $ 2,271.4 $ 2,034.9 $ 2,105.1 $ 1,762.8 $ 1,988.5 $ 1,895.6 Operating Income 442.5 391.4 466.0 400.0 501.0 448.2 495.3 443.7 Net Income 271.4 244.6 291.3 233.2 261.3 232.6 262.2 239.4 Net Income Attributable to Common Shareholders 269.5 242.8 289.4 231.3 259.5 230.7 260.4 237.4 Basic and Diluted EPS (1) $ 0.85 $ 0.76 $ 0.91 $ 0.73 $ 0.82 $ 0.73 $ 0.82 $ 0.75 (1) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2018 2017 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 785.0 $ 694.9 $ 865.0 $ 751.3 $ 732.3 $ 666.6 $ 774.8 $ 713.7 Operating Income 157.2 163.1 172.7 142.8 175.5 175.6 177.1 155.2 Net Income 98.6 99.7 100.3 79.1 90.2 91.3 96.1 99.1 NSTAR Electric Operating Revenues $ 770.1 $ 690.7 $ 939.5 $ 712.6 $ 733.8 $ 704.7 $ 851.9 $ 690.2 Operating Income 119.0 133.6 205.5 126.0 156.6 177.9 229.7 124.2 Net Income 77.1 87.9 140.6 77.5 83.4 95.0 125.8 70.5 PSNH Operating Revenues $ 267.4 $ 235.1 $ 290.2 $ 254.9 $ 253.2 $ 230.4 $ 250.0 $ 248.0 Operating Income 55.8 46.9 56.5 37.2 66.6 63.5 66.0 69.8 Net Income 35.1 25.8 40.7 14.3 34.3 31.6 33.7 36.4

SCHEDULE I - FINANCIAL INFORMAT

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT	SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT BALANCE SHEETS AS OF DECEMBER 31, 2018 AND 2017 (Thousands of Dollars) 2018 2017 ASSETS Current Assets: Cash $ 591 $ 521 Accounts Receivable from Subsidiaries 32,175 3,397 Dividend Receivable from Subsidiary — 150,000 Notes Receivable from Subsidiaries 991,400 844,500 Prepayments and Other Current Assets 26,861 18,568 Total Current Assets 1,051,027 1,016,986 Deferred Debits and Other Assets: Investments in Subsidiary Companies, at Equity 12,009,659 10,945,986 Notes Receivable from Subsidiaries 323,500 312,190 Accumulated Deferred Income Taxes 40,454 47,940 Goodwill 3,231,811 3,231,811 Other Long-Term Assets 73,669 58,313 Total Deferred Debits and Other Assets 15,679,093 14,596,240 Total Assets $ 16,730,120 $ 15,613,226 LIABILITIES AND CAPITALIZATION Current Liabilities: Notes Payable $ 631,500 $ 778,087 Long-Term Debt - Current Portion 378,883 32,114 Accounts Payable 286 292 Accounts Payable to Subsidiaries 8,432 18,242 Other Current Liabilities 57,591 56,601 Total Current Liabilities 1,076,692 885,336 Deferred Credits and Other Liabilities 134,614 118,176 Long-Term Debt 4,031,997 3,523,472 Common Shareholders' Equity: Common Shares 1,669,392 1,669,392 Capital Surplus, Paid in 6,241,222 6,239,940 Retained Earnings 3,953,974 3,561,084 Accumulated Other Comprehensive Loss (60,000 ) (66,403 ) Treasury Stock (317,771 ) (317,771 ) Common Shareholders' Equity 11,486,817 11,086,242 Total Liabilities and Capitalization $ 16,730,120 $ 15,613,226 See the Combined Notes to Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 18, "Common Shares," material obligations and guarantees as described in Note 12, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF INCOME FOR THE YEARS ENDED DECEMBER 31, 2018 , 2017 AND 2016 (Thousands of Dollars, Except Share Information) 2018 2017 2016 Operating Revenues $ — $ — $ — Operating Expenses: Other (6,552 ) (32,189 ) (39,453 ) Operating Income 6,552 32,189 39,453 Interest Expense 123,638 80,700 59,420 Other Income, Net: Equity in Earnings of Subsidiaries 1,049,748 993,063 922,321 Other, Net 47,581 23,339 4,267 Other Income, Net 1,097,329 1,016,402 926,588 Income Before Income Tax Benefit 980,243 967,891 906,621 Income Tax Benefit (52,757 ) (20,105 ) (35,681 ) Net Income $ 1,033,000 $ 987,996 $ 942,302 Basic Earnings per Common Share $ 3.25 $ 3.11 $ 2.97 Diluted Earnings per Common Share $ 3.25 $ 3.11 $ 2.96 Weighted Average Common Shares Outstanding: Basic 317,370,369 317,411,097 317,650,180 Diluted 317,993,934 318,031,580 318,454,239 STATEMENTS OF COMPREHENSIVE INCOME 2018 2017 2016 Net Income $ 1,033,000 $ 987,996 $ 942,302 Other Comprehensive Income/(Loss), Net of Tax: Qualified Cash Flow Hedging Instruments 1,756 1,974 2,137 Changes in Unrealized (Losses)/Gains on Marketable Securities (547 ) (350 ) 2,294 Change in Funded Status of Pension, SERP and PBOP Benefit Plans 5,194 (2,745 ) (2,869 ) Other Comprehensive Income/(Loss), Net of Tax 6,403 (1,121 ) 1,562 Comprehensive Income $ 1,039,403 $ 986,875 $ 943,864 See the Combined Notes to Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 18, "Common Shares," material obligations and guarantees as described in Note 12, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF CASH FLOWS FOR THE YEARS ENDED DECEMBER 31, 2018 , 2017 and 2016 (Thousands of Dollars) 2018 2017 2016 Operating Activities: Net Income $ 1,033,000 $ 987,996 $ 942,302 Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities: Equity in Earnings of Subsidiaries (1,049,748 ) (993,063 ) (922,321 ) Cash Dividends Received from Subsidiaries 569,500 753,300 724,877 Deferred Income Taxes 20,032 37,867 19,008 Other (31,093 ) (36,052 ) (27,963 ) Changes in Current Assets and Liabilities: Accounts Receivables from Subsidiaries (28,716 ) 29,405 (9,173 ) Taxes Receivable/Accrued, Net (20,207 ) 1,555 8,050 Accounts Payable, Including Affiliate Payables (9,817 ) 9,763 (6,908 ) Other Current Assets and Liabilities, Net 2,553 7,536 (7,433 ) Net Cash Flows Provided by Operating Activities 485,504 798,307 720,439 Investing Activities: Capital Contributions to Subsidiaries (955,700 ) (1,156,731 ) (589,500 ) Return of Capital from Subsidiary 530,000 — — (Increase)/Decrease in Notes Receivable from Subsidiaries (158,210 ) (192,100 ) 14,510 Other Investing Activities (1,149 ) 1,484 — Net Cash Flows Used in Investing Activities (585,059 ) (1,347,347 ) (574,990 ) Financing Activities: Cash Dividends on Common Shares (640,110 ) (602,083 ) (564,486 ) Issuance of Long-Term Debt 1,550,000 1,200,000 500,000 Retirements of Long-Term Debt (450,000 ) — — Decrease in Notes Payable (347,810 ) (42,690 ) (76,453 ) Other Financing Activities (12,455 ) (5,759 ) (4,484 ) Net Cash Flows Provided by/(Used in) Financing Activities 99,625 549,468 (145,423 ) Net Increase in Cash 70 428 26 Cash - Beginning of Year 521 93 67 Cash - End of Year $ 591 $ 521 $ 93 Supplemental Cash Flow Information: Cash Paid/(Received) During the Year for: Interest $ 118,533 $ 73,868 $ 58,018 Income Taxes $ (30,239 ) $ (59,526 ) $ (65,531 ) See the Combined Notes to Financial Statements in this Annual Report on Form 10-K for a description of significant accounting matters related to Eversource parent, including Eversource common shares information as described in Note 18, "Common Shares," material obligations and guarantees as described in Note 12, "Commitments and Contingencies," and debt agreements as described in Note 7, "Short-Term Debt," and Note 8, "Long-Term Debt."

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	12 Months Ended
	Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	SCHEDULE II EVERSOURCE ENERGY AND SUBSIDIARIES VALUATION AND QUALIFYING ACCOUNTS AND RESERVES FOR THE YEARS ENDED DECEMBER 31, 2018 , 2017 AND 2016 (Thousands of Dollars) Column A Column B Column C Column D Column E Additions (1) (2) Charged Charged to Balance as to Costs Other Deductions - Balance of Beginning and Accounts - Describe as of Description: of Year Expenses Describe (a) (b) End of Year Eversource : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2018 $ 195,708 $ 61,337 $ 48,671 $ 92,993 $ 212,723 2017 200,630 44,665 47,630 97,217 195,708 2016 190,680 69,466 45,452 104,968 200,630 CL&P: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2018 $ 78,872 $ 15,831 $ 29,524 $ 36,193 $ 88,034 2017 86,391 5,312 25,533 38,364 78,872 2016 79,479 17,572 28,801 39,461 86,391 NSTAR Electric: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2018 $ 69,666 $ 22,279 $ 14,971 $ 32,400 $ 74,516 2017 70,284 21,252 14,273 36,143 69,666 2016 66,676 31,728 11,253 39,373 70,284 PSNH : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2018 $ 10,481 $ 6,383 $ 953 $ 6,752 $ 11,065 2017 9,941 6,917 464 6,841 10,481 2016 8,733 7,288 498 6,578 9,941 (a) Amounts relate to uncollectible accounts receivables reserved for that are not charged to bad debt expense. The PURA allows CL&P and Yankee Gas to accelerate the recovery of accounts receivable balances attributable to qualified customers under financial or medical duress (uncollectible hardship accounts receivable) outstanding for greater than 180 days and 90 days, respectively. The DPU allows NSTAR Electric and NSTAR Gas to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. (b) Amounts written off, net of recoveries.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying consolidated financial statements of Eversource, NSTAR Electric and PSNH and the financial statements of CL&P are herein collectively referred to as the "financial statements." The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. Intercompany transactions between CL&P, NSTAR Electric, PSNH and the CYAPC and YAEC companies have been eliminated in consolidation of the Eversource financial statements. Eversource's utility subsidiaries' electric, natural gas and water distribution 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. Eversource's consolidated financial information includes the results of Aquarion and its subsidiaries beginning from the date of the acquisition on December 4, 2017. Certain reclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation. In accordance with accounting guidance on noncontrolling interests in consolidated financial statements, the Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric, which are not owned by Eversource or its consolidated subsidiaries and are not subject to mandatory redemption, have been presented as noncontrolling interests in the financial statements of Eversource. The Preferred Stock of CL&P and the Preferred Stock of NSTAR Electric are considered to be temporary equity and have been classified between liabilities and permanent shareholders' equity on the balance sheets of Eversource, CL&P and NSTAR Electric due to a provision in the preferred stock agreements of both CL&P and NSTAR Electric that grant preferred stockholders the right to elect a majority of the CL&P and NSTAR Electric Boards of Directors, respectively, should certain conditions exist, such as if preferred dividends are in arrears for a specified amount of time. The Net Income reported in the statements of income and cash flows represents net income prior to apportionment to noncontrolling interests, which is represented by dividends on preferred stock of CL&P and NSTAR Electric.
Accounting Standards	Accounting Standards Accounting Standards Issued but Not Yet Effective: In February 2016, the FASB issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842) , which changes existing lease accounting guidance and is required to be applied in the first quarter of 2019. The requirements of the new leases standard include balance sheet recognition of leases deemed to be operating leases and additional disclosure requirements. The recognition, measurement and presentation of expenses and cash flows are not significantly changed. The Company implemented the new leases standard in the first quarter of 2019 and applied the Topic 842 lease criteria to new leases and lease renewals entered into effective on or after January 1, 2019. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) - Targeted Improvements , allowing a transition method to adopt the new leases standard on a prospective basis as of the adoption date, with prior periods presented in the financial statements continuing to follow existing lease accounting guidance under Topic 840 (Leases) in the accounting literature. The Company adopted the prospective transition method allowed in ASU 2018-11. The Company has decided to elect the practical expedient package whereby it does not need to reassess whether or not an existing contract is or contains a lease or whether a lease is an operating or capital lease, and it does not need to reassess initial direct costs for leases. The Company has also elected the practical expedient to not reevaluate land easements existing at adoption if they were not previously accounted for as leases. The Company determined the impact the ASUs will have on its financial statements by reviewing its lease population and identifying lease data needed for the disclosure requirements. The Company implemented a new lease accounting system in 2019 to ensure ongoing compliance with the ASU’s requirements. Eversource recognized approximately $60 million , which includes approximately $25 million at NSTAR Electric, approximately $1 million at CL&P and approximately $1 million at PSNH, of operating lease liabilities and right-of-use assets on their respective balance sheets upon transition at January 1, 2019. Implementation of the new guidance will not have an impact on each company’s results of operations and cash flows. Accounting Standards Recently Adopted: On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted ASU 2014-09, Revenue from Contracts with Customers , which amended existing revenue recognition guidance, using the modified retrospective method (cumulatively at the date of initial application) applying it only to contracts that were not complete at January 1, 2018. Under this method of adoption, prior year reported results were not restated. Implementation of the ASU did not have a material effect on the results of operations, financial position or cash flows of Eversource, CL&P, NSTAR Electric or PSNH. See Note 22, "Revenues," for further information . The Company identified an item that was accounted for differently under the new revenue guidance, as compared to the previously existing guidance. As a result of applying guidance on the unit of account under the new standard, purchases of power from and sales of power to ISO-New England are now accounted for net by the hour, rather than net by the month. This change increased Operating Revenues and Purchased Power, Fuel and Transmission by $22.8 million for the year ended December 31, 2018, with no impact on net income. On January 1, 2018, Eversource adopted ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Liabilities . The ASU removed the available-for-sale designation for equity securities, whereby changes in fair value were previously recorded in accumulated other comprehensive income within shareholders' equity, and required changes in fair value of all equity securities to be recorded in earnings effective January 1, 2018. There was no cumulative effect of adoption. Unrealized losses recorded in Other Income, Net were $4.3 million for the year ended December 31, 2018. For further information, see Note 5, "Marketable Securities," to the financial statements. On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted ASU 2017-07, Compensation – Retirement Benefits: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost . The ASU required separate presentation of service cost from other components of net pension, SERP and PBOP costs, with the other components presented as non-operating income and not subject to capitalization. The ASU has been 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. As of December 31, 2018 , the non-service cost components of net pension, SERP and PBOP costs that were not capitalized in plant were recorded as an increase to regulatory liabilities of $39.8 million , as these amounts continue to be included in rates. See Note 1N, "Summary of Significant Accounting Policies - Other Income, Net," to the financial statements for the portion of pension, SERP and PBOP costs that are presented as non-operating income for the years ended December 31, 2018, 2017 and 2016. For the year ended December 31, 2017, the amounts, which were previously presented within Operations and Maintenance expense on the statements of income, totaled $29.9 million at Eversource, $1.8 million at CL&P, $19.2 million at NSTAR Electric and $5.9 million at PSNH, and have been retrospectively presented within Other Income, Net. For the year ended December 31, 2016, these amounts were $18.6 million at Eversource, $0.7 million at CL&P, $10.5 million at NSTAR Electric and $6.2 million at PSNH. On January 1, 2018, Eversource, CL&P, NSTAR Electric and PSNH adopted two accounting standards relating to the statement of cash flows; ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments, and ASU 2016-18, Restricted Cash. As a result of implementing ASU 2016-15, dividends from equity method investments of $19.1 million , $20.0 million , and $0.7 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively, are presented in operating activities at Eversource, for which the 2017 and 2016 amounts were previously classified in investing activities. ASU 2016-18 required that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash and restricted cash equivalents. Both standards were applied retrospectively, as required, and neither had a material impact on Eversource's, CL&P's, NSTAR Electric's or PSNH's statements of cash flows. See Note 1P, "Summary of Significant Accounting Policies - Supplemental Cash Flow Information," to the financial statements for a reconciliation of cash and cash equivalents as reported on the balance sheet to the statement of cash flows, which includes amounts described as restricted cash and restricted cash equivalents.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash on hand and short-term cash investments that are highly liquid in nature and have original maturities of three months or less. At the end of each reporting period, any overdraft amounts are reclassified from Cash and Cash Equivalents to Accounts Payable on the balance sheets.
Provision for Uncollectible Accounts	Provision for Uncollectible Accounts Eversource, including CL&P, NSTAR Electric and PSNH, 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 NSTAR Electric and NSTAR Gas to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets.
CL&P Energy Efficiency Loans	CL&P Energy Efficiency Loans In December 2018, CL&P transferred $41.3 million of its energy efficiency customer loan portfolio to two outside lenders in order to make additional loans to customers. CL&P remains the servicer of the loans and will transmit customer payments to the lenders. Under a three-year agreement with the lenders, additional energy efficiency loans will also be transferred with a maximum amount outstanding under this program of $55 million . The transaction did not qualify as a sale for accounting purposes, and the amounts of the loans ( $18.5 million and $22.8 million as of December 31, 2018 in current and long-term, respectively), included in Accounts Receivable, Net and Other Long-Term Assets, are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet.
Fuel, Materials, Supplies and Inventory	Fuel, Materials, Supplies and Inventory Fuel, Materials, Supplies and Inventory include natural gas inventory, materials and supplies purchased primarily for construction or operation and maintenance purposes, and RECs. Inventory is valued at the lower of cost or net realizable value. RECs are purchased from suppliers of renewable sources of generation and are used to meet state mandated Renewable Portfolio Standards requirements.
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, long-term debt and RRBs. Fair Value Hierarchy: In measuring fair value, Eversource uses observable market data when available in order to minimize the use of unobservable inputs. Inputs used in fair value measurements are categorized into three fair value hierarchy levels for disclosure purposes. The entire fair value measurement is categorized based on the lowest level of input that is significant to the fair value measurement. Eversource evaluates the classification of assets and liabilities measured at fair value on a quarterly basis, and Eversource's policy is to recognize transfers between levels of the fair value hierarchy as of the end of the reporting period. The three levels of the fair value hierarchy are described below: Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. Uncategorized - Investments that are measured at net asset value are not categorized within the fair value hierarchy. Determination of Fair Value: The valuation techniques and inputs used in Eversource's fair value measurements are described in Note 4, "Derivative Instruments," Note 5, "Marketable Securities," Note 6, "Asset Retirement Obligations," Note 10A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," Note 15, "Fair Value of Financial Instruments" and Note 24B, "Acquisition of Aquarion and Goodwill - Goodwill" to the financial statements.
Derivative Accounting	Derivative Accounting Many of the electric and natural gas companies' contracts for the purchase and sale of energy or energy-related products are derivatives. The accounting treatment for energy contracts entered into varies and depends on the intended use of the particular contract and on whether or not the contract is a derivative. For the regulated companies, regulatory assets or regulatory liabilities are recorded to offset the fair values of derivative contracts related to energy and energy-related products, as contract settlements are recovered from, or refunded to, customers in future rates. The application of derivative accounting is complex and requires management judgment in the following respects: identification of derivatives and embedded derivatives, election and designation of a contract as normal, and determination of the fair value of derivative contracts. All of these judgments can have a significant impact on the financial statements. The judgment applied in the election of a contract as normal (and resulting accrual accounting) includes the conclusion that it is probable at the inception of the contract and throughout its term that it will result in physical delivery of the underlying product and that the quantities will be used or sold by the business in the normal course of business. If facts and circumstances change and management can no longer support this conclusion, then a contract cannot be considered normal, accrual accounting is terminated, and fair value accounting is applied prospectively. The fair value of derivative contracts is based upon the contract terms and conditions and the underlying market price or fair value per unit. When quantities are not specified in the contract, the Company determines whether the contract has a determinable quantity by using amounts referenced in default provisions and other relevant sections of the contract. The fair value of derivative assets and liabilities with the same counterparty are offset and recorded as a net derivative asset or liability on the balance sheets. All changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.
Investments	Investments Investments are included in Other Long-Term Assets on the balance sheets and earnings impacts from these equity investments are included in Other Income, Net on the statements of income. Strategic, Infrastructure and Other Investments: As of December 31, 2018 and 2017 , Eversource had investments totaling $463.7 million and $277.6 million , respectively. As of December 31, 2018 and 2017 , Eversource's investments included a 50 percent ownership in Bay State Wind, an offshore wind project of $234.3 million and $30.2 million , respectively, a 15 percent ownership interest in a FERC-regulated natural gas transmission business of $155.0 million and $159.6 million , respectively, a 37.2 percent ( 14.5 percent of which related to NSTAR Electric) ownership interest in two companies that transmit hydro-electricity imported from the Hydro-Quebec system in Canada of $19.5 million and $17.7 million , respectively, other investments totaling $54.9 million and $38.8 million , respectively, and a 40 percent ownership interest in Access Northeast of $31.3 million as of December 31, 2017. NSTAR Electric's investments totaled $7.6 million and $6.9 million , respectively, as of December 31, 2018 and 2017 . Impairment of Access Northeast: Access Northeast is a natural gas pipeline and storage project jointly owned by Eversource, Enbridge, Inc. ("Enbridge") and National Grid plc ("National Grid"), through Algonquin Gas Transmission, LLC ("AGT"). Equity method investments are assessed for impairment when conditions exist that indicate that the fair value of the investment is less than book value. If the decline in value is considered to be other-than-temporary, the investment is written down to its estimated fair value, which establishes a new cost basis in the investment. Impairment evaluations involve a significant degree of judgment and estimation, including identifying circumstances that indicate an impairment may exist and developing undiscounted future cash flows. In 2015 and 2016, AGT sought to secure long-term natural gas pipeline capacity contracts with EDCs in Massachusetts, Connecticut, New Hampshire, Maine, and Rhode Island. Subsequently, in 2016, the Massachusetts Supreme Judicial Court and the NHPUC each ruled that state statutes precluded the state regulatory agencies from approving those contracts in Massachusetts and New Hampshire, respectively. The New Hampshire Supreme Court overruled the NHPUC decision in May 2018. Legislative changes are needed in Massachusetts to allow the DPU to approve natural gas pipeline capacity contracts. No such changes have occurred during any legislative session to date. In September 2018, a series of non-Eversource natural gas explosions in eastern Massachusetts resulted in widespread property and system damage, personal injuries, and a fatality. As a result of these events, compounded by the failure to secure Massachusetts legislation to date, we believe there is significant uncertainty around the future timing of, and ability to secure, needed legislative change affecting the natural gas industry and pipeline expansion, which may significantly delay the completion of the Access Northeast project. Eversource identified the September 2018 natural gas series of explosions, compounded by the adverse legislative environment, as negative evidence that indicated potential impairment. Our impairment assessment used a discounted cash flow approach, including consideration of the severity and duration of any decline in fair value of our investment in the project, and involved significant management judgment and estimation, including projections of the project’s discounted cash flows and assumptions about exit price. In the third quarter of 2018, management determined that the future cash flows of the Access Northeast project were uncertain and could no longer be reasonably estimated and that the book value of our equity method investment was not recoverable. As a result, Eversource recorded an other-than-temporary impairment of $32.9 million within Other Income, Net on our statement of income in 2018, which represented the full carrying value of our equity method investment. Regional Decommissioned Nuclear Companies : CL&P, NSTAR Electric and PSNH own common stock in three regional nuclear generation companies (CYAPC, YAEC and MYAPC, collectively referred to as the "Yankee Companies"), each of which owned a single nuclear generating facility that has been decommissioned. For CL&P, NSTAR Electric and PSNH, the respective investments in CYAPC, YAEC and MYAPC are accounted for under the equity method and are included in Other Long-Term Assets on their respective balance sheets. For CL&P, NSTAR Electric and PSNH, these investments totaled $1.3 million , $0.9 million and $0.3 million as of both December 31, 2018 and 2017 . Eversource consolidates CYAPC and YAEC because CL&P's, NSTAR Electric's and PSNH's combined ownership and voting interests in each of these entities is greater than 50 percent. For further information on the Yankee Companies, see Note 12C, "Commitments and Contingencies – Spent Nuclear Fuel Obligations – Yankee Companies," to the financial statements. Equity in Earnings and Dividends from Equity Method Investments: For the years ended December 31, 2018 , 2017 and 2016 , Eversource had equity in earnings, net of impairment, of unconsolidated affiliates of $3.8 million , $27.4 million , and $0.2 million , respectively. Eversource received dividends from its equity method investees of $22.3 million , $20.0 million and $0.1 million , respectively, for the years ended December 31, 2018 , 2017 and 2016 .
Allowance for Funds Used During Construction	Allowance for Funds Used During Construction AFUDC represents the cost of borrowed and equity funds used to finance construction and is included in the cost of the electric, natural gas and water companies' utility plant on the balance sheet. The portion of AFUDC attributable to borrowed funds is recorded as a reduction of Interest Expense, and the AFUDC related to equity funds is recorded as Other Income, Net on the statements of income. AFUDC costs are recovered from customers over the service life of the related plant in the form of increased revenue collected as a result of higher depreciation expense. The average AFUDC rate is based on a FERC-prescribed formula using the cost of a company's short-term financings and capitalization (preferred stock, long-term debt and common equity), as appropriate. The average rate is applied to average eligible CWIP amounts to calculate AFUDC.
Other Taxes	Other Taxes Eversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers.
Related Parties	Related Parties Eversource Service, Eversource's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, and other services to Eversource's companies. The Rocky River Realty Company, Renewable Properties, Inc. and Properties, Inc., three other Eversource subsidiaries, construct, acquire or lease some of the property and facilities used by Eversource's companies. As of both December 31, 2018 and 2017 , CL&P, NSTAR Electric and PSNH had long-term receivables from Eversource Service in the amounts of $25.0 million , $5.5 million and $3.8 million , respectively, which were included in Other Long-Term Assets on the balance sheets. These amounts related to the funding of investments held in trust by Eversource Service in connection with certain postretirement benefits for CL&P, NSTAR Electric and PSNH employees and have been eliminated in consolidation on the Eversource financial statements. Included in the CL&P, NSTAR Electric and PSNH balance sheets as of December 31, 2018 and 2017 were Accounts Receivable from Affiliated Companies and Accounts Payable to Affiliated Companies relating to transactions between CL&P, NSTAR Electric and PSNH and other subsidiaries that are wholly-owned by Eversource. These amounts have been eliminated in consolidation on the Eversource financial statements.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Provision for uncollectible accounts and uncollectible hardship accounts	The total provision for both uncollectible accounts and for uncollectible hardship accounts (the uncollectible hardship balance is included in the total provision) is included in Receivables, Net on the balance sheets, and is as follows: Total Provision for Uncollectible Accounts Uncollectible Hardship As of December 31, As of December 31, (Millions of Dollars) 2018 2017 2018 2017 Eversource $ 212.7 $ 195.7 $ 131.5 $ 122.5 CL&P 88.0 78.9 71.9 65.5 NSTAR Electric 74.5 69.7 42.5 40.3 PSNH 11.1 10.5 — — In accordance with new revenue accounting guidance, uncollectible expense associated with customers' accounts receivable included in Operations and Maintenance expense on the statements of income is as follows: For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Eversource $ 61.3 $ 44.5 $ 69.5 CL&P 15.8 5.3 17.6 NSTAR Electric 22.3 21.3 31.7 PSNH 6.4 6.7 7.3
Schedule of Utility Inventory	The carrying amounts of fuel, materials and supplies, and RECs, which are included in Current Assets on the balance sheets, were as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Fuel $ 33.1 $ — $ — $ — $ 29.7 $ — $ — $ — Materials and Supplies 126.1 44.5 48.6 24.3 117.1 44.4 45.1 18.5 RECs 78.8 — 65.6 13.2 76.3 4.0 50.4 21.8 Total - Current $ 238.0 $ 44.5 $ 114.2 $ 37.5 $ 223.1 $ 48.4 $ 95.5 $ 40.3
Costs related to fuel and natural gas	Costs related to fuel and natural gas included in Purchased Power, Fuel and Transmission on the statements of income were as follows: For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Eversource - Natural Gas and Fuel $ 442.6 $ 432.5 $ 372.2 PSNH - Fuel 7.9 43.4 45.0 PSNH completed the sale of its generation assets in 2018.
Weighted-average AFUDC rates	AFUDC costs and the weighted-average AFUDC rates were as follows: Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2018 2017 2016 Borrowed Funds $ 19.7 $ 12.5 $ 10.8 Equity Funds 44.0 34.4 26.2 Total AFUDC $ 63.7 $ 46.9 $ 37.0 Average AFUDC Rate 4.9 % 5.1 % 4.4 % For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars, except percentages) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Borrowed Funds $ 6.3 $ 7.8 $ 1.3 $ 5.1 $ 4.8 $ 0.7 $ 3.3 $ 5.3 $ 0.8 Equity Funds 12.2 15.6 — 12.1 10.2 — 6.3 10.2 0.3 Total AFUDC $ 18.5 $ 23.4 $ 1.3 $ 17.2 $ 15.0 $ 0.7 $ 9.6 $ 15.5 $ 1.1 Average AFUDC Rate 5.8 % 5.0 % 0.7 % 6.2 % 5.0 % 0.7 % 4.7 % 3.2 % 1.0 %
Other Income, Net	The components of Other Income, Net on the statements of income were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Pension, SERP and PBOP Non-Service Income Components (1) $ 60.8 $ 29.9 $ 18.6 AFUDC Equity 44.0 34.4 26.2 Equity in Earnings, Net of Impairment (2) 3.8 27.4 0.2 Investment Income/(Loss) (4.0 ) 7.5 8.5 Interest Income (3) 18.1 8.3 11.0 Gains on Sales of Property 5.1 — — Other 0.6 0.4 — Total Other Income, Net (1) $ 128.4 $ 107.9 $ 64.5 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Pension, SERP and PBOP Non-Service Income Components (1) $ 9.5 $ 36.0 $ 9.9 $ 1.8 $ 19.2 $ 5.9 $ 0.7 $ 10.5 $ 6.2 AFUDC Equity 12.2 15.6 — 12.1 10.2 — 6.3 10.2 0.3 Equity in Earnings 0.1 0.7 — — 0.3 — 0.1 0.3 — Investment Income/(Loss) (3.0 ) (0.5 ) (0.8 ) 4.5 2.6 1.6 (1.5 ) (0.3 ) (0.7 ) Interest Income (3) 3.7 0.8 14.1 4.6 1.8 2.2 8.6 0.6 1.8 Gain on Sale of Property — 0.5 4.4 — — — — — — Other 0.2 — 0.1 — — 0.1 — — — Total Other Income, Net (1) $ 22.7 $ 53.1 $ 27.7 $ 23.0 $ 34.1 $ 9.8 $ 14.2 $ 21.3 $ 7.6 (1) As a result of the adoption of new accounting guidance, the non-service related components of pension, SERP and PBOP benefit costs are presented as non-operating income and recorded in Other Income, Net on the statements of income. The 2017 and 2016 amounts, which were previously presented within Operations and Maintenance expense on the statements of income, have been retrospectively presented within Other Income, Net for the years ended December 31, 2017 and 2016. Eversource elected the practical expedient in the accounting guidance that allows the Company to use the amounts disclosed in its Pension Benefits and Postretirement Benefits Other Than Pension footnote for the prior period presentations as the estimation basis for applying the retrospective presentation requirements. (2) For the year ended December 31, 2018, equity in earnings, net of impairment, of unconsolidated affiliates includes an other-than-temporary impairment of $32.9 million in the Access Northeast project investment. See Note 1K, "Summary of Significant Accounting Policies - Investments," for further information. Equity in earnings includes $17.6 million and $9.7 million of unrealized gains in 2018 and 2017, respectively, and $1.7 million of unrealized losses in 2016 associated with an equity method investment in a renewable energy fund. (3) See Note 2, "Regulatory Accounting," for interest income recognized in 2018 for the equity return component of carrying charges on storm costs at PSNH.
Other Taxes	These gross receipts taxes are recorded separately with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the statements of income as follows: For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Eversource $ 161.9 $ 157.4 $ 162.7 CL&P 141.4 137.5 145.2
Supplemental Cash Flow Information	Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2018 2017 2016 Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 503.2 $ 419.1 $ 398.1 Income Taxes 158.8 30.8 (135.5 ) Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 435.9 379.5 301.5 As of and For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Cash Paid/(Received) During the Year for: Interest, Net of Amounts Capitalized $ 149.7 $ 122.1 $ 40.5 $ 144.6 $ 124.6 $ 45.9 $ 143.3 $ 112.9 $ 46.5 Income Taxes 66.1 120.0 27.3 68.8 95.5 26.1 (73.9 ) 66.0 (36.0 ) Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 106.1 116.5 81.7 132.5 116.5 44.4 116.2 87.0 37.9
Cash and cash equivalents as reported on the balance sheet	The following table reconciles cash and cash equivalents as reported on the balance sheets to the cash, cash equivalents, and restricted cash as reported on the statements of cash flows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Cash and Cash Equivalents as reported on the Balance Sheets $ 108.1 $ 87.7 $ 1.6 $ 1.4 $ 38.2 $ 6.0 $ 1.8 $ 0.9 Restricted cash included in: Prepayments and Other Current Assets 72.1 3.5 13.0 47.5 24.4 3.1 12.8 0.5 Marketable Securities 25.9 0.4 0.1 0.6 23.3 0.5 0.1 0.8 Other Long-Term Assets 3.2 — — 3.2 — — — — Cash, Cash Equivalents, and Restricted Cash reported on the Statements of Cash Flows $ 209.3 $ 91.6 $ 14.7 $ 52.7 $ 85.9 $ 9.6 $ 14.7 $ 2.2

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Schedule of Regulatory Assets	The components of regulatory assets were as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Benefit Costs $ 1,914.8 $ 424.7 $ 544.4 $ 169.6 $ 2,068.8 $ 469.2 $ 560.7 $ 212.3 Income Taxes, Net 728.6 454.4 105.9 8.3 768.9 453.8 113.2 21.7 Securitized Stranded Costs 608.4 — — 608.4 — — — — Deferred Costs from Generation Asset Sale — — — — 516.1 — — 516.1 Storm Restoration Costs, Net 576.0 302.6 212.9 60.5 404.8 216.7 146.6 41.5 Regulatory Tracker Mechanisms 316.0 33.2 169.1 67.3 509.9 85.3 273.0 116.4 Derivative Liabilities 356.5 356.5 — — 367.2 362.3 — — Goodwill-related 348.4 — 299.1 — 365.2 — 313.6 — Asset Retirement Obligations 89.2 32.3 42.2 3.3 101.0 30.3 39.0 17.0 Other Regulatory Assets 208.0 27.0 64.6 12.1 137.4 27.6 78.4 15.8 Total Regulatory Assets 5,145.9 1,630.7 1,438.2 929.5 5,239.3 1,645.2 1,524.5 940.8 Less: Current Portion 514.8 125.2 241.7 67.2 741.9 200.3 333.9 130.1 Total Long-Term Regulatory Assets $ 4,631.1 $ 1,505.5 $ 1,196.5 $ 862.3 $ 4,497.4 $ 1,444.9 $ 1,190.6 $ 810.7
Schedule of Regulatory Liabilities	The components of regulatory liabilities were as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH EDIT due to Tax Cuts and Jobs Act $ 2,883.0 $ 1,031.0 $ 1,103.7 $ 396.4 $ 2,882.0 $ 1,031.6 $ 1,087.9 $ 405.1 Cost of Removal 521.0 39.9 307.1 22.1 502.1 23.2 293.8 37.9 Benefit Costs 91.2 — 76.9 — 132.3 — 112.6 — Regulatory Tracker Mechanisms 309.0 89.5 163.7 48.3 136.7 34.6 77.8 5.0 AFUDC - Transmission 70.7 47.4 23.3 — 67.1 48.8 18.3 — Revenue Subject to Refund due to Tax Cuts and Jobs Act 24.6 — — 12.6 — — — — Other Regulatory Liabilities 80.2 24.0 29.2 4.2 45.2 12.9 3.7 2.7 Total Regulatory Liabilities 3,979.7 1,231.8 1,703.9 483.6 3,765.4 1,151.1 1,594.1 450.7 Less: Current Portion 370.2 109.6 190.6 55.5 128.1 39.0 79.6 6.3 Total Long-Term Regulatory Liabilities $ 3,609.5 $ 1,122.2 $ 1,513.3 $ 428.1 $ 3,637.3 $ 1,112.1 $ 1,514.5 $ 444.4

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Utility Property, Plant and Equipment	The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows: (Percent) 2018 2017 2016 Eversource 2.9 % 3.0 % 3.0 % CL&P 2.8 % 2.8 % 2.7 % NSTAR Electric 2.8 % 2.9 % 2.9 % PSNH 2.8 % 3.1 % 3.1 % The following tables summarize property, plant and equipment by asset category: Eversource As of December 31, (Millions of Dollars) 2018 2017 Distribution - Electric $ 15,071.1 $ 14,410.5 Distribution - Natural Gas 3,546.2 3,244.2 Transmission - Electric 10,153.9 9,270.9 Distribution - Water 1,639.8 1,558.4 Solar 164.1 36.2 Utility 30,575.1 28,520.2 Other (1) 778.6 693.7 Property, Plant and Equipment, Gross 31,353.7 29,213.9 Less: Accumulated Depreciation Utility (7,126.2 ) (6,846.9 ) Other (336.7 ) (286.9 ) Total Accumulated Depreciation (7,462.9 ) (7,133.8 ) Property, Plant and Equipment, Net 23,890.8 22,080.1 Construction Work in Progress 1,719.6 1,537.4 Total Property, Plant and Equipment, Net $ 25,610.4 $ 23,617.5 As of December 31, 2018 2017 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Distribution - Electric $ 6,176.4 $ 6,756.4 $ 2,178.6 $ 5,888.3 $ 6,479.0 $ 2,083.4 Transmission - Electric 4,700.5 4,065.9 1,338.7 4,239.9 3,821.2 1,161.3 Solar — 164.1 — — 36.2 — Property, Plant and Equipment, Gross 10,876.9 10,986.4 3,517.3 10,128.2 10,336.4 3,244.7 Less: Accumulated Depreciation (2,302.6 ) (2,702.0 ) (772.9 ) (2,239.0 ) (2,550.2 ) (751.8 ) Property, Plant and Equipment, Net 8,574.3 8,284.4 2,744.4 7,889.2 7,786.2 2,492.9 Construction Work in Progress 335.4 510.3 135.7 381.8 460.3 149.4 Total Property, Plant and Equipment, Net $ 8,909.7 $ 8,794.7 $ 2,880.1 $ 8,271.0 $ 8,246.5 $ 2,642.3 (1) These assets are primarily comprised of building improvements, computer software, hardware and equipment at Eversource Service. The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2018 (Years) Eversource CL&P NSTAR Electric PSNH Distribution - Electric 34.1 35.4 33.7 32.3 Distribution - Natural Gas 43.8 — — — Transmission - Electric 41.3 38.0 45.3 42.9 Distribution - Water 33.3 — — — Solar 24.9 — 24.9 — Other 12.9 — — —

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The following table presents the gross fair values of contracts, categorized by risk type, and the net amounts recorded as current or long-term derivative assets or liabilities: As of December 31, 2018 2017 (Millions of Dollars) Fair Value Hierarchy Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Commodity Supply and Price Risk Management Netting (1) Net Amount Recorded as a Derivative Current Derivative Assets: CL&P Level 3 9.6 (3.4 ) 6.2 9.5 (7.1 ) 2.4 Other Level 2 $ 1.5 $ (0.9 ) $ 0.6 $ — $ — $ — Long-Term Derivative Assets: CL&P Level 3 74.2 (2.3 ) 71.9 71.9 (5.3 ) 66.6 Current Derivative Liabilities: CL&P Level 3 (55.1 ) — (55.1 ) (54.4 ) — (54.4 ) Other Level 2 — — — (4.5 ) — (4.5 ) Long-Term Derivative Liabilities : CL&P Level 3 (379.5 ) — (379.5 ) (376.9 ) — (376.9 ) Other Level 2 — — — (0.4 ) — (0.4 ) (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 CL&P's Level 3 derivative contracts and the range of the significant unobservable inputs utilized in the valuations over the duration of the contracts: As of December 31, 2018 2017 CL&P Range Period Covered Range Period Covered Capacity Prices $ 4.30 — 7.44 per kW-Month 2022 - 2026 $ 5.00 — 8.70 per kW-Month 2021 - 2026 Forward Reserve 0.75 — 1.78 per kW-Month 2019 - 2024 1.00 — 2.00 per kW-Month 2018 - 2024
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation	. CL&P (Millions of Dollars) For the Years Ended December 31, 2018 2017 Derivatives, Net: Fair Value as of Beginning of Period $ (362.3 ) $ (420.5 ) Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities (32.0 ) (9.5 ) Settlements 37.8 67.7 Fair Value as of End of Period $ (356.5 ) $ (362.3 )

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities Reconciliation	The following is a summary of the available-for-sale debt securities, which are recorded at fair value and are included in current and long-term Marketable Securities on the balance sheets. As of December 31, 2018 2017 Eversource (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Debt Securities $ 190.0 $ 0.4 $ (4.0 ) $ 186.4 $ 284.9 $ 3.2 $ (1.1 ) $ 287.0
Investments Classified by Contractual Maturity Date	As of December 31, 2018 , 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) $ 30.5 $ 30.3 One to five years 29.2 28.9 Six to ten years 43.6 42.9 Greater than ten years 86.7 84.3 Total Debt Securities $ 190.0 $ 186.4 (1) Amounts in the Less than one year category include securities in the CYAPC and YAEC spent nuclear fuel trusts, which are restricted and are classified in long-term Marketable Securities on the balance sheets.
Marketable Securities Recorded at Fair Value	The following table presents the marketable securities recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Eversource (Millions of Dollars) As of December 31, 2018 2017 Level 1: Mutual Funds and Equities $ 244.0 $ 313.8 Money Market Funds 25.9 23.3 Total Level 1 $ 269.9 $ 337.1 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 79.6 $ 70.2 Corporate Debt Securities 39.5 50.9 Asset-Backed Debt Securities 14.0 21.2 Municipal Bonds 19.2 110.7 Other Fixed Income Securities 8.2 10.7 Total Level 2 $ 160.5 $ 263.7 Total Marketable Securities $ 430.4 $ 600.8

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Change in Asset Retirement Obligation	A reconciliation of the beginning and ending carrying amounts of ARO liabilities is as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Balance as of Beginning of Year $ 419.1 $ 31.5 $ 44.6 $ 25.0 $ 426.4 $ 36.0 $ 42.6 $ 23.5 Liabilities Incurred During the Year 11.3 — 11.3 — 0.2 0.1 0.1 — Liabilities Settled During the Year (36.6 ) — — (21.5 ) (19.3 ) (1.0 ) (0.2 ) — Accretion 25.5 2.0 2.2 0.5 26.3 2.3 2.1 1.5 Revisions in Estimated Cash Flows 46.9 — 14.3 — (14.5 ) (5.9 ) — — Balance as of End of Year $ 466.2 $ 33.5 $ 72.4 $ 4.0 $ 419.1 $ 31.5 $ 44.6 $ 25.0

SHORT-TERM DEBT (Tables)

SHORT-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Debt	The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding as of December 31, Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2018 2017 2018 2017 2018 2017 Eversource Parent Commercial Paper Program $ 631.5 $ 979.3 $ 818.5 $ 470.7 2.77 % 1.86 % NSTAR Electric Commercial Paper Program 278.5 234.0 371.5 416.0 2.50 % 1.55 % Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 7.875% 1994 Series D due 2024 $ 139.8 $ 139.8 5.750% 2004 Series B due 2034 130.0 130.0 5.625% 2005 Series B due 2035 100.0 100.0 6.350% 2006 Series A due 2036 250.0 250.0 5.750% 2007 Series B due 2037 150.0 150.0 6.375% 2007 Series D due 2037 100.0 100.0 5.650% 2008 Series A due 2018 — 300.0 5.500% 2009 Series A due 2019 250.0 250.0 2.500% 2013 Series A due 2023 400.0 400.0 4.300% 2014 Series A due 2044 475.0 475.0 4.150% 2015 Series A due 2045 350.0 350.0 3.200% 2017 Series A due 2027 300.0 300.0 4.000% 2018 Series A due 2048 500.0 — Total First Mortgage Bonds 3,144.8 2,944.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year (250.0 ) (300.0 ) Unamortized Premiums and Discounts, Net 10.2 11.5 Unamortized Debt Issuance Costs (21.5 ) (17.7 ) CL&P Long-Term Debt $ 3,004.0 $ 2,759.1 NSTAR Electric (Millions of Dollars) As of December 31, 2018 2017 Debentures: 5.750% due 2036 $ 200.0 $ 200.0 5.500% due 2040 300.0 300.0 2.375% due 2022 400.0 400.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 250.0 2.700% due 2026 250.0 250.0 3.200% due 2027 700.0 700.0 Total Debentures 2,400.0 2,400.0 Notes: 5.900% Senior Notes Series B due 2034 50.0 50.0 6.700% Senior Notes Series D due 2037 40.0 40.0 5.100% Senior Notes Series E due 2020 95.0 95.0 3.500% Senior Notes Series F due 2021 250.0 250.0 3.880% Senior Notes Series G due 2023 80.0 80.0 2.750% Senior Notes Series H due 2026 50.0 50.0 Total Notes 565.0 565.0 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net (2.5 ) (1.8 ) Unamortized Debt Issuance Costs (17.7 ) (19.4 ) NSTAR Electric Long-Term Debt $ 2,944.8 $ 2,943.8 PSNH (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 6.000% Series O due 2018 — 110.0 4.500% Series P due 2019 150.0 150.0 4.050% Series Q due 2021 122.0 122.0 3.200% Series R due 2021 160.0 160.0 3.500% Series S due 2023 325.0 325.0 Total First Mortgage Bonds 807.0 917.0 Pollution Control Revenue Bonds: Adjustable Rate Tax Exempt Series A due 2021 — 89.3 Less Amounts due Within One Year (150.0 ) (110.0 ) Unamortized Premiums and Discounts, Net — 0.2 Unamortized Debt Issuance Costs (1.8 ) (4.1 ) PSNH Long-Term Debt $ 655.2 $ 892.4 OTHER (Millions of Dollars) As of December 31, 2018 2017 Yankee Gas - First Mortgage Bonds: 3.020% - 8.480% due 2019 - 2048 $ 470.0 $ 520.0 NSTAR Gas - First Mortgage Bonds: 4.09% - 9.950% due 2020 - 2048 385.0 285.0 Eversource Parent and Other - Notes and Debentures: 4.500% Debentures due 2019 350.0 350.0 2.500% - 4.250% Senior Notes due 2021 - 2029 4,360.0 3,260.0 Unsecured Notes 3.570% - 6.430% due 2021 - 2037 289.5 290.9 Secured Debt 4.100% - 9.640% due 2021 - 2035 70.7 70.4 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 39.5 181.4 Fair Value Adjustment (1) 144.7 172.6 Less Fair Value Adjustment - Current Portion (1) (36.2 ) (35.4 ) Less Amounts due in One Year (401.1 ) (104.2 ) Commercial Paper Classified as Long-Term Debt — 201.2 Unamortized Premiums and Discounts, Net (4.2 ) 1.5 Unamortized Debt Issuance Costs (23.2 ) (12.8 ) Total Other Long-Term Debt $ 5,644.7 $ 5,180.6 Total Eversource Long-Term Debt $ 12,248.7 $ 11,775.9 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record the NSTAR long-term debt at fair value on the date of the 2012 merger and to record the Aquarion long-term debt at fair value on the date of the 2017 acquisition.

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Debt	The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding as of December 31, Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2018 2017 2018 2017 2018 2017 Eversource Parent Commercial Paper Program $ 631.5 $ 979.3 $ 818.5 $ 470.7 2.77 % 1.86 % NSTAR Electric Commercial Paper Program 278.5 234.0 371.5 416.0 2.50 % 1.55 % Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 7.875% 1994 Series D due 2024 $ 139.8 $ 139.8 5.750% 2004 Series B due 2034 130.0 130.0 5.625% 2005 Series B due 2035 100.0 100.0 6.350% 2006 Series A due 2036 250.0 250.0 5.750% 2007 Series B due 2037 150.0 150.0 6.375% 2007 Series D due 2037 100.0 100.0 5.650% 2008 Series A due 2018 — 300.0 5.500% 2009 Series A due 2019 250.0 250.0 2.500% 2013 Series A due 2023 400.0 400.0 4.300% 2014 Series A due 2044 475.0 475.0 4.150% 2015 Series A due 2045 350.0 350.0 3.200% 2017 Series A due 2027 300.0 300.0 4.000% 2018 Series A due 2048 500.0 — Total First Mortgage Bonds 3,144.8 2,944.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year (250.0 ) (300.0 ) Unamortized Premiums and Discounts, Net 10.2 11.5 Unamortized Debt Issuance Costs (21.5 ) (17.7 ) CL&P Long-Term Debt $ 3,004.0 $ 2,759.1 NSTAR Electric (Millions of Dollars) As of December 31, 2018 2017 Debentures: 5.750% due 2036 $ 200.0 $ 200.0 5.500% due 2040 300.0 300.0 2.375% due 2022 400.0 400.0 4.400% due 2044 300.0 300.0 3.250% due 2025 250.0 250.0 2.700% due 2026 250.0 250.0 3.200% due 2027 700.0 700.0 Total Debentures 2,400.0 2,400.0 Notes: 5.900% Senior Notes Series B due 2034 50.0 50.0 6.700% Senior Notes Series D due 2037 40.0 40.0 5.100% Senior Notes Series E due 2020 95.0 95.0 3.500% Senior Notes Series F due 2021 250.0 250.0 3.880% Senior Notes Series G due 2023 80.0 80.0 2.750% Senior Notes Series H due 2026 50.0 50.0 Total Notes 565.0 565.0 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net (2.5 ) (1.8 ) Unamortized Debt Issuance Costs (17.7 ) (19.4 ) NSTAR Electric Long-Term Debt $ 2,944.8 $ 2,943.8 PSNH (Millions of Dollars) As of December 31, 2018 2017 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 6.000% Series O due 2018 — 110.0 4.500% Series P due 2019 150.0 150.0 4.050% Series Q due 2021 122.0 122.0 3.200% Series R due 2021 160.0 160.0 3.500% Series S due 2023 325.0 325.0 Total First Mortgage Bonds 807.0 917.0 Pollution Control Revenue Bonds: Adjustable Rate Tax Exempt Series A due 2021 — 89.3 Less Amounts due Within One Year (150.0 ) (110.0 ) Unamortized Premiums and Discounts, Net — 0.2 Unamortized Debt Issuance Costs (1.8 ) (4.1 ) PSNH Long-Term Debt $ 655.2 $ 892.4 OTHER (Millions of Dollars) As of December 31, 2018 2017 Yankee Gas - First Mortgage Bonds: 3.020% - 8.480% due 2019 - 2048 $ 470.0 $ 520.0 NSTAR Gas - First Mortgage Bonds: 4.09% - 9.950% due 2020 - 2048 385.0 285.0 Eversource Parent and Other - Notes and Debentures: 4.500% Debentures due 2019 350.0 350.0 2.500% - 4.250% Senior Notes due 2021 - 2029 4,360.0 3,260.0 Unsecured Notes 3.570% - 6.430% due 2021 - 2037 289.5 290.9 Secured Debt 4.100% - 9.640% due 2021 - 2035 70.7 70.4 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 39.5 181.4 Fair Value Adjustment (1) 144.7 172.6 Less Fair Value Adjustment - Current Portion (1) (36.2 ) (35.4 ) Less Amounts due in One Year (401.1 ) (104.2 ) Commercial Paper Classified as Long-Term Debt — 201.2 Unamortized Premiums and Discounts, Net (4.2 ) 1.5 Unamortized Debt Issuance Costs (23.2 ) (12.8 ) Total Other Long-Term Debt $ 5,644.7 $ 5,180.6 Total Eversource Long-Term Debt $ 12,248.7 $ 11,775.9 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record the NSTAR long-term debt at fair value on the date of the 2012 merger and to record the Aquarion long-term debt at fair value on the date of the 2017 acquisition.
Schedule of Long-term Debt Instruments	The following table summarizes long-term debt issuances and repayments: (Millions of Dollars) Issue Date Issuances/(Repayments) Maturity Date Use of Proceeds for Issuances/ CL&P: 4.00% 2018 Series A First Mortgage Bonds March 2018 $ 500.0 April 2048 Repaid long-term debt that matured in 2018 and repaid short-term borrowings 5.65% 2008 Series A First Mortgage Bonds May 2008 (300.0 ) May 2018 Repaid at maturity on May 1, 2018 PSNH: 6.00% 2008 Series O First Mortgage Bonds May 2008 (110.0 ) May 2018 Repaid at maturity on May 1, 2018 2001 Series A Pollution Control Revenue Bonds December 2001 (89.3 ) May 2021 Redeemed on November 28, 2018 at a redemption price of $89.3 million Other: Eversource Parent 2.50% Series I Senior Notes (1) January 2018 200.0 March 2021 Repaid short-term borrowings Eversource Parent 3.30% Series M Senior Notes January 2018 450.0 January 2028 Repaid long-term debt that matured in 2018 Eversource Parent 3.80% Series N Senior Notes December 2018 400.0 December 2023 Repaid short-term borrowings Eversource Parent 4.25% Series O Senior Notes December 2018 500.0 April 2029 Repaid short-term borrowings Eversource Parent 1.60% Series G Senior Notes January 2015 (150.0 ) January 2018 Repaid at maturity on January 15, 2018 Eversource Parent 1.45% Series E Senior Notes May 2013 (300.0 ) May 2018 Repaid at maturity on May 1, 2018 Yankee Gas 4.13% Series O First Mortgage Bonds September 2018 50.0 October 2048 Repaid long-term debt that matured in 2018 Yankee Gas 6.90% Series J First Mortgage Bonds October 2008 (100.0 ) October 2018 Repaid at maturity on October 1, 2018 NSTAR Gas 4.09% Series P First Mortgage Bonds September 2018 100.0 October 2048 Repaid short-term borrowings (1) These notes are part of the same series issued by Eversource parent in March 2016. The aggregate outstanding principal amount of these notes is now $450 million .
Schedule of Maturities of Long-term Debt	Long-term debt maturities on debt outstanding for the years 2019 through 2023 and thereafter are shown below. These amounts exclude the CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2018 : (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 801.1 $ 250.0 $ — $ 150.0 2020 296.1 — 95.0 — 2021 1,033.5 — 250.0 282.0 2022 1,188.9 — 400.0 — 2023 1,665.2 400.0 80.0 325.0 Thereafter 7,977.7 2,615.3 2,140.0 50.0 Total $ 12,962.5 $ 3,265.3 $ 2,965.0 $ 807.0

RATE REDUCTION BONDS AND VARI_2

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES (Tables)	12 Months Ended
	Dec. 31, 2018
Rate Reduction Bonds and Variable Interest Entity [Abstract]
Schedule of Variable Interest Entities	The following tables summarize the impact of PSNH Funding on PSNH's balance sheet and income statement: (Millions of Dollars) Balance Sheet: As of December 31, 2018 Restricted Cash - Current Portion (included in Prepayments and Other Current Assets) $ 47.5 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 3.2 Securitized Stranded Cost (included in Regulatory Assets) 608.4 Other Regulatory Liabilities (included in Regulatory Liabilities) 5.8 Accrued Interest (included in Other Current Liabilities) 14.4 Rate Reduction Bonds - Current Portion 52.3 Rate Reduction Bonds - Long-Term Portion 583.3 (Millions of Dollars) Income Statement: For the Year Ended December 31, 2018 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 27.3 Interest Expense on RRB Principal (included in Interest Expense) 14.4

EMPLOYEE BENEFITS (Tables)

EMPLOYEE BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2018
Postemployment Benefits [Abstract]
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following table provides information on the Pension and SERP Plan benefit obligations, fair values of Pension Plan assets, and funded status: Pension and SERP As of December 31, 2018 As of December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) $ (5,242.3 ) $ (1,170.2 ) $ (1,217.3 ) $ (572.2 ) Service Cost (84.8 ) (21.4 ) (17.4 ) (11.2 ) (71.3 ) (18.5 ) (15.5 ) (9.7 ) Interest Cost (196.4 ) (41.8 ) (43.5 ) (22.0 ) (188.0 ) (41.6 ) (42.7 ) (21.2 ) Actuarial Gain/(Loss) 414.9 106.1 98.6 39.2 (548.7 ) (116.9 ) (143.5 ) (65.1 ) Benefits Paid - Pension 261.8 59.6 66.9 26.2 243.7 63.5 55.4 26.4 Benefits Paid - Lump Sum 14.2 — 7.1 — 18.4 — 6.8 — Benefits Paid - SERP 6.8 0.3 0.3 0.2 20.4 0.3 0.3 0.3 Employee Transfers — 12.0 2.5 (0.9 ) — 8.2 5.5 (0.7 ) Increase due to acquisition of Aquarion — — — — (168.7 ) — — — Benefit Obligation as of End of Year $ (5,520.0 ) $ (1,160.4 ) $ (1,236.5 ) $ (610.7 ) $ (5,936.5 ) $ (1,275.2 ) $ (1,351.0 ) $ (642.2 ) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of Beginning of Year $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 $ 4,076.0 $ 905.5 $ 1,088.3 $ 494.0 Employer Contributions 185.6 41.2 56.5 — 235.2 2.5 85.4 0.8 Actual Return on Pension Plan Assets (75.2 ) (14.2 ) (18.7 ) (7.6 ) 589.7 126.7 154.8 70.4 Benefits Paid - Pension (261.8 ) (59.6 ) (66.9 ) (26.2 ) (243.7 ) (63.5 ) (55.4 ) (26.4 ) Benefits Paid - Lump Sum (14.2 ) — (7.1 ) — (18.4 ) — (6.8 ) — Employee Transfers — (12.0 ) (2.5 ) 0.9 — (8.2 ) (5.5 ) 0.7 Increase due to acquisition of Aquarion — — — — 100.7 — — — Fair Value of Pension Plan Assets as of End of Year $ 4,573.9 $ 918.4 $ 1,222.1 $ 506.6 $ 4,739.5 $ 963.0 $ 1,260.8 $ 539.5 Funded Status as of December 31st $ (946.1 ) $ (242.0 ) $ (14.4 ) $ (104.1 ) $ (1,197.0 ) $ (312.2 ) $ (90.2 ) $ (102.7 ) The following table provides information on the PBOP Plan benefit obligations, fair values of plan assets, and funded status: PBOP As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) $ (810.0 ) $ (165.0 ) $ (270.0 ) $ (89.7 ) Service Cost (10.0 ) (1.9 ) (2.0 ) (1.1 ) (9.5 ) (1.9 ) (1.7 ) (1.3 ) Interest Cost (30.7 ) (5.8 ) (8.7 ) (3.4 ) (27.1 ) (5.3 ) (8.7 ) (3.0 ) Actuarial Gain/(Loss) 102.5 14.4 28.4 8.6 (81.8 ) (18.5 ) (13.2 ) (11.9 ) Benefits Paid 45.3 10.1 14.5 4.9 41.5 9.9 13.5 4.6 Employee Transfers — (0.1 ) 0.1 0.2 — 2.4 1.5 0.2 Increase due to acquisition of Aquarion — — — — (61.7 ) — — — Benefit Obligation as of End of Year $ (841.5 ) $ (161.7 ) $ (246.3 ) $ (91.9 ) $ (948.6 ) $ (178.4 ) $ (278.6 ) $ (101.1 ) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 922.2 $ 135.9 $ 405.5 $ 79.0 $ 815.8 $ 129.2 $ 361.6 $ 73.2 Actual Return on Plan Assets (36.6 ) (5.2 ) (17.4 ) (2.9 ) 118.0 18.1 52.9 10.4 Employer Contributions 9.3 — 5.2 — 7.6 — 5.3 — Benefits Paid (45.3 ) (10.1 ) (14.5 ) (4.9 ) (41.5 ) (9.9 ) (13.5 ) (4.6 ) Employee Transfers — — 0.3 — — (1.5 ) (0.8 ) — Increase due to acquisition of Aquarion — — — — 22.3 — — — Fair Value of Plan Assets as of End of Year $ 849.6 $ 120.6 $ 379.1 $ 71.2 $ 922.2 $ 135.9 $ 405.5 $ 79.0 Funded Status as of December 31st $ 8.1 $ (41.1 ) $ 132.8 $ (20.7 ) $ (26.4 ) $ (42.5 ) $ 126.9 $ (22.1 )
Schedule of Defined Benefit Plans Disclosures	The components of net periodic benefit expense for the PBOP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets on the balance sheets, are shown below. The service cost component of net periodic benefit expense and the intercompany allocations, less the capitalized portions, are included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit costs are included in Other Income, Net on the statements of income. PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include the intercompany allocations or the corresponding capitalized portion, as these amounts are cash settled on a short-term basis. PBOP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 10.0 $ 1.9 $ 2.0 $ 1.1 Interest Cost 30.7 5.8 8.7 3.4 Expected Return on Plan Assets (72.4 ) (10.4 ) (32.5 ) (6.0 ) Actuarial Loss 10.3 1.6 2.3 0.7 Prior Service (Credit)/Cost (23.6 ) 1.1 (16.9 ) 0.5 Total Net Periodic Benefit Income $ (45.0 ) $ — $ (36.4 ) $ (0.3 ) Intercompany Allocations N/A $ (1.0 ) $ (1.3 ) $ (0.4 ) PBOP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 9.5 $ 1.9 $ 1.7 $ 1.3 Interest Cost 27.1 5.3 8.7 3.0 Expected Return on Plan Assets (63.7 ) (9.7 ) (28.6 ) (5.5 ) Actuarial Loss 9.1 1.0 3.4 0.6 Prior Service (Credit)/Cost (21.6 ) 1.1 (17.0 ) 0.6 Total Net Periodic Benefit Income $ (39.6 ) $ (0.4 ) $ (31.8 ) $ — Intercompany Allocations N/A $ (0.7 ) $ (1.1 ) $ (0.5 ) PBOP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 12.2 $ 2.0 $ 3.4 $ 1.3 Interest Cost 32.9 5.3 13.3 2.9 Expected Return on Plan Assets (62.9 ) (10.1 ) (28.1 ) (5.5 ) Actuarial Loss 9.0 1.5 3.3 0.7 Prior Service (Credit)/Cost (9.1 ) 0.5 (7.1 ) 0.2 Total Net Periodic Benefit Income $ (17.9 ) $ (0.8 ) $ (15.2 ) $ (0.4 ) Intercompany Allocations N/A $ 0.3 $ (0.1 ) $ (0.1 ) As of December 31, 2018 and 2017 , the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 5,070.8 $ 1,031.0 $ 1,144.7 $ 543.1 2017 5,583.6 1,179.2 1,260.1 597.2 The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status:
Schedule of Assumptions Used	The following actuarial assumptions were used in calculating the Pension and SERP Plans' year end funded status: Pension and SERP As of December 31, 2018 2017 Discount Rate 4.22% — 4.45% 3.43% — 3.75% Compensation/Progression Rate 3.50% 3.50% The following actuarial assumptions were used to calculate Pension and SERP expense amounts: Pension and SERP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.85% — 4.62% 3.20% — 3.90% 3.27% — 4.89% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% Compensation/Progression Rate 3.50% 3.50% 3.50% The following actuarial assumptions were used to calculate PBOP expense amounts: PBOP For the Years Ended December 31, 2018 2017 2016 Discount Rate 3.28% — 3.94% 3.48% — 4.64% 2.88% — 4.09% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% The following actuarial assumptions were used in calculating the PBOP Plans' year end funded status: PBOP As of December 31, 2018 2017 Discount Rate 4.38% — 4.41% 3.55% — 3.70%
Schedule of Net Benefit Costs	Pension and SERP For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 84.8 $ 21.4 $ 17.4 $ 11.2 Interest Cost 196.4 41.8 43.5 22.0 Expected Return on Pension Plan Assets (391.6 ) (79.1 ) (104.9 ) (43.6 ) Actuarial Loss 145.7 29.1 41.1 11.6 Prior Service Cost 4.3 1.1 0.2 0.4 Total Net Periodic Benefit Expense/(Income) $ 39.6 $ 14.3 $ (2.7 ) $ 1.6 Intercompany Allocations N/A $ 6.1 $ 6.5 $ 1.9 Pension and SERP For the Year Ended December 31, 2017 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 71.3 $ 18.5 $ 15.5 $ 9.7 Interest Cost 188.0 41.6 42.7 21.2 Expected Return on Pension Plan Assets (334.1 ) (71.7 ) (87.6 ) (40.0 ) Actuarial Loss 135.2 27.7 41.1 11.6 Prior Service Cost 4.5 1.5 0.6 0.5 Total Net Periodic Benefit Expense $ 64.9 $ 17.6 $ 12.3 $ 3.0 Intercompany Allocations N/A $ 9.8 $ 9.1 $ 3.3 Pension and SERP For the Year Ended December 31, 2016 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Service Cost $ 75.0 $ 18.8 $ 16.3 $ 9.9 Interest Cost 185.5 41.6 42.2 20.7 Expected Return on Pension Plan Assets (317.9 ) (72.1 ) (85.1 ) (38.6 ) Actuarial Loss 125.7 25.4 39.9 9.9 Prior Service Cost 3.6 1.5 0.3 0.5 Total Net Periodic Benefit Expense $ 71.9 $ 15.2 $ 13.6 $ 2.4 Intercompany Allocations N/A $ 13.8 $ 11.4 $ 4.0
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and OCI as well as amounts recognized in Regulatory Assets and OCI that were reclassified as net periodic benefit (expense)/income during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses/(Gains) Arising During the Year $ 6.4 $ 44.8 $ (1.2 ) $ 2.6 Actuarial Losses Reclassified as Net Periodic Benefit Expense (9.9 ) (8.6 ) (0.4 ) (0.5 ) Actuarial Losses Securitized as Stranded Costs (1) (0.8 ) — — — Prior Service (Credit)/Cost Arising During the Year 1.3 (4.0 ) — (0.1 ) Prior Service Credit/(Cost) Reclassified as Net Periodic Benefit Income/(Expense) 23.6 22.3 — (0.7 ) Prior Service Cost Securitized as Stranded Costs (1) (1.3 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 207.3 $ 211.6 $ 9.9 $ 5.0 $ 6.6 $ 0.3 Prior Service (Credit)/Cost (197.6 ) (221.2 ) (23.6 ) 2.6 2.6 0.2 The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income ("OCI") as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented: Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2018 2017 2018 2017 Actuarial Losses Arising During the Year $ 48.6 $ 333.0 $ 0.7 $ 9.3 Actuarial Losses Reclassified as Net Periodic Benefit Expense (140.1 ) (129.5 ) (5.6 ) (5.7 ) Actuarial Losses Securitized as Stranded Costs (1) (36.7 ) — — — Prior Service Cost/(Credit) Arising During the Year — 1.0 — (0.4 ) Prior Service Cost Reclassified as Net Periodic Benefit Expense (3.9 ) (4.1 ) (0.4 ) (0.4 ) Prior Service Cost Securitized as Stranded Costs (1) (0.1 ) — — — (1) These amounts were reclassified to securitized regulatory assets in connection with the divestiture of PSNH's generation business. For further information see Note 2, "Regulatory Accounting" to the financial statements. The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2018 and 2017 , as well as the amounts that are expected to be recognized as components in 2019 : Regulatory Assets as of December 31, Expected 2019 Expense AOCI as of December 31, Expected 2019 Expense (Millions of Dollars) 2018 2017 2018 2017 Actuarial Loss $ 1,807.6 $ 1,935.8 $ 140.6 $ 80.8 $ 85.7 $ 5.6 Prior Service Cost 6.3 10.3 0.9 1.1 1.5 0.2
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans: (Millions of Dollars) 2019 2020 2021 2022 2023 2024 - 2028 Pension and SERP $ 308.5 $ 310.4 $ 318.8 $ 326.6 $ 335.6 $ 1,764.1 PBOP 58.4 58.5 58.6 58.3 57.8 277.4
Schedule of Allocation of Plan Assets	Management has assumed a 7 percent long-term rate of return for the Aquarion Plans. These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows: As of December 31, 2018 2017 Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Eversource Pension Plan and Tax-Exempt Assets Within PBOP Plan Target Asset Allocation Assumed Rate of Return Target Asset Allocation Assumed Rate of Return Equity Securities: United States 15.0 % 8.5 % 21.5 % 8.5 % Global 10.0 % 8.75 % — % — % Non-United States 8.0 % 8.5 % 11.0 % 8.5 % Emerging Markets 4.0 % 10.0 % 4.5 % 10.0 % Debt Securities: Fixed Income 13.0 % 4.0 % 11.0 % 4.0 % Public High Yield Fixed Income 4.0 % 6.5 % 4.0 % 6.5 % Private Debt 15.0 % 9.0 % 15.0 % 9.0 % Emerging Markets Debt — % — % 2.0 % 6.5 % Private Equity 15.0 % 12.0 % 15.0 % 12.0 % Real Assets 16.0 % 7.5 % 12.0 % 7.5 % Hedge Funds — % — % 4.0 % 6.0 % The following table presents, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Pension Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 443.4 $ — $ 1,377.8 $ 1,821.2 $ 535.4 $ — $ 1,653.3 $ 2,188.7 Fixed Income (2) 85.5 160.8 1,265.5 1,511.8 56.6 215.9 1,218.3 1,490.8 Private Equity 6.1 — 834.0 840.1 11.2 — 641.8 653.0 Real Assets (3) 62.9 — 569.1 632.0 101.6 — 539.9 641.5 Total $ 597.9 $ 160.8 $ 4,046.4 $ 4,805.1 $ 704.8 $ 215.9 $ 4,053.3 $ 4,974.0 Less: 401(h) PBOP Assets (4) (231.2 ) (234.5 ) Total Pension Assets $ 4,573.9 $ 4,739.5 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2018 2017 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 91.9 $ — $ 210.5 $ 302.4 $ 115.3 $ — $ 241.9 $ 357.2 Fixed Income (2) 22.0 40.3 123.0 185.3 23.4 44.0 133.9 201.3 Private Equity — — 32.7 32.7 — — 31.3 31.3 Real Assets (3) 27.5 — 70.5 98.0 22.4 — 75.5 97.9 Total $ 141.4 $ 40.3 $ 436.7 $ 618.4 $ 161.1 $ 44.0 $ 482.6 $ 687.7 Add: 401(h) PBOP Assets (4) 231.2 234.5 Total PBOP Assets $ 849.6 $ 922.2 (1) United States, Global, Non-United States and Emerging Markets equity securities that are uncategorized include investments in commingled funds and hedge funds that are overlayed with equity index swaps and futures contracts. (2) Fixed Income investments that are uncategorized include investments in commingled funds, fixed income funds that invest in a variety of opportunistic and fixed income strategies, and hedge funds that are overlayed with fixed income futures. (3) Real assets include real estate funds and hedge funds. (4) The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plan.
Schedule of Defined Contribution Plans	The total Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 38.4 $ 5.0 $ 9.7 $ 3.3 2017 34.5 4.6 8.5 3.7 2016 31.8 4.5 8.1 3.4
Schedule of Other Retirement Benefits	The actuarially-determined liability for these benefits, which is included in Other Long-Term Liabilities on the balance sheets, as well as the related expense included in Operations and Maintenance Expense on the income statements, are as follows: Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2018 2017 2016 Actuarially-Determined Liability $ 49.1 $ 53.4 $ 54.2 Other Retirement Benefits Expense 2.7 2.8 2.9 As of and For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Actuarially-Determined Liability $ 0.3 $ 0.1 $ 1.7 $ 0.3 $ 0.1 $ 1.9 $ 0.3 $ 0.1 $ 2.0 Other Retirement Benefits Expense 1.1 1.1 0.4 1.0 1.0 0.5 1.1 0.9 0.6

SHARE-BASED PAYMENTS (Tables)

SHARE-BASED PAYMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Disclosure of Share-based Compensation Arrangements by Share-based Payment	The total compensation expense and associated future income tax benefits recognized by Eversource, CL&P, NSTAR Electric and PSNH for share-based compensation awards were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Compensation Expense $ 21.4 $ 19.7 $ 23.6 Future Income Tax Benefit 5.4 8.0 9.6 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Compensation Expense $ 7.8 $ 7.7 $ 2.9 $ 7.0 $ 7.0 $ 3.2 $ 9.1 $ 8.2 $ 3.5 Future Income Tax Benefit 2.0 1.9 0.7 2.9 2.8 1.3 3.7 3.3 1.4
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Share Transactions	A summary of RSU transactions is as follows: RSUs (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 717,039 $ 49.29 Granted 286,315 $ 56.69 Shares Issued (201,386 ) $ 55.35 Forfeited (19,603 ) $ 56.78 Outstanding as of December 31, 2018 782,365 $ 50.25
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Summary of Share Transactions	A summary of performance share transactions is as follows: Performance Shares (Units) Weighted Average Grant-Date Fair Value Outstanding as of December 31, 2017 510,565 $ 55.45 Granted 184,355 $ 56.77 Shares Issued (178,258 ) $ 54.98 Forfeited (17,098 ) $ 56.18 Outstanding as of December 31, 2018 499,564 $ 56.08

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	The components of income tax expense are as follows: Eversource (Millions of Dollars) For the Years Ended December 31, 2018 2017 2016 Current Income Taxes: Federal $ 106.5 $ 58.9 $ 38.9 State 10.6 31.6 53.0 Total Current 117.1 90.5 91.9 Deferred Income Taxes, Net: Federal 122.6 433.0 427.9 State 52.2 58.6 38.6 Total Deferred 174.8 491.6 466.5 Investment Tax Credits, Net (2.9 ) (3.2 ) (3.4 ) Income Tax Expense $ 289.0 $ 578.9 $ 555.0 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Current Income Taxes: Federal $ 54.2 $ 79.3 $ 12.2 $ 50.9 $ 107.8 $ 18.6 $ 27.3 $ 86.4 $ (13.7 ) State 20.9 30.0 (0.5 ) 17.4 25.6 6.2 13.3 39.5 8.8 Total Current 75.1 109.3 11.7 68.3 133.4 24.8 40.6 125.9 (4.9 ) Deferred Income Taxes, Net: Federal 48.5 27.9 15.4 123.9 88.1 52.7 157.6 96.6 79.5 State 6.4 13.5 20.5 (4.6 ) 22.4 11.2 11.3 5.1 7.8 Total Deferred 54.9 41.4 35.9 119.3 110.5 63.9 168.9 101.7 87.3 Investment Tax Credits, Net (0.9 ) (1.8 ) — (1.0 ) (1.8 ) — (1.2 ) (1.8 ) — Income Tax Expense $ 129.1 $ 148.9 $ 47.6 $ 186.6 $ 242.1 $ 88.7 $ 208.3 $ 225.8 $ 82.4
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation between income tax expense and the expected tax expense at the statutory rate is as follows: Eversource (Millions of Dollars, except percentages) For the Years Ended December 31, 2018 2017 2016 Income Before Income Tax Expense $ 1,329.5 $ 1,574.4 $ 1,504.8 Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016 279.2 551.0 526.7 Tax Effect of Differences: Depreciation (30.8 ) (10.8 ) (3.4 ) Investment Tax Credit Amortization (2.9 ) (3.2 ) (3.4 ) Other Federal Tax Credits — — (3.5 ) State Income Taxes, Net of Federal Impact 44.4 47.7 56.2 Dividends on ESOP (5.1 ) (8.4 ) (8.4 ) Tax Asset Valuation Allowance/Reserve Adjustments 5.2 7.0 3.3 Excess Stock Benefit (1.5 ) (2.9 ) (19.1 ) Other, Net 0.5 (1.5 ) 6.6 Income Tax Expense $ 289.0 $ 578.9 $ 555.0 Effective Tax Rate 21.7 % 36.8 % 36.9 % For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars, except percentages) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Income Before Income Tax Expense $ 506.8 $ 532.0 $ 163.5 $ 563.4 $ 616.8 $ 224.7 $ 542.6 $ 576.6 $ 214.3 Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016 106.4 111.7 34.3 197.2 215.9 78.6 189.9 201.8 75.0 Tax Effect of Differences: Depreciation (1.2 ) (2.8 ) 0.1 (5.2 ) (3.0 ) 1.1 1.6 (3.1 ) 1.0 Investment Tax Credit Amortization (0.9 ) (1.8 ) — (1.0 ) (1.8 ) — (1.2 ) (1.8 ) — Other Federal Tax Credits — — — — — — — — (3.5 ) State Income Taxes, Net of Federal Impact 14.5 33.2 15.8 4.5 31.2 11.3 14.5 29.0 10.8 Tax Asset Valuation Allowance/Reserve Adjustments 7.1 1.2 — (9.5 ) — — 1.5 — — Excess Stock Benefit (0.1 ) (0.1 ) (0.1 ) (0.7 ) (0.7 ) (0.3 ) (0.9 ) (1.2 ) (0.4 ) Other, Net 3.3 7.5 (2.5 ) 1.3 0.5 (2.0 ) 2.9 1.1 (0.5 ) Income Tax Expense $ 129.1 $ 148.9 $ 47.6 $ 186.6 $ 242.1 $ 88.7 $ 208.3 $ 225.8 $ 82.4 Effective Tax Rate 25.5 % 28.0 % 29.1 % 33.1 % 39.2 % 39.5 % 38.4 % 39.2 % 38.4 %
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Deferred Tax Assets: Employee Benefits $ 388.2 $ 94.5 $ 35.0 $ 31.1 $ 442.1 $ 112.3 $ 34.0 $ 38.0 Derivative Liabilities 111.4 111.4 — — 111.8 110.5 0.3 — Regulatory Deferrals - Liabilities 299.3 38.6 195.5 16.1 205.6 12.0 139.8 17.9 Allowance for Uncollectible Accounts 54.0 23.1 17.8 3.0 50.1 20.6 17.3 2.9 Tax Effect - Tax Regulatory Liabilities 830.3 336.8 288.9 111.7 832.6 337.2 281.2 116.8 Net Operating Loss Carryforwards 28.5 — — 0.6 47.8 — — — Purchase Accounting Adjustment 64.2 — — — 69.9 — — — Other 166.2 81.1 15.6 33.4 149.5 70.7 4.9 49.6 Total Deferred Tax Assets 1,942.1 685.5 552.8 195.9 1,909.4 663.3 477.5 225.2 Less: Valuation Allowance 19.5 10.7 — — 14.6 6.3 — — Net Deferred Tax Assets $ 1,922.6 $ 674.8 $ 552.8 $ 195.9 $ 1,894.8 $ 657.0 $ 477.5 $ 225.2 Deferred Tax Liabilities: Accelerated Depreciation and Other Plant-Related Differences $ 3,724.2 $ 1,293.3 $ 1,342.4 $ 410.6 $ 3,562.0 $ 1,224.9 $ 1,229.2 $ 502.5 Property Tax Accruals 73.2 35.4 26.3 5.2 56.7 20.7 24.2 5.5 Regulatory Amounts: Regulatory Deferrals - Assets 1,025.9 320.1 277.4 213.8 924.9 310.6 267.1 103.6 Tax Effect - Tax Regulatory Assets 238.9 167.0 9.7 8.1 243.1 173.1 9.8 11.4 Goodwill Regulatory Asset - 1999 Merger 95.2 — 81.7 — 99.8 — 85.7 — Derivative Assets 20.1 19.9 — — 17.4 17.4 — — Other 251.1 5.9 109.8 39.4 288.4 13.7 137.3 45.7 Total Deferred Tax Liabilities $ 5,428.6 $ 1,841.6 $ 1,847.3 $ 677.1 $ 5,192.3 $ 1,760.4 $ 1,753.3 $ 668.7
Summary of Operating Loss Carryforwards	The following tables provide the amounts and expiration dates of state tax credit and loss carryforwards and federal tax credit and net operating loss carryforwards: As of December 31, 2018 2017 (Millions of Dollars) Eversource CL&P NSTAR PSNH Expiration Range Eversource CL&P NSTAR PSNH Expiration Range Federal Net $ 103.6 $ — $ — $ — 2033 - 2037 $ 197.3 $ — $ — $ — 2027 - 2037 Federal Charitable 2.2 — — — 2020 - 2022 18.7 — — — 2017 - 2022 State Net Operating Loss 80.7 — — — 2019 - 2038 82.8 — — — 2028 - 2037 State Tax Credit 148.9 107.0 — — 2018 - 2023 139.0 94.5 — — 2017 - 2022 State Charitable 9.6 — — — 2019 - 2023 31.4 — — — 2017 - 2022
Summary of Income Tax Contingencies	The amount of interest expense/(income) on uncertain tax positions recognized and the related accrued interest payable/(receivable) are as follows: Other Interest Expense/(Income) Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2018 2017 2016 2018 2017 Eversource $ (1.7 ) $ — $ (0.2 ) $ 0.1 $ 1.8 A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2016 $ 48.0 $ 13.5 Gross Increases - Current Year 9.9 3.9 Gross Increases - Prior Year 0.2 0.2 Lapse of Statute of Limitations (9.7 ) (2.3 ) Balance as of December 31, 2016 48.4 15.3 Gross Increases - Current Year 11.4 4.7 Gross Decreases - Prior Year (0.9 ) (0.5 ) Lapse of Statute of Limitations (7.2 ) (1.4 ) Balance as of December 31, 2017 51.7 18.1 Gross Increases - Current Year 9.2 3.2 Gross Decreases - Prior Year (6.5 ) (0.9 ) Lapse of Statute of Limitations (8.5 ) (2.2 ) Balance as of December 31, 2018 $ 45.9 $ 18.2
Summary of Income Tax Examinations	The following table summarizes Eversource, CL&P, NSTAR Electric and PSNH's tax years that remain subject to examination by major tax jurisdictions as of December 31, 2018 : Description Tax Years Federal 2018 Connecticut 2015 - 2018 Massachusetts 2015 - 2018 New Hampshire 2016 - 2018

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Environmental Loss Contingencies by Site	A reconciliation of the activity in the environmental reserves is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Balance as of January 1, 2017 $ 65.8 $ 4.9 $ 3.8 $ 5.3 Additions 6.2 0.5 1.8 1.0 Payments/Reductions (17.1 ) (0.7 ) (2.9 ) (0.6 ) Balance as of December 31, 2017 54.9 4.7 2.7 5.7 Additions 23.5 1.9 9.7 — Payments/Reductions (13.7 ) (1.2 ) (1.5 ) (0.3 ) Balance as of December 31, 2018 $ 64.7 $ 5.4 $ 10.9 $ 5.4 The number of environmental sites for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: Eversource CL&P NSTAR Electric PSNH 2018 60 15 16 9 2017 59 14 15 10
Long-term Purchase Commitment	The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2018 2017 2016 Purchased Power and Capacity $ 72.0 $ 103.9 $ 152.5 Renewable Energy 218.5 235.5 210.9 Peaker CfDs 20.9 38.7 47.7 Natural Gas Procurement 432.4 377.0 323.9 Transmission Support Commitments 23.4 19.8 15.9 Coal, Wood and Other (1) — 47.7 55.7 For the Years Ended December 31, 2018 2017 2016 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Purchased Power and Capacity $ 49.4 $ 4.4 $ 18.2 $ 81.0 $ 4.0 $ 18.9 $ 132.7 $ 0.7 $ 19.1 Renewable Energy 63.2 89.8 65.5 51.0 123.7 60.8 42.1 101.1 67.7 Peaker CfDs 20.9 — — 38.7 — — 47.7 — — Transmission Support Commitments 9.2 9.2 5.0 7.8 7.8 4.2 6.3 6.2 3.4 Coal, Wood and Other (1) — — — — — 47.7 — — 55.7 (1) PSNH previously entered into various arrangements for the purchase of coal, wood and the transportation services for fuel supply for its electric generating assets. On January 10, 2018, Eversource and PSNH completed the sale of PSNH's thermal generation assets. On August 26, 2018, Eversource and PSNH completed the sale of PSNH's hydroelectric generation assets. Upon sale, the remaining future contractual obligations were transferred to the respective buyers. See Note 13, "Generation Asset Sale," for further information. The estimated future annual costs of significant executed, non-cancelable, long-term contractual arrangements in effect as of December 31, 2018 are as follows: Eversource (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 68.3 $ 73.5 $ 69.1 $ 72.9 $ 74.1 $ 142.9 $ 500.8 Renewable Energy 262.4 261.0 238.9 240.5 217.2 1,662.0 2,882.0 Peaker CfDs 11.9 22.6 21.9 15.3 17.5 43.5 132.7 Natural Gas Procurement 243.8 227.7 183.6 149.2 135.1 1,039.7 1,979.1 Transmission Support Commitments 22.8 23.1 15.2 16.2 17.8 17.8 112.9 Total $ 609.2 $ 607.9 $ 528.7 $ 494.1 $ 461.7 $ 2,905.9 $ 5,607.5 CL&P (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 57.0 $ 69.7 $ 65.3 $ 69.1 $ 70.4 $ 123.9 $ 455.4 Renewable Energy 102.0 103.8 104.0 104.9 105.5 785.3 1,305.5 Peaker CfDs 11.9 22.6 21.9 15.3 17.5 43.5 132.7 Transmission Support Commitments 9.0 9.1 6.0 6.4 7.0 7.0 44.5 Total $ 179.9 $ 205.2 $ 197.2 $ 195.7 $ 200.4 $ 959.7 $ 1,938.1 NSTAR Electric (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 5.5 $ 3.1 $ 3.1 $ 3.1 $ 3.0 $ 19.0 $ 36.8 Renewable Energy 94.7 93.1 88.6 88.8 63.9 435.1 864.2 Transmission Support Commitments 9.0 9.1 6.0 6.3 7.0 7.0 44.4 Total $ 109.2 $ 105.3 $ 97.7 $ 98.2 $ 73.9 $ 461.1 $ 945.4 PSNH (Millions of Dollars) 2019 2020 2021 2022 2023 Thereafter Total Purchased Power and Capacity $ 5.8 $ 0.7 $ 0.7 $ 0.7 $ 0.7 $ — $ 8.6 Renewable Energy 65.7 64.1 46.3 46.8 47.8 441.6 712.3 Transmission Support Commitments 4.8 4.9 3.2 3.5 3.8 3.8 24.0 Total $ 76.3 $ 69.7 $ 50.2 $ 51.0 $ 52.3 $ 445.4 $ 744.9
Schedule of Guarantor Obligations	The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries to external parties, as of December 31, 2018 : Company Description Maximum Exposure (in millions) Expiration Dates On behalf of subsidiaries: Eversource Gas Transmission LLC Access Northeast Project Capital Contributions Guaranty (1) $ 184.9 2021 Various Surety Bonds (2) 41.9 2019 - 2021 Rocky River Realty Company and Eversource Service Lease Payments for Real Estate 6.3 2019 - 2024 Bay State Wind LLC Real Estate Purchase 2.5 2019 (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 authorized capital contributions for its investment in the Access Northeast project. The guaranty decreases as authorized 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.

GENERATION ASSET SALE (Tables)

GENERATION ASSET SALE (Tables)	12 Months Ended
	Dec. 31, 2018
Regulated Operations [Abstract]
Schedule of Generation Assets and Liabilities	As of December 31, 2018 , all generation assets had been sold and as a result, no generation assets were classified as held for sale. As of December 31, 2017, PSNH's generation assets held for sale, which were included in current assets on the Eversource and PSNH balance sheets, and were part of the Electric Distribution reportable segment, were as follows: (Millions of Dollars) As of December 31, 2017 Thermal Gross Plant $ 1,091.4 Hydroelectric Gross Plant 83.0 Accumulated Depreciation (575.4 ) Net Plant 599.0 Fuel and Inventory 87.7 Materials and Supplies 27.3 Emission Allowances 19.1 Other Assets 2.6 Deferred Costs from Thermal Generation Asset Sale (516.1 ) Total Generation Assets Held for Sale $ 219.6

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2018
Leases [Abstract]
Schedule of Rent Expense	Operating lease rental payments charged to expense are as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 10.8 $ 10.9 $ 11.8 $ 2.5 2017 10.5 11.7 11.3 3.3 2016 12.1 12.5 11.4 2.9
Schedule of Future Minimum Rental Payments for Operating Leases	Future minimum rental payments, excluding executory costs, such as property taxes, state use taxes, insurance, and maintenance, under long-term non-cancelable leases, as of December 31, 2018 are as follows: Operating Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 11.5 $ 1.5 $ 7.2 $ 0.5 2020 9.8 1.4 6.0 0.4 2021 8.7 1.2 5.3 0.4 2022 7.2 1.1 4.4 0.4 2023 4.7 0.5 3.1 0.2 Thereafter 32.7 0.2 29.5 0.3 Future minimum lease payments $ 74.6 $ 5.9 $ 55.5 $ 2.2
Schedule of Future Minimum Lease Payments for Capital Leases	Capital Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2019 $ 3.4 $ 2.0 $ 0.5 $ 0.1 2020 3.4 2.0 0.5 0.1 2021 2.9 1.5 0.5 0.1 2022 1.5 — 0.6 0.1 2023 0.7 — 0.6 0.1 Thereafter 13.9 — 13.4 0.5 Future minimum lease payments 25.8 5.5 16.1 1.0 Less amount to arrive at present value 13.8 1.0 12.4 0.1 Present value of future minimum lease payments $ 12.0 $ 4.5 $ 3.7 $ 0.9

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping	The fair values provided in the table below are classified as Level 2 within the fair value hierarchy. Carrying amounts and estimated fair values are as follows: Eversource CL&P NSTAR Electric PSNH (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value Carrying Amount Fair Value As of December 31, 2018: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 156.8 $ 116.2 $ 113.8 $ 43.0 $ 43.0 $ — $ — Long-Term Debt 13,086.1 13,154.9 3,254.0 3,429.2 2,944.8 3,024.1 805.2 819.5 Rate Reduction Bonds 635.7 645.8 — — — — 635.7 645.8 As of December 31, 2017: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 160.8 $ 116.2 $ 116.5 $ 43.0 $ 44.3 $ — $ — Long-Term Debt 12,325.5 12,877.1 3,059.1 3,430.5 2,943.8 3,156.5 1,002.4 1,038.2

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes in accumulated other comprehensive income/(loss) by component, net of tax, are as follows: For the Year Ended December 31, 2018 For the Year Ended December 31, 2017 Eversource (Millions of Dollars) Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Qualified Cash Flow Hedging Instruments Unrealized Defined Benefit Plans Total Balance as of January 1st $ (6.2 ) $ — $ (60.2 ) $ (66.4 ) $ (8.2 ) $ 0.4 $ (57.5 ) $ (65.3 ) OCI Before Reclassifications — (0.5 ) 0.3 (0.2 ) — (0.4 ) (7.2 ) (7.6 ) Amounts Reclassified from AOCI 1.8 — 4.8 6.6 2.0 — 4.5 6.5 Net OCI 1.8 (0.5 ) 5.1 6.4 2.0 (0.4 ) (2.7 ) (1.1 ) Balance as of December 31st $ (4.4 ) $ (0.5 ) $ (55.1 ) $ (60.0 ) $ (6.2 ) $ — $ (60.2 ) $ (66.4 )
Schedule of Comprehensive Income (Loss)	The following table sets forth the amounts reclassified from AOCI by component and the impacted line item on the statements of income: Amounts Reclassified from AOCI Eversource (Millions of Dollars) For the Years Ended December 31, Statements of Income Line Item Impacted 2018 2017 2016 Qualified Cash Flow Hedging Instruments $ (2.8 ) $ (3.3 ) $ (3.5 ) Interest Expense Tax Effect 1.0 1.3 1.4 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (1.8 ) $ (2.0 ) $ (2.1 ) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (6.0 ) $ (6.2 ) $ (5.6 ) Other Income, Net (1) Amortization of Prior Service Cost (0.4 ) (1.1 ) (0.8 ) Other Income, Net (1) Total Defined Benefit Plan Costs (6.4 ) (7.3 ) (6.4 ) Tax Effect 1.6 2.8 2.5 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (4.8 ) $ (4.5 ) $ (3.9 ) Total Amounts Reclassified from AOCI, Net of Tax $ (6.6 ) $ (6.5 ) $ (6.0 ) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 1N, "Summary of Significant Accounting Policies – Other Income, Net" and Note 10A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," for further information.

COMMON SHARES (Tables)

COMMON SHARES (Tables)	12 Months Ended
	Dec. 31, 2018
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 and PSNH that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2018 and 2017 Issued as of December 31, 2018 2017 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 $ 1 100,000,000 200 200 PSNH $ 1 100,000,000 301 301 Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Per Share Shares Outstanding as of December 31, As of December 31, Series 2018 2017 2018 2017 CL&P $1.90 Series of 1947 $ 52.50 163,912 163,912 $ 8.2 $ 8.2 $2.00 Series of 1947 $ 54.00 336,088 336,088 16.8 16.8 $2.04 Series of 1949 $ 52.00 100,000 100,000 5.0 5.0 $2.20 Series of 1949 $ 52.50 200,000 200,000 10.0 10.0 3.90% Series of 1949 $ 50.50 160,000 160,000 8.0 8.0 $2.06 Series E of 1954 $ 51.00 200,000 200,000 10.0 10.0 $2.09 Series F of 1955 $ 51.00 100,000 100,000 5.0 5.0 4.50% Series of 1956 $ 50.75 104,000 104,000 5.2 5.2 4.96% Series of 1958 $ 50.50 100,000 100,000 5.0 5.0 4.50% Series of 1963 $ 50.50 160,000 160,000 8.0 8.0 5.28% Series of 1967 $ 51.43 200,000 200,000 10.0 10.0 $3.24 Series G of 1968 $ 51.84 300,000 300,000 15.0 15.0 6.56% Series of 1968 $ 51.44 200,000 200,000 10.0 10.0 Total CL&P 2,324,000 2,324,000 $ 116.2 $ 116.2 NSTAR Electric 4.25% Series of 1956 $ 103.625 180,000 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 102.80 250,000 250,000 25.0 25.0 Total NSTAR Electric 430,000 430,000 $ 43.0 $ 43.0 Fair Value Adjustment due to Merger with NSTAR (3.6 ) (3.6 ) Other 6.00% Series of 1958 $ 100.00 23 23 $ — $ — Total Eversource - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

PREFERRED STOCK NOT SUBJECT T_2

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Preferred Stock	The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric and PSNH that were authorized and issued, as well as the respective per share par values: Shares Par Value Authorized as of December 31, 2018 and 2017 Issued as of December 31, 2018 2017 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 $ 1 100,000,000 200 200 PSNH $ 1 100,000,000 301 301 Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Per Share Shares Outstanding as of December 31, As of December 31, Series 2018 2017 2018 2017 CL&P $1.90 Series of 1947 $ 52.50 163,912 163,912 $ 8.2 $ 8.2 $2.00 Series of 1947 $ 54.00 336,088 336,088 16.8 16.8 $2.04 Series of 1949 $ 52.00 100,000 100,000 5.0 5.0 $2.20 Series of 1949 $ 52.50 200,000 200,000 10.0 10.0 3.90% Series of 1949 $ 50.50 160,000 160,000 8.0 8.0 $2.06 Series E of 1954 $ 51.00 200,000 200,000 10.0 10.0 $2.09 Series F of 1955 $ 51.00 100,000 100,000 5.0 5.0 4.50% Series of 1956 $ 50.75 104,000 104,000 5.2 5.2 4.96% Series of 1958 $ 50.50 100,000 100,000 5.0 5.0 4.50% Series of 1963 $ 50.50 160,000 160,000 8.0 8.0 5.28% Series of 1967 $ 51.43 200,000 200,000 10.0 10.0 $3.24 Series G of 1968 $ 51.84 300,000 300,000 15.0 15.0 6.56% Series of 1968 $ 51.44 200,000 200,000 10.0 10.0 Total CL&P 2,324,000 2,324,000 $ 116.2 $ 116.2 NSTAR Electric 4.25% Series of 1956 $ 103.625 180,000 180,000 $ 18.0 $ 18.0 4.78% Series of 1958 $ 102.80 250,000 250,000 25.0 25.0 Total NSTAR Electric 430,000 430,000 $ 43.0 $ 43.0 Fair Value Adjustment due to Merger with NSTAR (3.6 ) (3.6 ) Other 6.00% Series of 1958 $ 100.00 23 23 $ — $ — Total Eversource - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Years Ended December 31, 2018 2017 2016 Net Income Attributable to Common Shareholders $ 1,033.0 $ 988.0 $ 942.3 Weighted Average Common Shares Outstanding: Basic 317,370,369 317,411,097 317,650,180 Dilutive Effect 623,565 620,483 804,059 Diluted 317,993,934 318,031,580 318,454,239 Basic EPS $ 3.25 $ 3.11 $ 2.97 Diluted EPS $ 3.25 $ 3.11 $ 2.96

REVENUES (Tables)

REVENUES (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following table presents operating revenues disaggregated by revenue source: For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Revenue from Contracts with Customers Retail Tariff Sales Residential $ 3,766.6 $ 542.5 $ — $ 130.7 $ — $ — $ 4,439.8 Commercial 2,634.7 334.8 — 63.3 — (4.5 ) 3,028.3 Industrial 351.9 96.0 — 4.4 — (10.0 ) 442.3 Total Retail Tariff Sales Revenue 6,753.2 973.3 — 198.4 — (14.5 ) 7,910.4 Wholesale Transmission Revenue — — 1,308.9 — 47.3 (1,092.2 ) 264.0 Wholesale Market Sales Revenue 179.5 57.5 — 4.1 — — 241.1 Other Revenue from Contracts with Customers 65.9 (2.2 ) 12.6 7.2 889.0 (891.0 ) 81.5 Reserve for Revenue Subject to Refund (12.3 ) (8.3 ) — (3.7 ) — — (24.3 ) Total Revenue from Contracts with Customers 6,986.3 1,020.3 1,321.5 206.0 936.3 (1,997.7 ) 8,472.7 Alternative Revenue Programs (47.0 ) (1.2 ) (35.2 ) 5.4 — 31.9 (46.1 ) Other Revenue 17.9 3.1 — 0.6 — — 21.6 Total Operating Revenues $ 6,957.2 $ 1,022.2 $ 1,286.3 $ 212.0 $ 936.3 $ (1,965.8 ) $ 8,448.2 For the Year Ended December 31, 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH Revenue from Contracts with Customers Retail Tariff Sales Residential $ 1,828.2 $ 1,380.9 $ 557.5 Commercial 928.1 1,391.5 316.9 Industrial 147.7 124.9 79.3 Total Retail Tariff Sales Revenue 2,904.0 2,897.3 953.7 Wholesale Transmission Revenue 620.6 488.8 199.5 Wholesale Market Sales Revenue 48.3 76.1 56.6 Other Revenue from Contracts with Customers 35.0 28.9 15.5 Reserve for Revenue Subject to Refund — — (12.3 ) Total Revenue from Contracts with Customers 3,607.9 3,491.1 1,213.0 Alternative Revenue Programs (65.9 ) 0.9 (17.3 ) Other Revenue 8.5 8.3 1.1 Eliminations (454.3 ) (387.4 ) (149.2 ) Total Operating Revenues $ 3,096.2 $ 3,112.9 $ 1,047.6

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Eversource's segment information is as follows: For the Year Ended December 31, 2018 (1) Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 6,957.2 $ 1,022.2 $ 1,286.3 $ 212.0 $ 936.3 $ (1,965.8 ) $ 8,448.2 Depreciation and Amortization (671.8 ) (75.0 ) (231.8 ) (46.5 ) (49.1 ) 2.2 (1,072.0 ) Other Operating Expenses (5,548.6 ) (787.6 ) (375.5 ) (99.8 ) (831.5 ) 1,966.7 (5,676.3 ) Operating Income 736.8 159.6 679.0 65.7 55.7 3.1 1,699.9 Interest Expense (202.8 ) (44.1 ) (120.6 ) (34.3 ) (129.3 ) 32.3 (498.8 ) Interest Income 18.7 — 2.4 — 30.3 (33.3 ) 18.1 Other Income/(Loss), Net 67.5 7.1 31.1 (0.4 ) 1,185.3 (1,180.3 ) 110.3 Income Tax (Expense)/Benefit (160.2 ) (29.4 ) (161.8 ) (0.1 ) 62.5 — (289.0 ) Net Income 460.0 93.2 430.1 30.9 1,204.5 (1,178.2 ) 1,040.5 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income Attributable to Common Shareholders $ 455.4 $ 93.2 $ 427.2 $ 30.9 $ 1,204.5 $ (1,178.2 ) $ 1,033.0 Total Assets (as of) $ 21,389.1 $ 3,904.9 $ 10,285.0 $ 2,253.0 $ 17,874.2 $ (17,464.9 ) $ 38,241.3 Cash Flows Used for Investments in Plant $ 961.3 $ 351.5 $ 929.7 $ 102.3 $ 178.6 $ — $ 2,523.4 For the Year Ended December 31, 2017 (2) Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution (3) Other Eliminations Total Operating Revenues $ 5,542.9 $ 947.3 $ 1,301.7 $ 15.9 $ 931.0 $ (986.8 ) $ 7,752.0 Depreciation and Amortization (542.6 ) (72.9 ) (209.4 ) (3.7 ) (37.4 ) 2.2 (863.8 ) Other Operating Expenses (4,072.6 ) (716.4 ) (382.8 ) (8.3 ) (806.6 ) 986.7 (5,000.0 ) Operating Income 927.7 158.0 709.5 3.9 87.0 2.1 1,888.2 Interest Expense (186.3 ) (43.1 ) (115.1 ) (3.1 ) (90.0 ) 15.8 (421.8 ) Interest Income 7.3 0.1 1.8 0.1 15.7 (16.7 ) 8.3 Other Income/(Loss), Net 41.6 3.8 27.3 — 1,113.0 (1,086.0 ) 99.7 Income Tax Expense (288.3 ) (44.2 ) (228.7 ) (2.1 ) (15.5 ) (0.1 ) (578.9 ) Net Income/(Loss) 502.0 74.6 394.8 (1.2 ) 1,110.2 (1,084.9 ) 995.5 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income/(Loss) Attributable to Common Shareholders $ 497.4 $ 74.6 $ 391.9 $ (1.2 ) $ 1,110.2 $ (1,084.9 ) $ 988.0 Total Assets (as of) $ 19,250.4 $ 3,595.2 $ 9,401.2 $ 2,182.9 $ 16,220.9 $ (14,430.2 ) $ 36,220.4 Cash Flows Used for Investments in Plant $ 1,020.7 $ 298.2 $ 867.6 $ 16.0 $ 145.6 $ — $ 2,348.1 For the Year Ended December 31, 2016 (2) Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Operating Revenues $ 5,594.3 $ 857.7 $ 1,210.0 $ — $ 870.4 $ (893.3 ) $ 7,639.1 Depreciation and Amortization (504.7 ) (65.3 ) (185.8 ) — (33.5 ) 2.2 (787.1 ) Other Operating Expenses (4,173.0 ) (629.0 ) (321.3 ) — (779.2 ) 891.8 (5,010.7 ) Operating Income 916.6 163.4 702.9 — 57.7 0.7 1,841.3 Interest Expense (193.1 ) (41.3 ) (110.0 ) — (63.5 ) 6.9 (401.0 ) Interest Income 10.0 0.1 1.2 — 7.0 (7.3 ) 11.0 Other Income, Net 22.7 0.7 17.8 — 1,021.2 (1,008.9 ) 53.5 Income Tax (Expense)/Benefit (288.8 ) (45.2 ) (238.2 ) — 16.5 0.7 (555.0 ) Net Income 467.4 77.7 373.7 — 1,038.9 (1,007.9 ) 949.8 Net Income Attributable to Noncontrolling Interests (4.6 ) — (2.9 ) — — — (7.5 ) Net Income Attributable to Common Shareholders $ 462.8 $ 77.7 $ 370.8 $ — $ 1,038.9 $ (1,007.9 ) $ 942.3 Cash Flows Used for Investments in Plant $ 812.6 $ 255.3 $ 801.0 $ — $ 108.0 $ — $ 1,976.9 (1) Effective January 1, 2018, upon implementation of the new revenue accounting guidance, the electric distribution segment is presented gross and intercompany transmission billings are presented in the eliminations column, as Eversource believes that the electric distribution segment acts as a principal, rather than an agent, in its contracts with retail customers. Retail customers contract directly with the electric distribution utility and do not differentiate between distribution and transmission services. Therefore, the electric distribution segment revenues, which are derived from retail customer billings, are presented gross of the eliminations. Prior to 2018, the electric distribution segment presented intercompany electric transmission billings net, based on indicators of net presentation prior to the new revenue guidance. See Note 22 "Revenues," to the financial statements regarding accounting for revenues. (2) As a result of the adoption of new accounting guidance, the non-service related components of pension, SERP and PBOP benefit costs are presented as non-operating income and recorded in Other Income, Net on the statements of income. The 2017 and 2016 amounts, which were previously presented within Operations and Maintenance expense on the statements of income, have been retrospectively presented within Other Income, Net for the years ended December 31, 2017 and 2016. See Note 1C, "Summary of Significant Accounting Policies - Accounting Standards" and Note 1N, "Summary of Significant Accounting Policies - Other Income, Net," to the financial statements for further information. (3) The water distribution business was determined to be a reportable segment beginning in 2018. The 2017 segment information has been recast to conform to the current segment reporting structure.

ACQUISITION OF AQUARION AND G_2

ACQUISITION OF AQUARION AND GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Business Acquisition by Acquisition	The allocation of the cash purchase price was as follows: (Millions of Dollars) Current Assets $ 41.2 PP&E 1,034.9 Goodwill 907.9 Other Noncurrent Assets, excluding Goodwill 215.5 Current Liabilities (121.9 ) Noncurrent Liabilities (421.6 ) Long-Term Debt (778.3 ) Total Cash Purchase Price $ 877.7
Business Acquisition, Pro Forma Information	The unaudited pro forma financial information has been presented for illustrative purposes only and is not necessarily indicative of the consolidated results of operations that would have been achieved or the future consolidated results of operations of Eversource. For the Years Ended December 31, (Pro forma amounts in millions, except share amounts) 2017 2016 Operating Revenues $ 7,947.7 $ 7,849.0 Net Income Attributable to Common Shareholders 1,019.1 969.3 Basic EPS 3.21 3.05 Diluted EPS 3.20 3.04
Business Combination, Segment Allocation	The following table presents goodwill by reportable segment as of December 31, 2018 and 2017: (Billions of Dollars) Electric Distribution Electric Transmission Natural Gas Distribution Water Distribution Total Goodwill $ 2.5 $ 0.6 $ 0.4 $ 0.9 $ 4.4

QUARTERLY FINANCIAL DATA (UNA_2

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information	Quarter Ended Eversource (Millions of Dollars, except per share information) 2018 2017 March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, Operating Revenues $ 2,288.0 $ 1,853.9 $ 2,271.4 $ 2,034.9 $ 2,105.1 $ 1,762.8 $ 1,988.5 $ 1,895.6 Operating Income 442.5 391.4 466.0 400.0 501.0 448.2 495.3 443.7 Net Income 271.4 244.6 291.3 233.2 261.3 232.6 262.2 239.4 Net Income Attributable to Common Shareholders 269.5 242.8 289.4 231.3 259.5 230.7 260.4 237.4 Basic and Diluted EPS (1) $ 0.85 $ 0.76 $ 0.91 $ 0.73 $ 0.82 $ 0.73 $ 0.82 $ 0.75 (1) The summation of quarterly EPS data may not equal annual data due to rounding. Quarter Ended 2018 2017 (Millions of Dollars) March 31, June 30, September 30, December 31, March 31, June 30, September 30, December 31, CL&P Operating Revenues $ 785.0 $ 694.9 $ 865.0 $ 751.3 $ 732.3 $ 666.6 $ 774.8 $ 713.7 Operating Income 157.2 163.1 172.7 142.8 175.5 175.6 177.1 155.2 Net Income 98.6 99.7 100.3 79.1 90.2 91.3 96.1 99.1 NSTAR Electric Operating Revenues $ 770.1 $ 690.7 $ 939.5 $ 712.6 $ 733.8 $ 704.7 $ 851.9 $ 690.2 Operating Income 119.0 133.6 205.5 126.0 156.6 177.9 229.7 124.2 Net Income 77.1 87.9 140.6 77.5 83.4 95.0 125.8 70.5 PSNH Operating Revenues $ 267.4 $ 235.1 $ 290.2 $ 254.9 $ 253.2 $ 230.4 $ 250.0 $ 248.0 Operating Income 55.8 46.9 56.5 37.2 66.6 63.5 66.0 69.8 Net Income 35.1 25.8 40.7 14.3 34.3 31.6 33.7 36.4

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	Mar. 25, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)customer	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)companyutilityMW	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Feb. 08, 2019USD ($)	Jan. 01, 2019USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer			4,000,000
Goodwill		$ 4,427,266	$ 4,427,266		$ 4,427,266	$ 4,427,266
Other Income, Net					128,366	107,913	$ 64,505
Equity method investment		463,700	463,700		$ 463,700	277,600
Number of Companies That Transmit Electricity Imported From Hydro-Quebec System | company					2
Other-than-temporary impairment				$ 32,900	$ 32,900
Number of nuclear generation companies | company					3
Net of damages awarded	$ 26,100
The Connecticut Light And Power Company
Summary of Accounting Policies [Line Items]
Other Income, Net					$ 22,663	22,991	14,238
Period of accounts receivable recoverable under financial or medical duress					180 days
Equity method investment		1,300	1,300		$ 1,300
Net of damages awarded	13,600
Long term receivable		25,000	25,000		25,000	25,000
Transfer of loans receivable		41,300
Maximum loans receivable outstanding		55,000	55,000		55,000
Loans transferred receivable current		18,500	18,500		18,500
Loans transferred receivable non-current		22,800	22,800		$ 22,800
Yankee Gas Services Company
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress					90 days
NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Other Income, Net					$ 53,066	34,100	21,263
Equity method investment		900	900		900
Net of damages awarded	8,600
Long term receivable		5,500	5,500		5,500	5,500
Public Service Company Of New Hampshire
Summary of Accounting Policies [Line Items]
Other Income, Net					27,672	9,805	7,563
Equity method investment		300	300		300
Net of damages awarded	$ 3,900
Long term receivable		3,800	3,800		3,800	3,800
Eversource
Summary of Accounting Policies [Line Items]
Dividends					$ 22,300	20,000	100
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | utility					8
Northern Pass
Summary of Accounting Policies [Line Items]
Capacity required for transmission line | MW					1,090
Capitalized Costs, Proved Properties		$ 307,000	$ 307,000		$ 307,000
Bay State Wind LLC
Summary of Accounting Policies [Line Items]
Ownership interest		50.00%	50.00%		50.00%
Equity method investment		$ 234,300	$ 234,300		$ 234,300	$ 30,200
FERC Regulated Transmission Business
Summary of Accounting Policies [Line Items]
Ownership interest						15.00%
Equity method investment		$ 155,000	$ 155,000		$ 155,000	$ 159,600
Algonquin Gas Tansmsission LLC - Access Northeast
Summary of Accounting Policies [Line Items]
Ownership interest		40.00%	40.00%		40.00%
Equity method investment						31,300
Hydro-Quebec System
Summary of Accounting Policies [Line Items]
Ownership interest		37.20%	37.20%		37.20%
Equity method investment		$ 19,500	$ 19,500		$ 19,500	17,700
Hydro-Quebec System | NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Ownership interest		14.50%	14.50%		14.50%
Equity method investment		$ 7,600	$ 7,600		$ 7,600	6,900
Yankee Companies
Summary of Accounting Policies [Line Items]
Net of damages awarded					52,200
CYAPC and YAEC
Summary of Accounting Policies [Line Items]
Total amount of damages awarded					6,800
MYAPC
Summary of Accounting Policies [Line Items]
Net of damages awarded					14,400
Other Equity Method Investments
Summary of Accounting Policies [Line Items]
Equity method investment		54,900	54,900		54,900	38,800
Accounting Standards Update 2014-09
Summary of Accounting Policies [Line Items]
Operating Revenue and Purchased Power, Fuel and Transmission		$ 22,800	$ 22,800		22,800
Accounting Standards Update 2016-01
Summary of Accounting Policies [Line Items]
Unrealized gains recorded in other income					4,300
Accounting Standards Update 2017-07
Summary of Accounting Policies [Line Items]
Increase (Decrease) in Regulatory Liabilities					39,800
Accounting Standards Update 2016-15
Summary of Accounting Policies [Line Items]
Proceeds from Equity Method Investment, Distribution					19,100	20,000	700
Equity in Earnings
Summary of Accounting Policies [Line Items]
Other Income, Net					3,800	27,400	200
Equity in Earnings | The Connecticut Light And Power Company
Summary of Accounting Policies [Line Items]
Other Income, Net					100	0	100
Equity in Earnings | NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Other Income, Net					700	300	300
Equity in Earnings | Public Service Company Of New Hampshire
Summary of Accounting Policies [Line Items]
Other Income, Net					$ 0	$ 0	$ 0
Subsequent Event | Revolution Wind And South Fork Wind Power
Summary of Accounting Policies [Line Items]
Ownership interest								50.00%
Parent obligations								$ 127,600
Scenario, Forecast | Accounting Standards Update 2016-19
Summary of Accounting Policies [Line Items]
Right of use asset									$ 60,000
Scenario, Forecast | Accounting Standards Update 2016-19 | The Connecticut Light And Power Company
Summary of Accounting Policies [Line Items]
Right of use asset									1,000
Scenario, Forecast | Accounting Standards Update 2016-19 | NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Right of use asset									25,000
Scenario, Forecast | Accounting Standards Update 2016-19 | Public Service Company Of New Hampshire
Summary of Accounting Policies [Line Items]
Right of use asset									$ 1,000

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	$ 212,700	$ 195,700
Uncollectible Hardship	131,500	122,500
Bad debt expense associated with accounts receivable	$ 61,337	44,453	$ 69,466
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
Total Provision for Uncollectible Accounts	$ 88,000	78,900
Uncollectible Hardship	71,900	65,500
Bad debt expense associated with accounts receivable	15,831	5,312	17,572
NSTAR Electric Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	74,500	69,700
Uncollectible Hardship	42,500	40,300
Bad debt expense associated with accounts receivable	22,279	21,252	31,728
Public Service Company Of New Hampshire
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Provision for Uncollectible Accounts	11,100	10,500
Uncollectible Hardship	0	0
Bad debt expense associated with accounts receivable	$ 6,383	$ 6,704	$ 7,288

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fuel, Materials, Supplies and Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Inventory [Line Items]
Total - Current	$ 238	$ 223.1
Fuel
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	33.1	29.7
Materials and Supplies
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	126.1	117.1
RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	78.8	76.3
The Connecticut Light And Power Company
Public Utilities, Inventory [Line Items]
Total - Current	44.5	48.4
The Connecticut Light And Power Company | Fuel
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
The Connecticut Light And Power Company | Materials and Supplies
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	44.5	44.4
The Connecticut Light And Power Company | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	4
NSTAR Electric Company
Public Utilities, Inventory [Line Items]
Total - Current	114.2	95.5
NSTAR Electric Company | Fuel
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
NSTAR Electric Company | Materials and Supplies
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	48.6	45.1
NSTAR Electric Company | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	65.6	50.4
Public Service Company Of New Hampshire
Public Utilities, Inventory [Line Items]
Total - Current	37.5	40.3
Public Service Company Of New Hampshire | Fuel
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
Public Service Company Of New Hampshire | Materials and Supplies
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	24.3	18.5
Public Service Company Of New Hampshire | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	$ 13.2	$ 21.8

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Accounting Policies [Line Items]
Fuel power costs	$ 442.6	$ 432.5	$ 372.2
Public Service Company Of New Hampshire
Summary of Accounting Policies [Line Items]
Fuel power costs	$ 7.9	$ 43.4	$ 45

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 19.7	$ 12.5	$ 10.8
Equity Funds	44	34.4	26.2
Total AFUDC	$ 63.7	$ 46.9	$ 37
Average AFUDC Rate	4.90%	5.10%	4.40%
The Connecticut Light And Power Company
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 6.3	$ 5.1	$ 3.3
Total AFUDC	$ 18.5	$ 17.2	$ 9.6
Average AFUDC Rate	5.80%	6.20%	4.70%
NSTAR Electric Company
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 7.8	$ 4.8	$ 5.3
Total AFUDC	$ 23.4	$ 15	$ 15.5
Average AFUDC Rate	5.00%	5.00%	3.20%
Public Service Company Of New Hampshire
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 1.3	$ 0.7	$ 0.8
Total AFUDC	$ 1.3	$ 0.7	$ 1.1
Average AFUDC Rate	0.70%	0.70%	1.00%

SUMMARY OF SIGNIFICANT ACCOUN_9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 128,366	$ 107,913	$ 64,505
Interest Income	18,100	8,300	11,000
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	44,000	34,400	26,200
Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	60,800	29,900	18,600
Equity in Earnings
Summary of Accounting Policies [Line Items]
Other Income, Net	3,800	27,400	200
Equity in Earnings of Subsidiaries	17,600	9,700	1,700
Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	(4,000)	7,500	8,500
Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	5,100	0	0
Other
Summary of Accounting Policies [Line Items]
Other Income, Net	600	400	0
The Connecticut Light And Power Company
Summary of Accounting Policies [Line Items]
Other Income, Net	22,663	22,991	14,238
The Connecticut Light And Power Company | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	9,500	1,800	700
The Connecticut Light And Power Company | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	12,200	12,100	6,300
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	12,200	12,100	6,300
The Connecticut Light And Power Company | Equity in Earnings
Summary of Accounting Policies [Line Items]
Other Income, Net	100	0	100
The Connecticut Light And Power Company | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	(3,000)	4,500	(1,500)
The Connecticut Light And Power Company | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	3,700	4,600	8,600
The Connecticut Light And Power Company | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	0	0	0
The Connecticut Light And Power Company | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	200	0	0
NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Other Income, Net	53,066	34,100	21,263
NSTAR Electric Company | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	36,000	19,200	10,500
NSTAR Electric Company | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	15,600	10,200	10,200
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	15,600	10,200	10,200
NSTAR Electric Company | Equity in Earnings
Summary of Accounting Policies [Line Items]
Other Income, Net	700	300	300
NSTAR Electric Company | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	(500)	2,600	(300)
NSTAR Electric Company | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	800	1,800	600
NSTAR Electric Company | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	500	0	0
NSTAR Electric Company | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	0	0	0
Public Service Company Of New Hampshire
Summary of Accounting Policies [Line Items]
Other Income, Net	27,672	9,805	7,563
Public Service Company Of New Hampshire | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	9,900	5,900	6,200
Public Service Company Of New Hampshire | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	0	0	300
Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity	0	0	300
Public Service Company Of New Hampshire | Equity in Earnings
Summary of Accounting Policies [Line Items]
Other Income, Net	0	0	0
Public Service Company Of New Hampshire | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	(800)	1,600	(700)
Public Service Company Of New Hampshire | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	14,100	2,200	1,800
Public Service Company Of New Hampshire | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	4,400	0	0
Public Service Company Of New Hampshire | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 100	$ 100	$ 0

SUMMARY OF SIGNIFICANT ACCOU_10

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 161.9	$ 157.4	$ 162.7
Tax remittance to state for energy efficiency funds	46.8	25.4
The Connecticut Light And Power Company
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 141.4	$ 137.5	$ 145.2

SUMMARY OF SIGNIFICANT ACCOU_11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Supplemental Cash Flow [Line Items]
Cash and Cash Equivalents	$ 108,068	$ 108,068	$ 38,165
Cash Paid/(Received) During the Year for:
Interest, Net of Amounts Capitalized		503,200	419,100	$ 398,100
Income Taxes		158,800	30,800	(135,500)
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)		435,900	379,500	301,500
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	209,324	209,324	85,890	106,750	$ 67,996
DOE settlement payment	145,000	(145,000)	0	59,804
The Connecticut Light And Power Company
Schedule of Supplemental Cash Flow [Line Items]
Cash and Cash Equivalents	87,721	87,721	6,028
Cash Paid/(Received) During the Year for:
Interest, Net of Amounts Capitalized		149,700	144,600	143,300
Income Taxes		66,100	68,800	(73,900)
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)		106,100	132,500	116,200
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	91,613	91,613	9,619	8,403	2,205
NSTAR Electric Company
Schedule of Supplemental Cash Flow [Line Items]
Cash and Cash Equivalents	1,606	1,606	1,763
Cash Paid/(Received) During the Year for:
Interest, Net of Amounts Capitalized		122,100	124,600	112,900
Income Taxes		120,000	95,500	66,000
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)		116,500	116,500	87,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	14,659	14,659	14,708	15,507	12,821
Public Service Company Of New Hampshire
Schedule of Supplemental Cash Flow [Line Items]
Cash and Cash Equivalents	1,439	1,439	900
Cash Paid/(Received) During the Year for:
Interest, Net of Amounts Capitalized		40,500	45,900	46,500
Income Taxes		27,300	26,100	(36,000)
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)		81,700	44,400	37,900
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	52,723	52,723	2,191	$ 5,953	$ 4,088
Prepaid Expenses and Other Current Assets
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	72,100	72,100	24,400
Prepaid Expenses and Other Current Assets | The Connecticut Light And Power Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	3,500	3,500	3,100
Prepaid Expenses and Other Current Assets | NSTAR Electric Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	13,000	13,000	12,800
Marketable Securities
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	25,900	25,900	23,300
Marketable Securities | The Connecticut Light And Power Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	400	400	500
Marketable Securities | NSTAR Electric Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	100	100	100
Marketable Securities | Public Service Company Of New Hampshire
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	600	600	800
Other Noncurrent Assets
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	3,200	3,200	0
Other Noncurrent Assets | The Connecticut Light And Power Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	0	0	0
Other Noncurrent Assets | NSTAR Electric Company
Non-Cash Investing Activities:
Restricted Cash and Cash Equivalents	$ 0	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOU_12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	$ 108,068	$ 38,165
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	209,324	85,890	$ 106,750	$ 67,996
The Connecticut Light And Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	87,721	6,028
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	91,613	9,619	8,403	2,205
NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	1,606	1,763
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	14,659	14,708	15,507	12,821
Public Service Company Of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and Cash Equivalents	1,439	900
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	52,723	2,191	5,953	$ 4,088
Prepaid Expenses and Other Current Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	72,100	24,400
Prepaid Expenses and Other Current Assets | The Connecticut Light And Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	3,500	3,100
Prepaid Expenses and Other Current Assets | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	13,000	12,800
Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	25,900	23,300
Marketable Securities | The Connecticut Light And Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	400	500
Marketable Securities | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	100	100
Marketable Securities | Public Service Company Of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	600	800
Other Noncurrent Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	3,200	0
Other Noncurrent Assets | The Connecticut Light And Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	0	0
Other Noncurrent Assets | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	0	0
Variable Interest Entity, Primary Beneficiary | Prepaid Expenses and Other Current Assets | Public Service Company Of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	47,500	500
Variable Interest Entity, Primary Beneficiary | Other Noncurrent Assets | Public Service Company Of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents	$ 3,200	0
Accounting Standards Update 2016-18
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash and Cash Equivalents		$ 28,800	$ 32,400

REGULATORY ACCOUNTING - Compone

REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,145,900	$ 5,239,300
Less: Current Portion	514,779	741,868
Total Long-Term Regulatory Assets	4,631,137	4,497,447
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,914,800	2,068,800
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	728,600	768,900
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	608,400	0
Deferred Costs from Generation Asset Sale
Regulatory Assets [Line Items]
Total Regulatory Assets	0	516,100
Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	576,000	404,800
Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	316,000	509,900
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	356,500	367,200
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	348,400	365,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	89,200	101,000
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	208,000	137,400
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Total Regulatory Assets	1,630,700	1,645,200
Less: Current Portion	125,155	200,281
Total Long-Term Regulatory Assets	1,505,488	1,444,935
The Connecticut Light And Power Company | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	424,700	469,200
The Connecticut Light And Power Company | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	454,400	453,800
The Connecticut Light And Power Company | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light And Power Company | Deferred Costs from Generation Asset Sale
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light And Power Company | Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	302,600	216,700
The Connecticut Light And Power Company | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	33,200	85,300
The Connecticut Light And Power Company | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	356,500	362,300
The Connecticut Light And Power Company | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light And Power Company | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	32,300	30,300
The Connecticut Light And Power Company | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	27,000	27,600
NSTAR Electric Company
Regulatory Assets [Line Items]
Total Regulatory Assets	1,438,200	1,524,500
Less: Current Portion	241,747	333,882
Total Long-Term Regulatory Assets	1,196,512	1,190,575
NSTAR Electric Company | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	544,400	560,700
NSTAR Electric Company | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	105,900	113,200
NSTAR Electric Company | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric Company | Deferred Costs from Generation Asset Sale
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric Company | Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	212,900	146,600
NSTAR Electric Company | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	169,100	273,000
NSTAR Electric Company | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric Company | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	299,100	313,600
NSTAR Electric Company | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	42,200	39,000
NSTAR Electric Company | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	64,600	78,400
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Total Regulatory Assets	929,500	940,800
Less: Current Portion	67,228	130,134
Total Long-Term Regulatory Assets	862,288	810,677
Public Service Company Of New Hampshire | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	169,600	212,300
Public Service Company Of New Hampshire | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	8,300	21,700
Public Service Company Of New Hampshire | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets		0
Public Service Company Of New Hampshire | Deferred Costs from Generation Asset Sale
Regulatory Assets [Line Items]
Total Regulatory Assets	0	516,100
Public Service Company Of New Hampshire | Storm Restoration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	60,500	41,500
Public Service Company Of New Hampshire | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	67,300	116,400
Public Service Company Of New Hampshire | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
Public Service Company Of New Hampshire | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	3,300	17,000
Public Service Company Of New Hampshire | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 12,100	$ 15,800

REGULATORY ACCOUNTING - Narrati

REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 17, 2018	May 08, 2018
Regulatory Assets [Line Items]
Deferred storm restoration costs		$ 5,145,900	$ 5,239,300
Other Income, Net		128,366	107,913	$ 64,505
Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Deferred storm restoration costs		266,000
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Deferred storm restoration costs		929,500	940,800
Amount Of Recovery Approved In Storm Restoration Costs					$ 49,000
Other Income, Net		27,672	9,805	7,563
Public Service Company Of New Hampshire | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Deferred storm restoration costs		24,000
Other Income, Net	$ 8,700
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Deferred storm restoration costs		1,630,700	1,645,200
Other Income, Net		22,663	22,991	14,238
The Connecticut Light And Power Company | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Deferred storm restoration costs		148,000
NSTAR Electric Company
Regulatory Assets [Line Items]
Deferred storm restoration costs		1,438,200	1,524,500
Other Income, Net		53,066	$ 34,100	$ 21,263
NSTAR Electric Company | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Deferred storm restoration costs		$ 94,000
Rate Reduction Bonds | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Amount of securitized rate reduction bonds issued						$ 635,700

REGULATORY ACCOUNTING REGULATOR

REGULATORY ACCOUNTING REGULATORY ACCOUNTING - Regulatory Costs in Long-Term Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Amount of Regulatory Costs Not yet Approved	$ 122.9	$ 105.8
The Connecticut Light And Power Company
Amount of Regulatory Costs Not yet Approved	42.1	18.2
NSTAR Electric Company
Amount of Regulatory Costs Not yet Approved	49.3	42.7
Public Service Company Of New Hampshire
Amount of Regulatory Costs Not yet Approved	$ 12.2	$ 27.2

REGULATORY ACCOUNTING - Equity

REGULATORY ACCOUNTING - Equity Return on Regulatory Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet	$ 0.7	$ 1
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet	$ 12	42
Clean Air Project | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Equity return not recorded on the balance sheet		$ 25

REGULATORY ACCOUNTING - Compo_2

REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 3,979,700	$ 3,765,400
Less: Current Portion	370,230	128,071
Total Long-Term Regulatory Liabilities	$ 3,609,475	3,637,273
Amount of regulated EDIT liabilities, percentage	85.00%
Excess ADIT due to tax Cuts and Jobs Act [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 2,883,000	2,882,000
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	521,000	502,100
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	91,200	132,300
Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	309,000	136,700
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	70,700	67,100
Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	24,600	0
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	80,200	45,200
The Connecticut Light And Power Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,231,800	1,151,100
Less: Current Portion	109,614	38,967
Total Long-Term Regulatory Liabilities	1,122,157	1,112,136
The Connecticut Light And Power Company | Excess ADIT due to tax Cuts and Jobs Act [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,031,000	1,031,600
The Connecticut Light And Power Company | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	39,900	23,200
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	89,500	34,600
The Connecticut Light And Power Company | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	47,400	48,800
The Connecticut Light And Power Company | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
The Connecticut Light And Power Company | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	24,000	12,900
NSTAR Electric Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,703,900	1,594,100
Less: Current Portion	190,620	79,562
Total Long-Term Regulatory Liabilities	1,513,279	1,514,451
NSTAR Electric Company | Excess ADIT due to tax Cuts and Jobs Act [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,103,700	1,087,900
NSTAR Electric Company | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	307,100	293,800
NSTAR Electric Company | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	76,900	112,600
NSTAR Electric Company | Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	163,700	77,800
NSTAR Electric Company | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	23,300	18,300
NSTAR Electric Company | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
NSTAR Electric Company | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	29,200	3,700
Public Service Company Of New Hampshire
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	483,600	450,700
Less: Current Portion	55,526	6,251
Total Long-Term Regulatory Liabilities	428,069	444,397
Public Service Company Of New Hampshire | Excess ADIT due to tax Cuts and Jobs Act [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	396,400	405,100
Public Service Company Of New Hampshire | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	22,100	37,900
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	48,300	5,000
Public Service Company Of New Hampshire | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company Of New Hampshire | Revenue Subject to Refund [Member]
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	12,600	0
Public Service Company Of New Hampshire | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,200	$ 2,700
Minimum
Regulatory Liabilities [Line Items]
Estimated useful lives	35

REGULATORY ACCOUNTING - FERC RO

REGULATORY ACCOUNTING - FERC ROE Complaints (Details) - FERC ROE First and Second Complaints $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers	$ 39.1
The Connecticut Light And Power Company
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers	21.4
NSTAR Electric Company
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers	14.6
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers	$ 3.1

PROPERTY, PLANT AND EQUIPMENT_3

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Investment in Utility Property, Plant and Equipment By Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 15,071,100	$ 14,410,500
Distribution - Natural Gas	3,546,200	3,244,200
Transmission - Electric	10,153,900	9,270,900
Distribution - Water	1,639,800	1,558,400
Solar	164,100	36,200
Utility	30,575,100	28,520,200
Other Assets	778,600	693,700
Property, Plant and Equipment, Gross	31,353,700	29,213,900
Less: Accumulated Depreciation
Utility	(7,126,200)	(6,846,900)
Other	(336,700)	(286,900)
Total Accumulated Depreciation	(7,462,900)	(7,133,800)
Property, Plant and Equipment, Net	23,890,800	22,080,100
Construction Work in Progress	1,719,600	1,537,400
Total Property, Plant and Equipment, Net	25,610,428	23,617,463
The Connecticut Light And Power Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	6,176,400	5,888,300
Transmission - Electric	4,700,500	4,239,900
Solar	0	0
Property, Plant and Equipment, Gross	10,876,900	10,128,200
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,302,600)	(2,239,000)
Property, Plant and Equipment, Net	8,574,300	7,889,200
Construction Work in Progress	335,400	381,800
Total Property, Plant and Equipment, Net	8,909,701	8,271,030
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	6,756,400	6,479,000
Transmission - Electric	4,065,900	3,821,200
Solar	164,100	36,200
Property, Plant and Equipment, Gross	10,986,400	10,336,400
Less: Accumulated Depreciation
Total Accumulated Depreciation	(2,702,000)	(2,550,200)
Property, Plant and Equipment, Net	8,284,400	7,786,200
Construction Work in Progress	510,300	460,300
Total Property, Plant and Equipment, Net	8,794,700	8,246,494
Public Service Company Of New Hampshire
Property, Plant and Equipment [Line Items]
Distribution - Electric	2,178,600	2,083,400
Transmission - Electric	1,338,700	1,161,300
Solar	0	0
Property, Plant and Equipment, Gross	3,517,300	3,244,700
Less: Accumulated Depreciation
Total Accumulated Depreciation	(772,900)	(751,800)
Property, Plant and Equipment, Net	2,744,400	2,492,900
Construction Work in Progress	135,700	149,400
Total Property, Plant and Equipment, Net	$ 2,880,073	$ 2,642,274

PROPERTY, PLANT AND EQUIPMENT_4

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.90%	3.00%	3.00%
The Connecticut Light And Power Company
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	2.80%	2.70%
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	2.90%	2.90%
Public Service Company Of New Hampshire
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	3.10%	3.10%

PROPERTY, PLANT AND EQUIPMENT_5

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Distribution - Electric	34 years 1 month 6 days
Distribution - Natural Gas	43 years 9 months 18 days
Distribution - Natural Gas	$ 3,546.2	$ 3,244.2
Transmission - Electric	41 years 3 months 18 days
Distribution - Water	33 years 3 months 18 days
Solar	24 years 10 months 24 days
Other	12 years 10 months 24 days
The Connecticut Light And Power Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	35 years 4 months 24 days
Transmission - Electric	38 years
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	33 years 8 months 24 days
Transmission - Electric	45 years 3 months 18 days
Solar	24 years 10 months 24 days
Public Service Company Of New Hampshire
Property, Plant and Equipment [Line Items]
Distribution - Electric	32 years 3 months 18 days
Transmission - Electric	42 years 10 months 24 days

DERIVATIVE INSTRUMENTS - Schedu

DERIVATIVE INSTRUMENTS - Schedule of Gross Fair Value of Contracts (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Inputs, Level 2 | Current Derivative Assets
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	$ 1.5	$ 0
Netting	(0.9)	0
Net Amount Recorded as a Derivative	0.6	0
Fair Value, Inputs, Level 2 | Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	0	(4.5)
Netting (1)	0	0
Net Amount Recorded as a Derivative	0	(4.5)
Fair Value, Inputs, Level 2 | Long-Term Derivative Liabilities:
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	0	(0.4)
Netting (1)	0	0
Net Amount Recorded as a Derivative	0	(0.4)
The Connecticut Light And Power Company | Fair Value, Inputs, Level 3 | Current Derivative Assets
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	9.6	9.5
Netting	(3.4)	(7.1)
Net Amount Recorded as a Derivative	6.2	2.4
The Connecticut Light And Power Company | Fair Value, Inputs, Level 3 | Long-Term Derivative Assets
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	74.2	71.9
Netting	(2.3)	(5.3)
Net Amount Recorded as a Derivative	71.9	66.6
The Connecticut Light And Power Company | Fair Value, Inputs, Level 3 | Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(55.1)	(54.4)
Netting (1)	0	0
Net Amount Recorded as a Derivative	(55.1)	(54.4)
The Connecticut Light And Power Company | Fair Value, Inputs, Level 3 | Long-Term Derivative Liabilities:
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(379.5)	(376.9)
Netting (1)	0	0
Net Amount Recorded as a Derivative	$ (379.5)	$ (376.9)

DERIVATIVE INSTRUMENTS - Deriva

DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details) MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)MMBTUMWhMW	Dec. 31, 2017USD ($)MMBTU	Dec. 31, 2016USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company (as a percentage)	20.00%
Amount of power to be purchased under capacity-related contract (up to for 35 mw) (in mw) | MW	787
Amount of natural gas to be purchased under futures contracts (in MMBtu) | MMBTU	12.5	9.5
Loss deferred as regulatory costs | $	$ 25	$ 29	$ 125.5
The Connecticut Light And Power Company
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts (as a percentage)	80.00%
Amount of energy to be purchased under renewable energy contract (in mwh) | MWh	0.1

DERIVATIVE INSTRUMENTS - Unobse

DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - Fair Value, Inputs, Level 3 - $ / KWmo	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of Exit Price Premiums	4.20%
The Connecticut Light And Power Company | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	4.30	5
Forward Reserve (in USDPerKiloWattMonth)	0.75	1
Percentage of Exit Price Premiums	15.70%
The Connecticut Light And Power Company | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	7.44	8.70
Forward Reserve (in USDPerKiloWattMonth)	1.78	2

DERIVATIVE INSTRUMENTS - Variat

DERIVATIVE INSTRUMENTS - Variations Using Significant unobservable Inputs (Details) - Fair Value, Inputs, Level 3 - The Connecticut Light And Power Company - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (362.3)	$ (420.5)
Net Realized/Unrealized Losses Included in Regulatory Assets and Liabilities	(32)	(9.5)
Settlements	37.8	67.7
Ending balance	$ (356.5)	$ (362.3)

MARKETABLE SECURITIES - Equity

MARKETABLE SECURITIES - Equity Securities (Details) - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Payment to DOE	$ 145
Equity securities	44
Available-for-sale Securities, Equity Securities		$ 52.5
Amortized Cost	190	284.9
Pre-Tax Unrealized Gains	0.4	3.2
Pre-Tax Unrealized Losses	(4)	(1.1)
Fair Value	186.4	287
Equity Securities | YAEC
Debt Securities, Available-for-sale [Line Items]
Marketable securities held in nuclear decommissioning trusts	200	261.3
Debt Securities | YAEC
Debt Securities, Available-for-sale [Line Items]
Marketable securities held in nuclear decommissioning trusts	$ 143.9	$ 242.3

MARKETABLE SECURITIES - Contrac

MARKETABLE SECURITIES - Contractual Maturity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Debt Securities, Available-for-sale, Realized Gain	$ 9.8
Amortized Cost
Less than one year		$ 30.5
One to five years		29.2
Six to ten years		43.6
Greater than ten years		86.7
Amortized Cost	284.9	190
Fair Value
Less than one year		30.3
One to five years		28.9
Six to ten years		42.9
Greater than ten years		84.3
Total Debt Securities	$ 287	$ 186.4

MARKETABLE SECURITIES - Fair Va

MARKETABLE SECURITIES - Fair Value Measurement (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	$ 430.4	$ 600.8
Fair Value, Inputs, Level 1
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	269.9	337.1
Fair Value, Inputs, Level 1 | Mutual Funds and Equities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	244	313.8
Fair Value, Inputs, Level 1 | Money Market Funds
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	25.9	23.3
Fair Value, Inputs, Level 2
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	160.5	263.7
Fair Value, Inputs, Level 2 | U.S. Government Issued Debt Securities (Agency and Treasury)
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	79.6	70.2
Fair Value, Inputs, Level 2 | Corporate Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	39.5	50.9
Fair Value, Inputs, Level 2 | Asset-Backed Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	14	21.2
Fair Value, Inputs, Level 2 | Municipal Bonds
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	19.2	110.7
Fair Value, Inputs, Level 2 | Other Fixed Income Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	$ 8.2	$ 10.7

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligation	$ 466.2	$ 419.1	$ 426.4
CYAPC and YAEC
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligation	$ 339.9	$ 301.5

ASSET RETIREMENT OBLIGATIONS _2

ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	$ 419.1	$ 426.4
Liabilities Incurred During the Year	11.3	0.2
Liabilities Settled During the Year	(36.6)	(19.3)
Accretion	25.5	26.3
Revisions in Estimated Cash Flows	46.9	(14.5)
Balance as of End of Year	466.2	419.1
The Connecticut Light And Power Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	31.5	36
Liabilities Incurred During the Year	0	0.1
Liabilities Settled During the Year	0	(1)
Accretion	2	2.3
Revisions in Estimated Cash Flows	0	(5.9)
Balance as of End of Year	33.5	31.5
NSTAR Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	44.6	42.6
Liabilities Incurred During the Year	11.3	0.1
Liabilities Settled During the Year	0	(0.2)
Accretion	2.2	2.1
Revisions in Estimated Cash Flows	14.3	0
Balance as of End of Year	72.4	44.6
Public Service Company Of New Hampshire
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	25	23.5
Liabilities Incurred During the Year	0	0
Liabilities Settled During the Year	(21.5)	0
Accretion	0.5	1.5
Revisions in Estimated Cash Flows	0	0
Balance as of End of Year	$ 4	$ 25

SHORT-TERM DEBT - Narrative (De

SHORT-TERM DEBT - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Aug. 01, 2018	Jan. 08, 2018	Dec. 08, 2017	Nov. 30, 2017	Nov. 03, 2016
Short-term Debt [Line Items]
Amount of debt authorized			$ 800,000,000
Commercial Paper
Short-term Debt [Line Items]
Amount of commercial paper program	$ 0	$ 201,200,000
Line of Credit
Short-term Debt [Line Items]
Amount outstanding during period	0	0
Eversource | Commercial Paper
Short-term Debt [Line Items]
Amount of commercial paper program	1,450,000,000			$ 201,200,000	$ 1,450,000,000
Eversource | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	$ 1,450,000,000
Debt instrument term	5 years
The Connecticut Light And Power Company
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency						$ 600,000,000
Notes payable to related parties	$ 0	69,500,000
NSTAR Electric Company
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency						$ 655,000,000
Amount of debt authorized			$ 200,000,000
NSTAR Electric Company | Commercial Paper
Short-term Debt [Line Items]
Amount of commercial paper program	650,000,000
NSTAR Electric Company | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	$ 650,000,000
Debt instrument term	5 years
NPT
Short-term Debt [Line Items]
Amount of debt authorized							$ 800,000,000
Public Service Company Of New Hampshire
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency	$ 331,000,000
Notes payable to related parties	$ 57,000,000	262,900,000
Public Service Company Of New Hampshire | Short Term Debt Authorization Calculation
Short-term Debt [Line Items]
Interest rate stated percentage (up to) (as a percentage)	10.00%
Short-term debt borrowing calculation approved by regulatory agency	$ 60,000,000
Aquarion | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	$ 100,000,000
Short-term Debt		$ 76,000,000
Unsecured Debt | The Connecticut Light And Power Company
Short-term Debt [Line Items]
Period of maturity restricting provisions of debt	10 years
Total capitalization (as a percentage)	10.00%
Capacity available under preferred stock provisions	$ 758,100,000

SHORT-TERM DEBT - Schedule of D

SHORT-TERM DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Notes Payable	$ 910,000	$ 1,088,087
Parent Company
Line of Credit Facility [Line Items]
Notes Payable	631,500	778,087
Commercial Paper | Parent Company
Line of Credit Facility [Line Items]
Notes Payable	631,500	979,300
Available Borrowing Capacity	$ 818,500	$ 470,700
Weighted-Average discount (as a percentage)	2.77%	1.86%
Commercial Paper | NSTAR Electric Company
Line of Credit Facility [Line Items]
Notes Payable	$ 278,500	$ 234,000
Available Borrowing Capacity	$ 371,500	$ 416,000
Weighted-Average discount (as a percentage)	2.50%	1.55%

LONG-TERM DEBT - Narrative (Det

LONG-TERM DEBT - Narrative (Details)	1 Months Ended		12 Months Ended
	Dec. 31, 2018USD ($)	Jan. 31, 2018USD ($)issuance	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Aug. 01, 2018USD ($)	Jan. 08, 2018USD ($)	Dec. 08, 2017USD ($)
Debt Instrument [Line Items]
Repayments of Long-term Debt			$ 1,050,330,000	$ 745,000,000	$ 200,000,000
Current portion of long-term debt	$ 837,319,000		837,319,000	549,631,000
Amount of debt authorized						$ 800,000,000
Long-term debt outstanding	12,248,743,000		12,248,743,000	11,775,889,000
Payment to DOE	145,000,000
Interest included in payment to settle spent nuclear fuel obligation	29,000,000		29,000,000	132,600,000
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Repayments of Long-term Debt			300,000,000	250,000,000	0
Current portion of long-term debt	250,000,000		250,000,000	300,000,000
Long-term debt outstanding	3,004,016,000		3,004,016,000	2,759,135,000
NSTAR Electric Company
Debt Instrument [Line Items]
Repayments of Long-term Debt			0	400,000,000	200,000,000
Amount of debt authorized						$ 200,000,000
Long-term debt outstanding	2,944,846,000		2,944,846,000	2,943,759,000
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Repayments of Long-term Debt			199,250,000	70,000,000	0
Current portion of long-term debt	150,000,000		150,000,000	110,000,000
Long-term debt outstanding	655,173,000		655,173,000	892,438,000
Parent Company
Debt Instrument [Line Items]
Repayments of Long-term Debt			450,000,000	0	$ 0
Current portion of long-term debt	378,883,000		378,883,000	32,114,000
Long-term debt outstanding	4,031,997,000		4,031,997,000	3,523,472,000
Commercial Paper
Debt Instrument [Line Items]
Amount of commercial paper program	0		0	201,200,000
Commercial Paper | NSTAR Electric Company
Debt Instrument [Line Items]
Amount of commercial paper program	650,000,000		650,000,000
Commercial Paper | Parent Company
Debt Instrument [Line Items]
Current portion of long-term debt		$ 446,800,000
Number of Debt Issuances | issuance		2
Amount of commercial paper program	1,450,000,000		1,450,000,000				$ 201,200,000	$ 1,450,000,000
Senior Notes
Debt Instrument [Line Items]
Long-term debt	12,248,700,000		12,248,700,000	11,775,900,000
Senior Notes | NSTAR Electric Company
Debt Instrument [Line Items]
Long-term debt outstanding	565,000,000		565,000,000	565,000,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-term debt outstanding	$ 39,500,000		$ 39,500,000	$ 181,400,000

LONG-TERM DEBT - Schedule of Lo

LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($)	Dec. 31, 2018	Oct. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Jan. 31, 2018	Jan. 08, 2018	Dec. 31, 2017	Dec. 08, 2017	Jan. 31, 2015	May 31, 2013	May 31, 2008
Debt Instrument [Line Items]
Long-Term Debt	$ 12,248,743,000						$ 11,775,889,000
Less Amounts due Within One Year	$ (837,319,000)						(549,631,000)
Eversource Parent 2.50% Series I Senior Notes (2)
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)					2.50%
Eversource Parent 3.30% Series M Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)					3.30%
Eversource Parent 3.80% Series N Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.80%
Eversource Parent 4.25% Series O Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.25%
Eversource Parent 1.60% Series G Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)									1.60%
Eversource Parent 1.45% Series E Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)										1.45%
First Mortgage Notes | Yankee Gas - First Mortgage Bonds: 3.020% - 8.480% due 2019 - 2048
Debt Instrument [Line Items]
Long-Term Debt	$ 470,000,000						520,000,000
First Mortgage Notes | NSTAR Gas - First Mortgage Bonds: 4.09% - 9.950% due 2020 - 2048
Debt Instrument [Line Items]
Long-Term Debt	385,000,000						285,000,000
Unsecured Debt | 4.500% Debentures due 2019
Debt Instrument [Line Items]
Long-Term Debt	350,000,000						350,000,000
Unsecured Debt | 2.500% - 4.250% Senior Notes due 2021 - 2029
Debt Instrument [Line Items]
Long-Term Debt	4,360,000,000						3,260,000,000
Senior Notes
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	4,200,000						(1,500,000)
Unamortized Debt Issuance Costs	(23,200,000)						(12,800,000)
Long-term debt	12,248,700,000						11,775,900,000
Loans Payable
Debt Instrument [Line Items]
Less Amounts due Within One Year	(401,100,000)						(104,200,000)
Loans Payable | Unsecured Notes 3.570% - 6.430% due 2021 - 2037
Debt Instrument [Line Items]
Long-Term Debt	289,500,000						290,900,000
Loans Payable | Secured Debt 4.100% - 9.640% due 2021 - 2035
Debt Instrument [Line Items]
Long-Term Debt	70,700,000						70,400,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-Term Debt	39,500,000						181,400,000
Fair Value Adjustment
Debt Instrument [Line Items]
Long-Term Debt	144,700,000						172,600,000
Fair Value Adjustment - Current Portion
Debt Instrument [Line Items]
Long-Term Debt	(36,200,000)						(35,400,000)
Total Other Long-Term Debt
Debt Instrument [Line Items]
Long-Term Debt	5,644,700,000						5,180,600,000
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Long-Term Debt	3,004,016,000						2,759,135,000
Less Amounts due Within One Year	(250,000,000)						(300,000,000)
The Connecticut Light And Power Company | 5.650% 2008 Series A due 2018
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)											5.65%
The Connecticut Light And Power Company | 4.000% 2018 Series A due 2048
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)				4.00%
The Connecticut Light And Power Company | 4.375% Fixed Rate Tax Exempt due 2028
Debt Instrument [Line Items]
Long-Term Debt	120,500,000						120,500,000
The Connecticut Light And Power Company | First Mortgage Notes
Debt Instrument [Line Items]
Long-Term Debt	3,144,800,000						2,944,800,000
Unamortized Premiums and Discounts, Net	10,200,000						11,500,000
Unamortized Debt Issuance Costs	(21,500,000)						(17,700,000)
Long-term debt	$ 3,004,000,000						2,759,100,000
The Connecticut Light And Power Company | First Mortgage Notes | 7.875% 1994 Series D due 2024
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	7.875%
Long-Term Debt	$ 139,800,000						139,800,000
The Connecticut Light And Power Company | First Mortgage Notes | 5.750% 2004 Series B due 2034
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 130,000,000						130,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 5.625% 2005 Series B due 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.625%
Long-Term Debt	$ 100,000,000						100,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 6.350% 2006 Series A due 2036
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.35%
Long-Term Debt	$ 250,000,000						250,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 5.750% 2007 Series B due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 150,000,000						150,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 6.375% 2007 Series D due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.375%
Long-Term Debt	$ 100,000,000						100,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 5.650% 2008 Series A due 2018
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.65%
Long-Term Debt	$ 0						300,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 5.500% 2009 Series A due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.50%
Long-Term Debt	$ 250,000,000						250,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 2.500% 2013 Series A due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.50%
Long-Term Debt	$ 400,000,000						400,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 4.300% 2014 Series A due 2044
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.30%
Long-Term Debt	$ 475,000,000						475,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 4.150% 2015 Series A due 2045
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.15%
Long-Term Debt	$ 350,000,000						350,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 3.200% 2017 Series A due 2027
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 300,000,000						300,000,000
The Connecticut Light And Power Company | First Mortgage Notes | 2018 Series A First Mortgage Bonds Due 2048 [Member]
Debt Instrument [Line Items]
Long-Term Debt	$ 500,000,000						0
The Connecticut Light And Power Company | First Mortgage Notes | 4.000% 2018 Series A due 2048
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.00%
The Connecticut Light And Power Company | First Mortgage Notes | 4.375% Fixed Rate Tax Exempt due 2028
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.375%
NSTAR Electric Company
Debt Instrument [Line Items]
Long-Term Debt	$ 2,944,846,000						2,943,759,000
NSTAR Electric Company | NSTAR Gas 4.09% Series P First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)			4.09%
NSTAR Electric Company | Unsecured Debt
Debt Instrument [Line Items]
Long-Term Debt	2,400,000,000						2,400,000,000
Less Amounts due Within One Year	0						0
Unamortized Premiums and Discounts, Net	2,500,000						1,800,000
Unamortized Debt Issuance Costs	(17,700,000)						(19,400,000)
Long-term debt	$ 2,944,800,000						2,943,800,000
NSTAR Electric Company | Unsecured Debt | 5.750% due 2036
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.75%
Long-Term Debt	$ 200,000,000						200,000,000
NSTAR Electric Company | Unsecured Debt | 5.500% due 2040
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.50%
Long-Term Debt	$ 300,000,000						300,000,000
NSTAR Electric Company | Unsecured Debt | 2.375% due 2022
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.375%
Long-Term Debt	$ 400,000,000						400,000,000
NSTAR Electric Company | Unsecured Debt | 4.400% due 2044
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.40%
Long-Term Debt	$ 300,000,000						300,000,000
NSTAR Electric Company | Unsecured Debt | 3.250% due 2025
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.25%
Long-Term Debt	$ 250,000,000						250,000,000
NSTAR Electric Company | Unsecured Debt | 2.700% due 2026
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.70%
Long-Term Debt	$ 250,000,000						250,000,000
NSTAR Electric Company | Unsecured Debt | 3.200% due 2027
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 700,000,000						700,000,000
NSTAR Electric Company | Senior Notes
Debt Instrument [Line Items]
Long-Term Debt	$ 565,000,000						565,000,000
NSTAR Electric Company | Senior Notes | 5.900% Senior Notes Series B due 2034
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.90%
Long-Term Debt	$ 50,000,000						50,000,000
NSTAR Electric Company | Senior Notes | 6.700% Senior Notes Series D due 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.70%
Long-Term Debt	$ 40,000,000						40,000,000
NSTAR Electric Company | Senior Notes | 5.100% Senior Notes Series E due 2020
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.10%
Long-Term Debt	$ 95,000,000						95,000,000
NSTAR Electric Company | Senior Notes | 3.500% Senior Notes Series F due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.50%
Long-Term Debt	$ 250,000,000						250,000,000
NSTAR Electric Company | Senior Notes | 3.880% Senior Notes Series G due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.88%
Long-Term Debt	$ 80,000,000						80,000,000
NSTAR Electric Company | Senior Notes | 2.750% Senior Notes Series H due 2026
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.75%
Long-Term Debt	$ 50,000,000						50,000,000
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Long-Term Debt	655,173,000						892,438,000
Less Amounts due Within One Year	(150,000,000)						(110,000,000)
Public Service Company Of New Hampshire | 6.000% Series O due 2018
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)											6.00%
Public Service Company Of New Hampshire | First Mortgage Notes
Debt Instrument [Line Items]
Long-Term Debt	807,000,000						917,000,000
Less Amounts due Within One Year	(150,000,000)						(110,000,000)
Unamortized Premiums and Discounts, Net	0						(200,000)
Unamortized Debt Issuance Costs	(1,800,000)						(4,100,000)
Long-term debt	$ 655,200,000						892,400,000
Public Service Company Of New Hampshire | First Mortgage Notes | 5.600% Series M due 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	5.60%
Long-Term Debt	$ 50,000,000						50,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | 6.000% Series O due 2018
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	6.00%
Long-Term Debt	$ 0						110,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | 4.500% Series P due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.50%
Long-Term Debt	$ 150,000,000						150,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.05%
Long-Term Debt	$ 122,000,000						122,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | 3.200% Series R due 2021
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.20%
Long-Term Debt	$ 160,000,000						160,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | 3.500% Series S due 2023
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.50%
Long-Term Debt	$ 325,000,000						325,000,000
Public Service Company Of New Hampshire | First Mortgage Notes | Adjustable Rate Tax Exempt Series A Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-Term Debt	0						89,300,000
Yankee Gas Services Company | Yankee Gas 4.13% Series O First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)			4.13%
Yankee Gas Services Company | Yankee Gas 6.90% Series J First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)		6.90%
Commercial Paper
Debt Instrument [Line Items]
Commercial Paper Classified as Long-Term Debt	0						201,200,000
Commercial Paper | NSTAR Electric Company
Debt Instrument [Line Items]
Commercial Paper Classified as Long-Term Debt	$ 650,000,000
Minimum | First Mortgage Notes | Yankee Gas - First Mortgage Bonds: 3.020% - 8.480% due 2019 - 2048
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.02%
Minimum | First Mortgage Notes | NSTAR Gas - First Mortgage Bonds: 4.09% - 9.950% due 2020 - 2048
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.35%
Minimum | Unsecured Debt | 4.500% Debentures due 2019
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.50%
Minimum | Unsecured Debt | 2.500% - 4.250% Senior Notes due 2021 - 2029
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	2.50%
Minimum | Loans Payable | Unsecured Notes 3.570% - 6.430% due 2021 - 2037
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	3.57%
Minimum | Loans Payable | Secured Debt 4.100% - 9.640% due 2021 - 2035
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	4.10%
Parent Company
Debt Instrument [Line Items]
Long-Term Debt	$ 4,031,997,000						3,523,472,000
Less Amounts due Within One Year	(378,883,000)						$ (32,114,000)
Parent Company | Senior Notes | Eversource Parent 2.50% Series I Senior Notes (2)
Debt Instrument [Line Items]
Long-term debt	450,000,000
Parent Company | Commercial Paper
Debt Instrument [Line Items]
Less Amounts due Within One Year					$ (446,800,000)
Commercial Paper Classified as Long-Term Debt	$ 1,450,000,000					$ 201,200,000		$ 1,450,000,000

LONG-TERM DEBT - Schedule of Is

LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($)

1 Months Ended

12 Months Ended

Nov. 30, 2018

Oct. 31, 2018

Jan. 31, 2015

May 31, 2013

May 31, 2008

Dec. 31, 2001

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Sep. 30, 2018

Mar. 31, 2018

Jan. 31, 2018

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (1,050,330,000)

$ (745,000,000)

$ (200,000,000)

Senior Notes

Debt Instrument [Line Items]

Long-term debt

12,248,700,000

11,775,900,000

Senior Notes | Yankee Gas 4.13% Series O First Mortgage Bonds

Debt Instrument [Line Items]

Debt instruments, face amount

$ 50,000,000

Senior Notes | Yankee Gas 6.90% Series J First Mortgage Bonds

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (100,000,000)

Senior Notes | NSTAR Gas 4.09% Series P First Mortgage Bonds

Debt Instrument [Line Items]

Debt instruments, face amount

$ 100,000,000

The Connecticut Light And Power Company

Debt Instrument [Line Items]

Retirements of Long-Term Debt

(300,000,000)

(250,000,000)

0

The Connecticut Light And Power Company | Senior Notes | 2018 Series A First Mortgage Bonds Due 2048 [Member]

Debt Instrument [Line Items]

Debt instruments, face amount

$ 500,000,000

The Connecticut Light And Power Company | Senior Notes | 2008 Series A First Mortgage Bonds Due 2018 [Member]

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (300,000,000)

Public Service Company Of New Hampshire

Debt Instrument [Line Items]

Retirements of Long-Term Debt

(199,250,000)

(70,000,000)

0

Public Service Company Of New Hampshire | Senior Notes | 2008 Series O First Mortgage Bonds Due 2018 [Member]

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (89.3)

$ (110,000,000)

$ (89,300,000)

Parent Company

Debt Instrument [Line Items]

Retirements of Long-Term Debt

(450,000,000)

$ 0

$ 0

Parent Company | Senior Notes | Eversource Parent 2.50% Series I Senior Notes (2)

Debt Instrument [Line Items]

Debt instruments, face amount

400,000,000

$ 200,000,000

Long-term debt

450,000,000

Parent Company | Senior Notes | Series G Senior Notes Due 2018

Debt Instrument [Line Items]

Debt instruments, face amount

$ 500,000,000

$ 450,000,000

Parent Company | Senior Notes | Eversource Parent 1.60% Series G Senior Notes

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (150,000,000)

Parent Company | Senior Notes | Eversource Parent 1.45% Series E Senior Notes

Debt Instrument [Line Items]

Retirements of Long-Term Debt

$ (300,000,000)

LONG-TERM DEBT - Schedule of _2

LONG-TERM DEBT - Schedule of Long-term Debt Issuances and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2018
Debt Instrument [Line Items]
Repayments of debt		$ (1,050,330)	$ (745,000)	$ (200,000)
Eversource Parent 3.30% Series M Senior Notes
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)					3.30%
Eversource Parent 1.60% Series G Senior Notes (5)
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)	1.60%
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Repayments of debt		(300,000)	(250,000)	0
NSTAR Electric Company
Debt Instrument [Line Items]
Repayments of debt		$ 0	(400,000)	(200,000)
NSTAR Electric Company | Unsecured Debt | Unsecured Notes Due 2027
Debt Instrument [Line Items]
Interest rate stated percentage (up to) (as a percentage)		3.20%
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Repayments of debt		$ (199,250)	(70,000)	0
Parent Company
Debt Instrument [Line Items]
Repayments of debt		$ (450,000)	$ 0	$ 0
Parent Company | Senior Notes | Eversource Parent 1.60% Series G Senior Notes (5)
Debt Instrument [Line Items]
Repayments of debt	$ (150,000)

LONG-TERM DEBT - Schedule of _3

LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details) $ in Millions	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
2,019	$ 801.1
2,020	296.1
2,021	1,033.5
2,022	1,188.9
2,023	1,665.2
Thereafter	7,977.7
Total	12,962.5
The Connecticut Light And Power Company
Debt Instrument [Line Items]
2,019	250
2,020	0
2,021	0
2,022	0
2,023	400
Thereafter	2,615.3
Total	3,265.3
NSTAR Electric Company
Debt Instrument [Line Items]
2,019	0
2,020	95
2,021	250
2,022	400
2,023	80
Thereafter	2,140
Total	2,965
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
2,019	150
2,020	0
2,021	282
2,022	0
2,023	325
Thereafter	50
Total	$ 807

RATE REDUCTION BONDS AND VARI_3

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Narrative (Details) $ in Millions	May 08, 2018USD ($)
Debt Instrument [Line Items]
Weighted average interest rate	3.66%
Public Service Company Of New Hampshire | Rate Reduction Bonds
Debt Instrument [Line Items]
Amount of securitized rate reduction bonds issued	$ 635.7

RATE REDUCTION BONDS AND VARI_4

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 5,145,900	$ 5,239,300
Regulatory Liabilities	3,609,475	3,637,273
Accrued Interest (included in Other Current Liabilities)	823,006	738,222
Rate Reduction Bonds - Current Portion	52,332	0
Rate Reduction Bonds - Long-Term Portion	583,331	0
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	608,400	0
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	208,000	137,400
Public Service Company Of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	929,500	940,800
Regulatory Liabilities	428,069	444,397
Accrued Interest (included in Other Current Liabilities)	64,046	67,924
Rate Reduction Bonds - Current Portion	52,332	0
Rate Reduction Bonds - Long-Term Portion	583,331	0
Public Service Company Of New Hampshire | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)		0
Public Service Company Of New Hampshire | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	12,100	15,800
Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	608,400
Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	5,800
Accrued Interest (included in Other Current Liabilities)	14,400
Prepaid Expenses and Other Current Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash and Cash Equivalents	72,100	24,400
Prepaid Expenses and Other Current Assets | Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash and Cash Equivalents	47,500	500
Other Noncurrent Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash and Cash Equivalents	3,200	0
Other Noncurrent Assets | Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash and Cash Equivalents	$ 3,200	$ 0

RATE REDUCTION BONDS AND VARI_5

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 498,805	$ 421,755	$ 400,961
Public Service Company Of New Hampshire
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	60,634	$ 51,007	$ 50,040
Variable Interest Entity, Primary Beneficiary | Public Service Company Of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	27,300
Interest Expense on RRB Principal (included in Interest Expense)	$ 14,400

EMPLOYEE BENEFITS - Pension Pla

EMPLOYEE BENEFITS - Pension Plan Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Liability		$ 962,510	$ 1,228,091
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Increase in liability due to amendment in pension plan		465,000	390,000
Funded status of plan		$ (946,100)	(1,197,000)
Assumed rate of return		8.25%
Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		$ 8,100	(26,400)
Defined Benefit Plan, Increase in Discount Rate Resulting in Decrease in Liability		$ 88,000
Decrease in discount rate resulting in increase in liability			64,000
Taxable assets in equity securities (in percentage)		70.00%
Taxable assets in fixed income securities		30.00%
The Connecticut Light And Power Company
Defined Contribution Plan Disclosure [Line Items]
Liability		$ 282,771	354,469
The Connecticut Light And Power Company | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		(242,000)	(312,200)
The Connecticut Light And Power Company | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		(41,100)	(42,500)
Public Service Company Of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Liability		124,457	124,639
Public Service Company Of New Hampshire | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		(104,100)	(102,700)
Public Service Company Of New Hampshire | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		(20,700)	(22,100)
NSTAR Electric Company
Defined Contribution Plan Disclosure [Line Items]
Liability		14,145	89,995
NSTAR Electric Company | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		(14,400)	(90,200)
NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan		132,800	126,900
Other Current Liabilities
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan			8,900	$ 8,400
Other Noncurrent Assets | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Prepaid asset		33,400	13,100
Accrued Pension, SERP and PBOP | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Liability		$ 25,300	$ 39,500
Scenario, Forecast | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 112,000
Estimated future contributions in the next twelve months by other subsidiaries	46,000
Scenario, Forecast | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	11,000
Scenario, Forecast | The Connecticut Light And Power Company | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	44,000
Scenario, Forecast | Public Service Company Of New Hampshire | Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	10,000
Scenario, Forecast | NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 6,000

EMPLOYEE BENEFITS - Schedule of

EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	$ (5,936.5)	$ (5,242.3)
Service Cost	(84.8)	(71.3)	$ (75)
Interest Cost	(196.4)	(188)	(185.5)
Actuarial Gain/(Loss)	414.9	(548.7)
Benefits Paid - Pension	261.8	243.7
Benefits Paid - Lump Sum	14.2	18.4
Benefits Paid - SERP	6.8	20.4
Employee Transfers	0	0
Increase due to acquisition of Aquarion	0	(168.7)
Benefit Obligation as of End of Year	(5,520)	(5,936.5)	(5,242.3)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	4,739.5	4,076
Employer Contributions	185.6	235.2
Actual Return on Pension Plan Assets	(75.2)	589.7
Benefits Paid - Pension	(261.8)	(243.7)
Benefits Paid - Lump Sum	(14.2)	(18.4)
Employee Transfers	0	0
Increase due to acquisition of Aquarion	0	100.7
Fair Value of Pension Plan Assets as of End of Year	4,573.9	4,739.5	4,076
Funded Status as of December 31st	(946.1)	(1,197)
Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(948.6)	(810)
Service Cost	(10)	(9.5)	(12.2)
Interest Cost	(30.7)	(27.1)	(32.9)
Actuarial Gain/(Loss)	102.5	(81.8)
Benefits Paid - Pension	45.3	41.5
Employee Transfers	0	0
Increase due to acquisition of Aquarion	0	(61.7)
Benefit Obligation as of End of Year	(841.5)	(948.6)	(810)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	922.2	815.8
Employer Contributions	9.3	7.6
Actual Return on Pension Plan Assets	(36.6)	118
Benefits Paid - Pension	(45.3)	(41.5)
Employee Transfers	0	0
Increase due to acquisition of Aquarion	0	22.3
Fair Value of Pension Plan Assets as of End of Year	849.6	922.2	815.8
Funded Status as of December 31st	8.1	(26.4)
The Connecticut Light And Power Company | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,275.2)	(1,170.2)
Service Cost	(21.4)	(18.5)	(18.8)
Interest Cost	(41.8)	(41.6)	(41.6)
Actuarial Gain/(Loss)	106.1	(116.9)
Benefits Paid - Pension	59.6	63.5
Benefits Paid - Lump Sum	0	0
Benefits Paid - SERP	0.3	0.3
Employee Transfers	12	8.2
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(1,160.4)	(1,275.2)	(1,170.2)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	963	905.5
Employer Contributions	41.2	2.5
Actual Return on Pension Plan Assets	(14.2)	126.7
Benefits Paid - Pension	(59.6)	(63.5)
Benefits Paid - Lump Sum	0	0
Employee Transfers	(12)	(8.2)
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	918.4	963	905.5
Funded Status as of December 31st	(242)	(312.2)
The Connecticut Light And Power Company | Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(178.4)	(165)
Service Cost	(1.9)	(1.9)	(2)
Interest Cost	(5.8)	(5.3)	(5.3)
Actuarial Gain/(Loss)	14.4	(18.5)
Benefits Paid - Pension	10.1	9.9
Employee Transfers	(0.1)	2.4
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(161.7)	(178.4)	(165)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	135.9	129.2
Employer Contributions	0	0
Actual Return on Pension Plan Assets	(5.2)	18.1
Benefits Paid - Pension	(10.1)	(9.9)
Employee Transfers	0	1.5
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	120.6	135.9	129.2
Funded Status as of December 31st	(41.1)	(42.5)
NSTAR Electric Company | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,351)	(1,217.3)
Service Cost	(17.4)	(15.5)	(16.3)
Interest Cost	(43.5)	(42.7)	(42.2)
Actuarial Gain/(Loss)	98.6	(143.5)
Benefits Paid - Pension	66.9	55.4
Benefits Paid - Lump Sum	7.1	6.8
Benefits Paid - SERP	0.3	0.3
Employee Transfers	2.5	5.5
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(1,236.5)	(1,351)	(1,217.3)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	1,260.8	1,088.3
Employer Contributions	56.5	85.4
Actual Return on Pension Plan Assets	(18.7)	154.8
Benefits Paid - Pension	(66.9)	(55.4)
Benefits Paid - Lump Sum	(7.1)	(6.8)
Employee Transfers	(2.5)	(5.5)
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	1,222.1	1,260.8	1,088.3
Funded Status as of December 31st	(14.4)	(90.2)
NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(278.6)	(270)
Service Cost	(2)	(1.7)	(3.4)
Interest Cost	(8.7)	(8.7)	(13.3)
Actuarial Gain/(Loss)	28.4	(13.2)
Benefits Paid - Pension	14.5	13.5
Employee Transfers	0.1	1.5
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(246.3)	(278.6)	(270)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	405.5	361.6
Employer Contributions	5.2	5.3
Actual Return on Pension Plan Assets	(17.4)	52.9
Benefits Paid - Pension	(14.5)	(13.5)
Employee Transfers	(0.3)	0.8
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	379.1	405.5	361.6
Funded Status as of December 31st	132.8	126.9
Public Service Company Of New Hampshire | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(642.2)	(572.2)
Service Cost	(11.2)	(9.7)	(9.9)
Interest Cost	(22)	(21.2)	(20.7)
Actuarial Gain/(Loss)	39.2	(65.1)
Benefits Paid - Pension	26.2	26.4
Benefits Paid - Lump Sum	0	0
Benefits Paid - SERP	0.2	0.3
Employee Transfers	(0.9)	(0.7)
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(610.7)	(642.2)	(572.2)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	539.5	494
Employer Contributions	0	0.8
Actual Return on Pension Plan Assets	(7.6)	70.4
Benefits Paid - Pension	(26.2)	(26.4)
Benefits Paid - Lump Sum	0	0
Employee Transfers	0.9	0.7
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	506.6	539.5	494
Funded Status as of December 31st	(104.1)	(102.7)
Public Service Company Of New Hampshire | Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(101.1)	(89.7)
Service Cost	(1.1)	(1.3)	(1.3)
Interest Cost	(3.4)	(3)	(2.9)
Actuarial Gain/(Loss)	8.6	(11.9)
Benefits Paid - Pension	4.9	4.6
Employee Transfers	0.2	0.2
Increase due to acquisition of Aquarion	0	0
Benefit Obligation as of End of Year	(91.9)	(101.1)	(89.7)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of Beginning of Year	79	73.2
Employer Contributions	0	0
Actual Return on Pension Plan Assets	(2.9)	10.4
Benefits Paid - Pension	(4.9)	(4.6)
Employee Transfers	0	0
Increase due to acquisition of Aquarion	0	0
Fair Value of Pension Plan Assets as of End of Year	71.2	79	$ 73.2
Funded Status as of December 31st	$ (20.7)	$ (22.1)

EMPLOYEE BENEFITS - Schedule _2

EMPLOYEE BENEFITS - Schedule of Funded Status (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 5,070.8	$ 5,583.6
The Connecticut Light And Power Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,031	1,179.2
NSTAR Electric Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,144.7	1,260.1
Public Service Company Of New Hampshire
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 543.1	$ 597.2

EMPLOYEE BENEFITS - Schedule _3

EMPLOYEE BENEFITS - Schedule of Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.22%	3.43%
Compensation/Progression Rate	3.50%	3.50%
Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.45%	3.75%
Compensation/Progression Rate		4.00%
Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.38%	3.55%
Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.41%	3.70%
Pre-65 Plan | Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Health Care Trend Rate, Percentage		3.50%
Pre-65 Plan | Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Health Care Trend Rate, Percentage	6.75%
Post-65 Plan | Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Health Care Trend Rate, Percentage	3.50%
Post-65 Plan | Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Health Care Trend Rate, Percentage	5.00%

EMPLOYEE BENEFITS - Schedule _4

EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 84.8	$ 71.3	$ 75
Interest Cost	196.4	188	185.5
Expected Return on Pension Plan Assets	(391.6)	(334.1)	(317.9)
Actuarial Loss	145.7	135.2	125.7
Prior Service Cost	4.3	4.5	3.6
Total Net Periodic Benefit Income	39.6	64.9	71.9
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	10	9.5	12.2
Interest Cost	30.7	27.1	32.9
Expected Return on Pension Plan Assets	(72.4)	(63.7)	(62.9)
Actuarial Loss	10.3	9.1	9
Prior Service Cost	(23.6)	(21.6)	(9.1)
Total Net Periodic Benefit Income	(45)	(39.6)	(17.9)
The Connecticut Light And Power Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	21.4	18.5	18.8
Interest Cost	41.8	41.6	41.6
Expected Return on Pension Plan Assets	(79.1)	(71.7)	(72.1)
Actuarial Loss	29.1	27.7	25.4
Prior Service Cost	1.1	1.5	1.5
Total Net Periodic Benefit Income	14.3	17.6	15.2
Intercompany Allocations	6.1	9.8	13.8
The Connecticut Light And Power Company | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1.9	1.9	2
Interest Cost	5.8	5.3	5.3
Expected Return on Pension Plan Assets	(10.4)	(9.7)	(10.1)
Actuarial Loss	1.6	1	1.5
Prior Service Cost	1.1	1.1	0.5
Total Net Periodic Benefit Income	0	(0.4)	(0.8)
Intercompany Allocations	(1)	0.7	0.3
NSTAR Electric Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	17.4	15.5	16.3
Interest Cost	43.5	42.7	42.2
Expected Return on Pension Plan Assets	(104.9)	(87.6)	(85.1)
Actuarial Loss	41.1	41.1	39.9
Prior Service Cost	0.2	0.6	0.3
Total Net Periodic Benefit Income	(2.7)	12.3	13.6
Intercompany Allocations	6.5	9.1	11.4
NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2	1.7	3.4
Interest Cost	8.7	8.7	13.3
Expected Return on Pension Plan Assets	(32.5)	(28.6)	(28.1)
Actuarial Loss	2.3	3.4	3.3
Prior Service Cost	(16.9)	(17)	(7.1)
Total Net Periodic Benefit Income	(36.4)	(31.8)	(15.2)
Intercompany Allocations	(1.3)	1.1	(0.1)
Public Service Company Of New Hampshire | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	11.2	9.7	9.9
Interest Cost	22	21.2	20.7
Expected Return on Pension Plan Assets	(43.6)	(40)	(38.6)
Actuarial Loss	11.6	11.6	9.9
Prior Service Cost	0.4	0.5	0.5
Total Net Periodic Benefit Income	1.6	3	2.4
Intercompany Allocations	1.9	3.3	4
Public Service Company Of New Hampshire | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1.1	1.3	1.3
Interest Cost	3.4	3	2.9
Expected Return on Pension Plan Assets	(6)	(5.5)	(5.5)
Actuarial Loss	0.7	0.6	0.7
Prior Service Cost	0.5	0.6	0.2
Total Net Periodic Benefit Income	(0.3)	0	(0.4)
Intercompany Allocations	$ 0.4	$ 0.5	$ (0.1)

EMPLOYEE BENEFITS - Schedule _5

EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	7.00%
Expected Long-Term Rate of Return (in percentage)	7.00%
Compensation/Progression Rate (in percentage)	4.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percentage)		8.25%	8.25%
Compensation/Progression Rate (in percentage)		3.50%	3.50%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percentage)		8.25%	8.25%
Minimum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.85%	3.20%	3.27%
Expected Long-Term Rate of Return (in percentage)	8.25%
Compensation/Progression Rate (in percentage)	3.50%
Minimum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.28%	3.48%	2.88%
Expected Long-Term Rate of Return (in percentage)	8.25%
Maximum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	4.62%	3.90%	4.89%
Maximum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.94%	4.64%	4.09%

EMPLOYEE BENEFITS - Summary of

EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
OCI
Prior Service Costs Securitized as Stranded Costs		$ 0
Pension Plan
Net Regulatory Assets [Abstract]
Actuarial Losses Arising During the Year	$ 48.6	333
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(140.1)	(129.5)
Unamortized Securitized Stranded Costs	(36.7)	0
Prior Service Cost/(Credit) Arising During the Year	0	1
Prior Service Cost Reclassified as Net Periodic Benefit Expense	(3.9)	(4.1)
Actuarial Loss	1,807.6	1,935.8
Prior Service Cost	6.3	10.3
Expected Actuarial Loss Expense	140.6
Expected Prior Service Cost Expense	0.9
OCI
Actuarial Losses Arising During the Year	0.7	9.3
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(5.6)	(5.7)
Prior Service Cost Reclassified as Net Periodic Benefit Expense	0	0
Prior Service (Credit)/Cost Arising During the Year	0	(0.4)
Prior Service Cost Reclassified as Net Periodic Benefit Expense	0.4	0.4
Prior Service Costs Securitized as Stranded Costs	(0.1)	0
Actuarial Loss	80.8	85.7
Prior Service Cost	1.1	1.5
Actuarial Loss	5.6
Prior Service Cost	0.2
Other Postretirement Benefits Plan
Net Regulatory Assets [Abstract]
Actuarial Losses Arising During the Year	6.4	44.8
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(9.9)	(8.6)
Prior Service Cost/(Credit) Arising During the Year	1.3	(4)
Prior Service Cost Reclassified as Net Periodic Benefit Expense	(23.6)	(22.3)
Actuarial Loss	207.3	211.6
Prior Service Cost	(197.6)	(221.2)
Expected Actuarial Loss Expense	9.9
Expected Prior Service Cost Expense	(23.6)
OCI
Actuarial Losses Arising During the Year	1.2	(2.6)
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(0.4)	(0.5)
Prior Service Cost Reclassified as Net Periodic Benefit Expense	0	0.7
Prior Service (Credit)/Cost Arising During the Year	0	(0.1)
Prior Service Costs Securitized as Stranded Costs	(1.3)
Actuarial Loss	5	6.6
Prior Service Cost	2.6	2.6
Actuarial Loss	0.3
Prior Service Cost	0.2
Actuarial Gain (Loss) Securitized Stranded Costs, Regulatory Assets	(0.8)	0
Other Comprehensive Income, Defined Benefit Plan, Actuarial Losses Securitized Stranded Cost	$ 0	$ 0

EMPLOYEE BENEFITS - Schedule _6

EMPLOYEE BENEFITS - Schedule of Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2018USD ($)
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
2,019	$ 308.5
2,020	310.4
2,021	318.8
2,022	326.6
2,023	335.6
2023-2027	1,764.1
Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
2,019	58.4
2,020	58.5
2,021	58.6
2,022	58.3
2,023	57.8
2023-2027	$ 277.4

EMPLOYEE BENEFITS - Schedule _7

EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Long-term rate for Aquarion plans	0.07
Defined Benefit Plan, Equity Securities, US
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	21.50%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.50%	8.50%
Defined Benefit Plan, Debt Security, Public High Yield Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	6.50%	6.50%
Defined Benefit Plan, Debt Security, Private Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	9.00%	9.00%
Defined Benefit Plan, Debt Security, Emerging Markets Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	0.00%	2.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	0.00%	6.50%
Defined Benefit Plan, Equity Securities, Emerging Markets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.50%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	10.00%	10.00%
Fixed Income Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	13.00%	11.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	4.00%	4.00%
Defined Benefit Plan, Equity Securities, Global
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	10.00%	0.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.75%	0.00%
Defined Benefit Plan, Equity Securities, Non-US
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	8.00%	11.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	8.50%	8.50%
Private Equity
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	12.00%	12.00%
Real Assets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	16.00%	12.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	7.50%	7.50%
Hedge Funds
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	0.00%	4.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	0.00%	6.00%

EMPLOYEE BENEFITS - Schedule _8

EMPLOYEE BENEFITS - Schedule of Asset category (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 4,573.9	$ 4,739.5	$ 4,076
Uncategorized	4,046.4	4,053.3
Pension Plan | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,821.2	2,188.7
Uncategorized	1,377.8	1,653.3
Pension Plan | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,511.8	1,490.8
Uncategorized	1,265.5	1,218.3
Pension Plan | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	840.1	653
Uncategorized	834	641.8
Pension Plan | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	632	641.5
Uncategorized	569.1	539.9
Pension Plan | Total Assets Before 401
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	4,805.1	4,974
Pension Plan | 401 PBOP Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	(231.2)	(234.5)
Pension Plan | Fair Value, Inputs, Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	597.9	704.8
Pension Plan | Fair Value, Inputs, Level 1 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	443.4	535.4
Pension Plan | Fair Value, Inputs, Level 1 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	85.5	56.6
Pension Plan | Fair Value, Inputs, Level 1 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	6.1	11.2
Pension Plan | Fair Value, Inputs, Level 1 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	62.9	101.6
Pension Plan | Fair Value, Inputs, Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	160.8	215.9
Pension Plan | Fair Value, Inputs, Level 2 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan | Fair Value, Inputs, Level 2 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	160.8	215.9
Pension Plan | Fair Value, Inputs, Level 2 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan | Fair Value, Inputs, Level 2 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	849.6	922.2	$ 815.8
Uncategorized	436.7	482.6
Other Postretirement Benefits Plan | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	302.4	357.2
Uncategorized	210.5	241.9
Other Postretirement Benefits Plan | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	185.3	201.3
Uncategorized	123	133.9
Other Postretirement Benefits Plan | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	32.7	31.3
Uncategorized	32.7	31.3
Other Postretirement Benefits Plan | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	98	97.9
Uncategorized	70.5	75.5
Other Postretirement Benefits Plan | Total Assets Before 401
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	618.4	687.7
Other Postretirement Benefits Plan | 401 PBOP Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	231.2	234.5
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	141.4	161.1
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	91.9	115.3
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	22	23.4
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	27.5	22.4
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	40.3	44
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	40.3	44
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 0	$ 0

EMPLOYEE BENEFITS - Defined Con

EMPLOYEE BENEFITS - Defined Contribution Plan Narrative (Details)	12 Months Ended
	Dec. 31, 2018
Defined Contribution Plan, 401K
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution (as a percentage)	100.00%
Percentage of employees' pay (up to)	3.00%
Defined Contribution Plan, Alternate Contribution 401K
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution (as a percentage)	50.00%
Percentage of employees' pay (up to)	8.00%

EMPLOYEE BENEFITS - Schedule _9

EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 38.4	$ 34.5	$ 31.8
The Connecticut Light And Power Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	5	4.6	4.5
NSTAR Electric Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	9.7	8.5	8.1
Public Service Company Of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 3.3	$ 3.7	$ 3.4

EMPLOYEE BENEFITS - Schedule_10

EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	$ 49.1	$ 53.4	$ 54.2
Other Retirement Benefits Expense	2.7	2.8	2.9
The Connecticut Light And Power Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.3	0.3	0.3
Other Retirement Benefits Expense	1.1	1	1.1
NSTAR Electric Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.1	0.1	0.1
Other Retirement Benefits Expense	1.1	1	0.9
Public Service Company Of New Hampshire
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	1.7	1.9	2
Other Retirement Benefits Expense	$ 0.4	$ 0.5	$ 0.6

SHARE-BASED PAYMENTS - Narrativ

SHARE-BASED PAYMENTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted in incentive plan (up to) (in shares)	6,700,000
Shares available for issuance under incentive plan (in shares)	3,720,650	2,445,110
Shares outstanding (in shares)	424,119
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 56.72
Total unrecognized compensation expense	$ 22.3
Tax effect on total share-based payments (in percentage)	25.00%
Excess tax benefit	$ 1.5	$ 2.9	$ 19.1
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 56.69	$ 55.97	$ 54.67
Shares outstanding (in shares)		388,269
Weighted average shares outstanding (in dollars per share)	$ 56.57	$ 56.15
Restricted stock units available (in shares)	216,572
Restricted stock unit fully vested (in shares)	358,246
Additional restricted stock unit expected to vest (in shares)	402,913
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 56.77	$ 55.70	$ 53.64
Shares outstanding (in shares)	366,995	331,207
Weighted average shares outstanding (in dollars per share)	$ 56.17	$ 55.79
Restricted stock units available (in shares)	131,349
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 56.08
Restricted stock unit fully vested (in shares)	132,569
The Connecticut Light And Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 8.1
Period for recognition (in years)	1 year 8 months 23 days
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 8
Period for recognition (in years)	1 year 8 months 19 days
Public Service Company Of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 2.8
Period for recognition (in years)	1 year 8 months 19 days
Eversource
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition (in years)	1 year 8 months 23 days
Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	3 years
Board Members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period of graded vesting schedule under long-term incentive program	1 year

SHARE-BASED PAYMENTS - Eversour

SHARE-BASED PAYMENTS - Eversource Incentve Plan (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	717,039
Granted (in shares)	286,315
Shares issued (in shares)	(201,386)
Forfeited (in shares)	(19,603)
Ending balance (in shares)	782,365	717,039
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance (in dollars per share)	$ 49.29
Granted (in dollars per share)	56.69	$ 55.97	$ 54.67
Shares issued (in dollars per share)	55.35
Forfeited (in dollars per share)	56.78
Ending balance (in dollars per share)	$ 50.25	$ 49.29
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	510,565
Granted (in shares)	184,355
Shares issued (in shares)	(178,258)
Forfeited (in shares)	(17,098)
Ending balance (in shares)	499,564	510,565
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance (in dollars per share)	$ 55.45
Granted (in dollars per share)	56.77	$ 55.70	$ 53.64
Shares issued (in dollars per share)	54.98
Forfeited (in dollars per share)	56.18
Ending balance (in dollars per share)	$ 56.08	$ 55.45

SHARE-BASED PAYMENTS - Schedule

SHARE-BASED PAYMENTS - Schedule of Compensation Expense and Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 21.4	$ 19.7	$ 23.6
Future Income Tax Benefit	5.4	8	9.6
The Connecticut Light And Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	7.8	7	9.1
Future Income Tax Benefit	2	2.9	3.7
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	7.7	7	8.2
Future Income Tax Benefit	1.9	2.8	3.3
Public Service Company Of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	2.9	3.2	3.5
Future Income Tax Benefit	$ 0.7	$ 1.3	$ 1.4

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - State and Local Jurisdiction - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Valuation allowance for tax credit and operating loss carryforward	$ 19.5	$ 14.4
Eversource
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	5.2	9.9
The Connecticut Light And Power Company
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	$ 4.4	$ 1.8

INCOME TAXES - Components of In

INCOME TAXES - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Income Taxes:
Federal	$ 106,500	$ 58,900	$ 38,900
State	10,600	31,600	53,000
Total Current	117,100	90,500	91,900
Deferred Income Taxes, Net:
Federal	122,600	433,000	427,900
State	52,200	58,600	38,600
Total Deferred	174,812	491,630	466,463
Investment Tax Credits, Net	(2,900)	(3,200)	(3,400)
Income Tax Expense	288,972	578,892	554,997
The Connecticut Light And Power Company
Current Income Taxes:
Federal	54,200	50,900	27,300
State	20,900	17,400	13,300
Total Current	75,100	68,300	40,600
Deferred Income Taxes, Net:
Federal	48,500	123,900	157,600
State	6,400	(4,600)	11,300
Total Deferred	54,859	119,295	168,919
Investment Tax Credits, Net	(900)	(1,000)	(1,200)
Income Tax Expense	129,056	186,646	208,308
NSTAR Electric Company
Current Income Taxes:
Federal	79,300	107,800	86,400
State	30,000	25,600	39,500
Total Current	109,300	133,400	125,900
Deferred Income Taxes, Net:
Federal	27,900	88,100	96,600
State	13,500	22,400	5,100
Total Deferred	41,438	110,499	101,698
Investment Tax Credits, Net	(1,800)	(1,800)	(1,800)
Income Tax Expense	148,906	242,085	225,789
Public Service Company Of New Hampshire
Current Income Taxes:
Federal	12,200	18,600	(13,700)
State	(500)	6,200	8,800
Total Current	11,700	24,800	(4,900)
Deferred Income Taxes, Net:
Federal	15,400	52,700	79,500
State	20,500	11,200	7,800
Total Deferred	35,924	63,883	87,345
Investment Tax Credits, Net	0	0	0
Income Tax Expense	$ 47,576	$ 88,675	$ 82,364

INCOME TAXES - Reconciliation B

INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 1,329,491	$ 1,574,407	$ 1,504,818
Federal tax expense (in percentage)	21.00%	35.00%	35.00%
Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016	$ 279,200	$ 551,000	$ 526,700
Tax Effect of Differences:
Depreciation	(30,800)	(10,800)	(3,400)
Investment Tax Credit Amortization	(2,900)	(3,200)	(3,400)
Other Federal Tax Credits	0	0	(3,500)
State Income Taxes, Net of Federal Impact	44,400	47,700	56,200
Dividends on ESOP	(5,100)	(8,400)	(8,400)
Tax Asset Valuation Allowance/Reserve Adjustments	5,200	7,000	3,300
Excess Stock Benefit	(1,500)	(2,900)	(19,100)
Other, Net	500	(1,500)	6,600
Income Tax Expense	$ 288,972	$ 578,892	$ 554,997
Effective Tax Rate	21.70%	36.80%	36.90%
The Connecticut Light And Power Company
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 506,773	$ 563,372	$ 542,562
Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016	106,400	197,200	189,900
Tax Effect of Differences:
Depreciation	(1,200)	(5,200)	1,600
Investment Tax Credit Amortization	(900)	(1,000)	(1,200)
Other Federal Tax Credits	0	0	0
State Income Taxes, Net of Federal Impact	14,500	4,500	14,500
Tax Asset Valuation Allowance/Reserve Adjustments	7,100	(9,500)	1,500
Excess Stock Benefit	(100)	(700)	(900)
Other, Net	3,300	1,300	2,900
Income Tax Expense	$ 129,056	$ 186,646	$ 208,308
Effective Tax Rate	25.50%	33.10%	38.40%
NSTAR Electric Company
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 531,996	$ 616,811	$ 576,566
Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016	111,700	215,900	201,800
Tax Effect of Differences:
Depreciation	(2,800)	(3,000)	(3,100)
Investment Tax Credit Amortization	(1,800)	(1,800)	(1,800)
Other Federal Tax Credits	0	0	0
State Income Taxes, Net of Federal Impact	33,200	31,200	29,000
Tax Asset Valuation Allowance/Reserve Adjustments	1,200	0	0
Excess Stock Benefit	(100)	(700)	(1,200)
Other, Net	7,500	500	1,100
Income Tax Expense	$ 148,906	$ 242,085	$ 225,789
Effective Tax Rate	28.00%	39.20%	39.20%
Public Service Company Of New Hampshire
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 163,452	$ 224,671	$ 214,349
Statutory Federal Income Tax Expense at 21% in 2018 and 35% in 2017 and 2016	34,300	78,600	75,000
Tax Effect of Differences:
Depreciation	100	1,100	1,000
Investment Tax Credit Amortization	0	0	0
Other Federal Tax Credits	0	0	(3,500)
State Income Taxes, Net of Federal Impact	15,800	11,300	10,800
Tax Asset Valuation Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit	(100)	(300)	(400)
Other, Net	(2,500)	(2,000)	(500)
Income Tax Expense	$ 47,576	$ 88,675	$ 82,364
Effective Tax Rate	29.10%	39.50%	38.40%

INCOME TAXES - Temporary Differ

INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets:
Employee Benefits	$ 388.2	$ 442.1
Derivative Liabilities	111.4	111.8
Regulatory Deferrals - Liabilities	299.3	205.6
Allowance for Uncollectible Accounts	54	50.1
Tax Effect - Tax Regulatory Liabilities	830.3	832.6
Federal Net Operating Loss Carryforwards	28.5	47.8
Purchase Accounting Adjustment	64.2	69.9
Other	166.2	149.5
Total Deferred Tax Assets	1,942.1	1,909.4
Less: Valuation Allowance	19.5	14.6
Net Deferred Tax Assets	1,922.6	1,894.8
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	3,724.2	3,562
Property Tax Accruals	73.2	56.7
Regulatory Amounts:
Regulatory Deferrals - Assets	1,025.9	924.9
Tax Effect - Tax Regulatory Assets	238.9	243.1
Goodwill Regulatory Asset - 1999 Merger	95.2	99.8
Derivative Assets	20.1	17.4
Other	251.1	288.4
Total Deferred Tax Liabilities	5,428.6	5,192.3
Regulatory Liabilities	3,979.7	3,765.4
Refunds to customers	5
The Connecticut Light And Power Company
Deferred Tax Assets:
Employee Benefits	94.5	112.3
Derivative Liabilities	111.4	110.5
Regulatory Deferrals - Liabilities	38.6	12
Allowance for Uncollectible Accounts	23.1	20.6
Tax Effect - Tax Regulatory Liabilities	336.8	337.2
Federal Net Operating Loss Carryforwards	0	0
Purchase Accounting Adjustment	0	0
Other	81.1	70.7
Total Deferred Tax Assets	685.5	663.3
Less: Valuation Allowance	10.7	6.3
Net Deferred Tax Assets	674.8	657
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	1,293.3	1,224.9
Property Tax Accruals	35.4	20.7
Regulatory Amounts:
Regulatory Deferrals - Assets	320.1	310.6
Tax Effect - Tax Regulatory Assets	167	173.1
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	19.9	17.4
Other	5.9	13.7
Total Deferred Tax Liabilities	1,841.6	1,760.4
Regulatory Liabilities	1,231.8	1,151.1
NSTAR Electric Company
Deferred Tax Assets:
Employee Benefits	35	34
Derivative Liabilities	0	0.3
Regulatory Deferrals - Liabilities	195.5	139.8
Allowance for Uncollectible Accounts	17.8	17.3
Tax Effect - Tax Regulatory Liabilities	288.9	281.2
Federal Net Operating Loss Carryforwards	0	0
Purchase Accounting Adjustment	0	0
Other	15.6	4.9
Total Deferred Tax Assets	552.8	477.5
Less: Valuation Allowance	0	0
Net Deferred Tax Assets	552.8	477.5
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	1,342.4	1,229.2
Property Tax Accruals	26.3	24.2
Regulatory Amounts:
Regulatory Deferrals - Assets	277.4	267.1
Tax Effect - Tax Regulatory Assets	9.7	9.8
Goodwill Regulatory Asset - 1999 Merger	81.7	85.7
Derivative Assets	0	0
Other	109.8	137.3
Total Deferred Tax Liabilities	1,847.3	1,753.3
Regulatory Liabilities	1,703.9	1,594.1
Public Service Company Of New Hampshire
Deferred Tax Assets:
Employee Benefits	31.1	38
Derivative Liabilities	0	0
Regulatory Deferrals - Liabilities	16.1	17.9
Allowance for Uncollectible Accounts	3	2.9
Tax Effect - Tax Regulatory Liabilities	111.7	116.8
Federal Net Operating Loss Carryforwards	0.6	0
Purchase Accounting Adjustment	0	0
Other	33.4	49.6
Total Deferred Tax Assets	195.9	225.2
Less: Valuation Allowance	0	0
Net Deferred Tax Assets	195.9	225.2
Deferred Tax Liabilities:
Accelerated Depreciation and Other Plant-Related Differences	410.6	502.5
Property Tax Accruals	5.2	5.5
Regulatory Amounts:
Regulatory Deferrals - Assets	213.8	103.6
Tax Effect - Tax Regulatory Assets	8.1	11.4
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	0	0
Other	39.4	45.7
Total Deferred Tax Liabilities	677.1	668.7
Regulatory Liabilities	483.6	$ 450.7
Refunds to customers	4.4
Yankee Gas Services Company
Regulatory Amounts:
Refunds to customers	$ 0.6

INCOME TAXES - Tax Credits and

INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	$ 103.6	$ 197.3
Federal and State Charitable Contribution	2.2	18.7
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	148.9	139
Federal and State Charitable Contribution	9.6	31.4
Operating Loss Carryforwards	80.7	82.8
The Connecticut Light And Power Company | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
The Connecticut Light And Power Company | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	107	94.5
Federal and State Charitable Contribution	0	0
Operating Loss Carryforwards	0	0
NSTAR Electric Company | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
NSTAR Electric Company | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Operating Loss Carryforwards	0	0
Public Service Company Of New Hampshire | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Public Service Company Of New Hampshire | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
Federal and State Charitable Contribution	0	0
Operating Loss Carryforwards	$ 0	$ 0

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	$ 51.7	$ 48.4	$ 48
Gross Increases - Current Year	9.2	11.4	9.9
Gross Decreases - Prior Year		(0.9)	(0.2)
Gross Decreases - Prior Year	(6.5)
Lapse of Statute of Limitations	(8.5)	(7.2)	(9.7)
Ending Balance	45.9	51.7	48.4
The Connecticut Light And Power Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	18.1	15.3	13.5
Gross Increases - Current Year	3.2	4.7	3.9
Gross Decreases - Prior Year		(0.5)	(0.2)
Gross Decreases - Prior Year	(0.9)
Lapse of Statute of Limitations	(2.2)	(1.4)	(2.3)
Ending Balance	$ 18.2	$ 18.1	$ 15.3

INCOME TAXES - Interest Expense

INCOME TAXES - Interest Expense and Accrued Interest Payable on Uncertain Tax Positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Other Interest Expense/(Income)	$ (1.7)	$ 0	$ (0.2)
Accrued Interest Expense	$ 0.1	$ 1.8

INCOME TAXES - Open Tax Year (D

INCOME TAXES - Open Tax Year (Details)	12 Months Ended
	Dec. 31, 2018
Federal
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,018
Connecticut | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,015
Connecticut | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,018
Massachusetts | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,015
Massachusetts | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,018
New Hampshire | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,016
New Hampshire | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2,018

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	$ 54.9	$ 65.8
Additions	23.5	6.2
Payments/Reductions	(13.7)	(17.1)
Accrual for Environmental Loss Contingencies, Ending Balance	64.7	54.9
The Connecticut Light And Power Company
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	4.7	4.9
Additions	1.9	0.5
Payments/Reductions	(1.2)	(0.7)
Accrual for Environmental Loss Contingencies, Ending Balance	5.4	4.7
NSTAR Electric Company
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	2.7	3.8
Additions	9.7	1.8
Payments/Reductions	(1.5)	(2.9)
Accrual for Environmental Loss Contingencies, Ending Balance	10.9	2.7
Public Service Company Of New Hampshire
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	5.7	5.3
Additions	0	1
Payments/Reductions	(0.3)	(0.6)
Accrual for Environmental Loss Contingencies, Ending Balance	$ 5.4	$ 5.7

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)site	Dec. 31, 2017USD ($)site	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Number of Sites | site	60	59
Reserve | $	$ 64.7	$ 54.9	$ 65.8
The Connecticut Light And Power Company
Loss Contingencies [Line Items]
Number of Sites | site	15	14
Reserve | $	$ 5.4	$ 4.7	4.9
NSTAR Electric Company
Loss Contingencies [Line Items]
Number of Sites | site	16	15
Reserve | $	$ 10.9	$ 2.7	3.8
Public Service Company Of New Hampshire
Loss Contingencies [Line Items]
Number of Sites | site	9	10
Reserve | $	$ 5.4	$ 5.7	$ 5.3

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)site	Dec. 31, 2017USD ($)site	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Number of Sites | site	60	59
Reserve	$ 64.7	$ 54.9	$ 65.8
The Connecticut Light And Power Company
Loss Contingencies [Line Items]
Number of Sites | site	15	14
Reserve	$ 5.4	$ 4.7	4.9
NSTAR Electric Company
Loss Contingencies [Line Items]
Number of Sites | site	16	15
Reserve	$ 10.9	$ 2.7	3.8
Public Service Company Of New Hampshire
Loss Contingencies [Line Items]
Number of Sites | site	9	10
Reserve	$ 5.4	$ 5.7	$ 5.3
MGP Site accrual
Loss Contingencies [Line Items]
Reserve balances related to former MGP sites	$ 50.1	$ 49
Environmental Sites for Which a Range of Loss Exists
Loss Contingencies [Line Items]
Number of Sites | site	7
Reserve	$ 23.8
Best estimate of potential remediation costs (up to)	$ 20
Environmental Sites for Which a Range of Loss Exists | The Connecticut Light And Power Company
Loss Contingencies [Line Items]
Number of Sites | site	2
Reserve	$ 0.7
Best estimate of potential remediation costs (up to)	$ 1
Environmental Site for Which a Range is Too Early to Determine
Loss Contingencies [Line Items]
Number of Sites | site	12
Reserve	$ 11.1
Environmental Site for Which a Range is Too Early to Determine | The Connecticut Light And Power Company
Loss Contingencies [Line Items]
Number of Sites | site	4
Reserve	$ 1.9
Environmental Site for Which a Range is Too Early to Determine | NSTAR Electric Company
Loss Contingencies [Line Items]
Number of Sites | site	3
Reserve	$ 1.9
Evironmental Sites with Best Estimate
Loss Contingencies [Line Items]
Number of Sites | site	41
Reserve	$ 29.8
Evironmental Sites with Best Estimate | The Connecticut Light And Power Company
Loss Contingencies [Line Items]
Reserve	$ 2.8
Environmental site quantity remaining | site	9
Evironmental Sites with Best Estimate | NSTAR Electric Company
Loss Contingencies [Line Items]
Reserve	$ 9
Environmental site quantity remaining | site	13
Evironmental Sites with Best Estimate | Public Service Company Of New Hampshire
Loss Contingencies [Line Items]
Reserve	$ 5.4
Environmental site quantity remaining | site	9

COMMITMENTS AND CONTINGENCIES_4

COMMITMENTS AND CONTINGENCIES - Schedule of Estimated Future Annual Costs of Long term Contractual Agreement (Details) $ in Millions	Dec. 31, 2018USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	$ 609.2
2,020	607.9
2,021	528.7
2,022	494.1
2,023	461.7
Thereafter	2,905.9
Total	5,607.5
Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	68.3
2,020	73.5
2,021	69.1
2,022	72.9
2,023	74.1
Thereafter	142.9
Total	500.8
Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	262.4
2,020	261
2,021	238.9
2,022	240.5
2,023	217.2
Thereafter	1,662
Total	2,882
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	11.9
2,020	22.6
2,021	21.9
2,022	15.3
2,023	17.5
Thereafter	43.5
Total	132.7
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	243.8
2,020	227.7
2,021	183.6
2,022	149.2
2,023	135.1
Thereafter	1,039.7
Total	1,979.1
Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	22.8
2,020	23.1
2,021	15.2
2,022	16.2
2,023	17.8
Thereafter	17.8
Total	112.9
The Connecticut Light And Power Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	179.9
2,020	205.2
2,021	197.2
2,022	195.7
2,023	200.4
Thereafter	959.7
Total	1,938.1
The Connecticut Light And Power Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	57
2,020	69.7
2,021	65.3
2,022	69.1
2,023	70.4
Thereafter	123.9
Total	455.4
The Connecticut Light And Power Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	102
2,020	103.8
2,021	104
2,022	104.9
2,023	105.5
Thereafter	785.3
Total	1,305.5
The Connecticut Light And Power Company | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	11.9
2,020	22.6
2,021	21.9
2,022	15.3
2,023	17.5
Thereafter	43.5
Total	132.7
The Connecticut Light And Power Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	9
2,020	9.1
2,021	6
2,022	6.4
2,023	7
Thereafter	7
Total	44.5
NSTAR Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	109.2
2,020	105.3
2,021	97.7
2,022	98.2
2,023	73.9
Thereafter	461.1
Total	945.4
NSTAR Electric Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	5.5
2,020	3.1
2,021	3.1
2,022	3.1
2,023	3
Thereafter	19
Total	36.8
NSTAR Electric Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	94.7
2,020	93.1
2,021	88.6
2,022	88.8
2,023	63.9
Thereafter	435.1
Total	864.2
NSTAR Electric Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	9
2,020	9.1
2,021	6
2,022	6.3
2,023	7
Thereafter	7
Total	44.4
Public Service Company Of New Hampshire
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	76.3
2,020	69.7
2,021	50.2
2,022	51
2,023	52.3
Thereafter	445.4
Total	744.9
Public Service Company Of New Hampshire | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	5.8
2,020	0.7
2,021	0.7
2,022	0.7
2,023	0.7
Thereafter	0
Total	8.6
Public Service Company Of New Hampshire | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2,019	65.7
2,020	64.1
2,021	46.3
2,022	46.8
2,023	47.8
Thereafter	441.6
Total	712.3
Public Service Company Of New Hampshire | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2,019	4.8
2,020	4.9
2,021	3.2
2,022	3.5
2,023	3.8
Thereafter	3.8
Total	$ 24

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES - Long-Term Contractual Arrangement Narrative (Details)	12 Months Ended
	Dec. 31, 2018contractprojectMW	Dec. 31, 2008contractMW
Long-term Purchase Commitment [Line Items]
Number of capacity contracts for differences between CL&P and United Illuminated Company | contract	4
Amount of capacity contracts for differences between CL&P and United Illuminated Company (in MW) | MW	787
Number of generation projects between CL&P and United Illuminated Company | project	3
Number of demand response projects between CL&P and United Illuminated Company | project	1
Percentage of costs and benefits borne by United Illuminated Company	20.00%
Peaker Contracts For Differences
Long-term Purchase Commitment [Line Items]
Percentage of costs and benefits borne by United Illuminated Company		20.00%
Period of payment to generation facility owner		30 years
The Connecticut Light And Power Company | Peaker Contracts For Differences
Long-term Purchase Commitment [Line Items]
Number of capacity contracts | contract		3
Amount of capacity contracts | MW		500
Percentage of costs and benefits borne		80.00%
CL&P, NSTAR Electric and PSNH | Transmission Support Commitments
Long-term Purchase Commitment [Line Items]
Period of payment of annual operation and maintenance expense	30 years

COMMITMENTS AND CONTINGENCIES_6

COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Purchased Power and Capacity	$ 72	$ 103.9	$ 152.5
Renewable Energy	218.5	235.5	210.9
Peaker CfDs	20.9	38.7	47.7
Natural Gas Procurement	432.4	377	323.9
Coal, Wood and Other	0	47.7	55.7
Transmission Support Commitments	23.4	19.8	15.9
The Connecticut Light And Power Company
Long-term Purchase Commitment [Line Items]
Purchased Power and Capacity	49.4	81	132.7
Renewable Energy	63.2	51	42.1
Peaker CfDs	20.9	38.7	47.7
Coal, Wood and Other	0	0	0
Transmission Support Commitments	9.2	7.8	6.3
NSTAR Electric Company
Long-term Purchase Commitment [Line Items]
Purchased Power and Capacity	4.4	4	0.7
Renewable Energy	89.8	123.7	101.1
Peaker CfDs	0	0	0
Coal, Wood and Other	0	0	0
Transmission Support Commitments	9.2	7.8	6.2
Public Service Company Of New Hampshire
Long-term Purchase Commitment [Line Items]
Purchased Power and Capacity	18.2	18.9	19.1
Renewable Energy	65.5	60.8	67.7
Peaker CfDs	0	0	0
Coal, Wood and Other	0	47.7	55.7
Transmission Support Commitments	$ 5	$ 4.2	$ 3.4

COMMITMENTS AND CONTINGENCIES_7

COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details) - USD ($) $ in Millions	Mar. 22, 2017	Mar. 25, 2016
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		$ 26.1
Loss Contingency, Refunded Amount		56.5
Yankee Companies
Guarantor Obligations [Line Items]
Damages sought	$ 100
CYAPC
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		32.6
The Connecticut Light And Power Company
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		13.6
NSTAR Electric Company
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		8.6
Public Service Company Of New Hampshire
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		3.9
YAEC
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		19.6
MYAPC
Guarantor Obligations [Line Items]
Loss Contingency, Damages Awarded, Value		$ 24.6

COMMITMENTS AND CONTINGENCIES_8

COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details) - USD ($)	Feb. 08, 2019	Dec. 31, 2018
Guarantee Of Financial Obligations Of Npt
Loss Contingencies [Line Items]
Maximum exposure		$ 25,000,000
Guarantee Of Npt Letters Of Credit
Loss Contingencies [Line Items]
Maximum exposure		$ 14,000,000
Subsequent Event | Revolution Wind And South Fork Wind Power
Loss Contingencies [Line Items]
Equity Method Investments	$ 225,000,000
Equity method investment, ownership percentage	50.00%
Parent obligations	$ 127,600,000

COMMITMENTS AND CONTINGENCIES_9

COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details) $ in Millions	Dec. 31, 2018USD ($)
Access Northeast Project Capital Contributions Guaranty
Guarantor Obligations [Line Items]
Maximum Exposure	$ 184.9
Surety Bonds
Guarantor Obligations [Line Items]
Maximum Exposure	41.9
Lease Payments for Real Estate
Guarantor Obligations [Line Items]
Maximum Exposure	6.3
Bay State Wind LLC
Guarantor Obligations [Line Items]
Maximum Exposure	$ 2.5

COMMITMENTS AND CONTINGENCIE_10

COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details) $ in Millions	Oct. 06, 2017	Jun. 08, 2017	Jul. 15, 2016MW	Apr. 29, 2016	Sep. 30, 2018	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Mar. 26, 2014	Apr. 14, 2017	Oct. 15, 2014
Loss Contingencies [Line Items]
Loss Contingency, Percentage Of Base ROE Reasonably Justified					10.41%
Loss Contingency, Percentage Of Incentive Cap On Total ROE					13.08%
Capacity required for installation of distribution cable | MW			0.115
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Base ROE percentage challenged by complainants						11.14%
Loss Contingency, Base ROE Subsequently Authorized by FERC for First Complaint Period and Prospectively From October 2014					11.14%
Percentage of ROE for any incentive project		13.08%
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 First Complaint
Loss Contingencies [Line Items]
Percentage of ROE for any incentive project									11.74%
Refund payments						38.9
FERC ROE Second Complaint
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period								10.57%	10.57%
Loss contingency, estimate of possible earnings impact						39.1
Percentage of ROE for any incentive project								11.74%
FERC ROE Fourth Complaint
Loss Contingencies [Line Items]
Percentage of base ROE of complaint period				10.57%
Maximum percentage cap of ROE for incentive projects				11.74%
Original base ROE authorized by FERC at time of complaint	11.74%
Percentage of ROE for any incentive project	10.57%
The Connecticut Light And Power Company | FERC ROE First Complaint
Loss Contingencies [Line Items]
Refund payments						22.4
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
Loss Contingencies [Line Items]
Loss in period							$ 4.9
Base rate credit							$ 17.5
NSTAR Electric Company | FERC ROE First Complaint
Loss Contingencies [Line Items]
Refund payments						13.7
NSTAR Electric Company | FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact						14.6
Public Service Company Of New Hampshire | FERC ROE First Complaint
Loss Contingencies [Line Items]
Refund payments						2.8
Public Service Company Of New Hampshire | FERC ROE Second Complaint
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact						$ 3.1
Minimum
Loss Contingencies [Line Items]
Loss Contingency, Percentage Of Base ROE Reasonably Justified					9.60%
Minimum | FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of ROE for any incentive project										11.14%
Maximum
Loss Contingencies [Line Items]
Loss Contingency, Percentage Of Base ROE Reasonably Justified					10.99%
Maximum | FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of ROE for any incentive project										13.10%

COMMITMENTS AND CONTINGENCIES C

COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES - Schedule of Environmental Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018site	Dec. 31, 2017USD ($)site
Site Contingency [Line Items]
Environmental Site Quantity	60	59
The Connecticut Light And Power Company
Site Contingency [Line Items]
Environmental Site Quantity	15	14
NSTAR Electric Company
Site Contingency [Line Items]
Loss Contingency, Loss in Period | $		$ 4.9
Environmental Site Quantity	16	15
Loss Contingency, Base Rate Credit | $		$ 17.5
Environmental Site for Which a Range is Too Early to Determine
Site Contingency [Line Items]
Environmental Site Quantity	12
Environmental Site for Which a Range is Too Early to Determine | The Connecticut Light And Power Company
Site Contingency [Line Items]
Environmental Site Quantity	4
Environmental Site for Which a Range is Too Early to Determine | NSTAR Electric Company
Site Contingency [Line Items]
Environmental Site Quantity	3

GENERATION ASSET SALE - Narrati

GENERATION ASSET SALE - Narrative (Details) $ in Thousands	Jul. 16, 2018contract	Jan. 10, 2018USD ($)	Oct. 11, 2017USD ($)	Oct. 31, 2017USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Regulatory Assets [Line Items]
Purchase price in purchase sale agreement for thermal generation assets			$ 175,000
Purchase price in purchase sale agreement for hydroelectric assets			$ 83,000
Proceeds from the Sale of PSNH Generation Assets								$ 193,924	$ 0	$ 0
Number of purchase sale agreements | contract	6
Total Regulatory Assets								5,145,900	5,239,300
Pre-tax incmoe associated with generation assets								1,329,491	1,574,407	1,504,818
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Purchase price in purchase sale agreement for thermal generation assets		$ 175,000				$ 17,300
Purchase price in purchase sale agreement for hydroelectric assets				$ 83,000	$ 5,800
Purchase price is sale agreement adjusted for other expenses		$ 40,900
Proceeds from the Sale of PSNH Generation Assets						$ 116,800		193,924	0	0
Proceeds from assets held for sale					$ 77,200
Difference between book value of hydroelectric generation assets and expected proceeds from sale							$ 17,300
Total Regulatory Assets								929,500	940,800
Pre-tax incmoe associated with generation assets								$ 163,452	224,671	214,349
Domestic Tax Authority | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Pre-tax incmoe associated with generation assets							$ 9,900		$ 60,000	$ 65,300

GENERATION ASSET SALE - Schedul

GENERATION ASSET SALE - Schedule of Assets-Held-for-Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets [Line Items]
Thermal Gross Plant	$ 31,353,700	$ 29,213,900
Accumulated Depreciation	(7,462,900)	(7,133,800)
Total Property, Plant and Equipment, Net	25,610,428	23,617,463
Other Assets	778,600	693,700
Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Thermal Gross Plant	3,517,300	3,244,700
Accumulated Depreciation	(772,900)	(751,800)
Total Property, Plant and Equipment, Net	2,880,073	$ 2,642,274
Electricity Generation Plant, Non-Nuclear | Public Service Company Of New Hampshire
Regulatory Assets [Line Items]
Thermal Gross Plant	1,091,400
Hydroelectric Gross Plant	83,000
Accumulated Depreciation	(575,400)
Total Property, Plant and Equipment, Net	599,000
Fuel and Inventory	87,700
Materials and Supplies	27,300
Emission Allowances	19,100
Other Assets	2,600
Deferred Costs from Thermal Generation Asset Sale	(516,100)
Total Generation Assets Held for Sale	$ 219,600

LEASES - Operating Leases Renta

LEASES - Operating Leases Rental Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 10.8	$ 10.5	$ 12.1
The Connecticut Light And Power Company
Operating Leased Assets [Line Items]
Operating leases, rent expense	10.9	11.7	12.5
NSTAR Electric Company
Operating Leased Assets [Line Items]
Operating leases, rent expense	11.8	11.3	11.4
Public Service Company Of New Hampshire
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 2.5	$ 3.3	$ 2.9

LEASES - Future Minimum Rental

LEASES - Future Minimum Rental Payments, Operating and Capital Leases (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	$ 11.5
2,020	9.8
2,021	8.7
2,022	7.2
2,023	4.7
Thereafter	32.7
Future minimum lease payments	74.6
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	3.4
2,020	3.4
2,021	2.9
2,022	1.5
2,023	0.7
Thereafter	13.9
Future minimum lease payments	25.8
Less amount to arrive at present value	13.8
Present value of future minimum lease payments	12
The Connecticut Light And Power Company
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	1.5
2,020	1.4
2,021	1.2
2,022	1.1
2,023	0.5
Thereafter	0.2
Future minimum lease payments	5.9
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	2
2,020	2
2,021	1.5
2,022	0
2,023	0
Thereafter	0
Future minimum lease payments	5.5
Less amount to arrive at present value	1
Present value of future minimum lease payments	4.5
NSTAR Electric Company
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	7.2
2,020	6
2,021	5.3
2,022	4.4
2,023	3.1
Thereafter	29.5
Future minimum lease payments	55.5
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	0.5
2,020	0.5
2,021	0.5
2,022	0.6
2,023	0.6
Thereafter	13.4
Future minimum lease payments	16.1
Less amount to arrive at present value	12.4
Present value of future minimum lease payments	3.7
Public Service Company Of New Hampshire
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	0.5
2,020	0.4
2,021	0.4
2,022	0.4
2,023	0.2
Thereafter	0.3
Future minimum lease payments	2.2
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,019	0.1
2,020	0.1
2,021	0.1
2,022	0.1
2,023	0.1
Thereafter	0.5
Future minimum lease payments	1
Less amount to arrive at present value	0.1
Present value of future minimum lease payments	$ 0.9

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	$ 155,570	$ 155,570
Rate Reduction Bonds	583,331	0
Carrying Amount
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	13,086,100	12,325,500
Rate Reduction Bonds	635,700
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	156,800	160,800
Long-Term Debt	13,154,900	12,877,100
Rate Reduction Bonds	645,800
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
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	3,254,000	3,059,100
The Connecticut Light And Power Company | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	113,800	116,500
Long-Term Debt	3,429,200	3,430,500
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
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	2,944,800	2,943,800
NSTAR Electric Company | Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	43,000	44,300
Long-Term Debt	3,024,100	3,156,500
Public Service Company Of New Hampshire
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rate Reduction Bonds	583,331	0
Public Service Company Of New Hampshire | Carrying Amount
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	805,200	1,002,400
Rate Reduction Bonds	635,700
Public Service Company Of New Hampshire | Fair Value
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	819,500	$ 1,038,200
Rate Reduction Bonds	$ 645,800

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Changes in AOCI By Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 11,086,242	$ 10,711,734
OCI Before Reclassifications		(7,600)
Amounts Reclassified from AOCI		6,500
Net OCI		(1,100)
Ending balance	11,486,817	11,086,242
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(66,403)	(65,282)
OCI Before Reclassifications	(200)
Amounts Reclassified from AOCI	6,600
Net OCI	6,400
Ending balance	(60,000)	(66,403)
Qualified Cash Flow Hedging Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(6,200)	(8,200)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCI	1,800	2,000
Net OCI	1,800	2,000
Ending balance	(4,400)	(6,200)
Unrealized Losses on Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	400
OCI Before Reclassifications	(500)	(400)
Amounts Reclassified from AOCI	0	0
Net OCI	(500)	(400)
Ending balance	(500)	0
Defined Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(60,200)	(57,500)
OCI Before Reclassifications	300	(7,200)
Amounts Reclassified from AOCI	4,800	4,500
Net OCI	5,100	(2,700)
Ending balance	$ (55,100)	$ (60,200)

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Related tax effect recognized in AOCI	$ 0.2	$ 4.1	$ 4
Pre-tax amount reclassified from AOCI as a decrease to net income	2.5
Pre-tax amount reclassified from AOCI as a decrease to net income as a result of amortization of Pension, SERP and PBOP costs	6.3
NSTAR Gas
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income	0.7
Public Service Company Of New Hampshire
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income	$ 1.8

ACCUMULATED OTHER COMPREHENSI_5

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									$ (288,972)	$ (578,892)	$ (554,997)
Net Income/(Loss) Attributable to Common Shareholders	$ 231,300	$ 289,400	$ 242,800	$ 269,500	$ 237,400	$ 260,400	$ 230,700	$ 259,500	1,033,000	987,996	942,302
Defined Benefit Plan Costs:
Total Amounts Reclassified from AOCI, Net of Tax									6,600	6,500	6,000
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect									1,000	1,300	1,400
Qualified Cash Flow Hedging Instruments, Net of Tax | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income/(Loss) Attributable to Common Shareholders									(1,800)	(2,000)	(2,100)
Amortization of Actuarial Losses
Defined Benefit Plan Costs:
Reclassifications from AOCI									(6,000)	(6,200)	(5,600)
Amortization of Prior Service Cost
Defined Benefit Plan Costs:
Reclassifications from AOCI									(400)	(1,100)	(800)
Defined Benefit Plans
Defined Benefit Plan Costs:
Reclassifications from AOCI									(6,400)	(7,300)	(6,400)
Tax Effect									1,600	2,800	2,500
Total Amounts Reclassified from AOCI, Net of Tax									(4,800)	(4,500)	(3,900)
Interest Expense | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Qualified Cash Flow Hedging Instruments									$ (2,800)	$ (3,300)	$ (3,500)

DIVIDEND RESTRICTIONS - Narrati

DIVIDEND RESTRICTIONS - Narrative (Details) $ in Millions	Dec. 31, 2018USD ($)
Schedule of Restrictions on Retained Earnings [Line Items]
Consolidated total debt to total capital ratio (as a percentage)	0.65
Retained earnings subject to restrictions	$ 4,000
The Connecticut Light And Power Company
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	1,700
NSTAR Electric Company
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	2,100
Public Service Company Of New Hampshire
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	$ 627.3

COMMON SHARES - (Details)

COMMON SHARES - (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 5	$ 5	$ 5
Authorized (in shares)	380,000,000	380,000,000
Issued (in shares)	333,878,402	333,878,402
Treasury stock (in shares)	16,992,594	16,992,594
The Connecticut Light And Power Company
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 10	$ 10
Authorized (in shares)	24,500,000	24,500,000
Issued (in shares)	6,035,205	6,035,205
NSTAR Electric Company
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 1	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	200	200
Public Service Company Of New Hampshire
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 1	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	301	301
Common Shares
Class of Stock [Line Items]
Common stock outstanding (in shares)	316,885,808	316,885,808	316,885,808	317,191,249
Common Shares | The Connecticut Light And Power Company
Class of Stock [Line Items]
Common stock outstanding (in shares)	6,035,205	6,035,205	6,035,205	6,035,205
Common Shares | NSTAR Electric Company
Class of Stock [Line Items]
Common stock outstanding (in shares)	200	200	200	200
Common Shares | Public Service Company Of New Hampshire
Class of Stock [Line Items]
Common stock outstanding (in shares)	301	301	301	301

PREFERRED STOCK NOT SUBJECT T_3

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Narrative (Details)	Dec. 31, 2018$ / sharesshares
The Connecticut Light And Power Company
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares	9,000,000
Preferred stock par value per share (in dollars per share) | $ / shares	$ 50
NSTAR Electric Company
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares	2,890,000
Preferred stock par value per share (in dollars per share) | $ / shares	$ 100

PREFERRED STOCK NOT SUBJECT T_4

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Schedule of Preferred Stock by Class (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock value outstanding	$ 155.6	$ 155.6
The Connecticut Light And Power Company
Class of Stock [Line Items]
Shares outstanding (in shares)	2,324,000	2,324,000
Preferred stock value outstanding	$ 116.2	$ 116.2
The Connecticut Light And Power Company | Series of 1947 Preferred Stock at $1.90
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 1.90	$ 1.90
Redemption Price Per Share (in dollars per share)	$ 52.50
Shares outstanding (in shares)	163,912	163,912
Preferred stock value outstanding	$ 8.2	$ 8.2
The Connecticut Light And Power Company | Series of 1947 Preferred Stock at $2.00
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2	$ 2
Redemption Price Per Share (in dollars per share)	$ 54
Shares outstanding (in shares)	336,088	336,088
Preferred stock value outstanding	$ 16.8	$ 16.8
The Connecticut Light And Power Company | Series of 1949 Preferred Stock at $2.04
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.04	$ 2.04
Redemption Price Per Share (in dollars per share)	$ 52
Shares outstanding (in shares)	100,000	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company | Series of 1949 Preferred Stock at $2.20
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.20	$ 2.20
Redemption Price Per Share (in dollars per share)	$ 52.50
Shares outstanding (in shares)	200,000	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company | Series of 1949 Preferred Stock at 3.90%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	3.90%	3.90%
Redemption Price Per Share (in dollars per share)	$ 50.50
Shares outstanding (in shares)	160,000	160,000
Preferred stock value outstanding	$ 8	$ 8
The Connecticut Light And Power Company | Series E of 1954 Preferred Stock at $2.06
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.06	$ 2.06
Redemption Price Per Share (in dollars per share)	$ 51
Shares outstanding (in shares)	200,000	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company | Series F of 1955 Preferred Stock at $2.09
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 2.09	$ 2.09
Redemption Price Per Share (in dollars per share)	$ 51
Shares outstanding (in shares)	100,000	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company | Series of 1956 Preferred Stock at 4.5%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.50%	4.50%
Redemption Price Per Share (in dollars per share)	$ 50.75
Shares outstanding (in shares)	104,000	104,000
Preferred stock value outstanding	$ 5.2	$ 5.2
The Connecticut Light And Power Company | Series of 1958 Preferred Stock at 4.96%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.96%	4.96%
Redemption Price Per Share (in dollars per share)	$ 50.50
Shares outstanding (in shares)	100,000	100,000
Preferred stock value outstanding	$ 5	$ 5
The Connecticut Light And Power Company | Series of 1963 Preferred Stock at 4.5%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.50%	4.50%
Redemption Price Per Share (in dollars per share)	$ 50.50
Shares outstanding (in shares)	160,000	160,000
Preferred stock value outstanding	$ 8	$ 8
The Connecticut Light And Power Company | Series of 1967 Preferred Stock at 5.28%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	5.28%	5.28%
Redemption Price Per Share (in dollars per share)	$ 51.43
Shares outstanding (in shares)	200,000	200,000
Preferred stock value outstanding	$ 10	$ 10
The Connecticut Light And Power Company | Series G of 1968 Preferred Stock at $3.24
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 3.24	$ 3.24
Redemption Price Per Share (in dollars per share)	$ 51.84
Shares outstanding (in shares)	300,000	300,000
Preferred stock value outstanding	$ 15	$ 15
The Connecticut Light And Power Company | Series of 1968 Preferred Stock at 6.56%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	6.56%	6.56%
Redemption Price Per Share (in dollars per share)	$ 51.44
Shares outstanding (in shares)	200,000	200,000
Preferred stock value outstanding	$ 10	$ 10
NSTAR Electric Company
Class of Stock [Line Items]
Shares outstanding (in shares)	430,000	430,000
Preferred stock value outstanding	$ 43	$ 43
NSTAR Electric Company | Preferred Stock 4.25%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.25%	4.25%
Redemption Price Per Share (in dollars per share)	$ 103.625
Shares outstanding (in shares)	180,000	180,000
Preferred stock value outstanding	$ 18	$ 18
NSTAR Electric Company | Preferred Stock 4.78%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	4.78%	4.78%
Redemption Price Per Share (in dollars per share)	$ 102.80
Shares outstanding (in shares)	250,000	250,000
Preferred stock value outstanding	$ 25	$ 25
NSTAR Electric Company | Series of Preferred Stock at 6%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	6.00%	6.00%
Aquarion Water Company | Series of Preferred Stock at 6%
Class of Stock [Line Items]
Redemption Price Per Share (in dollars per share)	$ 100
Shares outstanding (in shares)	23	23
Preferred stock value outstanding	$ 0	$ 0
Fair Value Adjustment | NSTAR Electric Company
Class of Stock [Line Items]
Preferred stock value outstanding	$ 3.6	$ 3.6

COMMON SHARESHOLDERS' EQUITY _2

COMMON SHARESHOLDERS' EQUITY AND NONCONTROLLING INTERESTS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Dividends on preferred stock	$ 7,519	$ 7,519	$ 7,519
Preferred stock value outstanding	$ 155,600	$ 155,600

EARNINGS PER SHARE - Components

EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 231,300	$ 289,400	$ 242,800	$ 269,500	$ 237,400	$ 260,400	$ 230,700	$ 259,500	$ 1,033,000	$ 987,996	$ 942,302
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,370,369	317,411,097	317,650,180
Dilutive Effect (in shares)									623,565	620,483	804,059
Diluted (in shares)									317,993,934	318,031,580	318,454,239
Basic EPS (in dollars per share)									$ 3.25	$ 3.11	$ 2.97
Diluted EPS (in dollars per share)									$ 3.25	$ 3.11	$ 2.96

REVENUES (Details)

REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									$ 8,472,700
Operating Revenues	$ 2,034,900	$ 2,271,400	$ 1,853,900	$ 2,288,000	$ 1,895,600	$ 1,988,500	$ 1,762,800	$ 2,105,100	8,448,201	$ 7,751,952	$ 7,639,129
Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									4,439,800
Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									3,028,300
Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									442,300
Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									7,910,400
Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									264,000
Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									241,100
Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									81,500
Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(24,300)
Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(46,100)
Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									21,600
The Connecticut Light And Power Company
Disaggregation of Revenue [Line Items]
Operating Revenues	751,300	865,000	694,900	785,000	713,700	774,800	666,600	732,300	3,096,174	2,887,359	2,805,955
NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	712,600	939,500	690,700	770,100	690,200	851,900	704,700	733,800	3,112,926	2,980,629	3,041,588
Public Service Company Of New Hampshire
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 254,900	$ 290,200	$ 235,100	$ 267,400	$ 248,000	$ 250,000	$ 230,400	$ 253,200	1,047,619	981,624	959,482
Operating Segments | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									6,986,300
Operating Revenues									6,957,200
Operating Segments | Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									3,766,600
Operating Segments | Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									2,634,700
Operating Segments | Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									351,900
Operating Segments | Electric Distribution | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									6,753,200
Operating Segments | Electric Distribution | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Distribution | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									179,500
Operating Segments | Electric Distribution | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									65,900
Operating Segments | Electric Distribution | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(12,300)
Operating Segments | Electric Distribution | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(47,000)
Operating Segments | Electric Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									17,900
Operating Segments | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,020,300
Operating Revenues									1,022,200	947,300	857,700
Operating Segments | Natural Gas Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									542,500
Operating Segments | Natural Gas Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									334,800
Operating Segments | Natural Gas Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									96,000
Operating Segments | Natural Gas Distribution | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									973,300
Operating Segments | Natural Gas Distribution | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Natural Gas Distribution | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									57,500
Operating Segments | Natural Gas Distribution | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(2,200)
Operating Segments | Natural Gas Distribution | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(8,300)
Operating Segments | Natural Gas Distribution | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(1,200)
Operating Segments | Natural Gas Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									3,100
Operating Segments | Electric Transmission
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,321,500
Operating Revenues									1,286,300
Operating Segments | Electric Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Transmission | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Transmission | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,308,900
Operating Segments | Electric Transmission | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Electric Transmission | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									12,600
Operating Segments | Electric Transmission | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(35,200)
Operating Segments | Electric Transmission | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									0
Operating Segments | Water Distribution
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									206,000
Operating Revenues									212,000
Operating Segments | Water Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									130,700
Operating Segments | Water Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									63,300
Operating Segments | Water Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									4,400
Operating Segments | Water Distribution | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									198,400
Operating Segments | Water Distribution | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Water Distribution | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									4,100
Operating Segments | Water Distribution | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									7,200
Operating Segments | Water Distribution | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(3,700)
Operating Segments | Water Distribution | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									5,400
Operating Segments | Water Distribution | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									600
Operating Segments | Other
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									936,300
Operating Revenues									936,300
Operating Segments | Other | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									47,300
Operating Segments | Other | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									889,000
Operating Segments | Other | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Other | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									0
Operating Segments | Other | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									0
Operating Segments | The Connecticut Light And Power Company
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									3,607,900
Operating Segments | The Connecticut Light And Power Company | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,828,200
Operating Segments | The Connecticut Light And Power Company | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									928,100
Operating Segments | The Connecticut Light And Power Company | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									147,700
Operating Segments | The Connecticut Light And Power Company | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									2,904,000
Operating Segments | The Connecticut Light And Power Company | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									620,600
Operating Segments | The Connecticut Light And Power Company | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									48,300
Operating Segments | The Connecticut Light And Power Company | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									35,000
Operating Segments | The Connecticut Light And Power Company | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									3,491,100
Operating Segments | NSTAR Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,380,900
Operating Segments | NSTAR Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,391,500
Operating Segments | NSTAR Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									124,900
Operating Segments | NSTAR Electric Company | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									2,897,300
Operating Segments | NSTAR Electric Company | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									488,800
Operating Segments | NSTAR Electric Company | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									76,100
Operating Segments | NSTAR Electric Company | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									28,900
Operating Segments | NSTAR Electric Company | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Operating Segments | Public Service Company Of New Hampshire
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									1,213,000
Operating Segments | Public Service Company Of New Hampshire | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									557,500
Operating Segments | Public Service Company Of New Hampshire | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									316,900
Operating Segments | Public Service Company Of New Hampshire | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									79,300
Operating Segments | Public Service Company Of New Hampshire | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									953,700
Operating Segments | Public Service Company Of New Hampshire | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									199,500
Operating Segments | Public Service Company Of New Hampshire | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									56,600
Operating Segments | Public Service Company Of New Hampshire | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									15,500
Operating Segments | Public Service Company Of New Hampshire | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(12,300)
Segment Reconciling Items [Member] | The Connecticut Light And Power Company | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(65,900)
Segment Reconciling Items [Member] | The Connecticut Light And Power Company | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									8,500
Segment Reconciling Items [Member] | NSTAR Electric Company | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									900
Segment Reconciling Items [Member] | NSTAR Electric Company | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									8,300
Segment Reconciling Items [Member] | Public Service Company Of New Hampshire | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									(17,300)
Segment Reconciling Items [Member] | Public Service Company Of New Hampshire | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									1,100
Eliminations
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(1,997,700)
Operating Revenues									(1,965,800)	$ (986,800)	$ (893,300)
Eliminations | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Eliminations | Commercial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(4,500)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(10,000)
Eliminations | Total Retail Tariff Sale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(14,500)
Eliminations | Transmission Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(1,092,200)
Eliminations | Wholesale Revenue
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Eliminations | Other Revenue from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									(891,000)
Eliminations | Reserve for Revenue Subject to Refund
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customers									0
Eliminations | Alternative Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									31,900
Eliminations | Other Revenue
Disaggregation of Revenue [Line Items]
Operating Revenues									0
Consolidations Eliminations | The Connecticut Light And Power Company
Disaggregation of Revenue [Line Items]
Operating Revenues									(454,300)
Consolidations Eliminations | NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues									(387,400)
Consolidations Eliminations | Public Service Company Of New Hampshire
Disaggregation of Revenue [Line Items]
Operating Revenues									$ (149,200)

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)companysegment	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Number of companies that transmit hydro electricity | company	2
Amount of natural gas transmission purchased	$ 62.5
Number of reportable segments | segment	1
Transmission Merger Cost Recovery
Segment Reporting Information [Line Items]
Amount of recovery through transmission rates		$ 27.5

SEGMENT INFORMATION - Schedule

SEGMENT INFORMATION - Schedule of Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,034,900	$ 2,271,400	$ 1,853,900	$ 2,288,000	$ 1,895,600	$ 1,988,500	$ 1,762,800	$ 2,105,100	$ 8,448,201	$ 7,751,952	$ 7,639,129
Depreciation and Amortization									(1,072,000)	(863,800)	(787,100)
Other Operating Expenses									(5,676,300)	(5,000,000)	(5,010,700)
Operating Income	400,000	466,000	391,400	442,500	443,700	495,300	448,200	501,000	1,699,930	1,888,249	1,841,274
Interest Expense									(498,805)	(421,755)	(400,961)
Interest Income									18,100	8,300	11,000
Other Income/(Loss), Net									110,300	99,700	53,500
Income Tax Benefit									(288,972)	(578,892)	(554,997)
Net Income	233,200	291,300	244,600	271,400	239,400	262,200	232,600	261,300	1,040,519	995,515	949,821
Net Income Attributable to Noncontrolling Interests									(7,519)	(7,519)	(7,519)
Net Income/(Loss) Attributable to Common Shareholders	231,300	$ 289,400	$ 242,800	$ 269,500	237,400	$ 260,400	$ 230,700	$ 259,500	1,033,000	987,996	942,302
Total Assets (as of)	38,241,256				36,220,386				38,241,256	36,220,386
Cash Flows Used for Investments in Plant									2,523,371	2,348,105	1,976,867
Operating Segments | Eversource Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues									6,957,200	5,542,900	5,594,300
Depreciation and Amortization									(671,800)	(542,600)	(504,700)
Other Operating Expenses									(5,548,600)	(4,072,600)	(4,173,000)
Operating Income									736,800	927,700	916,600
Interest Expense									(202,800)	(186,300)	(193,100)
Interest Income									18,700	7,300	10,000
Other Income/(Loss), Net									67,500	41,600	22,700
Income Tax Benefit									(160,200)	(288,300)	(288,800)
Net Income									460,000	502,000	467,400
Net Income Attributable to Noncontrolling Interests									(4,600)	(4,600)	(4,600)
Net Income/(Loss) Attributable to Common Shareholders									455,400	497,400	462,800
Total Assets (as of)	21,389,100				19,250,400				21,389,100	19,250,400
Cash Flows Used for Investments in Plant									961,300	1,020,700	812,600
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating Revenues									1,022,200	947,300	857,700
Depreciation and Amortization									(75,000)	(72,900)	(65,300)
Other Operating Expenses									(787,600)	(716,400)	(629,000)
Operating Income									159,600	158,000	163,400
Interest Expense									(44,100)	(43,100)	(41,300)
Interest Income									0	100	100
Other Income/(Loss), Net									7,100	3,800	700
Income Tax Benefit									(29,400)	(44,200)	(45,200)
Net Income									93,200	74,600	77,700
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income/(Loss) Attributable to Common Shareholders									93,200	74,600	77,700
Total Assets (as of)	3,904,900				3,595,200				3,904,900	3,595,200
Cash Flows Used for Investments in Plant									351,500	298,200	255,300
Operating Segments | Eversource Electric Transmission
Segment Reporting Information [Line Items]
Operating Revenues									1,286,300	1,301,700	1,210,000
Depreciation and Amortization									(231,800)	(209,400)	(185,800)
Other Operating Expenses									(375,500)	(382,800)	(321,300)
Operating Income									679,000	709,500	702,900
Interest Expense									(120,600)	(115,100)	(110,000)
Interest Income									2,400	1,800	1,200
Other Income/(Loss), Net									31,100	27,300	17,800
Income Tax Benefit									(161,800)	(228,700)	(238,200)
Net Income									430,100	394,800	373,700
Net Income Attributable to Noncontrolling Interests									(2,900)	(2,900)	(2,900)
Net Income/(Loss) Attributable to Common Shareholders									427,200	391,900	370,800
Total Assets (as of)	10,285,000				9,401,200				10,285,000	9,401,200
Cash Flows Used for Investments in Plant									929,700	867,600	801,000
Operating Segments | Eversource Water
Segment Reporting Information [Line Items]
Operating Revenues									212,000	15,900	0
Depreciation and Amortization									(46,500)	(3,700)	0
Other Operating Expenses									(99,800)	(8,300)	0
Operating Income									65,700	3,900	0
Interest Expense									(34,300)	(3,100)	0
Interest Income									0	100	0
Other Income/(Loss), Net									(400)	0	0
Income Tax Benefit									(100)	(2,100)	0
Net Income									30,900	(1,200)	0
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income/(Loss) Attributable to Common Shareholders									30,900	(1,200)	0
Total Assets (as of)	2,253,000				2,182,900				2,253,000	2,182,900
Cash Flows Used for Investments in Plant									102,300	16,000	0
Operating Segments | Other Segments
Segment Reporting Information [Line Items]
Operating Revenues									936,300	931,000	870,400
Depreciation and Amortization									(49,100)	(37,400)	(33,500)
Other Operating Expenses									(831,500)	(806,600)	(779,200)
Operating Income									55,700	87,000	57,700
Interest Expense									(129,300)	(90,000)	(63,500)
Interest Income									30,300	15,700	7,000
Other Income/(Loss), Net									1,185,300	1,113,000	1,021,200
Income Tax Benefit									62,500	(15,500)	16,500
Net Income									1,204,500	1,110,200	1,038,900
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income/(Loss) Attributable to Common Shareholders									1,204,500	1,110,200	1,038,900
Total Assets (as of)	17,874,200				16,220,900				17,874,200	16,220,900
Cash Flows Used for Investments in Plant									178,600	145,600	108,000
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues									(1,965,800)	(986,800)	(893,300)
Depreciation and Amortization									2,200	2,200	2,200
Other Operating Expenses									1,966,700	986,700	891,800
Operating Income									3,100	2,100	700
Interest Expense									32,300	15,800	6,900
Interest Income									(33,300)	(16,700)	(7,300)
Other Income/(Loss), Net									(1,180,300)	(1,086,000)	(1,008,900)
Income Tax Benefit									0	(100)	700
Net Income									(1,178,200)	(1,084,900)	(1,007,900)
Net Income Attributable to Noncontrolling Interests									0	0	0
Net Income/(Loss) Attributable to Common Shareholders									(1,178,200)	(1,084,900)	(1,007,900)
Total Assets (as of)	$ (17,464,900)				$ (14,430,200)				(17,464,900)	(14,430,200)
Cash Flows Used for Investments in Plant									$ 0	$ 0	$ 0

ACQUISITION OF AQUARION AND G_3

ACQUISITION OF AQUARION AND GOODWILL - Narrative (Details) - USD ($)	Dec. 04, 2017	Oct. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Business Acquisition [Line Items]
Acquisition of Aquarion			$ 0	$ 877,652,000	$ 0
Operating Revenues				15,900,000
Pre-Tax Income				1,100,000
Goodwill			4,427,266,000	4,427,266,000
Impairment loss		$ 0
Aquarion Water Company
Business Acquisition [Line Items]
Consideration transferred	$ 1,675,000,000
Acquisition of Aquarion	880,000,000
Consideration transferred, liabilities incurred	795,000,000
Equity interest	745,000,000
Aquarion shareholder loan paid at closing	135,000,000
Operating Revenues				$ 7,947,700,000	$ 7,849,000,000
Goodwill	$ 900,000,000		$ 907,900,000
Line of Credit | Aquarion
Business Acquisition [Line Items]
Long-term Debt, Fair Value						$ 7,900,000

ACQUISITION OF AQUARION AND G_4

ACQUISITION OF AQUARION AND GOODWILL - Schedule of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 04, 2017
Business Acquisition [Line Items]
Goodwill	$ 4,427,266	$ 4,427,266
Aquarion Water Company
Business Acquisition [Line Items]
Current Assets	41,200
PP&E	1,034,900
Goodwill	907,900		$ 900,000
Other Noncurrent Assets, excluding Goodwill	215,500
Current Liabilities	(121,900)
Noncurrent Liabilities	(421,600)
Long-Term Debt	(778,300)
Total Cash Purchase Price	$ 877,700

ACQUISITION OF AQUARION AND G_5

ACQUISITION OF AQUARION AND GOODWILL - Schedule of Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Operating Revenues	$ 15.9
Aquarion Water Company
Business Acquisition [Line Items]
Operating Revenues	7,947.7	$ 7,849
Net Income Attributable to Common Shareholders	$ 1,019.1	$ 969.3
Basic EPS (in dollars per share)	$ 3.21	$ 3.05
Diluted EPS (in dollars per share)	$ 3.20	$ 3.04

ACQUISITION OF AQUARION AND G_6

ACQUISITION OF AQUARION AND GOODWILL - Schedule of Goodwill by Reportable Segments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 4,427,266
Goodwill	4,400,000
Ending balance	4,427,266
Electric Distribution
Goodwill [Roll Forward]
Goodwill	2,500,000
Electric Transmission
Goodwill [Roll Forward]
Goodwill	600,000
Natural Gas Distribution
Goodwill [Roll Forward]
Goodwill	400,000
Water Distribution
Goodwill [Roll Forward]
Goodwill	$ 900,000

QUARTERLY FINANCIAL DATA (UNA_3

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Line Items]
Operating Revenues	$ 2,034,900	$ 2,271,400	$ 1,853,900	$ 2,288,000	$ 1,895,600	$ 1,988,500	$ 1,762,800	$ 2,105,100	$ 8,448,201	$ 7,751,952	$ 7,639,129
Operating Income	400,000	466,000	391,400	442,500	443,700	495,300	448,200	501,000	1,699,930	1,888,249	1,841,274
Net Income	233,200	291,300	244,600	271,400	239,400	262,200	232,600	261,300	1,040,519	995,515	949,821
Net Income Attributable to Common Shareholders	$ 231,300	$ 289,400	$ 242,800	$ 269,500	$ 237,400	$ 260,400	$ 230,700	$ 259,500	1,033,000	987,996	942,302
Basic and Diluted EPS (in dollars per share)	$ 0.73	$ 0.91	$ 0.76	$ 0.85	$ 0.75	$ 0.82	$ 0.73	$ 0.82
The Connecticut Light And Power Company
Quarterly Financial Data [Line Items]
Operating Revenues	$ 751,300	$ 865,000	$ 694,900	$ 785,000	$ 713,700	$ 774,800	$ 666,600	$ 732,300	3,096,174	2,887,359	2,805,955
Operating Income	142,800	172,700	163,100	157,200	155,200	177,100	175,600	175,500	635,837	683,354	672,434
Net Income	79,100	100,300	99,700	98,600	99,100	96,100	91,300	90,200	377,717	376,726	334,254
NSTAR Electric Company
Quarterly Financial Data [Line Items]
Operating Revenues	712,600	939,500	690,700	770,100	690,200	851,900	704,700	733,800	3,112,926	2,980,629	3,041,588
Operating Income	126,000	205,500	133,600	119,000	124,200	229,700	177,900	156,600	584,123	688,440	663,731
Net Income	77,500	140,600	87,900	77,100	70,500	125,800	95,000	83,400	383,090	374,726	350,777
Public Service Company Of New Hampshire
Quarterly Financial Data [Line Items]
Operating Revenues	254,900	290,200	235,100	267,400	248,000	250,000	230,400	253,200	1,047,619	981,624	959,482
Operating Income	37,200	56,500	46,900	55,800	69,800	66,000	63,500	66,600	196,414	265,873	256,826
Net Income	$ 14,300	$ 40,700	$ 25,800	$ 35,100	$ 36,400	$ 33,700	$ 31,600	$ 34,300	$ 115,876	$ 135,996	$ 131,985

SCHEDULE I - FINANCIAL INFORM_2

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash	$ 108,068	$ 38,165
Prepayments and Other Current Assets	260,995	138,009
Total Current Assets	2,292,224	2,487,099
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	463,700	277,600
Goodwill	4,427,266	4,427,266
Other Long-Term Assets	862,693	605,692
Total Deferred Debits and Other Assets	10,338,604	10,115,824
Total Assets	38,241,256	36,220,386
Current Liabilities:
Notes Payable	910,000	1,088,087
Long-Term Debt – Current Portion	837,319	549,631
Accounts Payable	1,119,995	1,085,034
Other Current Liabilities	823,006	738,222
Total Current Liabilities	4,112,882	3,589,045
Total Deferred Credits and Other Liabilities	9,653,913	9,613,640
Capitalization:
Long-Term Debt	12,248,743	11,775,889
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid in	6,241,222	6,239,940
Retained Earnings	3,953,974	3,561,084
Accumulated Other Comprehensive Loss	(60,000)	(66,403)
Treasury Stock	(317,771)	(317,771)
Common Shareholders' Equity	11,486,817	11,086,242	$ 10,711,734	$ 10,352,215
Total Liabilities and Capitalization	38,241,256	36,220,386
Eversource
Current Assets:
Cash	591	521	$ 93	$ 67
Accounts Receivable from Subsidiaries	32,175	3,397
Dividend Receivable from Subsidiary	0	150,000
Notes Receivable from Subsidiaries	991,400	844,500
Prepayments and Other Current Assets	26,861	18,568
Total Current Assets	1,051,027	1,016,986
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	12,009,659	10,945,986
Notes Receivable from Subsidiaries	323,500	312,190
Accumulated Deferred Income Taxes	40,454	47,940
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	73,669	58,313
Total Deferred Debits and Other Assets	15,679,093	14,596,240
Total Assets	16,730,120	15,613,226
Current Liabilities:
Notes Payable	631,500	778,087
Long-Term Debt – Current Portion	378,883	32,114
Accounts Payable	286	292
Accounts Payable to Subsidiaries	8,432	18,242
Other Current Liabilities	57,591	56,601
Total Current Liabilities	1,076,692	885,336
Total Deferred Credits and Other Liabilities	134,614	118,176
Capitalization:
Long-Term Debt	4,031,997	3,523,472
Common Shareholders' Equity:
Common Shares	1,669,392	1,669,392
Capital Surplus, Paid in	6,241,222	6,239,940
Retained Earnings	3,953,974	3,561,084
Accumulated Other Comprehensive Loss	(60,000)	(66,403)
Treasury Stock	317,771	(317,771)
Common Shareholders' Equity	11,486,817	11,086,242
Total Liabilities and Capitalization	$ 16,730,120	$ 15,613,226

SCHEDULE I - FINANCIAL INFORM_3

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF INCOME (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 2,034,900	$ 2,271,400	$ 1,853,900	$ 2,288,000	$ 1,895,600	$ 1,988,500	$ 1,762,800	$ 2,105,100	$ 8,448,201	$ 7,751,952	$ 7,639,129
Operating Expenses:
Other									1,335,213	1,307,052	1,342,134
Operating Income	400,000	466,000	391,400	442,500	443,700	495,300	448,200	501,000	1,699,930	1,888,249	1,841,274
Interest Expense									498,805	421,755	400,961
Other Income, Net:
Other Income, Net									128,366	107,913	64,505
Income Before Income Tax Benefit									1,329,491	1,574,407	1,504,818
Income Tax Benefit									288,972	578,892	554,997
Net Income	$ 233,200	$ 291,300	$ 244,600	$ 271,400	$ 239,400	$ 262,200	$ 232,600	$ 261,300	$ 1,040,519	$ 995,515	$ 949,821
Basic Earnings Per Common Share (in dollars per share)									$ 3.25	$ 3.11	$ 2.97
Diluted Earnings Per Common Share (in dollars per share)									$ 3.25	$ 3.11	$ 2.96
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,370,369	317,411,097	317,650,180
Diluted (in shares)									317,993,934	318,031,580	318,454,239
Eversource
Condensed Income Statements, Captions [Line Items]
Operating Revenues									$ 0	$ 0	$ 0
Operating Expenses:
Other									(6,552)	(32,189)	(39,453)
Operating Income									6,552	32,189	39,453
Interest Expense									123,638	80,700	59,420
Other Income, Net:
Equity in Earnings of Subsidiaries									1,049,748	993,063	922,321
Other, Net									47,581	23,339	4,267
Other Income, Net									1,097,329	1,016,402	926,588
Income Before Income Tax Benefit									980,243	967,891	906,621
Income Tax Benefit									(52,757)	(20,105)	(35,681)
Net Income									$ 1,033,000	$ 987,996	$ 942,302
Basic Earnings Per Common Share (in dollars per share)									$ 3.25	$ 3.11	$ 2.97
Diluted Earnings Per Common Share (in dollars per share)									$ 3.25	$ 3.11	$ 2.96
Weighted Average Common Shares Outstanding:
Basic (in shares)									317,370,369	317,411,097	317,650,180
Diluted (in shares)									317,993,934	318,031,580	318,454,239

SCHEDULE I - FINANCIAL INFORM_4

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statement of Income Captions [Line Items]
Net Income	$ 233,200	$ 291,300	$ 244,600	$ 271,400	$ 239,400	$ 262,200	$ 232,600	$ 261,300	$ 1,040,519	$ 995,515	$ 949,821
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments									1,756	1,974	2,137
Changes in Unrealized (Losses)/Gains on Marketable Securities									(547)	(350)	2,294
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									5,194	(2,745)	(2,869)
Other Comprehensive Income/(Loss), Net of Tax									6,403	(1,121)	1,562
Comprehensive Income									1,039,403	986,875	943,864
Eversource
Condensed Statement of Income Captions [Line Items]
Net Income									1,033,000	987,996	942,302
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments									1,756	1,974	2,137
Changes in Unrealized (Losses)/Gains on Marketable Securities									(547)	(350)	2,294
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									5,194	(2,745)	(2,869)
Other Comprehensive Income/(Loss), Net of Tax									6,403	(1,121)	1,562
Comprehensive Income									$ 1,039,403	$ 986,875	$ 943,864

SCHEDULE I - FINANCIAL INFORM_5

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities:
Net Income	$ 233,200	$ 291,300	$ 244,600	$ 271,400	$ 239,400	$ 262,200	$ 232,600	$ 261,300	$ 1,040,519	$ 995,515	$ 949,821
Flows Provided by Operating Activities:
Deferred Income Taxes									174,812	491,630	466,463
Other									(111,225)	(204,421)	(118,195)
Accounts Receivables from Subsidiaries									(141,433)	(117,155)	(142,699)
Taxes Receivable/Accrued, Net									(67,770)	52,284	234,543
Other Current Assets and Liabilities, Net									78,226	91,545	13,737
Net Cash Flows Provided by Operating Activities									1,783,978	1,996,202	2,208,242
Investing Activities:
Other Investing Activities									6,754	5,479	36,211
Net Cash Flows Used in Investing Activities									(2,390,481)	(3,230,516)	(2,151,548)
Financing Activities:
Cash Dividends on Common Shares									(640,110)	(602,083)	(564,486)
Issuance of Long-Term Debt									2,200,000	2,500,000	800,000
Retirements of Long-Term Debt									(1,050,330)	(745,000)	(200,000)
Increase/(Decrease) in Short-Term Debt									(379,310)	72,810	(12,453)
Other Financing Activities									(28,457)	(4,754)	(33,482)
Net Cash Flows Provided by/(Used in) Financing Activities									729,937	1,213,454	(17,940)
Cash, Cash Equivalents and Restricted Cash - Beginning of Year				38,165					38,165
Cash, Cash Equivalents and Restricted Cash - End of Year	108,068				38,165				108,068	38,165
Cash Paid/(Received) During the Year for:
Interest									503,200	419,100	398,100
Income Taxes									158,800	30,800	(135,500)
Eversource
Operating Activities:
Net Income									1,033,000	987,996	942,302
Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries									(1,049,748)	(993,063)	(922,321)
Cash Dividends Received from Subsidiaries									569,500	753,300	724,877
Deferred Income Taxes									20,032	37,867	19,008
Other									(31,093)	(36,052)	(27,963)
Accounts Receivables from Subsidiaries									(28,716)	29,405	(9,173)
Taxes Receivable/Accrued, Net									(20,207)	1,555	8,050
Accounts Payable, Including Affiliate Payables									(9,817)	9,763	(6,908)
Other Current Assets and Liabilities, Net									2,553	7,536	(7,433)
Net Cash Flows Provided by Operating Activities									485,504	798,307	720,439
Investing Activities:
Capital Contributions to Subsidiaries									(955,700)	(1,156,731)	(589,500)
Return of Capital from Subsidiary									530,000	0	0
(Increase)/Decrease in Notes Receivable from Subsidiaries									(158,210)	(192,100)	14,510
Other Investing Activities									(1,149)	1,484	0
Net Cash Flows Used in Investing Activities									(585,059)	(1,347,347)	(574,990)
Financing Activities:
Cash Dividends on Common Shares									(640,110)	(602,083)	(564,486)
Issuance of Long-Term Debt									1,550,000	1,200,000	500,000
Retirements of Long-Term Debt									(450,000)	0	0
Increase/(Decrease) in Short-Term Debt									(347,810)	(42,690)	(76,453)
Other Financing Activities									(12,455)	(5,759)	(4,484)
Net Cash Flows Provided by/(Used in) Financing Activities									99,625	549,468	(145,423)
Net Increase/(Decrease) in Cash and Cash Equivalents									70	428	26
Cash, Cash Equivalents and Restricted Cash - Beginning of Year				$ 521				$ 93	521	93	67
Cash, Cash Equivalents and Restricted Cash - End of Year	$ 591				$ 521				591	521	93
Cash Paid/(Received) During the Year for:
Interest									118,533	73,868	58,018
Income Taxes									$ (30,239)	$ (59,526)	$ (65,531)

SCHEDULE II - VALUATION AND Q_2

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
The Connecticut Light And Power Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Period of accounts receivable recoverable under financial or medical duress	180 days
Yankee Gas Services Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Period of accounts receivable recoverable under financial or medical duress	90 days
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 195,708	$ 200,630	$ 190,680
Additions, Charged to Costs and Expense	61,337	44,665	69,466
Additions, Charged to Other Accounts	48,671	47,630	45,452
Deductions	92,993	97,217	104,968
Balance at end of period	212,723	195,708	200,630
Allowance for Doubtful Accounts | The Connecticut Light And Power Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	78,872	86,391	79,479
Additions, Charged to Costs and Expense	15,831	5,312	17,572
Additions, Charged to Other Accounts	29,524	25,533	28,801
Deductions	36,193	38,364	39,461
Balance at end of period	88,034	78,872	86,391
Allowance for Doubtful Accounts | NSTAR Electric Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	69,666	70,284	66,676
Additions, Charged to Costs and Expense	22,279	21,252	31,728
Additions, Charged to Other Accounts	14,971	14,273	11,253
Deductions	32,400	36,143	39,373
Balance at end of period	74,516	69,666	70,284
Allowance for Doubtful Accounts | Public Service Company Of New Hampshire
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	10,481	9,941	8,733
Additions, Charged to Costs and Expense	6,383	6,917	7,288
Additions, Charged to Other Accounts	953	464	498
Deductions	6,752	6,841	6,578
Balance at end of period	$ 11,065	$ 10,481	$ 9,941