Eversource Energy (ES) 10-K 17 Feb 21 2020 FY Annual report Financial data

COVER PAGE

COVER PAGE - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity Registrant Name	EVERSOURCE ENERGY
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	300 Cadwell Drive
Entity Address, City or Town	Springfield
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01104
City Area Code	800
Local Phone Number	286-5000
Entity File Number	1-5324
Entity Tax Identification Number	04-2147929
Title of 12(b) Security	Common Shares, $5.00 par value per share
Trading Symbol	ES
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 28,496,151,703
Entity Common Stock, Shares Outstanding		343,003,366
Documents Incorporated by Reference	Portions of the Eversource Energy and Subsidiaries 2019 combined Annual Report on Form 10-K and portions of the Proxy Statement relating to the Annual Meeting of Shareholders to be held on May 5, 2021, are incorporated by reference into Parts II and III of this Report. NSTAR Electric Company and Public Service Company of New Hampshire each meet the conditions set forth in General Instruction I(1)(a) and (b) of Form 10-K, and each is therefore filing this Form 10-K with the reduced disclosure format specified in General Instruction I(2) of Form 10‑K. Eversource Energy, The Connecticut Light and Power Company, NSTAR Electric Company and Public Service Company of New Hampshire each separately file this combined Form 10-K. Information contained herein relating to any individual registrant is filed by such registrant on its own behalf. Each registrant makes no representation as to information relating to the other registrants.
Entity Central Index Key	0000072741
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light and Power Company
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
Entity Registrant Name	THE CONNECTICUT LIGHT AND POWER COMPANY
Entity Incorporation, State or Country Code	CT
Entity Address, Address Line One	107 Selden Street
Entity Address, City or Town	Berlin
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06037-1616
City Area Code	800
Local Phone Number	286-5000
Entity File Number	0-00404
Entity Tax Identification Number	06-0303850
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		6,035,205
Entity Central Index Key	0000023426
NSTAR Electric Company
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
Entity Registrant Name	NSTAR ELECTRIC COMPANY
Entity Incorporation, State or Country Code	MA
Entity Address, Address Line One	800 Boylston Street
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02199
City Area Code	800
Local Phone Number	286-5000
Entity File Number	1-02301
Entity Tax Identification Number	04-1278810
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		200
Entity Central Index Key	0000013372
Public Service Company of New Hampshire
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
Entity Registrant Name	PUBLIC SERVICE COMPANY OF NEW HAMPSHIRE
Entity Incorporation, State or Country Code	NH
Entity Address, Address Line One	Energy Park
Entity Address, Address Line Two	780 North Commercial Street
Entity Address, City or Town	Manchester
Entity Address, State or Province	NH
Entity Address, Postal Zip Code	03101-1134
City Area Code	800
Local Phone Number	286-5000
Entity File Number	1-6392
Entity Tax Identification Number	02-0181050
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		301
Entity Central Index Key	0000315256

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash	$ 106,599	$ 15,432
Receivables, Net (net of allowance for uncollectible accounts of $358,851 and $224,821 as of December 31, 2020 and 2019, respectively)	1,195,925	989,383
Unbilled Revenues	233,025	181,006
Fuel, Materials, Supplies and REC Inventory	265,599	235,471
Regulatory Assets	1,076,556	651,112
Prepayments and Other Current Assets	252,439	342,135
Total Current Assets	3,130,143	2,414,539
Property, Plant and Equipment, Net	30,882,523	27,585,470
Deferred Debits and Other Assets:
Regulatory Assets	5,493,330	4,863,639
Goodwill	4,445,988	4,427,266
Investments in Unconsolidated Affiliates	1,107,143	871,633
Marketable Securities	456,617	449,130
Other Long-Term Assets	583,854	512,238
Total Deferred Debits and Other Assets	12,086,932	11,123,906
Total Assets	46,099,598	41,123,915
Current Liabilities:
Notes Payable	1,249,325	889,084
Long-Term Debt – Current Portion	1,053,186	327,411
Rate Reduction Bonds – Current Portion	43,210	43,210
Accounts Payable	1,370,647	1,147,872
Regulatory Liabilities	389,430	361,152
Other Current Liabilities	809,214	836,834
Total Current Liabilities	4,915,012	3,605,563
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	4,095,339	3,755,777
Regulatory Liabilities	3,850,781	3,658,042
Derivative Liabilities	294,535	338,710
Asset Retirement Obligations	499,713	488,511
Accrued Pension, SERP and PBOP	1,653,788	1,370,245
Other Long-Term Liabilities	948,506	810,553
Total Deferred Credits and Other Liabilities	11,342,662	10,421,838
Capitalization:
Long-Term Debt	15,125,876	13,770,828
Rate Reduction Bonds	496,912	540,122
Noncontrolling Interest - Preferred Stock of Subsidiaries	155,570	155,570
Common Shareholders' Equity:
Common Shares	1,789,092	1,729,292
Capital Surplus, Paid In	8,015,663	7,087,768
Retained Earnings	4,613,201	4,177,048
Accumulated Other Comprehensive Income	(76,411)	(65,059)
Treasury Stock	(277,979)	(299,055)
Common Shareholders' Equity	14,063,566	12,629,994
Commitments and Contingencies (Note 13)
Total Liabilities and Capitalization	46,099,598	41,123,915
The Connecticut Light and Power Company
Current Assets:
Cash	90,801	0
Receivables, Net (net of allowance for uncollectible accounts of $358,851 and $224,821 as of December 31, 2020 and 2019, respectively)	459,214	400,927
Unbilled Revenues	57,407	56,465
Fuel, Materials, Supplies and REC Inventory	57,924	50,700
Regulatory Assets	345,622	178,607
Accounts Receivable from Affiliated Companies	17,486	24,577
Prepayments and Other Current Assets	83,950	73,184
Total Current Assets	1,112,404	784,460
Property, Plant and Equipment, Net	10,234,556	9,625,765
Deferred Debits and Other Assets:
Regulatory Assets	1,866,152	1,557,261
Other Long-Term Assets	242,862	217,705
Total Deferred Debits and Other Assets	2,109,014	1,774,966
Total Assets	13,455,974	12,185,191
Current Liabilities:
Notes Payable to Eversource Parent	0	63,800
Long-Term Debt – Current Portion	0	0
Accounts Payable	451,240	374,698
Accounts Payable to Affiliated Companies	51,118	97,793
Obligations to Third Party Suppliers	49,967	56,952
Regulatory Liabilities	137,166	82,763
Derivative Liabilities	68,767	67,804
Other Current Liabilities	102,060	132,339
Total Current Liabilities	860,318	876,149
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,408,343	1,244,551
Regulatory Liabilities	1,204,942	1,164,991
Derivative Liabilities	294,535	338,594
Accrued Pension, SERP and PBOP	478,325	391,159
Other Long-Term Liabilities	133,690	147,586
Total Deferred Credits and Other Liabilities	3,519,835	3,286,881
Capitalization:
Long-Term Debt	3,914,835	3,518,136
Noncontrolling Interest - Preferred Stock of Subsidiaries	116,200	116,200
Common Shareholders' Equity:
Common Shares	60,352	60,352
Capital Surplus, Paid In	2,810,765	2,535,765
Retained Earnings	2,173,367	1,791,392
Accumulated Other Comprehensive Income	302	316
Common Shareholders' Equity	5,044,786	4,387,825
Commitments and Contingencies (Note 13)
Total Liabilities and Capitalization	13,455,974	12,185,191
NSTAR Electric Company
Current Assets:
Cash	102	52
Receivables, Net (net of allowance for uncollectible accounts of $358,851 and $224,821 as of December 31, 2020 and 2019, respectively)	403,045	346,785
Unbilled Revenues	38,342	37,482
Fuel, Materials, Supplies and REC Inventory	133,894	124,060
Regulatory Assets	399,882	285,591
Accounts Receivable from Affiliated Companies	30,095	29,914
Taxes Receivable	65,051	20,408
Prepayments and Other Current Assets	21,833	10,742
Total Current Assets	1,092,244	855,034
Property, Plant and Equipment, Net	10,123,062	9,472,770
Deferred Debits and Other Assets:
Regulatory Assets	1,304,019	1,250,029
Prepaid PBOP	204,138	166,058
Other Long-Term Assets	162,836	144,368
Total Deferred Debits and Other Assets	1,670,993	1,560,455
Total Assets	12,886,299	11,888,259
Current Liabilities:
Notes Payable	195,000	10,500
Notes Payable to Eversource Parent	21,300	30,300
Long-Term Debt – Current Portion	250,000	95,000
Accounts Payable	383,558	363,691
Accounts Payable to Affiliated Companies	95,703	96,307
Obligations to Third Party Suppliers	98,572	108,827
Renewable Portfolio Standards Compliance Obligations	127,536	150,429
Regulatory Liabilities	164,761	209,180
Other Current Liabilities	72,118	71,333
Total Current Liabilities	1,408,548	1,135,567
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,459,906	1,357,265
Regulatory Liabilities	1,550,390	1,516,585
Accrued Pension, SERP and PBOP	172,571	108,243
Other Long-Term Liabilities	337,245	320,629
Total Deferred Credits and Other Liabilities	3,520,112	3,302,722
Capitalization:
Long-Term Debt	3,393,221	3,247,086
Noncontrolling Interest - Preferred Stock of Subsidiaries	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,993,942	1,813,442
Retained Earnings	2,527,167	2,346,287
Accumulated Other Comprehensive Income	309	155
Common Shareholders' Equity	4,521,418	4,159,884
Commitments and Contingencies (Note 13)
Total Liabilities and Capitalization	12,886,299	11,888,259
Public Service Company of New Hampshire
Current Assets:
Cash	141	413
Receivables, Net (net of allowance for uncollectible accounts of $358,851 and $224,821 as of December 31, 2020 and 2019, respectively)	119,899	99,934
Unbilled Revenues	46,041	48,146
Fuel, Materials, Supplies and REC Inventory	26,829	24,957
Regulatory Assets	115,852	84,053
Accounts Receivable from Affiliated Companies	10,925	6,763
Special Deposits	36,767	32,513
Prepaid Property Taxes	26,257	15,768
Prepayments and Other Current Assets	10,788	3,663
Total Current Assets	393,499	316,210
Property, Plant and Equipment, Net	3,374,270	3,129,506
Deferred Debits and Other Assets:
Regulatory Assets	873,203	861,672
Other Long-Term Assets	23,733	43,270
Total Deferred Debits and Other Assets	896,936	904,942
Total Assets	4,664,705	4,350,658
Current Liabilities:
Notes Payable to Eversource Parent	46,300	27,000
Long-Term Debt – Current Portion	282,000	0
Rate Reduction Bonds – Current Portion	43,210	43,210
Accounts Payable	132,635	127,081
Accounts Payable to Affiliated Companies	43,397	37,946
Regulatory Liabilities	58,756	65,766
Accrued Interest	19,671	19,138
Other Current Liabilities	38,816	32,736
Total Current Liabilities	664,785	352,877
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	537,627	506,212
Regulatory Liabilities	383,183	413,381
Accrued Pension, SERP and PBOP	184,715	157,638
Other Long-Term Liabilities	37,874	37,075
Total Deferred Credits and Other Liabilities	1,143,399	1,114,306
Capitalization:
Long-Term Debt	817,070	951,620
Rate Reduction Bonds	496,912	540,122
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	928,134	903,134
Retained Earnings	615,018	490,306
Accumulated Other Comprehensive Income	(613)	(1,707)
Common Shareholders' Equity	1,542,539	1,391,733
Commitments and Contingencies (Note 13)
Total Liabilities and Capitalization	$ 4,664,705	$ 4,350,658

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Allowance for uncollectible accounts	$ 358,851	$ 224,821
The Connecticut Light and Power Company
Allowance for uncollectible accounts	157,447	97,348
NSTAR Electric Company
Allowance for uncollectible accounts	91,583	75,406
Public Service Company of New Hampshire
Allowance for uncollectible accounts	$ 17,157	$ 10,497

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues	$ 8,904,430	$ 8,526,470	$ 8,448,201
Operating Expenses:
Purchased Power and Transmission	2,987,840	3,040,160	3,138,969
Operations and Maintenance	1,480,252	1,363,113	1,335,213
Depreciation	981,380	885,278	819,930
Amortization of Regulatory Assets, Net	177,679	195,380	252,026
Energy Efficiency Programs	535,760	501,369	472,380
Taxes Other Than Income Taxes	752,785	711,035	729,753
Impairment of Northern Pass Transmission	0	239,644	0
Total Operating Expenses	6,915,696	6,935,979	6,748,271
Operating Income	1,988,734	1,590,491	1,699,930
Interest Expense	538,452	533,197	498,805
Other Income, Net	108,590	132,777	128,366
Income Before Income Tax Expense	1,558,872	1,190,071	1,329,491
Income Tax Expense	346,186	273,499	288,972
Net Income	1,212,686	916,572	1,040,519
Net Income Attributable to Noncontrolling Interests	7,519	7,519	7,519
Net Income Attributable to Common Shareholders	$ 1,205,167	$ 909,053	$ 1,033,000
Basic Earnings Per Common Share (in dollars per share)	$ 3.56	$ 2.83	$ 3.25
Diluted Earnings Per Common Share (in dollars per share)	$ 3.55	$ 2.81	$ 3.25
Weighted Average Common Shares Outstanding:
Basic (in shares)	338,836,147	321,416,086	317,370,369
Diluted (in shares)	339,847,062	322,941,636	317,993,934
The Connecticut Light and Power Company
Operating Revenues	$ 3,547,527	$ 3,232,551	$ 3,096,174
Operating Expenses:
Purchased Power and Transmission	1,369,196	1,188,202	1,095,187
Operations and Maintenance	572,897	549,167	506,448
Depreciation	320,709	301,188	278,557
Amortization of Regulatory Assets, Net	58,412	51,621	129,021
Energy Efficiency Programs	141,453	118,235	93,977
Taxes Other Than Income Taxes	344,451	342,489	357,147
Total Operating Expenses	2,807,118	2,550,902	2,460,337
Operating Income	740,409	681,649	635,837
Interest Expense	153,547	151,357	151,727
Other Income, Net	20,774	17,531	22,663
Income Before Income Tax Expense	607,636	547,823	506,773
Income Tax Expense	149,702	136,971	129,056
Net Income	457,934	410,852	377,717
NSTAR Electric Company
Operating Revenues	2,941,148	3,044,642	3,112,926
Operating Expenses:
Purchased Power and Transmission	879,244	1,064,289	1,257,073
Operations and Maintenance	534,118	468,436	462,100
Depreciation	319,468	296,500	276,372
Amortization of Regulatory Assets, Net	83,248	103,735	46,654
Energy Efficiency Programs	263,986	289,206	292,288
Taxes Other Than Income Taxes	206,764	195,586	194,316
Total Operating Expenses	2,286,828	2,417,752	2,528,803
Operating Income	654,320	626,890	584,123
Interest Expense	130,508	114,198	105,193
Other Income, Net	52,017	44,577	53,066
Income Before Income Tax Expense	575,829	557,269	531,996
Income Tax Expense	130,828	125,313	148,906
Net Income	445,001	431,956	383,090
Public Service Company of New Hampshire
Operating Revenues	1,079,095	1,065,936	1,047,619
Operating Expenses:
Purchased Power and Transmission	364,067	398,449	370,246
Operations and Maintenance	219,325	210,995	210,541
Depreciation	100,372	93,737	92,055
Amortization of Regulatory Assets, Net	52,804	57,732	80,978
Energy Efficiency Programs	37,583	25,982	20,105
Taxes Other Than Income Taxes	81,611	62,574	77,280
Total Operating Expenses	855,762	849,469	851,205
Operating Income	223,333	216,467	196,414
Interest Expense	58,127	60,666	60,634
Other Income, Net	13,786	19,222	27,672
Income Before Income Tax Expense	178,992	175,023	163,452
Income Tax Expense	31,680	40,975	47,576
Net Income	$ 147,312	$ 134,048	$ 115,876

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Income	$ 1,212,686	$ 916,572	$ 1,040,519
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,596	1,393	1,756
Changes in Unrealized Gains/(Losses) on Marketable Securities	342	1,166	(547)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(13,290)	(7,618)	5,194
Other Comprehensive (Loss)/Income, Net of Tax	(11,352)	(5,059)	6,403
Comprehensive Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Comprehensive Income Attributable to Common Shareholders	1,193,815	903,994	1,039,403
The Connecticut Light and Power Company
Net Income	457,934	410,852	377,717
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	(26)	(26)	51
Changes in Unrealized Gains/(Losses) on Marketable Securities	12	41	(19)
Other Comprehensive (Loss)/Income, Net of Tax	(14)	15	32
Comprehensive Income Attributable to Common Shareholders	457,920	410,867	377,749
NSTAR Electric Company
Net Income	445,001	431,956	383,090
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	437	437	437
Changes in Unrealized Gains/(Losses) on Marketable Securities	3	12	(5)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(286)	1,084	13
Other Comprehensive (Loss)/Income, Net of Tax	154	1,533	445
Comprehensive Income Attributable to Common Shareholders	445,155	433,489	383,535
Public Service Company of New Hampshire
Net Income	147,312	134,048	115,876
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,075	1,075	1,104
Changes in Unrealized Gains/(Losses) on Marketable Securities	19	69	(33)
Other Comprehensive (Loss)/Income, Net of Tax	1,094	1,144	1,071
Comprehensive Income Attributable to Common Shareholders	$ 148,406	$ 135,192	$ 116,947

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Adoption of New Accounting Standard	Common Shares	Capital Surplus, Paid In	Retained Earnings	Retained EarningsAdoption of New Accounting Standard	Accumulated Other Comprehensive Loss	Treasury Stock	The Connecticut Light and Power Company	The Connecticut Light and Power CompanyAdoption of New Accounting Standard	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 CompanyRetained EarningsAdoption of New Accounting Standard	The Connecticut Light and Power CompanyAccumulated Other Comprehensive Loss	NSTAR Electric Company	NSTAR Electric CompanyAdoption of New Accounting Standard	NSTAR Electric CompanyCommon Shares	NSTAR Electric CompanyCapital Surplus, Paid In	NSTAR Electric CompanyRetained Earnings	NSTAR Electric CompanyRetained EarningsAdoption of New Accounting Standard	NSTAR Electric CompanyAccumulated Other Comprehensive Loss	Public Service Company of New Hampshire	Public Service Company of New HampshireAdoption of New Accounting Standard	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 HampshireRetained EarningsAdoption of New Accounting Standard	Public Service Company of New HampshireAccumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2017			316,885,808								6,035,205							200							301
Beginning 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				377,717			383,090				383,090			115,876				115,876
Return of Capital																							(530,000)			(530,000)
Dividends on Common Stock	(640,110)				(640,110)				(60,000)				(60,000)			(228,000)				(228,000)
Dividends on Preferred Stock	(7,519)				(7,519)				(5,559)				(5,559)			(1,960)				(1,960)
Capital Contributions from Eversource Parent									300,000			300,000				130,500			130,500				365,000			365,000
Long-Term Incentive Plan Activity	(543)			(543)
Other Changes in Shareholders' Equity	1,825			1,825
Other Comprehensive Loss	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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	916,572				916,572				410,852				410,852			431,956				431,956			134,048				134,048
Dividends on Common Stock	(685,979)				(685,979)				(341,800)				(341,800)			(181,800)				(181,800)			(271,000)				(271,000)
Dividends on Preferred Stock	(7,519)				(7,519)				(5,559)				(5,559)			(1,960)				(1,960)
Capital Contributions from Eversource Parent	225,000								125,000			125,000				180,000			180,000							225,000
Issuance of Common Shares (in shares)			11,980,000
Issuance of Common Shares	868,550		$ 59,900	808,650
Long-Term Incentive Plan Activity	3,434			3,434
Issuance of Treasury Shares (in shares)			1,014,837
Issuance of Treasury Shares	69,474			50,758				18,716
Capital Stock Expense	(16,296)			(16,296)
Other Comprehensive Loss	$ (5,059)						(5,059)		15						15	1,533						1,533	1,144						1,144
Ending balance (in shares) at Dec. 31, 2019	329,880,645		329,880,645								6,035,205							200							301
Ending balance at Dec. 31, 2019	$ 12,629,994	$ (1,514)	$ 1,729,292	7,087,768	4,177,048	$ (1,514)	(65,059)	(299,055)	4,387,825	$ (900)	$ 60,352	2,535,765	1,791,392	$ (900)	316	4,159,884	$ (161)	$ 0	1,813,442	2,346,287	$ (161)	155	1,391,733	$ (300)	$ 0	903,134	490,306	$ (300)	(1,707)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,212,686				1,212,686				457,934				457,934			445,001				445,001			147,312				147,312
Return of Capital																							(22,300)				(22,300)
Dividends on Common Stock	(767,500)				(767,500)				(69,500)				(69,500)			(262,000)				(262,000)
Dividends on Preferred Stock	(7,519)				(7,519)				(5,559)				(5,559)			(1,960)				(1,960)
Capital Contributions from Eversource Parent									275,000			275,000				180,500			180,500				25,000			25,000
Issuance of Common Shares (in shares)			11,960,000
Issuance of Common Shares	949,660		$ 59,800	889,860
Long-Term Incentive Plan Activity	7,890			7,890
Issuance of Treasury Shares (in shares)			1,113,378
Issuance of Treasury Shares	71,888			50,812				21,076
Capital Stock Expense	(20,667)			(20,667)
Other Comprehensive Loss	$ (11,352)						(11,352)		(14)						(14)	154						154	1,094						1,094
Ending balance (in shares) at Dec. 31, 2020	342,954,023		342,954,023								6,035,205							200							301
Ending balance at Dec. 31, 2020	$ 14,063,566		$ 1,789,092	$ 8,015,663	$ 4,613,201		$ (76,411)	$ (277,979)	$ 5,044,786		$ 60,352	$ 2,810,765	$ 2,173,367		$ 302	$ 4,521,418		$ 0	$ 1,993,942	$ 2,527,167		$ 309	$ 1,542,539		$ 0	$ 928,134	$ 615,018		$ (613)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Dividends on Common Shares (in dollars per share)	$ 2.27	$ 2.14	$ 2.02
Par value of Common Shares (in dollars per share)	$ 5	$ 5

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net Income	$ 1,212,686	$ 916,572	$ 1,040,519
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	981,380	885,278	819,930
Deferred Income Taxes	257,154	209,812	174,812
Uncollectible Expense	53,461	63,446	61,337
Pension, SERP and PBOP Expense, Net	12,888	22,000	5,498
Pension and PBOP Contributions	(111,524)	(121,782)	(194,947)
Regulatory (Under)/Over Recoveries, Net	(516,411)	(124,870)	34,920
Amortization	177,679	195,380	252,026
Payments Related to CYAPC's DOE Pre-1983 Spent Nuclear Fuel Obligation	0	(29,000)	(145,000)
Proceeds from DOE Spent Nuclear Fuel Litigation	0	68,840	0
Impairment of Northern Pass Transmission	0	239,644	0
Other	(174,289)	(196,087)	(111,225)
Changes in Current Assets and Liabilities:
Accounts Receivables from Subsidiaries	(351,843)	(98,716)	(141,433)
Fuel, Materials, Supplies and REC Inventory	(15,404)	(8,074)	(831)
Taxes Receivable/Accrued, Net	43,819	(16,129)	(67,770)
Accounts Payable	122,567	14,866	24,481
Other Current Assets and Liabilities, Net	(9,591)	(11,603)	78,226
Net Cash Flows Provided by Operating Activities	1,682,572	2,009,577	1,830,543
Investing Activities:
Investments in Property, Plant and Equipment	(2,942,996)	(2,911,489)	(2,569,936)
Proceeds from Sales of Marketable Securities	434,124	566,592	900,749
Proceeds from Sales of Marketable Securities Used to Pay Pre-1983 Spent Nuclear Fuel Obligation	0	0	145,000
Purchases of Marketable Securities	(401,823)	(537,258)	(908,387)
Acquisition of Assets of Columbia Gas of Massachusetts, Net of Restricted Cash	(1,113,252)	0	0
Investments in Unconsolidated Affiliates, Net	(239,673)	(416,337)	(205,150)
Other Investing Activities	23,809	24,204	6,754
Net Cash Flows Used in Investing Activities	(4,129,275)	(3,274,288)	(2,437,046)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	928,992	852,254	0
Cash Dividends on Common Shares	(744,665)	(663,239)	(640,110)
Cash Dividends on Preferred Stock	(7,519)	(7,519)	(7,519)
Increase in Notes Payable	13,955	325,370
Decrease in Notes Payable			(379,310)
(Repayments)/Issuance of Rate Reduction Bonds	(43,210)	(52,332)	635,663
Issuance of Long-Term Debt	2,760,000	1,520,000	2,200,000
Retirement of Long-Term Debt	(327,236)	(801,078)	(1,050,330)
Other Financing Activities	14,273	(1,006)	(28,457)
Net Cash Flows Provided by/(Used in) Financing Activities	2,594,590	1,172,450	729,937
Net Increase/(Decrease) in Cash and Restricted Cash	147,887	(92,261)	123,434
Cash and Restricted Cash - Beginning of Year	117,063	209,324	85,890
Cash and Restricted Cash - End of Year	264,950	117,063	209,324
Hingham Water System
Investing Activities:
Proceeds from the Sale of Assets	110,536	0	0
PSNH Generation Assets
Investing Activities:
Proceeds from the Sale of Assets	0	0	193,924
The Connecticut Light and Power Company
Operating Activities:
Net Income	457,934	410,852	377,717
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	320,709	301,188	278,557
Deferred Income Taxes	144,527	54,005	54,859
Uncollectible Expense	12,882	15,948	15,831
Pension, SERP and PBOP Expense, Net	11,372	12,761	8,943
Pension and PBOP Contributions	(23,200)	(24,000)	(41,150)
Regulatory (Under)/Over Recoveries, Net	(279,941)	(24,653)	(53,372)
Amortization of Regulatory Assets, Net	58,412	51,621	129,021
Other	(115,213)	(80,266)	(69,786)
Changes in Current Assets and Liabilities:
Accounts Receivables from Subsidiaries	(126,638)	(52,746)	(67,334)
Fuel, Materials, Supplies and REC Inventory	(7,225)	(6,171)	3,909
Taxes Receivable/Accrued, Net	(12,014)	(23,089)	8,954
Accounts Payable	(17,028)	102,344	(76,924)
Other Current Assets and Liabilities, Net	(27,504)	(11,350)	18,846
Net Cash Flows Provided by Operating Activities	397,073	726,444	588,071
Investing Activities:
Investments in Property, Plant and Equipment	(833,973)	(917,532)	(864,136)
Other Investing Activities	573	714	209
Net Cash Flows Used in Investing Activities	(833,400)	(916,818)	(863,927)
Financing Activities:
Cash Dividends on Common Shares	(69,500)	(341,800)	(60,000)
Cash Dividends on Preferred Stock	(5,559)	(5,559)	(5,559)
Increase/(Decrease) in Notes Payable to Eversource Parent	(63,800)	63,800	(69,500)
Issuance of Long-Term Debt	400,000	500,000	500,000
Retirement of Long-Term Debt	0	(250,000)	(300,000)
Capital Contributions from Eversource Parent	275,000	125,000	300,000
Other Financing Activities	(4,976)	12,291	(7,091)
Net Cash Flows Provided by/(Used in) Financing Activities	531,165	103,732	357,850
Net Increase/(Decrease) in Cash and Restricted Cash	94,838	(86,642)	81,994
Cash and Restricted Cash - Beginning of Year	4,971	91,613	9,619
Cash and Restricted Cash - End of Year	99,809	4,971	91,613
NSTAR Electric Company
Operating Activities:
Net Income	445,001	431,956	383,090
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	319,468	296,500	276,372
Deferred Income Taxes	72,595	27,107	41,438
Uncollectible Expense	15,293	25,079	22,279
Pension, SERP and PBOP Expense, Net	(18,132)	(12,399)	(21,521)
Pension and PBOP Contributions	(650)	(6,359)	(61,751)
Regulatory (Under)/Over Recoveries, Net	(186,081)	(60,863)	149,647
Amortization of Regulatory Assets, Net	83,248	103,735	46,654
Other	(62,054)	(78,220)	(65,523)
Changes in Current Assets and Liabilities:
Accounts Receivables from Subsidiaries	(81,571)	(11,087)	(26,403)
Fuel, Materials, Supplies and REC Inventory	(9,834)	(9,858)	(18,685)
Taxes Receivable/Accrued, Net	(44,045)	14,147	(33,900)
Accounts Payable	25,573	(22,659)	37,140
Other Current Assets and Liabilities, Net	(32,997)	1,194	51,674
Net Cash Flows Provided by Operating Activities	525,814	698,273	780,511
Investing Activities:
Investments in Property, Plant and Equipment	(907,000)	(861,391)	(725,766)
Other Investing Activities	159	86	58
Net Cash Flows Used in Investing Activities	(906,841)	(861,305)	(725,708)
Financing Activities:
Cash Dividends on Common Shares	(262,000)	(181,800)	(228,000)
Cash Dividends on Preferred Stock	(1,960)	(1,960)	(1,960)
Increase in Notes Payable	184,500		44,500
Decrease in Notes Payable		(268,000)
Increase/(Decrease) in Notes Payable to Eversource Parent	(9,000)	30,300	0
Issuance of Long-Term Debt	400,000	400,000	0
Retirement of Long-Term Debt	(95,000)	0	0
Capital Contributions from Eversource Parent	180,500	180,000	130,500
Other Financing Activities	(4,915)	(3,855)	108
Net Cash Flows Provided by/(Used in) Financing Activities	392,125	154,685	(54,852)
Net Increase/(Decrease) in Cash and Restricted Cash	11,098	(8,347)	(49)
Cash and Restricted Cash - Beginning of Year	6,312	14,659	14,708
Cash and Restricted Cash - End of Year	17,410	6,312	14,659
Public Service Company of New Hampshire
Operating Activities:
Net Income	147,312	134,048	115,876
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	100,372	93,737	92,055
Deferred Income Taxes	7,337	15,917	35,924
Uncollectible Expense	5,164	6,726	6,383
Pension, SERP and PBOP Expense, Net	(1,255)	417	754
Pension and PBOP Contributions	(19,500)	(15,400)	0
Regulatory (Under)/Over Recoveries, Net	(45,830)	(26,288)	(27,264)
Amortization of Regulatory Assets, Net	52,804	57,732	80,978
Other	(4,842)	(28,228)	(15,363)
Changes in Current Assets and Liabilities:
Accounts Receivables from Subsidiaries	(33,612)	(210)	(19,307)
Fuel, Materials, Supplies and REC Inventory	(1,872)	1,902	16,928
Taxes Receivable/Accrued, Net	(6,942)	25,374	(19,970)
Accounts Payable	27,270	12,281	(10,147)
Other Current Assets and Liabilities, Net	(7,738)	(3,573)	3,028
Net Cash Flows Provided by Operating Activities	218,668	274,435	259,875
Investing Activities:
Investments in Property, Plant and Equipment	(342,586)	(308,993)	(323,910)
Proceeds from the Sale of Assets	0	0	193,924
Proceeds from the Sale of Property	0	0	4,782
Other Investing Activities	982	1,023	437
Net Cash Flows Used in Investing Activities	(341,604)	(307,970)	(124,767)
Financing Activities:
Cash Dividends on Common Shares	(22,300)	(271,000)	(150,000)
Increase/(Decrease) in Notes Payable to Eversource Parent	19,300	(30,000)	(205,900)
(Repayments)/Issuance of Rate Reduction Bonds	(43,210)	(52,332)	635,663
Return of Capital	0	0	(530,000)
Issuance of Long-Term Debt	150,000	300,000	0
Retirement of Long-Term Debt	0	(150,000)	(199,250)
Capital Contributions from Eversource Parent	25,000	225,000	365,000
Other Financing Activities	(2,987)	(4,168)	(89)
Net Cash Flows Provided by/(Used in) Financing Activities	125,803	17,500	(84,576)
Net Increase/(Decrease) in Cash and Restricted Cash	2,867	(16,035)	50,532
Cash and Restricted Cash - Beginning of Year	36,688	52,723	2,191
Cash and Restricted Cash - End of Year	$ 39,555	$ 36,688	$ 52,723

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2020
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, NSTAR Gas and Eversource Gas Company of Massachusetts (EGMA) (natural gas utilities) and Aquarion (water utilities). Eversource provides energy delivery and/or water service to approximately 4.3 million electric, natural gas and water customers through nine regulated utilities in Connecticut, Massachusetts and New Hampshire. On October 9, 2020, Eversource completed the acquisition of certain assets and liabilities that comprised NiSource’s natural gas distribution business in Massachusetts, which was previously doing business as Columbia Gas of Massachusetts (CMA). The natural gas distribution assets acquired from CMA were assigned to EGMA, an indirect wholly-owned subsidiary of Eversource formed in 2020. The LNG assets acquired from CMA were assigned to Hopkinton LNG Corp. The cash purchase price was $1.1 billion, plus a target working capital amount of $69.6 million, which is subject to adjustment to reflect actual working capital as of the closing date that has not yet been finalized. Eversource's consolidated financial information includes the results of EGMA beginning from the date of acquisition on October 9, 2020. See Note 24, "Acquisition of Assets of Columbia Gas of Massachusetts," for further information. 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, EGMA 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. NSTAR Gas and EGMA are engaged in the distribution and sale of natural gas to customers within Massachusetts and Yankee Gas is engaged in the distribution and sale of natural gas to customers within Connecticut. 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 all its thermal and hydroelectric generation assets in 2018. Eversource Service, Eversource's service company, and several wholly-owned real estate subsidiaries of Eversource, provide support services to Eversource, including its regulated companies. 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 the operations of CYAPC and YAEC, both of which are inactive regional nuclear power companies engaged in the long-term storage of their spent nuclear fuel. 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 holds several equity ownership interests that are not consolidated and are accounted for under the equity method. 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. 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. COVID-19 has adversely affected workers and the economy and caused volatility in the financial markets. Due to the inherent uncertainty of the unprecedented and evolving situation, we continue to closely monitor how COVID-19 related developments affect Eversource. Based on available information, we have not experienced significant impacts directly related to the pandemic that have adversely affected our current operations or results of operations. The extent of the impact to us in the future will vary and depend in large part on the duration, scope and severity of the pandemic and the timing and extent of COVID-19 relief legislation, and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of planned proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19. We believe that we have in place, or are developing, successful mechanisms with our state regulatory commissions that allow, or will allow, us to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses, while balancing the impact on our customers’ bills and our operating cash flows. See Note 1F, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of December 31, 2020 in light of the COVID-19 pandemic. An extended economic slowdown has resulted in lower demand for electricity, natural gas and/or water by our commercial and industrial customers. However, fluctuations in retail sales volumes for CL&P, NSTAR Electric, Yankee Gas, NSTAR Gas, EGMA, and our Connecticut water distribution business do not materially impact earnings due to their respective state regulatory commission-approved distribution revenue decoupling mechanisms. As of December 31, 2020, we did not identify indicators or triggering events for impairments to our goodwill, long-lived assets, available-for-sale debt securities, or equity method investment carrying values. Certain reclassifications of prior year data were made in the accompanying financial statements to conform to the current year presentation. As of December 31, 2020 and 2019, Eversource's carrying amount of goodwill was approximately $4.45 billion and $4.43 billion, respectively. Eversource performs an assessment for possible impairment of its goodwill at least annually. Eversource completed its annual goodwill impairment assessment for each of its reporting units as of October 1, 2020 and determined that no impairment exists. See Note 25, "Goodwill," for further information. C. Accounting Standards Accounting Standards Issued but Not Yet Effective: In December 2019, the FASB issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes , which eliminates certain exceptions to the general principles of current income tax guidance in ASC 740 and simplifies and improves consistency in application of that income tax guidance through clarifications of and amendments to ASC 740. The guidance is effective in the first quarter of 2021. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH. Accounting Standards Recently Adopted: On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (Topic 326), which provides a model for recognizing credit losses on financial instruments based on an estimate of current expected losses, requiring immediate recognition of credit losses expected over the life of a financial instrument. The Company determined the impacts of this standard on the allowance for credit losses on its financial instruments, primarily accounts receivable. As of January 1, 2020, the Company recorded increases to the allowance for uncollectible accounts for late fees and other receivable amounts of $1.6 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The impact to retained earnings, net of tax, was $1.5 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The Company also adjusted the allowance for uncollectible amounts of hardship receivables and other low-income assistance programs, which are ultimately collectible in rates at specified points in time under approved regulatory mechanisms. The impact on the allowance, which was offset in other long-term assets on the balance sheets, was an increase of $22.2 million and $21.3 million at Eversource and CL&P, respectively, and a decrease of $1.5 million at NSTAR Electric as of January 1, 2020. See Note 1F, “Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts,” for further information. The Company adopted ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment as of January 1, 2020 . The ASU simplified the accounting for goodwill impairment by removing a complex step in the goodwill impairment test. Under the guidance, goodwill impairment is measured as the amount by which its carrying value exceeds its fair value. The ASU did not have an impact on the financial statements of Eversource. On January 1, 2020, the Company adopted ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The ASU aligned the requirements for capitalizing costs incurred to implement a cloud computing arrangement with existing internal-use software guidance. The prospective implementation of this standard did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric or PSNH for the year ended December 31, 2020. On January 1, 2020, the Company prospectively adopted ASU 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The ASU modified fair value disclosure requirements . The standard includes new disclosure requirements for Level 3 unobservable inputs and eliminated the requirement to disclose certain information relating to transfers between levels. The modified disclosures are included in Note 1I, “Summary of Significant Accounting Policies - Fair Value Measurements,” and Note 4, “Derivative Instruments.” The Company adopted ASU 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General, Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans as of January 1, 2020. The guidance eliminated certain disclosures about defined benefit plans, added new disclosures, and clarified other requirements. This guidance is effective for fiscal years ending after December 15, 2020. Adoption of this guidance did not have a material effect on our annual financial statement disclosures. The modified disclosures are included in Note 11A, “Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pension.” D. Impairment of Northern Pass Transmission Northern Pass was Eversource's planned 1,090 MW HVDC transmission line that would have interconnected 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 a result of a final decision received on July 19, 2019 from the New Hampshire Supreme Court, whereby the court denied Northern Pass’ appeal and affirmed the NHSEC’s denial of Northern Pass’ siting application on NPT, Eversource concluded that construction of NPT was no longer probable and that there was no constructive path forward for the project. In 2019, Eversource terminated the project and permanently abandoned any further development. As a result, substantially all of the capitalized project costs, which totaled $318 million, certain of which were subject to cost reimbursement agreements, were impaired. Based on the conclusion that the construction of Northern Pass was no longer probable, Eversource recorded an impairment charge in 2019 for all of the project costs associated with Northern Pass, which were primarily engineering design, siting, permitting and legal costs, along with appropriate allowances for funds used during construction, and recognized a receivable for certain cost reimbursement agreements. Additionally, Eversource recorded an impairment charge associated with the land acquired to construct Northern Pass in order to recognize the land at its estimated fair value based on assessed values and transaction costs. In total, this resulted in a pre-tax impairment charge of $239.6 million within Operating Income on the statement of income for the year ended December 31, 2019 and was reflected in the Electric Transmission segment. The after-tax impact of the impairment charge was $204.4 million, or $0.64 per share, after giving effect to the estimated fair value of the related land, reimbursement agreements, and the impact of expected income tax benefits associated with the impairment charge. As a result of the decision to terminate the NPT project and permanently abandon any further development, Eversource does not expect any future cash expenditures associated with this project. E. Cash Cash includes cash on hand. At the end of each reporting period, any overdraft amounts are reclassified from Cash to Accounts Payable on the balance sheets. F. Allowance for Uncollectible Accounts Receivables, Net on the balance sheets primarily includes trade receivables from retail customers and customers related to wholesale transmission contracts, wholesale market sales, sales of RECs and property rentals. Receivables, Net also includes customer receivables for the purchase of electricity from a competitive third party supplier, the current portion of customer energy efficiency loans, property damage receivables and other miscellaneous receivables. There is no material concentration of receivables. Receivables are recorded at amortized cost, net of a credit loss provision (or allowance for uncollectible accounts). Receivables are presented net of expected credit losses at estimated net realizable value by maintaining an allowance for uncollectible accounts. Effective January 1, 2020, the current expected credit loss (CECL) model was applied to receivables for purposes of calculating the allowance for uncollectible accounts. This model is based on expected losses and results in the recognition of estimated expected credit losses, including uncollectible amounts for both billed and unbilled revenues, over the life of the receivable at the time a receivable is recorded. Receivables, net of reserves, increased $206.5 million ($58.3 million at CL&P, $56.3 million at NSTAR Electric, and $20.0 million at PSNH) in 2020, as compared to 2019, due primarily to an increase in delinquent receivables from customers attributable to the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Receivables, net of reserves, also increased due to the addition of EGMA of $65.8 million as of December 31, 2020. The allowance for uncollectible accounts is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. Factors in determining credit loss include historical collection, write-off experience, and management's assessment of collectability from customers, including current conditions, reasonable forecasts, and expectations of future collectability and collection efforts. Management continuously assesses the collectability of receivables and adjusts estimates based on actual experience and future expectations based on economic indicators, collection efforts and other factors. Management also monitors the aging analysis of receivables to determine if there are changes in the collections of accounts receivable. Receivable balances are written off against the allowance for uncollectible accounts when the customer accounts are no longer in service and these balances are deemed to be uncollectible. As of December 31, 2020, management evaluated the adequacy of the allowance for uncollectible accounts in light of the COVID-19 pandemic and the related economic downturn. This evaluation included an analysis of collection and customer payment trends, economic conditions, delinquency statistics, aging-based quantitative assessments, the impact on residential customer bills because of energy usage and change in rates, flexible payment plans and financial hardship arrearage management programs being offered to customers, and COVID-19 developments, including any potential federal governmental pandemic relief programs and the expansion of unemployment benefit initiatives, which help to mitigate the potential for increasing customer account delinquencies. Additionally, management considered past economic declines and corresponding uncollectible reserves as part of the current assessment. This evaluation has shown that our operating companies have experienced an increase in aged receivables and some lower cash collections from customers because of the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Based upon the evaluation performed, for the year ended December 31, 2020, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $31.5 million for Eversource ($2.8 million for CL&P, $11.0 million for NSTAR Electric, $2.3 million for PSNH and $15.4 million at our natural gas businesses). These COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs or deferred through existing regulatory tracking mechanisms that recover uncollectible energy supply costs, as management believes it is probable that these costs will ultimately be recovered from customers in rates. Management concluded that the reserve balance as of December 31, 2020 adequately reflected the collection risk and net realizable value for Eversource’s receivables. Management will continue to evaluate the adequacy of the uncollectible allowance in future reporting periods based on an ongoing assessment of accounts receivable collections, delinquency statistics, and analysis of aging-based quantitative assessments. 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. Management also believes that uncollectible hardship accounts receivable at EGMA will be recoverable in future rates. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. Hardship customers are protected from shut-off in certain circumstances, and historical collection experience has reflected a higher default risk as compared to the rest of the receivable population. As a result of the adoption of ASU 2016-13, management aligned the allowance for uncollectible hardship accounts across all regulatory jurisdictions, using a higher credit risk profile for this pool of trade receivables as compared to non-hardship receivables. Implementation impacts of the accounting standard on the allowance for uncollectible hardship accounts are reflected in the rollforward of the uncollectible allowance in the table below. The allowance for uncollectible hardship accounts is included in the total uncollectible allowance balance. The total allowance for uncollectible accounts is included in Receivables, Net on the balance sheets. The activity in the allowance for uncollectible accounts by portfolio segment is as follows: As of December 31, 2020 Eversource CL&P NSTAR Electric PSNH (Millions of Dollars) Hardship Accounts Retail (Non-Hardship), Total Allowance Hardship Accounts Retail (Non-Hardship), Total Allowance Hardship Accounts Retail (Non-Hardship), Total Allowance Total Allowance Beginning Balance $ 143.3 $ 81.5 $ 224.8 $ 80.1 $ 17.2 $ 97.3 $ 43.9 $ 31.5 $ 75.4 $ 10.5 ASU 2016-13 Implementation Impact on January 1, 2020 21.6 2.2 23.8 21.3 0.9 22.2 (1.6) 0.3 (1.3) 0.3 Increase due to CMA asset acquisition — 24.2 24.2 — — — — — — — Uncollectible Expense (1) — 53.5 53.5 — 12.9 12.9 — 15.3 15.3 5.2 Uncollectible Costs Deferred (2) 43.1 53.9 97.0 38.2 10.8 49.0 (1.7) 26.4 24.7 7.4 Write-Offs (14.7) (63.3) (78.0) (11.9) (17.8) (29.7) (0.9) (26.3) (27.2) (6.9) Recoveries Collected 1.5 12.1 13.6 1.4 4.3 5.7 — 4.7 4.7 0.7 Ending Balance $ 194.8 $ 164.1 $ 358.9 $ 129.1 $ 28.3 $ 157.4 $ 39.7 $ 51.9 $ 91.6 $ 17.2 (1) Uncollectible expense associated with customer and other accounts receivable is included in Operations and Maintenance expense on the statements of income. For the years ended December 31, 2019 and 2018, uncollectible expense included in Operations and Maintenance Expense was $63.4 million and $61.3 million for Eversource, $15.9 million and $15.8 million for CL&P, $25.1 million and $22.3 million for NSTAR Electric and $6.7 million and $6.4 million for PSNH, respectively. (2) The current period provision for expected credit losses is deferred as a regulatory cost on the balance sheets, as this amount is ultimately recovered in rates. Amounts include uncollectible costs for hardship accounts and other customer receivables, including uncollectible amounts related to COVID-19. G. Transfer of Energy Efficiency Loans CL&P has transferred a portion of its energy efficiency customer loan portfolio to 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, with a maximum amount outstanding under this program of $55 million. The amounts of the loans are included in Accounts Receivable, Net and Other Long-Term Assets, and are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet. The current and long-term portions totaled $12.9 million and $9.5 million, respectively, as of December 31, 2020, and $16.5 million and $18.2 million, respectively, as of December 31, 2019. H. Fuel, Materials, Supplies and REC Inventory Fuel, Materials, Supplies and REC 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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Fuel $ 38.2 $ — $ — $ — $ 26.7 $ — $ — $ — Materials and Supplies 151.3 57.9 62.1 22.5 132.9 50.7 54.7 18.5 RECs 76.1 — 71.8 4.3 75.9 — 69.4 6.5 Total $ 265.6 $ 57.9 $ 133.9 $ 26.8 $ 235.5 $ 50.7 $ 124.1 $ 25.0 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, long-lived assets, equity method investments, and AROs, and in the valuation of the acquisition of CMA in 2020. The fair value measurement guidance was also applied in estimating the 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. The levels of the fair value hierarchy are described below: Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products. 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, "Investments in Unconsolidated Affiliates," Note 7, "Asset Retirement Obligations," Note 11A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," Note 15, "Fair Value of Financial Instruments," Note 24, "Acquisition of Assets of Columbia Gas of Massachusetts," and Note 25, “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. 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. 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. 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. 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) 2020 2019 2018 Eversource - Natural Gas and Fuel $ 464.2 $ 462.1 $ 442.6 PSNH - Fuel (1) — — 7.9 (1) PSNH completed the sale of its generation assets in 2018. 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. AFUDC costs and the weighted-average AFUDC rates were as follows: Eversource For the Years Ended December 31, (Millions of Dollars, except percentages) 2020 2019 2018 Borrowed Funds $ 23.7 $ 25.6 $ 19.7 Equity Funds 42.0 45.0 44.0 Total AFUDC $ 65.7 $ 70.6 $ 63.7 Average AFUDC Rate 5.0 % 5.4 % 4.9 % For the Years Ended December

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	12 Months Ended
	Dec. 31, 2020
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, plus a return on investment. The application of accounting guidance for rate-regulated enterprises results in recording regulatory assets and liabilities. Regulatory assets represent the deferral of incurred costs that are probable of future recovery in customer rates. Regulatory assets are amortized as the incurred costs are recovered through customer rates. Regulatory liabilities represent either revenues received from customers to fund expected costs that have not yet been incurred or probable future refunds to customers. Management believes it is probable that each of the regulated companies will recover its respective investments in long-lived assets and the regulatory assets that have been recorded. If management were to determine that it could no longer apply the accounting guidance applicable to rate-regulated enterprises, or if management could not conclude it is probable that costs would be recovered from customers in future rates, the applicable 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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Benefit Costs $ 2,794.2 $ 632.3 $ 690.0 $ 267.6 $ 2,382.9 $ 539.0 $ 629.8 $ 218.2 Income Taxes, Net 747.1 458.9 110.4 15.2 725.8 458.8 108.0 12.8 Securitized Stranded Costs 522.1 — — 522.1 565.3 — — 565.3 Storm Restoration Costs, Net 765.6 515.1 186.4 64.1 540.6 274.6 200.6 65.4 Regulatory Tracker Mechanisms 850.5 246.6 332.2 95.3 411.5 78.3 207.1 65.8 Derivative Liabilities 296.3 293.1 — — 334.5 329.2 — — Goodwill-related 314.7 — 270.2 — 331.5 — 284.6 — Asset Retirement Obligations 118.4 32.1 58.6 3.9 97.2 30.8 50.3 3.6 Other Regulatory Assets 161.0 33.7 56.1 20.9 125.4 25.2 55.2 14.7 Total Regulatory Assets 6,569.9 2,211.8 1,703.9 989.1 5,514.7 1,735.9 1,535.6 945.8 Less: Current Portion 1,076.6 345.6 399.9 115.9 651.1 178.6 285.6 84.1 Total Long-Term Regulatory Assets $ 5,493.3 $ 1,866.2 $ 1,304.0 $ 873.2 $ 4,863.6 $ 1,557.3 $ 1,250.0 $ 861.7 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. See Note 11A, "Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pension," for further information on regulatory benefit plan amounts recognized and amortized during the year. 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 12, "Income Taxes," to the financial statements. Securitized Stranded Costs: In 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. For further information, see Note 10, "Rate Reduction Bonds and Variable Interest Entities." 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. Of the total deferred storm restoration costs, $591 million is either pending regulatory approval or has yet to be filed with the applicable regulatory commission (including $390 million at CL&P, $166 million at NSTAR Electric and $35 million at PSNH). Storm Event: On August 4, 2020, Tropical Storm Isaias caused catastrophic damage to our electric distribution system, which resulted in significant amounts and durations of customer outages, primarily in Connecticut. In terms of customer outages, this storm was one of the worst in CL&P’s history. PURA has opened an investigation into CL&P's response to Tropical Storm Isaias. PURA will also investigate the prudence of costs incurred by CL&P to restore service as part of its response. CL&P is fully participating in PURA’s investigations and believes that these storm restoration costs were prudently incurred and meet the criteria for cost recovery. As a result, management does not expect the storm costs to have a material impact on the results of operations of Eversource or CL&P. Based on current estimates, the storm resulted in deferred storm restoration costs on our balance sheets of approximately $228 million at CL&P and $245 million at Eversource as of December 31, 2020. The estimated cost of restoration will change as additional cost information becomes available, final storm costs are deferred or capitalized, and post-storm restoration work is completed. The majority of incremental storm costs relate to third-party vendors that are external field crews needed to restore power and address municipal priorities. CL&P’s current estimate of total storm costs includes its projection of the cost of such vendors, but that estimate will change as CL&P receives and examines all storm related invoices. 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 (including securitized RRB charges), 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, Yankee Gas, NSTAR Gas and EGMA 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. 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. CL&P Rate Suspension: On July 31, 2020, PURA temporarily suspended its June 26, 2020 approval of certain delivery rate components effective July 1, 2020, and ordered CL&P to restore rates to those in effect as of June 30, 2020 in order to allow PURA time to reexamine the rates to ensure that CL&P is not over-collecting revenues in the short-term. Rates were adjusted effective August 1, 2020. On December 2, 2020, PURA issued a final decision in which it adjusted the timing of the annual rate adjustments for the Revenue Decoupling Mechanism Charge, the Transmission Adjustment Clause charge, the Non-Bypassable Federally Mandated Congestion Charge, and the Electric System Improvements Tracker so that these rates take effect on May 1st of each year, as opposed to the current process of adjusting rates each January 1 and July 1. The temporary suspension of rates has resulted in a current period under-recovery of costs, which results in an increase to our regulatory assets, with no impact on the statement of income other than carrying charges, and a delay in the collection of our costs. This deferral is reflected within Regulatory Tracker Mechanisms in the table above. 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, 2020, there were 19 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 ARO 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 spent nuclear fuel storage costs of the CYAPC, YAEC and MYAPC decommissioned nuclear power 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 $196.9 million (including $84.1 million for CL&P, $69.8 million for NSTAR Electric and $4.3 million for PSNH) and $146.0 million (including $51.8 million for CL&P, $55.7 million for NSTAR Electric and $18.0 million for PSNH) of additional regulatory costs as of December 31, 2020 and 2019, 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. As of December 31, 2020, net incremental costs as a result of COVID-19 deferred by Eversource totaled $24.0 million, of which $15.8 million ($3.0 million at CL&P, $6.8 million at NSTAR Electric and $0.6 million at PSNH) was related to non-tracked uncollectible expense and $8.2 million ($1.7 million at CL&P, $5.1 million at NSTAR Electric and $0.5 million at PSNH) related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment. 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 $0.2 million and $0.5 million for CL&P as of December 31, 2020 and 2019, respectively, and $5.1 million and $6.5 million for PSNH as of December 31, 2020 and 2019, respectively. These carrying costs will be recovered from customers in future rates. Regulatory Liabilities: The components of regulatory liabilities were as follows: As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH EDIT due to Tax Cuts and Jobs Act of 2017 $ 2,778.6 $ 1,010.7 $ 1,044.0 $ 371.5 $ 2,844.6 $ 1,022.8 $ 1,071.2 $ 392.8 Cost of Removal 624.8 98.4 363.6 12.9 559.8 64.6 330.6 16.3 Benefit Costs 83.6 — 72.5 — 84.5 — 72.2 — Regulatory Tracker Mechanisms 366.5 148.9 139.7 47.8 325.1 94.8 165.6 57.0 AFUDC - Transmission 76.8 44.6 32.2 — 73.2 46.0 27.2 — Other Regulatory Liabilities 309.9 39.5 63.2 9.8 132.0 19.6 59.0 13.1 Total Regulatory Liabilities 4,240.2 1,342.1 1,715.2 442.0 4,019.2 1,247.8 1,725.8 479.2 Less: Current Portion 389.4 137.2 164.8 58.8 361.2 82.8 209.2 65.8 Total Long-Term Regulatory Liabilities $ 3,850.8 $ 1,204.9 $ 1,550.4 $ 383.2 $ 3,658.0 $ 1,165.0 $ 1,516.6 $ 413.4 EDIT due to Tax Cuts and Jobs Act of 2017: Pursuant to the Tax Cuts and Jobs Act of 2017, Eversource had remeasured its existing deferred federal income tax balances 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. EDIT liabilities related to property, plant, and equipment 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 PSNH (effective January 1, 2021), CL&P (effective May 1, 2019) and Yankee Gas (effective November 15, 2018), the refund of EDIT liabilities was incorporated into base distribution rates. For NSTAR Electric (effective January 1, 2019) and NSTAR Gas (effective February 1, 2019), the refund of EDIT liabilities occurred in rates through a new reconciling factor. The Connecticut water business has not yet begun to reflect the refund of EDIT in distribution rates. See " Recent Regulatory Developments " below for information on the PSNH 2020 rate settlement agreement and the impact on the EDIT balance. 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. FERC ROE Complaints : As of December 31, 2020, Eversource has a reserve established for the second ROE complaint period 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, 2020 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 13E, "Commitments and Contingencies – FERC ROE Complaints," for further information on developments in the pending ROE complaint proceedings. Recent Regulatory Developments : PSNH Distribution Rates: On December 15, 2020, the NHPUC approved an October 9, 2020 settlement agreement on permanent rates between PSNH and all parties to the proceeding. The NHPUC approved a permanent rate increase of $45.0 million effective January 1, 2021, inclusive of the temporary rate increase previously approved. PSNH was also permitted three step increases, effective January 1, 2021, August 1, 2021, and August 1, 2022, to reflect plant additions in calendar years 2019, 2020 and 2021, respectively. On December 23, 2020, the NHPUC approved the first step adjustment for 2019 plant in service to recover a revenue requirement of $10.6 million, subject to reconciliation after completion of an audit, effective January 1, 2021. The settlement agreement also established an authorized regulatory ROE of 9.3 percent with a 54.4 percent common equity ratio in PSNH’s capital structure and provided for a new tracker to recover regulatory assessments, vegetation management costs, property tax costs, and lost distribution revenue attributable to net metering. In addition, base distribution rates were adjusted to reflect the refund of EDIT from the Tax Cuts and Jobs Act of 2017. The settlement agreement allowed for the effect of the permanent rate increase to be extended back to the temporary rate period. In lieu of a customer rate increase for this recoupment of revenue, the NHPUC directed a portion of the total EDIT regulatory liability to offset bill impacts to customers. The impact of the settlement agreement resulted in an after-tax benefit to earnings in 2020 of $11.0 million at Eversource ($7.2 million at PSNH), due primarily to the reconciliation of permanent rates back to the temporary rate period resulting in a reduction of the EDIT regulatory liability, which reduced Income Tax Expense on the statement of income, and the allowed recovery of previously expensed costs. The earnings impact was partially offset by the negative impact from the over-refunding of the change in the 2018 federal corporate income tax rate as a result of the Tax Cuts and Jobs Act of 2017 that was reflected in temporary rates, which reduced Operating Revenues on the statement of income. PSNH Generation Asset Divestiture-Related Costs : On May 15, 2020, the NHPUC Audit Staff issued a final report on the audit of PSNH’s generation asset divestiture-related costs and resulting securitized and stranded costs. The findings in the audit report as well as other aspects of the divestiture process were further investigated by NHPUC Staff through the discovery phase, which was completed in July 2020. On September 30, 2020, PSNH filed a settlement agreement on the generation asset divestiture-related costs with the NHPUC Audit Staff. The settlement agreement resolved all issues with respect to PSNH’s divestiture of its generating assets and the recovery of $12.0 million of divestiture-related costs incurred above the $635.7 million amount previously securitized. On December 17, 2020, the NHPUC approved the additional $12.0 million proposed in the settlement agreement to be recovered over a one-year period through the SCRC rate beginning February 1, 2021. As a result of the settlement agreement, the $12.0 million of divestiture-related costs were transferred from Other Long-Term Assets to Regulatory Assets on the Eversource and PSNH balance sheets as of December 31, 2020. NSTAR Gas Rate Case : On October 30, 2020, the DPU approved a base distribution rate increase of $23.0 million effective November 1, 2020, compared to the original request of $38.0 million. NSTAR Gas' 2019 plant additions are allowed recovery beginning on November 1, 2021. Thus, the reduced revenue requirement reflects the removal of this recovery, among other adjustments. The DPU also approved NSTAR Gas' proposal to continue its ongoing Gas System Enhancement Program (GSEP), the inclusion of GSEP investments since 2015 into base rates, and the implementation of a 10-year performance-based ratemaking plan, which includes an inflation-based adjustment mechanism to annual base distribution rates. The decision allows an authorized regulatory ROE of 9.9 percent on a capital structure including 54.77 percent equity. The decision also approves a geothermal pilot program. The impact of the rate case decision resulted in a pre-tax charge to earnings in 2020 of $2.7 million at NSTAR Gas, primarily due to certain plant-related disallowances. EGMA Rate Settlement Agreement : On October 7, 2020, the DPU approved a rate settlement agreement, which approved the CMA asset acquisition as well as a rate stabilization plan, among other items. See Note 24, "Acquisition of Assets of Columbia Gas of Massachusetts" for further information.

PROPERTY, PLANT AND EQUIPMENT A

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	12 Months Ended
	Dec. 31, 2020
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) 2020 2019 Distribution - Electric $ 16,703.2 $ 15,880.0 Distribution - Natural Gas 6,111.2 3,931.1 Transmission - Electric 11,954.0 10,958.4 Distribution - Water 1,743.1 1,726.5 Solar 201.5 200.2 Utility 36,713.0 32,696.2 Other (1) 1,269.0 1,025.6 Property, Plant and Equipment, Gross 37,982.0 33,721.8 Less: Accumulated Depreciation Utility (8,476.3) (7,483.5) Other (477.6) (387.4) Total Accumulated Depreciation (8,953.9) (7,870.9) Property, Plant and Equipment, Net 29,028.1 25,850.9 Construction Work in Progress 1,854.4 1,734.6 Total Property, Plant and Equipment, Net $ 30,882.5 $ 27,585.5 As of December 31, 2020 2019 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH Distribution - Electric $ 6,820.7 $ 7,544.4 $ 2,378.4 $ 6,485.5 $ 7,163.7 $ 2,271.1 Transmission - Electric 5,512.0 4,701.3 1,742.4 5,043.0 4,411.9 1,498.7 Solar — 201.5 — — 200.2 — Property, Plant and Equipment, Gross 12,332.7 12,447.2 4,120.8 11,528.5 11,775.8 3,769.8 Less: Accumulated Depreciation (2,475.4) (3,074.1) (848.9) (2,385.7) (2,895.3) (799.9) Property, Plant and Equipment, Net 9,857.3 9,373.1 3,271.9 9,142.8 8,880.5 2,969.9 Construction Work in Progress 377.3 750.0 102.4 483.0 592.3 159.6 Total Property, Plant and Equipment, Net $ 10,234.6 $ 10,123.1 $ 3,374.3 $ 9,625.8 $ 9,472.8 $ 3,129.5 (1) These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company. On October 9, 2020, Eversource completed the CMA asset acquisition. EGMA’s net plant assets of $1.20 billion are reflected in the natural gas distribution asset category as of December 31, 2020. On July 31, 2020, Eversource sold its water system and treatment plant that supplies water to the towns of Hingham, Hull and North Cohasset to the town of Hingham, Massachusetts. Net property, plant and equipment of $63.9 million and goodwill of $23.6 million were included in determining the gain on sale. Proceeds from the sale were $110.5 million, with a pre-tax gain of $16.0 million (after-tax gain of $3.5 million) recognized within Operations and Maintenance Expense on the statement of income for the year ended December 31, 2020. The assets and liabilities associated with the sale of the business were previously reflected in the Water Distribution segment and reporting unit. Depreciation: 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) 2020 2019 2018 Eversource 3.0 % 3.0 % 2.9 % CL&P 2.8 % 2.8 % 2.8 % NSTAR Electric 2.8 % 2.8 % 2.8 % PSNH 2.8 % 2.8 % 2.8 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2020 (Years) Eversource CL&P NSTAR Electric PSNH Distribution - Electric 34.3 35.4 33.7 33.3 Distribution - Natural Gas 41.5 — — — Transmission - Electric 40.7 36.9 45.5 42.6 Distribution - Water 34.1 — — — Solar 24.3 — 24.3 — Other (1) 11.0 — — — (1) The estimated useful life of computer software, hardware and equipment primarily ranges from 5 to 15 years and of buildings is 40 years.

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 (Millions of Dollars) Fair Value Hierarchy Commodity Supply Netting (1) Net Amount Commodity Supply Netting (1) Net Amount Current Derivative Assets: CL&P Level 3 $ 13.7 $ (0.4) $ 13.3 $ 12.2 $ (0.4) $ 11.8 Long-Term Derivative Assets: CL&P Level 3 58.7 (1.8) 56.9 67.5 (2.1) 65.4 Current Derivative Liabilities: CL&P Level 3 (68.8) — (68.8) (67.8) — (67.8) Other Level 2 (3.3) 0.1 (3.2) (5.2) — (5.2) Long-Term Derivative Liabilities: CL&P Level 3 (294.5) — (294.5) (338.6) — (338.6) Other Level 2 — — — (0.1) — (0.1) (1) Amounts represent derivative assets and liabilities that Eversource elected to record net on the balance sheets. These amounts are subject to master netting agreements or similar agreements for which the right of offset exists. The business activities that result in the recognition of derivative assets also create exposure to various counterparties. As of December 31, 2020, 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 capacities of these contracts as of December 31, 2020 and 2019 were 675 MW and 676 MW, respectively. 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 had a contract to purchase 0.1 million MWh of energy per year through 2020. As of December 31, 2020 and 2019, Eversource had New York Mercantile Exchange (NYMEX) financial contracts for natural gas futures in order to reduce variability associated with the price of 8.9 million and 9.6 million MMBtu of natural gas, respectively. For the years ended December 31, 2020, 2019 and 2018, there were losses of $21.2 million, $20.7 million and $25.0 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 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 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, 2020 2019 CL&P Range Weighted Average (1) Period Covered Range Period Covered Capacity Prices $ 4.30 — 5.30 $ 4.63 per kW-Month 2024 - 2026 $ 3.01 — $ 7.34 per kW-Month 2023 - 2026 Forward Reserve 0.54 — 0.90 0.72 per kW-Month 2021 - 2024 0.80 — 1.90 per kW-Month 2020 - 2024 (1) Unobservable inputs were weighted by the relative future capacity and forward reserve prices and contractual MWs over the periods covered. Exit price premiums of 7.1 percent through 11.4 percent, or a weighted average of 10.3 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. The risk premium was weighted by the relative fair value of the net derivative instruments. 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, 2020 2019 Derivatives, Net: Fair Value as of Beginning of Period $ (329.2) $ (356.5) Net Realized/Unrealized Losses Included in Regulatory Assets (17.9) (15.0) Settlements 54.0 42.3 Fair Value as of End of Period $ (293.1) $ (329.2)

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2020
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. Equity Securities: Unrealized gains and losses on equity securities held in Eversource's non-qualified executive benefit trust are recorded in Other Income, Net on the statements of income. The fair value of these equity securities as of December 31, 2020 and 2019 was $40.9 million and $45.7 million, respectively. For the years ended December 31, 2020 and 2019, there were unrealized gains of $3.7 million and $9.8 million recorded in Other Income, Net related to these equity securities, respectively. Eversource's equity securities also include CYAPC's and YAEC's marketable securities held in spent nuclear fuel trusts, which had fair values of $205.1 million and $182.8 million as of December 31, 2020 and 2019, 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, 2020 2019 Eversource (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Debt Securities $ 213.1 $ 11.2 $ (0.1) $ 224.2 $ 228.4 $ 5.8 $ (0.1) $ 234.1 Eversource's debt securities include CYAPC's and YAEC's marketable securities held in spent nuclear fuel trusts in the amounts of $192.5 million and $198.1 million as of December 31, 2020 and 2019, 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, excluding amounts related to credit losses or losses on securities intended to be sold, which are recorded in Other Income, Net. There have been no significant unrealized losses and no credit losses for the years ended December 31, 2020 or 2019, and no allowance for credit losses as of December 31, 2020. Factors considered in determining whether a credit loss exists include adverse conditions specifically affecting the issuer, the payment history, ratings and rating changes of the security, and the severity of the impairment. For asset-backed debt securities, underlying collateral and expected future cash flows are also evaluated. Debt securities included in Eversource's non-qualified benefit trust portfolio are investment-grade bonds with a lower default risk based on their credit quality. As of December 31, 2020, the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Fair Less than one year (1) $ 43.6 $ 43.6 One to five years 57.4 59.7 Six to ten years 46.6 49.7 Greater than ten years 65.5 71.2 Total Debt Securities $ 213.1 $ 224.2 (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. 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, 2020 2019 Level 1: Mutual Funds and Equities $ 246.0 $ 228.5 Money Market Funds 41.2 46.0 Total Level 1 $ 287.2 $ 274.5 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 72.9 $ 96.8 Corporate Debt Securities 63.8 44.0 Asset-Backed Debt Securities 11.9 12.9 Municipal Bonds 24.0 26.7 Other Fixed Income Securities 10.4 7.7 Total Level 2 $ 183.0 $ 188.1 Total Marketable Securities $ 470.2 $ 462.6 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, 2020
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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Balance as of Beginning of Year $ 489.5 $ 32.0 $ 97.5 $ 4.2 $ 466.2 $ 33.5 $ 72.4 $ 4.0 Liability Assumed Upon CMA Asset Acquisition 20.1 — — — — — — — Liabilities Incurred During the Year 2.1 — 2.1 — 30.3 — 30.3 — Liabilities Settled During the Year (21.8) (0.7) (1.0) — (21.3) (3.6) — — Accretion 28.9 2.1 4.3 0.2 27.1 2.2 3.5 0.2 Revisions in Estimated Cash Flows (19.1) — (11.1) — (12.8) (0.1) (8.7) — Balance as of End of Year $ 499.7 $ 33.4 $ 91.8 $ 4.4 $ 489.5 $ 32.0 $ 97.5 $ 4.2 The ARO balance includes the current portion of $1.0 million for Eversource and NSTAR Electric as of December 31, 2019, which is included in Other Current Liabilities on the balance sheets. Eversource's amounts include CYAPC and YAEC's AROs of $330.3 million and $337.7 million as of December 31, 2020 and 2019, 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.

INVESTMENTS IN UNCONSOLIDATED A

INVESTMENTS IN UNCONSOLIDATED AFFILIATES	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
INVESTMENTS IN UNCONSOLIDATED AFFILIATES	INVESTMENTS IN UNCONSOLIDATED AFFILIATES Investments in entities that are not consolidated are included in 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. Eversource's investments included the following: Investment Balance as of December 31, (Millions of Dollars) Ownership Interest 2020 2019 Offshore Wind Business - North East Offshore and Bay State Wind 50 % $ 887.1 $ 649.3 Natural Gas Pipeline - Algonquin Gas Transmission, LLC 15 % 125.2 127.8 Renewable Energy Investment Fund 90 % 71.6 72.4 Other various 23.2 22.1 Total Investments in Unconsolidated Affiliates $ 1,107.1 $ 871.6 For the years ended December 31, 2020, 2019 and 2018, Eversource had equity in earnings, net of impairment, of unconsolidated affiliates of $14.2 million, $42.2 million, and $3.8 million, respectively. Eversource received dividends from its equity method investees of $21.8 million, $48.9 million, and $22.3 million, respectively, for the years ended December 31, 2020, 2019 and 2018. Investments in affiliates where Eversource has the ability to exercise significant influence, but not control, over an investee are initially recognized as an equity method investment at cost. Any differences between the cost of an investment and the amount of underlying equity in net assets of an investee are considered basis differences, and are determined based upon the estimated fair values of the investee's identifiable assets and liabilities. The carrying amount of Eversource’s offshore wind investments exceeded its share of underlying equity in net assets by $264.1 million and $240.3 million, respectively, as of December 31, 2020 and 2019. As of December 31, 2020, these basis differences are primarily comprised of $168.3 million of equity method goodwill that is not being amortized, intangible assets for PPAs, which will be amortized over the term of the PPAs, and capitalized interest. Offshore Wind Business: Eversource's offshore wind business includes ownership interests in North East Offshore and Bay State Wind, which together hold PPAs and contracts for the Revolution Wind, South Fork Wind, and Sunrise Wind projects, as well as offshore leases through BOEM. Eversource's offshore wind projects are being developed and constructed through a joint and equal partnership with Ørsted. On February 8, 2019, Eversource and Ørsted entered into an equal partnership to acquire key offshore wind assets in the Northeast. Eversource has a 50 percent ownership interest in North East Offshore, which holds the Revolution Wind and South Fork Wind projects, as well as a 257 square-mile lease off the coasts of Massachusetts and Rhode Island. Eversource also has a 50 percent ownership interest in Bay State Wind, which holds the Sunrise Wind project. Bay State Wind's separate 300-square-mile ocean lease is located approximately 25 miles south of the coast of Massachusetts adjacent to the North East Offshore area. NSTAR Electric: As of December 31, 2020 and 2019, NSTAR Electric's investments included a 14.5 percent ownership interest in two companies that transmit hydro-electricity imported from the Hydro-Quebec system in Canada of $8.6 million and $8.2 million, respectively. Impairment of Equity Method Investments: 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. During the year ended December 31, 2020, Eversource recorded an other-than-temporary impairment of $2.8 million within Other Income, Net on the statement of income, related to a write-off of an investment within a renewable energy fund.

SHORT-TERM DEBT

SHORT-TERM DEBT	12 Months Ended
	Dec. 31, 2020
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 and NSTAR Electric 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 October 25, 2019, 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, 2021. On December 18, 2019, 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 31, 2021. 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, 2020, PSNH's short-term debt authorization under the 10 percent of net fixed plant test plus $60 million totaled $383.9 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, 2020, CL&P had $907.6 million of unsecured debt capacity available under this authorization. Yankee Gas, NSTAR Gas and EGMA are not required to obtain approval from any state or federal authority to incur short-term debt. Short-Term Debt - Commercial Paper Programs and Credit Agreements : Eversource parent has a $2.00 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, Yankee Gas and Aquarion Water Company of Connecticut are parties to a five-year $1.45 billion revolving credit facility, which terminates on December 6, 2024. On October 21, 2020, Eversource parent and EGMA entered into a short-term $550 million re volving credit facility, which terminates on October 20, 2021. These revolving credit facilities serve to backstop Eversource parent's $2.00 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, which terminates on December 6, 2024. 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 Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2020 2019 2020 2019 2020 2019 Eversource Parent Commercial Paper Program $ 1,054.3 $ 1,224.9 $ 945.7 $ 225.1 0.25 % 1.98 % NSTAR Electric Commercial Paper Program 195.0 10.5 455.0 639.5 0.16 % 1.63 % There were no borrowings outstanding on the revolving credit facilities as of December 31, 2020 or 2019. On May 15, 2020, CL&P and PSNH entered into uncommitted line of credit agreements, which will expire by May 14, 2021. The CL&P agreements total $450 million and the PSNH agreements total $300 million. There are no borrowings outstanding on either the CL&P or PSNH uncommitted line of credit agreements as of December 31, 2020. Amounts outstanding under the commercial paper programs 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. Under the credit facilities described above, Eversource and its subsidiaries, including CL&P, NSTAR Electric, PSNH, NSTAR Gas, EGMA, Yankee Gas, and Aquarion Water Company of Connecticut, must comply with certain financial and non-financial covenants, including a consolidated debt to total capitalization ratio. As of December 31, 2020 and 2019, 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. The Company expects the future operating cash flows of Eversource, CL&P, NSTAR Electric and PSNH, along with existing borrowing availability and access to both debt and equity markets, will be sufficient to meet any working capital and future operating requirements, and capital investment forecasted opportunities.

LONG-TERM DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 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 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 500.0 500.0 4.000% 2018 Series A due 2048 800.0 800.0 0.750% 2020 Series A due 2025 400.0 — Total First Mortgage Bonds 3,794.8 3,394.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net 25.9 27.8 Unamortized Debt Issuance Costs (26.4) (25.0) CL&P Long-Term Debt $ 3,914.8 $ 3,518.1 NSTAR Electric (Millions of Dollars) As of December 31, 2020 2019 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 3.250% due 2029 400.0 400.0 3.950% due 2030 400.0 — Total Debentures 3,200.0 2,800.0 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 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 470.0 565.0 Less Amounts due Within One Year (250.0) (95.0) Unamortized Premiums and Discounts, Net (6.8) (4.1) Unamortized Debt Issuance Costs (20.0) (18.8) NSTAR Electric Long-Term Debt $ 3,393.2 $ 3,247.1 PSNH (Millions of Dollars) As of December 31, 2020 2019 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 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 3.600% Series T due 2049 300.0 300.0 2.400% Series U due 2050 150.0 — Total First Mortgage Bonds $ 1,107.0 $ 957.0 Less Amounts due Within One Year (282.0) — Unamortized Premiums and Discounts, Net (1.5) (0.7) Unamortized Debt Issuance Costs (6.4) (4.7) PSNH Long-Term Debt $ 817.1 $ 951.6 OTHER (Millions of Dollars) As of December 31, 2020 2019 Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050 $ 640.0 $ 620.0 NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050 500.0 460.0 Aquarion - Senior Note 4.000% due 2024 360.0 360.0 Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049 335.2 335.3 Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035 35.9 68.8 Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050 5,550.0 4,000.0 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 11.7 11.6 Fair Value Adjustment (1) 74.7 109.1 Less Fair Value Adjustment - Current Portion (1) (31.0) (31.3) Less Amounts due in One Year (490.2) (201.1) Commercial Paper Classified as Long-Term Debt — 346.3 Unamortized Premiums and Discounts, Net 46.5 (4.1) Unamortized Debt Issuance Costs (32.0) (20.6) Total Other Long-Term Debt $ 7,000.8 $ 6,054.0 Total Eversource Long-Term Debt $ 15,125.9 $ 13,770.8 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record long-term debt at fair value on the dates of the 2012 merger with NSTAR and the 2017 acquisition of Aquarion. Long-Term Debt Issuance Authorizations: On January 27, 2020, the DPU approved NSTAR Gas' request for authorization to issue up to $270 million in long-term debt through December 31, 2021. On July 31, 2020, the NHPUC approved PSNH's request for authorization to issue up to $200 million in long-term debt through December 31, 2020. On December 14, 2020, NSTAR Electric filed a petition with the DPU for authorization to issue $1.6 billion in long-term debt through December 31, 2023. On December 16, 2020, Aquarion Water Company of Connecticut filed an application with PURA for authorization to issue $100 million in long-term debt through December 31, 2021. Long-Term Debt Issuances and Repayments: The following table summarizes long-term debt issuances and repayments: (Millions of Dollars) Issuance/(Repayment) Issue Date or Repayment Date Maturity Date Use of Proceeds for Issuance/ CL&P: 0.75% Series A First Mortgage Bonds $ 400.0 December 2020 December 2025 Refinanced short-term borrowings, funded capital expenditures and working capital NSTAR Electric: 3.95% 2020 Debentures 400.0 March 2020 April 2030 Refinanced investments in eligible green expenditures, which were previously financed in 2018 and 2019 5.10% Series E Senior Notes (95.0) March 2020 March 2020 Paid at maturity PSNH: 2.40% Series U First Mortgage Bonds 150.0 August 2020 September 2050 Refinanced short-term borrowings, funded capital expenditures and working capital Other: Eversource Parent 3.45% Series P Senior Notes 350.0 January 2020 January 2050 Paid short-term borrowings Eversource Parent 3.45% Series P Senior Notes (1) 300.0 August 2020 January 2050 (2) Eversource Parent 0.80% Series Q Senior Notes 300.0 August 2020 August 2025 (2) Eversource Parent 1.65% Series R Senior Notes 600.0 August 2020 August 2030 (2) Eversource Parent 2.50% Series I Senior Notes (450.0) February 2021 March 2021 Paid on par call date in advance of maturity date NSTAR Gas 4.46% Series N First Mortgage Bonds (125.0) January 2020 January 2020 Paid at maturity NSTAR Gas 2.33% Series R First Mortgage Bonds 75.0 May 2020 May 2025 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes NSTAR Gas 3.15% Series S First Mortgage Bonds 115.0 May 2020 May 2050 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes NSTAR Gas 9.95% Series J First Mortgage Bonds (25.0) December 2020 December 2020 Paid at maturity Yankee Gas 4.87% Series K First Mortgage Bonds (50.0) April 2020 April 2020 Paid at maturity Yankee Gas 2.90% Series R First Mortgage Bonds 70.0 September 2020 September 2050 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes Aquarion Water Company of Massachusetts, Inc. and Aquarion Water Capital of Massachusetts, Inc. various term loans and general mortgage bonds (32.2) July 2020 Various Redeemed long-term debt in conjunction with the sale of assets to the Town of Hingham, Massachusetts (1) These senior notes are part of the same series issued by Eversource parent in January 2020. The aggregate outstanding principal amount of these senior notes is now $650 million. (2) The proceeds from these Eversource parent issuances funded a portion of the purchase price for the CMA asset acquisition and refinanced short-term borrowings. In January 2021, PSNH provided a redemption notice to the holders of the PSNH 4.050% Series Q First Mortgage Bonds that PSNH will redeem the $122 million of bonds on March 1, 2021, the par call date, in advance of the June 1, 2021 maturity date. 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 a portion of 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, NSTAR Gas and Aquarion. 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 Pollution Control Revenue Bonds (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. No long-term debt defaults have occurred as of December 31, 2020. CYAPC's 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, 2020 and 2019, as a result of consolidating CYAPC, Eversource has consolidated $11.7 million and $11.6 million, respectively, in pre-1983 spent nuclear fuel obligations to the DOE. In December 2019, CYAPC paid $29 million to the DOE to partially settle this obligation. The obligation includes accumulated interest costs of $8.7 million and $8.6 million as of December 31, 2020 and 2019, 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 2021 through 2025 and thereafter are shown below. These amounts exclude PSNH rate reduction bonds, CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2020: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2021 $ 1,022.2 $ — $ 250.0 $ 282.0 2022 1,175.2 — 400.0 — 2023 1,658.2 400.0 80.0 325.0 2024 1,049.9 139.8 — — 2025 1,400.0 400.0 250.0 — Thereafter 9,807.9 2,975.5 2,690.0 500.0 Total $ 16,113.4 $ 3,915.3 $ 3,670.0 $ 1,107.0

RATE REDUCTION BONDS AND VARIAB

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES	12 Months Ended
	Dec. 31, 2020
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: On May 8, 2018, PSNH Funding, a wholly-owned subsidiary of PSNH, 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 are 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 are 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 was formed solely to issue RRBs to finance PSNH's unrecovered remaining costs associated with the divestiture of its generation assets. PSNH Funding is considered a 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 sheets and income statements: (Millions of Dollars) As of December 31, Balance Sheet: 2020 2019 Restricted Cash - Current Portion (included in Current Assets) $ 36.8 $ 32.5 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 2.1 3.2 Securitized Stranded Cost (included in Regulatory Assets) 522.1 565.3 Other Regulatory Liabilities (included in Regulatory Liabilities) 9.1 5.6 Accrued Interest (included in Other Current Liabilities) 8.0 8.6 Rate Reduction Bonds - Current Portion 43.2 43.2 Rate Reduction Bonds - Long-Term Portion 496.9 540.1 (Millions of Dollars) Income Statement: For the Years Ended December 31, 2020 2019 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 43.2 $ 43.0 Interest Expense on RRB Principal (included in Interest Expense) 19.7 21.1 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, 2020
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 Pension Protection Act 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 meet 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) as an offset to 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, SERP 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. Funded Status: The Pension, SERP and 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. Although Eversource maintains marketable securities in a benefit trust, the SERP Plans do not contain any assets. For further information, see Note 5, "Marketable Securities," to the financial statements. The following tables provide information on the plan benefit obligations, fair values of plan assets, and funded status: Pension and SERP As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (6,321.7) $ (1,331.3) $ (1,397.3) $ (692.6) $ (5,520.0) $ (1,160.4) $ (1,236.5) $ (610.7) Service Cost (76.2) (21.8) (15.4) (8.2) (67.7) (18.0) (14.6) (7.1) Interest Cost (177.8) (37.3) (38.6) (19.4) (219.0) (45.7) (49.0) (24.0) Actuarial Loss (658.2) (152.3) (139.5) (62.1) (815.3) (176.6) (181.0) (84.5) Benefits Paid - Pension 279.3 63.6 59.4 33.5 273.0 60.2 67.1 30.3 Benefits Paid - Lump Sum 23.4 — 13.1 — 20.0 — 12.9 — Benefits Paid - SERP 7.3 0.3 0.2 0.4 7.3 0.3 0.1 0.4 Employee Transfers — 1.5 0.2 (0.3) — 8.9 3.7 3.0 Increase due to acquisition of CMA (121.4) — — — — — — — Benefit Obligation as of End of Year $ (7,045.3) $ (1,477.3) $ (1,517.9) $ (748.7) $ (6,321.7) $ (1,331.3) $ (1,397.3) $ (692.6) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of $ 4,968.6 $ 986.2 $ 1,288.8 $ 551.6 $ 4,573.9 $ 918.4 $ 1,222.1 $ 506.6 Employer Contributions 109.6 23.2 0.7 19.5 112.5 24.0 0.4 15.4 Actual Return on Pension Plan Assets 512.3 98.8 128.3 55.8 575.2 112.9 150.0 62.9 Benefits Paid - Pension (279.3) (63.6) (59.4) (33.5) (273.0) (60.2) (67.1) (30.3) Benefits Paid - Lump Sum (23.4) — (13.1) — (20.0) — (12.9) — Employee Transfers — (1.5) (0.2) 0.3 — (8.9) (3.7) (3.0) Increase due to acquisition of CMA 121.4 — — — — — — — Fair Value of Pension Plan Assets as of End of Year $ 5,409.2 $ 1,043.1 $ 1,345.1 $ 593.7 $ 4,968.6 $ 986.2 $ 1,288.8 $ 551.6 Funded Status as of December 31st $ (1,636.1) $ (434.2) $ (172.8) $ (155.0) $ (1,353.1) $ (345.1) $ (108.5) $ (141.0) For the year ended December 31, 2020, the increase in the benefit obligation was primarily attributable to a decrease in the discount rate, which resulted in an increase to Eversource's pension liability of $603.0 million. The increase in the benefit obligation was partially offset by the actual return on assets exceeding the expected asset return and changes in the mortality assumption. For the year ended December 31, 2019, the increase in the benefit obligation was primarily attributable to a decrease in the discount rate, which resulted in an increase to Eversource's pension liability of $813.1 million, which was partially offset by changes in actual plan experience and changes in other assumptions. The pension and SERP Plans' funded status includes the current portion of the SERP liability totaling $6.8 million and $8.7 million as of December 31, 2020 and 2019, respectively, which is included in Other Current Liabilities on the balance sheets. As of December 31, 2020 and 2019, the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2020 $ 6,669.4 $ 1,356.4 $ 1,449.4 $ 707.2 2019 5,963.4 1,205.4 1,340.8 646.7 PBOP As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (899.0) $ (172.7) $ (258.3) $ (93.0) $ (841.5) $ (161.7) $ (246.3) $ (91.9) Service Cost (10.2) (1.7) (2.1) (0.9) (7.8) (1.4) (1.7) (0.7) Interest Cost (24.6) (4.4) (6.6) (2.8) (32.7) (6.3) (9.5) (3.4) Actuarial Loss (82.8) (8.6) (7.4) (19.0) (67.0) (13.4) (15.2) (3.1) Benefits Paid 50.2 10.1 14.9 6.1 50.0 10.8 15.4 5.6 Employee Transfers — (1.3) (1.0) 0.1 — (0.7) (1.0) 0.5 Increase due to acquisition of CMA (27.5) — — — — — — — Benefit Obligation as of End of Year $ (993.9) $ (178.6) $ (260.5) $ (109.5) $ (899.0) $ (172.7) $ (258.3) $ (93.0) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 935.9 $ 126.3 $ 424.4 $ 76.0 $ 849.6 $ 120.6 $ 379.1 $ 71.2 Actual Return on Plan Assets 116.5 15.7 53.3 9.3 127.0 17.1 57.0 10.0 Employer Contributions 1.9 — — — 9.3 — 6.0 — Benefits Paid (50.2) (10.1) (14.9) (6.1) (50.0) (10.8) (15.4) (5.6) Employee Transfers — 2.2 1.8 0.2 — (0.6) (2.3) 0.4 Fair Value of Plan Assets as of End of Year $ 1,004.1 $ 134.1 $ 464.6 $ 79.4 $ 935.9 $ 126.3 $ 424.4 $ 76.0 Funded Status as of December 31st $ 10.2 $ (44.5) $ 204.1 $ (30.1) $ 36.9 $ (46.4) $ 166.1 $ (17.0) The Eversource PBOP funded status includes prepaid assets of $34.7 million and $62.7 million recorded in Other Long-Term Assets and liabilities of $24.5 million and $25.8 million included in Accrued Pension, SERP and PBOP on the balance sheets as of December 31, 2020 and 2019, respectively. For the year ended December 31, 2020, the increase in the benefit obligation was primarily attributable to a decrease in the discount rate, which resulted in an increase to the Eversource PBOP liability of $68.3 million, and by changes in our retirement assumptions. For the year ended December 31, 2019, the increase in the benefit obligation was primarily attributable to a decrease in the discount rate, which resulted in an increase to the Eversource PBOP liability of $88.6 million. The following actuarial assumptions were used in calculating the Pension, SERP and PBOP Plans' year end funded status: Pension and SERP PBOP As of December 31, As of December 31, 2020 2019 2020 2019 Discount Rate 2.4% — 2.7% 3.0% — 3.4% 2.5% — 2.6% 3.2% — 3.3% Compensation/Progression Rate 3.5% — 4.0% 3.5% — 4.0% N/A For the Eversource Service PBOP Plan, the health care cost trend rate is not applicable. For the Aquarion PBOP Plan, the health care cost trend rate for pre-65 retirees is 6.3 percent, with an ultimate rate of 5 percent in 2023, and for post-65 retirees, the health care trend rate and ultimate rate is 3.5 percent. Expense: Eversource charges net periodic benefit expense/(income) for the Pension, SERP and PBOP Plans 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 benefit 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/(income) for the Pension, SERP and PBOP 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/(income), less the capitalized portion, is included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit expense/(income), less the deferred portion, are included in Other Income, Net on the statements of income. Pension, SERP and 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 and deferred portion, as these amounts are cash settled on a short-term basis. Pension and SERP PBOP For the Year Ended December 31, 2020 For the Year Ended December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 76.2 $ 21.8 $ 15.4 $ 8.2 $ 10.2 $ 1.7 $ 2.1 $ 0.9 Interest Cost 177.8 37.3 38.6 19.4 24.6 4.4 6.6 2.8 Expected Return on Plan Assets (400.3) (79.2) (103.0) (44.7) (73.6) (9.9) (34.0) (5.7) Actuarial Loss 202.0 39.2 55.2 15.6 8.4 1.1 2.5 0.8 Prior Service Cost/(Credit) 1.2 — 0.3 — (21.2) 1.1 (17.0) 0.4 Total Net Periodic Benefit Expense/(Income) $ 56.9 $ 19.1 $ 6.5 $ (1.5) $ (51.6) $ (1.6) $ (39.8) $ (0.8) Intercompany Allocations N/A $ 9.1 $ 8.9 $ 2.9 N/A $ (1.1) $ (1.4) $ (0.5) Pension and SERP PBOP For the Year Ended December 31, 2019 For the Year Ended December 31, 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 67.7 $ 18.0 $ 14.6 $ 7.1 $ 7.8 $ 1.4 $ 1.7 $ 0.7 Interest Cost 219.0 45.7 49.0 24.0 32.7 6.3 9.5 3.4 Expected Return on Plan Assets (367.1) (73.2) (97.1) (40.7) (66.8) (9.2) (30.2) (5.4) Actuarial Loss 143.2 26.9 44.7 10.6 8.3 1.3 3.3 0.3 Prior Service Cost/(Credit) 0.9 — 0.3 — (23.5) 1.1 (16.9) 0.4 Total Net Periodic Benefit Expense/(Income) $ 63.7 $ 17.4 $ 11.5 $ 1.0 $ (41.5) $ 0.9 $ (32.6) $ (0.6) Intercompany Allocations N/A $ 8.5 $ 8.0 $ 2.3 N/A $ (0.9) $ (1.2) $ (0.4) Pension and SERP PBOP For the Year Ended December 31, 2018 For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 84.8 $ 21.4 $ 17.4 $ 11.2 $ 10.0 $ 1.9 $ 2.0 $ 1.1 Interest Cost 196.4 41.8 43.5 22.0 30.7 5.8 8.7 3.4 Expected Return on Plan Assets (391.6) (79.1) (104.9) (43.6) (72.4) (10.4) (32.5) (6.0) Actuarial Loss 145.7 29.1 41.1 11.6 10.3 1.6 2.3 0.7 Prior Service Cost/(Credit) 4.3 1.1 0.2 0.4 (23.6) 1.1 (16.9) 0.5 Total Net Periodic Benefit Expense/(Income) $ 39.6 $ 14.3 $ (2.7) $ 1.6 $ (45.0) $ — $ (36.4) $ (0.3) Intercompany Allocations N/A $ 6.1 $ 6.5 $ 1.9 N/A $ (1.0) $ (1.3) $ (0.4) The following actuarial assumptions were used to calculate Pension, SERP and PBOP expense amounts: Pension and SERP PBOP For the Years Ended December 31, For the Years Ended December 31, 2020 2019 2018 2020 2019 2018 Discount Rate 2.6% — 3.5% 2.7% — 3.6% 3.9% — 4.6% 2.7% — 3.6% 3.9% — 4.6% 3.3% — 3.9% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% 8.25% 8.25% 8.25% Compensation/Progression Rate 3.5% — 4.0% 3.5% — 4.0% 3.5% — 4.0% N/A N/A N/A For the Aquarion Pension and PBOP Plans, the expected long-term rate of return was 7 percent for the years ended December 31, 2020 and 2019. For the Aquarion PBOP Plan, the health care cost trend rate was a range of 3.5 percent to 6.5 percent for the year ended December 31, 2020, and 3.5 percent to 6.8 percent for the year ended December 31, 2019. 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: Pension and SERP PBOP Regulatory Assets OCI Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2020 (1) 2019 2020 2019 2020 (1) 2019 2020 2019 Actuarial Losses Arising During the Year $ 553.1 $ 591.6 $ 24.3 $ 15.4 $ 39.1 $ 4.6 $ 1.3 $ 2.3 Actuarial Losses Reclassified as Net Periodic Benefit Expense (194.3) (137.8) (7.7) (5.4) (8.0) (8.0) (0.4) (0.3) Prior Service Cost Arising During the Year 2.0 — — — — — — — Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income (1.0) (0.7) (0.2) (0.2) 21.3 25.1 (0.1) (1.6) (1) Amounts include the impact of the CMA asset acquisition from October 9, 2020 through December 31, 2020. 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, 2020 and 2019: Regulatory Assets as of December 31, AOCI as of December 31, (Millions of Dollars) 2020 2019 2020 2019 Pension and SERP Actuarial Loss $ 2,620.2 $ 2,261.4 $ 107.4 $ 90.8 Prior Service Cost 6.6 5.6 0.7 0.9 PBOP Actuarial Loss $ 235.0 $ 203.9 $ 7.9 $ 7.0 Prior Service (Credit)/Cost (151.2) (172.5) 0.9 1.0 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. 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) 2021 2022 2023 2024 2025 2026 - 2030 Pension and SERP $ 346.9 $ 355.6 $ 362.9 $ 397.5 $ 373.8 $ 1,883.2 PBOP 60.1 60.1 59.7 59.1 58.3 273.6 Eversource Contributions: Based on the current status of the Pension Plans and federal pension funding requirements, Eversource currently expects to make contributions of $130.0 million in 2021, of which $78.9 million will be contributed by CL&P. The remaining $51.1 million is expected to be contributed by other Eversource subsidiaries, primarily Eversource Service. Eversource currently estimates contributing $2.8 million to the PBOP Plans in 2021. 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. Management has assumed long-term rates of return of 8.25 percent for the Eversource Service Pension and PBOP Plan assets and a 7 percent long-term rate of return for the Aquarion Plans to estimate its 2021 Pension and PBOP costs. 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, 2020 2019 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 % 15.0 % 8.5 % Global 10.0 % 8.75 % 10.0 % 8.75 % Non-United States 8.0 % 8.5 % 8.0 % 8.5 % Emerging Markets 4.0 % 10.0 % 4.0 % 10.0 % Debt Securities: Fixed Income 13.0 % 4.0 % 13.0 % 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 % Private Equity 15.0 % 12.0 % 15.0 % 12.0 % Real Assets 16.0 % 7.5 % 16.0 % 7.5 % 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 Plan is 54 percent equity, 36 percent debt and 10 percent other. The target asset allocation for the Aquarion PBOP Plan is 54 percent equity, 41 percent debt and 5 percent other. 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) 2020 2019 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 630.8 $ — $ 1,321.7 $ 1,952.5 $ 592.6 $ — $ 1,349.9 $ 1,942.5 Fixed Income (2) 113.6 265.6 1,402.5 1,781.7 99.4 303.0 1,222.8 1,625.2 Private Equity 22.3 — 1,175.4 1,197.7 16.9 — 971.4 988.3 Real Assets (3) 158.4 — 580.8 739.2 58.7 — 615.0 673.7 Total $ 925.1 $ 265.6 $ 4,480.4 $ 5,671.1 $ 767.6 $ 303.0 $ 4,159.1 $ 5,229.7 Less: 401(h) PBOP Assets (4) (261.9) (261.1) Total Pension Assets $ 5,409.2 $ 4,968.6 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2020 2019 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 176.5 $ — $ 217.8 $ 394.3 $ 158.0 $ — $ 187.0 $ 345.0 Fixed Income (2) 16.0 43.2 152.9 212.1 15.8 39.6 148.1 203.5 Private Equity — — 31.5 31.5 — — 26.5 26.5 Real Assets (3) 82.1 — 22.2 104.3 51.2 — 48.6 99.8 Total $ 274.6 $ 43.2 $ 424.4 $ 742.2 $ 225.0 $ 39.6 $ 410.2 $ 674.8 Add: 401(h) PBOP Assets (4) 261.9 261.1 Total PBOP Assets $ 1,004.1 $ 935.9 (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 overlaid 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 overlaid 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 and corporate bonds, 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. 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 2020 $ 49.4 $ 6.6 $ 11.8 $ 4.1 2019 41.6 5.5 10.3 3.5 2018 38.4 5.0 9.7 3.3 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, 2020 and 2019, Eversource had 2,876,601 and 3,302,526 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 Capital Surplus, Paid In 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 Weighted Average Outstanding as of December 31, 2019 774,163 $ 54.43 Granted 208,937 $ 88.23 Shares Issued (301,938) $ 57.61 Forfeited (6,944) $ 60.95 Outstanding as of December 31, 2020 674,218 $ 63.42 The weighted average grant-date fair value of RSUs granted for the years ended December 31, 2020, 2019 and 2018 was $88.23, $67.91 and $56.69, respectively. As of December 31, 2020 and 2019, the number and weighted average grant-date fair value of unvested RSUs was 379,258 and $77.13 per share, and 439,293 and $63.06 per share, respectively. During 2020, there were 265,020 RSUs at a weighted average grant-date fair value of $62.99 per share that vested during the year and were either paid or deferred. As of December 31, 2020, 294,960 RSUs were fully vested and deferred and an additional 360,295 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 Weighted Average Outstanding as of December 31, 2019 486,907 $ 60.30 Granted 211,224 $ 75.36 Shares Issued (249,922) $ 55.72 Forfeited (404) $ 89.85 Outstanding as of December 31, 2020 447,805 $ 69.93 The weighted average grant-date fair value of performance shares granted for the years ended December 31, 2020, 2019 and 2018 was $75.36, $68.33 and $56.77, respectively. As of December 31, 2020 and 2019, the number and weighted average grant-date fair value of unvested performance shares was 404,698 and $70.85 per share, and 427,894 and $60.38 per share, respectively. During 2020, there were 233,426 performance shares at a weighted average grant-date fair value of $55.75 per share that vested during the year and were either paid or deferred. As of December 31, 2020, 43,107 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) 2020 2019 2018 Compensation Expense $ 33.9 $ 27.3 $ 21.4 Future Income Tax Benefit 8.9 7.0 5.4 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Compensation Expense $ 10.9 $ 11.3 $ 3.6 $ 9.8 $ 9.7 $ 3.3 $ 7.8 $ 7.7 $ 2.9 Future Income Tax Benefit 2.9 3.0 1.0 2.5 2.5 0.8 2.0 1.9 0.7 As of December 31, 2020, there was $19.3 million of total unrecognized compensation expense related to nonvested share-based awards for Eversource, including $3.6 million for CL&P, $5.7 million for NSTAR Electric, and $1.2 million for PSNH. This cost is expected to be recognized ratably over a weighted-average period of 1.74 years for Eversource, CL&P and PSNH, and 1.75 years NSTAR Electric. An income tax rate of 26 percent was used to estimate the tax effect on total share-based payments determined under the fair-value based method for all awards. Beginning in 2019, the Company began issuing treasury shares to settle fully vested RSUs and performance shares under the Company's incentive plans. For the years ended December 31, 2020, 2019 and 2018, excess tax benefits associated with the distribution of stock compensation awards reduced income tax expense by $6.6 million, $1.5 million, and $1.5 million, respectively, which increased cash flows from operating activities on the statements of cash flows. Eversource provides retirement and other benefits for certain current and past company officers. These benefits are accounted for on an accrual basis and expensed over a period equal to the service lives of the employees. The actuarially-determined liability for these benefits is included in Other Current and Long-Term Liabilities on the balance sheets. The related expense, which includes the allocation of expense associated with Eversource's service company officers that support CL&P, NSTAR Electric and PSNH, is included in Operations and Maintenance Expense on the income statements. The liability and expense amounts are as follows: Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2020 2019 2018 Actuarially-Determined Liability $ 45.7 $ 52.0 $ 49.1 Other Retirement Benefits Expense 3.3 2.7 2.7 As of and For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Actuarially-Determined $ 0.2 $ 0.1 $ 1.7 $ 0.2 $ 0.1 $ 1.7 $ 0.3 $ 0.1 $ 1.7 Other Retirement Benefits 1.2 1.1 0.5 1.0 0.9 0.4 1.1 1.1 0.4

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 2018 Current Income Taxes: Federal $ 73.6 $ 56.9 $ 106.5 State 19.1 10.5 10.6 Total Current 92.7 67.4 117.1 Deferred Income Taxes, Net: Federal 173.5 138.4 122.6 State 83.7 71.4 52.2 Total Deferred 257.2 209.8 174.8 Investment Tax Credits, Net (3.7) (3.7) (2.9) Income Tax Expense $ 346.2 $ 273.5 $ 289.0 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Current Income Taxes: Federal $ 12.0 $ 53.9 $ 20.6 $ 68.4 $ 82.6 $ 22.9 $ 54.2 $ 79.3 $ 12.2 State (6.1) 6.9 3.8 15.4 18.2 2.2 20.9 30.0 (0.5) Total Current 5.9 60.8 24.4 83.8 100.8 25.1 75.1 109.3 11.7 Deferred Income Taxes, Net: Federal 101.1 33.8 (1.3) 35.2 0.1 5.8 48.5 27.9 15.4 State 43.4 38.8 8.6 18.8 27.0 10.1 6.4 13.5 20.5 Total Deferred 144.5 72.6 7.3 54.0 27.1 15.9 54.9 41.4 35.9 Investment Tax Credits, Net (0.7) (2.6) — (0.8) (2.6) — (0.9) (1.8) — Income Tax Expense $ 149.7 $ 130.8 $ 31.7 $ 137.0 $ 125.3 $ 41.0 $ 129.1 $ 148.9 $ 47.6 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, 2020 2019 2018 Income Before Income Tax Expense $ 1,558.9 $ 1,190.1 $ 1,329.5 Statutory Federal Income Tax Expense at 21% 327.4 249.9 279.2 Tax Effect of Differences: Depreciation (11.1) 1.9 (30.8) Investment Tax Credit Amortization (3.7) (3.7) (2.9) State Income Taxes, Net of Federal Impact 44.9 24.6 44.4 Dividends on ESOP (5.1) (5.1) (5.1) Tax Asset Valuation Allowance/Reserve Adjustments 33.4 40.1 5.2 Excess Stock Benefit (6.6) (1.5) (1.5) EDIT Amortization (48.7) (37.4) (5.0) Other, Net 15.7 4.7 5.5 Income Tax Expense $ 346.2 $ 273.5 $ 289.0 Effective Tax Rate 22.2 % 23.0 % 21.7 % For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars, except percentages) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Income Before Income Tax Expense $ 607.6 $ 575.8 $ 179.0 $ 547.8 $ 557.3 $ 175.0 $ 506.8 $ 532.0 $ 163.5 Statutory Federal Income Tax Expense at 21% 127.6 120.9 37.6 115.0 117.0 36.8 106.4 111.7 34.3 Tax Effect of Differences: Depreciation 0.4 (3.7) (1.4) (0.2) (3.0) (0.8) (1.2) (2.8) 0.1 Investment Tax Credit Amortization (0.7) (2.6) — (0.8) (2.6) — (0.9) (1.8) — State Income Taxes, (1.2) 36.0 9.8 2.5 35.7 9.8 14.5 33.2 15.8 Tax Asset Valuation 30.7 — — 24.5 — — 7.1 1.2 — Excess Stock Benefit (2.3) (2.3) (0.8) (0.5) (0.5) (0.2) (0.1) (0.1) (0.1) EDIT Amortization (9.0) (20.4) (15.4) (5.8) (22.9) (4.0) — — (4.4) Other, Net 4.2 2.9 1.9 2.3 1.6 (0.6) 3.3 7.5 1.9 Income Tax Expense $ 149.7 $ 130.8 $ 31.7 $ 137.0 $ 125.3 $ 41.0 $ 129.1 $ 148.9 $ 47.6 Effective Tax Rate 24.6 % 22.7 % 17.7 % 25.0 % 22.5 % 23.4 % 25.5 % 28.0 % 29.1 % 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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Deferred Tax Assets: Employee Benefits $ 602.4 $ 144.5 $ 79.8 $ 56.6 $ 509.4 $ 125.4 $ 54.8 $ 46.7 Derivative Liabilities 92.6 91.8 — — 105.0 103.6 — — Regulatory Deferrals - Liabilities 259.8 30.2 161.8 13.4 267.0 37.1 165.7 19.0 Allowance for Uncollectible Accounts 87.5 42.3 20.9 4.6 56.7 25.7 17.7 2.8 Tax Effect - Tax Regulatory Liabilities 810.9 331.4 271.8 105.2 830.4 333.5 280.9 111.3 Net Operating Loss Carryforwards 12.7 — — — 9.1 — — — Purchase Accounting Adjustment 54.5 — — — 58.7 — — — Other 200.3 100.9 14.3 19.8 190.4 92.0 35.8 20.0 Total Deferred Tax Assets 2,120.7 741.1 548.6 199.6 2,026.7 717.3 554.9 199.8 Less: Valuation Allowance 48.3 33.7 — — 43.0 24.9 — — Net Deferred Tax Assets $ 2,072.4 $ 707.4 $ 548.6 $ 199.6 $ 1,983.7 $ 692.4 $ 554.9 $ 199.8 Deferred Tax Liabilities: Accelerated Depreciation and Other $ 4,153.6 $ 1,438.1 $ 1,489.4 $ 453.8 $ 3,901.0 $ 1,362.2 $ 1,391.9 $ 428.9 Property Tax Accruals 88.7 39.0 37.0 5.8 76.8 36.8 29.0 4.7 Regulatory Amounts: Regulatory Deferrals - Assets 1,376.7 444.8 324.4 263.4 1,155.6 340.7 276.2 260.9 Tax Effect - Tax Regulatory Assets 244.6 174.4 11.3 8.6 238.2 171.7 11.7 8.3 Goodwill Regulatory Asset - 1999 Merger 86.0 — 73.8 — 90.6 — 77.8 — Derivative Assets 17.8 17.8 — — 19.7 19.7 — — Other 200.3 1.6 72.6 5.6 257.6 5.9 125.6 3.2 Total Deferred Tax Liabilities $ 6,167.7 $ 2,115.7 $ 2,008.5 $ 737.2 $ 5,739.5 $ 1,937.0 $ 1,912.2 $ 706.0 2020 Federal Legislation: On March 27, 2020, President Trump signed the $2.2 trillion bipartisan Coronavirus Aid, Relief, and Economic Security (CARES) Act. Among other provisions, the CARES Act provides for loans and other benefits to small and large businesses, expanded unemployment insurance, direct payments to those with wages middle-income and below, new appropriations funding for health care and other priorities, and tax changes like deferrals of employer payroll tax liabilities coupled with an employee retention tax credit and rollbacks of Tax Cuts and Jobs Act of 2017 limitations on net operating losses and certain business interest limitation. For the year ended December 31, 2020, we have recorded a tax liability of approximately $39 million related to the deferral of employer payroll tax liability provision. Fifty percent of the deferral of employer payroll tax liability must be paid by December 31, 2021 and the remaining amount by December 31, 2022. Other than the cash flow benefit described, the CARES Act did not have a material impact. On December 27, 2020, President Trump signed into law H.R. 133, the “Consolidated Appropriations Act, 2021.” The House of Representatives and Senate previously passed the bill with overwhelming support. The legislation includes tax extenders as part of Division EE, the “Taxpayer Certainty and Disaster Tax Relief Act of 2020.” The provisions within the law include the extension of the Investment Tax Credit (ITC) for solar at 26 percent for facilities the construction of which begins through the end of 2022, at 22 percent for facilities the construction of which begins in 2023, and postponement of the date after which solar facilities placed in service receive only a 10 percent ITC to December 31, 2025, the extension of the ITC at 30 percent (with no phase-down) to offshore wind if construction begins by December 31, 2025 (qualifying offshore wind includes facilities located in the inland navigable waters or in the coastal waters of the U.S.), and the extension and expansion of the CARES Act employee retention tax credit for the period from January 1, 2021 through June 30, 2021, including increasing the credit rate from 50 percent to 70 percent of qualified wages, and increasing the per-employee creditable wages limit from $10,000 per year to $10,000 for each quarter. The tax credit provision impacts to Eversource are still being evaluated but are a significant positive development for the Company and provides the opportunity to generate additional tax credits in its renewable energy projects when the projects become operational. Carryforwards: The following table provides 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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Expiration Range Eversource CL&P NSTAR PSNH Expiration Range Federal Net Operating Loss $ — $ — $ — $ — — $ 19.8 $ — $ — $ — 2033 - 2037 State Net Operating Loss 183.4 — — — 2021 - 2040 65.5 — — — 2020 - 2038 State Tax Credit 186.6 133.4 — — 2020 - 2025 168.1 122.3 — — 2019 - 2024 State Charitable Contribution 10.2 — — — 2020 - 2024 9.9 — — — 2019 - 2023 In 2020, the company increased its valuation allowance reserve for state credits by $10.3 million ($8.8 million for CL&P), net of tax, to reflect an update for expiring tax credits. In 2019, the Company increased its valuation allowance reserve for state credits by $18.5 million ($14.2 million for CL&P), net of tax, to reflect an update for expiring tax credits. For 2020 and 2019, state credit and state loss carryforwards have been partially reserved by a valuation allowance of $48.3 million and $43.0 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, 2018 $ 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 Gross Increases - Current Year 12.1 4.0 Gross Increases - Prior Year 3.4 3.3 Lapse of Statute of Limitations (6.4) (2.4) Balance as of December 31, 2019 55.0 23.1 Gross Increases - Current Year 11.9 4.6 Gross Increases - Prior Year 1.4 0.7 Lapse of Statute of Limitations (6.5) (2.6) Balance as of December 31, 2020 $ 61.8 $ 25.8 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 Income Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2020 2019 2018 2020 2019 Eversource $ — $ — $ (1.7) $ 0.1 $ 0.1 Tax Positions: During 2020 and 2019, 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, 2020: Description Tax Years Federal 2020 Connecticut 2017 - 2020 Massachusetts 2017 - 2020 New Hampshire 2017 - 2020 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, 2020
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES A. Environmental Matters 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, 2019 $ 64.7 $ 5.4 $ 10.9 $ 5.4 Additions 26.5 7.0 0.5 2.8 Payments/Reductions (10.2) (1.0) (3.4) (0.7) Balance as of December 31, 2019 81.0 11.4 8.0 7.5 Increase Due to CMA Asset Acquisition 22.9 — — — Additions 8.4 4.2 0.7 — Payments/Reductions (9.9) (3.3) (4.0) (0.4) Balance as of December 31, 2020 $ 102.4 $ 12.3 $ 4.7 $ 7.1 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 2020 63 15 12 9 2019 57 15 15 9 The increase in the reserve balance was due primarily to the addition of nine MGP sites at the EGMA natural gas business resulting from the CMA acquisition and changes in cost estimates at the natural gas companies MGP sites and at CL&P for which additional remediation will be required. Included in the number of sites and reserve amounts above are former MGP sites that were operated several decades ago and manufactured natural 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 $92.2 million and $67.9 million as of December 31, 2020 and 2019, respectively, and related primarily to the natural gas business segment. As of December 31, 2020, for 6 environmental sites (1 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, 2020, $41.7 million (including $0.9 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 $33 million ($0.5 million at CL&P) may be incurred in executing current remediation plans for these sites. As of December 31, 2020, for 15 environmental sites (7 for CL&P and 2 for NSTAR Electric) that are included in the Company's reserve for environmental costs, management cannot reasonably estimate the exposure to loss in excess of the reserve, or range of loss, as these sites are under investigation and/or there is significant uncertainty as to what remedial actions, if any, the Company may be required to undertake. As of December 31, 2020, $17.5 million (including $2.6 million for CL&P and $0.4 million for NSTAR Electric) had been accrued as a liability for these sites. As of December 31, 2020, for the remaining 42 environmental sites (including 7 for CL&P, 10 for NSTAR Electric and 9 for PSNH) that are included in the Company's reserve for environmental costs, the $43.2 million accrual (including $8.8 million for CL&P, $4.3 million for NSTAR Electric and $7.1 million for PSNH) represents management's best estimate of the probable liability and no additional loss is anticipated at this time. Estimated Future Annual Costs: The estimated future annual costs of significant executed, non-cancelable, long-term contractual arrangements in effect as of December 31, 2020 are as follows: Eversource (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 650.0 $ 716.8 $ 652.3 $ 648.8 $ 651.5 $ 3,490.7 $ 6,810.1 Natural Gas Procurement 558.9 374.1 292.0 263.1 260.2 1,825.8 3,574.1 Purchased Power and Capacity 69.4 75.5 86.8 79.6 60.3 13.2 384.8 Peaker CfDs 30.0 34.2 46.9 41.6 31.3 102.4 286.4 Transmission Support Commitments 20.5 18.0 18.1 19.2 19.7 19.7 115.2 Total $ 1,328.8 $ 1,218.6 $ 1,096.1 $ 1,052.3 $ 1,023.0 $ 5,451.8 $ 11,170.6 CL&P (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 484.4 $ 548.3 $ 547.2 $ 549.1 $ 551.2 $ 2,645.5 $ 5,325.7 Purchased Power and Capacity 65.8 71.9 83.3 76.6 57.4 0.1 355.1 Peaker CfDs 30.0 34.2 46.9 41.6 31.3 102.4 286.4 Transmission Support Commitments 8.1 7.1 7.2 7.6 7.8 7.8 45.6 Total $ 588.3 $ 661.5 $ 684.6 $ 674.9 $ 647.7 $ 2,755.8 $ 6,012.8 NSTAR Electric (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 98.0 $ 100.0 $ 75.4 $ 72.9 $ 73.1 $ 522.1 $ 941.5 Purchased Power and Capacity 3.1 3.1 3.0 3.0 2.9 13.1 28.2 Transmission Support Commitments 8.1 7.1 7.1 7.5 7.7 7.7 45.2 Total $ 109.2 $ 110.2 $ 85.5 $ 83.4 $ 83.7 $ 542.9 $ 1,014.9 PSNH (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 67.6 $ 68.5 $ 29.7 $ 26.8 $ 27.2 $ 323.1 $ 542.9 Purchased Power and Capacity 0.5 0.5 0.5 — — — 1.5 Transmission Support Commitments 4.3 3.8 3.8 4.1 4.2 4.2 24.4 Total $ 72.4 $ 72.8 $ 34.0 $ 30.9 $ 31.4 $ 327.3 $ 568.8 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 2041 for both CL&P and NSTAR Electric and 2033 for PSNH. As required by 2018 regulation, CL&P and UI entered into ten-year contracts to purchase a combined total of approximately 9 million MWh annually from the Millstone Nuclear Power Station generation facility. On March 15, 2019, CL&P and UI each signed a ten-year contract with the owner of Millstone Nuclear Power Station in order to purchase a combined amount of approximately 50 percent of the facility's output (approximately 40 percent by CL&P). The Millstone Nuclear Power Station has a 2,112 MW nameplate capacity. PURA approved the contracts on September 18, 2019. Energy deliveries and payments under these contracts began in the fourth quarter of 2019. CL&P and UI were also required by 2018 regulation to enter into eight-year contracts to purchase a combined amount of approximately 18 percent of the facility's output (approximately 15 percent by CL&P) from the Seabrook Nuclear Power Plant beginning January 1, 2022. The Seabrook Nuclear Power Plant has an approximate 1,250 MW nameplate capacity. On November 22, 2019, CL&P and UI each signed an eight-year contract with the owner of the Seabrook Nuclear Power Plant. PURA approved the contracts on November 27, 2019. The total estimated future cost of the Millstone Nuclear Power Station and Seabrook Nuclear Power Plant energy purchase contracts are $3.6 billion and are reflected in the table above. CL&P sells the energy purchased under these contracts into the market and uses the proceeds from these energy sales to offset the contract costs. As the net costs under these contracts are recovered from customers in future rates, the contracts do not have an impact on the net income of CL&P. These contracts do not meet the definition of a derivative, and accordingly, the costs of these contracts are being accounted for as incurred. Excluded from the table above are long-term commitments of NSTAR Electric pertaining to the Massachusetts Clean Energy 83D contract, for which construction had not commenced by December 31, 2020. Estimated costs under this contract are expected to begin in 2023 and range between $150 million and $415 million per year under a 20-year contract, totaling approximately $6.7 billion. 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. Natural Gas Procurement: 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, which extend through 2045. Long-term purchases for natural gas procurement include contracts of EGMA, which was formed as a result of the CMA asset acquisition. Purchased Power and Capacity: These contracts include capacity CfDs of CL&P through 2026, and various IPP contracts or purchase obligations for electricity which extend through 2024 for CL&P, 2031 for NSTAR Electric and 2023 for PSNH. CL&P, along with UI, has three capacity CfDs consisting of two generation units and one demand response project. The combined capacities of these contracts as of December 31, 2020 and 2019 were 675 MW and 676 MW, respectively. 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 for the purchase of energy supply, the amounts of which vary with customers' energy needs. Peaker CfDs: CL&P, along with UI, has three peaker CfDs for a total of approximately 500 MW of peaking capacity through 2042. CL&P has a sharing agreement with UI, 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 are recovered from, or refunded to, CL&P's customers. Transmission Support Commitments: Along with other New England utilities, CL&P, NSTAR Electric and PSNH entered into a series of agreements in the 1980’s to support the costs of, and receive rights to use, transmission and terminal facilities that were built to import electricity from the Hydro-Québec system in Canada. CL&P, NSTAR Electric and PSNH were 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. On December 18, 2020, the parties to these agreements submitted to FERC an offer of settlement and amendments to these agreements implementing the terms of an extension for an additional 20-year period. The parties have requested these terms to be placed in effect as of January 1, 2021 or such other date as authorized by FERC. The estimated future annual costs included in the contractual obligations table above, are subject to the approval of these amendments by FERC and can vary as a result. The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2020 2019 2018 Renewable Energy $ 584.2 $ 320.8 $ 218.5 Natural Gas Procurement 453.4 448.5 432.4 Purchased Power and Capacity 62.7 62.1 72.0 Peaker CfDs 22.7 13.0 20.9 Transmission Support Commitments 22.1 21.8 23.4 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Renewable Energy $ 426.3 $ 88.8 $ 69.1 $ 160.6 $ 89.9 $ 70.3 $ 63.2 $ 89.8 $ 65.5 Purchased Power and Capacity 59.3 3.1 0.3 50.4 5.1 6.6 49.4 4.4 18.2 Peaker CfDs 22.7 — — 13.0 — — 20.9 — — Transmission Support Commitments 8.7 8.7 4.7 8.6 8.6 4.6 9.2 9.2 5.0 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 power facilities and are now engaged in the long-term storage of their spent fuel. The Yankee Companies fund these costs through litigation proceeds received from the DOE and, to the extent necessary, through wholesale, FERC-approved rates charged under power purchase agreements with several New England utilities, including CL&P, NSTAR Electric and PSNH. CL&P, NSTAR Electric and PSNH, in turn recover these costs from their customers through state regulatory commission-approved retail rates. The Yankee Companies collect 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 accept delivery of, and 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 previously awarded the Yankee Companies damages for Phases I, II and III of litigation resulting from the DOE's failure to meet its contractual obligations. These Phases covered damages incurred in the years 1998 through 2012, and the awarded damages have been received by the Yankee Companies with certain amounts of the damages refunded to their customers. DOE Phase IV Damages - On May 22, 2017, each of the Yankee Companies filed a fourth set of lawsuits against the DOE in the Court of Federal Claims. The Yankee Companies sought monetary damages totaling $104.4 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 of $103.2 million. The court awarded CYAPC, YAEC and MYAPC damages of $40.7 million, $28.1 million and $34.4 million, respectively. The DOE did not appeal the court's judgment and the decision became final on April 23, 2019. On June 12, 2019, each of the Yankee Companies received the damages proceeds. On June 12, 2019, the court accepted an offer of judgment in the amount of $0.5 million to settle the disputed amount of approximately $1 million in Phase IV contested damages. The Yankee Companies received the $0.5 million payment in July 2019. 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. Management does not anticipate a material impact to net income or cash flows as a result of these various guarantees and indemnifications. Guarantees issued on behalf of unconsolidated entities, including equity method offshore wind investments, for which Eversource parent is the guarantor, are recorded at fair value as a liability on the balance sheet at the inception of the guarantee. Eversource regularly reviews performance risk under these guarantee arrangements, and in the event it becomes probable that Eversource parent will be required to perform under the guarantee, the amount of probable payment will be recorded. The fair value of guarantees issued on behalf of unconsolidated entities are recorded within Other Long-Term Liabilities on the balance sheet, and was $0.5 million as of December 31, 2020. The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries and affiliates to external parties as of December 31, 2020: Company (Obligor) Description Maximum Exposure Expiration Dates North East Offshore LLC Construction-related purchase agreements with third-party contractors (1) $ 30.5 (1) Eversource Investment LLC Funding and indemnification obligations of North East Offshore LLC (2) — (2) Sunrise Wind LLC OREC capacity production (3) 2.2 (3) South Fork Wind, LLC Transmission interconnection 1.7 — Bay State Wind LLC Real estate purchase 2.5 2021 Various Surety bonds (4) 56.6 2021 - 2023 Rocky River Realty Company and Eversource Service Lease payments for real estate 5.2 2024 (1) Eversource parent issued guarantees on behalf of its 50 percent-owned affiliate, North East Offshore LLC (NEO), under which Eversource parent agreed to guarantee 50 percent of NEO’s performance of obligations under certain purchase agreements with third-party contactors, in an amount not to exceed $1.3 billion with an expiration date in 2025. Eversource parent also issued a separate guarantee to Ørsted on behalf of NEO, under which Eversource parent agreed to guarantee 50 percent of NEO’s payment obligations under certain offshore wind project construction-related agreements with Ørsted in an aggregate amount not to exceed $62.5 million. Any amounts paid under this guarantee to Ørsted will count toward, but not increase, the maximum amount of the Funding Guarantee described in Note 2, below. The guarantee expires upon the full performance of the guaranteed obligations. (2) Eversource parent issued a guarantee (Funding Guarantee) on behalf of Eversource Investment LLC (EI), its wholly-owned subsidiary that holds a 50 percent ownership interest in NEO, under which Eversource parent agreed to guarantee certain funding obligations and certain indemnification payments of EI under the Amended and Restated Limited Liability Company Operating Agreement of NEO, in an amount not to exceed $910 million. The guaranteed obligations include payment of EI's funding obligations during the construction phase of NEO’s underlying offshore wind projects and indemnification obligations associated with third party credit support for its investment in NEO. Eversource parent’s obligations under the Funding Guarantee expire upon the full performance of the guaranteed obligations. (3) On October 25, 2019, Eversource parent issued a guarantee on behalf of its 50 percent-owned affiliate, Sunrise Wind LLC, whereby Eversource parent will guarantee Sunrise Wind LLC's performance of certain obligations, in an amount not to exceed $15.4 million, under the Offshore Wind Renewable Energy Certificate Purchase and Sale Agreement (the Agreement). The Agreement was executed on October 23, 2019, by and between the New York State Energy Research and Development Authority (NYSERDA) and Sunrise Wind LLC. The guarantee expires upon the full performance of the guaranteed obligations. (4) 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. Letter of Credit : On September 16, 2020, Eversource parent entered into a guarantee on behalf of Eversource Investment LLC, which holds Eversource's investments in offshore wind-related equity method investments, under which Eversource parent would guarantee Eversource Investment LLC's obligations under a letter of credit facility with a financial institution that Eversource Investment LLC may request in an aggregate amount of up to approximately $25 million. 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 both December 31, 2020 and 2019. 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 both December 31, 2020 and 2019. 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. Initial briefs were filed by the NETOs, Complainants and FERC Trial Staff on January 11, 2019 and reply briefs were filed on March 8, 2019. The NETOs' brief was supportive of the overall ROE methodology determined in the October 16, 2018 order provided the FERC does not change the proposed methodology or alter its implementation in a manner that has a material impact on the results. The FERC order included illustrative calculations for the first complaint using FERC's proposed frameworks with financial data from that complaint. Those illustrative calculations indicated that for the first complaint period, for the NETOs, which FERC concludes are of average financial risk, the preliminary just and reasonable base ROE is 10.41 percent and the preliminary incentive cap on total ROE is 13.08 percent. If the results of the 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. These preliminary calculations are not binding and do not represent what we believe to be the most likely outcome of a final FERC order. On November 21, 2019, FERC issued Opinion No. 569 affecting the two pending transmission ROE complaints against the Midcontinent ISO (MISO) transmission owners, in which FERC adopted a new methodology for determining base ROEs. Various parties sought rehearing. On December 23, 2019, the NETOs filed supplementary materials in the NETOs' four pending cases to respond to this new methodology because of the uncertainty of the applicability to the NETOs' cases. On May 21, 2020, the FERC issued its order in Opinion No. 569-A on the rehearing of the MISO transmission owners' cases, in which FERC again changed its methodology for determining the MISO transmission owners' base ROEs. Various parties appealed the MISO transmission owners' opinion. On November 19, 2020, the FERC issued Opinion No. 569-B denying rehearing of Opinion No. 569-A and reaffirmed the methodology previously adopted in Opinion No. 569-A. The new methodology differs significantly from the methodology proposed by FERC in its October 16, 2018 order to determine the NETOs' base ROEs in its four pending cases. Given the significant uncertainty regarding the applicability of the FERC opinions in the MISO transmission owners' two complaint cases to the NETOs' pending four complaint cases, Eversource concluded that there is no reasonable basis for a change to the reserve or recognized ROEs for any of the complaint periods at this time. As well, Eversource cannot reasonably estimate a range of any gain or loss for any of the four complaint proceedings at this time. 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. A change of 10 basis points to the base ROE used to establish the reserves would impact Eversource’s after-tax earnings by an average of approximately $3 million for each of the four 15-month complaint periods. F. Eversource and NSTAR Electric Boston Harbor Civil Action In 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 against 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 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. Construction of the new distribution cable was completed in August 2019 and removal of the portions of the existing cable was completed in January 2020. All issues surrounding the current permit from the United States Army Corps of Engineers are expected to be resolved, and subsequently, such litigation then dismissed with prejudice. 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 in 2018. In connection with the new cable that was placed into service, a corresponding ARO was recognized for approximately $32 million within Other Long-Term Liabilities on the Eversource and NSTAR Electric balance sheets as of December 31, 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.

LEASES

LEASES	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
LEASES	LEASES Eversource, including CL&P, NSTAR Electric and PSNH, has entered into lease agreements as a lessee for the use of land, office space, service centers, vehicles, information technology, and equipment. These lease agreements are classified as either finance or operating leases and the liability and right-of-use asset are recognized on the balance sheet at lease commencement. Leases with an initial term of 12 months or less are not recorded on the balance sheet and are recognized as lease expense on a straight-line basis over the lease term. Eversource determines whether or not a contract contains a lease based on whether or not it provides Eversource with the use of a specifically identified asset for a period of time, as well as both the right to direct the use of that asset and receive the significant economic benefits of the asset. Eversource has elected the practical expedient to not separate non-lease components from lease components and instead to account for both as a single lease component, with the exception of the information technology asset class where the lease and non-lease components are separated. The provisions of Eversource, CL&P, NSTAR Electric and PSNH lease agreements contain renewal options. The renewal options range from one year to twenty years. The renewal period is included in the measurement of the lease liability if it is reasonably certain that Eversource will exercise these renewal options. For leases entered into or modified after the January 1, 2019 implementation date, the discount rate utilized for classification and measurement purposes as of the inception date of the lease is based on each company's collateralized incremental interest rate to borrow over a comparable term for an individual lease because the rate implicit in the lease is not determinable. 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 recognized as a lease liability on the balance sheet and are not reflected in the future minimum lease payments table below. Expense related to these contracts is included as variable lease cost in the table below. The expense and long-term obligation for these contracts are also included in Note 13B, "Commitments and Contingencies - Long-Term Contractual Arrangements," to the financial statements. The components of lease cost, prior to amounts capitalized, are as follows: For the Years Ended December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Financing Lease Cost: Amortization of Right-of-use-Assets $ 2.6 $ 0.7 $ 0.2 $ 0.1 $ 1.7 $ 0.7 $ 0.2 $ 0.1 Interest on Lease Liabilities 1.4 0.3 0.6 — 1.2 0.6 0.6 — Total Finance Lease Cost 4.0 1.0 0.8 0.1 2.9 1.3 0.8 0.1 Operating Lease Cost 11.1 0.6 2.1 0.1 11.7 0.5 3.4 0.1 Variable Lease Cost 57.8 12.2 — 45.6 60.5 13.3 — 47.2 Total Lease Cost $ 72.9 $ 13.8 $ 2.9 $ 45.8 $ 75.1 $ 15.1 $ 4.2 $ 47.4 Operating lease rental payments charged to expense in 2018 (which exclude CL&P's and PSNH's energy purchase contracts) were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 10.8 $ 10.9 $ 11.8 $ 2.5 Operating lease cost, net of the capitalized portion, is included in Operations and Maintenance (or Purchased Power, Fuel and Transmission expense for transmission segment leases) on the statements of income. Amortization of finance lease assets is included in Depreciation on the statements of income. Interest expense on finance leases is included in Interest Expense on the statements of income. Supplemental balance sheet information related to leases is as follows: As of December 31, 2020 (Millions of Dollars) Balance Sheet Classification Eversource CL&P NSTAR Electric PSNH Operating Leases: Operating Lease Right-of-use-Assets, Net Other Long-Term Assets $ 55.2 $ 0.3 $ 23.6 $ 0.3 Operating Lease Liabilities Operating Lease Liabilities - Current Portion Other Current Liabilities $ 9.5 $ 0.2 $ 0.7 $ — Operating Lease Liabilities - Long-Term Other Long-Term Liabilities 45.7 0.1 22.9 0.3 Total Operating Lease Liabilities $ 55.2 $ 0.3 $ 23.6 $ 0.3 Finance Leases: Finance Lease Right-of-use-Assets, Net Property, Plant and Equipment, Net $ 60.5 $ 0.7 $ 3.5 $ 0.8 Finance Lease Liabilities Finance Lease Liabilities - Current Portion Other Current Liabilities $ 5.0 $ 1.4 $ — $ 0.1 Finance Lease Liabilities - Long-Term Other Long-Term Liabilities 57.6 — 4.8 0.7 Total Finance Lease Liabilities $ 62.6 $ 1.4 $ 4.8 $ 0.8 As of December 31, 2019 (Millions of Dollars) Balance Sheet Classification Eversource CL&P NSTAR Electric PSNH Operating Leases: Operating Lease Right-of-use-Assets, Net Other Long-Term Assets $ 49.9 $ 0.7 $ 24.2 $ 0.4 Operating Lease Liabilities Operating Lease Liabilities - Current Portion Other Current Liabilities $ 8.6 $ 0.5 $ 0.7 $ 0.1 Operating Lease Liabilities - Long-Term Other Long-Term Liabilities 41.3 0.2 23.5 0.3 Total Operating Lease Liabilities $ 49.9 $ 0.7 $ 24.2 $ 0.4 Finance Leases: Finance Lease Right-of-use-Assets, Net Property, Plant and Equipment, Net $ 8.2 $ 1.9 $ 3.3 $ 0.9 Finance Lease Liabilities Finance Lease Liabilities - Current Portion Other Current Liabilities $ 2.4 $ 1.6 $ — $ 0.1 Finance Lease Liabilities - Long-Term Other Long-Term Liabilities 8.1 1.4 4.4 0.8 Total Finance Lease Liabilities $ 10.5 $ 3.0 $ 4.4 $ 0.9 The finance lease payments that NSTAR Electric will make over the next twelve months are entirely interest-related, due to escalating payments. As such, none of the finance lease payments over the next twelve months will reduce the finance lease liability. Other information related to leases is as follows (in millions of dollars, unless otherwise noted): As of December 31, 2020 2019 Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Weighted-Average Remaining Lease Term (Years): Operating Leases 10 3 19 8 12 2 20 9 Finance Leases 17 1 21 8 12 2 22 9 Weighted-Average Discount Rate (Percentage): Operating Leases 4.0 % 2.4 % 4.1 % 3.7 % 3.9 % 2.5 % 4.1 % 3.7 % Finance Leases 2.9 % 10.5 % 2.9 % 3.5 % 4.0 % 10.5 % 2.9 % 3.5 % Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2020 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 10.9 $ 0.6 $ 1.8 $ 0.1 Operating Cash Flows from Finance Leases 1.7 0.3 0.6 — Financing Cash Flows from Finance Leases 2.8 1.6 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 0.6 0.1 0.2 — Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 0.7 — 0.3 — Eversource also acquired $14.7 million of right-of-use assets in exchange for the assumption of new operating lease liabilities and $54.2 million of right-of-use assets in exchange for the assumption of new finance lease liabilities as a result of the CMA asset acquisition. Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2019 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 11.4 $ 0.4 $ 1.6 $ 0.1 Operating Cash Flows from Finance Leases 1.2 0.6 0.6 — Financing Cash Flows from Finance Leases 2.6 1.4 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 2.9 1.0 0.1 0.2 Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 2.0 — — — Future minimum lease payments, excluding variable costs, under long-term leases, as of December 31, 2020 are as follows: Operating Leases Finance Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Year Ending December 31, 2021 $ 11.4 $ 0.2 $ 1.6 $ 0.1 $ 7.2 $ 1.5 $ 0.6 $ 0.1 2022 9.0 0.1 1.6 0.1 5.7 — 0.6 0.1 2023 6.4 — 1.6 0.1 4.9 — 0.6 0.1 2024 4.5 — 1.7 — 4.8 — 0.7 0.1 2025 3.4 — 1.7 — 4.7 — 0.7 0.1 Thereafter 36.2 — 27.0 0.1 60.7 — 13.0 0.4 Future lease payments 70.9 0.3 35.2 0.4 88.0 1.5 16.2 0.9 Less amount representing interest 15.7 — 11.6 0.1 25.4 0.1 11.4 0.1 Present value of future minimum lease payments $ 55.2 $ 0.3 $ 23.6 $ 0.3 $ 62.6 $ 1.4 $ 4.8 $ 0.8
LEASES	LEASES Eversource, including CL&P, NSTAR Electric and PSNH, has entered into lease agreements as a lessee for the use of land, office space, service centers, vehicles, information technology, and equipment. These lease agreements are classified as either finance or operating leases and the liability and right-of-use asset are recognized on the balance sheet at lease commencement. Leases with an initial term of 12 months or less are not recorded on the balance sheet and are recognized as lease expense on a straight-line basis over the lease term. Eversource determines whether or not a contract contains a lease based on whether or not it provides Eversource with the use of a specifically identified asset for a period of time, as well as both the right to direct the use of that asset and receive the significant economic benefits of the asset. Eversource has elected the practical expedient to not separate non-lease components from lease components and instead to account for both as a single lease component, with the exception of the information technology asset class where the lease and non-lease components are separated. The provisions of Eversource, CL&P, NSTAR Electric and PSNH lease agreements contain renewal options. The renewal options range from one year to twenty years. The renewal period is included in the measurement of the lease liability if it is reasonably certain that Eversource will exercise these renewal options. For leases entered into or modified after the January 1, 2019 implementation date, the discount rate utilized for classification and measurement purposes as of the inception date of the lease is based on each company's collateralized incremental interest rate to borrow over a comparable term for an individual lease because the rate implicit in the lease is not determinable. 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 recognized as a lease liability on the balance sheet and are not reflected in the future minimum lease payments table below. Expense related to these contracts is included as variable lease cost in the table below. The expense and long-term obligation for these contracts are also included in Note 13B, "Commitments and Contingencies - Long-Term Contractual Arrangements," to the financial statements. The components of lease cost, prior to amounts capitalized, are as follows: For the Years Ended December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Financing Lease Cost: Amortization of Right-of-use-Assets $ 2.6 $ 0.7 $ 0.2 $ 0.1 $ 1.7 $ 0.7 $ 0.2 $ 0.1 Interest on Lease Liabilities 1.4 0.3 0.6 — 1.2 0.6 0.6 — Total Finance Lease Cost 4.0 1.0 0.8 0.1 2.9 1.3 0.8 0.1 Operating Lease Cost 11.1 0.6 2.1 0.1 11.7 0.5 3.4 0.1 Variable Lease Cost 57.8 12.2 — 45.6 60.5 13.3 — 47.2 Total Lease Cost $ 72.9 $ 13.8 $ 2.9 $ 45.8 $ 75.1 $ 15.1 $ 4.2 $ 47.4 Operating lease rental payments charged to expense in 2018 (which exclude CL&P's and PSNH's energy purchase contracts) were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 10.8 $ 10.9 $ 11.8 $ 2.5 Operating lease cost, net of the capitalized portion, is included in Operations and Maintenance (or Purchased Power, Fuel and Transmission expense for transmission segment leases) on the statements of income. Amortization of finance lease assets is included in Depreciation on the statements of income. Interest expense on finance leases is included in Interest Expense on the statements of income. Supplemental balance sheet information related to leases is as follows: As of December 31, 2020 (Millions of Dollars) Balance Sheet Classification Eversource CL&P NSTAR Electric PSNH Operating Leases: Operating Lease Right-of-use-Assets, Net Other Long-Term Assets $ 55.2 $ 0.3 $ 23.6 $ 0.3 Operating Lease Liabilities Operating Lease Liabilities - Current Portion Other Current Liabilities $ 9.5 $ 0.2 $ 0.7 $ — Operating Lease Liabilities - Long-Term Other Long-Term Liabilities 45.7 0.1 22.9 0.3 Total Operating Lease Liabilities $ 55.2 $ 0.3 $ 23.6 $ 0.3 Finance Leases: Finance Lease Right-of-use-Assets, Net Property, Plant and Equipment, Net $ 60.5 $ 0.7 $ 3.5 $ 0.8 Finance Lease Liabilities Finance Lease Liabilities - Current Portion Other Current Liabilities $ 5.0 $ 1.4 $ — $ 0.1 Finance Lease Liabilities - Long-Term Other Long-Term Liabilities 57.6 — 4.8 0.7 Total Finance Lease Liabilities $ 62.6 $ 1.4 $ 4.8 $ 0.8 As of December 31, 2019 (Millions of Dollars) Balance Sheet Classification Eversource CL&P NSTAR Electric PSNH Operating Leases: Operating Lease Right-of-use-Assets, Net Other Long-Term Assets $ 49.9 $ 0.7 $ 24.2 $ 0.4 Operating Lease Liabilities Operating Lease Liabilities - Current Portion Other Current Liabilities $ 8.6 $ 0.5 $ 0.7 $ 0.1 Operating Lease Liabilities - Long-Term Other Long-Term Liabilities 41.3 0.2 23.5 0.3 Total Operating Lease Liabilities $ 49.9 $ 0.7 $ 24.2 $ 0.4 Finance Leases: Finance Lease Right-of-use-Assets, Net Property, Plant and Equipment, Net $ 8.2 $ 1.9 $ 3.3 $ 0.9 Finance Lease Liabilities Finance Lease Liabilities - Current Portion Other Current Liabilities $ 2.4 $ 1.6 $ — $ 0.1 Finance Lease Liabilities - Long-Term Other Long-Term Liabilities 8.1 1.4 4.4 0.8 Total Finance Lease Liabilities $ 10.5 $ 3.0 $ 4.4 $ 0.9 The finance lease payments that NSTAR Electric will make over the next twelve months are entirely interest-related, due to escalating payments. As such, none of the finance lease payments over the next twelve months will reduce the finance lease liability. Other information related to leases is as follows (in millions of dollars, unless otherwise noted): As of December 31, 2020 2019 Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Weighted-Average Remaining Lease Term (Years): Operating Leases 10 3 19 8 12 2 20 9 Finance Leases 17 1 21 8 12 2 22 9 Weighted-Average Discount Rate (Percentage): Operating Leases 4.0 % 2.4 % 4.1 % 3.7 % 3.9 % 2.5 % 4.1 % 3.7 % Finance Leases 2.9 % 10.5 % 2.9 % 3.5 % 4.0 % 10.5 % 2.9 % 3.5 % Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2020 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 10.9 $ 0.6 $ 1.8 $ 0.1 Operating Cash Flows from Finance Leases 1.7 0.3 0.6 — Financing Cash Flows from Finance Leases 2.8 1.6 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 0.6 0.1 0.2 — Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 0.7 — 0.3 — Eversource also acquired $14.7 million of right-of-use assets in exchange for the assumption of new operating lease liabilities and $54.2 million of right-of-use assets in exchange for the assumption of new finance lease liabilities as a result of the CMA asset acquisition. Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2019 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 11.4 $ 0.4 $ 1.6 $ 0.1 Operating Cash Flows from Finance Leases 1.2 0.6 0.6 — Financing Cash Flows from Finance Leases 2.6 1.4 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 2.9 1.0 0.1 0.2 Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 2.0 — — — Future minimum lease payments, excluding variable costs, under long-term leases, as of December 31, 2020 are as follows: Operating Leases Finance Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Year Ending December 31, 2021 $ 11.4 $ 0.2 $ 1.6 $ 0.1 $ 7.2 $ 1.5 $ 0.6 $ 0.1 2022 9.0 0.1 1.6 0.1 5.7 — 0.6 0.1 2023 6.4 — 1.6 0.1 4.9 — 0.6 0.1 2024 4.5 — 1.7 — 4.8 — 0.7 0.1 2025 3.4 — 1.7 — 4.7 — 0.7 0.1 Thereafter 36.2 — 27.0 0.1 60.7 — 13.0 0.4 Future lease payments 70.9 0.3 35.2 0.4 88.0 1.5 16.2 0.9 Less amount representing interest 15.7 — 11.6 0.1 25.4 0.1 11.4 0.1 Present value of future minimum lease payments $ 55.2 $ 0.3 $ 23.6 $ 0.3 $ 62.6 $ 1.4 $ 4.8 $ 0.8

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	12 Months Ended
	Dec. 31, 2020
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 Fair Carrying Fair Carrying Fair As of December 31, 2020: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 169.1 $ 116.2 $ 123.4 $ 43.0 $ 45.7 $ — $ — Long-Term Debt 16,179.1 18,420.1 3,914.8 4,800.9 3,643.2 4,294.0 1,099.1 1,207.0 Rate Reduction Bonds 540.1 603.4 — — — — 540.1 603.4 As of December 31, 2019: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 162.0 $ 116.2 $ 117.8 $ 43.0 $ 44.2 $ — $ — Long-Term Debt 14,098.2 15,170.2 3,518.1 4,058.0 3,342.1 3,659.9 951.6 1,005.7 Rate Reduction Bonds 583.3 625.9 — — — — 583.3 625.9 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, 2020
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, 2020 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Qualified Unrealized Defined Total Qualified Unrealized Defined Total Balance as of January 1st $ (3.0) $ 0.7 $ (62.8) $ (65.1) $ (4.4) $ (0.5) $ (55.1) $ (60.0) OCI Before Reclassifications — 0.4 (19.6) (19.2) — 1.2 (13.3) (12.1) Amounts Reclassified from AOCI 1.6 — 6.3 7.9 1.4 — 5.6 7.0 Net OCI 1.6 0.4 (13.3) (11.3) 1.4 1.2 (7.7) (5.1) Balance as of December 31st $ (1.4) $ 1.1 $ (76.1) $ (76.4) $ (3.0) $ 0.7 $ (62.8) $ (65.1) 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 of the defined benefit plan OCI amounts before reclassifications recognized in AOCI were net deferred tax assets of $6.0 million and $4.4 million in 2020 and 2019, respectively, and deferred tax liabilities of $0.2 million in 2018. 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 2020 2019 2018 Qualified Cash Flow Hedging Instruments $ (2.5) $ (2.5) $ (2.8) Interest Expense Tax Effect 0.9 1.1 1.0 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (1.6) $ (1.4) $ (1.8) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (8.1) $ (5.7) $ (6.0) Other Income, Net (1) Amortization of Prior Service Cost (0.3) (1.8) (0.4) Other Income, Net (1) Total Defined Benefit Plan Costs (8.4) (7.5) (6.4) Tax Effect 2.1 1.9 1.6 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (6.3) $ (5.6) $ (4.8) Total Amounts Reclassified from AOCI, Net of Tax $ (7.9) $ (7.0) $ (6.6) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 1M, "Summary of Significant Accounting Policies – Other Income, Net" and Note 11A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," for further information.

DIVIDEND RESTRICTIONS

DIVIDEND RESTRICTIONS	12 Months Ended
	Dec. 31, 2020
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 agreements. Pursuant to the joint revolving credit agreement of Eversource, CL&P, PSNH, NSTAR Gas, Yankee Gas and Aquarion Water Company of Connecticut, the joint revolving credit agreement of Eversource and EGMA, 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, 2020, all companies were in compliance with such covenant and in compliance with all such provisions of the revolving credit agreements that may restrict the payment of dividends as of December 31, 2020. The Retained Earnings balances subject to dividend restrictions were $4.61 billion for Eversource, $2.17 billion for CL&P, $2.53 billion for NSTAR Electric and $615.0 million for PSNH as of December 31, 2020.

COMMON SHARES

COMMON SHARES	12 Months Ended
	Dec. 31, 2020
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 Authorized as of December 31, 2020 and 2019 Issued as of December 31, 2020 2019 Eversource $ 5 380,000,000 357,818,402 345,858,402 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 Common Share Issuances and 2019 Forward Sale Agreement: On June 15, 2020, Eversource completed an equity offering of 6,000,000 common shares at a price per share of $86.26. Eversource used the net proceeds of this offering to fund a portion of the purchase of the assets of CMA that closed on October 9, 2020. The issuance of these common shares resulted in proceeds of $509.2 million, net of issuance costs. In June 2019, Eversource completed an equity offering consisting of 5,980,000 common shares issued directly by the Company and 11,960,000 common shares issuable pursuant to a forward sale agreement with an investment bank. Under the forward sale agreement, 11,960,000 common shares were borrowed from third parties and sold by the underwriters. The forward sale agreement allowed Eversource, at its election and prior to May 29, 2020, to physically settle the forward sale agreement by issuing common shares in exchange for net proceeds at the then-applicable forward sale price specified by the agreement (initially, $71.48 per share) or, alternatively, to settle the forward sale agreement in whole or in part through the delivery or receipt of shares or cash. The forward sale price was subject to adjustment daily based on a floating interest rate factor and would decrease in respect of certain fixed amounts specified in the agreement, such as dividends. Eversource issued 6,000,000 common shares under the forward sale agreement in December 2019. On March 23, 2020, Eversource physically settled a portion of the forward sale agreement by delivering 1,500,000 common shares in exchange for net proceeds of $105.7 million. Subsequently, on March 26, 2020, Eversource physically settled the remaining portion of the forward sale agreement by delivering 4,460,000 common shares in exchange for net proceeds of $314.1 million. The forward sale price used to determine the cash proceeds received by Eversource was calculated based on the initial forward sale price, as adjusted in accordance with the forward sale agreement. The March and June 2020 common share issuances of 5,960,000 and 6,000,000, respectively, resulted in total proceeds of $929.0 million, net of issuance costs. The June and December 2019 common share issuances of 5,980,000 and 6,000,000, respectively, resulted in total proceeds of $852.3 million. These issuances were reflected in shareholders’ equity and as financing activities on the statements of cash flows. Issuances of shares under the forward sale agreement were classified as equity transactions. Accordingly, no amounts relating to the forward sale agreement were recorded in the financial statements until settlements took place. Prior to any settlements, the only impact of the forward sale agreement to the financial statements was the inclusion of incremental shares within the calculation of diluted EPS using the treasury stock method. See Note 21, "Earnings Per Share," to the financial statements for information on the forward sale agreement’s impact on the calculation of diluted EPS. Eversource used the net proceeds received from the direct issuance of common shares and the net proceeds received from settlement of the forward sale agreement to repay short-term debt under the commercial paper program, to partially fund the purchase of the assets of CMA, to fund capital spending and clean energy initiatives, and for general corporate purposes. Treasury Shares: As of December 31, 2020 and 2019, there were 14,864,379 and 15,977,757 Eversource common shares held as treasury shares, respectively. As of December 31, 2020 and 2019, there were 342,954,023 and 329,880,645 Eversource common shares outstanding, respectively. Eversource issues treasury shares to satisfy awards under the Company's incentive plans, shares issued under the dividend reinvestment and share purchase plan, and matching contributions under the Eversource 401k Plan. The issuance of treasury shares represents a non-cash transaction, as the treasury shares were used to fulfill Eversource's obligations that require the issuance of common shares.

PREFERRED STOCK NOT SUBJECT TO

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION	PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTIONThe 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. Details of preferred stock not subject to mandatory redemption are as follows (in millions, except in redemption price and shares): Redemption Price Shares Outstanding as of December 31, As of December 31, Series 2020 2019 2020 2019 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 - Noncontrolling Interest - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

COMMON SHAREHOLDERS' EQUITY AND

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	COMMON SHARES The following table sets forth the Eversource parent common shares and the shares of common stock of CL&P, NSTAR Electric and PSNH that were authorized and issued, as well as the respective per share par values: Shares Authorized as of December 31, 2020 and 2019 Issued as of December 31, 2020 2019 Eversource $ 5 380,000,000 357,818,402 345,858,402 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 Common Share Issuances and 2019 Forward Sale Agreement: On June 15, 2020, Eversource completed an equity offering of 6,000,000 common shares at a price per share of $86.26. Eversource used the net proceeds of this offering to fund a portion of the purchase of the assets of CMA that closed on October 9, 2020. The issuance of these common shares resulted in proceeds of $509.2 million, net of issuance costs. In June 2019, Eversource completed an equity offering consisting of 5,980,000 common shares issued directly by the Company and 11,960,000 common shares issuable pursuant to a forward sale agreement with an investment bank. Under the forward sale agreement, 11,960,000 common shares were borrowed from third parties and sold by the underwriters. The forward sale agreement allowed Eversource, at its election and prior to May 29, 2020, to physically settle the forward sale agreement by issuing common shares in exchange for net proceeds at the then-applicable forward sale price specified by the agreement (initially, $71.48 per share) or, alternatively, to settle the forward sale agreement in whole or in part through the delivery or receipt of shares or cash. The forward sale price was subject to adjustment daily based on a floating interest rate factor and would decrease in respect of certain fixed amounts specified in the agreement, such as dividends. Eversource issued 6,000,000 common shares under the forward sale agreement in December 2019. On March 23, 2020, Eversource physically settled a portion of the forward sale agreement by delivering 1,500,000 common shares in exchange for net proceeds of $105.7 million. Subsequently, on March 26, 2020, Eversource physically settled the remaining portion of the forward sale agreement by delivering 4,460,000 common shares in exchange for net proceeds of $314.1 million. The forward sale price used to determine the cash proceeds received by Eversource was calculated based on the initial forward sale price, as adjusted in accordance with the forward sale agreement. The March and June 2020 common share issuances of 5,960,000 and 6,000,000, respectively, resulted in total proceeds of $929.0 million, net of issuance costs. The June and December 2019 common share issuances of 5,980,000 and 6,000,000, respectively, resulted in total proceeds of $852.3 million. These issuances were reflected in shareholders’ equity and as financing activities on the statements of cash flows. Issuances of shares under the forward sale agreement were classified as equity transactions. Accordingly, no amounts relating to the forward sale agreement were recorded in the financial statements until settlements took place. Prior to any settlements, the only impact of the forward sale agreement to the financial statements was the inclusion of incremental shares within the calculation of diluted EPS using the treasury stock method. See Note 21, "Earnings Per Share," to the financial statements for information on the forward sale agreement’s impact on the calculation of diluted EPS. Eversource used the net proceeds received from the direct issuance of common shares and the net proceeds received from settlement of the forward sale agreement to repay short-term debt under the commercial paper program, to partially fund the purchase of the assets of CMA, to fund capital spending and clean energy initiatives, and for general corporate purposes. Treasury Shares: As of December 31, 2020 and 2019, there were 14,864,379 and 15,977,757 Eversource common shares held as treasury shares, respectively. As of December 31, 2020 and 2019, there were 342,954,023 and 329,880,645 Eversource common shares outstanding, respectively. Eversource issues treasury shares to satisfy awards under the Company's incentive plans, shares issued under the dividend reinvestment and share purchase plan, and matching contributions under the Eversource 401k Plan. The issuance of treasury shares represents a non-cash transaction, as the treasury shares were used to fulfill Eversource's obligations that require the issuance of common shares.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2020
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 and the equity forward sale agreement, as if they were converted into outstanding common shares. The dilutive effect of unvested RSU and performance share awards, as well as the equity forward sale agreement, 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. As described in Note 18, "Common Shares," earnings per share dilution, if any, related to the forward sale agreement is determined under the treasury stock method until settlement of the forward sale agreement. Under this method, the number of Eversource common shares used in calculating diluted EPS is deemed to be increased by the excess, if any, of the number of shares that would be issued upon physical settlement of the forward sale agreement less the number of shares that would be purchased by Eversource in the market (based on the average market price during the same reporting period) using the proceeds receivable upon settlement (based on the adjusted forward sale price at the end of that reporting period). Share dilution occurs when the average market price of Eversource's common shares is higher than the adjusted forward sale price. Eversource physically settled all remaining shares under the forward sale agreement as of March 26, 2020. For the year ended December 31, 2020, there were 39,560 antidilutive share awards excluded from the EPS computation, as their impact would have been antidilutive . Antidilutive shares pertained to a purchase option extended to underwriters in connection with Eversource's common share issuance on June 15, 2020. See Note 18, "Common Shares," for further information. There were no antidilutive share awards excluded from the computation for the years ended December 31, 2019 or 2018. 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, 2020 2019 2018 Net Income Attributable to Common Shareholders $ 1,205.2 $ 909.1 $ 1,033.0 Weighted Average Common Shares Outstanding: Basic 338,836,147 321,416,086 317,370,369 Dilutive Effect of: Share-Based Compensation Awards and Other 738,994 762,215 623,565 Equity Forward Sale Agreement 271,921 763,335 — Total Dilutive Effect 1,010,915 1,525,550 623,565 Diluted 339,847,062 322,941,636 317,993,934 Basic EPS $ 3.56 $ 2.83 $ 3.25 Diluted EPS $ 3.55 $ 2.81 $ 3.25

REVENUES

REVENUES	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES 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. A five-step model is used 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 tables present operating revenues disaggregated by revenue source: For the Year Ended December 31, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,951.5 $ 644.9 $ — $ 145.1 $ — $ — $ 4,741.5 Commercial 2,353.4 361.9 — 62.4 — (4.8) 2,772.9 Industrial 327.1 107.4 — 4.8 — (13.7) 425.6 Total Retail Tariff Sales Revenues 6,632.0 1,114.2 — 212.3 — (18.5) 7,940.0 Wholesale Transmission Revenues — — 1,557.3 — 74.2 (1,290.6) 340.9 Wholesale Market Sales Revenues 327.3 43.0 — 3.8 — — 374.1 Other Revenues from Contracts with Customers 74.7 3.6 13.3 7.3 1,161.7 (1,152.0) 108.6 Amortization of/(Reserve for) Revenues Subject to Refund 4.6 2.1 — (3.8) — — 2.9 Total Revenues from Contracts with Customers 7,038.6 1,162.9 1,570.6 219.6 1,235.9 (2,461.1) 8,766.5 Alternative Revenue Programs 88.1 44.7 (35.2) (4.7) — 37.1 130.0 Other Revenues 5.6 1.1 0.7 0.5 — — 7.9 Total Operating Revenues $ 7,132.3 $ 1,208.7 $ 1,536.1 $ 215.4 $ 1,235.9 $ (2,424.0) $ 8,904.4 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,723.7 $ 555.1 $ — $ 132.3 $ — $ — $ 4,411.1 Commercial 2,584.8 347.6 — 63.9 — (4.3) 2,992.0 Industrial 331.8 96.9 — 4.5 — (11.6) 421.6 Total Retail Tariff Sales Revenues 6,640.3 999.6 — 200.7 — (15.9) 7,824.7 Wholesale Transmission Revenues — — 1,293.3 — 61.3 (1,085.2) 269.4 Wholesale Market Sales Revenues 215.7 55.4 — 4.1 — — 275.2 Other Revenues from Contracts with Customers 54.8 2.8 13.2 7.0 967.2 (969.0) 76.0 Amortization of/(Reserve for) Revenues Subject to Refund 1.3 6.2 — (2.8) — — 4.7 Total Revenues from Contracts with Customers 6,912.1 1,064.0 1,306.5 209.0 1,028.5 (2,070.1) 8,450.0 Alternative Revenue Programs 45.9 (4.9) 81.8 4.6 — (74.2) 53.2 Other Revenues 18.5 3.1 0.7 1.0 — — 23.3 Total Operating Revenues $ 6,976.5 $ 1,062.2 $ 1,389.0 $ 214.6 $ 1,028.5 $ (2,144.3) $ 8,526.5 For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues 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 Revenues 6,753.2 973.3 — 198.4 — (14.5) 7,910.4 Wholesale Transmission Revenues — — 1,308.9 — 47.3 (1,092.2) 264.0 Wholesale Market Sales Revenues 179.5 57.5 — 4.1 — — 241.1 Other Revenues from Contracts with Customers 65.9 (2.2) 12.6 7.2 889.0 (891.0) 81.5 Reserve for Revenues Subject to Refund (12.3) (8.3) — (3.7) — — (24.3) Total Revenues 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 Revenues 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 Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 2,011.1 $ 1,365.8 $ 574.6 $ 1,837.1 $ 1,322.1 $ 564.5 $ 1,828.2 $ 1,380.9 $ 557.5 Commercial 878.3 1,176.8 299.9 922.9 1,349.4 314.6 928.1 1,391.5 316.9 Industrial 137.5 106.4 83.2 138.3 115.8 77.7 147.7 124.9 79.3 Total Retail Tariff Sales Revenues 3,026.9 2,649.0 957.7 2,898.3 2,787.3 956.8 2,904.0 2,897.3 953.7 Wholesale Transmission Revenues 754.8 576.5 226.0 587.1 517.3 188.9 620.6 488.8 199.5 Wholesale Market Sales Revenues 230.1 58.4 38.8 105.1 73.1 37.5 48.3 76.1 56.6 Other Revenues from Contracts 32.9 43.6 14.2 36.4 18.7 15.6 35.0 28.9 15.5 Amortization of/(Reserve for) — — 4.6 — — 1.3 — — (12.3) Total Revenues from Contracts 4,044.7 3,327.5 1,241.3 3,626.9 3,396.4 1,200.1 3,607.9 3,491.1 1,213.0 Alternative Revenue Programs (4.2) 54.5 2.6 77.5 41.6 8.6 (65.9) 0.9 (17.3) Other Revenues 2.2 3.5 0.6 10.3 7.0 1.9 8.5 8.3 1.1 Eliminations (495.2) (444.4) (165.4) (482.1) (400.4) (144.7) (454.3) (387.4) (149.2) Total Operating Revenues $ 3,547.5 $ 2,941.1 $ 1,079.1 $ 3,232.6 $ 3,044.6 $ 1,065.9 $ 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. 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 Revenues from Contracts with Customers: Other revenues from contracts with customers primarily include 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. Other revenues also include revenues from Eversource's service company, which is eliminated in consolidation. Amortization of/(Reserve for) Revenues Subject to Refund: Eversource has recorded a regulatory liability, recorded as a reduction to revenues, 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 of 2017, until rates billed to customers reflect the lower federal tax rate. The Connecticut water business has not yet reflected the change in the federal corporate income tax rate in distribution rates and continues to accrue the regulatory liability. CL&P and Yankee Gas each have fully refunded this regulatory liability by the end of 2018 and 2020, respectively, and in 2019, PSNH began to refund this regulatory liability to customers in rates. NSTAR Electric and NSTAR Gas were not required to make refunds to customers for 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 2018 rate changes. EGMA will begin refunding this amount in November 2021. 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 that are not considered revenue from contracts with customers. Other revenues also include lease revenues under lessor accounting guidance of $4.3 million ($0.8 million at CL&P and $2.7 million at NSTAR Electric) and $4.4 million ($1.0 million at CL&P and $2.7 million at NSTAR Electric) for the years ended December 31, 2020 and 2019, respectively. 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.

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION Eversource is organized into 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. 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, 5) the results of other unregulated subsidiaries, which are not part of its core business, and 6) Eversource parent's equity ownership interests that are not consolidated, which primarily include the offshore wind business, a natural gas pipeline owned by Enbridge, Inc., and a renewable energy investment fund. In the ordinary course of business, Yankee Gas, NSTAR Gas and EGMA purchase natural gas transmission services from the Enbridge, Inc. natural gas pipeline project described above. These affiliate transaction costs total $77.7 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. 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, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 7,132.3 $ 1,208.7 $ 1,536.1 $ 215.4 $ 1,235.9 $ (2,424.0) $ 8,904.4 Depreciation and Amortization (657.0) (87.9) (278.1) (44.2) (93.5) 1.6 (1,159.1) Other Operating Expenses (5,642.3) (913.8) (470.0) (86.6) (1,071.9) 2,428.0 (5,756.6) Operating Income 833.0 207.0 788.0 84.6 70.5 5.6 1,988.7 Interest Expense (216.0) (40.0) (126.8) (32.9) (161.0) 38.3 (538.4) Interest Income 3.2 0.9 4.7 — 37.8 (41.8) 4.8 Other Income, Net 58.0 3.1 23.3 2.0 1,382.9 (1,365.5) 103.8 Income Tax (Expense)/Benefit (129.6) (36.9) (183.8) (12.5) 16.6 — (346.2) Net Income 548.6 134.1 505.4 41.2 1,346.8 (1,363.4) 1,212.7 Net Income Attributable to Noncontrolling Interests (4.6) — (2.9) — — — (7.5) Net Income Attributable to Common Shareholders $ 544.0 $ 134.1 $ 502.5 $ 41.2 $ 1,346.8 $ (1,363.4) $ 1,205.2 Total Assets (as of) $ 24,981.9 $ 6,450.5 $ 11,695.0 $ 2,375.2 $ 22,089.4 $ (21,492.4) $ 46,099.6 Cash Flows Used for Investments in Plant $ 1,079.0 $ 494.4 $ 1,004.6 $ 118.8 $ 246.2 $ — $ 2,943.0 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 6,976.5 $ 1,062.2 $ 1,389.0 $ 214.6 $ 1,028.5 $ (2,144.3) $ 8,526.5 Depreciation and Amortization (651.3) (68.3) (253.3) (46.9) (63.2) 2.3 (1,080.7) Impairment of Northern Pass Transmission — — (239.6) — — — (239.6) Other Operating Expenses (5,525.1) (830.8) (411.2) (101.0) (891.3) 2,143.7 (5,615.7) Operating Income 800.1 163.1 484.9 66.7 74.0 1.7 1,590.5 Interest Expense (206.4) (47.4) (125.7) (34.6) (170.3) 51.2 (533.2) Interest Income 13.3 0.1 1.5 — 48.7 (50.8) 12.8 Other Income, Net 46.8 1.6 29.2 0.4 945.3 (903.3) 120.0 Income Tax (Expense)/Benefit (135.9) (21.2) (130.5) 2.4 11.7 — (273.5) Net Income 517.9 96.2 259.4 34.9 909.4 (901.2) 916.6 Net Income Attributable to Noncontrolling Interests (4.6) — (2.9) — — — (7.5) Net Income Attributable to Common Shareholders $ 513.3 $ 96.2 $ 256.5 $ 34.9 $ 909.4 $ (901.2) $ 909.1 Total Assets (as of) $ 22,541.9 $ 4,345.5 $ 10,904.0 $ 2,351.7 $ 18,843.7 $ (17,862.9) $ 41,123.9 Cash Flows Used for Investments in Plant $ 1,104.2 $ 460.2 $ 987.0 $ 118.0 $ 242.1 $ — $ 2,911.5 For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other (1) Eliminations (1) 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) 1,092.1 (1,087.1) 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 1,111.3 (1,085.0) 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 $ 1,111.3 $ (1,085.0) $ 1,033.0 Cash Flows Used for Investments in Plant $ 961.3 $ 351.5 $ 976.2 $ 102.3 $ 178.6 $ — $ 2,569.9 (1) On October 9, 2020, Eversource completed the CMA asset acquisition, with Yankee Energy System, Inc. (Yankee parent) as the acquiring entity. Yankee parent is the parent company of Yankee Gas, NSTAR Gas, EGMA and Hopkinton LNG Corp. As a result of the acquisition, in the fourth quarter of 2020, our chief operating decision maker assessed the performance of the Natural Gas Distribution segment including Yankee parent. Previously, Yankee parent was presented within Other and its equity in earnings were eliminated in consolidation. Prior comparative periods were revised to conform to the current period segment presentation.

ACQUISITION OF ASSETS OF COLUMB

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS	ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS On October 9, 2020, Eversource acquired certain assets and liabilities that comprised NiSource’s natural gas distribution business in Massachusetts, which was previously doing business as CMA, pursuant to an asset purchase agreement (the Agreement) entered into on February 26, 2020 between Eversource and NiSource Inc. (NiSource). The cash purchase price was $1.1 billion, plus a target working capital amount of $69.6 million, which is subject to adjustment to reflect actual working capital as of the closing date that has not yet been finalized. Eversource financed the acquisition through a combination of debt and equity issuances in a ratio that was consistent with our consolidated capital structure. The natural gas distribution assets acquired from CMA were assigned to EGMA, an indirect wholly-owned subsidiary of Eversource formed in 2020. The LNG assets acquired from CMA were assigned to Hopkinton LNG Corp. EGMA distributes natural gas to approximately 332,000 residential, commercial and industrial customers with over 5,000 miles of natural gas distribution pipeline across more than 60 communities in Massachusetts, adding to the approximately 303,000 natural gas customers that Eversource already serves in Massachusetts. The transaction required approval by the DPU, the Maine Public Utilities Commission, the FERC, and the Federal Communications Commission, and review under the Hart-Scott-Rodino Act. The liabilities assumed by Eversource under the Agreement specifically excluded any liabilities (past or future) arising out of, or related to, the fires and explosions that occurred on September 13, 2018 in Lawrence, Andover and North Andover, Massachusetts related to the delivery of natural gas by CMA, including certain subsequent events, all as described and in the DPU's Order on Scope dated December 23, 2019 (D.P.U. 19-141) (the Greater Lawrence Incident or GLI). The liabilities assumed also excluded any further emergency events prior to the closing of the acquisition related to the restoration and reconstruction with respect to the GLI, including any losses arising out of, or related to, any litigation, demand, cause of action, claim, suit, investigation, proceeding, indemnification agreements or rights. Eversource did not assume any of CMA's or NiSource Inc.'s third party debt obligations or notes payable. Rate Settlement Agreement : On October 7, 2020, the DPU approved a rate settlement agreement with Eversource, EGMA, NiSource, Bay State, the Massachusetts Attorney General's Office, the DOER and the Low-Income Weatherization and Fuel Assistance Program Network, which requested approval of the February 26, 2020 Agreement, as well as a rate stabilization plan, among other items. The settlement agreement included an authorized regulatory ROE of 9.70 percent as of January 1, 2021, a 53.25 percent equity component of its capital structure, and established rate base equal to $995 million as of the closing on October 9, 2020. The approved rate stabilization plan includes base distribution rate increases of $13 million on November 1, 2021 and $10 million on November 1, 2022. The settlement agreement includes two rate base resets during an eight-year rate plan, occurring on November 1, 2024 and November 1, 2027. The two rate base resets adjust distribution rates to account for capital additions (including the roll-in of GSEP capital additions), depreciation expense, property taxes, and return on rate base for capital additions placed into service through December 31, 2023, for the first rate base reset occurring on November 1, 2024, and through December 31, 2026, for the second rate base reset occurring on November 1, 2027. Notwithstanding the two distribution rate increases, the two rate base reset provisions, and potential adjustments for qualifying exogenous events, EGMA agreed not to file for an increase or redesign of distribution base rates effective prior to November 1, 2028. The settlement agreement also permits EGMA to seek recovery of both transaction and integration costs as a result of the asset acquisition after December 31, 2026, subject to DPU review and approval, and subject to certain conditions, such as demonstrating savings resulting from the acquisition. Preliminary Purchase Price Allocation : The allocation of the total purchase price to the estimated fair values of the assets acquired and liabilities assumed has been determined based on the accounting guidance for fair value measurements, which defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The preliminary allocation of the cash purchase price as of October 9, 2020 is as follows: (Millions of Dollars) Current Assets $ 145 Restricted Cash 57 PP&E 1,195 Goodwill 42 Other Noncurrent Assets, excluding Goodwill 128 Other Current Liabilities (81) Other Noncurrent Liabilities (317) Cash Purchase Price $ 1,169 The fair values of CMA's assets and liabilities were determined based on significant estimates and assumptions, including Level 3 inputs, that are judgmental in nature. The allocation of the total purchase price includes adjustments to reflect plant that will not earn a return and to reduce rate base to the allowed $995 million as specified in the rate settlement agreement. Eversource also recorded a $6.7 million liability for the future refund to customers for CMA's overcollection of the lower income tax rate beginning in 2018. The excess of the purchase price over the estimated fair values of the assets acquired and liabilities assumed was recognized as goodwill. The goodwill reflects the value paid by Eversource primarily for expanding its natural gas infrastructure within its existing jurisdiction. The goodwill resulting from the acquisition has been assigned to the Natural Gas Distribution reporting unit. Under the terms of the settlement agreement, a portion of the proceeds of the sale due to NiSource was withheld and used to establish an Energy Relief Fund comprised of two components, an Arrearage Forgiveness Fund and a fund which is restricted for energy efficiency and clean energy measures in the Merrimack Valley. As a result, Eversource funded restricted cash accounts and established a liability totaling $56.8 million on the acquisition date. By December 31, 2020, $15.4 million of the Arrearage Forgiveness Fund was credited back to customers and the remainder was paid back to NiSource. The purchase price included in investing cash outflows on the statement of cash flows of $1.11 billion reflects the payment to NiSource, excluding the restricted cash funds. Pro Forma Financial Information: The following unaudited pro forma financial information reflects the pro forma combined results of operations of Eversource and the CMA business acquired and reflects the amortization of purchase price adjustments assuming the acquisition had taken place on January 1, 2019. 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. Pro forma net income excludes the impact of assets and liabilities not assumed by Eversource, such as amounts directly associated with the GLI incident, and non-recurring costs associated with the transaction. For the Years Ended December 31, (Pro forma amounts in millions, except share amounts) 2020 2019 Operating Revenues $ 9,273 $ 9,103 Net Income Attributable to Common Shareholders 1,265 909 Basic EPS 3.73 2.83 Diluted EPS 3.72 2.82 Revenues and Net Income: The impact of CMA on Eversource's accompanying consolidated statement of income included operating revenues of $154.8 million and net income attributable to common shareholders of $13.9 million for the year ended December 31, 2020.

GOODWILL

GOODWILL	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill Disclosure	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's reporting units for the purpose of testing goodwill are Electric Distribution, Electric Transmission, Natural Gas Distribution and Water Distribution. 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 the CMA asset acquisition on October 9, 2020, resulting in the addition of approximately $42 million of goodwill, which was allocated to the Natural Gas Distribution reporting unit. On July 31, 2020, Eversource sold its water system and treatment plant that supplies water to the towns of Hingham, Hull and North Cohasset to the town of Hingham, Massachusetts, resulting in a reduction to goodwill of $23.6 million. This goodwill was previously reflected in the Water Distribution reporting unit. Eversource completed its annual goodwill impairment test for Electric Distribution, Electric Transmission, Natural Gas Distribution and Water Distribution reporting units as of October 1, 2020 and determined that no impairment existed. There were no events subsequent to October 1, 2020 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: (Millions of Dollars) Electric Electric Natural Gas Water Distribution Total Balance as of January 1, 2020 $ 2,544 $ 577 $ 399 $ 907 $ 4,427 Acquisition of CMA Assets — — 42 — 42 Sale of Hingham water system — — — (23) (23) Balance as of December 31, 2020 $ 2,544 $ 577 $ 441 $ 884 $ 4,446

SCHEDULE I - FINANCIAL INFORMAT

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2020
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, 2020 AND 2019 (Thousands of Dollars) 2020 2019 ASSETS Current Assets: Cash $ 434 $ 1,469 Accounts Receivable from Subsidiaries 39,645 25,070 Notes Receivable from Subsidiaries 996,300 1,376,000 Prepayments and Other Current Assets 19,043 33,546 Total Current Assets 1,055,422 1,436,085 Deferred Debits and Other Assets: Investments in Subsidiary Companies, at Equity 15,483,263 13,162,337 Notes Receivable from Subsidiaries 1,110,400 157,000 Accumulated Deferred Income Taxes 33,469 27,578 Goodwill 3,231,811 3,231,811 Other Long-Term Assets 90,735 92,394 Total Deferred Debits and Other Assets 19,949,678 16,671,120 Total Assets $ 21,005,100 $ 18,107,205 LIABILITIES AND CAPITALIZATION Current Liabilities: Notes Payable $ 1,054,325 $ 878,584 Long-Term Debt - Current Portion 473,933 23,933 Accounts Payable to Subsidiaries 18,424 4,333 Other Current Liabilities 103,477 62,385 Total Current Liabilities 1,650,159 969,235 Deferred Credits and Other Liabilities 163,053 149,637 Long-Term Debt 5,128,322 4,358,339 Common Shareholders' Equity: Common Shares 1,789,092 1,729,292 Capital Surplus, Paid in 8,015,663 7,087,768 Retained Earnings 4,613,201 4,177,048 Accumulated Other Comprehensive Loss (76,411) (65,059) Treasury Stock (277,979) (299,055) Common Shareholders' Equity 14,063,566 12,629,994 Total Liabilities and Capitalization $ 21,005,100 $ 18,107,205 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 13, "Commitments and Contingencies," and debt agreements as described in Note 8, "Short-Term Debt," and Note 9, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF INCOME FOR THE YEARS ENDED DECEMBER 31, 2020, 2019 AND 2018 (Thousands of Dollars, Except Share Information) 2020 2019 2018 Operating Revenues $ — $ — $ — Operating Expenses: Other 28,645 50,100 (6,552) Operating (Loss)/Income (28,645) (50,100) 6,552 Interest Expense 160,887 163,937 123,638 Other Income, Net: Equity in Earnings of Subsidiaries 1,309,630 1,001,526 1,049,748 Other, Net 38,546 68,137 47,581 Other Income, Net 1,348,176 1,069,663 1,097,329 Income Before Income Tax Benefit 1,158,644 855,626 980,243 Income Tax Benefit (46,523) (53,427) (52,757) Net Income $ 1,205,167 $ 909,053 $ 1,033,000 Basic Earnings per Common Share $ 3.56 $ 2.83 $ 3.25 Diluted Earnings per Common Share $ 3.55 $ 2.81 $ 3.25 Weighted Average Common Shares Outstanding: Basic 338,836,147 321,416,086 317,370,369 Diluted 339,847,062 322,941,636 317,993,934 STATEMENTS OF COMPREHENSIVE INCOME 2020 2019 2018 Net Income $ 1,205,167 $ 909,053 $ 1,033,000 Other Comprehensive (Loss)/Income, Net of Tax: Qualified Cash Flow Hedging Instruments 1,596 1,393 1,756 Changes in Unrealized Gains/(Losses) on Marketable Securities 342 1,166 (547) Change in Funded Status of Pension, SERP and PBOP Benefit Plans (13,290) (7,618) 5,194 Other Comprehensive (Loss)/Income, Net of Tax (11,352) (5,059) 6,403 Comprehensive Income $ 1,193,815 $ 903,994 $ 1,039,403 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 13, "Commitments and Contingencies," and debt agreements as described in Note 8, "Short-Term Debt," and Note 9, "Long-Term Debt." SCHEDULE I EVERSOURCE ENERGY (PARENT) FINANCIAL INFORMATION OF REGISTRANT STATEMENTS OF CASH FLOWS FOR THE YEARS ENDED DECEMBER 31, 2020, 2019 and 2018 (Thousands of Dollars) 2020 2019 2018 Operating Activities: Net Income $ 1,205,167 $ 909,053 $ 1,033,000 Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities: Equity in Earnings of Subsidiaries (1,309,630) (1,001,526) (1,049,748) Cash Dividends Received from Subsidiaries 485,800 883,000 569,500 Deferred Income Taxes (4,667) 13,382 20,032 Other 39,940 19,584 (31,093) Changes in Current Assets and Liabilities: Accounts Receivables from Subsidiaries (14,575) 7,105 (28,716) Taxes Receivable/Accrued, Net 35,300 (605) (20,207) Accounts Payable to Subsidiaries 14,091 (4,099) (9,817) Other Current Assets and Liabilities, Net 21,284 (2,503) 2,553 Net Cash Flows Provided by Operating Activities 472,710 823,391 485,504 Investing Activities: Capital Contributions to Subsidiaries (1,899,340) (1,039,000) (955,700) Return of Capital from Subsidiaries 80,000 — 530,000 Increase in Notes Receivable from Subsidiaries (264,300) (218,100) (158,210) Other Investing Activities (367) (1,799) (1,149) Net Cash Flows Used in Investing Activities (2,084,007) (1,258,899) (585,059) Financing Activities: Issuance of Common Shares, Net of Issuance Costs 928,992 852,254 — Cash Dividends on Common Shares (744,665) (663,239) (640,110) Issuance of Long-Term Debt 1,550,000 — 1,550,000 Retirement of Long-Term Debt — (350,000) (450,000) (Decrease)/Increase in Notes Payable (170,545) 593,370 (347,810) Other Financing Activities 46,480 4,001 (12,455) Net Cash Flows Provided by Financing Activities 1,610,262 436,386 99,625 Net (Decrease)/Increase in Cash (1,035) 878 70 Cash - Beginning of Year 1,469 591 521 Cash - End of Year $ 434 $ 1,469 $ 591 Supplemental Cash Flow Information: Cash Paid/(Received) During the Year for: Interest $ 140,694 $ 161,323 $ 118,533 Income Taxes $ (43,158) $ (63,227) $ (30,239) 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 13, "Commitments and Contingencies," and debt agreements as described in Note 8, "Short-Term Debt," and Note 9, "Long-Term Debt."

SCHEDULE II - VALUATION AND QUA

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES	12 Months Ended
	Dec. 31, 2020
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, 2020, 2019 AND 2018 (Thousands of Dollars) Column A Column B Column C Column D Column E Additions (1) (2) Description: Balance as of Beginning of Year Charged to Costs and Expenses Charged to Other Deductions -Describe (b) Balance as of End of Year Eversource : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2020 $ 224,821 $ 53,461 $ 145,005 $ 64,436 $ 358,851 2019 212,723 63,446 57,223 108,571 224,821 2018 195,708 61,337 48,671 92,993 212,723 CL&P: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2020 $ 97,348 $ 12,882 $ 71,223 $ 24,006 $ 157,447 2019 88,034 15,947 38,935 45,568 97,348 2018 78,872 15,831 29,524 36,193 88,034 NSTAR Electric: Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2020 $ 75,406 $ 15,293 $ 23,424 $ 22,540 $ 91,583 2019 74,516 25,079 12,556 36,745 75,406 2018 69,666 22,279 14,971 32,400 74,516 PSNH : Reserves Deducted from Assets - Reserves for Uncollectible Accounts: 2020 $ 10,497 $ 5,164 $ 7,692 $ 6,196 $ 17,157 2019 11,065 6,726 872 8,166 10,497 2018 10,481 6,383 953 6,752 11,065 (a) Amounts relate to uncollectible accounts receivables reserved for that are not charged to bad debt expense. CL&P, NSTAR Electric, NSTAR Gas and Yankee Gas are allowed to recover in rates, amounts associated with certain uncollectible hardship accounts receivable. Management also believes that uncollectible hardship accounts receivable at EGMA will be recoverable in future rates. CL&P, NSTAR Electric, PSNH, NSTAR Gas and EGMA are also allowed to recover uncollectible energy supply costs through regulatory tracking mechanisms. Amounts in this column also include a $24.2 million increase due to the CMA asset acquisition on October 9, 2020 at Eversource, and an increase due to the adoption of the credit loss accounting standard in 2020 of $23.8 million at Eversource, $22.2 million at CL&P, $0.3 million at PSNH, and a decrease of $1.3 million at NSTAR Electric.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2020
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 the operations of CYAPC and YAEC, both of which are inactive regional nuclear power companies engaged in the long-term storage of their spent nuclear fuel. 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 holds several equity ownership interests that are not consolidated and are accounted for under the equity method. 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. 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. COVID-19 has adversely affected workers and the economy and caused volatility in the financial markets. Due to the inherent uncertainty of the unprecedented and evolving situation, we continue to closely monitor how COVID-19 related developments affect Eversource. Based on available information, we have not experienced significant impacts directly related to the pandemic that have adversely affected our current operations or results of operations. The extent of the impact to us in the future will vary and depend in large part on the duration, scope and severity of the pandemic and the timing and extent of COVID-19 relief legislation, and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of planned proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19. We believe that we have in place, or are developing, successful mechanisms with our state regulatory commissions that allow, or will allow, us to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses, while balancing the impact on our customers’ bills and our operating cash flows. See Note 1F, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of December 31, 2020 in light of the COVID-19 pandemic. An extended economic slowdown has resulted in lower demand for electricity, natural gas and/or water by our commercial and industrial customers. However, fluctuations in retail sales volumes for CL&P, NSTAR Electric, Yankee Gas, NSTAR Gas, EGMA, and our Connecticut water distribution business do not materially impact earnings due to their respective state regulatory commission-approved distribution revenue decoupling mechanisms. As of December 31, 2020, we did not identify indicators or triggering events for impairments to our goodwill, long-lived assets, available-for-sale debt securities, or equity method investment carrying values.
Accounting Standards	Accounting Standards Accounting Standards Issued but Not Yet Effective: In December 2019, the FASB issued Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes , which eliminates certain exceptions to the general principles of current income tax guidance in ASC 740 and simplifies and improves consistency in application of that income tax guidance through clarifications of and amendments to ASC 740. The guidance is effective in the first quarter of 2021. The ASU is not expected to have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH. Accounting Standards Recently Adopted: On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (Topic 326), which provides a model for recognizing credit losses on financial instruments based on an estimate of current expected losses, requiring immediate recognition of credit losses expected over the life of a financial instrument. The Company determined the impacts of this standard on the allowance for credit losses on its financial instruments, primarily accounts receivable. As of January 1, 2020, the Company recorded increases to the allowance for uncollectible accounts for late fees and other receivable amounts of $1.6 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The impact to retained earnings, net of tax, was $1.5 million, $0.9 million, $0.2 million and $0.3 million at Eversource, CL&P, NSTAR Electric and PSNH, respectively. The Company also adjusted the allowance for uncollectible amounts of hardship receivables and other low-income assistance programs, which are ultimately collectible in rates at specified points in time under approved regulatory mechanisms. The impact on the allowance, which was offset in other long-term assets on the balance sheets, was an increase of $22.2 million and $21.3 million at Eversource and CL&P, respectively, and a decrease of $1.5 million at NSTAR Electric as of January 1, 2020. See Note 1F, “Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts,” for further information. The Company adopted ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), Simplifying the Test for Goodwill Impairment as of January 1, 2020 . The ASU simplified the accounting for goodwill impairment by removing a complex step in the goodwill impairment test. Under the guidance, goodwill impairment is measured as the amount by which its carrying value exceeds its fair value. The ASU did not have an impact on the financial statements of Eversource. On January 1, 2020, the Company adopted ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The ASU aligned the requirements for capitalizing costs incurred to implement a cloud computing arrangement with existing internal-use software guidance. The prospective implementation of this standard did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric or PSNH for the year ended December 31, 2020. On January 1, 2020, the Company prospectively adopted ASU 2018-13, Fair Value Measurement (Topic 820), Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement . The ASU modified fair value disclosure requirements . The standard includes new disclosure requirements for Level 3 unobservable inputs and eliminated the requirement to disclose certain information relating to transfers between levels. The modified disclosures are included in Note 1I, “Summary of Significant Accounting Policies - Fair Value Measurements,” and Note 4, “Derivative Instruments.” The Company adopted ASU 2018-14, Compensation – Retirement Benefits – Defined Benefit Plans – General, Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans as of January 1, 2020. The guidance eliminated certain disclosures about defined benefit plans, added new disclosures, and clarified other requirements. This guidance is effective for fiscal years ending after December 15, 2020. Adoption of this guidance did not have a material effect on our annual financial statement disclosures. The modified disclosures are included in Note 11A, “Employee Benefits - Pension Benefits and Postretirement Benefits Other Than Pension.”
Cash	CashCash includes cash on hand.  At the end of each reporting period, any overdraft amounts are reclassified from Cash to Accounts Payable on the balance sheets.
Provision for Uncollectible Accounts	Allowance for Uncollectible Accounts Receivables, Net on the balance sheets primarily includes trade receivables from retail customers and customers related to wholesale transmission contracts, wholesale market sales, sales of RECs and property rentals. Receivables, Net also includes customer receivables for the purchase of electricity from a competitive third party supplier, the current portion of customer energy efficiency loans, property damage receivables and other miscellaneous receivables. There is no material concentration of receivables. Receivables are recorded at amortized cost, net of a credit loss provision (or allowance for uncollectible accounts). Receivables are presented net of expected credit losses at estimated net realizable value by maintaining an allowance for uncollectible accounts. Effective January 1, 2020, the current expected credit loss (CECL) model was applied to receivables for purposes of calculating the allowance for uncollectible accounts. This model is based on expected losses and results in the recognition of estimated expected credit losses, including uncollectible amounts for both billed and unbilled revenues, over the life of the receivable at the time a receivable is recorded. Receivables, net of reserves, increased $206.5 million ($58.3 million at CL&P, $56.3 million at NSTAR Electric, and $20.0 million at PSNH) in 2020, as compared to 2019, due primarily to an increase in delinquent receivables from customers attributable to the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Receivables, net of reserves, also increased due to the addition of EGMA of $65.8 million as of December 31, 2020. The allowance for uncollectible accounts is determined based upon a variety of judgments and factors, including the application of an estimated uncollectible percentage to each receivable aging category. Factors in determining credit loss include historical collection, write-off experience, and management's assessment of collectability from customers, including current conditions, reasonable forecasts, and expectations of future collectability and collection efforts. Management continuously assesses the collectability of receivables and adjusts estimates based on actual experience and future expectations based on economic indicators, collection efforts and other factors. Management also monitors the aging analysis of receivables to determine if there are changes in the collections of accounts receivable. Receivable balances are written off against the allowance for uncollectible accounts when the customer accounts are no longer in service and these balances are deemed to be uncollectible. As of December 31, 2020, management evaluated the adequacy of the allowance for uncollectible accounts in light of the COVID-19 pandemic and the related economic downturn. This evaluation included an analysis of collection and customer payment trends, economic conditions, delinquency statistics, aging-based quantitative assessments, the impact on residential customer bills because of energy usage and change in rates, flexible payment plans and financial hardship arrearage management programs being offered to customers, and COVID-19 developments, including any potential federal governmental pandemic relief programs and the expansion of unemployment benefit initiatives, which help to mitigate the potential for increasing customer account delinquencies. Additionally, management considered past economic declines and corresponding uncollectible reserves as part of the current assessment. This evaluation has shown that our operating companies have experienced an increase in aged receivables and some lower cash collections from customers because of the moratorium on disconnections and the economic slowdown resulting from the COVID-19 pandemic. Based upon the evaluation performed, for the year ended December 31, 2020, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $31.5 million for Eversource ($2.8 million for CL&P, $11.0 million for NSTAR Electric, $2.3 million for PSNH and $15.4 million at our natural gas businesses). These COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs or deferred through existing regulatory tracking mechanisms that recover uncollectible energy supply costs, as management believes it is probable that these costs will ultimately be recovered from customers in rates. Management concluded that the reserve balance as of December 31, 2020 adequately reflected the collection risk and net realizable value for Eversource’s receivables. Management will continue to evaluate the adequacy of the uncollectible allowance in future reporting periods based on an ongoing assessment of accounts receivable collections, delinquency statistics, and analysis of aging-based quantitative assessments.
Transfer of Energy Efficiency Loans	Transfer of Energy Efficiency LoansCL&P has transferred a portion of its energy efficiency customer loan portfolio to 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, with a maximum amount outstanding under this program of $55 million.  The amounts of the loans are included in Accounts Receivable, Net and Other Long-Term Assets, and are offset by Other Current Liabilities and Other Long-Term Liabilities on CL&P’s balance sheet.
Fuel, Materials, Supplies and REC Inventory	Fuel, Materials, Supplies and REC InventoryFuel, Materials, Supplies and REC 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, long-lived assets, equity method investments, and AROs, and in the valuation of the acquisition of CMA in 2020. The fair value measurement guidance was also applied in estimating the 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. The levels of the fair value hierarchy are described below: Level 1 - Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities as of the reporting date. Active markets are those in which transactions for the asset or liability occur in sufficient frequency and volume to provide pricing information on an ongoing basis. Level 2 - Inputs are quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs are observable. Level 3 - Quoted market prices are not available. Fair value is derived from valuation techniques in which one or more significant inputs or assumptions are unobservable. Where possible, valuation techniques incorporate observable market inputs that can be validated to external sources such as industry exchanges, including prices of energy and energy-related products.
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. 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. 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. All changes in the fair value of derivative contracts are recorded as regulatory assets or liabilities and do not impact net income.
Allowance for Funds Used During Construction	Allowance for Funds Used During ConstructionAFUDC 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 TaxesEversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers. Separate from above were amounts recorded as Taxes Other Than Income Taxes at CL&P related to the remittance to the State of Connecticut of energy efficiency funds collected from customers of $21.4 million and $46.8 million in 2019 and 2018, respectively. Energy efficiency funds collected from customers after July 1, 2019 are no longer subject to remittance to the State of Connecticut. These amounts were recorded separately, with collections in Operating Revenues and with payments in Taxes Other Than Income Taxes on the Eversource and CL&P statements of income. As agents for state and local governments, Eversource's companies that serve customers in Connecticut and Massachusetts collect certain sales taxes that are recorded on a net basis with no impact on the statements of income.
Related Parties	Related Parties Eversource Service, Eversource's service company, provides centralized accounting, administrative, engineering, financial, information technology, legal, operational, planning, purchasing, tax, and other services to Eversource's companies. The Rocky River Realty Company and Properties, Inc., two other Eversource subsidiaries, construct, acquire or lease some of the property and facilities used by Eversource's companies. As of both December 31, 2020 and 2019, 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, 2020 and 2019 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. The Eversource Energy Foundation is an independent not-for-profit charitable entity and is not included in the consolidated financial statements of Eversource as the Company does not have title to, and cannot receive contributions back from, the Eversource Energy Foundation's assets. Eversource made contributions to the Eversource Energy Foundation of $6.4 million in 2020 and did not make any contributions in 2019 or 2018.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Provision for Uncollectible Accounts	The activity in the allowance for uncollectible accounts by portfolio segment is as follows: As of December 31, 2020 Eversource CL&P NSTAR Electric PSNH (Millions of Dollars) Hardship Accounts Retail (Non-Hardship), Total Allowance Hardship Accounts Retail (Non-Hardship), Total Allowance Hardship Accounts Retail (Non-Hardship), Total Allowance Total Allowance Beginning Balance $ 143.3 $ 81.5 $ 224.8 $ 80.1 $ 17.2 $ 97.3 $ 43.9 $ 31.5 $ 75.4 $ 10.5 ASU 2016-13 Implementation Impact on January 1, 2020 21.6 2.2 23.8 21.3 0.9 22.2 (1.6) 0.3 (1.3) 0.3 Increase due to CMA asset acquisition — 24.2 24.2 — — — — — — — Uncollectible Expense (1) — 53.5 53.5 — 12.9 12.9 — 15.3 15.3 5.2 Uncollectible Costs Deferred (2) 43.1 53.9 97.0 38.2 10.8 49.0 (1.7) 26.4 24.7 7.4 Write-Offs (14.7) (63.3) (78.0) (11.9) (17.8) (29.7) (0.9) (26.3) (27.2) (6.9) Recoveries Collected 1.5 12.1 13.6 1.4 4.3 5.7 — 4.7 4.7 0.7 Ending Balance $ 194.8 $ 164.1 $ 358.9 $ 129.1 $ 28.3 $ 157.4 $ 39.7 $ 51.9 $ 91.6 $ 17.2 (1) Uncollectible expense associated with customer and other accounts receivable is included in Operations and Maintenance expense on the statements of income. For the years ended December 31, 2019 and 2018, uncollectible expense included in Operations and Maintenance Expense was $63.4 million and $61.3 million for Eversource, $15.9 million and $15.8 million for CL&P, $25.1 million and $22.3 million for NSTAR Electric and $6.7 million and $6.4 million for PSNH, respectively. (2) The current period provision for expected credit losses is deferred as a regulatory cost on the balance sheets, as this amount is ultimately recovered in rates. Amounts include uncollectible costs for hardship accounts and other customer receivables, including uncollectible amounts related to COVID-19.
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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Fuel $ 38.2 $ — $ — $ — $ 26.7 $ — $ — $ — Materials and Supplies 151.3 57.9 62.1 22.5 132.9 50.7 54.7 18.5 RECs 76.1 — 71.8 4.3 75.9 — 69.4 6.5 Total $ 265.6 $ 57.9 $ 133.9 $ 26.8 $ 235.5 $ 50.7 $ 124.1 $ 25.0
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) 2020 2019 2018 Eversource - Natural Gas and Fuel $ 464.2 $ 462.1 $ 442.6 PSNH - Fuel (1) — — 7.9 (1) 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) 2020 2019 2018 Borrowed Funds $ 23.7 $ 25.6 $ 19.7 Equity Funds 42.0 45.0 44.0 Total AFUDC $ 65.7 $ 70.6 $ 63.7 Average AFUDC Rate 5.0 % 5.4 % 4.9 % For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars, CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Borrowed Funds $ 6.6 $ 9.1 $ 2.1 $ 7.1 $ 10.4 $ 2.8 $ 6.3 $ 7.8 $ 1.3 Equity Funds 13.8 21.5 4.2 13.2 19.8 3.4 12.2 15.6 — Total AFUDC $ 20.4 $ 30.6 $ 6.3 $ 20.3 $ 30.2 $ 6.2 $ 18.5 $ 23.4 $ 1.3 Average AFUDC Rate 5.9 % 5.7 % 4.7 % 6.3 % 5.7 % 4.6 % 5.8 % 5.0 % 0.7 %
Components of 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) 2020 2019 2018 Pension, SERP and PBOP Non-Service Income Components $ 44.4 $ 31.3 $ 60.8 AFUDC Equity 42.0 45.0 44.0 Equity in Earnings of Unconsolidated Affiliates (1) 14.2 42.2 3.8 Investment Income/(Loss) 1.1 0.8 (4.0) Interest Income 4.8 12.8 18.1 Gains on Sales of Property 1.8 0.3 5.1 Other 0.3 0.4 0.6 Total Other Income, Net $ 108.6 $ 132.8 $ 128.4 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Pension, SERP and PBOP Non-Service $ 3.8 $ 29.3 $ 7.0 $ 0.5 $ 23.5 $ 4.9 $ 9.5 $ 36.0 $ 9.9 AFUDC Equity 13.8 21.5 4.2 13.2 19.8 3.4 12.2 15.6 — Equity in Earnings of Unconsolidated Affiliates — 0.4 — 0.1 0.7 — 0.1 0.7 — Investment Income/(Loss) 1.1 (0.8) 0.1 2.3 (0.4) 0.3 (3.0) (0.5) (0.8) Interest Income 2.0 0.9 2.4 1.5 0.7 10.5 3.7 0.8 14.1 Gains on Sales of Property — 0.3 — — 0.1 — — 0.5 4.4 Other 0.1 0.4 0.1 (0.1) 0.2 0.1 0.2 — 0.1 Total Other Income, Net $ 20.8 $ 52.0 $ 13.8 $ 17.5 $ 44.6 $ 19.2 $ 22.7 $ 53.1 $ 27.7 (1) Equity in earnings of unconsolidated affiliates includes other-than-temporary impairments of $2.8 million related to a write-off of an investment within a renewable energy fund, and $32.9 million of the Access Northeast project investment for the years ended December 31, 2020 and 2018, respectively. See Note 6, "Investments in Unconsolidated Affiliates," for further information. Equity in earnings includes $2.4 million of primarily realized gains, and $20.4 million and $17.6 million of pre-tax unrealized gains, for the years ended December 31, 2020, 2019 and 2018, respectively, associated with an equity method investment in a renewable energy fund.
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) 2020 2019 2018 Eversource $ 170.6 $ 163.1 $ 161.9 CL&P 149.9 141.1 141.4
Supplemental Cash Flow Information	Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2020 2019 2018 Cash Paid During the Year for: Interest, Net of Amounts Capitalized $ 518.0 $ 532.4 $ 503.2 Income Taxes 48.9 56.0 158.8 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 367.2 379.4 389.3 As of and For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Cash Paid During the Year for: Interest, Net of Amounts Capitalized $ 149.0 $ 129.4 $ 54.5 $ 144.6 $ 121.9 $ 56.9 $ 149.7 $ 122.1 $ 40.5 Income Taxes 10.9 110.7 34.2 80.6 77.9 3.4 66.1 120.0 27.3 Non-Cash Investing Activities: Plant Additions Included in Accounts Payable (As of) 101.8 103.2 33.3 111.3 116.4 49.9 106.1 116.5 35.1
Cash and Cash Equivalents as Reported on the Balance Sheet	The following table reconciles cash as reported on the balance sheets to the cash and restricted cash balance as reported on the statements of cash flows: As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Cash as reported on the Balance Sheets $ 106.6 $ 90.8 $ 0.1 $ 0.1 $ 15.4 $ — $ 0.1 $ 0.4 Restricted cash included in: Special Deposits 73.6 8.7 17.2 36.8 52.5 4.6 6.2 32.5 Marketable Securities 41.2 0.3 0.1 0.6 46.0 0.4 — 0.6 Other Long-Term Assets 43.6 — — 2.1 3.2 — — 3.2 Cash and Restricted Cash reported on the $ 265.0 $ 99.8 $ 17.4 $ 39.6 $ 117.1 $ 5.0 $ 6.3 $ 36.7

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	12 Months Ended
	Dec. 31, 2020
Regulated Operations [Abstract]
Components of Regulatory Assets	The components of regulatory assets were as follows: As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Benefit Costs $ 2,794.2 $ 632.3 $ 690.0 $ 267.6 $ 2,382.9 $ 539.0 $ 629.8 $ 218.2 Income Taxes, Net 747.1 458.9 110.4 15.2 725.8 458.8 108.0 12.8 Securitized Stranded Costs 522.1 — — 522.1 565.3 — — 565.3 Storm Restoration Costs, Net 765.6 515.1 186.4 64.1 540.6 274.6 200.6 65.4 Regulatory Tracker Mechanisms 850.5 246.6 332.2 95.3 411.5 78.3 207.1 65.8 Derivative Liabilities 296.3 293.1 — — 334.5 329.2 — — Goodwill-related 314.7 — 270.2 — 331.5 — 284.6 — Asset Retirement Obligations 118.4 32.1 58.6 3.9 97.2 30.8 50.3 3.6 Other Regulatory Assets 161.0 33.7 56.1 20.9 125.4 25.2 55.2 14.7 Total Regulatory Assets 6,569.9 2,211.8 1,703.9 989.1 5,514.7 1,735.9 1,535.6 945.8 Less: Current Portion 1,076.6 345.6 399.9 115.9 651.1 178.6 285.6 84.1 Total Long-Term Regulatory Assets $ 5,493.3 $ 1,866.2 $ 1,304.0 $ 873.2 $ 4,863.6 $ 1,557.3 $ 1,250.0 $ 861.7
Components of Regulatory Liabilities	The components of regulatory liabilities were as follows: As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH EDIT due to Tax Cuts and Jobs Act of 2017 $ 2,778.6 $ 1,010.7 $ 1,044.0 $ 371.5 $ 2,844.6 $ 1,022.8 $ 1,071.2 $ 392.8 Cost of Removal 624.8 98.4 363.6 12.9 559.8 64.6 330.6 16.3 Benefit Costs 83.6 — 72.5 — 84.5 — 72.2 — Regulatory Tracker Mechanisms 366.5 148.9 139.7 47.8 325.1 94.8 165.6 57.0 AFUDC - Transmission 76.8 44.6 32.2 — 73.2 46.0 27.2 — Other Regulatory Liabilities 309.9 39.5 63.2 9.8 132.0 19.6 59.0 13.1 Total Regulatory Liabilities 4,240.2 1,342.1 1,715.2 442.0 4,019.2 1,247.8 1,725.8 479.2 Less: Current Portion 389.4 137.2 164.8 58.8 361.2 82.8 209.2 65.8 Total Long-Term Regulatory Liabilities $ 3,850.8 $ 1,204.9 $ 1,550.4 $ 383.2 $ 3,658.0 $ 1,165.0 $ 1,516.6 $ 413.4

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Utility Property, Plant and Equipment	The following tables summarize property, plant and equipment by asset category: Eversource As of December 31, (Millions of Dollars) 2020 2019 Distribution - Electric $ 16,703.2 $ 15,880.0 Distribution - Natural Gas 6,111.2 3,931.1 Transmission - Electric 11,954.0 10,958.4 Distribution - Water 1,743.1 1,726.5 Solar 201.5 200.2 Utility 36,713.0 32,696.2 Other (1) 1,269.0 1,025.6 Property, Plant and Equipment, Gross 37,982.0 33,721.8 Less: Accumulated Depreciation Utility (8,476.3) (7,483.5) Other (477.6) (387.4) Total Accumulated Depreciation (8,953.9) (7,870.9) Property, Plant and Equipment, Net 29,028.1 25,850.9 Construction Work in Progress 1,854.4 1,734.6 Total Property, Plant and Equipment, Net $ 30,882.5 $ 27,585.5 As of December 31, 2020 2019 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH Distribution - Electric $ 6,820.7 $ 7,544.4 $ 2,378.4 $ 6,485.5 $ 7,163.7 $ 2,271.1 Transmission - Electric 5,512.0 4,701.3 1,742.4 5,043.0 4,411.9 1,498.7 Solar — 201.5 — — 200.2 — Property, Plant and Equipment, Gross 12,332.7 12,447.2 4,120.8 11,528.5 11,775.8 3,769.8 Less: Accumulated Depreciation (2,475.4) (3,074.1) (848.9) (2,385.7) (2,895.3) (799.9) Property, Plant and Equipment, Net 9,857.3 9,373.1 3,271.9 9,142.8 8,880.5 2,969.9 Construction Work in Progress 377.3 750.0 102.4 483.0 592.3 159.6 Total Property, Plant and Equipment, Net $ 10,234.6 $ 10,123.1 $ 3,374.3 $ 9,625.8 $ 9,472.8 $ 3,129.5 (1) These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company. The depreciation rates for the various classes of utility property, plant and equipment aggregate to composite rates as follows: (Percent) 2020 2019 2018 Eversource 3.0 % 3.0 % 2.9 % CL&P 2.8 % 2.8 % 2.8 % NSTAR Electric 2.8 % 2.8 % 2.8 % PSNH 2.8 % 2.8 % 2.8 % The following table summarizes average remaining useful lives of depreciable assets: As of December 31, 2020 (Years) Eversource CL&P NSTAR Electric PSNH Distribution - Electric 34.3 35.4 33.7 33.3 Distribution - Natural Gas 41.5 — — — Transmission - Electric 40.7 36.9 45.5 42.6 Distribution - Water 34.1 — — — Solar 24.3 — 24.3 — Other (1) 11.0 — — — (1) The estimated useful life of computer software, hardware and equipment primarily ranges from 5 to 15 years and of buildings is 40 years.

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 (Millions of Dollars) Fair Value Hierarchy Commodity Supply Netting (1) Net Amount Commodity Supply Netting (1) Net Amount Current Derivative Assets: CL&P Level 3 $ 13.7 $ (0.4) $ 13.3 $ 12.2 $ (0.4) $ 11.8 Long-Term Derivative Assets: CL&P Level 3 58.7 (1.8) 56.9 67.5 (2.1) 65.4 Current Derivative Liabilities: CL&P Level 3 (68.8) — (68.8) (67.8) — (67.8) Other Level 2 (3.3) 0.1 (3.2) (5.2) — (5.2) Long-Term Derivative Liabilities: CL&P Level 3 (294.5) — (294.5) (338.6) — (338.6) Other Level 2 — — — (0.1) — (0.1) (1) Amounts represent derivative assets and liabilities that Eversource elected to record net on the balance sheets. These amounts are subject to master netting agreements or similar agreements for which the right of offset exists.
Fair Value Inputs, Liabilities, Quantitative Information	The following is a summary of 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, 2020 2019 CL&P Range Weighted Average (1) Period Covered Range Period Covered Capacity Prices $ 4.30 — 5.30 $ 4.63 per kW-Month 2024 - 2026 $ 3.01 — $ 7.34 per kW-Month 2023 - 2026 Forward Reserve 0.54 — 0.90 0.72 per kW-Month 2021 - 2024 0.80 — 1.90 per kW-Month 2020 - 2024
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation	The following table presents changes in the Level 3 category of derivative assets and derivative liabilities measured at fair value on a recurring basis. The derivative assets and liabilities are presented on a net basis. CL&P (Millions of Dollars) For the Years Ended December 31, 2020 2019 Derivatives, Net: Fair Value as of Beginning of Period $ (329.2) $ (356.5) Net Realized/Unrealized Losses Included in Regulatory Assets (17.9) (15.0) Settlements 54.0 42.3 Fair Value as of End of Period $ (293.1) $ (329.2)

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Eversource (Millions of Dollars) Amortized Pre-Tax Pre-Tax Fair Value Amortized Pre-Tax Pre-Tax Fair Value Debt Securities $ 213.1 $ 11.2 $ (0.1) $ 224.2 $ 228.4 $ 5.8 $ (0.1) $ 234.1
Investments Classified by Contractual Maturity Date	As of December 31, 2020, the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Fair Less than one year (1) $ 43.6 $ 43.6 One to five years 57.4 59.7 Six to ten years 46.6 49.7 Greater than ten years 65.5 71.2 Total Debt Securities $ 213.1 $ 224.2 (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, 2020 2019 Level 1: Mutual Funds and Equities $ 246.0 $ 228.5 Money Market Funds 41.2 46.0 Total Level 1 $ 287.2 $ 274.5 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 72.9 $ 96.8 Corporate Debt Securities 63.8 44.0 Asset-Backed Debt Securities 11.9 12.9 Municipal Bonds 24.0 26.7 Other Fixed Income Securities 10.4 7.7 Total Level 2 $ 183.0 $ 188.1 Total Marketable Securities $ 470.2 $ 462.6

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Balance as of Beginning of Year $ 489.5 $ 32.0 $ 97.5 $ 4.2 $ 466.2 $ 33.5 $ 72.4 $ 4.0 Liability Assumed Upon CMA Asset Acquisition 20.1 — — — — — — — Liabilities Incurred During the Year 2.1 — 2.1 — 30.3 — 30.3 — Liabilities Settled During the Year (21.8) (0.7) (1.0) — (21.3) (3.6) — — Accretion 28.9 2.1 4.3 0.2 27.1 2.2 3.5 0.2 Revisions in Estimated Cash Flows (19.1) — (11.1) — (12.8) (0.1) (8.7) — Balance as of End of Year $ 499.7 $ 33.4 $ 91.8 $ 4.4 $ 489.5 $ 32.0 $ 97.5 $ 4.2

INVESTMENTS IN UNCONSOLIDATED_2

INVESTMENTS IN UNCONSOLIDATED AFFILIATES (Tables)	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Summary of Investments	Eversource's investments included the following: Investment Balance as of December 31, (Millions of Dollars) Ownership Interest 2020 2019 Offshore Wind Business - North East Offshore and Bay State Wind 50 % $ 887.1 $ 649.3 Natural Gas Pipeline - Algonquin Gas Transmission, LLC 15 % 125.2 127.8 Renewable Energy Investment Fund 90 % 71.6 72.4 Other various 23.2 22.1 Total Investments in Unconsolidated Affiliates $ 1,107.1 $ 871.6

SHORT-TERM DEBT (Tables)

SHORT-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Borrowings Outstanding	The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2020 2019 2020 2019 2020 2019 Eversource Parent Commercial Paper Program $ 1,054.3 $ 1,224.9 $ 945.7 $ 225.1 0.25 % 1.98 % NSTAR Electric Commercial Paper Program 195.0 10.5 455.0 639.5 0.16 % 1.63 % Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2020 2019 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 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 500.0 500.0 4.000% 2018 Series A due 2048 800.0 800.0 0.750% 2020 Series A due 2025 400.0 — Total First Mortgage Bonds 3,794.8 3,394.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net 25.9 27.8 Unamortized Debt Issuance Costs (26.4) (25.0) CL&P Long-Term Debt $ 3,914.8 $ 3,518.1 NSTAR Electric (Millions of Dollars) As of December 31, 2020 2019 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 3.250% due 2029 400.0 400.0 3.950% due 2030 400.0 — Total Debentures 3,200.0 2,800.0 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 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 470.0 565.0 Less Amounts due Within One Year (250.0) (95.0) Unamortized Premiums and Discounts, Net (6.8) (4.1) Unamortized Debt Issuance Costs (20.0) (18.8) NSTAR Electric Long-Term Debt $ 3,393.2 $ 3,247.1 PSNH (Millions of Dollars) As of December 31, 2020 2019 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 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 3.600% Series T due 2049 300.0 300.0 2.400% Series U due 2050 150.0 — Total First Mortgage Bonds $ 1,107.0 $ 957.0 Less Amounts due Within One Year (282.0) — Unamortized Premiums and Discounts, Net (1.5) (0.7) Unamortized Debt Issuance Costs (6.4) (4.7) PSNH Long-Term Debt $ 817.1 $ 951.6 OTHER (Millions of Dollars) As of December 31, 2020 2019 Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050 $ 640.0 $ 620.0 NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050 500.0 460.0 Aquarion - Senior Note 4.000% due 2024 360.0 360.0 Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049 335.2 335.3 Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035 35.9 68.8 Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050 5,550.0 4,000.0 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 11.7 11.6 Fair Value Adjustment (1) 74.7 109.1 Less Fair Value Adjustment - Current Portion (1) (31.0) (31.3) Less Amounts due in One Year (490.2) (201.1) Commercial Paper Classified as Long-Term Debt — 346.3 Unamortized Premiums and Discounts, Net 46.5 (4.1) Unamortized Debt Issuance Costs (32.0) (20.6) Total Other Long-Term Debt $ 7,000.8 $ 6,054.0 Total Eversource Long-Term Debt $ 15,125.9 $ 13,770.8 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record long-term debt at fair value on the dates of the 2012 merger with NSTAR and the 2017 acquisition of Aquarion.

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Outstanding Long-Term Debt	The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding Available Borrowing Capacity as of December 31, Weighted-Average Interest Rate as of December 31, (Millions of Dollars) 2020 2019 2020 2019 2020 2019 Eversource Parent Commercial Paper Program $ 1,054.3 $ 1,224.9 $ 945.7 $ 225.1 0.25 % 1.98 % NSTAR Electric Commercial Paper Program 195.0 10.5 455.0 639.5 0.16 % 1.63 % Details of long-term debt outstanding are as follows: CL&P (Millions of Dollars) As of December 31, 2020 2019 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 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 500.0 500.0 4.000% 2018 Series A due 2048 800.0 800.0 0.750% 2020 Series A due 2025 400.0 — Total First Mortgage Bonds 3,794.8 3,394.8 Pollution Control Revenue Bonds: 4.375% Fixed Rate Tax Exempt due 2028 120.5 120.5 Less Amounts due Within One Year — — Unamortized Premiums and Discounts, Net 25.9 27.8 Unamortized Debt Issuance Costs (26.4) (25.0) CL&P Long-Term Debt $ 3,914.8 $ 3,518.1 NSTAR Electric (Millions of Dollars) As of December 31, 2020 2019 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 3.250% due 2029 400.0 400.0 3.950% due 2030 400.0 — Total Debentures 3,200.0 2,800.0 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 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 470.0 565.0 Less Amounts due Within One Year (250.0) (95.0) Unamortized Premiums and Discounts, Net (6.8) (4.1) Unamortized Debt Issuance Costs (20.0) (18.8) NSTAR Electric Long-Term Debt $ 3,393.2 $ 3,247.1 PSNH (Millions of Dollars) As of December 31, 2020 2019 First Mortgage Bonds: 5.600% Series M due 2035 $ 50.0 $ 50.0 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 3.600% Series T due 2049 300.0 300.0 2.400% Series U due 2050 150.0 — Total First Mortgage Bonds $ 1,107.0 $ 957.0 Less Amounts due Within One Year (282.0) — Unamortized Premiums and Discounts, Net (1.5) (0.7) Unamortized Debt Issuance Costs (6.4) (4.7) PSNH Long-Term Debt $ 817.1 $ 951.6 OTHER (Millions of Dollars) As of December 31, 2020 2019 Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050 $ 640.0 $ 620.0 NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050 500.0 460.0 Aquarion - Senior Note 4.000% due 2024 360.0 360.0 Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049 335.2 335.3 Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035 35.9 68.8 Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050 5,550.0 4,000.0 Pre-1983 Spent Nuclear Fuel Obligation (CYAPC) 11.7 11.6 Fair Value Adjustment (1) 74.7 109.1 Less Fair Value Adjustment - Current Portion (1) (31.0) (31.3) Less Amounts due in One Year (490.2) (201.1) Commercial Paper Classified as Long-Term Debt — 346.3 Unamortized Premiums and Discounts, Net 46.5 (4.1) Unamortized Debt Issuance Costs (32.0) (20.6) Total Other Long-Term Debt $ 7,000.8 $ 6,054.0 Total Eversource Long-Term Debt $ 15,125.9 $ 13,770.8 (1) The fair value adjustment amount is the purchase price adjustments, net of amortization, required to record long-term debt at fair value on the dates of the 2012 merger with NSTAR and the 2017 acquisition of Aquarion.
Schedule of Issuance and Repayments of Long-Term Debt	The following table summarizes long-term debt issuances and repayments: (Millions of Dollars) Issuance/(Repayment) Issue Date or Repayment Date Maturity Date Use of Proceeds for Issuance/ CL&P: 0.75% Series A First Mortgage Bonds $ 400.0 December 2020 December 2025 Refinanced short-term borrowings, funded capital expenditures and working capital NSTAR Electric: 3.95% 2020 Debentures 400.0 March 2020 April 2030 Refinanced investments in eligible green expenditures, which were previously financed in 2018 and 2019 5.10% Series E Senior Notes (95.0) March 2020 March 2020 Paid at maturity PSNH: 2.40% Series U First Mortgage Bonds 150.0 August 2020 September 2050 Refinanced short-term borrowings, funded capital expenditures and working capital Other: Eversource Parent 3.45% Series P Senior Notes 350.0 January 2020 January 2050 Paid short-term borrowings Eversource Parent 3.45% Series P Senior Notes (1) 300.0 August 2020 January 2050 (2) Eversource Parent 0.80% Series Q Senior Notes 300.0 August 2020 August 2025 (2) Eversource Parent 1.65% Series R Senior Notes 600.0 August 2020 August 2030 (2) Eversource Parent 2.50% Series I Senior Notes (450.0) February 2021 March 2021 Paid on par call date in advance of maturity date NSTAR Gas 4.46% Series N First Mortgage Bonds (125.0) January 2020 January 2020 Paid at maturity NSTAR Gas 2.33% Series R First Mortgage Bonds 75.0 May 2020 May 2025 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes NSTAR Gas 3.15% Series S First Mortgage Bonds 115.0 May 2020 May 2050 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes NSTAR Gas 9.95% Series J First Mortgage Bonds (25.0) December 2020 December 2020 Paid at maturity Yankee Gas 4.87% Series K First Mortgage Bonds (50.0) April 2020 April 2020 Paid at maturity Yankee Gas 2.90% Series R First Mortgage Bonds 70.0 September 2020 September 2050 Refinanced existing indebtedness, funded capital expenditures and for general corporate purposes Aquarion Water Company of Massachusetts, Inc. and Aquarion Water Capital of Massachusetts, Inc. various term loans and general mortgage bonds (32.2) July 2020 Various Redeemed long-term debt in conjunction with the sale of assets to the Town of Hingham, Massachusetts (1) These senior notes are part of the same series issued by Eversource parent in January 2020. The aggregate outstanding principal amount of these senior notes is now $650 million. (2) The proceeds from these Eversource parent issuances funded a portion of the purchase price for the CMA asset acquisition and refinanced short-term borrowings.
Schedule of Maturities of Long-Term Debt Outstanding	Long-term debt maturities on debt outstanding for the years 2021 through 2025 and thereafter are shown below. These amounts exclude PSNH rate reduction bonds, CYAPC pre-1983 spent nuclear fuel obligation, net unamortized premiums, discounts and debt issuance costs, and other fair value adjustments as of December 31, 2020: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2021 $ 1,022.2 $ — $ 250.0 $ 282.0 2022 1,175.2 — 400.0 — 2023 1,658.2 400.0 80.0 325.0 2024 1,049.9 139.8 — — 2025 1,400.0 400.0 250.0 — Thereafter 9,807.9 2,975.5 2,690.0 500.0 Total $ 16,113.4 $ 3,915.3 $ 3,670.0 $ 1,107.0

RATE REDUCTION BONDS AND VARI_2

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES (Tables)	12 Months Ended
	Dec. 31, 2020
Rate Reduction Bonds and Variable Interest Entity [Abstract]
Summary of the Impact of Funding on the Balance Sheets and Income Statements	The following tables summarize the impact of PSNH Funding on PSNH's balance sheets and income statements: (Millions of Dollars) As of December 31, Balance Sheet: 2020 2019 Restricted Cash - Current Portion (included in Current Assets) $ 36.8 $ 32.5 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 2.1 3.2 Securitized Stranded Cost (included in Regulatory Assets) 522.1 565.3 Other Regulatory Liabilities (included in Regulatory Liabilities) 9.1 5.6 Accrued Interest (included in Other Current Liabilities) 8.0 8.6 Rate Reduction Bonds - Current Portion 43.2 43.2 Rate Reduction Bonds - Long-Term Portion 496.9 540.1 (Millions of Dollars) Income Statement: For the Years Ended December 31, 2020 2019 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 43.2 $ 43.0 Interest Expense on RRB Principal (included in Interest Expense) 19.7 21.1

EMPLOYEE BENEFITS (Tables)

EMPLOYEE BENEFITS (Tables)	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following tables provide information on the plan benefit obligations, fair values of plan assets, and funded status: Pension and SERP As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (6,321.7) $ (1,331.3) $ (1,397.3) $ (692.6) $ (5,520.0) $ (1,160.4) $ (1,236.5) $ (610.7) Service Cost (76.2) (21.8) (15.4) (8.2) (67.7) (18.0) (14.6) (7.1) Interest Cost (177.8) (37.3) (38.6) (19.4) (219.0) (45.7) (49.0) (24.0) Actuarial Loss (658.2) (152.3) (139.5) (62.1) (815.3) (176.6) (181.0) (84.5) Benefits Paid - Pension 279.3 63.6 59.4 33.5 273.0 60.2 67.1 30.3 Benefits Paid - Lump Sum 23.4 — 13.1 — 20.0 — 12.9 — Benefits Paid - SERP 7.3 0.3 0.2 0.4 7.3 0.3 0.1 0.4 Employee Transfers — 1.5 0.2 (0.3) — 8.9 3.7 3.0 Increase due to acquisition of CMA (121.4) — — — — — — — Benefit Obligation as of End of Year $ (7,045.3) $ (1,477.3) $ (1,517.9) $ (748.7) $ (6,321.7) $ (1,331.3) $ (1,397.3) $ (692.6) Change in Pension Plan Assets: Fair Value of Pension Plan Assets as of $ 4,968.6 $ 986.2 $ 1,288.8 $ 551.6 $ 4,573.9 $ 918.4 $ 1,222.1 $ 506.6 Employer Contributions 109.6 23.2 0.7 19.5 112.5 24.0 0.4 15.4 Actual Return on Pension Plan Assets 512.3 98.8 128.3 55.8 575.2 112.9 150.0 62.9 Benefits Paid - Pension (279.3) (63.6) (59.4) (33.5) (273.0) (60.2) (67.1) (30.3) Benefits Paid - Lump Sum (23.4) — (13.1) — (20.0) — (12.9) — Employee Transfers — (1.5) (0.2) 0.3 — (8.9) (3.7) (3.0) Increase due to acquisition of CMA 121.4 — — — — — — — Fair Value of Pension Plan Assets as of End of Year $ 5,409.2 $ 1,043.1 $ 1,345.1 $ 593.7 $ 4,968.6 $ 986.2 $ 1,288.8 $ 551.6 Funded Status as of December 31st $ (1,636.1) $ (434.2) $ (172.8) $ (155.0) $ (1,353.1) $ (345.1) $ (108.5) $ (141.0) PBOP As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Change in Benefit Obligation: Benefit Obligation as of Beginning of Year $ (899.0) $ (172.7) $ (258.3) $ (93.0) $ (841.5) $ (161.7) $ (246.3) $ (91.9) Service Cost (10.2) (1.7) (2.1) (0.9) (7.8) (1.4) (1.7) (0.7) Interest Cost (24.6) (4.4) (6.6) (2.8) (32.7) (6.3) (9.5) (3.4) Actuarial Loss (82.8) (8.6) (7.4) (19.0) (67.0) (13.4) (15.2) (3.1) Benefits Paid 50.2 10.1 14.9 6.1 50.0 10.8 15.4 5.6 Employee Transfers — (1.3) (1.0) 0.1 — (0.7) (1.0) 0.5 Increase due to acquisition of CMA (27.5) — — — — — — — Benefit Obligation as of End of Year $ (993.9) $ (178.6) $ (260.5) $ (109.5) $ (899.0) $ (172.7) $ (258.3) $ (93.0) Change in Plan Assets: Fair Value of Plan Assets as of Beginning of Year $ 935.9 $ 126.3 $ 424.4 $ 76.0 $ 849.6 $ 120.6 $ 379.1 $ 71.2 Actual Return on Plan Assets 116.5 15.7 53.3 9.3 127.0 17.1 57.0 10.0 Employer Contributions 1.9 — — — 9.3 — 6.0 — Benefits Paid (50.2) (10.1) (14.9) (6.1) (50.0) (10.8) (15.4) (5.6) Employee Transfers — 2.2 1.8 0.2 — (0.6) (2.3) 0.4 Fair Value of Plan Assets as of End of Year $ 1,004.1 $ 134.1 $ 464.6 $ 79.4 $ 935.9 $ 126.3 $ 424.4 $ 76.0 Funded Status as of December 31st $ 10.2 $ (44.5) $ 204.1 $ (30.1) $ 36.9 $ (46.4) $ 166.1 $ (17.0)
Schedule of Defined Benefit Plans	As of December 31, 2020 and 2019, the accumulated benefit obligation for the Pension and SERP Plans is as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2020 $ 6,669.4 $ 1,356.4 $ 1,449.4 $ 707.2 2019 5,963.4 1,205.4 1,340.8 646.7
Schedule of Assumptions Used	The following actuarial assumptions were used in calculating the Pension, SERP and PBOP Plans' year end funded status: Pension and SERP PBOP As of December 31, As of December 31, 2020 2019 2020 2019 Discount Rate 2.4% — 2.7% 3.0% — 3.4% 2.5% — 2.6% 3.2% — 3.3% Compensation/Progression Rate 3.5% — 4.0% 3.5% — 4.0% N/A The following actuarial assumptions were used to calculate Pension, SERP and PBOP expense amounts: Pension and SERP PBOP For the Years Ended December 31, For the Years Ended December 31, 2020 2019 2018 2020 2019 2018 Discount Rate 2.6% — 3.5% 2.7% — 3.6% 3.9% — 4.6% 2.7% — 3.6% 3.9% — 4.6% 3.3% — 3.9% Expected Long-Term Rate of Return 8.25% 8.25% 8.25% 8.25% 8.25% 8.25% Compensation/Progression Rate 3.5% — 4.0% 3.5% — 4.0% 3.5% — 4.0% N/A N/A N/A
Schedule of Net Benefit Costs	The components of net periodic benefit expense/(income) for the Pension, SERP and PBOP 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/(income), less the capitalized portion, is included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit expense/(income), less the deferred portion, are included in Other Income, Net on the statements of income. Pension, SERP and 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 and deferred portion, as these amounts are cash settled on a short-term basis. Pension and SERP PBOP For the Year Ended December 31, 2020 For the Year Ended December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 76.2 $ 21.8 $ 15.4 $ 8.2 $ 10.2 $ 1.7 $ 2.1 $ 0.9 Interest Cost 177.8 37.3 38.6 19.4 24.6 4.4 6.6 2.8 Expected Return on Plan Assets (400.3) (79.2) (103.0) (44.7) (73.6) (9.9) (34.0) (5.7) Actuarial Loss 202.0 39.2 55.2 15.6 8.4 1.1 2.5 0.8 Prior Service Cost/(Credit) 1.2 — 0.3 — (21.2) 1.1 (17.0) 0.4 Total Net Periodic Benefit Expense/(Income) $ 56.9 $ 19.1 $ 6.5 $ (1.5) $ (51.6) $ (1.6) $ (39.8) $ (0.8) Intercompany Allocations N/A $ 9.1 $ 8.9 $ 2.9 N/A $ (1.1) $ (1.4) $ (0.5) Pension and SERP PBOP For the Year Ended December 31, 2019 For the Year Ended December 31, 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 67.7 $ 18.0 $ 14.6 $ 7.1 $ 7.8 $ 1.4 $ 1.7 $ 0.7 Interest Cost 219.0 45.7 49.0 24.0 32.7 6.3 9.5 3.4 Expected Return on Plan Assets (367.1) (73.2) (97.1) (40.7) (66.8) (9.2) (30.2) (5.4) Actuarial Loss 143.2 26.9 44.7 10.6 8.3 1.3 3.3 0.3 Prior Service Cost/(Credit) 0.9 — 0.3 — (23.5) 1.1 (16.9) 0.4 Total Net Periodic Benefit Expense/(Income) $ 63.7 $ 17.4 $ 11.5 $ 1.0 $ (41.5) $ 0.9 $ (32.6) $ (0.6) Intercompany Allocations N/A $ 8.5 $ 8.0 $ 2.3 N/A $ (0.9) $ (1.2) $ (0.4) Pension and SERP PBOP For the Year Ended December 31, 2018 For the Year Ended December 31, 2018 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 84.8 $ 21.4 $ 17.4 $ 11.2 $ 10.0 $ 1.9 $ 2.0 $ 1.1 Interest Cost 196.4 41.8 43.5 22.0 30.7 5.8 8.7 3.4 Expected Return on Plan Assets (391.6) (79.1) (104.9) (43.6) (72.4) (10.4) (32.5) (6.0) Actuarial Loss 145.7 29.1 41.1 11.6 10.3 1.6 2.3 0.7 Prior Service Cost/(Credit) 4.3 1.1 0.2 0.4 (23.6) 1.1 (16.9) 0.5 Total Net Periodic Benefit Expense/(Income) $ 39.6 $ 14.3 $ (2.7) $ 1.6 $ (45.0) $ — $ (36.4) $ (0.3) Intercompany Allocations N/A $ 6.1 $ 6.5 $ 1.9 N/A $ (1.0) $ (1.3) $ (0.4)
Schedule of Amounts Recognized in Regulatory Assets and OCI	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: Pension and SERP PBOP Regulatory Assets OCI Regulatory Assets OCI For the Years Ended December 31, For the Years Ended December 31, (Millions of Dollars) 2020 (1) 2019 2020 2019 2020 (1) 2019 2020 2019 Actuarial Losses Arising During the Year $ 553.1 $ 591.6 $ 24.3 $ 15.4 $ 39.1 $ 4.6 $ 1.3 $ 2.3 Actuarial Losses Reclassified as Net Periodic Benefit Expense (194.3) (137.8) (7.7) (5.4) (8.0) (8.0) (0.4) (0.3) Prior Service Cost Arising During the Year 2.0 — — — — — — — Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income (1.0) (0.7) (0.2) (0.2) 21.3 25.1 (0.1) (1.6) (1) Amounts include the impact of the CMA asset acquisition from October 9, 2020 through December 31, 2020. 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, 2020 and 2019: Regulatory Assets as of December 31, AOCI as of December 31, (Millions of Dollars) 2020 2019 2020 2019 Pension and SERP Actuarial Loss $ 2,620.2 $ 2,261.4 $ 107.4 $ 90.8 Prior Service Cost 6.6 5.6 0.7 0.9 PBOP Actuarial Loss $ 235.0 $ 203.9 $ 7.9 $ 7.0 Prior Service (Credit)/Cost (151.2) (172.5) 0.9 1.0
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) 2021 2022 2023 2024 2025 2026 - 2030 Pension and SERP $ 346.9 $ 355.6 $ 362.9 $ 397.5 $ 373.8 $ 1,883.2 PBOP 60.1 60.1 59.7 59.1 58.3 273.6
Schedule of Allocation of Plan Assets	These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows: As of December 31, 2020 2019 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 % 15.0 % 8.5 % Global 10.0 % 8.75 % 10.0 % 8.75 % Non-United States 8.0 % 8.5 % 8.0 % 8.5 % Emerging Markets 4.0 % 10.0 % 4.0 % 10.0 % Debt Securities: Fixed Income 13.0 % 4.0 % 13.0 % 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 % Private Equity 15.0 % 12.0 % 15.0 % 12.0 % Real Assets 16.0 % 7.5 % 16.0 % 7.5 % 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) 2020 2019 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 630.8 $ — $ 1,321.7 $ 1,952.5 $ 592.6 $ — $ 1,349.9 $ 1,942.5 Fixed Income (2) 113.6 265.6 1,402.5 1,781.7 99.4 303.0 1,222.8 1,625.2 Private Equity 22.3 — 1,175.4 1,197.7 16.9 — 971.4 988.3 Real Assets (3) 158.4 — 580.8 739.2 58.7 — 615.0 673.7 Total $ 925.1 $ 265.6 $ 4,480.4 $ 5,671.1 $ 767.6 $ 303.0 $ 4,159.1 $ 5,229.7 Less: 401(h) PBOP Assets (4) (261.9) (261.1) Total Pension Assets $ 5,409.2 $ 4,968.6 PBOP Plan Fair Value Measurements as of December 31, (Millions of Dollars) 2020 2019 Asset Category: Level 1 Level 2 Uncategorized Total Level 1 Level 2 Uncategorized Total Equity Securities (1) $ 176.5 $ — $ 217.8 $ 394.3 $ 158.0 $ — $ 187.0 $ 345.0 Fixed Income (2) 16.0 43.2 152.9 212.1 15.8 39.6 148.1 203.5 Private Equity — — 31.5 31.5 — — 26.5 26.5 Real Assets (3) 82.1 — 22.2 104.3 51.2 — 48.6 99.8 Total $ 274.6 $ 43.2 $ 424.4 $ 742.2 $ 225.0 $ 39.6 $ 410.2 $ 674.8 Add: 401(h) PBOP Assets (4) 261.9 261.1 Total PBOP Assets $ 1,004.1 $ 935.9 (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 overlaid 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 overlaid 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 2020 $ 49.4 $ 6.6 $ 11.8 $ 4.1 2019 41.6 5.5 10.3 3.5 2018 38.4 5.0 9.7 3.3
Summary of Share Transactions	A summary of RSU transactions is as follows: RSUs Weighted Average Outstanding as of December 31, 2019 774,163 $ 54.43 Granted 208,937 $ 88.23 Shares Issued (301,938) $ 57.61 Forfeited (6,944) $ 60.95 Outstanding as of December 31, 2020 674,218 $ 63.42 Performance Shares Weighted Average Outstanding as of December 31, 2019 486,907 $ 60.30 Granted 211,224 $ 75.36 Shares Issued (249,922) $ 55.72 Forfeited (404) $ 89.85 Outstanding as of December 31, 2020 447,805 $ 69.93
Schedule of Compensation Expense and Income Tax Benefit	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) 2020 2019 2018 Compensation Expense $ 33.9 $ 27.3 $ 21.4 Future Income Tax Benefit 8.9 7.0 5.4 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Compensation Expense $ 10.9 $ 11.3 $ 3.6 $ 9.8 $ 9.7 $ 3.3 $ 7.8 $ 7.7 $ 2.9 Future Income Tax Benefit 2.9 3.0 1.0 2.5 2.5 0.8 2.0 1.9 0.7
Schedule of Other Retirement Benefits	The liability and expense amounts are as follows: Eversource (Millions of Dollars) As of and For the Years Ended December 31, 2020 2019 2018 Actuarially-Determined Liability $ 45.7 $ 52.0 $ 49.1 Other Retirement Benefits Expense 3.3 2.7 2.7 As of and For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Actuarially-Determined $ 0.2 $ 0.1 $ 1.7 $ 0.2 $ 0.1 $ 1.7 $ 0.3 $ 0.1 $ 1.7 Other Retirement Benefits 1.2 1.1 0.5 1.0 0.9 0.4 1.1 1.1 0.4

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Income Tax Expense	The components of income tax expense are as follows: Eversource (Millions of Dollars) For the Years Ended December 31, 2020 2019 2018 Current Income Taxes: Federal $ 73.6 $ 56.9 $ 106.5 State 19.1 10.5 10.6 Total Current 92.7 67.4 117.1 Deferred Income Taxes, Net: Federal 173.5 138.4 122.6 State 83.7 71.4 52.2 Total Deferred 257.2 209.8 174.8 Investment Tax Credits, Net (3.7) (3.7) (2.9) Income Tax Expense $ 346.2 $ 273.5 $ 289.0 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Current Income Taxes: Federal $ 12.0 $ 53.9 $ 20.6 $ 68.4 $ 82.6 $ 22.9 $ 54.2 $ 79.3 $ 12.2 State (6.1) 6.9 3.8 15.4 18.2 2.2 20.9 30.0 (0.5) Total Current 5.9 60.8 24.4 83.8 100.8 25.1 75.1 109.3 11.7 Deferred Income Taxes, Net: Federal 101.1 33.8 (1.3) 35.2 0.1 5.8 48.5 27.9 15.4 State 43.4 38.8 8.6 18.8 27.0 10.1 6.4 13.5 20.5 Total Deferred 144.5 72.6 7.3 54.0 27.1 15.9 54.9 41.4 35.9 Investment Tax Credits, Net (0.7) (2.6) — (0.8) (2.6) — (0.9) (1.8) — Income Tax Expense $ 149.7 $ 130.8 $ 31.7 $ 137.0 $ 125.3 $ 41.0 $ 129.1 $ 148.9 $ 47.6
Summary of Reconciliation Between Income Tax Expense and Expected Tax	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, 2020 2019 2018 Income Before Income Tax Expense $ 1,558.9 $ 1,190.1 $ 1,329.5 Statutory Federal Income Tax Expense at 21% 327.4 249.9 279.2 Tax Effect of Differences: Depreciation (11.1) 1.9 (30.8) Investment Tax Credit Amortization (3.7) (3.7) (2.9) State Income Taxes, Net of Federal Impact 44.9 24.6 44.4 Dividends on ESOP (5.1) (5.1) (5.1) Tax Asset Valuation Allowance/Reserve Adjustments 33.4 40.1 5.2 Excess Stock Benefit (6.6) (1.5) (1.5) EDIT Amortization (48.7) (37.4) (5.0) Other, Net 15.7 4.7 5.5 Income Tax Expense $ 346.2 $ 273.5 $ 289.0 Effective Tax Rate 22.2 % 23.0 % 21.7 % For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars, except percentages) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Income Before Income Tax Expense $ 607.6 $ 575.8 $ 179.0 $ 547.8 $ 557.3 $ 175.0 $ 506.8 $ 532.0 $ 163.5 Statutory Federal Income Tax Expense at 21% 127.6 120.9 37.6 115.0 117.0 36.8 106.4 111.7 34.3 Tax Effect of Differences: Depreciation 0.4 (3.7) (1.4) (0.2) (3.0) (0.8) (1.2) (2.8) 0.1 Investment Tax Credit Amortization (0.7) (2.6) — (0.8) (2.6) — (0.9) (1.8) — State Income Taxes, (1.2) 36.0 9.8 2.5 35.7 9.8 14.5 33.2 15.8 Tax Asset Valuation 30.7 — — 24.5 — — 7.1 1.2 — Excess Stock Benefit (2.3) (2.3) (0.8) (0.5) (0.5) (0.2) (0.1) (0.1) (0.1) EDIT Amortization (9.0) (20.4) (15.4) (5.8) (22.9) (4.0) — — (4.4) Other, Net 4.2 2.9 1.9 2.3 1.6 (0.6) 3.3 7.5 1.9 Income Tax Expense $ 149.7 $ 130.8 $ 31.7 $ 137.0 $ 125.3 $ 41.0 $ 129.1 $ 148.9 $ 47.6 Effective Tax Rate 24.6 % 22.7 % 17.7 % 25.0 % 22.5 % 23.4 % 25.5 % 28.0 % 29.1 %
Schedule of Accumulated Deferred Income Tax Obligations	The tax effects of temporary differences that give rise to the net accumulated deferred income tax obligations are as follows: As of December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Deferred Tax Assets: Employee Benefits $ 602.4 $ 144.5 $ 79.8 $ 56.6 $ 509.4 $ 125.4 $ 54.8 $ 46.7 Derivative Liabilities 92.6 91.8 — — 105.0 103.6 — — Regulatory Deferrals - Liabilities 259.8 30.2 161.8 13.4 267.0 37.1 165.7 19.0 Allowance for Uncollectible Accounts 87.5 42.3 20.9 4.6 56.7 25.7 17.7 2.8 Tax Effect - Tax Regulatory Liabilities 810.9 331.4 271.8 105.2 830.4 333.5 280.9 111.3 Net Operating Loss Carryforwards 12.7 — — — 9.1 — — — Purchase Accounting Adjustment 54.5 — — — 58.7 — — — Other 200.3 100.9 14.3 19.8 190.4 92.0 35.8 20.0 Total Deferred Tax Assets 2,120.7 741.1 548.6 199.6 2,026.7 717.3 554.9 199.8 Less: Valuation Allowance 48.3 33.7 — — 43.0 24.9 — — Net Deferred Tax Assets $ 2,072.4 $ 707.4 $ 548.6 $ 199.6 $ 1,983.7 $ 692.4 $ 554.9 $ 199.8 Deferred Tax Liabilities: Accelerated Depreciation and Other $ 4,153.6 $ 1,438.1 $ 1,489.4 $ 453.8 $ 3,901.0 $ 1,362.2 $ 1,391.9 $ 428.9 Property Tax Accruals 88.7 39.0 37.0 5.8 76.8 36.8 29.0 4.7 Regulatory Amounts: Regulatory Deferrals - Assets 1,376.7 444.8 324.4 263.4 1,155.6 340.7 276.2 260.9 Tax Effect - Tax Regulatory Assets 244.6 174.4 11.3 8.6 238.2 171.7 11.7 8.3 Goodwill Regulatory Asset - 1999 Merger 86.0 — 73.8 — 90.6 — 77.8 — Derivative Assets 17.8 17.8 — — 19.7 19.7 — — Other 200.3 1.6 72.6 5.6 257.6 5.9 125.6 3.2 Total Deferred Tax Liabilities $ 6,167.7 $ 2,115.7 $ 2,008.5 $ 737.2 $ 5,739.5 $ 1,937.0 $ 1,912.2 $ 706.0
Summary of Tax Credits and Loss Carryforwards	The following table provides 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, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR PSNH Expiration Range Eversource CL&P NSTAR PSNH Expiration Range Federal Net Operating Loss $ — $ — $ — $ — — $ 19.8 $ — $ — $ — 2033 - 2037 State Net Operating Loss 183.4 — — — 2021 - 2040 65.5 — — — 2020 - 2038 State Tax Credit 186.6 133.4 — — 2020 - 2025 168.1 122.3 — — 2019 - 2024 State Charitable Contribution 10.2 — — — 2020 - 2024 9.9 — — — 2019 - 2023
Summary of Income Tax Contingencies	A reconciliation of the activity in unrecognized tax benefits, all of which would impact the effective tax rate if recognized, is as follows: (Millions of Dollars) Eversource CL&P Balance as of January 1, 2018 $ 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 Gross Increases - Current Year 12.1 4.0 Gross Increases - Prior Year 3.4 3.3 Lapse of Statute of Limitations (6.4) (2.4) Balance as of December 31, 2019 55.0 23.1 Gross Increases - Current Year 11.9 4.6 Gross Increases - Prior Year 1.4 0.7 Lapse of Statute of Limitations (6.5) (2.6) Balance as of December 31, 2020 $ 61.8 $ 25.8 Other Interest Income Accrued Interest Expense For the Years Ended December 31, As of December 31, (Millions of Dollars) 2020 2019 2018 2020 2019 Eversource $ — $ — $ (1.7) $ 0.1 $ 0.1
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, 2020: Description Tax Years Federal 2020 Connecticut 2017 - 2020 Massachusetts 2017 - 2020 New Hampshire 2017 - 2020

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2019 $ 64.7 $ 5.4 $ 10.9 $ 5.4 Additions 26.5 7.0 0.5 2.8 Payments/Reductions (10.2) (1.0) (3.4) (0.7) Balance as of December 31, 2019 81.0 11.4 8.0 7.5 Increase Due to CMA Asset Acquisition 22.9 — — — Additions 8.4 4.2 0.7 — Payments/Reductions (9.9) (3.3) (4.0) (0.4) Balance as of December 31, 2020 $ 102.4 $ 12.3 $ 4.7 $ 7.1 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 2020 63 15 12 9 2019 57 15 15 9
Schedule of Estimated Future Annual Costs of Long term Contractual Agreement	The estimated future annual costs of significant executed, non-cancelable, long-term contractual arrangements in effect as of December 31, 2020 are as follows: Eversource (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 650.0 $ 716.8 $ 652.3 $ 648.8 $ 651.5 $ 3,490.7 $ 6,810.1 Natural Gas Procurement 558.9 374.1 292.0 263.1 260.2 1,825.8 3,574.1 Purchased Power and Capacity 69.4 75.5 86.8 79.6 60.3 13.2 384.8 Peaker CfDs 30.0 34.2 46.9 41.6 31.3 102.4 286.4 Transmission Support Commitments 20.5 18.0 18.1 19.2 19.7 19.7 115.2 Total $ 1,328.8 $ 1,218.6 $ 1,096.1 $ 1,052.3 $ 1,023.0 $ 5,451.8 $ 11,170.6 CL&P (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 484.4 $ 548.3 $ 547.2 $ 549.1 $ 551.2 $ 2,645.5 $ 5,325.7 Purchased Power and Capacity 65.8 71.9 83.3 76.6 57.4 0.1 355.1 Peaker CfDs 30.0 34.2 46.9 41.6 31.3 102.4 286.4 Transmission Support Commitments 8.1 7.1 7.2 7.6 7.8 7.8 45.6 Total $ 588.3 $ 661.5 $ 684.6 $ 674.9 $ 647.7 $ 2,755.8 $ 6,012.8 NSTAR Electric (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 98.0 $ 100.0 $ 75.4 $ 72.9 $ 73.1 $ 522.1 $ 941.5 Purchased Power and Capacity 3.1 3.1 3.0 3.0 2.9 13.1 28.2 Transmission Support Commitments 8.1 7.1 7.1 7.5 7.7 7.7 45.2 Total $ 109.2 $ 110.2 $ 85.5 $ 83.4 $ 83.7 $ 542.9 $ 1,014.9 PSNH (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 67.6 $ 68.5 $ 29.7 $ 26.8 $ 27.2 $ 323.1 $ 542.9 Purchased Power and Capacity 0.5 0.5 0.5 — — — 1.5 Transmission Support Commitments 4.3 3.8 3.8 4.1 4.2 4.2 24.4 Total $ 72.4 $ 72.8 $ 34.0 $ 30.9 $ 31.4 $ 327.3 $ 568.8 The total costs incurred under these agreements were as follows: Eversource For the Years Ended December 31, (Millions of Dollars) 2020 2019 2018 Renewable Energy $ 584.2 $ 320.8 $ 218.5 Natural Gas Procurement 453.4 448.5 432.4 Purchased Power and Capacity 62.7 62.1 72.0 Peaker CfDs 22.7 13.0 20.9 Transmission Support Commitments 22.1 21.8 23.4 For the Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH CL&P NSTAR PSNH Renewable Energy $ 426.3 $ 88.8 $ 69.1 $ 160.6 $ 89.9 $ 70.3 $ 63.2 $ 89.8 $ 65.5 Purchased Power and Capacity 59.3 3.1 0.3 50.4 5.1 6.6 49.4 4.4 18.2 Peaker CfDs 22.7 — — 13.0 — — 20.9 — — Transmission Support Commitments 8.7 8.7 4.7 8.6 8.6 4.6 9.2 9.2 5.0
Schedule of Guarantor Obligations	The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries and affiliates to external parties as of December 31, 2020: Company (Obligor) Description Maximum Exposure Expiration Dates North East Offshore LLC Construction-related purchase agreements with third-party contractors (1) $ 30.5 (1) Eversource Investment LLC Funding and indemnification obligations of North East Offshore LLC (2) — (2) Sunrise Wind LLC OREC capacity production (3) 2.2 (3) South Fork Wind, LLC Transmission interconnection 1.7 — Bay State Wind LLC Real estate purchase 2.5 2021 Various Surety bonds (4) 56.6 2021 - 2023 Rocky River Realty Company and Eversource Service Lease payments for real estate 5.2 2024 (1) Eversource parent issued guarantees on behalf of its 50 percent-owned affiliate, North East Offshore LLC (NEO), under which Eversource parent agreed to guarantee 50 percent of NEO’s performance of obligations under certain purchase agreements with third-party contactors, in an amount not to exceed $1.3 billion with an expiration date in 2025. Eversource parent also issued a separate guarantee to Ørsted on behalf of NEO, under which Eversource parent agreed to guarantee 50 percent of NEO’s payment obligations under certain offshore wind project construction-related agreements with Ørsted in an aggregate amount not to exceed $62.5 million. Any amounts paid under this guarantee to Ørsted will count toward, but not increase, the maximum amount of the Funding Guarantee described in Note 2, below. The guarantee expires upon the full performance of the guaranteed obligations. (2) Eversource parent issued a guarantee (Funding Guarantee) on behalf of Eversource Investment LLC (EI), its wholly-owned subsidiary that holds a 50 percent ownership interest in NEO, under which Eversource parent agreed to guarantee certain funding obligations and certain indemnification payments of EI under the Amended and Restated Limited Liability Company Operating Agreement of NEO, in an amount not to exceed $910 million. The guaranteed obligations include payment of EI's funding obligations during the construction phase of NEO’s underlying offshore wind projects and indemnification obligations associated with third party credit support for its investment in NEO. Eversource parent’s obligations under the Funding Guarantee expire upon the full performance of the guaranteed obligations. (3) On October 25, 2019, Eversource parent issued a guarantee on behalf of its 50 percent-owned affiliate, Sunrise Wind LLC, whereby Eversource parent will guarantee Sunrise Wind LLC's performance of certain obligations, in an amount not to exceed $15.4 million, under the Offshore Wind Renewable Energy Certificate Purchase and Sale Agreement (the Agreement). The Agreement was executed on October 23, 2019, by and between the New York State Energy Research and Development Authority (NYSERDA) and Sunrise Wind LLC. The guarantee expires upon the full performance of the guaranteed obligations.

LEASES (Tables)

LEASES (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Components of Lease Cost	The components of lease cost, prior to amounts capitalized, are as follows: For the Years Ended December 31, 2020 2019 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Financing Lease Cost: Amortization of Right-of-use-Assets $ 2.6 $ 0.7 $ 0.2 $ 0.1 $ 1.7 $ 0.7 $ 0.2 $ 0.1 Interest on Lease Liabilities 1.4 0.3 0.6 — 1.2 0.6 0.6 — Total Finance Lease Cost 4.0 1.0 0.8 0.1 2.9 1.3 0.8 0.1 Operating Lease Cost 11.1 0.6 2.1 0.1 11.7 0.5 3.4 0.1 Variable Lease Cost 57.8 12.2 — 45.6 60.5 13.3 — 47.2 Total Lease Cost $ 72.9 $ 13.8 $ 2.9 $ 45.8 $ 75.1 $ 15.1 $ 4.2 $ 47.4
Schedule of Rent Expense	Operating lease rental payments charged to expense in 2018 (which exclude CL&P's and PSNH's energy purchase contracts) were as follows: (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH 2018 $ 10.8 $ 10.9 $ 11.8 $ 2.5
Supplemental Balance Sheet Information Related to Leases	Supplemental balance sheet information related to leases is as follows: As of December 31, 2020 (Millions of Dollars) Balance Sheet Classification Eversource CL&P NSTAR Electric PSNH Operating Leases: Operating Lease Right-of-use-Assets, Net Other Long-Term Assets $ 55.2 $ 0.3 $ 23.6 $ 0.3 Operating Lease Liabilities Operating Lease Liabilities - Current Portion Other Current Liabilities $ 9.5 $ 0.2 $ 0.7 $ — Operating Lease Liabilities - Long-Term Other Long-Term Liabilities 45.7 0.1 22.9 0.3 Total Operating Lease Liabilities $ 55.2 $ 0.3 $ 23.6 $ 0.3 Finance Leases: Finance Lease Right-of-use-Assets, Net Property, Plant and Equipment, Net $ 60.5 $ 0.7 $ 3.5 $ 0.8 Finance Lease Liabilities Finance Lease Liabilities - Current Portion Other Current Liabilities $ 5.0 $ 1.4 $ — $ 0.1 Finance Lease Liabilities - Long-Term Other Long-Term Liabilities 57.6 — 4.8 0.7 Total Finance Lease Liabilities $ 62.6 $ 1.4 $ 4.8 $ 0.8
Other Information Related to Leases	Other information related to leases is as follows (in millions of dollars, unless otherwise noted): As of December 31, 2020 2019 Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Weighted-Average Remaining Lease Term (Years): Operating Leases 10 3 19 8 12 2 20 9 Finance Leases 17 1 21 8 12 2 22 9 Weighted-Average Discount Rate (Percentage): Operating Leases 4.0 % 2.4 % 4.1 % 3.7 % 3.9 % 2.5 % 4.1 % 3.7 % Finance Leases 2.9 % 10.5 % 2.9 % 3.5 % 4.0 % 10.5 % 2.9 % 3.5 % Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2020 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 10.9 $ 0.6 $ 1.8 $ 0.1 Operating Cash Flows from Finance Leases 1.7 0.3 0.6 — Financing Cash Flows from Finance Leases 2.8 1.6 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 0.6 0.1 0.2 — Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 0.7 — 0.3 — Eversource CL&P NSTAR Electric PSNH For the Year Ended December 31, 2019 Cash Paid for Amounts Included in the Measurement of Lease Liabilities: Operating Cash Flows from Operating Leases $ 11.4 $ 0.4 $ 1.6 $ 0.1 Operating Cash Flows from Finance Leases 1.2 0.6 0.6 — Financing Cash Flows from Finance Leases 2.6 1.4 — 0.1 Supplemental Non-Cash Information on Lease Liabilities: Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities 2.9 1.0 0.1 0.2 Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities 2.0 — — —
Future Minimum Lease Payments under Long-Term Finance Leases	Future minimum lease payments, excluding variable costs, under long-term leases, as of December 31, 2020 are as follows: Operating Leases Finance Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Year Ending December 31, 2021 $ 11.4 $ 0.2 $ 1.6 $ 0.1 $ 7.2 $ 1.5 $ 0.6 $ 0.1 2022 9.0 0.1 1.6 0.1 5.7 — 0.6 0.1 2023 6.4 — 1.6 0.1 4.9 — 0.6 0.1 2024 4.5 — 1.7 — 4.8 — 0.7 0.1 2025 3.4 — 1.7 — 4.7 — 0.7 0.1 Thereafter 36.2 — 27.0 0.1 60.7 — 13.0 0.4 Future lease payments 70.9 0.3 35.2 0.4 88.0 1.5 16.2 0.9 Less amount representing interest 15.7 — 11.6 0.1 25.4 0.1 11.4 0.1 Present value of future minimum lease payments $ 55.2 $ 0.3 $ 23.6 $ 0.3 $ 62.6 $ 1.4 $ 4.8 $ 0.8
Future Minimum Lease Payments under Long-Term Operating Leases	Future minimum lease payments, excluding variable costs, under long-term leases, as of December 31, 2020 are as follows: Operating Leases Finance Leases (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Year Ending December 31, 2021 $ 11.4 $ 0.2 $ 1.6 $ 0.1 $ 7.2 $ 1.5 $ 0.6 $ 0.1 2022 9.0 0.1 1.6 0.1 5.7 — 0.6 0.1 2023 6.4 — 1.6 0.1 4.9 — 0.6 0.1 2024 4.5 — 1.7 — 4.8 — 0.7 0.1 2025 3.4 — 1.7 — 4.7 — 0.7 0.1 Thereafter 36.2 — 27.0 0.1 60.7 — 13.0 0.4 Future lease payments 70.9 0.3 35.2 0.4 88.0 1.5 16.2 0.9 Less amount representing interest 15.7 — 11.6 0.1 25.4 0.1 11.4 0.1 Present value of future minimum lease payments $ 55.2 $ 0.3 $ 23.6 $ 0.3 $ 62.6 $ 1.4 $ 4.8 $ 0.8

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Carrying Amounts and Estimated Fair Values of Financial Instruments	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 Fair Carrying Fair Carrying Fair As of December 31, 2020: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 169.1 $ 116.2 $ 123.4 $ 43.0 $ 45.7 $ — $ — Long-Term Debt 16,179.1 18,420.1 3,914.8 4,800.9 3,643.2 4,294.0 1,099.1 1,207.0 Rate Reduction Bonds 540.1 603.4 — — — — 540.1 603.4 As of December 31, 2019: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 162.0 $ 116.2 $ 117.8 $ 43.0 $ 44.2 $ — $ — Long-Term Debt 14,098.2 15,170.2 3,518.1 4,058.0 3,342.1 3,659.9 951.6 1,005.7 Rate Reduction Bonds 583.3 625.9 — — — — 583.3 625.9

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income/(Loss) by Component, Net of Tax	The changes in accumulated other comprehensive income/(loss) by component, net of tax, are as follows: For the Year Ended December 31, 2020 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Qualified Unrealized Defined Total Qualified Unrealized Defined Total Balance as of January 1st $ (3.0) $ 0.7 $ (62.8) $ (65.1) $ (4.4) $ (0.5) $ (55.1) $ (60.0) OCI Before Reclassifications — 0.4 (19.6) (19.2) — 1.2 (13.3) (12.1) Amounts Reclassified from AOCI 1.6 — 6.3 7.9 1.4 — 5.6 7.0 Net OCI 1.6 0.4 (13.3) (11.3) 1.4 1.2 (7.7) (5.1) Balance as of December 31st $ (1.4) $ 1.1 $ (76.1) $ (76.4) $ (3.0) $ 0.7 $ (62.8) $ (65.1)
Schedule of Amounts Reclassified from AOCI by Component	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 2020 2019 2018 Qualified Cash Flow Hedging Instruments $ (2.5) $ (2.5) $ (2.8) Interest Expense Tax Effect 0.9 1.1 1.0 Income Tax Expense Qualified Cash Flow Hedging Instruments, Net of Tax $ (1.6) $ (1.4) $ (1.8) Defined Benefit Plan Costs: Amortization of Actuarial Losses $ (8.1) $ (5.7) $ (6.0) Other Income, Net (1) Amortization of Prior Service Cost (0.3) (1.8) (0.4) Other Income, Net (1) Total Defined Benefit Plan Costs (8.4) (7.5) (6.4) Tax Effect 2.1 1.9 1.6 Income Tax Expense Defined Benefit Plan Costs, Net of Tax $ (6.3) $ (5.6) $ (4.8) Total Amounts Reclassified from AOCI, Net of Tax $ (7.9) $ (7.0) $ (6.6) (1) These amounts are included in the computation of net periodic Pension, SERP and PBOP costs. See Note 1M, "Summary of Significant Accounting Policies – Other Income, Net" and Note 11A, "Employee Benefits – Pension Benefits and Postretirement Benefits Other Than Pension," for further information.

COMMON SHARES (Tables)

COMMON SHARES (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Common Shares Authorized and Issued	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 Authorized as of December 31, 2020 and 2019 Issued as of December 31, 2020 2019 Eversource $ 5 380,000,000 357,818,402 345,858,402 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 Shares Outstanding as of December 31, As of December 31, Series 2020 2019 2020 2019 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 - Noncontrolling Interest - 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, 2020
Equity [Abstract]
Schedule of Preferred Stock Not Subject to Mandatory Redemption	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 Authorized as of December 31, 2020 and 2019 Issued as of December 31, 2020 2019 Eversource $ 5 380,000,000 357,818,402 345,858,402 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 Shares Outstanding as of December 31, As of December 31, Series 2020 2019 2020 2019 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 - Noncontrolling Interest - Preferred Stock of Subsidiaries $ 155.6 $ 155.6

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Components of Basic and Diluted EPS	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, 2020 2019 2018 Net Income Attributable to Common Shareholders $ 1,205.2 $ 909.1 $ 1,033.0 Weighted Average Common Shares Outstanding: Basic 338,836,147 321,416,086 317,370,369 Dilutive Effect of: Share-Based Compensation Awards and Other 738,994 762,215 623,565 Equity Forward Sale Agreement 271,921 763,335 — Total Dilutive Effect 1,010,915 1,525,550 623,565 Diluted 339,847,062 322,941,636 317,993,934 Basic EPS $ 3.56 $ 2.83 $ 3.25 Diluted EPS $ 3.55 $ 2.81 $ 3.25

REVENUES (Tables)

REVENUES (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following tables present operating revenues disaggregated by revenue source: For the Year Ended December 31, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,951.5 $ 644.9 $ — $ 145.1 $ — $ — $ 4,741.5 Commercial 2,353.4 361.9 — 62.4 — (4.8) 2,772.9 Industrial 327.1 107.4 — 4.8 — (13.7) 425.6 Total Retail Tariff Sales Revenues 6,632.0 1,114.2 — 212.3 — (18.5) 7,940.0 Wholesale Transmission Revenues — — 1,557.3 — 74.2 (1,290.6) 340.9 Wholesale Market Sales Revenues 327.3 43.0 — 3.8 — — 374.1 Other Revenues from Contracts with Customers 74.7 3.6 13.3 7.3 1,161.7 (1,152.0) 108.6 Amortization of/(Reserve for) Revenues Subject to Refund 4.6 2.1 — (3.8) — — 2.9 Total Revenues from Contracts with Customers 7,038.6 1,162.9 1,570.6 219.6 1,235.9 (2,461.1) 8,766.5 Alternative Revenue Programs 88.1 44.7 (35.2) (4.7) — 37.1 130.0 Other Revenues 5.6 1.1 0.7 0.5 — — 7.9 Total Operating Revenues $ 7,132.3 $ 1,208.7 $ 1,536.1 $ 215.4 $ 1,235.9 $ (2,424.0) $ 8,904.4 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,723.7 $ 555.1 $ — $ 132.3 $ — $ — $ 4,411.1 Commercial 2,584.8 347.6 — 63.9 — (4.3) 2,992.0 Industrial 331.8 96.9 — 4.5 — (11.6) 421.6 Total Retail Tariff Sales Revenues 6,640.3 999.6 — 200.7 — (15.9) 7,824.7 Wholesale Transmission Revenues — — 1,293.3 — 61.3 (1,085.2) 269.4 Wholesale Market Sales Revenues 215.7 55.4 — 4.1 — — 275.2 Other Revenues from Contracts with Customers 54.8 2.8 13.2 7.0 967.2 (969.0) 76.0 Amortization of/(Reserve for) Revenues Subject to Refund 1.3 6.2 — (2.8) — — 4.7 Total Revenues from Contracts with Customers 6,912.1 1,064.0 1,306.5 209.0 1,028.5 (2,070.1) 8,450.0 Alternative Revenue Programs 45.9 (4.9) 81.8 4.6 — (74.2) 53.2 Other Revenues 18.5 3.1 0.7 1.0 — — 23.3 Total Operating Revenues $ 6,976.5 $ 1,062.2 $ 1,389.0 $ 214.6 $ 1,028.5 $ (2,144.3) $ 8,526.5 For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues 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 Revenues 6,753.2 973.3 — 198.4 — (14.5) 7,910.4 Wholesale Transmission Revenues — — 1,308.9 — 47.3 (1,092.2) 264.0 Wholesale Market Sales Revenues 179.5 57.5 — 4.1 — — 241.1 Other Revenues from Contracts with Customers 65.9 (2.2) 12.6 7.2 889.0 (891.0) 81.5 Reserve for Revenues Subject to Refund (12.3) (8.3) — (3.7) — — (24.3) Total Revenues 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 Revenues 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 Years Ended December 31, 2020 2019 2018 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 2,011.1 $ 1,365.8 $ 574.6 $ 1,837.1 $ 1,322.1 $ 564.5 $ 1,828.2 $ 1,380.9 $ 557.5 Commercial 878.3 1,176.8 299.9 922.9 1,349.4 314.6 928.1 1,391.5 316.9 Industrial 137.5 106.4 83.2 138.3 115.8 77.7 147.7 124.9 79.3 Total Retail Tariff Sales Revenues 3,026.9 2,649.0 957.7 2,898.3 2,787.3 956.8 2,904.0 2,897.3 953.7 Wholesale Transmission Revenues 754.8 576.5 226.0 587.1 517.3 188.9 620.6 488.8 199.5 Wholesale Market Sales Revenues 230.1 58.4 38.8 105.1 73.1 37.5 48.3 76.1 56.6 Other Revenues from Contracts 32.9 43.6 14.2 36.4 18.7 15.6 35.0 28.9 15.5 Amortization of/(Reserve for) — — 4.6 — — 1.3 — — (12.3) Total Revenues from Contracts 4,044.7 3,327.5 1,241.3 3,626.9 3,396.4 1,200.1 3,607.9 3,491.1 1,213.0 Alternative Revenue Programs (4.2) 54.5 2.6 77.5 41.6 8.6 (65.9) 0.9 (17.3) Other Revenues 2.2 3.5 0.6 10.3 7.0 1.9 8.5 8.3 1.1 Eliminations (495.2) (444.4) (165.4) (482.1) (400.4) (144.7) (454.3) (387.4) (149.2) Total Operating Revenues $ 3,547.5 $ 2,941.1 $ 1,079.1 $ 3,232.6 $ 3,044.6 $ 1,065.9 $ 3,096.2 $ 3,112.9 $ 1,047.6

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Summary of Segment Information and Segmented Total Assets	Eversource's segment information is as follows: For the Year Ended December 31, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 7,132.3 $ 1,208.7 $ 1,536.1 $ 215.4 $ 1,235.9 $ (2,424.0) $ 8,904.4 Depreciation and Amortization (657.0) (87.9) (278.1) (44.2) (93.5) 1.6 (1,159.1) Other Operating Expenses (5,642.3) (913.8) (470.0) (86.6) (1,071.9) 2,428.0 (5,756.6) Operating Income 833.0 207.0 788.0 84.6 70.5 5.6 1,988.7 Interest Expense (216.0) (40.0) (126.8) (32.9) (161.0) 38.3 (538.4) Interest Income 3.2 0.9 4.7 — 37.8 (41.8) 4.8 Other Income, Net 58.0 3.1 23.3 2.0 1,382.9 (1,365.5) 103.8 Income Tax (Expense)/Benefit (129.6) (36.9) (183.8) (12.5) 16.6 — (346.2) Net Income 548.6 134.1 505.4 41.2 1,346.8 (1,363.4) 1,212.7 Net Income Attributable to Noncontrolling Interests (4.6) — (2.9) — — — (7.5) Net Income Attributable to Common Shareholders $ 544.0 $ 134.1 $ 502.5 $ 41.2 $ 1,346.8 $ (1,363.4) $ 1,205.2 Total Assets (as of) $ 24,981.9 $ 6,450.5 $ 11,695.0 $ 2,375.2 $ 22,089.4 $ (21,492.4) $ 46,099.6 Cash Flows Used for Investments in Plant $ 1,079.0 $ 494.4 $ 1,004.6 $ 118.8 $ 246.2 $ — $ 2,943.0 For the Year Ended December 31, 2019 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 6,976.5 $ 1,062.2 $ 1,389.0 $ 214.6 $ 1,028.5 $ (2,144.3) $ 8,526.5 Depreciation and Amortization (651.3) (68.3) (253.3) (46.9) (63.2) 2.3 (1,080.7) Impairment of Northern Pass Transmission — — (239.6) — — — (239.6) Other Operating Expenses (5,525.1) (830.8) (411.2) (101.0) (891.3) 2,143.7 (5,615.7) Operating Income 800.1 163.1 484.9 66.7 74.0 1.7 1,590.5 Interest Expense (206.4) (47.4) (125.7) (34.6) (170.3) 51.2 (533.2) Interest Income 13.3 0.1 1.5 — 48.7 (50.8) 12.8 Other Income, Net 46.8 1.6 29.2 0.4 945.3 (903.3) 120.0 Income Tax (Expense)/Benefit (135.9) (21.2) (130.5) 2.4 11.7 — (273.5) Net Income 517.9 96.2 259.4 34.9 909.4 (901.2) 916.6 Net Income Attributable to Noncontrolling Interests (4.6) — (2.9) — — — (7.5) Net Income Attributable to Common Shareholders $ 513.3 $ 96.2 $ 256.5 $ 34.9 $ 909.4 $ (901.2) $ 909.1 Total Assets (as of) $ 22,541.9 $ 4,345.5 $ 10,904.0 $ 2,351.7 $ 18,843.7 $ (17,862.9) $ 41,123.9 Cash Flows Used for Investments in Plant $ 1,104.2 $ 460.2 $ 987.0 $ 118.0 $ 242.1 $ — $ 2,911.5 For the Year Ended December 31, 2018 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other (1) Eliminations (1) 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) 1,092.1 (1,087.1) 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 1,111.3 (1,085.0) 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 $ 1,111.3 $ (1,085.0) $ 1,033.0 Cash Flows Used for Investments in Plant $ 961.3 $ 351.5 $ 976.2 $ 102.3 $ 178.6 $ — $ 2,569.9 (1) On October 9, 2020, Eversource completed the CMA asset acquisition, with Yankee Energy System, Inc. (Yankee parent) as the acquiring entity. Yankee parent is the parent company of Yankee Gas, NSTAR Gas, EGMA and Hopkinton LNG Corp. As a result of the acquisition, in the fourth quarter of 2020, our chief operating decision maker assessed the performance of the Natural Gas Distribution segment including Yankee parent. Previously, Yankee parent was presented within Other and its equity in earnings were eliminated in consolidation. Prior comparative periods were revised to conform to the current period segment presentation.

ACQUISITION OF ASSETS OF COLU_2

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS (Tables)	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Preliminary Allocation of the Cash Purchase Price	The preliminary allocation of the cash purchase price as of October 9, 2020 is as follows: (Millions of Dollars) Current Assets $ 145 Restricted Cash 57 PP&E 1,195 Goodwill 42 Other Noncurrent Assets, excluding Goodwill 128 Other Current Liabilities (81) Other Noncurrent Liabilities (317) Cash Purchase Price $ 1,169
Summary of Unaudited Pro Forma Financial Information	The following unaudited pro forma financial information reflects the pro forma combined results of operations of Eversource and the CMA business acquired and reflects the amortization of purchase price adjustments assuming the acquisition had taken place on January 1, 2019. 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. Pro forma net income excludes the impact of assets and liabilities not assumed by Eversource, such as amounts directly associated with the GLI incident, and non-recurring costs associated with the transaction. For the Years Ended December 31, (Pro forma amounts in millions, except share amounts) 2020 2019 Operating Revenues $ 9,273 $ 9,103 Net Income Attributable to Common Shareholders 1,265 909 Basic EPS 3.73 2.83 Diluted EPS 3.72 2.82

GOODWILL (Tables)

GOODWILL (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Goodwill by Reportable Segment	The following table presents goodwill by reportable segment: (Millions of Dollars) Electric Electric Natural Gas Water Distribution Total Balance as of January 1, 2020 $ 2,544 $ 577 $ 399 $ 907 $ 4,427 Acquisition of CMA Assets — — 42 — 42 Sale of Hingham water system — — — (23) (23) Balance as of December 31, 2020 $ 2,544 $ 577 $ 441 $ 884 $ 4,446

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ / shares in Units, $ in Thousands, customer in Millions	Oct. 09, 2020USD ($)	Dec. 31, 2020USD ($)customerutilityMW	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2017USD ($)
Summary of Accounting Policies [Line Items]
Number of electric and natural gas customers | customer		4.3
Goodwill		$ 4,445,988	$ 4,427,266
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 358,851	224,821
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Stockholders' equity		$ 14,063,566	12,629,994	$ 11,486,817		$ 11,086,242
Pre-tax impairment charge		0	239,644	0
After-tax impact of impairment charge			$ 204,400
After-tax impact of impairment charge (in dollars per share) | $ / shares			$ 0.64
Increase (decrease) in receivables		206,500
Operating lease liabilities		55,200	$ 49,900
Charitable contributions		6,400	0	0
Increase to operating cash inflows in accounts payable		(122,567)	(14,866)	(24,481)
Increase to investing cash outflows in investments in property, plant and equipment		2,942,996	2,911,489	2,569,936
Energy Relief Fund
Summary of Accounting Policies [Line Items]
Restricted cash		41,500
Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity		4,613,201	4,177,048	3,953,974		3,561,084
Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		164,100	81,500
CMA
Summary of Accounting Policies [Line Items]
Purchase price	$ 1,100,000
Goodwill	42,000
Target working capital amount	$ 69,600
Adoption of New Accounting Standard
Summary of Accounting Policies [Line Items]
Stockholders' equity			(1,514)
Adoption of New Accounting Standard | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity			(1,514)		$ 1,500
Adoption of New Accounting Standard | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts					1,600
The Connecticut Light and Power Company
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 157,447	97,348
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Stockholders' equity		$ 5,044,786	4,387,825	4,199,317		3,587,127
Increase (decrease) in receivables		58,300
Operating lease liabilities		$ 300	700
Period of accounts receivable recoverable under financial or medical duress		180 days
Maximum loans receivable outstanding		$ 55,000
Loans transferred receivable current		12,900	16,500
Loans transferred receivable non-current		9,500	18,200
Tax remittance to state for energy efficiency funds			21,400	46,800
Long term receivable		25,000	25,000
Increase to operating cash inflows in accounts payable		17,028	(102,344)	76,924
Increase to investing cash outflows in investments in property, plant and equipment		833,973	917,532	864,136
The Connecticut Light and Power Company | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity		2,173,367	1,791,392	1,727,899		1,415,741
The Connecticut Light and Power Company | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 28,300	17,200
The Connecticut Light and Power Company | Adoption of New Accounting Standard
Summary of Accounting Policies [Line Items]
Stockholders' equity			(900)
The Connecticut Light and Power Company | Adoption of New Accounting Standard | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity			(900)		900
The Connecticut Light and Power Company | Adoption of New Accounting Standard | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts					900
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]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 91,583	75,406
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Stockholders' equity		$ 4,521,418	4,159,884	3,730,155		3,446,080
Increase (decrease) in receivables		56,300
Operating lease liabilities		23,600	24,200
Long term receivable		5,500	5,500
Increase to operating cash inflows in accounts payable		(25,573)	22,659	(37,140)
Increase to investing cash outflows in investments in property, plant and equipment		907,000	861,391	725,766
NSTAR Electric Company | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity		2,527,167	2,346,287	2,098,091		1,944,961
NSTAR Electric Company | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		51,900	31,500
NSTAR Electric Company | Adoption of New Accounting Standard
Summary of Accounting Policies [Line Items]
Stockholders' equity			(161)
NSTAR Electric Company | Adoption of New Accounting Standard | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity			(161)		200
NSTAR Electric Company | Adoption of New Accounting Standard | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts					200
Public Service Company of New Hampshire
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 17,157	10,497
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member
Stockholders' equity		$ 1,542,539	1,391,733	1,302,541		1,350,594
Increase (decrease) in receivables		20,000
Operating lease liabilities		300	400
Long term receivable		3,800	3,800
Increase to operating cash inflows in accounts payable		(27,270)	(12,281)	10,147
Increase to investing cash outflows in investments in property, plant and equipment		342,586	308,993	323,910
Public Service Company of New Hampshire | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity		615,018	490,306	$ 627,258		$ 511,382
Public Service Company of New Hampshire | Adoption of New Accounting Standard
Summary of Accounting Policies [Line Items]
Stockholders' equity			(300)
Public Service Company of New Hampshire | Adoption of New Accounting Standard | Retained Earnings
Summary of Accounting Policies [Line Items]
Stockholders' equity			(300)		300
Public Service Company of New Hampshire | Adoption of New Accounting Standard | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts					$ 300
EGMA
Summary of Accounting Policies [Line Items]
Increase (decrease) in receivables		$ 65,800
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | utility		9
Northern Pass
Summary of Accounting Policies [Line Items]
Capacity required for transmission line | MW		1,090
Capitalized costs			318,000
Restatement Adjustment
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			23,800
Restatement Adjustment | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			2,200
Restatement Adjustment | Hardship Accounts and Other Low Income Assistance Programs
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		$ 22,200
Restatement Adjustment | The Connecticut Light and Power Company
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			22,200
Restatement Adjustment | The Connecticut Light and Power Company | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			900
Restatement Adjustment | The Connecticut Light and Power Company | Hardship Accounts and Other Low Income Assistance Programs
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		21,300
Restatement Adjustment | NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			(1,300)
Restatement Adjustment | NSTAR Electric Company | Retail Non Hardship Wholesaleand Other Receivables
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			300
Restatement Adjustment | NSTAR Electric Company | Hardship Accounts and Other Low Income Assistance Programs
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts		1,500
Restatement Adjustment | Public Service Company of New Hampshire
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts			$ 300
COVID 19
Summary of Accounting Policies [Line Items]
Accounts receivable		31,500
COVID 19 | The Connecticut Light and Power Company
Summary of Accounting Policies [Line Items]
Accounts receivable		2,800
COVID 19 | NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Accounts receivable		11,000
COVID 19 | Public Service Company of New Hampshire
Summary of Accounting Policies [Line Items]
Accounts receivable		2,300
COVID 19 | Natural Gas Businesses
Summary of Accounting Policies [Line Items]
Accounts receivable		$ 15,400

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Uncollectible Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 224,821
Increase due to CMA asset acquisition	24,200
Uncollectible Expense	53,461	$ 63,446	$ 61,337
Uncollectible Costs Deferred	97,000
Write-Offs	(78,000)
Recoveries Collected	13,600
Ending Balance	$ 358,851	224,821
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 23,800
Ending Balance		23,800
Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	143,300
Increase due to CMA asset acquisition	0
Uncollectible Expense	0
Uncollectible Costs Deferred	43,100
Write-Offs	(14,700)
Recoveries Collected	1,500
Ending Balance	194,800	143,300
Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	21,600
Ending Balance		21,600
Retail Non Hardship Wholesaleand Other Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	81,500
Increase due to CMA asset acquisition	24,200
Uncollectible Expense	53,500
Uncollectible Costs Deferred	53,900
Write-Offs	(63,300)
Recoveries Collected	12,100
Ending Balance	164,100	81,500
Retail Non Hardship Wholesaleand Other Receivables | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	2,200
Ending Balance		2,200
The Connecticut Light and Power Company
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	97,348
Increase due to CMA asset acquisition	0
Uncollectible Expense	12,882	15,948	15,831
Uncollectible Costs Deferred	49,000
Write-Offs	(29,700)
Recoveries Collected	5,700
Ending Balance	$ 157,447	97,348
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
The Connecticut Light and Power Company | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 22,200
Ending Balance		22,200
The Connecticut Light and Power Company | Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	80,100
Increase due to CMA asset acquisition	0
Uncollectible Expense	0
Uncollectible Costs Deferred	38,200
Write-Offs	(11,900)
Recoveries Collected	1,400
Ending Balance	129,100	80,100
The Connecticut Light and Power Company | Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	21,300
Ending Balance		21,300
The Connecticut Light and Power Company | Retail Non Hardship Wholesaleand Other Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	17,200
Increase due to CMA asset acquisition	0
Uncollectible Expense	12,900
Uncollectible Costs Deferred	10,800
Write-Offs	(17,800)
Recoveries Collected	4,300
Ending Balance	28,300	17,200
The Connecticut Light and Power Company | Retail Non Hardship Wholesaleand Other Receivables | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	900
Ending Balance		900
NSTAR Electric Company
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	75,406
Increase due to CMA asset acquisition	0
Uncollectible Expense	15,293	25,079	22,279
Uncollectible Costs Deferred	24,700
Write-Offs	(27,200)
Recoveries Collected	4,700
Ending Balance	$ 91,583	75,406
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
NSTAR Electric Company | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ (1,300)
Ending Balance		(1,300)
NSTAR Electric Company | Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	43,900
Increase due to CMA asset acquisition	0
Uncollectible Expense	0
Uncollectible Costs Deferred	(1,700)
Write-Offs	(900)
Recoveries Collected	0
Ending Balance	39,700	43,900
NSTAR Electric Company | Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	(1,600)
Ending Balance		(1,600)
NSTAR Electric Company | Retail Non Hardship Wholesaleand Other Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	31,500
Increase due to CMA asset acquisition	0
Uncollectible Expense	15,300
Uncollectible Costs Deferred	26,400
Write-Offs	(26,300)
Recoveries Collected	4,700
Ending Balance	51,900	31,500
NSTAR Electric Company | Retail Non Hardship Wholesaleand Other Receivables | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	300
Ending Balance		300
Public Service Company of New Hampshire
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	10,497
Increase due to CMA asset acquisition	0
Uncollectible Expense	5,164	6,726	$ 6,383
Uncollectible Costs Deferred	7,400
Write-Offs	(6,900)
Recoveries Collected	700
Ending Balance	$ 17,157	10,497
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Public Service Company of New Hampshire | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 300
Ending Balance		$ 300

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -Transfer of Energy Efficiency Loans (Details) - The Connecticut Light and Power Company - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum loans receivable outstanding	$ 55
Loans transferred receivable current	12.9	$ 16.5
Loans transferred receivable non-current	$ 9.5	$ 18.2

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fuel, Materials, Supplies and Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Public Utilities, Inventory [Line Items]
Total	$ 265.6	$ 235.5
Fuel
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	38.2	26.7
Materials and Supplies
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	151.3	132.9
RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	76.1	75.9
The Connecticut Light and Power Company
Public Utilities, Inventory [Line Items]
Total	57.9	50.7
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	57.9	50.7
The Connecticut Light and Power Company | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	0	0
NSTAR Electric Company
Public Utilities, Inventory [Line Items]
Total	133.9	124.1
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	62.1	54.7
NSTAR Electric Company | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	71.8	69.4
Public Service Company of New Hampshire
Public Utilities, Inventory [Line Items]
Total	26.8	25
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	22.5	18.5
Public Service Company of New Hampshire | RECs
Public Utilities, Inventory [Line Items]
Other inventory, capitalized costs, gross	$ 4.3	$ 6.5

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Operating Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Accounting Policies [Line Items]
Natural gas and fuel costs	$ 464.2	$ 462.1	$ 442.6
Public Service Company of New Hampshire
Summary of Accounting Policies [Line Items]
Natural gas and fuel costs	$ 0	$ 0	$ 7.9

SUMMARY OF SIGNIFICANT ACCOUN_9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 23.7	$ 25.6	$ 19.7
Equity Funds	42	45	44
Total AFUDC	$ 65.7	$ 70.6	$ 63.7
Average AFUDC Rate	5.00%	5.40%	4.90%
The Connecticut Light and Power Company
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 6.6	$ 7.1	$ 6.3
Equity Funds	13.8	13.2	12.2
Total AFUDC	$ 20.4	$ 20.3	$ 18.5
Average AFUDC Rate	5.90%	6.30%	5.80%
NSTAR Electric Company
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 9.1	$ 10.4	$ 7.8
Equity Funds	21.5	19.8	15.6
Total AFUDC	$ 30.6	$ 30.2	$ 23.4
Average AFUDC Rate	5.70%	5.70%	5.00%
Public Service Company of New Hampshire
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 2.1	$ 2.8	$ 1.3
Equity Funds	4.2	3.4	0
Total AFUDC	$ 6.3	$ 6.2	$ 1.3
Average AFUDC Rate	4.70%	4.60%	0.70%

SUMMARY OF SIGNIFICANT ACCOU_10

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 108,590	$ 132,777	$ 128,366
Unrealized gain associated with investment	14,200	42,200	3,800
Renewable Energy Fund
Summary of Accounting Policies [Line Items]
Other-than-temporary impairment			2,800
Access Northeast Project
Summary of Accounting Policies [Line Items]
Other-than-temporary impairment			32,900
Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	44,400	31,300	60,800
AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	42,000	45,000	44,000
Equity in Earnings of Unconsolidated Affiliates
Summary of Accounting Policies [Line Items]
Other Income, Net	14,200	42,200	3,800
Unrealized gain associated with investment	2,400	20,400	17,600
Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	1,100	800	(4,000)
Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	4,800	12,800	18,100
Gains on Sales of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	1,800	300	5,100
Other
Summary of Accounting Policies [Line Items]
Other Income, Net	300	400	600
The Connecticut Light and Power Company
Summary of Accounting Policies [Line Items]
Other Income, Net	20,774	17,531	22,663
The Connecticut Light and Power Company | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	3,800	500	9,500
The Connecticut Light and Power Company | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	13,800	13,200	12,200
The Connecticut Light and Power Company | Equity in Earnings of Unconsolidated Affiliates
Summary of Accounting Policies [Line Items]
Other Income, Net	0	100	100
The Connecticut Light and Power Company | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	1,100	2,300	(3,000)
The Connecticut Light and Power Company | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	2,000	1,500	3,700
The Connecticut Light and Power Company | Gains on Sales 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	100	(100)	200
NSTAR Electric Company
Summary of Accounting Policies [Line Items]
Other Income, Net	52,017	44,577	53,066
NSTAR Electric Company | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	29,300	23,500	36,000
NSTAR Electric Company | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	21,500	19,800	15,600
NSTAR Electric Company | Equity in Earnings of Unconsolidated Affiliates
Summary of Accounting Policies [Line Items]
Other Income, Net	400	700	700
NSTAR Electric Company | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other Income, Net	(800)	(400)	(500)
NSTAR Electric Company | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	900	700	800
NSTAR Electric Company | Gains on Sales of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	300	100	500
NSTAR Electric Company | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	400	200	0
Public Service Company of New Hampshire
Summary of Accounting Policies [Line Items]
Other Income, Net	13,786	19,222	27,672
Public Service Company of New Hampshire | Pension, SERP and PBOP Non-Service Income Components
Summary of Accounting Policies [Line Items]
Other Income, Net	7,000	4,900	9,900
Public Service Company of New Hampshire | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other Income, Net	4,200	3,400	0
Public Service Company of New Hampshire | Equity in Earnings of Unconsolidated Affiliates
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	100	300	(800)
Public Service Company of New Hampshire | Interest Income
Summary of Accounting Policies [Line Items]
Other Income, Net	2,400	10,500	14,100
Public Service Company of New Hampshire | Gains on Sales of Property
Summary of Accounting Policies [Line Items]
Other Income, Net	0	0	4,400
Public Service Company of New Hampshire | Other
Summary of Accounting Policies [Line Items]
Other Income, Net	$ 100	$ 100	$ 100

SUMMARY OF SIGNIFICANT ACCOU_11

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Other Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 170.6	$ 163.1	$ 161.9
The Connecticut Light and Power Company
Summary of Accounting Policies [Line Items]
Excise and sales taxes	$ 149.9	$ 141.1	$ 141.4

SUMMARY OF SIGNIFICANT ACCOU_12

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	$ 518	$ 532.4	$ 503.2
Income Taxes	48.9	56	158.8
Non-Cash Investing Activities:
Plant additionsincluded in accounts payable (as of)	367.2	379.4	389.3
The Connecticut Light and Power Company
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	149	144.6	149.7
Income Taxes	10.9	80.6	66.1
Non-Cash Investing Activities:
Plant additionsincluded in accounts payable (as of)	101.8	111.3	106.1
NSTAR Electric Company
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	129.4	121.9	122.1
Income Taxes	110.7	77.9	120
Non-Cash Investing Activities:
Plant additionsincluded in accounts payable (as of)	103.2	116.4	116.5
Public Service Company of New Hampshire
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	54.5	56.9	40.5
Income Taxes	34.2	3.4	27.3
Non-Cash Investing Activities:
Plant additionsincluded in accounts payable (as of)	$ 33.3	$ 49.9	$ 35.1

SUMMARY OF SIGNIFICANT ACCOU_13

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	$ 106,599	$ 15,432
Cash and Restricted Cash reported on the Statements of Cash Flows	264,950	117,063	$ 209,324	$ 85,890
The Connecticut Light and Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	90,801	0
Cash and Restricted Cash reported on the Statements of Cash Flows	99,809	4,971	91,613	9,619
NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	102	52
Cash and Restricted Cash reported on the Statements of Cash Flows	17,410	6,312	14,659	14,708
Public Service Company of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	141	413
Cash and Restricted Cash reported on the Statements of Cash Flows	39,555	36,688	$ 52,723	$ 2,191
Special Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	73,600	52,500
Special Deposits | The Connecticut Light and Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	8,700	4,600
Special Deposits | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	17,200	6,200
Special Deposits | Public Service Company of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	36,800	32,500
Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	41,200	46,000
Marketable Securities | The Connecticut Light and Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	300	400
Marketable Securities | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	100	0
Marketable Securities | Public Service Company of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	600	600
Other Long-Term Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	43,600	3,200
Other Long-Term Assets | The Connecticut Light and Power Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	0	0
Other Long-Term Assets | NSTAR Electric Company
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 0	0
Other Long-Term Assets | Public Service Company of New Hampshire
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash		$ 3,200

REGULATORY ACCOUNTING - Compone

REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,569,900	$ 5,514,700
Less:  Current Portion	1,076,556	651,112
Total Long-Term Regulatory Assets	5,493,330	4,863,639
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	2,794,200	2,382,900
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	747,100	725,800
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	522,100	565,300
Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	765,600	540,600
Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	850,500	411,500
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	296,300	334,500
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	314,700	331,500
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	118,400	97,200
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	161,000	125,400
The Connecticut Light and Power Company
Regulatory Assets [Line Items]
Total Regulatory Assets	2,211,800	1,735,900
Less:  Current Portion	345,622	178,607
Total Long-Term Regulatory Assets	1,866,152	1,557,261
The Connecticut Light and Power Company | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	632,300	539,000
The Connecticut Light and Power Company | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	458,900	458,800
The Connecticut Light and Power Company | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
The Connecticut Light and Power Company | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	515,100	274,600
The Connecticut Light and Power Company | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	246,600	78,300
The Connecticut Light and Power Company | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	293,100	329,200
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	32,100	30,800
The Connecticut Light and Power Company | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	33,700	25,200
NSTAR Electric Company
Regulatory Assets [Line Items]
Total Regulatory Assets	1,703,900	1,535,600
Less:  Current Portion	399,882	285,591
Total Long-Term Regulatory Assets	1,304,019	1,250,029
NSTAR Electric Company | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	690,000	629,800
NSTAR Electric Company | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	110,400	108,000
NSTAR Electric Company | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric Company | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	186,400	200,600
NSTAR Electric Company | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	332,200	207,100
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	270,200	284,600
NSTAR Electric Company | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	58,600	50,300
NSTAR Electric Company | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	56,100	55,200
Public Service Company of New Hampshire
Regulatory Assets [Line Items]
Total Regulatory Assets	989,100	945,800
Less:  Current Portion	115,852	84,053
Total Long-Term Regulatory Assets	873,203	861,672
Public Service Company of New Hampshire | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	267,600	218,200
Public Service Company of New Hampshire | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	15,200	12,800
Public Service Company of New Hampshire | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	522,100	565,300
Public Service Company of New Hampshire | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	64,100	65,400
Public Service Company of New Hampshire | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	95,300	65,800
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	3,900	3,600
Public Service Company of New Hampshire | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 20,900	$ 14,700

REGULATORY ACCOUNTING - Narrati

REGULATORY ACCOUNTING - Narrative (Details) - USD ($)	Dec. 23, 2020	Dec. 17, 2020	Dec. 15, 2020	Oct. 30, 2020	Oct. 07, 2020	Sep. 30, 2019	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	May 08, 2018
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							$ 196,900,000		$ 146,000,000
Regulatory assets							6,569,900,000		5,514,700,000
Deferred costs related to uncollectible expense incurred at our natural gas distribution segment							15,800,000
Deferred costs related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment							8,200,000
NHPUC
Regulatory Assets [Line Items]
After-tax benefit to earnings from settlement agreement							11,000,000
Increase in divestiture-related costs incurred to be recovered		$ 12,000,000				$ 12,000,000
Divestiture costs incurred to be recovered								$ 635,700,000
Recovery period		1 year
DPU
Regulatory Assets [Line Items]
Authorized regulatory ROE					9.70%
Authorized common equity ratio					53.25%
FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers							39,100,000
Regulatory Assets | NHPUC
Regulatory Assets [Line Items]
Divestiture costs incurred to be recovered							12,000,000
Long-Term Derivative Assets | NHPUC
Regulatory Assets [Line Items]
Divestiture costs incurred to be recovered							(12,000,000)
COVID 19
Regulatory Assets [Line Items]
Deferred costs							24,000,000
Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							591,000,000
Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets							$ 314,700,000		331,500,000
Recovery period							40 years
Remaining amortization							19 years
Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory assets							$ 765,600,000		540,600,000
Storm Restoration Costs, Net | Tropical Storm Isaias
Regulatory Assets [Line Items]
Regulatory assets							245,000,000
Public Service Company of New Hampshire
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							4,300,000		18,000,000
Regulatory assets							989,100,000		945,800,000
Deferred costs related to uncollectible expense incurred at our natural gas distribution segment							600,000
Deferred costs related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment							500,000
Equity return not recorded on the balance sheet							5,100,000		6,500,000
Public Service Company of New Hampshire | NHPUC
Regulatory Assets [Line Items]
Rate increase approved			$ 45,000,000
Revenue requirement	$ 10,600,000
Authorized regulatory ROE			9.30%
Authorized common equity ratio			54.40%
After-tax benefit to earnings from settlement agreement							7,200,000
Public Service Company of New Hampshire | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers							3,100,000
Public Service Company of New Hampshire | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							35,000,000
Public Service Company of New Hampshire | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets							0		0
Public Service Company of New Hampshire | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory assets							64,100,000		65,400,000
The Connecticut Light and Power Company
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							84,100,000		51,800,000
Regulatory assets							2,211,800,000		1,735,900,000
Deferred costs related to uncollectible expense incurred at our natural gas distribution segment							3,000,000
Deferred costs related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment							1,700,000
Equity return not recorded on the balance sheet							200,000		500,000
The Connecticut Light and Power Company | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers							21,400,000
The Connecticut Light and Power Company | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							390,000,000
The Connecticut Light and Power Company | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets							0		0
The Connecticut Light and Power Company | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory assets							515,100,000		274,600,000
The Connecticut Light and Power Company | Storm Restoration Costs, Net | Tropical Storm Isaias
Regulatory Assets [Line Items]
Regulatory assets							228,000,000
NSTAR Electric Company
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							69,800,000		55,700,000
Regulatory assets							1,703,900,000		1,535,600,000
Deferred costs related to uncollectible expense incurred at our natural gas distribution segment							6,800,000
Deferred costs related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment							5,100,000
NSTAR Electric Company | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers							14,600,000
NSTAR Electric Company | Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved							166,000,000
NSTAR Electric Company | Goodwill-related
Regulatory Assets [Line Items]
Regulatory assets							270,200,000		284,600,000
NSTAR Electric Company | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory assets							$ 186,400,000		$ 200,600,000
NSTAR Gas | DPU
Regulatory Assets [Line Items]
Rate increase approved				$ 23,000,000
Authorized regulatory ROE				9.90%
Authorized common equity ratio				54.77%
After-tax benefit to earnings from settlement agreement				$ 2,700,000
Rate increase requested				$ 38,000,000
Performance-based ratemaking plan period				10 years
Rate Reduction Bonds | Public Service Company of New Hampshire
Regulatory Assets [Line Items]
Amount of securitized rate reduction bonds issued										$ 635,700,000

REGULATORY ACCOUNTING - Compo_2

REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,240,200	$ 4,019,200
Less:  Current Portion	389,430	361,152
Total Long-Term Regulatory Liabilities	3,850,781	3,658,042
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,778,600	2,844,600
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	624,800	559,800
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	83,600	84,500
Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	366,500	325,100
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	76,800	73,200
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	309,900	132,000
The Connecticut Light and Power Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,342,100	1,247,800
Less:  Current Portion	137,166	82,763
Total Long-Term Regulatory Liabilities	1,204,942	1,164,991
The Connecticut Light and Power Company | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,010,700	1,022,800
The Connecticut Light and Power Company | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	98,400	64,600
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	148,900	94,800
The Connecticut Light and Power Company | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	44,600	46,000
The Connecticut Light and Power Company | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	39,500	19,600
NSTAR Electric Company
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,715,200	1,725,800
Less:  Current Portion	164,761	209,180
Total Long-Term Regulatory Liabilities	1,550,390	1,516,585
NSTAR Electric Company | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,044,000	1,071,200
NSTAR Electric Company | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	363,600	330,600
NSTAR Electric Company | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	72,500	72,200
NSTAR Electric Company | Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	139,700	165,600
NSTAR Electric Company | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	32,200	27,200
NSTAR Electric Company | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	63,200	59,000
Public Service Company of New Hampshire
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	442,000	479,200
Less:  Current Portion	58,756	65,766
Total Long-Term Regulatory Liabilities	383,183	413,381
Public Service Company of New Hampshire | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	371,500	392,800
Public Service Company of New Hampshire | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	12,900	16,300
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	47,800	57,000
Public Service Company of New Hampshire | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
Public Service Company of New Hampshire | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 9,800	$ 13,100

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, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 16,703,200	$ 15,880,000
Distribution - Natural Gas	6,111,200	3,931,100
Transmission - Electric	11,954,000	10,958,400
Distribution - Water	1,743,100	1,726,500
Solar	201,500	200,200
Utility	36,713,000	32,696,200
Other	1,269,000	1,025,600
Property, Plant and Equipment, Gross	37,982,000	33,721,800
Less:  Accumulated Depreciation
Utility	(8,476,300)	(7,483,500)
Other	(477,600)	(387,400)
Total Accumulated Depreciation	(8,953,900)	(7,870,900)
Property, Plant and Equipment, Net	29,028,100	25,850,900
Construction Work in Progress	1,854,400	1,734,600
Total Property, Plant and Equipment, Net	30,882,523	27,585,470
The Connecticut Light and Power Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	6,820,700	6,485,500
Transmission - Electric	5,512,000	5,043,000
Solar	0	0
Property, Plant and Equipment, Gross	12,332,700	11,528,500
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,475,400)	(2,385,700)
Property, Plant and Equipment, Net	9,857,300	9,142,800
Construction Work in Progress	377,300	483,000
Total Property, Plant and Equipment, Net	10,234,556	9,625,765
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	7,544,400	7,163,700
Transmission - Electric	4,701,300	4,411,900
Solar	201,500	200,200
Property, Plant and Equipment, Gross	12,447,200	11,775,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,074,100)	(2,895,300)
Property, Plant and Equipment, Net	9,373,100	8,880,500
Construction Work in Progress	750,000	592,300
Total Property, Plant and Equipment, Net	10,123,062	9,472,770
Public Service Company of New Hampshire
Property, Plant and Equipment [Line Items]
Distribution - Electric	2,378,400	2,271,100
Transmission - Electric	1,742,400	1,498,700
Solar	0	0
Property, Plant and Equipment, Gross	4,120,800	3,769,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(848,900)	(799,900)
Property, Plant and Equipment, Net	3,271,900	2,969,900
Construction Work in Progress	102,400	159,600
Total Property, Plant and Equipment, Net	$ 3,374,270	$ 3,129,506

PROPERTY, PLANT AND EQUIPMENT_4

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION -Narrative (Details) - USD ($) $ in Millions	Jul. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
After-tax gain (loss) on the sale of property, plant and equipment		$ 3.5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Hingham Water System
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 63.9
Goodwill	23.6
Proceeds from the sale of Hingham Water System	$ 110.5
Pre-tax gain (loss) on sale of property, plant and equipment		$ 16

PROPERTY, PLANT AND EQUIPMENT_5

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	3.00%	3.00%	2.90%
The Connecticut Light and Power Company
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	2.80%	2.80%
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	2.80%	2.80%
Public Service Company of New Hampshire
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service	2.80%	2.80%	2.80%

PROPERTY, PLANT AND EQUIPMENT_6

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Distribution - Electric	34 years 3 months 18 days
Distribution - Natural Gas	41 years 6 months
Transmission - Electric	40 years 8 months 12 days
Distribution - Water	34 years 1 month 6 days
Solar	24 years 3 months 18 days
Other	11 years
Computer Software, Hardware and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Computer Software, Hardware and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	15 years
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	40 years
The Connecticut Light and Power Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	35 years 4 months 24 days
Transmission - Electric	36 years 10 months 24 days
NSTAR Electric Company
Property, Plant and Equipment [Line Items]
Distribution - Electric	33 years 8 months 12 days
Transmission - Electric	45 years 6 months
Solar	24 years 3 months 18 days
Public Service Company of New Hampshire
Property, Plant and Equipment [Line Items]
Distribution - Electric	33 years 3 months 18 days
Transmission - Electric	42 years 7 months 6 days

DERIVATIVE INSTRUMENTS - Schedu

DERIVATIVE INSTRUMENTS - Schedule of Gross Fair Value of Contracts (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Level 2 | Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	$ (3.3)	$ (5.2)
Netting	0.1	0
Net Amount Recorded as a Derivative	(3.2)	(5.2)
Level 2 | Long-Term Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	0	(0.1)
Netting	0	0
Net Amount Recorded as a Derivative	0	(0.1)
The Connecticut Light and Power Company | Level 3 | Current Derivative Assets
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	13.7	12.2
Netting	(0.4)	(0.4)
Net Amount Recorded as a Derivative	13.3	11.8
The Connecticut Light and Power Company | Level 3 | Long-Term Derivative Assets
Current and Long-Term Derivative Assets
Commodity Supply and Price Risk Management	58.7	67.5
Netting	(1.8)	(2.1)
Net Amount Recorded as a Derivative	56.9	65.4
The Connecticut Light and Power Company | Level 3 | Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(68.8)	(67.8)
Netting	0	0
Net Amount Recorded as a Derivative	(68.8)	(67.8)
The Connecticut Light and Power Company | Level 3 | Long-Term Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(294.5)	(338.6)
Netting	0	0
Net Amount Recorded as a Derivative	$ (294.5)	$ (338.6)

DERIVATIVE INSTRUMENTS - Deriva

DERIVATIVE INSTRUMENTS - Derivative Contracts at Fair Value (Details) MWh in Millions, MMBTU in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)MWhMMBTUMW	Dec. 31, 2019USD ($)MMBTUMW	Dec. 31, 2018USD ($)
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) (in MW) | MW	675	676
Amount of natural gas to be purchased under futures contracts (in MMBtu) | MMBTU	8.9	9.6
Loss deferred as regulatory costs | $	$ 21.2	$ 20.7	$ 25
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
Minimum | Level 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	7.10%
Minimum | Level 3 | The Connecticut Light and Power Company
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	11.40%
Weighted Average | Level 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts	10.30%

DERIVATIVE INSTRUMENTS - Unobse

DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - The Connecticut Light and Power Company - Level 3 - $ / KWmo	Dec. 31, 2020	Dec. 31, 2019
Capacity Prices | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	4.30	3.01
Capacity Prices | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	5.30	7.34
Forward Reserve | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.54	0.80
Forward Reserve | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.90	1.90

DERIVATIVE INSTRUMENTS - Variat

DERIVATIVE INSTRUMENTS - Variations Using Significant unobservable Inputs (Details) - Level 3 - The Connecticut Light and Power Company - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (329.2)	$ (356.5)
Net Realized/Unrealized Losses Included in Regulatory Assets	(17.9)	(15)
Settlements	54	42.3
Ending balance	$ (293.1)	$ (329.2)

MARKETABLE SECURITIES - Equity

MARKETABLE SECURITIES - Equity Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Equity securities	$ 40.9	$ 45.7
Amortized Cost	213.1	228.4
Pre-Tax Unrealized Gains	11.2	5.8
Pre-Tax Unrealized Losses	(0.1)	(0.1)
Fair Value	224.2	234.1
CYAPC and YAEC
Debt Securities, Available-for-sale [Line Items]
Equity securities	205.1	182.8
Marketable securities held in nuclear decommissioning trusts	192.5	198.1
Accounting Standards Update 2016-01
Debt Securities, Available-for-sale [Line Items]
Unrealized gains recorded in other income	$ 3.7	$ 9.8

MARKETABLE SECURITIES - Contrac

MARKETABLE SECURITIES - Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Less than one year	$ 43.6
One to five years	57.4
Six to ten years	46.6
Greater than ten years	65.5
Amortized Cost	213.1	$ 228.4
Fair Value
Less than one year	43.6
One to five years	59.7
Six to ten years	49.7
Greater than ten years	71.2
Total Debt Securities	$ 224.2	$ 234.1

MARKETABLE SECURITIES - Fair Va

MARKETABLE SECURITIES - Fair Value Measurement (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	$ 470.2	$ 462.6
Level 1
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	287.2	274.5
Level 1 | Mutual Funds and Equities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	246	228.5
Level 1 | Money Market Funds
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	41.2	46
Level 2
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	183	188.1
Level 2 | U.S. Government Issued Debt Securities (Agency and Treasury)
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	72.9	96.8
Level 2 | Corporate Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	63.8	44
Level 2 | Asset-Backed Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	11.9	12.9
Level 2 | Municipal Bonds
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	24	26.7
Level 2 | Other Fixed Income Securities
Debt and Equity Securities, FV-NI [Line Items]
Total Marketable Securities	$ 10.4	$ 7.7

ASSET RETIREMENT OBLIGATIONS -

ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	$ 489.5	$ 466.2
Liability Assumed Upon CMA Asset Acquisition	20.1	0
Liabilities Incurred During the Year	2.1	30.3
Liabilities Settled During the Year	(21.8)	(21.3)
Accretion	28.9	27.1
Revisions in Estimated Cash Flows	(19.1)	(12.8)
Balance as of End of Year	499.7	489.5
The Connecticut Light and Power Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	32	33.5
Liability Assumed Upon CMA Asset Acquisition	0	0
Liabilities Incurred During the Year	0	0
Liabilities Settled During the Year	(0.7)	(3.6)
Accretion	2.1	2.2
Revisions in Estimated Cash Flows	0	(0.1)
Balance as of End of Year	33.4	32
NSTAR Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	97.5	72.4
Liability Assumed Upon CMA Asset Acquisition	0	0
Liabilities Incurred During the Year	2.1	30.3
Liabilities Settled During the Year	(1)	0
Accretion	4.3	3.5
Revisions in Estimated Cash Flows	(11.1)	(8.7)
Balance as of End of Year	91.8	97.5
Public Service Company of New Hampshire
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	4.2	4
Liability Assumed Upon CMA Asset Acquisition	0	0
Liabilities Incurred During the Year	0	0
Liabilities Settled During the Year	0	0
Accretion	0.2	0.2
Revisions in Estimated Cash Flows	0	0
Balance as of End of Year	$ 4.4	$ 4.2

ASSET RETIREMENT OBLIGATIONS _2

ASSET RETIREMENT OBLIGATIONS - Narrative (Details) $ in Millions	Jul. 15, 2016kV	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligations		$ 499.7	$ 489.5	$ 466.2
Amount of capacity required for installation of distribution cable (in kV) | kV	115
Eversource and NSTAR Electric | Other Current Liabilities
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligations			1
CYAPC and YAEC
Schedule of Asset Retirement Obligation [Line Items]
Asset retirement obligations		$ 330.3	$ 337.7

INVESTMENTS IN UNCONSOLIDATED_3

INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Summary of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affilitates	$ 1,107,143	$ 871,633
Offshore Wind Business - North East Offshore and Bay State Wind
Schedule of Equity Method Investments [Line Items]
Ownership interest	50.00%
Investments in unconsolidated affilitates	$ 887,100	649,300
Natural Gas Pipeline - Algonquin Gas Transmission, LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest	15.00%
Investments in unconsolidated affilitates	$ 125,200	127,800
Renewable Energy Investment Fund
Schedule of Equity Method Investments [Line Items]
Ownership interest	90.00%
Investments in unconsolidated affilitates	$ 71,600	72,400
Other
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affilitates	$ 23,200	$ 22,100

INVESTMENTS IN UNCONSOLIDATED_4

INVESTMENTS IN UNCONSOLIDATED AFFILIATES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)company	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Feb. 08, 2019mi²
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates, net of impairment	$ 14,200	$ 42,200	$ 3,800
Dividends received from equity method investees	$ 21,800	48,900	22,300
Number of companies that transmit hydro electricity imported from The Hydro-Quebec System in Canada | company	2
Payments to acquire investments	$ 239,673	416,337	205,150
Offshore Wind Business - North East Offshore and Bay State Wind
Schedule of Equity Method Investments [Line Items]
Carrying amount of equity method investments in excess of the underlying equity in net assets	264,100	240,300
Goodwill	$ 168,300
Ownership interest	50.00%
Revolution Wind And South Fork Wind
Schedule of Equity Method Investments [Line Items]
Ownership interest				50.00%
Area of land (in square miles) | mi²				257
Bay State Wind
Schedule of Equity Method Investments [Line Items]
Ownership interest				50.00%
Area of land (in square miles) | mi²				300
Hydro-Quebec System
Schedule of Equity Method Investments [Line Items]
Ownership interest	14.50%
Payments to acquire investments	$ 8,600	$ 8,200
Renewable Energy Fund
Schedule of Equity Method Investments [Line Items]
Other-than-temporary impairment			2,800
Access Northeast Project
Schedule of Equity Method Investments [Line Items]
Other-than-temporary impairment			$ 32,900

SHORT-TERM DEBT - Narrative (De

SHORT-TERM DEBT - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Oct. 21, 2020	May 15, 2020	Dec. 18, 2019	Oct. 25, 2019
Revolving Credit Facility
Short-term Debt [Line Items]
Amount of commercial paper program			$ 550,000,000
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	$ 2,000,000,000
Eversource | Line of Credit
Short-term Debt [Line Items]
Debt instrument term	5 years
Amount of commercial paper program	$ 1,450,000,000
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	63,800,000
The Connecticut Light and Power Company | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program				$ 450,000,000
Borrowings outstanding	0
NSTAR Electric Company
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency					$ 655,000,000
Notes payable to related parties	21,300,000	30,300,000
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]
Debt instrument term	5 years
Amount of commercial paper program	$ 650,000,000
Public Service Company of New Hampshire
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency	383,900,000
Notes payable to related parties	$ 46,300,000	$ 27,000,000
Public Service Company of New Hampshire | Short Term Debt Authorization Calculation
Short-term Debt [Line Items]
Interest rate	10.00%
Short-term debt borrowing calculation approved by regulatory agency	$ 60,000,000
Public Service Company of New Hampshire | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program				$ 300,000,000
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	$ 907,600,000

SHORT-TERM DEBT - Schedule of D

SHORT-TERM DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Borrowings Outstanding	$ 1,249,325	$ 889,084
Eversource Parent Commercial Paper Program
Line of Credit Facility [Line Items]
Borrowings Outstanding	1,054,325	878,584
Commercial Paper | Eversource Parent Commercial Paper Program
Line of Credit Facility [Line Items]
Borrowings Outstanding	1,054,300	1,224,900
Available Borrowing Capacity	$ 945,700	$ 225,100
Weighted-Average Interest Rate (as a percentage)	0.25%	1.98%
Commercial Paper | NSTAR Electric Company
Line of Credit Facility [Line Items]
Borrowings Outstanding	$ 195,000	$ 10,500
Available Borrowing Capacity	$ 455,000	$ 639,500
Weighted-Average Interest Rate (as a percentage)	0.16%	1.63%

LONG-TERM DEBT - Schedule of Lo

LONG-TERM DEBT - Schedule of Long-Term Debt Outstanding (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-Term Debt	$ 15,125,876	$ 13,770,828
Less Amounts due in One Year	(1,053,186)	(327,411)
Commercial Paper Classified as Long-Term Debt	0	346,300
Senior Notes
Debt Instrument [Line Items]
Unamortized Premiums and Discounts, Net	46,500	(4,100)
Unamortized Debt Issuance Costs	(32,000)	(20,600)
Long-Term Debt	15,125,900	13,770,800
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-Term Debt	11,700	11,600
Fair Value Adjustment
Debt Instrument [Line Items]
Long-Term Debt	74,700	109,100
Fair Value Adjustment - Current Portion
Debt Instrument [Line Items]
Long-Term Debt	(31,000)	(31,300)
Loans Payable
Debt Instrument [Line Items]
Less Amounts due in One Year	(490,200)	(201,100)
Total Other Long-Term Debt
Debt Instrument [Line Items]
Long-Term Debt	7,000,800	6,054,000
The Connecticut Light and Power Company
Debt Instrument [Line Items]
Long-Term Debt	3,914,835	3,518,136
Less Amounts due in One Year	$ 0	0
The Connecticut Light and Power Company | 4.375% Fixed Rate Tax Exempt due 2028
Debt Instrument [Line Items]
Interest rate	4.375%
Long-Term Debt	$ 120,500	120,500
The Connecticut Light and Power Company | First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	3,794,800	3,394,800
Unamortized Premiums and Discounts, Net	25,900	27,800
Unamortized Debt Issuance Costs	(26,400)	(25,000)
Long-Term Debt	$ 3,914,800	3,518,100
The Connecticut Light and Power Company | First Mortgage Bonds | 7.875% 1994 Series D due 2024
Debt Instrument [Line Items]
Interest rate	7.875%
Long-Term Debt	$ 139,800	139,800
The Connecticut Light and Power Company | First Mortgage Bonds | 5.750% 2004 Series B due 2034
Debt Instrument [Line Items]
Interest rate	5.75%
Long-Term Debt	$ 130,000	130,000
The Connecticut Light and Power Company | First Mortgage Bonds | 5.625% 2005 Series B due 2035
Debt Instrument [Line Items]
Interest rate	5.625%
Long-Term Debt	$ 100,000	100,000
The Connecticut Light and Power Company | First Mortgage Bonds | 6.350% 2006 Series A due 2036
Debt Instrument [Line Items]
Interest rate	6.35%
Long-Term Debt	$ 250,000	250,000
The Connecticut Light and Power Company | First Mortgage Bonds | 5.750% 2007 Series B due 2037
Debt Instrument [Line Items]
Interest rate	5.75%
Long-Term Debt	$ 150,000	150,000
The Connecticut Light and Power Company | First Mortgage Bonds | 6.375% 2007 Series D due 2037
Debt Instrument [Line Items]
Interest rate	6.375%
Long-Term Debt	$ 100,000	100,000
The Connecticut Light and Power Company | First Mortgage Bonds | 2.500% 2013 Series A due 2023
Debt Instrument [Line Items]
Interest rate	2.50%
Long-Term Debt	$ 400,000	400,000
The Connecticut Light and Power Company | First Mortgage Bonds | 4.300% 2014 Series A due 2044
Debt Instrument [Line Items]
Interest rate	4.30%
Long-Term Debt	$ 475,000	475,000
The Connecticut Light and Power Company | First Mortgage Bonds | 4.150% 2015 Series A due 2045
Debt Instrument [Line Items]
Interest rate	4.15%
Long-Term Debt	$ 350,000	350,000
The Connecticut Light and Power Company | First Mortgage Bonds | 3.200% 2017 Series A due 2027
Debt Instrument [Line Items]
Interest rate	3.20%
Long-Term Debt	$ 500,000	500,000
The Connecticut Light and Power Company | First Mortgage Bonds | 4.000% 2018 Series A due 2048
Debt Instrument [Line Items]
Interest rate	4.00%
Long-Term Debt	$ 800,000	800,000
The Connecticut Light and Power Company | First Mortgage Bonds | 0.750% 2020 Series A due 2025
Debt Instrument [Line Items]
Interest rate	0.75%
Long-Term Debt	$ 400,000	0
NSTAR Electric Company
Debt Instrument [Line Items]
Long-Term Debt	3,393,221	3,247,086
Less Amounts due in One Year	(250,000)	(95,000)
NSTAR Electric Company | Unsecured Debt
Debt Instrument [Line Items]
Long-Term Debt	3,200,000	2,800,000
Less Amounts due in One Year	(250,000)	(95,000)
Unamortized Premiums and Discounts, Net	(6,800)	(4,100)
Unamortized Debt Issuance Costs	(20,000)	(18,800)
Long-Term Debt	$ 3,393,200	3,247,100
NSTAR Electric Company | Unsecured Debt | 5.750% due 2036
Debt Instrument [Line Items]
Interest rate	5.75%
Long-Term Debt	$ 200,000	200,000
NSTAR Electric Company | Unsecured Debt | 5.500% due 2040
Debt Instrument [Line Items]
Interest rate	5.50%
Long-Term Debt	$ 300,000	300,000
NSTAR Electric Company | Unsecured Debt | 2.375% due 2022
Debt Instrument [Line Items]
Interest rate	2.375%
Long-Term Debt	$ 400,000	400,000
NSTAR Electric Company | Unsecured Debt | 4.400% due 2044
Debt Instrument [Line Items]
Interest rate	4.40%
Long-Term Debt	$ 300,000	300,000
NSTAR Electric Company | Unsecured Debt | 3.250% due 2025
Debt Instrument [Line Items]
Interest rate	3.25%
Long-Term Debt	$ 250,000	250,000
NSTAR Electric Company | Unsecured Debt | 2.700% due 2026
Debt Instrument [Line Items]
Interest rate	2.70%
Long-Term Debt	$ 250,000	250,000
NSTAR Electric Company | Unsecured Debt | 3.200% due 2027
Debt Instrument [Line Items]
Interest rate	3.20%
Long-Term Debt	$ 700,000	700,000
NSTAR Electric Company | Unsecured Debt | 3.250% due 2029
Debt Instrument [Line Items]
Interest rate	3.25%
Long-Term Debt	$ 400,000	400,000
NSTAR Electric Company | Unsecured Debt | 3.950% due 2030
Debt Instrument [Line Items]
Interest rate	3.95%
Long-Term Debt	$ 400,000	0
NSTAR Electric Company | Senior Notes
Debt Instrument [Line Items]
Long-Term Debt	$ 470,000	565,000
NSTAR Electric Company | Senior Notes | 5.900% Senior Notes Series B due 2034
Debt Instrument [Line Items]
Interest rate	5.90%
Long-Term Debt	$ 50,000	50,000
NSTAR Electric Company | Senior Notes | 6.700% Senior Notes Series D due 2037
Debt Instrument [Line Items]
Interest rate	6.70%
Long-Term Debt	$ 40,000	40,000
NSTAR Electric Company | Senior Notes | 5.100% Senior Notes Series E due 2020
Debt Instrument [Line Items]
Long-Term Debt	$ 0	95,000
NSTAR Electric Company | Senior Notes | 3.500% Senior Notes Series F due 2021
Debt Instrument [Line Items]
Interest rate	3.50%
Long-Term Debt	$ 250,000	250,000
NSTAR Electric Company | Senior Notes | 3.880% Senior Notes Series G due 2023
Debt Instrument [Line Items]
Interest rate	3.88%
Long-Term Debt	$ 80,000	80,000
NSTAR Electric Company | Senior Notes | 2.750% Senior Notes Series H due 2026
Debt Instrument [Line Items]
Interest rate	2.75%
Long-Term Debt	$ 50,000	50,000
Public Service Company of New Hampshire
Debt Instrument [Line Items]
Long-Term Debt	817,070	951,620
Less Amounts due in One Year	(282,000)	0
Public Service Company of New Hampshire | First Mortgage Bonds
Debt Instrument [Line Items]
Long-Term Debt	1,107,000	957,000
Less Amounts due in One Year	(282,000)	0
Unamortized Premiums and Discounts, Net	(1,500)	(700)
Unamortized Debt Issuance Costs	(6,400)	(4,700)
Long-Term Debt	$ 817,100	951,600
Public Service Company of New Hampshire | First Mortgage Bonds | 5.600% Series M due 2035
Debt Instrument [Line Items]
Interest rate	5.60%
Long-Term Debt	$ 50,000	50,000
Public Service Company of New Hampshire | First Mortgage Bonds | 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate	4.05%
Long-Term Debt	$ 122,000	122,000
Public Service Company of New Hampshire | First Mortgage Bonds | 3.200% Series R due 2021
Debt Instrument [Line Items]
Interest rate	3.20%
Long-Term Debt	$ 160,000	160,000
Public Service Company of New Hampshire | First Mortgage Bonds | 3.500% Series S due 2023
Debt Instrument [Line Items]
Interest rate	3.50%
Long-Term Debt	$ 325,000	325,000
Public Service Company of New Hampshire | First Mortgage Bonds | 3.600% Series T due 2049
Debt Instrument [Line Items]
Interest rate	3.60%
Long-Term Debt	$ 300,000	300,000
Public Service Company of New Hampshire | First Mortgage Bonds | 2.400% Series U due 2050
Debt Instrument [Line Items]
Long-Term Debt	150,000	0
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050
Debt Instrument [Line Items]
Long-Term Debt	$ 640,000	620,000
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050 | Minimum
Debt Instrument [Line Items]
Interest rate	2.23%
Yankee Gas | First Mortgage Bonds | Yankee Gas - First Mortgage Bonds: 2.230% - 8.480% due 2022 - 2050 | Maximum
Debt Instrument [Line Items]
Interest rate	8.48%
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050
Debt Instrument [Line Items]
Long-Term Debt	$ 500,000	460,000
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050 | Minimum
Debt Instrument [Line Items]
Interest rate	2.33%
NSTAR Gas | First Mortgage Bonds | NSTAR Gas - First Mortgage Bonds: 2.330% - 7.110% due 2025 - 2050 | Maximum
Debt Instrument [Line Items]
Interest rate	7.11%
Aquarion | Unsecured Debt | Aquarion - Senior Note 4.000% due 2024
Debt Instrument [Line Items]
Interest rate	4.00%
Long-Term Debt	$ 360,000	360,000
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049
Debt Instrument [Line Items]
Long-Term Debt	$ 335,200	335,300
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049 | Minimum
Debt Instrument [Line Items]
Interest rate	0.00%
Aquarion | Unsecured Debt | Aquarion - Unsecured Notes 0% - 6.430% due 2021 - 2049 | Maximum
Debt Instrument [Line Items]
Interest rate	6.43%
Aquarion | Secured Debt | Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035
Debt Instrument [Line Items]
Long-Term Debt	$ 35,900	68,800
Aquarion | Secured Debt | Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035 | Minimum
Debt Instrument [Line Items]
Interest rate	4.45%
Aquarion | Secured Debt | Aquarion - Secured Debt 4.450% - 9.290% due 2022 - 2035 | Maximum
Debt Instrument [Line Items]
Interest rate	9.29%
Eversource
Debt Instrument [Line Items]
Long-Term Debt	$ 5,128,322	4,358,339
Less Amounts due in One Year	(473,933)	(23,933)
Eversource | Unsecured Debt | Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050
Debt Instrument [Line Items]
Long-Term Debt	$ 5,550,000	$ 4,000,000
Eversource | Unsecured Debt | Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050 | Minimum
Debt Instrument [Line Items]
Interest rate	0.80%
Eversource | Unsecured Debt | Eversource Parent - Senior Notes 0.800% - 4.250% due 2021 - 2050 | Maximum
Debt Instrument [Line Items]
Interest rate	4.25%

LONG-TERM DEBT - Schedule of Is

LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Aug. 31, 2020	Jul. 30, 2020	May 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Repayments of debt									$ (327,236)	$ (801,078)	$ (1,050,330)
Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 15,125,900								15,125,900	13,770,800
The Connecticut Light and Power Company
Debt Instrument [Line Items]
Repayments of debt									0	(250,000)	(300,000)
The Connecticut Light and Power Company | Senior Notes | 0.75% Series A First Mortgage Bonds
Debt Instrument [Line Items]
Issuance	$ 400,000
NSTAR Electric Company
Debt Instrument [Line Items]
Repayments of debt									(95,000)	0	0
NSTAR Electric Company | Senior Notes | 3.95% 2020 Debentures
Debt Instrument [Line Items]
Interest rate							3.95%
Issuance							$ 400,000
NSTAR Electric Company | Senior Notes | 5.10% Series E Senior Notes
Debt Instrument [Line Items]
Interest rate							5.10%
Repayments of debt							$ (95,000)
Public Service Company of New Hampshire
Debt Instrument [Line Items]
Repayments of debt									$ 0	(150,000)	(199,250)
Public Service Company of New Hampshire | Senior Notes | 2.40% Series U First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate			2.40%
Issuance			$ 150,000
NSTAR Gas | Senior Notes | Eversource Parent Series I Senior Notes
Debt Instrument [Line Items]
Interest rate								2.50%
Repayments of debt								$ (450,000)
NSTAR Gas | Senior Notes | NSTAR Gas 4.46% Series N First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate								4.46%
Repayments of debt								$ (125,000)
NSTAR Gas | Senior Notes | NSTAR Gas 2.33% Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate					2.33%
Issuance					$ 75,000
NSTAR Gas | Senior Notes | NSTAR Gas 3.15% Series S First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate					3.15%
Issuance					$ 115,000
NSTAR Gas | Senior Notes | NSTAR Gas 9.95% Series J First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate	9.95%								9.95%
Repayments of debt	$ (25,000)
Yankee Gas | Senior Notes | Yankee Gas 4.87% Series K First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate						4.87%
Repayments of debt						$ (50,000)
Yankee Gas | Senior Notes | Yankee Gas 2.90% Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate		2.90%
Issuance		$ 70,000
Aquarion | Senior Notes | Aquarion Water Company of Massachusetts, Inc. and Aquarion Water Capital of Massachusetts, Inc. various term loans and general mortgage bonds
Debt Instrument [Line Items]
Repayments of debt				$ (32,200)
Eversource
Debt Instrument [Line Items]
Repayments of debt									$ 0	$ (350,000)	$ (450,000)
Eversource | Senior Notes | Eversource Parent 3.45% Series P Senior Notes
Debt Instrument [Line Items]
Interest rate			3.45%					3.45%
Issuance			$ 300,000					$ 350,000
Eversource | Senior Notes | Eversource Parent 0.80% Series Q Senior Notes
Debt Instrument [Line Items]
Interest rate			0.80%
Issuance			$ 300,000
Eversource | Senior Notes | Eversource Parent 1.65% Series R Senior Notes
Debt Instrument [Line Items]
Interest rate			1.65%
Issuance			$ 600,000
Eversource | The Connecticut Light and Power Company | Senior Notes | 4.00% 2018 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Long-term debt	$ 650,000								$ 650,000

LONG-TERM DEBT - Narrative (Det

LONG-TERM DEBT - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended
	Dec. 31, 2019	Jan. 31, 2021	Dec. 31, 2020	Dec. 16, 2020	Dec. 14, 2020	Jul. 31, 2020	Jan. 27, 2020
Debt Instrument [Line Items]
Long-term debt	$ 13,770,828		$ 15,125,876
Payment to DOE	29,000
Interest included in payment to settle spent nuclear fuel obligation	8,600		8,700
NSTAR Electric Company
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance					$ 1,600,000
Long-term debt	3,247,086		3,393,221
Public Service Company of New Hampshire
Debt Instrument [Line Items]
Amount of long-term debt approved for issuance						$ 200,000
Long-term debt	951,620		817,070
NSTAR Gas
Debt Instrument [Line Items]
Amount of long-term debt approved for issuance							$ 270,000
Aquarion Water Company
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance				$ 100,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-term debt	11,600		11,700
PSNH 4.050% Series Q First Mortgage Bond | Public Service Company of New Hampshire
Debt Instrument [Line Items]
Long-term debt	957,000		$ 1,107,000
PSNH 4.050% Series Q First Mortgage Bond | Public Service Company of New Hampshire | 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate			4.05%
Long-term debt	$ 122,000		$ 122,000
PSNH 4.050% Series Q First Mortgage Bond | Public Service Company of New Hampshire | Subsequent Event | 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate		4.05%
Face amount of debt		$ 122,000

LONG-TERM DEBT - Schedule of _2

LONG-TERM DEBT - Schedule of Long-term Debt Maturities (Details) $ in Millions	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
2021	$ 1,022.2
2022	1,175.2
2023	1,658.2
2024	1,049.9
2025	1,400
Thereafter	9,807.9
Total	16,113.4
The Connecticut Light and Power Company
Debt Instrument [Line Items]
2021	0
2022	0
2023	400
2024	139.8
2025	400
Thereafter	2,975.5
Total	3,915.3
NSTAR Electric Company
Debt Instrument [Line Items]
2021	250
2022	400
2023	80
2024	0
2025	250
Thereafter	2,690
Total	3,670
Public Service Company of New Hampshire
Debt Instrument [Line Items]
2021	282
2022	0
2023	325
2024	0
2025	0
Thereafter	500
Total	$ 1,107

RATE REDUCTION BONDS AND VARI_3

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Narrative (Details) - Public Service Company of New Hampshire - Rate Reduction Bonds	May 08, 2018USD ($)
Debt Instrument [Line Items]
Amount of securitized rate reduction bonds issued	$ 635,700,000
Weighted average interest rate	3.66%

RATE REDUCTION BONDS AND VARI_4

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 6,569,900	$ 5,514,700
Regulatory Liabilities	3,850,781	3,658,042
Accrued Interest (included in Other Current Liabilities)	809,214	836,834
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	496,912	540,122
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	522,100	565,300
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	161,000	125,400
Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	989,100	945,800
Regulatory Liabilities	383,183	413,381
Accrued Interest (included in Other Current Liabilities)	38,816	32,736
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	496,912	540,122
Public Service Company of New Hampshire | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	522,100	565,300
Public Service Company of New Hampshire | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	20,900	14,700
Variable Interest Entity, Primary Beneficiary | Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	496,900	540,100
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)	522,100	565,300
Variable Interest Entity, Primary Beneficiary | Public Service Company of New Hampshire | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	9,100	5,600
Accrued Interest (included in Other Current Liabilities)	8,000	8,600
Special Deposits
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	73,600	52,500
Special Deposits | Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	36,800	32,500
Special Deposits | Variable Interest Entity, Primary Beneficiary | Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	36,800	32,500
Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	43,600	3,200
Other Long-Term Assets | Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash		3,200
Other Long-Term Assets | Variable Interest Entity, Primary Beneficiary | Public Service Company of New Hampshire
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	$ 2,100	$ 3,200

RATE REDUCTION BONDS AND VARI_5

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 538,452	$ 533,197	$ 498,805
Public Service Company of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	52,804	57,732	80,978
Interest Expense on RRB Principal (included in Interest Expense)	58,127	60,666	$ 60,634
Variable Interest Entity, Primary Beneficiary | Rate Reduction Bonds | Public Service Company of New Hampshire
Condensed Income Statements, Captions [Line Items]
Amortization of Regulatory Assets, Net	43,200	43,000
Interest Expense on RRB Principal (included in Interest Expense)	$ 19,700	$ 21,100

EMPLOYEE BENEFITS - Schedule of

EMPLOYEE BENEFITS - Schedule of Pension Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	$ (6,321.7)	$ (5,520)
Service Cost	(76.2)	(67.7)	$ (84.8)
Interest Cost	(177.8)	(219)	(196.4)
Actuarial Loss	(658.2)	(815.3)
Benefits Paid	279.3	273
Benefits Paid - Lump Sum	23.4	20
Benefits Paid - SERP	7.3	7.3
Employee Transfers	0	0
Increase due to acquisition of CMA	(121.4)	0
Benefit Obligation as of End of Year	(7,045.3)	(6,321.7)	(5,520)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	4,968.6	4,573.9
Employer Contributions	109.6	112.5
Actual Return on Plan Assets	512.3	575.2
Benefits Paid - Pension	(279.3)	(273)
Benefits Paid - Lump Sum	(23.4)	(20)
Employee Transfers	0	0
Increase due to acquisition of CMA	121.4	0
Fair Value of Plan Assets as of End of Year	5,409.2	4,968.6	4,573.9
Funded Status as of December 31st	(1,636.1)	(1,353.1)
Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(899)	(841.5)
Service Cost	(10.2)	(7.8)	(10)
Interest Cost	(24.6)	(32.7)	(30.7)
Actuarial Loss	(82.8)	(67)
Benefits Paid	50.2	50
Employee Transfers	0	0
Increase due to acquisition of CMA	(27.5)	0
Benefit Obligation as of End of Year	(993.9)	(899)	(841.5)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	935.9	849.6
Employer Contributions	1.9	9.3
Actual Return on Plan Assets	116.5	127
Benefits Paid - Pension	(50.2)	(50)
Employee Transfers	0	0
Fair Value of Plan Assets as of End of Year	1,004.1	935.9	849.6
Funded Status as of December 31st	10.2	36.9
The Connecticut Light and Power Company | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,331.3)	(1,160.4)
Service Cost	(21.8)	(18)	(21.4)
Interest Cost	(37.3)	(45.7)	(41.8)
Actuarial Loss	(152.3)	(176.6)
Benefits Paid	63.6	60.2
Benefits Paid - Lump Sum	0	0
Benefits Paid - SERP	0.3	0.3
Employee Transfers	1.5	8.9
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(1,477.3)	(1,331.3)	(1,160.4)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	986.2	918.4
Employer Contributions	23.2	24
Actual Return on Plan Assets	98.8	112.9
Benefits Paid - Pension	(63.6)	(60.2)
Benefits Paid - Lump Sum	0	0
Employee Transfers	(1.5)	(8.9)
Increase due to acquisition of CMA	0	0
Fair Value of Plan Assets as of End of Year	1,043.1	986.2	918.4
Funded Status as of December 31st	(434.2)	(345.1)
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	(172.7)	(161.7)
Service Cost	(1.7)	(1.4)	(1.9)
Interest Cost	(4.4)	(6.3)	(5.8)
Actuarial Loss	(8.6)	(13.4)
Benefits Paid	10.1	10.8
Employee Transfers	(1.3)	(0.7)
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(178.6)	(172.7)	(161.7)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	126.3	120.6
Employer Contributions	0	0
Actual Return on Plan Assets	15.7	17.1
Benefits Paid - Pension	(10.1)	(10.8)
Employee Transfers	2.2	(0.6)
Fair Value of Plan Assets as of End of Year	134.1	126.3	120.6
Funded Status as of December 31st	(44.5)	(46.4)
NSTAR Electric Company | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(1,397.3)	(1,236.5)
Service Cost	(15.4)	(14.6)	(17.4)
Interest Cost	(38.6)	(49)	(43.5)
Actuarial Loss	(139.5)	(181)
Benefits Paid	59.4	67.1
Benefits Paid - Lump Sum	13.1	12.9
Benefits Paid - SERP	0.2	0.1
Employee Transfers	0.2	3.7
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(1,517.9)	(1,397.3)	(1,236.5)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	1,288.8	1,222.1
Employer Contributions	0.7	0.4
Actual Return on Plan Assets	128.3	150
Benefits Paid - Pension	(59.4)	(67.1)
Benefits Paid - Lump Sum	(13.1)	(12.9)
Employee Transfers	(0.2)	(3.7)
Increase due to acquisition of CMA	0	0
Fair Value of Plan Assets as of End of Year	1,345.1	1,288.8	1,222.1
Funded Status as of December 31st	(172.8)	(108.5)
NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(258.3)	(246.3)
Service Cost	(2.1)	(1.7)	(2)
Interest Cost	(6.6)	(9.5)	(8.7)
Actuarial Loss	(7.4)	(15.2)
Benefits Paid	14.9	15.4
Employee Transfers	(1)	(1)
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(260.5)	(258.3)	(246.3)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	424.4	379.1
Employer Contributions	0	6
Actual Return on Plan Assets	53.3	57
Benefits Paid - Pension	(14.9)	(15.4)
Employee Transfers	1.8	(2.3)
Fair Value of Plan Assets as of End of Year	464.6	424.4	379.1
Funded Status as of December 31st	204.1	166.1
Public Service Company of New Hampshire | Pension Plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation as of Beginning of Year	(692.6)	(610.7)
Service Cost	(8.2)	(7.1)	(11.2)
Interest Cost	(19.4)	(24)	(22)
Actuarial Loss	(62.1)	(84.5)
Benefits Paid	33.5	30.3
Benefits Paid - Lump Sum	0	0
Benefits Paid - SERP	0.4	0.4
Employee Transfers	(0.3)	3
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(748.7)	(692.6)	(610.7)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	551.6	506.6
Employer Contributions	19.5	15.4
Actual Return on Plan Assets	55.8	62.9
Benefits Paid - Pension	(33.5)	(30.3)
Benefits Paid - Lump Sum	0	0
Employee Transfers	0.3	(3)
Increase due to acquisition of CMA	0	0
Fair Value of Plan Assets as of End of Year	593.7	551.6	506.6
Funded Status as of December 31st	(155)	(141)
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	(93)	(91.9)
Service Cost	(0.9)	(0.7)	(1.1)
Interest Cost	(2.8)	(3.4)	(3.4)
Actuarial Loss	(19)	(3.1)
Benefits Paid	6.1	5.6
Employee Transfers	0.1	0.5
Increase due to acquisition of CMA	0	0
Benefit Obligation as of End of Year	(109.5)	(93)	(91.9)
Change in Pension Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	76	71.2
Employer Contributions	0	0
Actual Return on Plan Assets	9.3	10
Benefits Paid - Pension	(6.1)	(5.6)
Employee Transfers	0.2	0.4
Fair Value of Plan Assets as of End of Year	79.4	76	$ 71.2
Funded Status as of December 31st	$ (30.1)	$ (17)

EMPLOYEE BENEFITS - Pension Pla

EMPLOYEE BENEFITS - Pension Plan Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Liability	$ 1,653,788	$ 1,653,788	$ 1,370,245
Expected long-term rate of return		7.00%	7.00%
The Connecticut Light and Power Company
Defined Contribution Plan Disclosure [Line Items]
Liability	478,325	$ 478,325	$ 391,159
Public Service Company of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Liability	184,715	184,715	157,638
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Increase in liability due to amendment in pension plan	603,000		813,100
Funded status of plan	(1,636,100)	$ (1,636,100)	$ (1,353,100)
Expected long-term rate of return		8.25%	8.25%	8.25%
Estimated future employer contributions in next fiscal year	130,000	$ 130,000
Estimated future contributions in the next twelve months by other subsidiaries		51,100
Pension Plan | The Connecticut Light and Power Company
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan	(434,200)	(434,200)	$ (345,100)
Estimated future employer contributions in next fiscal year	78,900	78,900
Pension Plan | Public Service Company of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan	(155,000)	(155,000)	(141,000)
Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Increase in liability due to amendment in pension plan		68,300	88,600
Funded status of plan	10,200	$ 10,200	$ 36,900
Expected long-term rate of return		8.25%	8.25%	8.25%
Estimated future employer contributions in next fiscal year	2,800	$ 2,800
Other Postretirement Benefits Plan | The Connecticut Light and Power Company
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan	(44,500)	(44,500)	$ (46,400)
Other Postretirement Benefits Plan | Public Service Company of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan	(30,100)	(30,100)	(17,000)
Other Current Liabilities
Defined Contribution Plan Disclosure [Line Items]
Funded status of plan	6,800	6,800	8,700
Other Long-Term Assets | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Prepaid asset	34,700	34,700	62,700
Accrued Pension, SERP and PBOP | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Liability	$ 24,500	$ 24,500	$ 25,800
Pre-65 Plan | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		6.30%
Ultimate rate	5.00%	5.00%
Pre-65 Plan | Minimum | Other Postretirement Benefits Plan | Aquarion
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		3.50%	3.50%
Pre-65 Plan | Maximum | Other Postretirement Benefits Plan | Aquarion
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		6.50%	6.80%
Post-65 Plan | Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
Ultimate rate	3.50%	3.50%
Eversource Service Pension and PBOP Plans
Defined Contribution Plan Disclosure [Line Items]
Assumed rate of return		8.25%
Eversource PBOP Plan | Other Postretirement Benefits Plan | Equity Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	70.00%	70.00%
Eversource PBOP Plan | Other Postretirement Benefits Plan | Fixed-Income Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	30.00%	30.00%
Aquarion Plans
Defined Contribution Plan Disclosure [Line Items]
Assumed rate of return		7.00%
Aquarion Pension Plan | Pension Plan | Equity Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	54.00%	54.00%
Aquarion Pension Plan | Pension Plan | Debt Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	36.00%	36.00%
Aquarion Pension Plan | Pension Plan | Other Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	10.00%	10.00%
Aquarion PBOP Plan | Other Postretirement Benefits Plan | Equity Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	54.00%	54.00%
Aquarion PBOP Plan | Other Postretirement Benefits Plan | Debt Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	41.00%	41.00%
Aquarion PBOP Plan | Other Postretirement Benefits Plan | Other Securities
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	5.00%	5.00%

EMPLOYEE BENEFITS - Schedule _2

EMPLOYEE BENEFITS - Schedule of Funded Status (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 6,669.4	$ 5,963.4
The Connecticut Light and Power Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,356.4	1,205.4
NSTAR Electric Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,449.4	1,340.8
Public Service Company of New Hampshire
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 707.2	$ 646.7

EMPLOYEE BENEFITS - Schedule _3

EMPLOYEE BENEFITS - Schedule of Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.40%	3.00%
Compensation/Progression Rate	3.50%	3.50%
Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.70%	3.40%
Compensation/Progression Rate	4.00%	4.00%
Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.50%	3.20%
Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.60%	3.30%
Pre-65 Plan | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Health care trend rate	6.30%

EMPLOYEE BENEFITS - Schedule _4

EMPLOYEE BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 76.2	$ 67.7	$ 84.8
Interest Cost	177.8	219	196.4
Expected Return on Plan Assets	(400.3)	(367.1)	(391.6)
Actuarial Loss	202	143.2	145.7
Prior Service Cost/(Credit)	1.2	0.9	4.3
Total Net Periodic Benefit Expense/(Income)	56.9	63.7	39.6
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	10.2	7.8	10
Interest Cost	24.6	32.7	30.7
Expected Return on Plan Assets	(73.6)	(66.8)	(72.4)
Actuarial Loss	8.4	8.3	10.3
Prior Service Cost/(Credit)	(21.2)	(23.5)	(23.6)
Total Net Periodic Benefit Expense/(Income)	(51.6)	(41.5)	(45)
The Connecticut Light and Power Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	21.8	18	21.4
Interest Cost	37.3	45.7	41.8
Expected Return on Plan Assets	(79.2)	(73.2)	(79.1)
Actuarial Loss	39.2	26.9	29.1
Prior Service Cost/(Credit)	0	0	1.1
Total Net Periodic Benefit Expense/(Income)	19.1	17.4	14.3
Intercompany Allocations	9.1	8.5	6.1
The Connecticut Light and Power Company | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	1.7	1.4	1.9
Interest Cost	4.4	6.3	5.8
Expected Return on Plan Assets	(9.9)	(9.2)	(10.4)
Actuarial Loss	1.1	1.3	1.6
Prior Service Cost/(Credit)	1.1	1.1	1.1
Total Net Periodic Benefit Expense/(Income)	(1.6)	0.9	0
Intercompany Allocations	(1.1)	(0.9)	(1)
NSTAR Electric Company | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	15.4	14.6	17.4
Interest Cost	38.6	49	43.5
Expected Return on Plan Assets	(103)	(97.1)	(104.9)
Actuarial Loss	55.2	44.7	41.1
Prior Service Cost/(Credit)	0.3	0.3	0.2
Total Net Periodic Benefit Expense/(Income)	6.5	11.5	(2.7)
Intercompany Allocations	8.9	8	6.5
NSTAR Electric Company | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2.1	1.7	2
Interest Cost	6.6	9.5	8.7
Expected Return on Plan Assets	(34)	(30.2)	(32.5)
Actuarial Loss	2.5	3.3	2.3
Prior Service Cost/(Credit)	(17)	(16.9)	(16.9)
Total Net Periodic Benefit Expense/(Income)	(39.8)	(32.6)	(36.4)
Intercompany Allocations	(1.4)	(1.2)	(1.3)
Public Service Company of New Hampshire | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	8.2	7.1	11.2
Interest Cost	19.4	24	22
Expected Return on Plan Assets	(44.7)	(40.7)	(43.6)
Actuarial Loss	15.6	10.6	11.6
Prior Service Cost/(Credit)	0	0	0.4
Total Net Periodic Benefit Expense/(Income)	(1.5)	1	1.6
Intercompany Allocations	2.9	2.3	1.9
Public Service Company of New Hampshire | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0.9	0.7	1.1
Interest Cost	2.8	3.4	3.4
Expected Return on Plan Assets	(5.7)	(5.4)	(6)
Actuarial Loss	0.8	0.3	0.7
Prior Service Cost/(Credit)	0.4	0.4	0.5
Total Net Periodic Benefit Expense/(Income)	(0.8)	(0.6)	(0.3)
Intercompany Allocations	$ (0.5)	$ (0.4)	$ (0.4)

EMPLOYEE BENEFITS - Schedule _5

EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	7.00%	7.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	8.25%	8.25%	8.25%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return	8.25%	8.25%	8.25%
Minimum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.60%	2.70%	3.90%
Compensation/Progression Rate	3.50%	3.50%	3.50%
Minimum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.70%	3.90%	3.30%
Maximum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.50%	3.60%	4.60%
Compensation/Progression Rate	4.00%	4.00%
Maximum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.60%	4.60%	3.90%

EMPLOYEE BENEFITS - Summary of

EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Plan
Net Regulatory Assets [Abstract]
Actuarial Losses Arising During the Year	$ 553.1	$ 591.6
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(194.3)	(137.8)
Prior Service Cost Arising During the Year	2	0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(1)	(0.7)
Actuarial Loss	2,620.2	2,261.4
Prior Service Cost	6.6	5.6
OCI
Actuarial Losses Arising During the Year	24.3	15.4
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(7.7)	(5.4)
Prior Service Cost Arising During the Year	0	0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.2)	(0.2)
Actuarial Loss	107.4	90.8
Prior Service Cost	0.7	0.9
Other Postretirement Benefits Plan
Net Regulatory Assets [Abstract]
Actuarial Losses Arising During the Year	39.1	4.6
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(8)	(8)
Prior Service Cost Arising During the Year	0	0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	21.3	25.1
Actuarial Loss	235	203.9
Prior Service Cost	(151.2)	(172.5)
OCI
Actuarial Losses Arising During the Year	1.3	2.3
Actuarial Losses Reclassified as Net Periodic Benefit Expense	(0.4)	(0.3)
Prior Service Cost Arising During the Year	0	0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income	(0.1)	(1.6)
Actuarial Loss	7.9	7
Prior Service Cost	$ 0.9	$ 1

EMPLOYEE BENEFITS - Schedule _6

EMPLOYEE BENEFITS - Schedule of Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2020USD ($)
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
2021	$ 346.9
2022	355.6
2023	362.9
2024	397.5
2025	373.8
2026 - 2030	1,883.2
Other Postretirement Benefits Plan
Defined Contribution Plan Disclosure [Line Items]
2021	60.1
2022	60.1
2023	59.7
2024	59.1
2025	58.3
2026 - 2030	$ 273.6

EMPLOYEE BENEFITS - Schedule _7

EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)	Dec. 31, 2020	Dec. 31, 2019
United States
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Assumed Rate of Return	8.50%	8.50%
Global
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	10.00%	10.00%
Assumed Rate of Return	8.75%	8.75%
Non-United States
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	8.00%	8.00%
Assumed Rate of Return	8.50%	8.50%
Emerging Markets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.00%
Assumed Rate of Return	10.00%	10.00%
Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	13.00%	13.00%
Assumed Rate of Return	4.00%	4.00%
Public High Yield Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	4.00%
Assumed Rate of Return	6.50%	6.50%
Private Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Assumed Rate of Return	9.00%	9.00%
Private Equity
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	15.00%
Assumed Rate of Return	12.00%	12.00%
Real Assets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	16.00%	16.00%
Assumed Rate of Return	7.50%	7.50%

EMPLOYEE BENEFITS - Schedule _8

EMPLOYEE BENEFITS - Schedule of Asset Category (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 5,409.2	$ 4,968.6	$ 4,573.9
Uncategorized	4,480.4	4,159.1
Pension Plan | Total Assets Before 401
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	5,671.1	5,229.7
Pension Plan | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,952.5	1,942.5
Uncategorized	1,321.7	1,349.9
Pension Plan | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,781.7	1,625.2
Uncategorized	1,402.5	1,222.8
Pension Plan | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	1,197.7	988.3
Uncategorized	1,175.4	971.4
Pension Plan | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	739.2	673.7
Uncategorized	580.8	615
Pension Plan | 401 PBOP Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	(261.9)	(261.1)
Pension Plan | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	925.1	767.6
Pension Plan | Level 1 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	630.8	592.6
Pension Plan | Level 1 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	113.6	99.4
Pension Plan | Level 1 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	22.3	16.9
Pension Plan | Level 1 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	158.4	58.7
Pension Plan | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	265.6	303
Pension Plan | Level 2 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan | Level 2 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	265.6	303
Pension Plan | Level 2 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Pension Plan | 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	1,004.1	935.9	$ 849.6
Uncategorized	424.4	410.2
Other Postretirement Benefits Plan | Total Assets Before 401
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	742.2	674.8
Other Postretirement Benefits Plan | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	394.3	345
Uncategorized	217.8	187
Other Postretirement Benefits Plan | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	212.1	203.5
Uncategorized	152.9	148.1
Other Postretirement Benefits Plan | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	31.5	26.5
Uncategorized	31.5	26.5
Other Postretirement Benefits Plan | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	104.3	99.8
Uncategorized	22.2	48.6
Other Postretirement Benefits Plan | 401 PBOP Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	261.9	261.1
Other Postretirement Benefits Plan | Level 1
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	274.6	225
Other Postretirement Benefits Plan | Level 1 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	176.5	158
Other Postretirement Benefits Plan | Level 1 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	16	15.8
Other Postretirement Benefits Plan | Level 1 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | Level 1 | Real Assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	82.1	51.2
Other Postretirement Benefits Plan | Level 2
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	43.2	39.6
Other Postretirement Benefits Plan | Level 2 | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | Level 2 | Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	43.2	39.6
Other Postretirement Benefits Plan | Level 2 | Private Equity
Defined Contribution Plan Disclosure [Line Items]
Fair value of pension plan assets	0	0
Other Postretirement Benefits Plan | 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, 2020
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, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 49.4	$ 41.6	$ 38.4
The Connecticut Light and Power Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	6.6	5.5	5
NSTAR Electric Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	11.8	10.3	9.7
Public Service Company of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 4.1	$ 3.5	$ 3.3

EMPLOYEE BENEFITS - Share-Based

EMPLOYEE BENEFITS - Share-Based Payments Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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)	2,876,601	3,302,526
Shares outstanding (in shares)	379,258
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 62.99
Total unrecognized compensation expense	$ 19.3
Period for recognition	1 year 8 months 26 days
Tax effect on total share-based payments (in percentage)	26.00%
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 88.23	$ 67.91	$ 56.69
Shares outstanding (in shares)		439,293
Weighted average shares outstanding (in dollars per share)	$ 77.13	$ 63.06
Restricted stock units available (in shares)	265,020
Restricted stock unit fully vested (in shares)	294,960
Additional restricted stock unit expected to vest (in shares)	360,295
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 75.36	$ 68.33	$ 56.77
Shares outstanding (in shares)	404,698	427,894
Weighted average shares outstanding (in dollars per share)	$ 70.85	$ 60.38
Restricted stock units available (in shares)	233,426
Weighted average grant date fair value of restricted stock units (in dollars per share)	$ 55.75
Restricted stock unit fully vested (in shares)	43,107
The Connecticut Light and Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 3.6
Period for recognition	1 year 9 months
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 5.7
Period for recognition	1 year 9 months
Public Service Company of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense	$ 1.2
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

EMPLOYEE BENEFITS - Summary o_2

EMPLOYEE BENEFITS - Summary of RSU and Share Transactions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock Units (RSUs)
Units
Beginning balance (in shares)	774,163
Granted (in shares)	208,937
Shares issued (in shares)	(301,938)
Forfeited (in shares)	(6,944)
Ending balance (in shares)	674,218	774,163
Weighted Average Grant-Date Fair Value
Beginning balance (in dollars per share)	$ 54.43
Granted (in dollars per share)	88.23	$ 67.91	$ 56.69
Shares issued (in dollars per share)	57.61
Forfeited (in dollars per share)	60.95
Ending balance (in dollars per share)	$ 63.42	$ 54.43
Performance Shares
Units
Beginning balance (in shares)	486,907
Granted (in shares)	211,224
Shares issued (in shares)	(249,922)
Forfeited (in shares)	(404)
Ending balance (in shares)	447,805	486,907
Weighted Average Grant-Date Fair Value
Beginning balance (in dollars per share)	$ 60.30
Granted (in dollars per share)	75.36	$ 68.33	$ 56.77
Shares issued (in dollars per share)	55.72
Forfeited (in dollars per share)	89.85
Ending balance (in dollars per share)	$ 69.93	$ 60.30

EMPLOYEE BENEFITS - Schedule_10

EMPLOYEE BENEFITS - Schedule of Compensation Expense and Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 33.9	$ 27.3	$ 21.4
Future Income Tax Benefit	8.9	7	5.4
The Connecticut Light and Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	10.9	9.8	7.8
Future Income Tax Benefit	2.9	2.5	2
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	11.3	9.7	7.7
Future Income Tax Benefit	3	2.5	1.9
Public Service Company of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	3.6	3.3	2.9
Future Income Tax Benefit	$ 1	$ 0.8	$ 0.7

EMPLOYEE BENEFITS - Schedule_11

EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	$ 45.7	$ 52	$ 49.1
Other Retirement Benefits Expense	3.3	2.7	2.7
The Connecticut Light and Power Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.2	0.2	0.3
Other Retirement Benefits Expense	1.2	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	0.9	1.1
Public Service Company of New Hampshire
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	1.7	1.7	1.7
Other Retirement Benefits Expense	$ 0.5	$ 0.4	$ 0.4

INCOME TAXES - Components of In

INCOME TAXES - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current Income Taxes:
Federal	$ 73,600	$ 56,900	$ 106,500
State	19,100	10,500	10,600
Total Current	92,700	67,400	117,100
Deferred Income Taxes, Net:
Federal	173,500	138,400	122,600
State	83,700	71,400	52,200
Total Deferred	257,154	209,812	174,812
Investment Tax Credits, Net	(3,700)	(3,700)	(2,900)
Income Tax Expense	346,186	273,499	288,972
The Connecticut Light and Power Company
Current Income Taxes:
Federal	12,000	68,400	54,200
State	(6,100)	15,400	20,900
Total Current	5,900	83,800	75,100
Deferred Income Taxes, Net:
Federal	101,100	35,200	48,500
State	43,400	18,800	6,400
Total Deferred	144,527	54,005	54,859
Investment Tax Credits, Net	(700)	(800)	(900)
Income Tax Expense	149,702	136,971	129,056
NSTAR Electric Company
Current Income Taxes:
Federal	53,900	82,600	79,300
State	6,900	18,200	30,000
Total Current	60,800	100,800	109,300
Deferred Income Taxes, Net:
Federal	33,800	100	27,900
State	38,800	27,000	13,500
Total Deferred	72,595	27,107	41,438
Investment Tax Credits, Net	(2,600)	(2,600)	(1,800)
Income Tax Expense	130,828	125,313	148,906
Public Service Company of New Hampshire
Current Income Taxes:
Federal	20,600	22,900	12,200
State	3,800	2,200	(500)
Total Current	24,400	25,100	11,700
Deferred Income Taxes, Net:
Federal	(1,300)	5,800	15,400
State	8,600	10,100	20,500
Total Deferred	7,337	15,917	35,924
Investment Tax Credits, Net	0	0	0
Income Tax Expense	$ 31,680	$ 40,975	$ 47,576

INCOME TAXES - Reconciliation B

INCOME TAXES - Reconciliation Between Income Tax Expense and Expected Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 1,558,872	$ 1,190,071	$ 1,329,491
Statutory Federal Income Tax Expense at 21%	327,400	249,900	279,200
Tax Effect of Differences:
Depreciation	(11,100)	1,900	(30,800)
Investment Tax Credit Amortization	(3,700)	(3,700)	(2,900)
State Income Taxes,   Net of Federal Impact	44,900	24,600	44,400
Dividends on ESOP	(5,100)	(5,100)	(5,100)
Tax Asset Valuation   Allowance/Reserve Adjustments	33,400	40,100	5,200
Excess Stock Benefit	(6,600)	(1,500)	(1,500)
EDIT Amortization	(48,700)	(37,400)	(5,000)
Other, Net	15,700	4,700	5,500
Income Tax Expense	$ 346,186	$ 273,499	$ 288,972
Effective Tax Rate	22.20%	23.00%	21.70%
The Connecticut Light and Power Company
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 607,636	$ 547,823	$ 506,773
Statutory Federal Income Tax Expense at 21%	127,600	115,000	106,400
Tax Effect of Differences:
Depreciation	400	(200)	(1,200)
Investment Tax Credit Amortization	(700)	(800)	(900)
State Income Taxes,   Net of Federal Impact	(1,200)	2,500	14,500
Tax Asset Valuation   Allowance/Reserve Adjustments	30,700	24,500	7,100
Excess Stock Benefit	(2,300)	(500)	(100)
EDIT Amortization	(9,000)	(5,800)	0
Other, Net	4,200	2,300	3,300
Income Tax Expense	$ 149,702	$ 136,971	$ 129,056
Effective Tax Rate	24.60%	25.00%	25.50%
NSTAR Electric Company
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 575,829	$ 557,269	$ 531,996
Statutory Federal Income Tax Expense at 21%	120,900	117,000	111,700
Tax Effect of Differences:
Depreciation	(3,700)	(3,000)	(2,800)
Investment Tax Credit Amortization	(2,600)	(2,600)	(1,800)
State Income Taxes,   Net of Federal Impact	36,000	35,700	33,200
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	1,200
Excess Stock Benefit	(2,300)	(500)	(100)
EDIT Amortization	(20,400)	(22,900)	0
Other, Net	2,900	1,600	7,500
Income Tax Expense	$ 130,828	$ 125,313	$ 148,906
Effective Tax Rate	22.70%	22.50%	28.00%
Public Service Company of New Hampshire
Income Tax Contingency [Line Items]
Income Before Income Tax Expense	$ 178,992	$ 175,023	$ 163,452
Statutory Federal Income Tax Expense at 21%	37,600	36,800	34,300
Tax Effect of Differences:
Depreciation	(1,400)	(800)	100
Investment Tax Credit Amortization	0	0	0
State Income Taxes,   Net of Federal Impact	9,800	9,800	15,800
Tax Asset Valuation   Allowance/Reserve Adjustments	0	0	0
Excess Stock Benefit	(800)	(200)	(100)
EDIT Amortization	(15,400)	(4,000)	(4,400)
Other, Net	1,900	(600)	1,900
Income Tax Expense	$ 31,680	$ 40,975	$ 47,576
Effective Tax Rate	17.70%	23.40%	29.10%

INCOME TAXES - Temporary Differ

INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets:
Employee Benefits	$ 602.4	$ 509.4
Derivative Liabilities	92.6	105
Regulatory Deferrals - Liabilities	259.8	267
Allowance for Uncollectible Accounts	87.5	56.7
Tax Effect - Tax Regulatory Liabilities	810.9	830.4
Net Operating Loss Carryforwards	12.7	9.1
Purchase Accounting Adjustment	54.5	58.7
Other	200.3	190.4
Total Deferred Tax Assets	2,120.7	2,026.7
Less:  Valuation Allowance	48.3	43
Net Deferred Tax Assets	2,072.4	1,983.7
Deferred Tax Liabilities:
Accelerated Depreciation and Other   Plant-Related Differences	4,153.6	3,901
Property Tax Accruals	88.7	76.8
Regulatory Amounts:
Regulatory Deferrals - Assets	1,376.7	1,155.6
Tax Effect - Tax Regulatory Assets	244.6	238.2
Goodwill Regulatory Asset - 1999 Merger	86	90.6
Derivative Assets	17.8	19.7
Other	200.3	257.6
Total Deferred Tax Liabilities	6,167.7	5,739.5
Regulatory liabilities	4,240.2	4,019.2
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Amounts:
Regulatory liabilities	2,778.6	2,844.6
The Connecticut Light and Power Company
Deferred Tax Assets:
Employee Benefits	144.5	125.4
Derivative Liabilities	91.8	103.6
Regulatory Deferrals - Liabilities	30.2	37.1
Allowance for Uncollectible Accounts	42.3	25.7
Tax Effect - Tax Regulatory Liabilities	331.4	333.5
Net Operating Loss Carryforwards	0	0
Purchase Accounting Adjustment	0	0
Other	100.9	92
Total Deferred Tax Assets	741.1	717.3
Less:  Valuation Allowance	33.7	24.9
Net Deferred Tax Assets	707.4	692.4
Deferred Tax Liabilities:
Accelerated Depreciation and Other   Plant-Related Differences	1,438.1	1,362.2
Property Tax Accruals	39	36.8
Regulatory Amounts:
Regulatory Deferrals - Assets	444.8	340.7
Tax Effect - Tax Regulatory Assets	174.4	171.7
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	17.8	19.7
Other	1.6	5.9
Total Deferred Tax Liabilities	2,115.7	1,937
Regulatory liabilities	1,342.1	1,247.8
The Connecticut Light and Power Company | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Amounts:
Regulatory liabilities	1,010.7	1,022.8
NSTAR Electric Company
Deferred Tax Assets:
Employee Benefits	79.8	54.8
Derivative Liabilities	0	0
Regulatory Deferrals - Liabilities	161.8	165.7
Allowance for Uncollectible Accounts	20.9	17.7
Tax Effect - Tax Regulatory Liabilities	271.8	280.9
Net Operating Loss Carryforwards	0	0
Purchase Accounting Adjustment	0	0
Other	14.3	35.8
Total Deferred Tax Assets	548.6	554.9
Less:  Valuation Allowance	0	0
Net Deferred Tax Assets	548.6	554.9
Deferred Tax Liabilities:
Accelerated Depreciation and Other   Plant-Related Differences	1,489.4	1,391.9
Property Tax Accruals	37	29
Regulatory Amounts:
Regulatory Deferrals - Assets	324.4	276.2
Tax Effect - Tax Regulatory Assets	11.3	11.7
Goodwill Regulatory Asset - 1999 Merger	73.8	77.8
Derivative Assets	0	0
Other	72.6	125.6
Total Deferred Tax Liabilities	2,008.5	1,912.2
Regulatory liabilities	1,715.2	1,725.8
NSTAR Electric Company | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Amounts:
Regulatory liabilities	1,044	1,071.2
Public Service Company of New Hampshire
Deferred Tax Assets:
Employee Benefits	56.6	46.7
Derivative Liabilities	0	0
Regulatory Deferrals - Liabilities	13.4	19
Allowance for Uncollectible Accounts	4.6	2.8
Tax Effect - Tax Regulatory Liabilities	105.2	111.3
Net Operating Loss Carryforwards	0	0
Purchase Accounting Adjustment	0	0
Other	19.8	20
Total Deferred Tax Assets	199.6	199.8
Less:  Valuation Allowance	0	0
Net Deferred Tax Assets	199.6	199.8
Deferred Tax Liabilities:
Accelerated Depreciation and Other   Plant-Related Differences	453.8	428.9
Property Tax Accruals	5.8	4.7
Regulatory Amounts:
Regulatory Deferrals - Assets	263.4	260.9
Tax Effect - Tax Regulatory Assets	8.6	8.3
Goodwill Regulatory Asset - 1999 Merger	0	0
Derivative Assets	0	0
Other	5.6	3.2
Total Deferred Tax Liabilities	737.2	706
Regulatory liabilities	442	479.2
Public Service Company of New Hampshire | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Amounts:
Regulatory liabilities	$ 371.5	$ 392.8

INCOME TAXES - Tax Credits and

INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	$ 0	$ 19.8
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	186.6	168.1
Federal and State Charitable Contribution	10.2	9.9
Operating Loss Carryforwards	183.4	65.5
The Connecticut Light and Power Company | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0	0
The Connecticut Light and Power Company | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	133.4	122.3
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
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
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 - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Tax liability related to the deferral of employer payroll tax liability provision of the CARES Act			$ 39
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Valuation allowance for tax credit and operating loss carryforward	$ 48.3	$ 43
Eversource | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	10.3	18.5
The Connecticut Light and Power Company | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	$ 8.8	$ 14.2

INCOME TAXES - Reconciliation o

INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	$ 55	$ 45.9	$ 51.7
Gross Increases - Current Year	11.9	12.1	9.2
Gross Increases - Prior Year			(6.5)
Gross Increases - Prior Year	1.4	3.4
Lapse of Statute of Limitations	(6.5)	(6.4)	(8.5)
Ending Balance	61.8	55	45.9
The Connecticut Light and Power Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	23.1	18.2	18.1
Gross Increases - Current Year	4.6	4	3.2
Gross Increases - Prior Year			(0.9)
Gross Increases - Prior Year	0.7	3.3
Lapse of Statute of Limitations	(2.6)	(2.4)	(2.2)
Ending Balance	$ 25.8	$ 23.1	$ 18.2

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Other Interest Income	$ 0	$ 0	$ (1.7)
Accrued Interest Expense	$ 0.1	$ 0.1

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	$ 81	$ 64.7
Increase Due to CMA Asset Acquisition	22.9
Additions	8.4	26.5
Payments/Reductions	(9.9)	(10.2)
Accrual for Environmental Loss Contingencies, Ending Balance	102.4	81
The Connecticut Light and Power Company
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	11.4	5.4
Increase Due to CMA Asset Acquisition	0
Additions	4.2	7
Payments/Reductions	(3.3)	(1)
Accrual for Environmental Loss Contingencies, Ending Balance	12.3	11.4
NSTAR Electric Company
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	8	10.9
Increase Due to CMA Asset Acquisition	0
Additions	0.7	0.5
Payments/Reductions	(4)	(3.4)
Accrual for Environmental Loss Contingencies, Ending Balance	4.7	8
Public Service Company of New Hampshire
Accrual for Environmental Loss Contingencies [Roll Forward]
Accrual for Environmental Loss Contingencies, Beginning Balance	7.5	5.4
Increase Due to CMA Asset Acquisition	0
Additions	0	2.8
Payments/Reductions	(0.4)	(0.7)
Accrual for Environmental Loss Contingencies, Ending Balance	$ 7.1	$ 7.5

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details) - site	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Number of Sites	63	57
The Connecticut Light and Power Company
Loss Contingencies [Line Items]
Number of Sites	15	15
NSTAR Electric Company
Loss Contingencies [Line Items]
Number of Sites	12	15
Public Service Company of New Hampshire
Loss Contingencies [Line Items]
Number of Sites	9	9

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Environmental Matters Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)sitegasSite	Dec. 31, 2019USD ($)site	Dec. 31, 2018USD ($)
Loss Contingencies [Line Items]
Number of sites | site	63	57
Reserve	$ 102.4	$ 81	$ 64.7
Number Of Gas Sites Acquired | gasSite	9
The Connecticut Light and Power Company
Loss Contingencies [Line Items]
Number of sites | site	15	15
Reserve	$ 12.3	$ 11.4	5.4
NSTAR Electric Company
Loss Contingencies [Line Items]
Number of sites | site	12	15
Reserve	$ 4.7	$ 8	10.9
Public Service Company of New Hampshire
Loss Contingencies [Line Items]
Number of sites | site	9	9
Reserve	$ 7.1	$ 7.5	$ 5.4
MGP Site accrual
Loss Contingencies [Line Items]
Reserve balances related to former MGP sites	$ 92.2	$ 67.9
Environmental Sites for Which a Range of Loss Exists
Loss Contingencies [Line Items]
Number of sites | site	6
Reserve	$ 41.7
Best estimate of potential remediation costs (up to)	$ 33
Environmental Sites for Which a Range of Loss Exists | The Connecticut Light and Power Company
Loss Contingencies [Line Items]
Number of sites | site	1
Reserve	$ 0.9
Best estimate of potential remediation costs (up to)	$ 0.5
Environmental Site for Which a Range is Too Early to Determine
Loss Contingencies [Line Items]
Number of sites | site	15
Reserve	$ 17.5
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	7
Reserve	$ 2.6
Environmental Site for Which a Range is Too Early to Determine | NSTAR Electric Company
Loss Contingencies [Line Items]
Number of sites | site	2
Reserve	$ 0.4
Evironmental Sites with Best Estimate
Loss Contingencies [Line Items]
Number of sites | site	42
Reserve	$ 43.2
Evironmental Sites with Best Estimate | The Connecticut Light and Power Company
Loss Contingencies [Line Items]
Reserve	$ 8.8
Environmental site quantity remaining | site	7
Evironmental Sites with Best Estimate | NSTAR Electric Company
Loss Contingencies [Line Items]
Reserve	$ 4.3
Environmental site quantity remaining | site	10
Evironmental Sites with Best Estimate | Public Service Company of New Hampshire
Loss Contingencies [Line Items]
Reserve	$ 7.1
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, 2020USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	$ 1,328.8
2022	1,218.6
2023	1,096.1
2024	1,052.3
2025	1,023
Thereafter	5,451.8
Total	11,170.6
Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	650
2022	716.8
2023	652.3
2024	648.8
2025	651.5
Thereafter	3,490.7
Total	6,810.1
Natural Gas Procurement
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	558.9
2022	374.1
2023	292
2024	263.1
2025	260.2
Thereafter	1,825.8
Total	3,574.1
Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	69.4
2022	75.5
2023	86.8
2024	79.6
2025	60.3
Thereafter	13.2
Total	384.8
Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	30
2022	34.2
2023	46.9
2024	41.6
2025	31.3
Thereafter	102.4
Total	286.4
Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2021	20.5
2022	18
2023	18.1
2024	19.2
2025	19.7
Thereafter	19.7
Total	115.2
The Connecticut Light and Power Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	588.3
2022	661.5
2023	684.6
2024	674.9
2025	647.7
Thereafter	2,755.8
Total	6,012.8
The Connecticut Light and Power Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	484.4
2022	548.3
2023	547.2
2024	549.1
2025	551.2
Thereafter	2,645.5
Total	5,325.7
The Connecticut Light and Power Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	65.8
2022	71.9
2023	83.3
2024	76.6
2025	57.4
Thereafter	0.1
Total	355.1
The Connecticut Light and Power Company | Peaker CfDs
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	30
2022	34.2
2023	46.9
2024	41.6
2025	31.3
Thereafter	102.4
Total	286.4
The Connecticut Light and Power Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2021	8.1
2022	7.1
2023	7.2
2024	7.6
2025	7.8
Thereafter	7.8
Total	45.6
NSTAR Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	109.2
2022	110.2
2023	85.5
2024	83.4
2025	83.7
Thereafter	542.9
Total	1,014.9
NSTAR Electric Company | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	98
2022	100
2023	75.4
2024	72.9
2025	73.1
Thereafter	522.1
Total	941.5
NSTAR Electric Company | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	3.1
2022	3.1
2023	3
2024	3
2025	2.9
Thereafter	13.1
Total	28.2
NSTAR Electric Company | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2021	8.1
2022	7.1
2023	7.1
2024	7.5
2025	7.7
Thereafter	7.7
Total	45.2
Public Service Company of New Hampshire
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	72.4
2022	72.8
2023	34
2024	30.9
2025	31.4
Thereafter	327.3
Total	568.8
Public Service Company of New Hampshire | Renewable Energy
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	67.6
2022	68.5
2023	29.7
2024	26.8
2025	27.2
Thereafter	323.1
Total	542.9
Public Service Company of New Hampshire | Purchased Power and Capacity
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2021	0.5
2022	0.5
2023	0.5
2024	0
2025	0
Thereafter	0
Total	1.5
Public Service Company of New Hampshire | Transmission Support Commitments
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2021	4.3
2022	3.8
2023	3.8
2024	4.1
2025	4.2
Thereafter	4.2
Total	$ 24.4

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES - Long-Term Contractual Arrangement Narrative (Details) MWh in Millions, $ in Millions	Oct. 31, 2020	Nov. 22, 2019megawatt	Mar. 15, 2019megawatt	Dec. 28, 2018MWh	Dec. 31, 2020USD ($)contractprojectMW	Dec. 31, 2019MW
Long-term Purchase Commitment [Line Items]
Estimated cost of energy purchase contracts					$ 11,170.6
Number of capacity contracts for differences between CL&P and UI | contract					3
Amount of capacity contracts for differences between CL&P and UI (in MW) | MW					675	676
Number of generation projects between CL&P and United Illuminated Company | project					2
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%
Contract term					20 years
Construction in Progress
Long-term Purchase Commitment [Line Items]
Total construction contract cost					$ 6,700
Minimum
Long-term Purchase Commitment [Line Items]
Estimated costs under construction contract					150
Maximum
Long-term Purchase Commitment [Line Items]
Estimated costs under construction contract					415
Peaker Contracts For Differences
Long-term Purchase Commitment [Line Items]
Estimated cost of energy purchase contracts					$ 286.4
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
Long-term Purchase Commitment [Line Items]
Estimated cost of energy purchase contracts					$ 6,012.8
The Connecticut Light and Power Company | Peaker Contracts For Differences
Long-term Purchase Commitment [Line Items]
Estimated cost of energy purchase contracts					$ 286.4
Number of capacity contracts | contract					3
Amount of peaking capacity contracts (in MW) | 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	20 years				30 years
Millstone Nuclear Power Station and Seabrook Nuclear Power Plant
Long-term Purchase Commitment [Line Items]
Estimated cost of energy purchase contracts					$ 3,600
Milestone Nuclear Power Station
Long-term Purchase Commitment [Line Items]
Annual purchase requirement (in MWh) | MWh				9
Percent of the facility's output required to be purchased			50.00%
Nameplate capacity (in MW) | megawatt			2,112
Milestone Nuclear Power Station | The Connecticut Light and Power Company
Long-term Purchase Commitment [Line Items]
Contract term			10 years	10 years
Percent of the facility's output required to be purchased			40.00%
Milestone Nuclear Power Station | UI
Long-term Purchase Commitment [Line Items]
Contract term			10 years	10 years
Seabrook Nuclear Power Plant
Long-term Purchase Commitment [Line Items]
Percent of the facility's output required to be purchased		18.00%
Nameplate capacity (in MW) | megawatt		1,250
Seabrook Nuclear Power Plant | The Connecticut Light and Power Company
Long-term Purchase Commitment [Line Items]
Contract term		8 years		8 years
Percent of the facility's output required to be purchased		15.00%
Seabrook Nuclear Power Plant | UI
Long-term Purchase Commitment [Line Items]
Contract term		8 years		8 years

COMMITMENTS AND CONTINGENCIES_6

COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Long-term Purchase Commitment [Line Items]
Renewable Energy	$ 584.2	$ 320.8	$ 218.5
Natural Gas Procurement	453.4	448.5	432.4
Purchased Power and Capacity	62.7	62.1	72
Peaker CfDs	22.7	13	20.9
Transmission Support Commitments	22.1	21.8	23.4
The Connecticut Light and Power Company
Long-term Purchase Commitment [Line Items]
Renewable Energy	426.3	160.6	63.2
Purchased Power and Capacity	59.3	50.4	49.4
Peaker CfDs	22.7	13	20.9
Transmission Support Commitments	8.7	8.6	9.2
NSTAR Electric Company
Long-term Purchase Commitment [Line Items]
Renewable Energy	88.8	89.9	89.8
Purchased Power and Capacity	3.1	5.1	4.4
Peaker CfDs	0	0	0
Transmission Support Commitments	8.7	8.6	9.2
Public Service Company of New Hampshire
Long-term Purchase Commitment [Line Items]
Renewable Energy	69.1	70.3	65.5
Purchased Power and Capacity	0.3	6.6	18.2
Peaker CfDs	0	0	0
Transmission Support Commitments	$ 4.7	$ 4.6	$ 5

COMMITMENTS AND CONTINGENCIES_7

COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details) - USD ($) $ in Thousands	Jun. 12, 2019	Feb. 21, 2019	May 22, 2017	Dec. 31, 2019	Jul. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Net of damages awarded	$ 500
Remaining damages sought	$ 1,000
Damages paid					$ 500
DOE settlement payment				$ 29,000		$ 0	$ (29,000)	$ (145,000)
Yankee Companies
Guarantor Obligations [Line Items]
Damages sought			$ 104,400
YAEC
Guarantor Obligations [Line Items]
Net of damages awarded				2,800
Total amount of damages awarded				5,400
MYAPC
Guarantor Obligations [Line Items]
Net of damages awarded				5,000
Total amount of damages awarded				$ 21,000
CYAPC, YAEC, And MYAPC
Guarantor Obligations [Line Items]
Net of damages awarded		$ 103,200
CYAPC
Guarantor Obligations [Line Items]
Net of damages awarded		40,700
YAEC
Guarantor Obligations [Line Items]
Net of damages awarded		28,100
MYAPC
Guarantor Obligations [Line Items]
Net of damages awarded		$ 34,400

COMMITMENTS AND CONTINGENCIES_8

COMMITMENTS AND CONTINGENCIES - Schedule of Guarantees and Indemnifications (Details) - USD ($)	Dec. 31, 2020	Dec. 01, 2020	Oct. 25, 2019
Guarantor Obligations [Line Items]
Fair value of guarantees	$ 500,000
North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest		50.00%
Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum Exposure			$ 15,400,000
Ownership interest			50.00%
North East Offshore LLC | Construction-related Purchase Contracts with Third-Party Suppliers
Guarantor Obligations [Line Items]
Maximum Exposure	30,500,000
North East Offshore LLC | Performance Guarantee
Guarantor Obligations [Line Items]
Maximum Exposure	$ 1,300,000,000
Percent of obligations guaranteed	50.00%
North East Offshore LLC | Payment Guarantee
Guarantor Obligations [Line Items]
Maximum Exposure	$ 62,500,000
Percent of obligations guaranteed	50.00%
Eversource Investment LLC | North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest		50.00%
Eversource Investment LLC | Funding and Indemnification Obligations
Guarantor Obligations [Line Items]
Maximum Exposure	$ 0
Eversource Investment LLC | Funding and Indemnification Obligations | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum Exposure	910,000,000
Sunrise Wind LLC | OREC Capacity Production
Guarantor Obligations [Line Items]
Maximum Exposure	2,200,000
South Fork Wind, LLC | Transmission Interconnection
Guarantor Obligations [Line Items]
Maximum Exposure	1,700,000
Bay State Wind LLC | Real Estate Purchase
Guarantor Obligations [Line Items]
Maximum Exposure	2,500,000
Various | Surety Bonds
Guarantor Obligations [Line Items]
Maximum Exposure	56,600,000
Rocky River Realty Company and Eversource Service | Lease Payments for Real Estate
Guarantor Obligations [Line Items]
Maximum Exposure	$ 5,200,000

COMMITMENTS AND CONTINGENCIES_9

COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details) - USD ($)	Dec. 31, 2020	Sep. 16, 2020
Loss Contingencies [Line Items]
Fair value of guarantees	$ 500,000
Letter of Credit | Eversource Investment LLC
Loss Contingencies [Line Items]
Maximum borrowing capacity		$ 25,000,000

COMMITMENTS AND CONTINGENCIE_10

COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details) $ in Millions	Oct. 16, 2018complaint	Oct. 06, 2017	Apr. 29, 2016complaint	Dec. 31, 2020USD ($)	Apr. 14, 2017	Oct. 15, 2014	Jul. 31, 2014complaint
Loss Contingencies [Line Items]
Percentage of base ROE reasonably justified	10.41%
Percentage of incentive cap on total ROE	13.08%
FERC ROE Complaints
Loss Contingencies [Line Items]
Loss contingency, pending claims, number | complaint	4		4
Period of complaint				15 months
Basis point change				0.10%
Estimate of possible loss for each 10 basis point change to base ROE				$ 3
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Loss contingency, pending claims, number | complaint							3
Base ROE percentage challenged by complainants				11.14%
Percentage of ROE for any incentive project	13.08%
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%
Percentage of ROE for any incentive project				11.74%
Loss contingency, estimate of possible earnings impact				$ 39.1
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%
Percentage of ROE for any incentive project		10.57%
Original base ROE authorized by FERC at time of complaint		11.74%
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 | 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 | FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of ROE for any incentive project						11.14%
Maximum | FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Percentage of ROE for any incentive project						13.10%

COMMITMENTS AND CONTINGENCIE_11

COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details) $ in Millions	Jul. 15, 2016kV	Dec. 31, 2018USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Site Contingency [Line Items]
Amount of capacity required for installation of distribution cable (in kV) | kV	115
Asset retirement obligations		$ 466.2	$ 499.7	$ 489.5
Long-Term Derivative Liabilities
Site Contingency [Line Items]
Asset retirement obligations				32
NSTAR Electric Company
Site Contingency [Line Items]
Base rate credit for new cable		17.5
Asset retirement obligations		$ 72.4	$ 91.8	$ 97.5

LEASES - Narrative (Details)

LEASES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0.6	$ 2.9
Right-of-use assets in exchange for the assumption of new finance lease liabilities	0.7	2
CMA
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	14.7
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 54.2
Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
The Connecticut Light and Power Company
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0.1	1
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0	0
The Connecticut Light and Power Company | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
The Connecticut Light and Power Company | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
NSTAR Electric Company
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0.2	0.1
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0.3	0
NSTAR Electric Company | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
NSTAR Electric Company | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
Public Service Company of New Hampshire
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0	0.2
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0	$ 0
Public Service Company of New Hampshire | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
Public Service Company of New Hampshire | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years

LEASES - Components of Lease Co

LEASES - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Lease Cost:
Amortization of Right-of-use-Assets	$ 2.6	$ 1.7
Interest on Lease Liabilities	1.4	1.2
Total Finance Lease Cost	4	2.9
Operating Lease Cost	11.1	11.7
Variable Lease Cost	57.8	60.5
Total Lease Cost	72.9	75.1
The Connecticut Light and Power Company
Financing Lease Cost:
Amortization of Right-of-use-Assets	0.7	0.7
Interest on Lease Liabilities	0.3	0.6
Total Finance Lease Cost	1	1.3
Operating Lease Cost	0.6	0.5
Variable Lease Cost	12.2	13.3
Total Lease Cost	13.8	15.1
NSTAR Electric Company
Financing Lease Cost:
Amortization of Right-of-use-Assets	0.2	0.2
Interest on Lease Liabilities	0.6	0.6
Total Finance Lease Cost	0.8	0.8
Operating Lease Cost	2.1	3.4
Variable Lease Cost	0	0
Total Lease Cost	2.9	4.2
Public Service Company of New Hampshire
Financing Lease Cost:
Amortization of Right-of-use-Assets	0.1	0.1
Interest on Lease Liabilities	0	0
Total Finance Lease Cost	0.1	0.1
Operating Lease Cost	0.1	0.1
Variable Lease Cost	45.6	47.2
Total Lease Cost	$ 45.8	$ 47.4

LEASES - Operating Leases Renta

LEASES - Operating Leases Rental Payments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 10.8
The Connecticut Light and Power Company
Operating Leased Assets [Line Items]
Operating leases, rent expense	10.9
NSTAR Electric Company
Operating Leased Assets [Line Items]
Operating leases, rent expense	11.8
Public Service Company of New Hampshire
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 2.5

LEASES - Supplemental Balance S

LEASES - Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases:
Operating Lease Right-of-use-Assets, Net	$ 55.2	$ 49.9
Operating Lease Liabilities - Current Portion	9.5	8.6
Operating Lease Liabilities - Long-Term	45.7	41.3
Total Operating Lease Liabilities	55.2	49.9
Finance Leases:
Finance Lease Right-of-use-Assets, Net	60.5	8.2
Finance Lease Liabilities - Current Portion	5	2.4
Finance Lease Liabilities - Long-Term	57.6	8.1
Total Finance Lease Liabilities	$ 62.6	$ 10.5
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PublicUtilitiesPropertyPlantAndEquipmentNet	us-gaap:PublicUtilitiesPropertyPlantAndEquipmentNet
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
The Connecticut Light and Power Company
Operating Leases:
Operating Lease Right-of-use-Assets, Net	$ 0.3	$ 0.7
Operating Lease Liabilities - Current Portion	0.2	0.5
Operating Lease Liabilities - Long-Term	0.1	0.2
Total Operating Lease Liabilities	0.3	0.7
Finance Leases:
Finance Lease Right-of-use-Assets, Net	0.7	1.9
Finance Lease Liabilities - Current Portion	1.4	1.6
Finance Lease Liabilities - Long-Term	0	1.4
Total Finance Lease Liabilities	1.4	3
NSTAR Electric Company
Operating Leases:
Operating Lease Right-of-use-Assets, Net	23.6	24.2
Operating Lease Liabilities - Current Portion	0.7	0.7
Operating Lease Liabilities - Long-Term	22.9	23.5
Total Operating Lease Liabilities	23.6	24.2
Finance Leases:
Finance Lease Right-of-use-Assets, Net	3.5	3.3
Finance Lease Liabilities - Current Portion	0	0
Finance Lease Liabilities - Long-Term	4.8	4.4
Total Finance Lease Liabilities	4.8	4.4
Public Service Company of New Hampshire
Operating Leases:
Operating Lease Right-of-use-Assets, Net	0.3	0.4
Operating Lease Liabilities - Current Portion	0	0.1
Operating Lease Liabilities - Long-Term	0.3	0.3
Total Operating Lease Liabilities	0.3	0.4
Finance Leases:
Finance Lease Right-of-use-Assets, Net	0.8	0.9
Finance Lease Liabilities - Current Portion	0.1	0.1
Finance Lease Liabilities - Long-Term	0.7	0.8
Total Finance Lease Liabilities	$ 0.8	$ 0.9

LEASES - Other Information Rela

LEASES - Other Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Weighted-Average Remaining Lease Term (Years):
Operating Leases	10 years	12 years
Finance Leases	17 years	12 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	4.00%	3.90%
Finance Leases	2.90%	4.00%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 10.9	$ 11.4
Operating Cash Flows from Finance Leases	1.7	1.2
Financing Cash Flows from Finance Leases	2.8	2.6
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.6	2.9
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.7	$ 2
The Connecticut Light and Power Company
Weighted-Average Remaining Lease Term (Years):
Operating Leases	3 years	2 years
Finance Leases	1 year	2 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	2.40%	2.50%
Finance Leases	10.50%	10.50%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 0.6	$ 0.4
Operating Cash Flows from Finance Leases	0.3	0.6
Financing Cash Flows from Finance Leases	1.6	1.4
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.1	1
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0	$ 0
NSTAR Electric Company
Weighted-Average Remaining Lease Term (Years):
Operating Leases	19 years	20 years
Finance Leases	21 years	22 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	4.10%	4.10%
Finance Leases	2.90%	2.90%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 1.8	$ 1.6
Operating Cash Flows from Finance Leases	0.6	0.6
Financing Cash Flows from Finance Leases	0	0
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.2	0.1
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.3	$ 0
Public Service Company of New Hampshire
Weighted-Average Remaining Lease Term (Years):
Operating Leases	8 years	9 years
Finance Leases	8 years	9 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	3.70%	3.70%
Finance Leases	3.50%	3.50%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 0.1	$ 0.1
Operating Cash Flows from Finance Leases	0	0
Financing Cash Flows from Finance Leases	0.1	0.1
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0	0.2
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0	$ 0

LEASES - Future Minimum Lease P

LEASES - Future Minimum Lease Payments under Long-Term Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Leases
2021	$ 11.4
2022	9
2023	6.4
2024	4.5
2025	3.4
Thereafter	36.2
Future lease payments	70.9
Less amount representing interest	15.7
Present value of future minimum lease payments	55.2	$ 49.9
Finance Leases
2021	7.2
2022	5.7
2023	4.9
2024	4.8
2025	4.7
Thereafter	60.7
Future lease payments	88
Less amount representing interest	25.4
Present value of future minimum lease payments	62.6	10.5
The Connecticut Light and Power Company
Operating Leases
2021	0.2
2022	0.1
2023	0
2024	0
2025	0
Thereafter	0
Future lease payments	0.3
Less amount representing interest	0
Present value of future minimum lease payments	0.3	0.7
Finance Leases
2021	1.5
2022	0
2023	0
2024	0
2025	0
Thereafter	0
Future lease payments	1.5
Less amount representing interest	0.1
Present value of future minimum lease payments	1.4	3
NSTAR Electric Company
Operating Leases
2021	1.6
2022	1.6
2023	1.6
2024	1.7
2025	1.7
Thereafter	27
Future lease payments	35.2
Less amount representing interest	11.6
Present value of future minimum lease payments	23.6	24.2
Finance Leases
2021	0.6
2022	0.6
2023	0.6
2024	0.7
2025	0.7
Thereafter	13
Future lease payments	16.2
Less amount representing interest	11.4
Present value of future minimum lease payments	4.8	4.4
Public Service Company of New Hampshire
Operating Leases
2021	0.1
2022	0.1
2023	0.1
2024	0
2025	0
Thereafter	0.1
Future lease payments	0.4
Less amount representing interest	0.1
Present value of future minimum lease payments	0.3	0.4
Finance Leases
2021	0.1
2022	0.1
2023	0.1
2024	0.1
2025	0.1
Thereafter	0.4
Future lease payments	0.9
Less amount representing interest	0.1
Present value of future minimum lease payments	$ 0.8	$ 0.9

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
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	496,912	540,122
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	16,179,100	14,098,200
Rate Reduction Bonds	540,100	583,300
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	169,100	162,000
Long-Term Debt	18,420,100	15,170,200
Rate Reduction Bonds	603,400	625,900
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	3,914,800	3,518,100
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	123,400	117,800
Long-Term Debt	4,800,900	4,058,000
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	3,643,200	3,342,100
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	45,700	44,200
Long-Term Debt	4,294,000	3,659,900
Public Service Company of New Hampshire
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rate Reduction Bonds	496,912	540,122
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	1,099,100	951,600
Rate Reduction Bonds	540,100	583,300
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	1,207,000	1,005,700
Rate Reduction Bonds	$ 603,400	$ 625,900

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, 2020	Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 12,629,994	$ 11,486,817
OCI Before Reclassifications	(19,200)	(12,100)
Amounts Reclassified from AOCI	7,900	7,000
Net OCI	(11,300)	(5,100)
Ending balance	14,063,566	12,629,994
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(65,059)	(60,000)
Ending balance	(76,411)	(65,059)
Qualified Cash Flow Hedging Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(3,000)	(4,400)
OCI Before Reclassifications	0	0
Amounts Reclassified from AOCI	1,600	1,400
Net OCI	1,600	1,400
Ending balance	(1,400)	(3,000)
Unrealized Gains on Marketable Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	700	(500)
OCI Before Reclassifications	400	1,200
Amounts Reclassified from AOCI	0	0
Net OCI	400	1,200
Ending balance	1,100	700
Defined Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(62,800)	(55,100)
OCI Before Reclassifications	(19,600)	(13,300)
Amounts Reclassified from AOCI	6,300	5,600
Net OCI	(13,300)	(7,700)
Ending balance	$ (76,100)	$ (62,800)

ACCUMULATED OTHER COMPREHENSI_4

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Related tax effect recognized in AOCI	$ 6	$ 4.4	$ (0.2)
Pre-tax amount reclassified from AOCI as a decrease to net income	1.8
NSTAR Electric Company
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax amount reclassified from AOCI as a decrease to net income	0.5
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	$ 1.3

ACCUMULATED OTHER COMPREHENSI_5

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) - Schedule of Amounts Reclassified From AOCI By Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax Effect	$ (346,186)	$ (273,499)	$ (288,972)
Net Income Attributable to Common Shareholders	1,205,167	909,053	1,033,000
Defined Benefit Plan Costs:
Total Amounts Reclassified from AOCI, Net of Tax	(7,900)	(7,000)	(6,600)
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	900	1,100	1,000
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 Attributable to Common Shareholders	(1,600)	(1,400)	(1,800)
Amortization of Actuarial Losses
Defined Benefit Plan Costs:
Reclassifications from AOCI	(8,100)	(5,700)	(6,000)
Amortization of Prior Service Cost
Defined Benefit Plan Costs:
Reclassifications from AOCI	(300)	(1,800)	(400)
Defined Benefit Plans
Defined Benefit Plan Costs:
Reclassifications from AOCI	(8,400)	(7,500)	(6,400)
Tax Effect	2,100	1,900	1,600
Total Amounts Reclassified from AOCI, Net of Tax	(6,300)	(5,600)	(4,800)
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	$ (2,500)	$ (2,500)	$ (2,800)

DIVIDEND RESTRICTIONS (Details)

DIVIDEND RESTRICTIONS (Details) $ in Millions	Dec. 31, 2020USD ($)
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	$ 4,610
The Connecticut Light and Power Company
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	2,170
NSTAR Electric Company
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	2,530
Public Service Company of New Hampshire
Schedule of Restrictions on Retained Earnings [Line Items]
Retained earnings subject to restrictions	$ 615

COMMON SHARES - Common Shares A

COMMON SHARES - Common Shares Authorized and Issued (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 5	$ 5
Authorized (in shares)	380,000,000	380,000,000
Issued (in shares)	357,818,402	345,858,402
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 - Narrative (Deta

COMMON SHARES - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 15, 2020	Mar. 26, 2020	Mar. 23, 2020	Dec. 30, 2019	Dec. 31, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 15, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Equity offering (in shares)	6,000,000						5,980,000
Price per share (in dollars per share)	$ 86.26							$ 86.26
Net proceeds from common shares issued directly by the Company	$ 509,200	$ 314,100	$ 105,700					$ 929,000	$ 852,300	$ 928,992	$ 852,254	$ 0
Common shares issuable pursuant to forward sale agreement (in shares)	11,960,000	4,460,000	1,500,000		6,000,000
Forward sale price (in dollars per share)				$ 71.48
Common shares issued directly by the Company (in shares)						5,960,000
Treasury stock (in shares)					14,864,379				15,977,757	14,864,379	15,977,757
Common stock outstanding (in shares)					342,954,023				329,880,645	342,954,023	329,880,645

PREFERRED STOCK NOT SUBJECT T_3

PREFERRED STOCK NOT SUBJECT TO MANDATORY REDEMPTION - Narrative (Details)	Dec. 31, 2020$ / 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 (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 (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, 2020	Dec. 31, 2019
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)	$ 1,900,000	$ 1,900,000
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)	$ 2,000,000	$ 2,000,000
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)	$ 2,040,000	$ 2,040,000
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)	$ 2,200,000	$ 2,200,000
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)	$ 2,060,000	$ 2,060,000
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)	$ 2,090,000	$ 2,090,000
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)	$ 3,240,000	$ 3,240,000
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
Aquarion Water Company | Series of Preferred Stock at 6%
Class of Stock [Line Items]
Preferred stock, dividend rate (as a percentage)	6.00%
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 SHAREHOLDERS' EQUITY A_2

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Net income attributable to noncontrolling interests	$ 7,500	$ 7,500	$ 7,500
Noncontrolling interest - preferred stock of subsidiaries	$ 155,570	$ 155,570

EARNINGS PER SHARE - Narrative

EARNINGS PER SHARE - Narrative (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Antidilutive share awards excluded from the EPS computation (in shares)	39,560	0	0

EARNINGS PER SHARE - Components

EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 1,205,167	$ 909,053	$ 1,033,000
Weighted Average Common Shares Outstanding:
Basic (in shares)	338,836,147	321,416,086	317,370,369
Dilutive Effect of:
Share-Based Compensation Awards and Other (in shares)	738,994	762,215	623,565
Equity Forward Sale Agreement (in shares)	271,921	763,335	0
Dilutive Effect (in shares)	1,010,915	1,525,550	623,565
Diluted (in shares)	339,847,062	322,941,636	317,993,934
Basic EPS (in dollars per share)	$ 3.56	$ 2.83	$ 3.25
Diluted EPS (in dollars per share)	$ 3.55	$ 2.81	$ 3.25

REVENUES (Details)

REVENUES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 8,766,500	$ 8,450,000	$ 8,472,700
Alternative Revenue Programs	130,000	53,200	(46,100)
Other Revenues	7,900	23,300	21,600
Operating Revenues	8,904,430	8,526,470	8,448,201
Lease revenue	4,300	4,400
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	4,741,500	4,411,100	4,439,800
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,772,900	2,992,000	3,028,300
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	425,600	421,600	442,300
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,940,000	7,824,700	7,910,400
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	340,900	269,400	264,000
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	374,100	275,200	241,100
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	108,600	76,000	81,500
Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,900	4,700	(24,300)
The Connecticut Light and Power Company
Disaggregation of Revenue [Line Items]
Operating Revenues	3,547,527	3,232,551	3,096,174
Lease revenue	800	1,000
NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	2,941,148	3,044,642	3,112,926
Lease revenue	2,700	2,700
Public Service Company of New Hampshire
Disaggregation of Revenue [Line Items]
Operating Revenues	1,079,095	1,065,936	1,047,619
Operating Segments | Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,038,600	6,912,100	6,986,300
Alternative Revenue Programs	88,100	45,900	(47,000)
Other Revenues	5,600	18,500	17,900
Operating Revenues	7,132,300	6,976,500	6,957,200
Operating Segments | Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,951,500	3,723,700	3,766,600
Operating Segments | Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,353,400	2,584,800	2,634,700
Operating Segments | Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	327,100	331,800	351,900
Operating Segments | Electric Distribution | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,632,000	6,640,300	6,753,200
Operating Segments | Electric Distribution | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Distribution | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	327,300	215,700	179,500
Operating Segments | Electric Distribution | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	74,700	54,800	65,900
Operating Segments | Electric Distribution | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	4,600	1,300	(12,300)
Operating Segments | Natural Gas Distribution
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,162,900	1,064,000	1,020,300
Alternative Revenue Programs	44,700	(4,900)	(1,200)
Other Revenues	1,100	3,100	3,100
Operating Revenues	1,208,700	1,062,200	1,022,200
Operating Segments | Natural Gas Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	644,900	555,100	542,500
Operating Segments | Natural Gas Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	361,900	347,600	334,800
Operating Segments | Natural Gas Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	107,400	96,900	96,000
Operating Segments | Natural Gas Distribution | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,114,200	999,600	973,300
Operating Segments | Natural Gas Distribution | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Natural Gas Distribution | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	43,000	55,400	57,500
Operating Segments | Natural Gas Distribution | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,600	2,800	(2,200)
Operating Segments | Natural Gas Distribution | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,100	6,200	(8,300)
Operating Segments | Electric Transmission
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,570,600	1,306,500	1,321,500
Alternative Revenue Programs	(35,200)	81,800	(35,200)
Other Revenues	700	700	0
Operating Revenues	1,536,100	1,389,000	1,286,300
Operating Segments | Electric Transmission | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Transmission | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Transmission | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Transmission | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Transmission | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,557,300	1,293,300	1,308,900
Operating Segments | Electric Transmission | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Electric Transmission | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	13,300	13,200	12,600
Operating Segments | Electric Transmission | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Water Distribution
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	219,600	209,000	206,000
Alternative Revenue Programs	(4,700)	4,600	5,400
Other Revenues	500	1,000	600
Operating Revenues	215,400	214,600	212,000
Operating Segments | Water Distribution | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	145,100	132,300	130,700
Operating Segments | Water Distribution | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	62,400	63,900	63,300
Operating Segments | Water Distribution | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	4,800	4,500	4,400
Operating Segments | Water Distribution | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	212,300	200,700	198,400
Operating Segments | Water Distribution | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Water Distribution | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,800	4,100	4,100
Operating Segments | Water Distribution | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,300	7,000	7,200
Operating Segments | Water Distribution | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(3,800)	(2,800)	(3,700)
Operating Segments | The Connecticut Light and Power Company
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	4,044,700	3,626,900	3,607,900
Alternative Revenue Programs	(4,200)	77,500	(65,900)
Other Revenues	2,200	10,300	8,500
Operating Segments | The Connecticut Light and Power Company | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,011,100	1,837,100	1,828,200
Operating Segments | The Connecticut Light and Power Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	878,300	922,900	928,100
Operating Segments | The Connecticut Light and Power Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	137,500	138,300	147,700
Operating Segments | The Connecticut Light and Power Company | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,026,900	2,898,300	2,904,000
Operating Segments | The Connecticut Light and Power Company | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	754,800	587,100	620,600
Operating Segments | The Connecticut Light and Power Company | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	230,100	105,100	48,300
Operating Segments | The Connecticut Light and Power Company | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	32,900	36,400	35,000
Operating Segments | The Connecticut Light and Power Company | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,327,500	3,396,400	3,491,100
Alternative Revenue Programs	54,500	41,600	900
Other Revenues	3,500	7,000	8,300
Operating Segments | NSTAR Electric Company | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,365,800	1,322,100	1,380,900
Operating Segments | NSTAR Electric Company | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,176,800	1,349,400	1,391,500
Operating Segments | NSTAR Electric Company | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	106,400	115,800	124,900
Operating Segments | NSTAR Electric Company | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,649,000	2,787,300	2,897,300
Operating Segments | NSTAR Electric Company | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	576,500	517,300	488,800
Operating Segments | NSTAR Electric Company | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	58,400	73,100	76,100
Operating Segments | NSTAR Electric Company | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	43,600	18,700	28,900
Operating Segments | NSTAR Electric Company | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Operating Segments | Public Service Company of New Hampshire
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,241,300	1,200,100	1,213,000
Alternative Revenue Programs	2,600	8,600	(17,300)
Other Revenues	600	1,900	1,100
Operating Segments | Public Service Company of New Hampshire | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	574,600	564,500	557,500
Operating Segments | Public Service Company of New Hampshire | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	299,900	314,600	316,900
Operating Segments | Public Service Company of New Hampshire | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	83,200	77,700	79,300
Operating Segments | Public Service Company of New Hampshire | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	957,700	956,800	953,700
Operating Segments | Public Service Company of New Hampshire | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	226,000	188,900	199,500
Operating Segments | Public Service Company of New Hampshire | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	38,800	37,500	56,600
Operating Segments | Public Service Company of New Hampshire | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	14,200	15,600	15,500
Operating Segments | Public Service Company of New Hampshire | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	4,600	1,300	(12,300)
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,235,900	1,028,500	936,300
Alternative Revenue Programs	0	0	0
Other Revenues	0	0	0
Operating Revenues	1,235,900	1,028,500	936,300
Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Other | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Other | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Other | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Other | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	74,200	61,300	47,300
Other | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Other | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,161,700	967,200	889,000
Other | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(2,461,100)	(2,070,100)	(1,997,700)
Alternative Revenue Programs	37,100	(74,200)	31,900
Other Revenues	0	0	0
Operating Revenues	(2,424,000)	(2,144,300)	(1,965,800)
Eliminations | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Eliminations | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(4,800)	(4,300)	(4,500)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(13,700)	(11,600)	(10,000)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(18,500)	(15,900)	(14,500)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(1,290,600)	(1,085,200)	(1,092,200)
Eliminations | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Eliminations | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(1,152,000)	(969,000)	(891,000)
Eliminations | Amortization of/(Reserve for) Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0
Consolidations Eliminations | The Connecticut Light and Power Company
Disaggregation of Revenue [Line Items]
Operating Revenues	(495,200)	(482,100)	(454,300)
Consolidations Eliminations | NSTAR Electric Company
Disaggregation of Revenue [Line Items]
Operating Revenues	(444,400)	(400,400)	(387,400)
Consolidations Eliminations | Public Service Company of New Hampshire
Disaggregation of Revenue [Line Items]
Operating Revenues	$ (165,400)	$ (144,700)	$ (149,200)

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)segment
Segment Reporting Information [Line Items]
Number of reportable segments	1
Yankee Gas, NSTAR Gas and EGMA
Segment Reporting Information [Line Items]
Amount of natural gas transmission purchased | $	$ 77.7
The Connecticut Light and Power Company
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric Company
Segment Reporting Information [Line Items]
Number of reportable segments	1
Public Service Company of New Hampshire
Segment Reporting Information [Line Items]
Number of reportable segments	1

SEGMENT INFORMATION - Schedule

SEGMENT INFORMATION - Schedule of Segment Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Operating Revenues	$ 8,904,430	$ 8,526,470	$ 8,448,201
Depreciation and Amortization	(1,159,100)	(1,080,700)	(1,072,000)
Impairment of Northern Pass Transmission	0	(239,644)	0
Other Operating Expenses	(5,756,600)	(5,615,700)	(5,676,300)
Operating Income	1,988,734	1,590,491	1,699,930
Interest Expense	(538,452)	(533,197)	(498,805)
Interest Income	4,800	12,800	18,100
Other Income, Net	103,800	120,000	110,300
Income Tax (Expense)/Benefit	(346,186)	(273,499)	(288,972)
Net Income	1,212,686	916,572	1,040,519
Net Income Attributable to Noncontrolling Interests	(7,519)	(7,519)	(7,519)
Net Income Attributable to Common Shareholders	1,205,167	909,053	1,033,000
Total Assets (as of)	46,099,598	41,123,915
Cash Flows Used for Investments in Plant	2,942,996	2,911,489	2,569,936
Operating Segments | Electric Distribution
Segment Reporting Information [Line Items]
Operating Revenues	7,132,300	6,976,500	6,957,200
Depreciation and Amortization	(657,000)	(651,300)	(671,800)
Impairment of Northern Pass Transmission		0
Other Operating Expenses	(5,642,300)	(5,525,100)	(5,548,600)
Operating Income	833,000	800,100	736,800
Interest Expense	(216,000)	(206,400)	(202,800)
Interest Income	3,200	13,300	18,700
Other Income, Net	58,000	46,800	67,500
Income Tax (Expense)/Benefit	(129,600)	(135,900)	(160,200)
Net Income	548,600	517,900	460,000
Net Income Attributable to Noncontrolling Interests	(4,600)	(4,600)	(4,600)
Net Income Attributable to Common Shareholders	544,000	513,300	455,400
Total Assets (as of)	24,981,900	22,541,900
Cash Flows Used for Investments in Plant	1,079,000	1,104,200	961,300
Operating Segments | Natural Gas Distribution
Segment Reporting Information [Line Items]
Operating Revenues	1,208,700	1,062,200	1,022,200
Depreciation and Amortization	(87,900)	(68,300)	(75,000)
Impairment of Northern Pass Transmission		0
Other Operating Expenses	(913,800)	(830,800)	(787,600)
Operating Income	207,000	163,100	159,600
Interest Expense	(40,000)	(47,400)	(44,100)
Interest Income	900	100	0
Other Income, Net	3,100	1,600	7,100
Income Tax (Expense)/Benefit	(36,900)	(21,200)	(29,400)
Net Income	134,100	96,200	93,200
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income Attributable to Common Shareholders	134,100	96,200	93,200
Total Assets (as of)	6,450,500	4,345,500
Cash Flows Used for Investments in Plant	494,400	460,200	351,500
Operating Segments | Electric Transmission
Segment Reporting Information [Line Items]
Operating Revenues	1,536,100	1,389,000	1,286,300
Depreciation and Amortization	(278,100)	(253,300)	(231,800)
Impairment of Northern Pass Transmission		(239,600)
Other Operating Expenses	(470,000)	(411,200)	(375,500)
Operating Income	788,000	484,900	679,000
Interest Expense	(126,800)	(125,700)	(120,600)
Interest Income	4,700	1,500	2,400
Other Income, Net	23,300	29,200	31,100
Income Tax (Expense)/Benefit	(183,800)	(130,500)	(161,800)
Net Income	505,400	259,400	430,100
Net Income Attributable to Noncontrolling Interests	(2,900)	(2,900)	(2,900)
Net Income Attributable to Common Shareholders	502,500	256,500	427,200
Total Assets (as of)	11,695,000	10,904,000
Cash Flows Used for Investments in Plant	1,004,600	987,000	976,200
Operating Segments | Water Distribution
Segment Reporting Information [Line Items]
Operating Revenues	215,400	214,600	212,000
Depreciation and Amortization	(44,200)	(46,900)	(46,500)
Impairment of Northern Pass Transmission		0
Other Operating Expenses	(86,600)	(101,000)	(99,800)
Operating Income	84,600	66,700	65,700
Interest Expense	(32,900)	(34,600)	(34,300)
Interest Income	0	0	0
Other Income, Net	2,000	400	(400)
Income Tax (Expense)/Benefit	(12,500)	2,400	(100)
Net Income	41,200	34,900	30,900
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income Attributable to Common Shareholders	41,200	34,900	30,900
Total Assets (as of)	2,375,200	2,351,700
Cash Flows Used for Investments in Plant	118,800	118,000	102,300
Other
Segment Reporting Information [Line Items]
Operating Revenues	1,235,900	1,028,500	936,300
Depreciation and Amortization	(93,500)	(63,200)	(49,100)
Impairment of Northern Pass Transmission		0
Other Operating Expenses	(1,071,900)	(891,300)	(831,500)
Operating Income	70,500	74,000	55,700
Interest Expense	(161,000)	(170,300)	(129,300)
Interest Income	37,800	48,700	30,300
Other Income, Net	1,382,900	945,300	1,092,100
Income Tax (Expense)/Benefit	16,600	11,700	62,500
Net Income	1,346,800	909,400	1,111,300
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income Attributable to Common Shareholders	1,346,800	909,400	1,111,300
Total Assets (as of)	22,089,400	18,843,700
Cash Flows Used for Investments in Plant	246,200	242,100	178,600
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(2,424,000)	(2,144,300)	(1,965,800)
Depreciation and Amortization	1,600	2,300	2,200
Impairment of Northern Pass Transmission		0
Other Operating Expenses	2,428,000	2,143,700	1,966,700
Operating Income	5,600	1,700	3,100
Interest Expense	38,300	51,200	32,300
Interest Income	(41,800)	(50,800)	(33,300)
Other Income, Net	(1,365,500)	(903,300)	(1,087,100)
Income Tax (Expense)/Benefit	0	0	0
Net Income	(1,363,400)	(901,200)	(1,085,000)
Net Income Attributable to Noncontrolling Interests	0	0	0
Net Income Attributable to Common Shareholders	(1,363,400)	(901,200)	(1,085,000)
Total Assets (as of)	(21,492,400)	(17,862,900)
Cash Flows Used for Investments in Plant	$ 0	$ 0	$ 0

ACQUISITION OF ASSETS OF COLU_3

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Narrative (Details) mi in Thousands	Nov. 01, 2022USD ($)	Nov. 01, 2021USD ($)	Oct. 09, 2020USD ($)customermi	Oct. 07, 2020USD ($)resetrateIncrease	Oct. 01, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Oct. 31, 2020USD ($)
Business Acquisition [Line Items]
Number of customers | customer			303,000
Operating revenues										$ 154,800,000
Pre-tax income										$ 13,900,000
Impairment loss					$ 0
Cash outflows for the acquisition of CMA							$ 1,113,252,000	$ 0	$ 0
TSA
Business Acquisition [Line Items]
TSA and pre-TSA costs						$ 15,900,000
Energy Efficiency expense						$ 2,000,000
DPU
Business Acquisition [Line Items]
Authorized regulatory ROE				9.70%
Authorized common equity ratio				53.25%
Approved rate base				$ 995,000,000
Number of rate base resets in agreement | reset				2
Term of agreement				8 years
Number of distribution rate increases | rateIncrease				2
DPU | Forecast [Member]
Business Acquisition [Line Items]
Rate increase approved	$ 10,000,000	$ 13,000,000
CMA
Business Acquisition [Line Items]
Consideration transferred			$ 1,100,000,000
Number of customers | customer			332,000
Number of communities served | customer			60
Length of natural gas pipeline | mi			5
Operating revenues							9,273,000,000	$ 9,103,000,000
Contingent liability for future refund to customers			$ 6,700,000
Energy relief fund liability			$ 56,800,000
Arrearage Forgiveness Fund											$ 15,400,000
Cash outflows for the acquisition of CMA							$ 1,110,000,000

ACQUISITION OF ASSETS OF COLU_4

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Preliminary Allocation of the Cash Purchase Price (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Oct. 09, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Goodwill	$ 4,445,988		$ 4,427,266
CMA
Business Acquisition [Line Items]
Current Assets		$ 145,000
Restricted Cash		57,000
PP&E		1,195,000
Goodwill		42,000
Other Noncurrent Assets, excluding Goodwill		128,000
Other Current Liabilities		(81,000)
Other Noncurrent Liabilities		(317,000)
Cash Purchase Price		$ 1,169,000

ACQUISITION OF ASSETS OF COLU_5

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Schedule of Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Business Acquisition [Line Items]
Operating Revenues			$ 154.8
CMA
Business Acquisition [Line Items]
Operating Revenues	$ 9,273	$ 9,103
Net Income Attributable to Common Shareholders	$ 1,265	$ 909
Basic EPS (in dollars per share)	$ 3.73	$ 2.83
Diluted EPS (in dollars per share)	$ 3.72	$ 2.82

GOODWILL - Narrative (Details)

GOODWILL - Narrative (Details) - USD ($)	Oct. 01, 2020	Dec. 31, 2020
Goodwill [Line Items]
Goodwill acquired		$ 42,000,000
Goodwill disposed of		23,000,000
Impairment loss	$ 0
Natural Gas Distribution
Goodwill [Line Items]
Goodwill acquired		42,000,000
Goodwill disposed of		0
Water Distribution
Goodwill [Line Items]
Goodwill acquired		0
Goodwill disposed of		23,000,000
Water Distribution | Hingham Water System
Goodwill [Line Items]
Goodwill disposed of		$ 23,600,000

GOODWILL - Summary of Goodwill

GOODWILL - Summary of Goodwill by Reportable Segment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Goodwill [Roll Forward]
Balance	$ 4,427,266
Acquisition of CMA Assets	42,000
Sale of Hingham water system	(23,000)
Balance	4,445,988
Electric Distribution
Goodwill [Roll Forward]
Balance	2,544,000
Acquisition of CMA Assets	0
Sale of Hingham water system	0
Balance	2,544,000
Electric Transmission
Goodwill [Roll Forward]
Balance	577,000
Acquisition of CMA Assets	0
Sale of Hingham water system	0
Balance	577,000
Water Distribution
Goodwill [Roll Forward]
Balance	907,000
Acquisition of CMA Assets	0
Sale of Hingham water system	(23,000)
Balance	884,000
Natural Gas Distribution
Goodwill [Roll Forward]
Balance	399,000
Acquisition of CMA Assets	42,000
Sale of Hingham water system	0
Balance	$ 441,000

SCHEDULE I - FINANCIAL INFORM_2

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - BALANCE SHEET (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash	$ 106,599	$ 15,432
Prepayments and Other Current Assets	252,439	342,135
Total Current Assets	3,130,143	2,414,539
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	1,107,143	871,633
Goodwill	4,445,988	4,427,266
Other Long-Term Assets	583,854	512,238
Total Deferred Debits and Other Assets	12,086,932	11,123,906
Total Assets (as of)	46,099,598	41,123,915
Current Liabilities:
Notes Payable	1,249,325	889,084
Long-Term Debt – Current Portion	1,053,186	327,411
Other Current Liabilities	809,214	836,834
Total Current Liabilities	4,915,012	3,605,563
Deferred Credits and Other Liabilities	11,342,662	10,421,838
Capitalization:
Long-Term Debt	15,125,876	13,770,828
Common Shareholders' Equity:
Common Shares	1,789,092	1,729,292
Capital Surplus, Paid in	8,015,663	7,087,768
Retained Earnings	4,613,201	4,177,048
Accumulated Other Comprehensive Loss	(76,411)	(65,059)
Treasury Stock	(277,979)	(299,055)
Stockholders' equity	14,063,566	12,629,994	$ 11,486,817	$ 11,086,242
Total Liabilities and Capitalization	46,099,598	41,123,915
Eversource
Current Assets:
Cash	434	1,469	$ 591	$ 521
Accounts Receivable from Subsidiaries	39,645	25,070
Notes Receivable from Subsidiaries	996,300	1,376,000
Prepayments and Other Current Assets	19,043	33,546
Total Current Assets	1,055,422	1,436,085
Deferred Debits and Other Assets:
Investments in Subsidiary Companies, at Equity	15,483,263	13,162,337
Notes Receivable from Subsidiaries	1,110,400	157,000
Accumulated Deferred Income Taxes	33,469	27,578
Goodwill	3,231,811	3,231,811
Other Long-Term Assets	90,735	92,394
Total Deferred Debits and Other Assets	19,949,678	16,671,120
Total Assets (as of)	21,005,100	18,107,205
Current Liabilities:
Notes Payable	1,054,325	878,584
Long-Term Debt – Current Portion	473,933	23,933
Accounts Payable to Subsidiaries	18,424	4,333
Other Current Liabilities	103,477	62,385
Total Current Liabilities	1,650,159	969,235
Deferred Credits and Other Liabilities	163,053	149,637
Capitalization:
Long-Term Debt	5,128,322	4,358,339
Common Shareholders' Equity:
Common Shares	1,789,092	1,729,292
Capital Surplus, Paid in	8,015,663	7,087,768
Retained Earnings	4,613,201	4,177,048
Accumulated Other Comprehensive Loss	(76,411)	(65,059)
Treasury Stock	(277,979)	(299,055)
Stockholders' equity	14,063,566	12,629,994
Total Liabilities and Capitalization	$ 21,005,100	$ 18,107,205

SCHEDULE I - FINANCIAL INFORM_3

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF INCOME (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 8,904,430	$ 8,526,470	$ 8,448,201
Operating Expenses:
Other	1,480,252	1,363,113	1,335,213
Operating Income (Loss)	1,988,734	1,590,491	1,699,930
Interest Expense	538,452	533,197	498,805
Other Income, Net:
Equity in Earnings of Subsidiaries	14,200	42,200	3,800
Other Income, Net	108,590	132,777	128,366
Income Before Income Tax Expense	1,558,872	1,190,071	1,329,491
Income Tax Benefit	346,186	273,499	288,972
Net Income	$ 1,212,686	$ 916,572	$ 1,040,519
Basic Earnings Per Common Share (in dollars per share)	$ 3.56	$ 2.83	$ 3.25
Diluted Earnings Per Common Share (in dollars per share)	$ 3.55	$ 2.81	$ 3.25
Weighted Average Common Shares Outstanding:
Basic (in shares)	338,836,147	321,416,086	317,370,369
Diluted (in shares)	339,847,062	322,941,636	317,993,934
Eversource
Condensed Income Statements, Captions [Line Items]
Operating Revenues	$ 0	$ 0	$ 0
Operating Expenses:
Other	28,645	50,100	(6,552)
Operating Income (Loss)	(28,645)	(50,100)	6,552
Interest Expense	160,887	163,937	123,638
Other Income, Net:
Equity in Earnings of Subsidiaries	1,309,630	1,001,526	1,049,748
Other, Net	38,546	68,137	47,581
Other Income, Net	1,348,176	1,069,663	1,097,329
Income Before Income Tax Expense	1,158,644	855,626	980,243
Income Tax Benefit	(46,523)	(53,427)	(52,757)
Net Income	$ 1,205,167	$ 909,053	$ 1,033,000
Basic Earnings Per Common Share (in dollars per share)	$ 3.56	$ 2.83	$ 3.25
Diluted Earnings Per Common Share (in dollars per share)	$ 3.55	$ 2.81	$ 3.25
Weighted Average Common Shares Outstanding:
Basic (in shares)	338,836,147	321,416,086	317,370,369
Diluted (in shares)	339,847,062	322,941,636	317,993,934

SCHEDULE I - FINANCIAL INFORM_4

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Income Captions [Line Items]
Net Income	$ 1,212,686	$ 916,572	$ 1,040,519
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,596	1,393	1,756
Changes in Unrealized Gains/(Losses) on Marketable Securities	342	1,166	(547)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(13,290)	(7,618)	5,194
Other Comprehensive (Loss)/Income, Net of Tax	(11,352)	(5,059)	6,403
Comprehensive Income	1,193,815	903,994	1,039,403
Eversource
Condensed Statement of Income Captions [Line Items]
Net Income	1,205,167	909,053	1,033,000
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,596	1,393	1,756
Changes in Unrealized Gains/(Losses) on Marketable Securities	342	1,166	(547)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(13,290)	(7,618)	5,194
Other Comprehensive (Loss)/Income, Net of Tax	(11,352)	(5,059)	6,403
Comprehensive Income	$ 1,193,815	$ 903,994	$ 1,039,403

SCHEDULE I - FINANCIAL INFORM_5

SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details) - USD ($) $ in Thousands	Jun. 15, 2020	Mar. 26, 2020	Mar. 23, 2020	Jun. 15, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net Income						$ 1,212,686	$ 916,572	$ 1,040,519
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries						(14,200)	(42,200)	(3,800)
Deferred Income Taxes						257,154	209,812	174,812
Other						(174,289)	(196,087)	(111,225)
Accounts Receivables from Subsidiaries						(351,843)	(98,716)	(141,433)
Taxes Receivable/Accrued, Net						43,819	(16,129)	(67,770)
Other Current Assets and Liabilities, Net						(9,591)	(11,603)	78,226
Net Cash Flows Provided by Operating Activities						1,682,572	2,009,577	1,830,543
Investing Activities:
Other Investing Activities						23,809	24,204	6,754
Net Cash Flows Used in Investing Activities						(4,129,275)	(3,274,288)	(2,437,046)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	$ 509,200	$ 314,100	$ 105,700	$ 929,000	$ 852,300	928,992	852,254	0
Cash Dividends on Common Shares						(744,665)	(663,239)	(640,110)
Issuance of Long-Term Debt						2,760,000	1,520,000	2,200,000
Retirement of Long-Term Debt						(327,236)	(801,078)	(1,050,330)
Decrease in Notes Payable								(379,310)
Other Financing Activities						14,273	(1,006)	(28,457)
Net Cash Flows Provided by/(Used in) Financing Activities						2,594,590	1,172,450	729,937
Cash, Cash Equivalents and Restricted Cash - Beginning of Year						15,432
Cash, Cash Equivalents and Restricted Cash - End of Year					15,432	106,599	15,432
Cash Paid/(Received) During the Year for:
Interest						518,000	532,400	503,200
Income Taxes						48,900	56,000	158,800
Eversource
Operating Activities:
Net Income						1,205,167	909,053	1,033,000
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries						(1,309,630)	(1,001,526)	(1,049,748)
Cash Dividends Received from Subsidiaries						485,800	883,000	569,500
Deferred Income Taxes						(4,667)	13,382	20,032
Other						39,940	19,584	(31,093)
Accounts Receivables from Subsidiaries						(14,575)	7,105	(28,716)
Taxes Receivable/Accrued, Net						35,300	(605)	(20,207)
Accounts Payable to Subsidiaries						14,091	(4,099)	(9,817)
Other Current Assets and Liabilities, Net						21,284	(2,503)	2,553
Net Cash Flows Provided by Operating Activities						472,710	823,391	485,504
Investing Activities:
Capital Contributions to Subsidiaries						(1,899,340)	(1,039,000)	(955,700)
Return of Capital from Subsidiaries						80,000	0	530,000
Increase in Notes Receivable from Subsidiaries						(264,300)	(218,100)	(158,210)
Other Investing Activities						(367)	(1,799)	(1,149)
Net Cash Flows Used in Investing Activities						(2,084,007)	(1,258,899)	(585,059)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs						928,992	852,254	0
Cash Dividends on Common Shares						(744,665)	(663,239)	(640,110)
Issuance of Long-Term Debt						1,550,000	0	1,550,000
Retirement of Long-Term Debt						0	(350,000)	(450,000)
Decrease in Notes Payable						(170,545)	593,370	(347,810)
Other Financing Activities						46,480	4,001	(12,455)
Net Cash Flows Provided by/(Used in) Financing Activities						1,610,262	436,386	99,625
Net (Decrease)/Increase in Cash						(1,035)	878	70
Cash, Cash Equivalents and Restricted Cash - Beginning of Year						1,469	591	521
Cash, Cash Equivalents and Restricted Cash - End of Year					$ 1,469	434	1,469	591
Cash Paid/(Received) During the Year for:
Interest						140,694	161,323	118,533
Income Taxes						$ (43,158)	$ (63,227)	$ (30,239)

SCHEDULE II - VALUATION AND Q_2

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA asset acquisition	$ 24,200
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 358,851	$ 224,821
Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		23,800
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
Increase due to CMA asset acquisition	$ 0
Allowance for uncollectible accounts for late fees and other receivable amounts	157,447	97,348
The Connecticut Light and Power Company | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		22,200
NSTAR Electric Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA asset acquisition	0
Allowance for uncollectible accounts for late fees and other receivable amounts	91,583	75,406
NSTAR Electric Company | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		(1,300)
Public Service Company of New Hampshire
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA asset acquisition	0
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 17,157	10,497
Public Service Company of New Hampshire | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		300
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	$ 224,821	212,723	$ 195,708
Additions, Charged to Costs and Expense	53,461	63,446	61,337
Additions, Charged to Other Accounts	145,005	57,223	48,671
Deductions	64,436	108,571	92,993
Balance at end of period	358,851	224,821	212,723
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	97,348	88,034	78,872
Additions, Charged to Costs and Expense	12,882	15,947	15,831
Additions, Charged to Other Accounts	71,223	38,935	29,524
Deductions	24,006	45,568	36,193
Balance at end of period	157,447	97,348	88,034
Allowance for Doubtful Accounts | NSTAR Electric Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	75,406	74,516	69,666
Additions, Charged to Costs and Expense	15,293	25,079	22,279
Additions, Charged to Other Accounts	23,424	12,556	14,971
Deductions	22,540	36,745	32,400
Balance at end of period	91,583	75,406	74,516
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	10,497	11,065	10,481
Additions, Charged to Costs and Expense	5,164	6,726	6,383
Additions, Charged to Other Accounts	7,692	872	953
Deductions	6,196	8,166	6,752
Balance at end of period	$ 17,157	$ 10,497	$ 11,065