The Connecticut Light and Power Company (CNLPM) 10-Q 5 Nov 21 2021 Q3 Quarterly report Financial data

COVER PAGE

COVER PAGE - shares	9 Months Ended
	Sep. 30, 2021	Oct. 31, 2021
Document And Entity [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
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	001-05324
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		343,805,812
Entity Central Index Key	0000072741
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false
The Connecticut Light and Power Company
Document And Entity [Line Items]
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	000-00404
Entity Tax Identification Number	06-0303850
Entity Filer Category	Non-accelerated Filer
Entity Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Entity Central Index Key	0000023426
Current Fiscal Year End Date	--12-31
NSTAR Electric Company
Document And Entity [Line Items]
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	001-02301
Entity Tax Identification Number	04-1278810
Entity Filer Category	Non-accelerated Filer
Entity Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		200
Entity Central Index Key	0000013372
Current Fiscal Year End Date	--12-31
Public Service Company of New Hampshire
Document And Entity [Line Items]
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	001-06392
Entity Tax Identification Number	02-0181050
Entity Filer Category	Non-accelerated Filer
Entity Smaller Reporting Company	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		301
Entity Central Index Key	0000315256
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets:
Cash	$ 88,204	$ 106,599
Receivables, Net (net of allowance for uncollectible accounts)	1,288,758	1,195,925
Unbilled Revenues	176,325	233,025
Fuel, Materials, Supplies and REC Inventory	217,286	265,599
Regulatory Assets	1,016,304	1,076,556
Prepayments	177,869	105,620
Other Current Assets	108,807	146,819
Total Current Assets	3,073,553	3,130,143
Property, Plant and Equipment, Net	32,467,069	30,882,523
Deferred Debits and Other Assets:
Regulatory Assets	5,458,928	5,493,330
Goodwill	4,453,618	4,445,988
Investments in Unconsolidated Affiliates	1,356,313	1,107,143
Marketable Securities	466,628	456,617
Other Long-Term Assets	737,946	583,854
Total Deferred Debits and Other Assets	12,473,433	12,086,932
Total Assets	48,014,055	46,099,598
Current Liabilities:
Notes Payable	711,000	1,249,325
Long-Term Debt – Current Portion	798,880	1,053,186
Rate Reduction Bonds – Current Portion	43,210	43,210
Accounts Payable	1,289,225	1,370,647
Regulatory Liabilities	612,931	389,430
Other Current Liabilities	802,831	809,214
Total Current Liabilities	4,258,077	4,915,012
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	4,341,105	4,095,339
Regulatory Liabilities	3,907,582	3,850,781
Derivative Liabilities	256,569	294,535
Asset Retirement Obligations	505,005	499,713
Accrued Pension, SERP and PBOP	1,330,037	1,653,788
Other Long-Term Liabilities	974,497	948,506
Total Deferred Credits and Other Liabilities	11,314,795	11,342,662
Long-Term Debt	17,420,300	15,125,876
Rate Reduction Bonds	453,702	496,912
Noncontrolling Interest – Preferred Stock of Subsidiaries	155,570	155,570
Common Shareholders' Equity:
Common Shares	1,789,092	1,789,092
Capital Surplus, Paid In	8,050,872	8,015,663
Retained Earnings	4,906,151	4,613,201
Accumulated Other Comprehensive Income (Loss)	(71,865)	(76,411)
Treasury Stock	(262,639)	(277,979)
Common Shareholders' Equity	14,411,611	14,063,566
Commitments and Contingencies (Note 9)
Total Liabilities and Capitalization	48,014,055	46,099,598
The Connecticut Light and Power Company
Current Assets:
Cash	62,791	90,801
Receivables, Net (net of allowance for uncollectible accounts)	549,144	459,214
Accounts Receivable from Affiliated Companies	38,544	17,486
Unbilled Revenues	52,589	57,407
Fuel, Materials, Supplies and REC Inventory	54,894	57,924
Regulatory Assets	325,268	345,622
Prepaid Property Taxes	76,829	25,779
Other Current Assets	47,402	58,171
Total Current Assets	1,207,461	1,112,404
Property, Plant and Equipment, Net	10,598,836	10,234,556
Deferred Debits and Other Assets:
Regulatory Assets	1,981,805	1,866,152
Other Long-Term Assets	267,312	242,862
Total Deferred Debits and Other Assets	2,249,117	2,109,014
Total Assets	14,055,414	13,455,974
Current Liabilities:
Accounts Payable	473,287	451,240
Accounts Payable to Affiliated Companies	98,298	51,118
Obligations to Third Party Suppliers	53,183	49,967
Regulatory Liabilities	311,269	137,166
Derivative Liabilities	72,249	68,767
Other Current Liabilities	168,547	102,060
Total Current Liabilities	1,176,833	860,318
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,495,407	1,408,343
Regulatory Liabilities	1,213,469	1,204,942
Derivative Liabilities	256,569	294,535
Accrued Pension, SERP and PBOP	313,206	478,325
Other Long-Term Liabilities	154,249	133,690
Total Deferred Credits and Other Liabilities	3,432,900	3,519,835
Long-Term Debt	4,215,096	3,914,835
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	2,810,765
Retained Earnings	2,243,004	2,173,367
Accumulated Other Comprehensive Income (Loss)	264	302
Common Shareholders' Equity	5,114,385	5,044,786
Commitments and Contingencies (Note 9)
Total Liabilities and Capitalization	14,055,414	13,455,974
NSTAR Electric Company
Current Assets:
Cash	3,538	102
Receivables, Net (net of allowance for uncollectible accounts)	489,503	403,045
Accounts Receivable from Affiliated Companies	27,417	30,095
Unbilled Revenues	47,844	38,342
Fuel, Materials, Supplies and REC Inventory	83,667	133,894
Taxes Receivable	0	65,051
Regulatory Assets	388,408	399,882
Other Current Assets	22,490	21,833
Total Current Assets	1,062,867	1,092,244
Property, Plant and Equipment, Net	10,611,728	10,123,062
Deferred Debits and Other Assets:
Regulatory Assets	1,247,715	1,304,019
Prepaid PBOP	224,244	204,138
Other Long-Term Assets	185,555	162,836
Total Deferred Debits and Other Assets	1,657,514	1,670,993
Total Assets	13,332,109	12,886,299
Current Liabilities:
Notes Payable	138,000	195,000
Notes Payable to Eversource Parent	24,600	21,300
Long-Term Debt – Current Portion	0	250,000
Accounts Payable	338,369	383,558
Accounts Payable to Affiliated Companies	78,974	95,703
Obligations to Third Party Suppliers	137,211	98,572
Renewable Portfolio Standards Compliance Obligations	72,124	127,536
Regulatory Liabilities	205,771	164,761
Other Current Liabilities	118,747	72,118
Total Current Liabilities	1,113,796	1,408,548
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	1,494,976	1,459,906
Regulatory Liabilities	1,561,572	1,550,390
Accrued Pension, SERP and PBOP	110,752	172,571
Other Long-Term Liabilities	344,088	337,245
Total Deferred Credits and Other Liabilities	3,511,388	3,520,112
Long-Term Debt	3,984,724	3,393,221
Noncontrolling Interest – Preferred Stock of Subsidiaries	43,000	43,000
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	2,053,942	1,993,942
Retained Earnings	2,624,784	2,527,167
Accumulated Other Comprehensive Income (Loss)	475	309
Common Shareholders' Equity	4,679,201	4,521,418
Commitments and Contingencies (Note 9)
Total Liabilities and Capitalization	13,332,109	12,886,299
Public Service Company of New Hampshire
Current Assets:
Cash	3,869	141
Receivables, Net (net of allowance for uncollectible accounts)	136,481	119,899
Accounts Receivable from Affiliated Companies	13,866	10,925
Unbilled Revenues	46,854	46,041
Fuel, Materials, Supplies and REC Inventory	24,789	26,829
Regulatory Assets	97,948	115,852
Prepaid Property Taxes	5,987	26,257
Special Deposits	18,605	36,767
Other Current Assets	2,851	10,788
Total Current Assets	351,250	393,499
Property, Plant and Equipment, Net	3,529,050	3,374,270
Deferred Debits and Other Assets:
Regulatory Assets	829,848	873,203
Other Long-Term Assets	22,684	23,733
Total Deferred Debits and Other Assets	852,532	896,936
Total Assets	4,732,832	4,664,705
Current Liabilities:
Notes Payable to Eversource Parent	66,500	46,300
Long-Term Debt – Current Portion	0	282,000
Rate Reduction Bonds – Current Portion	43,210	43,210
Accounts Payable	108,243	132,635
Accounts Payable to Affiliated Companies	25,055	43,397
Regulatory Liabilities	96,817	58,756
Other Current Liabilities	61,883	58,487
Total Current Liabilities	401,708	664,785
Deferred Credits and Other Liabilities:
Accumulated Deferred Income Taxes	535,656	537,627
Regulatory Liabilities	389,426	383,183
Accrued Pension, SERP and PBOP	162,115	184,715
Other Long-Term Liabilities	35,564	37,874
Total Deferred Credits and Other Liabilities	1,122,761	1,143,399
Long-Term Debt	1,163,630	817,070
Rate Reduction Bonds	453,702	496,912
Common Shareholders' Equity:
Common Shares	0	0
Capital Surplus, Paid In	1,088,134	928,134
Retained Earnings	502,870	615,018
Accumulated Other Comprehensive Income (Loss)	27	(613)
Common Shareholders' Equity	1,591,031	1,542,539
Commitments and Contingencies (Note 9)
Total Liabilities and Capitalization	$ 4,732,832	$ 4,664,705

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Allowance for uncollectible accounts	$ 441,723	$ 358,851
The Connecticut Light and Power Company
Allowance for uncollectible accounts	195,463	157,447
NSTAR Electric Company
Allowance for uncollectible accounts	105,020	91,583
Public Service Company of New Hampshire
Allowance for uncollectible accounts	$ 16,996	$ 17,157

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Revenues	$ 2,432,794	$ 2,343,642	$ 7,381,172	$ 6,670,497
Operating Expenses:
Purchased Power, Fuel and Transmission	880,639	806,254	2,529,217	2,312,957
Operations and Maintenance	389,065	332,031	1,265,754	1,006,148
Depreciation	276,846	244,453	822,197	721,179
Amortization	45,236	57,515	158,860	130,687
Energy Efficiency Programs	143,796	145,047	460,814	408,794
Taxes Other Than Income Taxes	213,881	197,112	623,827	556,726
Total Operating Expenses	1,949,463	1,782,412	5,860,669	5,136,491
Operating Income/(Loss)	483,331	561,230	1,520,503	1,534,006
Interest Expense	147,962	134,066	431,162	403,067
Other Income, Net	43,768	29,218	124,588	83,565
Income Before Income Tax Expense	379,137	456,382	1,213,929	1,214,504
Income Tax Expense	94,091	108,242	294,461	275,621
Net Income	285,046	348,140	919,468	938,883
Net Income Attributable to Noncontrolling Interests	1,880	1,880	5,639	5,639
Net Income Attributable to Common Shareholders	$ 283,166	$ 346,260	$ 913,829	$ 933,244
Basic Earnings Per Common Share (in dollars per share)	$ 0.82	$ 1.01	$ 2.66	$ 2.77
Diluted Earnings Per Common Share (in dollars per share)	$ 0.82	$ 1.01	$ 2.65	$ 2.76
Weighted Average Common Shares Outstanding:
Basic (in shares)	344,023,846	343,076,614	343,848,905	337,375,172
Diluted (in shares)	344,669,782	343,773,602	344,480,056	338,424,100
The Connecticut Light and Power Company
Operating Revenues	$ 919,643	$ 994,270	$ 2,736,513	$ 2,711,394
Operating Expenses:
Purchased Power, Fuel and Transmission	392,301	399,117	1,073,712	1,089,232
Operations and Maintenance	137,816	147,487	465,630	417,717
Depreciation	85,304	80,583	253,132	238,735
Amortization of Regulatory Assets, Net	28,921	36,365	76,637	37,215
Energy Efficiency Programs	35,714	41,829	100,810	109,655
Taxes Other Than Income Taxes	99,901	97,715	275,178	260,571
Total Operating Expenses	779,957	803,096	2,245,099	2,153,125
Operating Income/(Loss)	139,686	191,174	491,414	558,269
Interest Expense	42,778	38,369	124,371	114,972
Other Income, Net	6,903	5,917	21,690	16,273
Income Before Income Tax Expense	103,811	158,722	388,733	459,570
Income Tax Expense	33,658	38,625	104,626	103,464
Net Income	70,153	120,097	284,107	356,106
NSTAR Electric Company
Operating Revenues	918,698	875,371	2,343,116	2,270,174
Operating Expenses:
Purchased Power, Fuel and Transmission	294,052	267,375	711,667	702,117
Operations and Maintenance	142,074	131,143	421,649	369,293
Depreciation	84,820	80,366	251,530	238,232
Amortization of Regulatory Assets, Net	8,073	22,527	23,963	69,139
Energy Efficiency Programs	86,699	85,244	226,071	210,666
Taxes Other Than Income Taxes	54,723	54,680	163,501	153,985
Total Operating Expenses	670,441	641,335	1,798,381	1,743,432
Operating Income/(Loss)	248,257	234,036	544,735	526,742
Interest Expense	37,329	31,029	106,829	95,000
Other Income, Net	20,215	12,802	58,941	38,152
Income Before Income Tax Expense	231,143	215,809	496,847	469,894
Income Tax Expense	53,692	50,081	114,560	106,309
Net Income	177,451	165,728	382,287	363,585
Public Service Company of New Hampshire
Operating Revenues	314,893	283,669	887,177	815,261
Operating Expenses:
Purchased Power, Fuel and Transmission	107,353	96,612	279,475	273,311
Operations and Maintenance	57,041	50,657	168,242	151,802
Depreciation	30,169	25,410	89,462	74,494
Amortization of Regulatory Assets, Net	17,922	7,360	62,744	39,034
Energy Efficiency Programs	10,762	11,081	30,475	29,231
Taxes Other Than Income Taxes	24,038	18,174	69,639	58,331
Total Operating Expenses	247,285	209,294	700,037	626,203
Operating Income/(Loss)	67,608	74,375	187,140	189,058
Interest Expense	14,321	14,942	42,774	44,029
Other Income, Net	3,171	4,065	11,598	10,882
Income Before Income Tax Expense	56,458	63,498	155,964	155,911
Income Tax Expense	12,315	16,347	32,512	37,527
Net Income	$ 44,143	$ 47,151	$ 123,452	$ 118,384

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Net Income	$ 285,046	$ 348,140	$ 919,468	$ 938,883
Other Comprehensive Income (Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	115	602	967	1,218
Changes in Unrealized (Losses)/Gains on Marketable Securities	(106)	(134)	(569)	295
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	2,468	1,693	4,148	3,149
Net OCI	2,477	2,161	4,546	4,662
Comprehensive Income Attributable to Noncontrolling Interests	(1,880)	(1,880)	(5,639)	(5,639)
Comprehensive Income Attributable to Common Shareholders	285,643	348,421	918,375	937,906
The Connecticut Light and Power Company
Net Income	70,153	120,097	284,107	356,106
Other Comprehensive Income (Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	(7)	(7)	(20)	(20)
Changes in Unrealized (Losses)/Gains on Marketable Securities	(2)	(4)	(18)	11
Net OCI	(9)	(11)	(38)	(9)
Comprehensive Income Attributable to Common Shareholders	70,144	120,086	284,069	356,097
NSTAR Electric Company
Net Income	177,451	165,728	382,287	363,585
Other Comprehensive Income (Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	5	109	293	327
Changes in Unrealized (Losses)/Gains on Marketable Securities	(1)	(1)	(5)	2
Changes in Funded Status of Pension, SERP and PBOP Benefit Plans	(40)	(43)	(122)	(129)
Net OCI	(36)	65	166	200
Comprehensive Income Attributable to Common Shareholders	177,415	165,793	382,453	363,785
Public Service Company of New Hampshire
Net Income	44,143	47,151	123,452	118,384
Other Comprehensive Income (Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments	109	268	673	806
Changes in Unrealized (Losses)/Gains on Marketable Securities	(6)	(8)	(33)	17
Net OCI	103	260	640	823
Comprehensive Income Attributable to Common Shareholders	$ 44,246	$ 47,411	$ 124,092	$ 119,207

CONDENSED CONSOLIDATED STATEM_3

CONDENSED 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)/Income	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)/Income	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)/Income	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)/Income
Balance (in shares) at Dec. 31, 2019			329,880,645								6,035,205							200							301
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	336,633				336,633				118,738				118,738			100,390				100,390			39,601				39,601
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(187,462)				(187,462)				(69,500)				(69,500)			(196,500)				(196,500)			(22,300)				(22,300)
Issuance of Common Shares (in shares)			5,960,000
Issuance of Common Shares	432,100		$ 29,800	402,300
Long-Term Incentive Plan Activity	(15,295)			(15,295)
Issuance of Treasury Shares (in shares)			570,542
Issuance of Treasury Shares	27,746			17,230				10,516
Capital Stock Expense	(12,314)			(12,314)
Other Comprehensive Income (Loss)	1,948						1,948		(1)						(1)	67						67	278						278
Balance (in shares) at Mar. 31, 2020			336,411,187								6,035,205							200							301
Balance at Mar. 31, 2020	13,209,956		$ 1,759,092	7,479,689	4,322,825		(63,111)	(288,539)	4,434,772		$ 60,352	2,535,765	1,838,340		315	4,063,190		$ 0	1,813,442	2,249,526		222	1,409,012		$ 0	903,134	507,307		(1,429)
Balance (in shares) at Dec. 31, 2019			329,880,645								6,035,205							200							301
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	938,883								356,106							363,585							118,384
Dividends on Preferred Stock	(5,600)
Other Comprehensive Income (Loss)	4,662								(9)							200							823
Balance (in shares) at Sep. 30, 2020			342,797,473								6,035,205							200							301
Balance at Sep. 30, 2020	13,980,017		$ 1,789,092	7,996,976	4,535,860		(60,397)	(281,514)	4,794,352		$ 60,352	2,660,765	2,072,928		307	4,325,539		$ 0	1,813,442	2,511,742		355	1,488,340		$ 0	903,134	586,090		(884)
Balance (in shares) at Mar. 31, 2020			336,411,187								6,035,205							200							301
Balance at Mar. 31, 2020	13,209,956		$ 1,759,092	7,479,689	4,322,825		(63,111)	(288,539)	4,434,772		$ 60,352	2,535,765	1,838,340		315	4,063,190		$ 0	1,813,442	2,249,526		222	1,409,012		$ 0	903,134	507,307		(1,429)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	254,112				254,112				117,271				117,271			97,468				97,468			31,632				31,632
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(190,964)				(190,964)
Issuance of Common Shares (in shares)			6,000,000
Issuance of Common Shares	517,560		$ 30,000	487,560
Long-Term Incentive Plan Activity	7,694			7,694
Issuance of Treasury Shares (in shares)			216,675
Issuance of Treasury Shares	16,548			12,524				4,024
Capital Stock Expense	(8,321)			(8,321)
Other Comprehensive Income (Loss)	553						553		3						3	68						68	285						285
Balance (in shares) at Jun. 30, 2020			342,627,862								6,035,205							200							301
Balance at Jun. 30, 2020	13,805,258		$ 1,789,092	7,979,146	4,384,093		(62,558)	(284,515)	4,550,656		$ 60,352	2,535,765	1,954,221		318	4,160,236		$ 0	1,813,442	2,346,504		290	1,440,929		$ 0	903,134	538,939		(1,144)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	348,140				348,140				120,097				120,097			165,728				165,728			47,151				47,151
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(194,493)				(194,493)
Capital Contributions from Eversource Parent									125,000			125,000
Long-Term Incentive Plan Activity	6,921			6,921
Issuance of Treasury Shares (in shares)			169,611
Issuance of Treasury Shares	13,910			10,909				3,001
Other Comprehensive Income (Loss)	2,161						2,161		(11)						(11)	65						65	260						260
Balance (in shares) at Sep. 30, 2020			342,797,473								6,035,205							200							301
Balance at Sep. 30, 2020	$ 13,980,017		$ 1,789,092	7,996,976	4,535,860		(60,397)	(281,514)	4,794,352		$ 60,352	2,660,765	2,072,928		307	4,325,539		$ 0	1,813,442	2,511,742		355	1,488,340		$ 0	903,134	586,090		(884)
Balance (in shares) at Dec. 31, 2020	342,954,023		342,954,023								6,035,205							200							301
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	368,023				368,023				98,398				98,398			93,924				93,924			44,676				44,676
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(206,913)				(206,913)				(70,100)				(70,100)			(206,400)				(206,400)			(25,200)				(25,200)
Long-Term Incentive Plan Activity	(15,727)			(15,727)
Issuance of Treasury Shares (in shares)			480,275
Issuance of Treasury Shares	25,163			16,182				8,981
Other Comprehensive Income (Loss)	1,188						1,188		(32)						(32)	61						61	255						255
Balance (in shares) at Mar. 31, 2021			343,434,298								6,035,205							200							301
Balance at Mar. 31, 2021	$ 14,233,420		$ 1,789,092	8,016,118	4,772,431		(75,223)	(268,998)	5,071,662		$ 60,352	2,810,765	2,200,275		270	4,408,513		$ 0	1,993,942	2,414,201		370	1,562,270		$ 0	928,134	634,494		(358)
Balance (in shares) at Dec. 31, 2020	342,954,023		342,954,023								6,035,205							200							301
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	919,468								284,107							382,287							123,452
Dividends on Preferred Stock	(5,600)
Other Comprehensive Income (Loss)	$ 4,546								(38)							166							640
Balance (in shares) at Sep. 30, 2021	343,774,324		343,774,324								6,035,205							200							301
Balance at Sep. 30, 2021	$ 14,411,611		$ 1,789,092	8,050,872	4,906,151		(71,865)	(262,639)	5,114,385		$ 60,352	2,810,765	2,243,004		264	4,679,201		$ 0	2,053,942	2,624,784		475	1,591,031		$ 0	1,088,134	502,870		27
Balance (in shares) at Mar. 31, 2021			343,434,298								6,035,205							200							301
Balance at Mar. 31, 2021	14,233,420		$ 1,789,092	8,016,118	4,772,431		(75,223)	(268,998)	5,071,662		$ 60,352	2,810,765	2,200,275		270	4,408,513		$ 0	1,993,942	2,414,201		370	1,562,270		$ 0	928,134	634,494		(358)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	266,400				266,400				115,556				115,556			110,912				110,912			34,633				34,633
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(206,893)				(206,893)				(70,100)				(70,100)			(76,800)				(76,800)			(185,200)				(185,200)
Capital Contributions from Eversource Parent																60,000			60,000				160,000			160,000
Long-Term Incentive Plan Activity	6,162			6,162
Issuance of Treasury Shares (in shares)			166,805
Issuance of Treasury Shares	13,799			10,679				3,120
Other Comprehensive Income (Loss)	881						881		3						3	141						141	282						282
Balance (in shares) at Jun. 30, 2021			343,601,103								6,035,205							200							301
Balance at Jun. 30, 2021	14,311,889		$ 1,789,092	8,032,959	4,830,058		(74,342)	(265,878)	5,115,731		$ 60,352	2,810,765	2,244,341		273	4,502,276		$ 0	2,053,942	2,447,823		511	1,571,985		$ 0	1,088,134	483,927		(76)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	285,046				285,046				70,153				70,153			177,451				177,451			44,143				44,143
Dividends on Preferred Stock	(1,880)				(1,880)				(1,390)				(1,390)			(490)				(490)
Dividends on Common Stock	(207,073)				(207,073)				(70,100)				(70,100)										(25,200)				(25,200)
Long-Term Incentive Plan Activity	6,478			6,478
Issuance of Treasury Shares (in shares)			173,221
Issuance of Treasury Shares	14,674			11,435				3,239
Other Comprehensive Income (Loss)	$ 2,477						2,477		(9)						(9)	(36)						(36)	103						103
Balance (in shares) at Sep. 30, 2021	343,774,324		343,774,324								6,035,205							200							301
Balance at Sep. 30, 2021	$ 14,411,611		$ 1,789,092	$ 8,050,872	$ 4,906,151		$ (71,865)	$ (262,639)	$ 5,114,385		$ 60,352	$ 2,810,765	$ 2,243,004		$ 264	$ 4,679,201		$ 0	$ 2,053,942	$ 2,624,784		$ 475	$ 1,591,031		$ 0	$ 1,088,134	$ 502,870		$ 27

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Dividends on Common Shares (in dollars per share)	$ 0.6025	$ 0.6025	$ 0.6025	$ 0.5675	$ 0.5675	$ 0.5675
Par value (in dollars per share)	$ 5				$ 5	$ 5

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENT OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities:
Net Income	$ 919,468	$ 938,883
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	822,197	721,179
Deferred Income Taxes	191,346	156,795
Uncollectible Expense	39,690	31,101
Pension, SERP and PBOP (Income)/Expense, Net	(10,882)	9,153
Pension and PBOP Contributions	(140,000)	(107,985)
Regulatory Over/(Under) Recoveries, Net	87,455	(29,287)
Charges at CL&P related to PURA Settlement Agreement and Storm Performance Penalty	103,583	0
Amortization	158,860	130,687
Other	(229,878)	(69,216)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(158,205)	(193,895)
Fuel, Materials, Supplies and REC Inventory	48,312	21,102
Taxes Receivable/Accrued, Net	44,003	89,759
Accounts Payable	(258,509)	(121,034)
Other Current Assets and Liabilities, Net	(97,167)	(81,033)
Net Cash Flows Provided by Operating Activities	1,520,273	1,496,209
Investing Activities:
Investments in Property, Plant and Equipment	(2,211,136)	(2,101,564)
Proceeds from Sales of Marketable Securities	334,619	386,712
Purchases of Marketable Securities	(313,961)	(391,368)
Proceeds from the Sale of Hingham Water System	0	110,536
Investments in Unconsolidated Affiliates, Net	(245,245)	(31,677)
Other Investing Activities	17,436	17,647
Net Cash Flows Used in Investing Activities	(2,418,287)	(2,009,714)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	0	929,025
Cash Dividends on Common Shares	(603,611)	(555,655)
Cash Dividends on Preferred Stock	(5,639)	(5,639)
Decrease in Notes Payable	(458,325)	(1,174,870)
Repayment of Rate Reduction Bonds	(43,210)	(43,210)
Issuance of Long-Term Debt	3,150,000	2,360,000
Retirement of Long-Term Debt	(1,142,500)	(302,236)
Other Financing Activities	(45,522)	18,030
Net Cash Flows (Used in)/Provided by Financing Activities	851,193	1,225,445
Net (Decrease)/Increase in Cash and Restricted Cash	(46,821)	711,940
Cash and Restricted Cash - Beginning of Period	264,950	117,063
Cash and Restricted Cash - End of Period	218,129	829,003
The Connecticut Light and Power Company
Operating Activities:
Net Income	284,107	356,106
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	253,132	238,735
Deferred Income Taxes	77,147	92,590
Uncollectible Expense	10,183	10,013
Pension, SERP and PBOP (Income)/Expense, Net	4,478	8,629
Pension and PBOP Contributions	(78,913)	(23,200)
Regulatory Over/(Under) Recoveries, Net	(19,404)	(32,051)
Charges at CL&P related to PURA Settlement Agreement and Storm Performance Penalty	103,583	0
Amortization of Regulatory Assets, Net	76,637	37,215
Other	(74,179)	(63,525)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(165,423)	(153,464)
Taxes Receivable/Accrued, Net	45,762	(1,515)
Accounts Payable	(54,226)	(1,976)
Other Current Assets and Liabilities, Net	(12,315)	(68,316)
Net Cash Flows Provided by Operating Activities	450,569	399,241
Investing Activities:
Investments in Property, Plant and Equipment	(563,234)	(609,690)
Other Investing Activities	251	496
Net Cash Flows Used in Investing Activities	(562,983)	(609,194)
Financing Activities:
Cash Dividends on Common Shares	(210,300)	(69,500)
Cash Dividends on Preferred Stock	(4,169)	(4,169)
Issuance of Long-Term Debt	425,000	0
Retirement of Long-Term Debt	(120,500)	0
Capital Contributions from Eversource Parent	0	125,000
Increase in Notes Payable to Eversource Parent	0	172,100
Other Financing Activities	(5,664)	(1,214)
Net Cash Flows (Used in)/Provided by Financing Activities	84,367	222,217
Net (Decrease)/Increase in Cash and Restricted Cash	(28,047)	12,264
Cash and Restricted Cash - Beginning of Period	99,809	4,971
Cash and Restricted Cash - End of Period	71,762	17,235
NSTAR Electric Company
Operating Activities:
Net Income	382,287	363,585
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	251,530	238,232
Deferred Income Taxes	12,905	13,436
Uncollectible Expense	12,477	11,321
Pension, SERP and PBOP Income, Net	(19,627)	(13,714)
Pension and PBOP Contributions	(10,000)	(650)
Regulatory Over/(Under) Recoveries, Net	86,111	(20,047)
Amortization of Regulatory Assets, Net	23,963	69,139
Other	(71,005)	(25,508)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(110,336)	(104,528)
Fuel, Materials, Supplies and REC Inventory	50,227	27,709
Taxes Receivable/Accrued, Net	109,561	55,405
Accounts Payable	(85,431)	(57,300)
Other Current Assets and Liabilities, Net	(15,322)	(54,481)
Net Cash Flows Provided by Operating Activities	617,340	502,599
Investing Activities:
Investments in Property, Plant and Equipment	(675,245)	(655,039)
Other Investing Activities	70	138
Net Cash Flows Used in Investing Activities	(675,175)	(654,901)
Financing Activities:
Cash Dividends on Common Shares	(283,200)	(196,500)
Cash Dividends on Preferred Stock	(1,470)	(1,470)
Increase in Notes Payable to Eversource Parent	3,300	6,300
Decrease in Notes Payable	(57,000)	50,000
Issuance of Long-Term Debt	600,000	400,000
Retirement of Long-Term Debt	(250,000)	(95,000)
Capital Contributions from Eversource Parent	60,000	0
Other Financing Activities	(10,367)	(4,931)
Net Cash Flows (Used in)/Provided by Financing Activities	61,263	158,399
Net (Decrease)/Increase in Cash and Restricted Cash	3,428	6,097
Cash and Restricted Cash - Beginning of Period	17,410	6,312
Cash and Restricted Cash - End of Period	20,838	12,409
Public Service Company of New Hampshire
Operating Activities:
Net Income	123,452	118,384
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Depreciation	89,462	74,494
Deferred Income Taxes	(13,385)	13,959
Uncollectible Expense	4,381	2,058
Pension, SERP and PBOP (Income)/Expense, Net	(2,664)	(894)
Pension Contributions	0	(19,500)
Regulatory Over/(Under) Recoveries, Net	29,029	(22,203)
Amortization of Regulatory Assets, Net	62,744	39,034
Other	(22,738)	(7,545)
Changes in Current Assets and Liabilities:
Receivables and Unbilled Revenues, Net	(25,607)	(24,562)
Fuel, Materials, Supplies and REC Inventory	2,040	(301)
Taxes Receivable/Accrued, Net	22,286	1,313
Accounts Payable	(42,654)	(29,388)
Other Current Assets and Liabilities, Net	10,826	4,363
Net Cash Flows Provided by Operating Activities	237,172	149,212
Investing Activities:
Investments in Property, Plant and Equipment	(217,414)	(248,899)
Other Investing Activities	431	1,969
Net Cash Flows Used in Investing Activities	(216,983)	(246,930)
Financing Activities:
Cash Dividends on Common Shares	(235,600)	(22,300)
Repayment of Rate Reduction Bonds	(43,210)	(43,210)
Issuance of Long-Term Debt	350,000	150,000
Retirement of Long-Term Debt	(282,000)	0
Capital Contributions from Eversource Parent	160,000	0
Increase in Notes Payable to Eversource Parent	20,200	2,100
Other Financing Activities	(2,961)	(2,965)
Net Cash Flows (Used in)/Provided by Financing Activities	(33,571)	83,625
Net (Decrease)/Increase in Cash and Restricted Cash	(13,382)	(14,093)
Cash and Restricted Cash - Beginning of Period	39,555	36,688
Cash and Restricted Cash - End of Period	$ 26,173	$ 22,595

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES A. Basis of Presentation Eversource Energy is a public utility holding company primarily engaged, through its wholly-owned regulated utility subsidiaries, in the energy delivery business. Eversource Energy's wholly-owned regulated utility subsidiaries consist of CL&P, NSTAR Electric 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. The unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P are herein collectively referred to as the "financial statements." The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the Combined Notes to Financial Statements included in Item 8, "Financial Statements and Supplementary Data," of the Eversource 2020 Form 10-K, which was filed with the SEC on February 17, 2021. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's and PSNH's financial position as of September 30, 2021 and December 31, 2020, and the results of operations, comprehensive income and common shareholders' equity for the three and nine months ended September 30, 2021 and 2020 and the cash flows for the nine months ended September 30, 2021 and 2020. The results of operations and comprehensive income for the three and nine months ended September 30, 2021 and 2020 and the cash flows for the nine months ended September 30, 2021 and 2020 are not necessarily indicative of the results expected for a full year. Eversource's consolidated financial information includes the results of the acquisition of the assets of Columbia Gas of Massachusetts (CMA) on October 9, 2020. The natural gas distribution assets acquired from CMA on October 9, 2020 were assigned to EGMA. 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. 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 customers, workers and the U.S. economy. We provide a critical service to our customers and have taken extensive measures to maintain its safety and reliability. We continue to address the impacts of the COVID-19 pandemic and how the related developments affect Eversource. We are in the re-entry phase of our pandemic response plan, in which the majority of our employees under remote work arrangements have transitioned back to the workplace. We have not experienced significant impacts directly related to the pandemic that have materially affected our current operations, our workforce, or results of operations. The extent of the impact to us in the future will vary, and depend on the duration, scope and severity of the pandemic and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of future proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses. Based on the status of our COVID-19 regulatory dockets, communications with our state regulatory commissions, and policies and practices in the jurisdictions in which we operate, we believe our state regulatory commissions in Connecticut and Massachusetts 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 1C, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of September 30, 2021 in light of the COVID-19 pandemic and Note 2, "Regulatory Accounting," for the amount of net incremental COVID-19 costs deferred on our balance sheets. Certain reclassifications of prior period data were made in the accompanying financial statements to conform to the current period presentation. B. Accounting Standards Accounting Standards Recently Adopted: On January 1, 2021, the Company adopted 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 ASU did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH. C. 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. The current expected credit loss (CECL) model is 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. 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 September 30, 2021, 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 lower cash collections from customers because of the length of the moratorium on disconnections in Connecticut and Massachusetts, and the economic slowdown resulting from the COVID-19 pandemic. In Connecticut, the moratorium on disconnections of commercial and non-hardship residential customers ended in June 2021 and September 2021, respectively, but is still in place for hardship residential customers. In Massachusetts, the moratorium on disconnections of commercial customers and residential customers ended in September 2020 and July 2021, respectively. Disconnection activities have resumed after these moratoria have expired, which has resulted in recent improved collection experience and more customers applying for, and receiving, hardship status. On July 7, 2021, the NHPUC issued an order to New Hampshire utilities that concluded that recovery of incremental bad debt or waived late fees related to the COVID-19 pandemic would be addressed in a future rate case to the extent those costs are relevant at that time. As a result of the order, in the first nine months of 2021, PSNH removed its $0.6 million deferral of net incremental COVID-19 costs. In New Hampshire, the moratorium on disconnections of non-hardship residential and commercial customers ended in late 2020 and for hardship residential customers ended in May 2021 and PSNH has resumed disconnection activities, which has resulted in improved collection of outstanding customer receivable balances. Based upon the evaluation performed, in the first nine months of 2021, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $25.8 million for Eversource (increase of $16.3 million for CL&P and $12.5 million at our natural gas businesses, and decrease of $1.8 million at NSTAR Electric). In the third quarter of 2021, the COVID-19 related allowance for uncollectible accounts decreased by $6.5 million at Eversource (increased $4.0 million at CL&P, and decreased $8.3 million at NSTAR Electric and $2.2 million at our natural gas businesses). The COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs at our Connecticut and Massachusetts utilities 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 future rates. As of September 30, 2021, the total amount incurred as a result of COVID-19 included in the allowance for uncollectible accounts was $57.0 million at Eversource ($20.1 million at CL&P, $8.5 million at NSTAR Electric, and $27.4 million at our natural gas businesses). Management concluded that the reserve balance as of September 30, 2021 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, NSTAR Gas and EGMA to recover in rates amounts associated with certain uncollectible hardship accounts receivable. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. 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. Management uses a higher credit risk profile for this pool of trade receivables as compared to non-hardship receivables. 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 as of September 30 th is as follows: 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 Three Months Ended 2021 Beginning Balance $ 210.7 $ 215.1 $ 425.8 $ 145.6 $ 43.2 $ 188.8 $ 35.9 $ 62.1 $ 98.0 $ 17.2 Uncollectible Expense — 12.0 12.0 — 3.6 3.6 — 5.1 5.1 1.2 Uncollectible Costs Deferred (1) 22.8 1.7 24.5 4.5 5.7 10.2 11.8 (3.5) 8.3 1.2 Write-Offs (3.9) (20.5) (24.4) (3.5) (5.4) (8.9) (0.1) (7.4) (7.5) (2.8) Recoveries Collected 0.3 3.5 3.8 0.2 1.6 1.8 — 1.1 1.1 0.2 Ending Balance $ 229.9 $ 211.8 $ 441.7 $ 146.8 $ 48.7 $ 195.5 $ 47.6 $ 57.4 $ 105.0 $ 17.0 Nine Months Ended 2021 Beginning Balance $ 194.8 $ 164.1 $ 358.9 $ 129.1 $ 28.3 $ 157.4 $ 39.7 $ 51.9 $ 91.6 $ 17.2 Uncollectible Expense — 39.7 39.7 — 10.2 10.2 — 12.5 12.5 4.4 Uncollectible Costs Deferred (1) 44.8 53.3 98.1 25.7 21.4 47.1 8.3 11.8 20.1 2.0 Write-Offs (10.6) (55.2) (65.8) (8.7) (14.8) (23.5) (0.4) (22.6) (23.0) (7.3) Recoveries Collected 0.9 9.9 10.8 0.7 3.6 4.3 — 3.8 3.8 0.7 Ending Balance $ 229.9 $ 211.8 $ 441.7 $ 146.8 $ 48.7 $ 195.5 $ 47.6 $ 57.4 $ 105.0 $ 17.0 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 Three Months Ended 2020 Beginning Balance $ 175.5 $ 94.5 $ 270.0 $ 116.3 $ 20.4 $ 136.7 $ 34.6 $ 34.1 $ 68.7 $ 11.8 Uncollectible Expense — 10.5 10.5 — 3.8 3.8 — 4.5 4.5 0.8 Uncollectible Costs Deferred (1) 10.1 20.4 30.5 11.2 4.9 16.1 (1.3) 10.4 9.1 3.2 Write-Offs (7.3) (11.8) (19.1) (2.6) (4.6) (7.2) (0.2) (6.3) (6.5) (2.0) Recoveries Collected 0.4 2.7 3.1 0.3 1.1 1.4 — 1.0 1.0 0.2 Ending Balance $ 178.7 $ 116.3 $ 295.0 $ 125.2 $ 25.6 $ 150.8 $ 33.1 $ 43.7 $ 76.8 $ 14.0 Nine Months Ended 2020 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 21.6 2.2 23.8 21.3 0.9 22.2 (1.6) 0.3 (1.3) 0.3 Uncollectible Expense — 31.1 31.1 — 10.0 10.0 — 11.3 11.3 2.1 Uncollectible Costs Deferred (1) 24.9 41.5 66.4 32.7 8.3 41.0 (8.4) 17.3 8.9 5.6 Write-Offs (12.3) (49.3) (61.6) (10.0) (14.0) (24.0) (0.8) (20.5) (21.3) (5.0) Recoveries Collected 1.2 9.3 10.5 1.1 3.2 4.3 — 3.8 3.8 0.5 Ending Balance $ 178.7 $ 116.3 $ 295.0 $ 125.2 $ 25.6 $ 150.8 $ 33.1 $ 43.7 $ 76.8 $ 14.0 (1) These expected credit losses are deferred as regulatory costs on the balance sheets, as these amounts are ultimately recovered in rates. Amounts include uncollectible costs for hardship accounts and other customer receivables, including uncollectible amounts related to COVID-19 and uncollectible energy supply costs. D. Fair Value Measurements Fair value measurement guidance is applied to derivative contracts that are not elected or designated as "normal purchases" or "normal sales" (normal) and to the marketable securities held in trusts. Fair value measurement guidance is also applied to valuations of the investments used to calculate the funded status of pension and PBOP plans, the nonrecurring fair value measurements of nonfinancial assets such as goodwill, long-lived assets, equity method investments, and AROs, and in the valuation of the acquisition of CMA's assets 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," and Note 10, "Fair Value of Financial Instruments," to the financial statements. E. Other Income, Net The components of Other Income, Net on the statements of income were as follows: For the Three Months Ended September 30, 2021 September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Pension, SERP and PBOP Non-Service $ 21.7 $ 4.2 $ 10.1 $ 2.5 $ 11.0 $ 0.9 $ 7.2 $ 1.8 AFUDC Equity 10.3 1.7 6.2 0.3 10.3 3.5 5.5 0.9 Equity in Earnings of Unconsolidated Affiliates (1) 4.9 — 0.1 — 3.9 — 0.1 — Investment (Loss)/Income (0.6) (0.3) (0.2) (0.1) 1.0 1.3 (0.2) 0.2 Interest Income 7.3 1.3 3.9 0.4 1.5 0.2 0.1 1.2 Gain on Sale of Property — — — — 1.5 — — — Other 0.2 — 0.1 0.1 — — 0.1 — Total Other Income, Net $ 43.8 $ 6.9 $ 20.2 $ 3.2 $ 29.2 $ 5.9 $ 12.8 $ 4.1 For the Nine Months Ended September 30, 2021 September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Pension, SERP and PBOP Non-Service $ 63.9 $ 11.2 $ 30.3 $ 7.9 $ 34.3 $ 3.0 $ 22.2 $ 5.2 AFUDC Equity 28.7 5.1 18.6 1.2 31.8 11.4 15.8 3.5 Equity in Earnings of Unconsolidated Affiliates (1) 13.3 — 0.3 — 13.8 — 0.4 — Investment Income/(Loss) 0.7 1.2 0.6 0.3 (1.5) — (1.5) 0.1 Interest Income 17.2 4.1 8.8 2.0 3.3 1.8 0.7 2.0 Gain on Sale of Property 0.1 — — 0.1 1.8 — 0.3 — Other 0.7 0.1 0.3 0.1 0.1 0.1 0.3 0.1 Total Other Income, Net $ 124.6 $ 21.7 $ 58.9 $ 11.6 $ 83.6 $ 16.3 $ 38.2 $ 10.9 (1) Equity in earnings of unconsolidated affiliates includes $2.1 million of pre-tax unrealized gains associated with an investment in a renewable energy fund for the nine months ended September 30, 2021. For the nine months ended September 30, 2020, equity in earnings of unconsolidated affiliates included $2.4 million of primarily realized gains associated with this investment. F. Other Taxes Eversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers. 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 Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Eversource $ 49.4 $ 48.4 $ 137.9 $ 129.1 CL&P 46.1 45.6 120.7 114.2 As agents for state and local governments, Eversource's companies that serve customers in Connecticut and Massachusetts collect certain sales taxes that are recorded on a net basis with no impact on the statements of income. G. Supplemental Cash Flow Information Non-cash investing activities include plant additions included in Accounts Payable as follows: (Millions of Dollars) As of September 30, 2021 As of September 30, 2020 Eversource $ 359.6 $ 357.4 CL&P 75.3 97.8 NSTAR Electric 94.2 92.6 PSNH 32.8 50.0 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 September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Cash as reported on the Balance Sheets $ 88.2 $ 62.8 $ 3.5 $ 3.9 $ 106.6 $ 90.8 $ 0.1 $ 0.1 Restricted cash included in: Special Deposits 55.5 8.7 17.2 18.6 73.6 8.7 17.2 36.8 Marketable Securities 29.7 0.3 0.1 0.5 41.2 0.3 0.1 0.6 Other Long-Term Assets 44.7 — — 3.2 43.6 — — 2.1 Cash and Restricted Cash as reported on the Statements of Cash Flows $ 218.1 $ 71.8 $ 20.8 $ 26.2 $ 265.0 $ 99.8 $ 17.4 $ 39.6 Special Deposits represent cash collections related to the PSNH RRB customer charges that are held in trust, required ISO-NE cash deposits, and CYAPC and YAEC cash balances. Special Deposits are included in Current Assets on the balance sheets. Restricted cash included in Marketable Securities represents money market funds held in trusts to fund certain non-qualified executive benefits and restricted trusts to fund CYAPC and YAEC's spent nuclear fuel storage obligations. Restricted cash included in Other Long-Term Assets includes $41.5 million related to an Energy Relief Fund for energy efficiency and clean energy measures in the Merrimack Valley, and an additional energy efficiency program established under the terms of the EGMA settlement agreement.

REGULATORY ACCOUNTING

REGULATORY ACCOUNTING	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Benefit Costs $ 2,566.1 $ 540.2 $ 638.4 $ 249.7 $ 2,794.2 $ 632.3 $ 690.0 $ 267.6 Income Taxes, Net 756.4 458.1 113.8 18.7 747.1 458.9 110.4 15.2 Securitized Stranded Costs 489.7 — — 489.7 522.1 — — 522.1 Storm Restoration Costs, Net 944.2 674.2 198.1 71.9 765.6 515.1 186.4 64.1 Regulatory Tracker Mechanisms 883.0 304.6 320.0 76.8 850.5 246.6 332.2 95.3 Derivative Liabilities 265.3 265.3 — — 296.3 293.1 — — Goodwill-related 302.0 — 259.3 — 314.7 — 270.2 — Asset Retirement Obligations 121.6 33.7 57.8 4.0 118.4 32.1 58.6 3.9 Other Regulatory Assets 146.9 31.0 48.7 16.9 161.0 33.7 56.1 20.9 Total Regulatory Assets 6,475.2 2,307.1 1,636.1 927.7 6,569.9 2,211.8 1,703.9 989.1 Less: Current Portion 1,016.3 325.3 388.4 97.9 1,076.6 345.6 399.9 115.9 Total Long-Term Regulatory Assets $ 5,458.9 $ 1,981.8 $ 1,247.7 $ 829.8 $ 5,493.3 $ 1,866.2 $ 1,304.0 $ 873.2 CL&P Deferred Storm Costs: In 2021 and 2020, multiple tropical and severe storms caused extensive damage to CL&P’s electric distribution systems and customer outages, along with significant pre-staging costs. These storms resulted in deferred pre-staging and storm restoration costs of $195 million for 2021 storms and $344 million for 2020 storms, including the catastrophic impact of Tropical Storm Isaias in August 2020, among others. Management believes all these storm costs were prudently incurred and meet the criteria for specific cost recovery. Regulatory Costs in Long-Term Assets: Eversource's regulated companies had $260.6 million (including $111.2 million for CL&P, $85.1 million for NSTAR Electric and $3.2 million for PSNH) and $196.9 million (including $84.1 million for CL&P, $69.8 million for NSTAR Electric and $4.3 million for PSNH) of additional regulatory costs as of September 30, 2021 and December 31, 2020, 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 September 30, 2021 and December 31, 2020, these regulatory costs included net incremental COVID-19 related costs deferred of $41.3 million and $24.0 million at Eversource, respectively, of which, $34.5 million and $15.8 million, respectively, related to non-tracked uncollectible expense and the remainder related to facilities and fleet cleaning, sanitizing costs and supplies for personal protective equipment. Net incremental COVID-19 related costs deferred at CL&P and NSTAR Electric totaled $15.9 million and $10.9 million, respectively, as of September 30, 2021, and $4.7 million and $11.9 million, respectively, as of December 31, 2020, and primarily related to deferred non-tracked uncollectible expense. Regulatory Liabilities: The components of regulatory liabilities were as follows: As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH EDIT due to Tax Cuts and Jobs Act of 2017 $ 2,737.1 $ 1,001.5 $ 1,025.6 $ 363.9 $ 2,778.6 $ 1,010.7 $ 1,044.0 $ 371.5 Cost of Removal 676.7 117.0 384.1 19.0 624.8 98.4 363.6 12.9 Benefit Costs 65.9 — 56.5 — 83.6 — 72.5 — Regulatory Tracker Mechanisms 484.5 208.9 180.6 87.5 366.5 148.9 139.7 47.8 AFUDC - Transmission 79.6 43.6 36.0 — 76.8 44.6 32.2 — CL&P Settlement Agreement and Storm 103.4 103.4 — — — — — — Other Regulatory Liabilities 373.3 50.4 84.6 15.8 309.9 39.5 63.2 9.8 Total Regulatory Liabilities 4,520.5 1,524.8 1,767.4 486.2 4,240.2 1,342.1 1,715.2 442.0 Less: Current Portion 612.9 311.3 205.8 96.8 389.4 137.2 164.8 58.8 Total Long-Term Regulatory Liabilities $ 3,907.6 $ 1,213.5 $ 1,561.6 $ 389.4 $ 3,850.8 $ 1,204.9 $ 1,550.4 $ 383.2 Recent Regulatory Developments: CL&P Tropical Storm Isaias Costs: On August 4, 2020, Tropical Storm Isaias caused catastrophic damage to our electric distribution system, which resulted in significant numbers 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 will investigate the prudence of costs incurred by CL&P to restore service in response to Tropical Storm Isaias. That investigation is expected to occur either in a separate proceeding not yet initiated or as part of CL&P’s next rate review proceeding. Tropical Storm Isaias resulted in deferred storm restoration costs of approximately $234 million at CL&P and $251 million at Eversource as of September 30, 2021. The estimated cost of restoration may continue to change as additional cost information becomes available and final post-storm costs are deferred or capitalized. Although PURA found that CL&P’s performance in its preparation for and response to Tropical Storm Isaias fell below applicable performance standards in certain instances, CL&P believes it will be able to present credible evidence in a future proceeding demonstrating there is no reasonably close causal connection between the alleged sub-standard performance and the storm costs incurred. While it is possible that some amount of storm costs may be disallowed by PURA in a future proceeding, any such amount cannot be estimated at this time. Eversource and CL&P continue to believe that these storm restoration costs associated with Tropical Storm Isaias were prudently incurred and meet the criteria for cost recovery; and as a result, management does not expect the storm cost review by PURA to have a material impact on the financial position or results of operations of Eversource or CL&P. CL&P Tropical Storm Isaias Response Investigation: On April 28, 2021, PURA issued a final decision on CL&P’s compliance with its emergency response plan that concluded CL&P failed to comply with certain storm performance standards and was imprudent in certain instances. The $28.4 million performance penalty assessed by PURA was recorded within current regulatory liabilities on CL&P’s balance sheet. See Note 9G, “Commitments and Contingencies - CL&P Regulatory Matters,” for further information.

PROPERTY, PLANT AND EQUIPMENT A

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION	PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION The following tables summarize property, plant and equipment by asset category: Eversource As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Distribution - Electric $ 17,257.3 $ 16,703.2 Distribution - Natural Gas 6,334.9 6,111.2 Transmission - Electric 12,396.2 11,954.0 Distribution - Water 1,771.1 1,743.1 Solar 200.4 201.5 Utility 37,959.9 36,713.0 Other (1) 1,430.5 1,269.0 Property, Plant and Equipment, Gross 39,390.4 37,982.0 Less: Accumulated Depreciation Utility (8,830.2) (8,476.3) Other (550.0) (477.6) Total Accumulated Depreciation (9,380.2) (8,953.9) Property, Plant and Equipment, Net 30,010.2 29,028.1 Construction Work in Progress 2,456.9 1,854.4 Total Property, Plant and Equipment, Net $ 32,467.1 $ 30,882.5 As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH Distribution - Electric $ 7,028.9 $ 7,798.8 $ 2,469.9 $ 6,820.7 $ 7,544.4 $ 2,378.4 Transmission - Electric 5,707.9 4,884.0 1,805.9 5,512.0 4,701.3 1,742.4 Solar — 200.4 — — 201.5 — Property, Plant and Equipment, Gross 12,736.8 12,883.2 4,275.8 12,332.7 12,447.2 4,120.8 Less: Accumulated Depreciation (2,574.6) (3,220.7) (895.4) (2,475.4) (3,074.1) (848.9) Property, Plant and Equipment, Net 10,162.2 9,662.5 3,380.4 9,857.3 9,373.1 3,271.9 Construction Work in Progress 436.6 949.2 148.7 377.3 750.0 102.4 Total Property, Plant and Equipment, Net $ 10,598.8 $ 10,611.7 $ 3,529.1 $ 10,234.6 $ 10,123.1 $ 3,374.3 (1) These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company.

DERIVATIVE INSTRUMENTS

DERIVATIVE INSTRUMENTS	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 As of December 31, 2020 (Millions of Dollars) Fair Value Hierarchy Commodity Supply and Price Risk Netting (1) Net Amount Commodity Supply and Price Risk Netting (1) Net Amount Current Derivative Assets: CL&P Level 3 $ 14.4 $ (0.4) $ 14.0 $ 13.7 $ (0.4) $ 13.3 Long-Term Derivative Assets: CL&P Level 3 51.1 (1.6) 49.5 58.7 (1.8) 56.9 Current Derivative Liabilities: CL&P Level 3 (72.2) — (72.2) (68.8) — (68.8) Other Level 2 — — — (3.3) 0.1 (3.2) Long-Term Derivative Liabilities: CL&P Level 3 (256.6) — (256.6) (294.5) — (294.5) (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. 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 both September 30, 2021 and December 31, 2020 were 675 MW. The capacity contracts extend through 2026 and obligate both CL&P and UI to make or receive payments on a monthly basis to or from the generation facilities based on the difference between a set capacity price and the capacity market price received in the ISO-NE capacity markets. As of December 31, 2020, 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 MMBtu of natural gas. These contracts were classified as Level 2 in the fair value hierarchy. NSTAR Gas terminated its financial contracts swap program in April 2021. For the three months ended September 30, 2021 and 2020, there were gains of $0.7 million and losses of $2.6 million, respectively, deferred as regulatory costs, which reflect the change in fair value associated with Eversource's derivative contracts. For the nine months ended September 30, 2021 and 2020, there were losses of $9.5 million and $20.6 million, respectively. Fair Value Measurements of Derivative Instruments 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 September 30, 2021 As of December 31, 2020 CL&P Range Weighted Average (1) Period Covered Range Weighted Average (1) Period Covered Capacity Prices $2.61 $ 2.61 per kW-Month 2025 - 2026 $ 4.30 — $5.30 $ 4.63 per kW-Month 2024 - 2026 Forward Reserve Prices $ 0.50 — $1.15 $ 0.82 per kW-Month 2022 - 2024 $ 0.54 — $0.90 $ 0.72 per kW-Month 2021 - 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 5.5 percent through 9.8 percent, or a weighted average of 8.7 percent, are also applied to these contracts and reflect the uncertainty and illiquidity premiums that would be required based on the most recent market activity available for similar type contracts. 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. 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 For the Three Months Ended September 30, For the Nine Months Ended September 30, (Millions of Dollars) 2021 2020 2021 2020 Derivatives, Net: Fair Value as of Beginning of Period $ (279.7) $ (322.0) $ (293.1) $ (329.2) Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets 0.7 (4.7) (10.9) (22.3) Settlements 13.7 14.9 38.7 39.7 Fair Value as of End of Period $ (265.3) $ (311.8) $ (265.3) $ (311.8)

MARKETABLE SECURITIES

MARKETABLE SECURITIES	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 was $39.2 million and $40.9 million, respectively. For the three months ended September 30, 2021 and 2020, there were unrealized losses of $0.5 million and unrealized gains of $1.6 million, respectively, recorded in Other Income, Net related to these equity securities. For the nine months ended September 30, 2021 and 2020, there were unrealized gains of $2.5 million and unrealized losses of $1.0 million, 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 $214.9 million and $205.1 million as of September 30, 2021 and December 31, 2020, 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 September 30, 2021 As of December 31, 2020 Eversource (Millions of Dollars) Amortized Cost Pre-Tax Pre-Tax Fair Value Amortized Cost Pre-Tax Pre-Tax Fair Value Debt Securities $ 217.5 $ 8.0 $ (0.2) $ 225.3 $ 213.1 $ 11.2 $ (0.1) $ 224.2 Eversource's debt securities include CYAPC's and YAEC's marketable securities held in spent nuclear fuel trusts in the amounts of $195.2 million and $192.5 million as of September 30, 2021 and December 31, 2020, 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 three and nine months ended September 30, 2021 and 2020, and no allowance for credit losses as of September 30, 2021. 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 September 30, 2021, the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Cost Fair Value Less than one year (1) $ 30.9 $ 30.9 One to five years 65.5 67.1 Six to ten years 41.8 43.9 Greater than ten years 79.3 83.4 Total Debt Securities $ 217.5 $ 225.3 (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 September 30, 2021 As of December 31, 2020 Level 1: Mutual Funds and Equities $ 254.1 $ 246.0 Money Market Funds 29.7 41.2 Total Level 1 $ 283.8 $ 287.2 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 98.9 $ 72.9 Corporate Debt Securities 63.4 63.8 Asset-Backed Debt Securities 13.4 11.9 Municipal Bonds 6.1 24.0 Other Fixed Income Securities 13.8 10.4 Total Level 2 $ 195.6 $ 183.0 Total Marketable Securities $ 479.4 $ 470.2 U.S. government issued debt securities are valued using market approaches that incorporate transactions for the same or similar bonds and adjustments for yields and maturity dates. Corporate debt securities are valued using a market approach, utilizing recent trades of the same or similar 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.

SHORT-TERM AND LONG-TERM DEBT

SHORT-TERM AND LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
SHORT-TERM AND LONG-TERM DEBT	SHORT-TERM AND LONG-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, EGMA and Aquarion Water Company of Connecticut are parties to a five-year $2.00 billion revolving credit facility, which terminates on October 15, 2026. This revolving credit facility serves 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 October 15, 2026. The revolving credit facility serves to backstop NSTAR Electric's $650 million commercial paper program. The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding as of Available Borrowing Capacity as of Weighted-Average Interest Rate as of September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 (Millions of Dollars) Eversource Parent Commercial Paper Program $ 653.0 $ 1,054.3 $ 1,347.0 $ 945.7 0.18 % 0.25 % NSTAR Electric Commercial Paper Program 138.0 195.0 512.0 455.0 0.10 % 0.16 % There were no borrowings outstanding on the revolving credit facilities as of September 30, 2021 or December 31, 2020. CL&P and PSNH have uncommitted line of credit agreements totaling $450 million and $300 million, respectively, which will expire on May 12, 2022. There are no borrowings outstanding on either the CL&P or PSNH uncommitted line of credit agreements as of September 30, 2021. 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. As a result of the NSTAR Gas long-term debt issuances in October 2021, $80.0 million of commercial paper borrowings under the Eversource parent commercial paper program were classified as Long-Term Debt as of September 30, 2021. 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. Intercompany Borrowings: Eversource parent uses its available capital resources to provide loans to its subsidiaries to assist in meeting their short-term borrowing needs. Eversource parent records intercompany interest income from its loans to subsidiaries, which is eliminated in consolidation. Intercompany loans from Eversource parent to its subsidiaries are eliminated in consolidation on Eversource's balance sheets. As of September 30, 2021, there were intercompany loans from Eversource parent to PSNH of $66.5 million, and to a subsidiary of NSTAR Electric of $24.6 million. As of December 31, 2020, there were intercompany loans from Eversource parent to PSNH of $46.3 million, and to a subsidiary of NSTAR Electric of $21.3 million. Intercompany loans from Eversource parent are included in Notes Payable to Eversource Parent and classified in current liabilities on the respective subsidiary's balance sheets. Availability under Long-Term Debt Issuance Authorizations: On March 31, 2021, the DPU approved NSTAR Electric's request for authorization to issue up to $1.60 billion in long-term debt through December 31, 2023. On September 10, 2021, the DPU approved EGMA’s request for authorization to issue up to $725 million in long-term debt through December 31, 2023. The remaining Eversource operating companies, including CL&P and PSNH, have utilized the long-term debt authorizations in place with the respective regulatory commissions. 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: 2.05% Series A First Mortgage Bonds $ 425.0 June 2021 July 2031 Repaid short-term debt, paid capital expenditures and working capital 4.38% Series A PCRB (120.5) September 2021 September 2028 Paid on par call date in advance of maturity NSTAR Electric: 3.10% 2021 Debentures 300.0 May 2021 June 2051 Refinanced investments in eligible green expenditures, which were previously financed in 2019 and 2020 3.50% Series F Senior Notes (250.0) June 2021 September 2021 Paid on par call date in advance of maturity date 1.95% 2021 Debentures 300.0 August 2021 August 2031 Repaid short-term debt, paid capital expenditures and working capital PSNH: 4.05% Series Q First Mortgage Bonds (122.0) March 2021 June 2021 Paid on par call date in advance of maturity date 3.20% Series R First Mortgage Bonds (160.0) June 2021 September 2021 Paid on par call date in advance of maturity date 2.20% Series V First Mortgage Bonds 350.0 June 2021 June 2031 Repaid short-term debt, including short-term debt used to redeem Series R First Mortgage Bonds, paid capital expenditures and working capital Other: Eversource Parent 2.50% Series I Senior Notes (450.0) February 2021 March 2021 Paid on par call date in advance of maturity date Eversource Parent 2.55% Series S Senior Notes 350.0 March 2021 March 2031 Repaid short-term debt, including short-term debt used to redeem Series I Senior Notes Eversource Parent 1.40% Series U Senior Notes 300.0 August 2021 August 2026 Repaid short-term debt Eversource Parent Variable Rate Series T Senior Notes (1) 350.0 August 2021 August 2023 Repaid short-term debt Aquarion Water Company of Connecticut 3.31% Senior Notes 100.0 April 2021 April 2051 Repaid 5.50% Notes, repaid short-term debt, paid capital expenditures and working capital Aquarion Water Company of Connecticut 5.50% Notes (40.0) April 2021 April 2021 Paid at maturity Yankee Gas 1.38% Series S First Mortgage Bonds 90.0 August 2021 August 2026 (2) Yankee Gas 2.88% Series T First Mortgage Bonds 35.0 August 2021 August 2051 (2) EGMA 2.11% Series A First Mortgage Bonds 310.0 September 2021 October 2031 (2) EGMA 2.92% Series B First Mortgage Bonds 240.0 September 2021 October 2051 (2) NSTAR Gas 2.25% Series T First Mortgage Bonds 40.0 October 2021 November 2031 (2) NSTAR Gas 3.03% Series U First Mortgage Bonds 40.0 October 2021 November 2051 (2) (1) On August 10, 2021, Eversource Parent issued $350 million of floating rate Series T Senior Notes with a maturity date of August 15, 2023. The notes have a coupon rate based on the Compounded SOFR plus 0.25%. (2) The use of proceeds from these various issuances refinanced existing indebtedness, funded capital expenditures and were for general corporate purposes. The EGMA indebtedness that was refinanced included $309.4 million of long-term debt.

RATE REDUCTION BONDS AND VARIAB

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES	9 Months Ended
	Sep. 30, 2021
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: In May 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 in January 2018 to recover remaining costs resulting from the divestiture of PSNH’s generation assets. 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) PSNH Balance Sheets: As of September 30, 2021 As of December 31, 2020 Restricted Cash - Current Portion (included in Current Assets) $ 18.3 $ 36.8 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 3.2 2.1 Securitized Stranded Cost (included in Regulatory Assets) 489.7 522.1 Other Regulatory Liabilities (included in Regulatory Liabilities) 8.0 9.1 Accrued Interest (included in Other Current Liabilities) 3.0 8.0 Rate Reduction Bonds - Current Portion 43.2 43.2 Rate Reduction Bonds - Long-Term Portion 453.7 496.9 (Millions of Dollars) PSNH Income Statements: For the Three Months Ended For the Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 10.8 $ 10.8 $ 32.4 $ 32.4 Interest Expense on RRB Principal (included in Interest Expense) 4.5 4.9 13.9 14.9

PENSION BENEFITS AND POSTRETIRE

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION	9 Months Ended
	Sep. 30, 2021
Postemployment Benefits [Abstract]
PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION	PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION Eversource provides defined benefit retirement plans (Pension Plans) that cover eligible employees. 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 components of net periodic benefit plan 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 plan 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 plan 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 intercompany allocations of net periodic benefit plan expense/(income), as these amounts are cash settled on a short-term basis. Pension and SERP PBOP For the Three Months Ended September 30, 2021 For the Three Months Ended September 30, 2021 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 21.5 $ 5.6 $ 4.0 $ 2.2 $ 3.3 $ 0.5 $ 0.6 $ 0.3 Interest Cost 32.5 6.7 6.7 3.7 4.3 0.8 1.1 0.4 Expected Return on Plan Assets (109.5) (21.7) (27.1) (11.9) (19.8) (2.5) (9.2) (1.6) Actuarial Loss 60.7 10.8 15.3 5.3 2.0 0.4 0.5 0.1 Prior Service Cost/(Credit) 0.3 — 0.1 — (5.3) 0.3 (4.3) 0.1 Total Net Periodic Benefit Plan Expense/(Income) $ 5.5 $ 1.4 $ (1.0) $ (0.7) $ (15.5) $ (0.5) $ (11.3) $ (0.7) Intercompany Expense/(Income) Allocations N/A $ 2.2 $ 2.4 $ 0.7 N/A $ (0.4) $ (0.5) $ (0.2) Pension and SERP PBOP For the Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2021 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 64.3 $ 17.4 $ 11.9 $ 6.6 $ 10.1 $ 1.7 $ 1.8 $ 0.9 Interest Cost 97.5 20.7 20.1 10.9 12.9 2.4 3.3 1.3 Expected Return on Plan Assets (328.0) (65.0) (81.1) (35.6) (59.3) (7.7) (27.7) (4.6) Actuarial Loss 183.1 34.6 46.1 15.4 5.9 1.2 1.6 0.4 Prior Service Cost/(Credit) 1.1 — 0.3 — (15.9) 0.8 (12.7) 0.3 Total Net Periodic Benefit Plan Expense/(Income) $ 18.0 $ 7.7 $ (2.7) $ (2.7) $ (46.3) $ (1.6) $ (33.7) $ (1.7) Intercompany Expense/(Income) Allocations N/A $ 5.8 $ 6.4 $ 1.9 N/A $ (1.3) $ (1.5) $ (0.5) Pension and SERP PBOP For the Three Months Ended September 30, 2020 For the Three Months Ended September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 18.7 $ 5.4 $ 3.8 $ 2.0 $ 2.4 $ 0.4 $ 0.5 $ 0.2 Interest Cost 44.4 9.3 9.7 4.8 6.1 1.1 1.7 0.7 Expected Return on Plan Assets (99.2) (19.8) (25.7) (11.1) (18.3) (2.5) (8.5) (1.4) Actuarial Loss 50.7 9.7 14.0 3.8 2.2 0.3 0.6 0.2 Prior Service Cost/(Credit) 0.2 — — — (5.3) 0.3 (4.2) 0.1 Total Net Periodic Benefit Plan Expense/(Income) $ 14.8 $ 4.6 $ 1.8 $ (0.5) $ (12.9) $ (0.4) $ (9.9) $ (0.2) Intercompany Expense/(Income) Allocations N/A $ 2.4 $ 2.3 $ 0.8 N/A $ (0.3) $ (0.4) $ (0.1) Pension and SERP PBOP For the Nine Months Ended September 30, 2020 For the Nine Months Ended September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 57.0 $ 16.5 $ 11.4 $ 6.2 $ 7.3 $ 1.3 $ 1.6 $ 0.6 Interest Cost 133.0 28.1 29.0 14.5 18.3 3.3 5.0 2.1 Expected Return on Plan Assets (298.8) (59.6) (77.2) (33.5) (55.1) (7.4) (25.5) (4.2) Actuarial Loss 150.7 29.4 41.3 11.8 6.3 0.9 1.8 0.6 Prior Service Cost/(Credit) 0.8 — 0.2 — (15.9) 0.8 (12.7) 0.3 Total Net Periodic Benefit Plan Expense/(Income) $ 42.7 $ 14.4 $ 4.7 $ (1.0) $ (39.1) $ (1.1) $ (29.8) $ (0.6) Intercompany Expense/(Income) Allocations N/A $ 6.7 $ 6.5 $ 2.2 N/A $ (0.9) $ (1.0) $ (0.4)

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2021
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. The number of environmental sites and related reserves for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: As of September 30, 2021 As of December 31, 2020 Number of Sites Reserve Number of Sites Reserve Eversource 62 $ 111.9 63 $ 102.4 CL&P 14 12.5 15 12.3 NSTAR Electric 12 3.7 12 4.7 PSNH 9 6.4 9 7.1 The increase in the reserve balance was due primarily to a change in cost estimates at an NSTAR Gas MGP site under investigation for which we now know of additional remediation that is 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 $102.4 million and $92.2 million as of September 30, 2021 and December 31, 2020, respectively, and related primarily to the natural gas business segment. 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. B. Long-Term Contractual Arrangements The following is an update to the current status of long-term contractual arrangements set forth in Note 13B of the Eversource 2020 Form 10-K. Renewable Energy : Renewable energy contracts include non-cancelable commitments under contracts of NSTAR Electric for the purchase of energy and RECs from renewable energy facilities. NSTAR Electric (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 27.1 $ 103.9 $ 230.5 $ 341.2 $ 348.1 $ 6,564.2 $ 7,615.0 The table has been updated to include long-term commitments of NSTAR Electric pertaining to the Massachusetts Clean Energy 83D contract, for which construction commenced in 2021. 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. C. Guarantees and Indemnifications In the normal course of business, Eversource parent provides credit assurances on behalf of its subsidiaries, including CL&P, NSTAR Electric and PSNH, in the form of guarantees. 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 $5.7 million as of September 30, 2021. The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries and affiliates to external parties: As of September 30, 2021 Company (Obligor) Description Maximum Exposure Expiration Dates North East Offshore LLC Construction-related purchase agreements with third-party contractors (1) $ 1,093.5 (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) Sunrise Wind LLC Construction-related purchase agreements with third-party contractors (4) 386.4 — South Fork Wind, LLC Transmission interconnection 1.2 — South Fork Wind, LLC Construction-related purchase agreements with third-party contractors (5) 40.6 2023 Bay State Wind LLC Real estate purchase 2.5 2022 Various Surety bonds (6) 67.5 2021 - 2023 Rocky River Realty Company and Lease payments for real estate 4.0 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 aggregate 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 aggregate 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) 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 aggregate 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) Eversource parent issued a guaranty 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 aggregate amount not to exceed $420.6 million, in connection with a construction-related purchase agreement. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) April 14, 2026 and (ii) full performance of the guaranteed obligations. (5) Eversource parent issued two guarantees on behalf of its 50 percent-owned affiliate, South Fork Wind, LLC, whereby Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations in connection with two construction-related purchase agreements. Under one guarantee, Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations, in an aggregate amount not to exceed $25.8 million. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) October 4, 2023 and (ii) full performance of the guaranteed obligations. Under the second guaranty, Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations, in an aggregate amount not to exceed $14.8 million. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) October 18, 2023 and (ii) full performance of the guaranteed obligations. (6) 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 EI, which holds Eversource's investments in offshore wind-related equity method investments, under which Eversource parent would guarantee EI's obligations under a letter of credit facility with a financial institution that EI may request in an aggregate amount of up to approximately $25 million. D. Spent Nuclear Fuel Obligations - Yankee Companies CL&P, NSTAR Electric and PSNH have plant closure and fuel storage cost obligations to the Yankee Companies, which have each completed the physical decommissioning of their respective nuclear 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, III and IV of litigation resulting from the DOE's failure to meet its contractual obligations. These Phases covered damages incurred in the years 1998 through 2016, and the awarded damages have been received by the Yankee Companies with certain amounts of the damages refunded to their customers. DOE Phase V Damages - On March 25, 2021, each of the Yankee Companies filed a fifth set of lawsuits against the DOE in the Court of Federal Claims. The Yankee Companies are calculating and will be seeking monetary damages for CYAPC, YAEC and MYAPC, resulting from the DOE's failure to begin accepting spent nuclear fuel for disposal covering the years from 2017 to 2020 (DOE Phase V). E. FERC ROE Complaints Four separate complaints were filed at the FERC by combinations of New England state attorneys general, state regulatory commissions, consumer advocates, consumer groups, municipal parties and other parties (collectively, the Complainants). In each of the first three complaints, filed on October 1, 2011, December 27, 2012, and July 31, 2014, respectively, the Complainants challenged the NETOs' base ROE of 11.14 percent that had been utilized since 2005 and sought an order to reduce it prospectively from the date of the final FERC order and for the separate 15-month complaint periods. In the fourth complaint, filed April 29, 2016, the Complainants challenged the NETOs' base ROE billed of 10.57 percent and the maximum ROE for transmission incentive (incentive cap) of 11.74 percent, asserting that these ROEs were unjust and unreasonable. The ROE originally billed during the period October 1, 2011 (beginning of the first complaint period) through October 15, 2014 consisted of a base ROE of 11.14 percent and incentives up to 13.1 percent. On October 16, 2014, the FERC set the base ROE at 10.57 percent and the incentive cap at 11.74 percent for the first complaint period. This was also effective for all prospective billings to customers beginning October 16, 2014. This FERC order was vacated on April 14, 2017 by the U.S. Court of Appeals for the D.C. Circuit (the Court). All amounts associated with the first complaint period have been refunded, which totaled $38.9 million (pre-tax and excluding interest) at Eversource and reflected both the base ROE and incentive cap prescribed by the FERC order. The refund consisted of $22.4 million for CL&P, $13.7 million for NSTAR Electric and $2.8 million for PSNH. Eversource has recorded a reserve of $39.1 million (pre-tax and excluding interest) for the second complaint period as of September 30, 2021 and December 31, 2020. 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 September 30, 2021 and December 31, 2020. 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. G. CL&P Regulatory Matters CL&P Tropical Storm Isaias Response Investigation: In August 2020, PURA opened a docket to investigate the preparation for and response to Tropical Storm Isaias by Connecticut utilities, including CL&P. On April 28, 2021, PURA issued a final decision on CL&P’s compliance with its emergency response plan that concluded CL&P failed to comply with certain storm performance standards and was imprudent in certain instances. Specifically, PURA concluded that CL&P did not satisfy the performance standards for managing its municipal liaison program, timely removing electrical hazards from blocked roads, communicating critical information to its customers, or meeting its obligation to secure adequate external contractor and mutual aid resources in a timely manner. Based on its findings, PURA ordered CL&P to adjust its future rates in a pending or future rate proceeding to reflect a monetary penalty in the form of a downward adjustment of 90 basis points in its allowed rate of return on equity (ROE), which is currently 9.25 percent. In its decision, PURA explained that additional monetary penalties and further enforcement orders pursuant to Connecticut statute would be considered in a separate proceeding that was initiated on May 6, 2021. On May 6, 2021, as part of the penalty proceeding, PURA issued a notice of violation that included an assessment of $30 million, consisting of a $28.4 million civil penalty for non-compliance with storm performance standards to be provided as credits on customer bills and a $1.6 million fine for violations of accident reporting requirements to be paid to the State of Connecticut’s general fund. On July 14, 2021, PURA issued a final decision in this penalty proceeding that included an assessment of $28.6 million, maintaining the $28.4 million performance penalty and reducing the $1.6 million fine for accident reporting to $0.2 million. The $28.4 million performance penalty is currently being credited to customers on electric bills beginning on September 1, 2021 over a one-year period. The $28.4 million is the maximum statutory penalty amount under applicable Connecticut law in effect at the time of Tropical Storm Isaias, which is 2.5 percent of CL&P’s annual distribution revenues. The liability for the performance penalty was recorded as a current regulatory liability on CL&P’s balance sheet and as a reduction to Operating Revenues on the nine months ended September 30, 2021 income statement. The after-tax earnings impact of this charge was $0.07 per share. CL&P Settlement Agreement: On October 1, 2021, CL&P entered into a settlement agreement with the DEEP, Office of Consumer Counsel (OCC), Office of the Attorney General (AG) and the Connecticut Industrial Energy Consumers, resolving certain issues that arose in pending regulatory proceedings initiated by the PURA. PURA approved the settlement agreement on October 27, 2021. In the settlement agreement, CL&P agreed to provide a total of $65 million of customer credits to be distributed based on customer sales over a two-month period from December 1, 2021 to January 31, 2022. CL&P also agreed to irrevocably set aside $10 million to fund various customer assistance initiatives as directed by PURA for disbursement to state-designated purposes, with the objective of disbursing the funds prior to April 30, 2022, including providing credits to existing hardship and non-hardship customers carrying arrearages and other purposes. In the third quarter of 2021, CL&P recorded a current regulatory liability of $75 million on the balance sheet associated with the provisions of the settlement agreement, with a $65 million pre-tax charge as a reduction to Operating Revenues associated with the customer credits and a $10 million charge to Operations and Maintenance expense associated with the customer assistance initiatives on the three months ended September 30, 2021 income statement. In exchange for the $75 million of customer credits and assistance, PURA’s interim rate reduction docket was resolved without findings. As a result of the settlement agreement, neither the 90 basis point reduction to CL&P’s return on equity introduced in PURA’s storm-related decision issued April 28, 2021, nor the 45 basis point reduction to CL&P’s return on equity included in PURA’s draft decision issued September 14, 2021 in the interim rate reduction docket, will be implemented. CL&P has also agreed that its current base distribution rates shall be frozen, subject to the customer credits described above, until no earlier than January 1, 2024. The rate freeze applies only to base distribution rates (including storm costs) and not to other rate mechanisms such as the retail rate components, rate reconciling mechanisms, formula rates and any other adjustment mechanisms. The rate freeze also does not apply to any cost recovery mechanism outside of the base distribution rates with regard to grid-modernization initiatives or any other proceedings, either currently pending or that may be initiated during the rate freeze period, that may place additional obligations on CL&P. The approval of the settlement agreement satisfies the Connecticut statute of rate review requirements that requires electric utilities to file a distribution rate case within four years of the last rate case. As part of the settlement agreement, CL&P agreed to withdraw with prejudice its pending appeals of PURA’s April 28, 2021 and July 14, 2021 decisions related to Storm Isaias and agreed to waive its right to file an appeal and seek a judicial stay of the final decision in the interim rate reduction docket. The settlement agreement assures that CL&P will have the opportunity to petition for and demonstrate the prudence of the storm costs incurred to respond to customer outages associated with Storm Isaias in a future ratemaking proceeding. The cumulative pre-tax impact of the settlement agreement and the Storm Isaias assessment imposed in PURA’s April 28, 2021 and July 14, 2021 decisions totaled $103.6 million, and the after-tax earnings impact was $85.8 million, or $0.25 per share, for the nine months ended September 30, 2021.

FAIR VALUE OF FINANCIAL INSTRUM

FAIR VALUE OF FINANCIAL INSTRUMENTS	9 Months Ended
	Sep. 30, 2021
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 Fair Carrying Fair Carrying Fair Carrying Fair As of September 30, 2021: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 165.5 $ 116.2 $ 121.4 $ 43.0 $ 44.1 $ — $ — Long-Term Debt 18,219.2 19,810.9 4,215.1 4,865.2 3,984.7 4,494.3 1,163.6 1,228.9 Rate Reduction Bonds 496.9 555.8 — — — — 496.9 555.8 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 Derivative Instruments and Marketable Securities: Derivative instruments and investments in marketable securities are carried at fair value. For further information, see Note 4, "Derivative Instruments," and Note 5, "Marketable Securities," to the financial statements. See Note 1D, "Summary of Significant Accounting Policies – Fair Value Measurements," for the fair value measurement policy and the fair value hierarchy.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	9 Months Ended
	Sep. 30, 2021
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 Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Qualified Unrealized Defined Total Qualified Unrealized Defined Total Balance as of Beginning of Period $ (1.4) $ 1.1 $ (76.1) $ (76.4) $ (3.0) $ 0.7 $ (62.8) $ (65.1) OCI Before Reclassifications — (0.6) (2.4) (3.0) — 0.3 (1.6) (1.3) Amounts Reclassified from AOCI 1.0 — 6.5 7.5 1.2 — 4.8 6.0 Net OCI 1.0 (0.6) 4.1 4.5 1.2 0.3 3.2 4.7 Balance as of End of Period $ (0.4) $ 0.5 $ (72.0) $ (71.9) $ (1.8) $ 1.0 $ (59.6) $ (60.4) 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.

COMMON SHARES

COMMON SHARES	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 Issued as of Par Value September 30, 2021 December 31, 2020 Eversource $ 5 380,000,000 357,818,402 357,818,402 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 Treasury Shares: As of September 30, 2021 and December 31, 2020, there were 14,044,078 and 14,864,379 Eversource common shares held as treasury shares, respectively. As of September 30, 2021 and December 31, 2020, Eversource common shares outstanding we re 343,774,324 and 342,954,023, respectively.

COMMON SHAREHOLDERS' EQUITY AND

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 Issued as of Par Value September 30, 2021 December 31, 2020 Eversource $ 5 380,000,000 357,818,402 357,818,402 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 Treasury Shares: As of September 30, 2021 and December 31, 2020, there were 14,044,078 and 14,864,379 Eversource common shares held as treasury shares, respectively. As of September 30, 2021 and December 31, 2020, Eversource common shares outstanding we re 343,774,324 and 342,954,023, respectively.

EARNINGS PER SHARE

EARNINGS PER SHARE	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHAREBasic EPS is computed based upon the weighted average number of common shares outstanding during each period. Diluted EPS is computed on the basis of the weighted average number of common shares outstanding plus the potential dilutive effect of certain share-based compensation awards as if they were converted into outstanding common shares. The dilutive effect of unvested RSU and performance share awards is calculated using the treasury stock method. RSU and performance share awards are included in basic weighted average common shares outstanding as of the date that all necessary vesting conditions have been satisfied. There were no antidilutive share awards excluded from the computation of diluted EPS for the three and nine months ended September 30, 2021 and the three months ended September 30, 2020. For the nine months ended September 30, 2020, there were 52,747 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. The following table sets forth the components of basic and diluted EPS: Eversource (Millions of Dollars, except share information) For the Three Months Ended For the Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Net Income Attributable to Common Shareholders $ 283.2 $ 346.3 $ 913.8 $ 933.2 Weighted Average Common Shares Outstanding: Basic 344,023,846 343,076,614 343,848,905 337,375,172 Dilutive Effect of: Share-Based Compensation Awards and Other 645,936 696,988 631,151 686,403 Equity Forward Sale Agreement — — — 362,525 Total Dilutive Effect 645,936 696,988 631,151 1,048,928 Diluted 344,669,782 343,773,602 344,480,056 338,424,100 Basic EPS $ 0.82 $ 1.01 $ 2.66 $ 2.77 Diluted EPS $ 0.82 $ 1.01 $ 2.65 $ 2.76

REVENUES

REVENUES	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES The following tables present operating revenues disaggregated by revenue source: For the Three Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,146.8 $ 81.7 $ — $ 39.1 $ — $ — $ 1,267.6 Commercial 748.8 59.0 — 17.2 — (1.4) 823.6 Industrial 96.2 28.6 — 1.1 — (4.8) 121.1 Total Retail Tariff Sales Revenues 1,991.8 169.3 — 57.4 — (6.2) 2,212.3 Wholesale Transmission Revenues — — 527.2 — 23.0 (408.5) 141.7 Wholesale Market Sales Revenues 133.8 12.2 — 1.1 — — 147.1 Other Revenues from Contracts with Customers 29.6 1.2 3.5 1.8 303.1 (301.4) 37.8 Reserve for Revenues Subject to Refund (1) (93.4) — — (0.9) — — (94.3) Total Revenues from Contracts with Customers 2,061.8 182.7 530.7 59.4 326.1 (716.1) 2,444.6 Alternative Revenue Programs (7.9) 2.7 (112.6) 2.3 — 102.0 (13.5) Other Revenues (2) 1.3 0.1 0.2 0.1 — — 1.7 Total Operating Revenues $ 2,055.2 $ 185.5 $ 418.3 $ 61.8 $ 326.1 $ (614.1) $ 2,432.8 For the Nine Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,094.9 $ 722.8 $ — $ 102.8 $ — $ — $ 3,920.5 Commercial 1,902.9 356.4 — 47.0 — (4.1) 2,302.2 Industrial 261.1 119.5 — 3.3 — (12.8) 371.1 Total Retail Tariff Sales Revenues 5,258.9 1,198.7 — 153.1 — (16.9) 6,593.8 Wholesale Transmission Revenues — — 1,338.4 — 62.5 (1,075.4) 325.5 Wholesale Market Sales Revenues 380.1 54.1 — 3.0 — — 437.2 Other Revenues from Contracts with Customers 68.4 3.6 10.2 5.5 936.6 (929.6) 94.7 Reserve for Revenues Subject to Refund (1) (93.4) — — (2.2) — — (95.6) Total Revenues from Contracts with Customers 5,614.0 1,256.4 1,348.6 159.4 999.1 (2,021.9) 7,355.6 Alternative Revenue Programs 14.9 21.3 (119.2) 1.3 — 103.0 21.3 Other Revenues (2) 3.2 0.1 0.7 0.3 — — 4.3 Total Operating Revenues $ 5,632.1 $ 1,277.8 $ 1,230.1 $ 161.0 $ 999.1 $ (1,918.9) $ 7,381.2 For the Three Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,183.9 $ 45.5 $ — $ 45.8 $ — $ — $ 1,275.2 Commercial 682.7 41.1 — 17.1 — (1.4) 739.5 Industrial 91.0 17.5 — 1.3 — (3.6) 106.2 Total Retail Tariff Sales Revenues 1,957.6 104.1 — 64.2 — (5.0) 2,120.9 Wholesale Transmission Revenues — — 458.2 — 19.0 (365.6) 111.6 Wholesale Market Sales Revenues 79.6 8.7 — 1.1 — — 89.4 Other Revenues from Contracts with Customers 20.7 1.3 3.2 0.7 303.3 (299.0) 30.2 Total Revenues from Contracts with Customers 2,057.9 114.1 461.4 66.0 322.3 (669.6) 2,352.1 Alternative Revenue Programs 1.7 (4.0) (72.3) (2.0) — 67.0 (9.6) Other Revenues (2) 0.7 0.1 0.2 0.1 — — 1.1 Total Operating Revenues $ 2,060.3 $ 110.2 $ 389.3 $ 64.1 $ 322.3 $ (602.6) $ 2,343.6 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,063.7 $ 399.6 $ — $ 113.2 $ — $ — $ 3,576.5 Commercial 1,815.7 243.5 — 47.7 — (3.7) 2,103.2 Industrial 248.4 67.0 — 3.6 — (10.1) 308.9 Total Retail Tariff Sales Revenues 5,127.8 710.1 — 164.5 — (13.8) 5,988.6 Wholesale Transmission Revenues — — 1,177.9 — 55.6 (981.4) 252.1 Wholesale Market Sales Revenues 231.1 31.9 — 2.9 — — 265.9 Other Revenues from Contracts with Customers 63.3 4.1 9.9 2.8 845.1 (838.0) 87.2 Total Revenues from Contracts with Customers 5,422.2 746.1 1,187.8 170.2 900.7 (1,833.2) 6,593.8 Alternative Revenue Programs 54.8 22.9 (52.7) (4.1) — 48.9 69.8 Other Revenues (2) 4.9 1.0 0.5 0.5 — — 6.9 Total Operating Revenues $ 5,481.9 $ 770.0 $ 1,135.6 $ 166.6 $ 900.7 $ (1,784.3) $ 6,670.5 For the Three Months Ended September 30, 2021 For the Three Months Ended September 30, 2020 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 572.0 $ 401.9 $ 172.9 $ 608.7 $ 415.4 $ 159.8 Commercial 249.4 411.3 88.5 244.7 358.3 80.1 Industrial 35.0 35.9 25.3 38.0 30.6 22.4 Total Retail Tariff Sales Revenues 856.4 849.1 286.7 891.4 804.3 262.3 Wholesale Transmission Revenues 268.2 171.0 88.0 233.3 153.1 71.8 Wholesale Market Sales Revenues 100.3 21.3 12.2 60.0 12.1 7.5 Other Revenues from Contracts with Customers 12.1 14.3 7.3 8.1 10.5 3.7 (Reserve for)/Amortization of Revenues Subject to Refund (1) (93.4) — — — — 2.3 Total Revenues from Contracts with Customers 1,143.6 1,055.7 394.2 1,192.8 980.0 347.6 Alternative Revenue Programs (82.0) (14.4) (24.1) (65.0) 8.2 (13.8) Other Revenues (2) 0.2 0.7 0.6 0.2 0.7 — Eliminations (142.2) (123.3) (55.8) (133.7) (113.5) (50.1) Total Operating Revenues $ 919.6 $ 918.7 $ 314.9 $ 994.3 $ 875.4 $ 283.7 For the Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2020 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,558.6 $ 1,069.0 $ 467.3 $ 1,567.9 $ 1,057.9 $ 437.9 Commercial 679.3 975.7 249.2 670.4 921.3 225.3 Industrial 100.2 89.5 71.4 105.3 82.1 61.0 Total Retail Tariff Sales Revenues 2,338.1 2,134.2 787.9 2,343.6 2,061.3 724.2 Wholesale Transmission Revenues 652.8 478.2 207.4 576.5 430.3 171.1 Wholesale Market Sales Revenues 278.1 64.7 37.3 163.9 39.8 27.4 Other Revenues from Contracts with Customers 28.8 36.8 14.9 25.1 32.4 10.9 (Reserve for)/Amortization of Revenues Subject to Refund (1) (93.4) — — — — 6.9 Total Revenues from Contracts with Customers 3,204.4 2,713.9 1,047.5 3,109.1 2,563.8 940.5 Alternative Revenue Programs (74.2) (11.3) (18.8) (27.8) 31.1 (1.2) Other Revenues (2) 0.3 2.5 1.1 2.0 2.8 0.6 Eliminations (394.0) (362.0) (142.6) (371.9) (327.5) (124.6) Total Operating Revenues $ 2,736.5 $ 2,343.1 $ 887.2 $ 2,711.4 $ 2,270.2 $ 815.3 (1) The Electric Distribution segment 2021 revenue subject to refund amount relates to an October 1, 2021 CL&P settlement agreement with the DEEP, OCC, AG and the Connecticut Industrial Energy Consumers, which resolved certain issues that arose in pending regulatory proceedings initiated by the PURA. In the third quarter of 2021, CL&P recorded a reduction to Operating Revenues of $65 million on the income statement for a reserve for customer credits associated with the provisions of the settlement agreement. Additionally, CL&P recorded a $28.4 million reserve in the first quarter of 2021 for a civil penalty for non-compliance with storm performance standards to be credited to customers. The penalty was reclassified from Operations and Maintenance expense to a reduction of Operating Revenues in the third quarter of 2021 in connection with the finalization of the settlement agreement. In total, the reserve for revenues subject to refund totaled $93.4 million and was recorded as a current regulatory liability on CL&P’s balance sheet and as a reduction to Operating Revenues on the nine months ended September 30, 2021 income statement. See Note 9G, “Commitments and Contingencies - CL&P Regulatory Matters,” for further information. Other Revenues also include lease revenues under lessor accounting guidance

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2021
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 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) the results of other unregulated subsidiaries, which are not part of its core business, and 5) 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 Three Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Operating Revenues $ 2,055.2 $ 185.5 $ 418.3 $ 61.8 $ 326.1 $ (614.1) $ 2,432.8 Depreciation and Amortization (179.8) (28.5) (75.4) (11.5) (28.0) 1.1 (322.1) Other Operating Expenses (1,640.5) (176.9) (122.4) (26.1) (275.2) 613.7 (1,627.4) Operating Income/(Loss) $ 234.9 $ (19.9) $ 220.5 $ 24.2 $ 22.9 $ 0.7 $ 483.3 Interest Expense $ (61.0) $ (15.7) $ (33.5) $ (8.0) $ (42.5) $ 12.7 $ (148.0) Other Income, Net 25.4 6.7 5.0 1.2 325.9 (320.4) 43.8 Net Income/(Loss) Attributable to Common 150.4 (22.0) 139.4 17.5 304.9 (307.0) 283.2 For the Nine Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 5,632.1 $ 1,277.8 $ 1,230.1 $ 161.0 $ 999.1 $ (1,918.9) $ 7,381.2 Depreciation and Amortization (534.1) (108.7) (223.4) (34.3) (83.7) 3.1 (981.1) Other Operating Expenses (4,531.3) (970.6) (359.6) (76.7) (860.3) 1,918.9 (4,879.6) Operating Income $ 566.7 $ 198.5 $ 647.1 $ 50.0 $ 55.1 $ 3.1 $ 1,520.5 Interest Expense $ (175.4) $ (44.2) $ (98.7) $ (24.0) $ (125.9) $ 37.0 $ (431.2) Other Income, Net 76.0 15.2 17.3 3.1 1,059.2 (1,046.2) 124.6 Net Income Attributable to Common Shareholders 365.4 129.6 412.4 30.0 982.5 (1,006.1) 913.8 Cash Flows Used for Investments in Plant 764.9 506.4 691.0 91.2 157.6 — 2,211.1 For the Three Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Distribution (1) Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 2,060.3 $ 110.2 $ 389.3 $ 64.1 $ 322.3 $ (602.6) $ 2,343.6 Depreciation and Amortization (182.0) (14.8) (70.6) (10.8) (24.1) 0.3 (302.0) Other Operating Expenses (1,577.0) (104.2) (120.6) (10.2) (271.5) 603.1 (1,480.4) Operating Income/(Loss) $ 301.3 $ (8.8) $ 198.1 $ 43.1 $ 26.7 $ 0.8 $ 561.2 Interest Expense $ (53.3) $ (10.1) $ (31.1) $ (8.0) $ (38.7) $ 7.1 $ (134.1) Other Income, Net 16.0 0.7 6.9 1.6 401.0 (397.0) 29.2 Net Income/(Loss) Attributable to Common 205.5 (15.4) 125.6 23.1 396.6 (389.1) 346.3 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Distribution (1) Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 5,481.9 $ 770.0 $ 1,135.6 $ 166.6 $ 900.7 $ (1,784.3) $ 6,670.5 Depreciation and Amortization (490.0) (55.1) (206.8) (33.1) (68.1) 1.2 (851.9) Other Operating Expenses (4,309.9) (592.0) (338.5) (60.7) (771.4) 1,787.9 (4,284.6) Operating Income $ 682.0 $ 122.9 $ 590.3 $ 72.8 $ 61.2 $ 4.8 $ 1,534.0 Interest Expense $ (160.7) $ (32.1) $ (93.8) $ (25.1) $ (119.0) $ 27.6 $ (403.1) Other Income, Net 44.9 2.5 22.7 1.7 1,087.9 (1,076.1) 83.6 Net Income Attributable to Common Shareholders 450.6 73.3 381.8 35.6 1,035.6 (1,043.7) 933.2 Cash Flows Used for Investments in Plant 781.2 322.8 732.4 84.0 181.2 — 2,101.6 (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. The following table summarizes Eversource's segmented total assets: Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total As of September 30, 2021 $ 25,604.2 $ 6,865.6 $ 12,123.5 $ 2,444.9 $ 21,624.5 $ (20,648.6) $ 48,014.1 As of December 31, 2020 24,981.9 6,450.5 11,695.0 2,375.2 22,089.4 (21,492.4) 46,099.6

ACQUISITION OF ASSETS OF COLUMB

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [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 the NiSource Inc. (NiSource) 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. The cash purchase price was $1.1 billion, plus a working capital amount of $68.6 million, as finalized in the first quarter of 2021. 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. Preliminary Purchase Price Allocation : The purchase price allocation reflects measurement period adjustments recorded in 2021 to reduce the fair values of certain regulatory and plant assets and certain liabilities acquired, resulting in a corresponding increase to Goodwill, based on new information received during the measurement period. The preliminary allocation of the cash purchase price is as follows: (Millions of Dollars) Current Assets $ 138 Restricted Cash 57 PP&E 1,184 Goodwill 50 Other Noncurrent Assets, excluding Goodwill 131 Other Current Liabilities (81) Other Noncurrent Liabilities (310) Cash Purchase Price $ 1,169

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation Eversource Energy is a public utility holding company primarily engaged, through its wholly-owned regulated utility subsidiaries, in the energy delivery business. Eversource Energy's wholly-owned regulated utility subsidiaries consist of CL&P, NSTAR Electric 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. The unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH include the accounts of each of their respective subsidiaries. Intercompany transactions have been eliminated in consolidation. The accompanying unaudited condensed consolidated financial statements of Eversource, NSTAR Electric and PSNH and the unaudited condensed financial statements of CL&P are herein collectively referred to as the "financial statements." The combined notes to the financial statements have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures included in annual financial statements prepared in accordance with GAAP have been omitted pursuant to such rules and regulations. The accompanying financial statements should be read in conjunction with the Combined Notes to Financial Statements included in Item 8, "Financial Statements and Supplementary Data," of the Eversource 2020 Form 10-K, which was filed with the SEC on February 17, 2021. The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. The financial statements contain, in the opinion of management, all adjustments (including normal, recurring adjustments) necessary to present fairly Eversource's, CL&P's, NSTAR Electric's and PSNH's financial position as of September 30, 2021 and December 31, 2020, and the results of operations, comprehensive income and common shareholders' equity for the three and nine months ended September 30, 2021 and 2020 and the cash flows for the nine months ended September 30, 2021 and 2020. The results of operations and comprehensive income for the three and nine months ended September 30, 2021 and 2020 and the cash flows for the nine months ended September 30, 2021 and 2020 are not necessarily indicative of the results expected for a full year. Eversource's consolidated financial information includes the results of the acquisition of the assets of Columbia Gas of Massachusetts (CMA) on October 9, 2020. The natural gas distribution assets acquired from CMA on October 9, 2020 were assigned to EGMA. 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. 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 customers, workers and the U.S. economy. We provide a critical service to our customers and have taken extensive measures to maintain its safety and reliability. We continue to address the impacts of the COVID-19 pandemic and how the related developments affect Eversource. We are in the re-entry phase of our pandemic response plan, in which the majority of our employees under remote work arrangements have transitioned back to the workplace. We have not experienced significant impacts directly related to the pandemic that have materially affected our current operations, our workforce, or results of operations. The extent of the impact to us in the future will vary, and depend on the duration, scope and severity of the pandemic and the resulting impact on economic, health care and capital market conditions. The future impact will also depend on the outcome of future proceedings before our state regulatory commissions to recover our incremental costs associated with COVID-19, which include uncollectible customer receivable expenses. Based on the status of our COVID-19 regulatory dockets, communications with our state regulatory commissions, and policies and practices in the jurisdictions in which we operate, we believe our state regulatory commissions in Connecticut and Massachusetts 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 1C, "Summary of Significant Accounting Policies - Allowance for Uncollectible Accounts," for discussion of our evaluation of the allowance for doubtful accounts as of September 30, 2021 in light of the COVID-19 pandemic and Note 2, "Regulatory Accounting," for the amount of net incremental COVID-19 costs deferred on our balance sheets. Certain reclassifications of prior period data were made in the accompanying financial statements to conform to the current period presentation.
Accounting Standards	Accounting Standards Accounting Standards Recently Adopted: On January 1, 2021, the Company adopted 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 ASU did not have a material impact on the financial statements of Eversource, CL&P, NSTAR Electric and PSNH.
Allowance 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. The current expected credit loss (CECL) model is 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. 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 September 30, 2021, 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 lower cash collections from customers because of the length of the moratorium on disconnections in Connecticut and Massachusetts, and the economic slowdown resulting from the COVID-19 pandemic. In Connecticut, the moratorium on disconnections of commercial and non-hardship residential customers ended in June 2021 and September 2021, respectively, but is still in place for hardship residential customers. In Massachusetts, the moratorium on disconnections of commercial customers and residential customers ended in September 2020 and July 2021, respectively. Disconnection activities have resumed after these moratoria have expired, which has resulted in recent improved collection experience and more customers applying for, and receiving, hardship status. On July 7, 2021, the NHPUC issued an order to New Hampshire utilities that concluded that recovery of incremental bad debt or waived late fees related to the COVID-19 pandemic would be addressed in a future rate case to the extent those costs are relevant at that time. As a result of the order, in the first nine months of 2021, PSNH removed its $0.6 million deferral of net incremental COVID-19 costs. In New Hampshire, the moratorium on disconnections of non-hardship residential and commercial customers ended in late 2020 and for hardship residential customers ended in May 2021 and PSNH has resumed disconnection activities, which has resulted in improved collection of outstanding customer receivable balances. Based upon the evaluation performed, in the first nine months of 2021, management increased the allowance for uncollectible accounts for amounts incurred as a result of COVID-19 by $25.8 million for Eversource (increase of $16.3 million for CL&P and $12.5 million at our natural gas businesses, and decrease of $1.8 million at NSTAR Electric). In the third quarter of 2021, the COVID-19 related allowance for uncollectible accounts decreased by $6.5 million at Eversource (increased $4.0 million at CL&P, and decreased $8.3 million at NSTAR Electric and $2.2 million at our natural gas businesses). The COVID-19 related uncollectible amounts were deferred either as incremental regulatory costs at our Connecticut and Massachusetts utilities 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 future rates. As of September 30, 2021, the total amount incurred as a result of COVID-19 included in the allowance for uncollectible accounts was $57.0 million at Eversource ($20.1 million at CL&P, $8.5 million at NSTAR Electric, and $27.4 million at our natural gas businesses). Management concluded that the reserve balance as of September 30, 2021 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, NSTAR Gas and EGMA to recover in rates amounts associated with certain uncollectible hardship accounts receivable. These uncollectible hardship customer account balances are included in Regulatory Assets or Other Long-Term Assets on the balance sheets. 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. Management uses a higher credit risk profile for this pool of trade receivables as compared to non-hardship receivables. The allowance for uncollectible hardship accounts is included in the total uncollectible allowance balance.
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's assets 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.
Other Taxes	Other TaxesEversource's companies that serve customers in Connecticut collect gross receipts taxes levied by the state of Connecticut from their customers. 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 incomeAs 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.
Restricted Cash	Special Deposits represent cash collections related to the PSNH RRB customer charges that are held in trust, required ISO-NE cash deposits, and CYAPC and YAEC cash balances. Special Deposits are included in Current Assets on the balance sheets. Restricted cash included in Marketable Securities represents money market funds held in trusts to fund certain non-qualified executive benefits and restricted trusts to fund CYAPC and YAEC's spent nuclear fuel storage obligations. Restricted cash included in Other Long-Term Assets includes $41.5 million related to an Energy Relief Fund for energy efficiency and clean energy measures in the Merrimack Valley, and an additional energy efficiency program established under the terms of the EGMA settlement agreement.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Allowance for Uncollectible Accounts	The activity in the allowance for uncollectible accounts by portfolio segment as of September 30 th is as follows: 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 Three Months Ended 2021 Beginning Balance $ 210.7 $ 215.1 $ 425.8 $ 145.6 $ 43.2 $ 188.8 $ 35.9 $ 62.1 $ 98.0 $ 17.2 Uncollectible Expense — 12.0 12.0 — 3.6 3.6 — 5.1 5.1 1.2 Uncollectible Costs Deferred (1) 22.8 1.7 24.5 4.5 5.7 10.2 11.8 (3.5) 8.3 1.2 Write-Offs (3.9) (20.5) (24.4) (3.5) (5.4) (8.9) (0.1) (7.4) (7.5) (2.8) Recoveries Collected 0.3 3.5 3.8 0.2 1.6 1.8 — 1.1 1.1 0.2 Ending Balance $ 229.9 $ 211.8 $ 441.7 $ 146.8 $ 48.7 $ 195.5 $ 47.6 $ 57.4 $ 105.0 $ 17.0 Nine Months Ended 2021 Beginning Balance $ 194.8 $ 164.1 $ 358.9 $ 129.1 $ 28.3 $ 157.4 $ 39.7 $ 51.9 $ 91.6 $ 17.2 Uncollectible Expense — 39.7 39.7 — 10.2 10.2 — 12.5 12.5 4.4 Uncollectible Costs Deferred (1) 44.8 53.3 98.1 25.7 21.4 47.1 8.3 11.8 20.1 2.0 Write-Offs (10.6) (55.2) (65.8) (8.7) (14.8) (23.5) (0.4) (22.6) (23.0) (7.3) Recoveries Collected 0.9 9.9 10.8 0.7 3.6 4.3 — 3.8 3.8 0.7 Ending Balance $ 229.9 $ 211.8 $ 441.7 $ 146.8 $ 48.7 $ 195.5 $ 47.6 $ 57.4 $ 105.0 $ 17.0 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 Three Months Ended 2020 Beginning Balance $ 175.5 $ 94.5 $ 270.0 $ 116.3 $ 20.4 $ 136.7 $ 34.6 $ 34.1 $ 68.7 $ 11.8 Uncollectible Expense — 10.5 10.5 — 3.8 3.8 — 4.5 4.5 0.8 Uncollectible Costs Deferred (1) 10.1 20.4 30.5 11.2 4.9 16.1 (1.3) 10.4 9.1 3.2 Write-Offs (7.3) (11.8) (19.1) (2.6) (4.6) (7.2) (0.2) (6.3) (6.5) (2.0) Recoveries Collected 0.4 2.7 3.1 0.3 1.1 1.4 — 1.0 1.0 0.2 Ending Balance $ 178.7 $ 116.3 $ 295.0 $ 125.2 $ 25.6 $ 150.8 $ 33.1 $ 43.7 $ 76.8 $ 14.0 Nine Months Ended 2020 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 21.6 2.2 23.8 21.3 0.9 22.2 (1.6) 0.3 (1.3) 0.3 Uncollectible Expense — 31.1 31.1 — 10.0 10.0 — 11.3 11.3 2.1 Uncollectible Costs Deferred (1) 24.9 41.5 66.4 32.7 8.3 41.0 (8.4) 17.3 8.9 5.6 Write-Offs (12.3) (49.3) (61.6) (10.0) (14.0) (24.0) (0.8) (20.5) (21.3) (5.0) Recoveries Collected 1.2 9.3 10.5 1.1 3.2 4.3 — 3.8 3.8 0.5 Ending Balance $ 178.7 $ 116.3 $ 295.0 $ 125.2 $ 25.6 $ 150.8 $ 33.1 $ 43.7 $ 76.8 $ 14.0 (1) These expected credit losses are deferred as regulatory costs on the balance sheets, as these amounts are ultimately recovered in rates. Amounts include uncollectible costs for hardship accounts and other customer receivables, including uncollectible amounts related to COVID-19 and uncollectible energy supply costs.
Components of Other Income, Net	The components of Other Income, Net on the statements of income were as follows: For the Three Months Ended September 30, 2021 September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Pension, SERP and PBOP Non-Service $ 21.7 $ 4.2 $ 10.1 $ 2.5 $ 11.0 $ 0.9 $ 7.2 $ 1.8 AFUDC Equity 10.3 1.7 6.2 0.3 10.3 3.5 5.5 0.9 Equity in Earnings of Unconsolidated Affiliates (1) 4.9 — 0.1 — 3.9 — 0.1 — Investment (Loss)/Income (0.6) (0.3) (0.2) (0.1) 1.0 1.3 (0.2) 0.2 Interest Income 7.3 1.3 3.9 0.4 1.5 0.2 0.1 1.2 Gain on Sale of Property — — — — 1.5 — — — Other 0.2 — 0.1 0.1 — — 0.1 — Total Other Income, Net $ 43.8 $ 6.9 $ 20.2 $ 3.2 $ 29.2 $ 5.9 $ 12.8 $ 4.1 For the Nine Months Ended September 30, 2021 September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Pension, SERP and PBOP Non-Service $ 63.9 $ 11.2 $ 30.3 $ 7.9 $ 34.3 $ 3.0 $ 22.2 $ 5.2 AFUDC Equity 28.7 5.1 18.6 1.2 31.8 11.4 15.8 3.5 Equity in Earnings of Unconsolidated Affiliates (1) 13.3 — 0.3 — 13.8 — 0.4 — Investment Income/(Loss) 0.7 1.2 0.6 0.3 (1.5) — (1.5) 0.1 Interest Income 17.2 4.1 8.8 2.0 3.3 1.8 0.7 2.0 Gain on Sale of Property 0.1 — — 0.1 1.8 — 0.3 — Other 0.7 0.1 0.3 0.1 0.1 0.1 0.3 0.1 Total Other Income, Net $ 124.6 $ 21.7 $ 58.9 $ 11.6 $ 83.6 $ 16.3 $ 38.2 $ 10.9 (1) Equity in earnings of unconsolidated affiliates includes $2.1 million of pre-tax unrealized gains associated with an investment in a renewable energy fund for the nine months ended September 30, 2021. For the nine months ended September 30, 2020, equity in earnings of unconsolidated affiliates included $2.4 million of primarily realized gains associated with this investment.
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 Three Months Ended For the Nine Months Ended (Millions of Dollars) September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Eversource $ 49.4 $ 48.4 $ 137.9 $ 129.1 CL&P 46.1 45.6 120.7 114.2
Non-cash Investing Activities	Non-cash investing activities include plant additions included in Accounts Payable as follows: (Millions of Dollars) As of September 30, 2021 As of September 30, 2020 Eversource $ 359.6 $ 357.4 CL&P 75.3 97.8 NSTAR Electric 94.2 92.6 PSNH 32.8 50.0
Reconciliation of Cash Balances to Cash and Restricted Cash	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 September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Cash as reported on the Balance Sheets $ 88.2 $ 62.8 $ 3.5 $ 3.9 $ 106.6 $ 90.8 $ 0.1 $ 0.1 Restricted cash included in: Special Deposits 55.5 8.7 17.2 18.6 73.6 8.7 17.2 36.8 Marketable Securities 29.7 0.3 0.1 0.5 41.2 0.3 0.1 0.6 Other Long-Term Assets 44.7 — — 3.2 43.6 — — 2.1 Cash and Restricted Cash as reported on the Statements of Cash Flows $ 218.1 $ 71.8 $ 20.8 $ 26.2 $ 265.0 $ 99.8 $ 17.4 $ 39.6

REGULATORY ACCOUNTING (Tables)

REGULATORY ACCOUNTING (Tables)	9 Months Ended
	Sep. 30, 2021
Regulated Operations [Abstract]
Components of Regulatory Assets	The components of regulatory assets were as follows: As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Benefit Costs $ 2,566.1 $ 540.2 $ 638.4 $ 249.7 $ 2,794.2 $ 632.3 $ 690.0 $ 267.6 Income Taxes, Net 756.4 458.1 113.8 18.7 747.1 458.9 110.4 15.2 Securitized Stranded Costs 489.7 — — 489.7 522.1 — — 522.1 Storm Restoration Costs, Net 944.2 674.2 198.1 71.9 765.6 515.1 186.4 64.1 Regulatory Tracker Mechanisms 883.0 304.6 320.0 76.8 850.5 246.6 332.2 95.3 Derivative Liabilities 265.3 265.3 — — 296.3 293.1 — — Goodwill-related 302.0 — 259.3 — 314.7 — 270.2 — Asset Retirement Obligations 121.6 33.7 57.8 4.0 118.4 32.1 58.6 3.9 Other Regulatory Assets 146.9 31.0 48.7 16.9 161.0 33.7 56.1 20.9 Total Regulatory Assets 6,475.2 2,307.1 1,636.1 927.7 6,569.9 2,211.8 1,703.9 989.1 Less: Current Portion 1,016.3 325.3 388.4 97.9 1,076.6 345.6 399.9 115.9 Total Long-Term Regulatory Assets $ 5,458.9 $ 1,981.8 $ 1,247.7 $ 829.8 $ 5,493.3 $ 1,866.2 $ 1,304.0 $ 873.2
Components of Regulatory Liabilities	The components of regulatory liabilities were as follows: As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH EDIT due to Tax Cuts and Jobs Act of 2017 $ 2,737.1 $ 1,001.5 $ 1,025.6 $ 363.9 $ 2,778.6 $ 1,010.7 $ 1,044.0 $ 371.5 Cost of Removal 676.7 117.0 384.1 19.0 624.8 98.4 363.6 12.9 Benefit Costs 65.9 — 56.5 — 83.6 — 72.5 — Regulatory Tracker Mechanisms 484.5 208.9 180.6 87.5 366.5 148.9 139.7 47.8 AFUDC - Transmission 79.6 43.6 36.0 — 76.8 44.6 32.2 — CL&P Settlement Agreement and Storm 103.4 103.4 — — — — — — Other Regulatory Liabilities 373.3 50.4 84.6 15.8 309.9 39.5 63.2 9.8 Total Regulatory Liabilities 4,520.5 1,524.8 1,767.4 486.2 4,240.2 1,342.1 1,715.2 442.0 Less: Current Portion 612.9 311.3 205.8 96.8 389.4 137.2 164.8 58.8 Total Long-Term Regulatory Liabilities $ 3,907.6 $ 1,213.5 $ 1,561.6 $ 389.4 $ 3,850.8 $ 1,204.9 $ 1,550.4 $ 383.2

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Summary of Property, Plant, and Equipment	The following tables summarize property, plant and equipment by asset category: Eversource As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Distribution - Electric $ 17,257.3 $ 16,703.2 Distribution - Natural Gas 6,334.9 6,111.2 Transmission - Electric 12,396.2 11,954.0 Distribution - Water 1,771.1 1,743.1 Solar 200.4 201.5 Utility 37,959.9 36,713.0 Other (1) 1,430.5 1,269.0 Property, Plant and Equipment, Gross 39,390.4 37,982.0 Less: Accumulated Depreciation Utility (8,830.2) (8,476.3) Other (550.0) (477.6) Total Accumulated Depreciation (9,380.2) (8,953.9) Property, Plant and Equipment, Net 30,010.2 29,028.1 Construction Work in Progress 2,456.9 1,854.4 Total Property, Plant and Equipment, Net $ 32,467.1 $ 30,882.5 As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) CL&P NSTAR PSNH CL&P NSTAR PSNH Distribution - Electric $ 7,028.9 $ 7,798.8 $ 2,469.9 $ 6,820.7 $ 7,544.4 $ 2,378.4 Transmission - Electric 5,707.9 4,884.0 1,805.9 5,512.0 4,701.3 1,742.4 Solar — 200.4 — — 201.5 — Property, Plant and Equipment, Gross 12,736.8 12,883.2 4,275.8 12,332.7 12,447.2 4,120.8 Less: Accumulated Depreciation (2,574.6) (3,220.7) (895.4) (2,475.4) (3,074.1) (848.9) Property, Plant and Equipment, Net 10,162.2 9,662.5 3,380.4 9,857.3 9,373.1 3,271.9 Construction Work in Progress 436.6 949.2 148.7 377.3 750.0 102.4 Total Property, Plant and Equipment, Net $ 10,598.8 $ 10,611.7 $ 3,529.1 $ 10,234.6 $ 10,123.1 $ 3,374.3 (1) These assets are primarily comprised of computer software, hardware and equipment at Eversource Service and buildings at The Rocky River Realty Company.

DERIVATIVE INSTRUMENTS (Tables)

DERIVATIVE INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross Fair Values and Net Amounts of Contracts	The following table presents the gross fair values of contracts, categorized by risk type, and the net amounts recorded as current or long-term derivative assets or liabilities: As of September 30, 2021 As of December 31, 2020 (Millions of Dollars) Fair Value Hierarchy Commodity Supply and Price Risk Netting (1) Net Amount Commodity Supply and Price Risk Netting (1) Net Amount Current Derivative Assets: CL&P Level 3 $ 14.4 $ (0.4) $ 14.0 $ 13.7 $ (0.4) $ 13.3 Long-Term Derivative Assets: CL&P Level 3 51.1 (1.6) 49.5 58.7 (1.8) 56.9 Current Derivative Liabilities: CL&P Level 3 (72.2) — (72.2) (68.8) — (68.8) Other Level 2 — — — (3.3) 0.1 (3.2) Long-Term Derivative Liabilities: CL&P Level 3 (256.6) — (256.6) (294.5) — (294.5) (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.
Summary of Level 3 Derivative Contracts and Significant Unobservable Inputs Used	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 September 30, 2021 As of December 31, 2020 CL&P Range Weighted Average (1) Period Covered Range Weighted Average (1) Period Covered Capacity Prices $2.61 $ 2.61 per kW-Month 2025 - 2026 $ 4.30 — $5.30 $ 4.63 per kW-Month 2024 - 2026 Forward Reserve Prices $ 0.50 — $1.15 $ 0.82 per kW-Month 2022 - 2024 $ 0.54 — $0.90 $ 0.72 per kW-Month 2021 - 2024 (1) Unobservable inputs were weighted by the relative future capacity and forward reserve prices and contractual MWs over the periods covered.
Changes in the Level 3 Category of Derivative Assets Measured at Fair Value on a Recurring Basis	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 For the Three Months Ended September 30, For the Nine Months Ended September 30, (Millions of Dollars) 2021 2020 2021 2020 Derivatives, Net: Fair Value as of Beginning of Period $ (279.7) $ (322.0) $ (293.1) $ (329.2) Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets 0.7 (4.7) (10.9) (22.3) Settlements 13.7 14.9 38.7 39.7 Fair Value as of End of Period $ (265.3) $ (311.8) $ (265.3) $ (311.8)

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Summary of 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 September 30, 2021 As of December 31, 2020 Eversource (Millions of Dollars) Amortized Cost Pre-Tax Pre-Tax Fair Value Amortized Cost Pre-Tax Pre-Tax Fair Value Debt Securities $ 217.5 $ 8.0 $ (0.2) $ 225.3 $ 213.1 $ 11.2 $ (0.1) $ 224.2
Contractual Maturities of Available-for-Sale Debt Securities	As of September 30, 2021, the contractual maturities of available-for-sale debt securities were as follows: Eversource (Millions of Dollars) Amortized Cost Fair Value Less than one year (1) $ 30.9 $ 30.9 One to five years 65.5 67.1 Six to ten years 41.8 43.9 Greater than ten years 79.3 83.4 Total Debt Securities $ 217.5 $ 225.3 (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 on a Recurring Basis by Level	The following table presents the marketable securities recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy: Eversource (Millions of Dollars) As of September 30, 2021 As of December 31, 2020 Level 1: Mutual Funds and Equities $ 254.1 $ 246.0 Money Market Funds 29.7 41.2 Total Level 1 $ 283.8 $ 287.2 Level 2: U.S. Government Issued Debt Securities (Agency and Treasury) $ 98.9 $ 72.9 Corporate Debt Securities 63.4 63.8 Asset-Backed Debt Securities 13.4 11.9 Municipal Bonds 6.1 24.0 Other Fixed Income Securities 13.8 10.4 Total Level 2 $ 195.6 $ 183.0 Total Marketable Securities $ 479.4 $ 470.2

SHORT-TERM AND LONG-TERM DEBT (

SHORT-TERM AND LONG-TERM DEBT (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Borrowings Outstanding and Available under the Commercial Paper Programs	The amount of borrowings outstanding and available under the commercial paper programs were as follows: Borrowings Outstanding as of Available Borrowing Capacity as of Weighted-Average Interest Rate as of September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 September 30, 2021 December 31, 2020 (Millions of Dollars) Eversource Parent Commercial Paper Program $ 653.0 $ 1,054.3 $ 1,347.0 $ 945.7 0.18 % 0.25 % NSTAR Electric Commercial Paper Program 138.0 195.0 512.0 455.0 0.10 % 0.16 %
Summary of Long-Term Debt Issuance 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: 2.05% Series A First Mortgage Bonds $ 425.0 June 2021 July 2031 Repaid short-term debt, paid capital expenditures and working capital 4.38% Series A PCRB (120.5) September 2021 September 2028 Paid on par call date in advance of maturity NSTAR Electric: 3.10% 2021 Debentures 300.0 May 2021 June 2051 Refinanced investments in eligible green expenditures, which were previously financed in 2019 and 2020 3.50% Series F Senior Notes (250.0) June 2021 September 2021 Paid on par call date in advance of maturity date 1.95% 2021 Debentures 300.0 August 2021 August 2031 Repaid short-term debt, paid capital expenditures and working capital PSNH: 4.05% Series Q First Mortgage Bonds (122.0) March 2021 June 2021 Paid on par call date in advance of maturity date 3.20% Series R First Mortgage Bonds (160.0) June 2021 September 2021 Paid on par call date in advance of maturity date 2.20% Series V First Mortgage Bonds 350.0 June 2021 June 2031 Repaid short-term debt, including short-term debt used to redeem Series R First Mortgage Bonds, paid capital expenditures and working capital Other: Eversource Parent 2.50% Series I Senior Notes (450.0) February 2021 March 2021 Paid on par call date in advance of maturity date Eversource Parent 2.55% Series S Senior Notes 350.0 March 2021 March 2031 Repaid short-term debt, including short-term debt used to redeem Series I Senior Notes Eversource Parent 1.40% Series U Senior Notes 300.0 August 2021 August 2026 Repaid short-term debt Eversource Parent Variable Rate Series T Senior Notes (1) 350.0 August 2021 August 2023 Repaid short-term debt Aquarion Water Company of Connecticut 3.31% Senior Notes 100.0 April 2021 April 2051 Repaid 5.50% Notes, repaid short-term debt, paid capital expenditures and working capital Aquarion Water Company of Connecticut 5.50% Notes (40.0) April 2021 April 2021 Paid at maturity Yankee Gas 1.38% Series S First Mortgage Bonds 90.0 August 2021 August 2026 (2) Yankee Gas 2.88% Series T First Mortgage Bonds 35.0 August 2021 August 2051 (2) EGMA 2.11% Series A First Mortgage Bonds 310.0 September 2021 October 2031 (2) EGMA 2.92% Series B First Mortgage Bonds 240.0 September 2021 October 2051 (2) NSTAR Gas 2.25% Series T First Mortgage Bonds 40.0 October 2021 November 2031 (2) NSTAR Gas 3.03% Series U First Mortgage Bonds 40.0 October 2021 November 2051 (2) (1) On August 10, 2021, Eversource Parent issued $350 million of floating rate Series T Senior Notes with a maturity date of August 15, 2023. The notes have a coupon rate based on the Compounded SOFR plus 0.25%. (2) The use of proceeds from these various issuances refinanced existing indebtedness, funded capital expenditures and were for general corporate purposes. The EGMA indebtedness that was refinanced included $309.4 million of long-term debt.

RATE REDUCTION BONDS AND VARI_2

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES (Tables)	9 Months Ended
	Sep. 30, 2021
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) PSNH Balance Sheets: As of September 30, 2021 As of December 31, 2020 Restricted Cash - Current Portion (included in Current Assets) $ 18.3 $ 36.8 Restricted Cash - Long-Term Portion (included in Other Long-Term Assets) 3.2 2.1 Securitized Stranded Cost (included in Regulatory Assets) 489.7 522.1 Other Regulatory Liabilities (included in Regulatory Liabilities) 8.0 9.1 Accrued Interest (included in Other Current Liabilities) 3.0 8.0 Rate Reduction Bonds - Current Portion 43.2 43.2 Rate Reduction Bonds - Long-Term Portion 453.7 496.9 (Millions of Dollars) PSNH Income Statements: For the Three Months Ended For the Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net) $ 10.8 $ 10.8 $ 32.4 $ 32.4 Interest Expense on RRB Principal (included in Interest Expense) 4.5 4.9 13.9 14.9

PENSION BENEFITS AND POSTRETI_2

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION (Tables)	9 Months Ended
	Sep. 30, 2021
Postemployment Benefits [Abstract]
Components of Net Periodic Benefit Expense/(Income)	The components of net periodic benefit plan 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 plan 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 plan 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 intercompany allocations of net periodic benefit plan expense/(income), as these amounts are cash settled on a short-term basis. Pension and SERP PBOP For the Three Months Ended September 30, 2021 For the Three Months Ended September 30, 2021 (Millions of Dollars) Eversource CL&P NSTAR Electric PSNH Eversource CL&P NSTAR Electric PSNH Service Cost $ 21.5 $ 5.6 $ 4.0 $ 2.2 $ 3.3 $ 0.5 $ 0.6 $ 0.3 Interest Cost 32.5 6.7 6.7 3.7 4.3 0.8 1.1 0.4 Expected Return on Plan Assets (109.5) (21.7) (27.1) (11.9) (19.8) (2.5) (9.2) (1.6) Actuarial Loss 60.7 10.8 15.3 5.3 2.0 0.4 0.5 0.1 Prior Service Cost/(Credit) 0.3 — 0.1 — (5.3) 0.3 (4.3) 0.1 Total Net Periodic Benefit Plan Expense/(Income) $ 5.5 $ 1.4 $ (1.0) $ (0.7) $ (15.5) $ (0.5) $ (11.3) $ (0.7) Intercompany Expense/(Income) Allocations N/A $ 2.2 $ 2.4 $ 0.7 N/A $ (0.4) $ (0.5) $ (0.2) Pension and SERP PBOP For the Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2021 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 64.3 $ 17.4 $ 11.9 $ 6.6 $ 10.1 $ 1.7 $ 1.8 $ 0.9 Interest Cost 97.5 20.7 20.1 10.9 12.9 2.4 3.3 1.3 Expected Return on Plan Assets (328.0) (65.0) (81.1) (35.6) (59.3) (7.7) (27.7) (4.6) Actuarial Loss 183.1 34.6 46.1 15.4 5.9 1.2 1.6 0.4 Prior Service Cost/(Credit) 1.1 — 0.3 — (15.9) 0.8 (12.7) 0.3 Total Net Periodic Benefit Plan Expense/(Income) $ 18.0 $ 7.7 $ (2.7) $ (2.7) $ (46.3) $ (1.6) $ (33.7) $ (1.7) Intercompany Expense/(Income) Allocations N/A $ 5.8 $ 6.4 $ 1.9 N/A $ (1.3) $ (1.5) $ (0.5) Pension and SERP PBOP For the Three Months Ended September 30, 2020 For the Three Months Ended September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 18.7 $ 5.4 $ 3.8 $ 2.0 $ 2.4 $ 0.4 $ 0.5 $ 0.2 Interest Cost 44.4 9.3 9.7 4.8 6.1 1.1 1.7 0.7 Expected Return on Plan Assets (99.2) (19.8) (25.7) (11.1) (18.3) (2.5) (8.5) (1.4) Actuarial Loss 50.7 9.7 14.0 3.8 2.2 0.3 0.6 0.2 Prior Service Cost/(Credit) 0.2 — — — (5.3) 0.3 (4.2) 0.1 Total Net Periodic Benefit Plan Expense/(Income) $ 14.8 $ 4.6 $ 1.8 $ (0.5) $ (12.9) $ (0.4) $ (9.9) $ (0.2) Intercompany Expense/(Income) Allocations N/A $ 2.4 $ 2.3 $ 0.8 N/A $ (0.3) $ (0.4) $ (0.1) Pension and SERP PBOP For the Nine Months Ended September 30, 2020 For the Nine Months Ended September 30, 2020 (Millions of Dollars) Eversource CL&P NSTAR PSNH Eversource CL&P NSTAR PSNH Service Cost $ 57.0 $ 16.5 $ 11.4 $ 6.2 $ 7.3 $ 1.3 $ 1.6 $ 0.6 Interest Cost 133.0 28.1 29.0 14.5 18.3 3.3 5.0 2.1 Expected Return on Plan Assets (298.8) (59.6) (77.2) (33.5) (55.1) (7.4) (25.5) (4.2) Actuarial Loss 150.7 29.4 41.3 11.8 6.3 0.9 1.8 0.6 Prior Service Cost/(Credit) 0.8 — 0.2 — (15.9) 0.8 (12.7) 0.3 Total Net Periodic Benefit Plan Expense/(Income) $ 42.7 $ 14.4 $ 4.7 $ (1.0) $ (39.1) $ (1.1) $ (29.8) $ (0.6) Intercompany Expense/(Income) Allocations N/A $ 6.7 $ 6.5 $ 2.2 N/A $ (0.9) $ (1.0) $ (0.4)

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Environmental Sites and Related Reserves	The number of environmental sites and related reserves for which remediation or long-term monitoring, preliminary site work or site assessment is being performed are as follows: As of September 30, 2021 As of December 31, 2020 Number of Sites Reserve Number of Sites Reserve Eversource 62 $ 111.9 63 $ 102.4 CL&P 14 12.5 15 12.3 NSTAR Electric 12 3.7 12 4.7 PSNH 9 6.4 9 7.1
Non-Cancelable Commitments under Purchase Commitment Contracts	Renewable energy contracts include non-cancelable commitments under contracts of NSTAR Electric for the purchase of energy and RECs from renewable energy facilities. NSTAR Electric (Millions of Dollars) 2021 2022 2023 2024 2025 Thereafter Total Renewable Energy $ 27.1 $ 103.9 $ 230.5 $ 341.2 $ 348.1 $ 6,564.2 $ 7,615.0
Summary of Exposure to Guarantees and Indemnifications	The following table summarizes Eversource parent's exposure to guarantees and indemnifications of its subsidiaries and affiliates to external parties: As of September 30, 2021 Company (Obligor) Description Maximum Exposure Expiration Dates North East Offshore LLC Construction-related purchase agreements with third-party contractors (1) $ 1,093.5 (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) Sunrise Wind LLC Construction-related purchase agreements with third-party contractors (4) 386.4 — South Fork Wind, LLC Transmission interconnection 1.2 — South Fork Wind, LLC Construction-related purchase agreements with third-party contractors (5) 40.6 2023 Bay State Wind LLC Real estate purchase 2.5 2022 Various Surety bonds (6) 67.5 2021 - 2023 Rocky River Realty Company and Lease payments for real estate 4.0 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 aggregate 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 aggregate 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) 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 aggregate 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) Eversource parent issued a guaranty 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 aggregate amount not to exceed $420.6 million, in connection with a construction-related purchase agreement. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) April 14, 2026 and (ii) full performance of the guaranteed obligations. (5) Eversource parent issued two guarantees on behalf of its 50 percent-owned affiliate, South Fork Wind, LLC, whereby Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations in connection with two construction-related purchase agreements. Under one guarantee, Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations, in an aggregate amount not to exceed $25.8 million. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) October 4, 2023 and (ii) full performance of the guaranteed obligations. Under the second guaranty, Eversource parent will guarantee South Fork Wind, LLC's performance of certain obligations, in an aggregate amount not to exceed $14.8 million. Eversource parent’s obligations under the guarantee expire upon the earlier of (i) October 18, 2023 and (ii) full performance of the guaranteed obligations.

FAIR VALUE OF FINANCIAL INSTR_2

FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Carrying Amounts and Estimated Fair Values of Financial Instruments	Carrying amounts and estimated fair values are as follows: Eversource CL&P NSTAR Electric PSNH (Millions of Dollars) Carrying Fair Carrying Fair Carrying Fair Carrying Fair As of September 30, 2021: Preferred Stock Not Subject to Mandatory Redemption $ 155.6 $ 165.5 $ 116.2 $ 121.4 $ 43.0 $ 44.1 $ — $ — Long-Term Debt 18,219.2 19,810.9 4,215.1 4,865.2 3,984.7 4,494.3 1,163.6 1,228.9 Rate Reduction Bonds 496.9 555.8 — — — — 496.9 555.8 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

ACCUMULATED OTHER COMPREHENSI_2

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Tables)	9 Months Ended
	Sep. 30, 2021
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 Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Qualified Unrealized Defined Total Qualified Unrealized Defined Total Balance as of Beginning of Period $ (1.4) $ 1.1 $ (76.1) $ (76.4) $ (3.0) $ 0.7 $ (62.8) $ (65.1) OCI Before Reclassifications — (0.6) (2.4) (3.0) — 0.3 (1.6) (1.3) Amounts Reclassified from AOCI 1.0 — 6.5 7.5 1.2 — 4.8 6.0 Net OCI 1.0 (0.6) 4.1 4.5 1.2 0.3 3.2 4.7 Balance as of End of Period $ (0.4) $ 0.5 $ (72.0) $ (71.9) $ (1.8) $ 1.0 $ (59.6) $ (60.4)

COMMON SHARES (Tables)

COMMON SHARES (Tables)	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 Issued as of Par Value September 30, 2021 December 31, 2020 Eversource $ 5 380,000,000 357,818,402 357,818,402 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

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2021
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 Three Months Ended For the Nine Months Ended September 30, 2021 September 30, 2020 September 30, 2021 September 30, 2020 Net Income Attributable to Common Shareholders $ 283.2 $ 346.3 $ 913.8 $ 933.2 Weighted Average Common Shares Outstanding: Basic 344,023,846 343,076,614 343,848,905 337,375,172 Dilutive Effect of: Share-Based Compensation Awards and Other 645,936 696,988 631,151 686,403 Equity Forward Sale Agreement — — — 362,525 Total Dilutive Effect 645,936 696,988 631,151 1,048,928 Diluted 344,669,782 343,773,602 344,480,056 338,424,100 Basic EPS $ 0.82 $ 1.01 $ 2.66 $ 2.77 Diluted EPS $ 0.82 $ 1.01 $ 2.65 $ 2.76

REVENUES (Tables)

REVENUES (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Operating Revenues Disaggregated by Revenue Source	The following tables present operating revenues disaggregated by revenue source: For the Three Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,146.8 $ 81.7 $ — $ 39.1 $ — $ — $ 1,267.6 Commercial 748.8 59.0 — 17.2 — (1.4) 823.6 Industrial 96.2 28.6 — 1.1 — (4.8) 121.1 Total Retail Tariff Sales Revenues 1,991.8 169.3 — 57.4 — (6.2) 2,212.3 Wholesale Transmission Revenues — — 527.2 — 23.0 (408.5) 141.7 Wholesale Market Sales Revenues 133.8 12.2 — 1.1 — — 147.1 Other Revenues from Contracts with Customers 29.6 1.2 3.5 1.8 303.1 (301.4) 37.8 Reserve for Revenues Subject to Refund (1) (93.4) — — (0.9) — — (94.3) Total Revenues from Contracts with Customers 2,061.8 182.7 530.7 59.4 326.1 (716.1) 2,444.6 Alternative Revenue Programs (7.9) 2.7 (112.6) 2.3 — 102.0 (13.5) Other Revenues (2) 1.3 0.1 0.2 0.1 — — 1.7 Total Operating Revenues $ 2,055.2 $ 185.5 $ 418.3 $ 61.8 $ 326.1 $ (614.1) $ 2,432.8 For the Nine Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,094.9 $ 722.8 $ — $ 102.8 $ — $ — $ 3,920.5 Commercial 1,902.9 356.4 — 47.0 — (4.1) 2,302.2 Industrial 261.1 119.5 — 3.3 — (12.8) 371.1 Total Retail Tariff Sales Revenues 5,258.9 1,198.7 — 153.1 — (16.9) 6,593.8 Wholesale Transmission Revenues — — 1,338.4 — 62.5 (1,075.4) 325.5 Wholesale Market Sales Revenues 380.1 54.1 — 3.0 — — 437.2 Other Revenues from Contracts with Customers 68.4 3.6 10.2 5.5 936.6 (929.6) 94.7 Reserve for Revenues Subject to Refund (1) (93.4) — — (2.2) — — (95.6) Total Revenues from Contracts with Customers 5,614.0 1,256.4 1,348.6 159.4 999.1 (2,021.9) 7,355.6 Alternative Revenue Programs 14.9 21.3 (119.2) 1.3 — 103.0 21.3 Other Revenues (2) 3.2 0.1 0.7 0.3 — — 4.3 Total Operating Revenues $ 5,632.1 $ 1,277.8 $ 1,230.1 $ 161.0 $ 999.1 $ (1,918.9) $ 7,381.2 For the Three Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,183.9 $ 45.5 $ — $ 45.8 $ — $ — $ 1,275.2 Commercial 682.7 41.1 — 17.1 — (1.4) 739.5 Industrial 91.0 17.5 — 1.3 — (3.6) 106.2 Total Retail Tariff Sales Revenues 1,957.6 104.1 — 64.2 — (5.0) 2,120.9 Wholesale Transmission Revenues — — 458.2 — 19.0 (365.6) 111.6 Wholesale Market Sales Revenues 79.6 8.7 — 1.1 — — 89.4 Other Revenues from Contracts with Customers 20.7 1.3 3.2 0.7 303.3 (299.0) 30.2 Total Revenues from Contracts with Customers 2,057.9 114.1 461.4 66.0 322.3 (669.6) 2,352.1 Alternative Revenue Programs 1.7 (4.0) (72.3) (2.0) — 67.0 (9.6) Other Revenues (2) 0.7 0.1 0.2 0.1 — — 1.1 Total Operating Revenues $ 2,060.3 $ 110.2 $ 389.3 $ 64.1 $ 322.3 $ (602.6) $ 2,343.6 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Revenues from Contracts with Customers Retail Tariff Sales Residential $ 3,063.7 $ 399.6 $ — $ 113.2 $ — $ — $ 3,576.5 Commercial 1,815.7 243.5 — 47.7 — (3.7) 2,103.2 Industrial 248.4 67.0 — 3.6 — (10.1) 308.9 Total Retail Tariff Sales Revenues 5,127.8 710.1 — 164.5 — (13.8) 5,988.6 Wholesale Transmission Revenues — — 1,177.9 — 55.6 (981.4) 252.1 Wholesale Market Sales Revenues 231.1 31.9 — 2.9 — — 265.9 Other Revenues from Contracts with Customers 63.3 4.1 9.9 2.8 845.1 (838.0) 87.2 Total Revenues from Contracts with Customers 5,422.2 746.1 1,187.8 170.2 900.7 (1,833.2) 6,593.8 Alternative Revenue Programs 54.8 22.9 (52.7) (4.1) — 48.9 69.8 Other Revenues (2) 4.9 1.0 0.5 0.5 — — 6.9 Total Operating Revenues $ 5,481.9 $ 770.0 $ 1,135.6 $ 166.6 $ 900.7 $ (1,784.3) $ 6,670.5 For the Three Months Ended September 30, 2021 For the Three Months Ended September 30, 2020 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 572.0 $ 401.9 $ 172.9 $ 608.7 $ 415.4 $ 159.8 Commercial 249.4 411.3 88.5 244.7 358.3 80.1 Industrial 35.0 35.9 25.3 38.0 30.6 22.4 Total Retail Tariff Sales Revenues 856.4 849.1 286.7 891.4 804.3 262.3 Wholesale Transmission Revenues 268.2 171.0 88.0 233.3 153.1 71.8 Wholesale Market Sales Revenues 100.3 21.3 12.2 60.0 12.1 7.5 Other Revenues from Contracts with Customers 12.1 14.3 7.3 8.1 10.5 3.7 (Reserve for)/Amortization of Revenues Subject to Refund (1) (93.4) — — — — 2.3 Total Revenues from Contracts with Customers 1,143.6 1,055.7 394.2 1,192.8 980.0 347.6 Alternative Revenue Programs (82.0) (14.4) (24.1) (65.0) 8.2 (13.8) Other Revenues (2) 0.2 0.7 0.6 0.2 0.7 — Eliminations (142.2) (123.3) (55.8) (133.7) (113.5) (50.1) Total Operating Revenues $ 919.6 $ 918.7 $ 314.9 $ 994.3 $ 875.4 $ 283.7 For the Nine Months Ended September 30, 2021 For the Nine Months Ended September 30, 2020 (Millions of Dollars) CL&P NSTAR Electric PSNH CL&P NSTAR Electric PSNH Revenues from Contracts with Customers Retail Tariff Sales Residential $ 1,558.6 $ 1,069.0 $ 467.3 $ 1,567.9 $ 1,057.9 $ 437.9 Commercial 679.3 975.7 249.2 670.4 921.3 225.3 Industrial 100.2 89.5 71.4 105.3 82.1 61.0 Total Retail Tariff Sales Revenues 2,338.1 2,134.2 787.9 2,343.6 2,061.3 724.2 Wholesale Transmission Revenues 652.8 478.2 207.4 576.5 430.3 171.1 Wholesale Market Sales Revenues 278.1 64.7 37.3 163.9 39.8 27.4 Other Revenues from Contracts with Customers 28.8 36.8 14.9 25.1 32.4 10.9 (Reserve for)/Amortization of Revenues Subject to Refund (1) (93.4) — — — — 6.9 Total Revenues from Contracts with Customers 3,204.4 2,713.9 1,047.5 3,109.1 2,563.8 940.5 Alternative Revenue Programs (74.2) (11.3) (18.8) (27.8) 31.1 (1.2) Other Revenues (2) 0.3 2.5 1.1 2.0 2.8 0.6 Eliminations (394.0) (362.0) (142.6) (371.9) (327.5) (124.6) Total Operating Revenues $ 2,736.5 $ 2,343.1 $ 887.2 $ 2,711.4 $ 2,270.2 $ 815.3 (1) The Electric Distribution segment 2021 revenue subject to refund amount relates to an October 1, 2021 CL&P settlement agreement with the DEEP, OCC, AG and the Connecticut Industrial Energy Consumers, which resolved certain issues that arose in pending regulatory proceedings initiated by the PURA. In the third quarter of 2021, CL&P recorded a reduction to Operating Revenues of $65 million on the income statement for a reserve for customer credits associated with the provisions of the settlement agreement. Additionally, CL&P recorded a $28.4 million reserve in the first quarter of 2021 for a civil penalty for non-compliance with storm performance standards to be credited to customers. The penalty was reclassified from Operations and Maintenance expense to a reduction of Operating Revenues in the third quarter of 2021 in connection with the finalization of the settlement agreement. In total, the reserve for revenues subject to refund totaled $93.4 million and was recorded as a current regulatory liability on CL&P’s balance sheet and as a reduction to Operating Revenues on the nine months ended September 30, 2021 income statement. See Note 9G, “Commitments and Contingencies - CL&P Regulatory Matters,” for further information. Other Revenues also include lease revenues under lessor accounting guidance

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Summary of Segment Information and Segmented Total Assets	Eversource's segment information is as follows: For the Three Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total Operating Revenues $ 2,055.2 $ 185.5 $ 418.3 $ 61.8 $ 326.1 $ (614.1) $ 2,432.8 Depreciation and Amortization (179.8) (28.5) (75.4) (11.5) (28.0) 1.1 (322.1) Other Operating Expenses (1,640.5) (176.9) (122.4) (26.1) (275.2) 613.7 (1,627.4) Operating Income/(Loss) $ 234.9 $ (19.9) $ 220.5 $ 24.2 $ 22.9 $ 0.7 $ 483.3 Interest Expense $ (61.0) $ (15.7) $ (33.5) $ (8.0) $ (42.5) $ 12.7 $ (148.0) Other Income, Net 25.4 6.7 5.0 1.2 325.9 (320.4) 43.8 Net Income/(Loss) Attributable to Common 150.4 (22.0) 139.4 17.5 304.9 (307.0) 283.2 For the Nine Months Ended September 30, 2021 Eversource (Millions of Dollars) Electric Distribution Natural Gas Distribution Electric Transmission Water Distribution Other Eliminations Total Operating Revenues $ 5,632.1 $ 1,277.8 $ 1,230.1 $ 161.0 $ 999.1 $ (1,918.9) $ 7,381.2 Depreciation and Amortization (534.1) (108.7) (223.4) (34.3) (83.7) 3.1 (981.1) Other Operating Expenses (4,531.3) (970.6) (359.6) (76.7) (860.3) 1,918.9 (4,879.6) Operating Income $ 566.7 $ 198.5 $ 647.1 $ 50.0 $ 55.1 $ 3.1 $ 1,520.5 Interest Expense $ (175.4) $ (44.2) $ (98.7) $ (24.0) $ (125.9) $ 37.0 $ (431.2) Other Income, Net 76.0 15.2 17.3 3.1 1,059.2 (1,046.2) 124.6 Net Income Attributable to Common Shareholders 365.4 129.6 412.4 30.0 982.5 (1,006.1) 913.8 Cash Flows Used for Investments in Plant 764.9 506.4 691.0 91.2 157.6 — 2,211.1 For the Three Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Distribution (1) Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 2,060.3 $ 110.2 $ 389.3 $ 64.1 $ 322.3 $ (602.6) $ 2,343.6 Depreciation and Amortization (182.0) (14.8) (70.6) (10.8) (24.1) 0.3 (302.0) Other Operating Expenses (1,577.0) (104.2) (120.6) (10.2) (271.5) 603.1 (1,480.4) Operating Income/(Loss) $ 301.3 $ (8.8) $ 198.1 $ 43.1 $ 26.7 $ 0.8 $ 561.2 Interest Expense $ (53.3) $ (10.1) $ (31.1) $ (8.0) $ (38.7) $ 7.1 $ (134.1) Other Income, Net 16.0 0.7 6.9 1.6 401.0 (397.0) 29.2 Net Income/(Loss) Attributable to Common 205.5 (15.4) 125.6 23.1 396.6 (389.1) 346.3 For the Nine Months Ended September 30, 2020 Eversource (Millions of Dollars) Electric Natural Gas Distribution (1) Electric Water Distribution Other (1) Eliminations (1) Total Operating Revenues $ 5,481.9 $ 770.0 $ 1,135.6 $ 166.6 $ 900.7 $ (1,784.3) $ 6,670.5 Depreciation and Amortization (490.0) (55.1) (206.8) (33.1) (68.1) 1.2 (851.9) Other Operating Expenses (4,309.9) (592.0) (338.5) (60.7) (771.4) 1,787.9 (4,284.6) Operating Income $ 682.0 $ 122.9 $ 590.3 $ 72.8 $ 61.2 $ 4.8 $ 1,534.0 Interest Expense $ (160.7) $ (32.1) $ (93.8) $ (25.1) $ (119.0) $ 27.6 $ (403.1) Other Income, Net 44.9 2.5 22.7 1.7 1,087.9 (1,076.1) 83.6 Net Income Attributable to Common Shareholders 450.6 73.3 381.8 35.6 1,035.6 (1,043.7) 933.2 Cash Flows Used for Investments in Plant 781.2 322.8 732.4 84.0 181.2 — 2,101.6 (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. The following table summarizes Eversource's segmented total assets: Eversource (Millions of Dollars) Electric Natural Gas Electric Water Distribution Other Eliminations Total As of September 30, 2021 $ 25,604.2 $ 6,865.6 $ 12,123.5 $ 2,444.9 $ 21,624.5 $ (20,648.6) $ 48,014.1 As of December 31, 2020 24,981.9 6,450.5 11,695.0 2,375.2 22,089.4 (21,492.4) 46,099.6

ACQUISITION OF ASSETS OF COLU_2

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS (Tables)	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Preliminary Allocation of the Cash Purchase Price	The preliminary allocation of the cash purchase price is as follows: (Millions of Dollars) Current Assets $ 138 Restricted Cash 57 PP&E 1,184 Goodwill 50 Other Noncurrent Assets, excluding Goodwill 131 Other Current Liabilities (81) Other Noncurrent Liabilities (310) Cash Purchase Price $ 1,169

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) customer in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)customerutility	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)
Summary of Accounting Policies [Line Items]
Number of electric, natural gas and water customers | customer		4.3
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 441.7	$ 441.7	$ 425.8	$ 358.9	$ 295	$ 270	$ 224.8
COVID-19
Summary of Accounting Policies [Line Items]
Increase (decrease) in the allowance for uncollectible accounts	(6.5)	25.8
Allowance for uncollectible accounts for late fees and other receivable amounts	57	57
CL&P
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	195.5	$ 195.5	188.8	157.4	150.8	136.7	97.3
Period of accounts receivable recoverable under financial or medical duress		180 days
CL&P | COVID-19
Summary of Accounting Policies [Line Items]
Increase (decrease) in the allowance for uncollectible accounts	4	$ 16.3
Allowance for uncollectible accounts for late fees and other receivable amounts	20.1	20.1
NSTAR Electric
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	105	105	98	91.6	76.8	68.7	75.4
NSTAR Electric | COVID-19
Summary of Accounting Policies [Line Items]
Increase (decrease) in the allowance for uncollectible accounts	(8.3)	(1.8)
Allowance for uncollectible accounts for late fees and other receivable amounts	8.5	8.5
PSNH
Summary of Accounting Policies [Line Items]
Allowance for uncollectible accounts for late fees and other receivable amounts	17	17	$ 17.2	$ 17.2	$ 14	$ 11.8	$ 10.5
PSNH | COVID-19
Summary of Accounting Policies [Line Items]
Reversal of deferred net incremental COVID-19 costs		0.6
EGMA | Other Long-Term Assets
Summary of Accounting Policies [Line Items]
Restricted cash	41.5	41.5
Natural Gas Businesses | COVID-19
Summary of Accounting Policies [Line Items]
Increase (decrease) in the allowance for uncollectible accounts	(2.2)	12.5
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 27.4	$ 27.4
Yankee Gas
Summary of Accounting Policies [Line Items]
Period of accounts receivable recoverable under financial or medical duress		90 days
Connecticut, Massachusetts and New Hampshire
Summary of Accounting Policies [Line Items]
Number of regulated utilities | utility		9

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 425,800	$ 270,000	$ 358,900	$ 224,800
Uncollectible Expense	12,000	10,500	39,690	31,101
Uncollectible Costs Deferred	24,500	30,500	98,100	66,400
Write-Offs	(24,400)	(19,100)	(65,800)	(61,600)
Recoveries Collected	3,800	3,100	10,800	10,500
Ending Balance	441,700	295,000	441,700	295,000
Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				23,800
CL&P
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	188,800	136,700	157,400	97,300
Uncollectible Expense	3,600	3,800	10,183	10,013
Uncollectible Costs Deferred	10,200	16,100	47,100	41,000
Write-Offs	(8,900)	(7,200)	(23,500)	(24,000)
Recoveries Collected	1,800	1,400	4,300	4,300
Ending Balance	195,500	150,800	195,500	150,800
CL&P | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				22,200
NSTAR Electric
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	98,000	68,700	91,600	75,400
Uncollectible Expense	5,100	4,500	12,477	11,321
Uncollectible Costs Deferred	8,300	9,100	20,100	8,900
Write-Offs	(7,500)	(6,500)	(23,000)	(21,300)
Recoveries Collected	1,100	1,000	3,800	3,800
Ending Balance	105,000	76,800	105,000	76,800
NSTAR Electric | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				(1,300)
PSNH
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	17,200	11,800	17,200	10,500
Uncollectible Expense	1,200	800	4,381	2,058
Uncollectible Costs Deferred	1,200	3,200	2,000	5,600
Write-Offs	(2,800)	(2,000)	(7,300)	(5,000)
Recoveries Collected	200	200	700	500
Ending Balance	17,000	14,000	17,000	14,000
PSNH | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				300
Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	210,700	175,500	194,800	143,300
Uncollectible Expense	0	0	0	0
Uncollectible Costs Deferred	22,800	10,100	44,800	24,900
Write-Offs	(3,900)	(7,300)	(10,600)	(12,300)
Recoveries Collected	300	400	900	1,200
Ending Balance	229,900	178,700	229,900	178,700
Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				21,600
Hardship Accounts | CL&P
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	145,600	116,300	129,100	80,100
Uncollectible Expense	0	0	0	0
Uncollectible Costs Deferred	4,500	11,200	25,700	32,700
Write-Offs	(3,500)	(2,600)	(8,700)	(10,000)
Recoveries Collected	200	300	700	1,100
Ending Balance	146,800	125,200	146,800	125,200
Hardship Accounts | CL&P | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				21,300
Hardship Accounts | NSTAR Electric
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	35,900	34,600	39,700	43,900
Uncollectible Expense	0	0	0	0
Uncollectible Costs Deferred	11,800	(1,300)	8,300	(8,400)
Write-Offs	(100)	(200)	(400)	(800)
Recoveries Collected	0	0	0	0
Ending Balance	47,600	33,100	47,600	33,100
Hardship Accounts | NSTAR Electric | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				(1,600)
Retail (Non-Hardship), Wholesale, and Other Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	215,100	94,500	164,100	81,500
Uncollectible Expense	12,000	10,500	39,700	31,100
Uncollectible Costs Deferred	1,700	20,400	53,300	41,500
Write-Offs	(20,500)	(11,800)	(55,200)	(49,300)
Recoveries Collected	3,500	2,700	9,900	9,300
Ending Balance	211,800	116,300	211,800	116,300
Retail (Non-Hardship), Wholesale, and Other Receivables | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				2,200
Retail (Non-Hardship), Wholesale, and Other Receivables | CL&P
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	43,200	20,400	28,300	17,200
Uncollectible Expense	3,600	3,800	10,200	10,000
Uncollectible Costs Deferred	5,700	4,900	21,400	8,300
Write-Offs	(5,400)	(4,600)	(14,800)	(14,000)
Recoveries Collected	1,600	1,100	3,600	3,200
Ending Balance	48,700	25,600	48,700	25,600
Retail (Non-Hardship), Wholesale, and Other Receivables | CL&P | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				900
Retail (Non-Hardship), Wholesale, and Other Receivables | NSTAR Electric
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	62,100	34,100	51,900	31,500
Uncollectible Expense	5,100	4,500	12,500	11,300
Uncollectible Costs Deferred	(3,500)	10,400	11,800	17,300
Write-Offs	(7,400)	(6,300)	(22,600)	(20,500)
Recoveries Collected	1,100	1,000	3,800	3,800
Ending Balance	$ 57,400	$ 43,700	$ 57,400	43,700
Retail (Non-Hardship), Wholesale, and Other Receivables | NSTAR Electric | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance				$ 300

SUMMARY OF SIGNIFICANT ACCOUN_6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Components of Other Income, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Summary of Accounting Policies [Line Items]
Other income, net	$ 43,768	$ 29,218	$ 124,588	$ 83,565
Pension, SERP and PBOP Non-Service   Income Components
Summary of Accounting Policies [Line Items]
Other income, net	21,700	11,000	63,900	34,300
AFUDC Equity
Summary of Accounting Policies [Line Items]
Other income, net	10,300	10,300	28,700	31,800
Equity in Earnings of Unconsolidated Affiliates (1)
Summary of Accounting Policies [Line Items]
Other income, net	4,900	3,900	13,300	13,800
Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other income, net	(600)	1,000	700	(1,500)
Interest Income
Summary of Accounting Policies [Line Items]
Other income, net	7,300	1,500	17,200	3,300
Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other income, net	0	1,500	100	1,800
Other
Summary of Accounting Policies [Line Items]
Other income, net	200	0	700	100
Equity In Earnings
Summary of Accounting Policies [Line Items]
Unrealized gain associated with investment			2,100	2,400
CL&P
Summary of Accounting Policies [Line Items]
Other income, net	6,903	5,917	21,690	16,273
CL&P | Pension, SERP and PBOP Non-Service   Income Components
Summary of Accounting Policies [Line Items]
Other income, net	4,200	900	11,200	3,000
CL&P | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other income, net	1,700	3,500	5,100	11,400
CL&P | Equity in Earnings of Unconsolidated Affiliates (1)
Summary of Accounting Policies [Line Items]
Other income, net	0	0	0	0
CL&P | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other income, net	(300)	1,300	1,200	0
CL&P | Interest Income
Summary of Accounting Policies [Line Items]
Other income, net	1,300	200	4,100	1,800
CL&P | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other income, net	0	0	0	0
CL&P | Other
Summary of Accounting Policies [Line Items]
Other income, net	0	0	100	100
NSTAR Electric
Summary of Accounting Policies [Line Items]
Other income, net	20,215	12,802	58,941	38,152
NSTAR Electric | Pension, SERP and PBOP Non-Service   Income Components
Summary of Accounting Policies [Line Items]
Other income, net	10,100	7,200	30,300	22,200
NSTAR Electric | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other income, net	6,200	5,500	18,600	15,800
NSTAR Electric | Equity in Earnings of Unconsolidated Affiliates (1)
Summary of Accounting Policies [Line Items]
Other income, net	100	100	300	400
NSTAR Electric | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other income, net	(200)	(200)	600	(1,500)
NSTAR Electric | Interest Income
Summary of Accounting Policies [Line Items]
Other income, net	3,900	100	8,800	700
NSTAR Electric | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other income, net	0	0	0	300
NSTAR Electric | Other
Summary of Accounting Policies [Line Items]
Other income, net	100	100	300	300
PSNH
Summary of Accounting Policies [Line Items]
Other income, net	3,171	4,065	11,598	10,882
PSNH | Pension, SERP and PBOP Non-Service   Income Components
Summary of Accounting Policies [Line Items]
Other income, net	2,500	1,800	7,900	5,200
PSNH | AFUDC Equity
Summary of Accounting Policies [Line Items]
Other income, net	300	900	1,200	3,500
PSNH | Equity in Earnings of Unconsolidated Affiliates (1)
Summary of Accounting Policies [Line Items]
Other income, net	0	0	0	0
PSNH | Investment Income/(Loss)
Summary of Accounting Policies [Line Items]
Other income, net	(100)	200	300	100
PSNH | Interest Income
Summary of Accounting Policies [Line Items]
Other income, net	400	1,200	2,000	2,000
PSNH | Gain on Sale of Property
Summary of Accounting Policies [Line Items]
Other income, net	0	0	100	0
PSNH | Other
Summary of Accounting Policies [Line Items]
Other income, net	$ 100	$ 0	$ 100	$ 100

SUMMARY OF SIGNIFICANT ACCOUN_7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Gross Tax Receipts [Line Items]
Gross receipts taxes	$ 49.4	$ 48.4	$ 137.9	$ 129.1
CL&P
Schedule of Gross Tax Receipts [Line Items]
Gross receipts taxes	$ 46.1	$ 45.6	$ 120.7	$ 114.2

SUMMARY OF SIGNIFICANT ACCOUN_8

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Non-cash Investing Activities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Schedule of Supplemental Cash Flow [Line Items]
Plant additions included in accounts payable	$ 359.6	$ 357.4
CL&P
Schedule of Supplemental Cash Flow [Line Items]
Plant additions included in accounts payable	75.3	97.8
NSTAR Electric
Schedule of Supplemental Cash Flow [Line Items]
Plant additions included in accounts payable	94.2	92.6
PSNH
Schedule of Supplemental Cash Flow [Line Items]
Plant additions included in accounts payable	$ 32.8	$ 50

SUMMARY OF SIGNIFICANT ACCOUN_9

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Reconciliation of Cash Balances to Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	$ 88,204	$ 106,599
Cash and Restricted Cash as reported on the Statements of Cash Flows	218,129	264,950	$ 829,003	$ 117,063
Special Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	55,500	73,600
Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	29,700	41,200
Other Long-Term Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	44,700	43,600
CL&P
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	62,791	90,801
Cash and Restricted Cash as reported on the Statements of Cash Flows	71,762	99,809	17,235	4,971
CL&P | Special Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	8,700	8,700
CL&P | Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	300	300
CL&P | Other Long-Term Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	0	0
NSTAR Electric
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	3,538	102
Cash and Restricted Cash as reported on the Statements of Cash Flows	20,838	17,410	12,409	6,312
NSTAR Electric | Special Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	17,200	17,200
NSTAR Electric | Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	100	100
NSTAR Electric | Other Long-Term Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	0	0
PSNH
Restricted Cash and Cash Equivalents Items [Line Items]
Cash as reported on the Balance Sheets	3,869	141
Cash and Restricted Cash as reported on the Statements of Cash Flows	26,173	39,555	$ 22,595	$ 36,688
PSNH | Special Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	18,600	36,800
PSNH | Marketable Securities
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	500	600
PSNH | Other Long-Term Assets
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 3,200	$ 2,100

REGULATORY ACCOUNTING - Compone

REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,475,200	$ 6,569,900
Less:  Current Portion	1,016,304	1,076,556
Total Long-Term Regulatory Assets	5,458,928	5,493,330
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	2,566,100	2,794,200
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	756,400	747,100
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	489,700	522,100
Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	944,200	765,600
Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	883,000	850,500
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	265,300	296,300
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	302,000	314,700
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	121,600	118,400
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	146,900	161,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,307,100	2,211,800
Less:  Current Portion	325,268	345,622
Total Long-Term Regulatory Assets	1,981,805	1,866,152
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	540,200	632,300
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	458,100	458,900
CL&P | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	674,200	515,100
CL&P | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	304,600	246,600
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	265,300	293,100
CL&P | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	33,700	32,100
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	31,000	33,700
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,636,100	1,703,900
Less:  Current Portion	388,408	399,882
Total Long-Term Regulatory Assets	1,247,715	1,304,019
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	638,400	690,000
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	113,800	110,400
NSTAR Electric | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	198,100	186,400
NSTAR Electric | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	320,000	332,200
NSTAR Electric | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	259,300	270,200
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	57,800	58,600
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	48,700	56,100
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	927,700	989,100
Less:  Current Portion	97,948	115,852
Total Long-Term Regulatory Assets	829,848	873,203
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	249,700	267,600
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	18,700	15,200
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	489,700	522,100
PSNH | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	71,900	64,100
PSNH | Regulatory Tracker Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	76,800	95,300
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	4,000	3,900
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 16,900	$ 20,900

REGULATORY ACCOUNTING - Narrati

REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	May 06, 2021
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 260,600	$ 196,900
Regulatory costs	6,475,200	6,569,900
Regulatory Liabilities	612,931	389,430
Unfavorable Regulatory Action
Regulatory Assets [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards			$ 28,400
Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	944,200	765,600
COVID-19
Regulatory Assets [Line Items]
Net incremental deferred costs related to non-tracked uncollectible expense	34,500	15,800
Net incremental deferred costs	41,300	24,000
Tropical Storm Isaias | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	251,000
CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	111,200	84,100
Regulatory costs	2,307,100	2,211,800
Regulatory Liabilities	311,269	137,166
CL&P | Loss from Catastrophes
Regulatory Assets [Line Items]
Deferred pre-staging and storm restoration costs	195,000	344,000
CL&P | Unfavorable Regulatory Action
Regulatory Assets [Line Items]
Regulatory Liabilities	75,000
CL&P | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	674,200	515,100
CL&P | COVID-19
Regulatory Assets [Line Items]
Net incremental deferred costs	15,900	4,700
CL&P | Tropical Storm Isaias | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	234,000
NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	85,100	69,800
Regulatory costs	1,636,100	1,703,900
Regulatory Liabilities	205,771	164,761
NSTAR Electric | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	198,100	186,400
NSTAR Electric | COVID-19
Regulatory Assets [Line Items]
Net incremental deferred costs	10,900	11,900
PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	3,200	4,300
Regulatory costs	927,700	989,100
Regulatory Liabilities	96,817	58,756
PSNH | Storm Restoration Costs, Net
Regulatory Assets [Line Items]
Regulatory costs	$ 71,900	$ 64,100

REGULATORY ACCOUNTING - Compo_2

REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,520,500	$ 4,240,200
Less:  Current Portion	612,931	389,430
Total Long-Term Regulatory Liabilities	3,907,582	3,850,781
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,737,100	2,778,600
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	676,700	624,800
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	65,900	83,600
Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	484,500	366,500
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	79,600	76,800
CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	103,400	0
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	373,300	309,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,524,800	1,342,100
Less:  Current Portion	311,269	137,166
Total Long-Term Regulatory Liabilities	1,213,469	1,204,942
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,001,500	1,010,700
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	117,000	98,400
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
CL&P | Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	208,900	148,900
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	43,600	44,600
CL&P | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	103,400	0
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	50,400	39,500
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,767,400	1,715,200
Less:  Current Portion	205,771	164,761
Total Long-Term Regulatory Liabilities	1,561,572	1,550,390
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,025,600	1,044,000
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	384,100	363,600
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	56,500	72,500
NSTAR Electric | Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	180,600	139,700
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	36,000	32,200
NSTAR Electric | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	84,600	63,200
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	486,200	442,000
Less:  Current Portion	96,817	58,756
Total Long-Term Regulatory Liabilities	389,426	383,183
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	363,900	371,500
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	19,000	12,900
PSNH | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Regulatory Tracker Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	87,500	47,800
PSNH | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 15,800	$ 9,800

PROPERTY, PLANT AND EQUIPMENT_3

PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Summary of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	$ 17,257,300	$ 16,703,200
Distribution - Natural Gas	6,334,900	6,111,200
Transmission - Electric	12,396,200	11,954,000
Distribution - Water	1,771,100	1,743,100
Solar	200,400	201,500
Utility	37,959,900	36,713,000
Other	1,430,500	1,269,000
Property, Plant and Equipment, Gross	39,390,400	37,982,000
Less:  Accumulated Depreciation
Utility	(8,830,200)	(8,476,300)
Other	(550,000)	(477,600)
Total Accumulated Depreciation	(9,380,200)	(8,953,900)
Property, Plant and Equipment, Net	30,010,200	29,028,100
Construction Work in Progress	2,456,900	1,854,400
Total Property, Plant and Equipment, Net	32,467,069	30,882,523
CL&P
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	7,028,900	6,820,700
Transmission - Electric	5,707,900	5,512,000
Solar	0	0
Property, Plant and Equipment, Gross	12,736,800	12,332,700
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(2,574,600)	(2,475,400)
Property, Plant and Equipment, Net	10,162,200	9,857,300
Construction Work in Progress	436,600	377,300
Total Property, Plant and Equipment, Net	10,598,836	10,234,556
NSTAR Electric
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	7,798,800	7,544,400
Transmission - Electric	4,884,000	4,701,300
Solar	200,400	201,500
Property, Plant and Equipment, Gross	12,883,200	12,447,200
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(3,220,700)	(3,074,100)
Property, Plant and Equipment, Net	9,662,500	9,373,100
Construction Work in Progress	949,200	750,000
Total Property, Plant and Equipment, Net	10,611,728	10,123,062
PSNH
Public Utility, Property, Plant and Equipment [Line Items]
Distribution - Electric	2,469,900	2,378,400
Transmission - Electric	1,805,900	1,742,400
Solar	0	0
Property, Plant and Equipment, Gross	4,275,800	4,120,800
Less:  Accumulated Depreciation
Total Accumulated Depreciation	(895,400)	(848,900)
Property, Plant and Equipment, Net	3,380,400	3,271,900
Construction Work in Progress	148,700	102,400
Total Property, Plant and Equipment, Net	$ 3,529,050	$ 3,374,270

DERIVATIVE INSTRUMENTS - Gross

DERIVATIVE INSTRUMENTS - Gross Fair Values and Net Amounts of Contracts (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Current Derivative Assets | CL&P | Level 3
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	$ 14.4	$ 13.7
Netting	(0.4)	(0.4)
Net Amount Recorded as a Derivative	14	13.3
Other Long-Term Assets | CL&P | Level 3
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	51.1	58.7
Netting	(1.6)	(1.8)
Net Amount Recorded as a Derivative	49.5	56.9
Current Derivative Liabilities | CL&P | Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(72.2)	(68.8)
Netting	0	0
Net Amount Recorded as a Derivative	(72.2)	(68.8)
Current Derivative Liabilities | Other | Level 2
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	0	(3.3)
Netting	0	0.1
Net Amount Recorded as a Derivative	0	(3.2)
Long-Term Derivative Liabilities | CL&P | Level 3
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(256.6)	(294.5)
Netting	0	0
Net Amount Recorded as a Derivative	$ (256.6)	$ (294.5)

DERIVATIVE INSTRUMENTS - Narrat

DERIVATIVE INSTRUMENTS - Narrative (Details) MMBTU in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021USD ($)MW	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)MW	Sep. 30, 2020USD ($)	Dec. 31, 2020MMBTUMW
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company			20.00%
Amount of power to be purchased under capacity-related contract (in MW) | MW	675		675		675
Amount of natural gas to be purchased under futures contracts | MMBTU					8.9
Gains (losses) on deferred as regulatory costs | $	$ 0.7	$ (2.6)	$ (9.5)	$ (20.6)
Level 3 | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts			5.50%
Level 3 | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts			9.80%
Level 3 | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts			8.70%
CL&P
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts			80.00%

DERIVATIVE INSTRUMENTS - Summar

DERIVATIVE INSTRUMENTS - Summary of Level 3 Derivative Contracts and Significant Unobservable Inputs Used (Details) - CL&P - Level 3 - $ / KWmo	Sep. 30, 2021	Dec. 31, 2020
Capacity Prices
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	2.61
Capacity Prices | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		4.30
Capacity Prices | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		5.30
Capacity Prices | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	2.61	4.63
Forward Reserve Prices | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.50	0.54
Forward Reserve Prices | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	1.15	0.90
Forward Reserve Prices | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.82	0.72

DERIVATIVE INSTRUMENTS - Change

DERIVATIVE INSTRUMENTS - Changes in the Level 3 Category of Derivative Assets Measured at Fair Value on a Recurring Basis (Details) - CL&P - Level 3 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivatives, Net [Rollforward]
Fair Value as of Beginning of Period	$ (279.7)	$ (322)	$ (293.1)	$ (329.2)
Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets	0.7	(4.7)	(10.9)	(22.3)
Settlements	13.7	14.9	38.7	39.7
Fair Value as of End of Period	$ (265.3)	$ (311.8)	$ (265.3)	$ (311.8)

MARKETABLE SECURITIES - Narrati

MARKETABLE SECURITIES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale equity securities	$ 39.2		$ 39.2		$ 40.9
Unrealized gain (loss) recorded in other income	(0.5)	$ 1.6	2.5	$ (1)
CYAPC and YAEC
Debt Securities, Available-for-sale [Line Items]
Available-for-sale equity securities	214.9		214.9		205.1
Marketable securities held in nuclear decommissioning trust	$ 195.2		$ 195.2		$ 192.5

MARKETABLE SECURITIES - Summary

MARKETABLE SECURITIES - Summary of Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Amortized Cost	$ 217.5	$ 213.1
Pre-Tax Unrealized Gains	8	11.2
Pre-Tax Unrealized Losses	(0.2)	(0.1)
Fair Value	$ 225.3	$ 224.2

MARKETABLE SECURITIES - Contrac

MARKETABLE SECURITIES - Contractual Maturities of Available-for-Sale Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Less than one year	$ 30.9
One to five years	65.5
Six to ten years	41.8
Greater than ten years	79.3
Amortized Cost	217.5	$ 213.1
Fair Value
Less than one year	30.9
One to five years	67.1
Six to ten years	43.9
Greater than ten years	83.4
Fair Value	$ 225.3	$ 224.2

MARKETABLE SECURITIES - Marketa

MARKETABLE SECURITIES - Marketable Securities Recorded at Fair Value on a Recurring Basis by Level (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 479.4	$ 470.2
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	283.8	287.2
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	195.6	183
Mutual Funds and Equities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	254.1	246
Money Market Funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	29.7	41.2
U.S. Government Issued Debt Securities (Agency and Treasury) | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	98.9	72.9
Corporate Debt Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	63.4	63.8
Asset-Backed Debt Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13.4	11.9
Municipal Bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	6.1	24
Other Fixed Income Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 13.8	$ 10.4

SHORT-TERM AND LONG-TERM DEBT -

SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 10, 2021	Mar. 31, 2021	Dec. 31, 2020
NSTAR Electric
Line of Credit Facility [Line Items]
Long-term Line of Credit, Noncurrent	$ 80,000,000
Notes payable to Eversource parent	24,600,000			$ 21,300,000
Amount of long-term debt requested for issuance			$ 1,600,000,000
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	66,500,000			46,300,000
Massachusetts Department of Public Utilities
Line of Credit Facility [Line Items]
Amount of long-term debt requested for issuance		$ 725,000,000
Line of Credit | CL&P
Line of Credit Facility [Line Items]
Maximum borrowing capacity	450,000,000
Amount outstanding under line of credit	0
Line of Credit | PSNH
Line of Credit Facility [Line Items]
Maximum borrowing capacity	300,000,000
Amount outstanding under line of credit	0
Commercial Paper | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Line of Credit
Line of Credit Facility [Line Items]
Amount outstanding under line of credit	0			$ 0
Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Eversource Parent | Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity	2,000,000,000
Eversource Parent | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 2,000,000,000
Debt instrument term	5 years
NSTAR Electric | Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Debt instrument term	5 years

SHORT-TERM AND LONG-TERM DEBT_2

SHORT-TERM AND LONG-TERM DEBT - Borrowings Outstanding and Available under the Commercial Paper Programs (Details) - Commercial Paper - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Borrowings outstanding	$ 653	$ 1,054.3
Available borrowing capacity	$ 1,347	$ 945.7
Weighted-average interest rate	0.18%	0.25%
NSTAR Electric
Debt Instrument [Line Items]
Borrowings outstanding	$ 138	$ 195
Available borrowing capacity	$ 512	$ 455
Weighted-average interest rate	0.10%	0.16%

SHORT-TERM AND LONG-TERM DEBT_3

SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands	Aug. 10, 2021	Oct. 31, 2021	Sep. 30, 2021	Aug. 31, 2021	Jun. 30, 2021	May 31, 2021	Apr. 30, 2021	Mar. 31, 2021	Feb. 28, 2021	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Repayments										$ (1,142,500)	$ (302,236)
Senior Notes | Eversource Parent 2.50% Series I Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage									2.50%
Repayments									$ (450,000)
Senior Notes | Eversource Parent 2.55% Series S Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage								2.55%
Issuances								$ 350,000
Senior Notes | Eversource Parent 1.40% Series U Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage				1.40%
Issuances				$ 300,000
Senior Notes | Eversource Parent Variable Rate Series T Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Issuances	$ 350,000			$ 350,000
Senior Notes | Eversource Parent Variable Rate Series T Senior Notes | Eversource Parent | Compounded SOFR
Debt Instrument [Line Items]
Basis spread on variable rate	0.25%
CL&P
Debt Instrument [Line Items]
Repayments										$ (120,500)	0
CL&P | Senior Notes | 2.05% Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage					2.05%
Issuances					$ 425,000
CL&P | Senior Notes | 4.38% Series A PCRB
Debt Instrument [Line Items]
Interest rate, stated percentage			4.38%							4.38%
Repayments			$ (120,500)
NSTAR Electric
Debt Instrument [Line Items]
Repayments										$ (250,000)	(95,000)
NSTAR Electric | Senior Notes | 3.10% 2021 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage						3.10%
Issuances						$ 300,000
NSTAR Electric | Senior Notes | 3.50% Series F Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage					3.50%
Repayments					$ (250,000)
NSTAR Electric | Senior Notes | 1.95% 2021 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage				1.95%
Issuances				$ 300,000
PSNH
Debt Instrument [Line Items]
Repayments										(282,000)	$ 0
PSNH | Senior Notes | 4.05% Series Q First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage								4.05%
Repayments								$ (122,000)
PSNH | Senior Notes | 3.20% Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage					3.20%
Repayments					$ (160,000)
PSNH | Senior Notes | 2.20% Series V First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage					2.20%
Issuances					$ 350,000
Aquarion | Senior Notes | Aquarion Water Company of Connecticut 3.31% Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage							3.31%
Issuances							$ 100,000
Aquarion | Senior Notes | Aquarion Water Company of Connecticut 5.50% Notes
Debt Instrument [Line Items]
Interest rate, stated percentage							5.50%
Repayments							$ (40,000)
EGMA | Senior Notes
Debt Instrument [Line Items]
Debt instrument, refinanced amount			$ 309,400							$ 309,400
EGMA | Senior Notes | EGMA 2.11% Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage			2.11%							2.11%
Issuances			$ 310,000
EGMA | Senior Notes | EGMA 2.92% Series B First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage			2.92%							2.92%
Issuances			$ 240,000
Yankee Gas | Senior Notes | Yankee Gas 1.38% Series S First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage				1.38%
Issuances				$ 90,000
Yankee Gas | Senior Notes | Yankee Gas 2.88% Series T First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage				2.88%
Issuances				$ 35,000
NSTAR Gas Company | Senior Notes | NSTAR Gas 2.25% Series T First Mortgage Bonds | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage		2.25%
Issuances		$ 40,000
NSTAR Gas Company | Senior Notes | NSTAR Gas 3.03% Series U First Mortgage Bonds | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage		3.03%
Issuances		$ 40,000

RATE REDUCTION BONDS AND VARI_3

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Narrative (Details) - PSNH - Rate Reduction Bonds	May 31, 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 - Summary of the Impact of Funding on the Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	$ 6,475,200	$ 6,569,900
Regulatory Liabilities	3,907,582	3,850,781
Accrued Interest (included in Other Current Liabilities)	802,831	809,214
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	453,702	496,912
Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	489,700	522,100
Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	146,900	161,000
Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	55,500	73,600
Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	44,700	43,600
PSNH
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	927,700	989,100
Regulatory Liabilities	389,426	383,183
Accrued Interest (included in Other Current Liabilities)	61,883	58,487
Rate Reduction Bonds - Current Portion	43,210	43,210
Rate Reduction Bonds - Long-Term Portion	453,702	496,912
PSNH | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Rate Reduction Bonds - Current Portion	43,200	43,200
Rate Reduction Bonds - Long-Term Portion	453,700	496,900
PSNH | Securitized Stranded Costs
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	489,700	522,100
PSNH | Securitized Stranded Costs | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	489,700	522,100
PSNH | Other Regulatory Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)	16,900	20,900
PSNH | Other Regulatory Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Regulatory Liabilities	8,000	9,100
Accrued Interest (included in Other Current Liabilities)	3,000	8,000
PSNH | Current Derivative Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	18,600	36,800
PSNH | Current Derivative Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	18,300	36,800
PSNH | Other Long-Term Assets
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	3,200	2,100
PSNH | Other Long-Term Assets | VIE
Condensed Balance Sheet Statements, Captions [Line Items]
Restricted Cash	$ 3,200	$ 2,100

RATE REDUCTION BONDS AND VARI_5

RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 147,962	$ 134,066	$ 431,162	$ 403,067
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	(17,922)	(7,360)	(62,744)	(39,034)
Interest Expense on RRB Principal (included in Interest Expense)	14,321	14,942	42,774	44,029
PSNH | VIE | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	10,800	10,800	32,400	32,400
Interest Expense on RRB Principal (included in Interest Expense)	$ 4,500	$ 4,900	$ 13,900	$ 14,900

PENSION BENEFITS AND POSTRETI_3

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION - Components of Net Periodic Benefit Expense/(Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension and SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 21.5	$ 18.7	$ 64.3	$ 57
Interest Cost	32.5	44.4	97.5	133
Expected Return on Plan Assets	(109.5)	(99.2)	(328)	(298.8)
Actuarial Loss	60.7	50.7	183.1	150.7
Prior Service Cost/(Credit)	0.3	0.2	1.1	0.8
Total Net Periodic Benefit Plan Expense/(Income)	5.5	14.8	18	42.7
PBOP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	3.3	2.4	10.1	7.3
Interest Cost	4.3	6.1	12.9	18.3
Expected Return on Plan Assets	(19.8)	(18.3)	(59.3)	(55.1)
Actuarial Loss	2	2.2	5.9	6.3
Prior Service Cost/(Credit)	(5.3)	(5.3)	(15.9)	(15.9)
Total Net Periodic Benefit Plan Expense/(Income)	(15.5)	(12.9)	(46.3)	(39.1)
CL&P | Pension and SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	5.6	5.4	17.4	16.5
Interest Cost	6.7	9.3	20.7	28.1
Expected Return on Plan Assets	(21.7)	(19.8)	(65)	(59.6)
Actuarial Loss	10.8	9.7	34.6	29.4
Prior Service Cost/(Credit)	0	0	0	0
Total Net Periodic Benefit Plan Expense/(Income)	1.4	4.6	7.7	14.4
Intercompany Expense/(Income) Allocations	2.2	2.4	5.8	6.7
CL&P | PBOP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.5	0.4	1.7	1.3
Interest Cost	0.8	1.1	2.4	3.3
Expected Return on Plan Assets	(2.5)	(2.5)	(7.7)	(7.4)
Actuarial Loss	0.4	0.3	1.2	0.9
Prior Service Cost/(Credit)	0.3	0.3	0.8	0.8
Total Net Periodic Benefit Plan Expense/(Income)	(0.5)	(0.4)	(1.6)	(1.1)
Intercompany Expense/(Income) Allocations	(0.4)	(0.3)	(1.3)	(0.9)
NSTAR Electric | Pension and SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	4	3.8	11.9	11.4
Interest Cost	6.7	9.7	20.1	29
Expected Return on Plan Assets	(27.1)	(25.7)	(81.1)	(77.2)
Actuarial Loss	15.3	14	46.1	41.3
Prior Service Cost/(Credit)	0.1	0	0.3	0.2
Total Net Periodic Benefit Plan Expense/(Income)	(1)	1.8	(2.7)	4.7
Intercompany Expense/(Income) Allocations	2.4	2.3	6.4	6.5
NSTAR Electric | PBOP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.6	0.5	1.8	1.6
Interest Cost	1.1	1.7	3.3	5
Expected Return on Plan Assets	(9.2)	(8.5)	(27.7)	(25.5)
Actuarial Loss	0.5	0.6	1.6	1.8
Prior Service Cost/(Credit)	(4.3)	(4.2)	(12.7)	(12.7)
Total Net Periodic Benefit Plan Expense/(Income)	(11.3)	(9.9)	(33.7)	(29.8)
Intercompany Expense/(Income) Allocations	(0.5)	(0.4)	(1.5)	(1)
PSNH | Pension and SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	2.2	2	6.6	6.2
Interest Cost	3.7	4.8	10.9	14.5
Expected Return on Plan Assets	(11.9)	(11.1)	(35.6)	(33.5)
Actuarial Loss	5.3	3.8	15.4	11.8
Prior Service Cost/(Credit)	0	0	0	0
Total Net Periodic Benefit Plan Expense/(Income)	(0.7)	(0.5)	(2.7)	(1)
Intercompany Expense/(Income) Allocations	0.7	0.8	1.9	2.2
PSNH | PBOP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	0.3	0.2	0.9	0.6
Interest Cost	0.4	0.7	1.3	2.1
Expected Return on Plan Assets	(1.6)	(1.4)	(4.6)	(4.2)
Actuarial Loss	0.1	0.2	0.4	0.6
Prior Service Cost/(Credit)	0.1	0.1	0.3	0.3
Total Net Periodic Benefit Plan Expense/(Income)	(0.7)	(0.2)	(1.7)	(0.6)
Intercompany Expense/(Income) Allocations	$ (0.2)	$ (0.1)	$ (0.5)	$ (0.4)

PENSION BENEFITS AND POSTRETI_4

PENSION BENEFITS AND POSTRETIREMENT BENEFITS OTHER THAN PENSION - Narrative (Details) $ in Millions	Sep. 30, 2021USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected pension plan contributions	$ 180
CL&P
Defined Benefit Plan Disclosure [Line Items]
Expected pension plan contributions	99
NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Expected pension plan contributions	$ 30

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)site	Dec. 31, 2020USD ($)site
Site Contingency [Line Items]
Number of Sites | site	62	63
Reserve | $	$ 111.9	$ 102.4
CL&P
Site Contingency [Line Items]
Number of Sites | site	14	15
Reserve | $	$ 12.5	$ 12.3
NSTAR Electric
Site Contingency [Line Items]
Number of Sites | site	12	12
Reserve | $	$ 3.7	$ 4.7
PSNH
Site Contingency [Line Items]
Number of Sites | site	9	9
Reserve | $	$ 6.4	$ 7.1

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Site Contingency [Line Items]
Reserve balance	$ 111.9	$ 102.4
MGP Sites
Site Contingency [Line Items]
Reserve balance	$ 102.4	$ 92.2

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Non-Cancellable Commitments under Purchase Commitment Contracts (Details) - Renewable Energy - NSTAR Electric $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]
2021	$ 27.1
2022	103.9
2023	230.5
2024	341.2
2025	348.1
Thereafter	6,564.2
Total	7,615
Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Total	$ 6,700
Contract term	20 years
Minimum | Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Estimated costs	$ 150
Maximum | Massachusetts Clean Energy 83D Contract
Unrecorded Unconditional Purchase Obligation [Line Items]
Estimated costs	$ 415

COMMITMENTS AND CONTINGENCIES_4

COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details) - USD ($)	Sep. 30, 2021	Sep. 16, 2020
Loss Contingencies [Line Items]
Fair value of guarantees	$ 5,700,000
Letter of Credit | Eversource Investment LLC
Loss Contingencies [Line Items]
Maximum borrowing capacity		$ 25,000,000

COMMITMENTS AND CONTINGENCIES_5

COMMITMENTS AND CONTINGENCIES - Guarantees and Indemnifications (Details) $ in Millions	Sep. 30, 2021USD ($)
North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 15.4
Ownership interest	50.00%
South Fork Wind, LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Eversource Investment LLC | North East Offshore LLC
Guarantor Obligations [Line Items]
Ownership interest	50.00%
Construction-related purchase agreements with third-party contractors | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 1,093.5
Construction-related purchase agreements with third-party contractors | Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	386.4
Construction-related purchase agreements with third-party contractors | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	40.6
Funding and indemnification obligations of North East Offshore LLC | Eversource Investment LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	0
Funding and indemnification obligations of North East Offshore LLC | Eversource Investment LLC | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	910
OREC capacity production | Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	2.2
Transmission interconnection | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	1.2
Real estate purchase | Bay State Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	2.5
Surety bonds | Various
Guarantor Obligations [Line Items]
Maximum exposure (up to)	67.5
Lease payments for real estate | Rocky River Realty Company and Eversource Service
Guarantor Obligations [Line Items]
Maximum exposure (up to)	4
Performance guarantee | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 1,300
Percent of obligations guaranteed	50.00%
Performance guarantee | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 14.8
Payment guarantee | North East Offshore LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 62.5
Percent of obligations guaranteed	50.00%
Payment guarantee | South Fork Wind, LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 25.8
Construction-Related Purchase Guarantee | Sunrise Wind LLC
Guarantor Obligations [Line Items]
Maximum exposure (up to)	$ 420.6

COMMITMENTS AND CONTINGENCIES_6

COMMITMENTS AND CONTINGENCIES - FERC ROE Complaints (Details) - USD ($) $ in Millions	Apr. 29, 2016	Oct. 16, 2014	Sep. 30, 2021	Oct. 15, 2014	Dec. 31, 2020
Loss Contingencies [Line Items]
Percentage of base ROE reasonably justified			10.41%
Percentage of incentive cap on total ROE			13.08%
FERC ROE First, Second and Third Complaints
Loss Contingencies [Line Items]
Base ROE subsequently authorized			11.14%
FERC ROE First, Second and Third Complaints | Minimum
Loss Contingencies [Line Items]
Percentage of maximum ROE for any incentive project				11.14%
FERC ROE First, Second and Third Complaints | Maximum
Loss Contingencies [Line Items]
Percentage of maximum ROE for any incentive project				13.10%
FERC ROE Complaints
Loss Contingencies [Line Items]
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 Fourth Complaint
Loss Contingencies [Line Items]
Base ROE percentage of complaint period	10.57%
Maximum percentage cap of ROE for incentive projects	11.74%
FERC ROE First Complaint
Loss Contingencies [Line Items]
Base ROE subsequently authorized		10.57%
Percentage of maximum ROE for any incentive project		11.74%
Amounts associated with first complaint refunded			38.9
FERC ROE First Complaint | CL&P
Loss Contingencies [Line Items]
Amounts associated with first complaint refunded			22.4
FERC ROE First Complaint | NSTAR Electric
Loss Contingencies [Line Items]
Amounts associated with first complaint refunded			13.7
FERC ROE First Complaint | PSNH
Loss Contingencies [Line Items]
Amounts associated with first complaint refunded			$ 2.8
FERC ROE Second Complaint
Loss Contingencies [Line Items]
Base ROE percentage of complaint period			10.57%
Percentage of maximum ROE for any incentive project			11.74%
Loss contingency, estimate of possible earnings impact			$ 39.1		$ 39.1
FERC ROE Second Complaint | CL&P
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact			21.4		21.4
FERC ROE Second Complaint | NSTAR Electric
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact			14.6		14.6
FERC ROE Second Complaint | PSNH
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact			$ 3.1		$ 3.1

COMMITMENTS AND CONTINGENCIES_7

COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details)	Jul. 15, 2016kV
Commitments and Contingencies Disclosure [Abstract]
Amount of capacity required for installation of distribution cable (in kV)	115

COMMITMENTS AND CONTINGENCIES_8

COMMITMENTS AND CONTINGENCIES - CL&P Tropical Storm Isaias Response Investigation (Details) - USD ($) $ / shares in Units, $ in Millions	Sep. 30, 2021	Jul. 14, 2021	May 07, 2021	May 06, 2021	Apr. 28, 2021
Loss Contingencies [Line Items]
Loss contingency, allowed rate of ROE					9.25%
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact				$ 30
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards				28.4
Loss contingency, estimate of possible earnings impact, accident reporting violation fines				$ 1.6
Non-compliance fine		$ 28.6
Loss contingency, accident reporting violation fines		$ 0.2
Loss contingency, penalty rate as a percent of distribution revenues			2.50%
Loss contingency, after-tax earnings impact per share (in dollars per share)	$ (0.25)	$ 0.07

COMMITMENTS AND CONTINGENCIES_9

COMMITMENTS AND CONTINGENCIES - CL&P Comprehensive Settlement Agreement (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Jul. 14, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Regulatory Liabilities		$ 612,931			$ 389,430
Loss related to litigation settlement		103,583	$ 0
CL&P
Loss Contingencies [Line Items]
Regulatory Liabilities		311,269			$ 137,166
Loss related to litigation settlement		103,583	$ 0
Subsequent Event
Loss Contingencies [Line Items]
Basis points reduction to return on equity, scenario one	0.90%
Basis points reduction to return on equity, scenario two	0.45%
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss related to litigation settlement		103,600
Loss related to litigation settlement, net of tax		$ 85,800
Loss contingency, after-tax earnings impact per share (in dollars per share)		$ 0.25		$ (0.07)
Unfavorable Regulatory Action | Sales
Loss Contingencies [Line Items]
Loss related to litigation settlement		$ 65,000
Unfavorable Regulatory Action | Oil and Gas, Operation and Maintenance
Loss Contingencies [Line Items]
Loss related to litigation settlement		10,000
Unfavorable Regulatory Action | CL&P
Loss Contingencies [Line Items]
Regulatory Liabilities		$ 75,000
Unfavorable Regulatory Action | Subsequent Event
Loss Contingencies [Line Items]
Customer credits	$ 65,000
Customer assistance initiatives	10,000
Customer credits and assistance	$ 75,000

FAIR VALUE OF FINANCIAL INSTR_3

FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
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	453,702	496,912
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	18,219,200	16,179,100
Rate Reduction Bonds	496,900	540,100
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	165,500	169,100
Long-Term Debt	19,810,900	18,420,100
Rate Reduction Bonds	555,800	603,400
CL&P
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	116,200	116,200
CL&P | 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	4,215,100	3,914,800
Rate Reduction Bonds	0	0
CL&P | Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	121,400	123,400
Long-Term Debt	4,865,200	4,800,900
Rate Reduction Bonds	0	0
NSTAR Electric
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 | 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	3,984,700	3,643,200
Rate Reduction Bonds	0	0
NSTAR Electric | Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	44,100	45,700
Long-Term Debt	4,494,300	4,294,000
Rate Reduction Bonds	0	0
PSNH
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Rate Reduction Bonds	453,702	496,912
PSNH | 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	1,163,600	1,099,100
Rate Reduction Bonds	496,900	540,100
PSNH | Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred Stock Not Subject to Mandatory Redemption	0	0
Long-Term Debt	1,228,900	1,207,000
Rate Reduction Bonds	$ 555,800	$ 603,400

ACCUMULATED OTHER COMPREHENSI_3

ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent [Roll Forward]
OCI Before Reclassifications							$ (3,000)	$ (1,300)
Amounts Reclassified from AOCI							7,500	6,000
Net OCI	$ 2,477	$ 881	$ 1,188	$ 2,161	$ 553	$ 1,948	4,546	4,662
Total
AOCI Attributable to Parent [Roll Forward]
Beginning balance			(76,400)			(65,100)	(76,400)	(65,100)
Net OCI	2,477	$ 881	1,188	2,161	$ 553	1,948
Ending balance	(71,900)			(60,400)			(71,900)	(60,400)
Qualified Cash Flow Hedging Instruments
AOCI Attributable to Parent [Roll Forward]
Beginning balance			(1,400)			(3,000)	(1,400)	(3,000)
OCI Before Reclassifications							0	0
Amounts Reclassified from AOCI							1,000	1,200
Net OCI							1,000	1,200
Ending balance	(400)			(1,800)			(400)	(1,800)
Unrealized Gains/(Losses) on Marketable Securities
AOCI Attributable to Parent [Roll Forward]
Beginning balance			1,100			700	1,100	700
OCI Before Reclassifications							(600)	300
Amounts Reclassified from AOCI							0	0
Net OCI							(600)	300
Ending balance	500			1,000			500	1,000
Defined Benefit Plans
AOCI Attributable to Parent [Roll Forward]
Beginning balance			$ (76,100)			$ (62,800)	(76,100)	(62,800)
OCI Before Reclassifications							(2,400)	(1,600)
Amounts Reclassified from AOCI							6,500	4,800
Net OCI							4,100	3,200
Ending balance	$ (72,000)			$ (59,600)			$ (72,000)	$ (59,600)

COMMON SHARES - Common Shares A

COMMON SHARES - Common Shares Authorized and Issued (Details) - $ / shares	Sep. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020
Class of Stock [Line Items]
Par value (in dollars per share)	$ 5		$ 5	$ 5
Authorized (in shares)	380,000,000	380,000,000
Issued (in shares)	357,818,402	357,818,402
CL&P
Class of Stock [Line Items]
Par value (in dollars per share)	$ 10
Authorized (in shares)	24,500,000	24,500,000
Issued (in shares)	6,035,205	6,035,205
NSTAR Electric
Class of Stock [Line Items]
Par value (in dollars per share)	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	200	200
PSNH
Class of Stock [Line Items]
Par value (in dollars per share)	$ 1
Authorized (in shares)	100,000,000	100,000,000
Issued (in shares)	301	301

COMMON SHARES - Narrative (Deta

COMMON SHARES - Narrative (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Equity [Abstract]
Treasury stock (in shares)	14,044,078	14,864,379
Common stock outstanding (in shares)	343,774,324	342,954,023

COMMON SHAREHOLDERS' EQUITY A_2

COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Equity [Abstract]
Dividends on preferred stock	$ 1,880	$ 1,880	$ 1,880	$ 1,880	$ 1,880	$ 1,880	$ 5,600	$ 5,600
Noncontrolling interest attributed to preferred stock of subsidiaries	$ 155,570						$ 155,570		$ 155,570

EARNINGS PER SHARE - Narrative

EARNINGS PER SHARE - Narrative (Details) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Antidilutive share awards excluded from the EPS computation (in shares)	0	0	52,747

EARNINGS PER SHARE - Components

EARNINGS PER SHARE - Components of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Income Attributable to Common Shareholders	$ 283,166	$ 346,260	$ 913,829	$ 933,244
Net Income Attributable to Common Shareholders	$ 283,200	$ 346,300	$ 913,800	$ 933,200
Weighted Average Common Shares Outstanding:
Basic (in shares)	344,023,846	343,076,614	343,848,905	337,375,172
Dilutive Effect of:
Share-Based Compensation Awards and Other (in shares)	645,936	696,988	631,151	686,403
Equity Forward Sale Agreement (in shares)	0	0	0	362,525
Total Dilutive Effect (in shares)	645,936	696,988	631,151	1,048,928
Diluted (in shares)	344,669,782	343,773,602	344,480,056	338,424,100
Basic EPS (in dollars per share)	$ 0.82	$ 1.01	$ 2.66	$ 2.77
Diluted EPS (in dollars per share)	$ 0.82	$ 1.01	$ 2.65	$ 2.76

REVENUES (Details)

REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	May 06, 2021
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 2,444,600	$ 2,352,100	$ 7,355,600	$ 6,593,800
Alternative Revenue Programs	(13,500)	(9,600)	21,300	69,800
Other Revenues	1,700	1,100	4,300	6,900
Operating Revenues	$ 2,432,794	$ 2,343,642	7,381,172	6,670,497
Loss related to litigation settlement			103,583	0
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 1,100	$ 1,100	3,800	3,200
Unfavorable Regulatory Action
Disaggregation of Revenue [Line Items]
Loss related to litigation settlement			103,600
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards					$ 28,400
Sales | Unfavorable Regulatory Action
Disaggregation of Revenue [Line Items]
Loss related to litigation settlement			65,000
CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 919,643	$ 994,270	2,736,513	2,711,394
Loss related to litigation settlement			103,583	0
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 200	$ 200	600	600
NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 918,698	$ 875,371	2,343,116	2,270,174
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 700	$ 700	2,500	2,100
PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 314,893	$ 283,669	887,177	815,261
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 1,267,600	$ 1,275,200	3,920,500	3,576,500
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	823,600	739,500	2,302,200	2,103,200
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	121,100	106,200	371,100	308,900
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,212,300	2,120,900	6,593,800	5,988,600
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	141,700	111,600	325,500	252,100
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	147,100	89,400	437,200	265,900
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	37,800	30,200	94,700	87,200
(Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(94,300)		(95,600)
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,143,600	1,192,800	3,204,400	3,109,100
Alternative Revenue Programs	(82,000)	(65,000)	(74,200)	(27,800)
Other Revenues	200	200	300	2,000
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,055,700	980,000	2,713,900	2,563,800
Alternative Revenue Programs	(14,400)	8,200	(11,300)	31,100
Other Revenues	700	700	2,500	2,800
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	394,200	347,600	1,047,500	940,500
Alternative Revenue Programs	(24,100)	(13,800)	(18,800)	(1,200)
Other Revenues	600	0	1,100	600
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	572,000	608,700	1,558,600	1,567,900
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	401,900	415,400	1,069,000	1,057,900
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	172,900	159,800	467,300	437,900
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	249,400	244,700	679,300	670,400
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	411,300	358,300	975,700	921,300
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	88,500	80,100	249,200	225,300
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	35,000	38,000	100,200	105,300
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	35,900	30,600	89,500	82,100
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	25,300	22,400	71,400	61,000
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	856,400	891,400	2,338,100	2,343,600
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	849,100	804,300	2,134,200	2,061,300
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	286,700	262,300	787,900	724,200
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	268,200	233,300	652,800	576,500
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	171,000	153,100	478,200	430,300
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	88,000	71,800	207,400	171,100
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	100,300	60,000	278,100	163,900
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	21,300	12,100	64,700	39,800
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	12,200	7,500	37,300	27,400
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	12,100	8,100	28,800	25,100
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	14,300	10,500	36,800	32,400
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,300	3,700	14,900	10,900
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(93,400)	0	(93,400)	0
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	2,300	0	6,900
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	326,100	322,300	999,100	900,700
Alternative Revenue Programs	0	0	0	0
Other Revenues	0	0	0	0
Operating Revenues	326,100	322,300	999,100	900,700
Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	23,000	19,000	62,500	55,600
Other | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	303,100	303,300	936,600	845,100
Other | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(716,100)	(669,600)	(2,021,900)	(1,833,200)
Alternative Revenue Programs	102,000	67,000	103,000	48,900
Other Revenues	0	0	0	0
Operating Revenues	(614,100)	(602,600)	(1,918,900)	(1,784,300)
Eliminations | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Eliminations | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(1,400)	(1,400)	(4,100)	(3,700)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(4,800)	(3,600)	(12,800)	(10,100)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(6,200)	(5,000)	(16,900)	(13,800)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(408,500)	(365,600)	(1,075,400)	(981,400)
Eliminations | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Eliminations | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(301,400)	(299,000)	(929,600)	(838,000)
Eliminations | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	(142,200)	(133,700)	(394,000)	(371,900)
Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	(123,300)	(113,500)	(362,000)	(327,500)
Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	(55,800)	(50,100)	(142,600)	(124,600)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,061,800	2,057,900	5,614,000	5,422,200
Alternative Revenue Programs	(7,900)	1,700	14,900	54,800
Other Revenues	1,300	700	3,200	4,900
Operating Revenues	2,055,200	2,060,300	5,632,100	5,481,900
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,146,800	1,183,900	3,094,900	3,063,700
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	748,800	682,700	1,902,900	1,815,700
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	96,200	91,000	261,100	248,400
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,991,800	1,957,600	5,258,900	5,127,800
Electric Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	133,800	79,600	380,100	231,100
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	29,600	20,700	68,400	63,300
Electric Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(93,400)		(93,400)
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	182,700	114,100	1,256,400	746,100
Alternative Revenue Programs	2,700	(4,000)	21,300	22,900
Other Revenues	100	100	100	1,000
Operating Revenues	185,500	110,200	1,277,800	770,000
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	81,700	45,500	722,800	399,600
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	59,000	41,100	356,400	243,500
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	28,600	17,500	119,500	67,000
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	169,300	104,100	1,198,700	710,100
Natural Gas Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Natural Gas Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	12,200	8,700	54,100	31,900
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,200	1,300	3,600	4,100
Natural Gas Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	530,700	461,400	1,348,600	1,187,800
Alternative Revenue Programs	(112,600)	(72,300)	(119,200)	(52,700)
Other Revenues	200	200	700	500
Operating Revenues	418,300	389,300	1,230,100	1,135,600
Electric Transmission | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	527,200	458,200	1,338,400	1,177,900
Electric Transmission | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,500	3,200	10,200	9,900
Electric Transmission | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	59,400	66,000	159,400	170,200
Alternative Revenue Programs	2,300	(2,000)	1,300	(4,100)
Other Revenues	100	100	300	500
Operating Revenues	61,800	64,100	161,000	166,600
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	39,100	45,800	102,800	113,200
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	17,200	17,100	47,000	47,700
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,100	1,300	3,300	3,600
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	57,400	64,200	153,100	164,500
Water Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Water Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,100	1,100	3,000	2,900
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,800	$ 700	5,500	$ 2,800
Water Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ (900)		$ (2,200)

SEGMENT INFORMATION - Narrative

SEGMENT INFORMATION - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)segment
CL&P
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric
Segment Reporting Information [Line Items]
Number of reportable segments	1
PSNH
Segment Reporting Information [Line Items]
Number of reportable segments	1
Affiliated Entity
Segment Reporting Information [Line Items]
Amount of natural gas transmission purchased | $	$ 77.7

SEGMENT INFORMATION - Summary o

SEGMENT INFORMATION - Summary of Segment Information and Segmented Total Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Operating Revenues	$ 2,432,794	$ 2,343,642	$ 7,381,172	$ 6,670,497
Depreciation and Amortization	(322,100)	(302,000)	(981,100)	(851,900)
Other Operating Expenses	(1,627,400)	(1,480,400)	(4,879,600)	(4,284,600)
Operating Income/(Loss)	483,331	561,230	1,520,503	1,534,006
Interest Expense	(147,962)	(134,066)	(431,162)	(403,067)
Other Income, Net	43,768	29,218	124,588	83,565
Net Income/(Loss) Attributable to Common Shareholders	283,166	346,260	913,829	933,244
Cash Flows Used for Investments in Plant			2,211,136	2,101,564
Assets	48,014,055		48,014,055		$ 46,099,598
Other
Segment Reporting Information [Line Items]
Operating Revenues	326,100	322,300	999,100	900,700
Depreciation and Amortization	(28,000)	(24,100)	(83,700)	(68,100)
Other Operating Expenses	(275,200)	(271,500)	(860,300)	(771,400)
Operating Income/(Loss)	22,900	26,700	55,100	61,200
Interest Expense	(42,500)	(38,700)	(125,900)	(119,000)
Other Income, Net	325,900	401,000	1,059,200	1,087,900
Net Income/(Loss) Attributable to Common Shareholders	304,900	396,600	982,500	1,035,600
Cash Flows Used for Investments in Plant			157,600	181,200
Assets	21,624,500		21,624,500		22,089,400
Eliminations
Segment Reporting Information [Line Items]
Operating Revenues	(614,100)	(602,600)	(1,918,900)	(1,784,300)
Depreciation and Amortization	1,100	300	3,100	1,200
Other Operating Expenses	613,700	603,100	1,918,900	1,787,900
Operating Income/(Loss)	700	800	3,100	4,800
Interest Expense	12,700	7,100	37,000	27,600
Other Income, Net	(320,400)	(397,000)	(1,046,200)	(1,076,100)
Net Income/(Loss) Attributable to Common Shareholders	(307,000)	(389,100)	(1,006,100)	(1,043,700)
Cash Flows Used for Investments in Plant			0	0
Assets	(20,648,600)		(20,648,600)		(21,492,400)
Electric Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	2,055,200	2,060,300	5,632,100	5,481,900
Depreciation and Amortization	(179,800)	(182,000)	(534,100)	(490,000)
Other Operating Expenses	(1,640,500)	(1,577,000)	(4,531,300)	(4,309,900)
Operating Income/(Loss)	234,900	301,300	566,700	682,000
Interest Expense	(61,000)	(53,300)	(175,400)	(160,700)
Other Income, Net	25,400	16,000	76,000	44,900
Net Income/(Loss) Attributable to Common Shareholders	150,400	205,500	365,400	450,600
Cash Flows Used for Investments in Plant			764,900	781,200
Assets	25,604,200		25,604,200		24,981,900
Natural Gas Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	185,500	110,200	1,277,800	770,000
Depreciation and Amortization	(28,500)	(14,800)	(108,700)	(55,100)
Other Operating Expenses	(176,900)	(104,200)	(970,600)	(592,000)
Operating Income/(Loss)	(19,900)	(8,800)	198,500	122,900
Interest Expense	(15,700)	(10,100)	(44,200)	(32,100)
Other Income, Net	6,700	700	15,200	2,500
Net Income/(Loss) Attributable to Common Shareholders	(22,000)	(15,400)	129,600	73,300
Cash Flows Used for Investments in Plant			506,400	322,800
Assets	6,865,600		6,865,600		6,450,500
Electric Transmission | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	418,300	389,300	1,230,100	1,135,600
Depreciation and Amortization	(75,400)	(70,600)	(223,400)	(206,800)
Other Operating Expenses	(122,400)	(120,600)	(359,600)	(338,500)
Operating Income/(Loss)	220,500	198,100	647,100	590,300
Interest Expense	(33,500)	(31,100)	(98,700)	(93,800)
Other Income, Net	5,000	6,900	17,300	22,700
Net Income/(Loss) Attributable to Common Shareholders	139,400	125,600	412,400	381,800
Cash Flows Used for Investments in Plant			691,000	732,400
Assets	12,123,500		12,123,500		11,695,000
Water Distribution | Operating Segments
Segment Reporting Information [Line Items]
Operating Revenues	61,800	64,100	161,000	166,600
Depreciation and Amortization	(11,500)	(10,800)	(34,300)	(33,100)
Other Operating Expenses	(26,100)	(10,200)	(76,700)	(60,700)
Operating Income/(Loss)	24,200	43,100	50,000	72,800
Interest Expense	(8,000)	(8,000)	(24,000)	(25,100)
Other Income, Net	1,200	1,600	3,100	1,700
Net Income/(Loss) Attributable to Common Shareholders	17,500	$ 23,100	30,000	35,600
Cash Flows Used for Investments in Plant			91,200	$ 84,000
Assets	$ 2,444,900		$ 2,444,900		$ 2,375,200

ACQUISITION OF ASSETS OF COLU_3

ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Narrative (Details) - CMA $ in Millions	Oct. 09, 2020USD ($)
Business Acquisition [Line Items]
Cash purchase price	$ 1,100
Target working capital amount	$ 68.6

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	Sep. 30, 2021	Dec. 31, 2020	Oct. 09, 2020
Business Acquisition [Line Items]
Goodwill	$ 4,453,618	$ 4,445,988
CMA
Business Acquisition [Line Items]
Current Assets			$ 138,000
Restricted Cash			57,000
PP&E			1,184,000
Goodwill			50,000
Other Noncurrent Assets, excluding Goodwill			131,000
Other Current Liabilities			(81,000)
Other Noncurrent Liabilities			(310,000)
Cash Purchase Price			$ 1,169,000

Uncategorized Items - es-202109

Label	Element	Value
Accounting Standards Update [Extensible Enumeration]	us-gaap_AccountingStandardsUpdateExtensibleList	Accounting Standards Update 2016-13 [Member]
The Connecticut Light And Power Company [Member]
Accounting Standards Update [Extensible Enumeration]	us-gaap_AccountingStandardsUpdateExtensibleList	Accounting Standards Update 2016-13 [Member]
NSTAR Electric Company [Member]
Accounting Standards Update [Extensible Enumeration]	us-gaap_AccountingStandardsUpdateExtensibleList	Accounting Standards Update 2016-13 [Member]
Public Service Company Of New Hampshire (PSNH) [Member]
Accounting Standards Update [Extensible Enumeration]	us-gaap_AccountingStandardsUpdateExtensibleList	Accounting Standards Update 2016-13 [Member]