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