SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details) - USD ($) $ in Thousands				4 Months Ended	7 Months Ended	12 Months Ended
	Jun. 15, 2020	Mar. 26, 2020	Mar. 23, 2020	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities:
Net Income						$ 1,228,046	$ 1,212,686	$ 916,572
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries						(14,200)	(14,200)	(42,200)
Deferred Income Taxes						347,056	257,154	209,812
Other						(64,640)	(25,957)	(42,610)
Accounts Receivables from Subsidiaries						(135,505)	(351,843)	(98,716)
Taxes Receivable/Accrued, Net						(110,621)	43,819	(16,129)
Other Current Assets and Liabilities, Net						5,569	(9,591)	(11,603)
Net Cash Flows Provided by Operating Activities						1,962,600	1,682,572	2,009,577
Investing Activities:
Other Investing Activities						22,178	23,809	24,204
Net Cash Flows Used in Investing Activities						(3,447,374)	(4,129,275)	(3,274,288)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	$ 509,200	$ 314,100	$ 105,700	$ 929,000	$ 852,300	0	928,992	852,254
Cash Dividends on Common Shares						(805,439)	(744,665)	(663,239)
Issuance of Long-Term Debt						3,230,000	2,760,000	1,520,000
Retirement of Long-Term Debt						(1,142,500)	(327,236)	(801,078)
Other Financing Activities						(46,625)	14,273	(1,006)
Net Cash Flows Provided by Financing Activities						1,440,832	2,594,590	1,172,450
Net (Decrease)/Increase in Cash and Restricted Cash						(43,942)	147,887	(92,261)
Cash and Restricted Cash - Beginning of Year						264,950	117,063	209,324
Cash and Restricted Cash - End of Year					117,063	221,008	264,950	117,063
Cash Paid/(Received) During the Year for:
Interest						568,700	518,000	532,400
Income Taxes						121,600	48,900	56,000
Eversource
Operating Activities:
Net Income						1,220,527	1,205,167	909,053
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Earnings of Subsidiaries						(1,345,199)	(1,309,630)	(1,001,526)
Cash Dividends Received from Subsidiaries						1,037,100	485,800	883,000
Deferred Income Taxes						20,293	(4,667)	13,382
Other						36,910	39,940	19,584
Accounts Receivables from Subsidiaries						(3,758)	(14,575)	7,105
Taxes Receivable/Accrued, Net						(19,455)	35,300	(605)
Accounts Payable to Subsidiaries						19,185	14,091	(4,099)
Other Current Assets and Liabilities, Net						8,144	21,284	(2,503)
Net Cash Flows Provided by Operating Activities						973,747	472,710	823,391
Investing Activities:
Capital Contributions to Subsidiaries						(1,033,000)	(1,899,340)	(1,039,000)
Return of Capital from Subsidiaries						178,800	80,000	0
Increase in Notes Receivable from Subsidiaries						(140,200)	(264,300)	(218,100)
Other Investing Activities						(3,196)	(367)	(1,799)
Net Cash Flows Used in Investing Activities						(997,596)	(2,084,007)	(1,258,899)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs						0	928,992	852,254
Cash Dividends on Common Shares						(805,439)	(744,665)	(663,239)
Issuance of Long-Term Debt						1,000,000	1,550,000	0
Retirement of Long-Term Debt						(450,000)	0	(350,000)
(Decrease)/Increase in Notes Payable						288,625	(170,545)	593,370
Other Financing Activities						(9,545)	46,480	4,001
Net Cash Flows Provided by Financing Activities						23,641	1,610,262	436,386
Net (Decrease)/Increase in Cash and Restricted Cash						(208)	(1,035)	878
Cash and Restricted Cash - Beginning of Year						434	1,469	591
Cash and Restricted Cash - End of Year					$ 1,469	226	434	1,469
Cash Paid/(Received) During the Year for:
Interest						164,568	140,694	161,323
Income Taxes						$ (51,277)	$ (43,158)	$ (63,277)