SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENT OF CASH FLOW (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Activities:
Net (Loss)/Income	$ (434,700)	$ 1,412,400	$ 1,228,000
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Losses/(Earnings) of Subsidiaries	(15,500)	(22,900)	(14,200)
Deferred Income Taxes	85,405	346,779	347,056
Other	(53,026)	(39,192)	(64,640)
Receivables and Unbilled Revenues, Net	(124,393)	(470,593)	(135,505)
Taxes Receivable/Accrued, Net	36,357	18,358	(110,621)
Other Current Assets and Liabilities, Net	(66,202)	(45,583)	3,710
Net Cash Flows Provided by Operating Activities	1,646,161	2,401,293	1,962,600
Investing Activities:
Other Investing Activities	(2,897)	20,420	22,178
Net Cash Flows Used in Investing Activities	(4,870,732)	(4,130,490)	(3,447,374)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	0	197,058	0
Cash Dividends on Common Shares	(918,995)	(860,033)	(805,439)
Issuance of Long-Term Debt	5,198,345	4,045,000	3,230,000
Retirement of Long-Term Debt	(2,008,470)	(1,175,000)	(1,142,500)
Other Financing Activities	(46,466)	(48,185)	(46,625)
Net Cash Flows Provided by Financing Activities	2,869,237	2,029,941	1,440,832
Net (Decrease)/Increase in Cash, Cash Equivalents and Restricted Cash	(355,334)	300,744	(43,942)
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	521,752	221,008	264,950
Cash, Cash Equivalents and Restricted Cash - End of Year	166,418	521,752	221,008
Cash Paid/(Received) During the Year for:
Interest	783,200	636,200	568,700
Income Taxes	39,200	77,900	121,600
Eversource
Operating Activities:
Net (Loss)/Income	(442,240)	1,404,875	1,220,527
Adjustments to Reconcile Net Income to Net Cash Flows Provided by Operating Activities:
Equity in Losses/(Earnings) of Subsidiaries	312,040	(1,565,474)	(1,345,199)
Cash Dividends Received from Subsidiaries	1,027,400	855,600	1,037,100
Deferred Income Taxes	(22,256)	25,823	20,293
Other	(12,834)	26,455	36,910
Receivables and Unbilled Revenues, Net	(6,853)	(9,935)	(3,758)
Taxes Receivable/Accrued, Net	(80,968)	(21,627)	(19,455)
Accounts Payable to Subsidiaries	4,521	(4,079)	19,185
Other Current Assets and Liabilities, Net	35,357	35,090	8,144
Net Cash Flows Provided by Operating Activities	814,167	746,728	973,747
Investing Activities:
Capital Contributions to Subsidiaries	(1,369,700)	(1,499,300)	(1,033,000)
Return of Capital from Subsidiaries	438,000	12,000	178,800
Increase in Notes Receivable from Subsidiaries	(1,578,100)	(724,400)	(140,200)
Other Investing Activities	147,567	(1,289)	(3,196)
Net Cash Flows Used in Investing Activities	(2,362,233)	(2,212,989)	(997,596)
Financing Activities:
Issuance of Common Shares, Net of Issuance Costs	0	197,058	0
Cash Dividends on Common Shares	(918,995)	(860,033)	(805,439)
Issuance of Long-Term Debt	3,350,000	2,800,000	1,000,000
Retirement of Long-Term Debt	(1,200,000)	(750,000)	(450,000)
Increase (Decrease) in Notes Payable to Eversource Parent	329,705	99,250	288,625
Other Financing Activities	(13,076)	(19,193)	(9,545)
Net Cash Flows Provided by Financing Activities	1,547,634	1,467,082	23,641
Net (Decrease)/Increase in Cash, Cash Equivalents and Restricted Cash	(432)	821	(208)
Cash, Cash Equivalents and Restricted Cash - Beginning of Year	1,047	226	434
Cash, Cash Equivalents and Restricted Cash - End of Year	615	1,047	226
Cash Paid/(Received) During the Year for:
Interest	366,645	215,053	164,568
Income Taxes	$ 23,984	$ (20,992)	$ (51,277)