NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONDENSED CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus, Paid In	Retained Earnings	Accumulated Other Comprehensive Loss	NSTAR Electric	NSTAR Electric Common Stock	NSTAR Electric Capital Surplus, Paid In	NSTAR Electric Retained Earnings	NSTAR Electric Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2023		349,540,266					200
Balance as of Beginning of Period at Dec. 31, 2023	$ 14,173,892	$ 1,799,920	$ 8,460,876	$ 4,142,515	$ (33,737)	$ 6,150,498	$ 0	$ 3,013,842	$ 3,136,612	$ 44
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						159,977			159,977
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(250,770)			(250,770)		(96,700)			(96,700)
Capital Contributions from Eversource Parent						300,000		300,000
Other Comprehensive Income						(16)				(16)
Ending balance (in shares) at Mar. 31, 2024		351,379,414					200
Balance as of End of Period at Mar. 31, 2024	14,543,588	$ 1,806,385	8,537,591	4,413,593	(28,534)	6,513,269	$ 0	3,313,842	3,199,399	28
Beginning balance (in shares) at Dec. 31, 2023		349,540,266					200
Balance as of Beginning of Period at Dec. 31, 2023	14,173,892	$ 1,799,920	8,460,876	4,142,515	(33,737)	6,150,498	$ 0	3,013,842	3,136,612	44
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						502,129
Other Comprehensive Income						(52)
Ending balance (in shares) at Sep. 30, 2024		363,891,973					200
Balance as of End of Period at Sep. 30, 2024	15,044,424	$ 1,866,385	9,263,434	4,118,654	(28,205)	6,382,205	$ 0	3,388,842	2,993,371	(8)
Beginning balance (in shares) at Mar. 31, 2024		351,379,414					200
Balance as of Beginning of Period at Mar. 31, 2024	14,543,588	$ 1,806,385	8,537,591	4,413,593	(28,534)	6,513,269	$ 0	3,313,842	3,199,399	28
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						157,603			157,603
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(252,104)			(252,104)		(297,200)			(297,200)
Other Comprehensive Income						(18)				(18)
Ending balance (in shares) at Jun. 30, 2024		354,566,071					200
Balance as of End of Period at Jun. 30, 2024	14,818,713	$ 1,820,954	8,710,844	4,496,830	(29,581)	6,373,164	$ 0	3,313,842	3,059,312	10
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						184,549			184,549
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(260,119)			(260,119)		(250,000)			(250,000)
Capital Contributions from Eversource Parent						75,000		75,000
Other Comprehensive Income						(18)				(18)
Ending balance (in shares) at Sep. 30, 2024		363,891,973					200
Balance as of End of Period at Sep. 30, 2024	$ 15,044,424	$ 1,866,385	9,263,434	4,118,654	(28,205)	6,382,205	$ 0	3,388,842	2,993,371	(8)
Beginning balance (in shares) at Dec. 31, 2024	366,608,052	366,608,052					200
Balance as of Beginning of Period at Dec. 31, 2024	$ 15,039,387	$ 1,878,622	9,428,905	3,929,141	(26,472)	6,915,806	$ 0	3,788,842	3,127,105	(141)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						167,175			167,175
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(276,229)			(276,229)		(436,000)			(436,000)
Capital Contributions from Eversource Parent						100,000		100,000
Other Comprehensive Income						(2)				(2)
Ending balance (in shares) at Mar. 31, 2025		367,307,083					200
Balance as of End of Period at Mar. 31, 2025	$ 15,341,257	$ 1,878,622	9,440,596	4,203,700	(23,949)	6,746,489	$ 0	3,888,842	2,857,790	(143)
Beginning balance (in shares) at Dec. 31, 2024	366,608,052	366,608,052					200
Balance as of Beginning of Period at Dec. 31, 2024	$ 15,039,387	$ 1,878,622	9,428,905	3,929,141	(26,472)	6,915,806	$ 0	3,788,842	3,127,105	(141)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						529,232
Other Comprehensive Income						(1)
Ending balance (in shares) at Sep. 30, 2025	375,096,584	375,096,584					200
Balance as of End of Period at Sep. 30, 2025	$ 16,028,250	$ 1,914,273	9,916,324	4,366,085	(23,075)	7,107,567	$ 0	3,888,842	3,218,867	(142)
Beginning balance (in shares) at Mar. 31, 2025		367,307,083					200
Balance as of Beginning of Period at Mar. 31, 2025	15,341,257	$ 1,878,622	9,440,596	4,203,700	(23,949)	6,746,489	$ 0	3,888,842	2,857,790	(143)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						168,929			168,929
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(276,513)			(276,513)
Ending balance (in shares) at Jun. 30, 2025		371,038,611					200
Balance as of End of Period at Jun. 30, 2025	15,665,791	$ 1,895,516	9,665,374	4,279,915	(23,912)	6,914,928	$ 0	3,888,842	3,026,229	(143)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income/(Loss)						193,128			193,128
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	$ (281,379)			(281,379)
Other Comprehensive Income						1				1
Ending balance (in shares) at Sep. 30, 2025	375,096,584	375,096,584					200
Balance as of End of Period at Sep. 30, 2025	$ 16,028,250	$ 1,914,273	$ 9,916,324	$ 4,366,085	$ (23,075)	$ 7,107,567	$ 0	$ 3,888,842	$ 3,218,867	$ (142)