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
Balance (in shares) at Dec. 31, 2020		342,954,023					200
Balance at Dec. 31, 2020	$ 14,063,566	$ 1,789,092	$ 8,015,663	$ 4,613,201	$ (76,411)	$ 4,521,418	$ 0	$ 1,993,942	$ 2,527,167	$ 309
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	368,023			368,023		93,924			93,924
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(206,913)			(206,913)		(206,400)			(206,400)
Other Comprehensive (Loss)/Income, Net of Tax	1,188				1,188	61				61
Balance (in shares) at Mar. 31, 2021		343,434,298					200
Balance at Mar. 31, 2021	14,233,420	$ 1,789,092	8,016,118	4,772,431	(75,223)	4,408,513	$ 0	1,993,942	2,414,201	370
Balance (in shares) at Dec. 31, 2020		342,954,023					200
Balance at Dec. 31, 2020	14,063,566	$ 1,789,092	8,015,663	4,613,201	(76,411)	4,521,418	$ 0	1,993,942	2,527,167	309
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	634,422					204,836
Dividends on Preferred Stock	(3,800)
Other Comprehensive (Loss)/Income, Net of Tax	2,069					202
Balance (in shares) at Jun. 30, 2021		343,601,103					200
Balance at Jun. 30, 2021	14,311,889	$ 1,789,092	8,032,959	4,830,058	(74,342)	4,502,276	$ 0	2,053,942	2,447,823	511
Balance (in shares) at Mar. 31, 2021		343,434,298					200
Balance at Mar. 31, 2021	14,233,420	$ 1,789,092	8,016,118	4,772,431	(75,223)	4,408,513	$ 0	1,993,942	2,414,201	370
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	266,400			266,400		110,912			110,912
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(206,893)			(206,893)		(76,800)			(76,800)
Capital Contributions from Eversource Parent						60,000		60,000
Other Comprehensive (Loss)/Income, Net of Tax	881				881	141				141
Balance (in shares) at Jun. 30, 2021		343,601,103					200
Balance at Jun. 30, 2021	$ 14,311,889	$ 1,789,092	8,032,959	4,830,058	(74,342)	4,502,276	$ 0	2,053,942	2,447,823	511
Balance (in shares) at Dec. 31, 2021	344,403,196	344,403,196					200
Balance at Dec. 31, 2021	$ 14,599,844	$ 1,789,092	8,098,514	5,005,391	(42,275)	4,973,019	$ 0	2,253,942	2,718,576	501
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	445,326			445,326		92,739			92,739
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(219,768)			(219,768)		(71,900)			(71,900)
Other Comprehensive (Loss)/Income, Net of Tax	704				704	(47)				(47)
Balance (in shares) at Mar. 31, 2022		344,850,272					200
Balance at Mar. 31, 2022	$ 14,836,690	$ 1,789,092	8,102,618	5,229,069	(41,571)	4,993,321	$ 0	2,253,942	2,738,925	454
Balance (in shares) at Dec. 31, 2021	344,403,196	344,403,196					200
Balance at Dec. 31, 2021	$ 14,599,844	$ 1,789,092	8,098,514	5,005,391	(42,275)	4,973,019	$ 0	2,253,942	2,718,576	501
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	739,068					212,177
Dividends on Preferred Stock	(3,800)
Other Comprehensive (Loss)/Income, Net of Tax	$ (589)					(74)
Balance (in shares) at Jun. 30, 2022	346,411,029	346,411,029					200
Balance at Jun. 30, 2022	$ 15,057,215	$ 1,796,056	8,242,346	5,301,054	(42,864)	5,090,341	$ 0	2,303,942	2,785,972	427
Balance (in shares) at Mar. 31, 2022		344,850,272					200
Balance at Mar. 31, 2022	14,836,690	$ 1,789,092	8,102,618	5,229,069	(41,571)	4,993,321	$ 0	2,253,942	2,738,925	454
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	293,742			293,742		119,437			119,437
Dividends on Preferred Stock	(1,880)			(1,880)		(490)			(490)
Dividends on Common Stock	(219,877)			(219,877)		(71,900)			(71,900)
Capital Contributions from Eversource Parent						50,000		50,000
Other Comprehensive (Loss)/Income, Net of Tax	$ (1,293)				(1,293)	(27)				(27)
Balance (in shares) at Jun. 30, 2022	346,411,029	346,411,029					200
Balance at Jun. 30, 2022	$ 15,057,215	$ 1,796,056	$ 8,242,346	$ 5,301,054	$ (42,864)	$ 5,090,341	$ 0	$ 2,303,942	$ 2,785,972	$ 427