NSTAR ELECTRIC COMPANY AND SUBSIDIARY CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Thousands	Total	Adoption of New Accounting Standard	Common Stock	Capital Surplus, Paid In	Retained Earnings	Retained Earnings Adoption of New Accounting Standard	Accumulated Other Comprehensive Loss	NSTAR Electric Company	NSTAR Electric Company Adoption of New Accounting Standard	NSTAR Electric Company Common Stock	NSTAR Electric Company Capital Surplus, Paid In	NSTAR Electric Company Retained Earnings	NSTAR Electric Company Retained Earnings Adoption of New Accounting Standard	NSTAR Electric Company Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2018			316,885,808							200
Beginning balance at Dec. 31, 2018	$ 11,486,817		$ 1,669,392	$ 6,241,222	$ 3,953,974		$ (60,000)	$ 3,730,155		$ 0	$ 1,633,442	$ 2,098,091		$ (1,378)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	916,572				916,572			431,956				431,956
Dividends on Preferred Stock	(7,519)				(7,519)			(1,960)				(1,960)
Dividends on Common Stock	$ (685,979)				(685,979)			(181,800)				(181,800)
Capital Contributions from Eversource Parent								$ 180,000			180,000
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-13 [Member]							Accounting Standards Update 2016-13 [Member]
Other Comprehensive Income/(Loss), Net of Tax	$ (5,059)						(5,059)	$ 1,533						1,533
Ending balance (in shares) at Dec. 31, 2019			329,880,645							200
Ending balance at Dec. 31, 2019	12,629,994	$ (1,514)	$ 1,729,292	7,087,768	4,177,048	$ (1,514)	(65,059)	4,159,884	$ (161)	$ 0	1,813,442	2,346,287	$ (161)	155
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,212,686				1,212,686			445,001				445,001
Dividends on Preferred Stock	(7,519)				(7,519)			(1,960)				(1,960)
Dividends on Common Stock	(767,500)				(767,500)			(262,000)				(262,000)
Capital Contributions from Eversource Parent	25,000							180,500			180,500
Other Comprehensive Income/(Loss), Net of Tax	$ (11,352)						(11,352)	154						154
Ending balance (in shares) at Dec. 31, 2020	342,954,023		342,954,023							200
Ending 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	1,228,046				1,228,046			476,569				476,569
Dividends on Preferred Stock	(7,519)				(7,519)			(1,960)				(1,960)
Dividends on Common Stock	(828,337)				(828,337)			(283,200)				(283,200)
Capital Contributions from Eversource Parent								260,000			260,000
Other Comprehensive Income/(Loss), Net of Tax	$ 34,136						34,136	192						192
Ending balance (in shares) at Dec. 31, 2021	344,403,196		344,403,196							200
Ending 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