CONSOLIDATED STATEMENTS OF COMMON SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Capital Surplus, Paid In	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	The Connecticut Light and Power Company	The Connecticut Light and Power Company Common Shares	The Connecticut Light and Power Company Capital Surplus, Paid In	The Connecticut Light and Power Company Retained Earnings	The Connecticut Light and Power Company Accumulated Other Comprehensive Loss	NSTAR Electric Company	NSTAR Electric Company Common Shares	NSTAR Electric Company Capital Surplus, Paid In	NSTAR Electric Company Retained Earnings	NSTAR Electric Company Accumulated Other Comprehensive Loss	Public Service Company of New Hampshire	Public Service Company of New Hampshire Common Shares	Public Service Company of New Hampshire Capital Surplus, Paid In	Public Service Company of New Hampshire Retained Earnings	Public Service Company of New Hampshire Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Dec. 31, 2016		316,885,808						6,035,205					200					301
Beginning balance at Dec. 31, 2016	$ 10,711,734	$ 1,669,392	$ 6,250,224	$ 3,175,171	$ (65,282)	$ (317,771)	$ 3,470,387	$ 60,352	$ 2,110,714	$ 1,299,374	$ (53)	$ 3,342,843	$ 0	$ 1,500,642	$ 1,844,195	$ (1,994)	$ 1,387,357	$ 0	$ 843,134	$ 549,286	$ (5,063)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	995,515			995,515			376,726			376,726		374,726			374,726		135,996			135,996
Dividends on Common Stock	(602,083)			(602,083)			(254,800)			(254,800)		(272,000)			(272,000)		(173,900)			(173,900)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Stock Expenses, Net							51		51
Capital Contributions from Eversource Parent												2,300		2,300
Long-Term Incentive Plan Activity	(10,834)		(10,834)
Other Changes in Shareholders' Equity	550		550
Other Comprehensive Income (Loss)	(1,121)				(1,121)		322				322	171				171	1,141				1,141
Ending Balance (in shares) at Dec. 31, 2017		316,885,808						6,035,205					200					301
Ending balance at Dec. 31, 2017	11,086,242	$ 1,669,392	6,239,940	3,561,084	(66,403)	(317,771)	3,587,127	$ 60,352	2,110,765	1,415,741	269	3,446,080	$ 0	1,502,942	1,944,961	(1,823)	1,350,594	$ 0	843,134	511,382	(3,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,040,519			1,040,519			377,717			377,717		383,090			383,090		115,876			115,876
Dividends on Common Stock	(640,110)			(640,110)			(60,000)			(60,000)		(228,000)			(228,000)
Dividends on Preferred Stock	(7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Return of Capital																	(530,000)		(530,000)
Capital Contributions from Eversource Parent	365,000						300,000		300,000			130,500		130,500					365,000
Long-Term Incentive Plan Activity	(543)		(543)
Other Changes in Shareholders' Equity	1,825		1,825
Other Comprehensive Income (Loss)	$ 6,403				6,403		32				32	445				445	1,071				1,071
Ending Balance (in shares) at Dec. 31, 2018	316,885,808	316,885,808						6,035,205					200					301
Ending balance at Dec. 31, 2018	$ 11,486,817	$ 1,669,392	6,241,222	3,953,974	(60,000)	(317,771)	4,199,317	$ 60,352	2,410,765	1,727,899	301	3,730,155	$ 0	1,633,442	2,098,091	(1,378)	1,302,541	$ 0	678,134	627,258	(2,851)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	916,572			916,572			410,852			410,852		431,956			431,956		134,048			134,048
Dividends on Common Stock	(685,979)			(685,979)			(341,800)			(341,800)		(181,800)			(181,800)		(271,000)			(271,000)
Dividends on Preferred Stock	$ (7,519)			(7,519)			(5,559)			(5,559)		(1,960)			(1,960)
Capital Contributions from Eversource Parent							125,000		125,000			180,000		180,000			225,000		225,000
Issuance of Common Shares (in shares)	11,980,000	11,980,000
Issuance of Common Shares	$ 868,550	$ 59,900	808,650
Long-Term Incentive Plan Activity	3,434		3,434
Issuance of Treasury Shares (in shares)		1,014,837
Issuance of Treasury Shares	69,474		50,758			18,716
Capital Stock Expense	(16,296)		(16,296)
Other Comprehensive Income (Loss)	$ (5,059)				(5,059)		15				15	1,533				1,533	1,144				1,144
Ending Balance (in shares) at Dec. 31, 2019	329,880,645	329,880,645						6,035,205					200					301
Ending balance at Dec. 31, 2019	$ 12,629,994	$ 1,729,292	$ 7,087,768	$ 4,177,048	$ (65,059)	$ (299,055)	$ 4,387,825	$ 60,352	$ 2,535,765	$ 1,791,392	$ 316	$ 4,159,884	$ 0	$ 1,813,442	$ 2,346,287	$ 155	$ 1,391,733	$ 0	$ 903,134	$ 490,306	$ (1,707)