SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Income Captions [Line Items]
Net Income	$ 1,212,686	$ 916,572	$ 1,040,519
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,596	1,393	1,756
Changes in Unrealized Gains/(Losses) on Marketable Securities	342	1,166	(547)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(13,290)	(7,618)	5,194
Other Comprehensive (Loss)/Income, Net of Tax	(11,352)	(5,059)	6,403
Comprehensive Income	1,193,815	903,994	1,039,403
Eversource
Condensed Statement of Income Captions [Line Items]
Net Income	1,205,167	909,053	1,033,000
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments	1,596	1,393	1,756
Changes in Unrealized Gains/(Losses) on Marketable Securities	342	1,166	(547)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans	(13,290)	(7,618)	5,194
Other Comprehensive (Loss)/Income, Net of Tax	(11,352)	(5,059)	6,403
Comprehensive Income	$ 1,193,815	$ 903,994	$ 1,039,403