SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net Income	$ 251,900	$ 320,800	$ 33,300	$ 310,600	$ 233,200	$ 291,300	$ 244,600	$ 271,400	$ 916,572	$ 1,040,519	$ 995,515
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments									1,393	1,756	1,974
Changes in Unrealized Gains/(Losses) on Marketable Securities									1,166	(547)	(350)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									(7,618)	5,194	(2,745)
Other Comprehensive (Loss)/Income, Net of Tax									(5,059)	6,403	(1,121)
Comprehensive Income Attributable to Common Shareholders									903,994	1,039,403	986,875
Eversource
Condensed Statement of Income Captions [Line Items]
Net Income									909,053	1,033,000	987,996
Other Comprehensive (Loss)/Income, Net of Tax:
Qualified Cash Flow Hedging Instruments									1,393	1,756	1,974
Changes in Unrealized Gains/(Losses) on Marketable Securities									1,166	(547)	(350)
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									(7,618)	5,194	(2,745)
Other Comprehensive (Loss)/Income, Net of Tax									(5,059)	6,403	(1,121)
Comprehensive Income Attributable to Common Shareholders									$ 903,994	$ 1,039,403	$ 986,875