SCHEDULE I - FINANCIAL INFORMATION OF REGISTRANT - STATEMENTS OF COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statement of Income Captions [Line Items]
Net Income	$ 233,200	$ 291,300	$ 244,600	$ 271,400	$ 239,400	$ 262,200	$ 232,600	$ 261,300	$ 1,040,519	$ 995,515	$ 949,821
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments									1,756	1,974	2,137
Changes in Unrealized (Losses)/Gains on Marketable Securities									(547)	(350)	2,294
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									5,194	(2,745)	(2,869)
Other Comprehensive Income/(Loss), Net of Tax									6,403	(1,121)	1,562
Comprehensive Income									1,039,403	986,875	943,864
Eversource
Condensed Statement of Income Captions [Line Items]
Net Income									1,033,000	987,996	942,302
Other Comprehensive Income/(Loss), Net of Tax:
Qualified Cash Flow Hedging Instruments									1,756	1,974	2,137
Changes in Unrealized (Losses)/Gains on Marketable Securities									(547)	(350)	2,294
Change in Funded Status of Pension, SERP and PBOP Benefit Plans									5,194	(2,745)	(2,869)
Other Comprehensive Income/(Loss), Net of Tax									6,403	(1,121)	1,562
Comprehensive Income									$ 1,039,403	$ 986,875	$ 943,864