DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document And Entity [Line Items]
Entity Registrant Name	EVERSOURCE ENERGY
Document Period End Date	Dec. 31, 2018
Document Type	10-K
Entity Central Index Key	0000072741
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		316,981,088
Entity Public Float			$ 18,544,847,538
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light And Power Company
Document And Entity [Line Items]
Entity Registrant Name	CONNECTICUT LIGHT & POWER CO
Entity Central Index Key	0000023426
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Entity Filer Category	Non-accelerated Filer
Public Service Company Of New Hampshire
Document And Entity [Line Items]
Entity Registrant Name	PUBLIC SERVICE CO OF NEW HAMPSHIRE
Entity Central Index Key	0000315256
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		301
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company
Document And Entity [Line Items]
Entity Registrant Name	NSTAR ELECTRIC CO
Entity Central Index Key	0000013372
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		200
Entity Filer Category	Non-accelerated Filer