DOCUMENT AND ENTITY INFORMATION - USD ($)	12 Months Ended
	Dec. 31, 2016	Jan. 31, 2017	Jun. 30, 2016
Document And Entity [Line Items]
Entity Registrant Name	EVERSOURCE ENERGY
Document Period End Date	Dec. 31, 2016
Document Type	10-K
Entity Central Index Key	0000072741
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		316,885,808
Entity Public Float			$ 18,939,770,997
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	FY
Amendment Flag	false
The Connecticut Light And Power Company [Member]
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 [Member]
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
Western Massachusetts Electric Company [Member]
Document And Entity [Line Items]
Entity Registrant Name	WESTERN MASSACHUSETTS ELECTRIC CO
Entity Central Index Key	0000106170
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding (in shares)		434,653
Entity Filer Category	Non-accelerated Filer
NSTAR Electric Company [Member]
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)		100
Entity Filer Category	Non-accelerated Filer