DOCUMENT AND ENTITY INFORMATION - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
Document And Entity [Line Items]
Entity Registrant Name	Eversource Energy
Entity Central Index Key	0000072741
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Trading Symbol	ES
Entity Common Stock, Shares Outstanding (in shares)		316,885,808
The Connecticut Light And Power Company
Document And Entity [Line Items]
Entity Registrant Name	The Connecticut Light and Power Company
Entity Central Index Key	0000023426
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		6,035,205
Public Service Company Of New Hampshire
Document And Entity [Line Items]
Entity Registrant Name	Public Service Company of New Hampshire
Entity Central Index Key	0000315256
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		301
Western Massachusetts Electric Company
Document And Entity [Line Items]
Entity Registrant Name	Western Massachusetts Electric Company
Entity Central Index Key	0000106170
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		434,653
NSTAR Electric Company
Document And Entity [Line Items]
Entity Registrant Name	NSTAR Electric Company
Entity Central Index Key	0000013372
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding (in shares)		100