FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value, by Balance Sheet Grouping

The fair values provided in the tables below are classified as Level 2 within the fair value hierarchy.  Carrying amounts and estimated fair values are as follows:

	As of December 31,
	2017				2016
Eversource (Millions of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Preferred Stock Not Subject to Mandatory Redemption	$	155.6	$	160.8	$	155.6	$	158.3
Long-Term Debt	12,325.5		12,877.1		9,603.2		9,980.5

	CL&P				NSTAR Electric				PSNH
(Millions of Dollars)	Carrying Amount		Fair Value		Carrying Amount		Fair Value		Carrying Amount		Fair Value
As of December 31, 2017:
Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	116.5	$	43.0	$	44.3	$	—	$	—
Long-Term Debt	3,059.1		3,430.5		2,943.8		3,156.5		1,002.4		1,038.2
As of December 31, 2016:
Preferred Stock Not Subject to Mandatory Redemption	$	116.2	$	114.7	$	43.0	$	43.6	$	—	$	—
Long-Term Debt	2,766.0		3,049.6		2,644.6		2,790.6		1,072.0		1,109.7