ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Change in Asset Retirement Obligation

A reconciliation of the beginning and ending carrying amounts of ARO liabilities are as follows:

Eversource (Millions of Dollars)	As of December 31,
	2017			2016
Balance as of Beginning of Year	$	426.4		$	430.1
Liabilities Incurred During the Year	0.2			1.3
Liabilities Settled During the Year	(19.3		)	(19.0		)
Accretion	26.3			22.9
Revisions in Estimated Cash Flows	(14.5		)	(8.9		)
Balance as of End of Year	$	419.1		$	426.4

	As of December 31,
	2017								2016
(Millions of Dollars)	CL&P			NSTAR Electric			PSNH		CL&P		NSTAR Electric			PSNH
Balance as of Beginning of Year	$	36.0		$	42.6		$	23.5	$	33.8	$	41.0		$	21.6
Liabilities Incurred During the Year	0.1			0.1			—		—		—			0.5
Liabilities Settled During the Year	(1.0		)	(0.2		)	—		—		(0.4		)	—
Accretion	2.3			2.1			1.5		2.2		2.0			1.4
Revisions in Estimated Cash Flows	(5.9		)	—			—		—		—			—
Balance as of End of Year	$	31.5		$	44.6		$	25.0	$	36.0	$	42.6		$	23.5