ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2016

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,
	2016			2015
Balance as of Beginning of Year	$	430.1		$	426.3
Liabilities Incurred During the Year	1.3			6.6
Liabilities Settled During the Year	(19.0		)	(18.2		)
Accretion	22.9			26.5
Revisions in Estimated Cash Flows	(8.9		)	(11.1		)
Balance as of End of Year	$	426.4		$	430.1

	As of December 31,
	2016										2015
(Millions of Dollars)	CL&P		NSTAR Electric			PSNH		WMECO			CL&P			NSTAR Electric			PSNH			WMECO
Balance as of Beginning of Year	$	33.8	$	35.3		$	21.6	$	5.7		$	35.3		$	34.3		$	20.6		$	5.9
Liabilities Incurred During the Year	—		—			0.5		—			—			6.2			0.4			—
Liabilities Settled During the Year	—		(0.3		)	—		(0.1		)	—			(1.5		)	—			(0.1		)
Accretion	2.2		1.7			1.4		0.3			2.2			1.8			1.3			0.4
Revisions in Estimated Cash Flows	—		—			—		—			(3.7		)	(5.5		)	(0.7		)	(0.5		)
Balance as of End of Year	$	36.0	$	36.7		$	23.5	$	5.9		$	33.8		$	35.3		$	21.6		$	5.7