ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2020

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Change in Asset Retirement Obligation

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

	As of December 31,
	2020								2019
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Balance as of Beginning of Year	$	489.5	$	32.0	$	97.5	$	4.2	$	466.2	$	33.5	$	72.4	$	4.0
Liability Assumed Upon CMA Asset Acquisition	20.1		—		—		—		—		—		—		—
Liabilities Incurred During the Year	2.1		—		2.1		—		30.3		—		30.3		—
Liabilities Settled During the Year	(21.8)		(0.7)		(1.0)		—		(21.3)		(3.6)		—		—
Accretion	28.9		2.1		4.3		0.2		27.1		2.2		3.5		0.2
Revisions in Estimated Cash Flows	(19.1)		—		(11.1)		—		(12.8)		(0.1)		(8.7)		—
Balance as of End of Year	$	499.7	$	33.4	$	91.8	$	4.4	$	489.5	$	32.0	$	97.5	$	4.2