EMPLOYEE BENEFITS (Tables)

12 Months Ended

Dec. 31, 2023

Postemployment Benefits [Abstract]

Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets

The following tables provide information on the plan benefit obligations, fair values of plan assets, and funded status:  

	Pension and SERP
	As of December 31,
	2023								2022
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Change in Benefit Obligation:
Benefit Obligation as of Beginning of Year	$	(5,220.1)	$	(1,030.0)	$	(1,110.4)	$	(556.2)	$	(6,729.7)	$	(1,330.9)	$	(1,448.4)	$	(721.0)
Service Cost	(43.1)		(12.3)		(7.8)		(4.3)		(70.1)		(18.7)		(13.8)		(6.9)
Interest Cost	(254.0)		(50.5)		(53.9)		(27.3)		(154.5)		(31.3)		(32.8)		(16.9)
Actuarial (Loss)/Gain	(110.4)		(19.7)		(17.6)		(11.6)		1,385.8		284.1		295.5		156.7
Benefits Paid - Pension	317.3		66.1		76.7		35.7		302.5		63.3		68.4		33.9
Benefits Paid - Lump Sum	28.9		—		5.3		1.0		33.0		—		14.8		1.0
Benefits Paid - SERP	43.0		0.3		0.2		0.4		12.9		0.3		0.2		0.4
Employee Transfers	—		(2.4)		0.5		—		—		3.2		5.7		(3.4)
Benefit Obligation as of End of Year	$	(5,238.4)	$	(1,048.5)	$	(1,107.0)	$	(562.3)	$	(5,220.1)	$	(1,030.0)	$	(1,110.4)	$	(556.2)
Change in Pension Plan Assets:
Fair Value of Pension Plan Assets as of   Beginning of Year	$	5,806.4	$	1,172.0	$	1,418.8	$	618.0	$	6,495.5	$	1,323.8	$	1,596.0	$	694.6
Employer Contributions	5.0		—		—		—		80.0		—		15.0		—
Actual Return on Pension Plan Assets	309.8		61.7		75.3		32.7		(433.6)		(85.3)		(103.3)		(45.1)
Benefits Paid - Pension	(317.3)		(66.1)		(76.7)		(35.7)		(302.5)		(63.3)		(68.4)		(33.9)
Benefits Paid - Lump Sum	(28.9)		—		(5.3)		(1.0)		(33.0)		—		(14.8)		(1.0)
Employee Transfers	—		2.4		(0.5)		—		—		(3.2)		(5.7)		3.4
Fair Value of Pension Plan Assets as of End of Year	$	5,775.0	$	1,170.0	$	1,411.6	$	614.0	$	5,806.4	$	1,172.0	$	1,418.8	$	618.0
Funded Status as of December 31st	$	536.6	$	121.5	$	304.6	$	51.7	$	586.3	$	142.0	$	308.4	$	61.8

	PBOP
	As of December 31,
	2023								2022
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Change in Benefit Obligation:
Benefit Obligation as of Beginning of Year	$	(693.7)	$	(127.9)	$	(189.5)	$	(74.6)	$	(884.3)	$	(165.5)	$	(238.4)	$	(92.3)
Service Cost	(7.6)		(1.3)		(1.2)		(0.7)		(11.6)		(2.0)		(2.0)		(1.1)
Interest Cost	(33.8)		(6.2)		(9.2)		(3.7)		(20.2)		(3.7)		(5.3)		(2.2)
Actuarial Gain/(Loss)	5.0		4.4		(5.8)		0.8		173.6		33.0		39.4		15.2
Benefits Paid	52.7		10.0		16.7		6.1		52.1		10.4		16.6		6.0
Employee Transfers	—		—		0.5		(0.1)		—		(0.1)		0.2		(0.2)
Plan Amendment	1.4		0.4		0.2		0.2		—		—		—		—
Impact of Acquisitions	—		—		—		—		(3.3)		—		—		—
Benefit Obligation as of End of Year	$	(676.0)	$	(120.6)	$	(188.3)	$	(72.0)	$	(693.7)	$	(127.9)	$	(189.5)	$	(74.6)
Change in Plan Assets:
Fair Value of Plan Assets as of Beginning of Year	$	970.1	$	120.6	$	456.1	$	72.3	$	1,138.3	$	145.7	$	530.0	$	88.0
Actual Return on Plan Assets	104.7		12.6		52.3		8.3		(119.6)		(15.0)		(57.0)		(9.8)
Employer Contributions	1.9		—		—		—		3.1		—		—		—
Benefits Paid	(52.3)		(10.0)		(16.7)		(6.1)		(51.7)		(10.4)		(16.6)		(6.0)
Employee Transfers	—		(0.2)		(1.3)		0.2		—		0.3		(0.3)		0.1
Fair Value of Plan Assets as of End of Year	$	1,024.4	$	123.0	$	490.4	$	74.7	$	970.1	$	120.6	$	456.1	$	72.3
Funded Status as of December 31st	$	348.4	$	2.4	$	302.1	$	2.7	$	276.4	$	(7.3)	$	266.6	$	(2.3)

Schedule of Defined Benefit Plans

As of December 31, 2023 and 2022, the accumulated benefit obligation for the Pension and SERP Plans is as follows:

(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH
2023	$	4,936.8	$	977.8	$	1,051.9	$	522.1
2022	4,911.6		960.7		1,055.1		516.9

A reconciliation of the prepaid assets and liabilities within the Eversource Pension, SERP and PBOP Plans’ funded status to the balance sheets is as follows:

	As of December 31,
	2023								2022
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Prepaid Pension	$	672.2	$	127.4	$	306.5	$	56.3	$	756.7	$	147.9	$	310.2	$	66.4
Prepaid PBOP	356.0		2.4		302.1		2.7		288.8		—		266.6		—
Prepaid Pension and PBOP	$	1,028.2	$	129.8	$	608.6	$	59.0	$	1,045.5	$	147.9	$	576.8	$	66.4
Accrued Pension	$	—	$	—	$	—	$	—	$	3.7	$	—	$	—	$	—
Accrued SERP	135.6		5.9		1.9		4.6		166.7		5.9		1.8		4.6
Accrued PBOP	7.6		—		—		—		12.4		7.3		—		2.3
Less: Accrued SERP - current portion	(19.4)		(0.3)		(0.2)		(0.4)		(47.3)		(0.3)		(0.2)		(0.4)
Accrued Pension, SERP and PBOP	$	123.8	$	5.6	$	1.7	$	4.2	$	135.5	$	12.9	$	1.6	$	6.5

Schedule of Assumptions Used

The following actuarial assumptions were used in calculating the Pension, SERP and PBOP Plans' year end funded status:

	Pension and SERP							PBOP
	As of December 31,							As of December 31,
		2023			2022			2023			2022
Discount Rate		4.9%	—	5.0%	5.1%	—	5.2%	5.0%	—	5.2%	5.2%
Compensation/Progression Rate		3.5%	—	4.0%	3.5%	—	4.0%	N/A

The following actuarial assumptions were used to calculate Pension, SERP and PBOP expense amounts:

	Pension and SERP									PBOP
	For the Years Ended December 31,									For the Years Ended December 31,
	2023			2022			2021			2023			2022			2021
Discount Rate	4.9%	—	5.3%	2.2%	—	3.2%	1.5%	—	3.0%	5.1%	—	5.4%	2.3%	—	3.3%	1.8%	—	3.1%
Expected Long-Term Rate of Return	8.25%			8.25%			8.25%			8.25%			8.25%			8.25%
Compensation/Progression Rate	3.5%	—	4.0%	3.5%	—	4.0%	3.5%	—	4.0%	N/A			N/A			N/A

Schedule of Net Benefit Costs

The components of net periodic benefit plan expense/(income) for the Pension, SERP and PBOP Plans, prior to amounts capitalized as Property, Plant and Equipment or deferred as regulatory assets/(liabilities) for future recovery or refund, are shown below. The service cost component of net periodic benefit plan expense/(income), less the capitalized portion, is included in Operations and Maintenance expense on the statements of income. The remaining components of net periodic benefit plan expense/(income), less the deferred portion, are included in Other Income, Net on the statements of income. Pension, SERP and PBOP expense reflected in the statements of cash flows for CL&P, NSTAR Electric and PSNH does not include intercompany allocations of net periodic benefit plan expense/(income), as these amounts are cash settled on a short-term basis.

	Pension and SERP								PBOP
	For the Year Ended December 31, 2023								For the Year Ended December 31, 2023
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Service Cost	$	43.1	$	12.3	$	7.8	$	4.3	$	7.6	$	1.3	$	1.2	$	0.7
Interest Cost	254.0		50.5		53.9		27.3		33.8		6.2		9.2		3.7
Expected Return on Plan Assets	(465.0)		(94.2)		(113.8)		(49.5)		(77.1)		(9.4)		(36.9)		(5.5)
Actuarial Loss	45.8		2.5		17.1		1.5		—		—		—		—
Prior Service Cost/(Credit)	1.3		—		0.3		—		(21.6)		1.1		(17.0)		0.4
Settlement Loss	12.4		—		—		—		—		—		—		—
Total Net Periodic Benefit Plan Income	$	(108.4)	$	(28.9)	$	(34.7)	$	(16.4)	$	(57.3)	$	(0.8)	$	(43.5)	$	(0.7)
Intercompany Income Allocations	N/A		$	(4.0)	$	(3.0)	$	(0.8)	N/A		$	(1.9)	$	(2.1)	$	(0.7)

	Pension and SERP								PBOP
	For the Year Ended December 31, 2022								For the Year Ended December 31, 2022
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Service Cost	$	70.1	$	18.7	$	13.8	$	6.9	$	11.6	$	2.0	$	2.0	$	1.1
Interest Cost	154.5		31.3		32.8		16.9		20.2		3.7		5.3		2.2
Expected Return on Plan Assets	(523.6)		(106.3)		(128.4)		(56.1)		(89.9)		(11.4)		(42.4)		(6.7)
Actuarial Loss	116.0		16.2		32.8		7.9		—		—		—		—
Prior Service Cost/(Credit)	1.4		—		0.3		—		(21.7)		1.1		(17.0)		0.4
Total Net Periodic Benefit Plan Income	$	(181.6)	$	(40.1)	$	(48.7)	$	(24.4)	$	(79.8)	$	(4.6)	$	(52.1)	$	(3.0)
Intercompany Income Allocations	N/A		$	(16.0)	$	(12.4)	$	(3.6)	N/A		$	(3.7)	$	(3.6)	$	(1.2)

	Pension and SERP								PBOP
	For the Year Ended December 31, 2021								For the Year Ended December 31, 2021
(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH		Eversource		CL&P		NSTAR Electric		PSNH
Service Cost	$	85.8	$	23.0	$	15.8	$	8.9	$	13.5	$	2.3	$	2.4	$	1.2
Interest Cost	130.0		27.3		26.8		14.5		17.4		3.2		4.4		1.8
Expected Return on Plan Assets	(437.5)		(86.8)		(108.1)		(47.5)		(79.1)		(10.3)		(36.9)		(6.1)
Actuarial Loss	243.9		45.5		61.6		20.7		8.9		1.8		2.4		0.7
Prior Service Cost/(Credit)	1.4		—		0.3		—		(21.2)		1.1		(17.0)		0.4
Total Net Periodic Benefit Plan Expense/(Income)	$	23.6	$	9.0	$	(3.6)	$	(3.4)	$	(60.5)	$	(1.9)	$	(44.7)	$	(2.0)
Intercompany Expense/(Income) Allocations	N/A		$	8.0	$	8.8	$	2.7	N/A		$	(1.6)	$	(1.9)	$	(0.6)

Schedule of Amounts Recognized in Regulatory Assets and OCI

The following is a summary of the changes in plan assets and benefit obligations recognized in Regulatory Assets and Other Comprehensive Income (OCI) as well as amounts in Regulatory Assets and OCI that were reclassified as net periodic benefit expense during the years presented:

	Pension and SERP								PBOP
	Regulatory Assets				OCI				Regulatory Assets				OCI
	For the Years Ended December 31,								For the Years Ended December 31,
(Millions of Dollars)	2023		2022		2023		2022		2023		2022		2023		2022
Actuarial (Gain)/Loss Arising During the Year	$	251.1	$	(431.6)	$	14.0	$	4.6	$	(32.0)	$	36.8	$	(0.3)	$	(0.8)
Actuarial Loss Reclassified as Net Periodic Benefit Expense	(38.8)		(107.0)		(7.0)		(9.0)		—		—		—		—
Settlement Loss	—		—		(12.4)		—		—		—		—		—
Prior Service Credit Arising During the Year	—		—		—		—		(0.9)		—		—		—
Prior Service (Cost)/Credit Reclassified as Net Periodic   Benefit (Expense)/Income	(1.2)		(1.2)		(0.1)		(0.2)		21.8		21.8		(0.2)		(0.1)

The following is a summary of the remaining Regulatory Assets and Accumulated Other Comprehensive Income amounts that have not been recognized as components of net periodic benefit expense as of December 31, 2023 and 2022:

	Regulatory Assets as of December 31,				AOCI as of December 31,
(Millions of Dollars)	2023		2022		2023		2022
Pension and SERP
Actuarial Loss	$	1,101.0	$	888.7	$	56.5	$	61.9
Prior Service Cost	2.9		4.1		0.3		0.4
PBOP
Actuarial Loss	$	49.8	$	81.8	$	2.4	$	2.7
Prior Service (Credit)/Cost	(87.4)		(108.3)		0.7		0.9

Schedule of Expected Benefit Payments

The following benefit payments, which reflect expected future service, are expected to be paid by the Pension, SERP and PBOP Plans:

(Millions of Dollars)	2024		2025		2026		2027		2028		2029 - 2033
Pension and SERP	$	370.2	$	367.1	$	370.8	$	373.8	$	375.0	$	1,864.3
PBOP	55.2		54.7		53.8		52.8		51.8		241.1

Schedule of Allocation of Plan Assets

These long-term rates of return are based on the assumed rates of return for the target asset allocations as follows:

	As of December 31,
	2023						2022
	Target Asset Allocation				Assumed Rate of Return		Target Asset Allocation		Assumed Rate of Return
	Eversource Pension Plan		Eversource PBOP Plan		Eversource Pension Plan and PBOP Plan		Eversource Pension Plan and PBOP Plan
Equity Securities:
United States	—	%	20.0	%	8.5	%	15.0	%	8.5	%
Global	20.0	%	—	%	8.75	%	10.0	%	8.75	%
Non-United States	—	%	11.0	%	8.5	%	8.0	%	8.5	%
Emerging Markets	—	%	6.0	%	10.0	%	4.0	%	10.0	%
Debt Securities:
Fixed Income	16.0	%	17.0	%	5.5	%	13.0	%	4.0	%
Public High Yield Fixed Income	5.0	%	—	%	7.5	%	4.0	%	6.5	%
United States Treasuries	11.0	%	—	%	4.5	%	—	%	—	%
Private Debt	10.0	%	13.0	%	10.0	%	13.0	%	9.0	%
Private Equity	23.0	%	18.0	%	12.0	%	18.0	%	12.0	%
Real Assets	15.0	%	15.0	%	7.5	%	15.0	%	7.5	%

The following tables present, by asset category, the Pension and PBOP Plan assets recorded at fair value on a recurring basis by the level in which they are classified within the fair value hierarchy:  

	Pension Plan
	Fair Value Measurements as of December 31,
(Millions of Dollars)	2023								2022
Asset Category:	Level 1		Level 2		Uncategorized		Total		Level 1		Level 2		Uncategorized		Total
Equity Securities	$	374.0	$	—	$	853.0	$	1,227.0	$	407.7	$	—	$	1,102.2	$	1,509.9
Fixed Income (1)	354.6		340.9		1,516.4		2,211.9		277.1		78.5		1,598.8		1,954.4
Private Equity	—		—		1,685.3		1,685.3		—		—		1,684.9		1,684.9
Real Assets	173.6		—		722.1		895.7		181.8		—		731.0		912.8
Total	$	902.2	$	340.9	$	4,776.8	$	6,019.9	$	866.6	$	78.5	$	5,116.9	$	6,062.0
Less:  401(h) PBOP Assets (2)							(244.9)								(255.6)
Total Pension Assets							$	5,775.0							$	5,806.4

	PBOP Plan
	Fair Value Measurements as of December 31,
(Millions of Dollars)	2023								2022
Asset Category:	Level 1		Level 2		Uncategorized		Total		Level 1		Level 2		Uncategorized		Total
Equity Securities	$	139.1	$	—	$	212.1	$	351.2	$	153.2	$	—	$	183.5	$	336.7
Fixed Income	33.4		43.0		159.8		236.2		18.2		40.2		141.1		199.5
Private Equity	—		—		87.7		87.7		—		—		70.9		70.9
Real Assets	70.5		—		33.9		104.4		71.2		—		36.2		107.4
Total	$	243.0	$	43.0	$	493.5	$	779.5	$	242.6	$	40.2	$	431.7	$	714.5
Add:  401(h) PBOP Assets (2)							244.9								255.6
Total PBOP Assets							$	1,024.4							$	970.1

(1)     Fixed Income investments classified as Level 1 as of December 31, 2023 and 2022 include pending purchases and pending redemption settlements of $31 million and $138 million, respectively.

(2)     The assets of the Pension Plan include a 401(h) account that has been allocated to provide health and welfare postretirement benefits under the PBOP Plan.

Schedule of Defined Contribution Plans

The total Eversource 401k Plan employer matching contributions, including the K-Vantage contributions, were as follows:

(Millions of Dollars)	Eversource		CL&P		NSTAR Electric		PSNH
2023	$	67.3	$	9.0	$	13.7	$	5.4
2022	59.9		7.7		12.8		4.8
2021	55.5		7.0		12.2		4.3

Summary of Share Transactions

A summary of RSU transactions is as follows:

	RSUs (Units)	Weighted Average Grant-Date Fair Value
Outstanding as of December 31, 2022	629,734	$	68.52
Granted	248,124	$	76.42
Shares Issued	(181,409)	$	87.09
Forfeited	(24,207)	$	83.43
Outstanding as of December 31, 2023	672,242	$	65.89

A summary of performance share transactions is as follows:

	Performance Shares (Units)	Weighted Average Grant-Date Fair Value
Outstanding as of December 31, 2022	547,290	$	87.49
Granted	278,983	$	83.39
Shares Issued	(125,677)	$	90.49
Forfeited	(36,172)	$	85.13
Outstanding as of December 31, 2023	664,424	$	85.33

Schedule of Compensation Expense and Income Tax Benefit

The total compensation expense and associated future income tax benefits recognized by Eversource, CL&P, NSTAR Electric and PSNH for share-based compensation awards were as follows:

Eversource	For the Years Ended December 31,
(Millions of Dollars)	2023		2022		2021
Compensation Expense	$	27.8	$	33.4	$	28.2
Future Income Tax Benefit	7.3		8.7		7.3

	For the Years Ended December 31,
	2023						2022						2021
(Millions of Dollars)	CL&P		NSTAR Electric		PSNH		CL&P		NSTAR Electric		PSNH		CL&P		NSTAR Electric		PSNH
Compensation Expense	$	8.7	$	8.7	$	3.0	$	10.0	$	10.7	$	3.6	$	8.8	$	9.0	$	3.0
Future Income Tax Benefit	2.3		2.3		0.8		2.6		2.8		0.9		2.3		2.3		0.8

Schedule of Other Retirement Benefits

The liability and expense amounts are as follows:

Eversource (Millions of Dollars)	As of and For the Years Ended December 31,
	2023		2022		2021
Actuarially-Determined Liability	$	32.6	$	43.4	$	42.8
Other Retirement Benefits Expense (1)	2.6		10.9		2.2

	As of and For the Years Ended December 31,
	2023						2022						2021
(Millions of Dollars)	CL&P		NSTAR Electric		PSNH		CL&P		NSTAR Electric		PSNH		CL&P		NSTAR Electric		PSNH
Actuarially-Determined Liability	$	0.2	$	—	$	1.1	$	0.2	$	0.1	$	1.3	$	0.2	$	0.1	$	1.5
Other Retirement Benefits Expense (1)	0.8		0.8		0.4		4.0		3.7		1.3		0.7		0.7		0.3

(1)    Other Retirement Benefits Expense in 2022 includes a one-time special retirement benefit payable of $9.2 million, which was paid in 2023.