REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Millions																3 Months Ended	12 Months Ended
	Dec. 30, 2025	Dec. 01, 2025	Nov. 05, 2025	Nov. 01, 2025	Oct. 29, 2025	Sep. 22, 2025	Sep. 11, 2025	Jul. 25, 2025	Dec. 23, 2024	Nov. 12, 2024	Nov. 07, 2024	Oct. 30, 2024	Aug. 01, 2024	Jun. 11, 2024	Dec. 31, 2023	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2027	Dec. 31, 2026	Sep. 19, 2025	Sep. 10, 2025	Sep. 09, 2025	Aug. 01, 2025	Jul. 10, 2025	Jul. 01, 2025	Mar. 28, 2024	May 31, 2018
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																$ 244.2	$ 244.2	$ 221.0
Deferred costs																123.2	123.2	92.5
NSTAR Electric and EGMA Settlement
Regulatory Assets [Line Items]
Public utilities, approved rate, gain (loss) on settlement		$ 64.8
Collection period		10 years
FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers																	39.1	39.1
CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																127.1	127.1	116.3
Deferred costs																57.0	57.0	47.2
General obligation bonds																					$ 107.8					$ 125.0
Reduce costs of hardship protection measures charged to retail customers (percent)																										67.00%
New general obligation bonds to fund the electric vehicle charging program (percentage)																										80.00%
CL&P | Forecast
Regulatory Assets [Line Items]
New general obligation bonds to fund the electric vehicle charging program																			$ 20.0	$ 30.0
CL&P | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers																	21.4	21.4
NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																51.0	51.0	41.1
Deferred costs																34.0	34.0	24.4
Rate increase approved	$ 1,340.0
Historical average term of capital additions (in years)	5 years								5 years
NSTAR Electric | NSTAR Electric and EGMA Settlement
Regulatory Assets [Line Items]
Public utilities, approved rate, gain (loss) on settlement		$ (17.5)
Collection period		1 year
NSTAR Electric | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers																	14.6	14.6
PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																5.4	$ 5.4	4.5
Public utilities, approved return on equity, percentage														9.50%			9.50%
Public utilities, approved equity capital structure, percentage														50.00%			75.00%
Final proposed rate increase														$ 103.0
Permanent annual base distribution rate increase								$ 100.7
Distribution revenue																								$ 519.0
Public utilities, approved equity capital structure, basis point on revenue																	0.25%
Pre-tax benefit to earnings, recoupment																						$ 9.1
Unrecovered storm costs														247.0
Storm costs recovered																						$ 19.0	$ 12.0
Impact of the rate, pre-tax benefit to earnings																15.6
PSNH | FERC ROE Complaints
Regulatory Assets [Line Items]
Cumulative pre-tax reserves which include impact of refunds given to customers																	$ 3.1	3.1
PSNH | Rate Reduction Bonds
Regulatory Assets [Line Items]
Face amount of debt																												$ 635.7
Yankee Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested										$ 193.0
Public utilities, approved rate, requirement of revenue			$ 802.2
Rate increase approved			$ 82.2
Public utilities, approved return on equity, percentage			9.32%
Public utilities, requested debt capital structure, percentage			9.48%
Public utilities, approved equity capital structure, percentage			53.00%
Public utilities, approved rate, annual cap on cost recovery			$ 139.9
Public utilities, approved rate, gain (loss) on settlement			(8.5)
NSTAR Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested				$ 447.7			$ 162.6
Rate increase approved												$ 12.7
Public utilities, approved rate, gain (loss) on settlement																12.2
Public utilities, credit to customer	$ 10.2
Public utilities, credit to customer payment period	10 months
NSTAR Gas | GSEP Investments
Regulatory Assets [Line Items]
Rate increase approved					$ 107.3
Eversource Parent and Other Companies excluding NSTAR Electric | NSTAR Electric and EGMA Settlement
Regulatory Assets [Line Items]
Business combination, transaction cost settlement gain (loss)																82.3
EGMA
Regulatory Assets [Line Items]
Rate increase approved											$ 76.8
EGMA | NSTAR Electric and EGMA Settlement
Regulatory Assets [Line Items]
Transaction and integration cost		$ 82.3
EGMA | GSEP Investments
Regulatory Assets [Line Items]
Rate increase approved											8.8				$ 34.0
Deferred Pre-Staging And Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																129.0	129.0
Deferred Pre-Staging And Storm Restoration Costs | CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																82.0	82.0
Deferred Pre-Staging And Storm Restoration Costs | NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																25.0	25.0
Deferred Pre-Staging And Storm Restoration Costs | PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																22.0	22.0
Deferred Storm Restoration Costs
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																2,060.0	2,060.0
Deferred Storm Restoration Costs | CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																1,190.0	1,190.0
Deferred Storm Restoration Costs | CL&P | Tropical Storm Isaias
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																232.0	232.0
Deferred Storm Restoration Costs | NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																409.0	409.0
Deferred Storm Restoration Costs | PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved																$ 456.0	$ 456.0
Catastrophic Storm Costs | CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved								$ 246.0										$ 173.0							$ 171.0		$ 634.0
Goodwill-related
Regulatory Assets [Line Items]
Recovery period (in years)																40 years	40 years
Remaining amortization (in years)																	14 years
Base Rate Adjustment | NSTAR Electric
Regulatory Assets [Line Items]
Rate increase approved	$ 55.1								$ 55.8
Base Rate Adjustment | PSNH
Regulatory Assets [Line Items]
Rate increase (decrease) requested														$ 181.9
Rate increase approved													$ 61.2
Base Rate Adjustment | Yankee Gas
Regulatory Assets [Line Items]
Rate increase approved			$ 95.7			$ 55.6
Return on equity revenue basis point on reductions			0.16%
Base Rate Adjustment | NSTAR Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested					45.0
Concession payment	2.0
Delayed recovery of capital pipeline investments	53.0
Base Rate Adjustment | NSTAR Gas | GSEP Investments
Regulatory Assets [Line Items]
Rate increase (decrease) requested							107.3
Base Rate Adjustment | NSTAR Gas | Non-GSEP Plant
Regulatory Assets [Line Items]
Rate increase (decrease) requested	45.0						45.0
Base Rate Adjustment | EGMA
Regulatory Assets [Line Items]
Rate increase approved											$ 85.6				$ 147.8
Public utilities, return on rate base, remaining revenue requirement				$ 62.2
Rate Credit | Yankee Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested			$ 37.4
Inflation Based Adjustment | NSTAR Electric
Regulatory Assets [Line Items]
Rate increase approved	25.2								35.3
Inflation Based Adjustment | NSTAR Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested							10.3
Rate increase approved					$ 10.3
K-Bar Adjustment | NSTAR Electric
Regulatory Assets [Line Items]
Rate increase approved	$ 29.9								$ 20.5
Capital Additions Adjustment | NSTAR Gas
Regulatory Assets [Line Items]
Rate increase (decrease) requested							$ 152.3