GENERATION ASSET SALE - Narrative (Details) - USD ($)				12 Months Ended
	Nov. 27, 2019	Aug. 26, 2018	Jan. 10, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 08, 2018
Regulatory Assets [Line Items]
Proceeds from the sale of thermal assets				$ 0	$ 193,924,000	$ 0
Securitized Stranded Cost (included in Regulatory Assets)				5,514,700,000	5,145,900,000
Recoverable Divestiture Related Costs	$ 654,000,000.0
Pre-tax incmoe associated with generation assets				1,190,071,000	1,329,491,000	1,574,407,000
PSNH
Regulatory Assets [Line Items]
Purchase price in purchase sale agreement for thermal generation assets			$ 175,000,000
Proceeds from the sale of thermal assets			116,800,000	0	193,924,000	0
Purchase price in purchase sale agreement for hydroelectric assets		$ 5,800,000	$ 83,000,000
Proceeds from assets held for sale		77,200,000
Gain in sale of proceeds		17,300,000
Securitized Stranded Cost (included in Regulatory Assets)				945,800,000	929,500,000
Pre-tax incmoe associated with generation assets				175,023,000	163,452,000	224,671,000
Domestic Tax Authority | PSNH
Regulatory Assets [Line Items]
Pre-tax incmoe associated with generation assets		$ 9,900,000				$ 60,000,000.0
Rate Reduction Bonds | PSNH
Regulatory Assets [Line Items]
Amount of securitized rate reduction bonds issued							$ 635,700,000
Securitized Stranded Costs
Regulatory Assets [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)				565,300,000	608,400,000
Securitized Stranded Costs | PSNH
Regulatory Assets [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)				565,300,000	608,400,000
Variable Interest Entity, Primary Beneficiary | Securitized Stranded Costs | PSNH
Regulatory Assets [Line Items]
Securitized Stranded Cost (included in Regulatory Assets)				$ 565,300,000	$ 608,400,000