Face (par) amount of debt instrument at time of issuance.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($)	1 Months Ended						12 Months Ended
	Nov. 30, 2018	Oct. 31, 2018	Jan. 31, 2015	May 31, 2013	May 31, 2008	Dec. 31, 2001	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Mar. 31, 2018	Jan. 31, 2018
Debt Instrument [Line Items]
Retirements of Long-Term Debt							$ (1,050,330,000)	$ (745,000,000)	$ (200,000,000)
Senior Notes
Debt Instrument [Line Items]
Long-term debt							12,248,700,000	11,775,900,000
Senior Notes \| Yankee Gas 4.13% Series O First Mortgage Bonds
Debt Instrument [Line Items]
Debt instruments, face amount										$ 50,000,000.0
Senior Notes \| Yankee Gas 6.90% Series J First Mortgage Bonds
Debt Instrument [Line Items]
Retirements of Long-Term Debt		$ (100,000,000)
Senior Notes \| NSTAR Gas 4.09% Series P First Mortgage Bonds
Debt Instrument [Line Items]
Debt instruments, face amount										$ 100,000,000.0
The Connecticut Light And Power Company
Debt Instrument [Line Items]
Retirements of Long-Term Debt							(300,000,000)	(250,000,000)	0
The Connecticut Light And Power Company \| Senior Notes \| 2018 Series A First Mortgage Bonds Due 2048 [Member]
Debt Instrument [Line Items]
Debt instruments, face amount											$ 500,000,000
The Connecticut Light And Power Company \| Senior Notes \| 2008 Series A First Mortgage Bonds Due 2018 [Member]
Debt Instrument [Line Items]
Retirements of Long-Term Debt					$ (300,000,000)
Public Service Company Of New Hampshire
Debt Instrument [Line Items]
Retirements of Long-Term Debt							(199,250,000)	(70,000,000)	0
Public Service Company Of New Hampshire \| Senior Notes \| 2008 Series O First Mortgage Bonds Due 2018 [Member]
Debt Instrument [Line Items]
Retirements of Long-Term Debt	$ (89.3)				$ (110,000,000)	$ (89,300,000)
Parent Company
Debt Instrument [Line Items]
Retirements of Long-Term Debt							(450,000,000)	$ 0	$ 0
Parent Company \| Senior Notes \| Eversource Parent 2.50% Series I Senior Notes (2)
Debt Instrument [Line Items]
Debt instruments, face amount							400,000,000					$ 200,000,000.0
Long-term debt							450,000,000
Parent Company \| Senior Notes \| Series G Senior Notes Due 2018
Debt Instrument [Line Items]
Debt instruments, face amount							$ 500,000,000					$ 450,000,000.0
Parent Company \| Senior Notes \| Eversource Parent 1.60% Series G Senior Notes
Debt Instrument [Line Items]
Retirements of Long-Term Debt			$ (150,000,000)
Parent Company \| Senior Notes \| Eversource Parent 1.45% Series E Senior Notes
Debt Instrument [Line Items]
Retirements of Long-Term Debt				$ (300,000,000)