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

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Contractual interest rate for funds borrowed, under the debt agreement.

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

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SHORT-TERM AND LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($)	1 Months Ended			6 Months Ended
	Jan. 31, 2015	May 31, 2013	May 31, 2008	Jun. 30, 2018	Jun. 30, 2017	Jan. 31, 2018
Debt Instrument [Line Items]
Repayments				$ (860,421,000)	$ (150,000,000)
The Connecticut Light and Power Company
Debt Instrument [Line Items]
Repayments				(300,000,000)	(150,000,000)
The Connecticut Light and Power Company \| Senior Notes \| 4.00% 2018 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Issuances				$ 500,000,000
Interest rate, stated percentage				4.00%
The Connecticut Light and Power Company \| Senior Notes \| 2008 Series A First Mortgage Bonds Due 2018
Debt Instrument [Line Items]
Repayments			$ (300,000,000)
Interest rate, stated percentage			5.65%
Public Service Company of New Hampshire
Debt Instrument [Line Items]
Repayments				$ (110,000,000)	$ 0
Public Service Company of New Hampshire \| Senior Notes \| 2008 Series O First Mortgage Bonds Due 2018
Debt Instrument [Line Items]
Repayments			$ (110,000,000)
Interest rate, stated percentage			6.00%
Eversource Parent \| Senior Notes \| Eversource Parent 2.50% Series I Senior Notes
Debt Instrument [Line Items]
Issuances						$ 200,000,000.0
Long-term debt				$ 450,000,000
Interest rate, stated percentage						2.50%
Eversource Parent \| Senior Notes \| 3.30% Series M Senior Notes
Debt Instrument [Line Items]
Issuances						$ 450,000,000.0
Interest rate, stated percentage						3.30%
Eversource Parent \| Senior Notes \| Eversource Parent 1.60% Series G Senior Notes
Debt Instrument [Line Items]
Repayments	$ (150,000,000)
Interest rate, stated percentage	1.60%
Eversource Parent \| Senior Notes \| Series E Senior Notes Due 2018
Debt Instrument [Line Items]
Repayments		$ (300,000,000)
Interest rate, stated percentage		1.45%