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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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

SHORT-TERM AND LONG - Long-Term Debt Issuance Authorization (Details) - Senior Notes [Member] - USD ($) $ in Millions	Mar. 30, 2017	Jan. 04, 2017
The Connecticut Light And Power Company [Member]
Debt Instrument [Line Items]
Amount of debt authorized (up to)		$ 1,325
NSTAR Electric Company [Member]
Debt Instrument [Line Items]
Amount of debt authorized (up to)	$ 700