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