SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts Narrative (Details)	6 Months Ended
Jun. 30, 2017
Maximum [Member] \| The Connecticut Light And Power Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of accounts receivable recoverable under financial or medical duress	180 days
Minimum [Member] \| Yankee Gas Services Company [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of accounts receivable recoverable under financial or medical duress	90 days

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.

No definition available.

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