SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	$ 1,182.6	$ 1,014.4	$ 783.2
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	508.2	472.5	564.1
CL&P
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	208.4	216.8	176.8
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	143.2	95.8	139.8
NSTAR Electric
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	232.4	215.1	182.8
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	160.5	155.4	178.9
PSNH
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	83.9	78.4	62.8
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	$ 59.2	$ 77.7	$ 65.9