SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	$ 636.2	$ 568.7	$ 518.0
Income Taxes	77.9	121.6	48.9
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	586.9	467.9	367.2
CL&P
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	167.2	161.5	149.0
Income Taxes	117.6	38.4	10.9
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	131.8	110.6	101.8
NSTAR Electric
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	152.8	141.6	129.4
Income Taxes	23.8	74.2	110.7
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	184.3	120.0	103.2
PSNH
Cash Paid During the Year for:
Interest, Net of Amounts Capitalized	58.3	56.5	54.5
Income Taxes	58.3	51.1	34.2
Non-Cash Investing Activities:
Plant Additions Included in Accounts Payable (As of)	$ 76.2	$ 68.7	$ 33.3