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DERIVATIVE INSTRUMENTS - Gross Fair Values and Net Amounts of Contracts (Details) - USD ($) $ in Millions | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Current Derivative Assets | CL&P | Level 3 |  |
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract] |  |
Commodity Supply and Price Risk Management | $ 14.4 | $ 13.7
Netting | (0.4) | (0.4)
Net Amount Recorded as a Derivative | 14.0 | 13.3
Other Long-Term Assets | CL&P | Level 3 |  |
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract] |  |
Commodity Supply and Price Risk Management | 51.1 | 58.7
Netting | (1.6) | (1.8)
Net Amount Recorded as a Derivative | 49.5 | 56.9
Current Derivative Liabilities | CL&P | Level 3 |  |
Current and Long-Term Derivative Liabilities |  |
Commodity Supply and Price Risk Management | (72.2) | (68.8)
Netting | 0.0 | 0.0
Net Amount Recorded as a Derivative | (72.2) | (68.8)
Current Derivative Liabilities | Other | Level 2 |  |
Current and Long-Term Derivative Liabilities |  |
Commodity Supply and Price Risk Management | 0.0 | (3.3)
Netting | 0.0 | 0.1
Net Amount Recorded as a Derivative | 0.0 | (3.2)
Long-Term Derivative Liabilities | CL&P | Level 3 |  |
Current and Long-Term Derivative Liabilities |  |
Commodity Supply and Price Risk Management | (256.6) | (294.5)
Netting | 0.0 | 0.0
Net Amount Recorded as a Derivative | $ (256.6) | $ (294.5)

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