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INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Deferred Tax Assets: |  |
Employee Benefits | $ 266.9 | $ 244.5
Derivative Liabilities | 19.6 | 33.0
Regulatory Deferrals - Liabilities | 508.7 | 452.0
Allowance for Uncollectible Accounts | 145.3 | 143.8
Tax Effect - Tax Regulatory Liabilities | 720.8 | 739.0
Net Operating Loss Carryforwards | 198.2 | 13.8
Purchase Accounting Adjustment | 52.1 | 56.7
Equity Method Wind Investments | 1,098.6 | 584.9
Other | 267.1 | 200.1
Total Deferred Tax Assets | 3,277.3 | 2,467.8
Less: Valuation Allowance | 558.2 | 328.1
Net Deferred Tax Assets | 2,719.1 | 2,139.7
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 5,493.3 | 5,103.3
Property Tax Accruals | 107.4 | 95.0
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 1,709.1 | 1,512.3
Tax Effect - Tax Regulatory Assets | 294.5 | 284.0
Goodwill-related Regulatory Asset - 1999 Merger | 67.5 | 72.2
Employee Benefits | 353.0 | 282.0
Derivative Assets | 3.8 | 6.4
Other | 101.7 | 88.2
Total Deferred Tax Liabilities | 8,130.3 | 7,443.4
Offshore Wind Business |  |
Regulatory Amounts: |  |
Impairment charge | 427.0 | 224.0
CL&P |  |
Deferred Tax Assets: |  |
Employee Benefits | 33.7 | 29.9
Derivative Liabilities | 19.6 | 33.0
Regulatory Deferrals - Liabilities | 128.0 | 94.4
Allowance for Uncollectible Accounts | 75.4 | 79.6
Tax Effect - Tax Regulatory Liabilities | 317.6 | 320.7
Net Operating Loss Carryforwards | 0.0 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Equity Method Wind Investments | 0.0 | 0.0
Other | 134.7 | 125.3
Total Deferred Tax Assets | 709.0 | 682.9
Less: Valuation Allowance | 104.1 | 80.6
Net Deferred Tax Assets | 604.9 | 602.3
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 1,820.3 | 1,703.4
Property Tax Accruals | 49.8 | 42.0
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 522.9 | 470.0
Tax Effect - Tax Regulatory Assets | 194.7 | 191.9
Goodwill-related Regulatory Asset - 1999 Merger | 0.0 | 0.0
Employee Benefits | 51.0 | 38.8
Derivative Assets | 3.8 | 6.4
Other | 15.2 | 9.9
Total Deferred Tax Liabilities | 2,657.7 | 2,462.4
NSTAR Electric |  |
Deferred Tax Assets: |  |
Employee Benefits | 83.5 | 66.8
Derivative Liabilities | 0.0 | 0.0
Regulatory Deferrals - Liabilities | 316.7 | 291.5
Allowance for Uncollectible Accounts | 26.5 | 21.5
Tax Effect - Tax Regulatory Liabilities | 214.3 | 227.1
Net Operating Loss Carryforwards | 0.0 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Equity Method Wind Investments | 0.0 | 0.0
Other | 31.5 | 25.0
Total Deferred Tax Assets | 672.5 | 631.9
Less: Valuation Allowance | 0.0 | 0.0
Net Deferred Tax Assets | 672.5 | 631.9
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 1,845.2 | 1,728.6
Property Tax Accruals | 44.5 | 39.8
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 519.9 | 474.5
Tax Effect - Tax Regulatory Assets | 10.0 | 10.5
Goodwill-related Regulatory Asset - 1999 Merger | 58.0 | 61.9
Employee Benefits | 175.4 | 146.7
Derivative Assets | 0.0 | 0.0
Other | 24.9 | 19.5
Total Deferred Tax Liabilities | 2,677.9 | 2,481.5
PSNH |  |
Deferred Tax Assets: |  |
Employee Benefits | 14.5 | 13.0
Derivative Liabilities | 0.0 | 0.0
Regulatory Deferrals - Liabilities | 19.6 | 23.8
Allowance for Uncollectible Accounts | 3.8 | 3.9
Tax Effect - Tax Regulatory Liabilities | 93.2 | 95.5
Net Operating Loss Carryforwards | 1.5 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Equity Method Wind Investments | 0.0 | 0.0
Other | 24.1 | 23.4
Total Deferred Tax Assets | 156.7 | 159.6
Less: Valuation Allowance | 0.0 | 0.0
Net Deferred Tax Assets | 156.7 | 159.6
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 618.4 | 566.5
Property Tax Accruals | 6.5 | 6.3
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 277.8 | 250.3
Tax Effect - Tax Regulatory Assets | 9.4 | 8.3
Goodwill-related Regulatory Asset - 1999 Merger | 0.0 | 0.0
Employee Benefits | 23.5 | 16.8
Derivative Assets | 0.0 | 0.0
Other | 2.7 | 2.9
Total Deferred Tax Liabilities | $ 938.3 | $ 851.1

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