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INCOME TAXES - Temporary Differences That Give Rise To Accumulated Deferred Income Tax Obligations (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
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Deferred Tax Assets: |  |
Employee Benefits | $ 270.8 | $ 602.4
Derivative Liabilities | 76.8 | 92.6
Regulatory Deferrals - Liabilities | 390.7 | 259.8
Allowance for Uncollectible Accounts | 104.1 | 87.5
Tax Effect - Tax Regulatory Liabilities | 783.4 | 810.9
Net Operating Loss Carryforwards | 7.5 | 12.7
Purchase Accounting Adjustment | 67.2 | 54.5
Other | 196.6 | 200.3
Total Deferred Tax Assets | 1,897.1 | 2,120.7
Less: Valuation Allowance | 61.5 | 48.3
Net Deferred Tax Assets | 1,835.6 | 2,072.4
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 4,426.0 | 4,153.6
Property Tax Accruals | 88.1 | 88.7
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 1,260.3 | 1,376.7
Tax Effect - Tax Regulatory Assets | 257.8 | 244.6
Goodwill Regulatory Asset - 1999 Merger | 81.4 | 86.0
Derivative Assets | 14.9 | 17.8
Other | 304.2 | 200.3
Total Deferred Tax Liabilities | 6,432.7 | 6,167.7
The Connecticut Light and Power Company |  |
Deferred Tax Assets: |  |
Employee Benefits | 23.9 | 144.5
Derivative Liabilities | 76.8 | 91.8
Regulatory Deferrals - Liabilities | 90.9 | 30.2
Allowance for Uncollectible Accounts | 48.8 | 42.3
Tax Effect - Tax Regulatory Liabilities | 328.2 | 331.4
Net Operating Loss Carryforwards | 0.0 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Other | 103.9 | 100.9
Total Deferred Tax Assets | 672.5 | 741.1
Less: Valuation Allowance | 44.5 | 33.7
Net Deferred Tax Assets | 628.0 | 707.4
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 1,509.5 | 1,438.1
Property Tax Accruals | 40.5 | 39.0
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 438.3 | 444.8
Tax Effect - Tax Regulatory Assets | 181.4 | 174.4
Goodwill Regulatory Asset - 1999 Merger | 0.0 | 0.0
Derivative Assets | 14.9 | 17.8
Other | 5.5 | 1.6
Total Deferred Tax Liabilities | 2,190.1 | 2,115.7
NSTAR Electric Company |  |
Deferred Tax Assets: |  |
Employee Benefits | 40.3 | 79.8
Derivative Liabilities | 0.0 | 0.0
Regulatory Deferrals - Liabilities | 215.4 | 161.8
Allowance for Uncollectible Accounts | 21.5 | 20.9
Tax Effect - Tax Regulatory Liabilities | 254.3 | 271.8
Net Operating Loss Carryforwards | 0.0 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Other | 21.7 | 14.3
Total Deferred Tax Assets | 553.2 | 548.6
Less: Valuation Allowance | 0.0 | 0.0
Net Deferred Tax Assets | 553.2 | 548.6
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 1,553.7 | 1,489.4
Property Tax Accruals | 33.7 | 37.0
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 337.6 | 324.4
Tax Effect - Tax Regulatory Assets | 10.9 | 11.3
Goodwill Regulatory Asset - 1999 Merger | 69.9 | 73.8
Derivative Assets | 0.0 | 0.0
Other | 126.9 | 72.6
Total Deferred Tax Liabilities | 2,132.7 | 2,008.5
Public Service Company of New Hampshire |  |
Deferred Tax Assets: |  |
Employee Benefits | 14.1 | 56.6
Derivative Liabilities | 0.0 | 0.0
Regulatory Deferrals - Liabilities | 24.3 | 13.4
Allowance for Uncollectible Accounts | 6.2 | 4.6
Tax Effect - Tax Regulatory Liabilities | 100.9 | 105.2
Net Operating Loss Carryforwards | 0.0 | 0.0
Purchase Accounting Adjustment | 0.0 | 0.0
Other | 22.9 | 19.8
Total Deferred Tax Assets | 168.4 | 199.6
Less: Valuation Allowance | 0.0 | 0.0
Net Deferred Tax Assets | 168.4 | 199.6
Deferred Tax Liabilities: |  |
Accelerated Depreciation and Other Plant-Related Differences | 482.9 | 453.8
Property Tax Accruals | 6.3 | 5.8
Regulatory Amounts: |  |
Regulatory Deferrals - Assets | 198.4 | 263.4
Tax Effect - Tax Regulatory Assets | 8.3 | 8.6
Goodwill Regulatory Asset - 1999 Merger | 0.0 | 0.0
Derivative Assets | 0.0 | 0.0
Other | 10.5 | 5.6
Total Deferred Tax Liabilities | $ 706.4 | $ 737.2

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