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FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2025 | Mar. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Purchases of Investments | $ 602.7 | $ 590.0
I&M |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Purchases of Investments | 601.2 | 588.5
Spent Nuclear Fuel and Decommissioning Trusts |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Proceeds from Investment Sales | 576.5 | 569.5
Purchases of Investments | 601.2 | 588.5
Gross Realized Gains on Investment Sales | 1.9 | 5.4
Gross Realized Losses on Investment Sales | 0.7 | 1.2
Spent Nuclear Fuel and Decommissioning Trusts | I&M |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Proceeds from Investment Sales | 576.5 | 569.5
Purchases of Investments | 601.2 | 588.5
Gross Realized Gains on Investment Sales | 1.9 | 5.4
Gross Realized Losses on Investment Sales | $ 0.7 | $ 1.2

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