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FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Purchases of Investments |  |  | $ 1,336.5 | $ 1,190.1
I&M |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Purchases of Investments |  |  | 1,330.0 | 1,187.1
Spent Nuclear Fuel and Decommissioning Trusts |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Proceeds from Investment Sales | $ 717.9 | $ 584.6 | 1,294.4 | 1,154.1
Purchases of Investments | 728.8 | 598.6 | 1,330.0 | 1,187.1
Gross Realized Gains on Investment Sales | 2.4 | 4.9 | 4.3 | 10.3
Gross Realized Losses on Investment Sales | 1.8 | 4.2 | 2.5 | 5.4
Spent Nuclear Fuel and Decommissioning Trusts | I&M |  |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |  |
Proceeds from Investment Sales | 717.9 | 584.6 | 1,294.4 | 1,154.1
Purchases of Investments | 728.8 | 598.6 | 1,330.0 | 1,187.1
Gross Realized Gains on Investment Sales | 2.4 | 4.9 | 4.3 | 10.3
Gross Realized Losses on Investment Sales | $ 1.8 | $ 4.2 | $ 2.5 | $ 5.4

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