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FAIR VALUE MEASUREMENTS - Narrative (Details) - Spent Nuclear Fuel and Decommissioning Trusts - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Adjusted cost of debt securities | $ 1,700 | $ 1,500
Adjusted cost of equity securities | 536 | 549
I&M |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Adjusted cost of debt securities | 1,700 | 1,500
Adjusted cost of equity securities | $ 536 | $ 549

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