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OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES - Other Income (Expense) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Other Income (Expense) |  |  |  |
Total Other Income | $ 5.3 | $ 5.5 | $ 15.1 | $ 20.0
Pension and Other Postretirement Benefit Plan Non-Service Credits |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.7 | 3.0 | 5.0 | 11.0
Interest and Investment Income |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 2.3 | 1.2 | 6.7 | 3.9
AFUDC - Equity |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.3 | 1.5 | 4.0 | 4.0
Other Income (Expense) |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | $ 0.0 | $ (0.2) | $ (0.6) | $ 1.1

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