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OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES - Other Income (Expense) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Other Income (Expense) |  |  |  |
Total Other Income | $ 5.2 | $ 5.9 | $ 9.8 | $ 14.5
Pension and Other Postretirement Benefit Plan Non-Service Credits |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.5 | 3.7 | 3.3 | 8.0
Interest and Investment Income |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 2.5 | 0.8 | 4.4 | 2.7
AFUDC - Equity |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.3 | 1.3 | 2.7 | 2.5
Other Income (Expense) |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | $ (0.1) | $ 0.1 | $ (0.6) | $ 1.3

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