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OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES - Other Income (Expense) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Other Income (Expense) |  |  |  |
Total Other Income | $ 5.5 | $ 68.7 | $ 20.0 | $ 75.3
Pension and Other Postretirement Benefit Plan Non-Service Credits |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 3.0 | 1.8 | 11.0 | 5.5
Interest and Investment Income |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.2 | 6.6 | 3.9 | 8.7
AFUDC - Equity |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 1.5 | 1.1 | 4.0 | 2.5
Gain on Arbitration Award |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | 0.0 | 58.4 | 0.0 | 58.4
Other Income (Expense) |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income | $ (0.2) | 0.8 | $ 1.1 | 0.2
Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling |  |  |  |
Other Income (Expense) |  |  |  |
Total Other Income |  | $ 5.1 |  | $ 5.1

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- Definition Amount of income (expense) related to nonoperating activities, classified as other. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
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