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Operations and Significant Accounting Policies - Other Income (Expense) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | $ 85.0 | $ 22.4 | $ 8.7
Pension and Other Postretirement Benefit Plan Non-Service Credit |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 8.9 | 9.8 | 6.1
Interest and Investment Income |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 10.3 | 0.0 | 2.3
AFUDC - Equity |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 3.6 | 2.7 | 2.6
Gain on Land Sales |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 0.2 | 0.0 | 0.1
PSA Liability |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 0.0 | 10.2 | 0.0
Gain on Arbitration Award |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 58.4 | 0.0 | 0.0
Other |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | 3.6 | $ (0.3) | $ (2.4)
Interest Income Related To Interest Awarded As Part Of An Arbitration Ruling |  |  |
Other Income (Expense) - Other [Line Items] |  |  |
Total Other Income (Expense) - Other | $ 5.1 |  |

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- Definition [Line Items] for Other Income (Expense) - Other [Table] + References No definition available. + Details
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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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