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Operations and Significant Accounting Policies - Other Income (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income |  | $ 2.5 | $ 12.1 |  | $ 6.6 | $ 14.1 |
Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] |  |  |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income | [1] | 1.7 | 2.7 |  | 3.7 | 5.3 |
Interest and Investment Income (Loss) [Member] |  |  |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income |  | 1.0 | (1.0) |  | 2.1 | (0.9) |
AFUDC - Equity [Member] |  |  |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income |  | 0.9 | 0.8 |  | 1.4 | 1.7 |
PSA Liability [Member] |  |  |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income |  | 0.0 | 10.2 | [2] | 0.0 | 10.2 | [2]
Other [Member] |  |  |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |  |  |
Total Other Income |  | $ (1.1) | $ (0.6) |  | $ (0.6) | $ (2.2) |
[1] | These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 9. Pension and Other Postretirement Benefit Plans.)
[2] | The gain on removal of the PSA liability for the Northern Wind project upon decommissioning of the legacy wind energy facility assets, which was more than offset by a reserve for an anticipated loss on the sale of the Northern Wind project that was recorded in Cost of Sales - Non-Utility on the Consolidated Statement of Income.

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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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