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Operations and Significant Accounting Policies - Other Income (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Other Income (Expense) - Other [Line Items] |  |  |  |  |
Total Other Income |  | $ 1.0 | $ 2.9 | $ 6.1 | $ 9.1
Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |
Total Other Income | [1] |  |  | 4.4 | 6.5
Interest and Investment Income (Loss) [Member] |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |
Total Other Income |  |  |  | 1.7 | 0.4
AFUDC - Equity [Member] |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |
Total Other Income |  |  |  | 1.7 | 1.8
Other [Member] |  |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |  |
Total Other Income |  |  |  | $ (1.7) | $ 0.4
[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.)

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.9) -URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227 + Details
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