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Operations and Significant Accounting Policies - Other Income (Expense) - Other (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other |  | $ 8.7 | $ 14.7 | $ 18.7
Pension and Other Postretirement Benefit Plans Non-Service Credit [Member] |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other | [1] | 6.1 | 8.6 | 7.7
Interest and Investment Earnings [Member] |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other |  | 2.3 | 1.6 | 4.4
AFUDC - Equity [Member] |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other |  | 2.6 | 1.9 | 2.3
Gain on Land Sales [Member] |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other |  | 0.1 | 0.4 | 2.1
Other Income (Expense) - Other [Member] |  |  |  |
Other Income (Expense) - Other [Line Items] |  |  |  |
Total Other Income (Expense) - Other |  | $ (2.4) | $ 2.2 | $ 2.2
[1] | These are components of net periodic pension and other postretirement benefit cost other than service cost. (See Note 11. Pension and Other Postretirement Benefit Plans.

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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 -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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