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Pension and Other Postretirement Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Pension |  |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |  |
Net Loss | $ 2.5 | $ 11.4
Amortization of Prior Service Credit | 0.1 | 0.1
Prior Service Credit Arising During the Period | 0.0 | 0.8
Amortization of Gain (Loss) | (5.7) | (11.4)
Amortization of Prior Service Credit | (0.1) | (0.1)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities | (3.1) | 0.9
Postretirement Health and Life Obligation and Funded Status |  |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |  |
Net Loss | (18.3) | 3.9
Prior Service Credit Arising During the Period | (29.1) | 0.0
Amortization of Prior Service Credit | 8.4 | 7.5
Amortization of Gain (Loss) | 2.7 | (0.4)
Amortization of Prior Service Credit | (8.4) | (7.5)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities | $ (36.3) | $ 11.0

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- Definition Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income from prior service cost (credit) of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (j) -SubTopic 10 -Topic 220 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-11 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, before tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 10A -Subparagraph (j) -SubTopic 10 -Topic 220 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-10A Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-11 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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