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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, 2024
Dec. 31, 2023
Pension    
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]    
Net (Gain) Loss $ (15.2) $ 2.5
Amortization of Prior Service Credit 0.1 0.1
Amortization of Prior Service Credit (0.1) (0.1)
Amortization of (Loss) Gain (6.5) (5.7)
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities (21.6) (3.1)
Postretirement Health and Life Obligation and Funded Status    
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]    
Net (Gain) Loss (5.6) (18.3)
Prior Service Credit Arising During the Period 0.0 (29.1)
Amortization of Prior Service Credit 11.7 8.4
Amortization of Prior Service Credit (11.7) (8.4)
Amortization of (Loss) Gain 3.2 2.7
Total Recognized in Other Comprehensive Income and Regulatory Assets or Liabilities $ 9.3 $ (36.3)