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Operations and Significant Accounting Policies - Other Income (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Other Income    
Total Other Income $ 8.6 $ 4.1
Pension and Other Postretirement Benefit Plan Non-Service Credits    
Other Income    
Total Other Income 4.3 2.0
Interest and Investment Income    
Other Income    
Total Other Income 1.9 1.1
AFUDC - Equity    
Other Income    
Total Other Income 1.2 0.5
Other    
Other Income    
Total Other Income $ 1.2 $ 0.5