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Regulatory Matters (Regulatory Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulated Operations [Line Items]    
Total Assets $ 2,477.3 $ 2,460.2
Regulatory Assets, Current 319.9 214.3
Regulatory Assets, Noncurrent 2,157.4 2,245.9
Unrecognized Pension Benefit And Other Postretirement Benefit Costs    
Regulated Operations [Line Items]    
Total Assets 485.3 561.6
Other Postretirement Costs    
Regulated Operations [Line Items]    
Total Assets 45.3 59.7
Environmental Costs    
Regulated Operations [Line Items]    
Total Assets 42.8 40.6
Regulatory Effects Of Accounting For Income Taxes    
Regulated Operations [Line Items]    
Total Assets 172.0 163.5
Underrecovered Gas And Fuel Costs    
Regulated Operations [Line Items]    
Total Assets 82.3 12.7
Depreciation    
Regulated Operations [Line Items]    
Total Assets 214.9 201.9
Post-In Service Carrying Charges    
Regulated Operations [Line Items]    
Total Assets 280.8 269.9
Safety Activity Costs    
Regulated Operations [Line Items]    
Total Assets 203.7 206.6
DSM Program    
Regulated Operations [Line Items]    
Total Assets 17.8 25.0
Retired coal generating stations    
Regulated Operations [Line Items]    
Total Assets 617.0 682.0
Deferred Derivative Gain (Loss)    
Regulated Operations [Line Items]    
Total Assets 6.5 24.4
Deferred Property Taxes    
Regulated Operations [Line Items]    
Total Assets 75.9 72.3
Renewable Energy Program    
Regulated Operations [Line Items]    
Total Assets 81.3 60.8
Other Assets    
Regulated Operations [Line Items]    
Total Assets 105.8 79.2
Work and Asset Management enterprise resourcing system    
Regulated Operations [Line Items]    
Total Assets 21.5 0.0
Customer Assistance Programs    
Regulated Operations [Line Items]    
Total Assets $ 24.4 $ 0.0