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Regulatory Matters (Regulatory Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Regulated Operations [Line Items]    
Total Assets $ 2,580.8 $ 2,492.2
Regulatory Assets, Current 233.2 206.2
Regulatory Assets, Noncurrent $ 2,347.6 2,286.0
Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided 50 years  
Unrecognized Pension Benefit And Other Postretirement Benefit Costs    
Regulated Operations [Line Items]    
Total Assets $ 607.5 512.1
Other Postretirement Costs    
Regulated Operations [Line Items]    
Total Assets 72.2 74.8
Environmental Costs    
Regulated Operations [Line Items]    
Total Assets 41.4 45.8
Regulatory Effects Of Accounting For Income Taxes    
Regulated Operations [Line Items]    
Total Assets 158.0 194.8
Underrecovered Gas And Fuel Costs    
Regulated Operations [Line Items]    
Total Assets 85.5 73.6
Depreciation    
Regulated Operations [Line Items]    
Total Assets 191.3 177.5
Post-In Service Carrying Charges    
Regulated Operations [Line Items]    
Total Assets 251.5 237.9
Safety Activity Costs    
Regulated Operations [Line Items]    
Total Assets 200.7 171.9
DSM Program    
Regulated Operations [Line Items]    
Total Assets 37.5 39.2
Retired coal generating stations    
Regulated Operations [Line Items]    
Total Assets 744.0 803.9
Deferred Derivative Gain (Loss)    
Regulated Operations [Line Items]    
Total Assets 10.0 9.6
Deferred Property Taxes    
Regulated Operations [Line Items]    
Total Assets 68.5 65.1
Renewable Energy Program    
Regulated Operations [Line Items]    
Total Assets 37.7 18.5
Other Assets    
Regulated Operations [Line Items]    
Total Assets $ 75.0 $ 67.5