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Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Dec. 31, 2021
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss $ 15.6 $ 23.9 $ 23.5
Current period provisions 27.1 36.0  
Write-offs charged against allowance 48.2 57.4  
Recoveries of amounts previously written off 12.8 21.8  
Gas Distribution Operations      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 8.2 17.2 18.9
Current period provisions 22.4 29.1  
Write-offs charged against allowance 43.9 52.1  
Recoveries of amounts previously written off 12.5 21.3  
Electric Operations      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 6.6 5.9 3.8
Current period provisions 4.7 6.9  
Write-offs charged against allowance 4.3 5.3  
Recoveries of amounts previously written off 0.3 0.5  
Corporate and Other      
Accounts Receivable Allowance For Credit Loss [Line Items]      
Accounts Receivable, Allowance for Credit Loss 0.8 0.8 $ 0.8
Current period provisions 0.0 0.0  
Write-offs charged against allowance 0.0 0.0  
Recoveries of amounts previously written off $ 0.0 $ 0.0