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Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2022
Jun. 30, 2021
Dec. 31, 2021
Dec. 31, 2020
Accounts Receivable Allowance For Credit Loss [Line Items]        
Accounts Receivable, Allowance for Credit Loss $ 28.5   $ 23.5 $ 52.3
Current period provisions 8.6 $ 7.2    
Write-offs charged against allowance 8.9 54.4    
Recoveries of amounts previously written off 5.3 18.4    
Gas Distribution Operations        
Accounts Receivable Allowance For Credit Loss [Line Items]        
Accounts Receivable, Allowance for Credit Loss 22.2   18.9 41.8
Current period provisions 5.8 5.8    
Write-offs charged against allowance 7.7 46.7    
Recoveries of amounts previously written off 5.2 18.0    
Electric Operations        
Accounts Receivable Allowance For Credit Loss [Line Items]        
Accounts Receivable, Allowance for Credit Loss 5.5   3.8 9.7
Current period provisions 2.8 1.4    
Write-offs charged against allowance 1.2 7.7    
Recoveries of amounts previously written off 0.1 0.4    
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