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Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Beginning Balance $ 469.7    
Accretion recorded as a regulatory asset 17.1 $ 16.0  
Additions 9.5 23.2  
Settlements (22.3) (11.2)  
Change in estimated cash flows (3.2) (11.2)  
Asset Retirement Obligation 513.5 512.4 $ 495.6
Ending Balance $ 478.1 $ 469.7