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New Accounting Standards (Details) - USD ($)
$ in Millions
Jan. 01, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Allowance for credit loss   $ 33 $ 24 $ 20
Retained earnings   $ (25) $ (271)  
EnerBank | Forecast | Accounting Standards Update 2016-13        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Allowance for credit loss $ 65      
Retained earnings $ 0