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Regulatory Matters (Narrative) (Details)
$ in Millions
1 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2020
USD ($)
Aug. 31, 2020
customer
Jun. 30, 2020
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2020
USD ($)
Regulatory Matters [Line Items]            
Credits issued to customers       $ (72) $ (12)  
Electric transmission cost recovery [Member] | IPL [Member]            
Regulatory Matters [Line Items]            
Credits issued to customers     $ 42      
DAEC PPA [Member]            
Regulatory Matters [Line Items]            
Buyout payment $ 110          
PPA term amendment 5 years          
Derecho windstorm [Member]            
Regulatory Matters [Line Items]            
Net regulatory liability, derecho windstorm $ 7     7    
Derecho windstorm [Member] | IPL [Member]            
Regulatory Matters [Line Items]            
Number of customers without power, derecho windstorm (number of customers) | customer   250,000        
Derecho windstorm repair and rebuilding costs $ 130     $ 130    
Derecho windstorm [Member] | Forecast [Member] | IPL [Member]            
Regulatory Matters [Line Items]            
Derecho windstorm repair and rebuilding costs           $ 140