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Debt (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]    
Line of credit facility, current borrowing capacity   $ 1,000
Non-recourse debt and hybrid securities consolidated capital maximum limit   15.00%
Parent Company [Member]    
Debt Instrument [Line Items]    
Line of credit facility, current borrowing capacity   $ 450
IPL [Member]    
Debt Instrument [Line Items]    
Line of credit facility, current borrowing capacity   250
WPL [Member]    
Debt Instrument [Line Items]    
Line of credit facility, current borrowing capacity   $ 300
Forecast [Member] | Parent Company [Member]    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 500  
Forecast [Member] | IPL [Member]    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity 400  
Forecast [Member] | WPL [Member]    
Debt Instrument [Line Items]    
Line of credit facility, maximum borrowing capacity $ 500