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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2020
Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Money market fund investments $ 41.2 $ 5.4
Money market fund investments interest rate, percentage 0.40%  
IPL [Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Money market fund investments $ 21.2 5.4
Money market fund investments interest rate, percentage 0.40%  
WPL [Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Money market fund investments $ 20.0 0.0
Money market fund investments interest rate, percentage 0.40%  
Credit Losses ASU [Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax   12.0
New accounting standard, cumulative effect adjustment to retained earnings, after-tax   $ 8.7