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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
Sep. 30, 2019
Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Money market fund investments $ 174.4 $ 0.0
Money market fund investments interest rate, percentage 2.00%  
IPL [Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Money market fund investments $ 173.7 $ 0.0
Money market fund investments interest rate, percentage 2.00%