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Fair Value Measurements (Schedule Of Financial Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets $ 0.0 $ 22.6
Total Financial Assets   22.6
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets   22.6
Total Financial Assets   22.6
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets   0.0
Total Financial Assets   0.0
Significant Unobservable Inputs (Level 3) [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Supplemental executive retirement plan assets   0.0
Total Financial Assets   $ 0.0