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Income Taxes (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2018
Dec. 31, 2018
Income Taxes [Line Items]                  
Effective income tax rate   54.60% 54.60%   24.40% 24.40%   78.10% 78.10%
Increase (Decrease) in Effective Tax Rate   30.20%     53.70%        
State regulatory proceedings, value $ 0.0     $ 9.5     $ 127.8    
Deferred Tax Assets, Operating Loss Carryforwards 602.1 $ 602.1 $ 602.1 765.9 $ 765.9 $ 765.9      
Deferred Tax Assets, Charitable Contribution Carryforwards 7.8 7.8 7.8            
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions 1.5     0.6     0.4    
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions 0.0     22.6     0.2    
Unrecognized Tax Benefits, Income Tax Penalties Expense 0.0     0.0     $ 0.0    
Unrecognized Tax Benefits, Income Tax Penalties Accrued 0.0 0.0 0.0 $ 0.0 $ 0.0 $ 0.0      
Deferred Tax Assets, Valuation Allowance 6.4 6.4 6.4            
Internal Revenue Service (IRS)                  
Income Taxes [Line Items]                  
Deferred Tax Assets, Operating Loss Carryforwards 520.8 520.8 520.8            
State and Local Jurisdiction                  
Income Taxes [Line Items]                  
Deferred Tax Assets, Operating Loss Carryforwards $ 81.4 $ 81.4 $ 81.4