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Goodwill and Other Intangible Assets (Gross and Net Intangible Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount $ 40.0 $ 46.1
Accumulated Amortization 6.2 11.4
Total 33.8 34.7
Customer contracts    
Finite-Lived Intangible Assets [Line Items]    
Gross Carrying Amount 0.0 7.7
Accumulated Amortization 0.0 7.2
Total $ 0.0 0.5
Customer relationships    
Finite-Lived Intangible Assets [Line Items]    
Weighted - Average Remaining Amortization Years 4 years  
Gross Carrying Amount $ 6.7 6.7
Accumulated Amortization 4.5 3.9
Total $ 2.2 2.8
Permits    
Finite-Lived Intangible Assets [Line Items]    
Weighted - Average Remaining Amortization Years 22 years  
Gross Carrying Amount $ 31.7 31.7
Accumulated Amortization 1.7 0.3
Total $ 30.0 31.4
Other    
Finite-Lived Intangible Assets [Line Items]    
Weighted - Average Remaining Amortization Years 30 years  
Gross Carrying Amount $ 1.6 0.0
Accumulated Amortization 0.0 0.0
Total $ 1.6 $ 0.0