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Asset Retirement Obligation (Details)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2020
USD ($)
Mar. 31, 2019
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
ARO Loss Contingencies [Line Items]        
Asset Retirement Obligation, Liabilities Incurred $ 3.4   $ 15.8  
Number Of Consent Decrees 2      
Asset Retirement Obligation $ 1,260.7   1,315.2 $ 1,160.1
Surety Bonds Outstanding Delivered To EPA     244.9  
Asset retirement obligations $ 1,113.2   1,160.8  
Number Of Decades Remaining For Trust 3      
Asset Retirement Obligation, Liabilities Settled $ (22.5)   (112.8)  
Accretion expense for asset retirement obligations 17.3 $ 15.3 62.4  
Asset Retirement Obligation, Revision of Estimate 1.2   191.0  
Asset Retirement Obligation, Foreign Currency Translation Gain (Loss) (53.9)   (1.3)  
Asset retirement obligations (147.5)   (154.4)  
Unfavorable Regulatory Action | 2015 Consent Decrees With EPA        
ARO Loss Contingencies [Line Items]        
Asset retirement obligations, undiscounted     1,600.0  
Asset Retirement Obligation 60.0   429.3  
Bonnie Facility Trust [Member]        
ARO Loss Contingencies [Line Items]        
Assets Held-in-trust, Current     21.0  
Plant City and Bonnie Facilities        
ARO Loss Contingencies [Line Items]        
Asset retirement obligations $ 208.1   $ 211.2