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Asset Retirement Obligation (Details)
$ in Millions
3 Months Ended 9 Months Ended
Mar. 31, 2020
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
ARO Loss Contingencies [Line Items]          
Asset Retirement Obligation, Liabilities Incurred $ 15.8 $ 8.8      
Number Of Consent Decrees   2      
Asset Retirement Obligation   $ 1,369.2   $ 1,315.2 $ 1,160.1
Surety Bonds Outstanding Delivered To EPA       244.9  
Asset retirement obligations   $ 1,183.1   1,160.8  
Number Of Decades Remaining For Trust   3      
Asset Retirement Obligation, Liabilities Settled (112.8) $ (87.0)      
Accretion expense for asset retirement obligations 62.4 50.7 $ 44.3    
Asset Retirement Obligation, Revision of Estimate 191.0 141.4      
Asset Retirement Obligation, Foreign Currency Translation Gain (Loss) $ (1.3) (59.9)      
Asset retirement obligations   (186.1)   (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   50.0   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   $ 254.1   $ 211.2