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Accounting for Asset Retirement Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]      
Asset retirement obligations, beginning of period $ 859.3 $ 849.9  
Asset Retirement Obligation, Period Increase (Decrease) 258.9 0.0  
Liabilities incurred 27.8 27.1  
Liabilities settled (69.6) (64.8)  
Accretion expense 48.0 25.7 $ 40.4
Revisions in estimated cash flows 78.2 15.7  
Foreign currency translation (42.5) 5.7  
Asset retirement obligations, end of period 1,160.1 859.3 $ 849.9
Less current portion 136.3 98.1  
Asset retirement obligations $ 1,023.8 $ 761.2