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Property, Plant, and Equipment Textuals (Details) - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Impaired Long-Lived Assets Held and Used [Line Items]        
Asset impairment charges $ 1,418,100,000 $ 0 $ 1,418,100,000 $ 0
Net book value of impaired assets 742,200,000   742,200,000  
At-risk assets 850,000,000   850,000,000  
Other US Mining Operations [Member]        
Impaired Long-Lived Assets Held and Used [Line Items]        
At-risk assets 0   0  
Property, plant, equipment, and mine development assets [Member]        
Impaired Long-Lived Assets Held and Used [Line Items]        
Asset impairment charges 1,393,700,000   1,393,700,000  
Operating lease right-of-use assets [Member]        
Impaired Long-Lived Assets Held and Used [Line Items]        
Asset impairment charges 19,900,000   19,900,000  
Contract-Based Intangible Assets [Member]        
Impaired Long-Lived Assets Held and Used [Line Items]        
Asset impairment charges $ 4,500,000   $ 4,500,000