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Contingencies (Details)
$ in Millions
 3 Months Ended
Apr. 17, 2015
Entity
Insurance_company
People
Plaintiff
Apr. 17, 2013
People
Mar. 31, 2016
mine
processingFacility
Sep. 30, 2021
USD ($)
Loss Contingencies [Line Items]        
Loss contingency, number of processing facilities | processingFacility     3  
Pending Litigation        
Loss Contingencies [Line Items]        
Number of people killed   15    
Number of people injured   200    
Number of plaintiffs | Plaintiff 400      
Number of entities that filed claims | Entity 9      
Number of people that filed claims 325      
Number of insurance companies that filed claims | Insurance_company 80      
Loss Contingency, Estimate of Possible Loss | $       $ 37
IDAHO        
Loss Contingencies [Line Items]        
Loss contingency, number of mines | mine     18