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Environmental Obligations - Narrative (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
site
operable_unit
party
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 1998
USD ($)
Dec. 31, 2020
USD ($)
Environmental Exit Cost [Line Items]          
Environmental reserves, excluding recoveries $ 601.8 $ 543.1      
Environmental loss contingencies, net of expected recoveries, in excess of accrual 240.0        
Charges to expense for new losses 152.3 104.8 $ 65.8    
Accrual for environmental loss contingencies 592.1 529.2 503.2   $ 564.4
Payments for attorney fees and unpaid permit fees $ 92.6 74.5 $ 121.8    
Number of operable units evaluated and proposed for CMAs | operable_unit 6        
Non-judicial process, parties involved | party 100        
Number of sites FMC is named as a potentially responsible party | site 28        
Number of sites FMC may be a potentially responsible party or equivalent | site 46        
Middleport Litigation          
Environmental Exit Cost [Line Items]          
Settlement payment $ 12.5 11.7      
Pending Litigation | Middleport Litigation          
Environmental Exit Cost [Line Items]          
Operable units | operable_unit 11        
Cash outflow, maximum, after year 2021 $ 10.0        
Pocatello          
Environmental Exit Cost [Line Items]          
Charges to expense for new losses 31.1        
Accrual for environmental loss contingencies $ 82.9 75.8      
Tribal permit fee       $ 1.5  
Discount rate 4.20%        
Estimated year three fees $ 1.5        
Expected aggregate undiscounted fees 75.0        
Middleport          
Environmental Exit Cost [Line Items]          
Accrual for environmental loss contingencies $ 130.8 $ 108.2