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Marketable Securities Held in Trusts (Details)
$ in Millions
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Aug. 31, 2016
USD ($)
Investments, Debt and Equity Securities [Abstract]      
Amount deposited by Mosaic into the RCRA Trusts     $ 630.0
Number Of Decades Remaining For Trust     3
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost $ 678.3 $ 710.3  
Gross Unrealized Gains 0.5 12.1  
Gross Unrealized Losses (28.7) (7.5)  
Total debt securities 650.1 714.9  
Cash And Cash Equivalents | Fair Value Inputs Level 1      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 7.7 8.1  
Gross Unrealized Gains 0.0 0.0  
Gross Unrealized Losses 0.0 0.0  
Total debt securities 7.7 8.1  
Corporate Debt Securities | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 203.8 198.8  
Gross Unrealized Gains 0.1 5.6  
Gross Unrealized Losses (17.1) (0.9)  
Total debt securities 186.8 203.5  
Municipal Bonds | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 197.0 198.1  
Gross Unrealized Gains 0.4 6.5  
Gross Unrealized Losses (8.0) (0.5)  
Total debt securities 189.4 204.1  
U.S. Government Bonds | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 269.6 305.3  
Gross Unrealized Gains 0.0 0.0  
Gross Unrealized Losses (3.6) (6.1)  
Total debt securities 266.0 $ 299.2  
Asset-Backed Securities | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 0.2    
Gross Unrealized Gains 0.0    
Gross Unrealized Losses 0.0    
Total debt securities $ 0.2