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Marketable Securities Held in Trusts (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
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 $ 712.3 $ 681.1  
Gross Unrealized Gains 1.5 15.3  
Gross Unrealized Losses (18.6) (12.8)  
Total debt securities 695.2 683.6  
Cash And Cash Equivalents | Fair Value Inputs Level 1      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 3.1 1.0  
Gross Unrealized Gains 0.0 0.0  
Gross Unrealized Losses 0.0 0.0  
Total debt securities 3.1 1.0  
Corporate Debt Securities | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 203.3 204.6  
Gross Unrealized Gains 0.8 1.9  
Gross Unrealized Losses (6.8) (8.4)  
Total debt securities 197.3 198.1  
Municipal Bonds | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 210.8 206.9  
Gross Unrealized Gains 0.7 1.9  
Gross Unrealized Losses (4.0) (4.1)  
Total debt securities 207.5 204.7  
U.S. Government Bonds | Fair Value Inputs Level 2      
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]      
Amortized Cost 295.1 268.6  
Gross Unrealized Gains 0.0 11.5  
Gross Unrealized Losses (7.8) (0.3)  
Total debt securities $ 287.3 $ 279.8