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Marketable Securities Held in Trusts (Details) $ in Millions | Sep. 30, 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 |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Amortized cost | $ 709.7 | $ 681.1 |
Gross unrealized gains | 10.4 | 15.3 |
Gross unrealized losses | (6.9) | (12.8) |
Debt Securities, Available-for-sale | 713.2 | 683.6 |
Cash and Cash Equivalents | Level 1 |  |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Amortized cost | 1.9 | 1.0 |
Gross unrealized gains | 0.0 | 0.0 |
Gross unrealized losses | 0.0 | 0.0 |
Debt Securities, Available-for-sale | 1.9 | 1.0 |
Corporate debt securities | Level 2 |  |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Amortized cost | 202.6 | 204.6 |
Gross unrealized gains | 3.6 | 1.9 |
Gross unrealized losses | (4.8) | (8.4) |
Debt Securities, Available-for-sale | 201.4 | 198.1 |
Municipal bonds | Level 2 |  |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Amortized cost | 208.9 | 206.9 |
Gross unrealized gains | 2.7 | 1.9 |
Gross unrealized losses | (2.1) | (4.1) |
Debt Securities, Available-for-sale | 209.5 | 204.7 |
U.S. government bonds | Level 2 |  |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Amortized cost | 296.3 | 268.6 |
Gross unrealized gains | 4.1 | 11.5 |
Gross unrealized losses | 0.0 | (0.3) |
Debt Securities, Available-for-sale | 300.4 | $ 279.8 |
Debt securities |  |  |
Available-for-sale Securities, Fair Value to Amortized Cost Basis |  |  |
Debt Securities, Available-for-sale | $ 711.3 |  |

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