Marketable Securities Held in Trusts (Details) $ in Millions	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	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	$ 748.6	$ 740.6
Gross unrealized gains	4.1	7.3
Gross unrealized losses	(7.4)	(4.6)
Debt Securities, Available-for-sale	745.3	743.3
Cash and Cash Equivalents \| Level 1
Available-for-sale Securities, Fair Value to Amortized Cost Basis
Amortized cost	4.5	4.8
Gross unrealized gains	0.0	0.0
Gross unrealized losses	0.0	0.0
Debt Securities, Available-for-sale	4.5	4.8
Corporate debt securities \| Level 2
Available-for-sale Securities, Fair Value to Amortized Cost Basis
Amortized cost	216.1	218.8
Gross unrealized gains	1.6	3.4
Gross unrealized losses	(3.4)	(2.8)
Debt Securities, Available-for-sale	214.3	219.4
Municipal bonds \| Level 2
Available-for-sale Securities, Fair Value to Amortized Cost Basis
Amortized cost	210.5	208.3
Gross unrealized gains	2.5	3.9
Gross unrealized losses	(1.7)	(1.3)
Debt Securities, Available-for-sale	211.3	210.9
U.S. government bonds \| Level 2
Available-for-sale Securities, Fair Value to Amortized Cost Basis
Amortized cost	317.5	308.7
Gross unrealized gains	0.0	0.0
Gross unrealized losses	(2.3)	(0.5)
Debt Securities, Available-for-sale	$ 315.2	$ 308.2

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