Marketable Securities Held in Trusts (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	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	$ 681.1	$ 678.3
Gross Unrealized Gains	15.3	0.5
Gross Unrealized Losses	(12.8)	(28.7)
Total debt securities	683.6	650.1
Cash And Cash Equivalents \| Fair Value Inputs Level 1
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	1.0	7.7
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Total debt securities	1.0	7.7
Corporate Debt Securities \| Fair Value Inputs Level 2
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	204.6	203.8
Gross Unrealized Gains	1.9	0.1
Gross Unrealized Losses	(8.4)	(17.1)
Total debt securities	198.1	186.8
Municipal Bonds \| Fair Value Inputs Level 2
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	206.9	197.0
Gross Unrealized Gains	1.9	0.4
Gross Unrealized Losses	(4.1)	(8.0)
Total debt securities	204.7	189.4
U.S. Government Bonds \| Fair Value Inputs Level 2
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	268.6	269.6
Gross Unrealized Gains	11.5	0.0
Gross Unrealized Losses	(0.3)	(3.6)
Total debt securities	$ 279.8	266.0
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

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- Definition

The amount of cash, securities, or other assets held by a third-party trustee pursuant to the terms of an agreement which assets are available to be used by beneficiaries to that agreement only within the specific terms thereof and which agreement is expected to terminate more than one year from the balance sheet date (or operating cycle, if longer) at which time the assets held-in-trust will be released or forfeited.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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