Total tonnes of finished product the joint venture expects to produce during a year.

No definition available.

Name:	mos_AnnualProductionOfFinishedProduct
Namespace Prefix:	mos_
Data Type:	num:weightItemType
Balance Type:	na
Period Type:	duration

- Definition

Proportion of the total amount of assets reported by an equity method investment of the entity represented by a specific equity method investee.

+ References

No definition available.

+ Details

Name:	mos_EquityMethodInvestmentProportionOfAssetsRepresentedBySpecificEquityMethodInvestee
Namespace Prefix:	mos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Proportion of the total amount of liabilities reported by an equity method investment of the entity represented by a specific equity method investee.

+ References

No definition available.

+ Details

Name:	mos_EquityMethodInvestmentProportionOfLiabilitiesRepresentedBySpecificEquityMethodInvestee
Namespace Prefix:	mos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total investment required by the joint venture to develop a phosphates greenfield mine and chemical complexes

+ References

No definition available.

+ Details

Name:	mos_InvestmentInPhosphatesGreenfieldMine
Namespace Prefix:	mos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of lenders or financial institutions in a credit facility.

+ References

No definition available.

+ Details

Name:	mos_NumberOfLendersInaCreditFacility
Namespace Prefix:	mos_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

After project completion, number of months of shareholder tax amounts and severance fees for which the joint venture parties may have exposure.

+ References

No definition available.

+ Details

Name:	mos_NumberOfMonthsAfterProjectCompletionForAdditionalExposureToJointVentureParties
Namespace Prefix:	mos_
Data Type:	xbrli:timeItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent of joint venture production Mosaic expects to market

+ References

No definition available.

+ Details

Name:	mos_PercentageOfTotalProductionExpectedToMarket
Namespace Prefix:	mos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, aggregate carrying value as of the balance sheet date of loans payable (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16)(a)(2))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LoansPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow associated with the investment in or advances to an entity in which the reporting entity shares control of the entity with another party or group.

+ References

+ Details

Name:	us-gaap_PaymentsToAcquireInterestInJointVenture
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount purchased during the period under an unrecorded unconditional purchase obligation (for example, under the take-or-pay or throughput contract).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 440
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121559207&loc=d3e25336-109308

+ Details

Name:	us-gaap_UnrecordedUnconditionalPurchaseObligationPurchases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_EquityMethodInvesteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=mos_MaadenWaadAlShamalPhosphateCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investments in Non-Consolidated Companies - MWSPC Joint Venture (Details) t in Millions, $ in Millions		6 Months Ended	12 Months Ended
	Jul. 01, 2016 USD ($)	Jun. 30, 2014 USD ($) financialinstitution	Dec. 31, 2020 USD ($) t	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2017 USD ($)
Schedule of Equity Method Investments
Equity in net (loss) of nonconsolidated companies			$ (93.8)	$ (59.4)	$ (4.5)
Investments in nonconsolidated companies			673.1	763.6
Purchases made under long-term commitments during the reporting period			$ 1,900.0	1,900.0	2,000.0
Equity Method Investee \| MWSPC
Schedule of Equity Method Investments
Payments to Acquire Equity Method Investments	$ 120.0
Proportion of assets represented by MWSPC			83.00%
Proportion of liabilities represented by MWSPC			80.00%
Equity in net (loss) of nonconsolidated companies			$ (97.3)	$ (62.1)	(9.5)
Aggregate cost of investment in phosphates greenfield mine including Mosaic's portion to date			$ 8,000.0
Annual production of finished product (Tonnes) \| t			3.0
Percentage Of Total Production Expected To Market			25.00%
Number of lenders in MWSPC credit facility \| financialinstitution		20
MWSPC line of credit facility, maximum borrowing capacity		$ 5,000.0			$ 506.0	$ 560.0
After project completion, number of months of shareholder tax amounts and severance fees for which the joint venture parties may have exposure			36
Loans Payable						$ 1,100.0
Investments in nonconsolidated companies			$ 770.0
Equity Method Investee \| MWSPC \| Maximum
Schedule of Equity Method Investments
Total cash investment from investors to acquire interest in MWSPC		$ 2,400.0