Significant Accounting Policies (Policies)	12 Months Ended
May 31, 2012
Significant Accounting Policies Disclosure [Abstract]
Basis of Consolidation	Statement Presentation and Basis of Consolidation The accompanying Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Throughout the Notes to Consolidated Financial Statements, amounts in tables are in millions of dollars except for per share data and as otherwise designated. References in this report to a particular fiscal year are to the twelve months ended May 31 of that year. The accompanying Consolidated Financial Statements include the accounts of Mosaic and its majority owned subsidiaries, as well as the accounts of certain variable interest entities (“VIEs”) for which we are the primary beneficiary as described in Note 13. Certain investments in companies where we do not have control but have the ability to exercise significant influence are accounted for by the equity method.
Accounting Estimates	Accounting Estimates Preparation of the Consolidated Financial Statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting periods. The more significant estimates made by management relate to the recoverability of non-current assets including goodwill, the useful lives and net realizable values of long-lived assets, environmental and reclamation liabilities including asset retirement obligations (“AROs”), the costs of our employee benefit obligations for pension plans and postretirement benefits, income tax related accounts including the valuation allowance against deferred income tax assets, Canadian resource tax and royalties, inventory valuation and accruals for pending legal and environmental matters. Actual results could differ from these estimates.
Revenue Recognition	Revenue Recognition Revenue on North American sales is recognized when the product is delivered to the customer and/or when the risks and rewards of ownership are otherwise transferred to the customer and when the price is fixed or determinable. Revenue on North American export sales is recognized upon the transfer of title to the customer and when the other revenue recognition criteria have been met, which generally occurs when product enters international waters. Revenue from sales originating outside of North America is recognized upon transfer of title to the customer based on contractual terms of each arrangement and when the other revenue recognition criteria have been met. Shipping and handling costs are included as a component of cost of goods sold.
Income Taxes	Income Taxes In preparing our Consolidated Financial Statements, we utilize the asset and liability approach in accounting for income taxes. We recognize income taxes in each of the jurisdictions in which we have a presence. For each jurisdiction, we estimate the actual amount of income taxes currently payable or receivable, as well as deferred income tax assets and liabilities attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred income tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which these temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is provided for those deferred tax assets for which it is more likely than not that the related tax benefits will not be realized. We evaluate our ability to realize the tax benefits associated with deferred tax assets by analyzing the relative impact of all the available positive and negative evidence regarding our forecasted taxable income using both historical and projected future operating results, the reversal of existing taxable temporary differences, taxable income in prior carry-back years (if permitted) and the availability of tax planning strategies. A valuation allowance will be recorded in each jurisdiction in which a deferred income tax asset is recorded when it is more likely than not that the deferred income tax asset will not be realized. Changes in deferred tax asset valuation allowances, including those established in our Combination, impact income tax expense. We recognize excess tax benefits or shortfalls associated with share-based compensation in equity only when realized. When assessing whether excess tax benefits or shortfalls relating to share-based compensation have been realized, we follow the with-and-without approach excluding any indirect effects of the excess tax effects. Under this approach, excess tax benefits or shortfalls related to share-based compensation are generally not deemed to be realized until after the utilization of all other applicable tax benefits or shortfalls available to us. Accounting for uncertain income tax positions is determined by prescribing a minimum probability threshold that a tax position must meet before a financial statement benefit is recognized. This minimum threshold is that a tax position is more likely than not to be sustained upon examination by the applicable taxing authority, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefit to be recognized is measured as the largest amount of benefit that is greater than a fifty percent likelihood of being realized upon ultimate settlement. We recognize interest and penalties within our provision for income taxes on our Consolidated Statements of Earnings. We have not recorded U.S. deferred income taxes on certain of our non-U.S. subsidiaries' undistributed earnings as such amounts are intended to be reinvested outside of the United States indefinitely. However, should we change our business and tax strategies in the future and decide to repatriate a portion of these earnings to one of our U.S. subsidiaries, including cash maintained by these non-U.S. subsidiaries, additional tax liabilities would be incurred. It is not practical to estimate the amount of additional U.S. tax liabilities we would incur.
Canadian Resource Taxes and Royalties	Canadian Resource Taxes and Royalties We pay Canadian resource taxes consisting of the Potash Production Tax and resource surcharge. The Potash Production Tax is a Saskatchewan provincial tax on potash production and consists of a base payment and a profits tax. The profits tax is calculated on the potash content of each tonne sold from each Saskatchewan mine, net of certain operating expenses and a depreciation allowance. We also pay a percentage of the value of resource sales from our Saskatchewan mines. In addition to the Canadian resource taxes, royalties are payable to the mineral owners with respect to potash reserves or production of potash. These resource taxes and royalties are recorded in our cost of goods sold. Our Canadian resource tax and royalty expenses were $327.1 million, $294.2 million and $127.9 million for fiscal 2012, 2011 and 2010, respectively.
Foreign Currency Translation	Foreign Currency Translation The Company's reporting currency is the U.S. dollar; however, for operations located in Canada and Brazil, the functional currency is the local currency. Assets and liabilities of these foreign operations are translated to U.S. dollars at exchange rates in effect at the balance sheet date, while income statement accounts and cash flows are translated to U.S. dollars at the average exchange rates for the period. For these operations, translation gains and losses are recorded as a component of accumulated other comprehensive income in equity until the foreign entity is sold or liquidated. Transaction gains and losses result from transactions that are denominated in a currency other than the functional currency of the operation, primarily accounts receivable in our Canadian entities denominated in U.S. dollars, and accounts payable in Brazil denominated in U.S. dollars. These foreign currency transaction gains and losses are presented separately in the Consolidated Statement of Earnings.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include short-term, highly liquid investments with original maturities of 90 days or less, and other highly liquid investments that are payable on demand such as money market accounts, certain certificates of deposit and repurchase agreements. The carrying amount of such cash equivalents approximates their fair value due to the short-term and highly liquid nature of these instruments.
Concentration of Credit Risk	Concentration of Credit Risk In the U.S., we sell our products to manufacturers, distributors and retailers primarily in the Midwest and Southeast. Internationally, our phosphate and potash products are sold primarily through two North American export associations. A concentration of credit risk arises from our sales and accounts receivable associated with the international sales of potash product through Canpotex. We consider our concentration risk related to the Canpotex receivable to be mitigated by their credit policy which requires the underlying receivables to be substantially insured or secured by letters of credit. As of May 31, 2012 and 2011, $200.7 million and $186.4 million, respectively, of accounts receivable were due from Canpotex. In fiscal 2012, 2011 and 2010, sales to Canpotex were $1.3 billion, $992.9 million and $602.1 million, respectively.
Receivables and Allowance for Doubtful Accounts	Receivables and Allowance for Doubtful Accounts Accounts receivable are recorded at face amount less an allowance for doubtful accounts. On a regular basis, we evaluate outstanding accounts receivable and establish the allowance for doubtful accounts based on a combination of specific customer circumstances as well as credit conditions and a history of write-offs and subsequent collections. Included in other assets are long-term accounts receivable of $16.9 million and $27.8 million as of May 31, 2012 and 2011, respectively. In accordance with our allowance for doubtful accounts policy, we have recorded allowances against these long-term accounts receivable of $13.5 million and $20.4 million, respectively.
Inventories	Inventories Inventories of raw materials, work-in-process products, finished goods and operating materials and supplies are stated at the lower of cost or market. Costs for substantially all finished goods and work-in-process inventories include materials, production labor and overhead and are determined using the weighted average cost basis. Cost for substantially all raw materials is determined using the first-in first-out cost basis. Market value of our inventory is defined as forecasted selling prices less reasonably predictable selling costs (net realizable value). Significant management judgment is involved in estimating forecasted selling prices including various demand and supply variables. Examples of demand variables include grain and oilseed prices, stock-to-use ratios and changes in inventories in the crop nutrients distribution channels. Examples of supply variables include forecasted prices of raw materials, such as phosphate rock, sulfur, ammonia, and natural gas, estimated operating rates and industry crop nutrient inventory levels. Results could differ materially if actual selling prices differ materially from forecasted selling prices. Charges for lower of cost or market are recognized in our Consolidated Statements of Earnings in the period when there is evidence of a decline of market value below cost. To determine the cost of inventory, we allocate fixed expense to the costs of production based on the normal capacity, which refers to a range of production levels and is considered the production expected to be achieved over a number of periods or seasons under normal circumstances, taking into account the loss of capacity resulting from planned maintenance. Fixed overhead costs allocated to each unit of production should not increase due to abnormally low production. Those excess costs are recognized as a current period expense. When a production facility is completely shut down temporarily, it is considered “idle”, and all related expenses are charged to cost of goods sold.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are stated at cost. Costs of significant assets include capitalized interest incurred during the construction and development period. Repairs and maintenance, including planned major maintenance and plan turnaround costs, are expensed when incurred. Depletion expenses for mining operations, including mineral reserves, are generally determined using the units-of-production method based on estimates of recoverable reserves. Depreciation is computed principally using the straight-line method over the following useful lives: machinery and equipment three to 25 years, and buildings and leasehold improvements three to 40 years. We estimate initial useful lives based on experience and current technology. These estimates may be extended through sustaining capital programs. Factors affecting the fair value of our assets may also affect the estimated useful lives of our assets and these factors can change. Therefore, we periodically review the estimated remaining lives of our facilities and other significant assets and adjust our depreciation rates prospectively where appropriate.
Leases	Leases Leases in which the risk of ownership is retained by the lessor are classified as operating leases. Leases which substantially transfer all of the benefits and risks inherent in ownership to the lessee are classified as capital leases. Assets acquired under capital leases are depreciated on the same basis as property, plant and equipment. Rental payments are expensed on a straight-line basis. Leasehold improvements are depreciated over the depreciable lives of the corresponding fixed assets or the related lease term, whichever is shorter.
Investments	Investments Except as discussed in Note 13 of our Notes to Consolidated Financial Statements, with respect to variable interest entities, investments in the common stock of affiliated companies in which our ownership interest is 50% or less and in which we exercise significant influence over operating and financial policies are accounted for using the equity method which includes eliminating the effects of any material intercompany transactions.
Recoverability of Long-Lived Assets	Recoverability of Long-Lived Assets Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount may not be recoverable. The carrying amount of a long-lived asset group is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset group. If it is determined that an impairment loss has occurred, the loss is measured as the amount by which the carrying amount of the long-lived asset group exceeds its fair value.
Goodwill	Goodwill Goodwill is carried at cost, not amortized, and represents the excess of the purchase price and related costs over the fair value assigned to the net identifiable assets of a business acquired. We test goodwill for impairment at the reporting unit level on an annual basis or upon the occurrence of events that may indicate possible impairment. The goodwill impairment test is performed in two phases. The first step compares the fair value of the reporting unit with its carrying amount, including goodwill. If the fair value of the reporting unit exceeds its carrying amount, goodwill of the reporting unit is considered not impaired. However, if the carrying amount of the reporting unit exceeds its fair value, the implied fair value of the reporting unit's goodwill would be compared with the carrying amount of that goodwill. An impairment loss would be recorded to the extent that the carrying amount of goodwill exceeds its implied fair value. We have established the second quarter of our fiscal year as the period for our annual test for impairment of goodwill and the test resulted in no impairment in the periods presented.
Environmental Costs	Environmental Costs Accruals for estimated costs are recorded when environmental remediation efforts are probable and the costs can be reasonably estimated. In determining these accruals, we use the most current information available, including similar past experiences, available technology, consultant evaluations, regulations in effect, the timing of remediation and cost-sharing arrangements.
Asset Retirement Obligations	Asset Retirement Obligations We recognize AROs in the period in which we have an existing legal obligation associated with the retirement of a tangible long-lived asset, and the amount of the liability can be reasonably estimated. The ARO is recognized at fair value when the liability is incurred. Upon initial recognition of a liability, that cost is capitalized as part of the related long-lived asset and depreciated on a straight-line basis over the remaining estimated useful life of the related asset. The liability is adjusted in subsequent periods through accretion expense which represents the increase in the present value of the liability due to the passage of time. Such depreciation and accretion expenses are included in cost of goods sold for operating facilities and other operating expense for indefinitely closed facilities.
Litigation	Litigation We are involved from time to time in claims and legal actions incidental to our operations, both as plaintiff and defendant. We have established what we currently believe to be adequate accruals for pending legal matters. These accruals are established as part of an ongoing worldwide assessment of claims and legal actions that takes into consideration such items as advice of legal counsel, individual developments in court proceedings, changes in the law, changes in business focus, changes in the litigation environment, changes in opponent strategy and tactics, new developments as a result of ongoing discovery, and past experience in defending and settling similar claims. The litigation accruals at any time reflect updated assessments of the then-existing claims and legal actions. The final outcome or potential settlement of litigation matters could differ materially from the accruals which we have established. For significant individual cases, we accrue legal costs expected to be incurred.
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits Mosaic offers a number of benefit plans that provide pension and other benefits to qualified employees. These plans include defined benefit pension plans, supplemental pension plans, defined contribution plans and other postretirement benefit plans. We accrue the funded status of our plans, which is representative of our obligations under employee benefit plans and the related costs, net of plan assets measured at fair value. The cost of pensions and other retirement benefits earned by employees is generally determined with the assistance of an actuary using the projected benefit method prorated on service and management's best estimate of expected plan investment performance, salary escalation, retirement ages of employees and expected healthcare costs.
Share-Based Compensation	Share-Based Compensation We measure the cost of employees' services received in exchange for an award of equity instruments based on grant-date fair value of the award, and recognize the cost over the period during which the employee is required to provide service in exchange for the award. Our granted awards consist of stock options that generally vest annually in equal amounts over a three-year period and have an exercise price equal to the fair market value of our common stock on the date of grant, restricted stock units that generally cliff vest after three years and have a fair value equal to the market price of our stock at the date of grant and performance units that vest after a three-year period and are recorded at their fair value at the grant date. We recognize compensation expense for awards on a straight-line basis over the requisite service period.
Derivative and Hedging Activities	Derivative Activities We periodically enter into derivatives to mitigate our exposure to foreign currency risks and the effects of changing commodity and freight prices. We record all derivatives on the Consolidated Balance Sheets at fair value. The fair value of these instruments is determined by using quoted market prices, third party comparables, or internal estimates. We net our derivative asset and liability positions when we have a master netting arrangement in place. Changes in the fair value of the foreign currency, commodity, and freight derivatives are immediately recognized in earnings because we do not apply hedge accounting treatment to these instruments.
Fair Value	We determine the fair market values of our derivative contracts and certain other assets based on the fair value hierarchy described below, which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. There are three levels within its hierarchy that may be used to measure fair value. Level 1: Values based on unadjusted quoted prices in active markets that are accessible at the measurement date for identical assets or liabilities. Level 2: Values based on quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model-based valuation techniques for which all significant assumptions are observable in the market. Level 3: Values generated from model-based techniques that use significant assumptions not observable in the market. These unobservable assumptions reflect our own estimates of assumptions that market participants would use in pricing the asset or liability. Valuation techniques include use of option pricing models, discounted cash flow models and similar techniques.

Disclosure of accounting policy for Canadian resource taxes and royalties, which may include its accounting policies for recognizing and measuring the Potash Production Tax, including calculation of the profits tax, and recording of the resource taxes and royalties.

No definition available.