OTHER (INCOME)/EXPENSES-NET (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
ScheduleOfOtherIncomeAndOtherExpenseNet [Line Items]
Foreign exchange (gains)/losses-net	$ 0.5	$ 9.3	$ (3.1)
Administrative penalty (China)	0mjn_AdministrativepenaltyChina	33.4mjn_AdministrativepenaltyChina	0mjn_AdministrativepenaltyChina
Severance and other costs	1.3mjn_SeveranceAndOtherCosts	2.2mjn_SeveranceAndOtherCosts	8.0mjn_SeveranceAndOtherCosts
Gain on Sale of Investments	(4.0)us-gaap_GainOnSaleOfInvestments	0us-gaap_GainOnSaleOfInvestments	0us-gaap_GainOnSaleOfInvestments
Gain on sale of non-strategic intangible asset		0us-gaap_OtherNonoperatingIncome	(6.5)us-gaap_OtherNonoperatingIncome
Legal settlements	(1.9)us-gaap_LegalFees	7.0us-gaap_LegalFees	0us-gaap_LegalFees
Pension curtailment gain	(5.4)us-gaap_DefinedBenefitPlanCurtailments	0us-gaap_DefinedBenefitPlanCurtailments	0us-gaap_DefinedBenefitPlanCurtailments
Other net	(2.8)us-gaap_OtherNonoperatingIncomeExpense	(3.4)us-gaap_OtherNonoperatingIncomeExpense	6.4us-gaap_OtherNonoperatingIncomeExpense
Other (income)/expenses—net	(12.3)mjn_OtherExpensesIncomeNet	48.5mjn_OtherExpensesIncomeNet	4.8mjn_OtherExpensesIncomeNet
VENEZUELA
ScheduleOfOtherIncomeAndOtherExpenseNet [Line Items]
Foreign exchange (gains)/losses-net	14.0
VENEZUELA \| Change in Accounting Method Accounted for as Change in Estimate [Member]
ScheduleOfOtherIncomeAndOtherExpenseNet [Line Items]
Foreign exchange (gains)/losses-net	6.1
Total operating segments
ScheduleOfOtherIncomeAndOtherExpenseNet [Line Items]
Gain on sale of non-strategic intangible asset	$ 0

Administrative penalty (China)

No definition available.

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- Definition

Other Expenses/(Income)—net [Abstract] operating and non-operating

+ References

No definition available.

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- Definition

The charge against earnings in the period for known and estimated costs of termination benefits provided to current employees that are involuntarily terminated under a benefit arrangement associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, excluding costs or losses pertaining to an entity newly acquired in a business combination or a discontinued operation as defined by generally accepted accounting principles, costs associated with one-time termination benefits and other costs not otherwise stated.

+ References

No definition available.

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- Definition

The amount of decrease that is related to an event that significantly reduces the expected years of future service of present employees or eliminates for a significant number of employees the accrual of defined benefits for some or all of their future services.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)(10)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Plan Curtailment

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 15

-Paragraph 6

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927

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- Definition

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

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-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30700-110894

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- Definition

The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

+ References

No definition available.

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- Definition

The amount of expense provided in the period for legal costs incurred on or before the balance sheet date pertaining to resolved, pending or threatened litigation, including arbitration and mediation proceedings.

+ References

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- Definition

The aggregate amount of other income amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) profits on securities (net of losses), and (d) miscellaneous other income items.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Article 5

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- Definition

The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 9

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.9)

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