2.2.0.25falsefalse41201 - Disclosure - Derivatives and Other Financial Instruments (Narrative) (Details)truefalseIn Millions, unless otherwise specifiedfalse1falsefalseUSDfalsefalse1/1/2011 - 3/31/2011 USD ($) USD ($) / shares $Duration_1_1_2011_To_3_31_2011http://www.sec.gov/CIK0001452575duration2011-01-01T00:00:002011-03-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit14Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0Unit13Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$2falsefalseUSDfalsefalse1/1/2010 - 3/31/2010 USD ($) USD ($) / shares $Duration_1_1_2010_To_3_31_2010http://www.sec.gov/CIK0001452575duration2010-01-01T00:00:002010-03-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit14Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0Unit13Standardhttp://www.xbrl.org/2003/instancepurexbrli0USDUSD$3falsefalseUSDfalsefalse1/1/2010 - 12/31/2010 USD ($) $Duration_1_1_2010_To_12_31_2010http://www.sec.gov/CIK0001452575duration2010-01-01T00:00:002010-12-31T00:00:00Unit12Standardhttp://www.xbrl.org/2003/iso4217USDiso42170Unit1Standardhttp://www.xbrl.org/2003/instancesharesxbrli0Unit14Dividehttp://www.xbrl.org/2003/iso4217USDiso4217http://www.xbrl.org/2003/instancesharesxbrli0USDUSD$2true0us-gaap_SummaryOfDerivativeInstrumentsAbstractus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringNo definition available.falsefalseDerivatives and Other Financial Instruments3false0mjn_TransfersBetweenLevelsInFairValueHierarchymjnfalsedebitdurationTransfers Between Levels In Fair Value Hierarchyfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse00falsetruefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse00falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryTransfers Between Levels In Fair Value HierarchyNo authoritative reference available.falsefalseTransfers between levels in the fair value4false0us-gaap_MaximumLengthOfTimeHedgedInForeignCurrencyCashFlowHedgeus-gaaptruenadurationNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1falsefalsefalse001818falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:stringItemTypestringMaximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(3) falsefalseMaximum length of forecasted transactions where foreign exchange contracts are used, in months5false0mjn_DiscontinuedCashFlowHedgesAfterForecastedDatemjnfalsenadurationDiscontinued cash flow hedges after forecasted datefalsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse00falsefalsefalsefalsefalse2truefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:integerItemTypeintegerDiscontinued cash flow hedges after forecasted dateNo authoritative reference available.falsefalseNumber of discontinued foreign currency cash flow hedges due to forecasted transaction probable of not occurring6false0us-gaap_NotionalAmountOfForeignCurrencyDerivativesus-gaaptruedebitinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsefalse137400000137.4falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse142000000142.0falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryAggregate notional amount of foreign currency exchange rate derivatives. Notional amount refers to the number of currency units specified in the foreign currency derivative contract.No authoritative reference available.falsefalseNotional value of foreign exchange derivative contracts7false0us-gaap_ForeignCurrencyDerivativeLiabilitiesAtFairValueus-gaaptruecreditinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalse1truefalsefalse47000004.7falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse23000002.3falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryFair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities on the balance sheet.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 10 falsefalseForeign exchange derivative contracts fair value in net liabilities8false0mjn_AccumulatedOtherComprehensiveIncomeLossCumulativeChangesInNetGainLossFromCashFlowHedgesBeforeTaxmjnfalsecreditinstantAccumulated pretax change in accumulated gains and losses from derivative instruments designated and qualifying as the...falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse-3400000-3.4falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryAccumulated pretax change in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's increase (decrease) in deferred hedging gains or losses.No authoritative reference available.falsefalseEffective portion of changes in fair value on foreign exchange forward contracts included in accumulated other comprehensive income (loss) pre-tax9false0mjn_CashFlowHedgeIncludedInAccumulatedOtherComprehensiveIncomeLossExpectedToBeReclassifiedIntoEarningsmjnfalsecreditdurationCash flow hedge included in accumulated other comprehensive income (loss) expected to be reclassified into earningsfalsefalsefalsefalsefalsefalsefalsefalsefalsefalselabel1truefalsefalse-3300000-3.3falsefalsefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryCash flow hedge included in accumulated other comprehensive income (loss) expected to be reclassified into earningsNo authoritative reference available.falsefalseCash flow hedge included in accumulated other comprehensive income (loss) expected to be reclassified into earnings10false0mjn_NumberOfIneffectiveFairValueHedgesmjnfalsenadurationNumber of ineffective fair value hedgesfalsefalsefalsefalsefalsefalsefalsefalsefalsefalseverboselabel1truefalsefalse00falsefalsefalsefalsefalse2truefalsefalse00falsefalsefalsefalsefalse3falsefalsefalse00falsefalsefalsefalsefalseOtherxbrli:integerItemTypeintegerNumber of ineffective fair value hedgesNo authoritative reference available.falsefalseNumber of ineffective fair value hedges11false0us-gaap_MoneyMarketFundsAtCarryingValueus-gaaptruedebitinstantNo definition available.falsefalsefalsefalsefalsefalsefalsefalsefalsefalseterselabel1truefalsefalse287800000287.8falsetruefalsefalsefalse2falsefalsefalse00falsefalsefalsefalsefalse3truefalsefalse246800000246.8falsetruefalsefalsefalseMonetaryxbrli:monetaryItemTypemonetaryInvestment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 falsefalseMoney market funds310Derivatives and Other Financial Instruments (Narrative) (Details) (USD $)MillionsUnKnownUnKnownUnKnowntruetrue