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PENSION AND OTHER POST-EMPLOYMENT BENEFIT PLANS (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Change in fair value of plan assets:      
Beginning fair value of plan assets $ 276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets    
Employer contributions 5.2us-gaap_DefinedBenefitPlanContributionsByEmployer 19.4us-gaap_DefinedBenefitPlanContributionsByEmployer 28.3us-gaap_DefinedBenefitPlanContributionsByEmployer
Fair value of plan assets at end of year 231.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets 276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets  
Amounts in the consolidated balance sheets include:      
Pension and Other Post-employment Liabilities (211.1)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent (161.8)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent  
Accumulated benefit obligation in excess of plan assets      
Projected benefit obligation 409.0us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation 366.3us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation  
Accumulated benefit obligation 405.0us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation 356.1us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation  
Fair value of plan assets 197.1us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets 210.8us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets  
Pension curtailment gain (5.4)us-gaap_DefinedBenefitPlanCurtailments 0us-gaap_DefinedBenefitPlanCurtailments 0us-gaap_DefinedBenefitPlanCurtailments
Weighted-average assumptions used to determine net periodic benefit cost      
Expected long term return on plan assets in next fiscal year (as a percent) 6.60%mjn_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssetsInNextFiscalYear    
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]      
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year 6.70%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear 6.90%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear 7.80%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate 4.50%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate 4.90%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate 4.90%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate 2024 2023 2023
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]      
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components 0.1us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents    
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components   0us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1  
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation 0.6us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation    
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation   (0.5)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1  
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 231.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets 276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets  
Period of notice for quarterly redemption of diversified hedge 60mjn_Periodofnoticeforquarterlyredemptionofdiversifiedhedge    
DefinedContributionBenefits [Abstract]      
Employer contributions 5.2us-gaap_DefinedBenefitPlanContributionsByEmployer 19.4us-gaap_DefinedBenefitPlanContributionsByEmployer 28.3us-gaap_DefinedBenefitPlanContributionsByEmployer
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]      
Defined Contribution Plan, Cost Recognized 22.5us-gaap_DefinedContributionPlanCostRecognized 19.9us-gaap_DefinedContributionPlanCostRecognized 21.3us-gaap_DefinedContributionPlanCostRecognized
Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 15.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
21.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 15.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
21.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 215.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
254.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 215.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
254.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Cash and Cash Equivalents [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 8.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
13.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 8.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
13.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 8.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
13.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 8.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
13.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CashAndCashEquivalentsMember
 
US large cap equity securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 37.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
16.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 37.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
16.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
US large cap equity securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
US large cap equity securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 37.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
16.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 37.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
16.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UslargecapequitysecuritiesMember
 
US mid cap growth equity securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
3.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
3.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
US mid cap growth equity securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
US mid cap growth equity securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
3.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
3.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UsmidcapgrowthequitysecuritiesMember
 
US small cap growth equity securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 4.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 4.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
US small cap growth equity securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
US small cap growth equity securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 4.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 4.9us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
0.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_UssmallcapgrowthequitysecuritiesMember
 
Emerging market equity securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 12.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
2.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 12.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
2.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
Emerging market equity securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
Emerging market equity securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 12.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
2.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 12.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
2.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketequitysecuritiesMember
 
Real estate investment trusts [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 6.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
5.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 6.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
5.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
Real estate investment trusts [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
Real estate investment trusts [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 6.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
5.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 6.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
5.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_RealestateinvestmenttrustsMember
 
International large cap value equity securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 45.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
37.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 45.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
37.0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
International large cap value equity securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 7.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
8.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 7.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
8.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
International large cap value equity securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 37.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
28.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 37.6us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
28.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_InternationallargecapvalueequitysecuritiesMember
 
Hedge Funds [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 15.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
17.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 15.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
17.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 15.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
17.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 15.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
17.4us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_HedgeFundsMember
 
Municipal Bonds [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 40.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
72.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 40.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
72.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 40.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
72.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 40.2us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
72.8us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_MunicipalBondsMember
 
Corporate Bond Securities [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 55.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
101.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 55.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
101.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
Corporate Bond Securities [Member] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
Corporate Bond Securities [Member] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 55.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
101.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 55.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
101.7us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= us-gaap_CorporateBondSecuritiesMember
 
Emerging markets Fixed Income [Domain]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 5.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
6.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 5.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
6.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
 
Emerging markets Fixed Income [Domain] | Fair Value, Inputs, Level 1 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
   
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
   
Emerging markets Fixed Income [Domain] | Fair Value, Inputs, Level 2 [Member]      
Change in fair value of plan assets:      
Fair value of plan assets at end of year 5.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
6.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
 
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 5.5us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
6.3us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ mjn_UsGaapDefinedBenefitPlanAssetCategoriesAxis
= mjn_EmergingmarketsFixedIncomeDomain
 
Pension Benefits      
Changes in net periodic benefit cost      
Percentage in total pension assets and obligations 84.00%mjn_DefinedBenefitPlanPercentageInPensionAssetsAndObligations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Changes in benefit obligations      
Beginning benefit obligations 404.0us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
463.6us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Service cost - benefits earned during the period 4.8us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
5.2us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.9us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Interest cost on projected benefit obligations 15.8us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
14.4us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
15.6us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Actuarial assumptions (gains) losses 44.9us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(25.7)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Settlements and curtailments (74.2)us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(50.4)us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Benefits paid (2.8)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(2.8)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Exchange rate changes (3.6)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(0.3)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Benefit obligations at end of year 388.9us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
404.0us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
463.6us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Change in fair value of plan assets:      
Beginning fair value of plan assets 276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
312.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Actual return on plan assets 20.7us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(1.4)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Employer contributions 4.8us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
18.5us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Settlements (65.1)us-gaap_DefinedBenefitPlanSettlementsPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(50.4)us-gaap_DefinedBenefitPlanSettlementsPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Benefits paid (2.8)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(2.8)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Exchange rate changes (2.6)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0.1us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Fair value of plan assets at end of year 231.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
312.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Underfunded status at end of year (157.8)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(127.9)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Amounts in the consolidated balance sheets include:      
Other assets 1.7us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Pension and Other Post-employment Liabilities (159.5)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(129.2)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Defined Benefit Plan, Amounts Recognized in Balance Sheet (157.8)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(127.9)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Amounts in accumulated other comprehensive loss include:      
Prior service (benefit) 0.9us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
1.2us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Transition obligation 0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetTransitionAssetsObligationsBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0.1us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetTransitionAssetsObligationsBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax 0.9us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Accumulated benefit obligation 353.4us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
375.7us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Accumulated benefit obligation in excess of plan assets      
Service cost - benefits earned during the period 4.8us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
5.2us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.9us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Interest cost on projected benefit obligations 15.8us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
14.4us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
15.6us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Expected return on plan assets (15.7)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(17.1)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(16.6)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Amortization of prior service (benefit) 0us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Amortization of transition cost 0.1us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0.1us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0.1us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Net periodic benefit cost 5.0mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
2.6mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.0mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Pension curtailment gain (5.4)us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(1.4)us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Settlements and curtailments 39.7us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(8.2)us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
56.3us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Total net periodic benefit cost 39.3us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
(5.6)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
57.9us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Weighted-average assumptions used to determine benefit obligations      
Discount rate (as a percent) 3.98%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
4.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Rate of compensation increase (as a percent) 3.24%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.22%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Weighted-average assumptions used to determine net periodic benefit cost      
Discount rate (as a percent) 4.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.26%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
4.03%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Expected long term return on plan assets (as a percent) 6.16%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
5.22%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
5.65%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Rate of compensation increase (as a percent) 3.22%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
3.59%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
4.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 231.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
276.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
312.1us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
DefinedContributionBenefits [Abstract]      
Required contributions estimated for 2015 U.S. Pension Plan 3mjn_Requiredcontributionsestimatedfor2015U.S.PensionPlan
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year 15us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Employer contributions 4.8us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
18.5us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]      
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months 29.5us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Two 28.6us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Three 29.6us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Four 30.2us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Five 29.3us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter 144.2us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Other Benefits      
Changes in net periodic benefit cost      
Percentage in total pension assets and obligations 73.00%mjn_DefinedBenefitPlanPercentageInPensionAssetsAndObligations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Changes in benefit obligations      
Beginning benefit obligations 32.6us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
35.1us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Service cost - benefits earned during the period 0.9us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.1us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Interest cost on projected benefit obligations 1.5us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Actuarial assumptions (gains) losses 17.2us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(3.8)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Settlements and curtailments 0us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Benefits paid (0.4)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1.3)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Exchange rate changes (0.2)us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.2us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Benefit obligations at end of year 51.6us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
32.6us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
35.1us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Change in fair value of plan assets:      
Beginning fair value of plan assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Actual return on plan assets 0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Employer contributions 0.4us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.9us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Settlements 0us-gaap_DefinedBenefitPlanSettlementsPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanSettlementsPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Benefits paid (0.4)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1.3)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Exchange rate changes 0us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.4us-gaap_DefinedBenefitPlanForeignCurrencyExchangeRateChangesPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Fair value of plan assets at end of year 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Underfunded status at end of year (51.6)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(32.6)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Amounts in the consolidated balance sheets include:      
Other assets 0us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Pension and Other Post-employment Liabilities (51.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(32.6)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Defined Benefit Plan, Amounts Recognized in Balance Sheet (51.6)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(32.6)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Amounts in accumulated other comprehensive loss include:      
Prior service (benefit) (0.2)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(0.3)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Transition obligation 0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetTransitionAssetsObligationsBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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0us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetTransitionAssetsObligationsBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax (0.2)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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(0.3)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Accumulated benefit obligation 51.6us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
32.6us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Accumulated benefit obligation in excess of plan assets      
Service cost - benefits earned during the period 0.9us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.1us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Interest cost on projected benefit obligations 1.5us-gaap_DefinedBenefitPlanInterestCost
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1.3us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Expected return on plan assets 0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Amortization of prior service (benefit) 0.2us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(0.2)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(0.2)us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Amortization of transition cost 0us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
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= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanAmortizationOfTransitionObligationsAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Net periodic benefit cost 2.6mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
2.2mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
2.1mjn_DefinedBenefitPlanNetPeriodicBenefitCostExcludingSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Pension curtailment gain 0us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Settlements and curtailments 17.2us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(3.8)us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
2.6us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Total net periodic benefit cost 19.8us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1.6)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.7us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Weighted-average assumptions used to determine benefit obligations      
Discount rate (as a percent) 4.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.98%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Rate of compensation increase (as a percent) 3.06%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Weighted-average assumptions used to determine net periodic benefit cost      
Discount rate (as a percent) 4.98%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.75%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.29%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Expected long term return on plan assets (as a percent) 0.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Rate of compensation increase (as a percent) 3.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.48%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.94%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
DefinedBenefitPlanFairValueofPlanAssets [Abstract]      
Defined Benefit Plan, Fair Value of Plan Assets 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
DefinedContributionBenefits [Abstract]      
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year 0us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Employer contributions 0.4us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0.9us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]      
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months 1.4us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Two 2.0us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Three 2.5us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Four 2.9us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Year Five 3.3us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter $ 17.9us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
U.S. Pension Plan | Equity Securities [Member]      
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Defined Benefit Plan, Target Allocation Percentage .6    
U.S. Pension Plan | Fixed Income [Member]      
Defined Benefit Plan, Assets, Target Allocations [Abstract]      
Defined Benefit Plan, Target Allocation Percentage .4