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Asbestos - Summary of Net Unfunded AFFA Liability, Net of Tax (Parenthetical) (Detail) In Millions, unless otherwise specified | 12 Months Ended
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Mar. 31, 2015 USD ($) | Mar. 31, 2015 AUD | Mar. 31, 2014 USD ($) | Mar. 31, 2013 USD ($) | Mar. 31, 2015 Other Assets and Liabilities [Member] USD ($)
Asbestos Claims [Line Items] |  |  |  |  |
Amounts offset against income tax payable | $ 22.0 jhx_AmountOfDeferredTaxAssetsAppliedToIncomeTaxPayable |  | $ 16.7 jhx_AmountOfDeferredTaxAssetsAppliedToIncomeTaxPayable |  |
Favorable effect of foreign currency exchange in respect of income taxes payable | 3.5 jhx_ForeignExchangeGainLossIncomeTaxesPayableAsbestos |  |  |  |
Provision for asbestos-related education and medical research contribution | 1.4 jhx_ProvisionForAsbestosRelatedEducationAndMedicalResearchContribution |  | 1.7 jhx_ProvisionForAsbestosRelatedEducationAndMedicalResearchContribution |  |
Net liability of AICF | (1.5)jhx_NetOtherAssetsAndLiabilitiesOfAsbestosInjuriesCompensationFund |  | (0.8)jhx_NetOtherAssetsAndLiabilitiesOfAsbestosInjuriesCompensationFund |  |
Effect of foreign currency exchange on other assets and liabilities | 144.7 jhx_AsbestosAdjustmentGainLossOnForeignExchange |  | 97.2 jhx_AsbestosAdjustmentGainLossOnForeignExchange | 0.2 jhx_AsbestosAdjustmentGainLossOnForeignExchange | 0.2 jhx_AsbestosAdjustmentGainLossOnForeignExchange / us-gaap_BalanceSheetLocationAxis = jhx_OtherAssetsAndLiabilitiesMember
Asbestos claims paid | $ 135.1 jhx_LiabilityForAsbestosClaimsNetClaimPaid | 154.3 jhx_LiabilityForAsbestosClaimsNetClaimPaid |  |  |

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- Definition Portion of deferred income tax asset that becomes available to the Company as an Australian tax deduction resulting from the Company's previous contributions to AICF. + References No definition available. + Details
Name: | jhx_AmountOfDeferredTaxAssetsAppliedToIncomeTaxPayable
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Gain (loss) on foreign exchange movements in the asbestos related assets and liabilities which are denominated in Australian dollars. + References No definition available. + Details
Name: | jhx_AsbestosAdjustmentGainLossOnForeignExchange
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | jhx_AsbestosClaimsLineItems
Namespace Prefix: | jhx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Foreign exchange gain or loss in income taxes payable due to change in closing exchange rates between the currencies at the beginning and ending balance sheet dates. + References No definition available. + Details
Name: | jhx_ForeignExchangeGainLossIncomeTaxesPayableAsbestos
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Liability for asbestos claims net claim paid. + References No definition available. + Details
Name: | jhx_LiabilityForAsbestosClaimsNetClaimPaid
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Net Other Assets And Liabilities Of Asbestos Injuries Compensation Fund + References No definition available. + Details
Name: | jhx_NetOtherAssetsAndLiabilitiesOfAsbestosInjuriesCompensationFund
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Provision to fund asbestos-related research and education initiatives for a period of 10 years, beginning in fiscal year 2007. + References No definition available. + Details
Name: | jhx_ProvisionForAsbestosRelatedEducationAndMedicalResearchContribution
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant