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Income Taxes - Reconciliation of Unrecognized Tax Benefits and Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Income Tax Disclosure [Abstract] |  |  |
Unrecognized tax benefits, Beginning balance | $ 0.5 us-gaap_UnrecognizedTaxBenefits | $ 1.5 us-gaap_UnrecognizedTaxBenefits | $ 2.6 us-gaap_UnrecognizedTaxBenefits
Unrecognized tax benefits, Additions for tax positions of the current year | 4.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Unrecognized tax benefits, Additions for tax positions of prior year | 0.2 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 2.6 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Unrecognized tax benefits, Expiration of statute of limitations |  |  | (2.8)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations
Unrecognized tax benefits, Settlements paid during the current period |  | (1.2)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities |
Unrecognized tax benefits, Other reductions for the tax positions of prior periods |  |  | (1.0)jhx_UnrecognizedTaxBenefitsOtherDecreasesResultingFromPriorPeriodTaxPositions
Unrecognized tax benefits, Ending Balance | 4.9 us-gaap_UnrecognizedTaxBenefits | 0.5 us-gaap_UnrecognizedTaxBenefits | 1.5 us-gaap_UnrecognizedTaxBenefits
Interest and Penalties, Beginning balance |  | 0.1 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued | 0.9 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued
Interest and Penalties, Additions for tax positions of the current year | 0.1 jhx_InterestAndPenaltiesAdditionsForTaxPositionsOfCurrentYear |  |
Interest and Penalties, Additions for tax positions of prior year | 0.2 jhx_InterestAndPenaltiesAdditionsDeletionsForTaxPositionsOfPriorYear |  | (0.1)jhx_InterestAndPenaltiesAdditionsDeletionsForTaxPositionsOfPriorYear
Interest and Penalties, Expiration of statute of limitations |  |  | (0.7)jhx_TaxExpensesOnInterestAndPenaltiesRelatedToLapsesInStatutesOfLimitationsAndAuditSettlements
Interest and Penalties, Settlements paid during the current period |  | 0 jhx_InterestAndPenaltiesSettlementsPaidDuringCurrentPeriod |
Interest and Penalties, Other reductions for the tax positions of prior periods |  | (0.1)jhx_InterestAndPenaltiesOtherDecreasesResultingFromPriorPeriodTaxPositions |
Interest and Penalties, Ending Balance | $ 0.3 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued |  | $ 0.1 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued

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- Definition Interest and penalties additions deletions for tax positions of prior year. + References No definition available. + Details
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- Definition Interest and penalties additions for tax positions of the current year. + References No definition available. + Details
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- Definition Interest and penalties other decreases resulting from prior period tax positions. + References No definition available. + Details
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- Definition Interest and penalties settlements paid during the current period. + References No definition available. + Details
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- Definition Tax expenses on interest and penalties related to lapses in statutes of limitations and audit settlements. + References No definition available. + Details
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- Definition Unrecognized tax benefits other decreases resulting from prior period tax positions. + References No definition available. + Details
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- Details
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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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