Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Long-Term Debt - Additional Information (Detail)

v2.4.1.9
Long-Term Debt - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Feb. 28, 2015
Nov. 30, 2014
May 31, 2014
Debt Instrument [Line Items]            
Weighted average interest rate on total outstanding debt 1.40%us-gaap_DebtWeightedAverageInterestRate           
Weighted average term of debt 2 years 4 months 24 days 2 years 4 months 24 days        
Amounts drawn under the combined credit facilities $ 75.0us-gaap_ProceedsFromLinesOfCredit           
Credit facilities 590.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity          
Repayments of long-term borrowings 642.0us-gaap_RepaymentsOfLongTermDebt   330.0us-gaap_RepaymentsOfLongTermDebt      
Debt covenant description in credit facility agreement At 31 March 2015, the Company was in compliance with all restrictive debt covenants contained in its credit facility agreements. Under the most restrictive of these covenants, the Company (i) must not exceed a maximum of net debt to earnings before interest, tax, depreciation and amortization, excluding all income, expense and other profit and loss statement impacts of AICF, The Former James Hardie Companies and Marlew Mining Pty Limited (“Marlew”) and excluding assets, liabilities and other balance sheet items of AICF, the Former James Hardie Companies and Marlew, (ii) must meet or exceed a minimum ratio of earnings before interest and taxes to net interest charges, excluding all income, expense and other profit and loss statement impacts of AICF, the Former James Hardie Companies and Marlew, and (iii) must ensure that no more than 35% of Free Cash Flow (as defined in the AFFA), in any given financial year (“Annual Cash Flow Cap”) is contributed to AICF on the payment dates under the AFFA in the next following financial year. The Annual Cash Flow Cap does not apply to payments of interest, if any, to AICF and is consistent with contractual obligations of James Hardie 117 Pty Ltd (the “Performing Subsidiary”) and the Company under the AFFA.          
Maximum percentage of Free Cash Flow contributed to AICF 35.00%jhx_MaximumPercentageOfFreeCashFlowContributedToAsbestosInjuriesCompensationFund          
Proceeds from long-term borrowings 717.0us-gaap_ProceedsFromIssuanceOfLongTermDebt   330.0us-gaap_ProceedsFromIssuanceOfLongTermDebt      
Senior Unsecured Notes Due 15 February 2023 [Member]            
Debt Instrument [Line Items]            
Repayments of long-term borrowings       317.0us-gaap_RepaymentsOfLongTermDebt
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Proceeds from long-term borrowings       325.0us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Frequency of payments Interest is payable semi-annually in arrears on 15 February and 15 August of each year          
Interest rate       5.875%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Interest commencing payment date Aug. 15, 2015          
Senior unsecured notes due Feb. 15, 2023          
Percent of offer price on par value       99.213%jhx_DebtInstrumentOfferingPricePercentage
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Original issue discount       2.6jhx_DebtDiscount
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Debt issuance costs       8.3jhx_DebtIssuanceCostsCapitalized
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
   
Discount and debt issuance costs amortization period       8 years    
Unamortized discount balance 2.5us-gaap_DebtInstrumentUnamortizedDiscount
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
         
Unamortized balance of debt issuance costs 8.1us-gaap_UnamortizedDebtIssuanceExpense
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
         
Debt instrument redemption terms Before 15 February 2018, the issuer may redeem up to 35% of the aggregate principal amount of the senior notes with the net cash proceeds of certain equity offerings at a redemption price of 105.875% of the principal amount plus accrued and unpaid interest, if any, to but excluding, the redemption date. The issuer may also redeem some or all of the senior notes before 15 February 2018 at a redemption price of 100% of the principal amount, plus accrued and unpaid interest, plus a make whole premium equal to the greater of: (i) 1.0% of the principal amount of such note; and (ii) the excess, if any, of (x) the present value of the sum of the principal amount and premium that would be payable on such note on 15 February 2018 and all remaining interest payments to and including 15 February 2018, discounted on a semi-annual basis from 15 February 2018 to the redemption date at a per annum interest rate equal to the applicable treasury rate plus 50 basis points, over (y) the outstanding principal amount of such note.          
Redemption price, percentage 101.00%us-gaap_DebtInstrumentRedemptionPricePercentage
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
         
Senior Unsecured Notes Due 15 February 2023 [Member] | Debt Instrument Redemption Period Before February 15, 2018 [Member]            
Debt Instrument [Line Items]            
Percentage of aggregate principal amount for redemption 35.00%jhx_PercentageOfPrincipalAmountOfSeniorNotesForRedemption
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= jhx_DebtInstrumentRedemptionPeriodBeforeFebruaryFifteenTwoZeroOneEightMember
         
Redemption price, percentage 100.00%us-gaap_DebtInstrumentRedemptionPricePercentage
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= jhx_DebtInstrumentRedemptionPeriodBeforeFebruaryFifteenTwoZeroOneEightMember
         
Senior Unsecured Notes Due 15 February 2023 [Member] | Redeem up to 35% of Aggregate Principal Amount [Member] | Debt Instrument Redemption Period Before February 15, 2018 [Member]            
Debt Instrument [Line Items]            
Redemption price, percentage 105.875%us-gaap_DebtInstrumentRedemptionPricePercentage
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
/ us-gaap_DebtInstrumentRedemptionPeriodAxis
= jhx_DebtInstrumentRedemptionPeriodBeforeFebruaryFifteenTwoZeroOneEightMember
/ us-gaap_LongtermDebtTypeAxis
= jhx_RedeemUpToThirtyFivePercentageOfAggregatePrincipalAmountMember
         
Senior Unsecured Notes Due 15 February 2023 [Member] | Maximum [Member]            
Debt Instrument [Line Items]            
Applicable premium as a percentage of principal amount 1.00%jhx_ApplicablePremiumAsPercentageOfPrincipalAmount
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
         
Senior Unsecured Notes Due 15 February 2023 [Member] | Treasury Rate [Member]            
Debt Instrument [Line Items]            
Debt instrument spread rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= jhx_SeniorUnsecuredNotesDueFifteenFebruaryTwoZeroTwoThreeMember
/ us-gaap_VariableRateAxis
= jhx_TreasuryRateMember
         
Bilateral Credit Facilities and Senior Unsecured Notes [Member]            
Debt Instrument [Line Items]            
Weighted average interest rate on total outstanding debt 5.04%us-gaap_DebtWeightedAverageInterestRate
/ us-gaap_LineOfCreditFacilityAxis
= jhx_BilateralCreditFacilitiesAndSeniorUnsecuredNotesMember
          
Weighted average term of debt 6 years 9 months 18 days 2 years 4 months 24 days        
Additional Term Facilities [Member]            
Debt Instrument [Line Items]            
Credit facilities           150.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_AdditionalTermFacilitiesMember
Term Facility Maturity April 2017 [Member]            
Debt Instrument [Line Items]            
Credit facilities 100.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneSevenMember
        25.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneSevenMember
Credit facilities, maturity period 2017-04          
Term Facility Maturity April 2019 [Member]            
Debt Instrument [Line Items]            
Credit facilities 50.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneNineMember
        50.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneNineMember
Credit facilities, maturity period 2019-04          
Term Facility Maturity May 2019 [Member]            
Debt Instrument [Line Items]            
Credit facilities 75.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityMayTwoZeroOneNineMember
        75.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityMayTwoZeroOneNineMember
Credit facilities, maturity period 2019-05          
Term Facility Maturity March 2019 [Member]            
Debt Instrument [Line Items]            
Credit facilities 40.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityMarchTwoZeroOneNineMember
        40.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityMarchTwoZeroOneNineMember
Credit facilities, maturity period 2019-03          
Term Facility Maturity March 2017 [Member]            
Debt Instrument [Line Items]            
Credit facilities, previous maturity period 2017-03          
Term Facility Maturity April 2016 [Member]            
Debt Instrument [Line Items]            
Credit facilities 150.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneSixMember
         
Credit facilities, maturity period 2016-04       2016-04  
Repayments of long-term borrowings         40.0us-gaap_RepaymentsOfLongTermDebt
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityAprilTwoZeroOneSixMember
 
Term Facility Maturity November 2017 [Member]            
Debt Instrument [Line Items]            
Credit facilities $ 125.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityNovemberTwoZeroOneSevenMember
      $ 125.0us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= jhx_TermFacilitiesMaturityNovemberTwoZeroOneSevenMember
 
Credit facilities, maturity period 2017-11       2017-11