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Operating Segment Information and Concentrations of Risk - Summary of Gross Sales by Major Customers (Detail) (USA & Europe Fiber Cement [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Segment Reporting Information [Line Items] |  |  |
Gross Sales of Major Customers | $ 320.8 jhx_GrossSalesMajorCustomers | $ 313.8 jhx_GrossSalesMajorCustomers | $ 360.7 jhx_GrossSalesMajorCustomers
Customer A [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Gross Sales of Major Customers | 177.4 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 174.2 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 223.0 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
Gross sales percentage | 10.70%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 11.70%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 16.90%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
Customer B [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Gross Sales of Major Customers | $ 143.4 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | $ 139.6 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | $ 137.7 jhx_GrossSalesMajorCustomers / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
Gross sales percentage | 8.70%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 9.30%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember | 10.40%jhx_MajorCustomerPercentageOfGrossSales / us-gaap_MajorCustomersAxis = jhx_CustomerBMember / us-gaap_StatementBusinessSegmentsAxis = jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember

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- Definition Gross sales of the Company's major customers that individually account for over 10% of the Company's net sales in one or all of the past three fiscal years. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Major customer percentage of the Company's total gross sales. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_MajorCustomersAxis=jhx_CustomerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |