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Asbestos - Summary of Net Unfunded AFFA Liability, Net of Tax 2 (Details) - 12 months ended Mar. 31, 2021 $ in Millions, $ in Millions | USD ($) | AUD ($)
--- | --- | ---
Asbestos Liability |  |
Asbestos Claims [Line Items] |  |
Asbestos claims paid | $ 105.3 | $ 146.5

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- Definition Asbestos Claims [Line Items] + References No definition available. + Details
Name: | jhx_AsbestosClaimsLineItems
Namespace Prefix: | jhx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Asbestos liability net claims paid. + References No definition available. + Details
Name: | jhx_AsbestosNetClaimPaidAdjustment
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=jhx_AsbestosLiabilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |