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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: