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Asbestos - Schedule of Net Unfunded AFFA Liability, Net of Tax (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Jun. 30, 2026 | Mar. 31, 2026
Net Unfunded AFFA Liability, net of tax |  |
Asbestos Net Liability [Roll Forward] |  |
Net Unfunded AFFA liability, net of tax, Beginning Balance | $ (392.7) |
AICF operating costs paid - non claims-handling | (0.6) |
Movement in income tax payable | (41.6) |
Other movements | 2.4 |
Effect of foreign exchange | (0.2) |
Net Unfunded AFFA liability, net of tax, Ending Balance | (432.7) |
Deferred Tax Assets |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, deferred tax assets, beginning balance | 276.3 | $ 282.5
Movement in income tax payable | (6.8) |
Other movements | (0.7) |
Effect of foreign exchange | 1.3 |
Asbestos, deferred tax assets, beginning balance | 276.3 |
Income Tax Payable |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, income tax payable, beginning balance | 40.2 |
Movement in income tax payable | (34.8) |
Other movements | (0.1) |
Effect of foreign exchange | 1.2 |
Asbestos, income tax payable, ending balance | 6.5 |
Net Unfunded AFFA Liability |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, net liability, beginning balance | (715.4) |
AICF operating costs paid - non claims-handling | (0.6) |
Other movements | 3.2 |
Effect of foreign exchange | (2.7) |
Asbestos net liability, ending balance | (715.5) |
Asbestos Liability |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, net liability, beginning balance | (1,008.6) |
Asbestos claims paid | 32.8 |
AICF claims-handling costs incurred (paid) | 0.3 |
Effect of foreign exchange | (4.7) |
Asbestos net liability, ending balance | (980.2) |
Insurance Receivables |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, net liability, beginning balance | 24.3 |
Insurance recoveries | (0.8) |
Effect of foreign exchange | 0.2 |
Asbestos net liability, ending balance | 23.7 |
Restricted Cash and Investments |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, net liability, beginning balance | 268.7 |
Asbestos claims paid | (32.8) |
AICF claims-handling costs incurred (paid) | (0.3) |
AICF operating costs paid - non claims-handling | (0.6) |
Insurance recoveries | 0.8 |
Other movements | 2.4 |
Effect of foreign exchange | 1.8 |
Asbestos net liability, ending balance | 240.0 |
Other Assets and Liabilities |  |
Asbestos Net Liability [Roll Forward] |  |
Asbestos, net liability, beginning balance | 0.2 |
Other movements | 0.8 |
Asbestos net liability, ending balance | $ 1.0 |

X
- Definition Portion of deferred income tax asset that becomes available to the Company as an Australian tax deduction resulting from the Company's previous contributions to AICF. + References No definition available. + Details
Name: | jhx_AmountOfDeferredTaxAssetsAppliedToIncomeTaxPayable
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Asbestos injuries compensation fund claims handling costs incurred or paid. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Asbestos Injuries Compensation Fund operating cost paid non claim handling. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Other movements in the asbestos liability, either increasing or decreasing the liability. + References No definition available. + Details
Name: | jhx_AsbestosLiabilityOtherChanges
Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Asbestos liability net claims paid. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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X
- Definition Asbestos net liability in accordance with the Amended and Restated Final Funding Agreement. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Asbestos net liability in accordance with the Amended and Restated Final Funding Agreement, net of tax. + References No definition available. + Details
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- Definition Asbestos Net Liability [Roll Forward] + References No definition available. + Details
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X
- Definition Non current portion of Australian tax benefits as of the balance sheet date that will be available to the Company in relation to the Company's contributions to the AICF. + References No definition available. + Details
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X
- Definition Foreign exchange gain or loss in the asbestos liability due to change in closing exchange rates between the currencies at the beginning and ending balance sheet dates. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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- Definition Australian tax deduction available to be taken by the Company resulting from the Company's previous contributions to AICF. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition The amount recovered from insurance related to asbestos claims. + References No definition available. + Details
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Namespace Prefix: | jhx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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