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Organization and Significant Accounting Policies - Narrative (Details)			12 Months Ended
	Jan. 01, 2026 USD ($)	Jul. 01, 2025 shares	Mar. 31, 2026 USD ($) director shares	Mar. 31, 2025 USD ($) shares	Mar. 31, 2024 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Goodwill and intangible asset impairment \| $	$ 0
Advertising costs \| $			$ 151,700,000	$ 99,400,000	$ 110,800,000
Number of trading days			20 days
Potential diluted common shares outstanding (in shares)			100,000	0	0
AZEK
Summary Of Significant Accounting Policies [Line Items]
James Hardie Common Shares issued (in shares)		148,861,787
Contingent Shares Not Expected To Vest
Summary Of Significant Accounting Policies [Line Items]
Potential diluted common shares outstanding (in shares)			1,100,000	600,000	600,000
Restricted Stock Units Service Vesting
Summary Of Significant Accounting Policies [Line Items]
Vesting period			3 years
Restricted Stock Units Performance Vesting
Summary Of Significant Accounting Policies [Line Items]
Vesting period			3 years
Restricted Stock Units (Market Condition)
Summary Of Significant Accounting Policies [Line Items]
Vesting period			3 years
Minimum
Summary Of Significant Accounting Policies [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			2 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Acquired finite-lived intangible assets, weighted average useful life			18 years
Asbestos Injuries Compensation Fund
Summary Of Significant Accounting Policies [Line Items]
Ownership interest rate percentage (as percent)			0.00%
Asbestos Injuries Compensation Fund
Summary Of Significant Accounting Policies [Line Items]
Number of directors appointed by Company \| director			3
Asbestos Injuries Compensation Fund \| New South Wales, Australia
Summary Of Significant Accounting Policies [Line Items]
Number of directors appointed by NSW government \| director			2