Share-Based Compensation - Assumptions Used to Fair Value Restricted Stock Grants (Details) - Restricted Stock Units (Market Condition)	12 Months Ended
Mar. 31, 2026 $ / shares shares
August 2024 Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (per annum)	0.00%
Expected volatility	37.90%
Risk free interest rate	3.90%
Expected life in years	3 years
JHX stock price at grant date (A$ per share) \| $ / shares	$ 51.99
Number of restricted stock units (in shares) \| shares	396,949
December 2025 Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (per annum)	0.00%
Expected volatility	45.90%
Risk free interest rate	3.50%
Expected life in years	2 years 8 months 12 days
JHX stock price at grant date (A$ per share) \| $ / shares	$ 29.95
Number of restricted stock units (in shares) \| shares	654,899
October 2025 Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (per annum)	0.00%
Expected volatility	44.00%
Risk free interest rate	3.60%
Expected life in years	2 years 9 months 18 days
JHX stock price at grant date (A$ per share) \| $ / shares	$ 32.83
Number of restricted stock units (in shares) \| shares	219,775
September 2025 Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield (per annum)	0.00%
Expected volatility	44.60%
Risk free interest rate	3.60%
Expected life in years	3 years
JHX stock price at grant date (A$ per share) \| $ / shares	$ 30.13
Number of restricted stock units (in shares) \| shares	427,450

Share based compensation arrangement by share based payment award fair value assumptions grant date stock price.

No definition available.

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- Definition

Share based compensation arrangement by share based payment award restricted stock units number.

+ References

No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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