XML 50 R91.htm IDEA: XBRL DOCUMENT
v3.20.1

Stock-Based Compensation - Assumptions Used for Restricted Stock Grants (Detail) - Restricted Stock Units (Market Condition) [Member] - $ / shares | 12 Months Ended
--- | ---
Mar. 31, 2020 | Mar. 31, 2019
February 2020 Grant |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Dividend yield (per annum) | 2.90% |
Expected volatility | 26.60% |
Risk free interest rate | 1.20% |
Expected life in years | 2 years 6 months |
JHX stock price at grant date (A$ per share)) | $ 29.54 |
Number of restricted stock units (in shares) | 6,676 |
September 2019 Grant |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Dividend yield (per annum) | 3.10% |
Expected volatility | 26.60% |
Risk free interest rate | 1.60% |
Expected life in years | 2 years 10 months 24 days |
JHX stock price at grant date (A$ per share)) | $ 24.69 |
Number of restricted stock units (in shares) | 477,979 |
August 2019 Grant |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Dividend yield (per annum) | 3.10% |
Expected volatility | 27.80% |
Risk free interest rate | 1.60% |
Expected life in years | 2 years |
JHX stock price at grant date (A$ per share)) | $ 21.68 |
Number of restricted stock units (in shares) | 18,518 |
September 2018 Grant |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Dividend yield (per annum) |  | 3.00%
Expected volatility |  | 26.80%
Risk free interest rate |  | 2.70%
Expected life in years |  | 2 years 10 months 24 days
JHX stock price at grant date (A$ per share)) |  | $ 20.87
Number of restricted stock units (in shares) |  | 49,381
August 2018 Grant |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Dividend yield (per annum) |  | 3.00%
Expected volatility |  | 28.10%
Risk free interest rate |  | 2.70%
Expected life in years |  | 3 years
JHX stock price at grant date (A$ per share)) |  | $ 22.00
Number of restricted stock units (in shares) |  | 663,738

X
- Definition Share based compensation arrangement by share based payment award fair value assumptions grant date stock price. + References No definition available. + Details
Name: | jhx_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsGrantDateStockPrice
Namespace Prefix: | jhx_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share based compensation arrangement by share based payment award restricted stock units number. + References No definition available. + Details
Name: | jhx_ShareBasedCompensationArrangementByShareBasedPaymentAwardRestrictedStockUnitsNumber
Namespace Prefix: | jhx_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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 Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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. + References No definition available. + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.D.2) -URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809 + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PlanNameAxis=jhx_February2020GrantDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=jhx_RestrictedStockUnitsMarketConditionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=jhx_September2019GrantDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=jhx_August2019GrantDomain
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=jhx_September2018GrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=jhx_August2018GrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |