Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Stock-Based Compensation - Assumptions Used for Restricted Stock Grants (Detail)

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