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

Operating Segment Information and Concentrations of Risk - Summary of Gross Sales by Major Customers (Detail)

v3.20.1
Operating Segment Information and Concentrations of Risk - Summary of Gross Sales by Major Customers (Detail)
$ in Millions
12 Months Ended
Mar. 31, 2020
USD ($)
Customer
Mar. 31, 2019
USD ($)
Mar. 31, 2018
USD ($)
Segment Reporting Information [Line Items]      
JHX_Number of Customer | Customer 1    
jhx_Percentage Of Gross Sales Per Customer Maximum 10.00%    
Sales Revenue, Net | Geographic Concentration Risk      
Segment Reporting Information [Line Items]      
Gross sales percentage (as percent) 34.00% 36.00% 22.00%
Customer A | Accounts Receivable | Customer Concentration Risk      
Segment Reporting Information [Line Items]      
Gross sales percentage (as percent) 6.00% 8.50%  
Customer A | North America Fiber Cement | Sales Revenue, Net | Customer Concentration Risk      
Segment Reporting Information [Line Items]      
Net sales | $ $ 306.0 $ 260.5 $ 246.9
Gross sales percentage (as percent) 12.00% 10.40% 12.00%