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

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail)

v2.4.1.9
Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 12, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation expense $ 12.5us-gaap_AllocatedShareBasedCompensationExpense $ 13.0us-gaap_AllocatedShareBasedCompensationExpense $ 10.8us-gaap_AllocatedShareBasedCompensationExpense
Liability Awards Expense [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation expense 3.3us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_LiabilityAwardsMember 		4.5us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_LiabilityAwardsMember 		3.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_LiabilityAwardsMember
Equity Awards Expense [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Total stock-based compensation expense $ 9.2us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_EquityAwardsMember 		$ 8.5us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_EquityAwardsMember 		$ 7.0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= jhx_EquityAwardsMember