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

Operating Segment Information and Concentrations of Risk - Operating Segments and Geographical Information (Detail)

v2.4.1.9
Operating Segment Information and Concentrations of Risk - Operating Segments and Geographical Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Segment Reporting Information [Line Items]      
Net sales $ 1,656.9us-gaap_SalesRevenueGoodsNet $ 1,493.8us-gaap_SalesRevenueGoodsNet $ 1,321.3us-gaap_SalesRevenueGoodsNet
Total operating income 335.0us-gaap_OperatingIncomeLoss 53.1us-gaap_OperatingIncomeLoss 29.5us-gaap_OperatingIncomeLoss
Net interest expense (7.5)us-gaap_InterestIncomeExpenseNet (1.1)us-gaap_InterestIncomeExpenseNet 2.4us-gaap_InterestIncomeExpenseNet
Other (expense) income (4.9)us-gaap_OtherNonoperatingIncomeExpense 2.6us-gaap_OtherNonoperatingIncomeExpense 1.8us-gaap_OtherNonoperatingIncomeExpense
Total Identifiable Assets 2,044.5us-gaap_Assets 2,104.0us-gaap_Assets  
General Corporate [Member]      
Segment Reporting Information [Line Items]      
Total operating income (19.0)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_GeneralCorporateMember
(240.6)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_GeneralCorporateMember
(151.8)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_GeneralCorporateMember
Total Identifiable Assets 784.7us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_GeneralCorporateMember
1,066.6us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_GeneralCorporateMember
 
USA [Member]      
Segment Reporting Information [Line Items]      
Net sales 1,238.5us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_US
1,094.6us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_US
923.8us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_US
Total Identifiable Assets 956.4us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_US
785.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_US
 
Australia [Member]      
Segment Reporting Information [Line Items]      
Net sales 267.7us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_AU
259.2us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_AU
272.0us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_AU
Total Identifiable Assets 223.4us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_AU
173.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_AU
 
New Zealand [Member]      
Segment Reporting Information [Line Items]      
Net sales 64.7us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_NZ
63.0us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_NZ
56.1us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= country_NZ
Total Identifiable Assets 25.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_NZ
29.4us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= country_NZ
 
Other Countries [Member]      
Segment Reporting Information [Line Items]      
Net sales 86.0us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_OtherCountriesMember
77.0us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_OtherCountriesMember
69.4us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_OtherCountriesMember
Total Identifiable Assets 54.2us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_OtherCountriesMember
48.4us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_OtherCountriesMember
 
Segments Total [Member]      
Segment Reporting Information [Line Items]      
Total operating income 354.0us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_SegmentsMember
293.7us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_SegmentsMember
181.3us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_SegmentsMember
Total Identifiable Assets 1,259.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_SegmentsMember
1,037.4us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_SegmentsMember
 
Worldwide Total [Member]      
Segment Reporting Information [Line Items]      
Net sales 1,656.9us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
1,493.8us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
1,321.3us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
Total operating income 322.6us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
54.6us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
33.7us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
Total Identifiable Assets 2,044.5us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
2,104.0us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_WorldwideMember
 
USA & Europe Fiber Cement [Member]      
Segment Reporting Information [Line Items]      
Net sales 1,276.5us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
1,127.6us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
951.4us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
Total operating income 285.9us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
237.0us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
145.6us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
Total Identifiable Assets 959.3us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
782.6us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_UnitedStatesOfAmericaAndEuropeFiberCementMember
 
Asia Pacific Fiber Cement [Member]      
Segment Reporting Information [Line Items]      
Net sales 380.4us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
366.2us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
369.9us-gaap_SalesRevenueGoodsNet
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
Total operating income 94.1us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
81.1us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
61.7us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
Total Identifiable Assets 279.8us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
235.1us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= jhx_AsiaPacificFiberCementMember
 
Research and Development [Member]      
Segment Reporting Information [Line Items]      
Total operating income (26.0)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_ResearchAndDevelopmentArrangementMember
(24.4)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_ResearchAndDevelopmentArrangementMember
(26.0)us-gaap_OperatingIncomeLoss
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_ResearchAndDevelopmentArrangementMember
Total Identifiable Assets $ 20.7us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_ResearchAndDevelopmentArrangementMember
$ 19.7us-gaap_Assets
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_ResearchAndDevelopmentArrangementMember