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

Property, Plant and Equipment - Components of Property, Plant and Equipment (Detail)

v2.4.1.9
Property, Plant and Equipment - Components of Property, Plant and Equipment (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance $ 1,317.7us-gaap_PropertyPlantAndEquipmentGross $ 1,284.5us-gaap_PropertyPlantAndEquipmentGross  
Additions 277.9us-gaap_PropertyPlantAndEquipmentAdditions 125.2us-gaap_PropertyPlantAndEquipmentAdditions  
Disposals (8.3)us-gaap_PropertyPlantAndEquipmentDisposals (2.2)us-gaap_PropertyPlantAndEquipmentDisposals  
Other   (61.3)us-gaap_PropertyPlantAndEquipmentOther  
Exchange differences (53.8)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross (28.5)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross  
Cost, Ending balance 1,533.5us-gaap_PropertyPlantAndEquipmentGross 1,317.7us-gaap_PropertyPlantAndEquipmentGross 1,284.5us-gaap_PropertyPlantAndEquipmentGross
Accumulated depreciation, Beginning balance (614.9)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment (625.6)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment  
Charge for the year (70.2)us-gaap_Depreciation (61.3)us-gaap_Depreciation (60.0)us-gaap_Depreciation
Disposals 7.1us-gaap_AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment 1.5us-gaap_AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment  
Other   52.4us-gaap_PropertyPlantAndEquipmentOtherAccumulatedDepreciation  
Exchange differences 24.6jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments 18.1jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments  
Accumulated depreciation, Ending balance (653.4)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment (614.9)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment (625.6)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
Net book amount 880.1us-gaap_PropertyPlantAndEquipmentNet 702.8us-gaap_PropertyPlantAndEquipmentNet  
Land [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 28.7us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
18.5us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Additions 41.5us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
11.7us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Other   (1.5)us-gaap_PropertyPlantAndEquipmentOther
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Cost, Ending balance 70.2us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
28.7us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Net book amount 70.2us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
28.7us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_LandMember
 
Buildings [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 212.5us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
210.2us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Additions 30.2us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
18.9us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Disposals (1.7)us-gaap_PropertyPlantAndEquipmentDisposals
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
   
Other   (15.6)us-gaap_PropertyPlantAndEquipmentOther
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Exchange differences (1.2)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
(1.0)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Cost, Ending balance 239.8us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
212.5us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Accumulated depreciation, Beginning balance (80.9)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
(85.2)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Charge for the year (9.3)us-gaap_Depreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
(9.1)us-gaap_Depreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Disposals 0.8us-gaap_AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
   
Other   12.4us-gaap_PropertyPlantAndEquipmentOtherAccumulatedDepreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Exchange differences 1.2jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
1.0jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Accumulated depreciation, Ending balance (88.2)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
(80.9)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Net book amount 151.6us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
131.6us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_BuildingMember
 
Machinery and Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 961.1us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
994.7us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Additions 72.7us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
39.8us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Disposals (6.6)us-gaap_PropertyPlantAndEquipmentDisposals
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
(2.2)us-gaap_PropertyPlantAndEquipmentDisposals
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Other   (43.7)us-gaap_PropertyPlantAndEquipmentOther
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Exchange differences (52.6)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
(27.5)jhx_PropertyPlantAndEquipmentForeignCurrencyTranslationAdjustmentsGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Cost, Ending balance 974.6us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
961.1us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Accumulated depreciation, Beginning balance (534.0)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
(540.4)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Charge for the year (60.9)us-gaap_Depreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
(52.2)us-gaap_Depreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Disposals 6.3us-gaap_AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
1.5us-gaap_AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Other   40.0us-gaap_PropertyPlantAndEquipmentOtherAccumulatedDepreciation
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Exchange differences 23.4jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
17.1jhx_PropertyPlantAndEquipmentAccumulatedDepreciationForeignCurrencyTranslationAdjustments
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Accumulated depreciation, Ending balance (565.2)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
(534.0)us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Net book amount 409.4us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
427.1us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_MachineryAndEquipmentMember
 
Construction in Progress [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 115.4us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
61.1us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
 
Additions 133.5us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
54.8us-gaap_PropertyPlantAndEquipmentAdditions
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
 
Other   (0.5)us-gaap_PropertyPlantAndEquipmentOther
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
 
Cost, Ending balance 248.9us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
115.4us-gaap_PropertyPlantAndEquipmentGross
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
 
Net book amount $ 248.9us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember
$ 115.4us-gaap_PropertyPlantAndEquipmentNet
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= us-gaap_ConstructionInProgressMember