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)

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Property, Plant and Equipment - Components of Property, Plant and Equipment (Detail) - USD ($)
$ in Millions
 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance $ 1,533.5 $ 1,317.7  
Additions 78.6 277.9  
Disposals (68.0) (8.3)  
Exchange differences (2.1) (53.8)  
Cost, Ending balance 1,542.0 1,533.5 $ 1,317.7
Accumulated depreciation, Beginning balance (653.4) (614.9)  
Charge for the year (76.3) (70.2) (61.3)
Disposals 51.6 7.1  
Exchange differences 3.1 24.6  
Accumulated depreciation, Ending balance (675.0) (653.4) (614.9)
Net book amount 867.0 880.1  
Land [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 70.2 28.7  
Additions   41.5  
Exchange differences (0.1)    
Cost, Ending balance 70.1 70.2 28.7
Net book amount 70.1 70.2  
Buildings [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 239.8 212.5  
Additions 27.0 30.2  
Disposals (0.7) (1.7)  
Exchange differences (0.1) (1.2)  
Cost, Ending balance 266.0 239.8 212.5
Accumulated depreciation, Beginning balance (88.2) (80.9)  
Charge for the year (10.7) (9.3)  
Disposals 0.5 0.8  
Exchange differences 0.2 1.2  
Accumulated depreciation, Ending balance (98.2) (88.2) (80.9)
Net book amount 167.8 151.6  
Machinery and Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 974.6 961.1  
Additions 155.5 72.7  
Disposals (65.8) (6.6)  
Exchange differences (1.9) (52.6)  
Cost, Ending balance 1,062.4 974.6 961.1
Accumulated depreciation, Beginning balance (565.2) (534.0)  
Charge for the year (65.6) (60.9)  
Disposals 51.1 6.3  
Exchange differences 2.9 23.4  
Accumulated depreciation, Ending balance (576.8) (565.2) (534.0)
Net book amount 485.6 409.4  
Construction in Progress [Member]      
Property, Plant and Equipment [Line Items]      
Cost, Beginning balance 248.9 115.4  
Additions (103.9) 133.5  
Disposals (1.5)    
Cost, Ending balance 143.5 248.9 $ 115.4
Net book amount $ 143.5 $ 248.9