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

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2010
Tax Credit Carryforward [Line Items]        
Foreign tax credit carry-forwards $ 123.9 $ 130.2    
Income tax expense (benefit) due to tax audit settlements and statute of limitations expiration 0.2 0.5    
Total amount of unrecognised tax benefits 1.5 2.6 185.5 7.7
Total amount of interest and penalties accrued 0.1 0.9 196.3 (26.9)
Interest and penalties recognised income tax expense 0.8 6.1    
Period for the amount of unrecognised tax benefits increase or decrease Next 12 months      
Australian [Member]
       
Tax Credit Carryforward [Line Items]        
Tax loss carry-forward 31.4      
Percentage of valuation allowance against loss carry-forwards 100.00%      
Capital loss carry-forwards 115.3      
European [Member]
       
Tax Credit Carryforward [Line Items]        
Tax loss carry-forward 24.1      
Tax loss carry-forwards available to offset future taxable income not subject to expiration 19.5      
Percentage of valuation allowance against loss carry-forwards 100.00%      
Operating loss carry-forwards subject to expiration 4.6      
USA [Member]
       
Tax Credit Carryforward [Line Items]        
Tax loss carry-forward 4.1      
US tax loss carry-forward expiration date 2031      
Foreign tax credit carry-forwards [Member]
       
Tax Credit Carryforward [Line Items]        
Percentage of valuation allowance against loss carry-forwards 100.00%      
Foreign tax credit carry-forwards 123.9      
Non-Irish subsidiaries [Member]
       
Tax Credit Carryforward [Line Items]        
Undistributed foreign earnings $ 654.6