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

Income Taxes - Reconciliation of Unrecognised Tax Benefits and Interest and Penalties (Detail)

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Income Taxes - Reconciliation of Unrecognised Tax Benefits and Interest and Penalties (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2011
Income Taxes [Line Items]      
Unrecognized tax benefits, Beginning balance $ 2.6 $ 185.5 $ 7.7
Unrecognized tax benefits, Additions for tax positions of the current year 0.1 0.2 0.1
Unrecognized tax benefits, Additions for tax positions of prior year 2.6   153.3
Unrecognized tax benefits, Settlements paid during the current period   (184.4)  
Unrecognized tax benefits, Expiration of statute of limitations (2.8)    
Other reductions for the tax positions of prior periods (1.0) (5.2) (0.4)
Unrecognized tax benefits, Foreign currency translation adjustment   6.5 24.8
Balance at 31 March 2013 1.5 2.6 185.5
Interest and Penalties, Beginning balance 0.9 196.3 (26.9)
Interest and Penalties, Additions for tax positions of the current year         
Interest and Penalties, Additions for tax positions of prior year (0.1) 6.1 195.8
Interest and Penalties, Settlements paid during the current period   (208.9)  
Interest and Penalties, Expiration of statute of limitation (0.7)    
Interest and Penalties, Other reductions for the tax positions of prior periods     (0.2)
Interest and Penalties, Foreign currency translation adjustment   7.4 27.6
Interest and Penalties, Ending Balance $ 0.1 $ 0.9 $ 196.3