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Summary of Performance Share Units Activity (Detail) (Performance Stock Units, USD $)
12 Months Ended
Jan. 31, 2014
Jan. 31, 2013
Jan. 31, 2012
Performance Stock Units
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 2,599,610    
Granted, Shares 1,462,000    
Vested, Shares       
Forfeited, Shares (352,385)    
Non-vested awards outstanding at end of year, Shares 3,709,225 2,599,610  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 17.42    
Granted, Weighted average fair value $ 25.13 $ 18.22 $ 16.21
Vested, Weighted average fair value       
Forfeited, Weighted average fair value $ 17.24    
Non-vested awards outstanding at end of year, Weighted average fair value $ 20.48 $ 17.42