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Summary of Performance Share Units Activity (Detail) - Performance Stock Units - $ / shares
12 Months Ended
Jan. 31, 2016
Jan. 31, 2015
Jan. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 3,992,209    
Granted, Shares 1,471,000 163,336  
Vested, Shares (435,996)    
Forfeited, Shares (843,915)    
Non-vested awards outstanding at end of year, Shares 4,183,298 3,992,209  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 21.32    
Granted, Weighted average fair value 18.94 $ 23.40 $ 25.13
Vested, Weighted average fair value 17.58    
Forfeited, Weighted average fair value 22.72    
Non-vested awards outstanding at end of year, Weighted average fair value $ 20.64 $ 21.32