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Summary of Performance Share Units Activity (Detail) - Performance Stock Units (PSUs) - $ / shares
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 3,050,734    
Granted, Shares 390,000    
Vested, Shares (200,000)    
Forfeited, Shares (573,473)    
Non-vested awards outstanding at end of year, Shares 2,667,261 3,050,734  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 17.98    
Granted, Weighted average fair value 23.38 $ 27.30 $ 18.94
Vested, Weighted average fair value 29.58    
Forfeited, Weighted average fair value 22.47    
Non-vested awards outstanding at end of year, Weighted average fair value $ 21.84 $ 17.98