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Summary of Performance Share Units Activity (Detail) - Performance Stock Units (PSUs) - $ / shares
12 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 2,667,261    
Granted, Shares 100,000    
Vested, Shares (468,525)    
Forfeited, Shares (943,109)    
Non-vested awards outstanding at end of year, Shares 1,355,627 2,667,261  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 21.84    
Granted, Weighted average fair value 34.76 $ 23.38 $ 27.30
Vested, Weighted average fair value 22.45    
Forfeited, Weighted average fair value 22.08    
Non-vested awards outstanding at end of year, Weighted average fair value $ 22.45 $ 21.84