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Summary of Performance Share Units Activity (Detail) - Performance Stock Units (PSUs) - $ / shares
12 Months Ended
Jan. 31, 2017
Jan. 31, 2016
Jan. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 4,183,298    
Granted, Shares 410,000   163,336
Vested, Shares (100,000)    
Forfeited, Shares (1,442,564)    
Non-vested awards outstanding at end of year, Shares 3,050,734 4,183,298  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 20.64    
Granted, Weighted average fair value 27.30 $ 18.94 $ 23.40
Vested, Weighted average fair value 25.37    
Forfeited, Weighted average fair value 15.92    
Non-vested awards outstanding at end of year, Weighted average fair value $ 17.98 $ 20.64