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Employee and Director Stock Plans - Summary of Restricted Stock Award and Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) and Performance Stock Units (PSUs) - $ / shares
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Unreleased restricted stock      
Unvested restricted stock units, beginning balance (in shares) 7,622,400    
Granted (in shares) 2,481,800    
Vested (in shares) (3,765,700)    
Canceled/Forfeited (in shares) (692,500)    
Performance adjustment (in shares) 24,700    
Unvested restricted stock, ending balance (in shares) 5,670,700 7,622,400  
Weighted average grant date fair value      
Beginning balance of unvested restricted stock units (in dollars per share) $ 60.13    
Granted (in dollars per share) 106.55 $ 65.95 $ 52.53
Vested (in dollars per share) 57.85    
Canceled/Forfeited (in dollars per share) 69.08    
Performance adjustment (in dollars per share) 61.79    
Ending balance of unvested restricted stock (in dollars per share) $ 82.94 $ 60.13  
Minimum      
Weighted average grant date fair value      
Performance shares payout   99.70%  
Maximum      
Weighted average grant date fair value      
Performance shares payout   114.70%