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Stock-based Compensation Expense (Additional Information) (Details)
$ in Millions
3 Months Ended
Apr. 30, 2020
USD ($)
period
shares
Apr. 30, 2019
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Allocated share-based compensation expense $ 98.2 $ 75.2
Settlement of liability-classified restricted stock units 28.7 0.0
Market capitalization $ 2,000.0  
Expected dividend yield (in percentage) 0.00%  
Restricted Stock Units (RSUs) and Performance Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Awards vested in period, fair value $ 111.4 50.3
Awards granted in period (shares) | shares 775,400  
Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Awards granted in period (shares) | shares 500,000  
Allocated share-based compensation expense $ 76.9 54.4
Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Awards granted in period (shares) | shares 300,000  
Allocated share-based compensation expense $ 7.4 $ 6.5
Award vesting period 3 years  
Expected dividend yield (in percentage) 0.00% 0.00%
1998 Employee Qualified Stock Purchase Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Employee stock purchase plan maximum percentage of compensation to purchase shares by eligible participants 15.00%  
Employee stock purchase plan minimum percentage of common stock fair value defined to purchase shares by eligible participants 85.00%  
Employee stock purchase plan, number of exercise periods | period 4  
Employee stock purchase plan, term of exercise period 6 months  
Employee stock purchase plan, term of offering period 24 months  
Expected dividend yield (in percentage) 0.00% 0.00%
Share-based Compensation Award, Tranche One | Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PSU annual vesting percentage 33.33%  
Share-based Compensation Award, Tranche Two | Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PSU annual vesting percentage 33.33%  
Share-based Compensation Award, Tranche Three | Performance Stock Unit    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
PSU annual vesting percentage 33.33%