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Unearned Revenue and Performance Obligations (Details) - USD ($)
$ in Millions
12 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2017
Oct. 31, 2018
Revenue from Contract with Customer [Abstract]        
Subscription revenue recognized that was included in total unearned revenue balance at beginning of period $ 1,400 $ 1,000 $ 738  
Subscriptions | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-02-01        
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Revenue is expected to be recognized from remaining performance obligations for subscription contracts       $ 4,470
Subscriptions | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-02-01        
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Recognition period       24 months
Subscriptions | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)        
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]        
Revenue is expected to be recognized from remaining performance obligations for subscription contracts       $ 6,700