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Unearned Revenue and Performance Obligations (Details) - USD ($)
$ in Millions
3 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Revenue from Contract with Customer [Abstract]    
Subscription revenue recognized that was included in total unearned revenue balance at beginning of period $ 642 $ 487
Subscriptions | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-05-01    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]    
Revenue is expected to be recognized from remaining performance obligations for subscription contracts $ 6,800  
Recognition period 24 months