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Unearned Revenue and Performance Obligations (Details) - USD ($)
$ in Millions
3 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Revenue from Contract with Customer [Abstract]    
Subscription revenue recognized that was included in total unearned revenue balance at beginning of period $ 487 $ 361
Revenue is expected to be recognized from remaining performance obligations for subscription contracts $ 5,200  
Recognition period 24 months