Revenue Recognition (Narrative) (Details) $ in Millions	6 Months Ended
	Jul. 31, 2020 USD ($) category	Jul. 31, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Number of revenue categories | category	3
Remaining performance obligation	$ 3,350
Contract with customer, liability, revenue recognized	1,430	$ 1,190
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-08-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 2,310
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation percentage	69.00%
Performance obligation, expected timing of satisfaction	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-02-01
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 1,040
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation percentage	31.00%
Performance obligation, expected timing of satisfaction	3 years