Intangible Assets Acquired Through Business Combinations and Goodwill (Intangible Assets Acquired From Business Combinations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Finite-lived Intangible Assets [Roll Forward]
Intangible assets, gross, beginning balance			$ 3,419
Accumulated amortization, beginning balance			(1,496)
Intangible assets, net, beginning balance			1,923
Additions and retirements, net			58
Expense and retirements, net			(256)
Intangible assets, gross, ending balance	$ 3,477		3,477
Accumulated amortization, ending balance	(1,752)		(1,752)
Intangible assets, net, ending balance	1,725		$ 1,725
Weighted average remaining useful life			5 years
Amortization of intangible assets	127	$ 119	$ 256	$ 188
Contract asset	268		268		$ 215
Other assets
Finite-lived Intangible Assets [Roll Forward]
Contract asset	81		81		$ 121
Acquired developed technology
Finite-lived Intangible Assets [Roll Forward]
Intangible assets, gross, beginning balance			1,429
Accumulated amortization, beginning balance			(889)
Intangible assets, net, beginning balance			540
Additions and retirements, net			33
Expense and retirements, net			(123)
Intangible assets, gross, ending balance	1,462		1,462
Accumulated amortization, ending balance	(1,012)		(1,012)
Intangible assets, net, ending balance	450		$ 450
Weighted average remaining useful life			2 years 7 months 6 days
Customer relationships
Finite-lived Intangible Assets [Roll Forward]
Intangible assets, gross, beginning balance			$ 1,938
Accumulated amortization, beginning balance			(560)
Intangible assets, net, beginning balance			1,378
Additions and retirements, net			25
Expense and retirements, net			(129)
Intangible assets, gross, ending balance	1,963		1,963
Accumulated amortization, ending balance	(689)		(689)
Intangible assets, net, ending balance	1,274		$ 1,274
Weighted average remaining useful life			5 years 10 months 24 days
Other
Finite-lived Intangible Assets [Roll Forward]
Intangible assets, gross, beginning balance			$ 52
Accumulated amortization, beginning balance			(47)
Intangible assets, net, beginning balance			5
Additions and retirements, net			0
Expense and retirements, net			(4)
Intangible assets, gross, ending balance	52		52
Accumulated amortization, ending balance	(51)		(51)
Intangible assets, net, ending balance	$ 1		$ 1
Weighted average remaining useful life			1 year