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, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Jan. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	$ 3,240		$ 3,240		$ 1,911
Additions and retirements, net			1,329
Accumulated Amortization	(1,264)		(1,264)		(1,084)
Expense and retirements, net			(188)
Intangible Assets, Net	1,976		$ 1,976		827
Useful Life			5 years 8 months 12 days
Amortization of intangible assets	119	$ 74	$ 188	$ 149
Acquired developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	1,268		1,268		1,027
Additions and retirements, net			241
Accumulated Amortization	(768)		(768)		(677)
Expense and retirements, net			(91)
Intangible Assets, Net	500		$ 500		350
Useful Life			3 years
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	1,917		$ 1,917		831
Additions and retirements, net			1,086
Accumulated Amortization	(452)		(452)		(359)
Expense and retirements, net			(93)
Intangible Assets, Net	1,465		$ 1,465		472
Useful Life			6 years 8 months 12 days
Other
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross	55		$ 55		53
Additions and retirements, net			2
Accumulated Amortization	(44)		(44)		(48)
Expense and retirements, net			(4)
Intangible Assets, Net	$ 11		$ 11		$ 5
Useful Life			1 year 10 months 24 days