Summary of Business and Significant Accounting Policies - Adoption of ASU 2014-09 (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Apr. 30, 2018	Apr. 30, 2017	Jan. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenues		$ 3,006	$ 2,397
Marketing and sales	[1],[2]	1,329	1,106
(Provision for) benefit from income taxes		(41)	11
Net income		$ 344	$ 1
Diluted net income per share (in dollars per share)		$ 0.46	$ 0.00
Accounts receivable, net		$ 1,763		$ 3,921
Costs capitalized to obtain revenue contracts, net		667		671
Prepaid expenses and other current assets		562		471
Costs capitalized to obtain revenue contracts, noncurrent, net		1,038		1,105
Other assets, net		392		384
Accounts payable, accrued expenses and other liabilities		1,691		2,047
Unearned revenue		6,201		6,995
Other noncurrent liabilities		836		846
Stockholders’ equity		$ 11,060		10,376
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenues			$ 2,388
Marketing and sales	[1],[2]		1,110
(Provision for) benefit from income taxes			14
Net income			$ (9)
Diluted net income per share (in dollars per share)			$ (0.01)
Accounts receivable, net				3,918
Costs capitalized to obtain revenue contracts, net				461
Prepaid expenses and other current assets				390
Costs capitalized to obtain revenue contracts, noncurrent, net				413
Other assets, net				396
Accounts payable, accrued expenses and other liabilities				2,010
Unearned revenue				7,095
Other noncurrent liabilities				796
Stockholders’ equity				9,389
Change | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenues			$ 9
Marketing and sales	[1],[2]		(4)
(Provision for) benefit from income taxes			(3)
Net income			$ 10
Diluted net income per share (in dollars per share)			$ 0.01
Accounts receivable, net				3
Costs capitalized to obtain revenue contracts, net				210
Prepaid expenses and other current assets				81
Costs capitalized to obtain revenue contracts, noncurrent, net				692
Other assets, net				(12)
Accounts payable, accrued expenses and other liabilities				37
Unearned revenue				(100)
Other noncurrent liabilities				50
Stockholders’ equity				$ 987

[1] Amounts include amortization of intangible assets acquired through business combinations, as follows: Three Months Ended April 30, 2018 2017Cost of revenues$39 $44Marketing and sales30 31

[2] Amounts include stock-based expense, as follows: Three Months Ended April 30, 2018 2017Cost of revenues$34 $32Research and development66 64Marketing and sales120 119General and administrative32 37