Revenues - Contract Balances, Unearned Revenue and Remaining Performance Obligation (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Jan. 31, 2020
Disaggregation of Revenue [Line Items]
Customer contract assets	$ 454		$ 449
Unearned Revenue [Roll Forward]
Unearned revenue, beginning of period	10,662	$ 8,564
Billings and other	3,305	2,714
Contribution from contract asset	5	44
Unearned revenue from business combinations	5	0
Unearned revenue, end of period	9,112	7,585
Remaining Performance Obligation
Current	14,500		15,000
Noncurrent	14,800		15,800
Total	29,300		$ 30,800
Revenue recognized ratably over time
Unearned Revenue [Roll Forward]
Revenue recognized	(4,453)	(3,488)
Revenue recognized over time as delivered
Unearned Revenue [Roll Forward]
Revenue recognized	(191)	(172)
Revenue recognized at a point in time
Unearned Revenue [Roll Forward]
Revenue recognized	$ (221)	$ (77)