Revenues - Contract Balances, Unearned Revenue and Remaining Performance Obligation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Jan. 31, 2020
Disaggregation of Revenue [Line Items]
Customer contract assets	$ 508		$ 508		$ 449
Unearned Revenue [Roll Forward]
Unearned revenue, beginning of period	9,112	$ 7,585	10,662	$ 8,564
Billings and other	4,632	3,396	7,937	6,110
Contribution from contract asset	54	7	59	51
Unearned revenue from business combinations	64	151	69	151
Unearned revenue, end of period	8,711	7,142	8,711	7,142
Remaining Performance Obligation
Current	15,200		15,200		15,000
Noncurrent	15,400		15,400		15,800
Total	30,600		30,600		$ 30,800
Revenue recognized ratably over time
Unearned Revenue [Roll Forward]
Revenue recognized	(4,657)	(3,736)	(9,110)	(7,223)
Revenue recognized over time as delivered
Unearned Revenue [Roll Forward]
Revenue recognized	(190)	(174)	(381)	(346)
Revenue recognized at a point in time
Unearned Revenue [Roll Forward]
Revenue recognized	$ (304)	$ (87)	$ (525)	$ (165)