Revenues - Contract Balances, Unearned Revenue and Remaining Performance Obligation (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
Disaggregation of Revenue [Line Items]
Contract asset	$ 268		$ 268		$ 215
Unearned Revenue [Roll Forward]
Unearned revenue, beginning of period	7,585	$ 6,201	8,564	$ 6,995
Billings and other	3,396	2,875	6,110	5,086
Contribution from contract asset	7	31	51	25
Unearned revenue from business combinations	151	57	151	64
Unearned revenue, end of period	7,142	5,883	7,142	5,883
Remaining Performance Obligation
Current	12,100		12,100		11,900
Noncurrent	13,200		13,200		13,800
Total	25,300		25,300		$ 25,700
Revenue recognized ratably over time
Unearned Revenue [Roll Forward]
Revenue recognized	(3,736)	(3,056)	(7,223)	(5,924)
Revenue recognized over time as delivered
Unearned Revenue [Roll Forward]
Revenue recognized	(174)	(162)	(346)	(299)
Revenue recognized at a point in time
Unearned Revenue [Roll Forward]
Revenue recognized	$ (87)	$ (63)	$ (165)	$ (64)