Net Income (Loss) Per Share - Reconciliation of Denominator Used in Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Oct. 31, 2020	Oct. 31, 2019
Numerator:
Net income (loss)	$ 1,081	$ 2,625	$ 99	$ (109)	$ 91	$ 392	$ 3,805	$ 374
Denominator:
Weighted-average shares outstanding for basic earnings per share (in shares)	911			879			905	809
Dilutive effect of employee stock awards (in shares)	28			0			21	20
Adjusted weighted-average shares outstanding and assumed conversions for diluted earnings (loss) per share (in shares)	939			879			926	829