Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended			79 Months Ended	90 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2020	Jul. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of the options exercised during the period	$ 799	$ 784	$ 373
Weighted-average remaining contractual life of vested and expected to vest options (in years)	4 years
Options vested (in shares)	14,000,000			14,000,000
Weighted average exercise price vested (in dollars per share)	$ 66.34			$ 66.34
Remaining contractual term (in years)	3 years
Total intrinsic value of vested options	$ 1,589			$ 1,589
Weighted-average fair value per share of grants (in dollars per share)	$ 0.001
Total shares available for future grant (in shares)	133,000,000			133,000,000
Fair value of shares vested in period	$ 1,900	$ 1,100	$ 1,000
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000		5,000,000
Preferred stock, shares outstanding (in shares)	0	0		0
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 107	$ 76
Weighted-average fair value per share of grants (in dollars per share)	$ 41.43	$ 32.90	$ 23.64
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,800
Term of stock options (in years)				7 years	5 years
Aggregate stock compensation, not yet recognized	$ 4,016			$ 4,016
Weighted-average fair value per share of grants (in dollars per share)	$ 39.59	$ 28.89	$ 22.71
Period for recognition	2 years
Performance-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Performance-based restricted stock units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	0.00%
Performance-based restricted stock units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage	200.00%
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period for recognition	4 years