Stockholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Billions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Jan. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share of grants (in dollars per share)	$ 48.50	$ 38.97	$ 40.06	$ 40.69
Share-based compensation expense			$ 1.1
Period for recognition			2 years
Total shares available for future grant (in shares)	148		148		133
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share of ESPP shares (in dollars per share)	$ 53.64	$ 38.88