Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Jan. 31, 2021	Jan. 31, 2020
Number of shares
Options outstanding, beginning balance (in shares)	13,448,026
Options granted (in shares)	1,427,362
Options exercised (in shares)	(1,839,723)
Options forfeited/cancelled (in shares)	(274,376)
Options outstanding, ending balance (in shares)	12,761,289	13,448,026
Options vested and exercisable (in shares)	6,817,037
Options vested and exercisable and expected to vest thereafter (in shares)	12,761,289
Weighted average exercise price
Options outstanding, beginning balance (in usd per share)	$ 40.64
Options granted (in usd per share)	181.18
Options exercised (in usd per share)	18.92
Options forfeited/cancelled (in usd per share)	123.50
Options outstanding, ending balance (in usd per share)	57.48	$ 40.64
Options vested and exercisable (in usd per share)	17.50
Options vested and exercisable and expected to vest thereafter (in usd per share)	$ 57.48
Weighted average remaining contractual term (in years), options outstanding	5 years	5 years 4 months 24 days
Weighted average remaining contractual term (in years), options vested and exercisable	2 years 10 months 24 days
Weighted average remaining contractual term (in years), options vested and exercisable and expected to vest thereafter	5 years
Aggregate intrinsic value (in millions)
Options outstanding	$ 2,794	$ 1,427
Options vested and exercisable	1,765
Options vested and exercisable and expected to vest thereafter	$ 2,794