Cash Equivalents and Investments - Schedule of Cash and Cash Equivalents and Investments Fair Value (Details) - USD ($) $ in Thousands	Oct. 31, 2020	Jan. 31, 2020
Cash equivalents:
Amortized Cost	$ 3,832,638	$ 54,295
Gross Unrealized Gains	9	2
Gross Unrealized Losses	(13)	0
Total cash equivalents	3,832,634	54,297
Investments:
Amortized Cost	1,161,018	330,082
Gross Unrealized Gains	843	295
Gross Unrealized Losses	(335)	(1)
Estimated Fair Value	1,161,526	330,376
Amortized Cost	4,993,656	384,377
Gross Unrealized Gains	852	297
Gross Unrealized Losses	(348)	(1)
Estimated Fair Value	4,994,160	384,673
U.S. government and agency securities
Investments:
Amortized Cost	982,899	259,738
Gross Unrealized Gains	397	216
Gross Unrealized Losses	(300)	(1)
Estimated Fair Value	982,996	259,953
Corporate notes and bonds
Investments:
Amortized Cost	111,751	30,642
Gross Unrealized Gains	402	57
Gross Unrealized Losses	(29)	0
Estimated Fair Value	112,124	30,699
Certificates of deposit
Investments:
Amortized Cost	45,285	12,592
Gross Unrealized Gains	28	12
Gross Unrealized Losses	(1)	0
Estimated Fair Value	45,312	12,604
Commercial paper
Investments:
Amortized Cost	20,837	17,006
Gross Unrealized Gains	15	2
Gross Unrealized Losses	(5)	0
Estimated Fair Value	20,847	17,008
Asset-backed securities
Investments:
Amortized Cost	246	10,104
Gross Unrealized Gains	1	8
Gross Unrealized Losses	0	0
Estimated Fair Value	247	10,112
U.S. government and agency securities
Cash equivalents:
Amortized Cost	3,778,216	32,470
Gross Unrealized Gains	9	2
Gross Unrealized Losses	(13)	0
Total cash equivalents	3,778,212	32,472
Money market funds
Cash equivalents:
Amortized Cost	54,422	21,379
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total cash equivalents	$ 54,422	21,379
Commercial paper
Cash equivalents:
Amortized Cost		446
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Total cash equivalents		$ 446