Income Taxes - Components Of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jan. 31, 2021	Jan. 31, 2020
Income Tax Disclosure [Abstract]
Stock-based compensation	$ 39.0	$ 32.8
Research and development tax credit carryforwards	220.4	263.4
Foreign tax credit carryforwards	69.9	253.9
Accrued compensation and benefits	3.4	3.4
Other accruals not currently deductible for tax	14.1	28.4
Purchased technology and capitalized software	48.2	37.7
Fixed assets	8.1	11.6
Lease liability	114.2	106.4
Tax loss carryforwards	65.5	241.2
Deferred revenue	501.5	29.2
Other	40.2	28.0
Total deferred tax assets	1,124.5	1,036.0
Less: valuation allowance	(186.5)	(883.4)
Net deferred tax assets	938.0	152.6
Indefinite lived intangibles	(83.1)	(76.5)
Right-of-use assets	(101.6)	(101.3)
Unremitted earnings of foreign subsidiaries	(1.6)	(0.9)
Total deferred tax liabilities	(186.3)	(178.7)
Deferred tax assets, net	$ 751.7
Net deferred tax assets (liabilities)		$ (26.1)