Income Taxes - Income Taxes Components Of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Jan. 31, 2017	Jan. 31, 2016
Income Tax Disclosure [Abstract]
Stock-based compensation	$ 37.6	$ 37.5
Research and development tax credit carryforwards	136.7	91.3
Foreign tax credit carryforwards	127.3	51.1
Accrued compensation and benefits	39.5	41.5
Other accruals not currently deductible for tax	18.7	23.6
Purchased technology and capitalized software	76.9	64.3
Fixed assets	24.3	18.6
Tax loss carryforwards	173.6	17.6
Deferred Revenue	128.3	56.7
Other	27.6	13.9
Total deferred tax assets	790.5	416.1
Less: valuation allowance	(748.0)	(398.0)
Net deferred tax assets	42.5	18.1
Indefinite lived intangibles	(70.1)	(54.1)
Unremitted earnings of foreign subsidiaries	0.0	(22.4)
Total deferred tax liabilities	(70.1)	(76.5)
Net deferred tax liabilities	$ (27.6)	$ (58.4)