Recently Issued Accounting Standards (Adoption of New Accounting Standard - Balance Sheet) (Details) - USD ($) $ in Millions	Jul. 31, 2018	Feb. 01, 2018	Jan. 31, 2018
Current assets:
Accounts receivable, net	$ 234.4		$ 438.2
Prepaid expenses and other current assets	194.6		116.5
Deferred income taxes, net	81.5		81.7
Other assets	195.4		170.9
Current liabilities:
Accrued income taxes	38.8		28.0
Deferred revenue	1,491.5		1,551.6
Other accrued liabilities	139.4		198.0
Long-term deferred revenue	308.0		403.5
Long-term income taxes payable	41.5		41.6
Long-term deferred income taxes	88.2		66.6
Accumulated deficit	(2,103.2)		$ (2,084.9)
Impact from the adoption of ASC 606 and 340-40 | Accounting Standards Update 2014-09
Current assets:
Accounts receivable, net	53.0
Prepaid expenses and other current assets	(70.1)
Deferred income taxes, net	11.0
Other assets	(18.0)
Current liabilities:
Accrued income taxes	(1.4)
Deferred revenue	99.1
Other accrued liabilities	2.4
Long-term deferred revenue	25.3
Long-term income taxes payable	(0.2)
Long-term deferred income taxes	(4.6)
Accumulated deficit	(144.7)	$ 179.4
As Adjusted
Current assets:
Accounts receivable, net	287.4
Prepaid expenses and other current assets	124.5
Deferred income taxes, net	92.5
Other assets	177.4
Current liabilities:
Accrued income taxes	37.4
Deferred revenue	1,590.6
Other accrued liabilities	141.8
Long-term deferred revenue	333.3
Long-term income taxes payable	41.3
Long-term deferred income taxes	83.6
Accumulated deficit	$ (2,247.9)