Recently Issued Accounting Standards (Adoption of New Accounting Standard - Balance Sheet) (Details) - USD ($) $ in Millions	Oct. 31, 2018	Feb. 01, 2018	Jan. 31, 2018
Current assets:
Accounts receivable, net	$ 309.0		$ 438.2
Prepaid expenses and other current assets	202.8		116.5
Deferred income taxes, net	71.7		81.7
Other assets	188.1		170.9
Current liabilities:
Accrued income taxes	44.6		28.0
Deferred revenue	1,517.6		1,551.6
Other accrued liabilities	126.4		198.0
Long-term deferred revenue	274.5		403.5
Long-term income taxes payable	40.9		41.6
Long-term deferred income taxes	96.5		66.6
Accumulated deficit	(2,189.9)		$ (2,084.9)
Impact from the adoption of ASC 606 and 340-40 | Accounting Standards Update 2014-09
Current assets:
Accounts receivable, net	60.8
Prepaid expenses and other current assets	(66.6)
Deferred income taxes, net	12.3
Other assets	(14.8)
Current liabilities:
Accrued income taxes	(2.3)
Deferred revenue	112.0
Other accrued liabilities	3.2
Long-term deferred revenue	29.6
Long-term income taxes payable	(0.2)
Long-term deferred income taxes	(11.9)
Accumulated deficit	(138.7)	$ 179.4
As Adjusted
Current assets:
Accounts receivable, net	369.8
Prepaid expenses and other current assets	136.2
Deferred income taxes, net	84.0
Other assets	173.3
Current liabilities:
Accrued income taxes	42.3
Deferred revenue	1,629.6
Other accrued liabilities	129.6
Long-term deferred revenue	304.1
Long-term income taxes payable	40.7
Long-term deferred income taxes	84.6
Accumulated deficit	$ (2,328.6)