Recently Issued Accounting Standards (Adoption of New Accounting Standard - Balance Sheet) (Details) - USD ($) $ in Millions	Apr. 30, 2018	Jan. 31, 2018
Current assets:
Accounts receivable, net	$ 206.7	$ 438.2
Prepaid expenses and other current assets	198.4	116.5
Deferred income taxes, net	67.0	81.7
Other assets	188.7	170.9
Current liabilities:
Accrued income taxes	24.6	28.0
Deferred revenue	1,469.2	1,551.6
Other accrued liabilities	127.8	198.0
Long-term deferred revenue	337.2	403.5
Long-term income taxes payable	41.7	41.6
Long-term deferred income taxes	84.8	66.6
Accumulated deficit	(1,995.8)	(2,084.9)
Impact from the adoption of ASC 606 and 340-40 | Accounting Standards Update 2014-09
Current assets:
Accounts receivable, net	(67.6)
Prepaid expenses and other current assets	77.2
Deferred income taxes, net	(10.6)
Other assets	21.7
Current liabilities:
Accrued income taxes	(2.4)
Deferred revenue	(103.3)
Other accrued liabilities	(2.1)
Long-term deferred revenue	(33.0)
Long-term income taxes payable	0.2
Long-term deferred income taxes	5.7
Accumulated deficit	155.6	$ 178.0
As Adjusted
Current assets:
Accounts receivable, net	274.3
Prepaid expenses and other current assets	121.2
Deferred income taxes, net	77.6
Other assets	167.0
Current liabilities:
Accrued income taxes	27.0
Deferred revenue	1,572.5
Other accrued liabilities	129.9
Long-term deferred revenue	370.2
Long-term income taxes payable	41.5
Long-term deferred income taxes	79.1
Accumulated deficit	$ (2,151.4)