Description of Business, Basis of Presentation, and Significant Accounting Policies (Schedule of Recast of Selected Unaudited Consolidated Balance Sheet) (Details) - USD ($) $ in Millions		Aug. 31, 2018	May 31, 2018
Assets
Accounts receivable, net of allowance for doubtful accounts		$ 535.2	$ 492.4	[1]
Prepaid expenses and other current assets		225.1	224.0	[1]
Long-term deferred costs		355.6	361.0	[1],[2]
Liabilities and stockholders' equity
Accounts payable		62.6	73.7	[1]
Deferred revenue		36.6	34.6	[1]
Deferred income taxes		155.5	154.4	[1]
Other long-term liabilities		91.0	89.1	[1]
Retained earnings		$ 1,268.1	1,262.6	[1]
ASU 2014-09 [Member] | As Previously Reported [Member]
Assets
Accounts receivable, net of allowance for doubtful accounts			531.4
Prepaid expenses and other current assets			75.8
Long-term deferred costs	[2]		18.5
Liabilities and stockholders' equity
Accounts payable			74.5
Deferred revenue			24.3
Deferred income taxes			48.8
Other long-term liabilities			84.8
Retained earnings			930.3
ASU 2014-09 [Member] | Adjustments [Member]
Assets
Accounts receivable, net of allowance for doubtful accounts			(39.0)
Prepaid expenses and other current assets			148.2
Long-term deferred costs	[2]		342.5
Liabilities and stockholders' equity
Accounts payable			(0.8)
Deferred revenue			10.3
Deferred income taxes			105.6
Other long-term liabilities			4.3
Retained earnings			$ 332.3

[1] Amounts have been adjusted to reflect the adoption of ASC Topic 606.

[2] Amounts were previously reported as a component of other long-term assets on the Consolidated Balance Sheets included in the Company's fiscal 2018 Form 10-K. Long-term deferred costs are separately stated on the Consolidated Balance Sheets contained in this Form 10-Q.