Quarterly report pursuant to Section 13 or 15(d)

Description of Business, Basis of Presentation, and Significant Accounting Policies (Schedule of Recast of Selected Unaudited Consolidated Statement of Cash Flow) (Details)

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Description of Business, Basis of Presentation, and Significant Accounting Policies (Schedule of Recast of Selected Unaudited Consolidated Statement of Cash Flow) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Nov. 30, 2018
Nov. 30, 2017
Nov. 30, 2018
Nov. 30, 2017
Cash flows from operating activities        
Net income $ 235.8 $ 198.8 [1],[2] $ 479.4 $ 409.2 [1],[2]
Provision for deferred income taxes     10.9 47.2 [1]
Accounts receivable     (71.6) (8.5) [1]
Prepaid expenses and other current assets     (26.7) (25.8) [1]
Accounts payable and other current liabilities     (30.2) (35.5) [1]
Deferred costs     7.3 10.6 [1]
Net change in other long-term assets and liabilities     $ (0.4) 1.1 [1]
ASU 2014-09 [Member] | As Previously Reported [Member]        
Cash flows from operating activities        
Net income   217.0   444.8
Provision for deferred income taxes       68.4
Accounts receivable       (56.5)
Accounts payable and other current liabilities       (34.3)
Deferred costs      
Net change in other long-term assets and liabilities       1.7
ASU 2014-09 [Member] | Adjustments [Member]        
Cash flows from operating activities        
Net income   $ (18.2)   (35.6)
Provision for deferred income taxes       (21.2)
Accounts receivable       48.0
Accounts payable and other current liabilities       (1.2)
Deferred costs       10.6
Net change in other long-term assets and liabilities       $ (0.6)
[1] Amounts have been adjusted to reflect the adoption of ASC Topic 606.
[2] Amounts have been adjusted to reflect the adoption of Accounting Standards Codification ("ASC") Topic 606, "Revenue from Contracts with Customers" ("ASC Topic 606").