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 Statements of Income and Comprehensive Income) (Details)

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Description of Business, Basis of Presentation, and Significant Accounting Policies (Schedule of Recast of Selected Unaudited Consolidated Statements of Income and Comprehensive Income) (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Feb. 28, 2019
Feb. 28, 2018
Feb. 28, 2019
Feb. 28, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue $ 1,047.4 $ 918.0 [1] $ 2,733.7 $ 2,486.2 [1]
Operating expenses 325.3 272.2 [1] 855.7 752.8 [1]
Selling, general and administrative expenses 315.8 294.9 [1] 879.6 789.8 [1]
Total expenses 641.1 567.1 [1] 1,735.3 1,542.6 [1]
Operating income 429.3 369.0 [1] 1,056.8 989.4 [1]
Income taxes 101.0 4.1 [1] 253.5 219.1 [1]
Net income $ 324.6 $ 367.2 [1],[2] $ 804.0 [3] $ 776.4 [1],[2],[3]
Basic earnings per share $ 0.90 $ 1.02 [1],[2] $ 2.24 $ 2.16 [1],[2]
Diluted earnings per share $ 0.90 $ 1.01 [1],[2] $ 2.22 $ 2.15 [1],[2]
As Previously Reported [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Net income       $ 705.2
As Previously Reported [Member] | ASU 2014-09 [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue   $ 848.4   2,464.0
Operating expenses   270.7   751.5
Selling, general and administrative expenses   303.3   788.6
Total expenses   574.0   1,540.1
Operating income   292.5   969.7
Income taxes   34.4   270.6
Net income   $ 260.4   $ 705.2
Basic earnings per share   $ 0.72   $ 1.96
Diluted earnings per share   $ 0.72   $ 1.95
Adjustments [Member] | ASU 2014-09 [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue   $ 69.6   $ 22.2
Operating expenses   1.5   1.3
Selling, general and administrative expenses   (8.4)   1.2
Total expenses   (6.9)   2.5
Operating income   76.5   19.7
Income taxes   (30.3)   (51.5)
Net income   $ 106.8   $ 71.2
Basic earnings per share   $ 0.30   $ 0.20
Diluted earnings per share   $ 0.29   $ 0.20
[1] Amounts have been adjusted to reflect the adoption of Accounting Standards Codification ("ASC") Topic 606, "Revenue from Contracts with Customers" ("ASC Topic 606").
[2] Amounts have been adjusted to reflect the adoption of ASC Topic 606.
[3] Amounts have been adjusted to reflect the adoption of Accounting Standards Update ("ASU") No. 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)."