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 6 Months Ended
Nov. 30, 2018
Nov. 30, 2017
Nov. 30, 2018
Nov. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue $ 840.6 $ 789.0 [1] $ 1,686.3 $ 1,568.2 [1]
Operating expenses 264.9 248.6 [1] 530.4 480.6 [1]
Selling, general and administrative expenses 286.8 251.3 [1] 563.8 494.9 [1]
Total expenses 551.7 499.9 [1] 1,094.2 975.5 [1]
Operating income 307.2 303.1 [1] 627.5 620.4 [1]
Income taxes 73.5 106.0 [1] 152.5 215.0 [1]
Net income $ 235.8 $ 198.8 [1],[2] $ 479.4 $ 409.2 [1],[2]
Basic earnings per share $ 0.66 $ 0.55 [1],[2] $ 1.34 $ 1.14 [1],[2]
Diluted earnings per share $ 0.65 $ 0.55 [1],[2] $ 1.33 $ 1.13 [1],[2]
As Previously Reported [Member] | ASU 2014-09 [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue   $ 812.5   $ 1,615.6
Operating expenses   248.7   480.8
Selling, general and administrative expenses   245.6   485.3
Total expenses   494.3   966.1
Operating income   332.2   677.2
Income taxes   116.9   236.2
Net income   $ 217.0   $ 444.8
Basic earnings per share   $ 0.60   $ 1.24
Diluted earnings per share   $ 0.60   $ 1.23
Adjustments [Member] | ASU 2014-09 [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Service revenue   $ (23.5)   $ (47.4)
Operating expenses   (0.1)   (0.2)
Selling, general and administrative expenses   5.7   9.6
Total expenses   5.6   9.4
Operating income   (29.1)   (56.8)
Income taxes   (10.9)   (21.2)
Net income   $ (18.2)   $ (35.6)
Basic earnings per share   $ (0.05)   $ (0.10)
Diluted earnings per share   $ (0.05)   $ (0.10)
[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.