Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2019	Aug. 31, 2018
Capitalized Contract Cost [Line Items]
Amortization	$ 46.0	$ 44.6	[1]
Costs To Obtain A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	464.3	455.0
Capitalization of costs	35.9	32.4
Amortization	(40.2)	(38.9)
Ending balance	460.0	448.5
Costs To Fulfill A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	66.1	65.4
Capitalization of costs	6.0	6.0
Amortization	(5.8)	(5.7)
Ending balance	$ 66.3	$ 65.7

[1] Amounts have been adjusted to reflect 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).”