Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2019	May 31, 2018		May 31, 2017	[1],[2]
Capitalized Contract Cost [Line Items]
Amortization	$ 180.2	$ 174.7	[1],[2]	$ 169.4
Costs To Obtain A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	455.0
Capitalization of costs	166.5
Amortization	(157.2)
Ending balance	464.3	455.0
Costs To Fulfill A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	65.4
Capitalization of costs	23.7
Amortization	(23.0)
Ending balance	$ 66.1	$ 65.4

[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 Update ("ASU") No. 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)."