Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Nov. 30, 2018	Nov. 30, 2018
Costs To Obtain A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	$ 448.5	$ 455.0
Capitalization of costs	37.9	70.3
Amortization	(39.1)	(78.0)
Ending balance	447.3	447.3
Costs To Fulfill A Contract [Member]
Capitalized Contract Cost [Line Items]
Beginning balance	65.7	65.4
Capitalization of costs	5.9	11.9
Amortization	(5.8)	(11.5)
Ending balance	$ 65.8	$ 65.8