Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Capitalized Contract Cost [Line Items]
Amortization			$ 143.0	$ 139.1
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 468.1	$ 456.9	473.6	464.3
Capitalization of costs	49.9	49.4	127.5	122.7
Amortization	(41.9)	(40.7)	(125.0)	(121.4)
Balance, end of period	476.1	465.6	476.1	465.6
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	67.4	66.4	67.3	66.1
Capitalization of costs	7.2	6.7	19.3	18.7
Amortization	(6.0)	(6.0)	(18.0)	(17.7)
Balance, end of period	$ 68.6	$ 67.1	$ 68.6	$ 67.1