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, 2021	Nov. 30, 2020	Nov. 30, 2021	Nov. 30, 2020
Capitalized Contract Cost [Line Items]
Amortization			$ 99.1	$ 95.1
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 70.2	$ 67.5	69.3	67.3
Capitalization of costs	6.5	6.0	13.6	12.1
Amortization	(6.2)	(6.1)	(12.4)	(12.0)
Balance, end of period	70.5	67.4	70.5	67.4
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	491.9	469.4	488.2	473.6
Capitalization of costs	52.4	40.4	99.0	77.6
Amortization	(43.8)	(41.7)	(86.7)	(83.1)
Balance, end of period	$ 500.5	$ 468.1	$ 500.5	$ 468.1