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, 2022	Nov. 30, 2021	Nov. 30, 2022	Nov. 30, 2021
Capitalized Contract Cost [Line Items]
Amortization			$ 107.5	$ 99.1
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 73.4	$ 70.2	72.3	69.3
Capitalization of costs	7.6	6.5	15.1	13.6
Amortization	(6.5)	(6.2)	(12.9)	(12.4)
Balance, end of period	74.5	70.5	74.5	70.5
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	560.6	491.9	550.2	488.2
Capitalization of costs	50.0	52.4	107.0	99.0
Amortization	(48.0)	(43.8)	(94.6)	(86.7)
Balance, end of period	$ 562.6	$ 500.5	$ 562.6	$ 500.5