Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Feb. 29, 2024	Feb. 28, 2023	Feb. 29, 2024	Feb. 28, 2023
Capitalized Contract Cost [Line Items]
Amortization			$ 173.4	$ 163.0
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 75.8	$ 74.5	75.3	72.3
Capitalization of costs	7.5	8.3	21.2	23.4
Amortization	(6.7)	(6.6)	(19.9)	(19.5)
Balance, end of period	76.6	76.2	76.6	76.2
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	605.0	562.6	597.5	550.2
Capitalization of costs	53.7	65.2	163.1	172.2
Amortization	(51.6)	(48.9)	(153.5)	(143.5)
Balance, end of period	$ 607.1	$ 578.9	$ 607.1	$ 578.9