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, 2023	Feb. 28, 2022	Feb. 28, 2023	Feb. 28, 2022
Capitalized Contract Cost [Line Items]
Amortization			$ 163.0	$ 150.2
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 74.5	$ 70.5	72.3	69.3
Capitalization of costs	8.3	7.4	23.4	21.0
Amortization	(6.6)	(6.3)	(19.5)	(18.7)
Balance, end of period	76.2	71.6	76.2	71.6
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	562.6	500.5	550.2	488.2
Capitalization of costs	65.2	70.1	172.2	169.1
Amortization	(48.9)	(44.8)	(143.5)	(131.5)
Balance, end of period	$ 578.9	$ 525.8	$ 578.9	$ 525.8