Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2022	Aug. 31, 2021
Capitalized Contract Cost [Line Items]
Amortization	$ 53.0	$ 49.1
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	72.3	69.3
Capitalization of costs	7.5	7.1
Amortization	(6.4)	(6.2)
Balance, end of period	73.4	70.2
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	550.2	488.2
Capitalization of costs	57.0	46.6
Amortization	(46.6)	(42.9)
Balance, end of period	$ 560.6	$ 491.9