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, 2022	Feb. 28, 2021	Feb. 28, 2022	Feb. 28, 2021
Capitalized Contract Cost [Line Items]
Amortization			$ 150.2	$ 143.0
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	$ 70.5	$ 67.4	69.3	67.3
Capitalization of costs	7.4	7.2	21.0	19.3
Amortization	(6.3)	(6.0)	(18.7)	(18.0)
Balance, end of period	71.6	68.6	71.6	68.6
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	500.5	468.1	488.2	473.6
Capitalization of costs	70.1	49.9	169.1	127.5
Amortization	(44.8)	(41.9)	(131.5)	(125.0)
Balance, end of period	$ 525.8	$ 476.1	$ 525.8	$ 476.1