Service Revenue (Summary of Changes in Deferred Costs to Obtain and Fulfill Contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2021	May 31, 2020	May 31, 2019
Capitalized Contract Cost [Line Items]
Amortization	$ 191.4	$ 186.1	$ 180.2
Costs To Fulfill Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	67.3	66.1
Capitalization of costs	26.2	24.9
Amortization	(24.2)	(23.7)
Balance, end of period	69.3	67.3	66.1
Costs To Obtain Contracts [Member]
Capitalized Contract Cost [Line Items]
Balance, beginning of period	473.6	464.3
Capitalization of costs	181.8	171.7
Amortization	(167.2)	(162.4)
Balance, end of period	$ 488.2	$ 473.6	$ 464.3