Supplemental Cash Flow Information (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Income taxes paid	$ 298.8	$ 317.9	$ 319.1
Interest expense paid	$ 38.0	$ 10.4	4.0
Common stock issued in connection to acquisition			33.2
HR Outsourcing Holdings, Inc. [Member]
Common stock issued in connection to acquisition			$ 33.2