Summary of Significant Accounting Policies - Treasury Stock (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	May 31, 2022	May 31, 2021	May 31, 2020
Shares repurchased (in shares)	1.0
Treasury Stock
Total increase (decrease) in treasury stock	$ 15.0	$ (8.6)	$ (5.0)
Repurchase of treasury shares	42.4		4.1
Restricted stock activity	8.1	5.6	0.8
Re-issuance of treasury stock upon exercise of stock options, net of shares withheld to satisfy statutory tax obligations	$ 19.3	$ 3.0	$ 8.3