Summary of Significant Accounting Policies - Restructuring and Other Exit Costs, Supplemental Information on Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
Supplemental Information on Cash Flows
Interest paid	$ 8.6	$ 8.8	$ 7.2
Income taxes paid	14.3	7.0	17.0
Income tax refunds and interest received	7.0	$ 6.4	$ 0.1
Cost of sales and services and Selling, general and administrative
Restructuring and Other Exit Costs
Severance and furlough-related costs	7.1
Accrued liabilities
Restructuring and Other Exit Costs
Remaining liability for severance and furlough-related costs	$ 5.5