Stock Plans (Narrative) (Details) $ in Millions	9 Months Ended
	Feb. 28, 2021 USD ($)
Share-based Compensation Allocation and Classification in Financial Statements [Abstract]
Unrecognized compensation expense related to non-vested stock options, restricted stock, and performance share units	$ 123.2
Unrecognized compensation expense on non-vested awards weighted average period of recognition	21 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Method Used	We estimate the fair value of each stock option on the grant date using a Black-Scholes option-pricing model. Black-Scholes option-pricing models require us to make predictive assumptions regarding future stock price volatility, employee exercise behavior, and dividend yield. We estimate our future stock price volatility using the historical volatility over the expected term of the option, excluding time periods of volatility we believe a marketplace participant would exclude in estimating our stock price volatility. We also have considered, but did not use, implied volatility in our estimate, because trading activity in options on our stock, especially those with tenors of greater than 6 months, is insufficient to provide a reliable measure of expected volatility. Our method of selecting the other valuation assumptions is explained in Note 12 to the Consolidated Financial Statements included in our Annual Report on Form 10-K for the fiscal year ended May 31, 2020.