Employee Benefit Plans - Reconciliation of Pension Assets (Details) - Defined Benefit Pension Plans - USD ($) $ in Millions	May 31, 2021	May 31, 2020	May 31, 2019
Employee benefit plans
Fair value of plan assets	$ 158.4	$ 131.8	$ 129.9
U.S. mutual funds | Total
Employee benefit plans
Fair value of plan assets	40.3	31.5
International mutual funds | Total
Employee benefit plans
Fair value of plan assets	11.1	7.6
Government securities and corporate bond mutual funds | Total
Employee benefit plans
Fair value of plan assets	13.3	13.1
Funds-of-funds | Total
Employee benefit plans
Fair value of plan assets	61.3	54.6
Insurance Annuities | Total
Employee benefit plans
Fair value of plan assets	15.6	11.7
Cash and cash equivalents | Total
Employee benefit plans
Fair value of plan assets	0.7	0.5
Total Investments | Total
Employee benefit plans
Fair value of plan assets	142.3	119.0
Total pension plan assets | Total
Employee benefit plans
Fair value of plan assets	158.4	131.8
Quoted prices in active markets (Level 1) | U.S. mutual funds
Employee benefit plans
Fair value of plan assets	40.3	31.5
Quoted prices in active markets (Level 1) | International mutual funds
Employee benefit plans
Fair value of plan assets	11.1	7.6
Quoted prices in active markets (Level 1) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets		8.4
Quoted prices in active markets (Level 1) | Cash and cash equivalents
Employee benefit plans
Fair value of plan assets	0.7	0.5
Quoted prices in active markets (Level 1) | Total Investments
Employee benefit plans
Fair value of plan assets	52.1	48.0
Significant other observable inputs (Level 2) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets	13.3	4.7
Significant other observable inputs (Level 2) | Funds-of-funds
Employee benefit plans
Fair value of plan assets	61.3	54.6
Significant other observable inputs (Level 2) | Total Investments
Employee benefit plans
Fair value of plan assets	74.6	59.3
Significant other unobservable inputs (Level 3) | Insurance Annuities
Employee benefit plans
Fair value of plan assets	15.6	11.7	$ 9.9
Significant other unobservable inputs (Level 3) | Total Investments
Employee benefit plans
Fair value of plan assets	15.6	11.7
Measured at net asset value | Other investments measured at net asset value | Total
Employee benefit plans
Fair value of plan assets	$ 16.1	$ 12.8