Employee Benefit Plans - Reconciliation of Pension Assets (Details) - Defined Benefit Pension Plans - USD ($) $ in Millions	May 31, 2020	May 31, 2019	May 31, 2018
Employee benefit plans
Fair value of plan assets	$ 131.8	$ 129.9	$ 134.5
Total
Employee benefit plans
Fair value of plan assets	131.8	129.9
U.S. mutual funds | Total
Employee benefit plans
Fair value of plan assets	31.5	31.1
International mutual funds | Total
Employee benefit plans
Fair value of plan assets	7.6	8.4
Government securities and corporate bond mutual funds | Total
Employee benefit plans
Fair value of plan assets	13.1	14.9
Funds-of-funds | Total
Employee benefit plans
Fair value of plan assets	63.1	60.9
Hedge Funds | Total
Employee benefit plans
Fair value of plan assets	4.3	4.2
Insurance Annuities | Total
Employee benefit plans
Fair value of plan assets	11.7	9.9
Cash and cash equivalents | Total
Employee benefit plans
Fair value of plan assets	0.5	0.5
Quoted prices in active markets (Level 1)
Employee benefit plans
Fair value of plan assets	48.0	49.0
Quoted prices in active markets (Level 1) | U.S. mutual funds
Employee benefit plans
Fair value of plan assets	31.5	31.1
Quoted prices in active markets (Level 1) | International mutual funds
Employee benefit plans
Fair value of plan assets	7.6	8.4
Quoted prices in active markets (Level 1) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets	8.4	9.0
Quoted prices in active markets (Level 1) | Cash and cash equivalents
Employee benefit plans
Fair value of plan assets	0.5	0.5
Significant other observable inputs (Level 2)
Employee benefit plans
Fair value of plan assets	59.3	58.9
Significant other observable inputs (Level 2) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets	4.7	5.9
Significant other observable inputs (Level 2) | Funds-of-funds
Employee benefit plans
Fair value of plan assets	54.6	53.0
Significant other unobservable inputs (Level 3)
Employee benefit plans
Fair value of plan assets	24.5	22.0	19.9
Significant other unobservable inputs (Level 3) | Funds-of-funds
Employee benefit plans
Fair value of plan assets	8.5	7.9	7.7
Significant other unobservable inputs (Level 3) | Hedge Funds
Employee benefit plans
Fair value of plan assets	4.3	4.2	4.4
Significant other unobservable inputs (Level 3) | Insurance Annuities
Employee benefit plans
Fair value of plan assets	$ 11.7	$ 9.9	$ 7.8