Employee Benefit Plans - Reconciliation of Pension Assets (Details) - Defined Benefit Pension Plans - USD ($) $ in Millions	May 31, 2019	May 31, 2018	May 31, 2017
Employee benefit plans
Fair value of plan assets	$ 129.9	$ 134.5	$ 118.8
Total
Employee benefit plans
Fair value of plan assets	129.9	134.5
U.S. mutual funds | Total
Employee benefit plans
Fair value of plan assets	31.1	32.8
International mutual funds | Total
Employee benefit plans
Fair value of plan assets	8.4	10.4
Government securities and corporate bond mutual funds | Total
Employee benefit plans
Fair value of plan assets	14.9	15.7
Funds-of-funds | Total
Employee benefit plans
Fair value of plan assets	60.9	61.3
Hedge funds | Total
Employee benefit plans
Fair value of plan assets	4.2	4.4
Insurance annuities | Total
Employee benefit plans
Fair value of plan assets	9.9	7.8
Cash and cash equivalents | Total
Employee benefit plans
Fair value of plan assets	0.5	2.1
Quoted prices in active markets (Level 1)
Employee benefit plans
Fair value of plan assets	49.0	61.0
Quoted prices in active markets (Level 1) | U.S. mutual funds
Employee benefit plans
Fair value of plan assets	31.1	32.8
Quoted prices in active markets (Level 1) | International mutual funds
Employee benefit plans
Fair value of plan assets	8.4	10.4
Quoted prices in active markets (Level 1) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets	9.0	15.7
Quoted prices in active markets (Level 1) | Cash and cash equivalents
Employee benefit plans
Fair value of plan assets	0.5	2.1
Significant other observable inputs (Level 2)
Employee benefit plans
Fair value of plan assets	58.9	53.6
Significant other observable inputs (Level 2) | Government securities and corporate bond mutual funds
Employee benefit plans
Fair value of plan assets	5.9
Significant other observable inputs (Level 2) | Funds-of-funds
Employee benefit plans
Fair value of plan assets	53.0	53.6
Significant other unobservable inputs (Level 3)
Employee benefit plans
Fair value of plan assets	22.0	19.9	14.1
Significant other unobservable inputs (Level 3) | Funds-of-funds
Employee benefit plans
Fair value of plan assets	7.9	7.7	7.3
Significant other unobservable inputs (Level 3) | Hedge funds
Employee benefit plans
Fair value of plan assets	4.2	4.4	$ 6.8
Significant other unobservable inputs (Level 3) | Insurance annuities
Employee benefit plans
Fair value of plan assets	$ 9.9	$ 7.8