Fair Value Measurements - Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Millions	Nov. 30, 2019	Jun. 01, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments, cost	$ 8.8	$ 8.7
Total investments, unrealized gain/(loss)	0.2	0.1
Total investments, market value	9.0	8.8
Mutual funds - fixed income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds - fixed income, cost	8.0	7.9
Mutual funds - fixed income, unrealized gain/(loss)	0.1	0.0
Mutual funds - fixed income, market value	8.1	7.9
Mutual funds - equity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mutual funds - equity, cost	0.8	0.8
Mutual funds - equity, unrealized gain/(loss)	0.1	0.1
Mutual funds - equity, market value	$ 0.9	$ 0.9