STOCK-BASED COMPENSATION - Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Feb. 28, 2021	Feb. 23, 2020	Feb. 28, 2021	Feb. 23, 2020
Compensation expense
Stock-settled compensation expense	$ 6.3	$ 5.6	$ 17.6	$ 18.2
Cash-settled RSUs				1.0
Total compensation expense	6.3	5.6	17.6	19.2
Income tax benefit	(1.1)	(1.1)	(3.1)	(3.7)
Total compensation expense, net of tax benefit	5.2	4.5	14.5	15.5
Stock-settled restricted stock units
Compensation expense
Stock-settled compensation expense	3.7	3.2	10.4	9.5
Performance shares
Compensation expense
Stock-settled compensation expense	$ 2.6	$ 2.4	$ 7.2	8.6
Stock options
Compensation expense
Stock-settled compensation expense				$ 0.1

Allocated Share-based Compensation Expense, Cash-settled Restricted Stock Units

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Allocated Share-based Compensation Expense, Stock-settled Compensation Expense

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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