PENSION AND POSTRETIREMENT BENEFITS - Components of Pension and Other Postretirement Costs (Benefit) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 31, 2020	Feb. 28, 2021	Feb. 23, 2020	Feb. 28, 2021	Feb. 23, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total pension cost (benefit)		$ (8.4)	$ (11.1)	$ (23.5)	$ (20.8)
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost		2.7	2.8	9.0	8.4
Interest cost		21.7	27.8	65.1	89.8
Expected return on plan assets		(35.0)	(42.0)	(105.0)	(124.7)
Amortization of prior service cost (benefit)		0.5	0.7	1.7	2.0
Curtailment loss (gain)	$ 0.2	0.0	0.2	0.0	0.8
Settlement gain		0.0	2.1	0.0	2.1
Total pension cost (benefit)		(10.1)	(12.6)	(29.2)	(25.8)
Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost		0.0	0.0	0.1	0.1
Interest cost		0.4	0.6	1.1	1.9
Amortization of prior service cost (benefit)		(0.5)	(0.5)	(1.5)	(1.5)
Recognized net actuarial gain		(0.8)	(1.1)	(2.6)	(3.4)
Total pension cost (benefit)		(0.9)	(1.0)	(2.9)	(2.9)
Multi-employer plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total pension cost (benefit)		$ 1.7	$ 1.5	$ 5.7	$ 5.0