PENSION AND POSTRETIREMENT BENEFITS - Components of Pension Benefit and Other Postretirement Benefit Costs (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 31, 2020	Feb. 23, 2020	Feb. 24, 2019	Feb. 23, 2020	Feb. 24, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total benefit cost (benefit)		$ (11.1)	$ (5.7)	$ (20.8)	$ (16.1)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost		2.8	2.8	8.4	8.3
Interest cost		27.8	34.0	89.8	98.7
Expected return on plan assets		(42.0)	(44.6)	(124.7)	(130.1)
Amortization of prior service cost		0.7	0.7	2.0	2.1
Curtailment loss	$ 0.2	0.2	0.0	0.8	0.0
Settlement gain		(2.1)	0.0	(2.1)	0.0
Total benefit cost (benefit)		(12.6)	(7.1)	(25.8)	(21.0)
Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost		0.0	0.0	0.1	0.1
Interest cost		0.6	1.0	1.9	2.9
Amortization of prior service cost		(0.5)	(0.5)	(1.5)	(1.5)
Recognized net actuarial gain		(1.1)	(0.4)	(3.4)	(1.2)
Curtailment loss		0.0	0.0	0.0	(0.6)
Total benefit cost (benefit)		(1.0)	0.1	(2.9)	(0.3)
Multi-employer plans | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total benefit cost (benefit)		$ 1.5	$ 1.4	$ 5.0	$ 4.9