PENSION AND POSTRETIREMENT BENEFITS - Components of Pension and Postretirement Plan Costs (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 31, 2020	Feb. 23, 2020	May 30, 2021	May 31, 2020	May 26, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total pension and postretirement cost (benefit)			$ (30.9)	$ 12.4	$ (16.4)
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost			11.6	11.5	10.9
Interest cost			86.8	118.4	132.6
Expected return on plan assets			(140.0)	(170.2)	(174.4)
Amortization of prior service cost (benefit)			2.3	2.7	3.1
Recognized net actuarial loss (gain)			0.8	44.8	5.1
Settlement gain		$ (2.1)		(2.1)
Curtailment loss (gain)	$ 0.2		0.2	0.8
Total pension and postretirement cost (benefit)			(38.3)	5.9	(22.7)
Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost			0.2	0.1	0.1
Interest cost			1.5	2.6	3.8
Amortization of prior service cost (benefit)			(2.1)	(2.1)	(2.2)
Recognized net actuarial loss (gain)			(3.5)	(4.6)	(1.4)
Settlement gain			(0.5)	(0.2)	(1.0)
Curtailment loss (gain)					(0.6)
Total pension and postretirement cost (benefit)			(4.4)	(4.2)	(1.3)
Multi-employer plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total pension and postretirement cost (benefit)			$ 7.4	$ 6.5	$ 6.3