PENSION AND POSTRETIREMENT BENEFITS - Components of Pension Benefit and Other Postretirement Benefit Costs (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jan. 31, 2020	Feb. 23, 2020	May 31, 2020	May 26, 2019	May 27, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total benefit (income) cost			$ 12.4	$ (16.4)	$ (49.0)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost			11.5	10.9	42.8
Interest cost			118.4	132.6	111.1
Expected return on plan assets			(170.2)	(174.4)	(218.3)
Amortization of prior service cost (benefit)			2.7	3.1	2.9
Recognized net actuarial loss (gain)			44.8	5.1	3.4
Settlement loss (gain)		$ (2.1)	(2.1)		1.3
Curtailment loss (gain)	$ 0.2		0.8		0.7
Total benefit (income) cost			5.9	(22.7)	(56.1)
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost			0.1	0.1	0.2
Interest cost			2.6	3.8	3.9
Amortization of prior service cost (benefit)			(2.1)	(2.2)	(3.4)
Recognized net actuarial loss (gain)			(4.6)	(1.4)
Settlement loss (gain)			(0.2)	(1.0)
Curtailment loss (gain)				(0.6)
Total benefit (income) cost			(4.2)	(1.3)	0.7
Multi-employer plans | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Total benefit (income) cost			$ 6.5	$ 6.3	$ 7.1