PENSION AND POSTRETIREMENT BENEFITS - Schedule of Fair Value of Plan Assets, Summarized by Level (Details) - USD ($) $ in Millions	May 31, 2020	May 26, 2019
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	$ 3,820.4	$ 3,601.5
Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	196.6	150.8
Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	3,382.8	3,204.8
Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Total
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	3,579.4	3,355.6
Measured at net asset value
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	241.0	245.9
Cash and cash equivalents
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	82.0	78.4
Cash and cash equivalents | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	10.1	0.7
Cash and cash equivalents | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	71.9	77.7
Cash and cash equivalents | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
U.S. equity securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	146.1	148.1
U.S. equity securities | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	63.9	56.3
U.S. equity securities | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	82.2	91.8
U.S. equity securities | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
International equity securities
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	93.1	88.2
International equity securities | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	92.4	87.8
International equity securities | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.7	0.4
International equity securities | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Government bonds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	743.9	748.3
Government bonds | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Government bonds | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	743.9	748.3
Government bonds | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Corporate bonds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	2,461.7	2,255.5
Corporate bonds | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Corporate bonds | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	2,461.7	2,255.5
Corporate bonds | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Mortgage-backed bonds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	22.4	31.1
Mortgage-backed bonds | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Mortgage-backed bonds | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	22.4	31.1
Mortgage-backed bonds | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Real estate funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.4
Real estate funds | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.4
Real estate funds | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Real estate funds | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Net receivables for unsettled transactions
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	30.2	5.6
Net receivables for unsettled transactions | Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	30.2	5.6
Net receivables for unsettled transactions | Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	0.0	0.0
Net receivables for unsettled transactions | Level 3
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Total pension plan assets	$ 0.0	$ 0.0