Retirement Benefits and Postemployment Benefits (Schedule of fair values of benefit plan assets and their respective levels in fair value heirarchy) (Details) - USD ($) $ in Millions	May 31, 2020	May 26, 2019	May 27, 2018
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	$ 6,993.2	$ 6,291.6	$ 6,177.4
Defined Benefit Pension Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	1,817.3	1,890.8
Defined Benefit Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	3,500.7	2,780.4
Defined Benefit Pension Plans [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	223.5	239.3
Defined Benefit Pension Plans [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.2	0.3
Defined Benefit Pension Plans [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	180.3	186.5
Defined Benefit Pension Plans [Member] | Assets measured at net asset value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	1,271.2	1,194.3
Defined Benefit Pension Plans [Member] | Fair value measurement of pension plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	5,722.0	5,097.3
Defined Benefit Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	3,276.6	3,227.6
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	1,039.6	1,226.2
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	1,833.3	1,635.5
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	223.4	179.4
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	180.3	186.5
Defined Benefit Pension Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	2,445.2	1,869.4
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	777.7	664.6
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	1,667.4	1,144.9
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.1	59.9
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.2	0.3
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.2	0.3
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	793.5	753.8	$ 726.1
Other Postretirement Benefit Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	46.9	66.8
Other Postretirement Benefit Plans [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	425.9	381.1
Other Postretirement Benefit Plans [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.1	0.3
Other Postretirement Benefit Plans [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	16.7	11.1
Other Postretirement Benefit Plans [Member] | Assets measured at net asset value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	303.9	294.5
Other Postretirement Benefit Plans [Member] | Fair value measurement of pension plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	489.6	459.3
Other Postretirement Benefit Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	174.3	151.1
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	157.5	139.7
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.1	0.3
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	16.7	11.1
Other Postretirement Benefit Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	315.3	308.2
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	46.9	66.8
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	268.4	241.4
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Real asset investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	$ 0.0	$ 0.0