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 27, 2018	May 28, 2017	May 29, 2016
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		$ 6,177.4	$ 5,925.2	$ 5,539.9
Defined Benefit Pension Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	2,504.6	2,554.2
Defined Benefit Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	1,979.0	1,694.1
Defined Benefit Pension Plans [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	344.3	348.9
Defined Benefit Pension Plans [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	0.3	0.3
Defined Benefit Pension Plans [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		124.4	174.2
Defined Benefit Pension Plans [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		4,952.6	4,771.7
Defined Benefit Pension Plans [Member] | Investments measured at net asset value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[5]	1,224.8	1,153.5
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	1,722.5	1,773.0
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	1,264.5	951.9
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	229.1	253.1
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	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		124.4	174.2
Defined Benefit Pension Plans [Member] | Level 1 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		3,340.5	3,152.2
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	782.1	781.2
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	714.5	742.2
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	115.2	95.8
Defined Benefit Pension Plans [Member] | Level 2 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	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 2 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		1,611.8	1,619.2
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	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	[2]	0.0	0.0
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	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	[4]	0.3	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
Defined Benefit Pension Plans [Member] | Level 3 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		0.3	0.3
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		726.1	694.8	$ 602.4
Other Postretirement Benefit Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	35.8	189.8
Other Postretirement Benefit Plans [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	364.6	194.1
Other Postretirement Benefit Plans [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	8.0	32.5
Other Postretirement Benefit Plans [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	0.0	0.0
Other Postretirement Benefit Plans [Member] | Cash and accruals [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		19.1	11.3
Other Postretirement Benefit Plans [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		427.5	427.7
Other Postretirement Benefit Plans [Member] | Investments measured at net asset value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[5]	298.6	267.1
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	0.0	122.3
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	241.0	34.1
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	8.0	18.0
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	0.0	0.0
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		19.1	11.3
Other Postretirement Benefit Plans [Member] | Level 1 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		268.1	185.7
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	35.8	67.5
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Fixed income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[2]	123.6	160.0
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	0.0	14.5
Other Postretirement Benefit Plans [Member] | Level 2 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	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 2 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		159.4	242.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[1]	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	[2]	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Real assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[3]	0.0	0.0
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Other investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets	[4]	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
Other Postretirement Benefit Plans [Member] | Level 3 [Member] | Total fair value measurement of plan assets in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value measurement of pension plan assets		$ 0.0	$ 0.0

[1] Primarily publicly traded common stock for purposes of total return and to maintain equity exposure consistent with policy allocations. Investments include: United States and international equity securities, mutual funds, and equity futures valued at closing prices from national exchanges, and commingled funds valued at unit values provided by the investment managers, which are based on the fair value of the underlying investments

[2] Primarily government and corporate debt securities and futures for purposes of total return, managing fixed income exposure to policy allocations, and managing duration targets. Investments include: fixed income securities an d bond futures generally valued at closing prices from national exchanges, fixed income pricing models, and independent financial analysts; and fixed income commingled funds valued at unit values provided by the investment managers, which are based on the fair value of the underlying investments.

[3] Publicly traded common stock and limited partnerships in the energy and real estate sectors for purposes of total return. Investments include: energy and real estate securities generally valued at closing pri ces from national exchanges, and commingled funds valued at unit values provided by the investment managers, which are based on the fair value of the underlying investments.

[4] Global balanced fund of equity, fixed income, and real estate securities fo r purposes of meeting Canadian pension plan asset allocation policies, and insurance and annuity contracts to provide a stable stream of income for retirees and to fund postretirement medical benefits. Fair values are derived from unit values provided by t he investment managers, which are generally based on the fair value of the underlying investments and contract fair values from the providers.

[5] Primarily private investments and common collective trusts that are measured at fair value using the net asse t value per share (or its equivalent) practical expedient and have not been classified in the fair value hierarchy.