Retirement Plans - Reconciliation of Changes In Pension And Postretirement Healthcare Plans Benefit Obligations And Fair Value Of Assets (Details) - USD ($) $ in Millions	12 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2018
U.S. Plans [Member]
Changes in PBO and Accumulated Postretirement Benefit Obligation (“APBO”)
Service cost	$ 768
Interest cost	1,000
Change in Plan Assets
Company contributions	1,000	$ 1,000
Pension Plans [Member]
Changes in PBO and Accumulated Postretirement Benefit Obligation (“APBO”)
PBO/APBO at the beginning of year	28,855
PBO/APBO at the end of year	32,441	28,855
Change in Plan Assets
Balance at beginning of year	24,898
Balance at end of year	28,691	24,898
Funded Status of the Plans	(3,750)	(3,957)
Pension Plans [Member] | U.S. Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation (“ABO”)	29,272	25,915
Changes in PBO and Accumulated Postretirement Benefit Obligation (“APBO”)
PBO/APBO at the beginning of year	26,554	22,653
Service cost	768	689	$ 679
Interest cost	1,000	951	1,115
Actuarial loss (gain)	2,817	3,016
Benefits paid	(940)	(755)
PBO/APBO at the end of year	30,199	26,554	22,653
Change in Plan Assets
Balance at beginning of year	23,320	22,057
Actual return on plan assets	3,530	984
Company contributions	1,068	1,034
Benefits paid	(940)	(755)
Balance at end of year	26,978	23,320	22,057
Funded Status of the Plans	(3,221)	(3,234)
Amount Recognized in the Balance Sheet at May 31:
Current pension, postretirement healthcare and other benefit obligations	(38)	(70)
Noncurrent pension, postretirement healthcare and other benefit obligations	(3,183)	(3,164)
Net amount recognized	(3,221)	(3,234)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost:
Prior service (credit) cost and other	(68)	(173)
Pension Plans [Member] | International Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation (“ABO”)	2,012	2,084
Changes in PBO and Accumulated Postretirement Benefit Obligation (“APBO”)
PBO/APBO at the beginning of year	2,301	2,167
Service cost	96	94	97
Interest cost	43	49	49
Actuarial loss (gain)	(87)	127
Benefits paid	(41)	(38)
Settlements	(6)	(13)
Other	(64)	(85)
PBO/APBO at the end of year	2,242	2,301	2,167
Change in Plan Assets
Balance at beginning of year	1,578	1,509
Actual return on plan assets	146	94
Company contributions	86	91
Benefits paid	(41)	(38)
Settlements	(6)	(13)
Other	(50)	(65)
Balance at end of year	1,713	1,578	1,509
Funded Status of the Plans	(529)	(723)
Amount Recognized in the Balance Sheet at May 31:
Noncurrent asset	142	82
Current pension, postretirement healthcare and other benefit obligations	(17)	(16)
Noncurrent pension, postretirement healthcare and other benefit obligations	(654)	(789)
Net amount recognized	(529)	(723)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost:
Prior service (credit) cost and other	(7)	(6)
Postretirement Healthcare Plans [Member]
Changes in PBO and Accumulated Postretirement Benefit Obligation (“APBO”)
PBO/APBO at the beginning of year	1,221	955
Service cost	42	35	36
Interest cost	44	40	39
Actuarial loss (gain)	85	266
Benefits paid	(127)	(123)
Other	49	48
PBO/APBO at the end of year	1,314	1,221	$ 955
Change in Plan Assets
Company contributions	77	73
Benefits paid	(127)	(123)
Other	50	50
Funded Status of the Plans	(1,314)	(1,221)
Amount Recognized in the Balance Sheet at May 31:
Current pension, postretirement healthcare and other benefit obligations	(104)	(87)
Noncurrent pension, postretirement healthcare and other benefit obligations	(1,210)	(1,134)
Net amount recognized	(1,314)	(1,221)
Amounts Recognized in AOCI and not yet reflected in Net Periodic Benefit Cost:
Prior service (credit) cost and other	$ 1	$ 1