Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Nov. 30, 2019	Jun. 01, 2019	May 31, 2019	Nov. 30, 2018	May 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 2,031		$ 2,319	$ 2,123	$ 3,265
Receivables, less allowances	9,709		9,116
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	1,458		1,651
Total current assets	13,198		13,086
PROPERTY AND EQUIPMENT, AT COST	62,715		59,511
Less accumulated depreciation and amortization	30,307		29,082
Net property and equipment	32,408		30,429
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	14,097	$ 14,100
GOODWILL	6,861		6,884
OTHER ASSETS	3,390		4,004
ASSETS	69,954		54,403
CURRENT LIABILITIES
Short-term borrowings	150
Current portion of long-term debt	16		964
Accrued salaries and employee benefits	1,632		1,741
Accounts payable	3,283		3,030
Operating lease liabilities	1,928
Accrued expenses	3,538		3,278
Total current liabilities	10,547		9,013
LONG-TERM DEBT, LESS CURRENT PORTION	18,691		16,617
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,072		2,821
Operating lease liabilities	12,432
Other liabilities	6,553		8,195
Total other long-term liabilities	22,057		11,016
COMMON STOCKHOLDERS’ INVESTMENT	18,659		17,757	19,294
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	69,954		54,403
Consolidation Eliminations [Member]
CURRENT ASSETS
Cash and cash equivalents	(9)		(46)	(62)	(15)
Receivables, less allowances	(99)		(227)
Total current assets	(108)		(273)
INTERCOMPANY RECEIVABLE	(3,181)		(2,472)
INVESTMENT IN SUBSIDIARIES	(40,068)		(39,174)
OTHER ASSETS	(524)		(591)
ASSETS	(43,881)		(42,510)
CURRENT LIABILITIES
Accounts payable	(106)		(263)
Accrued expenses	(2)		(10)
Total current liabilities	(108)		(273)
INTERCOMPANY PAYABLE	(3,181)		(2,472)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(524)		(591)
Total other long-term liabilities	(524)		(591)
COMMON STOCKHOLDERS’ INVESTMENT	(40,068)		(39,174)
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	(43,881)		(42,510)
Parent Company [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	394		826	688	1,485
Receivables, less allowances	348		56
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	128		366
Total current assets	870		1,248
PROPERTY AND EQUIPMENT, AT COST	27		25
Less accumulated depreciation and amortization	17		17
Net property and equipment	10		8
INTERCOMPANY RECEIVABLE	3,181		2,877
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	39
INVESTMENT IN SUBSIDIARIES	35,086		33,725
OTHER ASSETS	953		995
ASSETS	40,139		38,853
CURRENT LIABILITIES
Short-term borrowings	150
Current portion of long-term debt			959
Accrued salaries and employee benefits	87		143
Accounts payable	192		16
Operating lease liabilities	4
Accrued expenses	509		521
Total current liabilities	942		1,639
LONG-TERM DEBT, LESS CURRENT PORTION	18,362		16,322
OTHER LONG-TERM LIABILITIES
Operating lease liabilities	37
Other liabilities	2,139		3,135
Total other long-term liabilities	2,176		3,135
COMMON STOCKHOLDERS’ INVESTMENT	18,659		17,757
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	40,139		38,853
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	236		158	187	257
Receivables, less allowances	5,698		5,603
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	932		953
Total current assets	6,866		6,714
PROPERTY AND EQUIPMENT, AT COST	58,286		55,341
Less accumulated depreciation and amortization	28,139		27,066
Net property and equipment	30,147		28,275
INTERCOMPANY RECEIVABLE			(405)
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	11,844
GOODWILL	1,587		1,589
INVESTMENT IN SUBSIDIARIES	4,982		5,449
OTHER ASSETS	1,141		1,811
ASSETS	56,567		43,433
CURRENT LIABILITIES
Current portion of long-term debt	5		2
Accrued salaries and employee benefits	1,058		1,100
Accounts payable	1,505		1,469
Operating lease liabilities	1,476
Accrued expenses	2,023		1,853
Total current liabilities	6,067		4,424
LONG-TERM DEBT, LESS CURRENT PORTION	286		287
INTERCOMPANY PAYABLE	58
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,013		2,832
Operating lease liabilities	10,577
Other liabilities	3,439		3,965
Total other long-term liabilities	17,029		6,797
COMMON STOCKHOLDERS’ INVESTMENT	33,127		31,925
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	56,567		43,433
Non-guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	1,410		1,381	$ 1,310	$ 1,538
Receivables, less allowances	3,762		3,684
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	398		332
Total current assets	5,570		5,397
PROPERTY AND EQUIPMENT, AT COST	4,402		4,145
Less accumulated depreciation and amortization	2,151		1,999
Net property and equipment	2,251		2,146
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	2,214
GOODWILL	5,274		5,295
OTHER ASSETS	1,820		1,789
ASSETS	17,129		14,627
CURRENT LIABILITIES
Current portion of long-term debt	11		3
Accrued salaries and employee benefits	487		498
Accounts payable	1,692		1,808
Operating lease liabilities	448
Accrued expenses	1,008		914
Total current liabilities	3,646		3,223
LONG-TERM DEBT, LESS CURRENT PORTION	43		8
INTERCOMPANY PAYABLE	3,123		2,472
OTHER LONG-TERM LIABILITIES
Deferred income taxes	583		580
Operating lease liabilities	1,818
Other liabilities	975		1,095
Total other long-term liabilities	3,376		1,675
COMMON STOCKHOLDERS’ INVESTMENT	6,941		7,249
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	$ 17,129		$ 14,627