Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Aug. 31, 2019	Jun. 01, 2019	May 31, 2019	Aug. 31, 2018	May 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 2,389		$ 2,319	$ 2,369	$ 3,265
Receivables, less allowances	9,312		9,116
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	1,316		1,651
Total current assets	13,017		13,086
PROPERTY AND EQUIPMENT, AT COST	61,436		59,511
Less accumulated depreciation and amortization	29,826		29,082
Net property and equipment	31,610		30,429
OPERATING LEASE RIGHT-OF-USE ASSETS	13,819	$ 14,100
GOODWILL	6,821		6,884
OTHER ASSETS	3,185		4,004
ASSETS	68,452		54,403
CURRENT LIABILITIES
Current portion of long-term debt	35		964
Accrued salaries and employee benefits	1,522		1,741
Accounts payable	3,179		3,030
Operating lease liabilities	1,896
Accrued expenses	3,303		3,278
Total current liabilities	9,935		9,013
LONG-TERM DEBT, LESS CURRENT PORTION	18,726		16,617
OTHER LONG-TERM LIABILITIES
Deferred income taxes	2,953		2,821
Operating lease liabilities	12,137
Other liabilities	6,535		8,195
Total other long-term liabilities	21,625		11,016
COMMON STOCKHOLDERS’ INVESTMENT	18,166		17,757	19,173
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	68,452		54,403
Consolidation Eliminations [Member]
CURRENT ASSETS
Cash and cash equivalents	(69)		(46)	(42)	(15)
Receivables, less allowances	(139)		(227)
Total current assets	(208)		(273)
INTERCOMPANY RECEIVABLE	(3,075)		(2,472)
INVESTMENT IN SUBSIDIARIES	(39,409)		(39,174)
OTHER ASSETS	(552)		(591)
ASSETS	(43,244)		(42,510)
CURRENT LIABILITIES
Accounts payable	(203)		(263)
Accrued expenses	(6)		(10)
Total current liabilities	(209)		(273)
INTERCOMPANY PAYABLE	(3,074)		(2,472)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(552)		(591)
Total other long-term liabilities	(552)		(591)
COMMON STOCKHOLDERS’ INVESTMENT	(39,409)		(39,174)
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	(43,244)		(42,510)
Parent Company [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	684		826	938	1,485
Receivables, less allowances	335		56
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	40		366
Total current assets	1,059		1,248
PROPERTY AND EQUIPMENT, AT COST	26		25
Less accumulated depreciation and amortization	17		17
Net property and equipment	9		8
INTERCOMPANY RECEIVABLE	3,003		2,877
OPERATING LEASE RIGHT-OF-USE ASSETS	32
INVESTMENT IN SUBSIDIARIES	34,439		33,725
OTHER ASSETS	984		995
ASSETS	39,526		38,853
CURRENT LIABILITIES
Current portion of long-term debt			959
Accrued salaries and employee benefits	91		143
Accounts payable	191		16
Operating lease liabilities	4
Accrued expenses	512		521
Total current liabilities	798		1,639
LONG-TERM DEBT, LESS CURRENT PORTION	18,395		16,322
OTHER LONG-TERM LIABILITIES
Operating lease liabilities	30
Other liabilities	2,137		3,135
Total other long-term liabilities	2,167		3,135
COMMON STOCKHOLDERS’ INVESTMENT	18,166		17,757
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	39,526		38,853
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	176		158	180	257
Receivables, less allowances	5,575		5,603
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	949		953
Total current assets	6,700		6,714
PROPERTY AND EQUIPMENT, AT COST	57,131		55,341
Less accumulated depreciation and amortization	27,715		27,066
Net property and equipment	29,416		28,275
INTERCOMPANY RECEIVABLE	72		(405)
OPERATING LEASE RIGHT-OF-USE ASSETS	11,538
GOODWILL	1,582		1,589
INVESTMENT IN SUBSIDIARIES	4,970		5,449
OTHER ASSETS	1,019		1,811
ASSETS	55,297		43,433
CURRENT LIABILITIES
Current portion of long-term debt	26		2
Accrued salaries and employee benefits	985		1,100
Accounts payable	1,444		1,469
Operating lease liabilities	1,445
Accrued expenses	1,895		1,853
Total current liabilities	5,795		4,424
LONG-TERM DEBT, LESS CURRENT PORTION	286		287
OTHER LONG-TERM LIABILITIES
Deferred income taxes	2,929		2,832
Operating lease liabilities	10,257
Other liabilities	3,390		3,965
Total other long-term liabilities	16,576		6,797
COMMON STOCKHOLDERS’ INVESTMENT	32,640		31,925
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	55,297		43,433
Non-guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	1,598		1,381	$ 1,293	$ 1,538
Receivables, less allowances	3,541		3,684
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	327		332
Total current assets	5,466		5,397
PROPERTY AND EQUIPMENT, AT COST	4,279		4,145
Less accumulated depreciation and amortization	2,094		1,999
Net property and equipment	2,185		2,146
OPERATING LEASE RIGHT-OF-USE ASSETS	2,249
GOODWILL	5,239		5,295
OTHER ASSETS	1,734		1,789
ASSETS	16,873		14,627
CURRENT LIABILITIES
Current portion of long-term debt	9		3
Accrued salaries and employee benefits	446		498
Accounts payable	1,747		1,808
Operating lease liabilities	447
Accrued expenses	902		914
Total current liabilities	3,551		3,223
LONG-TERM DEBT, LESS CURRENT PORTION	45		8
INTERCOMPANY PAYABLE	3,074		2,472
OTHER LONG-TERM LIABILITIES
Deferred income taxes	576		580
Operating lease liabilities	1,850
Other liabilities	1,008		1,095
Total other long-term liabilities	3,434		1,675
COMMON STOCKHOLDERS’ INVESTMENT	6,769		7,249
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	$ 16,873		$ 14,627