Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Millions	Feb. 29, 2020	Jun. 01, 2019	May 31, 2019	Feb. 28, 2019	May 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 1,766		$ 2,319	$ 2,872	$ 3,265
Receivables, less allowances	9,323		9,116
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	1,452		1,651
Total current assets	12,541		13,086
PROPERTY AND EQUIPMENT, AT COST	64,305		59,511
Less accumulated depreciation and amortization	30,999		29,082
Net property and equipment	33,306		30,429
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	13,981	$ 14,100
GOODWILL	6,814		6,884
OTHER ASSETS	3,372		4,004
ASSETS	70,014		54,403
CURRENT LIABILITIES
Short-term borrowings	300
Current portion of long-term debt	35		964
Accrued salaries and employee benefits	1,472		1,741
Accounts payable	3,193		3,030
Operating lease liabilities	1,902
Accrued expenses	3,423		3,278
Total current liabilities	10,325		9,013
LONG-TERM DEBT, LESS CURRENT PORTION	18,973		16,617
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,101		2,821
Operating lease liabilities	12,232
Other liabilities	6,552		8,195
Total other long-term liabilities	21,885		11,016
COMMON STOCKHOLDERS’ INVESTMENT	18,831		17,757	19,894
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	70,014		54,403
Consolidation Eliminations [Member]
CURRENT ASSETS
Cash and cash equivalents	(16)		(46)	(41)	(15)
Receivables, less allowances	(85)		(227)
Total current assets	(101)		(273)
INTERCOMPANY RECEIVABLE	(3,213)		(2,472)
INVESTMENT IN SUBSIDIARIES	(40,427)		(39,174)
OTHER ASSETS	(487)		(591)
ASSETS	(44,228)		(42,510)
CURRENT LIABILITIES
Accounts payable	(100)		(263)
Accrued expenses	(1)		(10)
Total current liabilities	(101)		(273)
INTERCOMPANY PAYABLE	(3,213)		(2,472)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(487)		(591)
Total other long-term liabilities	(487)		(591)
COMMON STOCKHOLDERS’ INVESTMENT	(40,427)		(39,174)
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	(44,228)		(42,510)
Parent Company [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	246		826	1,413	1,485
Receivables, less allowances	71		56
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	207		366
Total current assets	524		1,248
PROPERTY AND EQUIPMENT, AT COST	28		25
Less accumulated depreciation and amortization	18		17
Net property and equipment	10		8
INTERCOMPANY RECEIVABLE	3,349		2,877
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	38
INVESTMENT IN SUBSIDIARIES	35,407		33,725
OTHER ASSETS	962		995
ASSETS	40,290		38,853
CURRENT LIABILITIES
Short-term borrowings	300
Current portion of long-term debt			959
Accrued salaries and employee benefits	87		143
Accounts payable	194		16
Operating lease liabilities	4
Accrued expenses	416		521
Total current liabilities	1,001		1,639
LONG-TERM DEBT, LESS CURRENT PORTION	18,298		16,322
OTHER LONG-TERM LIABILITIES
Operating lease liabilities	36
Other liabilities	2,124		3,135
Total other long-term liabilities	2,160		3,135
COMMON STOCKHOLDERS’ INVESTMENT	18,831		17,757
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	40,290		38,853
Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	203		158	204	257
Receivables, less allowances	5,752		5,603
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	895		953
Total current assets	6,850		6,714
PROPERTY AND EQUIPMENT, AT COST	59,777		55,341
Less accumulated depreciation and amortization	28,761		27,066
Net property and equipment	31,016		28,275
INTERCOMPANY RECEIVABLE	(136)		(405)
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	11,715
GOODWILL	1,587		1,589
INVESTMENT IN SUBSIDIARIES	5,020		5,449
OTHER ASSETS	1,134		1,811
ASSETS	57,186		43,433
CURRENT LIABILITIES
Current portion of long-term debt	27		2
Accrued salaries and employee benefits	975		1,100
Accounts payable	1,554		1,469
Operating lease liabilities	1,435
Accrued expenses	2,033		1,853
Total current liabilities	6,024		4,424
LONG-TERM DEBT, LESS CURRENT PORTION	634		287
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,016		2,832
Operating lease liabilities	10,378
Other liabilities	3,473		3,965
Total other long-term liabilities	16,867		6,797
COMMON STOCKHOLDERS’ INVESTMENT	33,661		31,925
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	57,186		43,433
Non-guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
CURRENT ASSETS
Cash and cash equivalents	1,333		1,381	$ 1,296	$ 1,538
Receivables, less allowances	3,585		3,684
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	350		332
Total current assets	5,268		5,397
PROPERTY AND EQUIPMENT, AT COST	4,500		4,145
Less accumulated depreciation and amortization	2,220		1,999
Net property and equipment	2,280		2,146
OPERATING LEASE RIGHT-OF-USE ASSETS, NET	2,228
GOODWILL	5,227		5,295
OTHER ASSETS	1,763		1,789
ASSETS	16,766		14,627
CURRENT LIABILITIES
Current portion of long-term debt	8		3
Accrued salaries and employee benefits	410		498
Accounts payable	1,545		1,808
Operating lease liabilities	463
Accrued expenses	975		914
Total current liabilities	3,401		3,223
LONG-TERM DEBT, LESS CURRENT PORTION	41		8
INTERCOMPANY PAYABLE	3,213		2,472
OTHER LONG-TERM LIABILITIES
Deferred income taxes	572		580
Operating lease liabilities	1,818
Other liabilities	955		1,095
Total other long-term liabilities	3,345		1,675
COMMON STOCKHOLDERS’ INVESTMENT	6,766		7,249
LIABILITIES AND COMMON STOCKHOLDERS' INVESTMENT	$ 16,766		$ 14,627