Condensed Consolidating Financial Statements (Details 2) - USD ($) $ in Millions	Aug. 31, 2016	May 31, 2016	Aug. 31, 2015	May 31, 2015
CURRENT ASSETS
Cash and cash equivalents	$ 2,989	$ 3,534	$ 3,543	$ 3,763
Receivables, less allowances	7,233	7,252
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	1,179	1,203
Total current assets	11,401	11,989
PROPERTY AND EQUIPMENT, AT COST	48,121	47,018
Less accumulated depreciation and amortization	23,317	22,734
Net property and equipment	24,804	24,284
Goodwill	6,783	6,747
Other assets	2,587	2,939
ASSETS	45,575	45,959
CURRENT LIABILITIES
Current portion of long-term debt	47	29
Accrued salaries and employee benefits	1,603	1,972
Accounts payable	2,851	2,944
Accrued expenses	2,973	3,063
Total current liabilities	7,474	8,008
LONG-TERM DEBT, LESS CURRENT PORTION	13,735	13,733
OTHER LONG-TERM LIABILITIES
Deferred income taxes	1,762	1,567
Other liabilities	8,462	8,867
Total other long-term liabilities	10,224	10,434
STOCKHOLDERS' INVESTMENT	14,142	13,784
LIABILITIES AND STOCKHOLDERS' INVESTMENT	45,575	45,959
Parent Company Member
CURRENT ASSETS
Cash and cash equivalents	1,308	1,974	2,224	2,383
Receivables, less allowances	1	1
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	74	233
Total current assets	1,383	2,208
PROPERTY AND EQUIPMENT, AT COST	22	22
Less accumulated depreciation and amortization	17	17
Net property and equipment	5	5
INTERCOMPANY RECEIVABLE	2,747	2,437
INVESTMENT IN SUBSIDIARIES	25,493	24,766
Other assets	3,398	3,359
ASSETS	33,026	32,775
CURRENT LIABILITIES
Accrued salaries and employee benefits	38	54
Accounts payable	111	8
Accrued expenses	877	883
Total current liabilities	1,026	945
LONG-TERM DEBT, LESS CURRENT PORTION	13,458	13,451
OTHER LONG-TERM LIABILITIES
Other liabilities	4,400	4,595
Total other long-term liabilities	4,400	4,595
STOCKHOLDERS' INVESTMENT	14,142	13,784
LIABILITIES AND STOCKHOLDERS' INVESTMENT	33,026	32,775
Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	327	326	446	487
Receivables, less allowances	4,517	4,461
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	839	724
Total current assets	5,683	5,511
PROPERTY AND EQUIPMENT, AT COST	44,777	43,760
Less accumulated depreciation and amortization	22,061	21,566
Net property and equipment	22,716	22,194
INTERCOMPANY RECEIVABLE	1,177	1,284
Goodwill	1,571	1,571
INVESTMENT IN SUBSIDIARIES	3,758	3,697
Other assets	858	967
ASSETS	35,763	35,224
CURRENT LIABILITIES
Current portion of long-term debt	29	13
Accrued salaries and employee benefits	1,115	1,377
Accounts payable	1,334	1,501
Accrued expenses	1,368	1,411
Total current liabilities	3,846	4,302
LONG-TERM DEBT, LESS CURRENT PORTION	245	245
OTHER LONG-TERM LIABILITIES
Deferred income taxes	4,645	4,436
Other liabilities	3,420	3,375
Total other long-term liabilities	8,065	7,811
STOCKHOLDERS' INVESTMENT	23,607	22,866
LIABILITIES AND STOCKHOLDERS' INVESTMENT	35,763	35,224
Non Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	1,391	1,277	917	971
Receivables, less allowances	2,760	2,831
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	266	246
Total current assets	4,417	4,354
PROPERTY AND EQUIPMENT, AT COST	3,322	3,236
Less accumulated depreciation and amortization	1,239	1,151
Net property and equipment	2,083	2,085
Goodwill	5,212	5,176
Other assets	1,580	1,851
ASSETS	13,292	13,466
CURRENT LIABILITIES
Current portion of long-term debt	18	16
Accrued salaries and employee benefits	450	541
Accounts payable	1,488	1,519
Accrued expenses	728	769
Total current liabilities	2,684	2,845
LONG-TERM DEBT, LESS CURRENT PORTION	32	37
INTERCOMPANY PAYABLE	3,924	3,721
OTHER LONG-TERM LIABILITIES
Deferred income taxes	366	369
Other liabilities	642	897
Total other long-term liabilities	1,008	1,266
STOCKHOLDERS' INVESTMENT	5,644	5,597
LIABILITIES AND STOCKHOLDERS' INVESTMENT	13,292	13,466
Consolidation Eliminations Member
CURRENT ASSETS
Cash and cash equivalents	(37)	(43)	$ (44)	$ (78)
Receivables, less allowances	(45)	(41)
Total current assets	(82)	(84)
INTERCOMPANY RECEIVABLE	(3,924)	(3,721)
INVESTMENT IN SUBSIDIARIES	(29,251)	(28,463)
Other assets	(3,249)	(3,238)
ASSETS	(36,506)	(35,506)
CURRENT LIABILITIES
Accounts payable	(82)	(84)
Total current liabilities	(82)	(84)
INTERCOMPANY PAYABLE	(3,924)	(3,721)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(3,249)	(3,238)
Total other long-term liabilities	(3,249)	(3,238)
STOCKHOLDERS' INVESTMENT	(29,251)	(28,463)
LIABILITIES AND STOCKHOLDERS' INVESTMENT	$ (36,506)	$ (35,506)