Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	Aug. 31, 2013	May 31, 2013	Aug. 31, 2012	May 31, 2012
CURRENT ASSETS
Cash and cash equivalents	$ 5,096	$ 4,917	$ 2,743	$ 2,843
Receivables, less allowances	4,990	5,044
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	803	780
Deferred income taxes	604	533
Total current assets	11,493	11,274
PROPERTY AND EQUIPMENT, AT COST	38,167	38,109
Less accumulated depreciation and amortization	19,730	19,625
Net property and equipment	18,437	18,484
GOODWILL	2,712	2,755
Other assets	1,031	1,054
ASSETS	33,673	33,567
CURRENT LIABILITIES
Current portion of long-term debt	254	251
Accrued salaries and employee benefits	1,366	1,688
Accounts payable	1,879	1,879
Accrued expenses	2,024	1,932
Total current liabilities	5,523	5,750
LONG-TERM DEBT, LESS CURRENT PORTION	2,739	2,739
OTHER LONG-TERM LIABILITIES
Deferred income taxes	1,820	1,652
Other liabilities	5,936	6,028
Total other long-term liabilities	7,756	7,680
STOCKHOLDERS' INVESTMENT	17,655	17,398
LIABILITIES AND STOCKHOLDERS' INVESTMENT	33,673	33,567
Parent Company Member
CURRENT ASSETS
Cash and cash equivalents	4,058	3,892	1,767	1,906
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	35	45
Total current assets	4,093	3,937
PROPERTY AND EQUIPMENT, AT COST	27	27
Less accumulated depreciation and amortization	21	21
Net property and equipment	6	6
INVESTMENT IN SUBSIDIARIES	19,131	18,739
Other assets	2,156	2,187
ASSETS	25,386	24,869
CURRENT LIABILITIES
Current portion of long-term debt	250	250
Accrued salaries and employee benefits	58	82
Accounts payable	51	4
Accrued expenses	457	355
Total current liabilities	816	691
LONG-TERM DEBT, LESS CURRENT PORTION	2,489	2,489
INTERCOMPANY PAYABLE	1,897	1,642
OTHER LONG-TERM LIABILITIES
Other liabilities	2,529	2,649
Total other long-term liabilities	2,529	2,649
STOCKHOLDERS' INVESTMENT	17,655	17,398
LIABILITIES AND STOCKHOLDERS' INVESTMENT	25,386	24,869
Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	431	405	442	417
Receivables, less allowances	3,993	3,989
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	714	681
Deferred income taxes	589	518
Total current assets	5,727	5,593
PROPERTY AND EQUIPMENT, AT COST	35,912	35,915
Less accumulated depreciation and amortization	18,555	18,469
Net property and equipment	17,357	17,446
INTERCOMPANY RECEIVABLE	711	439
GOODWILL	1,552	1,552
INVESTMENT IN SUBSIDIARIES	3,433	3,347
Other assets	767	822
ASSETS	29,547	29,199
CURRENT LIABILITIES
Current portion of long-term debt	4	1
Accrued salaries and employee benefits	1,132	1,402
Accounts payable	1,389	1,392
Accrued expenses	1,387	1,366
Total current liabilities	3,912	4,161
LONG-TERM DEBT, LESS CURRENT PORTION	250	250
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,883	3,798
Other liabilities	3,166	3,133
Total other long-term liabilities	7,049	6,931
STOCKHOLDERS' INVESTMENT	18,336	17,857
LIABILITIES AND STOCKHOLDERS' INVESTMENT	29,547	29,199
Non Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	723	717	671	636
Receivables, less allowances	1,041	1,084
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	54	54
Deferred income taxes	15	15
Total current assets	1,833	1,870
PROPERTY AND EQUIPMENT, AT COST	2,228	2,167
Less accumulated depreciation and amortization	1,154	1,135
Net property and equipment	1,074	1,032
INTERCOMPANY RECEIVABLE	1,186	1,203
GOODWILL	1,160	1,203
Other assets	228	191
ASSETS	5,481	5,499
CURRENT LIABILITIES
Accrued salaries and employee benefits	176	204
Accounts payable	599	609
Accrued expenses	180	211
Total current liabilities	955	1,024
OTHER LONG-TERM LIABILITIES
Deferred income taxes	57
Other liabilities	241	246
Total other long-term liabilities	298	246
STOCKHOLDERS' INVESTMENT	4,228	4,229
LIABILITIES AND STOCKHOLDERS' INVESTMENT	5,481	5,499
Consolidation Eliminations Member
CURRENT ASSETS
Cash and cash equivalents	(116)	(97)	(137)	(116)
Receivables, less allowances	(44)	(29)
Total current assets	(160)	(126)
INTERCOMPANY RECEIVABLE	(1,897)	(1,642)
INVESTMENT IN SUBSIDIARIES	(22,564)	(22,086)
Other assets	(2,120)	(2,146)
ASSETS	(26,741)	(26,000)
CURRENT LIABILITIES
Accounts payable	(160)	(126)
Total current liabilities	(160)	(126)
INTERCOMPANY PAYABLE	(1,897)	(1,642)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(2,120)	(2,146)
Total other long-term liabilities	(2,120)	(2,146)
STOCKHOLDERS' INVESTMENT	(22,564)	(22,086)
LIABILITIES AND STOCKHOLDERS' INVESTMENT	$ (26,741)	$ (26,000)