Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	Nov. 30, 2012	May 31, 2012	Nov. 30, 2011	May 31, 2011
CURRENT ASSETS
Cash and cash equivalents	$ 2,517	$ 2,843	$ 1,896	$ 2,328
Receivables, less allowances	5,202	4,704
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	930	976
Deferred income taxes	510	533
Total current assets	9,159	9,056
PROPERTY AND EQUIPMENT, AT COST	37,749	36,164
Less accumulated depreciation and amortization	19,400	18,916
Net property and equipment	18,349	17,248
GOODWILL	2,757	2,387
Other assets	1,047	1,212
ASSETS	31,312	29,903
CURRENT LIABILITIES
Current portion of long-term debt	1	417
Accrued salaries and employee benefits	1,297	1,635
Accounts payable	1,730	1,613
Accrued expenses	1,800	1,709
Total current liabilities	4,828	5,374
LONG-TERM DEBT, LESS CURRENT PORTION	2,241	1,250
OTHER LONG-TERM LIABILITIES
Deferred income taxes	973	836
Other liabilities	7,727	7,716
Total other long-term liabilities	8,700	8,552
STOCKHOLDERS' INVESTMENT	15,543	14,727
LIABILITIES AND STOCKHOLDERS' INVESTMENT	31,312	29,903
Parent Company Member
CURRENT ASSETS
Cash and cash equivalents	1,715	1,906	1,000	1,589
Receivables, less allowances		3
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	162	261
Total current assets	1,877	2,170
PROPERTY AND EQUIPMENT, AT COST	26	29
Less accumulated depreciation and amortization	20	20
Net property and equipment	6	9
INVESTMENT IN SUBSIDIARIES	18,069	17,163
Other assets	2,781	2,845
ASSETS	22,733	22,187
CURRENT LIABILITIES
Accrued salaries and employee benefits	66	83
Accounts payable	46	6
Accrued expenses	216	184
Total current liabilities	328	273
LONG-TERM DEBT, LESS CURRENT PORTION	1,991	1,000
INTERCOMPANY PAYABLE	697	1,847
OTHER LONG-TERM LIABILITIES
Other liabilities	4,174	4,340
Total other long-term liabilities	4,174	4,340
STOCKHOLDERS' INVESTMENT	15,543	14,727
LIABILITIES AND STOCKHOLDERS' INVESTMENT	22,733	22,187
Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	328	417	412	279
Receivables, less allowances	4,106	3,793
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	714	671
Deferred income taxes	491	514
Total current assets	5,639	5,395
PROPERTY AND EQUIPMENT, AT COST	35,659	34,301
Less accumulated depreciation and amortization	18,264	17,822
Net property and equipment	17,395	16,479
INTERCOMPANY RECEIVABLE		323
GOODWILL	1,554	1,553
INVESTMENT IN SUBSIDIARIES	3,238	2,978
Other assets	802	1,099
ASSETS	28,628	27,827
CURRENT LIABILITIES
Current portion of long-term debt	1	417
Accrued salaries and employee benefits	1,020	1,365
Accounts payable	1,347	1,276
Accrued expenses	1,386	1,406
Total current liabilities	3,754	4,464
LONG-TERM DEBT, LESS CURRENT PORTION	250	250
INTERCOMPANY PAYABLE	418
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,704	3,649
Other liabilities	3,343	3,193
Total other long-term liabilities	7,047	6,842
STOCKHOLDERS' INVESTMENT	17,159	16,271
LIABILITIES AND STOCKHOLDERS' INVESTMENT	28,628	27,827
Non Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	659	636	599	546
Receivables, less allowances	1,147	943
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	54	44
Deferred income taxes	19	19
Total current assets	1,879	1,642
PROPERTY AND EQUIPMENT, AT COST	2,064	1,834
Less accumulated depreciation and amortization	1,116	1,074
Net property and equipment	948	760
INTERCOMPANY RECEIVABLE	1,115	1,524
GOODWILL	1,203	834
Other assets	208	86
ASSETS	5,353	4,846
CURRENT LIABILITIES
Accrued salaries and employee benefits	211	187
Accounts payable	573	482
Accrued expenses	198	119
Total current liabilities	982	788
OTHER LONG-TERM LIABILITIES
Deferred income taxes	13	5
Other liabilities	210	183
Total other long-term liabilities	223	188
STOCKHOLDERS' INVESTMENT	4,148	3,870
LIABILITIES AND STOCKHOLDERS' INVESTMENT	5,353	4,846
Consolidation Eliminations Member
CURRENT ASSETS
Cash and cash equivalents	(185)	(116)	(115)	(86)
Receivables, less allowances	(51)	(35)
Total current assets	(236)	(151)
INTERCOMPANY RECEIVABLE	(1,115)	(1,847)
INVESTMENT IN SUBSIDIARIES	(21,307)	(20,141)
Other assets	(2,744)	(2,818)
ASSETS	(25,402)	(24,957)
CURRENT LIABILITIES
Accounts payable	(236)	(151)
Total current liabilities	(236)	(151)
INTERCOMPANY PAYABLE	(1,115)	(1,847)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(2,744)	(2,818)
Total other long-term liabilities	(2,744)	(2,818)
STOCKHOLDERS' INVESTMENT	(21,307)	(20,141)
LIABILITIES AND STOCKHOLDERS' INVESTMENT	$ (25,402)	$ (24,957)