Condensed Consolidating Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	May 31, 2013	May 31, 2012	May 31, 2011	May 31, 2010
CURRENT ASSETS
Cash and cash equivalents	$ 4,917	$ 2,843	$ 2,328	$ 1,952
Receivables, less allowances	5,044	4,704
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	780	976
Deferred income taxes	533	533
Total current assets	11,274	9,056
PROPERTY AND EQUIPMENT, AT COST	38,109	36,164
Less accumulated depreciation and amortization	19,625	18,916
Net property and equipment	18,484	17,248
GOODWILL	2,755	2,387	2,326
Other assets	1,054	1,212
ASSETS	33,567	29,903
CURRENT LIABILITIES
Current portion of long-term debt	251	417
Accrued salaries and employee benefits	1,688	1,635
Accounts payable	1,879	1,613
Accrued expenses	1,932	1,709
Total current liabilities	5,750	5,374
LONG-TERM DEBT, LESS CURRENT PORTION	2,739	1,250
OTHER LONG-TERM LIABILITIES
Deferred income taxes	1,652	836
Other liabilities	6,028	7,716
Total other long-term liabilities	7,680	8,552
STOCKHOLDERS' INVESTMENT	17,398	14,727	15,220	13,811
LIABILITIES AND STOCKHOLDERS' INVESTMENT	33,567	29,903
Parent Company [Member]
CURRENT ASSETS
Cash and cash equivalents	3,892	1,906	1,589	1,310
Receivables, less allowances		3
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	45	261
Total current assets	3,937	2,170
PROPERTY AND EQUIPMENT, AT COST	27	29
Less accumulated depreciation and amortization	21	20
Net property and equipment	6	9
INVESTMENT IN SUBSIDIARIES	18,739	17,163
Other assets	2,187	2,845
ASSETS	24,869	22,187
CURRENT LIABILITIES
Current portion of long-term debt	250
Accrued salaries and employee benefits	82	83
Accounts payable	4	6
Accrued expenses	355	184
Total current liabilities	691	273
LONG-TERM DEBT, LESS CURRENT PORTION	2,489	1,000
INTERCOMPANY PAYABLE	1,642	1,847
OTHER LONG-TERM LIABILITIES
Other liabilities	2,649	4,340
Total other long-term liabilities	2,649	4,340
STOCKHOLDERS' INVESTMENT	17,398	14,727
LIABILITIES AND STOCKHOLDERS' INVESTMENT	24,869	22,187
Guarantor Subsidiaries [Member]
CURRENT ASSETS
Cash and cash equivalents	405	417	279	258
Receivables, less allowances	3,989	3,793
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	681	671
Deferred income taxes	518	514
Total current assets	5,593	5,395
PROPERTY AND EQUIPMENT, AT COST	35,915	34,301
Less accumulated depreciation and amortization	18,469	17,822
Net property and equipment	17,446	16,479
INTERCOMPANY RECEIVABLE	439	323
GOODWILL	1,552	1,553
INVESTMENT IN SUBSIDIARIES	3,347	2,978
Other assets	822	1,099
ASSETS	29,199	27,827
CURRENT LIABILITIES
Current portion of long-term debt	1	417
Accrued salaries and employee benefits	1,402	1,365
Accounts payable	1,392	1,276
Accrued expenses	1,366	1,406
Total current liabilities	4,161	4,464
LONG-TERM DEBT, LESS CURRENT PORTION	250	250
OTHER LONG-TERM LIABILITIES
Deferred income taxes	3,798	3,649
Other liabilities	3,133	3,193
Total other long-term liabilities	6,931	6,842
STOCKHOLDERS' INVESTMENT	17,857	16,271
LIABILITIES AND STOCKHOLDERS' INVESTMENT	29,199	27,827
Non Guarantor Subsidiaries [Member]
CURRENT ASSETS
Cash and cash equivalents	717	636	546	443
Receivables, less allowances	1,084	943
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	54	44
Deferred income taxes	15	19
Total current assets	1,870	1,642
PROPERTY AND EQUIPMENT, AT COST	2,167	1,834
Less accumulated depreciation and amortization	1,135	1,074
Net property and equipment	1,032	760
INTERCOMPANY RECEIVABLE	1,203	1,524
GOODWILL	1,203	834
Other assets	191	86
ASSETS	5,499	4,846
CURRENT LIABILITIES
Accrued salaries and employee benefits	204	187
Accounts payable	609	482
Accrued expenses	211	119
Total current liabilities	1,024	788
OTHER LONG-TERM LIABILITIES
Deferred income taxes		5
Other liabilities	246	183
Total other long-term liabilities	246	188
STOCKHOLDERS' INVESTMENT	4,229	3,870
LIABILITIES AND STOCKHOLDERS' INVESTMENT	5,499	4,846
Consolidation Eliminations [Member]
CURRENT ASSETS
Cash and cash equivalents	(97)	(116)	(86)	(59)
Receivables, less allowances	(29)	(35)
Total current assets	(126)	(151)
INTERCOMPANY RECEIVABLE	(1,642)	(1,847)
INVESTMENT IN SUBSIDIARIES	(22,086)	(20,141)
Other assets	(2,146)	(2,818)
ASSETS	(26,000)	(24,957)
CURRENT LIABILITIES
Accounts payable	(126)	(151)
Total current liabilities	(126)	(151)
INTERCOMPANY PAYABLE	(1,642)	(1,847)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(2,146)	(2,818)
Total other long-term liabilities	(2,146)	(2,818)
STOCKHOLDERS' INVESTMENT	(22,086)	(20,141)
LIABILITIES AND STOCKHOLDERS' INVESTMENT	$ (26,000)	$ (24,957)