Condensed Consolidating Financial Statements (Details 2) - USD ($) $ in Millions	Nov. 30, 2015	May. 31, 2015	Nov. 30, 2014	May. 31, 2014
CURRENT ASSETS
Cash and cash equivalents	$ 3,647	$ 3,763	$ 2,266	$ 2,908
Receivables, less allowances	5,865	5,719
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	953	853
Deferred income taxes	687	606
Total current assets	11,152	10,941
PROPERTY AND EQUIPMENT, AT COST	45,242	42,864
Less accumulated depreciation and amortization	22,964	21,989
Net property and equipment	22,278	20,875
Goodwill	3,806	3,810
Other assets	1,135	1,443
ASSETS	38,371	37,069
CURRENT LIABILITIES
Current portion of long-term debt	14	19
Accrued salaries and employee benefits	1,510	1,436
Accounts payable	2,129	2,066
Accrued expenses	2,298	2,436
Total current liabilities	5,951	5,957
LONG-TERM DEBT, LESS CURRENT PORTION	8,481	7,249
OTHER LONG-TERM LIABILITIES
Deferred income taxes	1,759	1,747
Other liabilities	7,190	7,123
Total other long-term liabilities	8,949	8,870
STOCKHOLDERS' INVESTMENT	14,990	14,993
LIABILITIES AND STOCKHOLDERS' INVESTMENT	38,371	37,069
Parent Company Member
CURRENT ASSETS
Cash and cash equivalents	2,229	2,383	1,048	1,756
Receivables, less allowances	10	3
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	85	41
Total current assets	2,324	2,427
PROPERTY AND EQUIPMENT, AT COST	29	29
Less accumulated depreciation and amortization	23	23
Net property and equipment	6	6
INVESTMENT IN SUBSIDIARIES	24,371	23,173
Other assets	2,785	2,752
ASSETS	29,486	28,358
CURRENT LIABILITIES
Accrued salaries and employee benefits	49	34
Accounts payable	76	5
Accrued expenses	632	604
Total current liabilities	757	643
LONG-TERM DEBT, LESS CURRENT PORTION	8,217	6,978
INTERCOMPANY PAYABLE	2,236	2,249
OTHER LONG-TERM LIABILITIES
Other liabilities	3,286	3,495
Total other long-term liabilities	3,286	3,495
STOCKHOLDERS' INVESTMENT	14,990	14,993
LIABILITIES AND STOCKHOLDERS' INVESTMENT	29,486	28,358
Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	474	487	482	441
Receivables, less allowances	4,503	4,383
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	739	689
Deferred income taxes	651	571
Total current assets	6,367	6,130
PROPERTY AND EQUIPMENT, AT COST	43,125	40,364
Less accumulated depreciation and amortization	21,832	20,685
Net property and equipment	21,293	19,679
INTERCOMPANY RECEIVABLE	981	686
Goodwill	1,571	1,552
INVESTMENT IN SUBSIDIARIES	3,228	3,800
Other assets	708	898
ASSETS	34,148	32,745
CURRENT LIABILITIES
Current portion of long-term debt	6	7
Accrued salaries and employee benefits	1,251	1,208
Accounts payable	1,411	1,433
Accrued expenses	1,415	1,557
Total current liabilities	4,083	4,205
LONG-TERM DEBT, LESS CURRENT PORTION	248	248
OTHER LONG-TERM LIABILITIES
Deferred income taxes	4,263	4,206
Other liabilities	3,653	3,367
Total other long-term liabilities	7,916	7,573
STOCKHOLDERS' INVESTMENT	21,901	20,719
LIABILITIES AND STOCKHOLDERS' INVESTMENT	34,148	32,745
Non Guarantor Subsidiaries Member
CURRENT ASSETS
Cash and cash equivalents	988	971	869	861
Receivables, less allowances	1,405	1,385
Spare parts, supplies, fuel, prepaid expenses and other, less allowances	129	123
Deferred income taxes	36	35
Total current assets	2,558	2,514
PROPERTY AND EQUIPMENT, AT COST	2,088	2,471
Less accumulated depreciation and amortization	1,109	1,281
Net property and equipment	979	1,190
INTERCOMPANY RECEIVABLE	1,255	1,563
Goodwill	2,235	2,258
Other assets	343	477
ASSETS	7,370	8,002
CURRENT LIABILITIES
Current portion of long-term debt	8	12
Accrued salaries and employee benefits	210	194
Accounts payable	739	758
Accrued expenses	251	275
Total current liabilities	1,208	1,239
LONG-TERM DEBT, LESS CURRENT PORTION	16	23
OTHER LONG-TERM LIABILITIES
Deferred income taxes	197	225
Other liabilities	251	261
Total other long-term liabilities	448	486
STOCKHOLDERS' INVESTMENT	5,698	6,254
LIABILITIES AND STOCKHOLDERS' INVESTMENT	7,370	8,002
Consolidation Eliminations Member
CURRENT ASSETS
Cash and cash equivalents	(44)	(78)	$ (133)	$ (150)
Receivables, less allowances	(53)	(52)
Total current assets	(97)	(130)
INTERCOMPANY RECEIVABLE	(2,236)	(2,249)
INVESTMENT IN SUBSIDIARIES	(27,599)	(26,973)
Other assets	(2,701)	(2,684)
ASSETS	(32,633)	(32,036)
CURRENT LIABILITIES
Accounts payable	(97)	(130)
Total current liabilities	(97)	(130)
INTERCOMPANY PAYABLE	(2,236)	(2,249)
OTHER LONG-TERM LIABILITIES
Deferred income taxes	(2,701)	(2,684)
Total other long-term liabilities	(2,701)	(2,684)
STOCKHOLDERS' INVESTMENT	(27,599)	(26,973)
LIABILITIES AND STOCKHOLDERS' INVESTMENT	$ (32,633)	$ (32,036)