Condensed Consolidating Financial Statements (Details 2) - USD ($)
$ in Millions
Nov. 30, 2016
May 31, 2016
Nov. 30, 2015
May 31, 2015
CURRENT ASSETS        
Cash and cash equivalents $ 3,059 $ 3,534 $ 3,647 $ 3,763
Receivables, less allowances 7,575 7,252    
Spare parts, supplies, fuel, prepaid expenses and other, less allowances 1,418 1,203    
Total current assets 12,052 11,989    
PROPERTY AND EQUIPMENT, AT COST 48,918 47,018    
Less accumulated depreciation and amortization 23,611 22,734    
Net property and equipment 25,307 24,284    
Goodwill 6,921 6,747    
Other assets 2,068 2,939    
ASSETS 46,348 45,959    
CURRENT LIABILITIES        
Current portion of long-term debt 43 29    
Accrued salaries and employee benefits 1,765 1,972    
Accounts payable 2,954 2,944    
Accrued expenses 3,045 3,063    
Total current liabilities 7,807 8,008    
LONG-TERM DEBT, LESS CURRENT PORTION 13,553 13,733    
OTHER LONG-TERM LIABILITIES        
Deferred income taxes 2,148 1,567    
Other liabilities 8,309 8,867    
Total other long-term liabilities 10,457 10,434    
STOCKHOLDERS' INVESTMENT 14,531 13,784    
LIABILITIES AND STOCKHOLDERS' INVESTMENT 46,348 45,959    
Consolidation Eliminations Member        
CURRENT ASSETS        
Cash and cash equivalents (55) (43) (44) (78)
Receivables, less allowances (51) (41)    
Total current assets (106) (84)    
INTERCOMPANY RECEIVABLE (3,961) (3,721)    
INVESTMENT IN SUBSIDIARIES (29,525) (28,463)    
Other assets (2,892) (3,238)    
ASSETS (36,484) (35,506)    
CURRENT LIABILITIES        
Accounts payable (106) (84)    
Total current liabilities (106) (84)    
INTERCOMPANY PAYABLE (3,961) (3,721)    
OTHER LONG-TERM LIABILITIES        
Deferred income taxes (2,892) (3,238)    
Total other long-term liabilities (2,892) (3,238)    
STOCKHOLDERS' INVESTMENT (29,525) (28,463)    
LIABILITIES AND STOCKHOLDERS' INVESTMENT (36,484) (35,506)    
Parent Company Member        
CURRENT ASSETS        
Cash and cash equivalents 1,330 1,974 2,229 2,383
Receivables, less allowances 1 1    
Spare parts, supplies, fuel, prepaid expenses and other, less allowances 370 233    
Total current assets 1,701 2,208    
PROPERTY AND EQUIPMENT, AT COST 22 22    
Less accumulated depreciation and amortization 17 17    
Net property and equipment 5 5    
INTERCOMPANY RECEIVABLE 2,359 2,437    
INVESTMENT IN SUBSIDIARIES 25,967 24,766    
Other assets 3,041 3,359    
ASSETS 33,073 32,775    
CURRENT LIABILITIES        
Accrued salaries and employee benefits 43 54    
Accounts payable 112 8    
Accrued expenses 887 883    
Total current liabilities 1,042 945    
LONG-TERM DEBT, LESS CURRENT PORTION 13,281 13,451    
OTHER LONG-TERM LIABILITIES        
Other liabilities 4,219 4,595    
Total other long-term liabilities 4,219 4,595    
STOCKHOLDERS' INVESTMENT 14,531 13,784    
LIABILITIES AND STOCKHOLDERS' INVESTMENT 33,073 32,775    
Guarantor Subsidiaries Member        
CURRENT ASSETS        
Cash and cash equivalents 294 326 474 487
Receivables, less allowances 4,753 4,461    
Spare parts, supplies, fuel, prepaid expenses and other, less allowances 822 724    
Total current assets 5,869 5,511    
PROPERTY AND EQUIPMENT, AT COST 45,735 43,760    
Less accumulated depreciation and amortization 22,360 21,566    
Net property and equipment 23,375 22,194    
INTERCOMPANY RECEIVABLE 1,602 1,284    
Goodwill 1,571 1,571    
INVESTMENT IN SUBSIDIARIES 3,558 3,697    
Other assets 867 967    
ASSETS 36,842 35,224    
CURRENT LIABILITIES        
Current portion of long-term debt 26 13    
Accrued salaries and employee benefits 1,247 1,377    
Accounts payable 1,441 1,501    
Accrued expenses 1,434 1,411    
Total current liabilities 4,148 4,302    
LONG-TERM DEBT, LESS CURRENT PORTION 245 245    
OTHER LONG-TERM LIABILITIES        
Deferred income taxes 4,792 4,436    
Other liabilities 3,501 3,375    
Total other long-term liabilities 8,293 7,811    
STOCKHOLDERS' INVESTMENT 24,156 22,866    
LIABILITIES AND STOCKHOLDERS' INVESTMENT 36,842 35,224    
Non Guarantor Subsidiaries Member        
CURRENT ASSETS        
Cash and cash equivalents 1,490 1,277 $ 988 $ 971
Receivables, less allowances 2,872 2,831    
Spare parts, supplies, fuel, prepaid expenses and other, less allowances 226 246    
Total current assets 4,588 4,354    
PROPERTY AND EQUIPMENT, AT COST 3,161 3,236    
Less accumulated depreciation and amortization 1,234 1,151    
Net property and equipment 1,927 2,085    
Goodwill 5,350 5,176    
Other assets 1,052 1,851    
ASSETS 12,917 13,466    
CURRENT LIABILITIES        
Current portion of long-term debt 17 16    
Accrued salaries and employee benefits 475 541    
Accounts payable 1,507 1,519    
Accrued expenses 724 769    
Total current liabilities 2,723 2,845    
LONG-TERM DEBT, LESS CURRENT PORTION 27 37    
INTERCOMPANY PAYABLE 3,961 3,721    
OTHER LONG-TERM LIABILITIES        
Deferred income taxes 248 369    
Other liabilities 589 897    
Total other long-term liabilities 837 1,266    
STOCKHOLDERS' INVESTMENT 5,369 5,597    
LIABILITIES AND STOCKHOLDERS' INVESTMENT $ 12,917 $ 13,466