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SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]      
Decrease associated with reduction in corporate income Tax Reform $ 1,100    
Movement in Valuation Allowances and Reserves [Roll Forward]      
Reversal of valuation allowance for minimum tax credit carryforwords due to Tax Reform 371    
Valuation allowance for deferred tax assets      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Valuation Allowances and Reserves, Deductions (1,484)    
Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year 6,058 $ 4,183 $ 2,434
Additions Charged to Cost and Expense   1,852 1,749
Additons Charged to Other Accounts 1 23 0
Other Additions (Deductions) 0 0 0
Balance at End of Year 4,575 6,058 4,183
Reserve for Taxes, Other than Income Taxes [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Valuation Allowances and Reserves, Deductions (2) (3)  
Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at Beginning of Year 64 83 93
Additions Charged to Cost and Expense   13 9
Additons Charged to Other Accounts 0   0
Other Additions (Deductions) (4) (29) (19)
Balance at End of Year $ 58 $ 64 $ 83