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SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Allowance for doubtful accounts, deducted from accounts receivable      
Income tax valuation allowance, deducted from deferred tax assets      
Balance at Beginning of Period $ 32 $ 28 $ 28
Charged to Costs and Expenses 95 83 57
Charged to Other Accounts 0 0 0
Deductions (84) (79) (57)
Balance at End of Period 43 32 28
Income tax valuation allowance, deducted from deferred tax assets      
Income tax valuation allowance, deducted from deferred tax assets      
Balance at Beginning of Period 3,794 1,863 4,116
Charged to Costs and Expenses (3,543) 1,934 (151)
Charged to Other Accounts (9) (128) (15)
Deductions 0 125 (2,087)
Balance at End of Period $ 242 $ 3,794 $ 1,863