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Schedule II - Valuation and Qualifying Accounts (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Allowance for doubtful accounts      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at  Beginning of Period $ 132 $ 136 $ 157
Charged to Cost and and Expenses 42 16 54
Deductions (42) (20) (75)
Balance at End of Period 132 132 136
Deferred tax valuation allowance      
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at  Beginning of Period 192 348 178
Charged to Cost and and Expenses 12 (150) 75
Deductions 10 (6) 95
Balance at End of Period $ 214 $ 192 $ 348