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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 [Roll Forward]      
Balance at beginning of period $ 26 $ 48 $ 51
Additions charged to costs and expenses 8 0 1
Other additions 0 0 0
Deductions 2 22 4
Balance at end of period $ 32 $ 26 $ 48