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Receivables (Tables)
12 Months Ended
Dec. 31, 2019
Receivables [Abstract]  
Schedule of accounts receivable
As of December 31
(Dollars in millions)20192018
Receivables$256  $378  
Allowance at beginning of year(2) (2) 
Reversal of allowance —  
Addition to allowance(2) —  
Allowance at end of year(3) (2) 
Total receivables, net of allowance$253  $376