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Accounts Receivable (Tables)
 12 Months Ended
Dec. 31, 2017
Receivables [Abstract]  
Schedule of components of accounts receivable
The following table presents details of our accounts receivable balances:
 
As of December 31,
 
2017
 
2016
 
(Dollars in millions)
Trade and purchased receivables
$
2,245

 
1,882

Earned and unbilled receivables
436

 
299

Other
40

 
14

Total accounts receivable
2,721

 
2,195

Less: allowance for doubtful accounts
(164
)
 
(178
)
Accounts receivable, less allowance
$
2,557

 
2,017
Schedule of details of allowance for doubtful accounts
The following table presents details of our allowance for doubtful accounts:
 
Beginning
Balance
 
Additions
 
Deductions
 
Ending
Balance
 
(Dollars in millions)
2017
$
178

 
176

 
(190
)
 
164

2016
$
152

 
192

 
(166
)
 
178

2015
$
162

 
177

 
(187
)
 
152