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Accounts Receivable
12 Months Ended
Dec. 31, 2019
Receivables [Abstract]  
Accounts Receivable Accounts Receivable

The following table presents details of our accounts receivable balances:
 
As of December 31,
 
2019
 
2018
 
(Dollars in millions)
Trade and purchased receivables
$
1,971

 
2,094

Earned and unbilled receivables
374

 
425

Other
20

 
21

Total accounts receivable
2,365

 
2,540

Less: allowance for doubtful accounts
(106
)
 
(142
)
Accounts receivable, less allowance
$
2,259

 
2,398



We are exposed to concentrations of credit risk from residential and business customers. We generally do not require collateral to secure our receivable balances. We have agreements with other communications service providers whereby we agree to bill and collect on their behalf for services rendered by those providers to our customers within our local service area. We purchase accounts receivable from other communications service providers primarily on a recourse basis and include these amounts in our accounts receivable balance. We have not experienced any significant loss associated with these purchased receivables.

The following table presents details of our allowance for doubtful accounts:
 
Beginning
Balance
 
Additions
 
Deductions
 
Ending
Balance
 
(Dollars in millions)
2019
$
142

 
145

 
(181
)
 
106

2018
164

 
153

 
(175
)
 
142

2017
178

 
176

 
(190
)
 
164