Table:
|  | 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 |
Paragraphs:
(8) Accounts Receivable
The following table presents details of our accounts receivable balances:
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.
Question:
What are the types of accounts receivables highlighted in the table?
Answer: Trade and purchased receivables, Earned and unbilled receivables, Other