pre_text: (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.
table: As of December 31,
table: 2019 2018
table: (Dollars in millions)
table: Trade and purchased receivables $1,971 2,094
table: Earned and unbilled receivables 374 425
table: Other 20 21
table: Total accounts receivable 2,365 2,540
table: Less: allowance for doubtful accounts (106) (142)
table: Accounts receivable, less allowance $2,259 2,398
question: Analyse this data from a financial earnings document. What is the change in the earned and unbilled receivables?