Receivables (Tables)
 12 Months Ended
Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]  
Rollforward of Allowance for Bad Debts
The table below presents a rollforward of our global allowance for bad debts for 2017, 2018 and 2019.
Millions of dollars
Balance at Beginning of Period
Provision (a)

Other (b)
Balance at End of Period (c)
Year ended December 31, 2017
$
175

$
566

$
(16
)
$
725

Year ended December 31, 2018
725

57

(44
)
738

Year ended December 31, 2019
738

50

(12
)
776


(a) Represents increases to allowance for bad debts charged to costs and expenses, net of recoveries.
(b) Includes write-offs, balance sheet reclassifications, and other activity.
(c) The allowance for bad debts in all years is primarily comprised of a full reserve against accounts receivable with our primary customer in Venezuela.