Receivables (Tables)
 12 Months Ended
Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]  
Allowance for Credit Losses on Financing Receivables [Table Text Block] The following table presents a rollforward of our global allowance for bad debts for 2016, 2017 and 2018.
Millions of dollars
Balance at Beginning of Period
Provision (a)

Other (b)
Balance at End of Period
Year ended December 31, 2016
$
145

$
50

$
(20
)
$
175

Year ended December 31, 2017
175

566

(16
)
725

Year ended December 31, 2018
725

57

(44
)
738


(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.