Receivables (Tables)

12 Months Ended

Dec. 31, 2015

Receivables [Abstract]

Allowance for bad debts

Millions of dollars	Balance at Beginning of Period		Charged to Costs and Expenses		Write-Offs			Balance at End of Period
Year ended December 31, 2013	$	92	$	39	$	(14	)	$	117
Year ended December 31, 2014	117		26		(6		)	137
Year ended December 31, 2015	137		44		(36		)	145