Receivables (Tables)

12 Months Ended

Dec. 31, 2011

Receivables [Abstract]

Allowance for bad debts

	Balance at		Charged to
Millions of dollars	Beginning of		Costs and				Balance at
Allowance for bad debts	Period		Expenses		Write-Offs		End of Period
Year ended December 31, 2009:	$	60	$	37	$	(7)	$	90
Year ended December 31, 2010:		90		5		(4)		91
Year ended December 31, 2011:		91		53		(7)		137