Income Taxes (Tables)

3 Months Ended

Mar. 31, 2012

Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table summarizes the difference between income tax expense at the United States statutory rate of 35% and the income tax expense (benefit) at effective worldwide tax rates for the periods presented:

	Three Months Ended March 31,
Millions of dollars	2012			2011
Earnings before income taxes	$	133		$	154
Income tax expense computed at United States statutory tax rate	$	47		$	54
U.S. government tax incentive - Energy Tax Credits	—			(54		)
Foreign government tax incentive - BEFIEX	(4		)	(11		)
Other	(7		)	(13		)
Income tax expense (benefit) computed at effective worldwide tax rates	$	36		$	(24	)