Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2011

Notes to Financial Statements [Abstract]

Changes in Asset Retirement Obligations

Asset retirement obligations consist primarily of estimated costs of dismantlement, removal, site reclamation and similar activities associated with our oil and gas properties. Changes in asset retirement obligations were as follows:

	Nine Months Ended September 30,
	2011			2010
(millions)
Asset Retirement Obligations, Beginning Balance	$	253		$	232
Liabilities Incurred		2			14
Liabilities Settled		(19	)		(35	)
Revision of Estimate		9			11
Accretion Expense		15			13
Asset Retirement Obligations, Ending Balance	$	260		$	235